Mechanical Performance of PVC Pressure Pipes with a Bell-and-Spigot Joint
Water is a valuable resource for society, but it is not always used sustainably. In various cities across the globe, a great deal of water has been leaking from pipe networks, for example, due to corrosion-induced leakage, poor installation, and the distortion and opening of joints resulting from ground deformation. In recent years, PVC pipes have often been the choice for buried water mains. These pipes generally use gasketed bell-and-spigot joints to connect many segments into a watertight infrastructure. The presence of joints, however, presents a challenge to the ability of these structures to remain sealed when subjected to permanent ground settlements. This research project evaluates the leakage performance, deformations, and loads that develop across the joint of two segments of 150-mm-diameter DR-18 PVC pipes connected by a bell-and-spigot joint, when subject to permanent ground deformation. A Four-Point Bending apparatus was designed and used to determine the flexural rigidity (EI) of the PVC pipes, and two different apparatuses – the Split-box and the Joint Testing Frame – were used to produce controlled differential distortion of the pipe joint and barrels. One experiment, which simulated a buried PVC pipe subject to a normal ground fault (as a proxy for various kinds of permanent ground motion), was executed using the Split-box. While the pipe joint did not leak under internal water pressure of 1034 kPa, demands on the joint, the rotations and shear forces, were identified and quantified up to maxima of 0.95° and 14 kN respectively for maximum fault offset of 120 mm. A series of tests was then executed using the Joint Testing Frame, examining the joint in a commonly used PVC pipe product. The pipe samples were pressurized to internal water pressures of from 15 kPa to 400 kPa and then tested up to joint leakage or the deformation limits of the pipe or testing frame. Novel shear force versus rotation envelopes for leakage were developed for the pipe product. These envelopes reveal a range of water pressures and shear and rotation demands that induce joint leakage and permit the further understanding of why the buried pipe joint did not leak.