Numerical Investigation of the Capacity of Anchor Chain Links in Clay

Abstract

Offshore floating systems are held in position with chains that connect the floater to anchors embedded in the seabed. An essential component for calculating the overall mooring capacity is an accurate assessment of the holding resistance from the anchor chains. Existing studies generally simplify the (complex) chain geometry to that of a cylindrical bar, which does not account for the intricate geometry of the connected chain links. This paper reports on three-dimensional finite-element modeling that defined the capacity of a link of anchor chain in clay soil with consideration of the geometry of the chain links, including the influence from adjacent links. Both stud link and studless links were considered, along with the effect of embedment depth, link direction angle, and interface condition. The soil resistance acting on the chain links, represented by uniaxial bearing capacity factors Nn,max, Ns,max, and Nt,max along the normal, lateral, and axial directions of the chain link, respectively, were derived, and the soil failure mechanisms for these conditions are discussed. Equivalent bearing capacity factors Nq and Na were derived by converting the soil resistance to normal and tangential resistances (q and f) acting on an equivalent cylindrical bar. Ultimately, f/q was calculated to represent the friction coefficient, μ, which ranged from 0.2 to 0.4.