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Introduction of dams
Purposes of dams
Various types of dams
Force acting on gravity dams
Factors in site selection
General design consideration
Procedure to build a dam
Mode of failure and criteria for structural stability
Design of concrete gravity dams
Problems in construction
A dam may be
defined as an
obstruction or a
barrier built across a
stream or a river.
The pool of water is
formed at upstream
and which is used to
turn the blades of a
turbine to generate
Purpose of dams:
Generation of hydropower electricity
For agricultural and irrigation purposes
To prevent the flooding during high
water flows at high PMP
To diverse the water maintaining
Dams chosen in project to build:
Construction of concrete gravity
Concrete gravity dam is such a
dam that is designed in such a way that
its own weight resists the external
Factors in Siteselection
Topography: A narrow site will minimize the amount of material in
the dam thus reducing its cost, but such a site may be adaptable.
Geology: The foundation of the dam should be relatively free of
major faults and shears. If these are present, they may require
expensive foundation treatment.
Appurtenant: While the cost of these Structures is usually less
than the cost of the dam, economy in design may be obtained by
considering their effect at the time of site selection.
Local condition: Site of availability of water supply, sewage
disposal, electric power for construction purposes, telephone
service should be chosen.
Access: Accessibility of the site has a very definite effect on the
total cost. Easy excess is required for the contractor’s plant and
equipment near the site.
General design consideration
Availability of public facilities or utilities such as water supply, sewage
disposal, electric power for construction purposes, telephone service,
construction camp; and need for permanent buildings for operating
personnel should be well available.
Maps and photographs
Map should show existing towns, highways, roads, railroads, and
Ground & aerial photographs and general area map should be
obtained locating the general area within the State, together with
county and township lines.
Stream-flow records, Stream-flow and reservoir yield, Flood studies,
Sedimentation and water quality studies ,ground-water conditions are
to be collected.
A topographic map of the reservoir site is to be collected, annual
periodic fluctuations of reservoir levels , Area-capacity curves for
storage of the spillway design flood are to be calculated.
Weather Service records of mean monthly air temperatures, river
water temperatures at various times, Wind velocities and prevailing
direction, Amount and annual variance in rainfall are to be collected.
Concrete aggregates and properties
Availability of suitable aggregates usually processed from natural
deposits of sand, gravel, and cobbles in sufficient quantity to
construct the dam and its appurtenant structures.
Concrete mix having high cement content and admixtures like
pozzolans, fly ash etc. are prepared from hydraulic laboratory
model studies & environmental studies.
Water for construction purposes
An adequate supply of water for construction purposes such as
washing aggregates and cooling and batching concrete should be
The water used in the concrete mix should be reasonably free of
silt, organic matter, alkali, salts, and other impurities and
objectionable amounts of chlorides or sulphates.
Procedure to build a dam:
Step I: Dewatering the part of river valley at selected
site of dam which is achieved by diverting the river
through a tunnel.
1. Provision of diversion tunnel is made.
2. Construction of dams in two stages.
3. Construction of galleries in gravity dams
Step II: Work is started at river during summer i.e. when
river flow is low. Earth-moving equipments is used to
build small dam(cofferdam) on upstream of main
Pumping is regularly done to remove water that may
seeps through the cofferdams.
Diversion tunnels are not required in case of concrete
gravity dams and only if water is channeled through a
water pipe is satisfactorily.
Step III: Removal of loose rock and
rubble from the valley walls and
Concrete-faced rock-fill dams
require a footing to be
constructed around their
upstream edge. The plinth is
made from concrete and serves
as a foundation or connection
between the dams and valley
walls & floor.
The area under plinth is
waterproofed by drilling holes
and pumping cement grout into
cracks in the rock.
Step IV: During dam
associated power station
and intake works are also
being built if hydropower
generation is to be
Once, dams is completed,
diversion tunnel is closed
and lake begins to fill.
a) Appraisal investigations
It includes a preliminary selection of
the site and type of dam using geologic
and topographic maps, photographs of
the site area, and data from field
examinations of natural outcrops, road
cuts, and other surface conditions.
b) Feasibility investigations
The location of the dam is usually
finalized. The geologic mapping and
sections are reviewed and supplemented
by additional data such as new surveys
and additional drill holes.
c) Final design data
A detailed foundation investigation is conducted to obtain the
final design data. This investigation involves as many drill holes as
are necessary to accurately define :
(1) Strike, dip, thickness, continuity, and composition of all faults and
shears in the foundation.
(2) Depth of overburden.
(3) Depth of weathering throughout the foundation.
(4) Joint orientation and continuity.
(5) Lithologic variability.
(6) Physical properties of the foundation rock, including material in the
faults and shears
• Adequate attention is to be paid during blasting operation to assure
unnecessary shattering of rocks, loosening of bed of foundation.
• Foundations such as shales, chalk, mudstones require protection
against air and water slaking.
a) Shaping of canyon profile:
• If canyon profile for a dam is relatively narrow with steep sloping walls,
dam section will be deflected by reservoir load and result torsional
effect. To counteract this, uniformly varying profile is to be shaped.
b) Dental treatment:
• The procedure of reinforcing and stabilizing weak zones during driling
action and final excavation is called “dental treatment.”
c) Proper Protection against piping should be made for dam stability.
Holes are drilled at shallow as well as deep and cement
grouting is filled to establish an effective barrier to seepage under
the dam and to consolidate the foundation.
a) Consolidation grouting
Low-pressure grouting to fill voids, fracture zones, and cracks at
and below the surface of the excavated foundation is accomplished
by drilling and grouting relatively shallow holes.
b) Curtain grouting
Construction of a deep grout curtain near the heel of the dam to
control seepage is accomplished by drilling deep holes and grouting
them using higher pressure.
To decide whether dam is low or high:
The height of gravity dam,
f = permissible compressive stress of the dam material and
Sc= Sp. Gravity of the dam material
Then, dam will be a low gravity dam.
otherwise, high gravity dam.
H < f /[Yw(Sc+1)]
Force acting on gravity dams:
Pressure due to
Stabilizing force i.e.
weight of dam itself
Modes of failure and criteria for structural stability of
By overturning( or rotation) about the toe
By development of tension, causing
ultimate failure by crushing
By shear failure called sliding
Methods of temperature control
Restricting concrete placement during the hotter part of the day or the
hotter months of the year, to a full treatment of refrigerating the various
parts of the concrete mix to obtain a predetermined, maximum concrete
one method is to chill the aggregate in large tanks of refrigerated water for a
given period of time.
Artificially cooling mass concrete by circulating cold water through
embedded cooling coils on the top of each construction lift will materially
reduce the peak temperature of the concrete
c) Low heat producing cement and modified cement as per site
requirements should be used .
d) Use of pozzolans
Design considerations for temperature treatment
a)Shallow construction lifts
c) Surface cooling
It can be accomplished by circulating water in closed
spaced embedded cooling-pipe coils placed adjacent to and
parallel with the exposed surfaces, by use of cold water
d) Size of construction blocks
e) Concrete cooling systems
f) Lift thickness
g) Delays between placements
Problems in construction of dams:
Cracking of concrete in
concrete gravity dams
Pressure problem in
www. Google.com/dams construction
Qingchao GUO, Wenhong CAO: RESERVOIR
SEDIMENTATION AND ITS CONTROLIWHR China
ICOLD Bulletin 144 : Costs Savings in Dams (2010)
Manuals of Design of concrete gravity dams published