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

being

grouted

from

the

galleries

were

also fitted

with

valves.

The vent

returns

for

joints

being

grouted

from

the

downstream

face of the dam were fitted with

risers

(stand-pipes)

914:4 to

1219.2 mm

(3

to 4

ft)

in

height

and

the valves installed on

the

stand-pipes

at a height

of

457.2

mm

(18

in.).

The

valves

were

also

provided

on

outlet ends

of 25.4 mm

(l

in.) vent

headers near

faces

of

the

dam.

Gauges

were

installed on

vent returns in case of

joints

being

grouted

from

downstream

face of

the dam

and on

vent lines

in

case ofjoints being

grouted

from

galleries.

Grout

was

injected in

each

section of

joint

or

a

group

ofjoints in

a

grout

lift

in rotation by batches

or

in

such

quantities

as

necessary

to

keep

the

grout

level

in

each

joint

at the

same

approximate

elevation

and to

allow time

for

settlement. The

air,

water

and thin

grout

was bled

from the

top of the

joint

through

vent

pipes.

The

valve

for

the vent

returns

was closed when

the

grout

filled the

vent

grooves

at

the

top

of the lift

and

flowed out of the

vent

returns.

The

valves for

the

return

headers and vent

pipes

were

opened

periodically

to drain

off

any

water of thin

grout

accumulated

in

the

system

and

pressure

applied

as many times

as found

necessary

to force

out

all excess

water

from the

grout.

Injection

of

the

grout

was

continued

until

grout

almost

as thick

as

being

pumped

flowed

from

the

vent at the

top

of

the

lift. Maximum

allowable

pressure,s were

applied

after

closing

the

stopcock

valve

for

the

vent

pidrs.

Pumping continued

until the

gauge

at

the

vent

ieturn

or

vent

line reached

the

pre-determined maxi-

complete.

Dial-gauges

registering

to 0.0025

mm

(.0001

in.)

were

used

-to -measure

the

openin,e

and closing

of

the

joint

when

grouting was

in

progress.

2.12

Galleries

anil

Shafts

vated

rock

profile with a

1.52

m

(5

ft)

m-inimum

clearance

bet-ween the

gallery

floor

and

the

rock.

The

gallery has been

kept t.524mx2.134

m

(5

ft.x7

ft)

in

size to

accommodate

the

normal

portable

equipment

for

grouting

and

drilling.

Another

supp.lementary

foundation

-

gallery

is

provided

for

drainage

just

upstream

of

the

middle

claYstone.

32

Inspection

galleries

of

size

1.524

mx2.l34

m

(l

ftx7

ft)

have

been

provided

from

abutment

to

abutment

at

vertical

intervals

of

about

+15

m

(50

ft).

Two

shafts

have

been

provided

for

elevators

it each

end of

the

spillway

which-

connect

all the

galleries.

-

A

number

of

grouting

and

drainage

tunnels

have

been

excavated

longitudinatty

into

thJ

abutments

for

grouting

and

drainage

of

the abutment.

These

tunnels

are

more

or

less

extensions

of

the inspection

galleries

and

are

connected

to main

foundation

lallery.

-

There

are

special

galleries

for housing

mechanism

for controlling

jet

flow

gates

and

spillway

gates.

2.ll

River

Outlets

Sixteen

river outlets

have been

provided

through

the

body

9f lhe

dam

in

the

spillway porrion

for

the

purpose

of

effecting

controlled

releases

of water

from

the

reservoir

[FiguresT(b)

& 10]. These

outlets have

been

arranged in

two tiers

of

eight

outlets

each

at

elevation

402.3 m

(1,320

ft) and-432.8

m

(1,420

ft).

The

outlets

are controlled

by

means

of

jet-flow

gates,

located

in

galleries

within

the dam.

The

hoisting

equipment for

these regulating

gates

has been

l6cated

in

the

3.66

m

X

5.87

m

(12

ft x

19.25

ft)

gate

galleries

at El.

406.30

m

(El.

1,333

ft) MSL

and

El. 436.78 rn

(El.

1,433 ft)

MSL

respectively.

The

outlets are

protected

by

semi-circular

trash-rack

structures

located

on

the upstream

face

of

the

dam.

Two 3.34

m

x

3.34 m

(10.97

ftx

L0.97

ft)

emergency

gates

have

also

been

provided

for

closing

any

of

the

river outlet

orifices

whenever

required,

for

inspec-

tion and

servicing

of the

jet-flow

gates

and

also

for

emergency

closure

in the

event

of

failure

of

jet-flow

gates.

To

improve

hydraulic

performance

and

to

avoid

excessive

negative

pressures

along

the

conduit,

special

arrangements

have

been

made

to

introduce

adequate

quantities

of air

in

the regions likely

to be

subjected

to

negative

pressure.

The

air requirements

were

determined

by

means

of

model

experiments. A

header

of

2.44

m

(8

f0

diameter has been

provided

for

each

tier of

outlets

and air

inlets

at

four locations

have

been

installed along the

length

of

each

outiet.

The

trash-racks

at

the

upstream

end

keep out

any

large

size

debris

which might

damage

the

conduit.

Each

struct.ure

covers two

river

outlets

of

E-1. 432.83

m

(1,42C

ft)

tier and two

of

El. 402.34

m

(1,320

ft) MSL

tier

in one

construction

block

and

there are

four

trash-

rack structures.

The

gates

for

the

conduits at

El.

432.83

m

(1,420

ft)

MSL

(upper

tier) are

designed

for a

maximum

head

of

82.30

m

(270

ft) and

for conduit

at

El.

402.34 m

(1,320

ft)

MSL

(lower

tier)

are designed

for

a

maxi-

mum

head

of 112.78

m

(370

ft)

both corresponding

to

i11

the

reservoir

elevation

of 515.11

m

(1,690

ft)

MSL. All

the eight

gates

of each

tier

are

exactly

alike

and

have

the facitity

of

interchangeability

of

parts.

Each

gate

is

operated

by

an

independgn-t

hydraulic

hoist

instiiled

in ihe

3.66

in x 5.87

m

(12

ft

x'19.25

ft)

gate

gallery

provided

for

this

purpose directly

above

itre c6nduiis.-

The

gallery floor is at

El.

406.30m

(1,333

ft)

MSL

for

-lower

conduits

and El.

436.78

m

(1,433

ft)

MSL

for

uPPer

conduits.

2.L4

Radiat

Gate

Spillway

and Spillway

Britlge

Bhakra

Dam

spillway

was

first designed

in

1949

on

the

criterion

that a

flood

of

1l

,327

cumecs

(400,00O

iusecs;

may

pass

over the

dam

with maximum

reservoir

ilevation

i,f

S 13.59

m

(1,685

ft)

MSL.

The

discharge

iu"iiiiic

included

a

central

spillway,

river

outlets

and

an

inclined

tunnel

sPillwaY.

Later

otr,

other

alternative

arrangements

for

spill-

wat

were

investigated.

_Based

on

these

investigations,

a

icheme

consisting

of

a

centrally

lqcqted_

drum

gate

Y

on

ttie

left

abutment

of

th conduits

Passing

through

#:131,""X'I'J'H:T"H3}:I

t

works

provided

repair

facilities

to overflow

spitlway

apron

by

supplemen-ting

.the

Oit.iutg.

through

tlie

pbwer

plants

to-meet

the

irriga-

tioo

t.d'uirement-s

and

these

were

also

intended

to

pass

;il

irtigation

requirements

during

closure

of diversion

i""o.f,*"

provisi6n

for

an

open

spandrel

reinforced

concrete

bridge

in two

spans

across

the

drum

gate

spillway

was

also

made.

Due

to

constructional

difficulties

and

risks

involved

in

ltri

wotting

of

an

inclined

tunnel

spillway,

mo-{91

experiments

weie

carried

out

to

investigate-

the-

possibi-

ii;il;-i;tidinating

the

tunnel

spillwav'

-

In

1952,

the

ieft

abutment

(wfrire

the

inclin6d

tunhel

was

propo.sed

i"

-

U.

-

iocated)

was

also

observed

to

be

weak

and as

such

the

tunnel

spillway

was

omitted

after

thorough

_"a.t-iiitr-

The

disch

atge

capacity

of

central

spillway

;;-

-*;difi.o

for

u

max-imudr

flow

of 8,212

cumecs

(Z-gb,O0g

",r...r1

gn

-thq-pasis

of

flood

routing

studies.

il;

pt*iding

repair

facilities,

the central-spillway

w-as

oivioeo

into

twb

compartments

with

the

help

of

a

central

Partition

wall.

After

a thorough

examinations

of

the

various

allY

located

radial

gate

over-

ovided.

The

sPillwaY

has

a

m

(260

f0

between

the

two

an

effective

crest

width

of

I

into

four

baYs

of

1'5'24

m

rridge

piers of

4.57

P

(11

{t)

ers

of

4.t

t m

(13.5

ft)

thick-

ness.

The

spillway

has

been

divided

into

two

eq94

compartm.n,*

uy--'a

centra.l-

partition

wall

to

provide

iacifit'

for

repairi.

The spillway

is

controlled

by

f9.uT

-li.ri'

*

tSO

ftf

*iO"

and^14.48'm

(47

.5.ft).high

radiat

gu..*

with

iheir

trunnions

anchored

on

the

downstream

end

of the

spillway

bridge

piers.

The

spillway

discharges

on to

a

stilling

basin

suitably

designed to

dissipate

the energy

of the

falling

water

without

harmful

erosion.

The energy

dissipation is

entirely

due

to hydraulic

jump

and

except for

a 1,524 mm

(5

ft)

high sill

provided

at

the

end of

the

stilling

basin, no

other

device

has

been

considbred

necessary

either to

stabilize

the

jump

or for

preventing

the

downstream

eroslon.

The spillway

has a

crest elevation

of

501.46

m

(1645.1

fa)

MSL

and has suitable

profile designed

for

a

maximum

reservoir

elevation

of 515.11

m

(1690

ft)

MSL.

The downstream

face

of

the spillway

portion

of

the

dam

has slope

of

0.8

:

I

and

has

been

connected

with the stilling

basin

floor through

a

114.30

m

(375

ft)

radius curve.

The

16 river

outlets

arranged

in two

tiers

of 8

outlets

each

discharge

over the

spillway

face.

To

.prevent

spillway

wafer

interferilg,

with

the

outlets,

iaised

ey6browi

have

been

provided

above

the

outlet

opentngs.

Feasibility

of

reinforced

concrete

arch

bridge

and-

a steel

plate

girder

was

considered,

prrt

a

-.T-beam

reinforied

brJdge

in

four

spans

across

the

radial

gatg

spillway

has

been

provided

from

considerations

of

efononiy,

architecture

and

ease

of

construction.

Hydraulic

Features

At

various

stages

diflerent

studies

were

made,

reearding

flood

incidence,

flood

routing

and

spillway

."-p""itvi"quired,

for

which

data

relating

to flows

in

ini

nin.r

Suttej

at

Bhakra

has

been

collected

since

tgOg.

ln

1949-design,

a

provision of

11,865

cumecs

f0

MSL.

In

1952,

flood

frequency

studies

were

carried

out

afresh

and

on

the

baiis

of these

studies.

taking

into

:usecs)

and

of

1947

flood

as 8.212

cumecs

(290,000

With

the

elimination

flood

release

had

to be

Pas

and

the

overflow

sPillwaY'

to

restricted

width

of

the

6

maximum

sPillwaY

width

an

JJ

reservoir

elevation

of

512.07 m

(1680

ft)

MSL.

How-

ever,

in 1958,

it was

proposed

to

raise

the

maximum

reservoir

elevation to El.

515.ll m

(1,690

ft) MSL

for

impounding additional

supplies

by

encroaching

on the

free-board. Allowing a free-board

of

3.05

m

(10

ft)

from

top of

tF.

4u.,.it

was

considered

that

the maxi-

mum reservorr

elevation

could

be increased

from

El.

512.07

m

(1,680

ft)

MSL

to Et. 515.11

m

(1690

ft)

MSL. Consequently the

maximum

reservoir

elevation

was

fixed

at El.

515.11 m

(1,690

f0

MSL, subject

to

the

restriction of

not

allowing

any

increase

in

the

reservoir

elevation

on account

of absorption

of floods.

With

the advance

information

of a

flood

from

meteoro-

logical

stations

located

suitably on

the

catchment,

the

reservoir

with

intelligent regulation

would

be

depleted

in advance of a

flood

peak

so

that

the

marimum

reservoir elevation

during

the course

of flood

passage

dose

not

exceed El.

515.11

m

(1690

f0

MSL.

Finally

the

spillway

has been

designed for

a

maximum

overall

discharge

of

8,21I cumecs

(290,000

cusecs)

including

the flow contributed

by

the

river outlets

and can

cater

for

a

peak

inflow

in thp

reservoir

of

11,327

cumecs

(400,000

cusecs)

of

the

pattern

and duration

of maxi-

mum

t947

flood. The

discharge

passing

through

the

penstocks

is

in

addition.

Spillway Crest and

Profile:

The

design

of the

spillway

crest

was

tested

on hydraulic

models.

A review

of

the

!l

e

lower

nappe

of

the

sharp

crested weir

upstream

from'the

gate

and

as

a

parabola

downstream

fr-om the

radial

gate

having

an

equation

x1

-y

-

--EI.A-jn1-

+

0.4556

with

origin

as

radial

gate

sill. The

shape

of

the

crest

upstream

from

the

gate

has

been laid

by.drawing

the lower

nappe profile

and

fitting

to,it

a

series

of

circular

curvej

up

to

the

elevation

of

the

gate

sill.

34

EI. 335.29

ry

(1,100

ft)

MSL

has

also

been

provided

at

the

end

of

the

basin

as

shown

in

Figure

7.

Downstream

of

the

sill,

the

apron

joins

the river

bed

at a

slope

of

3

to

1.

2.!5

Penstocks

and

Head

Gates

Reinforcement

Around

penstock

Opening:

All pen_

stocks have

been

designed

for

the

fofiowin-g

operaiion

conditions :

Maximum

reservoir

level

at

81.513.59

m

(1,6g5

ft)

MSL.

Minimum

reservoir

level

at

El.

43g.91

m

(1,440

ft)

MSL.

-<--

'

v

nt

oF

4a

find

2rofik

afl* llucltiogr

tD

r-a

to

lfue

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EFIAKRA.

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SPILLWAY

CRE5'T

d

PI

ERS

our-L|NEs

FIGURE

II

_frr.r7,oo

t

(

+

a

E

I

t

a

{

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tv

{sl*'r

T' E.Q.'O

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t

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et

AXIS

OF DAM

Cn

E+OO'OO

Morimum

storoge

level

El.

169;

*1r_f=T=E:?==_€=l=E_€=_:=_:---_===?

hspection

gollery

6ote hoist

slructure

EI

t456A4

furctrck

tnshn_vF

C.

Pcnstoc* EL 146

Et.

t576.50

l5O Ton

gont

Q,.

rcoa*oy

E,

Hoist

gollery

'Penstock

olr

G.tnspwtlolT

gattery

i

EtE?L

['

l

lnspection

Fandotrbn

qtory

I

,I

tl

I

Speciol

praool-

ed

eoncrete

in

lrenches.

.l'-; i

'

I

'iiL\l*:

\{\\\|'

lon

gonlryl

crene

odwoy

EL

l7OO.25

'

gollety

rock

olr

trynl

3O'0

Oroinoge

through

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

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