Discrete element simulation of large-scale triaxial tests on soil-rock mixtures based on flexible loading of confining pressure

Based on the computer three-dimensional scanning and stochastic simulation technologies, the three-dimensional random meso-structure models and discrete element models for soil-rock mixture (S-RM) samples with different stone contents and spatial distributions are established. Considering the flexible loading of confining pressure, the large-scale numerical triaxial tests on the S-RM samples under different confining pressures based on the flexibly-bonded particles method are conducted by particle flow code, and the effects of the stone content and spatial distribution on their mechanical properties and deformation and failure characteristics are studied. The numerical simulation results show that the strengths and deformation resistibility capacities of the S-RM samples increase with the increase of stone content and confining pressure, and their internal friction angles and cohesions vary to a certain extent under the same content but different spatial distributions of stones. However on the whole, the internal friction angle increases linearly with the increase of stone content, while the cohesion decreases. Under the flexible loading of confining pressure, the S-RM samples show bulging deformation and failure mode, and the shear band formed after failure is a meandering strip with an asymmetric X-shaped distribution, whose thickness is about 1/3~1/2 times the height of the S- RM samples. Moreover, the failure mode and the thickness and shape of shear band are affected by the stone content and spatial distribution and the confining pressure. The shear band formation is accompanied by the rotations of the local particles in the S-RM sample. When the strain reaches the peak strain, the locally rotating particles are connected to each other, indicating that the shear band has basically formed at this time. Since then, as the axial strain increases continually, the rotations of the internal particles still change because of the effect of the bulging deformation after the peak, and the thickness and shape of the shear band also change accordingly.