Shear strength theory of granular materials based on rate-state model

Granular materials are very common in engineering applications. Thus, it is essential to develop an accurate strength theory for their description. In this paper, we establish a relationship between the strain components in the shear band based on the microscopic particle contact model. More specifically, we consider the shear strain caused by both the slip and the rotation of the particles. From the principle of energy, a coupled evolution model of the shear strength of granular materials was constructed. This model can be used to analyze the entire evolution process of the internal friction coefficient in granular materials with shear deformation. To verify the model, we used materials composed of glass beads with an average particle size of 0.15 mm. We conducted the shear tests under both constant normal stress and constant shear rate. The experimental results showed that the variation of the internal friction coefficient with shear displacement was consistent with the prediction of our theoretical model. The influences of shear rate and normal stress on the strength were studied by further detailing the model parameters. More specifically, we demonstrated that the shear strength of the granular material system did not strictly follow the Coulomb strength theory, and the dilatancy angle had a significant effect on the shear strength. The increase of normal stress in granular materials resulted in larger deformations before failure. Hence the toughness of granular material was significantly enhanced. The proposed model allowed to comprehensively consider more influencing factors of strength, improve the accuracy of the model, and further enrich the strength analysis theory of granular materials. © 2022, Science Press. All right reserved.