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

Abstract

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.

Upper Bound Solution for the Face Stability of Shield Tunnel below the Water Table

“…When shield tunnel locates under the water table line, the soil excavation often induces underground water seepage and apt to cause the collapse of shield tunnel face. The face stability analysis under seepage condition was studied by numerical simulation [22][23][24] or theoretical analysis which was based on the existing model. Anagnostou and Kovári [25] studied the influence of seepage on the stability of tunnel face based on the wedge model.…”

Coupled Mechanical and Hydraulic Analysis of the Effect of a Front High Hydraulic Conductivity Zone on Shield Tunnelling

“…The seepage force acting on the tunnel face can be modeled on the basis of the advance core concept [2,7]. As an advance core, a hypothetical cylinder has the cylindrical shape volume of the ground.…”

“…Hong [1,2] analyzed causes of several tunnel flooding cases and found that the presence of unforeseen high hydraulic conductivity zones with high water pressure (herein, termed as hazardous zones) was strongly associated with various flooding accidents. High water pressure in a fault breccia zone can lead to significant problems related to the stability of the tunnel face.…”

“…However, few studies exist regarding the effects of high water pressure on the stability of a tunnel face affected by a fracture zone ahead of the tunnel. Hong [2] carried out a series of three-dimensional steady-state seepage analyses to solve the problem, but it is not a fully coupled hydro-mechanical analysis.…”

Tunnel Face Stability and the Effectiveness of Advance Drainage Measures in Water-Bearing Ground of Non-uniform Permeability

“…Brekke and Selmer-Olsen 1965;Chang et al 2005;Anagnostou 2010; Zingg and Anagnostou 2012b); specific case histories (e.g. Ko ¨nz 1968;Barla 2000;Bezrodny et al 1992;Dahlø and Nilsen 1994;Nilsen 2010); or specific aspects such as the effect of pre-support (pipe roof) and grouting in fractured zones (Shi et al 2015) or the mechanism of punching failure (Hong et al 2010).…”