Abstract: The effect of density on mechanical properties of coarse granular material under three-dimensional stress was investigated by using large-scale true triaxial consolidation and drainage shear tests under equal minimum principal stress and equal proportional loading condition of four different initial dry densities. Test results showed that under the same minimum principle stress, the stress curve became higher and steeper with the increase of initial dry density, the softening property increased, the compression deformation decreased and the dilatancy increased. The ratio of volumetric strain increment to the strain increment in the direction of maximum principle stress declined with the increase of initial dry density. Volumetric increment ratio decreased gradually from a positive value and tended towards zero but greater than zero for strain hardening curve. When volumetric strain increment ratio reduced from a positive value to be a negative value, the volumetric strain changed from compression to dilatancy and stress curve belonged to strain softening type. When volumetric strain increment ratio reached the minimum negative value, the expansion developed to the fastest, the stress reached peak corresponding to failure state. For strain hardening curve, void ratio decreased monotonically with the increase of mean normal stress; for strain softening curve, void ratio first decreased and then increased. With the increases of initial dry density, void ratio reduction attenuated, the compression deformation decreased and the hardening property alleviated. The strength grew linearly with the increase of initial dry density or minimum principle stress.

Key words: coarse granular material, three-dimensional stress, large-scale true triaxial test, initial dry density, mechanical property, deformation, void ratio, strength