邻近工程施工卸载再加载对已建盾构隧道影响的风险分析

Risk analysis of existing shield tunnel caused by multistep unloading and re-loading of adjacent engineering activity

基坑开挖和上部结构施工引起的卸载和再加载会使邻近已建盾构隧道产生一定位移与变形.以上海已建地铁盾构隧道侧向和上方受基坑开挖和结构施工引起的卸载和再加载工况为背景,利用数值模拟方法,分析了隧道侧向和上方不同区域开挖和结构荷载施加过程中隧道的整体位移和隧道结构变形的发展规律.结果表明,隧道侧向与上方卸载,会使隧道位移与结构变形产生不同幅度的增加;而侧向与上方再加载,会减小因卸载而产生的隧道位移,但会增加部分隧道管片结构变形.因此只有综合分析隧道的位移与结构变形,才能合理预测分步卸载、再加载对已建盾构隧道的影响规律,减小因工程施工引发的已建盾构隧道结构安全风险.

The deep excavation and superstructure construction will induce the unloading and re-loading effect, respectively, on the adjacent existing shield tunnel. The unloading and re-loading caused by engineering activities will introduce additional displacement and cross-section deformation of adjacent existing shield tunnels. A case history in Shanghai was investigated using the numerical simulation to detect the behavior of the existing shield tunnel caused by the adjacent unloading and re-loading. The displacement of the tunnel, the tunnel rotation and opening of the tunnel segmental joint were used to describe the unloading and re-loading induced tunnel behavior. The results show that the above and lateral unloading will increase the tunnel displacement and cross-section deformation. Meanwhile, the above and lateral re-loading will decrease the tunnel displacement but increase the tunnel cross-section deformation. The potential risk caused by unloading and re-loading on existing shield tunnel can be evaluated in terms of the tunnel displacement, rotation and cross section deformation.