CE6301 ENGINEERING GEOLOGY VTHT D.ANJALA/AP/CIVIL VELTECH HIGH TECH Dr.RANGARAJAN Dr.SAKUNTHALA ENGINEERING COLLEGE AVADI, CHENNAI DEPARTMENT OF CIVIL ENGINEERING LECTURER NOTES YEAR/SEM :II/III SUBJECT CODE/TITLE :CE6301/ ENGINEERING GEOLOGY FACULTY NAME :ANJALA.D UNIT I PHYSICAL GEOLOGY Geology in civil engineering – branches of geology – structure of earth and its composition – weathering of rocks – scale of weathering – soils - landforms and processes associated with river, wind, groundwater and sea – relevance to civil engineering. Plate tectonics SCOPE OF GEOLOGY IN CIVIL ENGINERRING: It is defined as that of applied science which deal with the application of geology for a safe, stable and economic design and construction of a civil engineering project. Engineering geology is almost universally considered as essential as that of soil mechanics, strength of material, or theory of structures. The application of geological knowledge in planning, designing and construction of big civil engineering projects. The basic objects of a course in engineering geology are two folds. It enables a civil engineer to understand the engineering implications of certain condition should relate to the area of construction which is essentially geological in nature. It enables a geologist to understand the nature of the geological information that is absolutely essentially for a safe design and construction of a civil engineering projects. The scope of geology can be studied is best studied with reference to major activities of the profession of a civil engineer which are Construction Water resources development Town and regional planning GEOLOGY IN CONSTUCTION FIELD PLANNING Topographic Maps: It’s gives details of relief features and understands the relative merits and demerits of all the possible sides of proposed structure. Hydrological maps: This map gives broad details about distribution and geometry of the surface of water channel. Geological maps : The petrological characters and structural disposition of rock types this gives an idea about the availability of materials for construction.
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CE6301 ENGINEERING GEOLOGY VTHT
D.ANJALA/AP/CIVIL
VELTECH HIGH TECH Dr.RANGARAJAN Dr.SAKUNTHALA ENGINEERING
COLLEGE AVADI, CHENNAI
DEPARTMENT OF CIVIL ENGINEERING
LECTURER NOTES
YEAR/SEM :II/III
SUBJECT CODE/TITLE :CE6301/ ENGINEERING GEOLOGY
FACULTY NAME :ANJALA.D
UNIT I PHYSICAL GEOLOGY
Geology in civil engineering – branches of geology – structure of earth and its composition –
weathering of rocks – scale of weathering – soils - landforms and processes associated with river,
wind, groundwater and sea – relevance to civil engineering. Plate tectonics
SCOPE OF GEOLOGY IN CIVIL ENGINERRING:
It is defined as that of applied science which deal with the application of geology for a
safe, stable and economic design and construction of a civil engineering project.
Engineering geology is almost universally considered as essential as that of soil
mechanics, strength of material, or theory of structures.
The application of geological knowledge in planning, designing and construction of big
civil engineering projects.
The basic objects of a course in engineering geology are two folds.
It enables a civil engineer to understand the engineering implications of certain condition
should relate to the area of construction which is essentially geological in nature.
It enables a geologist to understand the nature of the geological information that is
absolutely essentially for a safe design and construction of a civil engineering projects.
The scope of geology can be studied is best studied with reference to major activities of
the profession of a civil engineer which are
Construction
Water resources development
Town and regional planning
GEOLOGY IN CONSTUCTION FIELD
PLANNING
Topographic Maps:
It’s gives details of relief features and understands the relative merits and demerits of all
the possible sides of proposed structure.
Hydrological maps:
This map gives broad details about distribution and geometry of the surface of water
channel.
Geological maps :
The petrological characters and structural disposition of rock types this gives an idea
about the availability of materials for construction.
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Introduction about Lithosphere:
Litho is a Greek word, which means stone. Accordingly the lithosphere is the part of the
earth, which is solid crust.
The thickness of lithosphere is approximately 50 km. The crustthickness is not the some
at allplaces.
It is thicker in the continent and thinner on the oceanfloors. Lithosphere is a source of
various minerals.
It contains variety of landforms such as mountains.plateous valleys, plains.
Plates:
The surface of the earth is the crust of the earth. It is made of interlocking pieces called
plates. The continents and oceans rest in these places and are separated by wide cracks. The
plates move constantly.
subdivisions in geology
The subdivisions are:
Physical geology
Geomorphology
Mineralogy
Petrology
Historical geology
Economic geology
Geohydrology
Engineering geology
Metrolog
Crust:
Early in the 20 th century the reality of earth crust was demonstrated by a scientist named
Mohorovicic.He noted that in measurements of seismic wave arriving from an earthquake, those
focus lay within 40km of the surface, seismographs within 800 km of the epicenter. Recorded
two distinct sets of P and S-waves. He concluded that one par of waves must have travelled from the focus to the station by a direct path whereas the other pair of waves had arrived slightly later
because they had been refracted.
There are two types of crust:
Continental crust
Oceanic crust.
Continental Crust:
The continental crust consists of two layers separated by a well-defined
discontinuityknown as Conard discontinuity. The layers have been defined on the
basis of seismic wavesvelocities and densities.
In the upper layers the velocity of seismic waves corresponds to the velocity
found byexperimental to be characteristic of granite. Hence they are called as
Granitic or silica layer.
Oceanic Crust:
The earths crust beneath the oceans consist of a low velocity layer of deep sea sediments
about 300-400m thick in pacific and 600-700 m in the Atlantic.
The Layer of intermediate velocity called basement about 0,8 km thick, composed of
compacted and indurated sediments and lave flows.
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The third layer is called the oceanic layer about 4.1 to 5.8 km thick and certain
composition. This three-layered oceanic crust is generally 5 to 8 km thick.
Mantle:
Materials making the earth become quite different in properties at the base of the crust.
This depth below the surface of the earth at which a striking change in the properties of
the
materials is observed has been named as Mohovorovicic discontinuity.
In geological literature itis often referred as M-discontinuity or simply as Moho.Hence
mantle is that zone within theearth that starts from M-discontinuity and continues up to a
depth of 2900km.Mantle is made up of extremely basic material called aptly ultra basic
that is very rich iniron and magnesium but quite poor in silica. The material of the mantle
is believed to be variably viscous in nature .
Core:
It is the third and the innermost structural shell of the earth as conclusively proved by the
seismic evidence. It starts at a depth of 2900 km below the surface and extends right up to
the
centre of the earth, at a depth of 6370km.
The core remains a mystery in many ways. Within the core the physical nature ands
composition of the material is not uniform throughout its depth. It has a very high density
at mantle core boundary above 10g/cc.The outer core behaves lime a liquid towards the
seismic waves. The inner core starting from 4800km and extending up to 6370 m is of
unknown nature but definitely of solid character and with properties resembling top a
metallic body.
Atmosphere:
The outer gaseous part of the earth starting from the surface and extending as far
as700km and even beyond is termed atmosphere. It makes only about one million part of the
totalmass of the earth.
Stratosphere:
It is the second layer of the atmosphere starting from the tropopause and extending up to
san average height of 50km.The stratosphere differs from the lower layer in following
respects.
The temperature becomes constant for a height of 20km and then starts increasing.
It contains almost the entire concentration of OZONE GAS that occurs above the earth
form of a well-defined envelope distinguished as the Ozone layer.
The stratosphere itself has a layered structure and there is no significant mixing or
turbulence of gases in this layer.
Branches of geology:
Geology is a relatively recent subject. In addition to its core branches, advances in
geology in allied fields have lead to specialized sciences like geophysics, geochemistery,
seismology, oceanography and remote sensing.
Main and Allied branches of geology:
The vast subject of geology has been subjected into the following branches:
Main Branches Allied Branches
Physical geology Engineering geology
Mineralogy Mining geology
Petrology Geophysics
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Structural geology Geohydrology
Stratigraphy Geochemistry
Paleontology
Economic geology
Physical geology:
This is also variously described as dynamic geology, geomorphology etc.
It deals with:
Different physical features of the earth, such as mountains, plateaus, valleys, rivers.lakes
glaciers and volcanoes in terms of their origin and development.
The different changes occurring on the earth surface like marine transgression, marine
regression, formation or disappearance of rivers, springs and lakes.
Geological work of wind, glaciers, rivers, oceans, and groundwater ands their role
inconstantly moulding the earth surface features
Natural phenomena like landslides, earthquakes and weathering.
Mineralogy:
It deals with the study of minerals. Minerals are basic units with different rocks andores
of the earth are made up of.Details of mode of formation, composition, occurrence, types,
association, properties
uses etc. of minerals form the subject matter of mineralogy. For example: sometimes quartzite
and marble resemble one another in shine, colour and appearance while marble disintegrates and
decomposes in a shorter period because of its mineral composition and properties.
Petrology:
Petrology deals with the study of rocks. The earths crust also called lithosphere is made
up of different types of rocks. Hence petrology deals with the mode of formation, structure,
texture, composition, occurrence, and types of rocks. This is the most important branch
ofgeology from the civil engineering point of view.
Structural geology:
The rocks, which from the earths crust, undergo various deformations, dislocations
anddisturbances under the influence of tectonic forces. The result is the occurrence of different
geological structures like folds, fault, joints and unconformities in rocks. The details of mode of
formation, causes, types, classification, importance etc of these geological structures from
thesubject matter of structural geology.
Stratigraphy:
The climatic and geological changes including tectonic events in the geological past
canalso be known from these investigations. This kind of study of the earth’s history through
thesedimentary rock is called historical geology. It is also called stratigraphy (Strata = a set
ofsedimementary rocks, graphy description).
Economic geology:
Minerals can be groupedas general rock forming minerals and economic minerals. Some
of the economic minerals like talc, graphite, mica, asbestos, gypsum, magnesite, diamond
andgems. The details of their mode of formation, occurrence, classification. Association,
varieties,concenteration, properties, uses from the subject matter of economic geology. Further
based onapplication of geological knowledge in other fields there is many other allied
branchescollectively called earth science.
Some of them described here are:
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Engineering geology
Mining geology
Geophysics
Geohydrology
Geochemistry
Engineering geology:
This deals with the application of geological knowledge in the field of civil
engineering,for execution of safe, stable and economic constructions like dams, bridges and
tunnels. Mining Geology:
This deals with the application of geological knowledge in the field of mining. A
miningengineer is interested in the mode and extent of occurrence of ores, their association,
propertiesetc. It is also necessary to know other physical parameters like depth direction
inclinationthickness and reserve of the bodies for efficient utilization. Such details of mineral
exploration,estimation and exploration are dealt within mining geology.
Geophysics:
The study of physical properties like density and magnetism of the earth or its parts.
Toknow its interior form the subject matter of geophysics. There are different types
ofgeophysical
investigations based ion the physical property utilized gravity methods, seismic
methods,magnetic methods. Engineering geophysics is a branch of exploration geophysics,which
aims atsolving civil engineering problems by interpreting subsurface geology of the area
concerned.Electrical resitivity methods and seismic refraction methods are commonly used in
solving civil engineering problems.
Geohydrology:
This may also be called hydrogeology. It deals with occurrence, movement and nature
ofgroundwater in an area. It has applied importance because ground water has many
advantagesover surface water. In general geological and geophysical studies are together taken
up forgroundwater investigations.
Geochemistry: This branch is relatively more recent and deals with the occurrence,
distribution,abundance, mobility etc, of different elements in the earth crust. It is not important
from the civilengineering point of view.
weathering and its significance in engineering construction
Weathering is defined as a process of decay, disintegration and decomposition of
rocksunder the influence of certain physical and chemical agencies.
Disintegration:
It may be defined as the process of breaking up of rocks into small pieces by
themechanical agencies of physical agents.
Decomposition:
It may be defined as the process of breaking up of mineral constituents to form
newcomponents by the chemical actions of the physical agents.
Denudation:
It is a general term used when the surface of the earth is worn away by the chemical as
well as mechanical actions of physical agents and the lower layers are exposed.
The process of weathering depends upon the following three factors:
Nature of rocks
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Length of time
Climate
Two Chief types of weathering are commonly distinguished on the basis of type of
agency involved in the process and nature of the end product. They are:
Physical or mechanical weathering
Chemical weathering
Physical weathering:
It is the physical breakdown of rock masses under the attack of certain atmospheric
agents.
A single rock block is broken gradually into smaller irregular fragments and then into
particles of still smaller dimensions.
It is the most active in cold, dry and higher areas of the earth
surface Temperature variations are responsible to a great extent of physical weathering.
Thermal effects:
The effect of change of temperature on rocks is of considerable importance in arid
andsemi arid regions where difference between daytime and nighttime temperature is often
veryhigh. Such temperature fluctuations produce physical disintegration in a normally expected
manner.
Expansion on heating followed by contraction on cooling. When the rock mass islayered
and good thickness additional disturbing stresses may be developed into by unequalexpansion
and contraction from surface to the lower regions. The rock sometimes is found tobreak off
intoconcentric shells.
This process is known as exfoliation.When weathering occurs part of the
disintegratedrock material is carried away by running wateror any other transporting agent.
Someof them are left on the surface of the bedrock as residualboulders. It is often seen that
boulders have an onion like structure. This kind of weathering iscalled spheroidal weathering.
Chemical weathering:
The chemical decomposition of the rock is called chemical weathering which is
nothingbut chemical reaction between gases of the atmosphere and minerals of the rocks.
The chemicalchanges invariably take place in the presence of water generally rainwaterin
which aredissolved many active gases from the atmosphere like C02, nitrogen,
Hydrogenetc.Theseconditions are defined primarily by chemical composition of the
rockshumidity and theenvironmental surrounding the rock under attack.Chemical weathering is
essentially a process of chemical reactions between gases of theatmosphere and the surface
rocks. For example:
1) 2CaCO3 + H2O + CO2 ------------------ 2 Ca (HCO3) 2
2) CaSO4 + 2H2O -------------------- CaSO42.H2O
Engineering importance of rock weathering:
As engineer is directly or indirectly interested in rock weathering specially when he hasto
select a suitable quarry for the extraction of stones for structural and decorative purposes.
Theprocess of weathering always causes a lose in the strength of the rocks or soil.For the
construction engineer it is always necessary to see that:
To what extent the area under consideration for a proposed project has been affected
byweathering and
What may be possible effects of weathering processes typical of the area on the
construction materials
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Major geologicalfeatures
The earth is surrounded by an envelop of gases called the atmosphere. The movement
ofthe atmosphere in a direction parallel to the earth surface is wind.i.e the air in motion is
calledwind whereas the vertical movement s of the atmosphere are termed as air currents.
Erosion by wind and developed features:
Wind erosion is generally caused by two erosion processes:
Deflation
Abrasion.
Deflation:
Deflation is the process of simply removing the loose sand and dust sized particles from as area,
by fast moving winds. Wind deflation can successfully operate in comparatively
dryregionswithlittle or no rainfall and where the mantle is unprotected due to absence
ofvegetation. Such a removal of loose fine particles may at certain places leave a denuded
surfaceconsistingmostly of hard rocks or coarse materials like gravel and is called lag gravel.
This gravel layerprevents further deflation.
Abrasion:
The wind loaded with such particles attains a considerable erosive power which helps
aconsiderable er4osive power which helps in eroding the rock surfaces by rubbing and grinding
actions and produce many changes. This type of wind erosion is known as abrasion.Vertical
column of rocks are thus more readily worm out towards their lower portions and aresult
pedestal rocks are formed which wider tops have supported on comparatively narrowerbases.
Such type of rock formations is called Pedestal or Mushroom rocks.
Transportation by wind:
The total sediment load carried by a wind can be divided into two parts.
Bed load
Suspended load
The larger and heavier particles such as sands or gravels, which are moved by the winds but not
lifted more than 30 to 60 cm of the earth surface constitute the bed load. Whereas the finer clay
or dust particles which are lifted by the moving winds by a distance of hundreds of meters above
the earths surface constitute the suspended load.
Deposition of sediment by wind and the developed features:
The sediments get dropped and deposited forming what are known as Aeolian deposits.
There are two types of Aeolian deposits;
a) Sand dunes
b) Loess
Sand dunes:
Sand dunes are huge heaps of sand formed by the natural deposition of wind blown sand
sometimes of characteristics and recognizable shape. Such deposits are often found to migrate
from one place to another due to change in the direction and velocity of wind.
The active dunes can be divided into three types:
Barchans or Crescent shaped dunes
Transverse dunes
Longitudinal dunes
Barchans:
These dunes that look like a new moon in plan are of most common occurrence. They are
triangular in section with the steep side facing away from the wind direction and inclined at an
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angle of about 300 to 330 to the horizontal.
The gently sloping side lies on the windward side, and makes an angle of about 10 to 150 with
the horizontal. They may have variable sizes, with a generally maximum height of about
335 meters and horn to horn width of say 350 meters.
Transverse Dunes:
A transverse dune is similar to a barchans in section but in plan it is not curved
likebarchans such that its longer axis is broadly transverse to the direction of the prevailing
winds.
Longitudinal dunes:
Longitudinal dunes are the elongated ridges of sand with their longer axis broadly
parallel to the direction of the prevailing wind. When seen in the side view they will appear to be
triangular on an average they may be 3 m height and 200 m long.
Loess:
The finest particles of dust travelling in suspension with the wind are transported to
aconsiderable distance. When dropped down under favourable conditions these have been found
to accumulate in the different constituents the form of paper-thin laminae, which haveaggregated
together to form a massive deposit known as Loess.
Engineering considerations:
In general no site is selected for any type of important work on the moving dunes because
such dunes are always a source of trouble to an engineer. It has been experienced that sometimes
the moving dunes damage certain important works. But if an engineer is compelled to select such
a site, special methods should be adopted to check the motion of the moving dunes. For ex:Either
to construct windbreaks or growing vegetation on the surrounding areas.
Hydraulic action:
It is the mechanical loosening and removal of the material from the rocks due to pressure
exerted by the running water. The higher the velocity the greater is the pressure of the running
water and hence greater is its capacity to bodily move out parts of the rock or grains of soil from
the parent body occurring along its base or sides. The river water flowing with sufficient velocity
often develops force strong enough to disintegrate a loose rock, displace the fragments so created
and lift them up and move forward as part of bed load.
Cavitation:
It is distinct and rare type of hydraulic action performed by running water. It
isparticularly observed where river water suddenly acquires exceptionally high velocity such as
at the location of a waterfall. In other words there is a spontaneous change fro a liquid to vapour
state and back to liquid state at that point. The phenomenon of cavitations is also observed in
hydropower generation projects.
Abrasion:
It is the principal method of stream erosion and involves wearing away of the bedrocks
and rocks along the banks of a stream or river by the running water with the help of sand grain,
pebbles and gravels and all such particles that are being carried by its as load. These particles
grains and rock fragments moving along with river water are collectively known as tolls
oferosion. The river valleys, water falls, escarpments, gorges and canyons and river terraces are
some of the so well known examples developed principally by river abrasion.
Attrition:
This term is used for wear and tear of the load sediments being transported by a moving
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natural agency through the process of mutual impacts and collisions which they suffer during
their transport. Every part of the sediment in load in suspension or being moved along the bed of
the stream receives repeated impacts from other particles,. Due to these mutual collusions, the
irregularities and angularities of the particles are worn out. These become spherical in outline
and rounded and polished at the surface. Some of the fragments any eventually get reduced to
very fine particles that rea easily carried along with the running water for considerable distances.
Corrosion:
The slow built steady chemical action of the stream water on the rocks is expresses by the
term corrosion. The extent of corrosion depends such on the composition of rocks and also on
the composition of flowing water. Thus all rocks are not equally susceptible to corrosive action
of stream water. Limestones, gypsum and rock salt bodies are soluble in water to varying
degrees. The steam may hardly corrode sandstones, quartzites, granites and gneisses.
causes, classification of earthquake:
The physical forces the surfaces are rearranging rock materials by shifting magmas about
altering the structures of solid rocks. The adjustment beneath the surface however involve
various crystal movements, some of which because of suddenness and intensity produce tremors
in the rocks and they are known as earthquake. The science dealing with the study of earthquakes
in all their aspects is called seismology.
Focus and epicenter:
The exact spot underneath the earth surface at which an earthquake originates is known
as its focus. These waves first reach the point at the surface, which is immediately above
thefocus or origin of the earthquake. This point is called epicenter. The point which is
diametricallyopposite to the epicenter is called anticenter.
Intensity and magnitude:
Intensity of an earthquake may be defined as the ratio of an earthquake based on actual
effects produced by the quakes on the earth.Magnitude of a tectonic earthquake may be defined
as the rating of an earthquake basedon the total amount of energy released when the over strained
rocks suddenly rebound, causingthe earthquake.
Causes of earthquake:
The earthquake may be caused due to various reasons, depending upon it
intensity.Following causes of earthquake are important:
1. Earthquakes due to superficial movements:
The feeble earthquakes are caused due to superficial movements.i.e, dynamic agencies,
and operation upon surface of the earth.
The dashing waves cause vibrations along the seashore.
Water descending along high water falls, impinges the valley floor and causes
vibrations along the neighbouring areas.
At high altitudes the snow falling down is an avalance.also causes vibrations
along the neighbouring areas.
Earthquake due to volcanic eruptions:
Most of the volcanoes erupt quietly and as consequence, initiate no vibration on the
adjoining area. But a few of them when erupt, cause feeble tremors in the surface of the earth.But
there may be still a volcanic eruption may cause a severe vibration on the adjoining area and
have really disastrous effects.
Earthquake due to folding or faulting:
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The earthquakes are also caused due to folding of the layers of the earth’s crust. if
theearthquakes are caused due to folding or faulting then such earthquakes are more disastrous
andare known as tectonic earthquakes and directly or indirectly change the structural features of
the earth crust.
Classification of earthquakes:
Earthquakes are classified on a no. Of basis. Of these the depth of focus, the cause
oforigin andintensity are important.
a) Depth of focus:
Three classes of earthquakes are recognized on this basis, shallow, intermediate and
deepseated. In the shallow earthquakes the depth of focus lies anywhere up to 50 km below the
surface. The intermediate earthquakes originate between 50 and 300 km depth below the surface.
b) Cause of origin:
i) Tectonic earthquakes are originated due to relative movements of crystal block
onfaulting, commonly, earthquakes are of this type.
ii) Non tectonic earthquakes: that owes their origin to causes distinctly different
fromfaulting, such as earthquakes arising due to volcanic eruptions or landslides.
C) Intensity as basis:
Initially a scale of earthquakes intensity with ten divisions was given by Rossi
andferel.Which was based on the sensation of the people and the damage caused. However it
wasmodified by Mercalli and later by wood and Neumann.
Engineering considerations:
The time and intensity of the earthquake can never be predicted. The only remedy thatcan
be done at the best, it is provide additional factors in the design of structure to minimize
thelosses due to shocks of an earthquake. This can be done in the following way:
To collect sufficient data, regarding the previous seismic activity in the area.
To assess the losses, which are likely to take place in furniture due to earthquake shocks
To provide factors of safety, to stop or minimize the loss due to sever earth shocks.
Following are the few precautions which make the building sufficiently earthquake proof.
The foundation of a building should rest on a firm rock bed. Grillage foundations should
preferably be provided.
Excavation of the foundation should be done up to the same level, throughout the
building.
The concrete should be laid in rich mortar and continuously
Masonry should be done with cement mortar of not les than 1:4 max.
Flat R.CC slab should be provided.
All the parts of building should be tied firmly with each other.
Building should be uniform height.
Cantilivers, projections, parapets, domes etc, should be provided.
Best materials should be used.
Ground water
Groundwater hydrology may be defined as the science of the occurrence, distribution and
movement of water below the surface of the earth. Ground water is the underground water that
occurs in the saturated one of variable thickness and depth below the earth’s
surface.Groundwater is an important source of water supply throughout the world. Its use in
irrigation,industries, urban and rural home continues to increase.
Origin of ground water:
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Almost all groundwater can be thought of as a part of hydrologic cycle, including
surfaceand atmospheric waters. Connate water is water entrapped in the interstices of
sedimentary rockat the time it was deposited. It may have been derived from the ocean or fresh
water sources andtypically is highly minimized.New water of magmatic, almost all ground water
can be thoughtof as a part of the hydrologic cycle, including surface volcanic or cosmic origin
added to theterrestrial water supply is juvenile water.
Ground water constitutes one portion of the earth water circulatory system known as the
hydrologic cycle. Water bearing formations, of the earth crust act as conduits for transmission
and as reservoirs for storage of water. Water enters these formations from the ground surface or
form bodies of surface water
After which it travels slowly for varying distances until it returns to the surface by action
of natural flow, plants or man. Ground water emerging into surface stream channels aids
insustaining stream flow when surface runoff is low or non-existent. Similarly water pumped
fromwells represents the sole water source in many regions during much of every year.
All ground water originates as surface water. Principal sources of natural recharge
include precipitation, stream flow, lakes and reservoirs. Other contributions known as
artificialrecharge occur from excess irrigation, seepage from canals and water purposely applied
to augment groundwater supplies. Discharge of ground water occurs when emerges from
underground.
Most natural discharge occurs as flow into surface water bodies such as streams,lakes and
oceans. Flow to the surface appears as spring. Groundwater near the surface may return directly
to the atmosphere by evaporation from the soil and by transpiration from
vegetation.
Occurrence of ground water:
Ground water occurs in permeable geologic formations known as aquifers. ie, formations
having structures that permit appreciable water to move through them under ordinary field
conditions.
Ground water reservoir and water bearing formation are commonly used synonyms. An
aquitard is a formation, which only seepage is possible and thus the yield is insignificant
compared to an aquifer. It is partly permeable.
An acquiclude is an impermeable formation
which may contain water but incapable of transmitting significant water quantities. An
aquifugeis an impermeable formation neither containing not transmitting water.
Porosity:
The portion of a rock or soil not occupied by solid mineral matter may be occupied by
groundwater. These spaces are known as voids, interstices, pores or pore space. Because
interstices can act as groundwater conduits they are of fundamental importance to the study of
groundwater.
Typically they are characterized by their size, shape, irregularity and distribution.
Original interstices were created by geologic process governing the origin of he geologic
formation and are found in sedimentary and igneous rocks. Secondary interstices developed after
the rock was formed.
Capilary interstices are sufficiently small so that surface tension fo4ces will hold water
within them. Depending upon the connection of interstices with others, they may be classed as
communicating or isolated. The amount of pore space per unit volume of the aquifer material is
called porosity.
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Permeability:
As stated above the ground water is stored in the pores of rock and will hence beavailable
in the ground rocks, only if they are sufficiently porous. The porosity of the rock, thusdefining
the maximum amount of water that can be stored in the rock. In fact the water can enterinto a
rock only if the rock permits the flow of water through it, it depends on whether the rock
ispermeable or not. The size of the pores is thus quite an important factor and it should
besufficiently large to make the rock permeable.
Vertical distribution of groundwater:
The subsurface occurrence of groundwater may be divided into:
Zones of saturation
Zones of aeration
In the Zones of Saturation water exists within the interstices and is known as the
groundwater.This is the most important zone for a groundwater hydraulic engineer, because
hehas to tap outthis water. Water in this zone is under hydrostatic pressure. The space above the
water and belowthe surface is known as the zone of aeration. Water exists in this zone by
molecular attraction.This zone is also divided into three classes depending upon the number of
intersticespresent. The capillary fringe is the belt overlying the zone of saturation and it does
contain some interstitial water and is thus a continuation to the zone of saturation while the depth
from the surface, which is penetrate.
GEOLOGICAL WORK OF EARTHQUAKE
An earthquake is a sudden vibration of earth surface by rapid release of energy
This energy released when two parts of rock mass move suddenly in relation of to
eachoher along a fault.
EFFECTS OF EARTHQUAKE:
Buildings are damaged
Roads are fissured, railway lines are twisted and bridges are destroyed
Rivers change their coarse
Landslides may occur in hilly region.
TERMINOLOGY:
FOCUS:
The point of origin of an earthquake within the earth crust is called focus.
It radiates earthquake waves in all direction
EPICENTRE:
The point lying vertically above the earth surface directly above focus is called epicentre.
In the epicentre the shaking is most intense
The intensity gradually decrease
ISOSEISMAL LINES:
The line connecting points of equal intensity on the ground surface are called isosesimal
lines
EARTHQUAKE INTENSITY:
It is a measure of the degree of distraction caused by an earthquake
It is expressed by a number as given in the earthquake intensity scale
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SESIMOGRAPHS:
Seismographs are instruments which detect and record earthquakes.
EARTHQUAKE WAVES (SEISMIC WAVES):
P-Waves(primary waves)
S-Waves(secondary waves)
L-Waves (surface waves)
During earthquake elastic waves are produced are called seismic waves.
P-Waves:
These are longitudinal waves having short wavelength
They travel very faster and reach seismic station first
Their velocity is 1.7 times greater than s-waves
They passes through solid, liquid, gaseous medium.
S-WAVES:
These are shear waves which are traverse in nature.
They travel only in solid medium.
L-WAVES:
When p and s- waves reached earth surface they are called l- waves.
Here velocity is much less.
CLASSIFICATION OF EARTHQUAKE:
CLASSIFICATION –I: Depending on mode of origin
1. DUE TO SURFACE CAUSES: Generated by land slopes and collapse of root of
underground waves
2. DUE TO VOLACANIC CAUSES: It may also produce earthquake but very feeble.
3. DUE TO TECTONIC PLATES: Most numerous and disastrous and caused by shocks
originated in earth crust due to sudden movement of faults.
CLASSIFICATION-II: Depending on depth of focus
1. SHALLOW FOCUS: Depth of focus upto 55kms.
2. INTERMEDIATE FOCUS: Depth between 55-300kms.
3. DEEP FOCUS; Depth from 300-600kms.
PHYSIOGRAPHIC DIVISION OF INDIA:
India can be divided into 3 main division which may differ from one another in
physiography, stratiography and structure.
1. Peninsular
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2. Indo-gangetic plain
3. Extra peninsular India
PENINSULAR:
It lies to the south of plain of India of ganga river Physiography:
Peninsular has extremely various physiography.they are plateaus, fold mountains, valleys and
coastal plains. Weatern ghats which form a premonient physiographic features Structure:
Peninsular:
India is nearly a stable pleatue which has unaffected by the orogenic movements
The normal and block faulting is however common
Stratigraphy:
Peninsular is primarily made up of rocks of Archean and Precambrian age
The Archean rocks have been metamorphosed to varying degree
QUARTZ GROUP:
It is an important rock forming mineral next to feldspar
It is a non- metallic efractory mineral
It is a silicate group
Physical Properties Of Quartz:
Crystal System: Hexagonal
Habit: Crystalline Or Amorphous
Fracture: Conchoidal
Hardness: 7
Specific Gravity: 2.65-2.66(Low)
Streak: No
Transparency: Transparent/Semi-Transparent/Opaque
Polymorphism Transformation: Quartz
VARIETIES:
Pure quartz is always colourless and transparent
Presence of impurities the mineral showing colour they
Amethyst:
purple or violet Smoky quartz: shades of grey Milky quartz: light brown, pure white,
opaque Rose quartz: rose cryptocrystalline forms of quartz: chalcedony: amorphous, waxy lustre
agate: a banded , variety having different colours jasper: dull red, yellow, massive flint: dark
grey, conchoidal fracture opal: amorphous quartz family minerals primary: Recrystalization
process
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PLATE TECTONICS
The theory of plate tectonics provides explanations for the past and present day tectonic
behaviousof the Earth, particularly the global distribution of mountains seismicity, and
volcanism in a series of linear bells, seafloor spreading, polar wandering and continental dirft.
From several lines of thought andevidences it is learnt that all of the natural phenomena of the
earth might be the result of a single basicmechanism, i.e., convection in the mantle. How
convection could cause such natural phenomena is discussed later in the chapter.
THE CONCEPT
The theory of plate tectonics supposes that the sphere of the earth is made up of 7 major
andseveral minor plates which are in constant motion relative to each other.
The motion of the plates refer tothe rigid slabs of the continental and oceanic crust that
slides over the plastic zone of asthenosphere of theupper mantle
A fractures egg shell forms a good analogy to the spherical plates of the earth.These
plates are bounded by active linear zones causing volcanism and earthquakes.
HISTORICAL BACKGROUND
The theory of plate tectonics has been a recently developed theory. Recent advancement
in the
ocean floor studies and rock magnetism piled information on the nature of the seafloor.
As with thegrowing data has grown the number of workers in the same filed.
Constitutions made by severalindividuals collectively gave birth to the theory of plate
tectonics. At present even scientists from Russianschool who at first were against the
theory, begin to show faith in the theory on seeing the evidencesaccumulating every day.
However there are a few flaws in the theory which are yet to the reasonablyexplained by
the theory. Thus it may need a modification to answer all questions about the
earth.Thetheory of plate tectonics has a fore runner of continental dirft.
Thus the entire idea that the Earth’s externalskin is subject to motion has come in to the
minds in scientists when they observed the striking similarity ofthe opposite coasts of
South America and Africa.In 17th century Francis Bacon wondered about the coastline
matching.
But no work was done tilllate 19th Century.
When the world map was redrawn in 19th century the spirit of questioning of
matchingcoasts got fire. Antonio snider pelligrini (1858, French), Frank B.Taylor (1901,
American) and affredWegener (1915, German) contributed a lot to the idea of lateral
motion of the continents over the face ofthe earth (chapter 22).
During 1950s magnetic data become available in support of continental drift andseafloor
spreading.
Later it is understood that the continents themselves do not move but they are
merepassengers over the sliding lithospheric slabs driven by the spreading seafloor. In
1968,Jason morganreplaced the title ‘new global tectonics’ by a new terminology ‘plate
tectonics’.
Despite a few shortcomings the theory of plate tectonics gains momentum among the
world scientists day by day by the overwhelmingevidences. The following sections deal
in details about the plate tectonics.
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ELEMENTS OF TECTONISM Seismology Permitted an insight into the Earth. As per the seismic data the Earth is
composed of
a few layer of different composition, density and physical nature.
The earth consists of three Principallayers, namely crust, mantel and Core.
Crust is divisible into oceanic and continental crust. The earth’smovements involve the
upper mantle also. in the upper mantle is a layer called low velocity zone which behaves
like a fluid. Thus it Possesses a plastic flow. The layer is also known as asthenosphere.
Continental Crust, Oceanic crust and a part of upper mantle constitute a plate which a
rigid part of thelithosphere.
Plates overlie the asthenosphere. Any movement in the underlying asthenosphere affects
the plates.
CHARACTERISTICS OF PLATES
A Plate consists of crust and a part of upper mantal.
Size and Shape of the plates are not constant.
One large plate may be fragmented into many small plates may unit to form a large one.
plates are spherical of curved and are independent.
Thickness of plates vary.It is 70 km beneath oceans and 150 km beneath
continents.
Plates are bounted by different boundaries distinguished by the relative
motion of the adjacent plates.
Plates are enclosed by Features like mid-oceanic ridges , oceanic trenches great faults
and fold mountain belts.
The length of the boundary is variable.
Plates move with respect to each other and to the axis of rotation.
Plates move with different velocity and in different directions. Even different parts of the
same plate move at different velocities.
Plate margins are subject to deformation .but interior of the plate is free from
deformation.
plates bearing continental crust will not be consumed at the boundaries.
Plates and boundaries are not permanent features.
WORLD PLATES
Geographical plates of the Earth are recognized as follows. Seven plates are larger and
many others are smaller .
LARGE PLATES
Antarctic plate
Pacific plate
Eurasian plate
African plate
North American Plate
South American Plate
indian/Australian plate
SMALL PLATES
China Plate
Philippine Plate
Arabian Plate
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Iran Plate
Nazca Plate
Cocos Plate
Caribbean Plate 8. Scotia Plate
PLATE BOUNDARIES
The surficial trace of the zone of motion is known as plate boundary. The end of the plate is
calledplate margin. Figure 20.2 shows the boundary and the margin There are three types of plate
boundaries.These are recognized on the basis of the movement associated with the plate
junctions. They are:
1.Divergent or Constructive boundaries or sources
2. Convergent or Destructive boundaries or Sinks
3.Transform fault boundaries or conservative boundaries. With the help of seismic observations
and / or magnetic lineation’s plate boundaries are mapped. And they are also used to find the
direction and the velocity of plate motion.
DIVERGENT BOUNDARY
Long the middle of the ocean floor their rises a ridge with a central ‘V’ shapped valley.
Theboundary line that separates the two plates runs along the valley bottom. Materials of the
twoflanks ofthese mid oceanic ridges move away from each other. This boundary is known as
divergent boundary asthe plates diverge with reference to the boundary line. But they are never
separated. Because newmaterial is poured out continuously and is accreted to the moving plate
margins material is symmetrically divided into two halves and mobilised. The symmetry may
beproduced in thisway: A new ribbon of material is added to the margins of separating plates.
The rigidity of the material islower and lower as the centre of the ribbon is approached. Splitting
may occur along the line of weak zone.Thus when the ribbon is subjected to tensional forces
(because of the mobile plates) it is brokensymmetrically as the plane of weakness occupies the
central part of the ribbon.
CONVERGENT BOUNDARY
This boundary is developed as two plates converge towards each other and thus it is known as
Convergent boundary. Since land area is lost along this type of boundary, it is known as
destructiveboundary. For the reason that the material is being sunken at these boundaries they are
also known assinks. Convergent Boundaries are marked by deep sea trenches and fold mountain
belts. They may beLocated along the northern and western border of the Pacific forming
Aleutian trench, Japan trench andTonga trench and Tonga trench, Western continent slope of the
South America forming Eru-Chile trench,Himalayas f India, Mediter- tanean trench and java
trench.
The convergence of plates occur in two ways:
1.subduction And
2. Continental collision depending upon the nature of plates that collide. Three cases of
plate collision my be expected accordingly the type of convergence differs as follows.
Crustal Types Of Plates Type Of Convergence
1. Oceanic and oceanic Subduction
2.Oceanic and Continental Subduction
3.Continental and Continental Continental Collision
When both the colliding plates hold oceanic crust any one of the plates slides down the
other
plates slide at approximately 45 degrees.
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The process of sliding of one of the plates beneath the otheralong the convergent
boundary is known as subduction.
When the colliding plates are oceanic andcontinental, then it is always the oceanic plate
that is subducted beneath the continental.
It happens sobecause of the greater density of the oceanic crust of the descending plate.
The plate being made up ofcontinental crust is lighter and always tend to float over the
oceanic crust holding plate
When both thecolliding plates are composed of continental crust neither/ of the plates
slips down because of low density.
But on collision continental crust is evolved into fold mountain systems. A classic
example of such acontinental collision belt is the Himalayan belt, produced during the
Cenozoic Era by the convergence ofthe Indian plate with Eurasian plate.
SUBDUCTION ZONE :
Subduction Zone are the zones where subduction of plates occur. Obviously a sinkor a
destructive boundary or a convergent boundary may be a subduction zone. Plunging stab
or thesubducted plate is of oceanic crust. Buoyancy plays as important role in subduction
zones. Back arebasins are the basins developed due to the subduction. Subduction zones
are characterized by active
volcanism earthquake and the development of deep ocean trenches. The down-going stab
is assimilatedin the mantle. However, partial melting of the oceanic crust of the
subducted plate generates mafic igneousintrusion. The sepentinized pillow basalts and
mafic intrusions with associated deep-sea sediments
occurring along with subduction zones is termed ophiolite suite. The zone where all kinds
of earthquakes(shal-low, intermediate, and deep) originate is termed the Benioff zone or
Benioff plane (named after hugoBenioff, and American Seismologist). Earthquakes are
generated as the plate plunges creating frictionalforce. The Benioff zone is a thin inclined
plane zone located on the top margin of the descending slab.
Benioff plane dips away from oceanic trenches and toward the adjacent island arcs and
continents andmarks the surficial trace of the slippage of overriding and descending
plates the subducted plate may bepartially melted and andesitic magma may be
ENGINEERING CONSIDERATIONS OF CLAY MINERALS: Montmorillonite is a dangerous type of clay cut it when found in road or tunnel since it
hasexpandable nature which causes slope or wall failure
Kaolinite is used in ceramic industry , it is not expandable and wont absorb water
Clay is used as important material in construction industries both as building material and
asfoundation or structure
It has poor drainage because the soil tends to stay wet and soggy when it is affected by
water,while it is wet it can be easily compacted
It has poor aeration because the soil particles are small and closely spaced, it is very
difficultfor air to enter or leave the soil
It has very high nutrients reserves, reducing the need for fertilization also because clayretains
water plants growing in it often more drought tolerant than plants growing in sandy soil
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UNIT III PETROLOGY
Classification of rocks, distinction between Igneous, Sedimentary and Metamorphic
rocks.Engineering properties of rocks. Description, occurrence, engineering properties,
distribution and uses of Granite, Dolerite, Basalt, Sandstone, Limestone, Laterite, Shale,
Quartzite, Marble, Slate, Gneiss and Schist.
ROCKS:
Defined as aggregates of minerals
Forms major part of earth crust Quartzite and marbles contain only one mineral but most are composed of variety of different
mineral
Classified Into 3 Groups. They Are
1. Igneous rocks
2. Sedimentary rocks
3. Metamorphic rocks
IGNEOUS ROCKS:
Formed by cooling and solidification of magma
“Magma”is a hot viscous, siliceous melt, contains water vapour and gases
Magma comes from great depth bellow earth surface it composed of O, Si, Al,Fe, Mg, Na and K When a magma comes out upon the earth surface such magma is called lava
CHEMICAL COMPOSITION: SiO2- 40-70% Al2O3- 10-20% Ca, Mg, Fe- 10% Magma are divided into 2 groups based on chemical composition
ACID MAGMA: Si, Na and K(rich) Ca, Mg and Fe(poor)
BASIC MAGMA: Ca, Mg and Fe (rich) Si, Na and K (poor)
LIQUID PORTION: melt SOLIDS: any silicate minerals
VOLATILES: dissolved gases in melt, including water vapour, CO2 and SO2
CRYSTALLIZATION OF MAGMA: Cooling results in systematic arrangements of ions
Silicate minerals resulting in crystallization forms in a predictable order and develop distinct
PLUTONIC ROCKS/ INTRUSIVE ROCKS: Rocks formed from magm at deep seated layer in earth HYPABYSSAL ROCKS: Rocks formed close to surface of earth
TEXTURE: Overall appearance of a rock based on the size, shape and arrangement of interlocking
minerals is called texture.
TYPES OF IGNEOUS TEXTURE: BASED OF VISIBLE CRYSTALLINITY: APHANITIC: Fine grained texture
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Rapid rate of cooling Microscopic crystal
May contain visicles
PHANERITIC:
Coarse grained texture Slow cooling
Large, visible crystals
GLASSY TEXTURE: Very rapid cooling of lava
Resulting rock is called obsidian
BASED ON VARIATION IN CRYSTAL SIZE: PORPHYRITIC TEXTURE: Large crystals (phenocrysts) are embedded in a matrix of smaller crystals
( ground mass)
EQUIGRANULAR TEXTURE: All crystals are of same size
INEQUIGRANULAR TEXTURE: Some of the crystals are larger than others BASED ON CRYSTAL SIZE: Coarse grained texture- crystal size >2mm Medium grained texture-
crystal size 2-0.06 mm Fine grained texture- <0.06 mm
OTHER TYPE OF TEXTURE:
PEGMATITIC TEXTURE: Coarse grained
Crystallization of granitic magma
PYROCLASTIC TEXTURE: Rock fragments thrown out during volcanic process are called pyroclastic.
Depending on size they are ash, lapilli and volcanic bombs
Properties Of Rocks Structures and textures are physical features associated with the rocks. These occur along with
theformation of rocks and are important in view of civil engineering point because
They contribute to the strength of rocks. They contribute to the weakness of rocks
They reveal mode of origin of rocks.
NOTE: The structures such as folds and faults are exempted though they are also structures since
these develop after the formation of rocks due to tectonic forces.
The term structure refers to certain large scale features
Vesicular structure: Amygdaloidal structure
Columnar structure
Sheet structure Flow structure
VESICULAR STRUCTURE: This structure is due to porous in nature commonly observed in
volcanicrocks. Most of the lava contains volatiles (gasses like CO2, water vapour) which escapes into
theatmosphere by creating various sizes and shapes of cavities near the surface of lava flow. These cavitiesare called vesicles.Eg: SCORIA is a volcanic rock of highly porous.Eg: PUMICE, a light rock
with porosity even that floats on water.
AMYGDALOIDAL STRUCTURE: when secondary minerals such as calcite, zeolites, hydrated formsof silica (chalcedony, agate, amethyst, opal) are filled in vesicles, in such a case it is said
Amygdaloidal structure. Eg: Deccan traps of India.( ie basalts).
COLUMNAR STRUCTURE: with uniform cooling and contraction causes a regular or hexagonal form,which may be interested by cross- joints. Eg: Columnar basalts, around 40 mts high areseen at
Andheri, Bombay.
SHEET STRUCTURE: In this structure, the rocks appear to be made up of a number of sheets,
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because of the development of horizontal cracks. When erosion takes place, the overlying stratagradually disappear and ultimately the plutonic rocks exposed to the surface resulting thedevelopment of joints /
cracks parallel to the surface. Thus, the horizontal joint planes aresometimesso closely spaced as to
produce a sheet structure. Eg: granite.
FLOW STRUCTURE: After eruption of the lava flows, some of the bands or lines are drawnoverthe surface of lava to the direction of lava flow. Eg: Rhyolite.The texture of a rock refers to the individual
mineral grains of size, shape, and mutual relations of mineralconstituentsand glassy matter in a rock.
Depending on the nature of cooling, theTEXTURES inigneous rocks are categorized into: 1. Degree of crystallinity - Rocks composed entirely of crystals are called holocrystalline;
thosecomposed entirely of glass are holohyalline; rocks that contain both crystals and glass
arehypocrystalline / hemicrystalline . 2. Grain size - Overall, there is a distinction between the grain size of rocks that havecrystallized atdepth
are medium to coarse grained (eg: gabbros) and those that crystallized at shallow deptharefiner grained
(eg: basalts).Phaneric texture: if minerals in the rock are big enough to seen by the naked eye,the texture
is said to be Phaneric. Eg: granite.Aphanitic texture: if mineralsare too fine to be seen the texture is said to be aphanitic.Eg:basalts.
3. Based on growth of crystals / Rock fabric - Fabric is the shape and mutual relationships among rock
constituents: 1. Euhedral, refer to grains that are bounded by crystal faces
by some crystal faces
3. Anhedral, when crystal faces are absent, it is called anhedral Hypidiomorphic / granular texture - the most common granular texture in which a mixture of
euhedral,subhedral, and anhedral grains are present.
Ophitic texture - is one where random plagioclase laths are enclosed by pyroxene or olivine. If
plagioclaseis larger and encloses the ferromagnesian minerals, then the texture is subophitic . eg: basalt.Porphyritic texture: Large crystals that are surrounded by finer-grained matrix are referred to
asphenocrysts. If the matrix or groundmass is glassy, then the rock has a vitrophyric texture.
Poikilitic texture- Small euhedral crystals that are enclosed within a large mineral. Glassy Texture. The rock displays with sharp edges like broken glass is known as Glassy Texture.
Noindividual crystals can be seen. Eg: obsidian.
GRANITE is a plutonic igneous rock, compact, massive and hard rock. Granites are unstratified
butcharacterized by joints. It is a holocrystalline (completely crystalline) and leucocratic (light
coloured)rock .
Composition: Granite consists of quartz ( > 20 – 30 %), Feldspars (60%) include alkali feldspars
(orthoclase, microcline) and plagioclase feldspars (oligoclase), micas as essential mineralsand
accessory minerals are mafic minerals such as hornblende, biotite / muscovite , pyroxenes of
Free Air Corrected Gravity (gfa ) - The free-air correction accounts for gravity variations
causedby elevation differences in the observation locations. The form of the Free-Air gravity
anomaly, gfa ,is given by:
gfa = gobs - gn+ 0.3086h (mGal)
where h is the elevation (in meters) at which the gravity station is above the datum
(typically sea level).
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Bouguer Slab Corrected Gravity (gb ) - The Bouguer correction is a first-order correction to
account for the excess mass underlying observation points located at elevations higher than
theelevation datum (sea level or the geoid). Conversely, it accounts for a mass deficiency at
observation points located below the elevation datum. The form of the Bouguer gravityanomaly,
gb, is given by:
gb = gobs - gn + 0.3086h - 0.04193r h (mGal)
where r is the average density of the rocks underlying the survey area.
Terrain Corrected Bouguer Gravity (gt ) - The Terrain correction accounts for variations in
theobserved gravitational acceleration caused by variations in topography near each observation
point. Because of the assumptions made during the Bouguer Slab correction, the terrain
correctionis positive regardless of whether the local topography consists of a mountain or a
valley. The formof the Terrain corrected, Bouguer gravity anomaly, gt , is given by:
gt = gobs - gn + 0.3086h - 0.04193r h + TC (mGal)
where TC is the value of the computed Terrain correction.
Assuming these corrections have accurately accounted for the variations in gravitational
acceleration theywere intended to account for, any remaining variations in the gravitational
acceleration associated with theTerrain Corrected Bouguer Gravity can be assumed to be caused
by geologic structure.
FAULTS:
A geological fold occurs when one or a stack of originally flat and planar surfaces, suchas
sedimentary strata, are bent or curved as a result of permanent deformation. Synsedimentary
folds arethose due to slumping of sedimentary material before it is lithified. Folds in rocks vary
in size frommicroscopic crinkles to mountain-sized folds.
They occur singly as isolated folds and in extensive fold trainsof different sizes, on a
variety of scales.Folds form under varied conditions of stress, hydrostatic pressure, pore
pressure, and temperaturegradient, as evidenced by their presence in soft sediments, the full
spectrum of metamorphic rocks, andeven as primary flow structures in some igneous rocks.
A set of folds distributed on a regional scaleconstitutes a fold belt, a common feature of
orogenic zones. Folds are commonly formed by shortening ofexisting layers, but may also be
formed as a result of displacement on a non-planar fault (fault bend fold),at the tip of a
propagating fault (fault propagation fold), by differential compaction or due to the effects of
ahigh-level igneous intrusion e.g. above a laccolith.
Fold types Anticline: linear, strata normally dip away from axial center, oldest strata in center
irrespective of orientation.
Syncline: linear, strata normally dip toward axial center, youngest strata in center
irrespective of orientation.
Antiform: linear, strata dip away from axial center, age unknown, or inverted.
Synform: linear, strata dip toward axial centre, age unknown, or inverted.
Dome: nonlinear, strata dip away from center in all directions, oldest strata in center.
Basin: nonlinear, strata dip toward center in all directions, youngest strata in center.
Monocline: linear, strata dip in one direction between horizontal layers on each side.
Chevron: angular fold with straight limbs and small hinges
Recumbent: linear, fold axial plane oriented at low angle resulting in overturned strata in
one limb
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Slump:
typically monoclinal, result of differential compaction or dissolution during
sedimentation and lithification.
Ptygmatic: Folds are chaotic, random and disconnected. Typical of sedimentary slump
folding, migmatites and decollement detachment zones.
Parasitic: short wavelength folds formed within a larger wavelength fold structure -
normally associated
with differences in bed thickness
Disharmonic: Folds in adjacent layers with different wavelengths and shapes
(A homocline involves strata dipping in the same direction, though not necessarily any
folding.)
Causes Of Folding
Folds appear on all scales, in all rock types, at all levels in the crust and arise from a variety of
causes.
Layer-parallel shortening
When a sequence of layered rocks is shortened parallel to its layering, this deformation
may be accommodated in a number of ways, homogeneous shortening, reverse faulting or
folding.
The responsedepends on the thickness of the mechanical layering and the contrast in
properties between the layers.
If the layering does begin to fold, the fold style is also dependent on these properties.
Isolatedthick competent layers in a less competent matrix control the folding and
typically generate classic roundedbuckle folds accommodated by deformation in the
matrix.
In the case of regular alternations of layers ofcontrasting properties, such as sandstone-
shale sequences, kink-bands, box-folds and chevron folds arenormally produced.Fault-
related foldingMany folds are directly related to faults, associate with their propagation,
displacement and the accommodation of strains between neighbouring faults.Fault bend
folding Fault bend folds are caused by displacement along a non-planar fault. In non-
vertical faults,
The hangingwalldeforms to accommodate the mismatch across the fault as displacement
progresses. Fault bend foldsoccur in both extensional and thrust faulting. In extension,
listric faults form rollover anticlines in theirhanging walls.
In thrusting, ramp anticlines are formed whenever a thrust fault cuts up section from
onedetachment level to another.
Displacement over this higher-angle ramp generates the folding.Fault propagation
foldingFault propagation folds or tip-line folds are caused when displacement occurs on
an existing fault withoutfurther propagation.
In both reverse and normal faults this leads to folding of the overlying sequence, oftenin
the form of a monoclineDetachment foldingWhen a thrust fault continues to displace
above a planar detachment without further faultpropagation, detachment folds may form,
typically of box-fold style.
These generally occur above a gooddetachment such as in the Jura Mountains, where the
detachment occurs on middle Triassicevaporites.Folding in shear zonesShear zones that
approximate to simple shear typically contain minor asymmetric folds, with the direction
ofoverturning consistent with the overall shear sense.
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Some of these folds have highly curved hinge lines andare referred to as sheath folds.
Folds in shear zones can be inherited, formed due to the orientation of
preshearinglayering or formed due to instability within the shear flowFolding in
sedimentsRecently deposited sediments are normally mechanically weak and prone to
remobilisation before theybecome lithified, leading to folding. To distinguish them from
folds of tectonic origin, such structures arecalled synsedimentary (formed during
sedimentation).
Slump folding: When slumps form in poorly consolidated sediments, they commonly
undergo folding,particularly at their leading edges, during their emplacement.
The asymmetry of the slump folds can beused to determine paleoslope directions in
sequences of sedimentary rocks.
Dewatering: Rapid dewatering of sandy sediments, possibly triggered by seismic
activity, can causeconvolute bedding.Compaction:
Folds can be generated in a younger sequence by differential compaction over older
structures such as fault blocks and reefs. Igneous intrusionThe emplacement of igneous
intrusions tends to deform the surrounding country rock.
In the case of highlevelintrusions, near the Earth's surface, this deformation is
concentrated above the intrusion and oftentakes the form of folding, as with the upper
surface of a laccolith.
Flow foldingThe compliance of rock layers is referred to as competence: a competent
layer or bed of rock can withstandan applied load without collapsing and is relatively
strong, while an incompetent layer is relatively weak.
When rock behaves as a fluid, as in the case of very weak rock such as rock salt, or any
rock that is burieddeeply enough, it typically shows flow folding (also called passive
folding, because little resistance isoffered): the strata appear shifted undistorted,
assuming any shape impressed upon them by surroundingmore rigid rocks.
The strata simply serve as markers of the folding. Such folding is also a feature of
manyigneous intrusions and glacier ice.
Types Of Faults And Their Influence On Dams And Tunnels:
A geological fold occurs when one or a stack of originally flat and planar surfaces, such
as sedimentary strata, are bent or curved as a result of permanent deformation.
Synsedimentary folds arethose due to slumping of sedimentary material before it is
lithified.
Folds in rocks vary in size frommicroscopic crinkles to mountain-sized folds. They occur
singly as isolated folds and in extensive fold trains of different sizes, on a variety of
scales.
Folds form under varied conditions of stress, hydrostatic pressure, pore pressure, and
temperaturegradient, as evidenced by their presence in soft sediments, the full spectrum
of metamorphic rocks, andeven as primary flow structures in some igneous rocks.
A set of folds distributed on a regional scaleconstitutes a fold belt, a common feature of
orogenic zones.
Folds are commonly formed by shortening ofexisting layers, but may also be formed as a
result of displacement on a non-planar fault (fault bend fold),at the tip of a propagating
fault (fault propagation fold), by differential compaction or due to the effects of ahigh-
level igneous intrusion e.g. above a laccolith.
Fold types
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Anticline: linear, strata normally dip away from axial center, oldest strata in center
irrespective of orientation.
Syncline: linear, strata normally dip toward axial center, youngest strata in center
irrespective of orientation.
Antiform: linear, strata dip away from axial center, age unknown, or inverted.
Synform: linear, strata dip toward axial centre, age unknown, or inverted.
Dome: nonlinear, strata dip away from center in all directions, oldest strata in center.
Basin: nonlinear, strata dip toward center in all directions, youngest strata in center.
Monocline: linear, strata dip in one direction between horizontal layers on each side.
Chevron: angular fold with straight limbs and small hinges
Recumbent: linear, fold axial plane oriented at low angle resulting in overturned strata in
one limb of the fold.
Slump: typically monoclinal, result of differential compaction or dissolution during
sedimentation and lithification.
Ptygmatic: Folds are chaotic, random and disconnected. Typical of sedimentary slump
folding, migmatites and decollement detachment zones.
Parasitic: short wavelength folds formed within a larger wavelength fold structure -
normally associated with differences in bed thickness
Disharmonic: Folds in adjacent layers with different wavelengths and shapes (A
homocline involves strata dipping in the same direction, though not necessarily any
folding.)Causes of folding Folds appear on all scales, in all rock types, at all levels in the
crust and arise from a variety of causes. Layer-parallel shorteningWhen a sequence of
layered rocks is shortened parallel to its layering, this deformation may be accommodated
in a number of ways, homogeneous shortening, reverse faulting or folding.
The response depends on the thickness of the mechanical layering and the contrast in
properties between the layers.
Ifthe layering does begin to fold, the fold style is also dependent on these properties.
Isolatedthick competent layers in a less competent matrix control the folding and
typically generate classic rounded buckle folds accommodated by deformation in the
matrix.
In the case of regular alternations of layers ofcontrasting properties, such as sandstone-
shale sequences, kink-bands, box-folds and chevron folds arenormally produced.Fault-
related foldingMany folds are directly related to faults, associate with their propagation,
displacement and the accommodation of strains between neighbouring faults.
Fault bend foldingFault bend folds are caused by displacement along a non-planar fault.
In non-vertical faults, the hangingwalldeforms to accommodate the mismatch across the
fault as displacement progresses.
Fault bend foldsoccur in both extensional and thrust faulting. In extension, listric faults
form rollover anticlines in theirhanging walls. In thrusting, ramp anticlines are formed
whenever a thrust fault cuts up section from onedetachment level to another.
Displacement over this higher-angle ramp generates the folding.
Fault propagation folding Fault propagation folds or tip-line folds are caused when
displacement occurs on an existing fault without further propagation. In both reverse and
normal faults this leads to folding of the overlying sequence, often in the form of a
monoclineDetachment folding When a thrust fault continues to displace above a planar
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detachment without further faultpropagation, detachment folds may form, typically of
box-fold style.
These generally occur above a good detachment such as in the Jura Mountains, where the
detachment occurs on middle Triassicevaporites.
Folding in shear zonesShear zones that approximate to simple shear typically contain
minor asymmetric folds, with the direction of overturning consistent with the overall
shear sense. Some of these folds have highly curved hinge lines and are referred to as
sheath folds.
Folds in shear zones can be inherited, formed due to the orientation of preshearing
layering or formed due to instability within the shear flow Folding in sediments Recently
deposited sediments are normally mechanically weak and prone to remobilisation before
they become lithified, leading to folding. To distinguish them from folds of tectonic
origin, such structures are called synsedimentary (formed during sedimentation). Slump
folding:
When slumps form in poorly consolidated sediments, they commonly undergo
folding,particularly at their leading edges, during their emplacement. The asymmetry of
the slump folds can beused to determine paleoslope directions in sequences of
sedimentary rocks.Dewatering:
Rapid dewatering of sandy sediments, possibly triggered by seismic activity, can
causeconvolute bedding.Compaction: Folds can be generated in a younger sequence by
differential compaction over olderstructures such as fault blocks and reefs.
Igneous intrusionThe emplacement of igneous intrusions tends to deform the surrounding
country rock. In the case of highlevel intrusions, near the Earth's surface, this
deformation is concentrated above the intrusion and often takes the form of folding, as
with the upper surface of a laccolith.Flow foldingThe compliance of rock layers is
referred to as competence: a competent layer or bed of rock can withstand an applied load
without collapsing and is relatively strong, while an incompetent layer is relatively weak.
When rock behaves as a fluid, as in the case of very weak rock such as rock salt, or any
rock that is burieddeeply enough, it typically shows flow folding (also called passive
folding, because little resistance isoffered):
the strata appear shifted undistorted, assuming any shape impressed upon them by
surroundingmore rigid rocks. The strata simply serve as markers of the folding.
Such folding is also a feature of manyigneous intrusions and glacier ice.
Principle Of The Seismic Methods Of Subsurface Investigation:
INTRODUCTION
Seismic refraction is a geophysical method used for investigating subsurface ground
conditions by utilizing surface-sourced seismic waves.
Data acquired on site is computer processed and interpreted to produce models of the
seismic velocity and layer thickness of the subsurface ground structure.
The method iscommonly used for measuring the thickness of overburden in areas where
bedrock is at depth, and assessing ripability parameters.
OPERATION
Pulses of low frequency seismic energy are emitted by a seismic source such as a
hammer-plate, weightdrop or buffalo gun.
The type of source is dependant on local ground conditions and requireddepthpenetration.
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Explosives are best for deeper applications but are constrained by environmental
regulations.The seismic waves propagate downward through the ground until they are
reflected or refracted offsubsurface layers.
Refracted waves are detected by arrays of 24 or 48 geophones spaced at regularintervals
of 1 - 10 metres, depending on the desired depth penetration of the survey.
Sources arepositioned at each end of the geophone array to produce forward and reverse
wave arrivals along thearray.
Additional sources may be used at intermediate or off-line positions for full coverage at
all geophonepositions.
DATA INTERPRETATION
Geophones output data as time traces which are compiled and processed by the
seismograph. The basiccomponents of a seismic trace are the direct wave, the reflected
wave and the critically refracted wave.
Wave refraction occurs at interfaces in the ground where the seismic velocity of the lower
layer is greaterthan the velocity of the overlying layer.
This condition normally applies in near surface site investigationswhere soil or fill
overlies bedrock.
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UNIT V GEOLOGICAL INVESTIGATION
Remote sensing for civil engineering applications; Geological conditions necessary for design
and construction of Dams, Reservoirs, Tunnels, and Road cuttings. Coastal protection structures.
Investigation of Landslides and earthquakes - causes and mitigation , seismic zonation – seismic
zones of India.
Introduction About Remote Sensing:
Every object on earth emits its own internal energy according to its molecular andatomic
structure, in addition to reflecting sun light during the day time. This radiationscan be registered
by sensors in several wavelengths, including those in the infrared andmicrowave regions of the
spectrum. When such sensors are installed on aircrafts or onsatellites they can record the earth’s
objects from for off distances. Such distant (Remote)acquisition of information about the objects
on the earth’s surface is known as remotesensing.
Aerial Photography & Imageries:
The photographs of the earth taken from aircrafts are called the aerial photographs,while the
pictures taken from the satellites are called the imageries.
Aerial Photographs: Aerial photographs of the region are taken by cameras placed in the aircrafts. Aerialphotos give
three dimension of the photographed area. These photos contain a detailedrecord of the ground at
the time exposure.
Satellite Imageries:
The satellite imageries can either be read manually like aerial photographs, or with the help of
computers.
Geographic Information System;
The modern computers can process maps and data with suitable computerprogrammer. The
process of integrating and analyzing various types of data with the helpof computer is known as
geographic information system.
Applications Of Remote Sensing:
General geological mapping, mineral prospecting, petroleum exploration, groundwater
exploration, engineering .uses of site rocks, disaster studies, coastal geologicalstudies.
Geological Considerations Involved In The Construction Of Buildings
Basic requirements of a building foundation, building foundation on soils, building foundation
carried to the deep hard rocks, building founded on surface bed rocks, types of settlement in
buildings.
Air Photos:
Shape and size, flight and photo data, scale.
Kinds Of Air Photos:
Vertical air photos, oblique air photos, anusaics, photostrips, stereoprain.
Stereo Meter:
The instrument is used under a mirror stereoscope for measuring heights and areas of objects
from air photos.
SEDIMENTARY ROCKS:
Mud cracks
Tensile shear joints
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METAMORPHIC ROCKS:
Mural joints
Sheet joints
Shear joints
One set of joint are dominant then they are called primary joints, engineering .
SIGNIFICANCE OF JOINTS:
Spacing of joints
Length of joints Block size
Width of joints
Seepage of water through joints
Filled materials and its nature
UNCONFORMITY:
It is defined as a surface of erosion or non deposition occurring within a sequence of rocks. TYPE
OF UNCONFIRMITY:
Angular unconformity Disconformity Non- conformity Local unconformity Regional unconformity
ANGULAR UNCONFORMITY: The different inclinations and structural features above and below
the surface of unconformity The sequence below the unconformity may be steeply inclined folded and faulted. This represent to older formation. T he sequence above the surface of unconformity represent the younger formation DISCONFORMITY: In this type of unconformity in which the beds lying below and above the surface of erosion are nonn deposition such an unconformity become evident only after through investigation involing drilling through the strata NON-CONFORMITY: In bedded sedimentary rocks overly the non beded igneous mass this structure is called non conformity
REMOTE SENSING TECHNIQUES
Remote sensing is the science, art and technology of obtaining information about the object,
throughthe analysis of data acquired by a device this is not in contact with the object under the
investigation.Various objects are identified with the help of variation in the reflected
electromagnetic radiation
reflected by different earth’s objects. A remote sensing system, therefore, must be sensitive
enough tocapture the changes in the reflected electromagnetic energy. An ideal remote sensing
may have thefollowing components.Source of electromagnetic energyMedium which interacts
with this energyGround objectsSensor to detect and record the changes in electro-magnetic
energyElectromagnetic radiation: Sun is the source of light. It radiates the heat and light energy
in the form ofelectromagnetic radiation, the EMR comprises various rays such as , X- rays UV,
Visible,Infrared, thermal inferred, microwave and radio wave. , X- rays and UV are observed
andreflected by upper layer of atmosphere, which is most useful for remote sensing hence it is
known asatmosphere window.
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The part of the electromagnetic radiation from visible to microwave is called electromagnetic
spectrum(EMS).
Various components of an electromagnetic spectrum with their wavelength and frequency
areshown in the above figure.
Principle:
All objective on the earth reflective absorb or radiate energy in the form of
electromagneticwaves coming directly from the sun.
The electromagnetic radiation (EMR) reflected from the objective istransmitted through
the atmosphere. The remotely placed sensors can pickup the transmitted energy,record
and form an image.
This image data is sent to the earth recording stations, where all the data isrecorded on
high density digital tapes.
Information about an object depends upon its spectralcharacteristic, which itself depends
upon the nature of the object and its environment.
The electromagnetic radiation travelling through the atmosphere gets modified by
absorption and or scattering
.
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Remote sensing plate form:
Plate form is defined as a stage of sensor or camera. They play vital role inremote sensing
data acquistation.
They are necessary to correctly position the sensors that collect datafrom the objects of
interest.
The platforms may be air-borne, or space-borne, depending upon theobjects under study
on earth surface and also on the sensor employed. Ballons, Aircraft, and Satellitesare the
common remote sensing platform.
Balloons: These are designed and used for specific projects. Through the use of balloon is
commonlyrestricted by meteorological factors, there application in resource mapping has been
significant useful.Balloons are usually of two types, a) Free balloons and b) Threaded balloons.
Aircraft: aircraft are commonly used as remote sensing plate forms for obtaining aerial
photographs.
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They considered useful for regional converge and large scale mapping.
Space born plate form:
Satellite has provided to be vital use in natural resource mapping,
meteorological and communication application applications.
Satellites are free- flying orbiting vehicles,whose motion is governed by the gravity, and
atmosphere based on well-known kepler’s law’s.
Broadly,satellites can be grouped under two categories depending upon the types of
orbits in which they move.
Geostationary satellite
Altitude - 35,000km
Orbital Movement - Parallel to Earth Rotation
Uses - Communication
Example - GOBS, GMS, INSAT etc
Sun-Synchronous or Polar orbiting satellite
Altitude - 800-900km
Orbital Movement - Pole to Pole
Uses - Earth Observation
Example - LANDSAT, SPOT, IRS, IKNAS, QUAKE BIRD etc
Sensor system:
In remote sensing, the acquisition of data is dependent upon the sensor system
used.Various remote sensing platforms are equipped with different sensor systems.
It is a device thatreceives electromagnetic radiation, converts it into a signal and presents
it in a form suitable forobtaining information about the land or earth resource as used by
an information gathering system.Sensor can be grouped, either on the basis of energy
source or on the basis of wave bonds employed.Based on the energy source, sensor are
classifies as follows.
Sensor Classification
Based on the energy source Sensor May be classifies in to the followings:
Active Sensors (Sensor which produce the EMR by its own i.e RADAR)
Nashri ( Jan 1982) Every year causes damage to the roads
Malori ( Jun 1995): National Highway 1-A damaged and 6 persons killed
West Bengal Region:
Kalimpong, Darjeeling (Aug 1993):40 persons killed with heavy loss of property
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Arunachal Pradesh Region:
Itanagar ( July 1993): 2 km road damaged and 25 persons killed
Mizoram region:
Aizwal ( May 1995): 25 persons killed and road extensively damaged Nagaland region:
Kohima ( Aug 1993): 200 houses and 5 km road damaged. 500 persons killed. Selected
landslides in South India are listed below: Major Land slides took place in the Nilgiri Hill region
include Runnymede, Glenmore, Coonoor areas. Amboori landslide in Kerala: On Nov 9th, 2001,
a disastrous land slide occurred around Amboori (20 km from Thiruvananthapuram ) due to
heavy rains and water logging.
PREVENTION OF LANDSLIDES:
Provision of adequate surface and subsurface to enable water to freely drain out .
Construction of suitable ditches and waterways along slopes to drain off the water from
the loose overburden.
Construction of retaining walls against slopes, so that the rock masses which rolls down
is not only prevented from further fall but also reduces the slope.
Modifying the slopes to stable angles.
Growing vegetation to hold the material together.
Avoiding heavy traffic and blasting operations near the vulnerable places naturally helps
in preventing the occurrence of landslides.
Case Studies Of Structural Failures, Discuss The Importance Of Geological
Investigations For The Design And Construction Of Large Civil Structures. Ground-related factors have often been the origin of contractual claims with significant
time and costoverruns on both large and small construction projects. According to
European statistics, between 80%and 85% of all building failures and damages are
related to unforeseen and unfavourable groundconditions.
Without adequate site investigation, clients are always exposed to the risk of costly
delays,redesign and late project delivery arising out of unforeseen ground conditions;
You pay for a groundinvestigation whether you have one or not . In 1994, the Latham
Report stated that risk ...can bemanaged, minimised, shared, transferred or accepted;
it cannot be ignored . Unfortunately, when it comes to the risk of unforeseen ground
conditions, ignorance on behalf of both the contractor andemployer often seems
commonplace. As unforeseen ground conditions represent a huge area of risk,
aconstruction contract either has to allocate the risk to a single party or distribute it
between the parties.
The traditional method of controlling such risks has been through the use of thorough site
investigationand competent geotechnical design, aiming to produce a robust scheme,
well-matched to the expectedground conditions.
When selecting the construction site of a hydro dam, many factors are involved such as
technical,social and environmental. In this paper we focus exclusively on the technical
aspects that concern thepre-construction stages and the volume of direct and indirect
exploration of the ground.
The purpose ofthe exploration is to obtain a geological model as clear as possible that
serve to characterize thegeotechnical site and so the planning, budgeting and perform the
structural design of the works as wellas obtain sufficient information to establish a safe
and economic project.
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Geological risk managementand its economic consequences can lead to major losses
beyond the physical repair of the work whichrely on a good investigation of the site .
Referring to geotechnical instrumentation and monitoringworks, Allen mentions difficult
conditions to detect (with exploration methods) the presence of lensesmade of soft
material, highly compressible areas and pockets of high pore pressure, which can
causefaulting in the rock mass. From here, it is important to remark the need of the
exploration as even forthe location of the monitoring zones must follow criteria based on
direct or indirect examination.
Thiswork shall consider direct exploration of the site though drilling (exploratory
boreholes), geotechnicaltesting of permeability in wells and excavations of galleries or
tunnels. Drilling is a great support todefine the stratigraphic and structural model for the
site and to identify basic geotechnical parametersfor design of the work, being carried out
on both margins and the river bed, according to the location ofthe works.
The objectives of the sampling site with exploratory drills with core recovery usually
includethe following: stratification on the site, vertical or lateral variations in subsurface
geological conditions,sampling for laboratory testing, verification of the interpretation of
geophysical measurements andplacement of instruments in situ for geotechnical,
geophysical and geohydrological testing.
Theinterpretation of the evidence can be presented to anticipate areas of instability
conditions.Geotechnical testing of permeability in the wells by injecting pressurized
water constitute a substantialproportion of direct examination and focuses on the
competition of the rock mass and its ability tofacilitate or prevent leakage of water from
the dam.
Natural disasters in India can be understood better and controlled well, if
geology is understood well.Give your opinion about this statement using
appropriate case studies. Landslides are very common indeed in the Lower Himalayas. The young age of the
region's hills resultin labile rock formations, which are susceptible to slippages.
Rising population and developmentpressures, particularly from logging and tourism,
cause deforestation. The result is denuded hillsideswhich exacerbate the severity of
landslides; since tree cover impedes the downhill flow of water.[3] Partsof the Western
Ghats also suffer from low-intensity landslides.
Avalanches occurrences are common inKashmir, Himachal Pradesh, and Sikkim.Floods
in India Floods are the most common natural disaster in India. The heavy southwest
monsoonrains cause the Brahmaputra and other rivers to distend their banks, often
flooding surrounding areas.
Though they provide rice paddy farmers with a largely dependable source of natural
irrigation andfertilisation, the floods can kill thousands and displace millions.
Excess, erratic, or untimely monsoonrainfall may also wash away or otherwise ruin
crops. Almost all of India is flood-prone, and extremeprecipitation events, such as flash
floods and torrential rains, have become increasingly common incentral India over the
past several decades, coinciding with rising temperatures. Meanwhile, the
annualprecipitation totals have shown a gradual decline, due to a weakening monsoon
circulation as a resultof the rapid warming in the Indian Ocean and a reduced land-sea
temperature difference.
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This meansthat there are more extreme rainfall events intermittent with longer dry spells
over central India in therecent decades.
Cyclones in India Intertropical Convergence Zone, may affect thousands of Indians living
in the coastalregions. Tropical cyclogenesis is particularly common in the northern
reaches of the Indian Ocean inand around the Bay of Bengal. Cyclones bring with them
heavy rains, storm surges, and winds thatoften cut affected areas off from relief and
supplies.
In the North Indian Ocean Basin, the cycloneseason runs from April to December, with
peak activity between May and November. Each year, anaverage of eight storms with
sustained wind speeds greater than 63 kilometres per hour (39 mph) form;of these, two
strengthen into true tropical cyclones, which have sustained gusts greater than
117kilometres per hour (73 mph).
On average, a major (Category 3 or higher) cyclone develops every otheryear.During
summer, the Bay of Bengal is subject to intense heating, giving rise to humid and
unstable airmasses that produce cyclones. Many powerful cyclones, including the 1737
Calcutta cyclone, the 1970Bhola cyclone, the 1991
Bangladesh cyclone and the 1999 Odisha cyclone have led to widespreaddevastation
along parts of the eastern coast of India and neighboring Bangladesh. Widespread
deathand property destruction are reported every year in exposed coastal states such as
Andhra Pradesh,Orissa, Tamil Nadu, and West Bengal.
India's western coast, bordering the more placid Arabian Sea,experiences cyclones only
rarely; these mainly strike Gujarat and, less frequently, Kerala.Intertropical Convergence
Zone, may affect thousands of Indians living in the coastal regions. Tropicalcyclogenesis
is particularly common in the northern reaches of the Indian Ocean in and around the
Bayof Bengal. Cyclones bring with them heavy rains, storm surges, and winds that often
cut affected areasoff from relief and supplies.
In the North Indian Ocean Basin, the cyclone season runs from April toDecember, with
peak activity between May and November. Each year, an average of eight storms
withsustained wind speeds greater than 63 kilometres per hour (39 mph) form; of these,
two strengthen intotrue tropical cyclones, which have sustained gusts greater than 117
kilometres per hour (73 mph). Onaverage, a major (Category 3 or higher) cyclone
develops every other year.
During summer, the Bay of Bengal is subject to intense heating, giving rise to humid and
unstable airmasses that produce cyclones. Many powerful cyclones, including the 1737
Calcutta cyclone, the 1970Bhola cyclone, the 1991 Bangladesh cyclone and the 1999
Odisha cyclone have led to widespreaddevastation along parts of the eastern coast of
India and neighbouring Bangladesh. Widespread deathand property destruction are
reported every year in exposed coastal states such as AndhraPradesh, Orissa, Tamil
Nadu, and West Bengal.
India's western coast, bordering the more placidArabian Sea, experiences cyclones only
rarely; these mainly strike Gujarat and, less frequently, Kerala.In terms of damage and
loss of life, Cyclone 05B, a supercyclone that struck Orissa on 29 October1999, was the
worst in more than a quarter-century. With peak winds of 160 miles per hour (257
km/h),it was the equivalent of a Category 5 hurricane. Almost two million people were
left homeless; another20 million people lives were disrupted by the cyclone. Officially,
9,803 people died from the storm;unofficial estimates place the death toll at over 10,100.
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LANDSLIDES.
The term landslide refers to the downward sliding of huge quantities of land masses.
Suchsliding occurs along steep slopes of hills or mountains.. It may be sudden or slow in
its occurrence. Also, in magnitude, it may be major or minor.Often, loose and
unconsolidated surface material undergoes sliding. But sometimes, huge
blocks of consolidated rocks may also be involved.
If landslides occur in places of importancesuch as highways, railway lines, valleys,
reservoirs, inhabited areas and agricultural lands leadsto blocking of traffic, collapse of
buildings, harm to fertile lands and heavy loss to life andproperty. In India, landslides
often occur in Kashmir, Himachal Pradesh and in the mountains of Uttar Pradesh.
CLASSIFICATION OF EARTH MOVEMENTS:
All movements of land masses are referred to aslandslides and grouped them under “earth
movements”. The classification of earth movements us as follows:
EARTH MOVEMENTS EARTH FLOWS
Solifluction
Creep
LANDSLIDES
Debris slides and slump
Rock slides
Rock falls
SUBSIDENCE
Compaction
Collapse
Earth Flows:
There are three types of earth flows viz., solifluction; creep and rapid flows.Solifluction
refers to the downward movement of wet soil along the slopes under the influenceof
gravity.Creep refers to the extremely slow downward movement of dry surface material.
This is veryimp from the civil engg point of view due to slow movement of mass.
On careful examination,bending of strata ; dislodgement of fence posts ; telephone poles,
curvature of tree trunks;broken retaining walls etc offer clues to recognize creep.
Rapid flows It is similar to creep but differ with reference to the speed. Rapid flows
generallyaccompany heavy rains.
Mud flows are similar to rapid flows.
Landslides
It is include Debris slides, rock slides and rock falls.
Debris slides are common along the steep sides of rivers, lakes.
Debris slides of small magnitude are called slumps.
Rock slides are the movements of consolidated material which mainly consists of
recentlydetached bedrocks.
For eg: a rock slide that took place at Frank, Alberta in 1903 killing 70people.Rock falls
refer to the blocks of rocks of varying sizes suddenly crashing downwards alongsteep
slopes. These are common in the higher mountain regions during the rainy seasons.
Subsidence
It is compaction of underlying material or due to collapse.
Subsidence due to compaction: Sediments often become compact because of load.
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Excessive pumping out of water and the withdrawal of oil from the ground also cause
subsidence.
Subsidence due to collapse: In regions where extensive underground mining has removed
alarge volume of material, the weight of the overlying rock may cause collapse and subsidence.
CAUSES OF LANDSLIDES:
Landslides occur due to internal causes (inherent). The internalcauses are again of various types
such as Effect of slope; Effect of water; Effect of Lithology;Effect of associated structures ;
Effect of human factors etc..
1.Effect of slope:
This is a very important factor which provides favourable conditions for landslide
occurrence.Steeper slopes are prone to land slips of loose overburdens due to gravity
influence.However, it should be remembered that hard consolidated and fresh rocks remain
stable evenagainst any slope.
2.Effect of water: The presence of water greatly reduces the intergranular cohesion of theparticles of
loose ground causing weakness of masses and prone to landslide occurrence.
Water, being the most powerful solvent, not only causes decomposition of
minerals but also
leaches out the soluble matter of rocks.
This reduces the compaction of rock body and makes
it a weak mass.
3.Effect of Lithology;
Rocks which are highly fractured, porous and permeable are prone
tolandslideoccurrence because they give scope for the water to play an effective
role.
In addition,rocks which contain clay minerals, mica calcite, glauconite, gypsum
etc are more prone tolandslide occurrence because, all these minerals are easily
leached out.
4.Effect if associated structures ;
The geological structures such as bedding planes,joints,faults or shear zones are
planes of weakness and cause landslide occurrence.
5.Effect of human factors:
Human beings sometimes, interfere with nature by virtue of their activities and
cause landslides. For eg: laying roads ; railway tracks etc..
When construction works are carried out on hill tops, the heavy loads on the loose
zone of overburden create a sliding of rock masses.