Types of Dams_eg Considerations

8/3/2019 Types of Dams_eg Considerations

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TYPES OF DAMS & ENGINEERINGTYPES OF DAMS & ENGINEERING

GEOLOGICAL CONSIDERATIONSGEOLOGICAL CONSIDERATIONS

BY

Dr. R. Anbalagan

PROFESSORDEPARTMENT OF EARTH SCIENCES

INDIAN INSTITUTE OF TECHNOLOGY

ROORKEE

UTTARAKHAND


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Dam - Solid barrier -

constructed across rivervalley at a suitable location

with a view to impoundbehind it


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OBJECTIVES OF DAM CONSTRUCTION

Generation of hydropower

Providing water for irrigation facilities

Silt control

Providing water supply for industrial uses and

domestic consumption

Fighting droughts and controlling of floods

Providing navigational facilities

Tourism purposes


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EFFECTS OF DAM CONSTRUCTION

Land submergence and rehabilitation

Development of fisheries - pisciculture

Bird Sanctuary

Climate effect

Reservoir induced seismicity (RIS)

Effect in wild life

Environmental Impacts

Socio-economic impacts


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PARTS OF DAM

Schematic section of a dam


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CONTD.

Foundation natural surface on which dam rests embraces

whole width and length of super structure at general level of

fresh rocks

Abutmentssloping sides of valley forming part of foundation

Heel u/s portion of dam where it contacts bearing surface

Toe d/s portion of dam - where it contacts bearing surface

Crest top of dam

Free board area between MRL and

crest of dam


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CONTD.

Axis of Dam an imaginary line drawn either along centre of

plan of crest of dam or line defined by contact of u/s part of crest

with u/s face of dam

Dead Storage Level (DSL) elevation of reservoir below which

water remains permanently determined by HRT or other outlets

Head Race Tunnel tunnel that supplies water to power house

Max. ReservoirLevel (MRL) highest

elevation up to which water can be stored

in reservoir without over-topping the dam or being released through spillway


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CONTD.

Tail Water Level level of water at d/s base of dam due to

release of water from spillway, power house, irrigation outlets, etc

Gross Storage storage up to MRL dead storage + live storage

Live Storage storage between MRL and DSL

Dead Storage Storage up to DSL

SpillWay Concrete structure used to

pass flood season discharge from

upstream of dam to downstream without

damaging the dam structure


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CLASSIFICATION OF DAMS

GRAVITY EMBANKMENT COMPOSITE

HOLLOW SOLIDEARTH-FILL ROCK-FILL

CONCRETE MASONRY

1. ST. GRAVITY

2. CURVED GRAVITY

3. BUTTRESS

4. ARCH

5. CUPOLA

DAMS

1. HOMOGENEOUS

2. MODIFIED

3. ZONED

4. HYDRAULICFILLED

1. CENTRAL CLAY CORE

2. SLOPING CLAY CORE

3. UPSTREAM SLOPINGCONCRETE DIAPHRAGM


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GRAVITY DAM

Gravity Da

m

Concrete or masonry structure which resists imposed

forces by its weight and section without relying on arch or

beam action.

Usage restricted to straight or slightly curved dams.

Heavy loads imposed on foundation.


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Cord-Height Ratio

C- H Ratio = Width of the Valley at the Contemplated Height of dam (W)

Contemplated Height of dam (H)

If C-H Ratio is

10 - Very wide


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HOLLOW GRAVITY DAM

Preferred if shortage for cement and/or aggregate

Low consumption of concrete materials due to hollow structure

Generally low height dams 5 for better storage capacity

Hard, massive foundation rocks for proper anchoring of structure

and water tightness

Light structure


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STRAIGHT GRAVITY DAM

Fairly wide to wide valleys preferred to accommodate main dam

and appurtenant structures C-H ratio >4Various types of geological conditions preferred

Hard massive rocks preferred moderately hard rocks also good

no faults or thrusts below dam max. load in river bed foundation

less number ofGeological discontinuitiesSeepage below dam should be minimum

Roller compacted dams also fall in this category

Less overburden on abutments and river bed preferred for

economic reason

All heights of dam possible

Ex Bhakra Nangal Dam 225m high


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MASONRY DAM

Same like straight gravity dam in structure

Constructed out of stone masonry blocks hard massive igneousrocks like granite, syenite etc. fine to medium grained rocks for

good strength & stability of structure

Valley size, foundation rocks same as straight gravity dam but

low to medium height dams - constructed on moderately hard tohard rocks - less number ofGeological discontinuities

Height in general preferable less than 50m sometimes up to

80m

Availability of sufficient reserves of masonry blocks near dam

site min. transportation

Availability of skilled mass power

Ex.. 63m high and 510m long Gandhisagar dam across Chambal

river in M. P


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CURVED GRAVITY DAM

More or less same like straight gravity dam but axis not straight

sometimes deviation close to abutment ends

Deviation to accommodate better topographical setting or to

avoid adverse geological conditions

Convex side upstream

Ex.. Jamrani Dam Uttrakhand under construction


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BUTTRESS DAMThin walled dam

Consists of thin upstream sloping deck, supported by buttresses

Wide, U-shaped valleys - preferred

Low height dams


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ARCH DAM

Thin walled dam continuously curved in plan with upstream

convex side, straight in section

Tight narrow gorges with C-H ratio 3 or less

- preferred

Arching action max. load to abutments so strong abutmentrocks narrow river section

Abutment rocks hard massive with

less geological discontinuities

Thin dam section more seepage below dam

Erosion of foundation rocks rocks resistant to erosion

e. g. Iduki dam in India across Periyar river in Kerala 169m

high, 365m long


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CUPOLA DAM

Curved in section as well as in plan

Same conditions like Arch dam

Transfer of load uniform throughout foundation

Design and construction challenging

E. g. Vajont dam, Italy, 1969


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EMBANKMENT DAMS

Loose naturally available material flexible soil or rock fill

All embankment dams composite in nature

Spillway made of concrete/masonry material

Generally flexible type of dams suitable over varying geological

conditions

Particularly in seismically active terrain more suitable


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HOMOGENEOUS DAM

Use of locally available soil generally silty soil

Ponds and tanks

Height ranging 3 to 5m max. up to 8m

Constructed across existing drainage

Provided with an over flowing spillway concrete or masonry

on existing drainage

Foundation - Soil or poor rocks

Compaction of embankment materials important factor

C-H ratio >10


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MODIFIED HOMOGENEOUS DAM

Filter provided on the d/s side of dam to prevent internal erosion

of embankment materials

Height normally up to 20m even more

An open drain at toe to collect seepage water

Filter fine to coarse grained sand


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A central clay core to prevent seepage through dam

More safe and stable dam - generally 30 to 40m height

E. g. Bargi dam in M. P.

ZONED HOMOGENEOUS DAM


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CENTRAL CLAY CORE ROCK-FILL DAM1. Central clay core

2. Filter

3. shell

Clay core 70% clay fractions - rest silt and other size fractions

Filter fine to medium grained sand fractions source RBMand old terrace materials

Shell gravel to big boulders source RBM and old terrace

materials foundation most of rocks suitable even soft rocks

water tightness below dam to be ensured

E. g. Rogum dam, Russia 335m highest in World; Nurek

Dam, Russia 300m high;


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CONTD.

Foundation treatments less

Flexible, self healing type of dam

Due to big dam section, load per unit area on foundation less

suitable in most lithological conditions

Cheap Worlds highest dams are of this type

Wide to very wide valleys C-H ratio >5

E. g. Kalagarh dam across Ramganga river 80m high,

Uttarakhand, India


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SLOPING CLAY CORE ROCK-FILL DAM

Same as above except with an u/s sloping clay core

Advantage shear strength of clay core improve by the weight of

overlying material

Ex.. - Tehri Dam 260.5m high across Bhagirathi river,Uttarakhand, India


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UPSTREAM SLOPING CONCRETE DIAPHRAGM

Consists of u/s sloping concrete diaphragm on rockfill material

Good compaction of rock-fill to avoid sinking of diaphragm

Comfortable height up to 70m, more in many cases in Japan

many dams between 30-50m

Topographical and geological conditions same as clay core rock-

fill dam - good rock in diaphragm area for preventing settlement

Very cheap fast construction easy operation

Good stability under seismic conditions

E. g. - Shubaiyah Dam, China 100m high


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Upstream sloping concrete diaphragm

CONTD.


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PHYSICAL FACTORS GOVERNING SELECTION

OF TYPES OF DAM

Topography

Geology and foundation condition

Materials available for construction

Hydrology

Spillway

Earthquake


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Documents

Types of Dams_eg Considerations