Abstract: The existing tunnel seepage analytical solution formula does not consider the threedimensional drainage system. Therefore, a tunnel seepage calculation model with drainage system is established, and the analytical formula of tunnel water inflow is deduced. In addition, the analytical solution is compared with the degradation formula and numerical simulation results to validate the rationality of the analytical solution, and further examine the influence of geotextile permeability, drainage pipe spacing, and surrounding rock permeability on tunnel water inflow. The results show the following: (1) The blockage of geotextile, the increase of drainage pipe spacing, and the decrease of surrounding rock permeability coefficient will lead to the decrease of water inflow. (2) When the geotextile permeability decreases in the range of 10-4 and 10-7 m/s, the tunnel water inflow reduces significantly. When the geotextile permeability is less than 10-7 m/s, the tunnel drainage system is blocked completely and the tunnel loses drainage capacity. (3) The most reasonable design spacing for drainage pipes is 8~12 m. (4) The smaller the permeability of surrounding rock, the less the tunnel water inflow. 

Key words: tunnel engineering, drainage system, water inflow, analytical solution, numerical simulation