Abstract: The formula of determining the critical angle of soil self-stabilizing is deduced based on upper bound theorem. A new method is presented to evaluate slope stability by using the ratio of soil self-stabilizing angle to slope angle. In addition to the known second slip surface, which is the potential slip surface involving the overall stability, a new slip surface, namely the first slip surface is testified to possibly exist in the active zones of soil nail walls for the first time. This slip surface is determined by soil self-stabilizing angle. A series of case studies have validated the method proposed in this study. This research reveals the mechanism of soil slide, and provides a new approach of determining the stability of slope and soil-nail wall.

Key words: slope, slip surface, soil nail wall