Numerical modelling of a hybrid skirted foundation under combined loading

Offshore foundations are subject to combinations of vertical, horizontal and moment (VHM) loading. Different foundation solutions are appropriate, depending amongst others, on the expected load combinations. This paper investigates in detail the soil failure mechanisms and resulting foundation capacity under undrained VHM loading of a hybrid foundation concept. Comprising of a skirted mat combined with an internal caisson compartment, this foundation design is found to provide significantly increased horizontal capacity that is often critical in offshore applications, with key influences for increased moment capacity identified as well. The numerical study investigated both variations in the geometry of the internal caisson compartment and the soil shear strength profile. The paper concludes by proposing expressions that allow slightly conservative prediction of the combined capacity of a hybrid foundation.