Rapid Penetration of Spudcans in Sand-Paper

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The study examines how rapid penetration affects the resistance of spudcan foundations in sand, a key issue when jack-up vessels operate in rougher sea conditions. Rapid touchdown can generate large forces in the vessel’s legs, but resistance is difficult to predict because soil drainage and pore pressures change with penetration rate.<br /><br />Researchers tested a model spudcan in dry sand at 1g and in saturated sand at 50g. Water and a highly viscous pore fluid were used to reproduce penetration conditions ranging from drained to partially drained and undrained. The tests separated viscous effects from consolidation effects and measured both penetration resistance and pore pressure.<br /><br />Viscous effects alone were modest: resistance increased by about 0.7–2.9% per tenfold increase in penetration rate. Consolidation had a much stronger influence. In dense sand, resistance rose by up to 120% as conditions shifted from drained to undrained, mainly because dilation generated negative excess pore pressures (suction). At the highest rates, resistance reached a plateau, consistent with cavitation limiting suction. The measured limiting pore pressure was about −30 kPa, below the theoretical cavitation pressure of −100 kPa, likely because cavitation began locally away from the measurement point.<br /><br />The authors developed a backbone curve relating normalized penetration resistance to a dimensionless velocity, allowing the transition across drainage regimes to be quantified. They conclude that consolidation effects dominate viscous rate effects and must be considered when assessing spudcan touchdown loads. The framework may support practical predictions based on cone penetrometer tests, with appropriate adjustments for differences in geometry, size and drainage conditions. Further experimental and numerical work is needed to clarify pore-pressure behaviour during rapid penetration and the role of cavitation.

Keywords

spudcan foundations

penetration resistance

sand

jack-up vessels

rapid touchdown

pore pressure

drainage conditions

consolidation effects

cavitation

cone penetrometer tests