Investigation on the seepage-stress field evolution mechanism and failure process of karst tunnels in water-rich areas

Water and mud inrush disasters are common disasters in tunnel engineering in karst areas. To study the evolution mechanism of seepage-stress field in tunnels when passing through karst caves, on-site investigation and numerical simulation methods are applied to analyze the evolution characteristics of water inflow, deformation of surrounding rock and lining mechanical performance during tunnel construction and operation. The results show that: As the excavation face of the tunnel approaches the karst area, the water inflow of the tunnel, the horizontal extrusion displacement of the excavation face and the range of the plastic zone rapidly increase, leading to a significant increase in the risk of water and mud inrush. Full section curtain grouting can effectively reduce the water inflow of karst tunnels and improve the stress environment of surrounding rock. As the thickness of the grouting circle increases, the deformation and plastic zone range of the surrounding rock decrease, the reduction ratio of the grouting circle to water pressure increases, and the tensile stress of the lining decreases. As the thickness of the waterproof rock slab in front of the excavation face gradually decreases, its waterproof effect gradually weakens, leading to an increase in water inflow, deformation and plastic zone. The maximum water inflow of the excavation face is 2.41 m³/h and the maximum horizontal extrusion displacement is only 2.6 mm when the thickness of waterproof rock slab is 6 m, which can effectively prevent water and mud inrush disasters. Increasing the density of drainage blind pipes can effectively reduce the water pressure of the lining. Compared with the blind pipe spacing of 10 m, the average water pressure of the lining decreases by 39.3%, and the maximum tensile stress of the lining decreases by more than 30% when the blind pipe spacing is 2 m. The research results can not only provide support for the study of the mechanism of water and mud inrush disasters in tunnels, but also provide useful references for tunnel construction in karst areas.