大断面顶管通道近接穿越下覆既有地铁隧道数值模拟与现场试验

南京某地下步行通道采用非开挖顶管法施工,顶管近距离穿越既有地铁区间隧道及城市主干道。为了保证隧道及主干道安全,施工前建立三维有限元计算模型,模拟施工全过程,预测施工可能引起的隧道及地表变形。根据数值模拟结果提出针对性控制措施,并制定合理的监测方案,分别对隧道竖向位移、水平位移、径向收敛和地表隆沉进行监测。基于监测数据分析隧道及地表变形规律,明确顶管施工期间隧道及地表变形的3个不同发展阶段。研究表明:隧道竖向位移主要表现为隆起,由通道内出土卸荷所引起,工作井基坑开挖对其影响几乎可以忽略;顶管施工过程中,下覆隧道竖向位移先后经历了初始下沉、隆起增强和隆起稳定3个阶段,地表竖向位移先后经历了隆起增强、隆起减弱和沉降3个阶段;同一监测断面内,地表最大沉降位于通道中心轴线上方,距离通道越远沉降越小;采用微欠挖工艺有效控制了隧道最终隆起和地表最终沉降。

Numerical simulation and field monitoring on a large cross-section pipe-jacking underpass traversing existing metro tunnels

A pedestrian underpass in Nanjing was constructed using pipe jacking method，which traverses both the existing metro tunnels and an urban main road in short distance. In order to ensure the safety of the tunnels and the road，a 3D FEM model was established before construction to simulate the whole construction process and to predict the possible deformation of tunnels and ground settlement. Based on the simulation results，the targeted measures to reduce the deformation were put forward，and a reasonable field monitoring scheme of tunnels and ground surface deformation was proposed. The monitored items included the vertical displacement，horizontal displacement，diameter convergence of tunnel and the ground settlement. The variation of tunnel and ground deformation was analyzed based on the observed data and three different stages that tunnel and ground surface experienced during construction were proposed. The results indicate that the vertical displacements of tunnel are mainly manifested as heaving induced by the unloading in the underpass. The influence of excavation of working shafts on the vertical displacement of tunnels is almost negligible. In the whole construction process，the vertical displacement of tunnel mainly experiences an initial settlement stage，a quick heaving stage and a steady heaving stage. The ground settlement goes through a heaving enhancing stage，a heaving weakening stage and an absolute settlement stage. In the same monitoring section，the maximum ground settlement occurs on the central line of underpass，and the settlement decreases away from the central line. The slight under-excavation method applied in the construction is effective in reducing the ultimate tunnel heaving and ground settlement.