A Numerical Simulation Study On The Effects Of Adjacent Pile Foundation Induced By Shield Tunneling

The subway has become one of the effective means to ease traffic pressure and speed up urban rhythm. With so many advantages, shield tunneling has become the most commonly used method in subway construction. The subway generally goes through the city center, with the neighboring high-rise buildings, overhead bridges and other buildings with pile foundations, so the subway tunnel inevitably construct with the adjacent pile foundations. Even using the most advanced construction methods, construction process will inevitably cause ground movement induced by ground loss, which will make pile produce additional axial and lateral force. And this will make the pile producing additional deformation and internal forces. If the internal forces and deformations are too large, it will cause the upper building tilt and wall cracking, etc., which will adversely affect the security and stability of the upper part of the buildings. Therefore, the shield tunnel excavation work on the nearby pile foundations has a very important practical signature.Based on the construction of shield tunnel of metro Line2of Tianjin, the international large finite element analytical software ABAQUS was employed to build a3-dimensional elastic-plastic FEM model. In the3-dimensional dynamic simulation with the add-remove method, different soil layers, nonlinearity of the soil, the void at the shield tail, the pressure applied by the shield, the friction between shield and soil, the synchronous grouting at the shield tail, interaction between liner and soil, pile and soil are all considered. This paper explored the settlement laws of ground surface and the effects of adjacent pile foundation induced by shield tunneling,The following conclusions can be obtained by numerical analysis. When the shield driving away from the excavation starting surface outside the scope of5D, the settlement of ground surface at tunnel excavation starting side is basically stable, and the surface displacement at the pile side is obviously smaller than the other side. The maximum subsidence of the vertical sedimentation tank was in the tunnel excavation starting plane. The maximum uplift existed in front of excavation face range of about ID, and move forward as the shield driving. Pile got its’ maximum deformation and internal forces near the axis of the tunnel. On the basis of this model by changing the pile length, pile spacing, pile diameter, explored the effect of pile foundation performance due to parameters changing. Besides, the performance of friction pile and end bearing pile were also compared. On the basis of the single pile model, this paper established a numerical model of the influence of neighboring pile group induced by Shield Tunneling, from which can summed up the variation laws of the piles in the pile group performance, and compared with the single pile case. And come to the conclusion, shielding effect in pile group obviously reduced horizontal deformation and internal forces increment, especially the back piles. Meanwhile, protection measures of the neighboring pile in the construction of tunnel was discussed. In addition, double-tube shield tunneling model was established to explore the impact regularity to surface settlement and the adjacent pile performance. The analysis found that the maximum settlement of the transverse settlement trough of this model occurs in single-peak curve of the centerline of the two tunnels. In the left tunnel excavation, the work performance of the pile which is3m far from the right tunnel outside diameter has little effect.