Dilatancy behaviour of rockfill materials and its description

The dilatancy equation plays a significant role in establishing an elastoplastic constitutive model for soils. The rockfills will show strain-softening or strain-hardening behaviour according to the testing confining pressure and/or initial void ratio. Therefore, a new dilatancy equation for rockfill materials incorporating strain hardening and strain softening was studied. A series of triaxial compression tests on rockfills were carried out to investigate the material constants and applicability of the proposed dilatancy equation (PDE). The material constants M-c, beta, a and c of the PDE were found to be independent of the initial void ratio and confining pressure. At the dilatancy point and critical state, the observed dilatancy of soils is zero, while the PDE was proved to fully meet these conditions. In addition, the PDE can well depict the trends of the observed dilatancy behaviour during the whole shearing, even though the dilatancy behaviour from the peak point to the critical state is difficult to be simulated for many existing equations. By comparing with three widely used dilatancy equations, the simulated strain-volume curves by a constitutive model using the PDE are significantly acceptable, no matter whether the rockfill is strain hardening or strain softening.