Ground and tunnel responses induced by partial leakage in saturated clay with anisotropic permeability

Finite element analysis was conducted to study the ground and tunnel response to partial tunnel leakage coupled with anisotropic soil permeability, a novel and little-known approach that was developed from in-situ inspections of shield tunnel leakage in the Shanghai Metro system. The ground and tunnel settlements, which were caused by water leaking into the tunnel, significantly degraded both the serviceability and safety of the tunnel and its surroundings. In a typical analysis, such leakage is commonly assumed to be uniform along the tunnel circumference with a soil permeability that is isotropic. Numerical simulation results obtained in this paper indicated that partial tunnel leakage in only one side of the shield tunnel caused a greater pore pressure reduction at the tunnel spring line and a larger ground surface settlement than otherwise caused by uniform tunnel leakage with the same rate of water inflow. Indeed, observations showed that partial leakage in only one side of the shield tunnel caused remarkable lateral movements of the tunnel. Our analysis showed that coupling leakage boundary conditions with favorable soil permeability anisotropy could significantly decrease the maximum ground settlements induced by the leakage, which leads to an increase in the width of the surface settlement trough. Furthermore, the effect of soil permeability anisotropy on ground settlement was found more profound for cases involving partial tunnel leakage boundary conditions. (C) 2015 Elsevier B.V. All rights reserved.