Predicting Leakage-induced Settlement of Shield tunnels in Saturated Clay

This paper suggests a new set of analytical solutions for predicting leakage-induced seepage field and ground settlement in saturated clay. A unique feature of the solutions presented is considering the effect of the tunnel lining through the relative permeability between the tunnel and the soil. Through the superposition method, the proposed method can be easily extended to twin parallel tunnels. The accuracy of the analytical solutions are verified with numerical simulations. Parametric studies reveal that the decrease of pore pressure and the consequent settlements of ground and tunnel is proportional to the relative permeability. Over 20% of the initial hydrostatic pore pressure will dissipate when the relative permeability exceeds 0.01. The pore pressure decreases more significantly within the zone of 1.3D above the tunnel crown, 2.5D underneath the tunnel invert and 2.0D from the tunnel springline horizontally when the relative permeability is less than 0.01. Consequently, 62% of the total settlement of the ground occurs within this zone, which is called the main compression zone. It also shows that the tunnel leakage will result in very significant tunnel settlement because 78% of the total settlement occurs in the ground underlying the shield tunnel. Thus, the mechanism of the leakage-induced settlements of the ground and the tunnel can then be explained. For a typical shield tunnel in Shanghai, the leakage-induced settlement accounts for 1/6 of the total post-construction settlement.