EARTHEN DAM
-PURPOSES OF DAM
-MATERIAL USED FOR EARTHEN DAM
-TYPES OF EARTHEN DAMS
-TYPICAL SECTION OF EARTHEN DAM
-SEEPAGE IN EARTHEN DAMS
-TYPES OF FAILURE IN EARTHEN DAMS
2. DAMS
A Dam is a hydraulic structure of fairly impervious
material built across the river to create a reservoir
on its upstream side for impounding water for
various purposes.
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3. PURPOSES OF DAM
1. Raise the level of the water upstream to enable
water to be diverted into a canal
2. Store water(basic purpose)
3. to increase ’hydraulic head’
4. Irrigation
5. Drought and Flood control
6. Hydropower generation
7. Navigation
8. To develop fisheries
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4. EARTHEN DAM
The earthen dam is the type of embankment dam that is
composed of the earth which is compacted into
subsequent layers of suitable thickness.
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5. MATERIAL USED FOR EARTHEN
DAM
1. Clayey Material : Black Cotton Soil
2. Sandy Material : Murum, Soft Rock, Sandy Silt
3. Rock masonry ( For pitching and Riprap)
5. Cement, steel, lime, and other materials: in a small
amount for the construction of spillways and outlets.
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6. TYPES OF EARTHEN DAMS
There are three types of earthen dams are as follows:
1. Homogeneous earthen dam
2. Diaphragm earthen dam
3. Zoned earthen dam
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7. Homogeneous Earthen Dam
1. Constructed by only one material.
2. Used for low or medium-high dams.
3. The dam creates a major problem of seepage.
4. earthen material is available in the local area the dam
construction is most economical.
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8. Diaphragm Earthen Dam
1. Impermeable layer is provided known as the diaphragm.
2. It prevents seepage and this layer is covered by earth and rock.
3. It constructed of wood, rock, stone, steel, and concrete.
4. The diaphragm is strong enough to prevent the dam from
seepage and it is located at the centre of the dam section.
5. This dam is better than the homogeneous dam.
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9. Zoned Earthen Dam
1. It is just a modification of both the previous dam.
2. The impermeable core is at the centre of the dam.
3. This transition is provided to avoid the crack on the piping and
installed at the central part of the dam.
4. The outer zone is also strong enough to protect the central
impermeable
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12. Hearting(core):
It is the central part of the dam constructed by the clayey
soil. The soil is compacted to tighten the soil and provide
shear strength to the dam against slipping.
Casing:
The core is surrounded by a layer and this layer is known
as casing, constructed by soft rock or sand and gravel. It
prevents it from cracking, slipping and provides stability to
the core layer.
Rock toe:
Rock toe is constructed of small stone or rock pieces
whose size is larger than 20cm. Rock toe provides stability
to the dam and prevents it from seepage.
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13. Pitching:
Stone of size 30cm can be used for layering (thickness 30cm -
45cm). This layer is known as pitching in dams and it prevents
sudden drawdown and provides stability.
Turfing:
Turfing is a process of planting a special type of grass called
doob or turfing grass on the downstream face of the dam. It
prevents water logging due to heavy rainfall.
Berms:
Berms are the offset provided on the downstream at 8m to
10m of the interval of width 3m to 5m. It is used to collect the
rainwater and dispose of it safely. It is constructed to provide
roadways for the vehicle, to reduce the flow of rainwater.
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14. Drain:
A series of drains is constructed containing different types
of drains that are longitudinal drains, cross drains and toe
drains on the downstream side of the dam.
Transition filters:
It is a filter provided in between the clayey soil layer and
sandy shell to avoid pore pressure.
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15. SEEPAGE IN EARTHEN DAMS
1. Flow of water takes place from pores of soil.
2. Seepage occurs through embankment called as
Horizontal Piping
3. Seepage occurs through foundation called as Vertical
Piping.
4. If seepage is not controlled it may causes failure of
dam.
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16. PHERATIC LINE OR SEEPAGE LINE
1. The top flow line of saturated soil mass is called the line.
2. Below the pheratic line, the seepage takes place.
3. The hydrostatic pressure is acts below the pheratic line.
4. In the earth dam, the pheratic line shapes like a parabola.
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17. CONTROL OF SEEPAGE THROUGH EMBANKMENT
A)Provision of impervious core
• Provide zone type section with impervious core.
• So seepage line shifted downward.
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18. B)Provision of Rock Toe
• It help to divert the seepage.
• It helps in preventing sloughing of d/w toe.
• Submerged area gets reduced.
C)Provision of Drainage Blanket
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19. CONTROL OF SEEPAGE THROUGH FOUNDATION
A)Provision of Cut off Trench
• Excavated bellow the hearting.
• Filled with impervious soil and compacted.
• Helps to reduce seepage up to 90%.
B)Provision of Cut off Wall
• Concrete or sheet pile
• Provided up to depth of pervious soil in foundation.
• So that seepage can be controlled effectively.
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20. TYPES OF FAILURE IN EARTHEN DAMS
1. Hydraulic Failure
2. Seepage Failure
3. Structural Failure
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21. 1. Hydraulic Failure
40% failure occurs due to hydraulic failure
Over Topping :
I. Insufficient free board.
II. Length of spillways is less.
III. Excess floodwater enters in to the reservoir.
Erosion :
I. At u/s slope: stone pitching is not provided.
II. At d/s slope: Due to rain water.
III. At d/s toe: stone pitching is not provided.
Cracking due to frost action:
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22. 2. Seepage Failure
33% failure occurs due to seepage failure.
Piping through body of the dam:
Piping through body of the dam:
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23. 3. Structural Failure
25% to 30% failure occurs due to Structural failure.
Sliding down u/s and d/s slope:
If slope is steeper or mot proper.
Faulty construction and Improper maintenance:
Wrong placement of materials in different zones.
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24. Prevention measures to avoid Failure of
Earthen Dam
1.Spillway designed for sufficient capacity.
2. Sufficient free board.
3. Operate spillway properly.
4. Provide stone pitching on u/s slope.
5. Provide rock toe on d/s slope.
6. Provide drainage blanket.
7. Provide cut off wall and cut off trenches.
8. Maintenance should be carried out at a regular interval.
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25. Advantages of Earthen dam
1. It can simply be constructed with locally available
material.
2. The design of the dam is also quite easy.
3. It is most economical because it is constructed with
locally available materials.
4. Where there is a wide layer of the valley it is suitable
to construct.
Disadvantages of Earthen dam
1. It causes a lot of leakage and soil erosion.
2. Due to improper capacity, it may fail.
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