Investigation of the vertical uplift capacity of deep water mudmats in clay

Subsea mudmats are used in deep water oil and gas fields to support seabed structures, such as pipelines, manifolds, and well heads. On soft soil, removing mudmats during maintenance or decommissioning may be difficult and costly due to the significant suction that develops at the mudmat-soil interface, considerably increasing the uplift resistance beyond the submerged self-weight of the mudmat. This paper describes a series of centrifuge tests performed to investigate the uplift resistance of plain mudmats resting on lightly overconsolidated clay. The model mudmat invert was instrumented with pore pressure transducers to monitor the suction developing at the mudmat invert at various uplift velocities, uplift eccentricities, and mudmat skirt lengths. The results show an increase in uplift resistance with pull-out velocity and the dominant role played by the uplift eccentricity in reducing suction at the mat invert. Simple predictive methods based on bearing capacity theory and combined loading interaction diagrams are provided.