Seepage through embankments can negatively impact their stability and surrounding areas. Effects include waterlogging, salinization, and piping erosion within the embankment. Several methods are used to control seepage, including increasing flow paths with cut-off walls, impermeable cores, and upstream blankets. Properly designed internal drainage systems like toe drains and chimney drains can also help control seepage by reducing pore pressures and intercepting water flows. The dimensions and permeability of drainage elements must be sufficient to safely carry anticipated seepage flows.

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2. USAMA HANIF
FA15-BCV-074 2

3. CONTROL OF SEEPAGE
THROUGH EMBANKMENTS 3

4. CONTENTS:
SEEPAGE.
EFFECTS OF SEEPAGE.
METHODS OF SEEPAGE CONTROL.
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5. SEEPAGE:
• Also known as leakage, leak, oozing or percolation.
• The slow escape of a liquid or gas through porous material or
small holes.
• First recorded in 1815-1825.
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6. SEEPAGE:
• Something that seeps or
leaks out.
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7. EFFECTS OF SEEPAGE:
Water losses in canals
contribute to:
• Water-logging.
• Salinization of valuable
irrigated areas.
• Reduce system
performance.
• Lead to increase in
water withdrawal.
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8. EFFECTS OF SEEPAGE:
All embankments dams
are subjected to
seepage.
Seepage may be
detrimental to the
stability of structure as
a result of excessive
pore water pressure or
by internal erosion.
Turbid flow is a
symptom of internal
erosion.
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9. WATER-LOGGING:
Waterlogging refers to
the saturation of soil
with water.
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10. SALINITY:
Measure of all the salts
dissolved in water.
The average
ocean salinity is 35ppt
and the average river
water salinity is 0.5ppt
or less.
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11. PIPING:
Internal erosion of the
foundation or
embankment caused by
seepage.
Erosion starts at the
downstream toe and
works back toward the
reservoir.
The channels or pipes
follow paths of
maximum permeability.
Time-taking process.
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12. PIPING:
Resistance of the embankment or foundation to piping depends on
the:
• Plasticity of the soil.
• Gradation.
• Degree of compactness.
• Plastic clays with a plasticity index >15 are most resistant to
piping.
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13. PIPING (CONTROL):
Piping can be avoided by lengthening the flow paths of water
within the dam and its foundations.
This decreases the hydraulic gradient of the water flow and hence
its velocity.
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14. PIPING (INCREASING FLOW-PATHS):
Flow-paths can be increased by:
• Cut-off walls.
• Impermeable cores.
• Impermeable blankets extending upstream from the upstream
face.
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15. PIPING (METHODS TO INCREASE FLOW-PATH):
Cut-off walls:
• Mitigate the flow of
groundwater.
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16. PIPING (METHODS TO INCREASE FLOW-PATH):
Impermeable core:
• A zone of low
permeability material in
an embankment dam.
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17. PIPING (METHODS TO INCREASE FLOW-PATH):
Impermeable upstream
blanket:
• An impervious layer
placed on the reservoir
floor upstream of a
dam.
• In the case of an
embankment dam, the
blanket may be
connected to the
impermeable element in
the dam.
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18. SEEPAGE CONTROL:
Seepage is the continuous movement of water (from u/s to d/s
face of dam).
The upper surface of this stream of percolating water is known as
the phreatic surface.
 The phreatic surface should be kept at or below the downstream
toe.
The phreatic surface within a dam can be controlled by properly
designed cores or walls.
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19. INTERNAL DRAIN SYSTEM:
Purpose:
• A homogeneous dam with a height of more than about 6 m to 8 m
should have some type of downstream drain:
1. To reduce the pore water pressures in the d/s portion of the dam
therefore increasing the stability.
2. To control any seepage that exits the d/s portion of the dam
(i.e., prevents piping).
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20. INTERNAL DRAIN SYSTEM:
Effectiveness:
• The effectiveness of the drain in reducing pore pressures depends
on its:
1. Location.
2. Extent.
• However, piping is controlled by ensuring that the grading of the
pervious material from which the drain is constructed meets the
filter requirements for the embankment material.
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21. TOE DRAINS:
The design of a d/s drainage system is controlled by the:
• Height of the dam.
• Cost and availability of permeable material.
• Permeability of the foundation.
For low dams, a simple toe drain can be used successfully.
For reservoir depths greater than 15 m, most engineers would
place a drainage system further inside the embankment.
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22. HORIZONTAL DRAINAGE BLANKET:
ADVANTAGES:
• Often used for dams of
moderate height.
• Frequently used over the
downstream one-half or one-
third of the foundation area.
DISADVANTAGES:
• An earth dam embankment
tends to be more pervious in
the horizontal direction than
in the vertical.
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23. CHIMNEY DRAINS:
• Prevent horizontal flow along relatively impervious stratified
layers.
• Intercept seepage water before it reaches the downstream slope.
• Useful in reducing pore water pressures.
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24. DIMENSIONS AND PERMEABILITY OF DRAINS:
• Must be adequate to carry away the anticipated flow with an
ample margin of safety for unexpected leaks.
• If the dam and the foundations are relatively impermeable, then
the expected leakage would be low.
• A drain should be constructed of material with a coefficient of
permeability of at least 10 to 100 times greater than the average
embankment material.
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25. THIN U/S SLOPING CORE:
• In an earth dam with an u/s sloping core of low permeability, the
foundation is assumed to be impermeable and in a steady state.
• For this type of dam the d/s shell must be several hundred times
more permeable than the core.
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26. PARTIAL CUT-OFFS:
• An earth dam constructed without a cut-off on permeable or semi-
permeable foundations of earth or rock may lead to seepage
beneath the dam creating unacceptable uplift pressures and
causing instability.
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27. THANK YOU!!! 27