Abstract: 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.