Theoretical Research of the Reduction Law of Water Pressure Loaded outside the Lining of High-Water Pressure Karst Tunnel

In order to optimize the waterproof and drainage design of the lining of a high-water pressure karst tunnel, taking the New Yuanliangshan Tunnel as the research background, based on the differential equation of the plane radial stable seepage of pressurized water, considering the water pressure reduction effect of shotcrete, a calculation formula for the water pressure of the tunnel lining is derived. The influence of factors such as the drainage capacity of the drainage pipe, the thickness and impermeability of the grouting ring on the water pressure of the lining was analyzed. The results indicate that: The magnitude of water pressure on the lining varies exponentially with the tunnel drainage capacity, grouting ring thickness and permeability coefficient. The drainage capacity of the tunnel has the greatest impact on the water pressure of the lining. Once the drainage pipe is blocked, the water pressure reduction coefficient becomes 1, and the lining will withstand static water pressure. Increasing the thickness of the grouting ring is beneficial for reducing the water pressure loaded on the lining, but the reduction effect gradually weakens. Strictly controlling the quality of grouting operations, improving the homogeneity of the grouting circle, and reducing the permeability coefficient of local short plate grouting bodies can effectively improve the water pressure resistance of the grouting circle and reduce the permeability pressure of the lining.