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EARTHEN DAM BY
- FS17CE008 - SHIVANI LAXMAN PAWAR
- FS17CE040 -SHWETA SUBHASH JADHAV
IRRIGATION ENGINEERING ASSIGNMENT NO. 4
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INDEX
SR. NO. CONTENT PG. NO.
1. INTRODUCTION 1
2. WHAT IS AN EARTHEN DAM 2
4. TYPES OF EARTHEN DAM 3
5. CRITERIA FOR SAFE DESIGN OF EARTHEN DAMS 6
6. COMPONENTS OF EARTHEN DAM 7
7. CAUSES OF FAILURES OF EARTHEN DAM 9
8. ENVIRONMENTAL EFFECTS OF EARTHEN DAM 13
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INTRODUCTION
- The first known dam was built in 2900 B.C.
across the Nile River to protect the city of
Memphis from flooding. Dam build was continued
into the time of the Roman empire, after which
dam construction was literally lost until the
1800s. - A dam is a barrier constructed to hold back
water and raise its level, forming a reservoir
used to generate electricity or as a water
supply. - A dam is a barrier that impounds water or
underground streams. - The reservoirs created by dams not only
suppress floods but provide water for various
needs to include irrigation, human consumption,
industrial use, aquaculture and navigability.
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WHAT IS AN EARTHEN DAM?
- Earth fill dam, also called Earthen Dam, or
Embankment Dam. - Dam built up by compacting successive layers of
earth, using the most impervious materials to
form a core and placing more permeable substances
on the upstream and downstream sides. - A dam built of soil materials (sand, loam,
clay, and so on), with a trapezoidal or nearly
trapezoidal cross section.
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TYPES OF EARTHEN DAM
- Based upon the method of construction, Earth dam
is divided into two categories - (i) Rolled fill dam
(ii) Hydraulic fill dam - (i)Rolled-fill Method-The embankment is
constructed by placing suitable soil materials in
thin layers (15 to 30 cm) and compacting them
with rollers. The soil is brought to the site
from burrow pits and spread by bulldozers, etc.
In layers. These layers are thoroughly compacted
by rollers of designed weights. - (ii)Hydraulic-fill Method-In this method of
construction, the dam body is constructed by
excavating and transporting soils by using water.
Pipes called flumes, are laid along the outer
edge of the embankment.
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- Rolled- fill dams are further sub-divided into
following categories - Homogeneous Embankment type
- Zoned Embankment type
- Diaphragm Embankment type .
- HOMOGENEOUS TYPE DAM-A purely homogeneous type
earth dam is composed of a single kind of
material, dams are usually built of impervious or
semi-impervious soils, but several successful
have been built of relatively pervious sands and
sand gravel mixture. These dams are used only for
low to moderate heights.
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- ZONED TYPE DAM-A zoned embankment dam is
composed of more than one kind of material. This
is most common type of a rolled fill dam in which
a central impervious core is flanked by zones of
materials considerably more pervious.
- DIAPHRAGM TYPE DAM-In a diaphragm type earth dam
the bulk of the dam is constructed of pervious
materials, (i.e. sand, gravel or rock) and a thin
core usually known as diaphragm of impervious
material is provided to check seepage. As such
these dams are also sometimes known as thin core
dams.
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CRITERIA FOR SAFE DESIGN OF EARTHEN DAM
- The dam should be safe against overtopping.
- The dam must have sufficient free board.
- The seepage line should be within the d/s face so
that sloughing cannot takes place. - The dam and foundation should be safe against
piping. - The u/s and d/s slope and crest must be protected
from wind and wave action.
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COMPONENTS OF EARTHEN DAM
- CREST/TOP WIDTH
- FREE BOARD
- CORE
- CASING/OUTER SHELL
- CUT-OFF TRENCH
- PITCHING
- TURFING
- BERMS
- TOE DRAIN
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- CREST/TOP WIDTH-It is the topmost plane of the
dam, sometimes used as roadways/pedestrians, etc. - FREE BOARD-The vertical distance between the
highest level of the water in the reservoir and
the top (crest) of the dam. - CORE-It is the central impervious section
constructed with clayey soil, silt, clay, loam,
etc. It controls the seepage flow through the
body of the dam. - CASING/OUTER SHELL- It is the outer portion of
the dam. It is constructed with murum soft rock
or sand and gravel, etc. It provides a cover to
the core protecting it from cracking. - CUT-OFF TRENCH- It is a trench constructed under
the foundation of dam to stop water from seeping
beneath the dam. - PITCHING- It is a layer 30 to 45 cm thick of
stones of size 30cmand 40 to 50 kg weight
provided on upstream face to prevent erosion of
material caused due to wave action. - TURFING-It is a layer of special type of grass
called harali on the downstream face of the dam
to protect the d/s slope from eroding action of
rain water. - BERMS- Berms are offset provide on downstream at
8 to 10 m vertical intervals from 3 to 5 m width
to reduce the velocity of rainwater falling on
slope. - TOE DRAIN- It is a drain constructed at the
downstream slope to collect and drain away the
seepage water.
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CAUSES OF FAILURES OF EARTHEN DAM
- HYDRAULIC FAILURES (40)
- OVERTOPPING
- WAVE EROSION
- TOE EROSION
- GULLYING
- SEEPAGE FAILURES(30)
- PIPING
- SLOUGHING
- STRUCTURAL FAILURES(30)
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- HYDRAULIC FAILURES- Above 40 of earthen dam
failures are due to hydraulic failures which
includes - OVER TOPPING The over topping of dam are caused
due to insufficient capacity of spillway and
insufficient free board or its spillway gates are
not operated properly. - WAVE EROSION Erosion is caused due to wave
action on the upstream slope and leads to its
slip. The slope should be properly protected by
providing pitching. - TOE EROSION The toe of the dam may be eroded due
to heavy cross-current coming from spillway
bucket or tail water. The d/s slope should be
protected by providing stone pitching or riprap. - GULLYING Downstream slope may fail due to
formation of gullies by heavy downpour. Proper
berms, turfing and good drainage system should be
provided to downstream side.
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- SEEPAGE FAILURES- More than 33 of earthen dam
failure are due to seepage. Seepage always occur
in earth dams. It does not harm its stability if
it is within the design limits. But excessive
seepage will lead to failure of the dam. - PIPING Piping takes place when water that seeps
through the dam carries soil particles away from
the embankment, filters, drains, foundation or
abutment of the dam causing a large number of
catastrophic failures. - SLOUGHING- Failure of earthen dam due to
sloughing is closely related to water level in
the reservoir. In full reservoir condition, the
downstream toe of the dam becomes fully
saturated, which is a failure by producing a
small slump or miniature slide.
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- STRUCTURAL FAILURES-
- Upstream and downstream slope failures due to
formation of excessive pore pressure. - Upstream failure due to sudden drawdown in the
reservoir water level. - Downstream failure at the time of full reservoir.
- Foundation slide.
- Failure of dam due to earthquake.
- Failure of dam due to unprotected side slope.
- Failure due to damage caused by burrowing animals
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ENVIRONMENTAL EFFECTS OF EARTHEN DAM
- POSITIVE IMPACTS-
- Water supply for Domestic and Industrial use.
- Meeting the agriculture Demand for Food supply.
- Regulates the river level and flooding.
- Recreation leads to tourist attraction.
- Generation of Hydropower.
- NEGATIVE IMPACTS-
- Resettlement and Relocation of villages.
- Dams reservoirs leads to seismic effects.
- Aquatic life is disturbed.
- Scouring of river beds and loss of river banks.
- Affects the human health living near the dam.
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- NEGATIVE IMPACTS-
- Resettlement and Relocation of villages.
- Dams reservoirs leads to seismic effects.
- Aquatic life is disturbed.
- Scouring of river beds and loss of river banks.
- Affects the human health living near the dam.
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