Punch-Through Analysis of Jack-Up Rig at a Site Off the East Coast of India—A Case Study

Abstract

Jack-up rigs are primarily used for carrying out offshore operations related to drilling for hydrocarbons. Geotechnical assessment is a pre-requisite for deployment of any jack-up rig at a new offshore site. When deployed for operations, jack-ups are supported by their legs which initially penetrate below the seafloor on loading. Majority of jack-up units have individual/independent foundation, called ‘spudcans’, at the bottom of their legs. This paper presents a case of deployment of a jack-up at a site off the east coast of India where the jack-up had a ‘punch-through’ during preloading. Punch-through is a sudden and uncontrolled penetration of the spudcan often causing structural damage of the unit. It may occur when the load becomes equal to bearing capacity for the spudcan while within a soil layer having relatively higher bearing capacity than the soil underlying that layer. The deployment of the rig was carried out on the basis of preliminary soil investigation report from the consultant on-board the geotechnical vessel deployed for soil investigation. The case is analysed and discussed. Computer program ‘MAHAJACK’ developed by the author for carrying out leg-penetration and punch-through analysis for foundation of jack-up rigs has been used for the analysis.