Abstract

In recent years there has been a surge in the development of new small scale offshore facilities, including minimum facility structures for oil and gas developments as well as offshore renewable energy devices such as offshore wind turbines. In these cases the loading applied to the structure and foundation is significantly different to that applied to more typical larger offshore structures. The weight of the structure is much lower, and the horizontal load and moment applied to the foundation is much higher as a proportion of the vertical load. Design guidance for the combined loading response of shallow foundations under low vertical loads is sparse, and in particular much guidance is drawn from work where the vertical load applied to the foundation is close to the vertical bearing capacity. This paper addresses this lack of data by presenting results of combined loading experiments at low vertical loads on novel shallow foundations known as suction caissons. The experiments are carried out on dry sand at a low relative density to explore the drained response of the foundation. The experiments are successfully interpreted within the framework of work hardening plasticity, and information on the shape of the yield surface and the post-yield behaviour of the foundation is deduced. One of the key results is that the foundation can sustain moments and horizontal loads even when a tension is applied to the foundation.