Granular discrete element simulation of the evolution characteristics of the shear band in soil–rock mixture based on particle rotation analysis

Based on the 3D laser scanning technology, the surface morphologies of the rock blocks collected from the soil–rock mixture (S–RM) were scanned. The numerical model of the S–RM with different rock block proportions were established. To study the deformation and failure characteristics of the S–RM during the formation and evolution of the shear band, the numerical large-scale direct shear tests under different normal stresses were performed on these S–RM samples, the failure points were recorded by the detection of contact failure. Base on the step accumulation of particle’s spin, the rotation angles of rock blocks were monitored in the simulation. A parameter \({P}_{\theta }\) is introduced to describe the evolution characteristics of the shear band. Results show that the, \({P}_{\theta }\) of the S–RM with the rock block proportion of 60% is obviously greater than the others. The formation and evolution process of the shear band in the S–RM was consistent with the evolution process of the local particle’s rotation. The rotation of the soils always preceded the rotation of the rock blocks, which reflects the “bully” deformation characteristic of S–RM in the shear band formation process. In the form of the failure distribution, the interior failure of the S–RM with low rock block proportions was mainly the thin band-shaped destruction between the soils. However, higher rock block proportion caused more interactions between soils and rock blocks in the S–RM, and the destruction presented a thick cloud-like distribution. The shear fractures in the soils and tensile fractures along the contact planes between soils and rock blocks are the main failure pattern of S–RM under shear tests.