Study on the shear characteristics of undrained circulation of rubber sand under traffic load

As a lightweight and environmentally friendly granular material, rubber-sand mixtures have been widely utilized in roadbed filling engineering due to their excellent vibration-damping performance. However, systematic and in-depth research on the dynamic response mechanisms of rubber–sand mixtures under traffic loading remains limited. In this study, hollow cylinder torsional shear tests were conducted to investigate the effects of varying rubber contents (0 %, 20 %, 40 %, and 60 %) on the dynamic shear characteristics of rubber sand subjected to traffic loading. Additionally, a three–dimensional discrete element method (DEM)–based undrained hollow cylinder torsional shear model was established to analyze the evolution of particle displacement, particle mechanical coordination number, strong chain percentage, and fabric anisotropy during the torsional shear process. The results indicate that at low and medium rubber contents (20 %, 40 %), liquefaction and reorganization of the particle skeleton trigger abrupt increases in axial strain and suppress the rebound effect. Meanwhile, horizontal shear–band reorientation accelerates axial strain accumulation. Under these conditions, as rubber content increases, the damping ratio rises linearly, while the shear modulus decreases. At the microscopic level, the particle contact network experiences a reduction in the ratio of mechanical coordination numbers and strong force chains, accompanied by an accelerated decay of normal contact forces in the vertical direction. However, when the rubber content reaches 60 %, the elastic continuous phase formed by densely packed rubber particles stabilizes the strain field and suppresses displacement localization, enhancing stiffness. Microscopically, the number of normal contacts increases, the percentage of strong chains stabilizes, and the rate of decay of vertical normal contact forces is significantly reduced.