The pressure field inside water-rich cracks of tunnel linings during high-speed train passing through tunnels using air-water two-phase flow simulation

Water-rich cracks are a common type of damage in high-speed railway tunnels. When high-speed trains passing through tunnels, the dramatic changing in aerodynamic pressure repeatedly acts on water-rich cracks, potentially causing further crack expansion or even more severe structural damages. This study employs the dynamic overlapping grid method and the volume of fluid (VOF) model to establish a multiphase flow coupling model of air-train-tunnel-water-rich cracks, analyzing the spatiotemporal variation characteristics, influencing factors, and mechanisms within water-rich cracks when a high-speed train passes through a tunnel. The main conclusions are as follows: (1) The pressure changes inside the water-rich cracks exhibit a significant pressure amplification phenomenon. Compared to the tunnel wall, the increase in positive peak value (Cp,max) and negative peak value (Cp,min) of the aerodynamic pressure near the crack tip is as high as 22.91 % and 51.71 %. (2) The pressure variation trend along the length direction inside the water-rich crack has a distinct one-dimensional feature, while along the depth direction is significantly different. The pressure waves do not change with depth of the crack in water-free section, but the pressure fluctuation amplitude in the water-rich section increases with the depth. (3) The positive and negative pressure waves exert thrust and suction forces on the water body inside the water-rich crack, leading to fluctuation in air density near the crack tip, thus causing oscillation and amplification in the pressure. The water in the water-rich cracks exhibits increased motion amplitude and peak acceleration with greater depth, causing the pressure in water also intensifies. (4) Compared to those outside the crack at 300 km/h, the Cp,max near the water-rich crack tip increased by 6.69 %, 77.98 %, and 62.03 % when the train speed is 300 km/h, 350 km/h, and 400 km/h, and the Cp,min increased by 57.71 %, 111.25 %, and 161.73 %, respectively. The maximum pressure fluctuation amplitude occurring at a water content of 80 %. The results can provide theoretical basis for the healthy and high-quality operation of high-speed railway tunnels.