Pressure-Cycled Installation of Suction Buckets in Sand and Layered Soil Profiles

Installation refusal is a key design consideration for suction buckets. Pressure cycling, whereby the bucket is cycled vertically by reversing the pump flow, has been identified as one of the potential strategies to overcome installation challenges by reducing the required suction. This paper considers experimental data from centrifuge and field installations in sand and sand/clay layered soil profiles to examine the effectiveness of pressure cycling in different seabed conditions. The data indicate that cycling in sand only reduces the required suction pressure when this pressure remains lower than the critical suction and at depths at which frictional resistance is the dominant component of penetration resistance. Pressure cycling in layered soils is viewed as effective when the suction pressure remains lower than that required for plug uplift. The effect of pressure cycling on the required suction pressure is captured by a prediction model based on cone penetration test (CPT) data, and that includes a friction degradation term that is quantified from cyclic CPT data. The model is shown to provide reasonably good agreement with pressure-cycled suction bucket installations at both centrifuge and field scale.