Design of large geotextile mat cofferdam over deep soft clay

This article describes an extensive investigation of the failure mechanisms of a large geotextile mat cofferdam over a deep soft clay layer, where the large geotextile mat was filled with sand. Finite element (FE) analysis was conducted to provide insight into the behaviour of large geotextile mats. The FE results were validated against 1 g model test data and centrifuge test data prior to undertaking a detailed parametric study. It is found that large geotextile mat cofferdam over deep soft clay has two distinctive types of failure mechanisms - global and local failure mechanisms. The global failure mechanism showed the whole dam sank downwards together, and the local failure mechanism included a central standing ridge with two dam sides sliding downwards. A formula, based on the results of the parametric study, was proposed to distinguish the potential failure mechanism of the dam and the foundation soil. For these two different failure mechanisms, both limiting fill height and safety factor of the dam could be predicted using the equations obtained from this study. Finally, a design framework was proposed to provide guidance for designing the large geotextile mat cofferdam over deep soft clay under construction.