Numerical investigation and design of suction caisson for on-bottom pipelines under combined V-H-M-T loading in normal consolidated clay

Abstract

The length-to-diameter ratio of suction caisson used as the foundation of the pipeline system in deep-water oilfields in the South China Sea is usually between 1 and 2. Suction caisson will bear combined V-H-M-T loading, including vertical force, horizontal force, moment and torsion from the upper manifold structure during pipeline installation and operation. The failure envelopes equation is generally used for caisson design, but existing equations are mainly suitable for suction caissons under combined V-H-M loading. This study uses a finite element numerical investigation to study the combined V-H-M-T bearing capacity calculation method. The torsion influences on vertical force, horizontal force, moment bearing capacity and combined VHM bearing capacity are discussed. The results showed that the primary function of torsion is to share the tangential force around the cylinder wall, which causes the VHM composite envelope surface of the suction caisson to decrease. This impact is quantified through regression analysis of the calculation results. The design method of suction caisson for on-bottom pipelines under combined V-H-M-T loading in normal consolidated clay is summarized.