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

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310

PHOTO

3 : Idukki

Arch Dam and

reservoir-view

from

left

bank top.

consultants

were

satisfied

that all works

have been

done

before

concreting

any lifr.

A number

of

forms were

developed

to

ensure

that

all

quality

control

operations

were

done in time.

This

ensured

placement

of

proper

quality

concrete

in the

dann.

Materials

of

Construction

Concrete

Swift and

systematic concrete control has been

exercised in

each

and

every

phase

of

construction of

Idukki

Dam.

The

quality

control

works

were

centred

around

a well equipped

laboratory established in the

field.

Cement

The

cement

required for

concrete

was obtained

mostly

from

Sankarnagar factory

near Tirunelveli

in

Tamil Nadu,

belonging

to M/s

India

Cements

Ltd.

Routine tests

to determine

the

quality

of cement

received

were

conducted.

1.25 lakh tonnes of

cement

was

used in the

construction

of Idukki Arch

Dam.

Aggregates

The

different

grades

of aggregates

required for

the

concreting

were

mainly

produced

out of

char-

nockite rock from

the

Central Hill

Quarry.

To

augment

production

a second

quarry

on the left

bank

of

Cheruthoni

Dam

also was

commissioned

for

some-time

The

following

tests on coarse

aggregates

were coD-

ducted

to

ensure

its

quality.

(1)

Specific

gravity.

(2)

Absorption.

(2)

Crushing

value.

31t

(4)

Impact

value.

(5)

Los

Angeles Abrasive

test.

(6)

Soundness

test.

(7)

Flakiness

index.

(8)

Bulk

density and

voids

content.

(9)

Moisture

content.

(10)

Tests

for

grading,

correction,

grading

require-

ment,

significant

oversize

and undersize.

On

the fine aggregates,

the tests for

specific

gravity

and

absorption were mainly done.

The

sand

produc-

ed

from

the

aggregate

processing

plant

was

analysed

every

hour

and required

corrections

were effected

immediately.

Moisture

content

and

gradation

of

sand

eollected

from the batch

bins also

was

found

every

hour

and

the mix corrected on this

basis.

Pozzolana

No

pozzolana

was used in tdukki Dam

concrete as

suitable

pozzolana

could

not be located.

Air-Entraining

Agent

The AEA

used

in

the

clncrete for

Idukki

Dam

was

prepared

at site

usin-e

caustic

soda

and

'K'

grade

resin.

The

dosa-ue of AEA

ryas

kept at 0.4

percent

by weight

of

cernent.

Other Adntixtures

No other

admixture

was

used

for

Idukki

Dam

concrete.

Concrete

MiXes

for

ldukki

Dam

)

,

For

Idukki

Dam,

the

design

strength

of concrete

tvas

fixed

at 281.2

kg/sq

cm

(4,000

p.s.i.)

on

45.7

cmx9l.4 cm

(18

in.x

36 in.)

cylinders

at365

days.

This

design strength

was

equivalent

to

281.2

kg/sq

cm

(4,000p.s.i.)

on

15.2 cmx30.48

cm

(6

in.x12

in.)

eylinders

at

90

days.

At the

beginning, a

cement content

of

250

kg/cu

yd

of

concrete was adopted.

By the quality

control

exercised,

it was

possible

to

bring down

the cement

content

from

250

kg

per

cu

yd

to

180

kgicu

yd.

Quality

control'

efforts

reSulted

in

substant'ial

savings in

the cement

used for

ldukki

Dam.

Grouting

For

the convenience

of

construction

and

to

prevent

formation

of

cracks

in

concrete

during

constiuction,

Idukki

Dam was

divided

into

24

blocks

of

approxi-

312

T.ate]y

lf

*

length

by

means

of

contraction

joints.

The

blocks are

odd

numbered

from I

to 27

on

tle left

(Figure

4).

Before

the

loads

are

brought

on the dam,

overall

monolithism

of

the structures

is

to

be

ensured for

transmitting

the load

to the

abutment

and

foundation

!y

effective

arch

and

cantilever

action.

Two indepen-

dent

systeTs

of

grouting

were

adopted

for Idirkki

Dam grouting.

-

The

first.systeq

€etq,lting

was

adopted

for

grout-

ling

the

joints

of Idukki

Dam

the

second

system

being kept as reserve

(Figure

7).

Tlr"

grggt

compartments

are

generally

of lg.3

m

(60

f0

hgight and

bounded

on

ail

sidei

by

p.V.C.

seals.

The

space

in-between

the

upstream

monel

water

seal

and the

downstream

p.V.C.

water

seal

fixed near the

upstream

face

of

the

dam

is

also

grouted.

The

transverse

joints

are

provided

with

keys.

The

layout

of the

qrout

tubing

do

not interfere

wittr

the

provision

of the

shear

keys

in

the

joints.

Construction

Survevs

The

steep

terrain

at ldukki

Gorge

made

it impossi_

ble

to successfully

carry

out

the

conventional

counter

survey at the

site. Professor

Konecney

of

Canada

was

commissioned

by-th-.

consultants

for

carrying

out

the

'uvork.

He

established

a

few

control

staiiois

in

gu-t

by

_

the

method

of

terrestrial

photogrammetry.

After

the orientation

has

been

estabtished

the Easl-

North co-ordinate

system

was

transformed

into

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o

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3t4

grt^q

syqlem

with

Y-axis

having

an

incrination

or.3gn

-9'-47.10"

to

the

North

lini.

Horizontal

control

of

block

-

Iayout

was

done

by

setting

out

refer,eSce.

poinls

calleJ"

-

e'

pJi"i

o,

.d'

p-oint

for

each

block.^

'A'

pornt

was

established

in

the

block

from various

control

stations

on

the

banks

outside

the

da.m

profire

by

intersection.

.B'

point

was

established

by

intersecting'the

oiagon"r,

"r.i.t,

block

at any

elevarion.

After

establishin;

;A,;Jilj

o.

.8,

point

on

a

block

lift,

a

theod;iil;

*;,

,'J'^ou.,

the

point

and

back.

sight

taken

on

an

externar

station

to

compute

the

azimuth.

Then

deflection

unei",

were

turned

from

the reference

rine

and

aiiiu"".,

iireasured

accu-rately

from

',A'

on

'B'

point

as

tt.

"*.-

may

be

l?^ll.

tj

poilqt

fixed

around

the

peripr*ry

of

jach

blocl(.

Six

points

each

on

the

upstream

aoO

down_

streLry

segments

and

one

point'

.u.tt

on

Jtr.

sides

totalling

14

points

define

ttr"

rnup.

oi

u"v

-llr,

in a

block.

-

Pr_.ggmputed

values

of

the

distances

and

angles

from'A'and

.B'point,

to

tn" p.ripi.ry*piin,,

of

all

lifts

in

all

blocks

were

made

use

of

foi

th;

brock

setting

out.

Other

Features

in

the

Dam

A^system

of-

25-cm (10

in.)

diameter

drain

holes

were

formed

in

the

dam

'.oncrete,

rouiln-.uln

block

to

relieve

pore

pressure

in

concrete.

These

o.uior'extend

from

near

top

of

tlre

dam

to

the

lowest

gallery

in

each

block.;A.

sygt-em

of drain

holes

driiled

f;;d;

out

into

the

foundation

and

abutment

rock

drain

the

foundation.

A

network

of gareries

is

inco-rporated

in

the

dam,

intended

to

accomplish

foundario-n

olirrinI,

Irouting

and

drainage

from

within

the

dam

and

,oji

-eatte.ies

-and

fq1

inspectiolpurposes.

The

termi;"i;;?

tfr.

"oot-

rltg

corls

(Figure

? *.rtO

-erouting

pipes

were

iaken

into

the-galleries

ro

facilitate

cooliilgli

the

;;;;;"

mass

and.grouting

of

contraction jointls

1ri-euies

6-Ell.

tu"

reading

panels

for

the

embedded

"insiiu-ilni,

are

located

on

the

gailery

faces

at serected-Grurions,

eventhough

the

readin-s

stations

wilr

urtim"iery

be

The

diversion

tunnel

for

the

construction

of Idukki

Dam

was

closed

on

14

March

1974.

rrii

riieruoir

rose

to

elevation62i-4

m

(2,045

ft)

by

the

beginntng

"r

June

connected

to

the^Readin-e

Station.located

in

a

Central

In

strumenrat

i on

cham bei

formed

i";iJ;

a;^o

i..

The parapets

of

the dam

are

precast

units.

These

precast

units

were

transported

and placed

in

position

by

the cableways.

Purt

lV-fnilial

ft'eserooir

Operation

and

Power

Generation

1974

with

flow

from

the

date

of

closure.

During

the

South-West

monsooL

of

.l?74,

the

reservoir

went

up

to

El.

679.8

m

(2,230

ft)

with

the

outlers

and low

blocks

3r5

discharging

water.

By

the

end

of

the

North-Easr

monsoon

in

December,

1974

the

reservoir

fell

to El.

670.6

m

Q.,200

ft)

(the

sill level of

Cherurhoni

outlet)

and

remained

mo.re

or

less

steady

at

that

level

till

the

corrmencement

of

the South-West

monsoon

in

1975.

The.

outlet

gates

were

erected

by

June-July

1975.

During

the

South-West

and

North-East

monsoons

of

!975

(from

June

to

December 1975)

there was

a

total

inflow

of

1670

M

ms

(59

TMC)

raising

the level

in

the

reservoir

to

704.8

m

(2,312

ft)

(Photo

4).

The

first generator

in

Idukki

Power

House was

commissioned

on 12 February

1976.

There

was

some

initial

teething trouble

and

as

a result

very

little

water

could

be_drawn for

power

generation

during

the

pegiod

from

February

to

end of

May

1976.

The

live

storage

available in

the

Idukki

Reservoir

before

the

beginning

of

the

SW

and

NE

monsoons

of

1976

was

of

the

order of

254.8

M

mB

(9

TMC),

reckoning

El.

692 m

(2,270

ft)

as

the

M.D.D.L.

for

running

three

generators

of 130

MW

each.

During

the SW and

NE monsoons

of 1976,

there

was

a total

inflow

of

877.8 M

ms

(31

TMC)

from

June

1976

to December

1976.

p<

period

was

641

million

436 M

mB

(I5.4

TMC)

of u

as on

1

January

1977

was

the

total

live

storage

avai

power

generation

688

M

m:

^ Tlrr

pgygl

generation

from

January

lg77

ro

end

of N{uy

1977

was

to

the

tune

ot736

*iriion

unirs,

drawing

a

total

of

51I.1

Mms(t80t-ii\,{Cjoi

water.

The

erection

of

the

radial

crest

gates

for

cheru-

thoni

Dam

spillways

had

been

"o*pl""t.o

u.io."

the

commencement

of

monsoon

rains

oi

tgll.

The

reser_

voir

level

before

the

monsoons

started

*ar

-zbl.+

,n

(2,307.6

ft)

(as

on

I

Jun

storage

of

283.2

M

mB

(10

T

monsoons

started

by

the

mir

ber

1977

the

reservoir

was

i

ft).

This

was

just

below

the

of

the

total inflow

of

1265.

the

SW

and NE

monsoo

{22.4

TMC)-

was

used

for.power

generation.

The power

generation

during

the

period

was

931 million

unirc.

PHoro

4:

Idukki

Reservoir

showing

Idukki

and cheruthoni

Dams.

From

January

1978

to

end

of May

tgTg

a

total

of

1061

million

"oI:

-9t

"l.rey

was,

generated

dra;d;

!36.? Y

*'

(26

TMC)

of

wiier

and

b.i"s,iltown

the

Ievel

of water

in

the..r.ruoir;;

tbt.g;?il-os_z

nl

The

monsoon

of

I97g

started

by

this

time

and

the

reservoir

level

went

up

to

?

middle

of

November.

Thr

monsoons

of

1978

(June

to

(54.5

TMC)

of

whiih

736.2

to

generate

1085

million

un

(Jncontrolled

reservoir

rise

was permitted

up

to

El.

7.]2.!^ry(2,360

f0.

Above

this

levit

upto

Br.

iZs.S

^

9r?89

ft)

g

lise

of.3.05

m

(10

ft) p.,

oi..t

unO'

uUou.

725.5.m.(2,380

_fr)

a rise

of

i.

j

*

(j

frt-per

week

was

insisted.

The

dam

has

not

so

iar

been

fully

loaded.

Seismographs

installed

around

the

Idukki

Reservoir

remors

and

other

shocks.

ound

to

be

on

the

increase

.he

reservoir.

The

first

felt

5,

having

an

intensity

of

hen

the.

reservoir

was

at

.

Neariy

Z0

shocks

were

Conclusion

3t7

TAPAR

DAM

Perfurnrance

of

Partial

Cutoff

in

Unifbrm

by

C.

PATEL

Secretary,

Department

of

lrrigation

T;:LIiff

ti:T

l,:i'*nT;

"

Sand

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

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