Consolidation around partially embedded seabed pipelines

When a pipeline is laid on a soft clay seabed, excess pore pressure is generated. During the subsequent dissipation process, the effective stress at the pipe–soil interface and the available axial pipe–soil resistance rise. This ‘set-up' of axial resistance is an important consideration in various aspects of pipeline design, including the mitigation of thermal and pressure-induced expansion, the stability of the pipeline on sloping ground and the assessment of pipe–soil forces during installation. A set of finite-element analyses has been conducted to assess the pore pressure dissipation and consolidation beneath partially embedded seabed pipelines, extending existing solutions for strip footings. It is shown that the curved shape of a pipeline increases the normalised rate of consolidation compared with a strip footing. Dissipation curves for various levels of embedment are presented and the calculated response is shown to compare well with data from a field test conducted on a soft clay. The dissipation curves have been used to derive the development of effective contact force between the pipe and the seabed as consolidation progresses. These results highlight the significant enhancement of this force – and therefore the available axial resistance – that arises from a ‘wedging effect' related to the curvature of the pipe–soil contact surface. This wedging effect leads to a beneficial enhancement of the axial resistance.