Capacity of Caissons in Dense Sand under Combined Loading

This paper presents the development of an improved plasticity model to define the combined vertical and horizontal capacity of suction caisson in sand under low vertical loads, conditions relevant for foundations of offshore wind turbines. Model tests following a variety of load paths were used to demonstrate the change of the shape of the yield surface as a function of the vertical load applied and to provide parameters for plasticity modelling. A new hardening law is proposed that accounts for capacity changes because of caisson lateral movement in addition to the vertical movements normally solely considered. An updated formulation for the yield surface is then presented based on a normalization by the new hardening parameter. The plastic model is subsequently validated by comparison with test results. The model can be used to assist in the prediction of the capacity of suction caisson under combined loading at low vertical loads.