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Skirted foundations are becoming an increasingly prevalent offshore foundation solution for the oil and gas and renewable energies industries. Their capacity under combined horizontal, vertical and moment loading must be found in order to ensure their stability under environmental loadings. As part of this process, knowledge of the vertical bearing capacity is required. In this paper, the vertical bearing capacity of skirted foundations on normally consolidated undrained soil was investigated using numerical and physical modelling. Finite element analyses were carried to investigate the vertical bearing capacity of foundations with different geometries for various embedment ratios. Accompanying upper bound plasticity analyses highlighted the mechanistic reasons for the varying response and allowed examination of the effect of changing skirt interface friction. Analyses showed that skirted foundation capacity under vertical load may be considered normally as if the foundation is rigid with an embedment depth equal to the skirt depth. Based on the numerical analysis, a design method is proposed to calculate vertical bearing capacity. Finally, good agreement with results from a series of centrifuge model tests partially validated the design method.

The behaviour of pile groups when adjacent surcharge loads are applied to a clay layer was studied using centrifuge model tests. Lateral soil movements due to the surcharge loading cause passive lateral pile pressures and traction under the pile cap. These loadings induce pile group displacement and rotation away from the surcharge load. This 3-d soil-structure interaction is complex and requires data upon which design rules can be based.