Meso-level and macro-level mechanical properties of slip zone soil with varying coarse grain contents

The physical and mechanical properties of coarse-grained slip zone soil are notably different from those of fine-grained slip zone soil, which is mainly composed of clay particles. Many scholars have been interested in the meso-level mechanical properties of coarse-grained slip zone soil. However, no regularity in results has been observed thus far. In this study, a series of medium-scale shear tests are conducted on slip zone soil specimens with different coarse grain contents based on a medium-scale shear apparatus. This apparatus was independently revamped and capable of real-time monitoring. The digital images of the sheared soil specimens were recorded in real time by a high-resolution camera and combined with particle image velocimetry (PIV) technology. A discrete element model involving numerical samples was established to analyze the meso- and macro-level mechanical properties. The results show that the coarse grain content (CGC) has a considerable influence on the shear deformation of slip zone soils and on the meso- and macro-level mechanical properties of the slip zone soil. Moreover, the precise thickness of the main shear band of the slip zone soil under the testing conditions was derived. The numerical sample with high CGC showed obvious dilatancy. The contact force chain network of particles is thick and complex, and the distribution range of the displacement field and the normal contact force are large. This indicates that the slip zone with a high CGC will have more significant uplift when a landslide failure occurs. This study innovatively integrated a variety of research methods, such as visual shear instrument, PIV, and discrete element numerical simulation, and provided important guidance and reference to reveal the influence of CGC on the macro-mesoscopic mechanical properties of slip zone soil and the evolution trends of landslide deformation with high CGC.