chiupawar

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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.