Enlargement of a failed area along a sliding surface

Abstract

Progressive failure in short-term slope stability is examined in this study. The relative displacement between a sliding mass and a basement in a landslide was monitored precisely. The onset time of relative displacement at each borehole was determined and the speed of propagation of local relative displacement was calculated. The lowest speed of propagation was 4.6 mhr -1. Stresses inside the specimen were measured in the direct shear apparatus with a 400 × 400 mm shear plane. Results show that the horizontal sliding surface determined by the apparatus does not coincide with the plane in which Mohr's failure criteria are first fulfilled, but with the plane of the maximum shear stress. Shear stress reductions were observed and the drop position migrated with the shear. Based on those results, we can explain the kinematic processes of formation of a sliding surface during landslides: First local rupture occurs at a certain position where stress conditions fulfill the rupture criteria. The rupture surface that is mobilized by this rupture, in general, does not coincide with the potential sliding surface. Plastic deformation resulting from local failure increases in terms of its area and amount until plastic deformation along the potential sliding surface is eventually mobilized throughout the potential sliding surface. The enlargement process is dependent on material characteristics, variations in external forces, and boundary conditions. The discrepancy between the orientation of local rupture surface is determined mainly by stress and the orientation of potential sliding surface, which are determined mainly by boundary conditions and heterogeneity of materials, which are essential factors for progressive failure during landslides. © 2007 Springer-Verlag Berlin Heidelberg.