Similar to Culmann?s method, friction circle method also assumes failure surface as arc of circle.

The two basic types of failure of a finite slope may occur: (i) slope failure (ii) base failure.

When slope is fully submerged, submerged density ??, and weighted frictional angle ?w should be used for computing stability number Sn.

Failure of finite slopes occurs along a curved surface. In stability computation, curve is represented by an arc of a circle or logarithmic scale.

In friction circle method, it is assumed that resultant reaction is tangential in friction circle, since error involved in this assumption is of small magnitude.

If Fc is factor of safety with respect to cohesion,
We have c × H / Fc × ?H2
= c / Fc ? H = Sn
The dimensional quantity c / Fc ? H is called as Taylor?s stability number Sn.

The ratio of total depth (H + D) to depth H is called depth factor Df.

In rectangular plot method if re are n-slices, total number of ordinates will be (n-1), ordinates at end of last strip being zero.

In Hilf?s equation hc refers to Henry?s constant of solubility of air in water by volume (= 0.02 at 68°F).

The factor of safety with respect to cohesive strength, based on assumption that frictional force has been fully mobilized, and equation is given by FC = C / Cm.