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 (Edf) decreases by 26.5%, while the steady-state damping ratio (ξdf) 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 Edf and a 237.5% increase in ξdf; and (3) rubber particle size further governs this trade-off, with an intermediate size range of 5–10 mm yielding the highest ξdf of 0.045 and the lowest Edf 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.