盾构法开挖隧道对桩基础影响的有限元分析

利用有限元软件ABAQUS，采用对隧道洞室周边及开挖面的土体施加由盾构机引起的各种荷载的方法模拟天津市地铁1号线盾构施工。计算结果表明，有限元模型能够很好地模拟盾构施工过程。利用此模型研究隧道开挖对桩基础的影响。隧道开挖引起的桩顶沉降、桩身侧移主要发生在盾构机推进面逐渐接近桩的过程中，当盾构机推进面通过桩所在的位置后桩顶沉降、桩身侧移增加不明显；与隧道水平距离相同时，由于长桩能够充分发挥桩身下部的侧摩阻力，隧道开挖引起的长桩的桩顶沉降小于短桩的桩顶沉降；隧道开挖过程中12 m长桩的桩身发生了整体倾斜，16、19 m长桩的桩身出现了弯曲变形，16、19 m长桩的桩身最大弯矩发生在地面下12～13 m之间，即在隧道轴线附近；开挖过程中桩顶出现沿隧道推进方向的往复位移；桩顶作用的竖向荷载越大，由隧道开挖引起的桩顶沉降越大

Finite element analysis of effects of shield driven tunneling on pile foundation

Process of shield driven in Tianjin Metro Line No.1 project is simulated by means of finite element method. Pressures and shearing forces are enforced on the soils to simulate the real reactions between shield driven machine and the surrounding soil during tunneling. Results from the model adopted here by the finite element method are fine agreement with those acquired in the Tianjin Metro Line No.1 project. Researches on the effects of shield driven tunneling on the pile foundation nearby are carried out with this model. The settlement at pile top and displacement along pile caused by shield driven tunneling nearly reach their maximum values during the process when the shield driven machine is approaching the pile; when it is leaving away from the pile, the increments of settlement and displacement are small. Under the same conditions, settlement at the top of long pile is small because the side resistances at the lower part of long pile can be exploited to a great extend. During the process of tunneling, pile with the length of 12 m inclines while piles with the length of 16m and 19 m bend and the maximum moments are at the position 12-13 m below the ground. During tunneling, there are back and forth displacements at pile top along the direction in which the tunnel is pushed forward. The greater the load applied at pile top, the larger the settlement caused by tunneling at pile top