Upper bound analysis of uplift capacity of a tapered plate anchor in cohesive soil

Abstract

Helical anchors are used widely onshore and have recently been mooted as an innovative foundation method for lightweight offshore structures. From structural considerations, as the load requirement for each plate on a helical anchor increases, it becomes necessary to increase the diameter ratio of the central shaft to the plate, and even to replace the flat helical plate by a tapered plate, thicker at the shaft than at the outer edge. This article presents a simple upper bound analysis for a tapered plate attached to a central shaft and embedded in clay, as a basis for enabling simple calculations for optimising the geometry and spacing of the plates for a helical anchor. The solutions are verified by comparison with existing analytical solutions for particular cases and against finite-element simulations. Parametric studies are provided to explore the effects of the interface friction ratio, the shaft–plate diameter ratio, and the taper angle of the plate.