Research on waterproofing and drainage optimization scheme for karst tunnel lining in water-rich areas

In the presence of heavy rainfall on the earth’s surface, a series of water-induced problems often appear in karst tunnels, such as lining cracks and invert uplift. An effective method of alleviating these problems is the adjustment of the tunnel drainage scheme. In this study, three waterproofing and drainage optimization schemes were studied using numerical simulation and model tests. Numerical results show that, when the conventional waterproofing and drainage scheme is adopted in water-rich karst tunnels, the water pressure at the tunnel invert cannot be effectively reduced by the drainage system. When the water head height of the tunnel crown is 50 m and the distance between circumferential drainage blind pipes is reduced from 5 to 2 m, the rate of water pressure reduction at the invert from 21 to 27%. When a longitudinal drainage blind pipe is added at the bottom of the invert, the rate of reduction is increased to 84%; however, it is increased to 96% when the central drainage ditch is set at the bottom of the invert. Therefore, placing the central drainage ditch at the bottom of the invert has the most significant effect on reducing the water pressure. Model test results indicate that when the water head height of the tunnel crown is 12 m, the reduction rates of water pressure at the invert corresponding to the placement of a central drainage ditch at the bottom of the invert are 66%. The model test results were found to be consistent with numerical results.