Numerical Study of Footprint Generation and Reinstallation of Jack-Up Footings

Abstract

Jack-up leg installation, extraction, and reinstallation near extraction-induced footprints are simulated using the coupled Eulerian-Lagrangian method with a strain-softening soil model. A typical footprint considering soil remolding is summarized based on 29 installation and extraction simulations. The reinstallation behavior of flat-base footings, spudcans, and skirted footings near extraction-induced and idealized conical or cylindrical footprints is compared. The horizontal force and bending moment induced by the footprint are explained in terms of predicted soil flow mechanisms and reaction loads acting on various footing surfaces. Considering soil remolding in a footprint, the results indicate that the soil on the near side of the footprint collapses earlier than that on the far side. The back flow soil on the near side of the footprint leads to obvious negative H loading on the footing leg. Two peaks in the M profile are observed. The first one is due to the footing touching the uneven seabed and the second is due to asynchronous collapse of the near-side and far-side walls of the footprint. The effects of the footing type and offset distance on the reinstallation behavior are discussed. The maximum values of H and M in both the positive and negative ranges during reinstallation are presented. Among the investigated footing types, the skirted footing has the greatest potential for mitigating the footing–footprint interaction problem because it provides the largest vertical resistance but induces the smallest horizontal forces and bending moments.