Comparative tests on the failure characteristics and mechanisms of slopes with curved surfaces

A number of landslides have occurred in the slopes with curved surfaces. Curved surfaces have the potential to accelerate the failure of slopes and are essential for the analysis of slopes as open pit slopes and waste dump slopes in mines. Reasonable analysis of curved slopes requires knowledge about their failure and deformation behavior, which are not thoroughly clarified so far. In this study, a series of base friction model tests were conducted comparatively on slopes with concave and convex section surfaces under gravitational loading conditions. An updated speckle analysis and displacement measurement system was developed to capture the slope deformation and failure process in the base friction model tests; thus, the behaviors and mechanism of the failure process of the slopes were studied considering the effect of shape and curvature. The results showed that both the concave and convex section slopes experienced a significant step-by-step failure process. The slip surface was caused by the development of deformation localization in the curved slopes, and the slip surface of the concave section slopes was nearly arced with an initial deformation at the crown, while for the convex section slopes, the slip surface was nearly linear and the deformation occurred first at the middle of the slope surface. The failure behavior was significantly influenced by the shape and curvature of a slope surface, and the deformation and failure process of slopes was divided into three phases: the uniform deformation phase, the strain localization phase, and the failure phase. Two characteristic test time are provided to illustrate the stability of curved slopes, demonstrating that the stability of concave section slopes was higher than that of convex section slopes, which was basically consistent with the other results. A strain analysis was conducted to investigate the strain localization of the slopes with curved surfaces by user-written code following the finite element method, and the deformation mechanism of the curved slopes was analyzed by volumetric strain and maximum shear strain. A novel index was proposed to analyze the relative degree of volumetric effect and shear effect acting on slopes during the test, which indicates that the more pronounced shear effect of the concave section slopes appeared in the crown area of the slope, while the significant shear effect appeared at the middle of the slope surface for the convex section slopes. The slip surface geometry and location of the slopes with curved surfaces were illustrated by numerical modeling combining the strength reduction method with the finite difference program FLAC3D. The failure characteristics of slopes with curved surfaces obtained from numerical modeling were nearly consistent with the base friction model test results. Furthermore, it was found that for slopes with concave, planar, and convex section surfaces, the slip surface of the slopes gradually transformed from circular failure to nearly linear failure. In engineering practice, scarps or local deformation could be signs of movements and thought of precursors of open pit and waste dump slope failures. These findings could provide solid support to understand the failure characteristics and mechanism and early identify landslide hazards of slopes with curved surfaces.