Effect of highly pervious geological features on ground-water flow into a tunnel

Current practice for estimating water inflow rate relies mostly on analytical solutions which assume a homogeneous, isotropic porous medium around a tunnel. Field measurements indicate that current engineering practice does not consistently make adequate estimate of ground-water flow into a tunnel during excavation due to various factors that analytical solutions do not properly take into account. Among the various factors affecting ground-water flow, the significance of a highly pervious feature located near the tunnel is discussed in this research. The highly pervious feature, which is located near an underground opening and connected to a large source of water, can provide a path for relatively high-head water to the joints intersecting the opening. This paper describes the influence of a highly pervious feature on the ground-water flow regime around a tunnel and the change of inflow rate as the tunnel approaches a highly pervious feature.

Research Highlights
► Significance of a highly pervious feature (HPF) on ground-water flow into a tunnel.
► High head water concentration mostly into tunnel, if tunnel intersected by HPF.
► Almost no impact on ground-water inflow, if HPF at 2-diameter distance from tunnel.
► High flush flow, fast bleed-off, if HPF not connected to large source of water.
► High flush flow, slow bleed-off, if HPF directly connected to large source of water.