Abstract: The resilient modulus tests of polymer rockfill materials were performed using a middle-scale triaxial instrument. Mechanical properties of polymer rockfill materials and their evolution laws of resilient modulus were analysed under unloading and reloading conditions. The results showed that the volume-contraction was influenced by the confining pressure and stress level significantly. The specimen gradually changed from the initial state of shear dilation to shear contraction with the increase of confining pressure. Under high confining pressure, the unloaded volume-contraction increased nonlinearly with the increase of the stress level. At the confining pressure of 100 kPa, the specimen presented a volume-dilation during unloading, and the values of unloaded volume-contraction were similar and smaller at different stress levels. The ratio of the average resilient modulus to initial Young’s modulus was approximately between 3.9 and 4.2 under different confining pressures. The corresponding resilient modulus at the stress level of 0.7 was similar to the average resilient modulus. The Duncan-Chang model was applied to simulate the resilient modulus of the polymer rockfill materials, and the resilient modulus coefficient was approximately 4.0 to 4.2 times of the initial Young’s modulus coefficient in the numerical calculation process.

Key words: polymer rockfill materials, volume-contraction in unloading, triaxial tests, resilient modulus