Theoretical analysis and model test for pipeline protection from dragged anchors

摘要

Submarine pipelines are exposed to the risk of damage from dragged anchors of ships that lose control during severe storms. Rock armor berms are commonly employed to protect the pipelines by deflecting the dragged anchors. Theoretical work and model tests are implemented in this study to understand the protection mechanism provided by rock berms. A limit equilibrium method is proposed to address the interaction between the dragged Hall anchor and the developed soil wedges. The total drag force on the anchor is obtained as the sum of the drag force on the anchor crown and that on the anchor fluke. Model tests are performed with three model anchors with different linear scales. The drag forces measured in the model tests agree well with those calculated by the theoretical approach. Results show that when the anchor is dragged into the rock armor berm from the soil foundation, an unbalanced moment is induced on the anchor; this moment causes the dragged anchor to rotate and the fluke tip to rise up. Such prediction and observations of behaviour may be helpful to berm designers.