A new theoretical model to locate the back scarp in landslides caused by strength reduction in slip zone soil

The location of the backscarp is important for determining the landslide range. This study aimed to propose a new theoretical model for calculating the location of the backscarp in landslides caused by strength reduction in slip zone soil. The new theoretical model was first presented based on a two-surface failure mechanism, which specifically means that the strength reduction in slip zone soil first generates a basic slip surface and eventually generates a backscarp. Then, nine landslide experiments were performed to validate the theoretical model, and the locations of backscarps in the nine experiments were calculated. Finally, the theoretical model was applied to three real landslides (Xierguazi, Jiangdingya, and Xibuding landslides). The calculations show that for each of the experimental and real landslides, there is a trough point at which the local lowest factor of safety attains its lowest value, which corresponds to the inclination of the critical backscarp, indicating that the critical backscarp is readily located by the theoretical model. Moreover, the location of the calculated critical backscarp generally agrees with that of the measured or published backscarp for each of the experimental and real landslides.