Numerical Investigation of Sequential Strut Failure on Performance of Deep Excavations in Soft Soil

Abstract

The structural support system is the key element in the design of any deep excavations, in particular, in difficult ground conditions, and an adequate safety margin is required to cover uncertainties inherent in geotechnical engineering. When deep excavations are supported, for example, by a diaphragm wall and, depending on the depth of excavation, multiple layers of struts, usually the struts are the critical elements and overall failure will, in general, occur if a complete strutting level fails. However, if the failure of an individual element occurs, the system should be robust enough not to fail due to 3D effects that allow for stress redistribution within the support system. An additional factor is the embedment depth of the wall. A parametric finite element study in 3D was carried out to demonstrate the consequences of individual struts failure by analyzing a 30 m deep excavation in marine clay supported by a diaphragm wall and multiple layers of struts. The following imperfections were investigated: insufficient embedment depth of the wall into the stiff soil layer and failure of individual struts. It was shown that provided a robust design was put in place, significant stress redistribution capacity was available to avoid catastrophic failure of the excavation when individual support elements failed.