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Submitted by: Saroj khadka

Shahbaz Ahamad

Vikram Gupta

Atul Srivastava

Nahne patel2

CONTENTS:

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

Foundation investigations

Foundation treatment

Mode of failure and criteria for structural stability

Design of concrete gravity dams

Problems in construction

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Dams:

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 electrical power.

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Purpose of dams:

Generation of hydropower electricity

For agricultural and irrigation purposes

For fishery

To prevent the flooding during high

water flows at high PMP

To diverse the water maintaining

required heights.

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Various types of dams

Earth dams

Rock-fill dams

Solid masonry gravity

dams

Hollow masonry gravity

dams

Timber dams

Steel dams

Arch dams

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Dams chosen in project to build:

Construction of concrete gravity

dams:

Concrete gravity dam is such a

dam that is designed in such a way that

its own weight resists the external

forces.

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Factors in Site selection

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.

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General design consideration

Local condition

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

shipping points

Ground & aerial photographs and general area map should be

obtained locating the general area within the State, together with

county and township lines.

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Hydrological data

Stream-flow records, Stream-flow and reservoir yield, Flood studies,

Sedimentation and water quality studies ,ground-water conditions are

to be collected.

Reservoir capacity

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.

Climatic effects

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.

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Construction materials

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

assured.

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.

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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

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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

construction area.

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.

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Step III: Removal of loose rock and

rubble from the valley walls and

river bed.

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.

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Step IV: During dam

construction, the

associated power station

and intake works are also

being built if hydropower

generation is to be

generated.

Once, dams is completed,

diversion tunnel is closed

and lake begins to fill.

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FOUNDATION INVESTIGATIONS

Field investigations

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.

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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

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Foundation treatment: Excavation:• 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 torsionaleffect. To counteract this, uniformly varying profile is to be shaped.

b) Dental treatment:

• The procedure of reinforcing and stabilizing weak zones during drilingaction and final excavation is called “dental treatment.”

c) Proper Protection against piping should be made for dam stability.

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Grouting:

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.

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To decide whether dam is low or high:

The height of gravity dam,

Where,

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.

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H < f /[Yw(Sc+1)]

Design of low concrete gravity dams:

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Design of high concrete gravity dams:

Force acting on gravity dams:

Water pressure

Uplift pressure

Pressure due to

earthquake forces

Silt pressure

Wave pressure

Ice pressure

Stabilizing force i.e.

weight of dam itself

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Modes of failure and criteria for structural stability of gravity dams:

By overturning( or rotation) about the toe

By crushing

By development of tension, causing

ultimate failure by crushing

By shear failure called sliding

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major issues: TEMPERATURE CONTROL OF CONCRETE

Methods of temperature control

a) Pre-cooling 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

placing temperature.

one method is to chill the aggregate in large tanks of refrigerated water for a given period of time.

b) Post-cooling 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

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Design considerations for temperature treatment

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a)Shallow construction lifts

b)Retarding agents

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

sprays

d) Size of construction blocks

e) Concrete cooling systems

f) Lift thickness

g) Delays between placements

Problems in construction of dams:

Fish problem

Cracking of concrete in

concrete gravity dams

Submergence problem

Pressure problem in

hydroelectric power

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Bibliography:

www. Google.com/dams construction

www.dams.com

Qingchao GUO, Wenhong CAO: RESERVOIR

SEDIMENTATION AND ITS CONTROLIWHR China

Q89-R.4, 2009

ICOLD Bulletin 144 : Costs Savings in Dams (2010)

Manuals of Design of concrete gravity dams published

by U.S.A

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