Drained Residual Shear Strength Power Function Coefficients a and b

Abstract Drained residual strength is the controlling shear strength for slopes that have experienced prior movement, contain colluvium, or have a continuous zone of slickensided material. This study provides correlations between power function coefficients a and b and soil index properties, e.g., liquid limit, plastic limit, and clay-size fraction, to represent the drained residual strength envelope. These correlations provide a prediction of the residual secant friction angle, ϕ’r, at any desired effective normal stress, which can be used to establish the residual strength envelope for stability analyses. The standard deviation of a and b coefficients and the corresponding trendlines were found using two statistical methods, with the Graphical Three-Sigma Rule Method providing a better representation of the data scatter than the Computational Method. Data from the literature were compiled and compared to the proposed a and b coefficients and there is favorable agreement.