Local scour effects on the bearing characteristics of the hybrid skirted foundation considering combined loads

This study investigates the effects of local scour on the load-bearing performance of the hybrid skirted foundations subjected to combined loading, using a series of finite element model analyses. A comprehensive numerical model was established and validated against existing field tests and previous numerical results. The influences of key factors including foundation aspect ratio, scour pit depth, and scour pit angle on the coupled bearing capacity were examined through a parameter study. It found that increasing scour severity significantly reduces the bearing capacity of hybrid skirted foundations, particularly in terms of horizontal and moment resistance. When scour extends to the mat level, the maximum bearing capacity loss reaches 20.3 %; when scour progresses to the inner caisson, the maximum bearing capacity loss reaches 73.6 %. This study reveals that the upper structural configuration of the foundation offers enhanced resistance to scour effects. A two-level bearing-capacity framework is proposed to predict the reduction in bearing capacity due to scour. The design approach presented in this study offers valuable reference for offshore platform construction where scour is a common challenge, and contributes to improved safety in practical engineering applications.