Abstract:

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.

Key words: deep tunnel, deep foundation pit, shield hoisting shaft, enlargement, construction process, numerical simulation