Modelling the Effects of Cyclically-Induced Consolidation on Spudcan Capacity-Paper

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The study examines whether consolidation following cyclic loading can restore or increase the bearing capacity of spudcan foundations used by jack-up platforms. Conventional design methods account for cyclic soil degradation caused by excess pore-pressure buildup but often omit the strength gains that may occur when those pressures dissipate during calmer periods.<br /><br />The authors modelled kaolin clay using a hypoplastic constitutive model with intergranular strain, coupled with finite-element analyses. Small-strain simulations represented cyclic loading and subsequent pore-pressure dissipation; large-deformation RITSS analyses predicted post-cyclic spudcan penetration resistance. The simulations included 25 cycles representing an idealised rough-sea event, followed by consolidation.<br /><br />Cyclic loading generated excess pore pressures and reduced subsequent bearing capacity by about 10% relative to the reference case. When some excess pore pressure was allowed to dissipate before penetration, capacity increased by 15% over the reference case and 26% over the cyclically degraded case. The results indicate that consolidation can occur even under small-amplitude cyclic loading, such as during calmer operating conditions.<br /><br />The time required to achieve these gains depends strongly on soil consolidation properties and foundation size. For the study’s assumed soil and 12 m spudcan, the modelled consolidation period was long; higher consolidation coefficients or smaller foundations could make the process substantially faster. The authors conclude that standard laboratory tests can support this modelling approach, offering a way to quantify consolidation-related strength gains and potentially offset cyclic degradation. Further work is needed to address model limitations, including the number of cycles and excess pore pressures that can be simulated.

Keywords

spudcan foundations

jack-up platforms

cyclic loading

consolidation

bearing capacity

kaolin clay

excess pore pressure

finite-element analysis

hypoplastic model

soil degradation