Abstract: In order to research microscopic changes of loess during triaxial shear process, the loess triaxial test model is established with PFC3D (particle flow code in 3 dimensions) software. And the triaxial shear tests are simulated under different confining pressures of 0 kPa, 50 kPa, 150 kPa and 300 kPa. Compared with the results of laboratory triaxial shear tests, the microscopic changes of particles from the beginning then to the peak and at last to the residual deformation of the stress-strain curve are simulated by PFC3D. And the variations of displacement field and contact stress field are more consistent with the macroscopic phenomena of laboratory triaxial tests. The researches indicate that some closely links are existed between the macroscopic parameters (elastic modulus, Poisson's ratio, peak strength) of laboratory model and microscopic parameters (normal stiffness, shear stiffness, friction coefficient) of numerical model. For example, the elastic modulus is controlled by the normal stiffness; the Poisson’s ratio is controlled by the ratio of normal stiffness and shear stiffness; the friction coefficient impacts on the peak strength of stress-strain curve. With the increase of confining pressure, strain energy increases and volume changes in expansion-to-reduction trend. The research result can provide some references for further study of stress-strain behavior and shear strength characteristics of loess.

Key words: loess, triaxial tests, particle flow, microscopic deformation