Abstract: The conventional design method of deep excavation retaining structure generally processes element by element, consequently, some retaining structures are probably lack of essential redundancy, which is one of the reasons that led to many catastrophic collapses of deep excavations. Discrete element method (DEM) is adopted for simulation of excavation collapse and study of retaining structure redundancy; and a simulation method based on local failure for analyzing redundancy is also proposed. Here the influence of prop connection on the retaining structure redundancy is selected as an example of redundancy research. The failure processes of two excavations with different types of prop connections are simulated; and the phenomena of progressive collapses in them are compared and analyzed. Furthermore, the simulation results are also validated by comparison with the realistic case of excavation collapse. It is indicated that the improvement of the retaining structure redundancy can effectively resist the progressive collapse in deep excavation, and then the transformation of a type of damage to other types of damages and the evolution of the local damage to entire collapse can be avoided. In addition, the simulation results also show that the excavation collapse using DEM is feasible and reasonable, so as to provide a reference for simulation of such collapse problems in underground engineering and further study of redundancy in deep excavations.

Key words: excavation, retaining structure, redundancy, connection node, discrete elements