Stress Cracking Behavior of High Density Polyethylene Geomembrane Seams

W. J. Francey and R. Kerry Rowe                                                                                                                                                    GeoEngineering Centre at Queen’s-RMC, Department of Civil Engineering, Queen’s University, Kingston, Ontario, Canada

High density polyethylene (HDPE) geomembranes are used extensively in barrier systems for landfills and mining applications. Shipped as rolls these geomembranes require in-situ seaming to create a continuous barrier against liquid and gas migration. The most commonly employed seaming techniques for HDPE geomembranes include dual track wedge welding and extrusion welding, both of which subject overlapped sections of geomembrane sheet to high temperatures and molten polymer during seaming. Currently, a paucity of data exists on the effect of these seaming practices on the performance, both short and long-term, of the geomembrane barrier. Reports have indicated cracking failures at the heat affected zone (HAZ) for both dual track wedge welds and extrusions welds, prompting interest into the examination of a geomembrane’s susceptibility to stress cracking following seaming. Stress crack resistance (SCR) tests of HDPE seams conducted on un-notched specimens are reported. The craze formation and failures times for seams created at a sheet temperature of 21℃ with varying welding speed and welding temperature combinations are examined. High welding temperatures and the formation of “squeeze-out” during the seaming process are shown to significantly decrease the un-notched stress crack resistance SCR of HDPE geomembrane seams. In particular, the presence of discontinuities within the “squeeze-out” of dual track wedge welder seams has the potential to decrease the un-notched SCR of a seam to less than that of the notched SCR of the sheet. The results will aid in the identification of high cracking risk dual track HDPE geomembrane seams.