Geology: Different branches
⚫ The word geology has been derived from the Greek word,”Geo” meaning earth and “logos” meaning study. The study of geology mainly concerns itself with the study of earth’s constitution, structure and history of development.
Different branches of geology
⚫ Physical Geology: deals with processes that bring about changes on the earth’s surface.
⚫ Structural Geology: deals with the configuration of the rocks in the earth’s crust produced by number of forces.
⚫ Petrology: deals with study of rocks.
⚫ Geomorphology: study of origin of landforms an their modification by dynamic processes.
⚫ Geophysics: application of principles of physics for the study of the geology.
⚫ Geochemistry: deals with chemical composition of earth, distribution and migration of elements in various parts of the earth.
⚫ Sedimentology: deals with the science of erosion and deposition of rock particles by water, wind, ice.
⚫ Mineralogy: deals with the study of minerals, their properties.
⚫ Economic geology: deals with the exploration and recovery of natural resources, like ores, precious gemstones.
⚫ Engineering Geology: Engineering geology deals with the application of geology in design, construction and performance of civil engineering works.
Definition of engineering geology
• According to IAEG (International Association for Engineering Geology)
1. IAEG statutes, Arnould, 1970
The application of the earth sciences to engineering planning, construction, prospecting, testing and processing of related materials.
2. IAEG statutes, 1992
The science devoted to the investigation, study and solution of the engineering and environmental problems which may arise as the result of the interaction between geology and the works and development of measures for prevention or remediation of geological hazard.
Definition: Civil Engineering
⚫ Civil engineering is field of engineering, related
to design, construction and maintenance of buildings, dams, bridges, tunnels, highways and any other structures by the use of physical laws, mathematical
equations and theories of mechanics.
Civil engineering is all about people. It’s the work that civil Engineers do to develop and improve the services and facilities we, the public, all use.
Scope of geology in civil engineering
⚫ Mining engineering
⚫ Water Resource Engineering
⚫ Geomechanics
⚫ Land use planning
⚫ Environmental engineering
⚫ Earthquake Engineering
⚫ Oceanography
⚫ Hydrogeological study
⚫ Construction material engineering
⚫ Tunneling
⚫ Foundation engineering - assessment of soil conditions
⚫ Construction materials engineering - quality of stones, lime,
cement etc.
⚫ Infrastructure engineering - location of bridges, tunnels, river
meandering zones
⚫ Disaster mitigation - seismic resistant structural design, flood
control, river training, waterway of bridges
⚫ Land-use engineering - soil erosion control, natural drainage
⚫ Water Resources engineering - hydrogeology, source and quality
of aquifer and water, desilting of reservoirs and channels
⚫ Environmental engineering - ecological balance, solid waste
management by landfill
Objectives and importance of geology in civil engineering:
⚫ Geology provides systematic approach to complete the constructions' groundwork smoothly and complete the civil engineering without any complications
⚫ The value of geology in Civil Engineering has been recognized only in comparatively
recent years.
⚫ Geology provides a systematic knowledge of construction material, its occurrence, composition, durability and other properties. Example of such construction materials is building stones, road metal, clay, limestones and laterite.
⚫ The knowledge of the geological work of natural agencies such as water, wind, ice and earthquakes helps in planning and carrying out major civil engineering works.
⚫ For example the knowledge of erosion, transportation and deposition helps greatly in solving the expensive problems of river control, coastal and harbour work and soil conservation.
⚫ Ground water is the water which occurs in the subsurface rocks.The knowledge about its quantity and depth of occurrence is required in connection with water supply, irrigation, excavation and many other civil engineering works.
⚫ The foundation problems of dams, bridges and buildings are directly concerned with the geology of the area where they are to be built. In these works drilling is commonly undertaken to explore the ground conditions. Geology helps greatly in interpreting the drilling data.
⚫ In tunneling, constructing roads, canals, docks and in determining the stability of cuts and slopes, the knowledge about the nature and structure of rocks is very necessary.
⚫ Before staring a major engineering project at a place, a detailed geological report which is accompanied by geological maps and sections, is prepared. Such a report helps in planning and constructing the projects.
⚫ The stability of civil engineering structure is considerably increased if the geological feature like faults, joints, bedding planes, folding solution channels etc in the rock beds are properly located and suitably treated.
Definition of Engineering Geology according to IAEG (1992)
⚫ Engineering geology, is defined by the IAEG as the science devoted to the investigation, study and solution of engineering and environmental problems which may arise as the result of the interaction between geology and the works or activities of man, as well as of the prediction of and development of measures for the prevention or remediation of geological hazards.
⚫ It simply refers to the application of geological principles to engineering studies.
Role and task of an engineering geologist
⚫ Consult geological maps and aerial photographs to advice on site selection.
⚫ Perform desk studies and assess site information sources prior to field investigations.
⚫ Assist with design of built structures, using specialized computer software and calculations.
⚫ Assess findings for construction engineers.
⚫ Collect data and produce engineering geological reports.
⚫ Oversee progress of specific contracts related to engineering geology.
⚫ Conduct engineering calculations.
⚫ Assist in preparation of construction plans, specifications and cost estimates including material
quantity calculations.
⚫ Provide construction oversight, documentation, interpretation of drawings and specifications and other support services.
⚫ Gather, analyze and publish field and laboratory data in geotechnical report.
⚫ Conduct field investigations as geologic mapping, geotechnical drilling and sampling.
⚫ Conduct engineering analyzes including slope stability.
⚫ Report geotechnical recommendations integral to successful design, construction and
maintenance of roads, airports and other engineered structures.
⚫ Perform logging and sampling drill holes and trenches, geological and structural mapping, and
installation and observation of down-hole instrumentation.
⚫ Collect, analyze and interpret geotechnical data.
Scope, objective and it’s importance in context of Nepal:
⚫ Nepal has diverse topography with Himalaya, hill and Terai which comprises of variable geology.
⚫ Tectonically active Himalaya range comprises of many unique landforms to be studied prior construction.
⚫ Different dynamic earth processes like weathering, erosion, landslides, earthquake makes the study of geology in nepal important before commencing any design.
⚫ Lack of better understanding of geology of a area may result in design
failure.
⚫ For the identification of different hazards study of geology is important for
Nepal.
⚫ Geology assist in the preliminary phase of investigation so that the implementation phase of design works which has not yet been possible in Nepal.
⚫ Geological study is therefore essential to avoid disasters, accidents and for the long lasting construction.
◾ Mountains: Large landmass stretching above the surrounding land in a limited area, usually to form a peak.
◾ It is usually steeper than a hill.
◾ They may be formed by tectonic force or volcanism.
Types of Mountains:
Types
Tectonic Mountains Originated due to internal forces from within the earth.
- Volcanic mountains
- Fault mountains
- Fold mountains
Residual mountains Formed due to differential erosion Wind, water, glacier involve in geological processes.
◾ Shield: Part of continental crust in which Precambrian igneous and high grade metamorphic rocks are exposed at the surface.
◾ Relatively flat areas and tectonically stable.
◾ Plateau: It is a highland formed by processes including upwelling of volcanic magma, extrusion of lava and erosion by water and glaciers.
Classification of Plateaus:
i) Intermontane: Between mountains. Example: Tibetan Plateau
ii) Piedmont: Piedmont: foot of mountain. Example: Patagonian plateau in Argentina
iii) Continental Plateau: Formed either by continental uplift or spread of horizontal lava completely covering the original topography. Example: Plateaus of Western Australia
iv)Volcanic Plateau: Produced by volcanic activity
◾ The internal structure of earth is
divided into:
(a) Crust
(b) Mantle and
(c) Core
The division is based on
physical & chemical properties,
thickness, depth, density, seismic data,
pressure-temperature and availability of metals.
◾ Evidence from seismology tells us that the earth has a layered structure.
◾ Seismic waves with varying velocities that depend on the type of wave and physical properties of medium for the wave travelling.
◾ Therefore, it is necessary to understand different types of waves.
Wave type Description
1. Body wave (2 types)
(a) Primary wave/ P-wave/Transverse wave
(b) Secondary wave/Shear
wave/Longitudinal wave -These waves travel through the body of the earth.
-The particles move to and fro in the
direction in which the wave is travelling.
-Can travel in all media(solid,liquid and gas).
-Short wavelength and high frequency.
-The particles move to and fro at right
angles to the path of the wave.
-Can travel in solid media only.
-Short wavelength and high frequency.
2. Surface wave
Rayleigh wave or Love wave -They travel along paths nearly parallel to
the surface.
-These are transverse wave.
-They are responsible for most of the
destructive earthquakes.
-They have low frequency, long wavelength
and low velocity.
Figure 1: Internal Structure of Earth
◾ It is the uppermost shell of the earth covering the rocks of the interior thinly.
◾ Average thickness of crust: 33 kms
◾ Thickness of Crust in Oceanic areas: 5 to 10 kms
in Continental areas: 35 kms in Orogenic belts: 55-70 kms
◾ The Mohorovicic discontinuity separates crust from mantle.
• Crust can be divided into two layers, the upper layer is called Sial and the lower one is called Sima. The boundary between the sial and sima is called Conrad Discontinuity.
Sial
-Also called upper continental
crust.
-Rich in silica and alumininim.
-Rock of this layer are of granitic
to grano dioritic in composition.
- Thickness: 11 kms (extends upto
Conrad discontinuity)
Sima
-Also called lower continental
crust.
-Rich in silica and magnesium.
-Rocks of this layer are basaltic in
composition.
-Thickness: 22 kms (extends from Conrad discontinuity to Mohorovicic discontinuity)
-Outer sima ( 11-19kms) has rocks
of intermediate composition.
-Inner sima( 19-33kms) has basic
to ultrabasic rocks)
Ocean Land
• Thinnest layer of the Earth that ranges from only 5-6 km in oceans, 30-35 km in continents and 60-70 km in mountains
• Made up of large amounts of silicon and aluminum
• Two types of crust: oceanic crust and continental crust
• Composed of plates on which the continents and oceans rest
• Crust divided into upper sail and lower sima.
• Sial is also known as upper continental crust and its thickness is 11 km, composed of
all types of rocks. The Cordinal Discontinuity which separates the sial from sima.
• Sima is also called lower continental crust and its thickness is about 22 km, it extends the
5
Cardinal Discontinuity upto the Mohorovic Discontinuity.
◾ Second major part of the earth.
◾ Source region of most of the earth’s internal energy .
◾ Mantle extends from below the Mohorovicic discontinuity upto a depth of 2900 kms ( Thickness: 2865 kms).
◾ Forms 83% of the earth by volume and 68% by mass.
◾ Composition of Mantle: Olivine- Pyroxene complex in solid
state.
◾ Mohorovicic discontinuity (at the depth of 33 kms) separates mantle from crust.
◾ Gutenberg-Weichert discontinuity ( at the depth of 2900 kms) separates mantle from core.
◾ Innermost part of the earth.
◾ Separated from the mantle by Gutenberg- Weichert
discontinuity and extends upto the center of the earth.
◾ Comprises of about 17% of the volume and 34% of the mass of
the earth.
◾ Outer core ( 2900-4982 kms) is said to be inn fluid state as it doesn’t transmit S-waves.
◾ Middle core (4982- 5121 kms) is in a fluid to semi fluid state.
◾ Inner core (5121-6371 kms) is said to be in solid state. It is
believed to contain metallic nickel and iron and is called- Nife.
◾ Temperature of the earth at it’s center: 6000◦ C
◾ Pressure of the earth at it’s center : 3 million atmosphere
◾ There is a sharp change in the density from about 5.5*103 kg m-3 in the mantle to about 10.6* 103 kg m-3 in the core.
◾ While at the center of the core the density increases to 12 or
13* 103 kg m-3.
◾ Crust of the earth ( Oceanic and Continental) together with the uppermost portion of mantle constitutes the lithosphere.
Part of the mantle comprises of the layer Asthenosphere which behaves plastically due to increased temperature and pressure.
The lithosphere is capable of moving bodily over the
asthenosphere.
Plates:
◾ A plate is a large, rigid slab of rock moving slowly over the
asthenosphere and they are usually of continental dimensions.
◾ According to Le Pichon, there are 6 major plates and smaller
plates can be incorporated within theses 6 plates. They are:
(a) Pacific Plate
(b) The American Plate
(c) The African Plate
(d) The Eurasian Plate/ Tibetan Plate
(e) The Indian Plate
(f) The Antarctic Plate
◾ Of the six plates, 5 contain part of continents in the lithosphere and only Pacific plate is made mostly of ocean floor.
◾ Plates are separated by faults and thrusts.
◾ Motion of the plates may be towards or away from each other.
◾ Two plate margins meet at a common plate boundaries and where three plate boundaries meet, it is called Triple- Junction.
◾ When two plates diverge, we find extensional features called ridges.
◾ When two plates converge and one is thrust beneath the other, we find the island arcs.
◾ When two plates slide past each other, there occurs transcurrent faults.
Plate boundries:
◾ Plate boundaries are the sites of intense geological activities
which are mainly due to the movement of plates.
◾ As the big listhospheric plates move by diverging or converging
along their boundaries, tremendous energies are released.
◾ Based on the movement of plates, there are 3 types of plate boundaries:
1. Constructive Boundaries 2.Destructive Boundaries
3. Conservative Boundaries
◾ Also called diverging plate boundaries.
◾ This is a zone along which two plates are in motion away from each other.
◾ As a result of the movement, a fissure develops allowing hot molten materials to come out from the mantle and to form new plate materials.
◾ Divergence of plates may take place in the
middle of an ocean or in the middle of a continent.
◾ Since new material or crust is created by the materials from the mantle, this type of plate boundary is known as constructive or divergent margin.
◾ Mid-oceanic ridges are
formed during oceanic divergence.
Figure 2: Divergent plate boundary
◾ Also called converging plate boundaries.
◾ These are the zones along which two plates are in motion towards each other.
◾ Along such boundaries, crust is destroyed and recycled back into the interior of the earth as one plate dives under another.
◾ This process of entrance of one plate( denser) under
another(rarer) is called subduction.
◾ There are 3 types of convergence processes:
(a) Ocean-Ocean Convergence
b) Ocean-Continent Convergence
(c) Continent-Continent Convergence
Destructive Plate boundaries
(a) (b)
(c)
Fig 4: (a) Ocean-Ocean Convergence (b) Ocean-continent convergence (c) Continent-Continent
convergence
Ocean- Ocean Convergence ( Figure 4 (a))
Subduction of plate and formation of oceanic trenches start.
Island-arcs are formed by the upwelling of melted lavas due to
the friction during subduction.
Also results in formation of undersea volcanoes.
Ocean-Continent Convergence( Figure 4 (b))
Oceanic crust is subducted under a continent due to the density.
Magma rises from the subduction zone forming Volcanic arcs.
Continent-Continent Convergence( Figure 4 (c))
It is also called continental collision where two continents
converge.
When two continents collide, new mountains are formed.
◾ These are boundaries where two continents converge.
◾ These boundaries are also called transform boundaries.
◾ Such boundaries have neither loss nor gain of surface areas so it is called conservative boundaries.
◾ They are represented by faults.
◾ The faults are of transcurrent or transform type ( Figure 4).
◾ Responsible for shallow earthquakes.
◾ San Andreas Fault of California is an example.
Figure 4: Conservative Plate Boundary (transform Fault)
◾ About 55 million years ago, the collision of the Indian Plate took
place with Tibetan (Eurasian) plate.
◾ Many scientists believed that during collision the northward moving Indian plate first touched the southern edge of the Tibetan plate.
◾ There was Tethys sea (oceanic crust) in between the Indian plate
and Eurasian plate which disappeared with collision.
◾ The mountain building process continued with the collision and is
still in progress.
◾ This is noticeable by present day northward movement of Indian plate at the rate of 5 cm per year and occurrences of frequent shakes all along the Himalayas.
Figure 5: Evolution of Himalayas
◾ In 1620, Francis Bacon spotted that west coast of Africa and east coast of South America looked as if they would fit together like a pieces of jigsaw.
◾ In 1912, Alfred Wegner published a theory explaining
why earth looked like a huge jigsaw from evidences:
i) Same type of fossils were found on both coast.
ii) Rocks of both coasts were similar., both in age and composition.
iii) Coal has been found in Antarctica and Britain in present day. But these places have cold climates and cold deposit is found in warm conditions only.
◾ So both places must be nearer to equator in past days.
MINERALOGY
Study of minerals including their
* formation,
* occurrence,
* properties,
* composition and
* classifications.
Definition of a Mineral:
Naturally occurring,
homogeneous solid,
inorganically formed,
with definite (but generally not fixed) chemical composition
and
highly ordered atomic arrangement.
Scope of Mineralogy:
To acquire the knowledge of importance of the minerals like
- rock forming minerals for geological study
- Ore forming minerals for economic importance
KRUSTALLOS = Clear ice; Quartz = Frozen ice
Introduction
Crystal:
-A homogeneous solid possessing long range, three-dimensional internal order.
May be defined as a polyhedral solid bounded by plane faces, which express an orderly internal arrangement
of atoms or molecules.
Examples of Crystalline substances
Quartz Crystal
Gold in Quartz
Flint
Crystallographic axes
Crystal faces are conveniently referred to imaginary lines or directions, which may be used to describe the position of a face or group of faces in space. These lines or directions are called xllographic axes.
The growth or development of the crystal is considered to take place along the axes.
Crystallographic axes and crystallographic angles
CRYSTAL SYSTEM
crystal systems are a method of classifying crystals according to their
atomic lattice or structure.
The atomic lattice is a three dimensional network of atoms that are
arranged in a symmetrical pattern.
The shape of the lattice determines not only which crystal system the stone belongs to, but all of its physical properties and appearance.
There are seven crystal system known which is based on
a. Length of the Crystallographic axes
b. Crystallographic angles
c. No. of crystallographic axes.
Tetragonal System
Two axes are of equal length and are in the same plane, the main axis is either longer or shorter, and all three intersect at right angles.
Based on a rectangular inner structure.
For eg: Zircon, Chalcopyrite, Rutile
Hexagonal System
Three out of the four axes are in one plane, of the same length, and intersect each other at angles of 60 degrees. The fourth axis is of a different length and intersects the others at right angles.
Based on a hexagonal (6-sided) inner structure.
For eg: Apatite, Beryl, Aquamarine
a1=a2=a3c;
a1a2 = a2 a3 = a3a1 = 1200, ac = 900
Trigonal System
Rhombohedral System) - Axes and angles in this system are similar to the Hexagonal System, and the two systems are often combined as Hexagonal.
In the cross-section of a Hexagonal crystal, there will be six sides. In the cross-section of a Trigonal crystal there will be three sides. Based on a triangular inner structure.
For eg. Agate, Amethyst, Tourmaline, Ruby, quartz.
Orthorhombic System
Rhombic System)Three axes, all of different lengths, are at right
angles to each other.
Based on a rhombic (diamond-shaped) inner structure.
For eg. Enstatite, Topaz, Andalusite
Monoclinic System
There are three axes, each of different lengths. Two are at right
angles to each other and the third is inclined.
Based on a parallelogram inner structure.
For eg. Azurite, Gypsum, Staurolite
Triclinic System
All three axes are of different lengths and inclined towards each
other.
Based on a 'triclinic' inner structure, meaning 'three inclined
angles'.
Crystal forms are usually paired faces.
For eg, Rhodonite, Kyanite
PHYSICAL PROPERTIES OF MINERALS
1. Color:
First and most easily observed properties.
Distinguishing criterion for many, but unreliable and changeable
for some.
Depends upon the absorption of some and the reflection of others of the colored rays or vibrations which compose ordinary white light.
Corundum (Al2O3)
Ruby: Deep red
absorbs all the other vibrations, except red Sapphire: Dark blue
absorbs all the other vibrations, except blue
Colour (contd.)
The true color of a pure mineral depends on:
- The nature and arrangement of the constituent
ions. e.g.
Al, Na, K, Ca, Mg, Ba -- generally colorless or light
colored
Fe, Cr, Mn, Co, Ti, Ni, V, Cu -- generally colored.
- Different types of bonding of carbon atoms are responsible for:
the colorless nature of diamond the black nature of graphite.
2. Streak:
Color of a finely powdered mineral (= constant color)
- done in streak plate (H7) - unglazed porcelain
Hematite - cherry red, Magnetite - black, Quartz - colorless
3. Luster:
Refers to the general appearance of a mineral surface in reflected light.
B) Non metallic Luster contd….
Type Nature Example
Adamantine Brilliant like diamond cerussite
Vitreous shiny like broken glass Quartz
Resinous appearance of resin sulphur
Pearly milky reflectance talc
Greasy oily appearance halite
Silky fibrous appearance asbestos
Dull or earthy no luster soil
C) Sub-metallic:-
Intermediate between metallic and non-metallic
e.g. chromite, cuprite etc.
4. Diaphaneity:
The amount of light, which is transmitted through a mineral, is a measure of its diaphaneity.
This physical characteristic is described as:
Transparent
Translucent
Opaque.
Specific gravity (G):
The ratio between the wt. of a substance and the wt. of an equal volume of water at 40C.
Important for fine crystals or gemstones.
G of a crystalline substance depends on:
i) the kind of atoms of which it is composed
ii) the manner in which the atoms are packed together.
Mineral Composition At.wt. of cation
Sp.Gr.
Aragonite CaCO3
40.08 2.95
Strontianite SrCO3 87.62 3.76
Witherite BaCO3 137.34 4.29
Cerussite PbCO3 207.19 6.55
Mineral Composition Crystal System Sp.Gr.
Diamond C Isometric 3.52
Graphite C Hexagonal 2.23
Calcite CaCO3 Rhombohedral 2.71
Aragonite CaCO3 Orthorhombic 2.95
Average Sp. Gr.:
Determined merely by lifting the specimen
Non-metallic minerals:
2.65 to 2.75 (quartz - feldspar) Metallic minerals:
5.0 and above (graphite 2.23, silver
10.5)
Cleavage:
Tendency of minerals to break parallel to atomic planes just as the faces of the external form of a crystal.
Recognized in two ways:
- On the basis of Nature and
- Structure of the crystals.
Cleavage (Contd.)
On the basis of Nature: Perfect = well developed Good = Less perfect Fair/ Poor = Not so distinct
On the basis of structure:
1 set,
2 set,
3 sets etc. or Cubic, Octahedral, Prismatic, Basal etc.
Fracture:
The form or kind of surface obtained by breaking in a direction other than that of cleavage in crystallized minerals, and in any direction in massive minerals.
Fracture is defined as:
Conchoidal: a concentric, dish-shaped fracture similar to the broken surface of a glass. e.g. quartz.
Fibrous or splintery: like fibres, e.g. serpentine
Hackly: jagged fractures with sharp-edges, e.g. cast iron
Even: flat surface, e.g. chert
Uneven or irregular: with rough and irregular surface, e.g. cassiterite (Tinstone)
Splintery: Forming sharp splinters, e.g. kyanite
Hardness:
The resistance that a smooth surface of a mineral offers to scratching is its hardness (H) = Scratchability.
Depends upon ionic bonding - Increase in hardness with decreasing ionic size and increasing ionic charge.
Hardness (contd.)
Hardness scale : Given by Australian Mineralogist F. Mohs in 1824;
1. Talc - Mg3Si4O10(OH)2
2. Gypsum – CaSO4.2H2O
3. Calcite – CaCO3
4. Fluorite – CaF2
5. Apatite - Ca5(PO4)3 (F,Cl,OH)
6. Orthoclase Feldspar – KAlSi3O8
7. Quartz – SiO2
8. Topaz - Al2SiO4(F,OH)2
9. Corundum – Al2O3
10. Diamond - C
Others:
Copper coin 3
Finger Nail 2 to 3
Pocket Knife 5 to 6
Steel Knife 6.5
Glass 5.5
Determination of (H):
Tested by rubbing the specimen over a tolerably fine cut file noting the amount of powder and
the degree of noise produced in the operation.
less the powder and greater the noise, harder is the mineral.
Tenacity:
The resistance that a mineral offers to
breaking,
crushing,
bending or
tearing,
in short its cohesiveness is known as tenacity.
Tenacity (Contd…)
Brittle: breaks and powders easily, e.g. pyrite, apatite
Malleable: that can be hammered out into thin sheets
Ductile: that can be hammered out into thin wires e.g. Ag, Au, Cu etc.
Sectile: can cut into thin layers with a knife, e.g. graphite, gypsum
Elastic: mica sheets
Plastic: Talc, chlorite etc.
Crystal Habits and Aggregates
The habit or appearance of a single crystal or aggregates of crystal or aggregates of crystals help to identify them. The term used to express habit and state of aggregation are given below:
Habits
Minerals in isolated or distinct crystals may be described as:
Type Nature Min.Ex.
a) Acicular – needle like cystals - natrolite
b) Capillary and filiform –hair like-millerite
c) Bladed – like a knife blade- kyanite
For group of distinct crystals:
a) Dendritic – divergent branches - gold
b) Reticulated – net like – rutiles in mica
c) Divergent or radiated –radiating-stilbite
d) Drusy – covered with small xl - quartz
Habits contd….
Parallel or radiating groups of individual crystals:
a) Columnar – column like - hornblende
b) Bladed – many blades - kyanite
c) Fibrous – fibres - asbestos
d) Stellated – star like - wavellite
e) Globular – small spherical- cassiterite
f) Botroidal – like bunch of grapes -chalcedony
g) Reniform – kidney shaped - hematite
h) Mammilary – large botroidal - malachite
i) Colloform – spherical forms - aragonite
Habit Contd….
A mineral aggregate composed of scales or lamellae:
a) Foliated – plates or leaves - gypsum
b) Micaceous – thin sheets - micas
c) Lamellar or tabular-flat, plate-wollastonite
d) Plumose- feather like - stibnite
Habit contd…
A mineral aggregate composed of grains = Granular
Miscellaneous terms :
Form Nature Mineral
a) Stalactite elongated cones limonite
b) Concentric superimposed talc
c) Oolitic formed of small spheres oolites
d) Banded bands of diff. colors - chert
e) Massive compact without any form- iron ores
f) Amygdaloidal sub-globular zeolites
g) Concretion accumulation about nucleus - flint
Rock forming minerals
*Silicates
The silicate minerals are classified into various groups on the basis of their atomic structure.
Subdivided into Hydrous(Containing hydrogen and oxygen in their chemical formulas) and anhydrous (no water):
Hydrous: Chlorite, talc,clay minerals,mica, hornblende, serpentite etc.
Anhydrous: Feldspar, Pyroxenes, Olivine, zeolite, garnet, Quartz
Non-silicate Minerals
ii. Non- silicate Minerals:
These are oxides, hydroxides, carbonates, sulphate etc. Among the non-silicates the oxides are the oxides are the most important since many of them occur as minor accessories of rocks. Some of them are listed below:
Oxides:
Corundum (Al2O3), Hematite (Fe2O3), ilmenite (FeTiO3), Limonite (Fe2O3.H2O), Magnetite (Fe3O4), Quartz (SiO2), etc.
Hydroxides:
Brucite, Geothite,Manganite Mno.(OH) etc
Carbonate
Calcite (CaO), dolomite – (CaMg (CO3)
Sulphate
Anhydrite , Gypsum etc.
Feldspar,Quartz, pyroxene, micas, Fe-Ti oxides, olivines and amphiboles are main minerals compried chiefly in all magmatic rocks (igneous rocks).
Minerals like Quartz, feldspar, mica, chlorite, calcite etc. are commonly found in metemorphic rocks. Some minerals like chlorite, garnet, kyanite, staurolite, andalusite, silliminite are index minerals to define the grade of metamorphism.
Engineering Significance of Rock Forming Minerals.
The activities of the engineering geologogists and civil engineers are directly or indirectly associated with rocks and rock forming minerals.
Clay minerals like Kaolinites Montmorillonites, illite swelling after saturation with water thereby creating hazardous side for engineering structure.
The different Rock forming Minerals and different degrees of weathering stability. Quartz grains Rockstar Rockstar that are mostly found in sedimentary rocks are more stable at surficial environment.
The rockforming carbonate minerals like calcite and dolomitedissolve completely in water that contains dissolved CO2.
Hollows may develop inside the ground that contains carbonate rocks due to water interactions. Areas are called karst topography. Internal drainage and collappse features are commonly observed in Karst area. So great consciousness is required in such areas during site selection.
Orientation of platy micas and foliated structures reduce the strength of Rock.
Deformed and fracture minerals found in metamorphic rocks may reduce the strength of Rock.
PETROLOGY
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Petrology
Petrology is a branch of geology which deals with the study of rocks (from the Greek peta means “rock” and logos means explanation: or “study )
OR
The branch of geology dealing with the origin, occurrence, structure, and
history of rocks.
Rock is defined as aggregate of minerals in compact from. It is a naturally
occurring.
Mineral is defined as naturally occurring solid generally formed by inorganic processes with an ordered internal arrangement of atoms and chemical composition and physical properties that either are fixed or that vary within some definiterange.
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Petrography:
The branch of geology dealing with the description and systematic classification of rocks, especially by microscopic examination of thin sections. Petrography is a subfield of Petrology.
Types of rocks
1. Igneous Rocks
2. Metamorphic Rocks
3. Sedimentary Rocks
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Rock Cycle
The rock cycle is a model that describes formation, breakdown and reformation and rock as a result of sedimentary, igneous and metamorphic processes, all rocks are made up of minerals.
Rock exposed to the atmosphere are unstable and subject to weathering and erosion. Weathering and erosion breaks the rock down. This fragmented material accumulates and is buried by additional materials. Each grain of sands is still member of the class of rocks .It was formed from weathering, but a rock made up such grains fused together if sedimentary.
Sedimentary rocks can formed from the lithification (process in which sediments compact. Under pressure, expel contact fluids and gradually became solid rock) of these buried smaller fragments (clastic), the accumulation and lithification of materials generated by living organisms (Biogenic/fossils) or lithification of chemically precipitated material from a mineral bearing solution due to evaporation (Precipitate).
The rock cycle can account for everything on our planet from sand to the Earth’s types of crust. It is greatly influenced by the other elements on our planted : water and air mainly. The most exciting thing about rock cycle is that it exists on other planets
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Igneous Rocks
The term igneous comes from Latin word “ignis” meaning fire. Igneous rock is one of the three main rock types that are made from hot molten material inside the earth called magma or lava when they formed after reaching to the ground.
Igneous rocks are formed by solidification of cooled magma (molten rock). They may form with or without crystallization, either below the surface or on the surface.
This magma can be derived from partial melts of pre- existing rocks in either the earht's mantle or crust.
In general, the melting is caused by one or more of the following processes: an increase in temperature, a decrease in pressure, or a change in composition.
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# Magma
Magma is defined as hot, viscous, molten silicate melt formed in the crust or upper mantle of the Earth. Magma is the main source to produce the igneous rocks. The magma consists of major elements such as O, Si, Al, Fe, Na, K, Mg, Ti (> 99%); trace elements (Mn, Sr, Ni, Ba, Rb, U, S, Cl, F) and volatiles (fugitive, e.g.; water, carbon dioxide, sulfur. Magma when comes out on the Earth’s surface, it is pronounced as lava.
Magma may be classified into four types on the basis of amount of elements and its
emplacement.
i. Granitic/acidic/felsic magma
Acidic magma is rich in Si, Al, Na and Kand originated in the crust, e.g. granite,
rhyolite.
ii. Basaltic/basic/mafic magma
Basic magma is rich in Fe, Mg and Caand originated in upper mantle, e.g. gabbro, basalt.
iii. Intermediate magma
It contains both felsic and mafic compositions, e.g. diorite, andesite, syenite,
trachyte.
iv. Ultramafic magma
It consists of abundant Fe and Mg, originated in mantle, e.g. dunite, peridotite,
pyroxetine.
Important features of igneous rocks
• Generally hard, massive, compact with interlocking grains
• Absence of fossils
• Absence of bedding plane and foliation plane.
• Enclosing rocks are backed.
• Usually contains much feldspar etc.
Classification of Igneous rocks
There are many bases of classification of igneous rocks
a) Classification based on mode of occurrence
b) Classification based on Silica contain
c) Mineralogical classification
d) IUGS Classification (or Triangular classification)
a) Classification based on mode of occurrence
i. Intrusive igneous rocks (Plutonic rocks): These rocks are formed by the slow cooling of great volume of magma inside the earth surface of significant depth. The erosion throughout the geological time remove the overlying rocks and exposed plutonic rocks at the surface. They are normally coarse grained. Typical example: Granite.
ii. Extrusive igneous rocks (Volcanic rocks): They have formed by rapid cooling of magma at the surface of the earth (from lava), and are fine grained. Typical example: Basalt.
Hypabyssal rocks: Rocks that have solidified from magma below the surface of the earth but not deep inside it, are called Hypabyssal rocks. They are medium grained. Typical example: Dolerite
b) Classification based on Silica contain
Rock Class Amount of silica Minerals
%
Acidic >65 Quartz, orthoclase, Na-plagioclase, muscovite,
biotite (±hornblende). Example: Granite
Intermediate 55-65 Plagioclase, biotite, hornblende, quartz, orthoclase
(± augite). Example: Diorite
Basic 45-55 Ca-plagioclase, augite (±olivine, ± hornblende).
Example: Basalt
Ultrabasic < 45 Ca-plagioclase, olivine (± augite)
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c. Mineralogical classification
i. Felsic rocks: composed of light colored minerals, rocks themselves are light- colored, composed of quartz, potassium feldspar, biotite and amphibole.
Examples: Rhyolite, Granite.
ii. Mafic rocks: also rich in mafic minerals with high specific gravity. They are black, dark gray or dark green in color, and composed primarily of olivine, feldspar and pyroxene. Example: Basalt, Gabbro.
iii. Intermediate rocks are medium-gray color, and composed of amphibole and feldspar together with some pyroxene and biotite. Example: Andesites, Diorite.
iv. Ultramafic rocks: rich in ultramafic minerals like olivine, pyroxene that are dark colored and have very high specific gravity.
Example: peridotite, dunite and pyroxenite. 13
IUGS Classification (or Triangular classification)
This is initially formulated by Albert Streckeisen, and later International Union of Geological Sciences (IUGS) elaborated this so that there exist an internationally accepted comprehensive system of classification.
Steps of classification:
1) First distinguished the rocks based on grain size: Phaneritic rocks (coarse grained) are classified as Plutonic, and Aphanitic (fine grained) are classified as Volcanic.
2) Within each group of these broad categories, the rocks are named based on the basis of mineral percentages of 3 minerals: Quartz or Foid minerals, Alkali Feldspar and Plagioclase.
3) Other mafic minerals are to be discarded so that only the 3
minerals make 100%.
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Foid minerals (feldspathoids): These are group of Na and K aluminosilicates that appear when an alkali rich magma is deficient in Silica. Example: Leucite: KAlSi2O6, Nephelene (Na, K)AlSiO4.
Some of the plutonic rocks are low in silica and contain feldspathoids rather than quartz. Quartz and such minerals never found together because they are chemically incompatible and react to form feldspar.
Limitations: The rock must contain at least 10 %of Q, A, Por feldspathoids, mafic minerals discarded.
IUGS Classification of igneous rocks
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Granite
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IUGS Classification( contd.)
If rock contains small amount of mafic minerals it can be indicated by leuco (like leuco granite), with large amount of mafic minerals the prefix is mela (like mela granite).
If mafic minerals are abundant, they can be denoted in the name like hornblende biotite granite.
Ultramafic rocks (>90% mafic minerals) are classified differently by alternate methods:
1) Peridotite: rock containing 40-100 % Olivine, remainder Pyroxene
and/or hornblende.
2) Dunite: Peridotite containing 90-100 % Olivine.
Remainder mostly Pyroxene, or less common hornblende.
3) Pyroxenite: Major is pyroxene, remainder Olivine and/or hornblende.
4) Hornblendite: Major is hornblende, remainder Pyroxene and/or
Olivine.
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Texture of igneous rocks
Texture is defined as the size, shape and arrangement of the grains of crystals in arock. On the basis of texture of igneous rocks, the emplacement of magma, rate of cooling magma and composition of magma can be determined.
The different types of igneous texture are briefly explainbelow.
a) On the basis of degree of crystallization.
All of the minerals present in the rock may be distinctly crystallized and be easily recognized by unaided eye or they may be very poorly crystalized or even glassy(i.e. non crystallized):
i. Holocrystalline: The rock consists of entirely crystals(i.e. 100% crystals) (in Greek word; holo-100% and crystalline-crystal). Magma cools slowly and completely crystallizes in larger and district crystals. Plutonic rocks are examples of holocrystaline texture.
ii. Holohyaline: the rocks contain entirely glass materials(Hyaline means glassy). It is also known as glassy texture. This texture may also result when magma is cooled so quickly that minerals have no opportunity to form. For example obsidian and pumice.
iii. Hypohyaline or hypo crystalline: The rocks both crystals and glass. The volcanic
rocks such asbasalt, rhyolite and so on.
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b) On the basis ofgranularity
The texture is categorized on the basis of grain size of minerals.
i. Absolute size:
The grain size of minerals is greater than 5 mm (coarse grained), 5 to 1 mm (medium
grained), less than 1 mm (fine grained).
ii. Relative size:
a. Equigranular:- The grain of minerals have more or less same sizes.
b. Inequigranular:- The grain of the minerals have variable size.
c. Phaneritic :- The mineral grain are visible to nakedeye.
d. Aphaneratic :- Mineral grains are not visible to naked eye and needto help of
standard petrological microscope to identify the minerals.
c) On the basis of shape of crystal
i. Euhedral:- The rock contains the crystal face with well developed outline in the minerals.
ii. Subhedral:- The rock contains both well developed crystal faces and irregular outline face of minerals.
iii. Anhedral:- The minerals of rocks do not contain crystal faces and all grains are irregular outline faced crystals.
d). Mutual relation among the crystals
i. Porphyritic texture: This texture contains of large crystals (phenocrysts).
embedded in a finely crystalline or glassy groundmass in a rock.
ii. Poikilitic texture: Large crystals(phenocrysts) contain the inclusion of other minerals in arock.
iii. Ophitic texture: The rock contains the texture consisting of euhedral to subhedral crystals of Plagioclase embedded in a single pyroxene (e.g. augite)
iv. Sub-ophitic texture: The feldspar (plagioclase) crystal is partially surrounded by pyroxene in a rock.
v. Intersertial texture: small interspaces between crystal are filled with glass.
vi. Trachytic texture: The texture contains of sub-parallel alignment of plagioclase in the groundmass of lavas.
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Form of igneous rocks
The size, shape and mode of formation of igneous rock is called form. It is predominantly governed by temperature, composition, viscosity and mode of formation of magma as well as nature of rocks into which they are injected. Also, chemical and physical properties, overburden load, and structure of pre-existing rock are governing factors for different forms of igneous rocks.
Form of igneous rocks broadly classified as
A. Concordant bodies
B. Discordant Bodies
A. Concordant bodies:
The intrusion in which magma is influenced by the structural features of the rocks into which it has been injected and solidified along the planes of weakness like bedding plane, foliation plane etc. are called concordant bodies.
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i. Sills:
Sills concordant, bodies that are emplaced essentially parallel to the foliation or bedding of the country rock. High degree of mobility is required to produce this sheet like for
basaltic are more fluid than granitic ones, therefore most sills are basaltic in composition.
ii. Laccolith
They are concordant, commonly mushroom shaped intrusions that range in diameter from about 1 to 8 Km with maximum thickness in the order of 1000 m.
They are created when magma rising upward through essentially horizontal layers in the earth’s crust encounter more resistant layer, magma spreads laterally under it forming a
dome in overlying layers.
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iii. Lopoliths
• It consists of a large, lenticular, centrally sunken, generally concordant, basin or funnel shaped intrusive mass.
• The diameter range from tens to hundreds of kilometers and thickness up to thousands of meters are mafic, ultramafic and few have upper siliceous layers
iv. Phacoliths
Phacoliths are intrusive concordant bodies associated with folded rocks
• Within an anticline, they are doubly convex upward, and in trough of a syncline they are convex downward. It iss assumed that it is passive i.e. magma fills and enlarges the open or
potentially open areas that develop and 26
B. DISCORDANT BODIES
i. Dikes
Dikes tabular plutons that cut across the foliation or bedding of the country rock. They are typically emplaced into preexisting joint system and my occur singly or in swarms. Occasionally, vertical - or outward dipping ring dykes or inward dipping cone sheets may be found distributed in circular or oval pattern.
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ii. Batholiths
• They are large intrusive plutons
with steeply dipping walls.
• They are often composed of silicic range size about hundred to several thousand square kilometers, they form the core of major mountain systems in the world. Although broadly concordant to the structure, highly discordant when mapped in detail, may contain minor intrusions.
iii. Stocks or Bosses
• Stocks are smaller bodies that are likely fed from deeper level batholiths.
• Their maximum surface area is of
100 km2. 28
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Transportation of sediments and formation of sedimentary rocks by mode of river water- deposition on the continent and on the ocean floor.
Fluvial deposits
Marine deposits
Sedimentary Rocks
Transportation of sediments and formation of sedimentary rocks by mode of river water - deposition on the continent and on the ocean floor.
Fluvial deposits
Marine deposits
SEDIMENTARY ROCKS: are the secondary rocks which are
formed from the loose fragments or detrital or clastic sediments produced by weathering of older rocks.
• Almost 90% of earth crust is made up of igneous rocks.
• 75% of land surface on the earth is covered by thin layer of
sediments or sedimentary rocks.
• These sediments are transported and deposited by river water, wind or by movement of glacial ice. Transportation is either in suspension or in solution.
• When settle down on the beds of ocean, river and lakes undergo compaction/cementation for millions of years to form SEDIMENTARY ROCKS.
IMPORTANCE OF SEDIMENTARY ROCK
“Present is the key to the past”
• Helps in knowing depositional environment viz. marine (ocean deposits), fluvial (river deposits), aeolian (wind deposits), glacial, estuarine, Lacustrine (lake deposits) etc.
• Helps in knowing the provenance (i.e. source area of the sediments); change in climatic conditions i.e. in knowing and understanding old climate = paleoclimate.
Importance Features of
Sedimentary Rock
• Generally soft and stratified.
• Fossils are commonly found.
• Various sedimentary structures (eg. Mud cracks or sun cracks, ripple marks, graded bedding, cross- bedding, stratification etc.) may be present.
• Quartz, clay minerals, calcite, dolomite, feldspar etc are common minerals found in sedimentary rocks.
TYPES OF SEDIMENTARY ROCKS
• Sandstones
• Conglomerates
• Breccia
• Shale/mudstones
CLASTIC ROCKS
• formed from broken rock fragments weathered and eroded by river, glacier, wind and sea waves. These clastic sediments are found deposited on floodplains, beaches, in desert and on the sea floors.
solidify Clastic rocks
• Clastic rocks are classified on the basis of the grain size: conglomerate, sandstone, shale etc.
GRAIN SIZE
Boulder: >256mm Cobble: 64-256 mm
Pebble: 4-64 mm
Granule: 2-4mm Fine gravel
• Clastic rocks mainly comprise broken fragment of older rock – they are also know as Terrigenous rocks
Degree of roundness helps in knowing the distance of transportation
• Angular clasts- short distance transport from the source
• Rounded clasts- long distance transport
Sorting of the sediments also suggest the mode of deposition and transportation.
Long distance transport= well-rounded and well-sorted sediments,
Short distance transport = poorly sorted angular grains.
Also helps in knowing the energy conditions of the river.
DIFFERENT CATERGORIES OF CLASTIC ROCKS
• RUDACEOUS ROCKS: made up of rounded or sub- rounded Pebbles and cobbles eg. Conglomerate.
• ARENACEOUS ROCKS: made up of mainly sand eg. Sandstone. These rocks are either accumulated by wind action or deposited under water action or marine or lake environment.
• ARGILLACEOUS ROCKS: made up of clay size sediments eg. Shale, mudstones, siltstones.
IMPORTANCE
• CONGLOMERATE comprise clastic sediments like pebbles and cobbles (heterogeneous)
• If the cementation is good (voids between the clasts) = then the conglomerate will be hard and competent hence act as strong foundation, but not good rock for ground water source.
• However, if the cementation is poor = it makes the rock more porous with high porosity = act as good reserve for ground water (aquifer), but is undesirable at the site for foundation of major CE structures.
• Due to heavy seepage along the conglomerate may result in failure by sliding. Eg. Failure of St. Francis dam, US.
Cementation:
• Cementing material is usually secondary Silica (Siliceous cement), Calcium carbonate (Carbonate cement), Iron rich (ferruginous cement).
• Cement itself to some extent is the source of weakness in the sedimentary rocks
• Because cementing material and the clastic sediments are usually of different composition, leading to heterogeneity in their physical characteristics.
• Hence such rock will not behave homogeneously under stress, resulting into development of cracks or fissures which develops in cementing material.
• If the cement is Calcium Carbonate- it is undesirable, because it is susceptible to dissolve in Carbon-dioxide in water
• However, if cementation process continuous for longer span of time, cementation will become more complete, which reduce the porosity and permeability in the rock mass and increase competence.
• Shape of grains: i.e. if coarser grains are rounded or subrounded, cement material will not have firm grip=such rocks behave as incompetent rocks
Arkose (Feldspar)
Graywacke/lithic arenite
EVAPORITIC ROCKS
These rocks are formed within the a depositional basin from chemical substances dissolved in the seawater or lake water.
Halite
CaSO4.2H20
(NaCl)
CARBONATE ROCKS
• Limestone: It is a non-clastic rock formed either chemically or due to precipitation of calcite (CaCO3) from organisms usually (shell). These remains will result in formation of a limestone.
• Limestones formed by chemical precipitation are usually fine grained, whereas, in case of organic limestone the grain size vary depending upon the type of organism responsible for the formation
– Chalk: which is made up of foraminefera is very fine grained
– Fossiliferous Limestone: which is medium to coarse grained, as it is formed out of cementation of Shells.
Chalk
• used as a building stone and in the manufacture of lime, carbon dioxide, and cement.
• Massive and compact lst. Are competent to support CE-structure
• However, if it occur in huge thickness then it is not advisable, because of its typical CAVING character.
Sedimentary structures
• Bedding is most imp. Feature of a sed. Rock
• Beds are usually > 1 cm
• Laminae < 1 cm
• Orientation of bedding helps in knowing the paleo-current direction of the old rivers
GRADED BEDDING
Fine gravelly lithounit
Laminated layers of fine silt and clay Cross-stratified sst.
Paleo-flow from
right to left
Sand Dunes
Typical cross stratification in
Ripple marks
Biogenic structures
Foot prints
Mud cracks
Metamorphic rocks
When rocks are baked by heat of molten magma or squeezed by the movements of huge tectonic plates or by the pressure of overlying thick succession of rocks
They are altered or changed beyond their recognition
i.e. change in Chemical composition, texture and structure
Metamorphic rocks
Metamorphism
Is the process that occur in rocks due to the effects of
High temperature
High pressure
Chemically active fluids
Temperature
The source of temperature is either from magma or due to the depth factor.
Metamorphism usually result into change in min. comp. and texture of rocks (Ig. and Sed.) which are subjected to temp. > 1000 C and pressure > 1000’s Mpa.
Low-grade metamorphism:
Occurs at about 1000 C to 5000 C.
High-grade metamorphism: Occurs at > 5000 C
Pressure
UNIFORM PRESSURE
- increases with depth due to
increase in overburden.
- acts vertically downwards and affects the volume of both liquid & solids.
- high temperature is also associated with depth factor.
- Lithostatic pressure- due to overburden
DIRECT or Differential PRESSURE
- increases with depth upto some extent, effective in the upper part of the crust.
- acts in all direction and affects only on solids resulting into deformation of shape and change in mineral composition
- high temperature is not always
associated to depth factor.
- Stress- due to tectonic
forces
min
max
inter
Differential Stress
Uniform Stress
Granite Granite-Gneiss
STRUCTURES IN METAMORPHIC ROCKS
Foliation: when platy, lamellar or flaky minerals (eg. sheet silicate minerals the micas: biotite and muscovite, chlorite, talc, and serpentine), occurring in rock orient themselves parallel to one another (i.e. perpendicular to the direction of maximum pressure or stress).
Random orientation Of minerals
Lineation:
when prismatic or rod-like minerals (eg. Hornblende, tourmaline etc.) occurring in a rock orient themselves parallel to one another (perpendicular to direction of maxi. Pressure or stress)
SLATY CLEAVAGE
- usually formed during the early stage of Low-grade Metamorphism due to lithostatic stress.
- New sheet-structure minerals tends to be parallel to the bedding planes during metamorphism.
- however, further deep burial along the continental margin; compressional forces will cause deformation (folding).
- hence, the sheet minerals as well as foliation will no longer be parallel to the bedding planes, such type of foliation in fine grained rocks is called slaty cleavage.
Shale Slate
PHYLLITES
- usually associated with intermediate grade of metamorphism; where the mineral grains grows large in size as compare to that seen in slates
-This develops a pronounced foliation where the preferred oriented
minerals are seen.
SCHISTOSE STRUCTURE
- usually formed during intermediate and high grade metamorphism
- Grain size increases and can be seen by naked eye; grains tends to enlarge with increasing grade of metamorphism; the coarse grained sheet-structure minerals show preferred orientation
- grain size is the main difference between the slaty structure and
schistos structure.
GNEISSIC STRUCTURE
- usually associated with high-grade regional metamorphism (where differential stress prevails i.e. tectonic forces)
- where the sheet silicates and other minerals like quartz/feldspars/hornblende/pyroxene are segregated in distinct bands in the rocks- known as gneissic banding.
Classification of Metamorphic rocks based on texture/structures
SLATE
- strongly cleaved rock
-cleavage planes are developed due to orientation of fine
phyllosilcate grains eg. Muscovite, biotite, chlorite etc.
-individual grains too fine to be visible with naked eye
-overall dull appearance .
PHYLLITE
-similar to slate, but slightly coarser phyllosilicate grains
-grains can be seen in hand specimen, giving silk appearance to
cleavage surfaces
-often cleavage planes less perfectly planar than slates
SCHIST
- parallel alignment of moderately coarse grains (fabric = schistocity).
- grains are visible by eye.
- mainly phyllosilicates and other minerals such as hornblende, kyanite
etc.
GNEISS
- Coarse grained rock (grain size several millimeters) and
- Foliated (planar fabric: either schistosity or compositional layering)
- Tendency for different minerals to segregate into layers parallel to foliation (gneissic layering): typically quartz and feldspar rich layers tend to separate from micaceous layers.
Varieties:
- Orthogneiss: rocks formed from Igneous rocks.
- paragneiss: rocks formed from Sedimentary rocks - metasedimentary gneisses.
QUARTIZITE
It comprise equidimensional minerals viz. quartz and feldspars
Non foliated; show GRANULOSE STRUCTURE (saccharoidal)
Cataclastic Metamorphism
This type of metamorphism occurs mainly due to direct pressure
eg. when two bodies of rock slide past one another along a fault zone. Heat is generated by the friction of sliding along the zone, and the rocks tend to crushed and pulverized due to the sliding.
Cataclastic metamorphism is mere mechanical breakdown of rocks without any new mineral formation, however, sometime due to intense shearing few new minerals are formed.
Contact Metamorphism-
This type of metamorphism occurs locally adjacent to the igneous intrusion; with high temp. and low stress
There is little change in bulk composition of the rock
Area surrounding the intrusion (Batholith) is heated by the magma; metamorphism is restricted to a zone surrounding the intrusion, this zone is know as METAMORPHIC AUREOLE.
The rocks formed are non-foliated fine-grained rocks called as
HORNFELS.
Regional Metamorphism-
metamorphism occurs covering larger area, which is subjected to intense deformation under direct or differential stress.
Rocks formed under such environment are usually strongly foliated, such as slates, schists, and gniesses.
The differential stresses result from tectonic forces,
eg. when two continental masses collide with one another resulting into mountain building activity. Compressive stresses result in folding of the rock.
Types of Metamorphic Rocks
FOLIATED
The common foliated rocks in the order of increasing grain size are
SLATE – PHYLLITE – SCHIST – GNEISS
NON-FOLIATED
Quartzites and hornfels
Importance of Metamorphic rocks-
SLATES
Fine grained impermeable, cleavable and soft
Incompetent; cannot withstand great loads
But since they are impermeable and split easily; thin large sized slabs of uniform thickness can be extracted for roofing purpose.
Economic importance: Since they are bad conductor of electricity– used in electrical industries for switch board base
GNEISS
Gneissic rocks are rich in SILICA i.e. predominantly Quartz and
Feldspars along with garnet, pyroxene, Hornblende etc.
Non-porous and impermeable nature increases the strength of the rock
Foliated character to some extend improves workability
Load perpendicular to foliated planes gives more stronger foundation
If mineral assemblage is more or less similar to Granite (with less %
mafic minerals) then:
It is used as building stone
As aggregate for making concrete
As road metals etc.
SCHIST
Mainly composed of prismatic or platy minerals, which contributes in development of Schistose Structure. Eg. Hornblende, tourmaline, sillimanite etc (prismatic); chlorite, muscovite, biotite, talc, kyanite etc. (platy)
Cleavable nature of Schists is the main reason for their weakness;
they are incompetent.
QUARTZITE
SANDSTONE (composed of quartz/feldspars/feldspathoid minerals) when under go metamorphism result into Quartzite.
Granulose texture/structure (Granoblastic) makes them most competent rock amongst all other metamorphic rocks.
Because metamorphism of Sst. Result disappearance of cementing
material, bedding planes, fossil content etc.
Quartzites are compact, hard and strong; very less porous and less permeable than the parent Sst.
Predominance of Quartz makes the rock very hard and suitable for road metal; can be used as concrete aggregate etc.
Acts as strong foundation for any CE structure.
MARBLE
Latin word “Marmor”– Shining stone.
Calcareous metamorphic rock
Though it shows granulose structure it is not as hard as Quartzite because of its Calcareous composition; but can withstand reasonable load.
Due to its pleasant color and brilliant appearance when polished it is extensively used as building stone.
Calcite
Structural Geology
As a branch of geology, it deals with “the study of structures found on rocks”. It is also known as tectonic geology or simply tectonics.
The study of structural geology in civil engineering play important role for selection of suitable sites for all types of projects such as multistored building, dams, tunnels, etc.
Deformation
The change in geometry of the rocks that includes, translation, distortion(change in
shape), rotation and dilation(change in volume).
In translation, all of the particular path are straight, constant length, and parallel to
each other. In rotation, the particle path are curved and concentric.
When a body of rock is stressed the individual particles that make up the body are
displaced to new position.
In general rocks are found in horizontal form in initial stage of deformation and after it is formed, is subjected to number of forces. The motion initiated in a body due to stress continues until the material reaches a configuration that is an equilibrium state.
The effect of stress is strain or deformation.
Strains are defined as the change in relative position of particles in a body at two different times. The body must be deformed or distorted in shape rather just moved as a rigid body.
Within the Earth, rocks are continually being subjected to force that tend to bend
them, twist them, or fracture them.
When rocks bend, twist of fracture then they deform (change in shape or size). The
force that cause deformation of rocks are referred to as stresses.
Stress
Stress is a force per unit area. One type of stress that in uniform in all direction, called pressure. A uniform stress is a stress wherein the force at equally from all direction. In the earth the pressure due to the weight of overlying rocks is a uniform stress, and is sometimes referred to as confining stress.
If stress is not equal from all directions then the stress is a differential
stress. Three kinds of differential stress occur. Compressive stress, which squeezes rock.
Tensional stress(Extensional stress), which stretches rock. Shear stress, which result in slippage and translation.
Stage of deformation When a rock is subjected to increasing stress it passes through three successive stages of deformation.
a. Elastic Deformation: where
in the stress is reversibale.
b. Ductile Deformation: where
in the strain is irreversible.
c. Fracture: Irreversible strain where in the material breaks.
Types of deformation
Elastic Deformation: In this deformation there is no permanent
distortion or there is recoverable deformation.
Anelastic deformation: In this deformation strain is recoverable but
takes a certain time.
Plastic deformation: In this deformation there is a large permanent deformation and strain is constantly achieved and independently of stress.
Brittle deformation: In this deformation breaking of material takes
place before plastic deformation.
Ductile Deformation: At higher P and T condition most of the rock show ductile behavior, in this deform action, rocks deform plastically but there is not constant strain as in plastic deformation. Most of the rock structures are fold, fault etc. are the result of ductile deformation of the rocks in the greater depth of the earth.
Fracture: irreversible strain where in the material break.
Factors(Reasons) of deformation
Following factors play vital role deformation of rocks.
Temperature:- At high temperature molecules and their bonds can stretch and move, thus materials will behave in more ductile manner. At low temperature, materials are brittle.
Confining Pressure:- At high confining pressure materials are less likely to fracture because the pressure of the surrounding tends to hinder the formation of fractures. At low confining stress, material will be brittle and tend to fracture sooner.
Strain rate:- At high strain rates material tends to fracture. At low strain rates more time is available for individual atoms to move and therefore ductile behavior is favored.
Composition:- Some minerals, like quartz, olivine, and feldspars are very brittle. Others, like clay minerals, micas, and calcite are more ductile. This is due to the chemical bond type that hold them together. Thus, the mineralogical composition of the rock will be a factor in presence or absence of water. Water appears to weaken the chemical bonds and forms films around minerals grains along which slippage can take place. Thus wet rock tends to behave in ductile manner, while dry rocks to behave in brittle manner.
Attitude of beds
Sedimentary rocks are found in layers after the compaction, consolidation and lithification of sediments that are deposited in large depositional basins like sea, lake or rivers. These layers are called beds and the planes generated in this way are called bedding planes. The metamorphic rocks originated from sedimentary rocks can preserve the layering structure of the sedimentary rocks and are called foliation planes. Since the basins are flat surface, at the time of formation, the sedimentary rocks are horizontal. However due to course of time, these horizontal beds got tilted and undergoes deformation as a result of tectonic forces acting in the earth. The inclination direction and the degree by which it is tilted depend on the direction and magnitude of operating forces and the nature of rock types. In order to know the distribution of particular rock layers, their stability and their physical as well as engineering properties, the orientation of rock beds are necessary to study.
Such orientation of bedding planes and the foliation planes are popurly known
as attitude of rock beds. Attitude covers two terms namely strike and dip.
Strike
Strike is the horizontal direction of slope. More precisely, strike may be defined as the direction of a line formed by the intersection of the bedding (or foliation) with a horizontal plane. In simple term, strike is the extension of a bed or it is perpendicular to the dip direction.
Dip
literature meaning of dip is slope or inclination but in geology it has two component namely dip amount and dip direction.
i. Dip amount(angle):-
It is the actual angle between an inclined plane and an imaginary plane, and is measured perpendicular to strike. Dip amount is the angle of inclination of the plane with horizontal, and therefore it can vary from o° to 90°. If the bed is horizontal, dip angle is 0° and if it is vertical dip angle is 90°.
ii. Dip direction:
Dip direction is just the direction toward which the plane is inclined.
Way of writing attitude
Attitude= strike/dip amount/dip direction
Outcrops
The exposed part of the rock in the field is called outcrops. The attitude of beds are measured on outcrop. In cut section by river, landslides or by artificial activities like road construction, outcrops may expose. In outcrops also measured the thickness of bedding, joints, micro- folding, faulting and associated features etc. on the basis of outcrop study; geological maps are prepared, fossils are collected, engineering stability are determined.
Geological Structures
1. Primary structures
2. Secondary structures
1. Primary Structures
Those which develop at the time of formation of the formation of the rocks (e.g.
sedimentary structures, some volcanic structures.
Which help to follow the environmental conditions of deposition.
Such sedimentary structures help to identify the water depth, current velocity and
direction of current.
Younger sequence is also determined by the help of sedimentary
structures.
A. Stratification or Bedding
The layered features is a typical structure of rocks and is called stratification or bedding.
Surface separating layers of sedimentary rocks. Each bedding plane marks termination of one deposit and beginning of another of different character, such as surface separating a sand bed from a shale layer. Rock tends to separate or break readily along bedding planes.
i. Rhythmic Bedding
Consists of alternating parallel layers having different properties.
Evidence of seasonal variation of sedimentary source.
ii. Cross-bedding
Cross-bedding is a feature that occurs at various scales, and is observed in conglomerates and sandstones. It reflects the transportation of gravels and sand by current that flow over the sediment surface (e.g. in a river channel). Sand in river channel or coastal environments.
iii. Gradded Bedding
Deposition of coarse to fine materials from bottom to top and forming a single layer is called gradded bedding.
It is formed when current velocity decrease and the layer or denser particles are
deposited first, followed by the smaller particles.
B. Surface features.
a. Ripple marks
Ripples are wave like, triangular, small structure formed by the sediments transported by water or wind current.
b. Mud cracks
• When unconsolidated sediments dries in contact, as a result typically breaks into polygonal shaped sediments separated by downward pointed cracks.
Most of these structures are observed in dried mud
c. Rain prints
• Rain drops form small rimmed
,
depression through
impact on the soft exposed surface of fine grained sediments.
2. Secondary Structures
Which are those that develop in rocks after their formation as a result of their subjection to external forces.
Folds
Foliations and lineations
Boudinages
Crenulation cleavage
Joints
faults
Folds
The bending of rock-strata due to compressional forces acting tangentially or horizontally towards a common point or plane from opposite direction is known as folding. It results in the crumbling of strata, forming wavy undulation on the surface of the earth which are known as folds.
Parts of fold
The following terms used to describe fold parts and orientation.
1. Axial plane- Imaginary plane that intersects the crest or trough of a fold to divide it
into 2 equal portions
2. Axis- the line formed by the intersection of the axial plane and bedding plane.
3. Limbs -the sides or legs of a fold
4. Plunge- The dip of the fold axis
5. Symmetrical folds- mirror image on either side of the axial plane.
6. Asymmetrical folds – one limb is steeper than the other.
7. Overturned folds- one limb has been titled beyond the vertical, but both limbs dip in the same direction.
8. Recumbent fold-axial plane is horizontal, so fold lies on its side .
9. Isoclinal fold- fold limbs are
parallel to one another
Classification of fold
1. On the basis of the shape of the fold and the relative age of the rocks.
2. On the basis of geographic orientation of axial surface and hinge line.
3. On the basis of mode of occurrence.
4. On the basis of behavior with depth.
5. On the basis of degree of compression.
6. On the basis of inter limbs angle.
On the basis of the shape of the fold and the relative age of the rocks.
On the basis of shape of fold and the relative age, folds are classified into:
a. Anticline fold
it is generally convex upward, the two limbs dip away from each other or in same direction at same or different angles. The older rocks are found in the core.
b. Syncline fold
It is generally convex downward, the two limbs dip towards each other and
the younger rocks are found in the core.
If the anticline or syncline folds got overturned, they can give rise to
synformal anticline and antiformal syncline respectively.
2. On the basis of geographic orientation of axial surface and hinge line.
A. Based on relation of axial plane and hinge line.
Following table shows classification of fold based on axial plane and hinge
line (after Turner and Weiss, 1963).
B. Symmetrical folds
In this fold the axial plane(A.P) is essentially vertical and the limbs dip equally through in opposite direction. Asymmetrical folds are those in which A.P is inclined the limbs dipping unequally.
C. Overturned Folds
In which the A.P is inclined and both the limbs dip at same direction usually at
different angles.
3. On the basis of mode of occurrence.
a. Anticlinorium
these are exceptionally large sized fold running several kilometers across and the trend of fold is anticlinal but limbs may be locally warped up into numerous small such fold of different types.
b. Synclinorium
These are just reverse of an anticlinorium and is defined as a large scale fold with a
synclinal outline, the limbs being themselves thrown into numerous minor undulation.
c. Dome and Basin
Domes are the anticlinal arches in which beds dip away in all directions from a common center. Basins are the reverse of domes and are characterized by beds dipping in from all directions.
4. On the basis of behavior with depth.
a. Similar folds
The fold in which the degree of folding is observed or assumed to be similar for indefinite depths are grouped as similar folds. The axial regions in such types are thicker than the limbs.
b. Parallel folds
It is also called concentric folds and are characterized by an equal thickness of the beds throughout the folded sequence. This feature results in a change in the shape of the surface and a corresponding change in the form of fold both in an upwards and downwards.
c. Drag folds
Drag folds are minor folds developed within the body of incompetent beds surrounded by competent beds during the process of major folding or faulting, generally when the competent bed slide away through incompetent beds.
5. On the basis of degree of compression.
a. Open fold
if the beds are slightly compressed during the act of folding, there will be no variation in the thickness of the constituent beds. Such folds are termed as open folds.
b. Closed fold
If the beds are severely compressed and cause the beds to thin out at the limbs and
thicken at the crests and troughs, the resulting folds are termed closed folds.
6. On the basis of inter-limbs angle
Classification of fold based on inter limbs angle (Fleuty, 1964) are
as follows
a. Isoclinal fold of recumbent fold: Folds with parallel limbs, dipping in the same general direction with equal angle is called isoclinal fold.
b. Tight Fold: Folds with less than 30° inter-limb angle.
c. Close fold: Folds with 30-70° inter-limb angle.
d. Open fold: Folds with 70-120° inter-limb angle.
e. Gentle fold: Folds with 120-180° inter-limb angle.
Recumbent fold
• AP horizontal
• In large scale recumbent fold, the strata in the normal limb are usually thicker than the corresponding beds in overturned limbs.
• Inner part of fold: core; Outer part of fold: Shell
Engineering significance of fold
It has been observed that the folded rocks are always under a considerable strain, and the same is released whenever the folds are disturbed by some external force of whenever excavation is done through them.
This release of energy may damage the site in many ways, depending upon the nature and intensity of the deformational stresses as well as nature of the rocks.
Thus the major project like a tunnel, a dam, a highway etc. a site which is highly folded should be avoided because the engineer may have to face much troubles sooner or later.
B. lineation and Foliation
Lineation are linear structural features within rocks. Lineation is the result of the parallelism of some directional property in the rock. Stretching lineation record primarily the vectors of greatest stretch, which is perpendicular to the principle plane of shortening.
During Metamorphism, the rock mass undergoes for elongations and shortenings.
As a result, new platy minerals will show sub parallel arrangement. Such structures
are called foliation.
Any type of planar fabric in rock, including bedding, cleavage, schistosity, foliations are penetrative (occurs through) in samples at 10’s of cm in scale. Thus faults are not foliation, nor are fractures and joints because the later are simply fractures and not related to internal structure of rocks.
C. Boudinage
Flattening of strong layers surrounded by week layers may cause
strong layers to “neck” and form boudins.
D. Crenulation Cleavage
Cleavage describe the tendency of rocks to break along preferred planes of weakness, caused by the development of planar fabric as a result of deformation.
In crenulation cleavage the fabric is dominated by the micro-folding of a pre-existing planar fabric.
E. Joints
A joint is a fracture in a rock in which there is no relative displacement between the sides. Joints are relatively smooth fracture; they are present in most consolidated rocks of igneous, metamorphic and sedimentary origin.
Terminology
1. Joint set: it is defined as a group of joints of common origin.
2. Joint system: The whole assemblage of joints present in an exposure or map area is called joint system.
3. Open joint: These are those joints in which the blocks are separated or ‘open’ for small widths in direction at the at the negative angle to the fracture surface.
3. Closed joints: Those joints in which there is no separation of open structure.
4. Continuous joints: If the joints are extended for considerable depths.
5. Discontinuous joint: If the joints are disappeared at short depth.
Causes of joints
Joints may form as a result of either diastrophism (tension) or contraction. Most joints are tight fractures initially. But because of weathering (oxidation, hydration, carbonation etc.) the joint may be enlarge into an open fissures.
Classification of joint
Joints may be classified either geometrically or genetically. A geometrical classification is strictly descriptive and comparatively easy to apply but it does not indicate the origin of joints. In the geometrical classification, the the joints may be classified on the basis of their attitude relative to the bedding.
1. Geometrical classification of joint
i. Strike Joints
These joints are those whose strikes are parallel to the strike of the bedding of a sedimentary rock, the schistosity of schist, the gneissic structure of gneiss or foliation plane of phyllite, slate etc.
ii. Dip Joints
These joints are those whose strikes are parallel or essentially parallel to the dip direction of bedding, foliation, schistosity or gneissic structure.
iii. Oblique or Diagonal Joints
The joints are those whose strike direction lies between the strike and direction
of dip of the associated rocks.
iv. Bedding Joints
2. Genetic Classification of Joints
i. Sheet Joints
They may originate due to unloading of the rock mass. The cover is removed through the process of erosion. Such joints are specially common in plutonic igneous intrusions such as granite.
ii. Shear joints
These are also known as tectonic joints. They are formed due to compression in a
rock body. They originate as a direct result of folding or thrusting in rocks.
iii. Tensional Joints
These are also known as shrinkage joints. In igneous rocks, they are produced as a result of contraction due to cooling. In sedimentary rocks tensional joints may develop due to tension caused by compaction or consolidation. Tensional joints may be also be due to deformation.
Importance in joint study in civil Engineering
Knowledge of joints is important in many kinds of geological studies as well as civil
engineering site selection.
Quarry operations are generally influenced by the joints.
The orientation and concentration of joints is very significant in engineering
projects.
Closely spaced horizontal joints are great concern in tunneling.
A large joint dipping into a highway cut is the site of potential landslide.
Wells drill in granites for water supply will be more productive in highly jointed rocks than in less jointed rocks.
Joints are the major causes of instability of the rock masses in the hilly regions.
The selection of sites for dams and reservoir and alignment for highway and tunnels through rocks requires very detail investigation of joints for arriving at safe and economic designs.
Joints are always to be considered as a source of weakness of rock and as pathway for the leakage of water through the rocks. Both these properties of joints destroy the inherent soundness of the rock to a great extent. If the roof or side rocks, in the case of tunnels are much fracture, slippage of rocks occurs along these fractures and leakage of water may become major troubles.
Treatment of joints
Treatment of joints will differ in different projects.
The characteristics of the joints in terms of their type, frequency, intensity, pattern of distribution and their extent highly influence the stability of area.
Therefore treatment is highly recommended before or during the construction of infrastructure. It involves grouting with a suitable grout material for increasing the strength of rock.
It also reduces the permeability of rock material.
F. Faults
A fault is a rupture (fracture) in rocks along which there has been a relative displacement of the two sides parallel to fracture plane. Fault is result of brittle deformation due to tensional or compressional forces.
The displacement may vary from a few centimeters to many kilometers depending upon the nature and magnitude of the stress and the resistance offered by the rocks.
Parts of fault
1. Fault zone: It is a tabular region containing many parallel or
anatomizing faults.
2. A share zone: This is a zone across which blocks of rock have been displaced in a fault like manner, but without prominent development of visible faults, are the regions of ductile deformation rather than brittle deformation as in fault zone.
3. Hanging wall: The rock immediately above any non-vertical fault is
referred as the hanging wall.
4. Foot Wall: The rock immediately below any non- vertical fault is referred as the footwall.
5. Net-slip: the displacement vector connecting originally continuous points in hanging wall and foot wall is called the net slip as measured along the fault plane.
6. Strike slip: It is defined as the net slip parallel to the strike of fault.
7. Dip slip: this is the net slip
parallel to the dip fault.
8. Dip : Fault plane may be vertical, inclined or even horizontal. The dip of the fault is its inclination with the horizontal.
Classification of fault
1. On the basis of net slip
i. Strike slip fault:- The fault in which the net slip is parallel to the strike of the fault.
ii. Dip slip fault:- The fault in which the net slip is parallel to the dip of the fault. Diagonal or oblique fault:- The fault in which the net slip is the net slip is diagonally up or down the fault plane.
2. On the basis of geometry
i. Normal fault
It is one in which the hanging wall goes down relative to the foot wall
ii. Reverse fault
It is one in which hanging wall appears to have gone up relative to the footwall.
iii. Strike slip fault
When the movement is parallel to the strike of fault plane such faults are called strike slip fault.
iv. Vertical faults
Faults in which the fault plane is vertical and the resulting movements of
block is also in vertical direction are termed as vertical faults.
3. Based on genetic classification
i. Reverse fault:
It is fault in which hanging wall has gone up and dips more than 45°.
ii. Thrust fault
It is a fault in which the hanging wall has gone up and dips less than 45° to 10°.
iii. Over thrust fault
It is fault in which the hanging wall has gone up and dips less than 10°. In this
case net slip is larger than in other faults.
iv. Detachment fault
It is used for low angle normal fault.
4. On the basis of attitude of fault relative to attitude of adjacent beds
i. Parallel faults
A series of faults that have same strike and dip.
ii. Enechelon fault:
These are relatively short faults which overlaps each other.
iii. Peripheral faults: Faults showing curved pattern.
iv. Radial Faults: Belongs to a system of faults that radiate out from a single point.
Criteria or evidence of Faulting ( Field identification of Faults)
Sometimes, the faults are clearly visible in the field, when the two blocks are visible along with the displacement of one block with respect to the other. In certain cases, sufficient data has collected in the field to know the exact nature, type of the fault. The criteria for recognition of fault may be considered under the following headings.
i. Discontinuity of structure
If strata suddenly end against different beds, a fault may be present.
ii. Repetition or omission of strata
The outcrop of a bed may be repeated in cyclic order or it may disappear altogether .
Such repetition or omission of beds often establishes a fault.
iii. Features characteristics of fault planes
a) Slickensides: The movement of one wall against another result in polishing and grooving of fault surfaces. These grooves are called “slickensides”. These are useful in knowing the direction of the latest movement on the fault surface.
b) Fault breccia and Gouge: Along some faults the rocks are found highly fractured or even crushed to angular fragments. Angular fragments embedded in a matrix of fines are “Fault Breccia”. Some of the rocks along a fault may be ground to fine clay like powder called the “Gouge”.
iv. Physiographical data
Like fault scarp, fault line, offset ridges, fault control of streams, lines of pond, springs
or water seeking plants.
Engineering significance of faults
Faults are important for a civil engineer in that these mark the sites where dislocation of the ground has occurred in the past and such dislocation can not be entirely ruled out future.
Faults cause very much shearing and crushing of the rocks located along or near the fault surfaces and zones. These rocks become weak and unstable on the one hand and porous and permeable on the other hand.
Once the fault zones become lubricated with water, they become potential areas for further slips and slides. They may create critical conditions if they happen to occur within the foundation or abutment zones of dams and reservoirs or in the roof and wall of the tunnels.
The products of fault like breccia and gouge create additional problem. The site for any major civil engineering project should be located as possible as away from an active fault and never on active faults.
Reactivation of faults generate seismic waves causing structural
damages.
Therefore engineering geologist must mention the presence of faults
and possible ways of controlling the hazards in the report.
Unconformity
An unconformity is defined as a surface of erosion or non-deposition occurring within a sequence of rocks. It indicates a gap or an interval of time in the geological history of the area during which the normal process of deposition was interrupted. It is structural features in the sense that rock formation lying above and below it generally represent different conditions of formation.
Formation of unconformity
It follows through three processes such as erosion, deposition and tectonic
activities. There are three stages are follows.
1. The formation of older rocks.
2. Upliftment and surficial erosion of the older rock.
3. Again the formation of younger succession of beds after long time
interval above a surface of erosion.
Types of unconformity
1. Disconformity
It is that type of unconformity in which beds lying below and above the surface of erosion are almost parallel. No tilting or folding of lower strata is indicated.
2. Angular unconformity
This is characterized by different inclination above and below the surface. The lower beds, which are older, may be steeply inclined or even folded and faulted. The upper sequence represents the younger rocks, which are gently inclined or horizontal. The surface separating the two sequence is angular unconformity.
3. Nonconformity
It is the term used for uniformity in a sequence of rocks composed of plutonic igneous rocks (like Granite) as older or underlying rocks and sedimentary or volcanic rock as the overlying younger rocks.
4. Local unconformity
In this case unconformity is traceable only in small area.
5. Regional unconformity
In this case unconformity is extended over a wide region.
Recognition in the field
A. Angular relations.
B. Basal conglomerate: when a layer of conglomerate signifying shallow water condition is distinctly traced between some formation, as unconformity at the base of conglomerate is indicated.
C. Residual Soil : The presence of a layer of residual soil (a product of weathering ) within a rock sequence of another reliable indication of unconformity
D. Miscellaneous evidence : The contrasting behavior of rocks on either side of a particular contact surface in terms of indurations, degree of metamorphism, intensity of folding etc. will confirm the
Penecontemporaneous Structure
Penecontemporaneous deformation structures comprise disturbed, distorted, or deformed sedimentary layers produced by inorganic agencies.
These features have been formed at the time of or very shortly after deposition of sediment, but in any case, before the consolidation of sediment.
Generally, such deformation features are of local character, being primarily confined to a single bed within undeformed beds.
(in a state of complete confusion and disorder)
Plane of discontinuities in rock masses.
Discontinuities are the plane of weakness that marks the change in physical or chemical characteristics in rock materials. The discontinuities are bedding plane, foliation plane, number of joints sets, faults, unconformities etc.
Characteristics of discontinuities
(i) Orientation
The orientation ( or attitude) of discontinuities on the rock mass play important role in slope stability. The rock slope failures that occurs in road cuts and in nature slopes are no less important from the engineering stand point. The orientation of multiple discontinuities are of major concern in infrastructure development.
(ii) Spacing
The spacing of discontinuities affects the rock mass strength or quality. Even the strongest rock is reduced to one of the little strength when closely spaced discontinuities are encountered. Conversely, where the spacing is great, the strength of the rock mass increases.
(iii) Continuity
The discontinuity may continuous throughout the block or it may terminate. The continuity (or length) of the discontinuities are measured on the exposed rock surface. But it may lead to the misinterpretation because only limited portion of rocks are exposed in the earth surface; the discontinuity may continue or terminate beneath the earth surface.
(iv) surface characteristics (waviness and roughness)
Waviness of discontinuities means the undulating surface which results in variations in orientation or attitude along the given discontinuities . Waviness has greater influence on rock mass strength. The roughness of the surface , which provides friction between two adjacent blocks.
ROCK MASS
Rock is involved in many civil engineering projects. The international Association of Engineering Geology (IAEG) provides the rock names and geologic characteristics for most engineering applications. In engineering requirement a more generic subdividing into two groups. These are intact rock and rock mass.
Intact rock:- It is the term applied to tock containing no discontinuities such as
joint or bedding.
Rock mass:- It is the mass of rock interrupted by discontinuities, with each
contstitute discrete block having intact rock properties.
Rock mass classification systems are developed to obtain quantities values from rock. Some rock mass classification have been developed and are of primary value only for a specific purpose, some of the rock mass classifications are described below.
Engineering Rocks
Intact rock
Rock mass: Rock mass is described with the
An intact specimen is described as characteristics of discontinuities
• Rock name
• Mineralogy
• Texture
• Degree and kind of cementation
• Weathering
• Orientation
• Spacing
• continuity
• surface characteristics
• separation of discontinuity surfaces
• thickness and nature of filling material
• seepage condition etc
Rock mass classification :
During the feasibility and preliminary design stages of a project when very little detailed information on the rocks mass, its stress and hydrologic characteristics is available, the use of a rocks mass classification scheme can be of considerable benefit
Name of classification
Authors (first version) Country of
Origin
Application
Rock load theory Terzaghi(1946) USA Tunnel with steel support.
Stand up time Lauffer (1958) Austria Tunneling
RQD Deere et al. (1967) USA core logging tunneling
RSR concept Wickham et al.(1972) USA tunnel with steel support
RMR system Bieniawski (1989) South Africa tunnel, mines foundation
Q-system Barton et al. (1974) Norway tunnel, large chamber
Mining RMR Laubscher (1977) NA Mining
Slope Mass Rating Romana (1995) Spain Slopes
Geological Strength Index, GSI Hoek et al. (1995) NA mines and tunnel
Rock Mass Index, RMI Palmstrom (1995) Norway rock engineering
Tunneling Quality, Q Stillborg (1994) NA tunnel, mining
1. Terzaghi's rock mass classification
The earliest reference to the use of rock mass classification for the design of tunnel support is in a paper by Terzaghi (1946) in which the rock loads, carried by steel sets, are estimated on the basis of a de- scriptive classification. While no useful purpose would be served by including details of Terzaghi's classification in this discussion on the design of support for underground hard rock mines, it is interesting to examine the rock mass descriptions included in his original paper, because he draws attention to those characteristics that dominate rock mass behaviour, particularly in situations where gravity constitutes the dominant driving force.
Terzaghi's descriptions
1. Intact rock contains neither joints nor hair cracks. Hence, if it breaks, it breaks across sound rock. On account of the injury to the rock due to blasting, spalls may drop off the roof several hours or days after blasting. This is known as a spalling condition. Hard, intact rock may also be encountered in the popping condition involving the spontaneous and violent detachment of rock slabs from the sides or roof.
2. Stratified rock consists of individual strata with little or no resistance against separation along the boundaries between the strata. The strata may or may not be weakened by transverse joints. In such rock the spalling condition is quite common.
3. Moderately jointed rock contains joints and hair cracks, but the blocks between joints are locally grown together or so intimately interlocked that vertical walls do not require lateral support. In rocks of this type, both spalling and popping conditions may be encountered.
4. Blocky and seamy rock consists of chemically intact or almost intact rock fragments which are entirely separated from each other and imperfectly interlocked. In such rock, vertical walls may require lateral support.
5. Crushed but chemically intact rock has the character of crusher run. If most or all of the fragments are as small as fine sand grains and no recementation has taken place, crushed rock below the water table exhibits the properties of a water-bearing sand.
6. Squeezing rock slowly advances into the tunnel without perceptible volume increase. A prerequisite for squeeze is a high percentage of microscopic and sub-microscopic particles of mica- ceous minerals or clay minerals with a low swelling capacity.
7. Swelling rock advances into the tunnel chiefly on account of expansion. The capacity to swell seems to be limited to those rocks that contain clay minerals such as montmorillonite, with a high swelling capacity.
Rock quality designation (RQD)
The rock quality designation index (RQD) was developed by Deere (Deere et.al.1967) to provide a quantitative estimate for rock mass quality from drill core logs.
RQD is defined as the percentages of intact core pieces longer than 10 cm (4 inches) in the total length of the core. The core should be at least
5.47cm or 2.15 inches in diameter and should be drilled with double tube core barrel
Requirements:-
• Length of core longer than 10 cm or 4 inches.
• Diameter of core at least 5.47 cm or 2.15 inches.
• Drill with double –tube core barrel.
The correct procedures for measurement of the length of core pieces and the calculation of RQD are summarized below figure.
At section A, the length of the core is zero because there is no core recovery.
At section B, there are two pieces and one is smaller then 10 cm in length but the total length of the two pieces is considered because of it is not a natural break. The identification of the natural break and artificial break it is must be identified. The small change in the length the change the value of RQD and which finally change the design of support requirement .
The natural break and the drilling break can be identified one the basis of break and pattern, weathering condition of newly brakes surface and the matching of the two opposite newly broken surface. Usually the drilling break has abnormal breaking pattern. The surface of natural break may contain weathering color of stain whereas the artificial break do not . The newly broken surface of opposite side exactly fit to each other.
At section D, the length of the core pieces is again zero, because all the core
pieces are smaller than 10 cm.
At other sections C, D, F the core longer than 10 cm in length and 5.47 cm in diameter and used for the RQD calculation
3. Parameter c, effect of groundwater inflow and Joint condition on the basis of
a. Overall rock mass quality on the basis of A and B Combined.
b. Joint condition (Good, Fair, Poor).
c. amount of water inflow ( in Gallons per minute per 1000 feet of tunnel.
Rock Mass Rating (RMR) or Geomechanics classification Bieniwski,1979 developed the rock mass rating system and modified in 1889(Bineiwski) for the classification of rock mass.
The following six parameters are used to classify a rock mass using the RMR system.
1. Uniaxial compressive strength of rock material.
2. Rock Quality Designation (RQD).
3. Spacing of discontinuities.
4. Condition of discontinuities.
5. Groundwater conditions.
6. Orientation of discontinuities.
In applying this classification system, the rock mass is divided into a number of structural regions and each region is classified separately. The boundaries of the structural regions usually coincide with a major structural feature such as a fault or with a change in rock type. In some cases, significant changes in discontinuity spacing or characteristics, within the same rock type, may necessitate the division of the rock mass into a number of small structural regions.
5. Rock Tunneling Quality(Q)
On the basis of an evaluation of a large number of case histories of underground excavations, Barton et al. (1974), of the Norwegian Geotechnical Institute proposed a Tunneling Quality Index (Q) for the determination of rock mass characteristics and tunnel support requirements. The numerical value of the index Q varies on a logarithmic scale from 0.001 to a maximum of 1,000, and is defined by:
In explaining the meaning of the parameters used to determine the value of Q, Barton et
al (1974) offer the following comments:
The first quotient (RQD/Jn), representing the structure of the rock mass, is a crude measure of the block or particle size. Probably the largest blocks should be several times this size and the smallest fragments less than half the size. (Clay particles are of course excluded).
The second quotient (Jr/Ja) represents the roughness and frictional characteristics of the joint walls or filling materials. This quotient is weighted in favour of rough, unaltered joints in direct contact. When rock joints have thin clay mineral coatings and fillings, the strength is reduced significantly. Nevertheless, rock wall contact after small shear displacements have occurred may be a very important factor for preserving the excavation from ultimate failure.
The third quotient (Jw/SRF) consists of two stress parameters. SRF is a measure of:
1) Loosening load in the case of an excavation through shear zones and clay bearing rock,
2) Rock stress in compe- tent rock, and
3) Squeezing loads in plastic incompetent rocks. It can be regarded as a total stress parameter. The parameter Jw is a measure of water pressure, which has an adverse effect on the shear strength of joints due to a reduction in effective normal stress. Water may, in addition, cause softening and possible out-wash in the case of clay-filled joints.
Assignment
1. Define fold and the different parts of fold. Discuses the importance of
fold while construction of any civil engineering structure.
2. How is the fault identify in the field? Explain the effect of fault that need
to be considered while construction of civil engineering structure.
3. What are joints and fractures? Discuses the various joints. Add a note
about its importance in civil engineering investigation.
4. What is disconformity? Describe the various parameters of discontinuities
in rocks.
5. What is rock mass classification? Describe the different system of rock
mass classification.
6. Write Short note a.Unconformity b.Plunging Fold
Q.N.7 Differentiate between
a. Joint and bedding plane
b. Syncline and anticline.
c. Rock mass and intact rock
Joint
• A joint is a break (Fracture) of natural origin in the continuity of either a layer or body of rock that lacks any visible or measurable movement parallel to the surface (plane) of the fracture.
• A joint set is family of parallel, evenly spaced joints that can be identified through mapping and analysis of the orientations, spacing, and physical properties.
• A joint system consists of two or more interlocking joint sets.
Causes of jointing in geological strata
• Joints result from brittle fracture of a rock body.
• As the result of tensile stresses.
• The rise of pore fluid pressure as the result of either external compression or fluid injection.
• The result of internal stresses induced by the shrinkage caused by the cooling.
Classification of joint
• Geometric classification my be classified on the basis of their attitude relative to the bedding or some similar structure in the rocks.
• Strike joint: Strike joints are those that strike parallel to the strike of the bedding or foliation plane.
• Dip joint: Dip joints are those that strike parallel to the direction in which the bedding or other similar structure dips.
• Diagonal joint: Those joint striking in a direction that lies between the strike and direction of dip of the associated rocks.
• Bedding joint: The joints are parallel to the bedding of the associated rocks.
Genetic classification
• This classification is depends upon the genesis of joint.
• Tensional joint: This is shrinkage joint.
• Shear joint: This joint is developed from the sliding history of geological strata.
• Tectonic joint: Joints developed from tectonic activities and categorized according to attitude of beds. Generally tectonic joints are,
Strike set: Longitudinal joints parallel to the fold axis.
Dip set: Joints perpendicular to the longitudinal joint.
Diagonal set: Jointing less than 45° to the direction of tectonic axis.
Significance of joints
• To understand the nature and sequence of deformation in an area.
• Joints commonly controls the drainage pattern of the area.
• May act as aquifers or reservoir in rocks for oil or natural gas or ground water.
• Help to find out the brittle deformation in an area of construction (dams, bridges, road, building and power plants).
• In mineral exploration, to find out the trend and type of fractures and joints that host mineralization which will help in exploration.
• Joints plays great role in soil formation through chemical (decomposition), physical (disintegration) and biological weathering.
• It lowers the stability of land.
Contd.
• Joints and fractures serve as the pumping system for ground water flow in many area and they are the only routes by which ground water can move through igneous and metamorphic rocks.
• Joints and fractures are important in porosity and permeability of rocks for water supplies and hydrocarbon reservoirs.
• Joints orientations in road cuts greatly affect both construction and maintenance. Those oriented parallel to or dip into a highway cut become hazardous during construction and later because they provide potential movement surfaces.
Rock Slope Engineering and Earth Processes.
Running Water as a geologic agent (The work of river)
Surface water flow, both over the slopes of the land and in stream channels, collectively designated as runoff. Runoff may be derived both from:
1. Direct surface accumulation of precipitation that does not infiltrate, and
2. From ground water discharge
Types of rivers
There are mainly three types of rivers
a. Straight river
b. Meandering river
c. Braided rivers.
a. Straight river
• Follow a straight path.
• The topography of the area is
characterized by steep relief.
• The gradient of the river path is also high
causing the flow velocity of water.
• Since the energy level of such river is high, erosion rate is intensely higher than the deposition of sediments.
• Deep scouring along the river path is
higher than the side cutting.
• Dominantly occurred in the higher
Himalaya region.
b. Meandering River
• Follow a zigzag path.
• The topography of the area is characterized by moderate relief.
• The gradient of the river path is so moderate causing the river strikes in one end and return to other direction making the path zigzag.
• The river is widened and flow with lower
velocity than that of the straight river.
• Since the energy level of such river is high, erosional rate is intensely higher than the deposition of sediments.
• The side cutting by the river is higher than
the deep scouring along the river path.
• In the striking bank, the side cutting is higher with higher erosional rate and opposite to strike bank is a depositional bank where depositional of sediments take place.
• Due to this system channel shifting is prominent is such type of river system.
• Meandering river are dominantly occurred in the midlands and lesser Himalayan
c. Braided River
• In this types of river, a single river path is diverted into several paths and may converge to single later.
• The topography of the area is characterized by low relief.
• The gradient of the river path is low and the river area is widened and flow with low velocity.
• Since the energy level of such river is low, the deposition rate of sediments is intensely higher than the erosional rate. Thick succession along the river path and river diverts to other sub paths for flow down.
Many channel bars occur along the river path. Due to this phenomenon, the channel shifting is prominent to such type of river system. Braided rivers are dominantly occurred in the Terai region.
Work of stream
Streams perform three closely interrelated forms of geologic work:
1. Erosion
2. Transportation
3. Deposition
These phases of geologic work can not be separated one from the other, because where erosion occurs, there must be at least some transportation and eventually the transported particles must come to rest.
Erosional landforms by Rivers
V- shaped Valley
- Formed by erosion from a river/stream.
- shape of the valley is “V” shaped.
- Vertical erosion by a river never
exceeds the lateral erosion.
- So the width of the river valley is greater than the depth giving rise to v-shaped valley.
Canyon or Gorges
- When the river erosion is confined to down - cutting of its channel only, it gives rise to a deep - cut narrow valley, with steep or vertical walls known as Gorge or Canyon, in which the confined water rushes with tremendous force.
- Canyon are deep gorges.
- Gorges are often smaller than canyon
Canyon Gorge
Hanging valley
• a valley which is cut across by a deeper valley or a cliff.
Rate of erosion
Erosion by a river in a given time depends upon:
a. Its volume and velocity of flow (influences the quantity of energy)
b. Character and size of its load
c. Rock type and geologic structures
d. Infiltration capacity of the area it drains
e. Vegetation which affects stability and permeability of the soil
Sediment Transportation
The load which a river carries is transported in four different ways:
1. Traction
2. Saltation
3. Suspension
4. Solution
Traction: The rolling of the coarsest fragments along the river bed.
Saltation: Without being in suspended load, a particle may rise a few cm to as much as 30 cm above the bottom, travel down some distance, and them be pulled back by gravity. Such movement is known as saltation (Jumping motion).
Suspension: Fine sand, silt and mud are transported in suspension.
Solution: Soluable material is carried in solution.
Deposition
A geologic agent that erodes and transports material can also function as a mechanism for depositing sediment. All stream deposited sediments are known as alluvium.
Depositional landforms of Rivers
1. Fans: Where a stream leaves a bed rock valleys in a high land block and enters an open low land in which its channel is free to change directions, it deposits fans. They are low, fan shaped cones of alluvial sands and gravels ranging from a few meters to many km in extent.
Cones: Width 26-260 km nearly flat (slope less than 1 ) moderate width (4-6). Small steep sided cones (up to 15 ) by short torrential rains.
Piedmont alluvial plains: For example Gangetic plain
Alluvial fan
2. Braided channels
In streams with highly variable discharge and easily erodable banks, the channels may become scattered with bars and islands, forming a pattern named braided stream. The process of building up the channel in this way is aggradation. (opposite of degradation, deepening of stream).
Braided streams typically are broad and shallow. Also formed by melting ice. Amazon and Ganges rivers are good examples.
channel
3. Deltas
When a stream flows into a lake or the ocean, its speed is checked and it deposits its sediment.
The body of stream laid sediment deposited at the mouth of a river is a delta (after the Greek letter delta became of triangular shape).
For example Nile river delta (but may have any shape)
Channel cut-off and oxbow lake
• An oxbow lake is a curved-shaped body of water formed when a
wide meander from the main stem of a river is cut off to create a
lake. A river creates a meander, due to the river’s eroding the bank through hydraulic action and abrasion/corrosion. After long period of time, the meander becomes very curved, and eventually the neck of the meander will touch the opposite side and the river will cut through the neck, cutting off meander to form the oxbow lake.
Natural levee
Groundwater
The two fundamental causes for groundwater's active role in nature are
• Its ability to interact with the ambient environment and
• The systematized spatial distribution of its flow.
Interaction and flow occur simultaneously at all scales of space and time, although at correspondingly varying rates and intensities. Thus, effects of groundwater flow are created from the land surface to the greatest depths of the porous parts of the Earth's crust, and from a day's length through geologic times.
Erosional landforms of groundwater
• Lapis: leaching of calcite in limestone on surface
• Sink holes:
• Caverns
• Stylolite: boundary between two soluble rocks
• Solution valley/Cavities
Depositional landforms of groundwater
Stalactites and stalagmites
formed when CaCo3 dissolved in groundwater.
Commonly found in limestone cave.
Glaciers
• A glacier is a flowing mass of ice that formed by the re- crystallization of snow, is powered by gravity, and has flowed outward beyond the snow line.
• For glaciers to form requires that the quantity of incoming
snowfall shall exceed the average quantity lost yearly by
melting and evaporation.
Northeast face of Everest, Rombuck Glacier.
Glacial Erosion
Glaciers are the most powerful agent of erosion. No agent of erosion is more potential than are advancing glaciers. A 2 - 4 km thick glacier can pull large blocks and grind and sculpt the land. In few centuries it can carve a landscape which may require million of years for wind and water.
Glacial Erosion
Land forms produced by glacial erosion
(evidence of glacial erosion)
Glaciers erode bed rocks and produce distinctive landforms:
1. Cirques (pronounced as seerk)
2. Horns
3. Roches moutonnees (French words, pronounced as Roash mootahn-ay):
4. U-shaped and hanging valleys and
fjords, and
5. Striations and groves, and smooth and
polished surfaces in bed rocks.
Glacier Erosion
Cirques (pronounced as seerk)
They are the most common mountain landscape created by glaciations.
It is like a steep-walled bowl shaped niche (khopa in Nepali) in which a valley glacier originate.
A cirque, which begins at the head of the valley lies in
the area above the snow line.
Erosion is deepest here as snow remains longer.
It is rimmed in three sides by mountain and forth side is
down hill opening through which glacier descends.
Arete (stop), Col and Horn
Glacial Erosion
Rarely does only one valley glacier exist in a mountainous area. Commonly, separate glaciers, each fed from snowfall at a peak, will move down different sides of the crest of the mountain chain. Eventually, each glacier forms its own cirque.
Adjacent cirques may grow until they are separated by only a relatively thin, vertical, rocky remnant. The remnant is called an arete (French word for stop). Eventually, gaps are eroded in the wall-like arete. A gap in an arete between two cirques is a col.
A mountain pinnacle may be left after the wearing away of several aretes. A pinnacle which overlooks three or more cirques, is called a horn. Two of the best known peaks are horns: Mt. Everest, which is bordered by four huge valley glaciers, and the Matterhorn in the Alps.
Erosion of an arete, making it flat, produces a col
Arete
A thin, vertical, rocky remnant between two adjacent glacier
is called an arete
Horns
Horns
Glacial Erosion
U-shaped valleys and hanging valleys:
A valley glacier characteristically alters the V-shaped profile created by running water. The result is a U-shaped profile, with steeper sides and a rounder bottom.
A main-valley glacier may be fed by tributary glaciers. Each tributary glacier has its own head or source and finds its own route until it joins the main tongue. As they are smaller and have less erosive power, they remain higher than the main glacier valley. After the main-valley glacier has melted away, the bottom of the main-valley may be several hundred meters lower than the bottoms of it tributaries. These higher tributaries, aptly called hanging valleys, are common in European Alps.
Glacial Erosion
Roches moutonnees (French words, pronounced as Roash mootahn-ay):
The combined action of abrasion, smoothing, and rounding on one side (the side up which the ice flowed) and quarrying on the opposite side (down stream side) creates asymmetrical rock hillocks known as roches moutonnees.
Glacial Erosion
Fjords
Near a coast line, glaciers can create U-shaped valleys that may be flooded by the sea after the glaciers have melted. Such glaciated valleys occupied by an arm of the sea are called fjords. Some fjords extend as far as 190 km inland.
Striations and grooves
The abrasive effect of glaciers on massive solid bedrock is to smooth and polish the surface and to sculpt it into large-scale rounded forms and grooves. No other geologic agent creates such features.
The result of one-directional flow is the rasping out of tiny linear grooves, named striation, or of larger troughs or deep grooves. The striations and grooves are parallel to the direction of the glacier’s flow.
Glacial grooves and striation
Glacial Landform
Glacier Landforms
A. Landforms produced by flowing ice:
1. Moraine : Rounded deposits of glacial hill.
2. Drumlins: Smooth and elliptical hills.
B. Landforms produced by melt-water from the glaciers:
3. Eskers: Build up bed of a sub glacial stream.
4. Kames: irregularly shaped mound
C. Others deposits:
5. Kettles
Moraines
Moraine is any glacially formed accumulation of unconsolidated glacial debris (regolith & rock) that occur in both currently and formerly glaciated regions on Earth (i.e. a past glacial maximum), through geomorphological processes
A large body of drift (consisting of till, stratified drift, or both) that has been shaped into a rounded ridge is a moraine. Several varieties are:
a. Terminal moraines
b. Recessional moraines or end moraines
c. Inter-lobate moraines
d. Lateral moraines
e. Medial moraines
f. Ground moraines
At the outer margin of a glacier that has reached its maximum extent, the ice pushes up debris into a ridge whose trend follows the edge of the ice. This ridge is known as terminal moraine.
A single glacier deposits only one terminal moraine- at the
point of its greatest extent.
During its retreat, it may deposit many other morainic ridges along its margins at places where the rate of retreat is temporarily slowed. These ridges are known as recessional moraines or end moraines.
Between adjacent ice lobes are inter-lobate moraines.
A lateral moraine is formed along the non-leading edges of a valley glacier. A medial moraine, the product of converging lateral moraines that flow together where two valley glaciers meet, occurs atop and within the glacier itself.
End moraine, Near Muktinath
T
E
Terminal moraines(T) and recessional or end moraine(E).
Drumlins:
A drumlin, from the Irish word droimnín ("littlest ridge"), is an elongated hill in the shape of an inverted spoon or half- buried egg formed by glacial ice acting on underlying unconsolidated till or ground moraine.
In contrast to a moraine, which can be considered the peripheral leaving of a glacier, a drumlin consists of till that a glacier has fashioned into a streamlined shape.
Characteristically, a drumlin is eroded into a elongated shape with its steepest slope facing the direction from which the glacier originated. Drumlins range in height from 15 to 60 meters and in length, up to a kilometer or more.
Esker: is a long, winding, continuous embankment composed of a layer of gravel beneath a low, narrow mound of sand and silt, that can stretch for more than 60 km. An esker is a distinctive deposit made by a stream of melt-water beneath a large block of stagnant ice.
First the stream erodes a sinuous tunnel. Then, the stream partially or fully fills this tunnel with melt-water deposits. After the ice has melted away, these deposits are left as an embankment standing above the surrounding lowlands. An esker would not be preserved if the ice began to flow as a glacier again after the stream had deposited the sediment.
Kames terraces are bodies of outwash built against stagnant blocks of ice. A kame is any steep hill of well-sorted glacial sand and gravel.
Kettles: Scattered within the outwash or the till deposited near the edge of a glacier may be large blocks of ice. These blocks may be buried and slowly melt away. As the ice disappears, the overlying surface is let down and, if no more sediment is added, a closed steep sided depression, known as a kettle, forms above the former block of ice. Kettle may fill with water and become small lakes (up to one km or more in diameter).
Titi Lake
A kettle on moraine near Kalapani( Kaligandaki river valley)
A kettle on Khumbu Glacier
Pleistocene glaciations
Geological work of wind:
- Wind erosion,
- Wind transportation,
- Wind deposition, and
- Landforms produced by wind
Geological importance of wind
• Wind is the least effective agent of erosion, although many desert landforms are mistakenly attributed to it. Even in the great deserts of the world, most erosional landforms are the product of running water of past ages.
• In addition to forming dunes in the great deserts of the world, wind activity is important in the formation of dunes along many coastal areas and in smaller “rain-shadow” deserts.
• Wind activity is also important in forming large deposits of wind- blown dust, called loess, that blanket millions of square kilometers in the mid-latitude continents.
• Soil on this loess is among the most productive in the world and is the foundation for a large percentage of the world’s food supply.
Wind as a geological agent
• Wind is an effective local geologic agent, capable of lifting and transporting loose sand and dust, but its ability to erode solid rock is limited.
• The main effects of wind, as a geologic agent, are the transportation and deposition of sand and dust.
• It is estimated that wind-blown dust covers one- tenth of the land surface. This fact is important because soils from these deposits are some of Earth’s richest farmland.
Desert also receives some precipitation !!!
The infrequent desert rains are often heavy. Without a continuous vegetative cover to protect the ground, the rapid runoff causes great erosion.
Remnant of the erosion in desert; imagine the extent of erosion !
Desert does not contain only sand! A more typical desert surface
consists of barren rock or expanses of stony ground.
Limited vegetation exists in desert area.
Wind erosion
For wind to be an effective agent of erosion:
- Chemical and mechanical weathering must disintegrate the solid rock into
small lose fragments.
- A dry climate is also necessary; in humid climate vegetation usually coves the surface, and wet material is usually cohesive because water tends to hold loose fragments together.
Wind erosion acts in two ways:
• Deflation: the lifting and removal of loose sand and dust particles from Earth’s surface. It commonly occurs in semi-arid regions where the protective cover of grass and shrubs has been removed by the activity of humans and animals. The results are broad shallow depression called deflation basins. The deflation basins also commonly develop where calcium carbonate cement, in sandstone formations, is dissolved by groundwater, leaving loose sand grains that picked up and transported by wind. Large deflation basins, covering areas of several hundred square kilometers, are associated with the great desert areas of the world particularly in North America near the Nile Delta. In general, wind can move only sand and dust-sized particles, so deflation leaves concentration of coarse material known as lag deposits, or desert pavements.
Desert pavement or lag deposit
Wind erosion
Abrasion: the sandblasting action of wind-blown sand. In areas
where soft, poorly consolidated rock is exposed, wind erosion can be both spectacular and distinctive.
Some pebbles called ventifacts ( literally meaning “wind– made”), are shaped and polished by the wind.
In some desert regions, distinctive liner ridges, called yardangs ( Turkistani word Yar, meaning “ridge” or “bank”), are produced by wind erosion.
Typical yardangs have the form of an inverted boat hull and commonly occur in clusters, oriented parallel to the prevailing wind that formed them.
Yardangs are generally restricted to most arid parts of deserts, which are relatively sand-poor and are areas where vegetation and soil are minimal.
Wind transport
Wind transports sand by
- Saltation,
- Surface creep (rolling and sliding), and
- Silt and dust-sized particles are carried in suspension.
Great dust storms sometimes reach elevations of 2500 m and
advance at speeds of up to 200 m/sec.
It has been estimated that 500 x 106 tons of wind-blown dust are carried from the deserts each year.
Sand dunes:
Wind deposition
• Sand dunes commonly originate in wind shadows. Any obstacle that diverts the wind, such as a bush or a fence post, crates eddies and reduces wind velocity. Wind-blown sand is deposited in protected area, and eventually enough sand accumulates in the wind shadow area to form a dune. The dune itself then acts as a barrier, making its own wind shadow, and thus causes additional accumulation of sand.
• Wind-blown sand commonly accumulates in dunes that migrate downwind.
• Many different kind of sand dunes result from variations in sand supply, wind direction, and velocity. The most significant types of dunes are:
- Transverse dunes, Barchan dunes, Longitudinal dunes, Star dunes, and Parabolic dunes.
Sand dune
Forest
Windward slope
Lee slope or slip face
Parabolic dunes: formed by strong onshore winds
Barchan dunes: develop where the wind direction is constant but the sand supply is limited
Transverse dunes: develop where the wind direction is constant
and the sand supply is large
Sand seas:
Wind deposition
• Although Earth is commonly called the water planet, several continents have vast areas where precipitations is rare, and the surface is covered with wind-blown sand. Some of these areas are so vast they are known as sand seas or ergs.
• It has been calculated that 99.8% of all wind-blown sand is in the great sand seas of the world.
Loess:
Loess is a deposit of wind-blown silt (dust) that accumulates slowly and ultimately blankets large areas, often masking preexisting landforms. It covers one-tenth of the world's present land surface. The dust is derived either from nearby deserts or from rock flour, near margins of recently glaciated areas.
Buff-colored deposit of wind-blown silt, known as loess
Geological work of sea and ocean :
- geological work of sea and ocean;
- and associated landforms.
Waves
• Shorelines are dynamic systems involving the energy of waves and currents.
• Wind-generated waves provide most of the energy for erosion, transportation, and deposition of sediment.
• Waves approaching a shore are bent, or refracted, so that energy is concentrated on headlands and dispersed in bays.
The bending of waves, called wave refraction, plays an important
part in shoreline processes.
Erosion along coasts
• Erosion along coasts results from the abrasive action of sand and gravel, moved by the waves and currents and, to a lesser extent, from solution and hydraulic action.
• The undercutting action of waves and currents typically produces sea cliffs. As a sea cliff recedes, a wave-cut platform develops.
• Minor erosional forms associated with the development of sea cliffs include sea caves, sea arches, and sea stacks.
When waves leave the stormy area where they formed, they continue on without relation to local winds and carry a storm's energy to distant shore
When the wave subsides, the compressed air rapidly expands, dislodging rock fragments and enlarging fractures.
Abrasion, the sawing & grinding action of the water armed with rock fragments also erodes the shore
Wave-cut cliff originated by the cutting action of the surf
against the base of the coastal land.
Gradually rocks overhanging the notch at the base of the cliff crumble and the cliff retreats. Eventually a flat beach-like surface, the wave-cut platform, is created.
Because of refraction, wave impact is concentrated against the sides and ends of headlands projecting into water and attack the headlands from three sides.
When the sides of the headlands are vigorously attacked, sea caves
develop and when they unite a sea arch results.
Sea cave
Sea arch
Sea stack
Collapse of a sea arch
Summary of costal erosion
Deposition along coasts
Sediment transported along the shore is deposited in
areas of low wave energy and produces
landforms, including a variety of
- Beaches;
- Spits;
- Baymouth bar;
- Tombolos; and
- Barrier islands.
Source of sediment in coastal system
Beach
Many beach consists of sand that was carried to the ocean by rivers and then distributed along the shore by beach drift and longshore current
Longshore currents can also produce a tombolo, a ridge of sand
that connects an island to the mainland
Tides
• The sea advances and retreats in a regular rhythm twice in approximately
24 hours. These changes are called the tides.
• The origin of tides was not known until Isaac Newton (1642-1727)
provided an explanation.
• Tides are produced by the gravitational attraction of the Moon and the
centrifugal force of the Earth-Moon system.
• Tides affect coasts in two major ways:
- by initiating a rise and fall of the water level; and
- by generating tidal currents.
• The major effect of the rise and fall of tides is the transportation of sediment along the coast and over the adjacent shallow seafloor.
• The difference in height between high tide and low tide is as much as 21
m.
Tsunamis
• Movement of the ocean floor by earthquakes, volcanic eruptions, or submarine landslides frequently produces an unusual wave called a tsunami (Japanese meaning large wave)
• In tsunami, energy is transferred to the water by displacement of the seafloor during vertical faulting or by disturbances from volcanic eruptions or submarine landslides.
• When the sea floor is displaced rapidly, the entire body of water above it is affected. Thus, the entire body of water, 5 to 6 km deep, participates in the wave motion. Consequently, where part of the ocean floor is uplifted or subsides, a bulge and its adjacent depression are produced on the ocean surface.
• Tsunami has long wavelength and travels across the open ocean at
high speeds.
• As a tsunami approaches shore, its wavelength decreases and its wave height increase; therefore, a tsunami can be a formidable agent of destruction along shorelines.
How the small, beautiful island was developed?
What is the name of the landform? How it is developed ?
What is the name of the landform ? How it is formed ?
THANK YOU
Course content:
Weathering: Erosion Subsidence Expansive soil Mass wasting Volcanism Earthquake
Weathering
• Weathering refers to the disintegration and decomposition of rocks,
whereas erosion involves the removal of debris produced by the
weathering.
• In weathering, rocks adjust and are altered to form more stable at low pressure, low and fluctuating temperatures, and the chemical environment with abundant water that prevails at Earth’s surface.
• Weathering is important both in geologic theory and in many ways that effect our everyday lives:
- Proof of operating geoclinal cycle today;
- Means of adjustment with prevailing environmental;
- Conversion of bed rock to regolith /soil;
- Creates complication to engineering works; and
- Give rise economically important deposits.
• Although weathering involves a multitude of physical, chemical, and biological processes, two main types are recognized: Physical and chemical weathering.
Physical weathering
• Physical weathering is the breakdown of rock into small fragments by physical processes without a change in chemical composition. No chemical elements are added to, or subtracted from, the rock.
• Thermal effect / Ice wedging: When water freezes in cracks or other opening in rocks, it expands about 9 %, exerting great pressure on the rock walls. This process breakdown the rock. Conditions: adequate supply of moisture, preexisting fractures in rocks, temperature fluctuations beyond the freezing points.
• Granular disintegration: The physical separation of the individual
mineral particles of a rock form one another.
• Sheeting joints /exfoliation: The buried rock body tends to expand once the overlying rock mass is removed by erosion/excavation. The internal stresses set up by expansion can cause a sheet of rock to burst up or to result expansion joints.
• Pressure from growing roots widens cracks and contributes to the rock breakdown.
Exposed area goes on increasing with crack development
Ice-wedging
Ice-wedging leading to soil formation
Ice-wedging is common in the Himalayan region (near Lukla, Solukhumbu district)
What caused the rock blocks detached for the slope ?
Chemical weathering
• Chemical weathering is the breakdown of rocks by chemical alteration of the constituent minerals. Rocks are decomposed, the internal structure of the minerals is destroyed, and new minerals are created.
• Dissolution: Rock materials (e.g. halite and gypsum) passes directly into solution. Calcite is not soluble in pure water but it is soluble if the water contains CO2 forming calcium bicarbonate.
H2O + CO2 H2CO3 (Carbonic acid); H2CO3 + CaCO3
Ca(HCO3)2
• Hydrations: A mineral reacts with the water’s H+ or OH- ions to produce a different minerals. When Plagioclase feldspar comes in contact with water containing carbon dioxide, it converts into clay minerals.
• Oxidation: is the chemical combination of oxygen with one mineral to form a completely new mineral. The iron of Olivine unites with oxygen to form the mineral hematite and silicic acid.
2Fe2SiO4 (olivine)+ 4H2O + O2 2Fe2O3(Hematite) + 2H4SiO4
Chemical weathering: formation of stalagmites and stalactites
Granite: quartz, feldspar, muscovite & tourmaline
Products of weathering
• Rock fragments:
• Shattering; rock fragments produced when bedrock is blasted with
explosive or due to ice wedging.
• Granular disintegration ; grain-by-grain breakdown of rocks.
• Spheroidal weathering; a rounded shape is produced because weathering attacks an exposed rock from all sides at once, and decomposition is most rapid along the corners and edges of the rocks.
• Exfoliation; the rock breaks apart by separation along a series of concentric shells or layers that look like cabbage leaves.
• Regolith; a layer of soft, disaggregated rock material formed in place by the decomposition and disintegration of the bedrock that lies beneath it.
• Soil: the uppermost layer of the regolith is the soil. Type and thickness
depend on climate, parent rock material, and topography.
• Ions in solution: Major source of ions in solution are carbonate rocks followed by evaporites- salts of potassium, sodium, magnesium, chlorine , and sulfate.
Climate and Weathering
• Temperature: freeze-thaw causes mechanical fragmentation. Amount of precipitation (including intensity, seasonal variation, infiltrations, runoff, rate of evaporation): Chemical reaction, such as hydration, dissolution, and oxidation requires water.
• Tropical climates typically support lush (luxuriant) vegetation that yields organic acids. Consequently, forested areas experience higher rates of chemical weathering than in otherwise similar areas that lack such growth. High temperature and abundant water can also increase the rate of bacterial activity, important in the production of acid.
• High temperature and high precipitations cause intense chemical weathering. Physical weathering dominates in regions of low temperature and low rainfall. Rate of weathering: depends on susceptibility of the constituent minerals to weathering, climates, and the amount of surface exposed to the atmosphere.
Weathering as controlled by temperature and precipitation
Erosion
• Erosion is the removal (transport) of weathered rock materials downslope, and away, from their original site of weathering. Erosion processes are driven primarily by the force of gravity, which may be aided by a flowing medium such as water (e.g. rivers), and ice (e.g. glaciers), or gravity may act alone (e.g. rockfalls). Wind can also remove weathered materials (e.g. deflation).
• During transportation of the weathered rock materials, the angular particles commonly abrade (rub or scour) the surfaces over which they pass, wearing away and lowering the rocks. Thus, landslide debris may erode the slope or channel along its course, the sediments in rivers erode the rocky sections of their beds, and the rock fragments in glaciers erode the valley floor.
Erosion Processes
• Erosion processes are usually considered under four distinct categories:
• Mass Wasting: the processes that occur on slopes, under the influence of gravity, in which water may play a part, although water is not the main transporting medium.
• Fluvial: the processes that involve flowing water, which can occur within the soil mass (e.g. soil piping), over the land surface (e.g. rills and gullies or in seasonal or permanent channels (e.g. seasonal streams and rivers).
• Wind: the processes that involve the action of rapidly moving air
streams in dry areas, which can be cold or hot deserts.
• Glacial: the processes that involve the presence of ice, either in the soil (e.g. solifluction), or as the transporting medium (e.g. glaciers).
Erosion Controls
• The type and magnitude of erosion depends upon several factors including:
• Climate: exerts a fundamental control on the types and rates of erosion in an area, because climate determines the amount and seasonal distribution of water (rainfall), the temperature (tropical, temperate or polar), and factors such as the sunshine hours, the wind strengths, and wind patterns.
• Topography: mountain areas have a higher elevation and thus greater potential energy than the lowlands. This, combined with the steeper slope angles, results in more dynamic erosion in upland areas than on the surrounding plains.
• Rock Type: the type of rock determines how susceptible an area is to erosion. Within the same climatic regime, each rock type responds differently to weathering and erosion, exhibiting a characteristic resistance or weakness to the prevailing conditions. Thus, some rocks are relatively resistant and form higher ground, whereas others are less-resistant and form valleys and lowlands.
• Rock Structure: highly jointed or faulted rocks are usually more intensely weathered along the lines of weakness in the rock mass. Consequently, these softer weathered materials are more easily eroded out, with the result that river valleys are usually located along the line of a major fault or joint set.
Subsidence
• Subsidence is the sudden sinking or gradual downward settling of the ground's surface with little or no horizontal motion. The definition of subsidence is not restricted by the rate, magnitude, or area involved in the downward movement.
• It may be caused by natural processes or by human activities.
The former include various karst phenomena, thawing
of permafrost, consolidation, oxidation of organic soils, slow crustal warping (isostatic adjustment), normal faulting, caldera subsidence, or withdrawal of fluid lava from beneath a
solid crust. The human activities include sub-surface mining or extraction of underground fluids, e. g. petroleum, natural gas, or groundwater. Ground subsidence is of global concern
to geologists, geotechnical engineers, surveyors, engineers, urban planners, landowners, and the public in general.
Subsidence Contd……
• Dissolution of limestone
• Mining
• Extraction of natural gas
• Earthquake
• Groundwater-related subsidence
• Faulting induced
• Isostatic subsidence
• Seasonal effects
Expansive soil
• Expansive soils present significant geotechnical and structural engineering challenges the world over, with costs associated with expansive behavior estimated to run into several billion annually.
• Expansive soils are soils that experience significant volume change associated with changes in water contents. These volume changes can either in the form of swell or in the form shrinkage and this is why they are sometime known as swell/shrink soils.
• Key aspects that need identification when dealing with expansive soils include: soil properties, suction/water conditions, water content variations temporal and spatial, e.g. generated by trees, and the geometry/stiffness of foundations and associated structures.
• Expansive soils can be found in humid environments where expansive problems occur with soils of high Plasticity Index or in arid/semi arid soils where soils of even moderate expansiveness can cause significant damage.
• Mitigation of the effects of expansive clay on structures built in areas with expansive clays is a major challenge in geotechnical engineering.
• Some areas mitigate foundation cracking by watering around the foundation with a soaker hose during dry conditions.
• This process can be automated by a timer, or using a soil moisture sensor controller. Even though irrigation is expensive, the cost is small compared to repairing a cracked foundation.
• Admixtures can be added to expansive clays to reduce the shrink-swell properties, as well.
Mass wasting
• Definition:
Mass wasting / mass movement is defined as the downslope movement of material under the influence of gravity. When the driving force acting on a slope exceeds the resisting force, slope failure / mass wasting takes place.
• The resisting force is due to shear strength of the slope material. The driving force is the component of the gravitational force acting parallel to the slope.
Mass movement..
• Influencing factors: Saturation of material with water, vibration from earthquakes, over-steepening of slopes, alternating freezing and thawing, geology, & vegetation cover.
Types of movement:
• Creep: is an extremely slow, almost imperceptible down slope movement of soil and rock debris that result from the constant minor rearrangements of the constituent particles.
• Debris flows: consist of mixtures of rock fragments, mud, and water that flow down slope as viscous fluids.
• Landslides: involve movement along well-defined slippage plane. It is differ from creep and debris flows in their mechanism of movement. A landslide block moves as a unit (or series of units) along definite fracture ( or system of fractures).
Varne’s classification of mass movement
Creep, Jharkot village, near Muktinath
Debris flows and rock avalanche
Vegetation controls the mass movement
Debris flow may block a river
Debris flow can destroy infrastructure (Phedi gaon in 1993 , Palung)
Why vegetation could not prevent debris flow at Matatirtha?
Why the house was not effected by the debris flow?
Landslide occurs along a well-defined plane.
Landslide or slumping
Krishnabhir, Prithivi Highway
Countermeasures:
• Surface water drainage,
• Groundwater drainage,
• Rock bolt,
• Pile works,
• Retaining structures, and
• Bioengineering
Surface water drainage
Retaining structures
Bioengineering: use of living plants for engineering purpose
Tree route anchors the soil mass
Nature of Volcanism
• It is directly related to plate tectonics, and most active
volcanoes are located near plate boundaries.
• Magma (molten rock, including a small component of dissolved gases) is produced in these regions as spreading or sinking lithospheric plates interact with other earth materials.
• About 80 % of all active volcanoes on Earth are located in the “ring of fire” that circumscribes the Pacific Ocean, an area corresponding to the Pacific plate.
• Characteristic of volcano is partly related to the magma’s viscosity that varies from about 50 to 70 % based on silica(SiO2) content and its temperature.
• Magma that has emerged from a volcanic vent is called
lava.
Types of Volcano
• Shield volcanoes: They are by far the largest volcanoes. Although they are shaped like a gentle arch, or shield, they are among the tallest mountains on Earth when measured from their bases, often on the ocean floor. Examples are Hawaiian volcano Kilauea. They are non-explosive due to low silica content (about 50 %).
• The common rock type of the magma is basalt which is composed mostly of
feldspar and ferromagnesian minerals.
• They are mainly built up by numerous lava flows but can also produce a lot of tephra (all types of volcanic debris explosively ejected from a volcano), also called pyroclast (Greek pyro, “fire” and klastos, “broken”) debris. Accumulation of tephra formed tephra cone or cinder cone.
• The slope of a shield volcano is very gentle near the top (about 3-50, but it
increases ( to about 100) on the flanks based on the viscosity of the lava.
• They may have a summit caldera, which is steep, walled basin often 10 km
or more in diameter, formed by collapse in which a lave lake may form.
Shield volcano
Shield volcano: Lava tube
Types of Volcano…..
• Composite volcanoes: are known for their beautiful cone shape. Example includes Mount St. Helens and Mt. Rainier both in the state of Washington.
• They are associated with intermediate silica content (about 60 %), thus more viscous than shield volcano.
• The common rock type of the magma is andesite, composed mostly of soda and lime-rich feldspar and ferromagnesian minerals with small amounts of quartz.
• They are characterized by a mixture of explosive activity and lave flows. As a result, these volcanoes are composed of alternating layers of pyroclastic deposits and lava flows and are also called stratovolcanoes. They have steep flanks or sides because the angle of repose for many pyroclastic deposits is about 30 to 35 degrees.
• They are responsible for most of the volcanic hazards that have caused death and destruction throughout history.
Types of Volcano…..
• Volcanic Domes: are characterized by viscous magma with a relatively high silica content ( about 70 %).
• The common rock type of the magma is rhyolite, composed mostly of potassium and soda – rich feldspar, quartz and minor ferromagnesian minerals.
• The activities are mostly explosive, making these volcanoes very dangerous. Mt. Lassen in northeastern California is a good example of a volcanic dome.
Origin of volcano
Volcanic features:
• Craters: the depression (a few km in diameter) found at the top of volcanoes. They form by explosion or collapse and may be flat-floored or funnel-shaped.
• Calderas:Circular depressions resulting from explosive ejection of magma and subsequent collapse of the upper portion of the volcanic cone. ( may be 20 km in diameter).
• Vents: are opening thorough which volcanic materials are erupted at the
surface of Earth.
• Hot springs and Geysers: Groundwater that comes into contact with hot rocks becomes heated and in some cases the heated water discharges at surface as a hot spring.
• A system of periodic release of steam and hot water at the surface is
called a geyser.
Volcanic materials
• Lava flows: occurs when magma reaches the surface and overflows the crater or a volcanic vent along the flanks of the volcano. Guess its velocity!
• Pyroclastic materials: tephra (all types of volcanic debris) blown from the volcanic vent. It includes ash fall, ash flows, and lateral blasts.
• Poisonous gases: Water vapor, carbon dioxide, carbon monoxide, sulfur dioxide, and hydrogen sulfide are emitted during volcanic activities.
• Debris Flows and Mudflows: are produced when a large volume of loose volcanic ash and other ejecta become saturated and unstable and moves suddenly down slope.
Lava Flow
Ash eruption
Ash flows
Mud flows
Inundated by mud flows
Earthquake-definition
Earthquakes are vibrations of Earth, caused by the rupture and sudden movement of rocks that have been strained beyond their elastic limits.
Following an earthquake, adjustments along a rupture / fault commonly generate a series of earthquakes referred to as aftershocks.
Earthquake-causes
The cause of most earthquakes is movement of Earth’s tectonic plates. Earthquakes particularly occur at plate boundaries. Movement of a plate may also cause “Intraplate Earthquakes”.
Plate tectonic explains the causes of earthquakes (divergent / convergent plate boundaries, direction and rate of plate movement)
• Majorities of all earthquakes (about 80 %) occur in circum-pacific belt followed by Mediterranean- Asiatic belt(about 15 %). The remaining 5 % of earthquakes occurs mostly in divergent plate boundaries.
Map of the world showing the major earthquake belts as shaded area
Causes of earthquake: Elastic rebound theory
• In 1911 American seismologist Harry Fielding Reid studied the effects of the April 1906 California earthquake. He proposed the elastic rebound theory to explain the generation of certain earthquakes that scientists now know occur in tectonic areas, usually near plate boundaries.
• This theory states that during an earthquake, the rocks under strain suddenly break, creating a fracture along a fault. When a fault slips, movement in the crustal rock causes vibrations.
• The slip changes the local strain out into the surrounding rock. The change in strain leads to aftershocks (smaller earthquakes that occur after the initial earthquake), which are produced by further slips of the main fault or adjacent faults in the strained region.
Elastic rebound theory…..
• The slip begins at the focus and travels along the plane of the fault, radiating waves out along the rupture surface. On each side of the fault, the rock shifts in opposite directions.
• The fault rupture travels in irregular steps along the fault; these sudden stops and starts of the moving rupture give rise to the vibrations that propagate as seismic waves.
• After the earthquake, strain begins to build again until it is greater than the forces holding the rocks together, then the fault snaps again and causes another earthquake.
Focus and epicenter
• The point within Earth where the initial rupture initiates and thus the energy is released is called Focus. The point on Earth’s surface that is directly above the focus is the Epicenter.
Seismicity-waves
• An earthquake generates two types of body wave: P-wave & S- wave. P- waves, or primary waves, are the fastest seismic waves and can travel through solids, liquids and gases. They are compressional, or push-pull waves and are similar to sound waves in that they move material forward and backwards along a line in the same direction that waves themselves are moving. Thus, the material p-wave travel through is alternately expanded and compressed as the wave moves through it and returns to its original volume after the wave passes by.
• S-waves, or secondary waves, are slower than P-wave and can only travels through solids. S-waves are shear waves because they move the materials perpendicular to the direction of travel, thereby producing shear stress in the material they move through. S-wave deform materials out of shape as they pass. Because liquids and gases are not rigid, they have no shear strength and S-wave can not be transmitted through them.
• Surface waves travel along the surface of the ground, or just below it along planes between rock layers, and are slower than body waves. Unlike the sharp jolting and shaking that body waves cause, surface waves produce a rolling or swaying motion, much like the experience of being on a boat.
The shaking and destruction resulting from earthquakes are caused by two different types of seismic waves: body waves, which travel through Earth and are somewhat like sound waves; and surface wave, which travel only along the ground surface and are analogous to ocean waves.
Intensity and Magnitude
• The strength of an earthquake is measured in two different ways. The first, intensity, is a qualitative assessment of the kinds of damage done by an earthquake. The second, magnitude, is a quantitative measurement of the amount of energy released by an earthquake.
• The intensity depends on several factors that includes the total amount of energy released, the distance from the epicenter, and the type of rock and degree of consolidation. Wave amplitude and destruction are greater in soft, unconsolidated materials than in dense, crystalline rock. The intensity is greatest close to the epicenter. The most common intensity scale used is the Modified Mercalli Intensity Scale, which has values ranging from I to XII.
• The Richter Magnitude Scale measures earthquake magnitude, which is the total amount of energy released by an earthquake at its source. Magnitudes are based on direct measurements of the size of seismic waves (amplitude) made with recording instruments.
• The difference between two consecutive whole numbers on the scale means an increase of 10 times in the amplitude of the earth's vibrations.A tenfold increase in the size of Earth’s vibration is caused
EARTHQUAKE
It is an natural disaster.
When the fault ruptures with a sudden movement energy is released that has built up over the years. This energy is released in the form of vibrations called 'seismic waves’… earthquakes!
It is actually when these seismic waves reach the surface of the earth that most of the destruction occurs, which we associate with earthquakes.
TYPES OF SEISMIC WAVES
Seismic
waves
Body waves
Surface wave
Primary wave
Secondary wave
Rayleigh wave
Love wave
PROPAGATION OF EARTHQUAKE WAVES
EARTHQUAKE CLASSIFICATION
Based on distance
1. Tele seismic earthquake
2. Regional earthquake
3. Local earthquake
Based on magnitude
> 1000 km
> 500 km
< 500 km
1. Great earthquake M > 8.0
2. Major / Large earthquake 7.0 > M < 8.0
3. Moderate earthquake 5.0 > M < 7.0
4. Small earthquake 3.0 > M < 5.0
5. Micro earthquake 1.0 > M < 3.0
6. Ultra micro earthquake M < 1.0
TYPES OF EARTHQUAKE
NATURE OF EARTHQUAKE
1. Tectonic
2. Volcanic
3. Collapse
4. explosion
1. Foreshock
2. Main shock
3. Aftershock
4. Earthquake swarm
5. Normal seismic
WHAT HAPPENS DURING AN EARTHQUAKE?
As tectonic plates grind together at a fault line, the rocks on either side stretch to absorb a certain amount of pressure. If the pressure becomes too great, the rocks shatter, releasing shock waves that shake the surface. Buildings then sway and topple, and fires may start as gas and electricity lines are ripped apart.
WHERE DO MOST EARTHQUAKES STRIKE?
Most earthquakes, and also volcanic eruptions, occur on or near the edges of Earth’s tectonic plates. They are most common in the “Ring of Fire,” the name given to the edge of the vast Pacific Plate that lies beneath the Pacific Ocean. Japan, the Philippines, New Zealand, and the western coastline of North and South America all lie in this major fault zone.
HOW ARE EARTHQUAKES MEASURED?
The study of earthquakes is called seismology. Scientists measure and record earthquakes using devices called seismometers. The size of an earthquake is measured according to its magnitude (the size of the shock waves and the energy produced) or its effects.
If you are in house;
• Don’t use lift for getting down from building.
• Be prepared to move with your family.
If you are in shop, school or office;
• Don’t run for an exit.
• Take cover under a disk/table.
• Move away from window glass.
• Do not go near electric point and cable. Keep away from weak portion of the building and false ceiling.
LANDSLIDES
CAUSES OF LANDSLIDE
Heavy rains
Earthquake
Volcano eruption
Floods
Ground water changes
Rapid snow melt
quarrying
CLASSIFICATION OF LANDSLIDES
Type
Surface slide
Shallow slide
Deep slide
Very deep slide
Maximum Depth
< 1.5
1.5 – 5
5 – 20
>20
TYPES OF LANDSLIDE
LANDSLIDE PREPAREDNESS AND SAFETY MEASURES16
A) Before a landslide:
Find out if landslides have happened in your area in the past.
Look out for landslide warning signs like doors or windows jammed for the first time, new cracks appear in walls, bricks, foundations, retaining walls, tilt of utility poles or trees.
Consider relocation in case your house is located in an area particularly vulnerable to landslides. While doing so, remember:
1. Do not build on or at the base of unstable slopes, on or at the base of minor drainage hollows, at the base or on top of an old fill slope, at the base or top of a steep cut slope.
ii) Do not cut down trees or remove vegetation or avoid
slope weakening. 17
iii) If the house cannot be relocated, then ensure proper drainage and proper retaining walls.
Always stay alert and awake!!! Listen to radio/television for warnings of intense rainfall, storm and damp weather. These usually trigger landslides/debris or mudflow.
Make an evacuation plan in case of a landslide with all
the emergency items.
B) During a landslide:
Listen to any unusual sounds that 18
might indicate moving debris, such
as trees cracking or boulders knocking together. A trickle of flowing or falling
mud or debris may precede larger flows.
While you are outdoors during a landslide
Try to get out of the path of the landslide or mudflow by running
to the nearest high ground or away
from the path.
If you are near a river, be alert for any sudden increase or decrease in water flow or for a change from clear to muddy water. Such changes may indicate landslide upstream. So move quickly to safer areas.
If the rocks and other debris are approaching, run to the nearest shelter such as group of trees o1r9 a building.
While you are indoors during a landslide
Stay inside and remain alert. Listen to radio/ television for any update. i.e. if landslide occurs outside.
If your house falls apart due to landslide and if there is no escape, hold on to something strong and protect your head.
C) After a landslide:
Stay away from the landslide area as there may be danger
of additional slides. Do not drive through.
Watch for flooding which may occur after a landslide.
Check for injured or trapped persons near the slide, without entering the slide area. Direct rescuers to their locations.
Help neighbours who may require 20
special assistance– infants,
elderly people and disabled people.
Listen to local radio/television stations for the latest emergency information.
Look for and report broken utility
lines to appropriate authorities.
Check the building foundation, walls and surrounding land for damage. The safety of the areas needs to be assured before reoccupation.
PREVENTION & MITIGATION
Increase in vegetation
Engineered fill
Retaining walls
Removal of top
Debris basin
Buttress
debris flow heading toward neighborhood
WHAT IS TSUNAMI?
A tsunami is a wave train, or series of waves, generated in a body of water by an impulsive disturbance that vertically displaces the water column.
Earthquakes, landslides, volcanic eruptions, explosions, and even the impact of cosmic bodies, such as meteorites, can generate tsunamis.
Tsunamis can savagely attack coastlines, causing devastating property damage and loss of life.
WHAT IS TSUNAMI?
PLAN FOR A TSUNAMI
Develop a Family Disaster Plan
Learn about tsunami risk in your community
If you are visiting an area at risk from tsunamis, check with the hotel, motel, or campground operators for tsunami evacuation information
Plan an evacuation route from your home, school, workplace, or any other place you'll be where tsunamis present a risk.
Practice your evacuation route
Use a NOAA Weather Radio with a tone-alert feature to
keep you informed of local watches and warnings.
Discuss tsunami with your family
Assemble a Disaster Supplies Kit
HOW TO PROTECT YOUR PROPERTY
• Avoid building or living in buildings within several hundred feet of the coastline. These areas are more likely to experience damage from tsunamis, strong winds, or coastal storms.
• Make a list of items to bring inside in the event of a tsunami. A list will help you remember anything that can be swept away by tsunami waters.
• Elevate coastal homes. Most tsunami waves are less than 10 feet. Elevating your house will help reduce damage to your property from most tsunamis.
• Follow flood preparedness precautions. Tsunamis are large
amounts of water that crash onto the coastline, creating floods.
• Have an engineer check your home and advise about ways to make it more resistant to tsunami water. There may be ways to divert waves away from your property. Improperly built walls could make your situation worse. Consult with a professional for advice.
WHAT TO DO AFTER A TSUNAMI
• Continue listening to a NOAA Weather Radio, Coast Guard emergency frequency station, or other reliable source for emergency information
• Help injured or trapped persons
• Use the telephone only for emergency calls
• Stay out of the building if waters remain around it
• Examine walls, floors, doors, staircases, and windows to make
sure that the building is not in danger of collapsing.
• Inspect foundations for cracks or other damage
Look for fire hazards.
Check for gas leaks
Look for electrical system damage.
Check food supplies. Any food that has come in contact with
flood waters may be contaminated and should be thrown out.
IMPORTANT CAUSES OF ACCIDENT
Roof/ side fall
Winding
Haulage
Dumper
Conveyer
Explosive
Electricity
Dust / gas
Fall of object/ person
inundation
RECOMMENDATION FOR MINE DISASTER PREVENTION AND CONTROL
Mining program
Mine disaster prevention and control research
Mine management
Safety monitoring in mining
USE OF TECHNOLOGIES TO REDUCE THE NUMBER OF ACCIDENTS
Chapter 7 Hydrogeology
Morphology of river channel
Hydrogeology
Hydrogeology is a branch of geology that refers the study of groundwater (water under the
ground) and the geologic process of surface water.
A river is defined as a body of running water carrying sediments which flows along a definite path. The path of is the river valley. The flow of water in a river is expressed in terms of the volume passing through a point in a given time. This is known as discharge; which can be calculated as:
Discharge= velocity x channel cross-sectional area.
There are two types of flow i.e. laminar and turbulent.
Laminar flow is possible when the river is having a flat gradient and low velocity. The movement of
glacier and ground water are generally laminar in nature.
In turbulent flow the motion is random and edding.
A river’s work capacity is governed by its kinetic energy i.e. K = mv2/2, where, m = mass of water
(discharge).
The geological activity of river is divided chiefly into three parts as:
A. Erosion
B. Transportation and
C. Deposition
A. Erosion
The term erosion is applied for rock breakdown by the dynamic action of any geomorphic agents like water, wind
or glacier etc. when rainfalls, the water infiltrates to fill up the spaces lying within the soil and rock.
When these materials becomes saturated with water, no more water can infiltrate. In this condition, water flows on the surface. In the beginning, water flows random down the slope and erode the thin sheet of entire slope causing sheet erosion. As it advances, the surface water tends to flow in a in narrow channel called rill or gully.
During this stage surface water makes gully erosion. These gullies become winder and deeper and drain their water into other stream.
Erosional process of river
Hydraulic action
Abrasion
Attrition
Cavitation
Corrosion
Erosional landform produced by river
i. Pot-holes: Bowl like depressions in the rocky beds of streams due to abrasion.
ii. Water fall
iii. Gullies: Hillside are more prone to gullying when they are cleaned of vegetation, through deforestation,
overgrazing.
iv. V-shaped valley: Vertical erosion by a river never exceeds the lateral erosion. So the width of the river
valley is greater than the depth giving rise to v-shaped valley.
v. Canyon or Gorges: when the river erosion is confined to down - cutting of its channel only, it gives rise to a deep - cut narrow valley, with steep or vertical walls known as Gorge or Canyon, in which the confined water rushes with tremendous force.
vi. Channel cut-off and oxbow lake
An oxbow lake is a curved-shaped body of water formed when a wide meander from the main stem of a river is cut off to create a lake. A river creates a meander, due to the river’s eroding the bank through hydraulic action and abrasion/corrosion. After long period of time, the meander becomes very curved, and eventually the neck of the meander will touch the opposite side and the river will cut through the neck, cutting off meander to form the oxbow lake.
v. Escarpments: There are erosion land forms produced by rivers in regions composed of alternating beds of hard and soft rocks. The differential erosion of rocks give rise to a steep slope, called escarpment. This is usually developed in dipping beds with harder rocks overlying the soft ones.
vi. Hogbacks: The hogbacks are the sharp crested often sawtooth ridge formed of the upturned edge of the resistant rock layer of sandstone, limestone, or lava and slope excess of 45°.
vii. Cuestas: These erosional landforms are developed on resistant strata having low to moderate
dip.
viii. Mesa and Butte: these are erosional features made up essentially of horizontally layered rocks having a cap of hard and resistant rocks that have escaped erosion. Large sized caps are called mesa where comparatively small sized and isolated patches are called butte or kopjees.
ix. River terraces
These are erosional features consisting of several step-like plains along of a river valley. Cotton (1940) has suggested that river terraces may be either cyclic or non-cyclic. Cyclic terrace represent former valley floors formed during periods when valley deepening had stopped and lateral erosion had become dominant. These terraces are paired. Non-cyclic terrace are non- paired terrace, and are formed by lateral shifting of the river.
B. Transportation
The work carried out by river is related to the energy available to it. Each river has a certain quantity of potential energy determined by the height of source region and amount of water entering the river system. This energy is converted to kinetic energy as it moves through the system.
The load carried by river can be subdivided as follows.
1 Chemical transportation (carried in solution as dissolved load)
1. Mechanical transportation (carried mechanically due to the force of the current of the flow as sediment)
a. Carried in suspension as suspended load.
b. Carried along the bed as bed-load.
C. River deposition
Deposition of transported materials takes place where the river’s capacity or transporting ability is reduced. It
usually occurs when the following conditions are met
a. Decrease in the velocity of the river,
b. Decrease in slope or gradient.
c. Decrease in volume of water i.e. discharge.
d. Change in channels,
e. Chemical precipitation.
Depositional landform produced by river deposition
1. Alluvial fans and cone
When streams flow abruptly from steeper to gentle gradient, as at the base of mountain or ridge, its velocity is checked and huge quantities of materials carried by the river are dropped there giving rise to broad, low cone-shaped deposit called an alluvial fan.
2. Flood plain deposit
Flood plains are areas of low and relatively flat land bordering the channel on one or both sides, at bank level.
A number of features are associated with the flood plains, which are as follows.
a. Meanders and oxbow lake.
b. Natural levees: these are broad, low ridge formed along the bank of the river during floods. During flood, when the entire flood plain is inundated, water spreads from the main channel over adjacent flood plain deposit . When the flood retreats, sand and silt etc. are deposited in a zone adjacent to the channel flowing low ridge that parallel a river course.
3. Braided River
4. Delta
Deltas are basically features of river deposition. A river enters a lake or sea of permanent body of water it velocity is checked rapidly and the process of deposition is accelerated. The coarse and heavier material is laid down first and finer and lighter materials is carried further out. Thus the load brought by river gets deposited at its mouth, which gives rise to what is known as a delta; because these deposits are triangular in outline and resemblance the Greek letter delta.
Types of rivers
There are mainly three types of
rivers
a. Straight river
b. Meandering river
c. Braided rivers.
a. Straight river
• Follow a straight path.
• The topography of the area is characterized by steep relief .
• The gradient of the river path is also high causing the flow
velocity of water
• Since the energy level of such river is high, erosion rate is intensely higher than the deposition of sediments
• .deep scouring along the river path is higher than the
side cutting
• Dominantly occurred in the higher Himalaya region
b. Meandering River
• Follow a zigzag path.
• The topography of the area is characterized by moderate relief.
• The gradient of the river path is so moderate causing the river strikes in one end and return to other direction making the path zigzag.
• The river is widened and flow with lower velocity than
that of the straight river.
• Since the energy level of such river is high, erosional rate
is intensely higher than the deposition of sediments.
• The side cutting by the river is higher than the deep
scouring along the river path.
• In the striking bank, the side cutting is higher with higher erosional rate and opposite to strike bank is a depositional bank where depositional of sediments take place.
• Due to this system channel shifting is prominent is such type of river system.
• Meandering river are dominantly occurred in the
midlands and lesser Himalayan region.
c. Braided River
• In this types of river, a single river path is
diverted into several.
paths and may converge to single later.
• The topography of the area is characterized by low relief.
• The gradient of the river path is low and the river area is widened and flow with low velocity.
• Since the energy level of such river is low, the deposition rate of sediments is intensely higher than the erosional rate. Thick succession along the river path and river diverts to other sub paths for flow down. Many channel bars occur along the river path. Due to this phenomenon, the channel shifting is prominent to such type of river system. Braided rivers are dominantly occurred in the Terai region.
Engineering significance of different types of river channels
For construction, different types of civil engineering structure as well as for the survey of availability of
construction materials has to face by civil engineers.
In straight river channel if bridge is to In meandering river, if bridge In Braided river condition, a span
constructed, it is not applicable to make is constructed at the curve of bridge is high with many pillars
a foundation in the river channel as portion, foundation on the on the river path. In the low land
scouring is intense along the path striking bank many be braided river condition, the
affected. hydropower
As side cutting is lower in such cases, an In such condition, the site of Project may be unfeasible due to
arc bridge may be good options. the bridge may be proposed low gradient and high
Eg-Meeteri Bridge constructed above in the bridge may be sedimentation problems.
Bhotekoshi river is an arc bridge which proposed in the straight May irrigation project are
joins the boarder of Nepal and china. portion of meandering river. unfeasible due to low gradient
For hydropower site, in straight river Run off and reservoir may be and high sedimentation
condition, runoff type hydropower is proposed according to problems. In such cases the
applicable. site methods of sediment trap must
condition for be greatly considered .
hydropower site.
The availability of construction materials also detect the construction structures . Eg – presence of granite boulder, a gravity dam is constructed to make a reservoir for kulekhani hydropower project.
The subsurface geology controls the distribution and movement of groung water. Almost all ground water can be through as a part of the hydraulic cycle. Ground water is not a static collection of water body inside. It is moving slowly in its natural state. This movement is governed by hydraulic principles. The flow through aquifers can be expressed in terms of Darcy’s law is applicable to know ground water flow rates and directions. Henary Darcy a French hydraulic engineer, investigated, the flow of water through horizontal beds of sand to be used for water filtration.
Statement:
The flow rate through porous media is proportional to the head loss and inversely proportional to the
length of the flow path i.e.
Q ᾳ hL (i)
Q ᾳ 1/L (ii)
Introducing a proportionality constant K leads to the equation:
Q = -KAhL/L (iii)
Where, K is the hydraulic conductivity which is constant and is a measure of permeability of the porous
medium.
Where, A = cross-sectional area of a cylinder. hL = head loss
L = Length of flow path.
Eqn (iii) can be expressed in general terms.
The –ve sigh indicates that the flow of water in the direction of decreasing head. Q = -KA dh/dl
Q/A = -K dh/dl
or V = -K dh/dl (iv)
Where, V is the Darcy velocity of specific discharge.
The factors dh/dl is called hydraulic gradient. Equation (iv) states the Darcy’s law in its simplest form that the flow velocity (V) equals to the product of hydraulic conductivity (K) and the hydraulic gradient (dh/dl). The head loss is the independent of inclination of the cylinder.
Actually, the flow is limited by pore space so that the average velocity is given by:
Va = Q/A ᾳ (v)
Where, ᾳ = porosity.
Validity of Darcy’s law
Darcy’s law applied to laminar flow in porous media. For flow in pipes and other large sections, the Reynolds numbers serve as a critetian to distinguish between laminar and turbulent flow. It is dimensionless ratio of intertial to viscous forces i.e.
NR = δ VD/μ (vi)
Where = NR = Reynold number δ =
Fluid density.
V = Velocity
D = Diameter of a pipe μ = Viscosity of fluid.
Experiments show that Darcy’s law is valid for NR<1 does not depart seriously upto NR = 10, which represents an
upper limit to the validity of Darcy law.
Fortunately, most naturally underground flow occurs where with NR<1, Darcy law is applicable. Deviation from Darcy law can occurs where steep hydraulic gradient exist, such as near pumped wells. Also turbulent flow can be found in rocks such as basalt and limestone that contain large under ground opening.
a. Aquifers
Aquifer
Ground water holding strata are called aquifers. The water bearing geologic formation or strata which yield significant quantity of water for economic extraction from wells are called aquifers. They contain sufficient permeable material and yield significant quantities of water to wells and springs. This implies that aquifers have an ability to store and transmit water. Unconsolidated sands and gravels are good examples of aquifers. Aquifers are generally extensive and may be overlying or underlying by a confining bed which is relatively impermeable material.
b. Acquiclude
A saturated but relatively impermeable material that does not give appreciable quantity of water to wells, is called acquiclude. Such aquifer can only store water but cannot transmit significant amounts. Shale and clay are good examples of acquiclude.
c. Piezometric Level
The piezometric surcace or potentiometric surface of a confined aquifer is an imaginary surface coinciding with hrdrostatic pressure level of the water in the aquifer. The water level in a well penetrating a confined aquifer defines the elevation of the pizometric surface at that point. If the piezometric surface, a flowing well results.
Confined and unconfined aquifer
a. Confined Aquifer
Confined aquifer occur where ground water is confined under pressure greater than atmospheric by
overlying impermeable strata. Confined aquifer are also called artesian or pressure aquifer.
In a well penetrating such an aquifer, the water level will rise above the bottom of the confining bed. Water enters a confined aquifer from an area which is exposed to the surface. At the exposed part to the ground it becomes unconfined aquifer. A region supplying water to a confined aquifer is known as a ‘Recharged Area’.
It should be noted that a confided aquifer becomes an unconfined aquifer when the piezometric surface
falls below the bottom of the upper confining bed.
b. Unconfined aquifer
As open aquifer that is not overlaying by an impermeable materials and contain water essentially at atmospheric pressure is called an unconfined aquifer. The water in it is also called free groundwater i.e. water table varies in undulating form. Rises and falls in a water table correspond to changed in volume of water an aquifer.
A special case of an unconfined aquifer involves some impermeable strata any where and can preserve certain volume of water. This water may also from a level called ‘Perched Water table’.
(from Keller, 2000, Figure 10.9)
C. Other Aquifers
Aquitard a confining bed that retards does not completely stop the flow of water to or from an adjacent aquifer is called aquitard. Although it does not readily release water to well or springs, it may function as a storage chamber of groundwater.
Aquifuge: A rock body or rock layer having no interconnected opening or interstices and which
thus neither absorbs nor conducts water is called aquifuge.
Leaky Aquifer: An aquifer which receives leaked water from aquitard (i.e. Aquifer below
aquitard) is called leaky aquifer.
Artesian well: An artesian well is simply a well that doesn't require a pump to bring water to
the surface; this occurs when there is enough pressure in the aquifer.
Perched Aquifer: A perched aquifer is a special case of an unconfined aquifer where a saturated lens forms above the main unconfined aquifer and has its own perched groundwater table.
Spring
a. Springs are usually developed when the ground water oozing out from the ground surface . The
main types of springs are mentioned below.
i. Contact spring: If permeable bed meets the sloping surface of the natural ground hill, Springs
may develop. This types of spring is called contact spring.
ii. Dike springs: When a sloping permeable bed (aquifer) is intersected by a dyke, springs may
develop. This types of spring is called dike springs.
iii. Fault Spring: when a sloping permeable bed which is covered by impermeable bed is faulted, then spring may developed and such types springs are called fault springs. Water is also released from fissures developed on rocks, called fissure springs
iv. Artesian Springs: these are springs formed of confined ground water forced upward by hydraulic pressure
v. Karst spring: in limestone regions, ground water forms springs at the surface through widened joint or bedding plane that opens to that surface water to the surface. These are associated with volcanic activity and, or radian actively. Hot springs are common in geothermal regions.
vi. Fracture spring: discharge from faults, joints, or fissures in the earth, in which springs have followed a natural course of voids or weaknesses in the bedrock.
vii. Depression spring: formed where the ground surface intersects the water surface.
Karst spring
Contact Spring
Significance of subsurface water movement
Subsurface water is often a critical factor in various engineering works.
It may pose problems not only during the construction stage but it has a potential to affect
the safe functioning of an engineering project.
Almost every engineering project like, buildings, highway pavements, airport runways, dams, underground structures, structures on rock and soil slopes may be affected in one way or other by the subsurface water, which may lead to failure of such projects, thus causing loss of life and property.
Therefore it is an important aspect of any engineering geological investigation to assess the possible adverse effects of the subsurface water on the proposed engineering projects.
In fact it is not only the subsurface water which will be affecting the engineering structures but in many cases the construction of engineering structures will be responsible in changing the subsurface water regimes. Particularly the underground structures and the reservoir projects have a potential to change the subsurface water regimes considerably.
Therefore, it becomes important that engineering geological investigation of a proposed site must address and evaluate the possible impact of construction on existing subsurface water regime conditions and of existing subsurface water regimes on the proposed construction.
Another purpose is to anticipate what can be expected during construction besides to develop criteria for design and construction.
Subsurface water affects site selection, cost, durability and even the safety of the structures. Subsurface water plays a prominent part in slope movement, volume changes by shrinkage and swelling and collapse of loose soils. It may also erode the foundation of the structures, Rocks and soil properties, which forms the foundation of the structures, are often changed by groundwater
Subsurface water may influence excavation and construction methods by flowing into excavations, by producing seepage forces and uplift pressures and also by its corrosive action. Subsurface water conditions may also affect underground waste disposal.
Natural subsurface water regimes may be directly influenced by hydraulic structures. Therefore, one aim of engineering geological investigation is to facilitate by the provision of subsurface water data/ information, is the prediction of undesirable changes in the subsurface water regime and the recommendation of procedures to avoid them.
In engineering geological investigation the following important information on subsurface water
conditions should be evaluated;
The distribution of sub-surface water.
Water content
Direction and velocity of subsurface water flow.
Springs and seepages from individual water bearing horizons.
Depth to water table and its range of fluctuation.
Regions of confined water and piezometric levels.
Hydrochemical properties such as pH, salinity, corrosiveness.
Presence of bacterial or other pollutants.
Subsurface water conditions are significant for three major aspects of civil engineering works; subsurface water may pose a problem to construction, it may be an erosive agent that degrades the foundation of the structure and subsurface water may be critical to the functioning of the
SITE INVESTIGATION
Elements of an investigation
Types of site investigation (Direct and Indirect Methods)
Study of topographic, geological and engineering geological maps)
Geological investigation for different engineering structures like dam, reservoir, road, building, bridges and tunnel
Engineering Geological Site Investigation
Site investigation is a process of site exploration consisting of boring, sampling and testing so as to obtain geotechnical information for a safe, practical and economical geotechnical evaluation and design. Generally it is an exploration or discovery of the ground conditions especially on untouched site.
Geomorphology, topography, lithology, soli type, secondary sedimentary structures (i.e. joint, fold, fault, thrust, unconformity), surface and subsurface water condition, orientation of bedding/foliation planes, discontinuities, instability condition are major parameters for site investigation which can influence safety, economic and construction period of infrastructures.
Therefore, site investigation is most important task for civil engineers to
determine the feasibility of the project, design and cost estimation of infrastructures.
From the site investigation the engineering geological information which can be quantified are used as input parameters in design and cost
Important of Site investigation
Site investigations assist to evaluate the feasibility, economics, design and safety of a project by
• developing sufficient understanding of geology and hydrogeology for project design and construction,
• providing rock, soil and hydrological design
parameters,
• providing data for selecting major structures locations, alignment, excavation methods and determining the most economical alignment,
• providing data for minimizing uncertainties
georisks and cost estimation,
• establishing the most economical design, tender document preparation and construction program,
• improving the safety of the work
< 5 % Site investigation reduces the bid cost by 10 to 15% (Parker, 1996)
Mountainous terrains
Accessibility and transportation
Limited facilities and technology in-house
Air lift facilities ?
Tendency of less investment in site investigation
Difficult deep drilling > 300m
Very Difficult for Long and deep tunnel > 400m cover
Limited drilling facilities
Only few geophysical test company
No rock lab tests and in situ tests facilities in-house
Difficult to construct of precise geological model
Types of site investigation
There may be two phases of engineering geological site investigation:
• Surface Investigation
• Subsurface Investigation
Surface Investigation
Surface investigation also two components:
1. Direct surface investigation
2. Indirect surface investigation
Indirect Surface Investigation
It is the type of investigation in which preliminary idea can be obtained about any specific site by not visiting directly in the site. There may be different means by which such investigation can be carried out:
• Review of previous literature
• Topographical map analysis : slope, drainage network existing structure etc.
• Remote sensing : interpretation of the image like aerial photographs,
satellite images (Landsat imagery) etc.
Direct Surface Investigation
It includes the investigation carried out by visiting the actual site. Information is collection and documented by observation, measurement, interpretation. In engineering geological investigation, the following data are to be collected within direct surface investigation.
• Types of rocks or soil, and major component minerals on them.
• Attitude (orientation) of rock.
• Thickness of soil or rock.
• Weathering grade of rock.
• Numbers & types of discontinuities and their attitude.
• Strength of rock.
• Geological structure like bedding, foliation , joints, faults, folds,
unconformity etc.
• Slope stability factors, natural slope and landslides.
• Presences or absences of existing engineering structure like canals, dams,
tunnel etc.
• Topography, drainage system, catchments area, flood level etc .
Subsurface Investigation
Subsurface investigation may also have two component :
a. Indirect subsurface investigation:
Is the type of investigation in which subsurface data are obtained by not directly looking at the subsurface materials and structure . The major means of indirect subsurface investigation is the geophysical exploration method, which includes seismic method , electric, resistivity method, gravity and magnetic surveys. From these methods, the type of material (rock, soil) within the surface of the earth can be determined by carefully interpreting the geophysical data. Groundwater level, presences of aquifers, or other structures like fault , fold can be find out. Similarly economically valuable materials can be searched by this method
b. Direct subsurface investigation
A. Exploratory excavation: Digging pits or trenches , dozer cuts, tunneling etc.
B. Bore hole exploration: Core drilling logging etc.
Depending upon the important of project ,cost available and the extent of details information needed, the spacing of drilling or digging may vary.
Hence, subsurface exploration may be project specific and cost specific. From this method, depth thickness, type of soil and rock, presence or absences of discontinuities, weathering grade, water table conditions and aquifers parameters, porosity, permeability and major geological structures like folds, faults, joints etc. can be find out
Types of site investigation
Surface investigation Subsurface investigation
It may be project specific and cost specific from this method, depth, thickness , types of soil and rocks, presence and absence of discontinuities, weathering grade, water table conditions and aquifers parameters, porosity permeability and major geological structures like folds, faults, joints etc can be find out .
Direct Indirect Direct Indirect
With visiting the actual site, investigation carried out. With out visiting directly in the site, preliminary idea can be collected. There are different means- 1. Exploratory excavation : digging pits or trenches, dozer cuts, tunneling etc The major means is the geophysical exploration method includes seismic method, electric resistivity method,
Information is collected and documented by observation, measurement and interpretation Following data are to be collected
1. Rock and soil types and major component minerals on them
2. Attitude of
rocks
3. Thickness of soil
and rock
4. Weathering
grade of rock
5. Numbers and types of discontinuities and
1. Review of previous literature
2. Topographical map analysis : slope, drainage networks , existing structures
3. Remote
sensing: interpretation of the image like – aerial photographs , satellite image (landsat imagery) etc
2. Borehole
exploration
:core drilling,
logging etc.
3. Depending upon the importance of project, cost available and the extend of detail information needed, the spacing of drilling of digging may vary .
Gravity and magnetic surveys. From these methods, types of materials (rock, soil) within the surface
of earth can be determined carefully interpreting the geophysical data. Groundwater level, presence of aquifers, or other structures like fault, fold can be find out
. Similarly , economically valuable materials can be searched by this method
Their attitude
6. Strength of rock.
7. Geological structure like bedding, foliation , joints faults , folds, unconformity etc
8. Slope stability factors natural
slope and landslides
9. Presence or absence of existing engineering structure like-canals, dams , tunnels
10. Topography, drainage system,
catchments area, flood level
etc.
Site exploration Drilling, test methods
and borehole logs
1. DRILLING
it is the direct method of subsurface exploration. It is carried out to find the nature of soil, type of rock, presence of structure in the rock and their engineering quality. It is important to find out the porosity and permeability of soil and rock and also to detect the depth of the water table. A borehole into the surface of earth is drilled upto a required, predetermined depth using suitable technics. In the simplest case, soil and rock sample are obtained from the ground below as the drilling progresses. Deep drilling are preformed either by cable tools method or by one of the several rotary methods. Each method has practical advantages, so experienced drillers endeavor to have equipment available for a diversity of drilling approaches.
The most important drilling methods are the following.
1. Percussion or cable tool method.
2. Rotary method
3. Rotary –percussion method
4. Reserves circulation rotary method
5. Auger boring method
1. Percussion or cable tool method.
Percussion drilling is a drilling technique in which a drills bit is attach to rope or cable is repeatedly raised and lowered impacting soil and rock and making a hole deeper. It is frequently used to drill wells or for mineral prospecting activities. It has been used for hundreds of year and adapted to whatever technology is available Drills can be simple apparatus consisting of a heavy bit and a rope and operated by hand modern version are also called cable drilling and uses an engine and cable to drill holes, that may be hundreds of deep
Applications :-
• Suitable for all types or wide range of geological environment
• Most simplest , easiest, most reliable and the economic method
• Due to it's simplicity of design, maintenance and repairs of rigs and tool is easy and fast
• Mare accurate sampling
• Greater depth can be achieved
2. Rotary method: It is one of the rapid method for drilling in unconsolidated strata with diameter up to 45 cm or more. This method operates continuously with a hollow rotating bit through which mixture of clay and water or drilling mud is forced. Materials loosened by the bit is carried, upward in the hole by raising mud
Drilling mud consist of a suspension up water, bentonite, clay and various organic activities, rotary drilling is employed for oil wells and its application to water -well drilling is steadily increasing . Advantages are rapid drilling rate the avoidance of placement of a causing during drilling and the convinces of electric logging. Disadvantages include high equipment cost, more complex operation, the need to remove cake during well development and the problem of lost circulation in highly permeable or covetous geologic formations.
3. Rotary –percussion method:- It is the fasted method for drilling in hard –rock formation and uses air as the drilling fluid. A rotating bit, with the action of a phenamatic hammer delivers 10 to 15 impacts per second to the bottom up the hole. Penetration rate can be up to 0.3 miter/min. A change to conventional rotary drilling with mud is implied where caving formation or large quantities of water are encounter. The maximum depth bored through this method is 600 m, however, greater depth can be reached with heaver equipment and the diameter ranges from 30- 15 cm steel or wrought iron –pipe is used as casing materials and used in irrigation industrial and municipal purposes it is a type of very fast drilling which combines rotary and percussion method. It is now used in oil exploration and would be economical for deep water well.
4. Reserves- circulation rotary method:-
It is used on surface having silt, sand, gravel and cobble with water table at 2-30m, the maximum depth gained by this method is 60m and diameter is about 40-120cm. Steel or wrought iron pipe is used as casing materials and is used for irrigation industrial and municipal purposes. It is effective for large diameter of holes in unconsolidated and partially consolidated deposit. It required a lage volume of readily available water. It can drill up to the depth to the 125 m or more and are usually gravel packed.
OTHERS TEST METHODS
i. Test pit
it is an exploratory pit or hole excavated for determining the nature and fitness of the engineering works. Test pits with cross-sectional dimensions 1 m x 1 m to 2 m x 3 m usually are dug by hand labour to explore soil strata. Such pits are helpful to examine the nature of soil and subsoil materials, their contacts and soil-bedrock contacts and in some cases ground water conditions.
ii. Trench
it is the long narrow shallow excavation in the ground for visual inspection and
sampling.
The common dimensions of trenches are:
Hand dug- 1-2 m. Bulldozer- 3-5 m.
Trenching machine- upto 3 m.
Dragline- upto 10 m.
The trenches provide a continuous profile of soil strata, an excellent view of overburden bedrock contact, structural features and defects in bedrock and obtain in situ soil sample. iii.Boring
1. Auger boring method;- It has two types . they are
a. Hand auger : it is best suited where the materials of surface is clay silt sand, and gravel is less than 2cm and water table is at depth of 2-9 m. the maximum depth bored by this method is about 10m and diameter ranges from 5-20cm . it is most effective for penetrating and removing the clay but it is limited by gravel over 2cm . causing is required if materials is loose.
b. Power auger : it is used on suited where the materials of surface is clay silt sand, and gravel is less than 5cm and water table is at depth of 2-15 m. the maximum depth bored by this method is about 25m and diameter ranges from 15-90cm.
2. Wash boring method:- In this method a steel chopping bit is churned inside a cashing 5-15 cm to break the rock, and the cutting are floated up through the casing by wash water. The cutting then are discharged into a slump for examination. The bit is driven by driving weight from cable and wash pipe is rotated while driving down.
iv. Core sampling:- These are the cylindrical samples of rock obtained through the use of hollow drill bit which cuts and retains a section of rock underground. They are used to determined the subsurface geology and ground conditions. It is also used to identify in situ properties, petrographic characteristics and bearing capacity of formations. By planning a series of holes it is possible to determine the dip, strike, thickness, structure, deformations, and permeability of rock formations and their potentialities.
BORE HOLE LOG
The drilling subsurface earth materials (soils/rocks) are collected according to the depth of drilling called core. This core material is recorded in the sheet of a paper (graphical representation in scale) according to the depth called core logging or bore- hole logs. During core logging types of soil, rock and their different properties are described. Logging charts clearly show the thickness of individual rock or soil formations and their characteristics.
Geophysics
It is branch of geological science which is application of concepts of physics to the study of the interior of the earth. The indirect methods of subsurface explorations are used extensively and involve application of geological techniques for obtaining fairly
accurate idea of subsurface geology. These methods provide subsurface geology especially, buried metallic objects, construction materials, water table, depth of bed rock, thickness of rocks or soils (overburden), degree of consolidation, faults, buried channels etc.
Types of Geophysical methods
a. Seismic methods
i. Seismic refraction
ii. Seismic reflection
b. Electrical Resistivity methods
c. Self potential methods
d. Electromagnetic methods
e. Multi Channel Analysis of Surface Waves (MASW)
Methods Provide information Application
Seismic refraction Thickness of soil layers
Location of groundwater table Location of rock head Location of low velocity zones
Estimation of rock mass quality Extensively used and limited for shallow
depth.
Density and elastic moduli which determine the propagation velocity of seismic waves.
Seismic reflection Location of different layers of soil, rock,
sea bottom, etc.
Soil and rock structure Interpretation for great depths and
expansive.
Density and elastic moduli which determine the propagation velocity of seismic waves.
Electric resistivity / tomography Thickness of soil layers Location of ground water table Location of rock head
Location of weak zones and failure plan
Estimation of rock mass quality Location karst topography Extensively used and interpretation uncertainty.
Conductivity and capacitance which determines resistance of ground.
Self potential Location of water leakage
Estimation of ground water velocity Electrical conductivity
Electromagnetic
(Radar) Location of ground water table
Soil structures Openings Limited used and restricted to soft
ground
Multi Channel Analysis of Surface Waves (MASW) Bearing capacity, density
Dynamic parameters (modulus of elasticity, shear modulus, Poisson’s, P wave velocity ) Foundation, rock head and earth quake engineering.
Shear wave velocity used to calcula
soil and rock parameters.
Phages of site investigation
Preliminary Details Implementation
Initial phase of site In this phase, site In this phase, the study
investigation which exploration is carried out permits change in
support the feasibility of which provides expected condition that
a project necessary details about are incorporated in
prevailing site condition design modification and
for project for design, evaluation of completed
planning prior to work that supports actual
construction , construction of project.
In this phase, direct and In this phase, besides
indirect surface direct surface
investigation methods are investigation , direct and
carried out. indirect subsurface
investigation method are
carried out.
Interpretation of Topographic map
Map
A map is graphical representation of data obtained from the measurement of specific field site on plain paper in certain scale (depends upon purpose) with reference to north. A map shows natural earth features, man made features like infrastructure road, urban, reservoir, canal, railways, bridges etc
A topographic map is a two-dimensional representation of a portion of the three- dimensional surface of the earth . Topographic is the shape of the land surface, and topographic maps exist to represent the land surface.
Topographic map are tools used in geologic studies because they show the
configuration of the earth’s surface.
General information
The terms below indicate what information is contained on a topographic map,
and where it can be found.
Map scale : Maps come is a variety of scales, converging areas ranging from the entire earth to a city block ( or less). If the actual distances are considerably decreased on the map, it is celled small scale map. The opposite would be a large scale map. Eg- 1cm=1 m is a small scale map. 1 cm = 50 m is a large scale map.
Vertical scale ( contour interval ) : All maps have a horizontal scale. Topographic maps also have a vertical scale to allow the determination of a point in three dimensional space.
Contour Lines: Contour lines are used to determine elevations and are lines on a map that are produced from connecting points of equal elevation (elevation refers to height if feet, or meters, above sea level).
The following are general characteristics of contour lines:
1. Contour lines do not cross each other, divide or split.
2. Closely spaced contour lines represent steep slopes, conversely,
contour line that are spaced far apart represent gentle slopes.
3. Contour lines trend up valleys and form a “V” or a “U” where they
cross a stream.
On most topographic maps, index contour lines are generally darker and are marked with their elevations. Lighter contour lines do not have elevations, but can be determined by counting up or down from the nearest index contour line and multiplying by the contour interval The contour interval is stated on every topographic map and is usually located below the scale.
Published geological maps
Published Geological Map with a scale of
1:1 000 000;1:50 000; 1:10 000.
In case of Nepal 1:50 000 and 1:25 000
Geological maps are constructed to show:
- The stratigraphic names, and thus the relative age, of the geological formations in the area mapped,
- The distribution of these formations within the area mapped,
- The geological structure of the area mapped.
- The lithology of the formations, Geomorphological features in the area, such as major landslides, features resulting from the activities of man, such as mines and quarries.
It also accompanied a geolgocial cross-section along a given line which shows the underground geology along that specific line.
Geological map provides incomplete infromation for engineers, For example
Geologigical map indicates that there is Kuncha Formation in the area of his/her interest- What does he/she undestand with this information?
If a geoloigical map is to be interpreted for engineering purposes, scales of 1:10000 or larger are required and the map must have contours.
Geological Map Making Process
Geological traverses along rivers and road cut sections
Collecting geological data: rock types, geological structures, mineralogy, etc.
Preparing geological map Preparing geological cross-section Preparing stratigaraphical column
Geological mapping at a large scale
Small scale map ( e.g. 1: 25,000 or 1:50,000 are useful just to know the regional geology. But for engineering purpose, we need large scale map.
Large-scale maps are those devoted to the depiction of relatively small surface areas in great detail and range from about 1:1 000 (for the geology of a dam site) to about 1:50 (for a rock slope or tunnel). They are prepared for an engineering geological purpose.
Interpretation of geological maps for engineering purpose
Rock types and their distribution
Geological structures like faults, unconformities, and fold axis, and their distribution
Geological contacts and its distribution
Dip and strike of the strata
Relative age relationships of the various layers
Nature of rock and soil materials and the way in which they were deposited or intruded.
Published engineering geological maps
Engineering geological maps shows, among others, features like:
-The lithology of the strata, and the thickness of the layers and their depth below surface, and the depth to the water table;
-The location of significant geomorphologic features, such as the presence of karsts features in limestone, landslides, active faults etc.,
- Hazards remaining as the result of past industry, such as abandoned mines, old quarries, and areas of toxic fill etc.,
- Location of construction materials.
Information depicted in an engineering geological map differs with the purpose of its construction. For example, it may depict;
Site geology and geomorphology in such a way as to aid resolution of a particular engineering problem. Such maps may contain geotechnical data or, at the very least, the description of the features mapped will be in engineering geological terms.
Record the site geology uncovered during construction, again using an engineering geological descriptive vocabulary rather than ordinary geological terms. Such maps are based upon data recovered during site work by an engineering geologist working for a contractor or consultant.
What should be shown in an engineering geological map ?
1. A legible and complete topographic background, showing roads, towns, streams, prominent buildings etc. Contour lines should be shown. The map should include marginal comment giving the date of publication of the topographic base map.
2. The grid co-ordinate network appropriate to the project or country.
3. The scale of the map given both in figures and as a linear scale. If the original map was in units of feet, miles etc. then the linear scale should be both in these units and in meters.
4. North points; these should be true north, grid north and magnetic north. The annual change of magnetic declination should be given.
What should be shown in an engineering geologicla map ? ......
5. The map should be dated giving both the date of preparation of the map and the date of publication. The dates should be accurate to the nearest month.
6. A legend showing the meaning of all the symbols shown on the map.
7. The names of those responsible for the preparation of the
map.
Symbology in Engineering Geological Map
• Maps must be ‘user friendly’, easily understood and easily read
• As far as possible follow the symbology suggested by ,the Working Party of the Engineering Group of the Geological Society of London who has produced a catalogue of recommended symbols in their report in 1972 (Geological Society Engineering Group 1972).
• Since any standard system of symbols may not be adequate for a particular purpose and a mapmaker will have to modify or add additional symbols to the standard list.
Geological investigation for different engineering structures
• Tunnels:
Tunnels are underground router or passages driven through the rock of soft ground
without disturbing the overlying soil or rock cover
1. Horizontal or slightly dipping rock with strike parallel to the axis of the tunnel.
2. Steeply dipping formations with the strike perpendicular to the axis of the
tunnel
3. Location will be better in an anticline is favorable since the vertical pressure relived and due arch action by the upward than is syncline, since there will be increase in pressure. Also the water flows from anticline arch where as water flows into the tunnels if located in syncline
4. Fault : first to consider whether the faulting is recent (active), possibility of new fault is to be considered . If a tunnel intersects an active fault, nothing can be done to protect the structure: hence the tunnel alignment should be shifted. Also in any considerable water in flow. Fault gouge can be swelled and hence may carry displacement .
5. If the tunnel is located under the water table, a kind of sand like
suspension may rush into the tunnel.
6. Fractures and joint : joint spacing and joint sets should be less.
7. Effects of water on rocks whether it dissolves the rock, deteriorate it or
produce no effect. If produce no effect it will be favorable.
8. Strength of rock.
9. Lost: if blasting required, what part of the tunnel needs support & if what types,
is water likely to be encountered and if no in what portion.
Bridges
1. Bank scouring : The site should be at minimum bank scouring of the river.
Due to
water velocity, the support (bridge) are also scored
2. Beds should be competent
3. Narrow span (width ) of the river is favorable.
4. Bedding should be (strike) across the river flow.
5. Less jointed, less fractured.
6. Fracture filling should not be clay.
7. The effects of structure to the surrounding region.
8. Should be avoided the geological structure like fault, fold, thrust etc.
9. Expensive soils should be studied. Particular attention should be given to
the origin, discharge and periods of water.
Dams
Dams are solid barriers constructed across a river valley with a view of impounding water. Different types: Gravity dam. Area dam etc,
Characteristics to be considered for dam sites:
• Unusual accumulation of large masses of building materials and water on a limited area the earths surface and hence heavy pressures or the foundation.
• Destructive influences of the water in the reservoir on the foundation and
on the structure itself, which may cause leakage, erosion even failure.
• Emplacement always in a valley, hence dam depends on environmental
conditions.
Sliding problem
• If W and P represent the sum of all vertical and horizontal forces respectively, force P tends to displace the dam horizontal and to make slide. Since the forces W and P undergo changes both during and after construction.
• Most unfavorable combination will be when P/W= Maximum. The smaller the P/W value should be less than the co-efficient of friction.
• The rock should be competent ( strong enough) and less porous avoid
fractures and joint .
Dam site
• Topographically – River valley is most suitable.
• Technical –String, impermeable and stable.
• The site should be not far off. From deposits of materials.
• Lithology should not be varied at the site i.e. there should not be
material boundary.
• Stress if acted normal to the bedding plane the strength of rock would be high, hence horizontal beds are best and dip should be gently upstream. Most unfavorable direction of the bed is strike to resultant stress.
• Fault should be avoided. But if we don’t have any alternatives, small
scale faults can be treated by grounding.
• Axial plane of the fold should be avoided. In synclinal folds, water leakage.
from beneath the dam may occur.
• Mostly hard, massive igneous rocks are best massive siliceous cementing materials having sedimentary rocks are also food, massive varieties are good.
Reservoirs
A reservoirs meant to hold water; hence the principle geological criterion of the suitability of a reservoir site is that rocks and soils around and below if form an impervious basin without need of excessive and expensive grounding. Other point to consider include:
A. Change in water level after the reservoir fills due to siltation
B. Leakage sources:
• Permeable soils
• Rock aquifers
• Along fault and joint
C. Limestone, and to a lesser extent sandstone with a calcareous cement may present serious hazard
D. The rocks below and at the sides of the dam should impervious.
E. The syncline fold plunging upstream will be favorable ; but anticline is
unfavorable.
For Reservoirs sites the following factors are to be studied :
F. Ground water conditions: High water table conditions are favorable since there is flow of water from rocks of reservoir bank to the reservoir. Low water table regions are unfavorable and dangerous since there is possibility of flow of water from the reservoir to the rock.
G. Permeability Investigation
Impervious and impermeable rocks are better.
If permeable layer present, should be treated.
Igneous rocks unjointed, massive limestone and impermeable sandstone etc. are less permeable, whereas coarse sandstone, gravels, sands and glacial deposits are highly permeable.
H. Siltation
Sedimentation of the reservoir with passage of time .
Siltation will make the project failure by reducing storage capacity.
Stream velocities along with the natural of tributaries and rock type through which of flows affect.
Topography, climate, vegetation may affect.
Check dams, installation of outlets, silt basin and watershed improvement are methods of checking siltation .
Geology of Nepal
Geological division of Nepal
Engineering geological problem of each geological division of Nepal
Major rock type, soil type, construction material and geological structure
found in different geological division of Nepal
Geological Division of Nepal
• The Geology of Nepal is dominated by the Himalaya the highest, youngest and a very highly active mountain range (Upreti 2014). Himalaya is a type locality for the study of on- going continent - continent collision tectonics.
• Since 55 Ma the Himalayan orogeny beginning with the collision of Indian subcontinent and Eurasia at
the Paleocene/Eocene epoch (Rowley 1996), has thickened the Indian crust to its present thickness of 70 m (230 ft) (Le Fort 1975).
• The Himalaya range is about 2400 km. long and extends from Indus rive of Pakistan in the west to Assam in east. The Himalaya belt is the results of collision of two tectonic plates, Indian plate and Tibetan plate on the north. Before the collision of the plates, the place was occupied by Tethys Sea. The collision of the plates was still going on.
Geological division of Nepal
Geologically Nepal Himalayas can sub-divide in to five tectonic zones from south to north. The tectonic are extending east to west and almost parallel to sub-parallel. The zones are as follows.
1. Indo-gangetic plain or terai zone
2. Sub Himalayas or siwaliks or churia zone
3. Lesser Himalayan zone
4. Higher Himalayan zone
5. Tibetan-Tethys-zone
Geological Map of Nepal
Indo-Gangetic plain
• The gangetic plain is also called the Terai which is a rich, fertile and ancient
land in the southern parts of Nepal.
• It represents Holocene/Recent sedimentation belt where fluvial sedimentation is still in progress.
• This plain is less than 200 m above sea level and has thick (about 1500 m)
alluvial deposit.
• The alluvial deposits mainly consists of boulders, gravel, sand, silt and clay.
• It is a foreland basin which consists of the sediments brought down from
the northern part of Nepal.
• It is the Nepalese extension of the Indo-Gangetic Plains, which covers most of northern and eastern India, the most populous parts of Pakistan, and virtually all of Bangladesh. The Plains get their names from the rivers Ganges and Indus.
• The vast alluvial plains of the Indo-Gangetic Basin evolved as a foreland basin in the southern part of the rising Himalaya, before breaking up along a series of steep faults known as the Himalayan Frontal Fault (Nakata 1989) or the Main Frontal Thrust (HFT) (Gansser 1981).
• It comprises several sub-basins and all of them are quite shallow towards
the south, but rather deep in the northern sections.
Sub-Himalaya (Siwaliks)
• The Sub-Himalayan Sequence borders the Indo-Gangetic Floodplain along the Himalayan Frontal Fault and is dominated by thick Late Tertiary mollassic deposits known as the Siwaliks that resulted from the accumulating fluvial deposits on the southern front of the evolving Himalaya.
• In Nepal, it extends throughout the country from east to west in the southern part.
• It is delineated by the Himalayan Frontal Thrust (HFT) and Main Boundary Thrust (MBT) in south and north respectively.
• The youngest sediments on the top are the conglomerates, and the sandstones and mudstones are dominant in the lower portions.
• The upward coarsening sequence of the sediments obviously exhibit the time-history in the evolution and growth of the Himalaya during the early Tertiary time (Gansser 1964).
• The Sub Himalayan zone is the 10 to 25 km wide belt of Neogene Siwaliks (or Churia) group rocks forming the topographic front of the Himalaya.
Siwalik Contd……..
• It rises from the fluvial plains of the active foreland basin, and this front generally mapped as the trace of the Main Frontal Thrust (MFT).
• The Siwaliks Group consists of upward-coarsening successions of fluvial mudstone, siltstone, sandstone, and conglomerate.
• According to lithology, this unit is further divided into three zones as follows:-
• Upper Siwaliks: consists of Conglomerate
• Middle Siwaliks: consists of coarse sandstone
• Lower Siwaliks: consists of fine sandstone, mudstone
Lesser Himalayas
• The Lesser Himalayas lies in between the Sub-Himalayas and Higher Himalayas separated by the Main Boundary Thrust (MBT) and the Main Central Thrust (MCT) respectively.
• The total width ranges from 60–80 km. The Lesser Himalayas is made up mostly of the unfossiliferous sedimentary and metasedimentary rocks; such as shale, sandstone,
conglomerate, slate, phyllite, schist, quartzite, limestone and dolo mite.
• The rocks range in age from Precambrian to Miocene. The geology is complicated due to folding, faulting and thrusting and are largely unfossiliferous.
• Tectonically, the entire Lesser Himalayas consists of two sequences of rocks: allochthonous, and autochthonous-paraautochthonous units; with various nappes, klippes and tectonic windows.
• The northernmost boundary of the Siwaliks Group is marked by the Main Boundary Thrust (MBT), over which the low-grade metasedimentary rocks of the Lesser Himalaya overlie.
Contd……..
• The Lesser Himalaya, also called the Lower Himalaya, or the Midlands, is a thick (about 7 km) section of para-autochthonous crystalline rocks made up of low- to medium grade rocks.
• These lower Proterozoic clastic rocks (Parrish & Hodges 1996) are subdivided into two groups.
• Argillo-arenaceous rocks dominate the lower half of the succession, whereas the upper half consists of
both carbonate and siliciclastic rocks (Hagen (1969); Le Fort 1975; Stöcklin 1980).
• The Lesser Himalaya thrust over the Siwaliks along the MBT to the south, and is overlained by the allochthonous thrust sheets of Kathmandu and HHC along the MCT.
• The Lesser Himalaya is folded into a vast post- metamorphic anticlinal structure known as the Kunchha-
Gorkha anticlinorium (Pêcher 1977). The southern flank of the anticlinorium is weakly metamorphosed, whereas the northern flank is highly metamorphosed.
Higher Himalaya
• It consists of huge pile of strongly high grade metamorphosed rocks and is situated in between the fossiliferous Tibetan sedimentary zone in the north and MCT in south.
• It consists of about 10km thick succession of crystalline rock of Himalaya extending continuously along the entire length of the country, whereas the width is about 20 km.
• It consists of essentially high grade crystalline rocks including various kinds of gneiss, schist and magnetite in Nepal.
• This zone covers 14 peaks of Himalaya.
• The age of rocks found in Higher Himalaya zone is Pre- Cambrian and the granite was intruded in Tertiary period as determined by radio-metric dating.
• Ganser (1964) has divided the Higher Himalaya Zone into two sections:
• a) Kaligandaki Section
• b) Everest Section
Tibetan-Tethys Himalayas
• The Tibetan-Tethys Himalayas generally begins from the top of the Higher Himalayan Zone and extends to the north in Tibet.
• In Nepal these fossiliferous rocks are well developed in Thak Khola (Mustang), Manang and Dolpa area.
• This zone is about 40 km wide and composed of fossiliferous sedimentary rocks such as shale, sandstone and limestone etc.
• The area north of the Annapurna and Manaslu ranges in central Nepal consists of metasediments that overlie the Higher Himalayan zone along the South Tibetan Detachment system.
• It has undergone very little metamorphism except at its base where it is close to the Higher Himalayan crystalline rocks.
• The thickness is currently presumed to be 7,400 m (Fuchs, Widder & Tuladhar 1988).
• The rocks of the Tibetan Tethys Series (TSS) consist of a thick and nearly continuous lower Paleozoic to lower Tertiary marine sedimentary succession. The rocks are considered to be deposited in a part of the Indian passive continental margin (Liu & Einsele 1994).
Engineering Geological Problem
Terai
• The Terai is made up of recent river deposits and consists of coarse sediment in the north, near to the base of Siwaliks Range and fine in the south, near to the Indian border to Nepal. The elevation of Terai ranged from 65 m in eastern Nepal to 200 m in western Nepal with broad plain area.
• All rivers of Nepal drain to the Ganga River of India through the Terai. As a result, every year, Terai is facing extreme problems of floods and river bank erosion.
• Area near to the Siwaliks Range is also confronting problems of debris flows. Moreover, both small and large rivers have shown channel shifting nature in the last 300 years.
• Riverbeds in the Terai may rise at annual rates of 15 to 30 cm, and satellite imagery clearly shows that the Koshi River in eastern Nepal has shifted about 125 km west of its original course in 250 years (Joshi, 1985). Thus, river channel management during road construction is main geological engineering issue of Terai.
• In 18 August, 2008, the Koshi River now changed its route and started to flow through the channel before 51 year ago. As a results, nearly 150,00,000 people were displaced from the area both in India and Nepal.
Siwalik
• The Siwalik (Churia) Range is made up of geologically very young
sedimentary rocks such as mudstones, shale, sandstones, siltstones and conglomerates. These rocks are soft, unconsolidated and easily disintegrable.
• The Upper Siwalik contains thick beds of conglomerates and they are loose and fragile.
• Similarly Lower Siwalik and Middle Siwalik have problem from alternating beds of mudstones and sandstone. In such alternating bands, mudstone can flow when saturated with water which results overhanging sandstone beds. Such overhang jointed sandstone beds easily disintegrate into blocks.
• Similarly, throughout Nepal, the rainfall within Churia Range is normally in the range of 2000 to 2500 mm per year. As a result, geological conditions and the climate render the Churia Range highly susceptible for landslides processes.
• Basically, rock failures, shallow slides and debris flows are common in
Lesser Himalaya
• The Mahabharat Range is belongs to the Lesser Himalayan Zone. It is the most important barrier of the monsoon clouds and it greatly influences the rainfall distribution pattern in Nepal.
• Almost in whole Nepal, southern face of Mahabharata Range gets extensive
rainfall in comparison to Midland.
• The annual rainfall in Mahabharat Range area is comparatively higher and the frequency of high intensity rainfall is also high. Thus, these areas are getting extensive problem of floods, debris flows and shallow landslides. These events are periodically causing big disasters.
• Disaster of south and south east Kathmandu in 1993 and disaster of the
Mugling-Narayanghat Road in 2003 are examples of such problems.
• Not only rainfall but geological condition and very steep slopes also plays major role to soil slips and debris flows in the Mahabharat Range.
• It is noticed that the area made up of rocks such as limestone, dolomite marble and granites, the slopes are more stable in the Mahabharat Range whereas area consisting of rocks such as phyllites, slates, intercalation of phyllites and quartzites render the terrain most prone to landslides.
Higher Himalaya
• The Fore Himalaya is a northern part of Midlands and it is the frontal portion of the
Higher Himalaya.
• Geologically, it is generally belongs to the Lesser Himalayan Zone in many places and in some places it is the Higher Himalayan Zone. Thus, main rock types of this province are phyllites, schists, marble, quartzites, and gneisses.
• Tectonically, this zone is very active and uplifting at a high rate and the topography is steep and rugged. Similarly, like the south faced slope of the Mahabharat Range, the Fore Himalaya also gets high rainfall in the range between 2000 to 3500 mm.
• This province is also another vulnerable area for landslide occurrence, but because of less soil on steep slope, mainly rock related failure problems are very frequent.
• Deep seated landslides are also common in this zone. Some landslide dams can be
also noticed in narrow river valleys of this province.
Tibetan-Tethys Himalayan
• The province behind (north) the Higher Himalaya is called Trans Himalaya. Geologically, this province
belongs to the Tibetan-Tethys Himalayan Zone.
• This area is situated in the rain shadow zone of the greater Himalayan Range.
• This zone has average annual rainfall very low in comparison to the Midlands and the Fore Himalaya.
• Thus soil related landslides are less frequent but debris flow in a snow fed stream is quite common.
• The river bank made of alluvial and glacial moraine possesses bank failure problem.
Soil and Types
• Terai Alluvium
• Mountain soil
• Residual soil
• Colluvium soil
Structures
• HFT
• MBT
• CCT
• MCT
• STDs
• Others
• Primary and secondary structures
• Major and minor folds
• Joint, cracks, fractures etc
• Others Faults/thrusts
Terai
• Main hazard: River flooding
• Control
– Use of civil engineering structures.
– Proper drainage management.
Siwalik
• Main hazard: Soil erosion, especially sheet, rill and gully erosion and
landslide.
• Causes:
– Soft and fragile nature of rocks
– High slope
– active tectonic stress (MFT),
– Immature topography
– Toe cutting of Rivers
– Hill cutting during road constructions etc.
• Control:
• By using civil engineering structures
• Bio- engineering
• Drainage managemant
• Detail geological investigation before construction works.
• Main hazard:
Lesser Himalaya
– Landslide i.e. mainly slope failure and debris flow
– Soil erosion
– Toe cutting action of rivers
Cause
High slope
Presence of geological structure such as folds, faults, joints etc.
Activity of MBT and MCT (Seismicity)
Inherently weak geological setting (i.e. harder rocks above softer)
Concentrated precipitation
Deforestation
Improper landuse etc.
Control
By using civil engineering structure ( Retaining structure)
management of drainage
Bio engineering
Detail site investigation before construction work.
Higher Himalaya
• Main Hazards
– Rock fall
– GOLF ( Glacier Lake Outburst Floods)
Control
By using civil engineering structure
By monitoring, locating and controling the possible glacier lakes.
Mineral Reserves
• Mineral reserves are resources known to be economically feasible for extraction. Reserves are either Probable Reserves or Proved Reserves. A Probable Ore Reserve is the part of indicated, and in some circumstances, measured mineral resources that can be mined in an economically viable fashion.
Types of reserves
PROBABLE RESERVE
• Estimates made on the basis of measurements from widely spaced sampling points and exploratory openings (borehole/ pit/ trenches) with reasonable extrapolation on geological grounds.
• The shape, thickness variation, likely persistence, geological structure are broadly known. Some information on mineralogy, petrography of the host rock and wall rocks, ore dressing characteristics.
• The error of estimation of tonnage should be in the range of 20-30 %.
• This category implies a clearly lower status to the ore reserve in terms of degree of assurance, in spite of being still within the direction of economic considerations.
Possible Reserve
The Possible Reserve have the following characteristics:-
• The grade estimate of a possible reserve is a broad indication of the likely
quality.
• The possible reserve contains only very general information on the mode
of occurrence of geological structure and ore behavior.
• The ‘Possible Reserve’ may have an error level of 30 to 50 %.
• Proved Reserves: In this case, the reserves are estimated from dimensions revealed in outcrops, trenches, mine workings and boreholes and the extension of the same for reasonable distance not exceeding 200m on geological evidence. Where little or no exploratory work has been done, and where the outcrop exceeds one km in length, another line drawn roughly 200m in from outcrop will define a block of coal that may be regarded as proved on the basis of geological evidence. (Boreholes at 400 m and borehole density of 8-9 per Sq.Km.)
* Indicated Reserves: In the case of indicated reserves, the points of observation are 1,000 m apart, but may be 2,000 m for beds of known geological continuity . Thus a line drawn 1,000 to 2,000 m from an outcrop will demarcate the block of coal to be regarded as indicated (Boreholes at 1 to 2 km and borehole density of 1-2 per Sq.Km.)
* Inferred reserves : This refers to coal for which quantitative estimates are based largely on broad knowledge of the geological character of the bed, but for which there are no measurements. The estimates are based on an assumed continuity for which there is geological evidence, and more than 1,000 to 2,000 m from the outcrop. (Boreholes at > 1 Km)
RESERVE ESTIMATION METHODS
For moderately to steeply dipping tabular ore body
Cross section method
Longitudinal section method
Level plan method
For bedded/ horizontal or low dipping deposits
Included area method
Extended area method
Triangle method
Polygon method
Method of isoline
Isopach maps method
• Proved Reserves: In this case, the reserves are estimated from dimensions revealed in outcrops, trenches, mine workings and boreholes and the extension of the same for reasonable distance not exceeding 200m on geological evidence. Where little or no exploratory work has been done, and where the outcrop exceeds one km in length, another line drawn roughly 200m in from outcrop will define a block of coal that may be regarded as proved on the basis of geological evidence. (Boreholes at 400 m and borehole density of 8-9 per Sq.Km.)
* Indicated Reserves: In the case of indicated reserves, the points of observation are 1,000 m apart, but may be 2,000 m for beds of known geological continuity . Thus a line drawn 1,000 to 2,000 m from an outcrop will demarcate the block of coal to be regarded as indicated (Boreholes at 1 to 2 km and borehole density of 1-2 per Sq.Km.)
* Inferred reserves : This refers to coal for which quantitative estimates are based largely on broad knowledge of the geological character of the bed, but for which there are no measurements. The estimates are based on an assumed continuity for which there is geological evidence, and more than 1,000 to 2,000 m from the outcrop. (Boreholes at > 1 Km)
cross section method
• In this method, cross sections of the ore body are prepared on which are plotted the intersections or projections of mine workings and drill holes. The cross sections may be vertical, horizontal, or at right angles to the dip, usually parallel to each other, and often are spaced equal distances apart.
Cross section method
The cross-section or traverse section prepared across the ore body represent
the actual geological features in shape and quality
For the calculation of the reserve by this method the area of influence and quality is
considered on the basis of the rule of nearest point
In the cross section area method the reserve is calculated for individual opening and the area of influence of that opening is measured on the cross section or calculated by measuring actual thickness and dip length.
RL in mt.
188
180
171
164
Distance in Meter
• Isopath method
• Extended area method
• Block method
Block Method
• The block model is created using geostatistics and the geological data gathered through drilling of the prospective ore zone. The block model is essentially a set of specifically sized "blocks" in the shape of the mineralized orebody. Although the blocks all have the same size, the characteristics of each block differ. The grade, density, rock type and confidence are all unique to each block within the entire block model. Once the block model has been developed and analyzed, it is used to determine the ore resources and reserves (with project economics considerations) of the mineralized orebody. Mineral resources and reserves can be further classified depending on their geological confidence.
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