Exploring the microscale mechanism of granular soil under triaxial testing: Insights from coupled discrete-continuum approach

Abstract

[Objective] The rigid boundaries of the discrete element model for sand in triaxial tests have difficulty in reflecting the deformation and failure of the specimen. To simulate the flexible deformation of sand and the lateral confining rubber membrane and conduct an in-depth study on the micro-mechanical characteristics at the particle scale in the triaxial test of sandy soil, [Methods]the discrete-continuous coupling method was adopted. Based on the finite difference program FLAC^3D and the discrete element program PFC^3D, the deformable continuous membrane(Shell) element and the rigid discrete particle(Ball) element were used to simulate the rubber membrane and sand particles respectively, and a coupling model was established to deeply investigate the evolution laws of particle rolling and sliding as well as the distribution characteristics of normal and tangential contact forces during the shear failure process. [Results] The results show that, the coupling model exhibits a strain softening trend during the triaxial shearing process, and its stress-strain curve is similar to the real laboratory test result, well reproducing the deformation and failure process of the sand in the laboratory triaxial test. During loading, the average contact number of particles in the specimen gradually increases, and the microstructure tends to be stable. The shear deformation of the specimen is mainly caused by particle rolling, while the number of sliding particles increases during the failure softening stage. After compression, the normal contact force of the specimen particles shows significant anisotropy, the tangential contact force is evenly distributed, and the normal contact force plays a dominant role in bearing the deviator stress. [Conclusion] The discrete-continuous coupling model can effectively simulate the micro-mechanical behavior of sand in triaxial tests. The model takes into account the deviation of test conditions caused by the traditional coupling algorithm and solves the problem of difficultly accurately simulating test conditions in the traditional coupling algorithm by correcting the equilibrium conditions of discrete elements and the overall coupling system, achieving a more realistic and accurate characterization of the micro-mechanical characteristics of sand at the particle scale, providing a new perspective and a more solid theoretical support for in-depth understanding of the macro and micro mechanical behaviors of sand and related engineering applications.

Keywords

discrete-continuum coupling / sand / triaxial shear / microscopic characteristics / particle structure / mechanical properties / deformation