A study of failure mechanisms of deep excavations in soft clay using the finite element method

In this study, four failure mechanisms of excavations were investigated using the finite element method (FEM) with reduced shear strength. Center posts were considered in this finite element model. Both the elastic and elastoplastic support systems were used for comparison. The results showed that when the elastoplastic support system was used, reasonable stability of the excavations was estimated by the FEM. The yielding of the support system caused failures of the excavations. When the elastic support system was used, the FEM overestimated the stability of the excavations. The failures of these excavations were due to a large soil heave present at the excavation bottoms. For the two excavations in thick clay, the horizontal struts were bent until yield due to an upward movement of the center posts and a downward sinking of the wall. The yielding of the struts was followed by the yielding of the wall and failures of the excavations. For the remaining two excavations, which had either a shallow hard stratum or an insufficient support system, the failure was caused by the yielding of the wall due to an inward movement of the soil and the yielding of the struts because of the transfer of a large axial load from the wall.