DEM-aided study of Coulomb and Roscoe theories for shear band inclination

In general, there are two classical solutions in soil mechanics to predict the shear band orientation in dense granular materials: the Coulomb and Roscoe theories. The present paper by using the inherent capabilities of the discrete element method, DEM, introduces a local approach to evaluate the above solutions. The local approach uses local stresses and strains within shear bands. The conventional plane compression test (PSC test) and other boundary value problems (BVPs), including active and passive wall movements as well as reverse and normal faulting, are employed to develop shear bands. These BVPs, which received less attention in previous studies, could produce shear bands under various stress paths, boundary conditions, confining stresses and deformation directions, which all affect shear band angles. The results of the present study show that the Roscoe theory by the local approach compared with the Coulomb (and Arthur) solutions could predict shear band orientations more accurately regardless of the initial confining pressure and void ratio, type of test, stress path, etc., confirming that shear bands follow the zero extension line. Moreover, the results indicate that errors of the Coulomb (and Arthur) solutions in the prediction of shear band angles of the BVPs are remarkably greater than those of the PSC tests. This could be attributed to the higher degree of non-coaxiality of shear bands in the BVPs.