The Effect of Two-Way Pressure Cyclic Installation on the Tensile Capacity of Suction Caissons in Sand – Part III

Suction caissons are being increasingly considered as foundations for offshore wind turbine jacket structures. Suction caissons are installed through self-weight and application of under pressure, achieved by pumping water from the caisson interior. However, in some instances alternative installation strategies need to be considered to ensure complete installation. This paper considers one such strategy, in which two-way pressure cycling is applied in an attempt to promote penetration. The response of suction caissons to two-way pressure cycling in sand was investigated through a series of model scale tests conducted in a geotechnical centrifuge in medium dense and dense silica sand samples. Two-way pressure cycling led to a small but discernible reduction in the required suction pressure over the last 30% of skirt embedment. Pressure cycling had a negligible effect on the short term vented capacity in medium dense sand but caused a reduction of approximately 20% in dense sand. Allowing a time interval of a day or more between installation and extraction increased the vented tensile capacity for tests in both samples involving monotonic installation. For the tests involving pressure cycling, the vented tensile capacity increased by 11% after approximately 1 day and by 34% after 4 days for the tests in the dense sample, whereas there was negligible change in vented tensile capacity after about a day for the tests in the medium dense sample.