Micromechanical study of the uplift resistance of offshore rock berm protected pipelines

Offshore rock dumping in water depths up to 200m to create rockberms is routinely used in both the oil and gas and wind power sectors to provide protection and stability to products laid directly on the seabed, e.g. pipelines, umbilicals and cables. There are significant benefits to be gained from optimising the rockdump volumes used for these purposes including cost reduction, a reduction in the environmental impact on the seafloor and use of primary quarried materials. A key parameter in the design of the rockberms, particularly where they are being used to restrain the product on the seabed from buckling, is the uplift resistance provided by the rockdump. This paper considers the application of the discrete element method (DEM) to model the granular nature of rockdump materials and explores pipeline rock berm interaction to predict the uplift resistance. The non-spherical particle shapes used in the study are obtained through image analysis and laser scanning. The contact model is calibrated using, tilt table and interface testing and validated using angle of repose tests. A 3D DEM plane strain model is developed and the advantages/disadvantages in terms of model construction times and impact on the quality of the results are discussed. The predicted uplift resistance is then compared to physical model tests from the literature and analytical design methods.