On the Behaviour of Pipe-Clamping Mattresses to Arrest Pipeline Walking-Paper

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The paper investigates pipe-clamping mattresses (PCMs), a concrete structure designed to clamp onto subsea pipelines and limit cumulative axial movement, or “pipeline walking.” Although PCMs have successfully stopped walking at the Malampaya project, their performance in other seabed soils—and the effects of settlement over time—had not been established.<br /><br />Researchers conducted five centrifuge tests at 30g using reconstituted deepwater Gulf of Mexico clay. Model pipelines were subjected to repeated axial movements, first without a PCM and then with a clamp and added log-mattress ballast. The tests examined changes in axial resistance, consolidation, and settlement, including whether settlement could cause the clamp to loosen.<br /><br />The PCM increased total axial restraint by more than tenfold compared with the pipeline alone. Resistance generally strengthened with cyclic loading and consolidation. However, excess pore pressure generated during PCM installation initially reduced friction; resistance increased as the pore pressure dissipated. Longer consolidation before cycling produced higher initial and overall friction.<br /><br />Substantial settlement occurred in the soft clay: pipe embedment exceeded one pipe diameter in every test and increased with PCM weight. Despite this, the researchers observed no relative axial slippage between the PCM and pipe and no evidence that the clamp unlocked. The findings indicate that PCMs can provide effective restraint in this soil, but their early-life performance depends strongly on installation-induced pore-pressure dissipation. Further testing and analysis, including work in other soil types, were ongoing.

Keywords

pipe-clamping mattresses

subsea pipelines

pipeline walking

axial restraint

deepwater Gulf of Mexico clay

centrifuge testing

consolidation

settlement

pore pressure dissipation

axial resistance