Undrained failure envelope for skirted spudcan foundations in clay under combined loading

Abstract

Skirted spudcan foundations can effectively provide a considerable bearing capacity and moment fixity to withstand the complex combined vertical, horizontal, and moment loadings encountered in offshore engineering practices. The failure envelope is a general solution that characterizes the bearing capacities of offshore foundations under combined loading conditions. In this study, a series of probe tests were carried out using finite element analysis to investigate the undrained failure envelope of skirted spudcan foundations in soft clay. Particular attention was paid to exploring the influences of the soil strength heterogeneity, the footing–soil interface roughness, and the embedment depth ratio. The analysis results indicate that the envelope's size is influenced by these conditions to varying degrees, while the envelope’s shape is only slightly influenced. The failure envelope associated with smooth interface conditions provides conservative results, particularly for the deeply embedded scenarios. A closed-form algebraic expression was derived to describe the failure envelope of skirted spudcan foundations, which takes proper account of the soil strength heterogeneity, footing–soil interface roughness, and embedment depth ratio.