Axial interaction between anchor chain and sand. Part II: Cyclic loading test

Abstract

Cyclic axial interaction between anchor chain and sand directly influences the tension variation of mooring line in service. In Part I (Rui et al., 2021a), a series of monotonic loading tests have been conducted, but the cyclic interaction between chain and sand is still unrevealed. This paper developed an element testing database of cyclic chain-sand interaction results. The influences of cyclic amplitude, confining stress, chain nominal diameter, sand particle size and relative density on cyclic interaction were thoroughly investigated. It is found that the axial resistances in post-cyclic loading tests are always higher than the monotonic results. Cyclic amplitude has a significant influence on the chain-sand cyclic interaction. When cyclic displacement is less than half of the chain nominal diameter (db), the axial resistance gradually stabilizes after a few cycles. But when cyclic displacement is larger than db, the axial resistance shows an increasing trend due to the particle breakage, and stabilizes when the sand particle size distribution remains unchanged. A type of adjustment plateau with small constant axial resistance appears between unloading and reloading phases in chain-sand cyclic interaction curves. Stress release behind the chain link due to “soil arching” effect can explain the appearance of adjustment plateau.