Experimental and Numerical Studies of Spudcan-Pile Interaction

Abstract

Abstract In a JIP, extensive studies have been performed to evaluate the interactionbetween a jack-up spudcan foundation and adjacent piled foundation supportingthe permanent jacket platform in soft clay. Centrifuge modeling technique wasemployed to examine the induced stresses on the piles due to spudcan movement. Subsequent to the validation of the numerical model, extensive parametricstudies were conducted to supplement the experimental data. While full details of the studies would be reported elsewhere due to spaceconstraint, this paper aims to summarize the key findings from the centrifugemodel and numerical studies. The potential practical applications of thefindings are highlighted such that offshore geotechnical engineers may make useof the findings to make a preliminary judgment on the spudcan-pile interactionissue for the installation and extraction of jack-up at a given site with softclay. The induced loading on the pile decreases with increasing clearance between thespudcan and the pile. The study on the effect of pile length shows that at ashallow penetration depth, the bending moment has a peak value at mid-pile. Thestudy on the effect of pile socket length in sand in a dual layered soilprofile reveals that with an increasing pile socket length, the induced maximumbending moment during spudcan penetration decreases. Numerical studies indicatethat the shapes of the pile bending profiles corresponding to different clayrigidity indices are similar while the magnitude of maximum bending momentdecreases with increasing rigidity indices. The change in the magnitude of thebending moment is less than the corresponding change in pile bendingstiffness. The findings covering the influence of spudcan-pile clearance, effect of pilelength for a floating pile, effect of pile socket length for a socketed pile, effect of upper clay thickness for a dual layered soil profile, influence ofrigidity index and influence of pile stiffness are systematically presented indimensionless charts. These charts, which are currently not available in theindustry, will enable offshore geotechnical engineers to perform quickpreliminary estimates on the severity of spudcan-pile interaction problems invarious field conditions. Introduction Jack-up rigs are often deployed in close proximity to jacket platforms inshallow water oil and gas production. A jack-up rig is founded on spudcans andcantilevered over the adjacent jacket platform to drill new wells or work overexisting wells. During spudcan installation and extraction, large volume ofsoil is displaced and consequently severe stresses may be induced on adjacentpiles supporting the jacket platform [Mirza et al., 1988, Le Tirant and Pérol,1993]. Relatively few studies [Siciliano et al., 1990; Craig, 1998; Stewart,2005] have been performed to investigate the soil flow mechanism during spudcanpenetration and extraction as well as its effects on adjacent piles. With the aim of extending the understanding of spudcan-pile interaction at afundamental level, five companies have funded the Spudcan-Pile InteractionJoint Industry Project (JIP) in 2006. Extensive experimental and numericalstudies were performed at the National University of Singapore (NUS) toevaluate the interaction between a spudcan foundation and an adjacent piledfoundation supporting a permanent jacket platform in soft clay during spudcaninstallation. Both half spudcan and full spudcan centrifuge tests wereperformed on the NUS geotechnical beam centrifuge. The half spudcan testsenabled the soil flow mechanism around the spudcan to be investigated. Theinduced stresses on the piles and the associated pile response due to spudcaninstallation were examined through full spudcan tests (Leung et al., 2006).