The response of 160-mm-diameter shallow-buried unplasticised polyvinylchloride pipes to surface loading has been investigated in full-scale experiments in a reinforced box. Standard installation and loading conditions were adopted. Measurements of pipe-wall strain and pipe deformation were taken to determine the influence of the surrounding soil on the mode of pipe deformation. The shape of the pipes when deformed varied with the stiffness of the soil at each level within the trench. Pipe deformation in soils offering little support was roughly elliptical, whereas in stiffer soil configurations the deformation deviated markedly from elliptical. In addition, the deviation from an ellipse was far more pronounced under static loading, subsequent cyclic loading causing an additive component of elliptical deformation. Four deformation modes have been isolated and data from other researchers have been included to confirm the observations. A clear relationship between pipe-wall strain and vertical diametral strain was found, indicating that inference of deformation from strain gauge measurements is possible if care is used. The assumption of elliptical pipe deformation in both theoretical and experimental work on flexible pipes should be avoided and allowance for significant deviations from an ellipse should be made in predictions of deformation measurement.
Abstract