The paper develops a model to predict water flow into the tunnels, using the concept of an exponential decrease of hydraulic conductivity against the depth. The influences of surface hydraulic conductivity, hydraulic conductivity gradient, tunnel diameter, tunnel depth and hydrostatic total head to water inflows of the tunnel are investigated. In the formulation the Fourier transformation is applied to solving the governing equation of steady-state groundwater flow, and then the sensitivity analysis of the analytical solution of the model is discussed. The results indicate that inflows at first increase against depth, and then decrease as the tunnel becomes deeper. Finally, the analytical solution was applied to predicting the water inflow in Pin-Lin tunnel, Taiwan. It is shown that the great amount of groundwater inflow in Pin-Lin tunnel is associated with the tunnel depth and the existence of fractured rock zone that may be submerged by the ubsurface water.
