软土地基中大直径土压盾构掘进面局部失稳机理及支护压力研究

It has become a new tendency to build the large diameter tunnels in the underground traffic construction in the developed coastal areas. The large diameter shield is chosen for this kind of tunneling to void the disturbance to the ground and decrease the concomitant pollution especially in the soft ground which is widely distributed in these areas. However, the local failure of tunnel face easily comes out in tunneling because of the large diameter excavation. In this research, the large scale model test is firstly used to investigate the behavior of the working face in large diameter tunneling. By use of the technology of particle image velocity and sensor detection, the whole test process is observed carefully. As a result, the criterion for critical status of local failure is proposed by multi-parameter analysis. The criterion is embedded into the finite differential code FLAC3D to investigate the mechanism of local failure of working face as well as the pattern of local failure. The influences of geological conditions and support pressure on the working face stability are also analyzed. Consequently, the analytical model for the local failure of working face is proposed and the estimation of limit support pressure is derived. The technology of maintenance of face stability in practical large diameter tunneling will be benefited from this research.

建设大直径隧道已成为沿海发达地区地下快速交通发展的新趋势。软土地基在东南沿海及三角洲地区分布范围广,为了提高地层适应性，减小开挖对软土地层扰动和环境污染，大直径土压隧道主要采用盾构法施工。然而由于开挖直径大，盾构掘进时极易发生掘进界面局部坍塌失稳。本研究首先采用大型物理模型试验对大直径盾构隧道掘进界面行为进行模拟，通过颗粒数字测量系统和多种传感器对试验过程进行观测，提出基于多参数分析的掘进面局部失稳临界状态判定准则。基于该准则，采用动态差分数值软件FLAC3D对大直径盾构隧道掘进行数值模拟，研究掘进界面局部失稳机理和失稳模式，并分析地质条件变化和支护压力波动对掘进界面稳定性的影响。提出掘进界面局部失稳理论分析模型，并推导极限支护压力计算方法。本研究将为大直径盾构隧道施工掘进面稳定控制技术提供研究基础。

本项目对大直径盾构掘进面失稳问题进行研究。项目首先进行盾构隧道掘进面失稳事故案例调研搜集整理工作，通过工程案例分析对比，选取典型工程案例研究。在现有理论模型基础上，通过考虑成层地层和地下水渗流因素作用，提出复杂水文地质条件下，盾构开挖面失稳极限支护压力计算方法。项目展开了大比例尺物理模型试验研究，自主设计并建设了适用于大直径盾构的物理模型试验槽，自主研发了地层失稳综合观测技术，实现了砂性土中大直径盾构掘进面失稳试验模拟，揭示了砂性土盾构掘进面失稳机制及特征。以此为基础对掘进面失稳理论模型进行修正，提出了极限支护压力比计算方法。项目补充性地进行了黏土中隧道掘进面失稳物理模型试验，自主设计了黏土中开挖面失稳物理模型槽，通过综合观测技术揭示了粘土中隧道掘进面失稳机制及特征，研究了超前加固对失稳的影响。为了进步对盾构掘进面失稳研究进行深化，项目展开盾构隧道掘进面被动失稳理论研究。根据盾构开挖面受力机制，分别构建了被动失稳二维和三维机动场模型，利用上限分析法得到被动失稳极限支护压力上限解，并揭示了失稳初期特征和失稳模式。