非对称基坑开挖对下卧地铁隧道影响的离心试验

非对称基坑开挖引起的卸载－再加载作用常常对下方已建地铁隧道产生不利影响。为明确基坑施工过程对既有隧道的扰动作用，运用土工离心试验系统开展离心模型试验，试验中考虑非对称基坑开挖的卸载－再加载过程，以及基坑与隧道的相对位置，并结合卸载－再加载过程的桩-土-隧道荷载传递机制，分析了不同开挖步和荷载施加对既有隧道位移和受力的影响。结果表明：基坑开挖引起了明显的地层损失，非对称卸载作用导致隧道发生上浮和偏移，基坑初次开挖对隧道的扰动较小，随开挖深度增加，扰动作用逐渐加强；距离基坑中心线近的左线隧道扰动作用更加明显，离基坑越远，基坑卸载－再加载扰动作用越不明显；荷载施加后，由于桩基荷载传递作用和隧道加筋阻拦作用，使得隧道衬砌应力重分布；位于两桩之间的断面扰动较明显，而位于桩侧附近的断面扰动较小，说明群桩效应对隧道扰动更明显。

Centrifugal test on influence of asymmetric foundation excavation to an underlying subway tunnel

The unloading-reloading conditions during an asymmetric foundation excavation usually are harmful to the underlying subway tunnel. To verify the disturbance of foundation excavation, the modified centrifugal system was used to simulate different excavation steps, and the load transfer of foundation-soil-tunnel, considering the relative position of tunnel and foundation pit. The results show ground loss due to the excavation, tunnel float and offset induced by asymmetric unload. The disturbance of first excavation step was small, and became stronger as the excavation depth increases; the left tunnel close to foundation center was disturbed more significantly. Longer distance to the foundation and tunnel generates weaker the disturbance by unload-reload. The force of tunnel lining was redistributed because of the foundation load influence after loading. The disturbance of the section lying between piles was obvious. The section lying one-sided pile was small, the disturbance of pile group effect was more obvious.