开挖与渗流耦合条件下基坑支护系统破坏机理与安全评价研究

There are many large-scale, deep foundation pits with complex environment, which often experience failure and lead to serious harm. The foundation pit support system, which consists of the retaining structures and reinforced soil, exhibited comprehensive deformation and failure mechanisms with application of coupling of excavation and seepage that appeared commonly in practice. The objective of this research program is to investigate these mechanisms on the basis of achievements in the theoretical study of progressive failure, including: to develop experimental devices and measurement techniques to simulate the coupling loading of excavation and seepage at high centrifugal accelerations; to conduct systematic centrifuge model tests on the deformation and failure behaviors under the coupling loading conditions of excavation and seepage, together with field observations, soil element tests, and finite element analysis; to discover the interaction mechanism between the retaining structure and soil, and the progressive failure mechanism of foundation pit support system with coupling application of excavation and seepage using the research scheme "integrated analysis of failure and deformation" through which the failure process can be quantitatively tracked by using the measurable displacement; to propose new stability analysis method of foundation pit support system and develop earth pressure theory of the retaining structure based on the mechanism analysis, which are confirmed by centrifuge model tests and thereafter applied to real-world projects. The research achievements are of great significance to improve the safety and economy of the foundation pits.

基坑工程的深度和规模不断增大，其环境复杂、事故多发且危害严重。开挖和渗流耦合条件下，由支挡结构和所支护的土体构成的基坑支护系统的变形破坏机理复杂。拟在已有渐进破坏理论研究基础上、以离心模型试验为主要手段开展深入研究。研发以模拟超重力场中开挖与渗流耦合加载为核心的离心模型试验设备与测量技术，开展系统的开挖与渗流耦合条件下基坑支护系统变形破坏特性的离心模型试验，并进行有针对性的现场观测、土力学试验和有限元模拟。采用"变形与破坏过程集成分析"的研究思路，通过"可测的变形"追踪土体渐进破坏过程，揭示开挖与渗流耦合条件下支挡结构与土体相互作用机理、基坑支护系统渐进破坏机理等两个关键科学问题。在此基础上建立新的基坑支护系统稳定性分析方法和支挡结构土压力计算方法，通过离心模型试验等结果验证方法的有效性并用于工程实际。研究成果对提高基坑工程的安全性和经济性具有重要意义。

本项目在研制试验设备、完善测量技术的基础上，以离心模型试验为主要研究手段，结合现场观测和数值模拟，研究揭示了开挖与渗流条件下基坑的变形破坏机理、支挡结构与土体相互作用机理两个关键科学问题，提出了基坑安全判断和土压力计算的新方法。取得的新成果如下：（1）基于对基坑应力状态和路径分析提出了新的模拟原理，自主研制了超重力场基坑开挖模拟设备，能够在离心模型试验高离心加速度条件下合理模拟基坑开挖与渗流的耦合作用，获国家发明专利；（2）模拟多种开挖与渗流条件下，进行了系统的基坑支护系统变形破坏的离心模型试验、现场观测和数值模拟，阐明了开挖、渗流及其他影响因素对基坑变形和支护结构土压力的影响规律；（3）揭示了挡墙变位特性和基坑土体变形过程及其阶段性特征，阐明了开挖与渗流条件下基坑土体变形特性并给出了变形区域经验确定方法，刻画了基坑土体变形局部化发展过程，提出了基坑支护系统整体稳定分析方法；（4）阐明了支挡结构土压力与基坑土体的变形局部化和潜在滑裂面的关系，揭示了支挡结构与土体相互作用机理；（5）比较分析了土压力实测结果与传统方法计算结果的异同和原因，提出了分区计算土压力的改进算法，通过与离心模型试验对比初步验证了算法的有效性，能考虑基坑的变形局部化和潜在滑裂面特性，能反映支挡结构偏转对土压力的影响，参数易于确定，可用于实际工程。