为解决周边既有建(构)筑物对工程总体筹划的影响,在上软下硬复杂地质条件下调整施工顺序完成超深盾构吊出井施工的问题,在常规浅基坑“坑中坑”施工经验的基础上,以国内首个深层排水隧道———广州市深层隧道排水系统东濠涌试验段工程为依托,对采用不同施工顺序和方式的2 种施工方案(2 次“坑中坑”分步完成和一次“坑中坑”一步到位)进行对比分析,并利用 ABAQUS 有限元软件对这2 种方案中的关键工序(小圆井的后扩挖与先扩挖)进行计算模拟。结合实际施工过程和监测记录,最终得出结论: 1)对于与深层隧道工作井类似的超深基坑的坑中竖井结构形式,采用与浅基坑相反的先小后大和先深后浅的施工顺序更加有利; 2)采用先建后拆,2 次或多次“坑中坑”施工方案优于一步到位、一次成型的施工方案。

In order to reduce the influence of surrounding existing structures on the overall planning of the project, the construction sequence is adjusted to complete the construction of ultra-deep shield tunnel hoisting shaft under complex geological conditions of upper soft and lower hard strata. And then the construction experience of " pit in pit" in the conventional shallow foundation pit is introduced by taking Donghaochong Test Section of Guangzhou Deep Tunnel Drainage System as an example; the two construction schemes with different construction sequences and methods, i. e. twice "pit in pit" step by step and one-time " pit in pit", are comparatively analyzed. Finally, the finite element software ABAQUS is used to calculate and simulate the key processes in the two schemes (post-expansion and preexpansion of small circular shaft). The actual construction process and monitoring records show that: (1) For the shaft structure in the ultra-deep foundation pit, it is more advantageous to adopt the construction sequence of small shaft first and then enlarging and deep shaft first and then shallow one, which is opposite to the shallow foundation pit. (2) The construction plan of twice "pit in pit" is better than that of one-time completion.