中文摘要：

传统的基坑水平支护设计理论是基于构件进行强度设计，没有考虑大面积复杂基坑支护系统的连续破坏问题，对基坑支护体系冗余度的评价方法及冗余度指标等也缺乏针对性研究。以环梁形式的水平支撑体系为典型，设置了不同的环梁支撑平面布置方案，利用离散元软件PFC，通过FISH语言二次开发定义了钢筋混凝土杆件的破坏准则，实现了局部构件破坏时水平支撑结构体系的连续破坏模拟以及整体破坏荷载确定。在此基础上，进一步提出了一种考虑水平支撑设计荷载的冗余度评价指标，并对有、无角撑支撑体系的冗余度进行了定量分析对比，同时表明此指标可以更为直观地体现水平支撑体系在局部破坏的情况下是否能够继续承担设计荷载而不至于发生连续破坏直至整体破坏，具有更明确的理论与实用意义。针对环梁水平支撑体系的研究还表明，对于要求变形和受力尽量均匀的环梁支撑体系来说，在满足刚度均匀的前提条件下合理增加传力路径来提高冗余度尤为重要，否则，不合理地增加传力路径可能反而造成环梁支撑体系的受力和变形更为不利。建议对重要、复杂的基坑水平支撑体系进行冗余度分析及优化，并在施工过程中对关键构件进行重点监测与保护。

英文摘要：

The traditional design theory of horizontal supporting structures of excavations is based on the element design, and it cannot guarantee sufficient redundancy of the entire supporting systems. In the meantime, the researches on the redundancy of supporting structures, e.g., evaluation methodology and index, are insufficient. The ring-beam supporting structure is adopted as the representative example, and different plan configurations of this kind of structure are designed. Through the secondary development with FISH, the failure criteria of reinforced concrete beams are defined in DEM software, PFC. Furthermore, the progressive collapse of partially damaged supporting structures is simulated using PFC, and the collapse loads of the four types of structures are determined. A new redundancy index is proposed, and the redundancy in terms of the system redundancy index of two ring beam supporting systems is analyzed and compared. The research results show that the number of loading paths is an important factor that can influence the redundancy of retaining structures essentially, and that the progressive collapse simulation and redundancy analysis are necessary for the determination of key elements. It is suggested that redundancy analysis and optimization should be carried out in the design process of large and complex retaining structures, and that key elements should be monitored and protected intensively during the construction process.