Effect of a front high hydraulic conductivity zone on hydrological behavior of subsea tunnels

This study focuses on the hydrological behavior of the ground ahead of a tunnel face. A localized high hydraulic conductivity zone with high water pressure is denoted as a hazardous zone. To analyze the impact of the hazardous zone on the face stability, a new indicator (TSR: the ratio of the driving force to the resisting force) is proposed on the basis of the “advance core” concept (Lunardi, 2000). A series of three-dimensional steady-state seepage analyses are performed to estimate the distribution of the TSR of the ground ahead of the tunnel face. The analyses results show that the hydrostatic pore water pressure acts on the most of the hazardous zones throughout all of the tunnelling stages. When the distance between the tunnel face and the hazardous zone (d h ) value is approximately five times the excavated tunnel radius, the influence of the hazardous zone increases rapidly.