Mumbai University > Civil Engineering > Sem 7 > Irrigation Engineering

Marks: 6M

Year: Dec 2015, May 2016

The causes of failure of earth dam are as follows:

1. Hydraulic failures.
2. Seepage failures.
3. Structural failures.

Hydraulic failures:-

Hydraulic failure include the following :

a) Overtopping b) Wave erosion c) Toe erosion d) Gullying

• Overtopping: - The earth dam may get overtopped if the design flood is under-estimated, or if the spillway is of insufficient capacity. Faulty operation of spillway gates, etc. may also sometimes lead to overtopping.

• Wave erosion:- The effect of wave is to notch out earth from the upstream slope in absence of proper slope protection in the form of riprap. Rollers are developed in the waves which try to scoop out the earth. Waves can also causes upstream slips

• Toe erosion: - Toe erosion may occur due to two reasons a) erosion due to tail water, and b) erosion due to cross currents that may come from spillway buckets or from exit areas of outlets.

• Gullying: - Downstream slope may fail due to the formation of gullies by heavy downpour.

Seepage Failures: -

Seepage failure may be due to

a) Piping b) Sloughing.

• Piping: - The seepage of water through the body and foundation of earth dams may lead to piping or progressive erosion of concentrated leaks, causing a large number of catastrophic failures.

• Sloughing: - Failure due to progressive sloughing or raveling is closely related to piping. Under the full reservoir condition, the downstream toe remains saturated and may erode, producing a small slump or miniature slide.

Structural failures: -

Structural failures may be due to the following reasons:-

• Upstream and downstream slope failure due to construction pore pressure.
• Upstream slope failure due to sudden drawdown.
• Foundation slide
• Failure by spreading.
• Slope protection failures.
• Failures due to earthquake.
• Slope protection failures.
• Failure due to damage caused by burrowing animals.