Indian National Committee on Large Dams. Design and Construction Features of Selected Dams in India

'oo

2t66.OO

[zRodiol

go|re a{ x25'

K.

R.L.19

70

K

R.

L

.t84?.

E

o

!

lF

o

x

Non

overflow

section

KOynO

K.R.

L.Zlo9

K. R.Lr900

FIGURE

5.1

:

Koyna

Dam

section.

Crest

KR.L.2r33.5

2O95'OO

tongent

point

,o.#H44e8--

Dom

section

ovenflow

section

1956-61

K.R.L.1906

Modified

for

98pOO

fvtcf

t

(finor

I

I-

98,OOO

M

cft.(finol section

os

constructedl

II-

73,OOO M.

cft

lll-

98,OOO

M.

cft.

-t(#

(er(inoll

-

Figule

5.1

shows

the

three superimposed

sections

of

overflow

and

non-overflow

dam

for

2,773.4

M

cu

q

(98,000

M cu

ft), for 2,066

M

cu

m

(73,000

M

cu ft)

gross

storages.

5.4 It will

be

noted

that

the

foundation

of

the over-

flow

dam

went

down

to

about 1,840,

i.e., about

18.3

m

(60

ft)

below

exposed

rock

bed due

to

revela-

tion of

thick

inter

trappean

softer

rocks,

and inadequate

good

rock

cover.

5.5 By

1957-58

it

came to

be

realised

that

the

Stage

I

block

of

power

would

be sold

out

as

soon as

it is

generated

and that

the l0-year

gap

between

the two

stage

earlier

anticipated

has

disappeared.

Accordingly

step

by step it was

decided

to

construct

the

dam

relevant

to 2;066

M

cu m

(73,000

M

cu

ft)

gross

storage

in

one

go

but

excavate the

foundations

to a

width

relevant

to 2773.4

M

cu m

(98,000

M

cu

fr) storage

and

cover

it with

concrete,

and leave

a ledge to start

the shaping

for 2,066

M

cu

m

(73,000

-M

cu ft)

storage.

No

such

horizontal

ledge

was

possible

in

the

spillway portion.

generator

during

the

fair

weather

196l-62.

This

target was

achieved

in

monsoon

l96L

and

the first

unit went

on line

in

the

middle

of April 1962.

5.7 In

1958-59

a

good

suggestion was

made

to

do

ull blocks

(non-overflow

an0

overflow)

to a

shape

relevant

to

2773.4

M

cu

m (98,000

M

cu ft)

gross

storage,

as it

would

be

(t)

much

cheaper

to

do so'now

than

by

adding

concrete

at the

back

at a

later

date.

\.v*Fe

+*d

r47

(r'r)

thg

ba-g$ng

concrete

in

the spillway

will

be

both

difficult

and full

of

problems,

-including

rehabilitating

gates,

unlesi

otherwise

conver-

ted

into

orifices

by

a

bellmouth

breast wall.

(ttr)

The

extra

cost

of the

additional

concrete will

be

a

viable

investment

because

of

the increase

in

the

.

average

operational

head

for

power

generation

due

to

the minimum

dralidown

level

rising

from

El.

2,000

to

about

EI. 2.0g0

or

so.

Tbe

advice

was

no doubt

excellent,

but

it

involved

a_n

extra

placement

of

slightly more

than

2g,3g0

cu m

(l

M

cu

ft)

of

concrete

to achieve

the

one machine

acceptable

to

the

power

utility

(it

is

at

that time

the

only

-utility

to

be

served).

The-irrefutable good

advice

could

not

therefore be

accepted.

5.8

In

March

196l

when

it

was

foreseen

thar

the

interim

target

of

one

machine

storage

for

2 months

5.10

Once

the

overflorv

section

needed

no

backing,

a

deeper

study

was

made of the

non-overflow

section.

Except

increased

density

no other

redeeming

feature

was

available.

Then

it

came to be remembered

that

at

148

(f)

lake

at

minimum

drawdown

level

of

Er.

2000

or

at sluice

sill

level

of

El.

1960.

(ii)

lake

at

MWL

of

2773.4

M

cu m (9g,000

M

cu

ft)

gross

storage.

5.14

The

amended

and

adopted

cross-sections

of

the

dam superimposed

over

old

ones

can be

seen

in

Figure

5.2.

The

economy

caused

in

the

quantity

of

concrete is

easy

to note.

5.15 Figure

5.2

is

a longitudinal

section

of the dam

shorving the levels

reached

on

the various

blocks

from

1958 to

1963.

5.16

All

this change

was

conceived,

computed and

got

sanctioned

in

the

tense

period

when

Maharashtra

was

confronted

with

a

disister

due

to

the

failure

of

the Panshet

Dam

in

early

July

1961. Financial

and

administration

procedures

to

defermine

supplemental

contracts at Koyna

added

to

the

severe

tensions of the

umes.

to

!

C

o

0

o

tr

No

ro@99!

cl

FIGURE

5.2

:

Koyna Dam-Progress

of

concreting.

trlonolith

o

N

99

Con61g1g

plocernenl

Nt

t957-

58

r

t958-59

trl

t95g-60

-Et

t9@-6r

NI

t96t

-62

wa

tg62-63

El

Rorrdom

rubble

t,l('sonry

trgN

'.

l,

,t,

5.17

It

was

never even

dreamt

(1961

and

1962)

that

this area

would

soon turn out

to be seismically

active

and that

an

abrupt

and

severe change

ofl

slope

on the

downstream

face

at

El.

2,060 and an

increased

inertia

mass

at

top due

to

wider

top

widths

are

undesirable

features

under severe dynamic

conditions

and

from a

stress concentration

ioint

of view.

5.18

It

was

in

this

period

that

the l95l

dispensation

of

the

Planning

Commission limitirrg

diversion

to

1911.6

million

cu

m

(67,500

M

cu

ft) for

power

genera-

tion at

Koyna, was

held

as

legally

void.

The

Krishna

Basin

participant

States

(1962),

viz.,

Andhra Pradesh,

Maharashtra

and

Mysore

(now

Karnataka) could

not

come

to

a

mutual

agreement

in

regard

to

sharing

of

the

75

percent

dependable

annual

runoff of

Krishna

Basin.

The matter

got

ultimately

referred to

an

Inter-

States River

Disputes

Tribunal.

Till the award

was

declared

in

1974,

Maharashtra

could

divert

as

much

as

it

could for

power

generation.

It

did

not cause

any

adverse

effects'because

many

projects were

jet'to

be

undertaken

in

the basin

states

and

the few

that

were

started were

incomplete.

Expeditious

completion

of

Koyna Dam

with

gates

by

(1965-66)

and installation

of

the

second

stage 4

units of

75

MW each

by

1966,

enabled

an annual

generation

far

in excess

of

the

original

concept

with

a

limit

on

quantity of

water

to

be diverted,

and

thus enable

the

project

costs

to

be

amortised very much

earlier

than envisaged.

t49

t

a

6.1

In

the

1962

monsoon,

the lake

was

filled

upto

about El. 2075.

Mild

tremors

accompanied

by

sounds

started

being felt thereafter. Three

seismo-

graphical

stations could be

established

around

the

Iake

by

,1964

and

a fourth

one in

the dam

itself.

6.2

This

phenolnenon

was

the

subject

matter

of

C-13

to

ICOLD

Congress

September

L967

at Istambul

where

Q-35

"Dams

in Earthquake

,Zones

or

other

Unfavourable

Situations"

was

Scheduled

for

discussions.

Dr.

Shunzo

Okamoto,

Emeritus"

Professor

in

Japan

9g

Earthquake

Engineering

was

the

general

reporter.

Most

papers

were

theoretical

dissertations

and none

was

a

case

study of the

behaviour

of rigid

gravity

dams

FIGURE

6.1 :

Epicentres

of

some of

the

earth tremors

recorded

at seismological

observatories

,

around

Shivajisagar

lake.

I50

Seetion

lzI-S

eismie

phenomena

during

and after

an

earthquake

with

an epicentre

very

near

the dam.

Most

papeis

dealt with

either concrete

arch

dams or

earthfill

dams,

but

none

touched

concrete

or masonry

gravity

dams

under earthquake

conditions.

Thil

is reflected

in the

subjects

posedfor

discussion by

the General

Reporter.

"(f)

Antiseismic

design

criteria

for arch dams.

(if)

Further

research

and survey

required

to be

carried

out in

regard

to

earthquake resistant

problems

of

fill

type ilams."

6.3

While

at Koyna

(the

famous city

where Maulana

Jalaludin

Rumi expounded

and

established

Sufism)

during

the

study tour

that

followed

the Congress

(September

1967

at

Istambul)

the two senior

authors

of this

paper

learnt

through radio

news that

a

fairly

severe

shock

was felt

at Koyna on 13th September

1967.

Earlier

Dr. S.

Okamoto was

requested

to

break

journey

at

Bombay

on his way

back to visit

the Koyna

Dam site.

He

did oblige.

6.4

About

154 shocks

were recorded

from

10th

September

L967

to

lzth September

1967.

Their

magnitude

varied

from 2 to 3

in the Richter

scale

as

illustrated

in

Figures

6.1 and 6.2.

On

13th

September

1967

it

culminated

in two

shocks

(origin

times

06-23-31

and

06-48-25

GMT) of magnitude

5 to

5.5

(as

deter-

mined

by

Indian Seismic

Observatories)

with epicentres

near

the

dam.

The

focal

depths were

to be

5

km

deep

seismologically

or

l0

km

deep

according

to

intensity

and

value

of

magnitude.

de'signs

as

a

check

up.

'

-

that

the

worst

was over.

60

50

.^ 40

L

\J

E

q)

L

b30

t-

o

-o

E

l

zzo

I

9:

ol

fl

@r

cl

+'l

LI

8l

cl

ol

>i

,r

t-

I

r

L

i-

I

F

I

F

i-

I

r

I

F

I

F

I

r

F

I

rO

explained

either

as

"There

were

two

shocks-

one

with a

deep

focus,

and the other

with

a

shallo$ier

hypocentre.

The

first

one €used

the

shock

to

be felt

at

long

distances,

while

the

second

one

explained

the

large

intensity

in the

epicentral

area."

or

in

the

epicentral

area".

-*ozlri-e-ozlte-c"6

r4'967lti{-6

FIGURE

6.2

: Frequency

distribution

of

foreshocks

and aftershocks

obtained from

instruments

of Koyna

observatorY.

,-tli,

!--1

,

-,

ee e.orialecrl2cc$rl

6.8

The

earthquake

tazed

to the

ground

the

Koynana-

gar

construction

township causing about

180

deaths

of

mostly

young

people

and

children

fast a sleep

(04.2i

A.M.)

and

the total

deaths including

those that

occurred

in the

nearby

villages

was

assessed

at

about

270. Photos 6.1,6.2 and 6.9

illustrate

the damages

in

to

the country

side and

Photos 6.4,

6.5,6.6

6.7,6.8

and

6.9

illustrate the damage

effect

on the dam.

6.9

The frequency

and

distribution

of foreshock

and

aftershocks

in December 1967

are as

shown

in

Figurc

6.3.

6.10

Due to

cut-off

of

power,

the

accelerograph

in

tion for

which

the safety

of dam

was

checked.

6.ll

The

lake

was near full

at El.

2144,

4.35 m

(14.5

f0

below

FRL.

That

the

dam

withstood

the

Doys

-.'-t##

151

PHOTO

6.1

:

Crack

in

the road

near

Koynanagar.

PHOTO

6.2

:

Collapse

of

a

house

at

Koynanagar.

pHOTO

6.3

:

Collapsed

bridge

near

Helwak.

most

unexpected

reve-rest

shock,

but

with

minor

bruises

is

the

Giace

of

God.

-

d;;;;uld

rather

swoon

rhan

think

of

the

damage

trrui.ourd

h;;;b;ei'clusea

uy

the

failure

of

.the -&gr.

--iiJxposed

the

large

areas

of

ignorance

in

F"

g.fie"

*ri..pt

and

approach

to

dynamic

stability

of

da'ms.

-""'

6.12

Other

works

of

the

water

conductor

system

from

the

intake

to

the power

ho;;;"J;;ffi;;ili'i

po*r,

h

o

u se

co

m

pr

ex

.

.rrvit

h

stoo

;

]G;h

";i;fr

u".ll[rv

well

with

negligible

distress.

rators,

tripped

on

overspeed

were

on

low

load

(4

AM)

no

overspeeding

even

if

all

i,erspeed.

gear

operated

pre-

;yroscopic

action

of

ine_

.e

the

major

shock.

Minor

lngs

were

not

serious.

6'14

In

the

outdoor

switchyard

the

six

insurated

porcelain

disc

stacks

rigfdry'mounted

on

steel

lattice

pedestals

broke

due

to

osiittutory

actions.

)rators

were

hand

tripped,

ped

for

safety.

The

whole

'

statlon

was

plunged

into

reratron

personnel

was

low.

but

no

deaths

in

the

lower

ris

staff

rallied

to

serve

and

0 hours

after

the

disastrous

'of

the

little

damage

to

the

ralanced).

There

lfter

the

service

at

one

day

or two

r52

1..€%@€%*

eiilq

&

+4*J+FrFtfff

153

PHoTo

6.4

:

Dor'nstream

face elevation

of

Koyna

Dam

shorving

leakage

spots.

j

--

+n'.

-

,:

PHoro

6'5

:

Enlarged photo

of

leakage

on

downstream

face

of

Kolna

Dam

(left

bank)

monoliths

24-30.

PHOTO

6.6

:

A dry

crack

on

the

dorrnstream face

about the level

of

change

of

slope.

t54

PHOTO

6.7

:

Damage

at the

bearing of

T-beams

of

spillnay

bridge.

PHOTO 6.9

:

Crack at

the root

ioint

of

pier

with

ogee

cresl

PHOTO

6.8 : f)amage to hoist

tower.

52

48

4

40

e36

c

?sz

o

L

-28

oza

L

c)

€ro

2'.

t2

I

9lrol

tl

Ddc

DoYs--

(Jon

19681

FIGURE

6.3 :

Frequency distribution

of

foreshocks andaftershocks

obtained from

instruments

of Koyna

observatorY.

3P

155

ACCELEROGRAM

RECORDED

AT

BLOCI< I-A

OF

KOYNA

DAM

ON

DEC. I t.t967

AT

O4-2r LS.T

HORIZONTAU

COMPONENT

TRA,SVERSE

TO

DAM AXIS

THIS

PART

OF

RECORD

FAINT

VERTICAL

COMPONENT

HORIZONTAL

COMPONENT

ALONG

DAM AXIS

oro2c

304c,

TIME-SECONDS

,

r

,

r r

o

o.5

t.o

ACCELERATION-9

NOTE:

l. col"lPARED

wlrH oRIGINAL

AND

coRREcrED

oN ApRtL

3,

t96B

AT

scHooL

o.F RESEARCH

AND

ThAtNtNc

tN

EARTHoUAKE

ENGG,RooRKEE

By

pRoF'A.s.

ARYA

ANo

pRoF.

c.

TAMURA.

2.TRACING

tN tNK,

cHECKED

By v.p.

GuprA AND a.S.

anva.

FIGURE 6.4.

156

Indian National Committee on Large Dams. Design and Construction Features of Selected Dams in India

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