Geotechnical analysis and design of earth dams

There are many geotechnical considerations that are considered in the geotechnical analysis and design of earth dams.
Following are the major considerations in analysis and design of earthen dams.

Seepage

The most important reason for seepage analysis is to asses the potential for piping.

Piping is the formation of channels inside the dam due to internal erosion.

Silty soils are especially prone to piping. This type of failure is avoided by including filter and drain zones that control seepage and prevent soil migration.

Slope stability

Slope stability is the most important consideration in the analysis and design of earth dams. Land slides in either the upstream or downstream face of an earthen dam can be disastrous. These slopes must satisfy the stability requirements.

Rapid drawdown failure :
This type of failure occurs when the exterior water level has been at a certain elevation for a long time then quickly drops to a lower elevation.

If the soils have low hydraulic conductivity, the ground water table inside the slope cannot drop nearly as rapidly as the water outside so high pore water pressure inside the slope remain unchange and thus result in the land slide.

Causes of dam failure

35 percent were a direct result of floods that exceeded the spill way capacity. 25% were due to geotechnical problems such as seepage piping, high pore water pressure, fault movement, excessive settlement or land slides. The remaining 40 % were from a variety of problems including the use of poor construction materials or practices, wave action, acts of war and poor maintenance.

Reference : Geotechnical engineering principal and practices by Donald P Coduto