In recent years the frequent geological disasters make deep research on deformation mechanism for rockfill increasingly urgent and important. Rockfill has the characteristics of irregular shape and prominent interlock behavior; and a simple program is used to generate arbitrary shape of particle clusters. Taking tetrahedron as core

arbitrary shape of particle clusters are generated by crystal cell reproduction method. The particle clusters are used as basic unit to generate aggregation of particles so as to simulate the large scale triaxial drained shear test for rockfill and study the mesoscopic mechanism of rockfill deformation by analyzing the change law of mesoscopic parameters in experiment. The analysis shows that the stress-strain curves and volumetric deformations from numerical simulation are in agreement well with the test results; and the arbitrary shaped clusters are much better than circle particles in simulating the rockfill. The breakage rate is the bridge linking the properties of macroscopic parameters and mesoscopic parameters. With the analysis of the change law of mesoparameters among four stages of particle breakage

the mechanism of rockfill deformation is given.