Method to Evaluate Effect of Spudcan Penetration on Adjacent Jacket Piles

Abstract

When a jack-up drilling rig operates near an adjacent jacket platform, the effect of the large-diameter spudcan penetration on adjacent platform piles should be evaluated if the spudcan-pile clearance is less than one spudcan diameter. In this study, a method is developed to calculate the response of a pile subjected to spudcan penetration-induced load and pile head load transmitted from upper structure. The spudcan penetration-induced lateral pile deflection is first determined by large deformation finite element calculation. The spudcan penetration-induced load along pile shaft is then determined by transforming the pile lateral deflection into equivalent nodal loads in a nonlinear foundation beam finite element model. The pile response is finally calculated using an isolated pile finite element model subjected to penetration-induced loads and pile head loads transmitted from the upper structure or an overall finite element model which includes the upper structure and piles. Centrifuge model tests under 50g condition are conducted to verify the validity of the proposed method. To further investigate the applicability of the proposed method, the effects of pile head constraint, lateral pile head load magnitude and its direction, spudcan-pile clearance and undrained shear strength are studied. The effect of spudcan penetration on an adjacent pile is found to increase with rotation stiffness at the pile head. Spudcan penetration affects the adjacent piles most when the lateral pile head load is facing back to the spudcan. The effect of spudcan penetration decreases significantly when the spudcan-pile clearance is larger than the diameter of the spudcan and decreases with increasing undrained shear strength. Furthermore, the spudcan penetration has more influence on the pile deflection than the bending moment.