上软下硬地层盾构隧道围岩应力释放率研究

为解决盾构隧道在上软下硬地层中掘进时开挖面应力释放率难以确定的问题，基于一种既有的体积损失率迭代求解应力释放率的方法，依托广州地铁21号线盾构穿越上软下硬地层实际工程，通过数值模拟研究掌子面不同软硬岩比例、不同埋深条件下的应力释放率变化趋势，并结合现场实测资料进行对比分析。研究结果表明： 1）在盾构隧道掘进穿越上软下硬地层分界面的过程中，围岩的初次应力释放率范围基本保持在24%~36%，且随掌子面硬岩比例的增加呈线性增加趋势； 2）相对于围岩条件而言，埋深对应力释放率的影响更小。此外，在盾构隧道穿越上软下硬地层的全过程模拟中，根据围岩变化情况随不同开挖步动态调整应力释放率这一做法较全程取一固定应力释放率值更为合理。

Surrounding Rock Stress Release Rate of Shield Tunnel in Upper Soft and Lower Hard Strata

To determine the stress release rate of shield tunneling face in upper soft and lower hard strata, the variation rules of the stress release rate of surrounding rock under various proportions of hard and soft rocks on the tunnel face and buried depths are studied via numerical simulations using an existing stress release rate calculation method by volume loss rate iteration. The results are compared with the field data collected for Guangzhou metro line 21. The results indicate the following: (1) For shield tunneling in the interface between hard and soft rocks, the initial stress release rate of surrounding rock ranges from 24% to 36%, and it linearly increases with the proportion of hard rocks on tunnel face. (2) Compared with the strata condition, the influence of the buried depth on the stress release rate is less. In addition, in the simulation of shield tunnel passing through upper soft and lower hard strata, dynamically adjusting the stress release rate under different excavation steps according to the changes in surrounding rocks is feasible.