Compressive Failure Mechanisms of Thermoplastic Pipeline Systems in Response to Seismically Representative Compressive Loading

As water distribution infrastructure ages, providers seek to improve water distribution systems’ ability to accommodate the significant ground deformations associated with earthquakes, fault rupture, landslides, liquefaction-induced lateral spreading, and other natural hazards. To address this susceptibility to damage from large ground movement, municipalities and design engineers are considering improved materials and jointing mechanisms, some of which have been seismically assessed through full-scale testing. This paper reports on a series of full-scale compressive loading tests performed on thermoplastic pipe at the University of Colorado Boulder’s Center for Infrastructure, Energy, and Space Testing. The full-scale compressive loading tests provide a framework for interpretation of experimental results through a seismic resiliency lens. The tests identify and interpret the pipeline’s axial response to, and failure mechanisms under, compressive loading when paired with various coupling types such as reinforced internal gaskets, external restraint systems, and traditional bell-spigot connections. Testing performed on 6-in. (150-mm) diameter iPVC (DR14) with varying coupling types is discussed and illustrates the axial response mechanisms of traditional continuous and segmented systems, as well as pipeline connections that exhibit combined behavior. Failure modes discussed include global/local buckling, joint telescoping, and bell fracturing, and are considered in the context of large ground deformation due to natural hazards. Displacement and strain measurements are employed to capture simulated pipeline response to ground movement parallel to the buried system as well as considerations for internal pressure build up due to axial loads. The presented failure modes provide guidance relative to an ongoing ASCE/UESI committee on seismic evaluation of pipeline systems as well as for seismically classifying axial response for the developing ASCE/UESI Manual of Practice (MOP) on Seismic Design of Water and Wastewater Pipelines. Procedures for interpreting experimental results and the implications for seismic design are discussed.