Stability analysis of cut slope with shear band propagation along a weak layer

Abstract

Retrogressive spreading failure occur frequently in sensitive clay deposits due to triggering such as gradual natural erosion and degradation or artificial cut. The large scale of failure observed in retrogressive landslides have been attributed to quasi-horizontal shear band propagation along a weak layer. This study explores the critical conditions for such failure and develops the criteria for catastrophic propagation of quasi-horizontal shear band in infinite slopes accounting for unidirectional uphill shear band propagation and removal of downslope support. The critical conditions and criteria, with respect to pre-existing softened zone length and gravity shear stress ratio, for catastrophic shear band propagation in cut slopes are influenced by the front angle of cut slope, the softened zone length and the post-peak degradation relationship. The proposed criteria are justified by a large deformation finite element analysis. A framework for stability analysis of cut slopes in sensitive clays is established based on the criteria for catastrophic shear band propagation. The 1994 Sanite-Monique landslide in Quebec Canada is re-visited using the proposed framework, with the calculated factor of safety and failure mechanism compared with an upper bound limit analysis.