Particle flow modelling of deformation and failure mechanism of soil-rock mixture under different loading modes of confining pressure

Soil-rock mixture (S-RM) is a kind of discontinuous and inhomogeneous multiphase materials. Its deformation and failure are significantly affected by the loading mode of confining pressure due to the internal nonuniform deformation under axial loading. Considering different loading modes of confining pressure, the biaxial tests on S-RM samples with different contents and spatial distributions of rock blocks are conducted by the particle flow code (PFC^2D), and their deformation and failure characteristics are investigated under different loading modes. The numerical results show that the S-RM exhibits different mechanical behaviors after the peak under different loading modes of confining pressure owing to the effects of different lateral deformation constraints, and the peak deviatoric stress under the rigid loading mode is higher than that under the flexible one. Meanwhile, the formation and evolution of the localized shear band in the S-RM under different loading modes are also different, and the shape of its shear band depends on the loading modes and the content and spatial distribution of rock blocks. The shape of the shear band shows the type of complex multi-cross under the rigid loading mode and that of asymmetrical single-cross under the flexible loading mode, and with the increase of the content of rock blocks, it shifts from the type of single-cross to that of multi-cross. The shear