Asynchronous Mobilization of Shear Resistance in Slope Failures

Abstract

This paper focuses on the case study of the 2014 embankment failure at the Mount Polley TSF in Canada to study deformation-controlled mechanisms of instability leading to the asynchronous mobilization of shear strength and causing progressive failure. Three such mechanisms were identified in this failure: strain-weakening, the delayed mobilization of shear strength in the shell owing to stiffness incompatibility, and a reduction of mobilized shear resistance in the extending regions of the slide due to loss of confinement. Changes associated with these mechanisms were identified in the numerical analysis to help diagnose the impending collapse. These are: the emergence in the strain-weakening unit of a substantive area on the brink of strain-weakening, the depletion of reserve strengths in the foundation materials, and the extension of the unit above the strain-weakening zone owing to differential shear displacements within and outside the failure zone. Safety factor calculations do not adequately capture the stability of the Mount Polley embankment in the year preceding its collapse, and limit equilibrium methods overestimate the three-dimensional stability effects present in this slope. The findings underscore the importance of adopting numerical analysis for assessing slope behavior.