Geotechnical Centrifuge Investigation of the Effectiveness of a Novel Spudcan in Easing Spudcan–Footprint Interactions

The interaction between a spudcan and an existing footprint is one of the major concerns during the reinstallation of jack-up rigs. This paper reports the results from a series of centrifuge model tests undertaken to assess the efficiency of a recently developed novel spudcan shape with a flat base and four holes through the base to ease spudcan–footprint interactions. The experimental program was carried out at $200\mathit{g}$ in a beam centrifuge. The footprints were created either manually using a cutting tool or through spudcan penetration and extraction allowing a typical operation period as well as an elapsed time prior to reinstallation. While the former allowed a consistent evaluation of the benefits of spudcan shape, removing the additional variability due to soil strength heterogeneity, the latter allowed for examining the effect of real field footprints. For manually created shallow footprints in soft clay, comparing the responses with those on a generic spudcan, it was possible to show that the novel spudcan reduced the maximum horizontal force and moment by up to 47%–62% and 28%–36%, respectively. The critical offset distance was found at $0.75D$. For manually created deep footprints in stiff clay, the reductions were 20%–59% and 9%–45%, respectively. The critical offset distance was found at $0.5D$. For footprints created by penetrating and extracting a spudcan, the critical offset distance was identified at $0.75D$. The efficiency of the novel spudcan was calculated with the reduction of maximum horizontal force and moment by 42%–59% and 21%–62%, respectively.