Test and DEM analysis of rubber content and torsional shear stress ratio on torsional shear characteristics of rubber sand

In roadbed engineering, rubber sand used as a fill material is prone to uneven settlement under long-term traffic loading. To comprehensively analyze the dynamic response characteristics of rubber-modified sand under cyclic loading conditions, a hollow cylindrical torsional shear apparatus was employed to examine the effects of varying rubber contents (0 % and 20 %) and cyclic torsional shear stress ratios (0, 1/6, 1/3, and 1/2) on its dynamic shear performance. Simultaneously, a three-dimensional discrete element undrained hollow cylindrical torsional shear model was developed to reveal the intrinsic relationship between the material's macroscopic mechanical response and microstructural evolution. The results indicate that incorporating 20 % rubber particles significantly enhances the liquefaction susceptibility of the specimens, accelerates the accumulation of excess pore pressure and axial strain, and causes earlier onset of shear bands and bulging. Rubber particles enhance the energy dissipation capacity of the system, evidenced by a rapid decline in dynamic shear modulus, a substantial increase in damping ratio, and a more pronounced hysteresis curve. As the cyclic torsional shear stress ratio (η) increases, the coordination number, force chain length, and strength progressively decrease, leading to the gradual disintegration of strong contact chains and a notable reduction in structural stability. During the cyclic loading process, the distribution of particle contacts is markedly reorganized, a horizontal shear band gradually forms, the proportion of vertical contacts under high η conditions significantly increases, and the inclusion of rubber further promotes the development of a vertical load-bearing structure.