Soil-pipe interaction studies leading to the evaluation of settlement of pipelines is not new. Nevertheless, pipeline failures still occur due to differential ground movements between a heavy yielding structure and a pipeline firmly connected to it. Such differential movements induce excessive stress concentrations in the pipeline. Plastics pipes fail as a consequence of such movements, though their flexibility can make them less vulnerable than rigid pipes. This paper presents two extreme case studies of failure; a 100mm diameter polyvinyl chloride (PVC) domestic sewer pipe and 2700mm diameter glass reinforced plastic (GRP) intake pipeline. By treating the pipelines as beams on elastic foundation, the magnitude and location of the maximum bending moments arising from yielding of the heavy structure can be determined. The provision of rocker pipe joints that entertain a permissible rotation helps to redistribute the bending moments to acceptable levels and thereby alleviate distress in the pipeline.

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