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

Th-r

dynamic

behaviour

of

Idukki

Arch

Dam

has

again

been

examined

at

the

cement

Research

l-rxtitute,

New

Delhi,

on

the

basis

of

theoreti"ui

;;ryri,

using

finite

element

analysis.

Basic

Assumptions

and

Design

Criteria

The

basic

assumptions

adopted

for

different

anary-

sis

are

as

follows

:

concrete

is

considered

as a hom-ogeneous,

isotropic

and

elastic

material.with

the

followioE

.rr*u.tJr-istics

:

Modulus

of Elasticity

Coefficient

of

thermal

expansion

Poisson's

ratio

3.0

x

106 p.s.i.

5.5

x 106/"F

0.20

Unit

weight

2400

ks/m'

(150

tb/cu

ft)

The

modulus

of erasticity

and

poisson's

ratio

for

the

foundation

rock

was

assumed

ru,o.

-u,

-thut

of

concrete.

_ Th"

hydrostatic

pressu

(62.5

1b/f0

of

head

-

(l

tc

the

upstream

surface'

of

pressure

due

to

silt

and

wal

lb)

below

elevarion

640

m

The

maximum

ailowabre

working

stress

for

con-

crete

in

the

case

of

normal

loads

*ir

taten

as 70.3

kg_p_e19m2

(1090

p.s.i;)

in

compression

and

7.O3kel

cmz

(100

p.s.i.)

in

rension-

Structural

Behaviour

Testing

Apparatus

,

Recognising

llt.

importance

for

surveillance

of

a

Iarge

arch

dam

like

Idukki

for

which

a

great

deal

of

design

extrapolations

have

been

made,

it"was

decided

to plan

the

structurar

behaviour

monitoring

system

in

.a

large

ya.y

to

verify

that

the

behavioui

oFtne

oam

under

conditio'l

-of .

.loading

complies

-

*itt

safetv.

requirements

and design

assumptions.

.Surveying

methods,

viz.,

triangulation,

levelling

and

collimation

are

employed

to

measure

movements

of

the

dam

and

its

foundations

ieratiue-

io fixed

reference

points

on

earths'

surface.

ih;.

-rJ...o."

points

for

regular

observation

of

the

movlments

of

the

dam

are located

within

trvo

nets

identified

zts

'area

net'

(situated

in the

area

around

the reser-

voir

and

the

dam)

and'dam net'

(located

in

the

imme-

diate

vicinity

of

the

dam).

The

two

nets

are tied

in

periodically

to

determine the amount

of

ground

movement

produced

by

the

weight

of the

dam

and the

reservolr.

First

order

triangulation techniques

are

employed

to

measure

horizontal

movements

of

tar-eets fixed on

the downstream

face of the dam.

Vertical

movements

of the

dam

or its

foundation

is

measured

by

pnecision

levelling.

A

network

of control

bench

marks

have

been established

downstream

of

Idukki

Dam

which

have

been

connected

to

points

out-

side

the

assumed zone

of deformation.

Bench marks

have

also

been established

in

the

dam

galleries

and

drift

tunnels

and

connected

to the

downstream control

bench

marks

to find out

the

vertical

deformation.

Collimation

method

is employed

to

measure

the

deflection

of

the

crest of

the

d;m.

A

line of

sight

pqssing

through

two

reference

points

on the

right ind

left

abutment

rock

is

established

in

space

ancl

move-

Teqt-s

of_

points

on

the

dam crest

with respect

to

the

line

of

sight

are determined.

Plumb

lines

are

made

use of to measure

the rela-

tive

horizontal

displacements

ofthe

crest

of

the

arch

dam

with

reference

to its base.

Horizontat displace-

ments

relative

to

a

point

deep

in the

foundation rock

is

measured

by means

of an inverted

pendulum.

Rotation

with

reference

to

vertical

or horizontal

planes

are measured

by means of

Clinometer.

Geodetic

methods,

viz., triangulation,

levelling and

collimation

can measure

the

absolute movement

of

the

dam

and

foundation rock

with

respect

to

flxed

points

on

earth's

surface

whereas

ordinary

plumb

lines

measure

the

relative

displacements between

two

points

in

the

dam

structure.

The

structural

behaviour

measuring

instruments in-

stalled

in

Idukki

Dam

include

the followine

:

Strain

metre

groups

83

(4

metres

in

each

group)

No

stress-strain

meter

14

Stress

meter

52

Rock

targets

30

Pendulums

-Upright

Pendulum-Inverted

Clinometer

,ResistancA

type

thermometer

9

Vibrating

wire

type

thermometer

63

The

embedded

instruments

fall within

two

basic

groups,

viz.,

resistance

type

and

vibrating

wire

type

or accoustic

type.

These

instruments

help

to measure

the

reactions

of

the

dam structure

to infiuences sucle

as

temperature,

--

gravity

loads,

water loads,

volume

change of

concrete,

etc.

The

distribution

of

the different

types

of instru,

ments

in

the

dam

is

so

arranged

that

t[rere

is counter-

check

between

the-

readings

obtained

from

one

system

of instruments

and

those

obtained

from other

syltems

of

instruments.

Further,

the

instrument

loiations

cover

all

critical

points

and

the

readings

obtained

from

the instruments

can

be

directly

coinpared with

theoretical

results

(Figure

3).

The

foundatio_n

drainage

network

made up

of

199

drille<i

drain

holes

totalling

approximately

Z,OOO m is

Tgnitored

regularly

for

upliff

pressure

and-seepage.

'v'

notch

weirs

constructid

in

the

-ealleries

eira6ie

measurement

of

total

volume

of

seepage in the dam

and

its

foundation.

Level

of

water

^iri

the reservoir

is

read

every

day

and

regular

and

detailed visual

inspection

is

carried

out

for

detecting

cracks, if any,

in

the

galleries

and exposed

faces

of

tlie dam.

Seismic Net

The Idukki

reservoir

formed

by three high

dams

and

having

?

waterspread

area

of

60 sq

[m

and

storage

of

about

2,000

million

ms

of water

(at

F.R.L.)

exerts

a water

load

of

trvo

billion

tons on the

crust of

earth below

the

reservoir.

This

extra

load

would

naturally

tend to

adjust

the rock

structure

beneath

and

surrounding

the reservoir

and

may

induce

certain

structural adjustments

resulting

in

selsmic activity.

An

elaborate

seismic

net

is

installed

for

Idukki

Project

to

study

the

variation

in

seismiciry

of the

area

consequent

on

the

formation

of

Idukki reservoir.

The

Idukki seismic

net

consists

of eight seismorogical

stations

forming (l)

a local

strong

m-otion net

and

(2)

a regional

net

designed

for

both

s'trong motion

i.tiui(

and micro-seismicitv.

Different

types

-

of

seismographs

to measure

the

actual

glound

displacement

velocity

and

acceleration

generated

in

earthquakes

are

instailed

in

each

station.

Basemeter

Joint

meter-Electrical

J.oint

meter-Mechanical

4

l2

47

I

301

INSTRTJMENT

DISTRTBUTIOT{

RIGHT

BANK

20fA

,6

ta

O

a

6

.r

?

LEFT

BANK

1315t7eet23A

ar

ELocKs

DOI^/NSTRE

AM

ELEVAT

IO

N

DEvtLOPraEi?

ALOtrrG TtC

VERT|CAL

CYL|NOER

DEFINCO

EYTHC

UPSTREATi

CRES|T

ARC|r

-

g

50 I}o

60

2OO

-

AX|S

Of

DA

I

3t79

F

lrl

IL

z

o

F

s

lrJ

lr,

_

b__::

_-.|I:

:-Ul

O

DIVERSIoN

TUNNEL

*rr,

r*aa

a

22

HETCR

FONTS

rne

pnovrproe

FER

alocr.Tff,y

ent

rm;rtuEoirEn

CRq'NNG

OPERATIONS.

FROI

TTGGALL-

EF|ES

rcLrqflNGTt{C

ROCK

coNcntrE

INTENFACE

CLINOMETER

A

cLlNor4€TEn

is rrrrEo

tN

BLock

r

rr

EtEvettox

?,rooi

PENOULUMS

THREE

PENOULUM

AXIS ARE

PR(MO€O

rN

SLOCKS

g

r

ero

z. THE

EXTERTOR

rED

lT r'ro

rctGHT

tN

THE

lNirn

ia..

IEO

uFr TermET

rFr

of

El€tr

It{GcctPAnTr.€NT

ts F|TTEO

wf?}l

rrGrr6pq4Es

AJflXG TlrE

FreST

Sclsq.r

potn

urb

comelFruExr

Lr7t|3

An€

{.sO ,rSTnutENTED.

D

t.ty

f

rilo

tf tcttrcc,ornrnncrrrs.

THEY

INC

fITTEO

MOA€

STESLY

^S

Tlc

cncsT

Ei

AppROAclrGo.

rtrERS

AnE

Of rrc

rvpeS,:tgGrg-

CAt

tnex3or,rctls

].oat.

oR TwrN

cto-

ICLTTD

I'A

I

_-srRftN

rEEt

rEs

ANE

PLAC€O

NCAR

Tr€

fiOCK

IXTE(FACE,

NEAR

THE

SOTTOM

OF

Clclr

SLOCK

A

T€MPERATUR€

COit-

tcMs

TtlGi

oEvrcE

ts F|TTEo

wtTll

SO|rE

1O,SETTES

.

.ffiffiruRErr€rE*s

ARE

PLACED

oN

Tfl€

uPSTRE,A{

sUR.

FrcE

AT

ELEVAT'ONS

I9OO,.2OOO,

lloo,

22OO,

2?5O,

e1oo,e35o

axo

:aoo

tN

ELoCX

I

PENTUU.N|S

ARE 3OOFT

IN

LENGTH

AN

INTI

RMEOI.ATE

REAOTT{G

TAELE'

AT

LA/EL

23OO

TH€

CE^|TRAL

PENOUUA{

Axrs

ccNsrsTSOFTrngE

sEP RATE

P€rsturMs

88T16511

t€VEtS

?4OO.

23OO.2rooaNcr

tgooAt{o

oF

AN

TNVER_

TEO

PENq,fUM

OOWN

TO

TIf

NOMINAL

LE\GL

OF

I72O.

ROCK TARGETS

c

4l

rARG€TS

ane rrireo.ev

GRorrps

oF

'5TO9.lN€AcH

yuxxLl

L€ADtNc

FRSM

JlE SA!l|

tN

TH€

LEFT

ANO RIGHT

EANK

TxE

TARGETS

aR€

s€T

or

rxe

oouni_

!rlE4!

FAGE

OF

rht

TUNNELS

tN

rHE

PATT€RN

SHOWN.

FIGURE

3

:

General layout

of Instrumentation-Idukki

Arch

Dam.

DETAILS

OF

INSTALLATION

ffi

02

The

different

types

of instruments

installed in

the

Idukki

seismologichi

net

includes

the

following

:

(t)

Wood

Anderson Seismograph

with

photo-

graphic

recording

system.

(2)

High

Frequency

Electromagnetic

Seismograph

with

visible

recording

system.

(3)

Strong

motion Accelerograph (SMA-1)

(4)

Ranger

Seismograph

with

visible

recording

system.

(5)

Electromagnetic

Seismograph.

(6)

Benioff

Vertical

Seismo_sraph.

(7)

RFT

250

Accelerograph

Altogether

26 instruments

are installed

in

the

net

(Figure

3).

The

seismic

data

so

far

collected indicate

that some

relation

exists

between

loading

of

the reservoir

and

the

number

of

microtremors

being recorded.

The

frequency

of

microtremors

increases

at

times with

1is_ing

reservoir

level.

A few shocks

of

ma_enitude

2.5 in

the

Richter

Scale, or less

were

felt around

the

reservoir

area

since

the

impounding

of

the

reservoir

began.

Dam

Electrical

System

illumination

level

required in

the

various

areas

of the

dam

and related

structures

is

prescribed

based on

accepted

standards

Design

Spillway

No

openings

are

provided

in

the Idukki

Dam

for

flood

water

releases.

It

is accomplished through

spillway

and

outlets

provided

in

the adjacent

Cheru-

thoni

Dam. The

maximum design flood

for

the

catch-

ment

of

Idukki

reservoir

is

worked

out as

8,014

cumecs

(2.83

lakh

cusecs).

Someflood

absorption-

capacity is'

provided

in

the Idukki reservoir.

The design

flood

of

8,014 cumecs

(2.53

lakh

cusecs)

is moderated

to

4,928 cumecs

(l.74lakh

cusecs).

Five spillway

radial

crest

gates

of

sizes 12.19

mx

10.36

m

(40

ft

x

34

f0 are

installed in

Cheruthoni

Dam.

The

spillway

is located

in

the

river

portion.

It

has

an

ogeg

cre_st

with

an

upstream

lip

as

control

structure

and

a

freg

flip

bucket

as

termiial

structure.

The

crest

of

the

spilrwiv

lq

"t

Er,.-

Tiazaf-

<i,ili

ril

and

the

bucket

of

the

middle

thgec

ventways

having

;

radius

of 18.29

m

(60

ft)

is

at

n[

obg.iHliooO"nl.

tle

sa.qe

gnillwav

arrangemenr

is

pt*ioio

-b"

each

side

with

bucketi

at

El.

6tz.z

m

lz,cizs

rt)

uoa

o'ts.g

-

(2,939

{0

respect-ivety.

Sufficient

igchoiat",

g-uti"e

and

drainage

facilities

are

provided

rod.i

th;

bu;[e;

portion

to

overcome

uplift.

-

Longitudinal

contraction

joints

separate

the

bucicet portion

from

the

Oan.'

I}.-fpjllway

gales

_are

operated

by

hoists

located

at

EI-

739.5

m

(2,426

ft). i'tre

pratlforms'

ioi

these

hoists

and

the

roadway

are

ieinrorceo

-.on.rrt,

constructions.

The

design

for

spillway

buckets

were

finalised

after

conducting

hydraulic

model

studies

af-

tt e

-

Kerala

Engineering

Research

Institute,

peechi.

Outlets

Idukki Dam

does

not

contain

and

outlet.

However

the

outlets

for

the

reservoir

are rocated

in

cheruthoni

Dam

and Kulamavu

Dam.

Two

unusually

large

size

outlets

are

provided

in

Cheruthoni

Dam

io mEet

the

following requirements

:

(l)

Emptying

the

reservoir

during

emergencies.

(2)

Control of reservoir

levels

during

construction

of

the

dam.

(3)

Systematic

regulation

of reservoir

elevation

for controlled loading

of

Idukki

Arch

Dano

above

El.

701.2

m

(2,300

ft).

(a)

Supplementing

the

spillway

capacity

provided.

The capacity

of the

outlets

is dictated by

the

requirement

(3)

mentioned

above.

It was required to

design the outlets for a flow of

424.8

cumecs

(15,000

cusecs)

from

each

when

the

water

surface

is at

elevation

716;.4

m

(2,350

f0. This

requirement

was

found out

after

imposing

certain

constraints

in

respect

of rise

in reservoir

during

flash

flood

and

time

of

evacuating

the

flash

flood

during

initial

loading of

Idukki

Arch Dam.

The

discharge

capacity

of

each

outlet

is

450.3

cumecs

(15,900

cusecs)

for reservoir elevation

716.4 m

(2,350

ft) and

566.6 cumecs

(20,000

cusecs)

for

M.W.L.

734.3 m

(2,408.5

ft).

303

Part

lfl-Construetion

CONTR

ACT

A DM

INISTRATION

Maior

Contracts

The

contract

for

the

construction

of

Idukki

Arch

9u*

was

awarded

to

M7i-Hindustan

construcrion

Company

ltd,,

one

of

the

,ouj--

.i"if

-J"gineering

eontracors

in

rhecounrry.,

du-ring

-oecimu.i'i'qoo.

tt.

construction

of

cheruihoni

concrete

-eravity

dam

also

was

entrusted

with

ttri

same

contractors.

The

simultaneous

award-of

two

-uior

contracts

to

the

same

contracror

resulted

in

the

reduition

of ,ai.i.---

'-

-

The

contract

varue

of

the

rvork

carried

our

through

M/s

Hindustan

Cc

rn

respect

of

Idukki

Dam

i

the

total

estimated

cost

01

cement

for

concrete

was

su

tricity

Board

and

its

cost

crores.

Organisrfion

d"1T,i1'i,#iliilll

i,,;",j","l.firara,srare

Erecrrj-

$*Xflff1"1"1i':i+::&:ilXItX';tii[flfr'Tl;i

;:{'-**l*'.1':::lT.*xil#:li#

fl*l;i:l

Ji'ffi1"'f"if';1T",1n".'#.0,,'".,31

.:Je'ffi;;fi#

During

the

period

of

number

of

strikes

and

li

on

with

the

work

the

C

the

projtict

area

as

a

.p

entry

- -into

the

project

!

prevailing

necessitated

co,

the

securitl'

arra n,ee

m

en ts.

r:

The persistent

labour

unrest

and

the

various

labour

dlsputes

necessitated

rhe

srationing

of

a

District

Labour

officer

with.

his

"o-fi.-.n-tury'

,rim

at

rhe

project

site.

In

addition

to this,

the Bo#d;;;;n

per-

sonnel

wing

also

was

stationed

at

the

p.oj..i,ii..

-

Land

acquisition

and

eviction

probrems

necessita-

ted

the

services

of

a furt

time

land

u"quirition-

offi...

with

his

staff

stationed

in

the proje;

e;;i;;ihe

entire

period

of

project

construction.

Forest

clearance

required

for

the

project

works

as well

as

for

the

res.rnolr

area

crearanie

-luii.a

for

the

services

of

a

Divisionat

Forest

officer

with

co'r-

plementary

staff.

This

was

in

addirio"

io-it.'r.rui..,

rendered

by

regular

personnet

of

the

por.it

ilepart_

ment.

304

The

Central

Water and

Power

Research

Station,

i:

,

Contractor's

Organisation

Messrs

Hindustan

Construction

Ltd..

was the

contractors

for the construction

of

both

Idukki

and

Cheruthoni

Dams,

Tbey had a team

of

well

qualified

and

exierienceci engineers

established

at site

to

manage

the

woiks.

A

team of experienced

supervisors

and

a

labour force

rich in skilted

personnel

assisted

the

engineers

in carrying

out the

work.

Nearly'

3,300

people

consisting

of

engineers,

super-

visors,

sl<illed

and

unskilled

labourers

were employed

for Cheruthoni

Dam construction

also.

+

The contractors

had their

own

office

to

detail

the

construction

drawings,

prepare

the

bills, etc.

They

had

a

personnel

wing

also to

look after

labour

welfare.

They

had

well equipped

automobile

workshop,

car-

peniry

workshop,

saw-

mill, electrical

and

mechanical

workshops,

etc., established

at

site.

Review

Board

In

order to

solve

major

problems

affecting

rhe

progress

of

the

work

and

to carry

on

with the

project

works

smoothly,

it

became

necessary

to

constitute

a

hieh

level

bod-v

-

and

as a

result the

Review

Board

for

ldukki

Project

was costituteci

under the

Chairmanship

of

the

Hon'ble

Minister

of

Electricity, Government

of

Kerala.

The

Minister

for Irrigation and

Power,

Government

of

India

anC the Chief Minister

of

Kerala

lvere

always

invited

for

the Review

Board

Meetings.

Thev

took

active

interest in it

and

this enabled

the

.mo-oth

functioning

of the

Review

Board.

resulting

in

quick

decision

and

action.' The

Canadian Govern-

ment

and

CIDA

also

were participating

in Review

Board

meetings

as

specia[

invitees.

Disputes

between

the

Department

and

contractors

which

were

not

very

common

in

the

construction

field

in

-

ttte

State

arose

during

the construction

ot' Idukki

iroject

and

arbitrations

have to be

resorted to-

The organisational

requirements for carrying out

the contruction of ldukki Project wag

so large

and

complex

in

structure

and unprecedented

in

the

history

of

construction activities

in

the State.

Construction of

I)am

,

"

In

order

to

expedite

the

construction of th"

dam

the

initial excavation

of

the dam

was

carried

out

when

the

main

contract for

construction was

settled

and

awarded to

M/s

Hindustan Construc.tion Company

Ltd.,

in

December 1966.

'

,

The

preliminary

and enabling

works

required for

the

construction

of the

dam

like,

establishment

of con-

tractor's

camp,

opening

up

of

quarry,

erection

of cons-

truction

tools

and

plant,

construction

of access

roads

to

quarry,

camp and work

sites,

electrification

and

water

supply

arrangements and other

moving

in

operations

were

completed

by the

beginning

of 1969.

The

first

bucket of

concrete in

tdukki Dam was

laid

on

30

April

1969.

(Photo

2).

The

foundation

of

fhe dam

was carefully

blasted

using

the

pre-split

technique in

order

that

the

foun-

dation

is

not

shattered

during

excavation.

The remo-

val

of

the flnal

layer

of foundation rock

was

always

done

by

wedging and barring

and

other

approved

methods.

Concrete in the

dam was

laid

immediately

after

the

removal

of

the

final

layer

of

rock

and

foundation

preparation

on ac€ount of

the

spalling

nature

of

the

rock.'

Fully mechanised methods

were

adopted

for

manu-

facturing

and

placing

concrete.

The concrete

placed

was

pre-cooled and

post-cooled.

The contraction

joints

which divided the

dam into

monoliths

of

about

15

m

width

were

grouted

after cooling the

concrete

to

pre-

determined

temperature.

The

dam

was

drained inter-

nally

with

the help

of

formed drains.

The

foundation

drainage

was effected

through

a system

of drain

holes

drilled

in the

foundation

(Figures

4,

5

and

6).

The

contractors

had

planned

the

aggregate

produc-

tion

for Idukki

and

Cheruthoni

Dams from

a common

quarry situated

in the common hill between

the

two

dams.

While

the

bulk of

the

aggregates

were

pro-

duced

from this

quarry,

in order

to

enhance

the

production

of aggregates

the

contractors opened

up, a

new

quarry

on the

left bank of

Cheruthoni

Dam for

some

time.

The

aggregates

were

transported

to

the

respective

batching

plants

through cooling

tunnels

constructed

before

the respective batching

plants'

The concrete

manufactured

in the

Johnson

Batching

Plant

were

placed

in

the

blocks

using

lO-tonne

cableway.

The concreting

of Idukki

Dam

was carried

out

in

fi.ve working

seasons, commencing

with

the season

L969-70.

Each

working

season commenced

around

305

PHOTO

2

:

Photograph

showing

the

Idukki

Arch

Dam

under

construction.

September

after

the s.w.

monsoons

and

came

to a

close

around

June

or

July,

just

before

the

onset

of

monsoon.

The

construction

of

the

dam

was

completed

in

lg74

(Photo

3).

The

delay

in

construction

is'

attributable

to

the

time

required

for

obtaining

certain

essential

items

ol

construction

equioment

from

Canada

and

due to

the

labour

unrest

in the

project.

Concrete

Production

and

Placement

_

The

aggregates

for

production

of

concrete

for

both

the

dams

were

manufactured

from

blasted

rubble

obtained

from

the

common

quarry

in

the

central

hill.

The

aggregates

required

for

both-{he

dams

were pre-

pared

by

a

common

aggregates

probessing

plant.

Th_e quarries

were

fully mechanised.

Drilling

was

carried

out

by

10.1

cm

(a

in.)

wagon

mouoted-

rock

drills

and

blasting

done with

modein

explosives

using

electric

detonators.

For

loading

and

transport

of rubblE

to

the

nearby processing

plant

1.91

cu

-m

(2$

cu

yd)

power

showels

and

15

tonnes

dump

trucks

ri'eie

usbd.

306

Rubble

from

the

left

bank

q.uarry,

_

after

primary

crushing

inro

ls.z

cm

(6

in.)

.oubr.t

-*.rJ

truor-

ported

to the

co.mmo,n

stock pire

in

the

centiai

hitt

ro,

further

processing

by

-eu^nr

of

a r,ooo

-

Iong

ropeway.

The

aggregate processing

prant

and

sand

manufac-

turing pla_nt

also

were

mechanised.

The

aggr.gui"

pro-

99ss!ng

plant

consisted

of

9t.4

cm

uif

iG.T'cm

(36

in.

and 42

in.).

P-riTaly.Jaw

crushers

uoo

cyrurory

crushers,

122

cm

(4q

in.)

Secondary

and

tertiary

Crushers,

91.4

cm^(36

in.)

Gyraspheres

and- Kubit

breakers

for manufacturing

diherent

sizes

of

uggr.-

gates.

Rod

mills

and

sand

sizers

were

used

for pro-

duction

and

sizing

of

crushed

sand.

-

Thg aggregates

were

produced

in

six

different

gta_

des,

viz.,

152.4

mm-76.2

mm,

j6.2

mm-3g.1

rim,

38.1 mm-19.05

mm,

19.05

mm-9.52

mm.

9.52 mm-

4.76

mm

and

below

4.76

lnm (6

in.-3'in.,

3

in.-

1+

in_., -1$

i1.;31.4

in.,

314

in.-3l8'in.,

3/8

in.-31t6

in.

and

below 3/16

in.).

The

aggregates,

Uottr

coarse

and

€

o

N

F

I

n

av

')

|o

(\t

I

l|

f\J

a

n,

-

\n

'o;

6rd

{'E

ru

J

@

b

o

J

GI

a

I

L

,:(

.tl

E

I

o

(tr

q)

€

tr

o

h

$

&

p

e

tr

C

!t

o

F

o

tl

A

T

o

6

x

C

tl

rJ

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F

g

U

4

F

o

)

o

1

\o

o

J

la,

'|

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JJ

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,QJ

JU

,{\

)n

dX

t\n

I e--

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-!R='

;[i>

,t

j?l

307

Reference

to Figure

4

oo,:oor+ffii

E)

LEFT

BANK

RIGHT

BANK

JOINT

EL.EI

EL.

Eg

JOINT

oor

ooz

J.l-2

J.

1-3

J.

3-5

J.5-7

J.7-9

J.9-11

J. 11-13

J. 13-15

I.

r5-t7

J. l7-t 9

J.

19

-21

J.2t-23

J.23-2s

i.25

-27

10,000.0000

1o,oo2.2665

10,008.9931

ro;or9.9732

10,034.8992

10,053.4028

10,075.0945

to,ogg.5932

1o,L26.3448

10,155.63 t 6

10,186.5753

10,219.1353

10,253;1056

10,288.3107

J0,000.0000

10,049.9315

10,099.4605

10,148.2248

10,t95.9314

10,242.3697

10,287.4090

10,330.9972

10,373.0942

t0,4t3.7569

10,453.0262

10,490.9672

t0,527.6516

10,563.1534

24rs

0.000000

,,

5.187350

,,

10.250437

,,

15.092951

,,

19.607977

,,

23.781753

,,

27.599952

,,

31.039316

,,

34.151127

2'

36.953606

,,

39.477742

,,

41.754259

,,

43.91l96g

,,

45.676998

J. r-2

J.2-4

J. 4-6

J.

6-8

J.

8-10

J. 10-12

J.

12-14

r. i+-le

J.

16-18

J.

18-20

10,000

0000

70,oo2.2665

10,008.993

t

t0,0t9.9732

r0.034.8992

10,053.4028

10,o75.0945

10,o99.5932

10,126.5448

10,155.6316

10,000.0000

9,950.0685

9,900.5394

9,951.7752

9,804.0696

9,757.6303

9,7t2.5909

9,6e9.0128

9,626.9058

9,586.2431

1850

0.000000

1850

26.164t67

1900

36.984932

1900

4s.to37M

2000

44.788s76

2050

46.010446

2100

46.448479

21sO

46.428876

2200

46.149188

2200

48.400188

22sO

47.808960

2300

47.232410

2300 4a.gs+sso

23s0

48.392714

fine

were stocked

in separatc

piles

for

each

fraction.

Tbe

different

sizes

of

aggregates

wero drawn from the

main

stock

pile

through

belt conveyors and

stored in

separate

bins.

These

were

transported through

cooling

tunnels where

the

aggregates

wer'e

cooled.

The

coarse

aggregate up to

19.05 mm-9.52

mm

Gla

in.-318 io.)

fraction were

cooled

by spraying

of

chilled water and

the

aggregates

below

fraction

9.52

mm-4.76

mm

(3/8

in-l/t0

in.)

were

chilled

by

circulating

cold

alr.

A

Johnson's

make

batching

plant

consisting of

4

Nos.

1.53

cu

m

(2

cu

yd)

capacity

mixers

and capable

of

mixing 122.3

cu

m

(160

cuyd)

of concrete

per

hour

Jras

used

for-mixing

the

concrete

for

Idukki

Dam.

The

concrete so

mixed

was conveyed

in

3

cu m

(4

cu

yd)

buckets with

the

help

of

two

'Henderson'

Cableways

of I0

tonnes

capacity

each and

placed

in

position

and

consolidated by

electrically

operated

heavy

duty vibra-

tors.

The

double

curvature

of

Idukki

Dam

necessitated

special

type

of

form

work. The

form

works were

manufactured

in

steel

and

in

small

panels

to

suit con-

308

venience

in construction.

The

form work

is capable

of

being

jacked

into

required

shape

by.

nreans

of

mechanical

jacks

fitted

onto

structural

frame-rvork

of

shutters,

called

'soldiers'.

This

facility

contributed

largely

to

the

speed

o[

the rvork

and the

finish

of

the

exposed

faces.

Because

of the

shape of

the dam

and

limitation

of

the

cableway

a

portion

on

the

right

bank

of the

dam

was

out

of

reach for the cablewavs.

A tower

crane

embedded

on

the

dam

block

was macle

use

of

to

concrete

this

area.

Printed

checklists were

used

to

check

the

various

items

of

works

involved

before

the

placement

of

con-

crete.

Checklist

for

foundation prepiiration

ensuted

that

the

foundation was

checked

and

approved

by

the Geologist,

consulting

Engineers

and Kerala

Stat-e

Electricity

Board's

Engineers.

Another

checklist

ensu-

red that

form

work was

placed

in

position

and

correctly

aligned,

all

embedments

in

the

block

were placed

correctly

the lift surface

has

been

prepared

neatly

and

measurements

of

all relevant

items

were

taken and

that

Kerala

State

Electricity

Board Engineers

and

I

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

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