Resistance factors for design of slopes in a homogenous soil layer

Traditionally, the factor of safety (FOS) is widely used to account for uncertainties in the design of slopes within the framework of working stress design. As the uncertainties involved in the design of slopes vary, the same FOS may correspond to the different levels of reliability. In this study, the advanced first order reliability method is used to determine the resistance factors for design of slopes in a homogenous soil layer. It is found that the resistance factors depend on the target reliability index, the height of the slope, and the variability of the soil strength parameters. It is difficult to suggest a unique set of resistance factors for design of slopes. Analytic solutions are developed to determine the resistance factors for design of slopes assuming the random variables are normally distributed. An approximate method based on the concept of equivalent target reliability index is also suggested to determine the resistance factors for design of the slope when the soil strength parameters are lognormally distributed. The method suggested in this paper provides a practical way to perform load and resistance factors design of slopes.