Stability assessment of slopes with cracks using limit analysis

Cracks are a common occurrence in soil slopes, and a method is described for including the presence of cracks in stability assessment based on the kinematic approach of limit analysis. While many cracks may be present in a slope, the failure mechanism typically involves one crack, whose location has the most adverse influence on stability. A translational mechanism, typical of rock slope failures, is demonstrated to illustrate the method, followed by a rotation collapse analysis that is more appropriate for soils. Pre-existing (open) cracks are considered, as well as the cracks that form as part of the slope collapse mechanism. The maximum crack depth is determined by stability of the vertical crack boundary. This maximum crack depth may be reduced significantly by seepage forces in the slope. The most adverse location of the crack is determined from an optimization procedure where the minimum of the slope critical height is sought. The presence of water is included in the analysis, and stability charts are developed. The influence of the presence of cracks on stability of gentle slopes was not found to be significant, but the effect on the outcome of the analysis increases with an increase in inclination angle and the presence of pore-water pressure. The difference in the critical height of a 60 slope with an open crack and without one can be as much as 50%.