Abstract
Two failure deep excavations in soft clay were investigated in this study using the finite element method (FEM) with reduced shear strength. A comprehensive model of support system was built as regard the existence of wall, struts, and center posts. In order to determine the causes of collapse of the excavations, both elastic and elastoplastic behaviors of support system were analyzed. Result shows that failure of the excavations starts from large soil heave at the final excavation grade as considering an elastic behavior of support system and from yielding of support system if its behavior is elastoplastic. A failure mechanism is proposed for deep excavations in soft clay. Due to an upward movement of center posts, secondary bending moment on struts will reduce their capacity, originally designed for bearing axial load. Yielding of struts is followed by yielding of wall and then failure of excavation. Factors of safety estimated by FEM with modeling elastoplastic support system are also in good agreement with stability of the excavations observed in the field.
