Numerical Study of Spudcan Penetration Induced Loading on an Adjacent Jacket Pile in Soft Clays

摘要

A mobile jackup is an important facility in offshore oil and gasdevelopment and often works in close proximity to a permanent jacketplatform. The unique operation method and foundation tip (spudcan)configurations of jackups have induced a number of geotechnicalchallenges. Among them, an important issue is that the spudcan willdisplace a large volume of soil during penetration and may inducesevere stresses on adjacent piles supporting the jacket platform. Thoughhaving general principals, the current industry code does not providedetailed guidance that engineers can follow specifically in practice toquantify this effect. Thus, a practical approach was developed in thispaper in which the complicated phenomenon was numerically solved intwo steps: Firstly, the soil displacement of free field around the spudcanwas numerically studied using the large deformation technology. Theinduced soil displacement was found heavily dependent on the soildeformation characteristics such as e_(50). Secondly, the conventionalbeam-column method using P-Y soil springs was adopted to computethe soil displacement induced loading on the jacket pile. On thecontrary, the induced pile loading was found not sensitive to thevariation of soil e_(50) within a reasonable range, provided that thematching P-Y curves to the soil displacement in free field are used inthe sequential analysis. The above approach was validated bycentrifugal experiment results published in the past. In addition, thepaper discussed how to set up an appropriate boundary condition at thepile head where the pile is connected with the jacket structures, andhow to combine the spudcan induced loading with the upstructuralloading to determine the ultimate status of a jacket pile. Both itemshave been neglected in the past study but may have profound effect onthe final results.