Effect of anisotropic hydraulic conductivity on groundwater seepage into a rectangular tunnel in submerged sand

Managing groundwater seepage around tunnels is critical to tunnel design, particularly when the tunnel is constructed below the water table. Accurate seepage flow patterns and water inflow prediction under ordinary and critical conditions are imperative to mitigate potential tunnel construction and service disasters. In the past, an in-depth study on the anisotropic hydraulic conductivity of the soil mass that may affect the seepage condition has not been carried out. In this work, this aspect has been investigated numerically for a rectangular tunnel submerged within a homogeneous sand mass, considering the anisotropic hydraulic conductivity ratio (kz / kx, kz = vertical hydraulic conductivity and kx = horizontal hydraulic conductivity) varying from 0.25 to 1. This study has presented the changes in the flow patterns of groundwater around a rectangular tunnel for different values of kz / kx, and the variation of water inflow rates along the crown, invert and walls of the tunnel. The results indicate that as kz / kx decreases from 1 to 0.25, the water inflow rate into the tunnel reduces linearly and the invert of the tunnel experiences the highest inflow rate. The total water inflow into the tunnel when kz / kx = 1 is three times the inflow rate for kz / kx = 0.25. An illustrative example has been included to help tunnel designers and construction engineers utilize the findings of this study for practical lining and permanent tunnel drainage systems.