The effect of deformation rate in progressive slope failure

Abstract

For understanding the processes acting during the triggering and evolution of a landslide in sensitive clay, it is of importance to account for the material response in the failed state. This includes the rate of strain softening and the level of residual resistance. Through a review of new experimental data it is illustrated here that these properties depend on the displacement rate in the case of shear band formation. Higher rate increases the brittleness both in terms of a steeper softening response and a lower residual level. These observations are attributed to processes of local drainage and dissipation of pore pressure gradients in the vicinity of the shear band. Viscous effects, which yield higher resistance for higher rates of deformation, are also apparent. These aspects of material failure in sensitive clay are utilized in the context of progressive slope failure in order to explain observations from case records and to quantify the impact of the rate dependent softening response on the resistance of a slope. The strong brittleness of sensitive clay at high displacement rates under shear band formation motivates a recommendation of using a design approach close to a first yield criterion if the construction situation might include such high rates.