Suffusion in shield tunnel surrounding soils under train vibration using an improved DEM-PNM coupling method

Tunnel leakage facilitates the infiltration of sand particles into the tunnel, thereby inducing suffusion phenomena. Furthermore, train vibrations exert substantial dynamic effects on both particle and fluid phases around the tunnel, amplifying the suffusion. This soil erosion not only compromises the tunnel’s structural stability but also elevates risks to adjacent surface structures. Nevertheless, the impact of vibration on suffusion remains incompletely understood. This study employs an improved DEM-PNM coupling framework to investigate the mechanisms of vibration on suffusion in gap-graded soils from a microscopic perspective. A representative element-scale model replicating suffusion conditions of tunnels is developed. Vibration loads with varying amplitudes and frequencies derived from field measurements are applied to the model base. Based on this model, this study reveals the impact of vibration on suffusion and investigates its mechanisms from four perspectives: geometric, hydraulic, mechanical conditions, and pore-scale suffusion process. Furthermore, the impact of multiple train passes on suffusion around tunnels is further explored. Results suggest that train vibration exacerbates the suffusion around tunnels, inducing a significant increase in mass loss and particle migration distance compared to static conditions. Vibration has significant impacts on the geometric, mechanical, hydraulic conditions, and pore clogging states of soil. Higher frequencies and amplitudes result in more mass loss. Suffusion intensifies whenever the train passes, indicating that the long-term risks of suffusion to shield tunnels under vibration. This study gives critical insights into train vibration-driven suffusion for urban underground infrastructure.