Perforation drilling for easing spudcan-footprint interaction issues

The interaction between a spudcan and an existing footprint is a major concern during jack-up rig installation. No guidelines were provided in the recently finalised version of ISO guidelines 19905-1 in regards to mitigating spudcan-footprint interaction issues except some proposed considerations due to scarce of detailed investigation. This paper reports a measure for easing spudcan-footprint interaction issues, with the efficiency of perforation drilling tested through model tests carried out at 1 g. The soil conditions tested simulate soft seabed strength profiles close to the mudline, varying the undrained shear strength. The most critical reinstallation locations of 0.5D and 1D (D=spudcan diameter) and existing footprint depth of 0.33D were investigated. The removal of soil (through perforation) inside the spudcan perimeter, with an area of 9% perforated, reduced the induced maximum moment, horizontal force, and horizontal sliding distance by up to 80%, 83%, and 76% respectively.