Abstract: In slope stability analysis, one needs to calculate the factor of safety and determine the slip surface. The strength reduction method can yield reasonable value of the safety factor, but it cannot depict correctly the critical slip surface. This paper proposes an approach to determining the critical slip surface based on the displacement filed analysis during the sliding movement. It is shown that the displacement contours near the slip surface are the densest at the critical state of slope. The points along the potential slip surface represent those points at which the change rate of displacement along the direction perpendicular to the critical slip surface reaches the maximum in the vertical direction. By comparing the proposed method with the Spencer method and physical model test of rock slopes, it is shown that the proposed method yields good results in searching the slip surfaces. In addition, the effects of some other factors such as geometrical shape, degree of density and discrete point spacing on the slip surface are discussed.

Key words: strength reduction method, slope stability, critical slip surface, safety factor, change rate of displacement