Irrigation, Water Power and Water Resources

Engi eacrihniegve
354
imperviousness of concrete. Considerable economy can
concrete, such as workability and also
because quantity of cement is reduced. be
low-heat cement is used in
To reduce heat of hydration, sometimes special place of
portland cement. Sometimes retarding agents are added to the concrete at the time of mixing tothe
rate of heat generation so
that most of heat is lost from the concrete surface. TearmdormaA
4. Miscellaneous methods The following miscellaneous methods are generally used to
temperature.
() By reducing the lifts from the usual 1:5 mto 1·0 mor so, temperature can be
contro he.
extent. As the volume of concrete in the lift is reduced. less heat is generated. But the
construction joints will increase and the progress of work will be slower.
control ednumberto some of
(ii) By increasing the time period between the successive lifts to about 4 to 5
cooling time is available for dissipation of heat from the surface. However, the progress ofdays, suf icien
slow. Work becomES
(ii) As far as possible, curing by water should be done, as it reduces the surface
Moreover, when the water used for curing evaporates, if further lowers the surface
in dissipation of heat. temperaturetemperandatuherlegs
11:36GALLERIES IN GRAVITY DAMS
Agallery is asmall passage in a dam for providing an access to the interior of the dam. The galler
is usually rectangular in shape with its top and bottom either flat or semi-circular. For a gallery with
L15m top and bottom flat, it is necessary that all the
FLAT
-SEMI - corners should be rounded to reduce the strese
CIRCULAR concentration Fig. 11·55 (a)]. fthe gallerr is
with a semi-circular bottom, it is filled with
unbonded concrete at the base to provide a
flat surface for the walkway [Fig1155 (b)]).
2-2 m The gallery should be sufficiently large
to serve the required purpose. It should provoe
adequate working space and access for the
equipment for normal maintenance. If it is to be
WALKWAY
used for foundation grouting, it should be
WALK WAY sufficiently wide to accommodate the drilling
rig. The width of the gallery generally vanes
DRAINAGE
TROUGH from 1·5 to 1-8 m, The height of the gallery s
generally between 2-2 to2:4 m so that aperson
shoud bt
(a)
Fig., 11·55
(b)
can casily walk inside it. However, it feasible
noted that galleries are weak spots in the dam and they should be made as small as practicallyand1-80
to reduce the weakening effect. The usual sizes of the galleries are 1·5 mwidth x 2:2 mheight,
m width x 2-4 m height.
Functions of a gallery The gallery may serve one or more of the following purposes. from
percolating
1. The gallery can be used as a drainage gallery to permit drainage of water
upstream of the dam into the body of the dam or its foundation. and
groutin8
2. Agallery can be used for providing space for equipment requiredfor drilling holes
the holes to form a grout curtain in the foundation. maintenance.
3. A gallery provides an access to the interior of the damn for inspection and its
structu
study
4. Agallery also provides space for installing various instruments in the damto
behaviour.
 355
.GravityDams

Agallery can provide space for the mechanical and electrical equipment forthe operation of gates
5. penstocks or spillways.
outlet conduits,
for piping system for postcooling of concrete can be accommodated in the gallery.
The
6. TI joints.
gallery can be used for placing equipment used for grouting of contraction
7. The provides an access through the dam for control cable and power cables.
gallery
8. The provides access to the interior of the dam to the visitors.
gallery
9. The galleries Depending upon the purpose served, the galleries can be classified as follows:
Types of 1. Foundation gallery 2. Drainage gallery
3. Grouting gallery 4. Inspection gallery
5. Gate gallery the dam.
foundation gallery is provided at or near the foundation levelTheof bed level
gallery The for the full length of the dam.
1, Foundationextends from one abutment to the other valley. Its alignment is
gallery usually to conform to the transverse profile of the dam for its effective
The can slightly change close to the upstream face of the
of the gallery to the axis of the dam. It is provided the upstream face of the
dam and the gallery
usually parallel thickness of concrete between greater. Moreover,
However, the minimum depth of water in the dam or 6 m, whichever is gallery and the
use. of the maximum between the floor of the
should be at least 19%
minimum thickness of 1·5 m of concrete
there should be a percolating through the dam
foundation rock. drainage of the water
foundation gallery is mainly used for the upstream face of the body of dam is intercepted
The
The water percolating through the construction and carried to the gallery. In the
and the foundation. the time of holes drilled in
formed in the concrete atfoundation is intercepted by vertical drain
by the vertical drains seeping through the dam and foundation are usually 12-5
the
same manner, the water to the gallery. The verticaldrains in collected in the drainage gallery flows
carried water
the foundation and have a spacing of about 3 m. The provided at one end of the dam, from
and sump
to 30 cm in diameter (or gutter) and is collected in
a
nrough a drainage trough provided
where it is pumped out. and grouting holes for the grout curtain height
drilling
The foundation gallerypressureis also used for done through a gallery only after sufficient
Oundation. The high
grouting can be
recuired weight to counteract the grouting pressue.
gallery.
constructed so as to provide the discussed above, also acts as a drainage
ue damhas been gallery, as a supplementary
2. Drainage gallery The foundation also called the drainage gallery. Sometimes, downstream portion of the
sometimesthe foundation gallery is the
Therefore,
drainage provided in the case of high dams for draining
located downstream of the
foundation
gallery is also
dam and foundation. The supplementary drainage gallery is
usually
measured fromthe
upstream edge.
the dam, dam and is,
gallery at a distance of about two-thirds of the base width ofonly in the deepest portion of the foundation
This supplementary drainage gallery is usually providedThe drainage holes are drilled into the
therefore, not continuous from oneofabutnent to the other.
from the gallery for the draining the downstream portion of the dam. the
earlier, is also used for grouting
3. discussed
gallery The foundation gallery, as
foundationGrouting
to form a grout curtain near the upstream face.
for grouting the contraction joints of the
supply.
gallery. is provided upstream face. The
Sometimes,
dam from
within
a supplementary grouting them for the
the dam because it becomes difficult to grout the gallery which is located near
the
return and vent headers of the grout piping System are placed in galleriesin the vertical
Op of each 15 m supplementary grouting
lift of
concrete. Thus the spacing of the concrete. The piping
direction
system
is about 15 m. The
required grouting galleries are also helpful for post-cooling
for post cooling 1s arranged so as to terminate in these galleries.
of
the dam for
4. to the interior of
lhspectioInspection
access the
gallery inspection gallery is used to provide taking observations of
n of the dam from An inside. The inspection gallery is also used for
356 Irrigation, Water Power and Water Resources Engineering
various instruments installed in the dam to study its structural behaviour. Generally, no
gallery is provided in a dam. The galleries provided for other purposes are also used separate
as iinspection
galleries. In small dams, only one gallery is usually provided which serves all the purposes. nspection
5. Gate gallery In some gravity dams, aseparate gallery is provided to instal the
electrical equipment required for the operation of gates of the outlets, penstocks or spillway.mechanical
The loct and
and size of the gallery depend upon the requirements of the equipment to be housed in the gate palle
The gate gallery usually connects the hoisting chamber located just over the control gates of c
(outlets) and penstocks.
Design of a gallery A gallery is an opening (hollow space) in the body of the dam and hencs i
creates a discontinuity in an otherwise continuous concrete mass. The gallery alters the normal. stress
pattern in the body of the dam and a stress concentration occurs at the boundaries of the gallery. In order
to locate tension and compression zones around the gallery, the theory of elasticity is commonly used.
The stress concentration aroundacircular gallery can be determined by assuming that the dam is an
infinite plate and the gallery is a small circular hole. It is wellestablished that when an infinite plate with
a hole is subjected to a vertical compressive stress f, a maximum compressive stress of3foccurs On te
horizontal axis of a hole and tensile stress of f occurs on the vertical axis of the hole (F1g. 1I
However, the tensile stress changes to compressive stress at a height of about 1·70 r from tne couu
the hole where r is the radius of the hole. around
Because of the tensile stresses develop
-COMPRESSION the hole, the total tension is given by .(1-85)
TENSION
T=0.25fr stress andr
isthe
where fisthe vertical compressive
-3f radius of the hole.
given by . (1l86)
.
Theextra compression is
holeare
C=fr stresses due to a
the hole.
-COMPRESSION However, these extra closeto
tensionTis
narroW Zone
limited to a relatively thetotal depthcqual
gallery,
In the design ofa distributed over aThe. the
reguired
be
generally assumed toheight of the gallery.
resist
to 1S
zone
reinforcement
to one-quarter ofthe placedinthis
tensile reinforcement isEq. ll·85. The force. the
mpressive
possibIe.
by
total tension given the gallery as The
remainng
to ided
 360
Irrigation, Water Power and Water
Resources
concrete surface is not ready, or if the anchor bolts are not properly installed at the
or if they have been damaged by
subsequent opcrations. Sometimes weld plates aretime oi ErConcrngine ertiinngg
concrete and the anchor bolts (or stud bolts) are later welded to these plates at the time
of the gates. These weld plates can be of embedded in the
require ipinsetrcial antgionof
placed in the concrete, as they do not
casily
the sheathing of the formwork.
11-39 FOUNDATION GROUTING
As already mentioned, foundation grouting is generally required for most of the
improve the characteristics of the foundation materials and to reduce the uplift pressure. gravity
The dams to
grouting is usually of two types:
1. Consolidation grouting
1. Consolidation grouting
2. Curtain grouting fooundation
Consolidation grouting is done to improve the characteristics ofa
foundation rock and to inincrease its strength. Consolidation grouting is done on the entire
the dam. Shallow holes (also calledbase B-holes,
area of
fe12m-12mt -12 m -12m are drilled through the
on a grid pattern (Fig.foundation rOck usually
these holes is usually 11·58). 3The depth of
between to 15 m. The
12 m o spacing of the primary holes is kept large, about
12 to 30 m. After the
intermediate secondarygrouting
of
these holes
holes are drilled and
grouted. If necessary tertiary holes are drilled
12m o afterwards between the secondary holes and
grouted.
Prior to the
holes, all the holescommencement
of grouting of
are thoroughly washed with
PLAN alternate use of water and compressed air to
D=PRIMARY O=SECONDARY remove all loose material and drill
cuttings, etc.
HOLES HOLES =TERTIARY The holes are then tested with water
HOLES
pressure to check the watertightness of theunder
Fig. 11-58 or to locate seams or other openings in the rock
rock,
The consistency of the grout which are to be plugged.
required depends upon the
cement and water in the grout is suitably
are generally grouted using a watertightness
adjusted. The ratio usually varies
of the rock. The rati0 0
is relatively low as pressure of 300 to 400 kN/m² (3 to 4 between 1:3 to 1:3. The nol
compared to that in the curtain grouting, keflcm2). Because the pressure useu
pressure grouting. consolidation grouting is also known as
Consolidation grouting causes a general consolidation of the
increase in the bearing
or less capacity of the foundation. Moreover, the foundation, which results
monolithic
helps in checking the
mass by bonding together foundation
the jointed or shattered is consolidated into a more
leakage
of high rocks. Consolidation grouting also
pressure grout used later in the curtain
2. Curtain
grouting Curtain grouting (or high pressure grouting. curtain wall
or an impervious barrier in the
foundation
is to reduce the uplift pressure on the
grouting)
just d/s of the heel of the is done to form a deep grouting
dam. It also dam. Th¹ purpose of curtain
Holes required foor curtain grouting are quite helps in reducing through the foundation.
vertical, but sometimes these are deep. seepage
These holes are called 4-holes. The are usually
inclined. Inclined holes are required to
the rock to develop an effective grout the
holes joints in
inclined
curtain.
of the dam is sufficient. However, in the case of Generally,
very high only
dams,one
another intercept
line ofsetgrout
of holes mayparallel
alsobe the axis
torequired
after the first set has been grouted at a
holes
relatively lower pressure.
GravityDams
361
The primary series of holes in aline is
upon the nature of
usually first drilled. These holes
7-5 m, depending rock. These holes are washed, have aspacing of 4.5 m
to holes is then drilled between the tested and
series of
are then washed, tested and
primary holes to reduce the spacing to grouted. Asecondary
secondary holes: thus reducing the spacinggrouted.
These holes Atertiary series of
holes one-half of the original.
is then drilled
to one-fourth of the original. between the
grouted, as in the case of the These holes are also
(ested and consolidation
The depth of holes depends upon the nature of the grouting.
rock and the height of the
washed.
the holes is
generally taken 30 to 40% of the dam. The depth of
depth of water in the
However, for relatively poor rock foundations, the reservoir for
Curtain grouting is generally done in depth of holes may be upto 70% ofstrong foundations.
1 stages in depths of 15 m or so in one stage. the depth of water.
3routing pressure is quite high, curtain
grouting pressure can be carried out from
height of the dam had
only after some been galleries
foundation strata due to grouting pressure. constructed to avoid lifting up or
founeorally. the grouting pressure is limitedHowever, sometimes it is done from the dislocation of the
the depth inupstream face of the
to 25 D (kN/m), where D is
hole below the surface. metres of
Eor oravity dams of height grouting
greater
rout curtain usually consists of a multiple than 6Om or for those constructed on poor rock
Drainage system downstream of the grout line arrangement of holes. foundations, the
menally reduces the uplift on the dam and the curtain A well-designed and executed grouting system
tn provide an absolutely perfect seepage through the foundation. However, it is
system is usually provided impervious barrier and some seepage does occur. A suitableimpossible
through the foundation evendownstream
of the grout curtain to drainage
after the construction of the grout remove the water which has seeped
The drainage system usually curtain.
20 to 40% of the depth of water inconsists of a series of holes drilled in one row to a depth varying from
the reservoir. The spacing of the
2-0 m. The distances of the holes
from the upstream face is about 10% ofholes the
is generally between 1·5 to
holes are connected to the drainage gallery to depth of water. The drainage
gallery is collected in a sump through a gutter and discharge the water. The water collected in the drainage
of holes. pumped out. Sometimes, there are two or more rows
Drainage in the body of the dam Water percolating through the
1S usually collected through concrete of the body of the dam
open-jointed
near the upstream face of the dam throughout the
pipes embedded in the body of the dam at a suitable spacing
height of the dam. Sometimes, pipes are formed in the
COncrete of the dam. These pipes are called formed pipes. The water
he dam is collected by these pipes and which seeps through the body of
ll-40 discharged into the gallery.
NSTRUMENTATION IN GRAVITY DAMS
nstrumentation in gravity dams is generally required to study the structural behaviour and to
SS safety when subjected to different loads. The engineer can take
defects in the dam indicated timely action to rectify the
by the instruments. The performance data obtained from various instruments
are also useful for
help in examining the adequacy of various design parameters and assumptions. The data also
modifications of the design procedures and analytical techniques. Moreover, these instruments
monitor the actual performance of the dams.
There are basically two types of instruments used in gravity dams.
1.
Imbedded and internal instruments 2. Surveying instruments.
1.
of the Imbedded and internal instruments These instruments are imbedded or placed inside the body
dam, The following instruments are commonly used to measure various parameters.
(i) Strain meters The strain meters are used to measure strains at various points in the body of the
Canhe measuredinto
can be converted strains are converted
stresses using theintoequations
electricalofsignals, whichofare
the theory recorded. The measured strains
elasticity.
(i) Stresspressure
are basically meters The stress meters
transducers which directly
directlymeasure
measure the
thecompressive stress in the concrete. These
normnal stresses.
 362
Irrigation, Water Power and Water
Water Resources E

he stresses may also be indirectly calculated from the strain meter data by using
theory of elasticity. The strain data is useful for the determination of the stress pattern. the
Engi
formulae
of he
ne rig
(ut) Pressure meter. The pressure transducers are used to measure hydrostatic pressure
pores of concrete behind steel liners of penstocks or service gates. These are also used
developed
pressure at various points. Porous-tube piezometers are usually installed in holes drilledto measure thhein the
the foundation gallery. These are used to
measure pore pressure and uplift pressure.
in uplif
concrete through
gauges are usually connected to the uplift pressure pipes and are used
(iv) Resistance thermometers. Resistance
thermometers are
to measure uplift pressure
used to measure the
Bourdon pressure
temperature on the upstream and to measure the temperature of concrete. reservoir water
(V) Displacement meters. The displacement
meters are used to measure
adjacent blocks of concrete. relative displacements between
(vi) Inclinometers and plumb bobs.
Iso used to determine the tilt. The Inclinometers are used to measure tilt of the dam. Plumb bohs are
plumb
(vii) Deformation meters. The bobs are installed in vertical shafts, as already
deformation meters are used to
discussed
foundation. These are measure
along the axis of the dam as well as at deformation or settlement of the
complete picture of theinstalled
deformation pattern. right angles to the axis to obtain a
(viiil) Load transducers.
dam. Hollow load cells are The load transducers are used to measure the loads acting on the base of the
(ix) Water level meters. commonly
Water
uscd for this purpose.
are basically level meters are used to measure the water level in
2. Surveyingpore-pressure transducers. the reservoir. These
the targets fixed onInstruments. Precise surveying instruments are
the top of the dam, on generally used to take measurements on
fixed in galleries and in the vertical the abutments, and on the
deformation of the dam. shafts. The measurements taken aredownstream face. The targets are also
used for the computation of lt and
Measurements are done with respect to
These off-dam reference points are some control points already
established at an elevation higher than established before the construction of theestablished
dam is
away from the dam.
established at the other abutment such that the top of the dam near one started. They should be
abutment. A
point is approximately parallel to the axis ofthe line joining it with the instrument referenceat target is aso
Electronic theodolites and precise the dam. station the reterence
Total-station instruments are levelling instruments are used for
conducted to determine the quite convenient for this purpose. taking the measurements.
Precise levelling and riangulation are
deformation, precise levellinghorizontal, vertical and
is conducted across the cross-deformation. or the of the vertical
variations in levels. For the dam.
determination cross-deformation
of
determination
Several cross-sections are taken to determine the
and slopes, triangulation is used.
 Grvity
Dams
the low
= base width of dam, H,, =height of the 349
whereB,
fopof
the
the first strip, y, =height of the low dam,
first strip, and G = W, =total weight of dam
sbove Obviously, the increase of the base
width on the d/s side isspecific gravity of the damand water
3. procedure is repeated for other
The strips till the base of the given by z, =(B, - Bo) material.
- x,
JOINTS IN GRAVITY DAMS dam is reached.
I1.33 dam is a huge concrete
As a gravity
Depending upon the location and the structure, it is
essential to provide suitable joints at
places.
L.Construction joints purpose served, the joints are appropriate
2. Contraction joints(a) Transverse joints (b) Longitudinal joints.
classified as follows:
Construction Joints Construction joints are
1. construction
of the dam. They also provided for
in permit systematic,
convenient and economical construction of the dam. It is the usual
practice to placethe concrete in a gravity dam in lifts sO as to avoid
CNcOSS0Ve heat of hydration of cement.Consequently, horizontal
joints areintroduced between the successive -HJOiNTS
ORIZONTAL
lifts of
Fig l149).(Thelift is the height by which the dam is raisedconcrete
in one CONSTRUCTICN.
aontinuous operation by pouring of concrete (or laying of
The nrocess is not stopped unless the lift height of one masonry),
block is
nmpleted. The layer of concrete just over the foundation rock has
msualr a smaller lift of about 075 m, whereas all other layars
pSualy have a lift of about 1·50 m.
Todevelop proper bond between the two lifts, the top HEEL -STEPS TOE
f the concrete already laid in the lower lift is freed of surface
all foreign
materials by brushing. The surface is sometimes cleaned with high Fig. 11-49
velocity jets of water and air. Sometimes, wet-sand
a thick layer of rich cement mortar is applied to blasting is used. The surface is roughened and a 125
the roughened surface to develop a proper bond
Ie conCrete of the lower lift and the new
concrete. This treatment of the concrete surface makes between
iotzontal construction joint between the lifts fairly watertight. Before the
, Suihcicnt time should be allowed for the placing the concrete in the new
previously
50 that it becomes fairly hard, Thus horizontal
placed concrete to cool and to attain its initial
de between the sucoessive lifts of constuction joints are also necessary to allow adequate
concrete for dissipation of heat.
lo reveat thc onjoints. Contraction joints are provided to relieve the themal streses in the concree and
prevent
OCcur in
Concretedevelopment of haphazard cracks in the body of the dam. Considerable volumetric changcs
when it shrinks at the tíme of drying. Tensile stresses develop in concrete if the volumetric
Changes
also
are not permitted to occur. These tensile stresscs cause cracks in the concrete. Volumeric changes
occur arca
when there are large
the surface lemperature variations. Becausc of the difference of temperalures between
concrete and the interior of the concree, cracks may ccur at the surface of the
of the
COncrcte. Surface cracks.
may also once formed, gradually progresS deep into the interior of the dan. Deep cracks
TIse in the OCcur in the interior of the dam due to thc hcat of hydration of cement and consequcnt temperature
of the interior of the dam. Asteep lemperature gradicnt betwecn thc interior of the dam and the surface
dam develops, which may lead to the formation of cracks even after a long period.
f the
cracks
aphazarithidc and unsiof ghtly. These cracks also cause considerable stress concentration. They destroy the
Onol
are not properly controlled by providing suitable contraction joints, they are quite

tributiontheaction
\Oisreduce is also affect
the estructure
d by theseandcracks.
affect Suitable contraction joints are provided in the gravity dam
the load-carryingcapacity of the dam. The internal
stress

ints. cracks. There are two types of contraction joints. (a) Transverse
joints (b) Longitudinal
350 Irrigation, Water Power and Water Resources
(a)
Engineering
Transverse joints Transverse joints
-TOP 0F DAM are provided normal to the axiS of the da
(Fig.11.50). These joints are vertical and
extend from the foundation to the top of the
dam. These are also continuous from the
upstream to the downstream face of the dam
In other words, the transverse joints
the entire length of the dam in differentseparate
blocks
They allow the contraction of concrete in two
-TRANSVERSE JOINTS blocks between which they are provided, and
LONGITUDINAL SECTION OF DAM thus prevent the development of the
haphazard transverse cracks in the dam, In
Fig. 11S0 Longitudinal Section of dam fact, the transverse joints are man-made
cracks.
The spacing of the transverse joints depends uponanumber of factors, such as topography of the
site, temperature variations and capacity of the concreting plant. It also depends upon the requirements
of the associated structures, such as spillway gates, outlets, penstocks and spillway bridge piers. The
usual spacing of the joints for concrete dams is between 12 and 18 m. However, for masonry dams, it is
generally greater. The edges of the transverse joints are usually chamfered on the downstream face of
the dam to give a pleasing appearence and to avoid spalling of concrete. Water stops are provided across
the transverse joints to check leakage of water from the upstream to the downstream. The
transverse joints
may be grouted or left as it is without any grouting. In the case of the grouted joints, the
are called grout stops because they also prevent the flow of grout to the water stops
upstream of the water stop.
Vertical keys are generally provided over the entire surface of the adjacent blocks of the
These keys provide shearing resistance at the joint and also reduce the leakage. Keys transverse
and water
joints.
are discussed in detail in Sect. 11:34. stops
(b) Longitudinal joints In high gravity dams, the width of the
vertical cracksmay develop parallel to the axis of the dam. To prevent dam section is quite large and the
joints are provided in high dams, in addition to the transverse joints. uncontrolled
These
cracking, longitudinal
to the axis of the dam. As these joints approach the d/s face or joints are provided parallel
the ws face, they are turned normal to
the face of the dam to avoid feather-edging of concrete.
at right angles but are terminated at the point when theySometimes, the longitudinal joints are not turned
are within 5 to 6 m of the face of the dam. This
arrangement is preferred in the case of longitudinal joints which extend upto the
face. The longitudinal joints are usually staggered in adjacent points near the upstream
blocks.
transverse joints but are not continuous all along the length of the dam in They run between the two adjacent
practice to stagger the longitudinal joints in the adjacent blocks by a different blocks. It is the usual
The spacing of the longitudinal joints generally varies minimum distance of about 8
foundation conditions and convenience of construction. The between 15 and 30 m, depending upon tne
formed by the transverse joints into smaller longitudinal longitudinal ioints sub-divide the blockS
same purpose in one block of the dam as the blocks. Thus the longitudinal joints serve
transverse joints serve in the dam as a whole. Tue
longitudinal joints are provided only in high dams. In India, they have been provided
As the height of the dam increases, the base width also onty at Bhakra Da
increases, and a stage joints
is reached beyond which
vertical cracks parallel to the axis of the dam will develop if the longitudinal are not provided.
Horizontal keys are invariably provided on all along longitudinal
joints over
the joints. These joints are grouted so that each block between adjacent transverse jointstheactsentire
as asurta
monolithic
mass. The present practice is not to provide the longitudinal joints even in high dams. The longitudinal
joints introduce weak planes in the block and it may not act as a monolithic block as assumed in the
design unless a high degree of perfection is achieved in providing the horizontal keys at thejoints and
grouting the joints. Instead of providing the longitudinal joints, suitable measures are taken to achieve
a better temperature control by pro-cooling the concrete or by post cooling it. as discussed Sect. 11-35.
 351
GravityDams

AND WATER STOPS IN GRAVITY DAMS

KEYS
at the joints in gravity dams.
already mentioned, keys and water stops are provided
IL34
As
are interlocking projections of concrete provided at the surfaces of the
joints to
Keys
1. Keysloadfrom one part to the other.
the
transfer (a) In transverse joints, vertical
horizontal
keys are provided to transfer assist
shear (Fig. 11-51). These keys also
from the
water
inreducing the leakage of downstream
upstream of the dam to the
HEIGHT through the transverse joints.
OF joints. horizontal
(b) In longitudinal transfer
BLOCK vertical
keys are provided to

TOP BLOCK KEY

095m,02mn
0.40D

OF BLOCK
SIDE ELEVAT ION BOTTOM BLOCK
WIDTH
OF BLOCK
BLOCK O15m D/S
II BLOCK LONGITUDINAL
LKEY ELEVATION
030m0.15 0-30m -TRANSVERS JOINT SECTIONAL JOINT
PLAN
Fig. 11 -52

Fig. 11·51
aligned, as far as possible, approximately
horizontal keys should be
there are no shear stresses on
The faces of the so that
shear (See Fig. 11·52). for the reservoir full condition vary from the upstream face to the
Parallel with the
principal planes
directions of principal planes Therefore, complete conformity of
However. the the top of the dam. of keys, which
would
e Taces of the keys. foundation to unlimited shapes horizontal
downstream face and also from the planes would require an practice to providethedownstream
the faces of the keys with the principal un-economical. It is the usual
stresses in the lower
not be practicable, besides being highly direction of principal
tothe general
keys of only one shape Corresponding
stress is a
maximumn.
contraction joints and not in the
shear
portion of the dam where the vertical longitudinal
provide keys only in the upstream
The modern practice is to joints near the
ansverse contraction joints. transverse when
seals) are provided across reservoir to the downstream
2. Water stops Water stops (or water water from the
stops
leakage of are grouted, the waterusually
faceheof the dam. These stops prevent the
However, when the
transverse joints
grouting. The water stops
are
transverse
Prevent
joints are not grouted.
the flow of grout to the upstream of the stops
at the timne of
u the
following four types . Rubber stops (iv) PVC stops. mmthick, of annealed soft
(i) Metal stops (ii) Asphalt stops (iii) l:5
sheets, about 1to shapes: (a) Z-shape (b) M-
(i) Metal stops The metal stops are made of thin two
stops are usually of
Copper,
Shape. Themonelmetalmetal
stopsor are
stainless steel. The
commonly
metal
used in practice. required for the formation of a Z-type metal stop.
lef
length is About 8 cm of the str1p is
(u) A metal strip of about 30
cm
it is bcing cast. next block when
Ahou Z-shupe
1| cm of the
strip IS cmbcdded in
one block when
| | cm of the
strip is embedded in the

bciwc n lhe blocks uncmbcdded and the

remaining
 Irrigation, Water Power and Water
Resources
352

-UWS FACE
-U/S FACE -UIS FACE cast. Thus a
E
of the letter Ziswater stop of
A Z-shape
ngiIn
he
e
formed (Fig. shape
ring
Jlcm
water stop
in design and it is is
ME TAL cm
8cm
ME TAL
-DRAINAGE
WELL
spliced. However,
easi
1t
l
can
y insta l esdim:ge
STRIP-Z |STRIP-M 20 cm DIA
only a relatively small accommodo
J45cm ment. This type of water
erally used as
\atsteroapl ismve
joint is grouted.
a grott
stop whengn-
LTRANSVERSE JOINT -TRANSVERSE JOINT
<TRANSVERSE JOINT
(c)
(b) M-shape In
the case of aM.
(a) (b) type metal stop, a 38
Fig. 11:53
required. About 11 cmcmof strip is long
embedded in one block when cast, 16 cm of the strip length is folded at the middle and left the strip is
blocks and the remaining llcm of the strip is embedded in the adjacent block when cast. the
Thus betaween
stop is formed [Fig. 11:53 (6)]. The M-type water stop is difficult to instal and splice, but it can accommM-shate
relatively large lateral movement. This type of water stop is generally used for ungrouted joints
Fig. 1153 (c). shows an arrangement in which two Z-type water stops are used to confipe
drainage well. The drainage well is later filled with melted asphalt or grouted.
(i) Asphalt stops An asphalt stop consists of two semi-circular grooves (or semi-tectan oml
groove) ncar the upstream face of the dam in the transverse joint (Fig. 11.54 (a)]. The groove is filled with
asphalt, which is melted by electric heating coils laid earlier in the groove. The molten asphalt flls the
groove and also a portion of the joint on either side of the groove. To prevent excessive spreading of
the asphalt in the transverse
125 cm
-U/S FACE UIS FACE ASPHALIC JOINT joint, a Z-type water stop is
FILLER provided on either side of the
groove. The asphalt stop can
19mm DIA -38 mm DIA accommodate only arelativ
HOLE HOLE
GROOVE ely small lateral movement.
FILLED
WITH (ii) Rubber stops The
ASPIHALI
RUBBER 25 mm DIA rubber stop consists of a225
SHEET
cm long and 0.95 cm thick
rubber sheet. There is a
-TRANSVERSE JOINT LTRANSVERSE OINT central hollow bulb of 3.8 cm
-22.5cm
(a) diameter with a central hole
(b)
of 1:9 cm diameter in the
Fig 11-54 sheet. There are solid bulbS
either
end of the rubber sheet (Fig. of 2-5 cm diameter at
11·54 (6)]. The rubber sheet is embedded adjacent
in the However,
blocks near the upstream face. Arubber stop can accommodate symmetrically
a very large lateral movement.
it is not durable when not
always kept wet in
(iv) PVC stops Recently water stops madedarkness.
of polyvinyl chloride (PVC) have been used in some
dams. In these stops, a PVC sheet 22-5 cm wide and 125 cm thick is used. It has asaw-like cutsallalong
the edges and a central bulb. For very high dams, PVC sheets of large size (30-5 cm) are generallyused.
11:35
TEMPERATURE CONTROL IN DAMS
When cement concrete sets, alarge amount of heat is liberated. This heat raises the temperature
within the body of the dam, whereas the outside temperature remains equal to the atmospheric temperature
Thus atemperature gradient develops due to the difference of temperatures. This results in the development