Mitigation Effect of Perforation Drilling on the Sliding Risk during Spudcan Installation Close to Footprints

Abstract

Perforation drilling is a promising technique to mitigate the sliding risk of jack-up units installed around footprints. Based on the coupled Eulerian−Lagrangian (CEL) method, a 1/2 finite element model, including a rigid Lagrangian spudcan and a Eulerian soil part, was established, and the contact interface was modelled with the Coulomb friction model. Validated against an indoor perforation test, the model was adopted to investigate the mitigation mechanism and effects of the borehole diameter, number, depth, and the drilling range. The simulations reveal that the mitigation efficiency increases with the borehole diameter, number, and depth. However, it shows little improvement if the borehole depth increases beyond double footprint depth. The semi-drilling at the outer side of the footprint is a little more effective than the full-drilling at both the inner and outer sides of the footprint. The present work emphasizes the effects of perforation drilling parameters on the mitigation efficiency, which are of great significance to guide the engineering practice and guarantee the safe operation of the jack-up reinstallation close to existing footprints.

Keywords

• perforation drilling
• jack-up unit
• footprint
• sliding risk
• coupled eulerian–lagrangian method