Spudcan-pile interaction in thick soft clay and soft clay overlying sand: A simplified numerical solution

Abstract

A drilling jack-up is often deployed to perform drilling activities or well intervention at an existing fixed jacket platform. Depending on the clearance distance between the aft spudcan and the nearest pile, the installation of the spudcan may have an adverse effect on the platform pile which in turn could compromise the integrity of the jacket structure. This paper presents a simplified method for assessing the effect of spudcan installation on the pile foundation of a jacket platform in thick soft clay and soft clay overlying sand layers. Adopting a two-stage uncoupled approach, in which predetermined free-field lateral soil displacements are applied to a beam-column model with soil modelled using p-y curves, the soil displacements around a penetrating spudcan is estimated by an analytical solution derived from spherical cavity expansion theory. With appropriate consideration for the volume of soil displaced by the penetrating spudcan for the cases of thick soft clay and consideration for soil squeezing for soft clay overlying sand, the computed free-field lateral soil displacements are in fair agreement with the measured profiles in centrifuge tests and can be used in a beam-column model to estimate the induced bending moment in the pile in practice. The pile response to the free-field lateral soil displacements is assessed using a beam-column model incorporating p–y curves, considering the effect of soil remoulding caused by the installation of the spudcan where appropriate. A numerical model which considers the evolving lateral soil displacements due to the progressive advancement of the penetrating spudcan is also studied. The computed pile bending moment profiles are consistent with the measured profiles in the centrifuge tests and those computed by 3D large deformation finite element (LDFE) model. The proposed practical method is simple but yet effective to assess the influence of the installation of a spudcan foundation on an adjacent pile of a jacket platform in thick soft clay and soft clay overlying sand.