Discrete element analysis of the evolution of macro and micro characteristics of strain localization in the sand under triaxial shear

It is very important for evaluating the instability of geotechnical structures to investigate soil deformation and the spatial evolution of shear bands. For this aim,this paper employs the distinct element method(DEM) to simulate conventional triaxial tests on sand with flexible boundaries,analyzes the evolution of macroscopic and microscopic characteristics within and outside the shear bands,and tries to establish an upscale association between the macro and micro behaviors. Firstly,the DEM employed a complete microscopic contact model that accounts for the effect of particle shape on the macro-mechanical response by incorporating rolling and twisting resistances. Secondly,a flexible membrane boundary was used in the simulations of triaxial compression tests to enable the complete development of the shear band. Finally,the DEM simulation results were compared with the experimental results available,and analyzed from the macro and micro viewpoints. The DEM results indicate that the employment of the complete contact model and flexible boundaries is able to accurately reproduces stress-strain and volume responses of the sand sample and capture the evolution of the shear band in the simulations. There are significant differences in the average particle rotation rate(APR),porosity,mechanical average coordination numbers,and anisotropy coefficients within and outside shear bands. With the increase of axial strain,the APR and porosity inside the shear band are larger than the outside,on the contrary,the mechanical average coordination number outside the shear band is greater than the inside. In addition,the local porosity and anisotropy within the shear band have significant influences on the global evolution of void and anisotropy in the sand sample. © 2024 Academia Sinica. All rights reserved.