Dynamic response and long-term effects of tunnels in expansive mudstone under high-speed train loading

Expansive mudstone is highly susceptible to swelling upon water exposure, leading to significant deformation and localized stress concentration in tunnel linings. The periodic dynamic loads induced by high-speed trains further exacerbate these adverse effects, thereby compromising the operational safety of the tunnel. However, existing research on the dynamic response of high-speed trains in tunnels predominantly focuses on non-expansive rock formations. Studies addressing vehicle-induced vibration in expansive rock strata remain comparatively scarce, especially lacking exploration of local surrounding rock expansion which may cause more unfavorable stress concentration. A vehicle-track-tunnel dynamic calculation model was developed based on a high-speed railway tunnel traversing expansive mudstone strata. This model analyzed the dynamic response variations in the tunnel lining under moving train load when expansive deformation occurred at different locations in the surrounding mudstone rock (i.e., vault, sidewall, or invert). Subsequently, the fatigue life and long-term settlement (LTS) patterns of the tunnel were predicted under various expansion conditions. The results show that when the surrounding rock at the vault, sidewall, or invert expands, the respective maximum principal stresses (MAPS) of lining are 5.03 MPa, 7.24 MPa, and 0.86 MPa, respectively, and the respective peak minimum principal stresses (MIPS) are -10.33 MPa, -10.80 MPa, and -5.52 MPa, respectively. The MAPS exceeds the safety threshold when the surrounding mudstone rock at vault or sidewall expands. Moreover, the fatigue life of the lining under different expansion conditions follows the order: no expansion > the surrounding rock expansion at invert > the surrounding rock expansion at vault > the surrounding rock expansion at sidewall. The predicted fatigue life of the lining indicates that local expansion of the surrounding mudstone induces significant stress concentration in the lining, thereby shortening its service life. Furthermore, the LTS prediction shows that after 100 years of operation, the LTS at the tunnel base under the conditions of no expansion, the surrounding rock expansion at vault, the surrounding rock expansion at sidewall, and the surrounding rock expansion at invert are 8.43 mm, 13.01 mm, 11.24 mm, and 6.38 mm, respectively. Notably, the LTS caused by surrounding rock expansion at invert is lower than that under other conditions because such deformation partially offsets the settlement induced by train load. These findings offer critical insights for the design and maintenance of similar tunnels in expansive mudstone strata.