The types of failure surface are: i) Planar failure surface ii) circular failure surface iii) Non-circular failure surface.

Collin observed that the rupture mass slide down a sliding surface, in a definite pattern resembling that of a cycloid.

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

If the failure occurs along a sliding that intersects the slopes at or above its toe, the slide is known as slope failure.

For toe failure, Df = 1; for base failure, Df > 1.

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

Planar failure surface may commonly occur in a soil deposit or embankment with a specific plane of weakness.

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

The stability of a finite slope can be investigated by the following methods:

According to Bennet (1951), non-circular or composite slip surface may arise in homogeneous dam have foundation of infinite depth, rigid boundary planes of maximum and presence of stronger or weaker layer.