Measured spudcan fixity: analysis of instrumentation data from three North Sea jack-up units and correlation to site assessment procedures

Including spudcan fixity in a jack-up site assessment enhances the performance of the rig with respect to standard acceptance criteria, and hence expands the operating envelope of the unit. Monitoring of three harsh environment jack-up units over the period from 1991 to 1996 has yielded a significant quantity of data from which clear conclusions can be drawn about the degree of spudcan fixity experienced by this units in typical North Sea conditions. Generic methods currently used in the industry are shown to be consistently conservative with respect to the measured performance, and hence the data provide justification for the safe use of greater fixity in the future assessment of these units. No attempt is made in this paper to draw general conclusions about the conservatism of current methods with respect to other rig designs or different foundation conditions. Instead, the paper demonstrates how a well-executed, long term measurement program can be used to improve upon the generic methods and thereby extend the operating parameters for a specific jack-up design in a certain range of bottom conditions.