Effect of Soil-Pile-Structure Interaction on Behaviour of Offshore Jacket Structure

Abstract

Offshore jacket structures are generally supported on pile foundations. Studies have evaluated the effect of soil-pile interaction on design of foundation; however, effect of soil-pile-structure interaction on behaviour of jacket structure has received little attention. Hence, present study focuses on understanding the influence of soil conditions, soil-pile interaction and foundation modeling approach on deformation characteristics and member forces of jacket structure. Linear static analysis on a typical 4-legged battered jacket structure is performed using STAAD Pro., subjected to dead/live loads and environmental loads. The water depth of 120 m and wave heights of 5 m, 10 m and 15 m are considered for this study. Morison’s equation considering Stokes 5th order wave theory is used for calculation of wave forces on jacket structure. The supports are modelled as skirted pile groups. The piles are represented by springs, with stiffness calculated using soil-pile interaction analysis. The soil conditions used in the study are varied for different compaction states of sand and different consistency states of clay and various parameters such as lateral/vertical deflection, support reactions, forces in leg, beams and bracings have been compared. It is concluded that ignoring soil-pile-structure interaction during analysis of jacket structure would underestimate the lateral/vertical deflections, support reactions, shear force and bending moment for leg, and axial forces in beam and plan bracing of the structure. No substantial impact of the interaction on other member forces is observed. Jacket structure founded on clayey soil exhibits higher deformation and member forces as compared to sand in general. The study is expected to help structural engineers in adopting an appropriate modelling approach, considering soil-pile-structure interaction, to obtain more realistic response for jacket structures.