Revisiting seismic slope stability: intermediate or below-the-toe failure?

This technical note presents a novel procedure, discretisation-based kinematic analysis, to investigate the seismic slope stability at limit state. Such a procedure combines the merits of highly efficient kinematic analysis with an adaptive discretisation technique for the generation of a kinematically admissible failure mechanism for non-uniform soil slopes with varying soil strength parameters, which cannot be readily solved in conventional limit analysis. Apart from shallow toe failure, the below-the-toe and intermediate failure modes are also likely to occur, particularly for gentle slopes. Considering the latter two modes, the proposed approach is applied to a non-uniform soil slope with linearly increasing soil properties and a layered soil profile to demonstrate the adaptability of the procedure for wider applications. The upper-bound formulations of yield seismic acceleration and/or limit surcharge are derived based on the balance of work rate. Through an optimisation procedure, the least upper-bound solutions are sought under given parameters, and the critical failure mechanism can be characterised simultaneously.