A Study of the Failure Mechanism of Braced Excavations Using 3D Finite-Element Analysis

This study aims to investigate the failure mechanism of structural support systems in braced excavations. The three-dimensional finite-element method (FEM) was used to model the complexity of real geometry by considering the elastoplastic structural support system. Because failure could occur at the connection between walls and struts, a new model of a strut-wall connection was considered in the analysis to represent the actual condition of excavation failure. Three failure case histories were studied to investigate the performance of strut-wall connections by calibrating their strength parameters until the factor of safety was close to unity. It was found that a good result of stability analysis could be obtained in the FEM by considering this model. The yielding of the strut-wall connection model initiated the collapse of the bracing system in all case histories, followed by the yield of struts and failure of soils. A robust failure mechanism was also obtained, in which the yielding of the structural support system at failure initially developed at the middle section toward the corner of excavation geometry.