Abstract: A complete 3D numerical simulation by using FLAC3D is developed to investigate the features of surrounding rock deformation and stress field in squeezing ground excavation by double shield tunnel boring machine(TBM). The TBM model was based on the real geometry and the nonuniform gap between the shield and the ground. A great emphasis is placed on the key steps to simulate TBM tunneling in accordance with the practical construction. In this paper, we mainly studied the characteristics of displacement field, stress field and the plastic zone on the cross section and the longitudinal section profile of the tunnel. The results obtained in numerical modeling indicate that the surrounding rock which located in the lower part of the wall is contact to the shield of TBM, whereas the crown is not. Three loading and unloading phenomena are observed in the surrounding rock of floor, which can be attributed to the impact of the geometry of size difference on the cutter head and shield and the conicity of the front shield and the rear shield. Moreover, the circumferential stress and the radial stress in floor is greater than the crown; and the wall and the orientation of major principal stress is severely perturbed and obliquely crossing the radial of the tunnel. But the ground on the lower part of 70° is in elasticity. The plastic zone outside the front shield gradually decreases from top to bottom on transverse section and increases with the greater distance away from the excavation face. But, it has no obvious change in ground outside the rear shield.

Key words: double shield tunnel boring machine, nonuniform gap, characters of ground deformation, stress field, plastic zone