A new back analysis of strength parameters from single slips

For a given homogeneous slope with an arbitrary geometry, unit weight and pore water pressure distribution, the position of a critical failure surface will remain unique for a specified value of c′/tanϕ′. Based on this theoretical relationship between c′ and ϕ′ and the critical slip surface, a straightforward back analysis method is proposed to estimate the magnitude of c′/tanϕ′ from a known position of the failure surface observed in the field slope. The back analysis of c′/tanϕ′ can easily be implemented by incorporating the method into existing limit equilibrium slope stability analysis software. When the c′/tanϕ′ value is obtained, a pair of c′ and ϕ′ can uniquely be determined by considering the fact that the factor of safety is equal to unity.