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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

generated. Igneous activity, crustal deformation,mountain

building and metamorphism are associated with convergent boundaries. Partial fusion of

oceanic crust that plunges in to the mantle generates granitic magma and continental in

the roots of mountains. Sincesediments of low density accretes to the overriding plate, the

plate grows and thus it become constructive.

Although the growth rate is 1 mm/year geologically it is significant. In the two plates of a

destructive

boundary plate is constructed and the other destroyed.

CONTINENTAL COLLISION : According to mattauer, intra-continental subduction can occur

in three ways :

1.Crusts may be stacked one over the other;

2. Crust-mantle decollement may occur

3. Continental lithospheric subduction may also occur.

Collision of then Asian plate and Indian plate provides a best example for intra-

continental subduction.


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The results of the recent investigations on Himalayas reveal the occurrence of subduction

of continental plates in contrast to the general belief that the continental crust cannot sink

owing to it low density.

During initial periods of collision thickening of crust occurred along the boundary

continued collision developed two strike slip faults between which a triangular northeast

of India might have occupied a northern frontal location of Indian plate before collision.

As collision still persists the broken plate margins of both the plates plunge into the

mantle. It is estimated that about 1500km of Indian continental lithosphere has

disappeared into the mantle. The rates of subduction also vary with time.

During upper carboniferous period Indian plate moved at the rate of 10 cm per year. It

was 5 cm per year in Eocene. But it moves 1 to 2 cm per year at present.


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UNIT II MINEROLOGY

Physical properties of minerals – Quartz group, Feldspar group, Pyroxene - hypersthene and

augite, Amphibole – hornblende, Mica – muscovite and biotite, Calcite, Gypsum and Clay

minerals.

Introduction About Mineralogy:

It is a branch ofgeology, which deals with the various aspects related to minerals such as their

individualproperties their mode of formation and mode of occurrence.

It is defined as naturally occurring inorganic solid substance that is characterized with a

definitechemical composition and very often with a definite atomic structure.

Their colour, streak, hardness, cleavage, crystal form, specific gravity and luste generally

identify minerals. The symmetry elements are:

i) Plane of symmetry

ii) Axis of symmetry

iii) Centre of Symmetry

physical properties :

i) Colour

ii) Lustre

iii) Streak

iv) Hardness

v) Cleavage

vi) Fracture

vii) Tenacity

viii) Structure

ix) Specific gravity

x) Form

xi) Miscellaneous


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Color:

Color is not constant in most of the minerals and commonly the color is due to stain or impurities

in the minerals some minerals show peculiar phenomena connected with color.

Play of colors: It is the development of a series of prismatic colors shown by some minerals or

turning about in light.

Change of colors: It is similar to play of colors that rate of change of colors on rotation is rather

slow.

Iridescene: Some minerals show rainbow colors either in their interior on the surface. This is

termed iridescence.

Streak:


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The streak, which is the color of the mineral powder, is more nearly constant than the color. The

streak is determined by marking unglazed porcelain or simply by scratching it with a knife and

observing the color of the powder.

Lustre:

It is the appearance of a fresh surface of a mineral in ordinary reflected light. The following are

the important terms used to denote the lustre of minerals.

Classy or vitreous lustre - Lustre like a broken glass

Metallic lustre - When a mineral has lustre like metal.

Pearly luster - Lustre like pearls

Structure:

This is a term used to denote the shape and form of minerals. The following are the important

terms used to denote the structures of minerals.

Columnar Structure - The mineral has a thick or thin column like

Structures

Bladed Structure - The mineral has blade like structure.

Radiated structure - For columnar of fibrous diverging from central

Points.

Lamellar structure - The mineral made of separable plates.

Botroidal structure - For an aggregate like bunch of grapes.

Reniform structure - For kindney shaped aggregate.

Hardness:

It is the resistance of mineral offers to abrasion or scratching and is measured relative to a

standard scale of ten minerals known as Moh’s scale of hardness.

Hardness Name of the mineral

01 Talc

02 Gypsum

03 Calcite

04 Fluorite

05 Apatite

06 Orthoclase

07 Quartz

The scale comprises ten minerals arranged to order of ascending hardness; the softest is assigned

a value of 1 and the hardest value of 10. Hardness of any mineral will lie in between these

twlimits.

Specific gravity:

It may be defined as the density of the mineral compared to the density of water and as such

represents a ratio.ie specific gravity of a mineral is the ratio of its weight of an equal volume of

water. Specific gravity of a mineral depends upon the weight and spacing of its atoms.

Cleavage:

It is defined as the tendency of a crystallized mineral to break along certain definite planes

yielding more or less smooth surfaces. Cleavage is related to the internal structure of a mineral.

The cleavage planes area always parallel to some faces of the crystal form typical mineral. It is

also described on the basis of perfection or the degree of easiness with which minerals can split

along the cleavage planes.

Fracture:


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The fractures of a mineral may be defined as the appearance of its broken surface. Common

types of fractures are: Conchodal fracture - The broken surfaces shows concentric rings Or

curved surface. Even fracture - When the broken surface is smooth and flat. Uneven fracture -

When the mineral breaks with an irregular

Surface. It is a common fracture of many Minerals. Splintery structure - When the mineral

breaks with a rough.

Tenacity:

Important properties related to tenacity of the minerals are expressed by the terms like balances,

flexibility, elasticity, sectility and mellability etc. when a mineral can be cut with a knife it is

termed “sectile” and if the slice cut out from it can be flattened under a hammer. It is also said

“mellable” “brittle” minerals. Term elastic is used if it regains its former shape as the pressure is

released.

Form:

The internal atomic arrangement of a mineral is manifested outwardly by development if

geometrical shapes or crystal characters. The forms may be following three types:

i crystallized – When the mineral occurs in the form of well defined crystals.

ii Amorphous - When it shows absolutely no signs or evidence of crystallization.

IiiCrystalline - when well-defined crystals are absent but a marked tendency

Towards crystallization.

Miscellaneous:

Some of the special properties are mentioned below:

Magnetism:

Some minerals are highly magnetic,e,g magnetic, whereas few others may be feebly magnetic

like spinals and tourmaline.

Electricity:

Some minerals an electric charge may be developed by heating in some others same effect

results by applying pressure.

Fluorescence:This term express property of some minerals to emit light when exposed to

radiation.

Phosphorescence: It is similar to fluorescence in essential character but in this case light is

emitted not during the act of exposure to radiation but after the substance is transferred rapidly to

dark place.

i) Symmetry

ii) Crystallographic axis Symmetry:

Symmetry is understood a sort of regularity in the arrangement of faces on the body of a crystal.

Symmetry is a property of fundamental importance for a crystal. It can be studied with reference

to three different characters, commonly called elements of symmetry. These are:

A plane of symmetry

An axis of symmetry

Centre of symmetry

A plane of symmetry

Any imaginary plane passing through the centre of a crystal in such a way that it divides the

crystal in two exactly similar halves is called plane of symmetry. In other words, a plane of

symmetry is said to exist in a crystal when for each face, edge or solid angle there is


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anothersimilar face, edge or solid angle occupying identical position on the opposite side of this

plane.

An axis of symmetry:

It is defined as an imaginary line in a crystal passing through its centre in such a way that when a

crystal is given a complete rotation along this line a certain cryatl face comes to occupy the same

position at least twice. The nature of the axis of the symmetry into one of four types:

Axis of Binary or twofold symmetry

This requires that a crystal must be rotated by an angle of 180o to bring the reference face occupy

the same position.

Axis of Trigonal or threefold symmetry

It is that axis on which a crystal must be rotated by an angle of 120o for a reference face to

occupy the same position again in space.

Axis of tetragonal or fourfold symmetry

It is that axis on which the crystal must be rotated by an angle of 900 to bring a reference face in

the same position in space.

Axis of hexagonal or six fold symmetry: In which a rotation of 600 is required to fulfil the

condition of repetition of reference face.

Centre of symmetry

A crystal said to possess a centre of symmetry if on passing an imaginary line from some definite

face, edge or corner on one side of the crystal through its centre another exactly similar face or

edge or corner is found on the other side at an equal distance from the centre.

Ii) Crystallographic Axes

These are also termed as axes of reference and are simply certain imaginary lines arbitrarily

selected in such a way that all of them pass though centre of an ideal crystal. The concept of axes

of reference is based on the fact that exact mathematical relations exist between all the faces on a

given crystal with reference to its centre.

In crystallography following general assumptions have been universally agreed upon regarding

these crystallographic lines:

a) Three Straight Lines, essentially passing though a common centre and varying in mutual

relationships with respect to their lengths and angular inclinations from: all equal, Interchangable

and it right to all unequal and inclined with each other.

b) Four straight lines, essentially passing through a common centre; one vertical, being unequal

to the other three but at right angles to them. The three horizontal axes are separated from each

other at 1200 The concept of crystallographic axis has been the basis of classifying all, the

crystallinesubstances into six crystal systems.

i) Parameter

ii) Indices

iii) Symbols

iv) Forms

The numerical expression for such a relationship of a given crystal face with the

crystallographicaxes is variously termed as Parameters, index or a symbol each term having its

own significance.

Parameters

The relative intercepts made by a crystal face on the three crystallographic axes areknown as its

parameters. For instance in the three crystallographic axes are represented byXOX’,YOY’ and


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ZOZ’. With their relative lengths as Ox=a, Oy=b and Oz= cLet us consider a face represented by

a plane ijk occurring on this crystal. The intercepts of this

plane with the three axes are oi, oj and ok. Which expressed in ters of the lengths of the axes

is1a, 1/3b, 1/2c. Therefore 1a.1/3b and 1.2c are parameters of the face. These are

generallyexpressed as parametrical ratios as 1a:1/3b:1/2c

Indices

In common practice the relationship of a crystal face with the crystallographic axes isexpressed

in simple whole numbers, which are called indices. These indices are however alwaysbased on

and derived from the parameters. There are a number of methods for deriving indicesfrom

parameters such as the Neumann system and Miller system.In the miller system the indices for a

given crystal face are derived from its parameters intwo simple steps:

By taking the reciprocals of the parameters actually obtained for the given face.

By clearing fractions if any by simplifications and omitting the letters for the axes

in the final expression.

Symbol

It is the simplest and most representative of the indices for a set of similar faces thatconstitute a

crystallographic form. For instance in this fig there are six exactly identical crystalfaces, which

have same mathematical relationship with all the three crystallographic axes.Obviously the six

faces together make a form in which each face has an identical mathematicalrelationship with the

three axes. This statement can also be mathematically written as 100 whichas generalization for

all the six face of this particular form.

FormsAny group of similar faces showing identical mathematical relations with crystallographic

axes makes a form. Forms are further distinguished into following types:holohedral form

hemihedral form, and hemomorphic form, enantimorphic form, andfundamental form, open and

closed form.

Holohedral form

It is that form in a crystal system which shows development of all the possible faces in

itsdomain. For instance, octahedron is a holohedral form because it shows all the eight

facesdeveloped on the crystal; generally holohedral forms develop in the crystals of highest

symmetryin a crystal system. Such class of highest symmetry in a system is called its normal

class.

Hemihedral form

It shows as the name indicates only half the number of possible faces of a

correspondingholhedral form of the normal class of the same system. As such all

hemihedralforms may beassumed to have been derived form holohedral forms. The two

complimentary hemihedral formswill necessarily embrace all the faces and characters of the

parent holohedral form.

Hemimorphic form

It is also derived from a holohedral form and has only half the number of faces as inhemihedral

form. In this case however all the faces of the form are developed only i-on oneextremity of the

crystal. Being absent form the other extremity. In other words such a crystal willnot be

symmetrical with reference to a centre of the symmetry.

Enantiomorphous form

It is composed of faces placed on two crystals of the same mineral in such a way thatfaces on

one crystal become the mirror image of the form of faces on the other crystal. The formsand the

corresponding crystal showing these forms are referred as left and right handed.


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Fundamental form

It is also called a unit form. It designates that type of any given form in which

theparametersessentially correspond to the unit lengths of the crystallographic axes. A form

havinga symbol is essentially a fundamental form whereas another form also intercepting the

three axesat different lengths.

Open and closed forms

A form is defined as closed when on full development it makes a fully enclosed solid. Inan open

form space cannot be fully enclosed by it and entry from one or more sides is possible.

Elements Of The Symmetry And Minerals : i) Isometric system

ii) Hexagonal system

iii) Monoclinic system

Isometric system:

Definition:

All those crystals that can be referred to three crystallographic axes, which are essentially equal

in length at right angles to each other, and mutually interchangeable, are said to belong to the

isomeric or cubic system.

Axial diagram

Since all the three axes are equal and interchangeable these are represented by the letter a. In the

study position however the axes may be designated as a1,a2 and a3 the last being vertical.

Classes

Five symmetry classes fall in the Isometric system by virtue of their country The normal class is

known as galena type. It has got the following symmetry.

a) Axes of symmetry: 13 in all

3 are axes of four-fold symmetry

4 are axes of three-fold symmetry

6 are axes two fold of symmetry

b) Planes of Symmetry: 9 in all

3 planes of symmetry are at right angles to each other and are termed the principal planes; 6

planes f symmetry are diagonal in position and bisect the angles between the principal

planes.

c) It has centre of symmetry.

Forms

Following are the forms that commonly develop in the crystals belonging to isometric system.

1. Cube: A form bounded by six similar square faces each of which is parallel to two of three

crystallographic axes and meets the third axis.

2. Octahedron: A form bounded by eight similar faces each of the shape of an equilateral triangle

each meeting the three crystallographic axes at equal distances.

3. Dodecahdraon: It is form with twelves similar faces each of which is parallel to one of the

three crystallographic axes and meets the other two at equal distances.

4. Trisoctahedron: A form of twenty four faces; each face meeting two axes at unit length and to

the third at greater that unity.

5. Trapezohedran: A forms of 24 faces each faces meeting one axes at unit length and to the

other two at greater than unity.

6. Hexaoctahedran: 48 faces; each face meets the three axis at unequal distances.


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7. Tetra hexahedron: 24 faces each face meeting one axes and meet other to at unequal distance

which are simple multiple of each other.

Other classes:

Isometric system comprises five symmetry classes in all. Beside the normal class following three

classes are also represented among the minerals.

1. Pyritohedral Class

a) Symmetry 7 axes of symmetry of which 3 are axial axesof two fold symmetry 4 are

diagonal axes oftwo fold symmetry,3 planes of symmetry. Acentre of

symmetry.

b) Forms Pyritohedran and Diploid are two typical formsof this symmetry

class.Diploid is a closed form of twenty-four facesthat typically occur in

pairs.

2. Tetrahedral class

a) Symmetry 7 axes of symmetry, 6 planes of symmetry diagonal, no centre symmetry.

b) Forms Most typical form of this class is a four-sided solid in which each face is

an equilateral triangle. It is termed tetrahedron. It has a general symbol.

Hexagonal system

All those crystals, which can be referred to four crystallographic axes of which

i) Three axes are horizontal, equal, interchangeable and intersecting each other at 1200 between

the positive ends.

ii) The fourth axes are vertical and at right angles to the three horizontal axes are grouped under

the hexagonal system.

Axial diagram

The horizontal axes all being equal are designated by the letter a(a1,a2,a3)and the vertical axis by

the letter ‘c’ as usual.

Forms

Forms of hexagonal system differ in character from forms of all the other systems in that their

parameters, indices and symbols are determined with respect to four crystallographic axes. Thus

the general form expresses the relation of any hexagonal form.

1. Base: An open form of two faces in which each face meets the vertical axis only.

2. Prisms: A prism as defined earlier is an open form in which each face is essentially parallel to

the vertical axis. Following three types of prisms are met with in the hexagonal system.

a) Prism of 1st order. An open form of six faces in which each face is parallel to one of the three

horizontal axes besides the vertical axis. It cuts the two horizontal axes at unit length.

b) Prism of 2nd order. An open form of six faces like prism of 1st order but in this case each face

cuts all the three horizontal axes, two axes at equal length and to the third at greater length.

c) Prism of 3rd order: It is also called a dihexagonal prism as it has double the number of

faces compared to the six faces of prism of 1st order.

Monoclinic system

The monoclinic system includes all those forms that can be referred to three crystallographic

axes which are essentially unequal in length and further that can be of these is always inclined.

Axial diagram

All the three axes are unequal, they are designated by the letters a, b and c. The c axis is always

vertical. The inclined axis is a- axis. It is inclined towards the observer and is also referred as

clino axis.


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Normal class symmetry

There are three symmetry classes placed in monoclinic system. The symmetry of the normal

class is as given below:

a) Axis of Symmetry 1 axis of two fold symmetry only

b) Planes of symmetry 1 plane of symmetry only. And a centre of symmetry.

The plane of symmetry is that plane which contains the crystallographic axes a and c

Forms

The common forms of this system are

1) Pinacoid

it is an open from of two faces, each face being parallel to the two axes and cutting the third at a

unit length .Three pinacoids are distinguished in the monoclinic system.

i) a- pinacoid

ii) b-pinacoid

iii) c-pinacoid

2. Domes

A dome is also form of two faces, each face meeting the vertical axis and one of the other two

axes. It is a parallel to the third axis. Two types of domes are recognized:

i) Orthodome

ii) Clinodome

3. Prisms

There are three types of prisms is there;

i) Unit prism

ii) Orthoprism

iii) Clinoprism

4. Pyramid

These are closed forms and in these each face meets all the three axes.

i) Unit pyramid

ii) Orthopyrmaid

iii) Clinopyramid

Twinning and types of twin and common twin laws: A group of two crystals mutually united and intimately related are called TWINS and the

phenomenon of their formation is called twinning. Terminology

Terms commonly used in the explanation of twin Laws are: Twin plane, Twin axis, and

composition plane.

Twin plane:

It is such a plane in a twin crystal, which is common to both the halves of the crystal and across

which one half may appear to be the reflection of the other.

Twin axis:

It is a crystallographic direction along which a rotation of some degrees seems to have produced

the resultant twins. The twin axis is other than the axis of two fold, four fold, and symmetry.

Types of twins:

The following types are:

Contact Twins:

In this type the component parts of a twin crystal are held together along a well defined

composition plane.


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Penetration twins:

In these twins the contact plane is not well defined. In fact the two parts of twin crystalmay

appear to be inter penetrating to each other.

Simple Twins:

When a twin crystals has very well defined two halves held together according to

easilyunderstanding relationships these may be said as simple twins.

Common twin laws

Following is a brief outline of the most commonly observed twin laws in

differentcrystallographic system.

Isometric system

Spinal law:

It is so named because of its presence in minerals of spinal group. In this law, octahedralface is

the twin palce, which is also in most cases.

Tetragonal system

Rutile law

The face of pyramid of IInd order is the twinning plane. This is the most common law for the

crystals of the tetragonal system.

Hexagonal system

Brazilian Law:

In this law the prism of IInd order is a twin plane. Quartz shows development of twinsaccording

to this law.

Dauphine law:

In this law c-axis is the twinning axis. Twins are generally intergrown. Some quartz twinalso

based on this law.

Japanese law:

Contact twins result on this law in which pyramid is a twinning plane.

Orthorhombic system

In this system, crystals show twinning in a variety of ways of which following are more

common.

a) When the prism angle is about 600 and the twinning is repeated.

b) When the prism angle is 700

Staurolite Twinning. This mineral shows cruciform twins of two types.

Right angled cross: These result when the face is a twinning plane

Sea horse twin in which the face is a twin plane.

In both cases the twins are of penetration type.

Monoclinic system

The following laws are the most common and in no case exclusive.

Carlsbad law:

The c-axis is the twinning axis. The minerals commonly show interpenetration or contact

type of twinning.

Baveno law:

The mineral shows twining with clino dome as the twinning plane.

Man Bach law:

Here, the basal pinacoid is a twinning plane.

Triclinic system

Albite law


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In this plane parallel to b-pinacoid is the twinning plane.

Per cline law

The twinning axis is easily defined as the one parallel to b-axis. The twins may be repeated

polysynthetic type.

classification and formation of coal: The term coal is generally applied to a sedimentary formation of highly carbonaceous character

that is derived from vegetable matter involving set of process such as burial, compaction and

biochemical transformation.

Classification

A number of classifications for coals are available of these the one most widely adopted is based

on the rank of coal that defines degree of transformation of wood into coal through the natural

processes of deposition, compaction and biochemical changes.

Peat

It is essentially a partly changed vegetable mater in the first stage of transformation to coal. The

vegetable structure is easily visible and the evidence of its being in the processes of

transformation. to coal. Peat is generally composed of remains of moss like plants but

occasionally may contain reeds and partially altered portions of trees of higher order. Types:

Two types of peat are commonly recognized:

Bog Peat, which is evolved out of lower type of vegetation, like

mosses.

Mountain Peat that is decomposed and partially altered form of

higher type’s of trees.

Uses:

Peat is a low value fuel in its application .It finds uses where available in abundance as

i)Domestic fuel ii) gas purifier iii) For steam raising.

Lignite

It is a variously coloured variety of coal of lowest rank. In lignite transformation of vegetable

matter to coal like material is almost complete. Fibrous texture is also shown by some lignite’s.

Composition: Typical lignite has following composition:

Fixed Carbon : 50 percent; oxygen 20-25 percent

Hydrogen : 05 perecnt;nitrogen 02-05 percent

Sulphur: 01-02 percent.

Uses: These are used as domestic fuels and also in industry for distillation and gasification. This

variety of coal has also been used in steam locomotives and for producing gas.

Bituminous

It is also known as the common coal,someties as coking coal and is ,in fact, the most common

and important variety commercial coals. These are commonly black in colour, compactin

structure breaking into almost cubical fragments when struck with hammer. They have a black

streak. Bituminous coals burn freely leaving only a small mineral residue.

Types and composition:

The common bituminous coal is sometimes distinguished into three different types on the basis

of its carbon content: sub-bituminous, bituminous and semi-bituminous coals.

Anthracite

It is a coal highest rank in which original organic source has been completely transformed into

carbonaceous substance. It is very hard, jet black in colour, compact in structure and showing an

almost metallic luster.


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Uses:

Anthracite is a favourite domestic fuel where available. It is also used for steam raising and

other heating purposes. However because of its very low volatile matter content it is not suitable

for making coke.

Formation of coal

There is absolutely no doubt regarding the nature of the source material form which coal is

derived it is certainly always vegetable matter of one type or another. The two types of sources

yielded vegetable material for the formation of the coal.

i) The higher vegetation:

It including herbs, shrubs and trees, growing on the plains, plateaus, sub-mountaineousand areas

and characterized with wood tissue rich in cellulose and lignin and protein this type ofsource has

been named as the humic sediment.

ii) The lower vegetation:

It comprising chiefly plank tonic algae, as soften found at the bottom of lakes and

seas,submerged under water. This source has been named as sapropelic sediments.On the basis

of place of accumulation of the source material, the environment could be

distinguished as:

Geosynclinal type:

When accumulation took place in great sea basins characterized with considerable depth.

Intermediate type:

When deposition of source material took place along the sea shores at shallower depths.

Platform type:

Such as lagoons, lake basins and marshes and swamps.

In these littoral environments decomposition of cellulose from humic organic matter is an

easilyaccomplished process. IN other environment also the process may take the route of

transport ofsource material its accumulation, compaction, dehyfdration and polymerisation to

bituminouscoal to anthracite are all environment dependent. These are completed in an better

manner ingeosynclinal situations that is under great depths in the presence of heat and pressure

and seldom reach completion in littoral conditions. Summarisingly the transformation of organic

source material into coal takes place due to:

Bio chemical decomposition which is achieved by certain type of bacteria and

involves breakdown of organic matter of wood into coal constituents.

Dynamo chemical transformation which involves alteration of original coal structure

into more compact, metamorphosed varieties chiefly under the influence of

temperature and pressure factors. FELSPAR GROUP: It is most abundant of all minerals

It is used for making more than 50% by weight crust of earth

It is non-metallic and silicate minerals

CHEMICAL COMPOSITION: Potash feldspar KAlSi3 O8 Soda-lime feldspar NaAlSi3O8 (OR)

CaAl2Si2O8 VARITIES OF POTASH FELSPAR: Orthoclase Sanidine Microcline SODA LIME

FELSPAR: Albite Oligoclase Andecine Amarthitite Labrodorite

GENERAL PHYSICAL: CRYSTAL SYSTEM: monoclinic,triclinic HABIT: Tabular (crystalline) CLEAVAGE: Perfect( 2- directional)

FRACTURE: Conchoidal or uneven

COLOUR: White, grey, pink, green, red


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LUSTRE: Vitreous HARDNESS: 6-6.5

SPECIFIC GRAVITY; 2.56-2.58(low)

STREAK: No OCCURRENCE: Igneous rock

USES: Ceramics, glass, tableware, enamels, electric porcelain, false teeth POTASH FELSPAR: ORTHOCLASE:

CRYSTAL SYSTEM: monoclinic

COLOUR: red

CHEMICAL COMPOSITION: KAlSi3O8

MICROCLINE: CRYSTAL SYSTEM: triclinic

COLOUR: flesh red

CHEMICAL COMPOITION:KAlSi8 O8 USES: ceramic semiprecious

SODA LIME FELSPAR: ALBITE: CRYSTAL SYSTEM: Triclinic COLOR: Whitish or pinkish white

COMPOSITION: NaAlSi3 O8 USES: Ceramic, ornamental stone

ANORTHITE: CRYSTAL SYSTEM: Triclinic COLOR: white

COMPOSITION: Ca Al2Si2O8 (90%), NaAlSi3O8 (10%)

USES: ceramic, ornamental stone

OCCURRENCE: all types of rocks PYROXENES GROUP:

It is important group of rock forming minerals

They are commonly occur in dark colours, igneous and metamorphic rocks

They are rich in calcium, magnesium, iron, silicates

It show single chain structure of silicate

It is classified into orthopyroxene and clinopyroxene. It is based on internal atomic structure

ORTHOPYROXENE: Enstatite (MgSiO3) Hyperthene [(Mg,Fe)SiO3]

CLINOPYROXENE: Augite [(Ca, Na) (Mg, Fe, Al) (Al, Si)2O6]

Diopside [CaMgSi2O6] Hedenbergite[CaFeSi2O6]

AUGITE: CRYSTAL SYSTEM: Monoclinic

HABIT: Crystalline CLEAVAGE: Good ( primastic cleavage)

FRACTURE: Conchoidal

COLOUR: shades of greyish green and black

LUSTRE: vitreous

HARDNESS: 5-6

SPECIFIC GRAVITY: medium

STREAK: white

OCCURRENCE: ferro magnesium mineral of igneous rock (dolerite)

USES: rock forming mineral

COMPOSITON: [(Ca, Na) (Mg, Fe, Al) (Al, Si)2O6]

TRANSPARENCY: Translucent/opaque AMIPHOBLE GROUP:

These are closely related to pyroxene group

It shows double chain silicate structure

Rich in calcium, magnesium, iron oxide and Mn, Na, K and H

CLASSIFICATION: Orthorhombic

Monoclinic

Hornblende


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Tremolite

Actinolite

HORNBLENDE: (COMPOUND-COMPLEX SILICATE)

CRYSTAL SYSTEM: Monoc;inic

HABIT: crystalline

CLEAVAGE: good(prismatic) FRACTURE: conchoidal

COLOUR: dark green, dark brown black

LUSTRE: vitreous HARDNESS: 5 to 6

SPECIFIC GRRAVITY: 3 to 3.5 (medium)

STREAK: colourless or white COMPOSITION: hydrous silicates of Ca, Na, Mg, Al

TRANSPARENCY: translucent/opaque

OCCURRENCE: found in igneous rocks USES: road material

MICA GROUP: Form sheet like structure

Can be spilt into very thin sheets along one direction Aluminium and magnesium are rich

Occupy 4% of earth crust

Shows basal cleavage

CLASSIFICATION: LIGHT MICA:

Muscovite-KAL2(AlSi2O10)(OH)2-Potash mica

Paragonite-NaAl2(AlSi3O10)(OH)2-Soda mica

Lepidolite-KLiAl(Si4O10)(OH)2 –Lithium mica CLAY MINERAL GROUP:

These are phyllosilicates minerals

Essentially hydrous aluminium silicates

These are common weathering products Very common in sedimentary rock

CLASSIFICATION: There are four group, 1. Kaolin

a. Kaolinite b. Dictite

c. Nacrite

d. Halloysite

2. Smectite a. Montmorillonite

b. Nontronite

c. Hectorite 3. Illite

4. Chorite

PHYSICAL PROPERTIES: KAOLIN GROUP: KAOLINITE:

It is formed by weathering of aluminate- silicate minerals. The feldspar rick rocks are commonly

weathered to kaolinite.

Crystal system: Triclinic


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Habit: Massive Colour: White sometimes brown

Cleavage: Perfect Fracture: Even

Streak: White Lustre: Dull earthy

Hardness: 2 Specific gravity: 2.6(low)

Transparency: Translucent

Composition: Al2Si2O5(OH)4

Occurrence: secondary mineral formed by alternation of alkali feldspar Uses: ceramic industries,

medicine, cosmetics and main components in porcelain

HALLOYSITE: Crystal system: Monoclinic Habit: Massive

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

texture and structure

BASIC CLASSIFICATION: VOLCANIC ROCKS/ EXTRUSIVE ROCKS:

Rocks formed from lava on earth surface

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

hypersthenes; augite ; diopside ; magnetite / haematite, rutile, zircon, apatite, garnet..


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Texture: Granites exhibit phaneric texture ( coarse grained ), or graphic texture (similar

toArabicwriting ). Granites are usually equigranular but some times show inequigranular texture

in case ofPorphyritic texture (feldspars occur as phenocrysts). Hand specimen: Granite is grayish

or pinkish in color. Feldspar appears with white or brownish – red color. Quartz looks colorless.

Biotite is jet black and is found as small shining flakes. Hornblende is dark greenish black.

Varieties: When quartz decreases and increase in mafic minerals, granite passes over to

GRANODIORITE and then DIORITE. When both the alkali feldspars and plagioclase feldspars

are equal in quantity, the granite rock is called as ADAMELLITE. If hypersthene is more in

granite then it is known as CHARNOCKITE. If feldspars and quartz are very large in size and

exhibit interlocking texture, then it is called as PEGMATITE. Occurrence of large sized beryl,

tourmaline crystals is another diagnostic feature ofpegmatite.

RHYOLITE is very fined grained rock and is the volcanic equivalent of granite. When the

accessory minerals present more in quantity than normally such rocks are named as eg; biotite-

granite, hornblende-granite. Based on the color of feldspars, the granites are termed as Pink

granite; grey granite.

DOLERITE

Dolerite is a dark, fine grained black or dark greenish black igneous rock. It is intermediate in

composition and melanocratic (dark coloured) rock . Mineralogically and chemically, dolerite is

similar to Gabbro and basalt.

SPECIAL FEATURES: The compact nature and rich in mafic minerals make the rock emit

metallicsound when hit with a hammer. Dolerite occurs in nature as an intrusive rock ie as dyke.

ENGINEERING POINT OF VIEW: Dolerites are not common as building stones. They are

suitable asroad metal, railway ballast, bitumen aggregate, concrete purposes. At foundation sites

of dam like structures, the presence of dolerite is considered undesirable as they become a cause

for weak planes.

BASALT is a black volcanic, massive, fine grained, melanocratic rock. .

COMPOSITION: Basalt consist of plagioclase feldspars ( labradorite), Pyroxenes (Augite) and

iron oxides (magnetite or ilmenite). Biotite, hornblende and hypersthenes are the other accessory

minerals.Pyrite may also seen sometimes. Either quartz or olivine may appear in small amounts

depending on the silica content of parent lava.

Structures & Textures: Vesicular and amygdaloidal structures are common in basalts. However,

Columnar and flow structures are also observed in some cases. Basalts exhibit aphanitic texturein

hand specimens. ( ie the minerals are too fine). Appearance in Hand specimens: Basalt is

typically black or greenish grey or greenish black. Nonvesicular, massive in nature.

Engineering Properties Of Rocks:

Field testing and, to a lesser extent, geophysical surveying are major sources of both qualititive

andquantitative data relating to the ground conditions. In spite of the fact that in most cases field

testing is more expensive to carry out than sampling and laboratory testing, it forms an essential

part of many site investigations. There are several reasons for this, probably the most important

of which is because it provides, for design purposes, parameters which represent a more

realistic appraisal of geotechnical Two types of penetration tests are recognized (Anon 1975 and

1981). The standard penetration test (SPT) is a dynamic method in which a 51 mm external

diameter split tube sampler connected to drilling rods, is driven into the ground by a series of

hammer blows delivered at the surface. The test is conducted atintervals during the course of

boring and it provides a distributed sample for identification purposes. In the static penetration


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test a conical point is driven into the ground by means of a steady pressure on the top of the rods.

Both tests provide an indirect measure of shear strength since the action of the tests produces a

complex failure surface within the soil.Shear strength tests Various means of obtaining a direct

indication of the in situ shear strength are available. Probably the most widely used of these is

the shear vane test but brief reference will also be made to direct shear and triaxial tests. Shear

vane test rotation of the vane and allowing a short period of time for pore pressures to

dissipate. The test is used for very soft to firm, saturated, nonfissured, homogeneous clays. Plate

loading tests

Mineralogical Composition, Texture, Engineering Properties And Uses Of

Dolerite,Laterite, Sandstone And Limestone

DOLERITE



similar to Gabbro and basalt.

Composition: Dolerite consists of Plagioclase Feldspars and pyroxene (augite). Iron oxides,

hypersthenes and biotite occur as common accessory minerals. Olivine is some times found if the

parent magma was deficit of silica.

Texture: Dolerite is a massive and compact rock. It is neither porous nor permeable. The texture

in dolerites is generally equigranular. Interlocking texture is also common in dolerite. Under the

microscope dolerite exhibit Ophitic or subophitic texture.

Hand specimen: Dolerite is a fine grained rock with greenish black or black coloured. Presence

of pyroxene (augite) contributes the black color of a rock. Feldspars can be observed by means

of their cleavage surfaces and biotite if present appears as small, jet black..

Varieties: When all the minerals of dolerite are totally altered for eg: plagioclase into zoisite or

epidote and augite into chlorite / hornblende and olivine into serpentine then the rock is called

DIABASE.

Plutonic equivalent of dolerite is called Gabbro.

Volcanic equivalent of dolerite is called Basalt.

Glassy equivalent of dolerite is called trachylyte.


metallic sound when hit with a hammer. Dolerite occurs in nature as an intrusive rock ie as dyke.


suitable as road metal, railway ballast, bitumen aggregate, concrete purposes. At foundation sites

of dam likestructures, the presence of dolerite is considered undesirable as they become a cause

for weak planes.

Sandstones

Sandstones are abundant among sedimentary rocks but are next to shales. Sandstones are made

up of sand and described as Arenaceous rocks. Sandstones are stratified and sometimes

fossiliferous too. Compositionally, sandstones consist of sand grains ( 90% quartz ) with

accessory minerals of such as mica, ilmenite, magnetite, garnet, zircon, rutile, feldspars cover the

rest. In a hand specimen of sandstone, the size of sand grains may be coarse, medium or fine

grained and other grains appear in different colors due to the presence of cementing material:

Grains Appears as

Quartz Colorless, fresh with vitreous luster Mica flakes White colour with perfect cleavage


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Ilmenite / magnetite Jet black Garnet Red with shining Zircon; rutile White color with shining

Feldspars Pale colours of brown, red, white, grey with a dull lustre

Pyroxenes & amphiboles Pale colors Sandstones are generally porous and permeable and

considered one of the best aquifers. By virtue of their porosity and permeability, they are not

only capable of holding a good quantity of groundwater but also yield the same when tapped.

LIMESTONES

LIMESTONES: In hand specimens, limestones show different colours of white, gray, buff,

cream, pink, yellow and black. In nature, limestones occur both as porous and massive types. On

the otherhand, shell limestones care common and may be porous.

Types of Limestones:

Chalk: A soft, white fine grained calcareous deposit with dull lustre. It is also consists of fossils

viz., foraminifera.Stalactites result from the process when surface water with dissolved calcium

carbonate passthrough minute fractures and grows downwards from the roof of a cave. If the rate

of percolation of solution is excess than required evaporation, the solution falls on floorand form

as a cone like deposit which grows upwards from the floor is called as Stalagmites.If growth

continues stalactites and stalagmites may come together after some time producing apillar like

structure , called a DRIP STONE. Fossiliferous or Shell limestone: These are formed organically

with hard parts of marine organisms of coral reefs or gasteropods or lamellibranchs or

brachiopods etc.

Engineering Properties And Uses Of Granite 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 ofhypersthenes; augite ; diopside ; magnetite / haematite, rutile, zircon, apatite,

garnet..

Texture: Granites exhibit phaneric texture ( coarse grained ), or graphic texture (similar to

Arabicwriting ). Granites are usually equigranular but some times show inequigranular texture in

case of Porphyritic texture (feldspars occur as phenocrysts).

Hand specimen: Granite is grayish or pinkish in color. Feldspar appears with white or brownish

–red color. Quartz looks colorless. Biotite is jet black and is found as small shining flakes.

Hornblende is dark greenish black.Varieties: When quartz decreases and increase in mafic

minerals, granite passes over toGRANODIORITE and then DIORITE.

When both the alkali feldspars and plagioclase feldspars are equal in quantity, the granite rock is

called as ADAMELLITE.

If hypersthene is more in granite then it is known as CHARNOCKITE.

If feldspars and quartz are very large in size and exhibit interlocking texture, then it is called as

PEGMATITE. Occurrence of large sized beryl, tourmaline crystals is another diagnostic feature

of pegmatite.

RHYOLITE is very fined grained rock and is the volcanic equivalent of granite.

When the accessory minerals present more in quantity than normally such rocks are named as

eg; biotite-granite, hornblende-granite. Based on the color of feldspars, the granites are termed as

Pink granite; grey granite.

SPECIAL FEATURES:

Specific gravity of granite is 2.6 – 2.8


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Density = 2500 – 2650 kg/cm3; compressive strength = 1000 – 2500 kg /sq cm

ENGINEERING POINT OF VIEW: By virtue of many desirable qualities, granite can be used

infoundations of civil structures, building stone, road metal,. Tunneling through granite does not

require any lining.

Igneous Rock, Metamorphic Rock And Sedimentary Rock On The Basis Of Structure And

Texture

CLASSIFICATION OF IGNEOUS ROCKS:

Igneous rocks are the first formed rocks in the earth’s crust and hence these are called

PRIMARY ROCKS, even though igneous rocks have formed subsequently also. Igneous rocks

are the most abundant rocks in the earth crust and are formed at a very high temperature directly

as a result of solidification of magma since magma is the parent material of igneous rocks. The

temperature increases proportionately with the depth --- this is one of the reasons for the

formation of igneous rocks.

Igneous rocks are usually massive, unstratified, unfossiliferous and often occur as intrusive

cutting across other rocks ( country rocks or host rocks ). The igneous rocks are classified based

on silica%, silica saturation and depth of formation.

METAMORPHIC ROCKS


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Igneous and sedimentary rocks which are formed under a certain physico-chemical environment,

(theywere in equilibrium) in terms of temperature, pressure and chemically active fluids.

Subsequent to theirformation if any of these factors changes, the existing equilibrium gets disturb

in the constituent minerals ofparent rocks by metamorphism. As a result of Metamorphism

Granite changes to Granitic Gneiss

Peridotite (Ultrabasic) changes to Serpentine / Talc Schist.

Gabbro / Dunite changes to Hornblende Schist.

Sandstone changes to Quartzite.

Limestone changes into Marble.

Shale changes into Slate

The process of metamorphism occuring in rocks due to the effect of high temperature, pressure

andMchemically active fluids and are known as metamorphic agents. These three act together to

causeMmetamorphism and sometimes any one or two of them dominate and play an active role.

Temperature: Metamorphic changes mainly take place in the temperature range of 350°C to

850°C.Pressure: Uniform pressure ( vertically downwards) increases with depth and effect on

liquids and solidsat greater depths whereas the direct pressure (stress) due to tectonic forces acts

in any direction i.e.,upwards, downwards and side wards and effect only on solids.

Chemically inactive fluids: The most common liquid is water. Also the magma or hot

hydrothermalsolutions (containing various chemicals) may react directly with those rocks when

they come in contact.

Types of Metamorphism:

1. Thermal Metamorphism (Heat predominant)

2. Dynamic/Cataclastic Metamorphism: When direct pressure is predominant and acts, rocks are

forcedto move past resisting in their crushing and granulation.

3. Geo-Thermal Metamorphism: Uniform pressure is predominant alongwith heat brings changes

inoceanic salt deposits but not changes in silicate rocks.

4. Metasomatic Metamorphism (chemically active fluids predominant): This Metamorphism

alters thecomposition of the rock significantly. Hydrothermal solutions are hot (upto 400°C) and

cause forproviding new minerals such as Pb, Zn, Mn etc. Tourmaline, topaz and fluorspars are

produced whenthe volatiles involved .Eg: When Granite is attacked by watervapour, Boron,

fluorine will suffer mineralogical changes whereby feldspars replaced by tourmaline, the

resultant rock may be Tourmaline Granite.

5. Dynamothermal Metamorphism: (Direct pressure and Heat pressure): When an argillaceous

rock(shale) undergo Dynamo Thermal Metamorphism different minerals are produced. Eg.

Gneisses andschists.Chlorite Biotite Garnet Staurolite Kyanite Sillimanite

The presence of chlorite and biotite in a metamorphic rock indicates that it had been

formed under low

grade Metamorphism.

Presence of Garnet and Staurotite indicates medium grade of Metamorphism.

Occurrence of Kyanite and Sillimanite indicates high grade of Metamorphism.


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Mineral Composition: Following are the common minerals found in metamorphic rocks:

Cordite, Staurotite, Andaulusite; Sillimanite, Kyanite, idocrase formed during Metamorphism.

Garnet,Chlorite, Talc, Epidote, Quartz, Feldspars, Pyroxenes, Calcite, Mica, Hornblende also

occur in differentways due to Metamorphism.

FORMATION OF SEDIMENTARY ROCKS:

Sedimentary rocks are formed by simple or complex mechanical or chemical processes.

Biological activity is often involved in many cases in association with these processes.

Sedimentary rocks are broadly grouped into three classes depending upon their mode of

formation: clastic rocks (mechanically formed); chemically formed and organically

formed sedimentary rocks.

Mechanical weathering is the breakdown of rock into particles without producing

changes in the

chemical composition of the minerals in the rock. Ice is the most important agent of

mechanical weathering.

Water percolates into cracks and fissures within the rock, freezes, and expands. The force

exerted by the expansion is sufficient to widen cracks and break off pieces of rock.

Heating and cooling of the rock, and the resulting expansion and contraction, also aids

the process. Mechanical weathering contributesfurther to the breakdown of rock by

increasing the surface area exposed to chemical agents.

Chemical weathering is the breakdown of rock by chemical reaction. In this process the

minerals within the rock are changed into particles that can be easily carried away. Air

and water are both involved in many complex chemical reactions.

Outline the various Engineering properties of rocks:

Field testing and, to a lesser extent, geophysical surveying are major sources of both qualitative

and quantitative data relating to the ground conditions. In spite of the fact that in most cases field

testing is more expensive to carry out than sampling and laboratory testing, it forms an essential

part of many site investigations.


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There are several reasons for this, probably the most important of which is because it

provides, for design purposes, parameters which represent a more realistic appraisal of

geotechnical Two types of penetration tests are recognized (Anon 1975 and 1981).

The standard penetration test (SPT) is a dynamic method in which a 51 mm external

diameter split tube sampler connected to drilling rods, is driven into the ground by a

series of hammer blows delivered at the surface. The test is conducted at intervals during

the course of boring and it provides a distributed sample for identification purposes. In

the

static penetration test a conical point is driven into the ground by means of a steady

pressure on the top of the rods. Both tests provide an indirect measure of shear strength

since the action of the tests produces aMcomplex failure surface within the soil. Shear

strength tests

Various means of obtaining a direct indication of the in situ shear strength are available.

Probably the most widely used of these is the shear vane test but brief reference will also

be made to direct shear and triaxial tests.

Shear vane test provide an indication of both peak and remoulded undrained shear

strengths. Undrained shear strength is calculated from the relationship between torque

and angular rotation, the vane dimensions and the maximum torque applied. Remoulded

shear strength is measured similarly, after remoulding by rapid rotation of the vane and

allowing a short period of time for pore pressures to dissipate.

The test is used for very soft to firm, saturated, nonfissured, homogeneous clays. Plate

loading tests

Mineral Composition, Texture, Origin, Engineering Properties And Uses

(i)Granite (ii) Dolerite

(i) 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 minerals and

accessory minerals are mafic minerals such as hornblende, biotite / muscovite , pyroxenes of

hypersthenes; augite ; diopside ; magnetite / haematite, rutile, zircon, apatite, garnet.

Texture: Granites exhibit phaneric texture ( coarse grained ), or graphic texture (similar to

Arabic writing ). Granites are usually equigranular but some times show inequigranular texture

in case ofPorphyritic texture (feldspars occur as phenocrysts). Hand specimen: Granite is grayish

or pinkish in color. Feldspar appears with white or brownish – red color.

Quartz looks colorless. Biotite is jet black and is found as small shining flakes. Hornblende is

dark greenish black. Varieties: When quartz decreases and increase in mafic minerals, granite

passes over to

GRANODIORITE and then DIORITE.

When both the alkali feldspars and plagioclase feldspars are equal in quantity, the granite rock is


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called as ADAMELLITE.

If hypersthene is more in granite then it is known as CHARNOCKITE.

If feldspars and quartz are very large in size and exhibit interlocking texture, then it is called as

PEGMATITE. Occurrence of large sized beryl, tourmaline crystals is another diagnostic feature

ofpegmatite.

RHYOLITE is very fined grained rock and is the volcanic equivalent of granite.

When the accessory minerals present more in quantity than normally such rocks are named as

eg; biotite-granite, hornblende-granite. Based on the color of feldspars, the granites are termed as

Pink granite; grey granite.

SPECIAL FEATURES:

Specific gravity of granite is 2.6 – 2.8

Density = 2500 – 2650 kg/cm3; compressive strength = 1000 – 2500 kg /sq cm

ENGINEERING POINT OF VIEW: By virtue of many desirable qualities, granite can be used in

foundations of civil structures, building stone, road metal,. Tunneling through granite does not

require any lining.

(ii) DOLERITE



similar toGabbro and basalt.Composition: Dolerite consists of Plagioclase Feldspars and

pyroxene (augite). Iron oxides, hyperstheneand biotite occur as common accessory minerals.

Olivine is some times found if the parent magmawas deficit of silica.Texture: Dolerite is a

massive and compact rock. It is neither porous nor permeable. The texture indolerites is

generally equigranular. Interlocking texture is also common in dolerite. Under themicroscope

dolerite exhibit Ophitic or subophitic texture.

Hand specimen: Dolerite is a fine grained rock with greenish black or black coloured. Presence

ofpyroxene (augite) contributes the black color of a rock. Feldspars can be observed by means

of their cleavage surfaces and biotite if present appears as small, jet black..

Varieties: When all the minerals of dolerite are totally altered for eg: plagioclase into zoisite or

epidote and augite into chlorite / hornblende and olivine into serpentine then the rock is called

DIABASE.

Plutonic equivalent of dolerite is called Gabbro.

Volcanic equivalent of dolerite is called Basalt.

Glassy equivalent of dolerite is called trachylyte.


metallicsound when hit with a hammer. Dolerite occurs in nature as an intrusive rock ie as dyke.


suitable asroad metal, railway ballast, bitumen aggregate, concrete purposes. At foundation sites

of dam likestructures, the presence of dolerite is considered undesirable as they become a cause

for weak

planes.


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Quartz Granite Dolerite

Mineral Composition, Texture, Origin, Engineering Properties And Uses:

BASALT is a black volcanic, massive, fine grained, melanocratic rock.

COMPOSITION: Basalt consist of plagioclase feldspars ( labradorite), Pyroxenes (Augite) and

ironoxides (magnetite or ilmenite). Biotite, hornblende and hypersthenes are the other accessory

minerals.Pyrite may also seen sometimes. Either quartz or olivine may appear in small amounts

dependingon the silica content of parent lava.Structures & Textures: Vesicular and amygdaloidal

structures are common in basalts. However,

Columnar and flow structures are also observed in some cases. Basalts exhibit aphanitic texture

inhand specimens. ( ie the minerals are too fine).

Appearance in Hand specimens: Basalt is typically black or greenish grey or greenish black.

Nonvesicular,massive in nature. Exhibit a typical aphanitic texture ie extremely fine grained with

or without vesicles. Basalts are always unstratified, unfossiliferous and do not react with acids.

VESICULAR BASALT: it is characterized by the presence of empty cavities or vesicles.

AMYGDALOIDAL BASALTS is a vesicular basalt with cavities filled up by secondary

minerals ofsilica (quartz, amethyst, opal, agate); zeolites, calcite. Among these, silica minerals

may be used assemi-precious gemstones.

SPILLITE is a soda-rich basalt in which plagioclase feldspar is albite or oligoclase in stead of

labradorite.

Dolerite is the hypabyssal equivalent of basalt .

Gabbro is plutonic equivalent of Basalt .

Trachylite is equivalent of glassy basalt

Alkali Basalt is unsaturated basalt

Tholeite is oversaturated basalt

Uses: Massive basalts are highly durable and strongest having highest load bearing capacity.

Usedas building stones. Basalts are excellent for macadam and bitumen Roads.

A number of tunnels have been made across through the Deccan traps for railway lines near

Bombay.

They need no lining except sealing where the weak planes or joints are observed

toprevent seepage.Rhyolite is an igneous, volcanic rock of felsic (silica-rich) composition

(> 69% SiO2 ). It may have anytexture from glassy to aphanitic . The mineral assemblage

is usually quartz, alkalifeldspar and plagioclase. Hornblende is a common accessory

mineral.

Rhyolite can be considered as the extrusive equivalent to the plutonic granite rock, and

consequently,outcrops of rhyolite may bear a resemblance to granite.


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Rhyolites that cool too quickly to grow crystals form a natural glass or vitrophyre, also

called obsidian.Slower cooling forms microscopic crystals in the lava and results in

textures such as

flow foliations, spherulitic, nodular etc.. Some rhyolite is highly vesicular pumice..

Gabbro refers to a large group of dark, coarse-grained, intrusive mafic igneous rocks

chemically equivalentto basalt. The rocks are plutonic, formed when molten magma is

trapped beneath the Earth's surface and Cools into a crystalline mass.

The vast majority of the Earth's surface is underlain by gabbro within the oceanic crust,

produced by basaltmagmatism at mid-ocean ridges.

Gabbro is dense, greenish colored and contains pyroxene, plagioclase, amphibole, and

olivine (olivinegabbro when olivine is present in a large amount).

The pyroxene is mostly clinopyroxene; small amounts of orthopyroxene may be present.

If the amount oforthopyroxene is substantially greater than the amount of clinopyroxene,

the rock is thena norite. Quartz gabbros are also known to occur and are probably derived

from magma that was oversaturatedwith silica.

Essexites represent gabbros whose parent magma was under-saturated with silica,

resulting in theformation of the feldspathoid mineral nepheline. valuable amounts of

chromium, nickel, cobalt, gold, silver, platinum,and copper sulfides.

Syenite is a coarse-grained intrusive igneous rock of the same general composition as

granite but withthe quartz either absent or present in relatively small amounts (<5%).

Sandstones

Sandstones are abundant among sedimentary rocks but are next to shales. Sandstones are

made

up of sand and described as Arenaceous rocks. Sandstones are stratified and sometimes

consist of sand grains ( 90% quartz ) with accessoryminerals of such as mica, ilmenite,

magnetite, garnet, zircon, rutile, feldspars cover the rest

Clastic Rocks: These sedimentary rocks are formed through a number of steps.

(a) Decay and disintegration: preexisting rocks everywhere on the surface of the earth are

exposedto natural process of decay and disintegration like weathering and erosion. The original

hard coherent rocksare loosened, decomposed in some cases and the grains and particles so

obtained are transported toplaces of deposition (sea floor, lake basins and river channels). The

disintegrated product is often calleddetritus. Hence, these rocks are also sometimes called detrital

rocks.

(b) Gradual deposition: the sediments as produced through weathering and erosion and

transportedto depositional basin start settling there. Those sediments which are carried in

suspension settle down onthe floor of the basin in accordance with their density, size and shape,

forming layers. The particles thathave been transported in solution are first precipitated due to

evaporation and then settle down. Depositiongenerally takes place under ordinary temperature

and pressure conditions.

(c) Compaction and consolidation - diagenesis: the sediments accumulate at first in the form of

layers or heaps but gradually these get transformed into cohesive, hard and massive rocks when

conditions are favorable. This process of transformation of loose particles into hard cohesive


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rock- like masses is Called diagenesis. It may be achieved by either of the two methods: welding

or cementation.

Welding is the process of compaction and consolidation of the sediments accumulated in a basin

due to pressure.

Cementation is the process by which lose grains in a sedimentary deposit are held together by a

foreign binding or cementing material. These binding substances are commonly supplied by

percolatingwaters which are rich in carbonates of calcium and magnesium, oxides of iron and

silicon, and clay.

CHEMICALLY FORMED (NON_CLASSIC)ROCKS

Water is a great solvent. Water from springs, streams, river, lakes and seas dissolves many

compounds from the rocks with which it comes into contact. Under favorable conditions, a stage

isreached when a part of this water may become saturated with one or more of the dissolved

components. This may be followed by precipitation of salts as crystalline substances and their

gradual accumulation inthe basin. The Rock Salt (NaCl) is formed more or less by this method.

(c) ORGANICALLY FORMED (NON-CLASTIC) ROCKS:

More than 70 per cent of the globe is covered by oceans and seas. These extensive and immense

water bodies contain a variety of animal and plant life. The hard parts of many sea organisms are

constituted chiefly of carbonates of calcium.

Sediment Texture

Clastic sediment textures have been described in previous modules (i.e. Advanced

LoggingProceduresWorkbook), and a complete understanding is necessary for both cuttings

sample and coredescriptions.This description will form the basis of all subsequent interpretation

of the cuttings, the rock and theformation. The most commonly described clastic textures

include:

Grain Shape: Shape describes the geometric form of particles, which reflects the origin, history,

andinternal lattice structure of the particles. Many times qualitative information on processes can

be obtainedfrom the shape of particles. Particle shape is modified by abrasion during transport,

being dependent upon;

(1) initial shape when liberated from the source rock, (2) composition, (3) hardness, brittleness,

ortoughness, (4) inherited partings, (5) size, (6) agent of transport, (7) rigors of transport, and (8)

otherrandom effects.

Grain Texture: Transport in running water does not significantly affect the shape of hard sand-

sizeparticles. However, transport by water, wind, and glacial ice does affect the surface textures.

Abrasioncreates pits, fractures and various surface markings reflect the origin of the particle.

frameworkparticles, and the presence of any cementing agentm between the particles. The fabric

is affected by themanner in which the particles were laid down and the resulting structure of the

inter pore connections.

Sphericity: The degree to which a particle approximates the shape of a sphere. This expresses

how equalthe three mutually perpendicular dimensions of a particle are to one another. The rock

type controls thesphericity.

Porosity and Permeability

When one discusses porosity and permeability in the oil fields, the primary concerns are the

concepts ofabsolute and effective porosity. A reservoir will have a given amount of void space.

If these voids are notconnected, production will be limited.

Mudrocks


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Although sandstones and limestones are of primary concern in oil and gas exploration, the most

abundantsediments are mudrocks (shales, claystones, etc.). These comprise about half of all the

sediments.

Mudrocks (Table 1-1) are deposited in practically every environment, with the primary

environments ofdeposition being river floodplains, lakes, large deltas, the continental shelves and

platforms, and the oceanfloors Another major type of clay mineral is the three layer group. These

have sheetstructures composed oftwo layers of silica tetrahedra interleaved with aluminum di-

and tri-octahedra. The most widely knownexamples are the smectite and illite groups.

Sedimentary facies

Sedimentary environments usually exist alongside each other in certain natural successions. A

beach, where sand and gravel is deposited, will usually be bounded by a deeper marine

environment a littleoffshore, where finer sediments are deposited at the same time. Behind the

beach, there can be dunes(where the dominant deposition is well sorted sand) or a lagoon (where

fine clay and organic material isdeposited). Every sedimentary environment has its own

characteristic deposits. The typical rock formed ina certain environment is called its sedimentary

facies.

Sedimentary Structures

Sedimentary structures are used to identify the agents of deposition and the resulting changes in

that depositional environments that the sediments experienced after they were laid down). At the

wellsite, one of the most important structure that can be recognized from cores and, at times,

cuttings samples is the bedding type.

Structures Of Sedimentary Rocks The terms structure includes some large scale features developed in the rocks during the process

of their formation. These can be studied under following three headings.

Mechanical structures

These are the most prevalent structure includes some large scale features developed in the rocks

during the process of their formation. These can be studied under following three specific types.

Stratification: by stratification is understood a layered arrangement in a sedimentary rock. This

may bedeveloped very prominently a can be seen from a distance or only slightly and may be

detected after closeexamination. The different layers (also called beds or strata) may be of

similar or similar or dissimilarcolour, grain size and composition. The beds are separated from

each other by planes of weakness- thebending planes.

Bedding

Bedding is probably the most important feature of a sedimentary rock, and as such is the most

widely used

term in describing a sedimentary sequence. A “single bed” is generally described as a

sedimentation unit

which has been deposited under essentially constant physical conditions.

1. Regular or massive bedding

2. Laminated bedding

3. Graded bedding

4. Current or cross-bedding

5. Slump, or convolute bedding

For example, regular bedding is indicated by parallel bedding surfaces; that is, those divisions in

the lithology indicating a pause in the normal process of sedimentation. Between a given set of

bedding surfaces, formations are normally uniform, indicating a constant source and transport of


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sediments Another way of describing bedding is through analysis of the lithology's thickness and

its lateral continuity. This allows the division of beds into four gross classifications:

Beds more or less equal in thickness.

Beds that are not equal in thickness and are laterally uniform and continuous.

Beds that are unequal in thickness, but still continuous.

Beds that are unequal in thickness and are laterally variable and discontinuous.

Although there is no absolute correlation between bed thickness and grain size, there is a

significant relationship. If you look at turbidites as a case in point, the further you go away from

the suprafan channel, the finer the grains will be. This is primarily due to a significant drop in the

energy available fortransportation. For this same reason, the overall thickness of those beds will

be less. This relation of grainsize, bedding thickness, and energy (mode) of transport is true for

most of the depositional processes. Thedip of the bedding surfaces is characteristic and

structurally significant when recognized in a core sample inthe same way it is in a outcrop.

Remember, the long axis of the core represents a section offormation cu parallel to the well bore

and probably won't be vertical. Because the drill string will likely rotate during thecoring

process, it is impossible to determine the actual strike of the bedding, unless the core was

takenusing a specially oriented core barrel. Other than a bed's thickness and areal extent, the next

significantfeatures that can be examined are the internal structures. Two major types of structures

are recognized,cross bedding and graded bedding (Figure 2-2). These structures can be identified

in most clastic rocks,regardless of the grain size.

Cross bedding: it is a sedimentary structure in which layers lying one above another are not

parallel butbear an irregular, inclined relationship. Such a structure results in shallow-water

deposits when the stream. The structure is sometimes referred as false bedding orcurrent

bedding. it is further distinguished into following types:

(a) Tabular: a type of cross-bedding in which the top and bottom surfaces are essentially

parallel but the intervening strata are inclined differently.

(b) Lenticular: a type of cross-bedding in which the layers show extreme irregularity in their

shape and disposition; each layer or set of beds may be intersected by many others lying at

different angles.

(c) Wedge shaped: in this case the structure is highly complex; there are sets of May layers

bearing angular relationship. The layers in each set, however, are parallel to each other. The sets

are inclined mutually in such a way that they give the appearance of interwoven wedges in

vertical cross section.

Graded bedding, or the progressional change in grain size throughout a bed's thickness, is very

important to geologists in determining the original top and bottom of a bed as it was laid down.

This is especially true in deep water turbidite deposits, where the gradation from coarse to fine

sand, or an opposite These beds may range from several centimeters to more than a meter thick,

and usually the thicker the graded bed, the coarser the sediments will be at the unit's base.

Sometimes, the basal rock is composed of gravel. Graded beds are best described using a

depositional model known as the “Bouma Cycle” (Figure 2-5). Bouma recognized during his

study of turbidites that the “ideal” graded bed is composed of five basicparts: 1. Thelowest unit

is definitely graded and is usually the thickest part of the sequence. 2. The second section

commonly displays rippled cross lamination. 3. The third unit is composed of indistinctly

laminated sandy or silty politic sediments.


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Mud cracks: these are common structural features of many fine-grained sedimentary rocks.

These polygonal or irregular cracks are developed in drying muds. Subsequently, these cracked

muds are covered by further layers of sediments but the cracked structure is preserved.

Rain prints: these are marks (depressions of irregular, small crater-like shape) left on the top,

dried surface of fine grained muds. Like mud cracks, these also get preserved when the particular

layer is covered by subsequent deposits.

Ripple marks: these are also common sedimentary structures of mechanical origin in deposits

made in shallow waters. They are defined as symmetrical or unsymmetrical, wavelike

undulations or irregularities in a layer. Ripple marks generally unsymmetrical, wavelike

undulations or irregularities in a layer. Ripple marks generally result due to wind or wave action

on the process of deposition. The fine sediments are dragged from their normal course by the

waves developed in the water due to prevailing winds. Later on, these are deposited at places

where the waves become weaker or die out.

Bio-genic Sedimentary Structures

Bio-genic structures result from bioturbation, the post-depositional disturbance of sediments by

living organisms. This can occur by the organisms moving across the surface of sediment or

burrowing into the first few centimeters. It is usually contemporaneous with deposition (Figure

2-10). The magnitude of the structures vary, from the surface trails left by large terrestrial

vertebrates to burrows of small marine invertebrates.


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UNIT IV STRUCTURAL GEOLOGY AND GEOPHYSICAL METHODS

Geological maps – attitude of beds, study of structures – folds, faults and joints – relevance to

civil engineering. Geophysical methods – Seismic and electrical methods for subsurface

investigations.

STRUCTURAL FEATURES:

Out crop

Strike

Dip

OUTCROP:

The rock exposure on the surface of the earth.

STRIKE:

The trend of the rock bed on the ground surface is strike.

DIP: The angle of inclination of a rock bed with the horizontal plane is called dip.

It measured in a plane perpendicular to the stripe line.

There are two types of dip.

True dip

Apparent dip.

TRUE DIP:

It is a perpendicular plane to the strike line.

APPARENT DIP:

It is a dip measured in any other direction than the true dip is called apparent dip.

FOLDS

Investigation of dam site:

Preliminary investigation is done on the site to collect the information about the disadvantages or

advantages of the site. This is more flexible because the detailed investigation will be more

expensive,extensive and laborious. The important information collected at this stage is based on

the factors asfollowed:

Lithology

Structure

Physiography (Topography)

Ground water Conditions.


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Lithology provides the details of rocks types occurring in the dam site. The details include the

types of rockpresent, their nature and extent of weathering, the occurrence of soil, rock debris,

etc.

Lithology also givesa broad idea of the presence or absence of competent rocks, the weathering

it has undergone and otherrelated information.

The Structural study gives information on the strike and dip of the beds. It also reveals the

occurrence ofgeological structures like folds, faults, joints, unconformities and foliation. Details

of these features are veryimportant because they have a great influence on the suitability of site

for dam.

Topography (Physiography) gives information about important surface features like

valleys, hills, the trend of the river course, slopesand terraces present in the area.

These details indicate the stability of the slope and the slope of theoccurrence of

landslides.

Topographic studies also help in rough assessment of the depth of the bedrock at the site.

The nature of seismic activity in the region can also be known by suitable studies.

Groundwater conditions are related tothe study of occurrence of springs, seepages,

swamps, wells etc. present in the selected area.

This type ofstudy indicates the water table position and the scope for leakage of water

from the associated reservoir.

This also indicates the occurrence of solution cavities, if any, in the area.

Detailed Investigation: If the Dam Sites is found to be good in the preliminary

investigations,then it is take up for detailed investigation. This process comprises of surface and

subsurface investigations.

Surface investigations:

The surface investigations include closer examination of lithology,

structure,physiography and groundwater conditions.

The thorough investigation of the above factors, with the support

of laboratory studies of the materials at the dam site will reveal the conditions of

outcrops, faults, joints,folds, & their attitudes, weathering details, soil occurrences,

engineering properties like compressivestrength, tensile strength, porosity, permeability

and durability.


D.ANJALA/AP/CIVIL

Subsurface investigations: These also include the factors of investigations as said above. But

the studiesinclude the study of deeper layers of the dam site for ensuring the standards and safety

of the dam.

Tunnels: Tunnels are the underground passages or routes through hills, mountains or earth crust

used for different purposes. These passages are made by excavating rocks below the surface or

through the hills,mountains.

Types of tunnels: Tunnels are basically made to serve some specific purposes.

For instance:

1. Transportation tunnels: tunnels made across hills or high lands to lay roads or railwaytracks

for regular traffic and transportation purpose.

2. Traffic tunnels: Tunnels laid to reduce the distancebetween places of interest across natural

obstacles like hills, to save time and provide convenience arecalled traffic tunnels. These have

the advantage of leaving the ground surface undisturbed so that it can be

used as desired.

3. Diversion tunnels: The tunnels layed for diverting normal flow of river waterto keep the

dam site dry are called diversion tunnels.

4. Pressure tunnels: these are also called as hydropower tunnels.These are used to allow water to

pass through them under force, used for power generation.

5. Dischargetunnels: These are meant for conveying water from one point to another under

gravity force, like across hill.

6. Public utility tunnels: These are the tunnels layed for public supplies like drinking water

supply, cableslaying, sewage discharge or oil supply etc.

Effect of tunnelling on the ground:

Deterioration of the physical conditions of the ground is the commoneffect of tunnelling.

This happens because due to heavy and repeated blasting during excavatin, the rocksget

shattered to a great extent and develop numerous cracks and fractures.

This reduces the cohesivenessand compactness of rocks.

At normal conditions the earth crust or underground rocks are under greatpreassre

(overburden) or they will be in association with some geological structures like folding

will be at equilibrium stress holding the previaling strain intact.

When the tunnel is created, such rocks which are atequilibrium gets distrubed resulting in

the collapse of the roof. Freequent bursts may also occur.

Thisphenomenon of fall of rocks in brittle and hard rocks is called Popping. Due to

tunnelling, the overlying Rocks deprive of support from the bottom and may become

unstable.

Such unstable conditions becomestill more precarious if the tunnelled beds are incompetent or

loose or unconsolidated or saturated with ground water

Lining of tunnels:


D.ANJALA/AP/CIVIL

When tunnels are made through weak or loose or unconsolidated formations, they

areprovided with suitable lining for safety and stability. Lining refers to the support porvided

totunnel.

Lining may be in the form of steel structures or concrete. The main purposes of lining are to

resist the pressuresfrom the surroundings and to protect the shape of tunnel. It takes care of

the weaknesses of the ground.

It also helps in checking leakage of ground water into tunnel. The thickness of concrete

lining dependes onthe extent of protection required, and the degree of weakness of the

ground. It also depends on theoverbreak phenomenon. Lining is provided to support

weakparts of the tunnel. Lining is also provided insuch places where the seepage of water

into the tunnel occurs and creating problems.

In the case of veryweak rocks with unfavorable geological structures, lining may be

necessary through out the length of the

tunnel.

The zones of faulting or shearing also need suitable lining to impart strength to them.

Overbreak:During tunneling the excavations normally involve the removal of extra rocks or

matter around the tunnel.The quantity of rock broken and removed, in excess of what is

required by the perimeter of the proposedtunnel, is known as overbreak.

Factors governing the amout of overbreak: The nature of the rocks.

The orientation and spacing of jointsor weak zones in them.

In the case of sedimentary rocks, the orientation of the bedding planes

Thickness of the beds with respec to the alignment of the tunnel.

Geological factors influencing theoverbreak: Massive and soft rocks of a homogenous nature

cause less overbreak than harder

rocks withwell developed joints or weak zones. In sedimentary rocks, thin formations and

those with alternating hardand soft strata

produce more overbreak. This is because, during excavation, softer rocks yield more than

the hard rocks.

Electrical Methods Used For Sub Surface Investigations.

The electrical geophysical methods are used to determine the electrical resistivity of the

earth's subsurface.Thus, electrical methods are employed for those applications in which a

knowledge of resistivity or theresistivity distribution will solve or shed light on the problem at

hand. The resolution, depth, and areal extentof investigation are functions of the particular

electrical method employed.

Once resistivity data have beenacquired, the resistivity distribution of the subsurface can be

interpreted in terms of soil characteristicsand/or rock type and geological structure.

Resistivity data are usually integrated with other geophysicalresults and with surface and

subsurface geological data to arrive at an interpretation.

Electrical methods can be broadly classified into two groups: those using a controlled

(human-generated)energy source and those using naturally occurring electrical or

electromagnetic energy as a source.

Thecontrolled source methods are most commonly used for shallow investigations, from

characterizing surficialmaterials to investigating resistivities down to depths as great as 1 to 2

km, although greater depths ofinvestigation are possible with some techniques and under

some conditions.


D.ANJALA/AP/CIVIL

The natural sourcemethodsare applicable from depths of tens of meters to great depths well

beyond those of interest to hydrocarbondevelopment.

Possible applications of electrical methods for the development geologist range from the

investigation ofsoil contaminants and the monitoring of enhanced oil recovery (EOR)

projects to reservoir delineation andthe evaluation of geological stratigraphy and structure.

The application of electrical methods has beenprimarily confined to the onshore

environment.

The offshore use of some techniques is possible,particularly for permafrost delineation and

shallow marine geotechnical investigations.Electrical properties of materials

The application, interpretation, and understanding of electrical methods requires a familiarity

with the relationship between soil and rock characteristics and the resistivities obtained from

electrical data.

Theresistivity of subsurface rock formations is one of the physical properties determined

through the process oflogging that is performed on most oil and gas wells, utilizing

instrumentation inserted into the wellbore.

Theconcept of formation resistivity plays an important part in log analysis. Although there is

a correlationbetween rock resistivities measured by well logs and those measured by

electrical methods, the log is used to investigate properties only in the immediate vicinity of

the wellbore while electrical methods yieldinformation on bulk properties averaged over a

considerable volume of material.

The resistivity of most soils and rocks (including virtually all of the rocks of interest to

hydrocarbonexploration) at the frequencies utilized by electrical methods is controlled by the

fluids contained within therock[1] (see Determination of water resistivity).

This is because the dry soil or rock matrix is a virtualinsulator at DC and near DC

frequencies. The pore fluid is in most cases water, with dissolved salts.

Thesalinity is the primary factor in determining the resistivity of the pore fluid, with pore

configuration alsoplaying a part. Of lesser importance at oil reservoir depths is the

temperature of the formation.

Oil and/or gas, when present, occur over such limited formation thicknesses that their effects

on bulkaverageresistivity is, in most cases, undetectable.

Faulting or fracturing of porous sedimentary formations in most instances has little effect on

the bulk average resistivity since the additional fracture porosity changes the already high

porosity by only a smallpercentage.

However, in very tight rocks, such as igneous, metamorphic, and nonporous carbonate

rocks,where intrinsic porosity is very low, the fluids in joints, cracks, and faulted zones may

become the primaryconducting paths (see Porosity).

In summary, the factors affecting in situ average resistivity are the total porosity, including

fault and fractureporosity, and the resistivity of the fluids present within the rock. The

average resistivity can be considered

constant over the frequency range of interest to most of the methods under consideration

here.Controlled source methodsControlled source methods use generated currents or

electromagnetic fields as energy sources.

Anadvantage is the control over energy levels and the attendant positive effects on signal to

noise ratio in areas of high cultural noise.


D.ANJALA/AP/CIVIL

A disadvantage of controlled source methods is that the complex nature of thesource field

geometry (the geometry of the electromagnetic field or currents induced with the earth by

thetransmitter) may present quantitative interpretation problems in areas of complex

geology.In the DC method, a current (usually a very low frequency square wave and not

actually direct current) isinjected into the earth through a pair of current electrodes, and the

resulting potential field is mapped.

Various geometries of current and potential electrodes have been employed, with the choice

primarilybased upon the depth and geometry of the survey target.

The measured surface potential field isinterpreted in terms of the subsurface resistivity

distribution through modeling and inversiontechniques.

Induced polarization (IP) and complex resistivity (CR) techniques are special cases ofthe DC

method in which the induced potential field is measured and interpreted in termsof

mineralogy and/or soil characteristics.

IP and CR have been applied with some success to hydrocarbon

exploration through the measurement of geochemical alteration halos that have been found to

be related toreservoirs under some conditions.

In the electromagnetic (EM) method, an electromagnetic field is produced on or above the

surface of theground.

This primary EM field induces currents in subsurface conductors. The induced currents in

turnreradiate secondary EM fields.

These secondary fields can be detected on or above the surface as either adistortion in the

primary field (frequency domain methods) or as they decay following the turning off of

theprimary field (time domain methods). Both loops and grounded wires are used to generate

the source field.

Resistivities are calculated from the observed electromagnetic field data using modeling and

inversiontechniques.EM techniques have been adapted to a variety of surface and airborne

configuration, with the airborneinstruments generally limited in penetration to 100 to 200 m.

Airborne electromagnetic surveys have provenvery effective for mapping the shallow

resistivity distribution, leading to cost-effective surveys over largeareas.

Surface loop or grounded wire systems are applicable to depths well in excess of 1 km,

althoughhigh power transmitters are required as depth increases.

The resolution attainable is normally consideredas a percentage of penetration depth, such

that absolute resolution decreases with depth.In the controlled source magnetotelluric

(CSMT) method, a low frequency electromagnetic wave isgenerated, and the electrical and

magnetic fields are measured at some distance from the transmitter.

Thewave impedance of the electromagnetic wave at the receiver is calculated from the

electrical and magneticfield values as a function of frequency and then interpreted in terms of

the subsurface resistivity distribution.

Depths of penetration in excess of 1 to 2 km are attainable under suitable conditions.

Ground probing radar (GPR) is used for detailed investigations of the shallow subsurface. An

extremelyshort pulse is generated and transmitted into the earth and reflections are received

from interfaces betweenmaterials of differing resistivity and dielectrical constant.

GPR instrumentation is sophisticated but highlyportable.


D.ANJALA/AP/CIVIL

Depth of penetration is limited from less than 0.3 m in silty soils to over 100 m in

permafrost,freshwater-saturated sand, and some very low porosity rocks. Successful

applications include the

measurement of ice thickness, the location of cracks in ice, permafrost studies, the detailed

mapping of thebedrock surface, the examination of soil stratification, and the mapping of

contaminant plumes in theshallow subsurface.

An important application of GPR is locating buried pipes, tanks, and other objects thatreflect

the radar pulse.

Natural source methodsNatural source methods take advantage of naturally occurring

electrical potentials and electromagneticfields as energy sources.

Advantages of natural source methods are that there is no dependence on anartificial energy

source and that the natural electromagnetic field is well understood.

The principaldisadvantages are the unpredictability and lack of control over energy levels

and the attendant effects ofcultural noise on the signal to noise ratio.

The self-potential (SP) method examines the slowly varying surface potential field caused by

electrochemical and electrokinetic actions in near-surface materials.[4] Potentials can form,

for example, atinterfaces between materials containing fluids with different ion contents, or

they can be caused by movinggroundwater or by differential oxidation of ore bodies.

The method has been applied successfully ingeothermal and mineral exploration and in the

delineation of certain groundwater contaminants. Fieldprocedures are straightforward, with

the potential measured between carefully designed electrodes using

what is essentially a highly sensitive DC voltmeter. The potential field is mapped along

profiles or on a gridof measurement stations. Interpretation is generally qualitative, with SP

anomalies interpreted in terms ofthe shape and depth of the causative body or fluid flow.

Magnetotellurics:

(MT) is an electrical method of geophysical exploration that makes use of

naturallyoccurring electromagnetic energy propagating into the earth to determine the

electrical resistivity of thesubsurface.

The low frequency electromagnetic field is measured, and the wave impedance

iscalculated and expressed in terms of the resistivity of the subsurface.

The depth of investigation is afunction of the frequency of the electromagnetic wave,

taking advantage of the fundamental principle that

the lower the frequency of a wave, the deeper the penetration into the crust. MT surveys

generally involveapplications that range in depth from a few hundred meters to 10 km or

more.

The resistivity versus depth cross section developed from MT data can be interpreted in

terms of rock type.

Spatial variations in the resistivity-depth relationship observed at closely spaced locations

on the surfacecan be interpreted in terms of subsurface geological structure.

While MT cannot be used to detect oildirectly, the identification of favorable rock types

and the presence of geological structure capable oftrapping hydrocarbons is critical to

successful exploration.

MT data are interpreted using forward andinverse modeling techniques. Resolution is

considered low when compared with exploration or exploitationseismology, but may be

adequate in certain instances to provide valuable information


D.ANJALA/AP/CIVIL

concerninreservoirgeometry, rock characteristics, and a regional geological framework

For the larger deep

reservoirs, MT may be considered as a possible candidate for EOR monitoring if model studies

indicatethat the resistivity changes over time associated with the operation are within the

resolving power of themethod.Applications for development geology

The following is a brief summary of some of the many possible applications of electrical

methods of interestto the development geologist:

Evaluation of various characteristics of the shallow environment. Examples of such

characteristics arethe classification of unconsolidated materials based on their electrical

properties, the identification ofa lateral and/or vertical freshwater-saltwater boundary, the

depth to bedrock, and the identification andmapping of conductive groundwater

contaminants.

Monitoring of reservoir stimulation and enhanced recovery projects, where the stimulants

and propants or flood materials can be expected to modify the resistivity of the

formations.

Investigation of permafrost and ice characteristics in the Arctic.

Investigation of stratigraphy and structure, in particular as an adjunct to seismic data and

in thoseareas where seismic data are poor or unreliable.

Seafloor geotechnical mapping, as an adjunct to high resolution seismic studies.

Folds In Rocks And Folds In The Design Of 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 trainsof different sizes, on a variety of scales.Folds form

under varied conditions of stress, hydrostaticpressure, 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


D.ANJALA/AP/CIVIL

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 oforientation.

Syncline: linear, strata normally dip toward axial center, youngest strata in center

irrespective oforientation.

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

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 associatedwith 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. 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 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 folding

Many 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.


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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 faultwithout further 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 fault propagation, 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 zones

Shear zones that approximate to simple shear typically contain minor asymmetric folds,

with the direction ofoverturning consistent with the overall shear sense.

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 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 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.


D.ANJALA/AP/CIVIL

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 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.

Electrical Methods About Sub Surface Features During Civil Engineering Investigations.

The electrical geophysical methods are used to determine the electrical resistivity of the earth's

subsurface.Thus, electrical methods are employed for those applications in which a knowledge of

resistivity or theresistivity distribution will solve or shed light on the problem at hand. The

resolution, depth, and areal extentof investigation are functions of the particular electrical

method employed.

Once resistivity data have beenacquired, the resistivity distribution of the subsurface can be

interpreted in terms of soil characteristicsand/or rock type and geological structure.

Resistivity data are usually integrated with other geophysicalresults and with surface and

subsurface geological data to arrive at an interpretation.

Electrical methods can be broadly classified into two groups: those using a controlled (human-

generated)energy source and those using naturally occurring electrical or electromagnetic energy

as a source.

Thecontrolled source methods are most commonly used for shallow investigations, from

characterizing surficialmaterials to investigating resistivities down to depths as great as 1

to 2 km, although greater depths ofinvestigation are possible with some techniques and

under some conditions.

The natural source methodsare applicable from depths of tens of meters to great depths

well beyond those of interest to hydrocarbondevelopment.

Possible applications of electrical methods for the development geologist range from the

investigation ofsoil contaminants and the monitoring of enhanced oil recovery (EOR)

projects toreservoirdelineation andthe evaluation of geological stratigraphy and structure.

The application of electrical methods has beenprimarily confined to the onshore

environment.

The offshore use of some techniques is possible, particularly for permafrost delineation

and shallow marine geotechnical investigations.


D.ANJALA/AP/CIVIL

Electrical properties of materials

The application, interpretation, and understanding of electrical methods requires a

familiarity with therelationship between soil and rock characteristics and the resistivities

obtained from electrical data. Theresistivity of subsurface rock formations is one of the

physical properties determined through the process oflogging that is performed on most

oil and gas wells, utilizing instrumentation inserted into the wellbore.

Theconcept of formation resistivity plays an important part in log analysis.

Although there is a correlationbetween rock resistivities measured by well logs and those

measured by electrical methods, the log is usedto investigate properties only in the

immediate vicinity of the wellbore while electrical methods yieldinformation on bulk

properties averaged over a considerable volume of material.

The resistivity of most soils and rocks (including virtually all of the rocks of interest to

hydrocarbonexploration) at the frequencies utilized by electrical methods is controlled by

the fluids contained within therock (see Determination of water resistivity).

This is because the dry soil or rock matrix is a virtualinsulator at DC and near DC

frequencies.

The pore fluid is in most cases water, with dissolved salts. Thesalinity is the primary

factor in determining the resistivity of the pore fluid, with pore configuration alsoplaying

a part.

Of lesser importance at oil reservoir depths is the temperature of the formation.

Oil and/orgas, when present, occur over such limited formation thicknesses that their

effects on bulk averageresistivity is, in most cases, undetectable.

Faulting or fracturing of porous sedimentary formations in most instances has little effect

on the bulkaverage resistivity since the additional fracture porosity changes the already

high porosity by only a smallpercentage.

However, in very tight rocks, such as igneous, metamorphic, and nonporous carbonate

rocks,where intrinsic porosity is very low, the fluids in joints, cracks, and faulted zones

may become the primaryconducting paths (see Porosity).

In summary, the factors affecting in situ average resistivity are the total porosity,

including fault and fractureporosity, and the resistivity of the fluids present within the

rock.

The average resistivity can beconsidered onstant over the frequency range of interest to

most of the methods under consideration here.

Controlled source methods

Controlled source methods use generated currents or electromagnetic fields as energy

sources.

Anadvantage is the control over energy levels and the attendant positive effects on signal

to noise ratio inareas of high cultural noise.

A disadvantage of controlled source methods is that the complex nature of thesource field

geometry (the geometry of the electromagnetic field or currents induced with the earth by

thetransmitter) may present quantitative interpretation problems in areas of complex

geology.In the DC method, a current (usually a very low frequency square wave and not

actually direct current) isinjected into the earth through a pair of current electrodes, and

the resulting potential field is mapped.


D.ANJALA/AP/CIVIL

Various geometries of current and potential electrodes have been employed, with the

choice primarilybased upon the depth and geometry of the survey target.

The measured surface potential field isinterpreted in terms of the subsurface resistivity

distribution through modeling and inversiontechniques.

Induced polarization (IP) and complex resistivity (CR) techniques are special cases ofthe

DC method in which the induced potential field is measured and interpreted in termsof

mineralogy and/or soil characteristics.

IP and CR have been applied with some success to hydrocarbonexploration through the

measurement of geochemical alteration halos that have been found to be related

toreservoirs under some conditions.

In the electromagnetic (EM) method, an electromagnetic field is produced on or above

the surface of theground.

This primary EM field induces currents in subsurface conductors. The induced currents

in turnreradiate secondary EM fields. These secondary fields can be detected on or above

the surface as either adistortion in the primary field (frequency domain methods) or as

they decay following the turning off of theprimary field (time domain methods). Both

loops and grounded wires are used to generate the source field.

Resistivities are calculated from the observed electromagnetic field data using modeling

andinversiontechniques.

EM techniques have been adapted to a variety of surface and airborne configuration, with

the airborneinstruments generally limited in penetration to 100 to 200 m.

Ground probing radar (GPR) is used for detailed investigations of the shallow subsurface.

An extremelyshort pulse is generated and transmitted into the earth and reflections are

received from interfaces betweenmaterials of differing resistivity and dielectrical

constant. GPR instrumentation is sophisticated but highlyportable.

Depth of penetration is limited from less than 0.3 m in silty soils to over 100 m in

permafrost,freshwater-saturated sand, and some very low porosity rocks. Successful

applications include the

measurement of ice thickness, the location of cracks in ice, permafrost studies, the

detailed mapping of thebedrock surface, the examination of soil stratification, and the

mapping of contaminant plumes in theshallow subsurface. An important application of

GPR is locating buried pipes, tanks, and other objects thatreflect the radar pulse.

Natural source methods

Natural source methods take advantage of naturally occurring electrical potentials and

electromagneticfields as energy sources.

Advantages of natural source methods are that there is no dependence on anartificial

energy source and that the natural electromagnetic field is well understood.

The principaldisadvantages are the unpredictability and lack of control over energy levels

and the attendant effects ofcultural noise on the signal to noise ratio.The self-potential

(SP) method examines the slowly varying surface potential field caused by

electrochemical and electrokinetic actions in near-surface materials.

Potentials can form, for example, atinterfaces between materials containing fluids with

different ion contents, or they can be caused by movinggroundwater or by differential

oxidation of ore bodies.


D.ANJALA/AP/CIVIL

The method has been applied successfully ingeothermal and mineral exploration and in

the delineation of certain groundwater contaminants.

Fieldprocedures are straightforward, with the potential measured between carefully

designed electrodes usingwhat is essentially a highly sensitive DC voltmeter.

The potential field is mapped along profiles or on a gridof measurement stations.

Interpretation is generally qualitative, with SP anomalies interpreted in terms ofthe shape

and depth of the causative body or fluid flow.

Magnetotellurics (MT) is an electrical method of geophysical exploration that makes use

of naturallyoccurring electromagnetic energy propagating into the earth to determine the

electrical resistivity of thesubsurface.

The low frequency electromagnetic field is measured, and the wave impedance

iscalculated and expressed in terms of the resistivity of the subsurface.

The depth of investigation is afunction of the frequency of the electromagnetic wave,

taking advantage of the fundamental principle thatthe lower the frequency of a wave, the

deeper the penetration into the crust.

MT surveys generally involveapplications that range in depth from a few hundred meters

to 10 km or more.

The resistivity versus depth cross section developed from MT data can be interpreted in

terms of rock type.Spatial variations in the resistivity-depth relationship observed at

closely spaced locations on the surfacecan be interpreted in terms of subsurface

geological structure.

While MT cannot be used to detect oildirectly, the identification of favorable rock types

and the presence of geological structure capable oftrapping hydrocarbons is critical to

successful exploration.

MT data are interpreted using forward andinverse modeling techniques. Resolution is

considered low when compared with exploration or exploitationseismology, but may be

adequate in certain instances to provide valuable information concerning

reservoirgeometry, rock characteristics, and a regional geological framework.

For the larger deep reservoirs, MT may be considered as a possible candidate for EOR

monitoring if model studies indicatethat the resistivity changes over time associated with

the operation are within the resolving power of themethod.Applications for development

geology

The following is a brief summary of some of the many possible applications of electrical

methods of interestto the development geologist:

Evaluation of various characteristics of the shallow environment. Examples of such

characteristics arethe classification of unconsolidated materials based on their electrical

properties, the identification ofa lateral and/or vertical freshwater-saltwater boundary, the

depth to bedrock, and the identification andmapping of conductive groundwater

contaminants.

Monitoring of reservoir stimulation and enhanced recovery projects, where the stimulants

and propantsor flood materials can be expected to modify the resistivity of the

formations.

Investigation of permafrost and ice characteristics in the Arctic.

Investigation of stratigraphy and structure, in particular as an adjunct to seismic data and

in thoseareas where seismic data are poor or unreliable.


D.ANJALA/AP/CIVIL

Seafloor geotechnical mapping, as an adjunct to high resolution seismic studies.

Gravity Method In Geophysics:

For human exploration of the solar system, instruments must meet criteria of low mass,

low volume, lowpower demand, safe operation, and ruggedness and reliability (Meyer et

al., 1995; Hoffman, 1997; Budden,1999).

Tools used for planetary exploration will need to address fundamental scientific questions

andidentify precious resources, such as water.

The primary goal of studying detailed gravity data is to provide a better understanding of

the subsurfacegeology.

The gravity method is a relatively cheap, non-invasive, non-destructive remote sensing

methodthat has already been tested on the lunar surface.

It is also passive – that is, no energy need be put into theground in order to acquire data;

thus, the method is well suited to a populated setting such as Taos, and aremote setting

such as Mars.

The small portable instrument also permits walking traverses – ideal, in viewof the

congested tourist traffic in Taos.

Measurements of gravity provide information about densities of rocks underground.

There is a wide rangein density among rock types, and therefore geologists can make

inferences about the distribution of strata.In the Taos Valley

we are attempting to map subsurface faults.

Because faults commonly juxtapose rocks of differing densities, the gravity method is an

excellent exploration choice.

This is a generalized summary of the types of corrections that we have applied to the

Taosgravity data

The Gal (for Galileo) is the cgs unit for acceleration where one Gal equals 1 centimenter

per second squared.

Because variations in gravity are very small, units for gravity surveys are generally in

milligals (mGal) where 1 mGal is one thousandth of 1cm/s2. Standard gravity ( gnor g0 ) is

taken as the freefall accelleration of an object at sea level at a latitude of 45.5° and is

980.665 cm/s2 (or equivalently 9.80665 m/s2).

Standard gravity is therefore 980.665 Gal or 980665 mGal. It is useful to remember that 1

mGal is just a bit more than 1 millionth of gn (1.01972 x 10-6 gn). Observed Gravity (gobs )

- Gravity readings observed at each gravity station after corrections have been applied for

instrument drift and earth tides.

Latitude Correction (gn ) - Correction subtracted from gobs that accounts for Earth's elliptical

shape and rotation. The gravity value that would be observed if Earth were a perfect (no geologic

or topographic complexities), rotating ellipsoid is referred to as the normal gravity.gn =

978031.85 (1.0 + 0.005278895 sin2(lat) + 0.000023462 sin4(lat)) (mGal)

where lat is latitude

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).


D.ANJALA/AP/CIVIL

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.


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.









Recumbent: linear, fold axial plane oriented at low angle resulting in overturned strata in

one limb


D.ANJALA/AP/CIVIL

Slump:

typically monoclinal, result of differential compaction or dissolution during


Ptygmatic: Folds are chaotic, random and disconnected. Typical of sedimentary slump



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.



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.


D.ANJALA/AP/CIVIL

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.



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.


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


D.ANJALA/AP/CIVIL

Anticline: linear, strata normally dip away from axial center, oldest strata in center










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


Ptygmatic: Folds are chaotic, random and disconnected. Typical of sedimentary slump



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.



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


D.ANJALA/AP/CIVIL

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.



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.


D.ANJALA/AP/CIVIL

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.


D.ANJALA/AP/CIVIL

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


D.ANJALA/AP/CIVIL

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.


D.ANJALA/AP/CIVIL

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

.


D.ANJALA/AP/CIVIL

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.


D.ANJALA/AP/CIVIL

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)

Passive Sensors (Sensor depends the suns EMR i.e., MSS, TM, XS, LISS, PAN, WiPS

etc)


D.ANJALA/AP/CIVIL

Passive Sensor further divided into number of following types based on function of

sensor in EMR>

Photographic Camera (Operated in single band from 0.4-0.7mm)

Return Beam Vidcon (Operated in Green, Red, NIR)- RBV in Landsat and TV in

Bhaskara

Thermal Sensor (Operated in Thermal Infrared Region)

Optical and Mechanical Sensors (Operated in 0.5-1.1 mm) MSS and XS Radar and

MicrowaveSensor (Operated in Microwave Region) SLAR, SAR

Advanced Remote Sensor (Operated in GBR and IR) LISS-II, LISS-III, LISS-IV, WiPS,

PAN,

TMParameter of sensor:

Spatial Resolution : The minimum detectable area on the ground by a detector placed on a

sensor

Spectral Resolution : The small amount of spectral changes be detected by the sensor.

Radiometric Resolution : The presence of grey level

Temporal Resolution : Smaller period of repetitive coverage

Remote Sensing Satellite: Remote sensing, as conceived today for natural resource mapping

was

started with the launching of the first earth resource.

Technology’s satellite (ERTS) now known as LANDSAT-1, by USA in 1972 since then, with

the advancement in sensor technology, a number ofremote sensing earth resource satellite have

been launched. The important milestones crossed so farin achieving end-to-end capability are

LANDSAT Series, 1, 2, 3, 4, 5, 6 and 7; Frances satellite 1, 2,and 3, Indian polar satellite

Bhashkara 1&2, IRS 1A/ IRS 1B/IRS 1C/IRS 1D/IRS P2/IRS P3/IRS P4/IRSP5/IRS P6& Indian

meteorological satellite INSAT 1A/1B/1C/1D and 2A/2B/2C/2D/2E etc.,

Factors Of Landslides.

LANDSLIDES

A temporary instability of superficial mass of soil and rocks, consolidated or unconsolidated,

may leavetheir original position abruptly or extremely slowly and start either a downward

movement or verticallydownward sinking thus giving rise to baffling situation. These

movements may entitle to loss toproperty and life. Such movements of the ground have been

termed as Landslides or Land slip or MassMovement

Type of Landslides

The landslides can be classified into three namely

1) Flowage

2) Sliding and

3) Subsidence

based onthe rate of movement, nature of the mass involved in failure and degree of

saturation where applicable

Flowage: It is defined as downgrade movement of mass along no defined surface of failure.

Massinvolved in this type of failure is primarily unconsolidated or loosely packed or

disintegrated and decaymaterials and these materials behave as if it has its own shear failure

surface. The result is that themovement is highly irregular (Fig). Flowage is further distinguished

into slow and rapid flowage. In thefirst group, is not easily perceptible. The rapid flowage,

however the movement of failing mass may beeasily visible and it moves few meters a day


D.ANJALA/AP/CIVIL

Translational slides: The surface of failure is generally planner in character, speed of failure is

quiterapid and the nature of mass involved in failing may be rock block, rock slab, debris and

soil cover or even a mixture of all of them.

Radial Slides: In such slides, the failing surface is generally curved in character and the speed of

failure is also quite rapid. The materials involved in failure tilt at the rear end and heaves up at

the front or toe.

Rock Toppling and falls: Surface layer of rock and soils on the steep slopes that are likely to

fail in the

form of falls.

Subsidence: It is defined as sinking or setting of the ground in almost variously downward

directionwhich may occur because of removal of natural support from the underground or due to

compaction ofthe weaker rocks under the load from overlying mass. As a result the natural

ground fill suffers a sinking, downward movement.

Causes of Landslides:

Many factors are known to cooperate in causing a mass of materials to flow or fail or fall, some

of themplay a direct role and are easily understood whereas other are indirectly responsible for

the instabilityof the land mass, Bases on this the land landslides operated by internal forces and

external forcesInternal Forces: It includes nature of the slope and the water content are very

crucial in defining thestability of ground anywhere. The composition of the ground materials and


D.ANJALA/AP/CIVIL

the geological character ofthe area are other two internal factors that determine to a great extent

if a land mass in a given areawould be stable or not. The role these natural factors play in the

stability of the land mass are as follow.

The Nature of Slope: Some slopes are very stable even when very steep, whereas others are

inherently unstable, and may fail repeatedly even at very gently angles. Since a great majority of

massfailures are confined to slope only, it is reasonable to conclude the nature of a slope may be

a decidingfactor in defining the stability or otherwise of a land mass.

The Role of Water: Both surface and subsurface water causing mass movement. Water that

penetratesthe soil and rocks thought seepage and moves into the pores of the mass may be the

causes of uplift orpore-pressure within the mass under consideration.

Water that accumulates at the back of a mass mayexert a pressure, parallel to the direction of

flow and add to the shearing forces causing instability.

Composition of the Mass:

Some materials are stable in a given set of conditions of slope and watercontent whereas

other may be unstable.

Crystalline igneous rocks like granites and gabbros,metamorphic rock like marbles,

quartzite and gneisses may be stable even with vertical slopes whereasthe same cannot be

said about chalk- a soft variety of limestone, or shale or clay stone or soil.

It is,therefore, obvious that a fundamental character that is responsible for the stability of

mass is itscomposition, which has both physical and chemical implication.

Geological Structure:

Geological structures are of great significance in defining the stability of mass,especially in

rocks. These structures may be divided into three classes,

The bedding plane in structure,

The Schistosity and

The jointing Structure

i). Bedding plane in structure:

Many sedimentary rocks are layered or stratified and thickness of layersmay range from a

few centimeters to many meters.

The dip of the stratified rocks exerts very importantinfluence on the stability of slopes. If

the layer is horizontal, such rock slopes of the natural valleys andartificial cuts are stable

at all the angle up to 90°.

When they fall it may be due to presence ofsecondary joints or related features.


D.ANJALA/AP/CIVIL

If the layers are inclined, in such a situation, assuming that the rock is free from any other type of

discontinuities, the stability of a slope will depend primarily on the condition whether the layer

aredipping backwards into the mountain or forward into the valley.

ii). Schistosity: Schisotsity, foliation and cleavage structures are behaving as surface of

weakness andare prone to failure. This is primarily due to the fact that weathering in these rocks

takes placealongthese planes.

iii). The Jointing structures: Joints of any type are always to be studied with great caution in

rocksmaking slope for two reasons:

Firstly, very few rocks are free from these structures which may occur due to tension,

compression orshear to which these rocks have been subjected since their formation.Secondly,

they occur in sets or groups effecting the rock from the surface to considerable depth

andeventually reducing the shear strength of the rock mass considerably.

External Forces: The external features are also influence the cause of landslides.

Vibration:

A mass perched on slope may be stable but critically; the gravitative forces have

not yetovercome its frictional resistance.

A slight vibration or jerk to the mass may be sufficient to disturb thisequilibrium

and the mass becomes unstable.

Such vibrations are easily available from heavy blastingand heavy traffic on hill

roads.

Another important external factor is the removal of the support at the foot of the

slope, as duringexcavation for road widening, without due regard to the critical

condition of stability.

The slope thatmight have been previously stable becomes hazardous after such an

excavation.

Geological Processes That Result In Coastal Erosion

COASTAL PROTECTION

Coast is defined as a boundary between sea and mainland. It has been shaped by varying

influence oftectonic activity and instability of sea level.

Coast is associated with the sea and may include areas ofcliffs, dune, beaches and even

hills and plains and it has been affected by marine processes such astides, winds, waves

and current. In general coasts that are composed of soft, unconsolidated materials,such as

sand which changes more rapidly than coasts composed of rock.

Types of Coast

According to Johnson, the coast may be classified in to two types that is

a) Submerged coast and

b)Emerged coast.


D.ANJALA/AP/CIVIL

It is based on sea level related with climate and tectonic activity.

The submerged coastis the coastal interior; the land immediately behind the shore

zone (whose inner limit is defined by thehighest storm and tide waves) has an

intermediate inner limit.

The erosional features like Cliffs, Sheetsand Gullies are seen along the erosional

coast.

While in the case of an emerged coast, the coastal tractwhere the seaward

migration of the coastal tract is a low land, depositional features like

deltaicsedimentation, estuarine, marsh and sand dunes are the characteristic

features.

Importance of Coast

The coastal environment is very dynamic with many cyclic and random processes

owing to a variety ofresources and habitats.

Further the coastal ecosystems are the most productive ecosystems on earth.About

60 percent of world population lives near the coast and in one way or other

depends directly orindirectly on the coastal zone and its resources (Like Coral

reefs, Mangrove, Seaweeds, Sea grass,Salt marsh, Beach etc).

Thus the coastal zone plays a vital role on the nation’s economy.

Coastal Problems in India

The coastal area in India faces a wide range of problems. A recent regional survey

conducted by

International Ocean Institute, Operational Center at Chennai revealed several problems.

As per thesurvey, in India, population pressure has been considered as the most important

problem. For example, in the state of Tamilnadu, the population density in coastal area is

528 per sq.km against 372 per sq.km which is state average.

In parts of coastal metros like Bombay, Calcuttaand Madras, the population pressure led

to resource depletion and environmental degradation.The major activities that are

responsible for coastal population in India are discharge and disposal ofdomestic and

industrial wastes, discharging of coolant waters, harbor activities such as dredging,

cargohandling, dumping of ship wastes, spilling of cargo’s such as chemical and metal

ores, oil transport andfishing activity, etc.

Domestic waters are discharged mostly in untreated conditions due to lake oftreatment

facilities in most of t he cities or towns.

India is one of the largest industrialized nations in theVisakhapatnamand Calcutta are

situated on or near the coastline.

The estimated total quantity of waste discharged bythese industries is estimated to be

approximately 700 million cu.m

The coastal erosion is caused by wave braking, reduction in sediment input to coast,

tectonic

upheavals and rise in sea level. These causes are not only natural, but also, due to human

influence.

Inwest coast, erosion is very severe along Kerala coast. In Karnataka, about 73 km of the

coast isaffected by erosion.

Along the east coast the coastal erosion is moderate. In Tamilnadu, about 80 km ofthe

coastline is affected.


D.ANJALA/AP/CIVIL

In Orissa, about 30 to 40 km are affected. In West Bengal, erosion occurs in180 km,

along the coastline stretching from the confluence of the river Hooghly in the west to

theconfluence of the river Jadgan in the east.

The rate of erosion is as high as 30 m/year.

In India, nearly 150 million people are prone to natural hazard in coastal areas. Bay of

Bengal is one ofthe five cyclone prone areas of the world.

The coastal regions surrounding this bay are frequentlyaffected by flooding from the sea

as well as the rivers due to tropical cyclones and related storm surgesand heavy rainfall.

Between the year 1990 and 1995 in the state of Andhra Pradesh, more than 1100human

lives were lost and properly worth of Rs.23, 000 million were damaged.

In Tamilnadu during theyear 1990 and 1995, the damages caused to property were worth

of Rs. 5, 800 million and the loss ofhuman lives was more than 500.

Shoreline Erosion and Accretion

Shoreline is one of the most rapidly changing landforms of the earth. The geomorphic processes

oferosion and accretion, periodic storms, flooding and sea level changes continuously modify the

shoreline. The rate of shoreline-change varies depending upon the intensity of the causative

forces,warming up of oceanic water and melting of continental ice sheets etc, which result in

submergence oremergence of land.The coastal erosion and accretion processes are not

newphenomena.

Generally the main causes ofthese processes can be thought of

(i) beach configuration

(ii) tectonic movements in the coastal beltand the near shore

(iii) presence of mud blanks

(iv) gradual climate changes

(v) reduction in thedischarging of sediments from rivers and

(vi) manmade activities along the coast.

Tamil Nadu with a coastal length of 980 km is the second largest coast in India. This state

experiencetwo monsoon periods, one is active from mid-June to mid-September (i.e, southwest

monsoon) and theother is active from mid-October to mid-January (i.e., northeast monsoon). All

the districts of the studyarea are affected by cyclonic storms almost every alternative year (For

example, during the period1877-1977, the coast has been hit by the storms for at least 50 times).

During certain years, the coasthas been hit by cyclonic storms even more then once.

Management measures of Coastal protection

The following measures are some management measures for coastal protection:

To create awareness among the coastal communities in the study area, in order to protect

and

conserve the coastal area through effective involvement of educational institutions and

NGOS

Stringent measures need to be under taken with immediate effect to ban coastal and coral

mining and to take into task those involved in or those who encourage the exploitation of

corals

for any purpose. Patrolling the coast to check coral and coastal mining should be carried

out.

Law should be enacted to regulate and stop trawl boat operation in the zone earmarked

for


D.ANJALA/AP/CIVIL

non-mechanized boat. The Department of Forest and the Department of Fisheries should

take

steps to stop anchoring of vessels on coral reefs, pair trawling and dynamite fishing.

Indiscriminate picking of budding seaweeds need to be banned.

Commercial shell collection should be controlled and closely monitored.

Marine Resource Management Centers should be established to improve the skills of

fishermen communities in areas other than coastal mining, which in turn will lead to

efficient management of coast.

Deforestation along the coast and islands should be banned. The forest Department

should

take up a forestation along the coast and islands to protect soil erosion.

Discharging of untreated sewage and urban wastes into the coastal waters should be

totally banned.

Construction of embankment walls along the coast to prevent the coastal erosion etc.

Coastal protection structures

Necessity for protection

Incessant natural phenomena such as winds, waves,currents and cyclones occurring continuously

affect the shore line . due to these phenomena there may be erosion or accretion of shore

materials.Change in the shore line caused due to excessive siltation at ports, demand removal of

excess materialb dredging. On the other hand erosion may lead to scoring of neighbouring

structures. Compared tostructures in the interior land , costal structures are subjected to more

severe forces and need constantmaintenance. Hence the shore line has to be protected so as to

maintain the requirement.

Shore protection works

Shore protection works are involved in

To protect an exposed beach line

To stabilize the existing beach

To restore eroded beach

To create and stabilize artificial beach

Shore protection wors in general are:

Sea walls and bulheads

Protective beaches

Sand dunes

Groynes

Off shore breakwater


These are the structures constructed parallel to the shore line special to separate

land area from waterarea. These are constructed to stop further recession of shore

line.

Alignment of such wall should be straight as far as possible and may be curves.

Abrupt change

in direction may cause added wave forces. Bulk head are meant to retain the earth

behind from slidingand also provides a wave protection device.

Sea walls are used where the land to be protected in a developed one and waves

effects aresevere. Sea walls are ver massive and expensive. These walls prevent


D.ANJALA/AP/CIVIL

shoreward movements of highwater line. sheet pile walls or solid reinforcement

mason walls ma be used.

Inclined shores are provided with stone rivertment.lie sea walls revetments are

used mainl to

protect the land and upland propert against wave action and also function as a

retaining wall.

Protective beaches

Beaches of suitttable dimensions are effective in dissipating energy and alsop

provide

protection to the adjacent upland. Eroded beaches an be wade good b planning

beach fill so as toensuresandsuppl at the required rate.

Periodic repleinishment of stockpile is called artificial beach nourishments. It also

maes good

the deficiencies in natural sand suppl and protects the shore beond the beach at a

low cost.

Sand dunesThe are formed along the coast which prevent the free movement of

tides and wavws into the areabehind it. Sand dunes with time may migrate to the

adjacent areas and damage the propert. Dune sandma stabilize by vegetation.

Under severe weather conditions the formation will be different.GyronesIt is

another shore protection tructures. This is used to built a protection beach to

retard erosion.it alsoprotect the toe sea walls or bulkheads

Gyrones are constructed well into the sea perpendicular to shore line .Gyrones

Ma also be constructed with certain angle to shore line.

A series of Gyrones acting together to protect a shore line is called Gyronessstem.

Spacing

between Gyrones is such that the length and spacing are in the ratio of 1:1 to 1:3.

Closer spacing andspacing beond 1: 3 are inefficient.

Gyrones are expected to resist wave action and sand pressure. Gyrones can be

constructed of

timber piles or steel sheet piles.

Off-shore breakwaters

Off-shore breakwaters serve in several wasy such as,

1. Protecting an area from wave action

2. Shore protection structure

3. Acts as a trap for littoral drift

These are of mound type breakwaters which provide protection to harbor

entrances. Some timesoffshore breakwaters are constructed off shore of sea walls so as to reduce

the determined forces onthe sea walls. Littoral movements are very effectively intercepted by off

shore break waters

4. Using case studies, explain how groundwater investigation and exploration is carries out

by civilengineers. [AU NOV/DEC 2015]

GROUNDWATER INVESTIGATIONS

In addition to pumping tests, Groundwater Engineering provides a complete service for a wide

range ofgroundwater investigation techniques.

Desk top studies and research into existing information can be a very cost effective way to

identifygroundwater problems at an early stage. Numerical groundwater modelling can be used


D.ANJALA/AP/CIVIL

to assess likelyflow rates, distance of influence and the potential for adverse environmental

impacts.

INSTALLATION OF MONITORING WELLS

Monitoring wells and specialist piezometers installed in advance of dewatering works can

providevaluable information on hydrogeological conditions at a site.

PUMPING TESTS

Pumping tests are a reliable way of determining the mass permeability of soils and rocks, and of

providing other information on groundwater conditions.

BOREHOLE PERMEABILITY TESTS

A range of tests can be carried out in individual boreholes, including rising and falling head tests,

constant head tests, Lugeon tests, Lefranc tests and packer tests. When carried out in accordance

withrelevant published standards and interpreted appropriately, such tests can provide some

indication ofpermeability values and groundwater conditions.

GROUNDWATER MONITORING SYSTEMS

Groundwater monitoring systems can play an important role in construction projects to

allowgroundwater conditions to be monitored and to provide data for design purposes.

Groundwater potential evaluation for a given area/basin requires integrated approach.

Detailed quantification of theamount of groundwater demand a detailed water balance

study and defining the boundary conditions, establishmentof the lateral and vertical

extent of aquifers and confining beds. In the absence of detailed hydro meteorological

andhydrogeological data, groundwater potential evaluation tends to be more semi-

quantitativemainly based ongeophysical investigation.

The method followed in this study, for the most part, was depending on the short-term

field hydrogeologicalinvestigation and surface geophysical surveying. Both approaches

provide information on the availability ofgroundwater in a semi-quantitative

sense.Geophysics provides no information on the exact amount of groundwater available

in the subsurface.

The amount canonly be estimated when the geophysical survey is supported by the local

hydrogeological features such as rechargepotential, availability of permeable rocks,

catchments areas, etc.All the interpretations shown in the geophysical part of this study

are made semi-quantitatively by integrating thehydrogeological field observations with

the geophysical signature obtained from the VES data.

The recommendationsof the likely depth of drilling are made on the basis of the VES data

and the nearby well data. The supervisor/ hydrogeologist can recommend the accurate

drilling depth during the drilling operation.

For instance in some sites wheregeophysics does not give conclusive answers on the total

depth of the aquifers, yield of the well can be defined byusing provisional tests with the

compressor of the drilling machine.

Causes Of Inherent Weakness In Rocks

In the majority of cases the main trigger of landslides is heavy or prolonged rainfall. Generally

this takesthe form of either an exceptional short lived event, such as the passage of a tropical

cyclone or eventhe rainfall associated with a particularly intense thunderstorm or of a long

duration rainfall event withlower intensity, such as the cumulative effect of monsoon rainfall in

South Asia.

In the former case it isusually necessary to have very high rainfall intensities, whereas in

the latter the intensity of rainfall maybe only moderate - it is the duration and existing


D.ANJALA/AP/CIVIL

pore water pressure conditions that are important. Theimportance of rainfall as a trigger

for landslides cannot be underestimated. A global survey of landslideoccurrence in the 12

months to the end of September 2003 revealed that there were 210 damaginglandslide

events worldwide. Of these, over 90% were triggered by heavy rainfall.

One rainfall event forexample in Sri Lanka in May 2003 triggered hundreds of landslides,

killing 266 people and renderingover 300,000 people temporarily homeless.

In July 2003 an intense rain band associated with theannual Asian monsoon tracked

across central Nepal, triggering 14 fatal landslides that killed 85 people.

The reinsurance company Swiss Re estimated that rainfall induced landslides associated

with the1997-1998 El Nino event triggered landslides along the west coast of North,

Central and South Americathat resulted in over $5 billion in losses.

Finally, landslides triggered by Hurricane Mitch in 1998 killedan estimated 18,000

people in Honduras, Nicaragua, Guatemala and El Salvador. So why does rainfalltrigger

so many landslides? Principally this is because the rainfall drives an increase in pore

waterpressures within the soil.

The Figure A illustrates the forces acting on an unstable block on a slope.Movement is

driven by shear stress, which is generated by the mass of the block acting under

gravitydown the slope. Resistance to movement is the result of the normal load.

When the slope fills withwater, the fluid pressure provides the block with buoyancy,

reducing the resistance to movement. Inaddition, in some cases fluid pressures can act

down the slope as a result of groundwater flow toprovide a hydraulic push to the

landslide that further decreases the stability.

Whilst the example givenin Figures A and B is clearly an artificial situation, the

mechanics are essentially as per a reallandslide.

Dam Disaster

Dams may be defined as a solid barrier constructed at a suitable geological location across a river

valley.

Objectives of Dam Construction

The followings are the objectives of the dam construction:

Generating the hydroelectricity

Providing water for irrigation

Providing water supply for industries

Fighting drought and controlling of floods

Providing navigational facilities

Classification of Dams

Dams are classified 1) Gravity Dams, 2) Arch Dams and 3) Embankment Dams. This

classification isbased on design, materials, and size of the construction.

Gravity Dams: It is a solid masonry or concrete structure, generally of a triangular profile,

which is sodesigned that it can withhold a particulate volume of water by virtue of its weight. All

force arising insuch a dam as due to the thrust of the impound water and the massive weight of

the dam materials areassumed to the foundation rocks. This kind of dams is always very

important and costly structure,therefore its design and construction should always be done very

carefully.


D.ANJALA/AP/CIVIL

Arc Dams: It is arc-Shaped solid structure mostly of concrete, which is designed in such a way

that amajor part of the thrust forces acting on the dam are transmitted mainly by the arch action,

on to theabutment rocks, that is rock forming the left and right sides of the stream valley. Hence

such damescan be built even on those sites where the foundation rocks may not be sufficiently

strong.

Embankment or Earth Dams: The embankment dams are generally trapezoidal in section

constructedof selected soil or earth obtained from the borrow pits of the adjoining areas.

Sometimes anembankment dams also contains a hard rock-fill, depending upon the height, base

width and length ofthe dam as shown in the figure.


D.ANJALA/AP/CIVIL

Suitable Geological Site for Dam Construction

To select suitable site for dam construction some preliminary geological survey of the entire

catchmentsarea to be done followed by detailed geological mapping by remote sensing method.

It can gives theinformation of

1) Topographic features,

2) Natural Drainage pattern,

3) General Character,

4) Structuralfeatures of rocks, such as fold, fault and joints and

5) trend and rate of weathering.

Such a study wheninterpreted properly, would ruled out some sites for the dam placement

and help in identifying the mostsuitable locations topographically and economically, where

further detailed geological investigationcould be carried out. For obtaining the above

information, remote sensing and conventional geologicalsurvey need to be conducted.Geology of

the site

Lithology: To understanding the lithology of the area is very important to select the site for dam

construction. It can be possible through conventional and remote sensing methods. Such study

revealsthe type, composition and texture of the rocks exposed along the valley floor, yet it is of

greatsignificance to know what class of rocks makes up the area; igneous, sedimentary or

metamorphic.Lithology interpretation is to identify information of rock unit with reference to

their physicalcharacteristics, topography, etc. This is based primary on photo-interpretation

elements, e.g, tone,pattern, size, texture, shape and relationship condition in photos and image

and terrain parameters andassociated features with convergence of evidence.

Examples: Intrusive rocks can be identified from satellite imagery using the following

interpretation key:

Colour/Tone - Light tone or medium red

Texture - Coarse to fine

Pattern - Sub dendrite

Bedding - Non-bedding

Boundary - Round cliffs

Structure - Lineament, syncline and anticline.

Structure: The interpretation of structural features is very important for sit selection for

dam.

Thestructural features like folding, faulting, joints, shear zones and fault zone and

associated features canbe identified through remote sensing method.

Example: The fault is easy to pick up on aerial data and satellite image by sharp topographic break

andlinear alignments of structure, water bodies or vegetation.

Dip and Strike, Fault, Folds and Joints aresome important features of rocks for dam

foundation.

Dip and Strike:

The bedded rocks are stronger in composition, and can bear greater stress when

applied normal to the bedding planes than the stress applied along the bedding planes.

Thus the desired conditions are that the resultant thrust, should be perpendicular to the

bedding plane.


D.ANJALA/AP/CIVIL

The bedding generally upstream offer best resistance to the resultant thrust and also

obstructs the leakageof water than those dipping down-stream as shown in figures.

Folds: The folded rocks are always under a considerable strain, and the same is released wheneverany

kind of excavation is done through them or they are distributed by some external forces or stress.

It is therefore desirable that a highly folded rock should always be avoided. If the engineer is

compelled to a dopt such a site, he should see that the foundations of his dam should rest on the

upstream limbs ofthe fold, if the fold is anticlinal in nature as shone in figure. But the fold is

synclinal in nature; thefoundations of the dame should rest on the downstream limbs of the fold

as shown in figure.

Different possible positions of a gravity dam A. On horizontal bed rocks – suitable condition

B. On down stream dipping rocks – unsafe

C. On upstream dipping condition – safe against R

Effect of folding on dam site

Fault: It is always to avoid risk by rejecting a site on a fault, as the movement along the existing

faultplane is much easier than along the any other plans. Even a slight disturbance may damage

thestructure constructed on Fault.

If the engineer is completed by the circumstances to adopt such asituation, then he

should see that the site has the fewest disadvantages or no serious defects. It isadvisable in such

cases to place the foundation of a dame upstream of the fault and not downstream ofit as shown

in figure.Joints: No sites are totally free from joining.


D.ANJALA/AP/CIVIL

Hence, sites cannot be abandoned, even if profuselyjointed. However, the detailed

mapping of the aspects and character of joints as developed in the rockof proposed site

has to be taken up with the great caution.

The geometry of joints, their intensity, natureand continuity with depths all must be

established, and their effect on the site rocks are to be evaluatedand remedial

measurement to be taken in advance.

Occurrence of micro joints has to be source ofmany risks.Engineering

propertiesLithological and structural studies are not sufficient for the selection of site for

dam.

A through testingboth in laboratory and in situ of the site rock for their most important

engineering properties has to becarried out such as compressive strengths, shear strength,

modulus of elasticity, porosity andpermeability and resistant to disintegration on repeated

weathering and drying.

Effects Of The Action Of Sea Waves On The Coastal Zones

Introduction About Coast

Coast is defined as a boundary between sea and mainland. It has been shaped by varying

influence oftectonic activity and instability of sea level.

Coast is associated with the sea and may include areas ofcliffs, dune, beaches and even

hills and plains and it has been affected by marine processes such astides, winds, waves

and current.

In general coasts that are composed of soft, unconsolidated materials,such as sand which

changes more rapidly than coasts composed of rock.

Types of Coast:

According to Johnson, the coast may be classified in to two types that is

Submerged coast and

b)Emerged coast.

It is based on sea level related with climate and tectonic activity.

The submerged coast is the coastal interior; the land immediately behind the shore zone

(whose inner limit is defined by thehighest storm and tide waves) has an intermediate

inner limit. The erosional features like Cliffs, Sheetsand Gullies are seen along the

erosional coast.

While in the case of an emerged coast, the coastal tractwhere the seaward migration of

the coastal tract is a low land, depositional features like deltaicsedimentation, estuarine,

marsh and sand dunes are the characteristic features.

Importance of Coast

The coastal environment is very dynamic with many cyclic and random processes owing

to a variety ofresources and habitats.

Further the coastal ecosystems are the most productive ecosystems on earth.About 60

percent of world population lives near the coast and in one way or other depends directly

orindirectly on the coastal zone and its resources (Like Coral reefs, Mangrove, Seaweeds,

Sea grass,Salt marsh, Beach etc). Thus the coastal zone plays a vital role on the nation’s

economy.

Coastal Problems in India


D.ANJALA/AP/CIVIL

The coastal area in India faces a wide range of problems.

A recent regional survey conducted byInternational Ocean Institute, Operational Center

at Chennai revealed several problems. As per thesurvey, in India, population pressure has

been considered as the most important problem.

Environmental degradation such as destruction of mangroves along with pollution and

urbanization isconsidered as the next serious problem.

Traditionally, coastal areas are highly populated and developed. In India, out of the 3-

mega cities withpopulation more than 10 million, Delhi (13.2 M), Bombay (16 M) and

Calcutta (16.5 M) two are coastalcities i.e., Bombay and Calcutta. The population density

is also more coastal areas than the nationalaverage.

For example, in the state of Tamilnadu, the population density in coastal area is 528

persq.km against 372 per sq.km which is state average. In parts of coastal metros like

Bombay, Calcuttaand Madras, the population pressure led to resource depletion and

environmental degradation.

The major activities that are responsible for coastal population in India are discharge and

disposal of domestic and industrial wastes, discharging of coolant waters, harbor

activities such as dredging, cargohandling, dumping of ship wastes, spilling of cargo’s

such as chemical and metal ores, oil transport andfishing activity, etc.

Domestic waters are discharged mostly in untreated conditions due to lake oftreatment

facilities in most of t he cities or towns. India is one of the largest industrialized nations

in theworld. Major industrial cities and town such as Surat, Bombay, Cochin, Chennai

and Visakhapatnamand Calcutta are situated on or near the coastline.

The estimated total quantity of waste discharged bythese industries is estimated to be

approximately 700 million cu.mThe coastal erosion is caused by wave braking, reduction

in sediment input to coast, tectonicupheavals and rise in sea level.

These causes are not only natural, but also, due to human influence. Inwest coast, erosion

is very severe along Kerala coast. In Karnataka, about 73 km of the coast isaffected by

erosion.

Along the east coast the coastal erosion is moderate.

In Tamilnadu, about 80 km ofthe coastline is affected. In Orissa, about 30 to 40 km are

affected.

In West Bengal, erosion occurs in180 km, along the coastline stretching from the

confluence of the river Hooghly in the west to theconfluence of the river Jadgan in the

east.

The rate of erosion is as high as 30 m/year.

In India, nearly 150 million people are prone to natural hazard in coastal areas. Bay of

Bengal is one ofthe five cyclone prone areas of the world.

The coastal regions surrounding this bay are frequentlyaffected by flooding from the sea

as well as the rivers due to tropical cyclones and related storm surgesand heavy rainfall.

Between the year 1990 and 1995 in the state of Andhra Pradesh, more than 1100human

lives were lost and properly worth of Rs.23, 000 million were damaged.

In Tamilnadu during theyear 1990 and 1995, the damages caused to property were worth

of Rs. 5, 800 million and the loss ofhuman lives was more than 500.Shoreline

Erosion and Accretion


D.ANJALA/AP/CIVIL

Shoreline is one of the most rapidly changing landforms of the earth. The geomorphic

processes oferosion and accretion, periodic storms, flooding and sea level changes

continuously modify the shoreline.

The rate of shoreline-change varies depending upon the intensity of the causative forces,

warming up of oceanic water and melting of continental ice sheets etc,

which result in submergence oremergence of land.The coastal erosion and accretion

processes are not new phenomena.

Generally the main causes ofthese processes can be thought of

Beach Configuration;

Tectonic Movements In The Coastal Beltand The Near Shore

Presence Of Mud Blanks,

Gradual Climate Changes,

Reduction In Thedischarging Of Sediments From Rivers And

Manmade activities along the coast.

Tamil Nadu with a coastal length of 980 km is the second largest coast in India. This state

experiencetwo monsoon periods, one is active from mid-June to mid-September (i.e, southwest

monsoon) and theother is active from mid-October to mid-January (i.e., northeast monsoon). All

the districts of the studyarea are affected by cyclonic storms almost every alternative year (For

example, during the period1877-1977, the coast has been hit by the storms for at least 50 times).

During certain years, the coasthas been hit by cyclonic storms even more then once.

Management measures of Coastal protection

The following measures are some management measures for coastal protection:

To create awareness among the coastal communities in the study area, in order to

protect and

conserve the coastal area through effective involvement of educational institutions

and NGOS

Stringent measures need to be under taken with immediate effect to ban coastal and

coral

mining and to take into task those involved in or those who encourage the

exploitation of corals

for any purpose. Patrolling the coast to check coral and coastal mining should be

carried out.

Law should be enacted to regulate and stop trawl boat operation in the zone

earmarked for

non-mechanized boat. The Department of Forest and the Department of Fisheries

should take

steps to stop anchoring of vessels on coral reefs, pair trawling and dynamite fishing.

Indiscriminate picking of budding seaweeds need to be banned.

Commercial shell collection should be controlled and closely monitored.

Marine Resource Management Centers should be established to improve the skills of

fishermen communities in areas other than coastal mining, which in turn will lead to

efficient management of coast.

Deforestation along the coast and islands should be banned. The forest Department

should

take up a forestation along the coast and islands to protect soil erosion.


D.ANJALA/AP/CIVIL

Discharging of untreated sewage and urban wastes into the coastal waters should be

totally

banned.

Construction of embankment walls along the coast to prevent the coastal erosion etc.

Coastal protection structures

Necessity for protectionIncessant natural phenomena such as winds, waves,currents

and cyclones occurring continuously

affect the shore line . due to these phenomena there may be erosion or accretion of

shore materials.Change in the shore line caused due to excessive siltation at ports,

demand removal of excess materialb dredging. On the other hand erosion may lead to

scoring of neighbouring structures. Compared tostructures in the interior land , costal

structures are subjected to more severe forces and need constantmaintenance. Hence

the shore line has to be protected so as to maintain the requirement.

Shore protection works

Shore protection works are involved in

To protect an exposed beach line

To stabilize the existing beach

To restore eroded beach

To create and stabilize artificial beach

Shore protection wors in general are:


Protective beaches

Sand dunes

Groynes

Off shore breakwater


These are the structures constructed parallel to the shore line special to separate land area

from waterarea.

These are constructed to stop further recession of shore line.

Alignment of such wall should be straight as far as possible and may be curves. Abrupt

change

in direction may cause added wave forces. Bulk head are meant to retain the earth behind

from slidingand also provides a wave protection device.

Sea walls are used where the land to be protected in a developed one and waves effects

aresevere. Sea walls are ver massive and expensive. These walls prevent shoreward

movements of high water line.

sheet pile walls or solid reinforcement mason walls ma be used.

Inclined shores are provided with stone rivertment.lie sea walls revetments are used

mainl to

protect the land and upland propert against wave action and also function as a retaining

wall.

Protective beaches

Beaches of suitttable dimensions are effective in dissipating energy and alsop provide

protection to the adjacent upland.

Eroded beaches an be wade good b planning beach fill so as


D.ANJALA/AP/CIVIL

toensuresandsuppl at the required rate.Periodic repleinishment of stockpile is called

artificial beach nourishments. It also maes good the deficiencies in natural sand suppl and

protects the shore beond the beach at a low cost.

Sand dunes

The are formed along the coast which prevent the free movement of tides and wavws into

the areabehind it. Sand dunes with time may migrate to the adjacent areas and damage the

propert.

Dune sandma stabilize by vegetation. Under severe weather conditions the formation will

be different.GyronesIt is another shore protection tructures.

This is used to built a protection beach to retard erosion.it alsoprotect the toe sea walls or

bulkheads Gyrones are constructed well into the sea perpendicular to shore line .Gyrones

Ma also be constructed with certain angle to shore line.

A series of Gyrones acting together to protect a shore line is called Gyronessstem.

Spacingbetween Gyrones is such that the length and spacing are in the ratio of 1:1 to 1:3.

Closer spacing andspacing beond 1: 3 are inefficient.

Gyrones are expected to resist wave action and sand pressure.

Gyrones can be constructed of timber piles or steel sheet piles.

Off-shore breakwaters

Off-shore breakwaters serve in several wasy such as,

Protecting an area from wave action

Shore protection structure

Acts as a trap for littoral drift

These are of mound type breakwaters which provide protection to harbor entrances. Some times

offshore breakwaters are constructed off shore of sea walls so as to reduce the determined forces

onthe sea walls. Littoral movements are very effectively intercepted by off shore break waters

List The Causes Of Landslides. The term landslide refers to the downward sliding of huge quantities of land masses of

earth.

sliding 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 un

consolidatedsurface material undergoes sliding. But sometimes, hugeblocks

ofconsolidated 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 as landslides and grouped them under “earth

movements”. The classification of earth movements us as follows:

Earth Movements

Earth Flows

Solifluction

Creep

Rapid Flows

Landslides


D.ANJALA/AP/CIVIL

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 influence of

gravity.Creep refers to the extremely slow downward movement of dry surface material.

This is very imp 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 are similar to creep but differ with reference to the speed.

Rapid flows generally accompany heavy rains. Mud flows are similar to rapid flows.

Landslides 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

may take place to the compaction of underlying material or due to collapse. Subsidence

due to compaction:

Sediments often become compact because of load.

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 a large 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 internal causes 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 forlandslide

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 alsoleaches out the soluble

matter of rocks. This reduces the compaction of rock body and makes


D.ANJALA/AP/CIVIL

it a weak mass.

3.Effect of Lithology;

Rocks which are highly fractured, porous and permeable are prone tolandslide occurrence

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

ofoverburden create a sliding of rock masses.Land slides in India: Land slides are

reported in the hilly terrains in different regions of India.The most disastrous land slides

that have taken place in recent past are in the Himalayanterrain in the North and the

Nilgiri hill region in south.

In July 1970, heavy debris from Patalganga valley has been transported into Alaknanda in

theGarhwal region of Uttaranchal. The flooding in Alaknanda due to these landslides has

resulted ina silt and rock fragment accumulation of about 9 M cum.

Another disastrous land slide took place on 18th Aug 1998 in Malpa village which is

located on

the banks of Kali River in Pithorgarh district of Kumaon Himalayas. The piled debris was

around 20 m in height.

In 1968, numerous landslides occurred during heavy rainfall of about 500 to 1000 mm in

theDarjeeling and Sikkim regions where the 60 km highway between Darjeeling (West

Bengal) andGangtok (Sikkim) was disrupted.

EFFECTS OF LANDSLIDES:

From the civil engineering point of view, landslides may cause

disruption of transport

damaging roads and railways and telegraph poles

obstruction to the river flow in valleys

damaging sewage and other pipe lines.

destruction of buildings and civil structures

Recent landslides in the Himalaya terrain are listed below:

Himachal Pradesh region:

Nathpa (Nov 1989): Road destroyed about a km

Kullu (Sep 1995): Road 1km destroyed and 32 persons killed

Uttaranchal region:

Kalisaur ( July 1968): Road damaged extensively

Malpa (Aug 1998): Road to Manasarovar damaged & 205 persons killed

Jammu & Kashmir region:

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


D.ANJALA/AP/CIVIL

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.


D.ANJALA/AP/CIVIL

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.


D.ANJALA/AP/CIVIL

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.


D.ANJALA/AP/CIVIL

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.


D.ANJALA/AP/CIVIL

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.

unit i physical geology€¦ · 2019-11-22 · ce6301 engineering geology vtht d.anjala/ap/civil...

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