An experimental study to evaluate scour mitigation options for pipe-clamping mattresses

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Pipe clamping mattresses (PCMs) are a relatively new solution to anchor pipelines against axial walking. They comprise a hinged concrete structure that clamps onto a section of the installed pipeline, with concrete ballast logs then placed on top to secure the clamping action and with 100% of the submerged weight of the PCM contributing to enhanced axial friction, they represent a highly efficient solution.  However, questions remain over how suitable they are when installed on an erodible seabed with scour potentially leaving long sections of pipe at the PCM location unsupported. Assessing this issue is the subject of the current paper, in which experiments undertaken in the Large O-Tube at The University of Western Australia were performed to first understand the risk, and then develop an effective mitigation solution. Testing was undertaken in three phases (i) an investigation into if/how scour resulted around PCMs when subjected to ambient current and storm conditions without any scour protection; (ii) experiments to evaluate the performance of various full protection systems placed around the PCMs; and (iii) further study of a falling apron type rock berm solution that allows an acceptable (and predictable) level of scour to develop. This paper presents a selection of the results from each phase of testing and summarises key observations / conclusions for application to future PCM installations.

5th International Symposium on Frontiers in Offshore Geotechnics (ISFOG2025)

15 - Mooring lines, Cables, Pipelines, Immersed tunnels and Risers