Re-installation of jack-up close to footprints created by previous spudcan installations can be problematic. Instead of purely vertical loading during normal installation, the spudcan footing is subjected to eccentric and inclined loading arising from the combined effect of uneven seabed and shear strength variation in the vicinity of the footprint. Several mitigation measures have been proposed to alleviate this problem but so far only limited study has been conducted to investigate the effectiveness of these measures.

Reaming, otherwise known as leg-working or leg reciprocation, is the mitigation measure considered in this paper. Very limited information is available in literature regarding the procedure of reaming. This paper will present the results from centrifuge model tests and large deformation finite element analysis in an attempt to systematically investigate the efficacy of reaming technique for jack-up re-installation close to existing footprint in normally consolidated clay.

Several reaming strategies involving different amplitudes of leg penetration-extraction cycles were investigated. The induced vertical, horizontal and moment forces during reaming were compared with that of a generic spudcan re-installation. It is found that for reaming technique to be effective, reaming should be executed with small amplitude of penetration-extraction cycle. Moreover, the number of cycles for a particular leg penetration-extraction increment does not appear to play an important role in increasing the reaming effectiveness against footprint interaction. Back analysis using three-dimensional large deformation finite element analysis reveals a good agreement with centrifuge test data.

This study using centrifuge model coupled with large deformation finite element analysis provides insightful information pertaining the mechanisms and efficacy of reaming as a mitigation measure for re-installation of jack-up close to existing footprints.

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