Experimental study on formation mechanism of the trailing edge failure surface of retrogressive landslide

Retrogressive slide of natural slopes is often caused by the down-cutting of valley and excavation in the toe of slope and further forms multi-stage trailing edge tension crack surfaces in the rear of slope body. And the formation mechanism of the trailing edge failure surfaces plays a pivotal role in the stability analysis of the retrogressive landslide. So, model tests and theoretical analysis are carried out to research on the formation mechanism in this paper. A test device is developed to simulate both the softening effect of the groundwater on the sliding zone and progressive failure characteristics of the landslide. The sectional sliding surface, which is a part of this device and composed of several permeable boxes, can simulate sliding surfaces with different geometric shapes. The sliding zone can be simulated to be saturated and softened in stages by injecting water into different permeable boxes, so that the various failure modes can be simulated. Four kinds of test schemes are designed to simulate the circular, fold line and linear sliding surfaces. Meanwhile, three steps and two steps of slope surfaces are also simulated. Considering three stages of the landslide condition, every fracture angle of the trailing edge of the slip body is measured. The model test results indicate that the experimental value of the inclination of the trailing edge is obviously affected by the thickness of the sliding body and the location of the unstable slip section. It is assumed that the possible formation mechanism of the trailing edge of retrogressive landslide may be the overall sliding, the sliding tension crack and sliding shear failure, and the inclinations of the trailing edge are calculated. The results show that the calculated values of the sliding tension crack mechanism are the closest to the experimental ones, and the relative error is less 10% than the experimental value. It is considered according to the results that the formation mechanism of the trailing edge of the retrogressive landslide is: the bottom of the slip surface loses its stability and slides down, and tensile failure zone appears at the location of sliding body corresponding to the end of the unstable slide surface. The tensile stress is controlled by the minimum principal stress, and the direction of the tensile failure surface is basically in agreement with the maximum principal stress. © 2018, Science Press. All right reserved.