Pressure amplification and water–air two-phase flow in rough cracks of high-speed railway tunnel linings

To investigate the pressure amplification effect and water–air two-phase flow characteristics in rough cracks of high-speed railway tunnel linings, this study introduces a methodological innovation by coupling the successive random addition method for rough crack surface reconstruction with a two-phase Volume of Fluid model, which enables quantitative analysis of the interplay between multi-scale crack roughness and transient water–air flow dynamics under train-induced aerodynamic loads, revealing the spatial evolution of pressure amplification and the inertial overshoot mechanism of water movement. Crack position and orientation effects on pressure are examined. The main conclusions are as follows: The amplitude and rate of train-induced pressure waves are significantly enhanced in water-rich cracks while uniformity decreases; the positive and negative pressure peaks at the crack tip are 1.74 and 1.36 times those at the entrance; the standard deviation of the pressure peak approaches zero at the crack tip due to the geometric constraint. The positive peak of rate of pressure change is largest at the tip, and the negative peak is largest at the end section of the air area. The magnitude and rate of pressure change at the crack tip correlate positively with water displacement and velocity; owing to water inertia, the water movement overshoots the equilibrium position, resulting in larger displacement and consequently the pressure amplification effect. Positive pressure amplification is strongest in longitudinal and sidewall cracks; negative in crown; circumferential weakest due to gravity. The results provide a basis for the treatment of lining cracks in high-speed railway tunnels.