The laterite formations consist of top layers that are highly porous, followed by a lithomargic soil layer over the weathered residual soil and parent rock. The excavated slopes are stable during summer, but the slopes with exposed lithomargic soils have failed during rainy season even when safety factor was more than one. The present study considers the effect of erosion in the lithomargic layer of soil while analyzing the stability of slopes. Janbu’s GPS (Generalized Procedure of Slices) method in conjunction with a genetic algorithm is used to analyse the slope stability and to locate the noncircular critical slip surface. A failed slope from the Yekkur site was considered for the study considering three possible failure mechanisms (Mechanism I, II and III) of slopes due to progressive erosion of fines in the lithomargic soil layer. It is observed that the lithomargic soil’s vulnerability to erosion depends on a critical combination of sand content and hydraulic gradient causing piping. Mechanism III is more critical as compared to other mechanisms and a similar observation was made from failed slopes in the field. The failure in lateritic soil slopes is mainly due to piping of lithomargic soil, which reduces the length of the critical slip surface, and failure due to erosion is progressive.
Rao et al. (Wed,) studied this question.