Optimal Design of the Seepage Control for Xianglushan Diversion Tunnel Under High External Water Pressure

The high external water pressure in the deep tunnel has an adverse impact on the lining, resulting in disasters such as water inrush, mud inrush and tunnel collapse. In order to study the seepage control of the diversion tunnel under high external water pressure, a nonlinear softening model and an evolution equation of the permeability coefficient were deduced. Based on ABAQUS software platform, a three-dimensional numerical calculation program was compiled. Taking Xianglushan diversion tunnel in the Central-Yunnan Water Diversion Project as the background, the effects of lining, grouting layer and drainage hole on the seepage pressure in the surrounding rock and the lining were calculated and analyzed. The results showed that the permeability coefficient and thickness of the lining could significantly affect the seepage pressure distribution in the surrounding rock and the lining. The grouting layer broke the gradient distribution of the seepage pressure in the surrounding rock. With the increase of the grouting layer thickness and the decrease of the permeability coefficient, the seepage pressure on the outer wall of the lining gradually decreased. Drainage holes could directly affect the seepage pressure distribution in the surrounding rock and the lining. The more the drainage hole was, the greater the depth of drainage holes was, and the smaller the seepage pressure was. According to the calculation results, the optimal parameters of the seepage control for Xianglushan diversion tunnel were obtained, and the maximum seepage pressure on the outer wall of the lining was reduced to 0.4 MPa, which could meet the specified requirements.