The document discusses causes of failure for weirs and barrages built on permeable foundations, including piping/undermining, uplift pressure, hydraulic jump, and scouring. It explains that piping occurs when water percolates through the foundation and erodes soil particles, creating a hollow channel. Uplift pressure from percolating water can also cause failure if the structure's weight cannot counterbalance it. Hydraulic jump and high-velocity surface flow can produce suction pressures and scour soil. The document recommends increasing the seepage path using sheet piles, increasing floor thickness to resist uplift, and using energy dissipaters and filters to prevent soil loss and structural failure.

1. Failure of weir and barrage
DIVYA VISHNOI
Assistant Professor

2. Causes of Failure of weir or barrage
on permeable foundation
The combined effect of surface flow and surface flow may
cause the failure of the weir or barrage.
(i) Failure due to subsurface flow
(a) By piping or undermining: The water from the
upstream side continuously percolates through the bottom
of the foundation and emerges at the downstream end of
the weir or barrage floor. The force of percolating water
removes the soil particles by scouring at the point of
emergence. As the process of removal of soil particles goes
on continuously, a depression is formed which extends
backwards towards the upstream through the bottom of
the foundation. A hollow pipe like formation thus develops
under the foundation due to which the weir or barrage
may fail by subsiding. This phenomenon is known as
failure by piping or undermining.

3. By Piping or Undermining

4. By Piping or Undermining

5. Causes of Failure of weir or barrage
on permeable foundation
(b) By uplift Pressure: The percolating water exerts an upward pressure
on the foundation of the weir or barrage. If this uplift is not
counterbalanced by the self weight of the structure, it may fail by
rapture.
2. Failure by Surface Flow:
(a) By Hydraulic Jump: When the water flows with a very high velocity
over the crust of the weir or over the gates of the barrage, then
hydraulic jump develops. This hydraulic jump causes a suction
pressure or negative pressure on the downstream side which acts in
the direction of uplift pressure. If the thickness of the impervious floor
is not sufficient, then the structure fails by rapture.
(b) By Scouring During floods: The gates of the barrage are kept open
and the water flows with high velocity. The water may also flow with
very high velocity over the crest of the weir. Both the cases can result
in scouring effect on the downstream and on the upstream side of the
structure. Due to scouring effect on the downstream and on the
upstream side of the structure, its stability gets endangered by shearing.

6. By Uplift Pressure

7. By Hydraulic Jump

8. By Scouring During floods

9. Causes of Failure of Weir, and
Remedies
• If a weir is constructed on permeable soil, weir may fail
by piping, uplift force, suction caused by standing wave
and scouring on both upstream and downstream of the
weir.
• When hydraulic gradient or exit gradient exceeds the
critical value of soil, surface soil at down end starts
boiling first and is washed away by percolating water.
This process of removal or washing out of soil continuous
and eventually a channel in the form of pipe is formed by
seepage water. This is called piping which may cause the
failure of foundation. Similarly uplift force of percolating
water is acting on ther floor from bottom and if the
weight of floor is not enough to resist this uplift force,
floor may fail by cracking or bursting.

10. Causes of Failure of Weir, and
Remedies
• The main remedies against failure are:
• Path of percolation or creep length of seepage
water should be increased by providing sheet
piles at upstream, downstream or at
intermediate point to reduce the hydraulic
gradient.
• Floor thickness should be increased to
increase its self weight to balance the uplift
force.

11. Precautions Against Failure
• The following precautions can be taken to prevent
failure.
• (a) The length of the impervious layer should be
carefully designed so that the path of the percolating
water is increased consequently reducing the exit
gradient.
• (b) Sheet piles should be provided on the upstream
side and the downstream side of the impervious
floor to increase to the length of percolating water
so that the uplift pressure is considerable reduced.
• (c) The thickness of the impervious floor should be
such that the weight of the floor is a sufficient to
counterbalance the uplift pressure.

12. Precautions Against Failure
• (d) Energy dissipater blocks like friction
blocks, impact blocks, should be provided.
• (e) Inverted filter should be provided with
concrete blocks on the top so that the
percolating water does not wash out the soil
particles.
• Deep foundation like well foundation should
be provided for the barrage piers

13. Precautions Against Failure

14. Precautions Against Failure

15. Energy Dissipater Blocks

16. Increasing Floor
Thickness

17. References
• Irrigation Engineering & Water Power Engineering
– By Prof B.C.PUNMIA
– Laxmi Publication
• Irrigation Engineering & Hydraulic Structures
– By Prof. Santosh Kumar Garg
– Khanna Publishers
• Irrigation, Water Power Engineering & Hydraulic Structures
– By Prof K.R. Arora
– Standard Publishers Distributions
• Internet Websites
• http://www.aboutcivil.org/
• http://nptel.ac.in/courses/105105110/

18. Thanks