Earthen slopes may be found in nature. It may be man made. This is required for the construction of Roads, railway lines, dams, and irrigation works etc. failure of these are caused loss of life and property.

Causes of Failure

Failure is as we know a land slide.

  • Gravitational forces that is weight of soil acting downwards tangential component of which must be within the safe limits. Factor of safety is restraining force/sliding force
  • Seepage of water through the soil mass
  • Progressive disintegration of soil mass
  • Excavation near the base 

Failures of earthen slopes happens slowly or suddenly

Stability Analysis

Determine the potential failure surface and the forces tending to cause the slip. There is a restoring force or to stabilize the soil mass of earth. Find these forces is the analysis of slope failure. We can find a factor of safety. Seepage forces can also found from flow net and shearing strength of soil. There is infinite and finite slope. An infinite slope is the slope surface of semi infinite soil mass. Finite slope is finite extent bounded by a top surface.

Infinite slopes

If the height of the slope is very large it may be considered as infinite slope. It is assumed that the soil is homogenous in its properties. If strata present it may consider to be parallel. Failure occurred only along a plane parallel to the surface. In this case analysis is simple for cohesion less soil. Purely cohesive and cohesive frictional soil is also exists. Seepage forces also there for cohesion less soil.

Suppose angle of slope is B, and angle of friction is A. then it can be shown that for safety A=B. Thus, the maximum inclination of an infinite slope in cohesion less soil is equal to angle of internal friction of the soil. Stability is independent of unit weight and water content if seepage forces do not present. Cohesive frictional soil is most frequently occurred  

If we consider a finite vertical element at a finite depth factor of safety against slippage on a parallel plane to the surface at that depth is crucial.

Finite Slopes

A finite slope has a base and a top, the height being limited. The inclined surfaces of earthen dams, embankments,, excavations are examples for finite slopes. For the analysis of the stability of finite slopes it is assumed that a slip surface is possible. Study the equilibrium of forces in the failure surface. The slip surface is along a circular arc. A lot of methods are available to analyze including Swedish method of slices or Bishop method.