The behavior of anchor lines embedded in layered soils

Abstract

The behavior of deepwater anchors in the seabed is significantly affected by the anchor lines embedded in soils, whether in anchor installation or in mooring. Unlike the anchor lines submerged in seawater, the ones embedded in soils exhibit special and complex behaviors due to soil resistance in either tension transmitting or profile properties of the lines. This problem becomes more complicated when encountering a complex seabed condition, such as the layered soils with both cohesive and cohesionless layers. Full knowledge of the anchor lines embedded in layered soils is imperative for anchor installation and safe operation of mooring systems. The literature review indicates that the relevant studies apply only to a single layer of either cohesive or cohesionless soil. This highlights the importance of the present study and also the challenge to deal with the problem in layered soils composed of both cohesive and cohesionless layers. In the present work, a mechanical model as well as analytical procedures is proposed to analyze the tension transmitting and profile properties of anchor lines embedded in layered soils. This model can well capture the complexity of seabed conditions, applying to not only the layered soils with both cohesive and cohesionless layers, but also the cohesive or cohesionless layers with different soil strengths. To gain further knowledge of the behavior of anchor lines embedded in layered soils, numerous cases of layered soils are designed and analyzed by the present model. The results indicate that, the configuration of the embedded anchor line presents complex and various reverse catenary shapes due to different strengths of layered soils; companying with increasing curvature of the reverse catenary configuration, both the tension loss and the tension angle at the shackle of the anchor increase with increasing proportion of cohesionless layers. These phenomena exhibit the complexity and variety of the behavior of anchor lines embedded in layered soils. A specific case of such problems can be efficiently solved by the present model to gain quantitative analytical results.