Effects of geometry and soil properties on type and retrogression of landslides in sensitive clays

Flowslide and spread are two common types of landslides in sensitive clays. Empirical criteria, based on single or multiple soil properties and slope geometry, have been proposed for a rough assessment of potential landslide type and retrogression distance. A large variation has been found in the comparison of retrogression distance between empirical equations and field data. In the present study, flowslides and spreads are simulated using a Eulerian-based large-deformation finite-element (FE) method. In addition to strain-softening, a strain-rate-dependent undrained shear strength model that elevates the strain rate effects on the shear strength of liquefied clay flowing at high speed is used. In flowslides, a higher rate of increase in undrained shear strength with depth reduces the depth of subsequent slides, and thereby the retrogression distance. The maximum retrogression occurs for a uniform shear strength profile. The increase in the ratio of horizontal to vertical stress, resistance to downslope movement of the debris and decrease in soil brittleness and slope steepness change the failure pattern from a flowslide to a spread.

Automated summary

In this study, flowslides and spreads in sensitive clays were simulated using a Eulerian-based large-deformation finite-element method. A strain-rate-dependent undrained shear strength model was used to consider the strain rate effects on liquefied clay. The rate of increase in undrained shear strength with depth in flowslides reduces the depth of subsequent slides, leading to a smaller retrogression distance. The ratio of horizontal to vertical stress, resistance to downslope movement, soil brittleness, and slope steepness changes the failure pattern from flowslides to spreads.