Pullout behaviour of plate anchor in clay with linearly increasing strength

Plate anchors are widely adopted to provide uplift resistance for structures. For most offshore seabeds, the undrained shear strength profile can be reasonably approximated as varying linearly with depth. At present, there are two possible approximate approaches to determine uplift capacity of a square plate anchor in such a profile, but the validity of both approaches cannot be ascertained due to unavailability of a rigorous solution. This study addresses these uncertainties by establishing the capacity factors for a square anchor in a linearly increasing strength profile using a three-dimensional large-deformation finite element approach for a wide range of geometric and material combinations. It was found that both approaches give the correct solution only under specific conditions. Earlier studies on the uplift capacity of a plate anchor typically follow a classical path of deriving the solution for a weightless soil and extending this solution to a soil with self-weight. The applicability of such an approach to the uplift of a square anchor is examined in this study. A direct design method for a square plate anchor embedded in a linearly increasing strength profile, which enables the capacity factors for a square anchor to be directly obtained without any simplified assumptions, is then proposed.