This document discusses methods for controlling seepage through embankments. It defines seepage and describes its effects, such as waterlogging, salinization, and reducing system performance. Methods to control seepage discussed include increasing flow paths through cut-off walls, impermeable cores, and upstream blankets. Internal drainage systems like toe drains and horizontal drainage blankets are also described. Dimensions and permeability of drains are important factors. Thin upstream sloping cores and partial cut-offs can also help control seepage in embankments.

1. CONTROL OF SEEPAGE
THROUGH EMBANKMENTS

2. Vasu Goel (2817602) Jai Sharma (2818971)
Vishant Singhal (2817615) Mahapara Manzoor (2817609)
Nikhil (2817603)
Presented By :-

3. CONTENTS:
SEEPAGE.
EFFECTS OF SEEPAGE.
METHODS OF SEEPAGE CONTROL.

4. 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.

5. SEEPAGE:
• Something that seeps or
leaks out.

6. 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.

7. 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.

8. WATER-LOGGING:
Waterlogging refers to the
saturation of soil with water.

9. 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.

10. 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.

11. 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.

12. 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.

13. PIPING (INCREASING FLOW-PATHS):
Flow-paths can be increased by:
• Cut-off walls.
• Impermeable cores.
• Impermeable blankets extending upstream from the upstream face.

14. PIPING (METHODS TO INCREASE FLOW-PATH):
Cut-off walls:
Mitigate the flow of groundwater.

15. PIPING (METHODS TO INCREASE FLOW-PATH):
Impermeable core:
A zone of low permeability material in an
embankment dam.

16. 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.

17. 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.

18. 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. Toreduce the pore water pressures in the d/s portion of the dam
therefore increasing the stability.
2. Tocontrol any seepage that exits the d/s portion of the dam (i.e.,
prevents piping).

19. 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.

20. 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.

21. HORIZONTAL DRAINAGE BLANKET:
Advantages Disadvantages
• Often used for dams of
moderate height.
• Frequently used over the
downstream one-half or one-
third of the foundation area.
• An earth dam embankment
tends to be more pervious in the
horizontal direction than in the
vertical.

22. 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.

23. 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.

24. 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.

25. 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.

26. THANK
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