Estimation of shield tunnelling-induced ground surface settlements by virtual image technique

The accurate estimation of ground surface subsidence induced by shield tunnelling is crucial to the protection of buildings or structures in the vicinity. Under the hypothesis that the soil is a homogeneous isotropic incompressible linear-elastic semi-infinite half-space, equations for calculation of tunnelling-induced ground surface settlements under different surrounding soil intrusion models are derived based on the virtual image technique. Compared with those of numerical integration methods, the predicted results by the proposed method are more accurate. For the soil in reality is anisotropic, layered and compressible, the transverse ground surface settlement trough width is over-estimated both by this study and the numerical integration method. A modification parameter of trough width is introduced into the deduced formula. The modified method is proved by the field observations to be an easy and reliable method for prediction of ground surface settlements resulting from ground loss during construction of shield-driven tunnels.