Vibration mitigation of rubber–sand mixture-filled soilbags as subgrade cushions

This study proposes a subgrade cushioning approach using rubber–sand mixture (RSM)-filled soilbags to improve the vibration-mitigation performance of pavement structures under cyclic loading. Cyclic unconfined compression tests were conducted to characterise the resilient modulus and damping ratio of RSM-filled soilbags. Results indicate that: (1) as the dynamic stress ratio (defined as the ratio of cyclic load amplitude to static load) increases from 0.1 to 0.3, the steady-state resilient modulus (E_df) decreases by 26.5%, while the steady-state damping ratio (ξ_df) increases by 87.5%, revealing a pronounced stiffness–damping trade-off in RSM-filled soilbags; (2) rubber content exerts a strong compositional control on material performance, with increasing rubber content from 0% to 45% leading to a 64.5% reduction in E_df and a 237.5% increase in ξ_df; and (3) rubber particle size further governs this trade-off, with an intermediate size range of 5–10 mm yielding the highest ξ_df of 0.045 and the lowest E_df of 30.3 MPa among the tested particle sizes. To extend these experimental results to the system level, the derived cyclic properties were incorporated into numerical simulations, demonstrating that RSM-filled soilbags outperform conventional sand-filled soilbags in vibration attenuation, with further improvement achieved by increasing soilbag thickness.