富水地层大直径土压平衡盾构隧道开挖面破坏机理研究

To provide sufficient supporting force for soil of excavation face is crucial to ensure the face stability and successful construction. The existing models for the stability analysis of excavation face mostly hypothesize that supporting force is evenly distributed on the whole excavation face, which is fairly acceptable when the shield is with a small diameter. With the increase of the diameter, however, supporting force constantly increases with the growing depth. Thus, the increment of the error in the even distribution of supporting force hypothesis is unavoidable, particularly in water-rich stratum. The impact that ground water distribution and seepage has on the environment of engineering mechanics and the safety of construction has always been one of big problems for engineering construction. This project aims to do research on the distribution law of the supporting force applied to the excavation face of large-diameter shield tunnel. This study focused on the effect of ground water on the stability of the excavation face. In addition, the upper limit method is adopted to solve the three-dimensional failure model of the large diameter EPB shield driven tunnels.Nnumerical simulation will be adopted to carry out numerical modeling analysis by PFC and FLAC software., and a comprehensive analysis of the theoretical models, model tests and numerical modeling results will be made, so as to optimize the theoretical models and parameters.

为盾构开挖面土体提供足够的支撑力是保证开挖面稳定和成功施工的关键；现有的盾构开挖面稳定分析模型中，大都假设支撑力是均匀地分布在整个开挖面上，在盾构直径较小的时候是可以接受的；但随着直径增大，支撑压力沿深度方向连续增加，支撑力均匀分布的假设的误差连续增大，尤其是在富水的地层中，地下水赋存与渗流状态对工程力学环境和施工安全的影响，是工程建设中的一大难题。本项目将研究富水地层大直径盾构隧道开挖面支撑力的分布规律，重点分析地下水对开挖面稳定性的影响，并采用极限分析上限法求解大直径土压平衡盾构隧道开挖面的三维破坏模型；通过对典型的大直径土压平衡盾构隧道施工现场监测数据进行分析研究，并采用PFC、FLAC等计算程序进行数值建模分析，把理论模型、现场测试数据以及数值计算结果进行综合对比分析。

近年来，随着城市建设的快速发展，土压平衡盾构在城市地铁隧道建设中的应用范围越来越广，而且随着施工范围扩大，所遇到地层的复杂程度不断增加，特别是在砂-粘复合地层中，开挖面稳定性的预测与控制都非常困难，因此复杂地层土中压平衡盾构开挖面稳定性问题得到了广泛的关注，成为盾构隧道施工掘进的核心问题之一。.基于极限分析上限法，构建了旋转破坏模型，拟合了开挖面破坏区域。通过土压平衡盾构室内大型相似模型试验，探究了盾构开挖面失稳过程中开挖面支护压力变化规律和破坏模式。通过采用能够考虑大变形、渐进破坏的FLAC3D程序对土压平衡盾构施工力学过程进行了三维数值模拟，探究了开挖面失稳破坏形式、开挖面变形、极限支护力以及地表变形的影响规律。