Stress-induced anisotropy of coarse-grained soil by true triaxial tests based on PFC

Based on the results of laboratory tests on coarse-grained soil and the theory of three-dimensional particle flow code, a numerical model for true triaxial tests is obtained with mixed particles containing Clump particle. The Clump particle is generated with the tool of PFC and improvement of program code, to solve the insufficient shear strength problem on simulation of coarse grained soil by balls. A series of unilateral loading tests based on the PFC are performed, and the characteristics of complex stress-induced anisotropy of coarse-grained soil are studied from the macro-micro angle. The results indicate that the significant anisotropy showed by the macro parameters, meso parameters and stress-strain curves in the direction of three principal stresses is mainly induced by complex stress state. The deformation in the loading direction is compressive one in all cases, while the deformations in the other two lateral directions are complicated and greatly influenced by the value of B. Moreover, both the anisotropy of Poisson’s ratio and the stress-strain curve in the direction of a certain principal stress are easily affected by the value of B. In a mesoscopic view, the micro parameters in the direction of each principal stress like coordination number or porosity are very different, and their change trend can reflect the type of deformation and their values have a strong influence on the peak strength. It is also shown that the anisotropy of coarse-grained soil is due to the microstructure change caused by confining pressure difference.