Multi-scale pullout behaviour of strip anchor plates embedded in marine hydrate bearing sediments

Anchor plates are widely used in offshore platform infrastructure due to their great pullout bearing capacity. With the increasing extraction activities of oil and gas resources in sub-marine environments, strip anchor plates are likely to be embedded inside existing hydrate bearing sediments, which will inevitably change its pullout behaviour and bring hidden safety risks to the infrastructure. This paper establishes both DEM models and FEM models of the interaction between a strip anchor plate and the marine hydrate bearing sediments. The mechanical responses of the strip anchor plate subjected to vertical pullout loads are investigated under the conditions of different hydrate saturations and embedded depths. The failure modes obtained by both numerical methods are analyzed and discussed from both the macro and micro perspectives. The results show that the presence of hydrate significantly improves the pullout bearing capacity of the strip anchor plate. In the DEM simulations, the hydrate bearing sediment presents a brittle failure and develops shear bands which extend from both side-edges of the anchor plate to the ground. In the FEM simulations, hydrate bearing sediments are controlled by the ductile failure mode. The angle between the shear band and the vertical direction in the hydrate bearing sediment is controlled by the friction angle of the sediment.