Experimental Study on Couse of Progressive Formation of Retrogressive Landslide

To study the progressive failure mechanism of retrogressive landslides, a test device was developed to simulate the sectional unstable sliding of landslide mass. The main body of the device was composed of several permeable boxes, and could simulate sectional sliding surfaces with different geometric shapes. The sliding zone could be softened in multiple stages by the injection of water into different permeable boxes. This caused a reduction in the shear strength of the soil in the sliding zone, which led to graded instability sliding of the landslide mass. In this manner, the progressive failure process of the retrogressive landslide could be simulated. Twelve types of test schemes were designed, and sliding surfaces and slope lines of different shapes, as well as various slope materials, were used in the simulations. The sliding zone was softened gradually from the front to the rear, forming unstable sliding sections, and then the deformation characteristics of the landslide and the shapes of the trailing-edge fractures were observed. The results show that the unstable slip section at every level corresponds to one main fracture. The properties of the sliding mass and the shapes of the slope have a significant influence on the progressive failure mechanism of the landslide. The slops in a two-section slope shape the most obvious slope deformation. The inclinations of the trailing edge are generally steep dip angles, and 77.42%of the dip angles are in the rang of 58°-88°. The inclination of the trailing edge increases as the length of the first unstable sliding zone decreases or the slope shape and sliding surface are steeper.