A numerical and intelligent driven method for the drainage arrangement around a deep-buried tunnel in fractured rocks

The rational arrangement of the tunnel drainage system is crucial for the distribution of pore pressure around the tunnel lining, especially for deep-buried tunnels with high groundwater levels. This study proposes a numerical and intelligent driven method for optimization the drainage arrangement around deep-buried tunnels with discrete fracture networks. The hydrodynamic process in drainage holes is characterized by the pipe-flow model, while the fracture network system is described by the non-Darcy flow model. These two systems are combined considering the flow exchange along interfaces. A non-linear hydro-mechanical coupled model for the tunnel system with varied numbers of drainage holes in the fractured rock is then developed and solved in the finite element framework. Benchmark tests are conducted against analytical results and field data collected from a diversion tunnel at the Jinping II Hydropower Station on the Yalong River to demonstrate the reliability of the proposed model. The influence of different parameters related to the arrangement of the drainage system (the penetration depth of drainage holes into the rock, the drainage holes’ number, the spacing property of drainage holes) on the distribution of pore pressure around tunnel linings is investigated. The optimization design for the drainage system of the diversion tunnel of the Jinping II Hydropower Station is further carried out based on an intelligent analysis method using 1,500 sets of numerical results of the seepage distribution obtained from the proposed model. • A non-linear hydro-mechanical coupled model for the tunnel system with embedded drainage holes in the fractured rock is proposed and numerically solved. • The influence of the arrangement of the drainage system on the seepage stability is investigated in a diversion tunnel of the Jinping II Hydropower Station. • An efficient intelligent analysis for optimizing the drainage arrangement is operated based on numerical results.