Landslide-pipeline interaction for onshore slopes in silty sand
Onshore oil and gas pipelines are often routed through hazardous terrain owing to the need to traverse large distances and inevitably crosses large slopes and river valleys. A type of linear critical infrastructure, pipelines must be designed to withstand the soil forces created by landslides, among other geohazards. The quantification of soil forces on buried pipe, termed strain demand, can take the form of a simplified Winkler-beam style interaction, more commonly called soil-springs. Despite this simplified concept compared to more numerically intensive coupled continuum analysis, it is favored by industry. The previous work to quantify pipe-soil interaction has been limited to horizontal ground and does not consider the inclined slope acting in multiple directions, as soil is redistributed and shears past the pipe, as is the case for pipes intersecting landslides. Physical modelling utilizing a drum centrifuge was undertaken to recreate the environments where onshore landslides in granular soil occur. A model pipeline was constructed to match the structural stiffness of a real world pipeline. Novel instrumentation was employed to capture the full field pipe and soil strain, making use of a high-definition fiber optic sensing to capture the strain every 2.6 mm at model scale. Imaging technology was developed for use in a geotechnical centrifuge, including single board computers (Raspberry Pi). Twelve of these cameras were used to capture the subsurface soil strain and 3D photogrammetry of the slope surface. The resulting soil spring curves are both non-linear in space across the slope and in time, with varying behaviour of the soil structure interaction observed for pre-landslide phases during soil saturation. The SSI showed both a drained and undrained response through the landslides. Pipe designers and geohazard specialists should plan for both the permanent ground deformations typical of geohazards, but also the slower drained movement of slopes subjected to seasonal variation in climate-soil interaction.
centrifuge modelling, fiber-optic strain sensing, geohazards, geotechnical engineering, landslides, physical modelling, pipelines, raspberry pi, soil-structure interaction
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