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FAILURE OF EARTHEN DAMS

NAME- SABYASACHI SWAIN
SUBJECT- THEORY OF SEEPAGE
M.TECH 1ST YEAR
BRANCH- WRD & IE
ROLL NO- 13244...
FAILURE OF EARTHEN DAMS
• Earth dams are less rigid and hence more
susceptible to failure.

• An earthen dam may fail due ...
FAILURE OF EARTHEN DAMS
• The various causes leading to the failure
of earth dam can be grouped into
following three categ...
FAILURE OF EARTHEN DAMS
1. HYDRAULIC FAILURES-

• About 40% of earth dam failures have
been attributed to these causes.
• ...
FAILURE OF EARTHEN DAMS
a) Overtopping failure:
The water may overtop the dam , if
•
•
•



The design flood is under-est...
FAILURE OF EARTHEN DAMS
b) Erosion of upstream face:
• The wave action due to the wind and tides will
cause the erosion of...
FAILURE OF EARTHEN DAMS
Safety measures:
Upstream stone pitching .
Provision of riprap.

Proper design.
FAILURE OF EARTHEN DAMS
c) Cracking due to frost action:
• Frost in the upper portion of the dam may
cause heaving and cra...
FAILURE OF EARTHEN DAMS
d) Erosion of the downstream slope by
gully formation:
• Heavy rains falling over the downstream f...
FAILURE OF EARTHEN DAMS
Proper maintenance.
Filling the cuts from time to time , especially
during rainy season.
Grassi...
FAILURE OF EARTHEN DAMS

Provision of berms in an earthen dam
FAILURE OF EARTHEN DAMS
e) Toe erosion:
• Similar to the wave action at the upstream of
the dam, downstream dam slope is a...
FAILURE OF EARTHEN DAMS
Provision of a downstream slope pitching or a
riprap up to a height slightly above the normal
tai...
FAILURE OF EARTHEN DAMS
2. SEEPAGE FAILURES• Uncontrolled or concentrated seepage
through dam body or foundation may lead ...
FAILURE OF EARTHEN DAMS
• Piping is the progressive erosion and
subsequent removal of soil grains from within
the body or ...
FAILURE OF EARTHEN DAMS
(a)Piping through foundations:
• When highly permeable cavities or strata of
coarse sand or gravel...
FAILURE OF EARTHEN DAMS

Piping through the dam foundation
FAILURE OF EARTHEN DAMS
(b) Piping through dam body:
• When concentrated flow channels get
developed in the body of the da...
FAILURE OF EARTHEN DAMS

Piping through the dam body
FAILURE OF EARTHEN DAMS
All these can be removed by better
construction and better maintenance of dam
embankment.

Thoro...
FAILURE OF EARTHEN DAMS
(c) Sloughing:
• If the seepage line exists at the downstream
face of the dam, the portion of the ...
FAILURE OF EARTHEN DAMS
3. STRUCTURAL FAILURES• About 25% of overall dam failures.
• Generally, these are caused by shear ...
FAILURE OF EARTHEN DAMS
(a)Failure due to the pore water pressure:
• Excessive pore water pressure in confined seams
of sa...
FAILURE OF EARTHEN DAMS
(b) Upstream slope failure:
• Steep slope, weak embankment soil, sudden
drawdown of reservoir.
• C...
FAILURE OF EARTHEN DAMS

Upstream slope slide due to sudden drawdown
FAILURE OF EARTHEN DAMS
(c) Downstream slope failure:
• When the reservoir is at maximum level and if
the steady stage see...
FAILURE OF EARTHEN DAMS

Downstream slope slide during full reservoir condition
FAILURE OF EARTHEN DAMS
(d) Foundation slide:
• The dam body as a whole may slide, if the
foundation is from the silt or s...
FAILURE OF EARTHEN DAMS

Sliding due to soft or weak foundation
FAILURE OF EARTHEN DAMS
(e) Other modes:
• Failure by spreading.
• Failure by leaching.
• Failure due to earthquake – most...
REFERENCES
Garg, S.K., (2012), “Irrigation Engineering and
Hydraulic Structures.” 24th Edition, Khanna
Publishers.
Walling...
THANK YOU
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FAILURE OF EARTHEN DAMS (SEEPAGE THEORY)

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Presentation st sabya

  1. 1. FAILURE OF EARTHEN DAMS NAME- SABYASACHI SWAIN SUBJECT- THEORY OF SEEPAGE M.TECH 1ST YEAR BRANCH- WRD & IE ROLL NO- 13244006
  2. 2. FAILURE OF EARTHEN DAMS • Earth dams are less rigid and hence more susceptible to failure. • An earthen dam may fail due to improper designs, faulty constructions, or lack of maintenance etc.
  3. 3. FAILURE OF EARTHEN DAMS • The various causes leading to the failure of earth dam can be grouped into following three categories1. Hydraulic failures 2. Seepage failures 3. Structural failures
  4. 4. FAILURE OF EARTHEN DAMS 1. HYDRAULIC FAILURES- • About 40% of earth dam failures have been attributed to these causes. • The failure under this category may occur due to the following reasons:
  5. 5. FAILURE OF EARTHEN DAMS a) Overtopping failure: The water may overtop the dam , if • • •  The design flood is under-estimated. The spillway is of insufficient capacity. The spillway gates are not properly operated. Sufficient freeboard should, therefore be provided.
  6. 6. FAILURE OF EARTHEN DAMS b) Erosion of upstream face: • The wave action due to the wind and tides will cause the erosion of the dam material at the upstream face, if the material could not sustain wave velocity. • It will lead to washing out of the dam material or overturning of the protection slab or slip of the upstream face.
  7. 7. FAILURE OF EARTHEN DAMS Safety measures: Upstream stone pitching . Provision of riprap. Proper design.
  8. 8. FAILURE OF EARTHEN DAMS c) Cracking due to frost action: • Frost in the upper portion of the dam may cause heaving and cracking of the soil with dangerous seepage and consequent failure. An additional freeboard allowance should be provided for dams in areas of low temperatures.
  9. 9. FAILURE OF EARTHEN DAMS d) Erosion of the downstream slope by gully formation: • Heavy rains falling over the downstream face • The erosive action of moving water • The formation of gullies on the downstream face , leading to dam failure.
  10. 10. FAILURE OF EARTHEN DAMS Proper maintenance. Filling the cuts from time to time , especially during rainy season. Grassing the slopes. Providing proper berms at suitable heights.
  11. 11. FAILURE OF EARTHEN DAMS Provision of berms in an earthen dam
  12. 12. FAILURE OF EARTHEN DAMS e) Toe erosion: • Similar to the wave action at the upstream of the dam, downstream dam slope is also susceptible for erosion by the downward water. • Erosion due to the cross-currents that may come from the spillway buckets. • Erosion due to tailwater.
  13. 13. FAILURE OF EARTHEN DAMS Provision of a downstream slope pitching or a riprap up to a height slightly above the normal tail water depth. By providing the rock toe drainage. Sidewalls of the spillway must be of sufficient height and length.
  14. 14. FAILURE OF EARTHEN DAMS 2. SEEPAGE FAILURES• Uncontrolled or concentrated seepage through dam body or foundation may lead to failure of the dam. • Piping (through foundation and dam body) • Sloughing
  15. 15. FAILURE OF EARTHEN DAMS • Piping is the progressive erosion and subsequent removal of soil grains from within the body or foundation of the dam. • Sloughing is the progressive removal of soil from the wet downstream face. • More than one-third of the earth dams have failed due to these reasons.
  16. 16. FAILURE OF EARTHEN DAMS (a)Piping through foundations: • When highly permeable cavities or strata of coarse sand or gravel are present in the foundation, water may seep at a huge rate through them. • This concentrated flow at a high gradient may erode the soil. • Increased flow of water and soil results in creation of hollows below the foundation, into which the dam may sink down.
  17. 17. FAILURE OF EARTHEN DAMS Piping through the dam foundation
  18. 18. FAILURE OF EARTHEN DAMS (b) Piping through dam body: • When concentrated flow channels get developed in the body of the dam, soil may be removed as in case of foundation piping. • Formation of hollows in the dam body and subsequent subsidence of the dam body. • Flow channels develop due to faulty construction, insufficient compaction, cracks in embankment due to settlement, shrinkage cracks etc.
  19. 19. FAILURE OF EARTHEN DAMS Piping through the dam body
  20. 20. FAILURE OF EARTHEN DAMS All these can be removed by better construction and better maintenance of dam embankment. Thorough compaction of soils near the outlet conduits and preventing the leakage through them to avoid contact seepage. For pervious seams in foundation, relief drain with filter can be provided.
  21. 21. FAILURE OF EARTHEN DAMS (c) Sloughing: • If the seepage line exists at the downstream face of the dam, the portion of the toe of the dam below the exit point will always remain in the wet condition. • This will cause the reduction of the stability of the slope and small size sliding may occur. • The repetition of wetting and sliding will continue further to cause dam failure, termed as sloughing.
  22. 22. FAILURE OF EARTHEN DAMS 3. STRUCTURAL FAILURES• About 25% of overall dam failures. • Generally, these are caused by shear failures leading to sliding.
  23. 23. FAILURE OF EARTHEN DAMS (a)Failure due to the pore water pressure: • Excessive pore water pressure in confined seams of sand and silt, artesian pressure in abutments, etc. may reduce shear strength of soil. • Loose sand foundation may fail by liquefaction or flow slides. Adequate compaction of soil.
  24. 24. FAILURE OF EARTHEN DAMS (b) Upstream slope failure: • Steep slope, weak embankment soil, sudden drawdown of reservoir. • Cause the seepage force acting along the sliding direction causing increase of the driving force for slope direction. • Seldom lead to catastrophic failures. Can be avoided by flatten slopes, provision of rock berms and better operating rules.
  25. 25. FAILURE OF EARTHEN DAMS Upstream slope slide due to sudden drawdown
  26. 26. FAILURE OF EARTHEN DAMS (c) Downstream slope failure: • When the reservoir is at maximum level and if the steady stage seepage is at maximum rate, the downstream slope is more vulnerable to slide due to seepage force acting in the direction of driving force for the sliding. Flatten slope, better soil, increased compaction, internal drainage with protective filters and surface drainage facilities.
  27. 27. FAILURE OF EARTHEN DAMS Downstream slope slide during full reservoir condition
  28. 28. FAILURE OF EARTHEN DAMS (d) Foundation slide: • The dam body as a whole may slide, if the foundation is from the silt or soft soil. • The slow consolidation process and expansion of clay soils due to the saturation will decrease the shear strength of the foundation soil. Flatten slopes, broad berms, stabilization of soil, deep drain trenches with protective filters for drainage, relief wells.
  29. 29. FAILURE OF EARTHEN DAMS Sliding due to soft or weak foundation
  30. 30. FAILURE OF EARTHEN DAMS (e) Other modes: • Failure by spreading. • Failure by leaching. • Failure due to earthquake – most devastating of all types of failures. Proper design, regular inspection and better operating rules.
  31. 31. REFERENCES Garg, S.K., (2012), “Irrigation Engineering and Hydraulic Structures.” 24th Edition, Khanna Publishers. Wallingford H.R.,(2008), “Dam Breach Floods – An Introduction”, www.hrwallingford.com. Dam Failure- Wikipedia, the free encyclopedia. en.wikipedia.org/wiki/Dam_failure. Creager, W.P., Justin, J.D. and Hinds, J., (1955), “Engineering for Dams.” Vol. 3, 1st Edition, John Wiley & Sons,INC., Chapman & Hall, LTD.
  32. 32. THANK YOU

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