Microscopic Mechanism of Coarse-Grained Soil Under Triaxial Test Based on PFC-FLAC Coupling Method

This study investigated the microscopic mechanism of coarse-grained soil under triaxial loading using the Particle Flow Code (PFC) – Fast Lagrangian Analysis of Continua (FLAC) coupling method. A numerical model considering the influence of flexible membrane deformation under triaxial loading was established according to the gradation of the material. Then, the validity and reliability of the numerical model were verified by comparison with the laboratory triaxial test results. On this basis, the motion law of particles and the change law of the force chain between the particles were analyzed from the mesoscopic perspective. The coordination number, meso-mechanism of deformation, failure (number of cracks), and energy variation during the loading process were investigated. The deformation mechanism of coarse-grained soil is explained from the mesoscopic perspective: coarse-grained soil mainly depends on a skeleton consisting of particles to bear loads. The deformation of soil is caused by the movement of particles, filling of voids, and change of the particle skeleton structure. The coordination number develops as the axial strain increases. The cracks in the model were mainly shear cracks, which is consistent with the results of the laboratory triaxial test. Finally, the loading process of the coarse-grained soil was closely related to the variation of energy.