Global jack-up rig behaviour next to a footprint

Abstract

This paper reports the effect of the global behaviour of three-legged jack-up rigs due to the reinstallation of spudcan footings next to seabed footprints. Two reinstallation scenarios are discussed: (i) two legs first installed on flat ground, and then the third leg installed near a footprint (representing what is known as leg-by-leg preloading); and (ii) the three legs installed simultaneously (representing simultaneous preloading). The spudcan-soil interaction was simulated using a coupled Eulerian-Lagrangian (CEL) approach. A simplified global jack-up model was developed by considering an equivalent beam model for the hull and legs. The results of the jack-up installations are compared against the responses of the more common modelling of a spudcan with a fixed head condition. A detailed parametric study assessing the consequences of spudcan-footprint interactions, such as the risk of the jack-up and spudcan sliding towards the footprint centre, overturning of the jack-up rig and of structural failure of the jack-up leg due to excessive stresses, is also discussed. The ability of a recently developed novel spudcan with a flat base and 4 holes, coupled with the global jack-up model, to mitigate the consequences of spudcan-footprint interactions is highlighted.