Enginnering Geology- N Chennakesavulu

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2 n d

Edition

... t o .

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I


5/407Copynqhted -natena t

This book is meant for educational and learning purposes. The aulhor{ s} of the book has/have taken all reasonable care

to ensure that

the

contents of the book do not violate any existing copy

righ

t or other intellectual p

ro

perty

ri

ghts of any

person in any manner whatsoe

v

er: In the eve

nt

the authoi(

s}

has/have been unable

1 0

lrae

k

any source and i

f

any copyright

has been inadvertently infringed. p l ease not

i

fy the

publi

sher in writing for corrective ac

ti

on,

Printed

a

t Baba

B ar

kha Nath Printers

37, MIE,

Bahadurgarh,

Haryana t2

4

507

Typeset by Sri Krishna Graphics

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, Sou

th Ganesh

Nagar,

Delhi

110 092

Pu b li

shed by Rajiv

B

eni

for

Macmi l lan Publ i she

rs

India Ltd.

2110

,

Ansari Road,

Daryaganj ,

Ne w

D e l

hi

110 002

ISBN

I0: 0230-

63870

-8

ISBN

13:

978.0230-63870-9

Com

panies and

representativ

es throughout the world

MACMILLA

N PUBLISHERS INDIA LTD.

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hi

Bang

alore Chennai

Kolkata

Mu m b a i

Ahmedabad Bhopa l Cha nd

i

garh Coimbatore

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k

Guwaha t i Hubl i Hyderabad Ja ipur Lucknow Madura i

Nagpur

Patn

a Pune

Th

i ruvananthapuram

V is a

khapatnam

First published, 1993

Reprin

ted, 1 9 9 7

2

007

eight times)

Se

c

ond edition, 1 2 009

.

All r ights

reserved

.

No part

of th i

s publicat ion may

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reproduced or

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in

any

fo

rm or

b

y any

mea ns

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without

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Any

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o rized act in re lation to th i

s

publicat ion

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ay be l iable to criminal

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t ion and

c ivi l cl

aims for

damages

.

C

N Chenna Kes avulu, 1993

,

2 0 0 9


6/407Gopynghted material

5

.4 Sequence

of

Formation of Diff

e

r

ent

G

r

oups

of

Rocks

5 . 5

Ro

c

k

Cycle

5.

6 Civil

E

ngin

ee

ring

I

mportance

of

Petrology

5 .

2

Definit ion

of a R oc

k

5 3

Cl

as s ification of R

oc

k

s

5

I

S

h

ell Stn1c n1re of rhe Earth

5

. PETROl.oGY

4.

4

Impo

rt an

t

D

e

t

ails

of

C

ommon

R

o

c

k-fo

rmin

g

M

i

nerals

4.3 Brief S k

et

ch of Common R ock-

fo

rming M in erals

4

.

2

S

pe

c ial Fea tu res of S

il i

cate

M

in erals

4

. 1 Type

s

of

Roc k

-f

orming M i

ne

rals

4. COMMON

R

OCK

-

FORMJNG

M INERA

LS

3 .

7

D i

a gn

o

s

tic or

D is

tin gu i

s

hing

P

h y s ical

P

roperties

3 .6

Sig

n ifican

c

e of D ifferent P h ysica l

Prope

rt ies in M ineral

3.5

D

ifferent M ethods of

S

tu d

y

of M

in

eral

s

3

.4 C o m m o

n

R oc

k

-f

orming M i

ne

rals

an

d Their A

b

u n

d

anc

e

3

3

Mode

of

Foan

a t

i

o

n

o

f

M

in

era l

s

3

.

2

Defini t

io n

of a Crystal

3

1 Defiojt

oo of a Min

era

3.

M

IN E R A L O GY

2.3

R iv

e

r

a

s a G

eo l

ogi

c

al A g

e

nt

2.2 Weathering of R

o

c

ks

2 . 1 G

e

olog i

c

al

Agents

2 GEN E

R

Al.GFOlOGY

1 .

3

Sc o

pe

of

G

e

ology

1 .2 I m portance of

G

eology

in

Civil Engineering

Vil

IX

1

2

5

7

11

1

2

1 4

2

7

39

39

41

4

3

44

4

5

I

d

entif i

c

a

tion

48

(j()

61

61 I

6

1

65

6 8

94

94

95

96

1

00

IO I

1 02

I.

M ain and Allie

d Bra n

ches of

G

eology

Pre

ce

t

o th e

Sec

ond

Ed

ition

Prece o th e F irst Edition

1.

GEOLOGY

CO

NTENTS


7/407CDpynghted rnaierial

256

1.9 G

ro

u

nd Water

P

otential

in D

iffe

re

nt Parts of India

253

254

I 1.7

Geo

l

ogical Controls on G round Water Mo veme

n

t

I I

.8 F

lu c tua tion of the Water Table Level in

U n

confined A qu ifers

248

250

1

1.5

Cla

s

sification of Rocks B ased on

Poros

ity and

P

e

rm

eability

1

1.6

W ater

T ab

le and

Ty

pes of

G

rou

nd

W ater

244

245

1 1

.3 D

istri

bu tion of

Rain

fall

1 1 .4 Porosity and

P

e rme a b ili ty

242

1 1 A d vantages of U s ing

G ro

u nd Water

24 1

I.

Source

s

of

G

r

ou nd Water Su pp

l

y

240ntroduction

240

I

.

GROUNDWATER

2360.3 Effects of Joints and Their C ivil

E n g i

neering Importance

232

0

.

2 Effects of

Fault in

g an

d

Their Civil

E n

gineering

Im

portance

228

0

. I Effects of Fo lding and Their Civil Engin

e

ering Im portance

227ntroduction

2270.

IMP

OR T A N

C

EOFGEO

LOGI

CAL

S

TRUCTURES

226

.6 Common Symbols to

Indicat

e S ome G

e

o l

o g

ical Structures

222

. 5

U nc onf o rm

ity

Causes for Deve lop me

n

t of Structures

190

171

175

176

190

8.2 C o m

m o

n Structures and

T ex

tures

of

M etamorph

ic R oc

ks

8.3 C lassification of M e tamorp

hic R

oc

k

s

8.4 Descr ip t ive Study of C o m m on M e t am o

rphi

c R

oc

ks

9.

SIRU

CTURALGEOLOGY

162

.

1

M e ta m

o

rphism

1 6 1

nt

roduc

ti

on

1

61

7

.4

D

escriptiv e Study of

Co m m o

n

S

e

d im

entary

R

ocks

8. METAMORPHICROCKS

150

135

145

7

.2

Cl

assification of Sedimentary

R

ocks

7.3 Common Structures and

T

extures of

Sedim

entary R ocks

134

.

1

Sedimentary Rocks on the Earth's Crust

1 34

ntr

od11ct

i

on

134

1 2 3

125

6

.6 Suitability of Igneous

R

ocks for Building an

d F

oundation

6.7 M egascopic De sc r i

p

tion of Relatively C o m m o

n

Igneo

u

s

R

oc

k Types

7. SEOIME

NTARYROCK

S

109

1 II

Ill

1 1 5

6.2 M iscellaneous

6.3 C o m m o

n

Igneo

u

s Rocks and R ela tio

n

of

T

heir

C

onstituent M inerals

6.4 Class ificatio n of

I

gneous

R oc

ks

6

5 Stn

c t11r

es an

d Texh1res

103

103

1 04

6. IGNEOUS ROCKS

Introduction

6

.

1 Form s of

I

gneous

R oc

k

s

xu

Contents


8/407

c,opvnghted mater ia l

16 .2 Seismic Refraction M ethod

16 . 1 E le ct r i cal R es is tivity M et

h

od

Introdu

ct

i

on

15.3

Principles of E xp loration

G eoph y

sics

I 5.4 Classification of Geophysical Methods

15.5 Well-logging

1

6

.

GE

OPHYSICAi. I

NVE

STIGAT

IONS OF C

I

YII

.

EN

GINEE

RI

N

G IMPDR

TA

NCE

15. GEOPHY

S

I

C

AL

I

NV

EST

IG ATIONS

I n t roduc t

i

on

15.

I

B ranches

of

G e o p

h

ysics

15.2 Necessity of

Geoph

ysical

Inves t i

gations

14

. LANDS

LID

E

S

Introd

uction

14

. 1 I

m

po r t

ance of

L an

dslides

14.2 Class i f i c

a

tion of Earth M ovements

14.3 Causes of Landslides

1

44 Effects

of

Landslides

14.5 Preventive Measures for L a n d s lides

13.9 Determining the De

p

th of the Focus of an Earthquake

13.10 Effects of Earthquakes

13

.

1 1

Civil Engineering Considerations in Seismic Areas

13

.

1

2 Plate

Tec

tonics

an

d E ar t

h

q

u

ake D is

t

rib

u

tion

13.8 L oca

ting th

e

E

p

icentre of an E

a

rthq

uake

13.6 Intensity of Earthquakes

13 .7 M agnitude

o

f the Ear th qu akes

13 .5

E a

rt

h q

u

a

ke W aves

13.4 E a rthqu

a

k

e

s a nd

Fa

u lt ing

13.3 S

e

ismic

B

elts

a

nd Shield A r ea s

13.2 Class i f i ca

t

ions and

Ca

uses of E ar t

hq

u akes

1

3.

I

E a

rt

h

q

uake

Te

rm

in

o

l

o

gy

I

nt

rod

uction

1

3. E

AR

T

HQU

AKES

12 .6 Importance of the

Stu

dy of Stratigraphy from the Civ il Engineering

Poin t

o

f V iew

12.3

Geo

log i ca l T ime Scale

12

.4

G eo

l

og i ca

l

D iv

isions of

In d

ia

12 .2 Princ i

p

les of Stra t igrap

h

y

I

I.IO Ground W ater Ex

plo

ration

11.11 Effects of Excessive Tapping of G ro und W ater

11.12 Waterlogging

12. S T R A

TI

G RAPHY

I

ntroduction

12 .

I A

ims of Str

a

tigraphy

C on

te

n

ts

XIII

257

260

260

2 6 )

261

2 6

2

262

264

267

268

284

2 8

5

285

286

286

28

8

28

8

289

290

29 1

293

294

294

295

298

300

300

300

3

01

303

306

306

308

30

8

308

309

311

312

329

331

33

1

332

345

1

2 .

5 M ajor

S

t rat

i

graph

i

cal

U n

its

of

In d

i

a


9/407

Copvnghted maienal

Index

443

ibliography

441

0.7 A Few E xa

mp

l

es of Tunne

l

s of Interest and Importance

428

429

4 2 9

430

4 3 0

440

2 0 . I Purposes of Tunnelling

20.2 Effects of Tunnelling on the Ground

20.3 Lining of Tunnels

20.4

Economical

Aspects of Tunnelling

20.5 Geological Considerations for Successful Tunnelling

20

.6

Overbr

eak

427

ntroduction

42

7

0. TUNNEL

S

425

9 .

7 L a n d s l ide Occurre;ices

4 2 5

9 .6 S e

i

s m

i

c Activity in R eservoir Areas

413

420

19 .4 Water-tightness and Influencing Factors

19 . 5 Reservoir Silting

4 1 2

9 .3 Effect of Evaporation

412

9 2 Capacity

of

t

h

e Reservoi

r

4 1 2

9 .

I Co ns

iderations for

Successf

ul Reservoirs

411

ntrodu

ctjoo

4JJ9, RESERVOIRS

398

8 ,7 Case Histories

3 8 4

3 9 6

18.5 Geological Considerations in the Selection of a Dam Site

18 .6 Stages of Investigation in the Selection of a Dam Site

383

8

.4 Purposes of Dams

3 8 0

381

18.2 A Dam and Its Parts

1 8.3 TYPes of Dams and Beari

n

g of Geology of Site in Their Se lection

3 7 7

8

.

1 I

mportance of

Geol

ogy in Dam Construction

376

nt roduct io n

376

8

. DAMS

37

1

7

.4 Tests for Rocks Used as

Aggrega

t

es

3 5 8

3 6 2

17

.2 Tests for Rocks Used as Foundation Sites of Constructions

1 7.3 Tests for Rocks Used as Building Stones

3 5 7

7 . 1 D

i

fferent Engineering Property Tests for Rocks

3 5 6ntroduction

356

7. ENG

l

NEER

I

NG PROPERTIES OF ROCKS

xiv

Contents


10/407C ' pyn ht ld mat ri ti

Geo logy is the science of the earth (geo = earth, logos =

s t ud

y or science

)

. It deals with different

a

spects of the earth as a w h o le such as (i

)

origin, age, interior structure and history of

th

e earth;

(ii)

evoluti

o

n and

modi f i c

ation of various

s

urface

fea t

u res like

rivers , m ou n

tains and lakes along

w

ith

their causes; and

(iii)

materials making up the earth

.

G e o logy

is

a rela tively recen t s

ubjec

t.

I

n addition to its core branch es, advances in g

e

ology in

allied fields have led to spec ia lized sc iences like geo physics,

g e o c h e m i

stry,

geohydro1ogy

,

glac io logy

,

se i smo log

y , oceanography,

r

ock mec han i c s, pho

t

ogeology , and remote sens in g .

t

Similar

l

y

,

based on the applied importance of geology in o

th

er

f ie lds , re

l

a t

ed su

bjec

ts s u ch as

engineering geology, mining geology and so on h ave

c

ome into existence.

INTRODUCTION

A i

ms

: T he a

im

s of this chapter are:

1 .

T

o introduce the subject.

2.

T

o list out the main and allied branches of

geo logy

, explain their

s

ubject matter and to briefly

indicate their

r

elevance from the

c

ivi l engineering

poin

t of view

.

3

.

Toexp lore the scope of geology in terms of its academic s ign i f icance . It is purely meant to inculcate

interest and curiosity in

th

e subject

matter

.

4.

T

o give the importance of geology in the fields o

f:

(a)

e

xplo

r

ation, es

t imatio

n and ex

plo i

tation

of

e

conomic mineral depos i ts . and mining ; (b) ground water s t ud ies, t own

-

p lanning; (c) civi l

engineering, and so on.

Int

r

oducti

on; I.

I

Main and Allied Branches of

Geology

; I. I.

I

Physical Geol

ogy

;

1.1.2 Mineralogy

;

1.1.3 Petro

l

ogy; 1.1.4 Structural Geology

;

1.1.5 Historical G

e

ology

;

l.1.

6

Palaeont

o

logy

; 1.1.7 Economic Geology;

1.1.8

Engineering

Geology

; 1.1.9 Mining

Geology

;

I. I. I0 G e o p h ysics; I. I. I G eohydrology; 1.1.12 Geochemistry

;

1.2 Importance of Geology in Civil

E ngi

neeri

ng ; 1.3 Scope of

Geology

;

1.3.1 A ca

demic

I

mportance of Geology; 1.3.2 Importance of

Applied Geology in Differe

n

t F

i

elds.

GEOLOGY

1



1

.1

.2 Mineralogy

This

de

als with the

s

tu d

y of

m

i

ner

al

s.

Minera l

s are basic

un

i

ts

w

ith whi

c

h

di

ffe

rent

r

o

ck

s

a

nd

o

res

of the earth are made up of. Details of mode of form

a

tion

,

composition

, oc

c

u

rrence

,

types

, a

s sociation

,

properties, uses, etc ., of

minera

ls form the

s

ubject matter of

mi

neralogy.

Knowledge in th is branch of geology

is

neces sary for a civil engineer because the properties of

rocks

- (

which he is g

o

i

n

g to make use

of

in different w a y s ) are to a

larg

e extent contri

b

ut

e

d by the

properties and composition of their constituent minerals. For example, s

om

etimes quartz

i

te and marble

resemble one another in shine, colour and appearance.

B

u t quartzite by virtue of its mineralcom

pos

it ion

is very hard, tough, s trong and

dur

able, while marble dis in tegrates and decom poses in a shorter period

b e

cause

of

its mineral

c

ompos it ion and properties.

1

.

1

1

Phy

s i

cal Geology

This is also variously described

a

s dy

n

amic

geo

logy. geomorphology,etc. As the

n

ame suggests it deals

with: (i

)

different physical features of the earth, such as

mo

untains, p lateaus, vall

e

ys, riv ers, l akes,

glac

iers

, and vo

l c anoe

s

i

n terms of their origin and

deve

l

opment

, (ii

)

the different c h

an

ges

oc c

urring

on the earth 's s

u

rface

,

like marine transgression

,

mar i

n

e regres s ion

,

formation or disappea rance

of

r ivers, springs and lakes, (ii i) geological work

of

wind, glaciers

,

rivers, oceans, ground water, and their

ro

l

e

i

n

co

nstant

l

y moulding the

earth'

s surface features, and

( i

v) natural phenomena like

l and s lide

s,

earth

q

uakes,

an

d weathering

.

The main

c

ause for s

u

rface changes is weatheri

n

g This is a natural phenomenon

resu l

ting di rec tly

o

r

indir

ectly

du

e to

change

s

in

t

h

e atmosphere.

I

t

dis

i

ntegrat

es and decomposes

rock

s

.

T h i

s

as pe

ct

i

s

of special importance from the civil engineering point of view,

b e c a u s

e colour,

appearanc

e, s trength

and durability of rocks are adversely affected by weath ering.

Thu

s even granite which

is

considered

ideal for most

of

the civil engineering w

o

r

k

s beco

m

es weak and friable on thorou gh wea ther ing.

re

n

derin g it u s el

e

ss.

Civil engineers d

e

al with structures like darns which are artificial barriers to the natu ral

fl

ow of

rivers. Proper understanding of the geological work of a river and its features will lead to thei

r

bett

e

r

utilization for engin

e

ering applications.

All

ie

d branches:

E ngineering geology

Mining

g

eology

Geophysics

Geohydrology

Geoch

e

m istry

Main

bra

nches:

Physical geology

Mineralogy

Petr

olo

gy

Structural geology

Historical geology (stratigraphy

)

Palaeontology

Economic geo

l

ogy

The vast

s

ubject of geology has been subdivided into the following branches for the sake of

s ys temat i

c

s tu dy:

1 .1 MAIN AND ALLIED BRANCHES OF

GEOLOG

Y

2 Textbook of Engineering

G

eology


12/407Lopynghted m2tennl

1

.1

.

6

Palaeo

ntology

If

,

u nder favourable conditions,

an ima l

or p

l

an

t

life

get

s embedded in

s

ediments, it will be preserved

partly or

c

ompletely. S

uc

h reli

c

s and remnants of ancient life pre served in roc

k

s

b

y natural

p

rocesses

are known as "fo s s ils". D e tails of the m ode of formation of fossi

ls

, their types, occurrence, etc. , form

the sub ject matter of palaeontolo

g

y.

L

ik

e stratigraphy, this is also

a

n importa

n

t branch of geolo

gy

.

though it

is

not of much importance from the civil engineering point of view. But as fossils are rare

1.1 .5

H is to

rical

G e

ology (

S

tratigra

ph

y)

T

he

earth

's sur

f

ace was a

l

w ays u n

eve

n and provided

s

u itab le conditi ons for the

depos iti

on of

sedime

n

ts

a

t

s

ome

p

l

ac

e or

th

e

o

ther

.

T h erefore

,

th

e

r

e are

s

edim

e

ntary

roc k

s

o

n

t

h

e earth

rep

r

esent

i

ng the entire

p

eriod of the earth 's

h i

s tory. Pr

op

er

in ve

stig

a

ti

o

ns of these rocks reveal the chronologi

c

al sequence

of formation of rocks,

evolu t i

on-migrati on -extinction details of different plant and animal life during

the

diff

erent periods of the

earth

's history. In

addit io

n , the

climati

c and geographical c hanges

inc lu

d ing

tectonic even ts in the geological

p

ast can also be known from these

inve

stigations. T h is kind of s tu

d

y

of th e

eart

h 's history through the sedimentary rocks is called historical geology. It is also ca l led

s

trati

graphy

strat

a

= a set of

sed im

entary

ro c

ks;

graphy =description) b e c a u

se th is subject d

ea l

s with

deiails and

de

scription of sedim entary rock sequences

.

This is a major branch of

ge

ology

, h

aving a

l

o

t

of ac

ademic

an

d applied importance. From the ci

v

il

e

n gi

ne

ering

poin

t

of vi

ew also it is relevant

that except for the fact th a t o lder

r

oc

ks are in general more stable (like sh ie ld areas of th e Arch

aea

n

era) and more competent due to more compaction and

cementat

i

on.

F

urther,

s

tudy of

s

tratigra

p

hy can

b e utilized in predic ting the

unde r l

ying s trata w h i

c

h m ay be very important in some s

pe

cific civil

engineering

con

s tructions .

1 .

1.

4

S

truc tural G eo

lo

gy

T he rocks w

h i

ch form

th

e

e

arth'

s c ru st undergo

v

ar ious de fo rma t io

n

s,

di

s locations and disturba

n

ces

under the inf luence of tectonic fo rces.

Th

e

r

esult is th e occurr

e

nce of

diff

erent geo logical structures

like folds, fau l ts , joints

a

nd u nconfo

rmi t i

es in rock s . The d

e

tails of m ode of forrnation,causes, types,

classification, importance,

etc

. , of th ese geological s truct

u re

s form the subject matter of structural

geology.

From the

c

iv i l engin eerin g poin t of v iew, it is as im portant

a

s

petro

logy because th ese geological

structures

mod

ify the inherent ph y sical

c

haracters of rocks

render in

g th

e

m more suitable or unsuitable

for civil engineering

purpo

ses.For example, at a d

a

m s ite s

e

d imentary rocks with upstream dip

provi

de

a

d

es

i rab

le

g

eol

o

gical set-up

, w h

ile t

h

e sam e r

o

cks with downstream dip make the geological set-up

m o

s t u ndes irable.

1.1 .

3

Petrolo

gy

Petr

o = rock,

lo

g

o

s =

s

tud

y

)

Petrology d

eal

s with the

s tu

dy of rocks. The earth 's crust, also called litho

s

phere, is made up of different

types of rocks. Petrology dea ls with mode of

fo rm

ation,

s

tr u c ture,

texture

, c

ompos

ition ,

oc

currence,

types, e tc

.

,

of

rocks.

T

h

e

compo

s

it i

o

n

an

d textural characters

o

f

roc k

s primarily

contrib

u

t

e to

t

h

eir

inhe

r

ent

s

trength

and durab

i

lity.

R

ocks b ased on their

sui tabi l

ity can be u

s

ed as foundation for dams, for tunnelling and

as materials of construc

t

ion. Hence th is

i

s the

m o s t

important branch of geology from the c

i

vi

l

engineering point of view.

Geology 3


13/407~opyngh ma

n 8 1

1 .

1

.

9

Mini

ng

Ge

olo

gy

T

hi

s deals with the

a

pplic

atio

n of

geol

ogical know

led

ge

in

the field of min

i

ng. A mining

e

ng

inee

r

is interes ted in the mode and extent of occurrence of ores, th eir association, tenor,

propertie

s, etc. It

i

s also necessary to know oth

e

r ph

ys

ica

l param

eters

li

ke d

e

pth, direction (strike),

i

nclination (d ip),

thi

ckness and reserve of

or

e bodies

f

or efficient utilization. Such details of min

e

ral

e

x

p

loration,

estimation and e

xploi

tation are dealt with in mining geo

l

ogy.

The

i

m

po

rtance of geology

i

n

minin

g

m

ay be cited with the following

example

. Sometimes, the

lode

s or seams of

economi

c min

e

ra

l

s sudd

e

n ly

ge

t

terminated

. This

mig

ht happen e ither due to the

natural

l

imit of the ore body or

du

e to f

aultin

g. Geological s tudies will

solv

e

this p

ro

blem and, if it

1 .1.8 Engin

ee

ring Geo

l

ogy

This

deal

s with th e application of geol

ogi

cal

knowledg

e in th e

fi

eld of civil

e

ng

ineering

, for

exec

ution

of safe, stable and

eco

nomic

c

onstructions like

dam

s,

brid

ges and tunn

e

ls .

A

s

thi

s

i

s the branch with

whi

c

h we are most

co

n

cerned

, it has been

e

xplained

i

n

de

tail separately (refer to

S

ec. 1 .2) .

1.

1

.7 Economic Geology

Mi

nerals can be

gr

ouped as

g

enera l

rock-f

orming

mi

ne

r

als

a

nd economic

mi

ne

ral

s.

S

om e o

f

the

economic minerals like

talc

,

gr

a

ph i

te, mica,

as

b

estos

, gypsum,

m

agnesite, barytes,

dia

mond

a

nd gems

are useful

a

s

suc

h or as

r

aw

material

s in different indus

trie

s

.

Some

other

s

lik

e hem

a

tit

e , c

hromite,

galen

a

and pyro

lus

ite

a

re used

a

s ores for the extr

a c t

ion of various

meta

ls, the uses of whi

c

h are well known.

Th

e prosper ity

o

f a nation depends

t

o a

l

arge ext

e

nt on the

ric

h

res

erves of economic mineral depos its

i

t

ha

s. (

F

or

e

xample, Gulf

c

ountries are rich

be

cause of th

e

ir oil deposi

t

s;

S

outh

Afri

c

a

i

s rich because

of its

go

ld and d

i

amond de

po

s its.)

The

det

ails oftheir mode offormati

on, occ

urrence, c

l

a s s

if ic

ation

,

associ

a tion,

varieti

e

s

, concentration

,

p

ro

perti

es

, uses, etc. , fo rm the subject

matt

er of "econo

m

ic

ge

o

l

ogy". This branch of ge

ol

ogy, though

it

i

s very

imp

o

rtant by v

irt

ue

o

f

i

ts

econ

o

mic

im

port

a

n

c

e

, is no

t r

elevant

f

or

civ

il

enginee

rs for

o

bv

iou

s

reasons. It will be enough for them to know a few deta

il

s as in the

c

ase of fossils, so that they will

not be ignorant of

the

m as and when they

c

ome

a

cross these

i

n course of their civil engineering works

like tunnelling and

ro

ad

c

ut t ing.

E

ac

h of the

fo

rego

in

g b

ra

nches deals with specific subject matter and comprises the

m

ain branches

of g

eolo

gy proper . Furth

er

, based on

applicati

on of g

eol

ogical knowledge in

othe

r

fiel

ds there

ar

e

man

y

other all ied branches co

ll ec ti

vely called

e

arth sci

e

nces.

Some of them d

esc ri

bed here are:

En

gi

neering geo

logy.

Minin

g geolo gy.

G

eophysics

.

Geohydr

ology.

G

eochemis try.

a

nd

thr

ow much

li

ght on

th

e

pas

t history of

th

e earth

,

a

civil

en

gi

neer should know s

om

e d

etail

s

r

egarding them so that he recogn

i

zes them as

foss

il

s . Whenever he c

o

mes

a

cross such finds

duri

ng

h is w

ork

, he

sh

ould

re

port

th

e m atter to th e person

concerned

,

fo

r

necess

ary act

i

on.

4 Te

xtboo

k

o f

E n

g

in ee

ri

ng G eolo gy


14/407< " ' pynghted ma nal

The civil en g

i

neers

ai

m

a

t s

afety,

stab

i

lity, e

c

onomy and life

of th

e

s

tructures that they construct.

Civil

engineering co

ns

t ruc tions

l

ike dams

a

nd b ridg

e

s w ill have their fo

u

ndations on geo

l

ogical formations

of the earth's surfac

e

.

Therefore

, their

s

t

abi

lity

a

nd

s

afety depend on the competence of the in s

i

tu

rocks of t

h

e s ites

concerned

. A

l

s o ,

t

o be

econom

ical, s

u

ch competent foundation rocks s

h

o

u

ld be at

a shallow d

e

p

t

h

.

Further

,

fo

r

h u ge con

structi

on

s

l

ik e

dams, b u i

l

d

i

ng materi

a

l

s

are required in very large

1.2 IMPORTANCE OF GEOLOGY IN

C

IVIL E NGINEERING

1 .1

12

Geoc

he

m

is

try

This b ranch is r

e

lative

l

y

mo

re recent and deals

wit

h the oc

c

urrence, distribut

i

on , abundance, mobil

i

ty,

etc.,

of

different

element

s

in the

earth'

s

c

ru

s

t.

It

is not important

fro

m the

c

i

v

il

engi

n

ee

ri

ng

p

o

i

n

t

of

view.

1.1.

11

Geo

hydrology

Thi

s may

a

l

s

o be called

a

s hydrogeology.

I

t

dea

l

s with

occurrence, moveme

n

t

and nature

(i.e , qual

i

ty

and

quantity

) of ground

wate

r in an area. It

h

as a

p

plied importance because ground

w

ater

h a

s many

advantage

s over surface water. This b ranc

h i

s

c

lo

s

ely related to geo

l

ogy becau se the very

exis

tence,

m

ovement of ground water,

etc

. , are directly rela

t

ed to

p

orosity, permeability, structure, texture and

composition of the surface and underground roc

k

s. Dy

ke

s may control t

h

e occurre

n

ce

an

d movement

of ground water. In

general

, geo

l

ogical, geophysical (electrical

res

istivity method)

an

d hydro

l

ogical

s

tudies are

t

o

gether taken

u

p for ground

wa

t

er

i

n

ve

s

tigat

ions.

1 .1.10 Geophysics

The study of ph y

s

ical properties like density and magnetism of the earth or

i

ts parts, to know i

t

s interior

,

forms the subject matter of geophys

i

cs. Broadly it is subdivi

d

ed i

n

to general (or pure) geop

h

ysics and

e

x

ploration (or app

l

ied) geophys

i

cs.

P u

re

geoph y

s ics deals with genera

l

aspects of the earth as a

whol

e

and

explor

ation geo

ph y

s

ic

s

deal

s with the

s

tudy of u

p

per

la

yers of the

earth

's crus t inorder to (i

)

solve

so

m

e civil engineering

probl

e

m

s, (ii) locate oil and goes

deposits, (

iii) locate grou nd water

, (

iv) explore

an

d

es

timate the ore depos its, etc., of u

ndergr

ound.

The

re are different types of geophys ical

investi

gations based on the

ph

ysical

pr

operty utili

zed

,

vi

z

. grav

ity

methods

,

s

eismic meth

od

s,

magn

etic

methods. Since these are quic

k

ly and easily done on t

h

e surface, large areas can be investigated

economically and

efficientl

y

.

Engineering

geoph y

s ic s is a bran

c

h of exploration

geo ph y

s ic s which aims at s

o

lvin g

civ

i l

engineering problems by in t

erpreti

ng s

u b

surface

ge

ology of t

h

e

area

s concerned.

Geoph y

s

ic

al

investigations are very u

se

ful

in

solving foundation problems, alignment of

struct

u res, leakage

probl

em

s

alo

ng canals, locat

i

ng building materials like stones (where they are not available on the

s

urface

), etc. E

lectric

a

l

resistivity methods and seismic

refraction method

s are commonly used

i

n

s

o

l

v

in

g c i

v

il engineering

p

roblems.

is due to fau

l

ting, the continuity can be traced by ascertaining the

d

irection and extent of displacement

caused by fau

l

ting.

The geological knowledge

h el

ps in planning the

me

t

hod of mi n ing or

quarrin

g a depo

s i

t

in

an

advan

t

ageous way.

Geology S



With Reference to Reservoirs

Th

e

J

erome reservoir of Idaho and the

H

ondo reservoir of New Mexico are two examples of failures

due to geological reasons.

As in the case of dam sites, se

l

ection of suitab

l

e sites for locating reservoirs needs geological

studies to make them successful. Unfavourablegeological conditions lead to quick siJtiog of reservoirs,

th

ere

b y decreasing its life, and profuse leakage of stored

water.

Intense weathering in the rocks upstream causes silting prob lems . Porosity

an

d permeability

of

rocks, occurrence

of

fau l t s

, joints and other weak

p

lanes ca

u

se leakage

prob lems

. Grou

n

d water

co

n

ditions also play a key ro

l

e

i

n

i

n

fluencing

l

eakage

.

Th

u

s proper

s tu

di

es

of

geological conditions

at any proposed

r

e

s

ervoir site will fo

r

ewarn a

n

en

gin ee

r of the prob

l

ems,

if

any.

With Reference to Tunnels

R

amganga diversion tunnel

(

Hi

m a l a y a s )

,

U m i a m -

Barapani stage

I tu

n

n

e l

( Megha laya ) ,

Key

n

a ID stage

tail race t unne l , and B a s s ein creek tunnel (Bom

b

ay) are some

of

th e e

x

amples where geolog ical

c

o

nd

itio

n

s posed

se r i

ou

s

p

rob lems.

C o m p e

te

nc

e of the roc

k

s , associated

g eo

logical structures like

b e d d i

n

g, fau lts, joints, porosity

an

d

permeability of rocks, and ground water conditions are the geological c

o

nditions w h ich

n ee

d to be

t

h o

roughly s tu died to solve such problems.

With

Refe

rence to

D a 1 1 1 s

T

he fo ll owing are a few examples

of

fail

u

res of

d

ams. T hese failures have occurredonly due to adverse

geological conditions a

n

d not due to technical lapses:

l. St. Francis dam of California.

2

. Lafayette

d

am of California.

3

.

A u

s

tin dam

of

Texas

.

In

addition to these

fa i lures ,

there are

a ls

o a

n u m b e

r of examples w here the cost of construction

b

ecame very high in order to overcome the associated geological drawbacks.

Hales

b

ar dam (

o

n Tennessee

r

iver) , Camarassa

d

am (Spain), Dokan dam (Iraq); Chickm a

u

ga dam

(USA), Val l G allina dam (Italy) are a few examples of this kind.

The aforementioned exam

p

les amply illustrate that serious conse

q

u

ences are likely to resu lt if

proper attention is no

t

paid to the geological conditions occurring at the dam site.

Geological studies at the dam site will also suggest which design will be suitable for a given

geological context.

F

o

r

example,

grav

ity dams need very strong and competent fou

n

dation

roc

ks; for

buttress

d a m s ,

relatively less strong foundation rocks are

enoug

h ; arch dams

n ee

d very strong and stable

abutment

rock

s; for earth dams, even weak

foundatio

n rocks meet

t

h

e

r

e

quire

ments.

qu a

ntities near the

s

ite. Otherwise, the cost of construction will increase.

Thes

e critical details of c ivil

engineering importance, i

.e .

, durability and competence of foundatio n roc

k

s, their depth

of

occurrence,

availability of b u i lding material near project s ites, can be re lia

b

ly

ob ta ine

d from

g eo

logical a

n

d

geophysical studies .

The significance of geology w ith reference to civil engineering w il l be better appreciated if the

consequences of ignoring geological studies are also

quo ted

. Therefore, a few specific e

x

amples of

fa i lures of

d

iffe

r

ent kindsofimportant

c iv il

constructions are

li

sted now. Further details ofthese failures

are given unde

r r

e

s

pective chapters.

6

Textbook of Engineering Geology


16/407Copvr iqh ted mater c t l

1.3 .

1 A cadem ic

Im

portance of Geo

l

og

y

The stu dy

of

details of academic s ignificance of geology

is

no t

w it

h in the p

u rv

iew

of

the subject of

enginee

ri

ng geo

l

ogy.

B u

t at the same

ti

me,

i

t

i

s worth knowing from cu rios

i

ty and

i

ntere

s t po i

nts of

view some

o

f the

u nb e

lievable

a

nd s

tart

l i

n

g

fac

ts

ab

out

ou

r earth a

n

d its his to ry

,

which

a

re given as

follows:

I. The H im alayas, the tal lest m o

u n ta in

s

of th

e

p

rese

n

t d

ay

, are relati

ve

ly

o

f rece

n

t geological age

whose

grow

th was witnessed by m an . They are m ade up of mar ine

fo rmat ion

s s ugges ting th at t

h e

ir

p lace w as once occupied b y a narrow sea

(Tethy

s).

G

eol

ogy

is

one of the

m o s t

in

t

eresting and useful su bjec ts for the

l

ayman and the knowledge

ab l

e

peopl

e

alike. This is the only su b ject which gives information about the earth. Some

of

the details regar

di

ng

its

ac a

demic and

a

pplied im portance are

a

s follows.

1.3 S C

OP

E

O

F GEOLOGY

With R

eferen

ce to Roads and

R

a

ilway

s

The erstw h ile problem of freq

uen

t bou ld

erfa

lls al

on

g some sections of Bor G

h

at

o

n the Bombay-Pune

line

is

one of the examples that may be quoted to highligh t the importance of geological studies at

the s

it e .

Thus, to

ens

u

re safety

,

s t ab i lity

,

s

u

c c e ss

a

nd eco

n

omy i

n a

l l majo r civil

en

gineering co

n

structio

n

s ,

geo

log

ical

s t

u d ies are very important. The most im portant

an

d common geol

og i

c

al fa

c

tors

wh

ich

co

n tr i

but

e to the

s

u

i tabi l i

ty or

unsuita

b il

i

ty of a

s i

te for a given pu rpose are existing

roc

k types,

as

s

ocia

t

ed geological

s

truct

u

re

s and ground

wa

t

e

r con

di

tion

s

.

Occ

u r rence

s of

l

ands li d

es

,

earth

qu ak

e

s,

land

s

u b s id

e

nces, high snowfall,

w ate rl

ogging, type ofnatural forces like rivers,

e

t

c., at the propos

e

d

s ite are some other geological factors w

h

ich may need spec ial study f

o

r taking

p

recautio

n

ary measures.

Geological know l

e

dge can also be utilized w h

e

n n

ec e

s sary in dea ling with h uge b u ildings,

runways, te

rr

ain

eva

lu

atio

n for military operation

s

and d

efe

nce purposes.

It is to

b

e borne in mind that the role of geology in civil e

n

gineer i

n

g is to

in d

icate (at

d

ifferent

stages like d

e

signing

a

nd con

s t

ruction) in adv

a

nce the existing

draw

b acks, if

a

ny , of the sites, so that

suitab

l

e precau ti onary steps are taken to

over

come them and sites are

m a

de safe for u n

de

rtaking

cons truction.

It

i

s no

t

a

ru l

e that

geo log i

cal

co

nd

i

ti o ns

s

h ou ld be adverse e

veryw

h

ere

,

th o

u gh in practice ideal

s it

es are rare. Failures of

vario

us

earl

ier

struct

ures due to

di f fe re

nt

geo l

og

i

cal causes

h

ave now made

it m

a

ndatory to have

geologic

al clear

a

nce before taking up m

a

jor con s tr u c tions.

This

w ill

ens

u re risk

free

i

nvestment of time,

m o

ney and

ene

rgy.Nat

i

onal organizations like the Geo

l

ogical Su rvey of In dia

an

d the Natio

n

al Geop

h y

sical Research Institute

d

o t

h

e

n

eedful in th is regard.

With R

ef

erence to Bridges

The failure of a bridge near Cornwall (Canada

)

and

di f f icu

lti

e

s faced in the con s tr uction of the Georges

ri

ver b

r i

dge il lustrate the consequences of im proper or

incom

plete study of geo

l

og

i

cal cond

i

tions of

th

e s ites concer

n

ed.

S

tro

n

g

an

d

s

t ab l

e

ro c k

s are

n eed

ed for

fou

n

da

t

io

n

s

an

d

ab

utme

nts. Adverse geo

l

ogical

s

tr u

ct

u

res

sho

u

ld

no

t occur

a

t the

site

.

Geolog

y 7


17/407Lopynghted m2tennl

2.

T

he Indo

-G ange t i

c

plain s ,

the most fertile la

n

d of our co

u

ntry, and the seat of power of many

dynasties are su rprisi

ng

ly of th e most recent origin in geologica l t e rms .

3.

In contrast to this, the D eccan

p

lateau, w hich is ad

j

acent to the Indo-G a

n

getic

p

la ins , represe

n

ts

the oldest age and may be a piece of the primordial

crust

i

tsel

f.

4.

Th

e fossils pr

e

se

n

t i

n rocks of different geological ages

provid

e

c

o

nvincing proof of evol

u ti o

n

of

life from the beg inn in g to the present d

ay

. L ife originated in the sea and then extended to la

n

d.

Th

e trend was as follows:

s

o

e

>- U

n g

8 s

: : > "

e s


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142/407~opyngh ma

n 8 1

P

r

operti

es and Uses

C

hamockit

es are

hard

, s trong

an

d durab

l

e roc

k

s with a high

lo ad

-bearing

capacity

. Like

o

ther

pl

utonic

rocks t

h

ese are also

n

on-porous and

impermeable

. They do not have

a

ny weak

p

lanes like

bedding

,

s ignificant banding or foliation. They are suitable for

a ll

civil engineering wor

k

s . H

o

wever, their colour

is

b

lackish.

M

ahabalipuram temples (Tamil Na

du

) were constructed many centuries ago from

charnoc

kites.

The

chamockite

s of peninsular India are claimed to

b

e

o n

e

among

st

th

e stronges

t

and the most

durable s tones of t

h

e

wor

l

d

.

Structure and Texture

Li

k

e other

p

lutonic rocks

chamockite

s also are

compac t

, massive, dense and

n o n

-porous (

imperviou

s ) .

Texturally, these are

phane

ric coarse

g

r

a

ined. Fol

i

ation and bandi

n

g

o

c

c

ur sometimes o

n

ly for s hort

l

e

ngths.

A

vailabili

ty

C

harnockite

s

,

w h

ich are Archaean in age , occu r

w i

d ely d

i

st

ri

buted in peninsu

l

ar India and form a

portion o

f

the Nilgiri hills and so

u

thern parts

of

the

E

astern and W e

s

tern gh

a

t

s . Ta

mil Nadu

,

Karnatak

a

a nd

,

to

s

ome

extent

,

A

n

dhra Pradesh have

l

arge and good

ou

t

cro

p

s

of

c

ha

rn oc k

ite

s

.

Appearance

of

C harnockite in Hand Specim ens

Mega

s

copically, i.e. , in hand spec i

m

ens, all c

h

amocki

t

es, irrespective of

t

heir composition,

ar

e

melanocrati

c , i.

e.

, b lack coloured. All are p

h

an

e

ric coarse grained and equigranular with shining laths

of f

e

l

d

spar.

l

n acidic varietie

s

, greasy looking bluish grey quartz oc

c

urs.

Mine

rals

Presen t

A

ll chamoc

kite s

ar

e cha

r

acteri

z

ed by an abundance of feld spars and

pyroxenes

, particularly

h y

persthene.

Acid

i

c chamockites are like hypersthene

granite

s

, rnineralogically,

i.e.

,

they

ma

in l

y contain

feld

s

par

s,

quartz and hypersthe

n

e. The

i

n

ter

media

t

e and basic types are equivalent to

qu

artz norites and norites

res

pecti

v

el

y

. (Norite is like gabbro. The

d

iffere

n

ce

i

s t

h

at the

py

roxene present in gabb

r

o

i

s

augit

e,

but in

nori

te the pyroxene is

hypersthene

. Both have the la

b

radorite type of plagiocl

as

e

f

eldspar in

addition.) T

h

e ultrabasic ( i .

e.

, silica-poor) type of chamockite is

e

quivalent to pyroxenite.

Mode of Origin

Though chamocki

t

es are con

s

idered as igneous rocks, they

s

how peculiar characters diagnostic of both

igneou

s and

met

amorphic rocks. Hence

t

here

i

s a controversy about their origin. Throwing off tongues

and veins

in

t

o

surrounding rocks b y the

c

hamoc

ki

te body and occurrence

of

features

ind

icative

of

partial

a

ss

i

mi

l

ation

an

d

h

ybri

d

ism

strong

l

y support

t

h

e intrusive and

igneou

s origin

of

c h

amockit

es

.

But (i)

t

he occurrence (though occ a

s

ion

a

lly) of typical metamorphic minerals Like cordierite and garnet,

(i i)

th

e occurre

n

ce of gneissose stru c tu re

, (

ii

i

)

t

he myrmek itic growth of quartz and

fe l

dspar and

(iv

) sporadic

ro

und quartz grains

en

closed by

fe lds

par

s

tr

o

ngly support the metamorphic

or

igin

o

f

charnockite

s .

Cbamockites are believed

t

o have been formed

o

ut of recrys l31lization of igneous roc

k

s

u n d

er

condition

s of

high temperature and

pre

ssure (i .e.

, of

p

l

utonic

metamorphi

sm).

in colour and texture. These genetically related rocks are called c

h a

mockite series. This series

i

s a

l

so

call

e

d N il

g

iri gneiss or mountain

gneis

s .

Ig neous Rocks 13 3


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171/407~opyngh ma

n 8 1

Pressur

e

The pressure

w h i

ch

cause

s metamorphism

i

s of two different kinds, namely, uniform pre

s

sure and

dir

ected pressure. .

Uniform

pre

ssu r

e increas

es with depth (i.e., with increasing overburden), I

t

acts vertically

'

do

wnw

ards and affects the

volum

e of both liquids and solid

s

. Naturally, its effect is significant only

at great depths, but not at or near the surface. This also means that high temperatures will also be

as s

o

ciated (d u e to th e depth fac tor) with high uniform

p

ressure. So, both of them act together

an

d

bring about

m

e tamorphi

s

m in rock

s .

T

e

m p

e

ratur

e

The source of temperature w hich is res

pon

s ible for metamorphism is either due to depth or due to

the contact with magma (i.e., magma chamber or magmatic intrusion). The metamorphic changes

mainly take place in the temperature range of 350

-

850 C. The temperature rise also increases the

c

hemical

acti

v

ity in rocks and

f ac i

l

itates reacti

o

ns during metamorphism.

8.1 .

1

Metamor

phi

c

A

gents

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

c

hemic

a

lly active fluids. These three are known as metamorphic agents. Generally, all these three

a

ct

tog

ether and

cau

se meta

morphis

m.

But

, sometimes, any one or two of them may dominate and p

la

y

an active role. The

follow

ing are a few relevant details about metamorphic agents.

The word metamorphism means c

h

ange of form

m

e

ta =

change;

morpb =

form).

In

petrology, it

indicates the e

c

t

of

temperature

,

pres

s

ure and chemically active s o lutions over the texture

,

minerals

and compo

s

ition of parent rocks. Igneous and sedimentary rocks which serve as parent

r

ocks are formed

und

e

r a certain

phy

s

i

cochemical

enviro

n

ment,

i

.

e

.,

at the

t

i

me

of

their formation, they were

in

equilibrium with their

surroundin

gs in terms of temperature, pressure and chemically active fluids

.

Subsequent to their formation,

i

f any of these fac

to

rs c hanges significantly, the equilibrium gets u pset

and necessary metamorphism, i.e , textural, compositional and m ineralog

i

cal c

h

anges take place to

create a new equilibrium. This means the constituent minerals, texture and composition of parent rocks

b y

metamorphis

m change over to new minerals or new textures or new compositions which are more

s

table and

s

uitable under new conditions. For example: As a result of metamorphi

s

m (i)

gra

n ite, one

of tile mos

t

abunda

n

t igneous rocks, changes to granite gneiss; (i i) periodotite, an

u l

trabasic igneous

rock, changes to serp

entin

e and talc sc

h ist

; (iii) gabb

r

o (or

dolerite)

, an intermediate igneous rock,

ch anges into

hornbl

ende

schis

t. Among sedimentary rocks (iv)

sandston

e changes into quartzite;

(v) limestone

c

hang

es into

marble

;

(

vi

)

s

hale changes into

s

late and

s

o

on.

The

ran

ge

of

temperatur

e

and

pre

ssure w h ich occurs

i

n nature is very w

i

de

.

The normal surface

te

mper

a

tu

re and pre

s s

ure affect the rocks by

caus

ing weathering At the other extreme, intense heat

in the

s

ub

s

urface

(

at great

depth

s) melts the ro

c

ks and produces magma. As accepted by many, the

term

m

etamo rph i

s

m does not include either weathering of rocks or magma formation. The extreme

s tate

s

of

metamorphi

s

m ar

e

represented by palingenesis or

ultrametamorphi

sm

or anatexi

s. In these

the

inten

sity of temperature and

pre

ssure will be

s

o high that it

involve

s partial melting and mixing

of rocks. Since the identity of the altered

roc

ks

i

s not totally destroyed, in these

s tates

, they come under

metamorph

is

m

They are next only to the formation o

f

new

magma

8

1 MET

A

MORPHISM

162 Tex

tbook

of

E ng

ineering

G eo lo

gy


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book.


198/407Copyright~ m rial

~~

c

"tl .

0 1 ; l

~

~

-

e

o

O .

5 ~

" . , ,

. , . ,

O - -

3 Q, c :

e

e

.

.,,

0::

"O

c

-

~

}

" '

.

. , ,

a

~

i

5

" ' -

~

"

c

c 0

-

vi

- "tl

" "

a

'l

ti)

. , , "

" ' -

l a

. .

~

0

~ ~

t \

0

o-o

- -

M

-

'

8

~- 0 ":

- "'

; ; ,

-

. , .

"'

- "'

M 0 ':.

-

- "'

. .

0

-

" '

. , .

s

0

"'

-

-

00

: : a

" '

0

E

oo

. . , .

~

N

"'

oS

-

-o

"'

" '

~ 0

" ' -

.

- e-

"'

00

" '

0'

- -

00

e-- a-

'

-

So~

oo

~

.

~

" "

c E

~~

'- ~

.

0 "

., c O

~~

co~

c:

a

:;I ..

0

0: :

""

- 0

r - :

ci - -

0

-: 0 .

-

- ;;;

Ci

"' . , ,

0 ~ Q

-

-

-

" '

II

O

N

~

: 1 O ' E

" c

c r S :) ,. . Ii)

.&: - -

bO u

f

c

:;I .....

0

0

c >

F ~


199/407

have

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200/407

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have

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202/407Copyright~ m rial

Case

I: When beds d

i

p in the direction opposite to the s

lo

pe o

f

the valley: V po ints

u

p the

va ll

ey

.

Case 2 : When beds

d

ip in the same di

re

c t ion as the

s

lope of th e

v

alley

an

d at a greater angle:

V po ints

down

the

vall

e

y .

C ase 3: When beds are horizo

n

tal or dip

i

n the same

dire

ction as the s lope of the valley and

at a

smal le

r angle: V p oi n ts up the va l ley and is longer than in Case I.

Fig.

9.2

Valleys and

s

hapes of outcrops

Case 3

1 0 0 0 i;'"~~ti:::::. . . .

J

r T

T

500

,_

Case 2

500

1000

Case 1

500

1000

any direction

a

l features.

H e n c e

, such rocks even if fo lded or faulted do not provide any indication

of

them. Therefore, they are unsu i t ab le fo r study

of

geological s t ruc tures . For a similar r ea son ,

metamorph ic rocks , such as m a r b les and qu artz ites, which bear a predominantly granulose s t

ru

cture,

are also unsuitable for

t

he s tu dy of th ese

type

s of

st ruc ture

s.

Structural Geolog

y

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Enginnering Geology- N Chennakesavulu

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