* Hydraullic Failure
* Seepage Failure
* Structural Failure
Due to ,
* Overtopping (design level is underestimated)
* Erosion of U/S face (wave action – height)
* Cracking in upper portion of dam due to frost action (additional freeboard allowance up to 1.5 m) * Erosion of D/S face due to rain action (maintenance – berms - grass)
By overtopping: the water may overtop the dam ,if the design flood is under-estimated or if the spillway is of insufficient capacity or if the spillway gates are not properly operated. Sufficient freeboard should, therefore ,be provided as an additional safety measure. Erosion of upstream face: The waves developed near the top water surface due to the winds, try to notch-out the soilfrom the u/s face and may even, sometimes, cause the slip of the u/s slope. U/s stone pitching or riprap should ,therefore, be provided to avoid such failures. 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 addition freeboard allowance upto a maximum of say 1.5 m should therefore, be provided for dams in areas of low temperatures. Erosion of Down stream(D/S) face by gully formation: Heavy rains falling directly over the d/s face and the erosive action of the moving water, may lead to the formation of gullies on the downstream face, ultimately leading to the dam failure .This can be avoinded by proper maintenance, filling the cuts from time to time especially during rainy season, by grassing the slopes and providing proper berms at suitable heights so that water has not to flow for considerable distances. The proper drainage arrangement are made for the removal of rain water collected on the horizontal berms. So the provision of berms may be helpful to reduce runoff and decrease the velocity.
* Uncontrolled seepage...