Abstract: The mechanical properties of rockfill materials are not only depend on stress state, but also relate to degree of compaction or material state of rockfill materials. Large-scale triaxial tests under isotropic consolidation and drained shear were carried out to investigate the effect of dry density on mechanical properties of rockfill materials. Test results show that the forms of stress-strain relationships depend on the combined effect of density and confining pressure. Before failure state, the strength and deformation of rockfill materials are determined by density and confining pressure. When the strain is large enough, as in the asymptotic state or critical state, the effect of initial dry density on stress and volumetric strain of rockfill materials decreases until it disappears. For stress softening curve, the stress of phase transformation state is less than the stress of asymptotic state, and the stress of asymptotic state is less than the stress of failure state. Regardless of the value of confining pressure, the hardening of the stress-strain curve gradually decreases and the softening is gradually enhanced as the initial dry density increases.

Key words: rockfill materials, dry density, mechanical properties, phase transformation state, critical state, asymptotic state, stress-strain relationship