Risk assessment of slope failure considering multiple slip surfaces

For a slope with a large number of potential slip surfaces, the consequence of slope failure along different slip surfaces could be quite different. When the soil parameters are uncertain, the location of the slip surface with minimum factor of safety is also uncertain, making the consequence of slope failure also uncertain. The traditional equation for risk assessment may only be suitable for slope failure along a given slip surface, but may not be directly applicable to slope failure with a large number of potential slip surfaces. In this study, a new equation is suggested for risk assessment of slope failure considering the system failure probability. A response surface method is used to enhance the computational efficiency. Three slopes are studied to illustrate the proposed method. It is found that the consequence of slope failure is an important weighting factor in the risk assessment of slope failure. A slip surface with a larger failure probability but small consequence may be associated with a smaller risk. Hence, the most probable failure surface may not always be the slip surface with the largest risk. For the three examples studied in this paper, the risk of slope failure are all governed by the representative slip surfaces. Therefore, the risk of slope failure can then be assessed in a simplified manner by taking into account only the representative slip surfaces. Both the reliability method and empirical method can be used for representative slip surfaces identification.