Inverse catenary load attenuation along embedded ground chain of mooring lines

Abstract

The present paper presents an investigation of the static load attenuation emerging from the soil frictional forces acting on the embedded part of an anchor chain. Mooring line tension makes the embedded chain segment to develop an inverse catenary shape between the deep down point (DDP) and the padeye. Both the shape of the catenary and the mobilized frictional forces have significant influence on the total loading capacity of the anchoring system. The work is based on laboratory tests using a scale reduced model, designed to evaluate the catenary development and the load attenuation in respect to the installation depth, nominal chain angle and soil mechanical properties. As the experiments comprehend both loading and unloading cycles, the results provide a substantial database for confrontation of constitutive models for soil-chain interaction. In the literature, the usual assumption to relate frictional (F) and transversal (Q) forces in a catenary segment, ds, is a direct proportionality. However, present results indicate that such a simple relation is an oversimplification of a far more complex relation that cannot be accurately used for modeling the catenary development. Besides an hysteretic behavior, the mean relation F/Q presents a dependence on the undrained soil shear strength, su, also contradicting the usual assumption that F and Q are both linearly dependent on this parameter.