Analysis of ground surface settlement due to shallow shield tunnels

Abstract

When shallow tunnels are constructed under streets and buildings, surface settlement due to the tunnelling and its control becomes essential to prevent any environmental problems. This paper deals with finite element analysis and a simplified numerical method for computing the surface settlement due to tunnelling. The computed results are compared with the observations made during the construction of the shield tunnel through the diluvium deposit. The surface settlements due to the shield tunnel opening in the relatively shallow diluvium deposit are analyzed using the finite element method. The surface settlement computed from the elastic finite element analysis are added to the one from the empirical equation based on the lowering panel test. Non-linear finite element analysis was also carried out in order to account for the non-linearity of the soil. The analytical results are compared with the observed surface settlement obtained from the field measurement at the shield tunnelling site. In the sandy ground, it was noted that the elastic and plastic deformations occurred rapidly and that 95% of the final settlement was reached within 2 weeks. It was also noted that the non-linear finite element analysis using the hyperbolic representation of stress-strain relation gave a good estimate of the pattern of surface settlement. Finally, when only the final surface settlement due to the tunnel opening is required, it can be easily estimated from the summation of the elastic settlement and the settlement caused by local yielding.