A gas leak at a residence caused an explosion. It was hypothesized that thesoil shrink/swell potential caused a break in the polyethylene (PE) gas pipe-couplerconnection, which subsequently resulted in a leak and an explosion. However, thisclaim was without any scientific reasoning or engineering principles such as soilstructureinteraction. Review of prior information indicated that sometime prior to theexplosion a water line was installed below the PE gas pipeline and a BOMAG multipurposecompactor was used to compact the backfill in the water pipe trench. Thewaterline and PE gas pipeline were perpendicular to each other.Using finite element method (FEM) analysis of the soil-pipe system and thescientific method using site-specific soil, geophysical, and geotechnical data it wasshown that the break in the PE pipeline and coupler was due to deformation(displacement) of the soils in the trench area, where the PE gas service line waspresent and not due to soil movement alone. This deformation is the result of externaland applied loads from the BOMAG compactor in the static and dynamic compactionmodes.A field re-creation of the construction sequence on a later date corroboratedvery similar pipe displacements as that predicted by the numerical modeling. Thisconfirmed the results from numerical modeling and confirmed that the constructionactivities during the installation of water service and/or sewer lines underneath thegas line caused the gas line to sag and pull out at the adjacent pipe-couplerconnection.
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