Indian National Committee on Large Dams. Design and Construction Features of Selected Dams in India
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Illsni
IDum
1.
Ilistory
The
River
T+ptabour
720
km
long
is
one of
the
largest
rivers
of
India,
flowing
from
.irt
to
-ivest
and
jojning
the
Arabian
sea.
It
iises
in
the
dense
forests
of
Madhya
Pradesh,
near
Multai
and no*,
about
265.
km through-
Madhya
,pradesh,
230
km through
Maharashtra
and
225
km
through
Gujarat
State.
The
necessity
of
large_
lcale iqrigation
was
keenly
felt at
the end
of
second
world
w"i
when
acute
foo&
shortage
was
experienced.
The
erstwhile
Bombay
State,
therefore,
approached
the C.W.
and
p.C.
in
gaa
to
investigate
and
formulate
schemes
for
-utilising
the
unused
water
resources
of Narmada
and Tapi
Sasins
for
flood
control,
irrigation
and
power
geoeration.
It
was
also
decided-thaf
such
parts
br
tne
Sasin
develop-
ment
plal,
ryhich
would
produce
quick
results
ariO
later
on
fit wirh
the
overall
^
plan
of
ihe
basin
should
be
taken
up
in
advance
of thi
rest
of
the
plan.
An
ad hoc
committee
of
experts
was
appointed,
in
1948
ty
the
Government
of lirdia,
undei
ihe chair-
manship_of
Shri
A.N.
Khosla
to
examine
the
pro_
posals.
The
committee
recommended
to take
up
the
proposed
scheme
of weir
at
Kakrapar
at
the first
instance
and
coasider
the storage
dam
it ukai at
a later
date. The
survgv-s
a1d investigations
were,
therefore,
taken up in
1948
for
lower
Tapl
basin,
i.e.,'
Kakru.p^i
weir
and canals..
Tt..
projectleport
was
subs"qu"titty
prepare-d
and
administratively
approved
by
Govern_
ment
of
Bombay
in
June 1949
foi
its.
6.27
irores.
The
l9y.r
Tapi
-project
comprised
a
masonry
weir
at
Kakrapa-r
and
two
canals,
one
on
right
bank,
65 km
long
and
the
other
on
left
bank
tOd'
km
long,
both,
having
an
irrigable
command
area
of
2,l4Vg0
h;
Purt
f-Preliminarry
(5,30,000
acres)-
T!-.
construction
of
Kakrapbr
weir
was
starred
in
l952iand
completed
io
f
g5Zl'-'-
in
May
19_56.
This
pro_
tilisation
of
0.274
M
ha
m
minary
works
on
colonies,
Iune
1956.
.
However,
considerilg
inter-State
aspects
the
plan-
ning
commission
F"qtti
creired-
the
ii[ai-
proi..t
in
A_ugust
196l
with
F.R.L.
roi.
r
io
.,
vi.r5^Ji
r.
r:z
M.
fa-m
(9.18
M
acre--ft)
and
a
cost
of lis.
jb.2i
"ror.*,
with
break
up
as
under':
Rs.
Miilion
(r)
Dam
and
appurtenant
works
357.1
(ii)
Main
canal
and
branches
(tii)
Hydro
electric
installation
r
13.5
111.5
Total
582.1
_
The
dam
was
finally
complete
d in 1972.
The
work
of
canals
was
however
in
prog..*
up to rgTg-7g.
Most
of
the
canal
works
are
no*
c"ompleted.
^
The
project
cost
is
being
revised
on
account
of
rise
ot
construction
cost,
increase
in
installed
capacity
of
239
i"""Hii:XTi!fi;
and
the
latesr
cosr
of
the
project
,,^-Ih1
Ind.e1
Map
of
the
revi
Figure
r
anJii,
sarient
riuiu*'#fr%i$:?if,'J;r
l"
(l)
Dam
and
appurtenant
works
(li)
Main
canal
and
branches
(ur)
HyOro-electric
installation
...
Tapi
...(*qr,
Distt,
Surat
t_rularat
Miyogom
_r
Rojpipfo
Brooch
!-Ironsm
issron
ti
ne
(.
Kim
R.
oi
Dorn
Tofal
Rs.
Mitlion
762.2
371.4
22s.5
-
1359.
I
Salient
Features-Ilkai
project
Location
of
Dam
l.
River
2.
Village
Fort
Songoahl
_
\
\
J1
ropf
Mindhof
o
4L
'R
*i
Purno
R.-
Eilimoro
r
Ambiko
R.-,
Aursngq
R
--
Por
R,J
Roif woytA'-
J
YI^,1
g:
r,o
^
J
;
;;
"-_
_-_-_
b
Tronsmissio;,,";;_'_
-
Ln
Slote
Doundorv_
_ _
o
o
E
o
(D
'E
o
L
TL
lUkoi
R.e.M.C.{
kropor
R.8.M.C.
KoNrqpqr
Weir
240
FIGURE
I
:
Index
map_Ukai
project.
Hydrology
l.
Drainage
area
of
the
river
above
the
dam
site
2.
Mean
annual
runoff
at
the
darn
site
3.
Observed
maximum
flood
at dam
site
4.
Design
flood
5.
Maxirnum
regutated
outflow
from
the reservoir
Reservoir'
l.
Dead
storage
2.
Live
storage
ar
F.R.L.
105.156
3.
Maximum
storage
level
(F.R.L.)
4.
Water
spread
at F.R.L.
5.
Villages
affected
by
submergence
Dam
l.
Total
length
of
dam
(i)
Earth
dam
(ii)
I{asonry
dam
2.
Maximum
height
of
earth
dam
above
bed
3.
Maximum
height
of
masonry
dam
above
foundation
4.
Top
of
dam
Spillway
l.
Crest level
of
spillway
2.
Length
of
spillway
(pier
thickness
3.962
m
3. Top
of
crest gares
4.
Type
of
gate
...62,225
kmz
...1.722x
106
ha m
...42,470
m3/s
in
Aug. 1968
..-
19,490
m3/s
...22,650
mt/s
...0.
14185
x 106
ham
...0.70930
x
106
ham
...EL.
105.156
(R.L.
34s.00)
...60.095
ha
...175
Nos.
5.
Size
and
No.
of
Gates
6.
H.F.L.
Power
Section
I.
Size
of
penstock
2.
Installation-4
75
MW
each
3.
Generation
at
factor
4.
Annual
energy
generated
units
of
35o/o
load
(units)
Canal
System
l.
Gross
command
Y;iil;it
area
ha
2.
Annual
irrigated
...10,540
area
ha
3.
Length
of
main
canal
and
branches
...1260
km
4.
Length
of
distri-
butaties
and
minors
._
370.15
km
Utilisation
l.
Annual
utilisation
ex_storage
including
reservoir
losses
-o
Estimate
of
Cost
1.
Unit-I
dam
works
and
appurtenant
2. Unit
II
main
canal
and
branches
3.
Unit
III
Hydro-electric
works
...22
Nos.
(15.54
m x
14.78
m)
...EL.
106.98
m
...4
Nos.
7-01
m
diameter
..
.300
MW
...193
MW
...670
x
106
kwh
U.R.B.C.
Total
36,3I0
7,57,72O
ha
ha
76,730
1,47,270
ha
ha
1220
km
2480
km
2t7.2s
s87.40
km
km
...4926.83
m
...4,059
m
...868.83
m
..
68.58
. ..66.14
m
...EL.
I1I.25
m
...EL.9t.135
m
. . .425.196
m
(13
ft)...42s.196
m
..
EL.
105.
461
...Radial
Benefits
t.
.Firming
up Irrigation
in
Kakrapar
Command
2.
Annual
irrigation
in
Extended (Ukai)
Command
3. Perennial
irrigation
in
Kakrapar
and
Ukai
system
4-
_FirT
power
(at
35"/"
load
factor)
...7.081x
103
mg
...Rs.
in Million
762.2
"'') ))
))
37
t.4
,)
t,
Total
225,5
1359.
I
2,27,430
ha
1,52,400
ha
47,290
ha
1,93,000
kw
241
Fr-h-
_
_
2.
Hydrology
2.2
Rainfail
'-tn
generally
starts
during
bout
90 percent
of
the
rainl
monsoon-
period
extending
he
special
characteristics
o?
:
heavy
rainstorTs
generally
st
to
the
end
of Sep-tember.
manmum
and
minimum
W
and
256
mm
respectively.
2.3
Runof
The
River
is
being gauged
_
at
Kakrapar
weir
and
5:L*::_s_1uge
.sitesl
"f[E-
"ur.rurJ--dGe
'o-ata
at
6-al(rapar
weir
site
from
1953
to
1959
aid--at
iiathore
bridge-site
availabrr
r"itn.
priioo
from
rg3g
to
1959
ar_e
the
principar
data
used
fbi-
computations
oi yierd
series.
The
data
have
been
anatysii;-
t*"
Jrpu.ur,
fl."-ipj,]_t1,
(i)
runoff
during
monsoon
and
(n)
runoff
qurrng
post-monsoon
period.-
Monsoon
fu"?lf
,
The
monsoon
yield
is
worked
out
from
the
statistiiartv
a.riueJ
curvilinear
correration
between
rainfall
and
iunon
-rt.
relation
at
Kathore
bridge
site
is
computed
io
F.p.s.
units
as
under
:
statistical
method
of
murtiple
correration.
The
estab_
lished
retationship
in
FJ:E';;ir,
;;;,"0#i
X:0.261
A+0.441
8_O.Zs
where,
X:p.M.
runoff
in
M
acre-ft
(@
Kathore)
I
:Monsoon
precipitation
index.
.B:p.
M,
-rainfall
in
excess
of
l.Z7
cm
(0-5
inch)
per
_o"tt.
'Based
on
the
above
correli
2.4
Flood
Estimation
ysiography
of
a
catchment
R:0.01722
x /1.es86
(at
Kathore
bridge
,sauge
site)
Where,
R:
runoff
in
M
acre-ft.
/:
W.M.R.
in
inches.
ment
between
ukai
and
Kakrapar
is
insignificant
compared
to
the
size
of
the
whole
"at.hm"ent.
An
average.
unit
hy_drograph
with
a
peak
of
l
i,065
cumecs
yas
.
adopted
fo,r.
lvolking.
out-
the
standard projeci
fl9od,
while
the
highest
uiit
t1i-arogiuph
-ilth
"
peak
of
12,282
cumecs
was
deriveo
from-if,"
nGii"flood
of
over
l0
cm
over
the
entire
catchment."--rti,
unit
l:j::ql"fh _*,"r
utilised
*itroui-;t
per""ntage
Increase
rn
working
out
the
maximum
poisibie
flood.
pesign
Flood
Hydrograph
:'the
rainfa[
data
for
the
period
l89l
to
1959
*e1e'examined
u"J
-o;;
-;;r;
the
entire
catchment
were
rtitative
.estimate
of
design
the
catchment
is
elongated
the
hills,
depth-area
dura-
rtr
method
have
not
been
Le
design
storm
was
arrived
:ion
method.
The
maximum
rainfa[
varues
in
catchment
for
l
day,
2.days
ald
I
days
were
found
out
bt
-b;ilh-
Doru_
tion
method.
The
catchment
rainfail
for
.rii."
severe
storms.
experienced
between
lggl
to
1959
*ir.
used
lor
cre'vrlg
the
Depth
Duration
curves
as
well
as
an
Eny.lop
Curves.
T!9
s.torg
defths
for
i
duvl
2
days,
?lq:
days
were
obtained
ur' ii.:o-;;,
-it'J-
urro
19.30
cm
respectively
from
Depth
Ourai-i&
"u*"r.
2.5
Flood
Routing
TABLE
II.1
Fr
o
od
tJff:"
"?:iiil,
.esur
ts.
sl.
No.
Return
period
in
years
Probabilitv
of
flood
in
percentage
Remarks
to
196g
(Thousand
cumecs)
-
For
accurate
flood
studies,
the
storm
distribution
tgr
worst
effect
is
required.
as
the
O";;;;;
the
rur wursr
enect
ts
requrred.
As
the
data
for
the
{iffere-nt
region
are
not
available.
the
"U.,ro"
n.r"tr,
ble,
the
above
Depth
Duration
curve
was
utilisra
;iih
severar ,*.,,-r"7;11''o^'
was
adopted
for
the
basin
for
maiimisati
vvcr-J
<r'\r,prcu
rof
tne
Dasrn
lor
maxlmisation
of moisture
adjustment.
The
storm
depttrs
were
increased
bv
were
increased
bv
multiplying
the
above
factor.'
-rn.
udu.
tJ;;;-";
In
order
to
find
out
physical
upper
limit
of
the
flood,
the
maximum
problbie
flood
-"i"r-
o.ii".o
uft*
maximising
th.e
storm
depths.
In
absenc.
oi -.t.ororo-
grcal
ooservations,
a
moisture
adjustment
factor
of r.2
l.
2.
3.
5
9
l0
t5
20
30
50
100
150
200
250
500
750
1000
20
1l
l0
6.7
5
aa
J.J
2
I
0.67
0.5
0.4
0.2
0.13
0.I0
24.01
probabitity
26.51
of
flood
in
29.00
percentage
31.55
100
34.80
:
-return
period
38.20
in
Years
42.51
48.23
5t.77
54.t2
56.10
60.63
64.80
67.63
probable
flood
was
59,gg3
cumecs (Z,iiO,OOO.ure"s;.
243
hical
Survey
(i)
A^dvance
depletion
of
rh
I03.33
m
(339
ft)
up
to
the
(rr)
[U1ry
of reservoir
at the
\u.:z
ftl4ay)
in
the
month
o
n-fl
up
the
reservoir
froE
ll
(33ri":;;
fri'"'|r
r.(,ur
r'
!&._ij,f;ffi"n:,1iT*:?:":r,ff:i
Q,il
!:.IT
as
possibte
restrir
_9}1
in
lle
c,iln-oLna
il-;i"tili
24'6f0
cumecs
the
safe
d
ted
on
village
map.
drscharge
carrying
capacity.
storage
level,
as
od
is
known
to
be
7 )
",
tn,
_."iiJ,,"-
t.z
Eydrological
Survey
li#?:",'tgf
l?
-Jll?ti,":'^P,:nt,
there
are
65
rainspuge
starions
any
mrerm€diale
rz'rla
records
for
these
are
uuuitu6t"
itl.-riiil
'from
Jhe
_rese_r-
Sitt
Load
anit
l'T,,tli""l,*X;
:lh*j;_i{i,#i:;
3.
survey
aod
Inyestigarion
e
routed'
;t;"*r"tr*
fl*:l
and
especially
d
uriri
r""
llXtt"il!ryJf
,tvpes
or major
survevs
were
ca*ied
$:trJ#"li
6#
r.
ropographicar
surveys.
ili:3fir|eff"":T
2.
Hydrological
surveys.
ved
in
1954.'
'
l.
3lilll#,j,ill;l*;:"':;.o,""".
3.3
Borrow
Area
rnvestisation
5.
so'survey.
hrcfrlifial;,:i*:_ifiTr".,ff*":f
,,*f,k;,ii."s
244
for
all
the
samples
in
of
classification-of
soil
left
bank
borrow
area,
a
basis
was
derived
as
given
below:
-
sl.
No.
Zone
Clay
.
Atterberg's
content
tests
Proctor
standard
Permeabi-
lity
value
cm/sec
sl.
No.
Borrow
area
Earth
Dam
Situation
Area
(sq
km)
Reach
Qty.
M.
cu
m
L. L.
P.
I.
M.D.D.
O.M.C.
ke/cm
%
I.
Impervious
t5-30
40-60
I5-30
<t680
>t8
t_2xtO_6
zone
Semi
per-
5-15
30-40
5-15
1680_
t0_ 0.5_5x
lO_4
vrous
zone
lgl0
tg
Pervious
<5 30
N.p.
>1920
<t0
l0-g
7,f|11^
l.
Left
bank
2.
Right
bank
3.
Right
bank
saddle.
borrow
area
3.86
|
1,32
2.05
rarth
dam
on
Ieft
flank
Earth
dam
on
right
bank
and
main
gorge
Right
bank
saddle
dam
6.0
14.0
3.0
J.
'For
exploration
of
the
borrow
area,
the
grid
lines
.were 13.ngeq
every
l50
m
on
the
upstream
oT
the
dam
lrne.
'l'he
tirst
grid
line
was
takbn
roughly
at a
distance
of
l0
ave_rage
water
depth
from
thE
ufstream
19e -of
hearting.
with
a
view
to
preserve
the
'natural
blanket
on
the
upstream
for
reduciion
of seepage.
.
Along
the
g-rid
lines
rrial
pits
at 300
m cf c, i.e..
alternate
g$d
polnts,
were
taken
5 m
deep
or
upio'hard
strata
whichever
is
earlier.' The
samples
iollected
from
these.trial pits
were
tested
for
gradition,
compaction
and
Atterberg's
limit
tests.
on the
baiis
of
'
broad
classfications,
detailed
surveys
were
done
in
the
borrow
area
by
excavating
the-
remaining
trial
pits
ai
300
m
centres,
- _
Samples
from
trial
pits
were
collected
at every
1.5
--depth
interval
or
c[ange
of horizon, whichever
is
earlier.
Composite
samfles
were
taken
at the
rate
of one
for
each
trial pit
or
each cut
which
is
to
be
operated
at
one
time
ol
shovelling. With
the
help
of
above
method,
it
had
been
posiible
to
collect
one
sample
for
every
35.4
thousand
cu m
strata.
Borrow
area
investigation
was
carried
out
for
quantity
as
1.5
times
the
actual
requirement
to
cover
any
uncertain-
e
ties
during
operation
of
borrow
area.
Looking
to_the quantity
of
earth
work involved,
a
programme
for
investigation
and
testing was
framed
and
adopted
at
the
proJect
to
arrive af realistic
and
Jgpr€sentative
soil constants
for design
of earth
dam.
Various
tests,
viz.,
mechanical
anallsis,
AtterQerg's
limit
tests,
qroctor
compactioo,
pernieability
tests
a-nd
shear
tests
including
these
in-
iarge
she#
box
for
material
larger
than
4.75 mm
weie
carried out
on
representative
samples.
Atter
studying
the tast results
The
soil
was
classified
accordingly.
3.4
Other
Construction
Material
Survey
The
main
source
of
sand
was
river
and
small
tribu-
taries
of
River
Tapi.
3.5
Soil
Survey
in the
Command
Area
The
left
bank
command
area
has
rich
agricurturar
soils
The
soil
syTv-ey.
done
in
ruki"pur-i;ft
bank
command
area,
which
is
too near
the
ulai
t.n
uuoli
command
area)
revealed
that
the
soluble
ialts
in
245
rajor
portion
of
the
area
is
a
salt
content
ranging
from
rjff
:' l":::,T
i il
tn,", ;:
:i:
i;
se?.
.
rhe
predo
m
inant
;'i.,"B3l;";'liilg.,?:3
;lT"
"::
sulphates,
the
recfamation
of
the"area
wirrliot
present
much
difficulry.
The
observations
of
sub-soir
water-tabre
was
made
in I
19 wells
in
rhe
lefr
bank-
command
area
and
r
16
wells
in-rhe
right
bank
command
ur"a.
Wit..
levels
were
observed
in
these
weils
ouring'Nau..n
to June
1954
and
Febr-uary
ro
March
1955
on
the
left
bank
qnd.$g{1g Februar.yro
May
1950
u"O
-F.Uruu.y
ro
April
1954
on
the
right
ban(.
lble
varies
between
4.5
to
lne,
in
the
left
bank
canal.
as,
depth
of
sub_soil
water_
and
is
about
4.5
to
6.10
m
'to
May.
The
water
in
werrs
in
the
reft
bank
area
is
genera'y
potable-
on
the
right
bank
the
warer
in
the
weil
is
F-:T:I?]lf
saline
and
as
such
has
rimiiei
ipori""tion
for
tfrrgatron
purposes.
3'6
climate
and
Agricurturar
Conditions
in
trte
com-
mand
Area
ons
in
the
command
area,
:rature
and
other
weather
rfall)
are
collected,
i.e.,
nd
area
and
Bharuch
foi
The
area
lies
in
the
area
of
.high
tentperature.
In
Bharuch,
the
annual
mean
-u*rrru-
temperature
is
96'F
and
mean
minimum-
1.,rip.rutur.
is
70.F.
The
highest
maximum
of
tta"p
-iias
been
recorded
but
temperature
over
115"F
are
not
uncommon
over
this
hot
area.
The
lowest
minimum
temperature
recorded
it^(il^l_Vears
recorO)
is
+l;F
U"t
minimum
remperarure
of
40"F
and
tower
over
the
area
i;
ilI;t
^'
rvuvi
The
rainfall
data
of
over
50
years
is
available
for
most
of
the
raingau_ge
stations
but
of
15
stations
in
Surar
district
and
liilBh";u".t
oirtri.t.
In
the
command
area
of
Ukai
left
bank
canal,
the
rainfall
varies
f1o-T-rs2l^
oin''
to
2032
mm.
In
the
command
area
of
,y{li
right
bank,
the
rainfall
varies
from
889
mm
to
,a:
mfi'.-
ile
go
percent
of
rainfa,
246
:::qtt
during
.Julq
and
September
in
rhe
area
and
receives
from
Arabian
Sea.
-'--
From
Mav
to
September
the
south_west
winds
from
Arabian-Sea
prevails.
The
command
falls
in
the
area
of.
the
wind
speed
befow
140
km/hour._-Th";;;"
aaifv--*int"
speed
varies
between
5
to
lf
mTfrour]
4.
Geology
rend
E_W
and
NNE_SSW
rly
jointed;
the
joints
are
lnd
horizontal
tob.
exploration,a
90
m
wide
llill
No.
a
z.
'lo
'7t{'ieo"
o
f)
-.<r#-
Lefl
bOnk
eorth 6lqrn
--
Uos
Re f e
r
e n
c
e s
Overburden-----F^
"f
Amygdotoidot
bosott--@a
Sheor
zone
-
____-
Wmn
Weothered
rock--
Iw
wl
Purple
Amygdotoidof
lle
vrl
porphyritic
Amygdotoidot_llVz
vzl
Dol€rite
dyke--
ITIEI
bosolt
J
bosolt
)
FIGURE
2:
Geological
lorrgitudinal
section
along
dam
alignment
of
Ukai
project.
Right
bonk
eorth
dom--------.+/
Frocture
zone--
W
Red bote
oeo-.
lffi|
Mossive
bosoft. E
or
the
minimum
6
m
thick
cover
of
good
rock
was
left
over
such
features.
,
I.*
shear
zones
varying
in width
from
5
to
22
cm
consisting
of
fractured
rock-
and
yellowish
clay
gouge
was
excavated
either
up
to
good
rock
level
oi
to
tfie
depth
equal to
twice
its
-width
and
backfilled
with
c_oncrete,
and
further
treated
by
grouting.
For
treating
the
joints,
the
pattern
for
lo-nsoridaiion
g-uti"E
was
holes
9
m
deep
spaced
at
7.6
m
centre
ti centre
and were
gr-og1e{
under
3.5
kg/cms
pressure.
Additionat
holes
were
drilled
as warranlted
by
geologicaicondi-
tions.
This
was
done
after
raising
The
frurooty
to
3
m
_height.
The
curtain
groutingl
holes
**
24
m
to
3.7
m-
deep
?nd
grouted
at fiigh
pressure.
The
spacing
of
these
holes
was
6
m,
and
Orittea
through
drainage
gallery.
Later
on
the
drainage
holes were
drilled.
In
block
2
ofl the
left
transition
dam.
the fina,l
foundation
was
inclined
towards
downstream with
an
elevation
difference
of
l
l m
at
the heel and
toe.
The rock
surface
wag
quite
rough,
and the desigr,r
calculations
indicated
that it
was-safe
against
slidiig.
Ver
toom
bp
of
don
R.L.lrr.asm(3osft.l
F
Spillwoy
-1
LF.
R.L.
ro5.ts6m(34sft.l
247
As
a.pre-cautio:rary
measure,
a
2
m
deep
trench
was
provided
at
the
downstream
toe
with
a
fillet
at
the
ance.
4.3
Spillway
The
spillway
is
designed
for
49,50Q
cumecs
and
maximum
probable
flood
of
59,920
fo"ie.s.
bor
the
energy
dissipation
arrangement,
two
altelnatives
were
considered,
viz.,
(a)
stilling
basin,
and
(D)-s[i-;u-p.
^.The-
stilling
basin
needed
excavation
of 0.4
M
ms
ot
hard
rock.
An
exploratory
trench
of
30 m
x 15
m
excavated
in
the
impact
area-of
the
ski-jump
indicated
that
the
rocks
in
this
area
were
basafts
and
dolerite
pVkes.
It
was
thus
considered
to
have
a
ski-
jutp
beca.use
of the
rocky
;;u
in
the
downsrream
in
the
tail
channel-.
and
-keep
a
watch
on
the
perfor-
mance
and
do
remedial
treatm^ent
required.
ning
since
1973.
In
some
7
mx
15
m
and
about
30 m
filled
up
by
debris
during
th
4.4
Earthen
Dam
(it)
Tg
p-rovide
a
pratform
of
sand
berow
the
seat
of
the
9ur..
lieeping
its
top-ui-iUbut
J
m
above
standing
pool
t"u.i,'url-
ir:ouioiog
a
cut-off
through-this
sano.
(iii)
Driving
-sheet
piles
could
have
been
an
obvio'rs
choice,
but
for
the numlrous
horders
occurring
in
the
overburden.
(tv)
To
rely
on
the
concrete
diaphragm
berow
the
diversion
dam
to
provide
;
#rd;enicut_otr
(v)
T.o
provide
a
g.rout
curtain
with
suitable grouts
Iike
clay-chemicat
and
chemi.;i
jili
uprtr.u.
of
the
diversion
dam.
OR
.
To
construct
a
second
line
of diaphragm
some
disrance
upstream
by
way
or-pioiio;"g--i
further
safety
factor.
'
(vi)
To grout
the
sand
in
between
the
above
mentioned
two
lines
of
concrete
diaph*grn
with
suitable
grouts.
OR
To
-
provide
a
positive
earthfill
cut-off
down
to
rock
between
the
two
diaphragms.
^ $s
per
the
construction
schedure,
the
downstream
of
the
earth
section
was
raised
utio-urti-ui;it;-th.
open-cut-off
down
to
the
rock
was provided-between
the
diaphragms.
In
the
foundation
of
the
dam
right
bank
smal
saddle
dam
excavated
as
much
as
g
"m
;;6,
there
wasa
1.5
m
wide-f1u-rt
cutting
across
the
foririoation
and
also
0.3
m
thick
red
bole
bed was
pr;;o1
The
fault
zone
was
excavated
to
a depth
oi s
*lnd
an
impervious
blanket
-was
proviO.J-6"
iir.
ilprtream
covering
the
fault
and
the
red
bole
layer
6;.
--'
In
the
case
of rig_ht
bank
saddle
dam,,the
cut-off
depth
varied
froq
fz
to ts
m,
and
is
in
-weathered
to
mo'erately
flesh
basart,
wheie
red
bore
*ur
**"o-
tered,
the
cut-off
was
taken
below
it.
In
some
of
the
sections
of
the
cut-off,
there
were
vertical.
steps
of
about
6
t.o
g
m,
slope
*ui
-"0"
bt
a
plastic
concrete
consisting
'or
demeni,
*il
and
crushed
aggregates
mixed
with-bentonite.
terminated
was
very
depth
of
to i0
m.
much
as
as35m
The
existence
of
a
tl
gravel
and
boulders
be
water
in
the
channel
and
overburden
with
underlying
bank
terrace
had
presenti
positive
cut-off
for
the
eart
Cut-off
in the
river
channel
was
decided
to
be
done,by
opgn
excavation
after
considering
the
follow-
mg
atternatrves
:
(i)
Two
coffer
dams
without
sheet
piles
and pum-
pjng
out
warer-Two
seasons
frior
to
diver-
ston.
4.5
Seismicity
In
the
background
of
the
Koyna
Earthquake
of
I
I
December,
[gel
of
rhe
malnitude
-
oi"iiog
I
rke
of
23
March,
l9Z0-
of
mic
coefficient
was
revised
'izontal).
The
epicentre
of
km
NW
of
the
Utcai
Dam.
ory
has
been
functioning