Numerical Analysis of Anchor Dragging Impact on Rock-Covered Pipeline Using CEL Method

Abstract

Abstract Subsea pipelines located in harbour areas and shipping lanes are subjected to potential damage due to impact of anchor dragging. Such pipelines are usually covered with rock berms for protection. Due to the high costs associated with the installation of offshore rock berms, there is a need to optimise the rock berm size such that the rock quantities are reduced while still providing adequate protection for the pipeline. Analysis of anchor dragging near a rock-covered pipeline involves quantifying the complex interaction between the anchor, the anchor chain, the soil and the pipeline-rock system. In the present study, Coupled Eulerian-Lagrangian (CEL) finite element method is used to simulate the complex soil deformation and flow during the anchor dragging, thereby providing better understanding of the underlying mechanisms of the problem. This paper presents results of CEL analyses of anchor dragging near a pipeline covered by rock berms of different sizes. The simulated trajectories of the anchor during the dragging are shown to be in good agreement with the experimental results of Gaudin et al. (2009). This shows the ability of the present method in giving more rigorous solutions and better predictions of rock berm protective capacities. This paper also illustrates the use of the present analysis for optimizing the rock berm design and hence enabling significant cost savings.