Abstract: Based on the preliminarily designed construction plan of a soil-rockfill dam for Longwangding tailing dam project in Shaxi Copper Mine, the soil-rockfill materials with three different stone contents (5%, 15% and 30%) are compounded. A series of large-scale triaxial compression tests under various confining pressures are conducted on the soil-rockfill materials. The test results show that the soil-rockfill materials exhibit shear-dilatation and shear-comtraction deformations under low and high confining pressures, respectively. With the increase of stone content from 5% to 30%, the stress-strain curves are similar, but the strength and dilatation effects obviously increase. Based on the test result analysis, the plastic loading and flow direction vectors are constructed to build an elastoplastic mechanical model within the generalized plasticity framework. The method for determining the model parameters is described. Then, the model is applied to the simulations of the large-scale triaxial compression tests, and satisfactory simulation on the shear-comtraction/dilatation deformations of the soil-rockfill materials is obtained.