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

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'*'

BHAKRA

POWER

PLANT-I

ULTIMATE

INSTALLAT1ON

LOflGITUDINAL

SECTIOII

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BIIAXRA

POWER PLAI{X-I

ULflHATE

'fNSTALLATION

T

YPICAL

TRANSVERSE

SECTION

FIG

URE

I4

Penstock

discharge

7l

cumecs

(2,500

cusecs)

rvhen

reservoir

level

is

at El.

513.59

m

(1,6g5

ft) MSf.

In

the

9ody

of

the

dam,

concrete

surrounding

the

penstocks

is

subjected

to the

following

stresses

:

(i)

Vertical

and

horizontal

normal

stresses

due

to

dead

load,

hydrostatic

pressure

and

earthquake

acceleration

on

the

dam

;

and

the

hydr.odyna-

mic

effect

of

water

on

it

;

(fi)

Horizontal

normal

stresses

acting

on

vertical

traverse

qlanes due

to

grouting

pressure

and

beam

action

of

horizontal

elemEnis

;

(ttt)

Stresses

due

to

temperature

differential

;

and

(lu)

Stressei

due

to

internal pressures

and water

hammer

in

penstocks.

In

the

case

of

penstock

No. 10

in

the

elbow

portion

reinforcement

has

been

provided

for

fufl

internal pres-

sure

and

anchorage

for

ihe centrifugal

force.

Contac

t and

Consolidation

Grout

ing

After

the in_stall,ution.,

of

penstock

liner

and

setting

of

concrete

around

it,

the

cbntact

between

the

liner

and

the

concrete

has

been grouted

"oo

teitea

bt

hammering

the

inside

of

the line-r.

Th;

p.iti""

which

glve

hollow

sound

wer.e.

regrouted

und.,

"

pr.rr,rr.

of

2812

gisq

cm

(40

p.s.i.).

For

the

penstockr.q

Io

10, grouting

pressure

up

to

5273

e/sq

cm

(75

p.s.i.)

had

b&n

prt".itt.o

-*itt

the

use

of

special

spiders.

In

the

dam

portion,2S.4

mm

(l

in.) grout

inlets

ygle

provided.

all

along

the

length

of

thelenstock

at

1^,.521Tm

(5

fr)

centres,

both

6t

top arid

bottom.

similarly,

to

erable

contact

grouting

ue'twein

*n.r.t,

lini_ne.

and

rock

for

the

tunnEl

porti6ns,

foui

:-S.

r

mm

(1.5.

in,)_

d_iameter

glour

inreti

were

provided

at

each

section,

1524

mp^(5

f!)

apart

ail

alon!

the-l;tth

o]

the

-penstock.

After

the iompretion

Jr

tti

$duting,

steel

plug-s

were

screwed

ano

werded

to

tf,i

grour

Iftl

u19

ground

flush

with

the

liner.

fit

voids

between

the liner

and

the

concrete

detected

by knock-

!1g

wittr

a hammer,

have

been

grouted

afte;'tapping

25.4

mm

(l

in.)

diameter

holes

ii

the linei,

-

Rock

around

the

tunners

for

penstock

Nos.

2

to

5

'

grouting

through

4.57

m

ngs

having

four

such

holes

%l'

:J?,

"li?F,.ll;,"li"

fil

cover

over

them

was

ress

""a?ilru*.]flt"fo"i&.,?ioln'

Expansion

Couplings

Due

to

the left power

plant

being

founded

partly

on

claystone

and

paitty

on

sandstonE.

two

eipansion

couplings

with

a

suspended

piece

of

pensto.k

hun.

been_

provided

to

allbw

not

onry

for

ixpansion

but

also

for

a

-considerable

amount

oi

settlemeni

of the

power

plant

structure.

Penstocks

from

Nos.

l

to

5

have

been

provided

with

two

3.96

m

(13

ft)

diameter

dresser

tybe

expansion

couplings

3.96

m (t3

ft)

apart

before

ttreii

connections

with

scroll

cases

and

aiter

the reducer piecei.

The

downstream

expansion

couplings

are l.iZ

m

(26

ft)

upstream

from

the

centre

line-

of

the units.

'

This

arrangement

can

take

upto 76.2

mm (3

in.)

of

horizontal

and

vertical

differential

movement

and

a

corresponding

rotational

movement

of l"-6'

at

each

end

^of

thE

.3.96

m

(13

ft)

long

piece

of

the

penstock

suspended

between

the

two

coupiings.

.

Single

4.27

m

(14

fr) diameter

expansion

couplings

luy.

been

provided

in

penstock

Nbs.

6 ro 10,

jfit

before.the

penstocks

enter

the

right bank

power

plint,

in which

case

no

differential

settlemenf

is

a'ntici-

pated.

'-ddt4t

39

FTGURE

15

:

photograph

shorving

the inside

of

the

Left

power

frouse.

Mechanlcal

Features

(!)

Head

Gates

and

Gate

Frames

:

One 3.5g

m

f1_11 *l !y,7 9z

m

(25

ft) fixed

wheel

type

head

gate

rs

rnsrarrecl

at

the

entrance

of

each

of

ttre

penstock=

on

40

the

.upstream

face

of

the

dam.

The

-

head gares

are

used

for

emergency

closures,

in

case

"iO"rugE*to

the

penstocks

or

hydrauric

turbines

and

for

J"*ut.riug

the

penstocks,

tb

permit

inif""tion

and

maintenance.

2.16

PowerPlants-Civil

Structure.s

Two

above

sround

power

plants,

one

on

each

side

of

-

the

centrally*

located

.piri*uv,

,near

the

toe

of

the

dam, have

been

provided

to

futty-trarness

the

available

hydro-power

porential

at

Bhakri

(plgu..

i5l.

-

The

left

bank

power

n]aqt.

(power

plant

No.

l)

(Figure

14)

construction

or

*nicir

was

taten

up

in

t[.

firsr

phasg,

consisrs

of

five

unirs

or

q0

Mw

,i""1.

lh9.

n.gy.r

p]qnt

was

commissioned

in

December

l96l

(Figure

l5).

FIGURE

16

: Photograph

showing

the inside

of

the

Right

power

House.

The

constructiort

of

tle

right

bank power

qlant

installed

capacity

of

the

units

a

(Power

Plant

No.

2)

was

taken

up

r_n

the

seiond

fhase

studiis

were

carried

out

from

time

to

and it

houses

five units

of 120

MW

each

(Figure

i6).

The

initial

water power

studies

2O-year

record

of

rivef

flow

for

the

1947

and

on

the

assumptions

that

reservoir

shall

be

governed

primaril

considerations.

umber

of

water

were

based

on

a

period

1927

to

eases

from

the

from

irrigation

The

two

power

houses

are

interconnected

for

integrated

working.

Water Power

Studies

:

To

estimate

the firm

power

which

could

be

_senerated

at

Bhakra

and the

desired

These

indicated

an

available

firm

wer

of

165

MW

for

Bhakra

units

out

of

a

total

firm

er of

265

MW

including

Nangal

Canal

units.

The

^s

udies

also

indi-

cated

that

for

89

percent

of time

the

would

be

257 MW

ar

Bhakra

and

14

Canal

units

and

would

require

616.7

power

available

MW

for

Nangat

million

m3

(0.5

4l

million

acre-feet)

of

additionar

warer

to

firm

it

up for

100

percent

time.

nexpectedly

fast

growth

of

power

studies

were

taken

suitable

means

of

increasing

,

These

studies

were

carried

for

rhe

period

l9l2

to

l9S4

r

made purely

on

irrigation

;,

ffiT?l';'il

*?1",

fi:'ili?:

feeder

and

replacing

the

areas

commanded

bv_

Bhakra

water

with

it,

in"

"nr-

power

at

Bhakra

andNangut

"outo-

be

incriaiia

to

z+s Mw

and

from

Nangal

units

to

120

MW.

ffr"r"

iotut nr-

power

potential

of

365

Mw

was

accepted

foi further

planning

of

the

units.

_

In

1959

while

plannir

Bank

Power

Flant

a-set

of

were

made

to

determine

units

so

as

to

utilize

to

water

power

potential

whic

m.

The

firm

power

poten-

he

capacity

of

Beas-Sutlej

0

cusecs)

worked

out

to

water

power

studies

were

power

potential

at

Bhakra

"orage

level

from 438.91

m

m

(El.

IAGZ)

MSL.

The

re

to

.raising

of

the dead

I

m

(El.

1440)

MSL

to

post-right

bank

power

n,ffiu:Lr:"'""?'

ji

,Y# ;A

pre-right

bank

power

plant

stage.

Number

of

(Inits

and

size

:

Based

on

the

1955

)n was

made

for

ten

units

90

MW

were

installed

in

ly

with

the

completion

of

ere

aligned

to correspond

18.29

m

(60

ft)

which

was

commodate

the units

of the

or the

construction

of right

power

studies

indicated

the

of

higher

capacity.

Keep-

'the

site

in

view

and

cavita-

city

of

70

MW

for

each

minimum

head

79.96

m

:he

rated

capacitv

of the

ade

for

the

friturj

possible

power

as well

as

the

cavi-

tation

and

transport

considerations.

A maximum

rated

capacity_

of

170,000

B.H.p.

for-rhe

;;i;"t

a net

head

of

tZt.92

m (400-

ft)

at

opening

was

adoptid.

The

mi

of

turbine

was

kept

ai

rated

hiaO

of

The

generator

was

rated

at

-iZO

M

factor

with

synchronous

.f.rd

of

ta,

Layout

and^Type

of

Structure

:

Various

possible

arrangemenrs

of

the

units

and

type

of

structures

for

the

power

plants_

were

considered^.

conuiniio"at

tyfi

of

above ground

structure

for

Uoitr;il

;;;;;

phnts

:,=3{_rlted,

as

consrruction

of

underf-uoO

iril;

plants

was

ruled

out

due

to

weak

nature

'of

the

abut-

ment

rocks

and

the

construction

of

po*

plant

within

the

body

of

the

dam

would

have resulted

in

high

concentration

of

foundation

itir*r.r

-

ou.

to

power

plant

opening

for

which

foundations

are

not

competent.

Righl

Bank

power

plant:

The

RightBank

power

P.lant

-(Po,wer

P]ant

No.

II)

has

beei

tocaied

on

the

right

bank

of

River

.sutlei

uoju.""i

t;id;pillway

a,pr9n

with

its

centre

rine

of

gerieratinguniirzbl.lT

m

(660

f0

downstream

from

and"parallel

to the

axis

of the

lly

Thjs

places

the

srructuri

on

massive

sandstoni,

;ust

up_qtream

of

the

claystone

stratum

of

Hanerie

choe.

with

this

rocation

ih"

f.nrtock

length

is

kefi

to

a minimum

as

well

as

the^righr

rb;tfi;;t

of

the

dam is

not

subjected

to

heavy

excavations.

In.selecting

the finar

rocation

of

this power

plant

it

was

decided

to..prace-.it

upstream

of

'the

claystone

stratum,

to

avoid

the

differential

settlements

ano

the

extensive

consolidation

treatment

and cut-off

walls

required

to

confine

the

claystone

foundations.

rlant

structure

also

accommodates

t bays

and

a

service

bay with

the left

rwer

plant

forming part

of

the

right

rall

and

the

service

bay

on

the

rilht

r

plant.

This

arrangement

is bist

stock

alignment

tailiace

excavation

I

rail-road

access

to

the

power

plant.

Ttrq

general

arrangement

of

servic.

UiV,

tiunrfor*r,

deck

;

rail-road

and road

approarh,

"i".,-ir

ti-ilu,

to

that of

power

plant

No.

I.'

-

.

Th.

g.enerating

units

in

this

case

consist

of

radial

axial

vertical

turbines

of

127

MW

cap;;iii-

^;;;;rt;;

head

of

12192

m

coupled

to

a r

2ol6i'Mw,li+

r"rVe,

11 kV,

187.5

rjp.m.

generators.

The

un-it

'rpu"ing

hai

been

kept

18.29

m

(60

rt)

in

rhis

case

arso.

Because

of

less

space

available

on-'the

right

"oJor

fui, po*"t

p.lant

duc

to very

steep

hilr

sroies

and

nearniss

of

the

right

diversion

tunnel,ihe

service

bay in-ir,ii-""r.

is

of wedge

shape

and

abuts

against

the

iock

"utiin

,.

42

3.1

Excavation

of

the

Diversion

Tunnels

The

excavation

of

the

huge

diversion

tunnels

through the

poo_r

rock

strata

posed

many

serious prob-

lems. About

40

percent

length

of

the

tunnels

was

were met

in

enlarging

-the

pilot

headings.

According

to the origin-al

proposal,

the

pilot

heading

was

to

be

enlarged

to

full

section

by

installing

temporary

steel

supports. Light

steel

ribs,

203.20

mmx203.20

mm

Part

rrr-rrain,

hnstruation

Featares

(8

in.

x

8

in.) at

l5.qq

lg

(3S

pounds),

consisting

7 curved

segments,

cold

bent

to

a radius

of

8.33

(27

ft.

4 in.)

and

2

straight

footings

each

3.05

m

(10

f0 long

were

proposed

in

the

good

rock

reaches

side,

trenches

were

excavated to

a 1evel2.44

m

(S

ft)

above the

centre line, below

which

the

excavation

was

almost

vertical.

Light steel

ribs consisting

of

5

of

m

43

FIGURE

17

:

Photograph

showing

the

view

of

the

17.6

m

(58

ft)

iliam-.ter

diversion

tunnel under

construction.