On the behaviour of pipe-clamping mattresses to arrest pipeline walking

A novel solution to mitigate pipeline walking, namely the use of pipe-clamping mattresses(PCMs), was first developed for the Malampaya project. Comprising a hinged concrete structure designed to clamp onto a section of pipeline, and supporting (post-installed) ballast weight that is transferred directly to the pipeline, PCMs are potentially a highly efficient alternative to more traditional solutions such as rock dump or concrete mattresses. The original PCM geotechnical design was based primarily on analyses extrapolated from pipeline-seabed interaction, supported by a standard suite of classification and interface tests. Physical model testing was not performed. While observations (taken since installation) show that the PCMs have effectively mitigated pipeline walking in the seabed conditions at Malampaya, their performance in other soil types has not been investigated. To provide further evidence on the effectiveness of PCMs in other soils types, and investigate their performance over time, a series of centrifuge tests was performed in a soil sample representative of deep-water Gulf of Mexico conditions. In each test, a model representing the PCM was installed on the pipeline section, which was then subjected to cyclic axial displacement. Settlement of the pipeline-PCM system, as well as changes in axial resistance, were directly measured and are reported in this paper.