Performance of High-Density Polyethylene and Bituminous Geomembranes in Physically Aggressive Applications

Abstract

Two physically aggressive geomembrane (GMB) applications are examined along with two non-conventional geomembranes which have been proposed as solutions for them: (1) High-temperature formulated polyethylene GMBs for use in elevated temperature landfills and; (2) Bituminous geomembranes (BGMs) for use in heap leach mining which is a physically demanding application in terms of gravel puncture and strain. First, the durability of four HDPE geomembranes, each with a different formulation is examined in municipal solid waste leachate at a range of temperatures (40–95°C). Two were formulated for high temperatures and used polyethylene of raised temperature resistance (PE-RT) while two used conventional HDPE GMB formulations. Depletion of antioxidants and stabilizers was monitored using standard and high-pressure oxidative induction time (OIT) tests. All four GMBs had very high off-the-roll stress crack resistance (SCRo) that decreased to stable, more representative values shortly after immersion. The time to nominal failure (tNF) is predicted using Arrhenius modelling and the representative SCR values. Despite all four GMBs having similar tNF at constant elevated temperatures (65–95°C), it is shown that one of the PE-RT GMBs could have an extended life in situations like elevated temperature landfills where there is a time-temperature history to be accommodated by the GMB. Second, experiments simulating a BGM lined heap leach pad were conducted to quantify the short-term punctures and gravel-induced tensile strains. Vertical pressures ranging from 500 to 2,000 kPa were examined with attention focused on the effect of the underliner soil type (subgrade) on a 4.1-mm-thick BGM’s response when overlain by a coarse drainage layer. Two other BGMs and a conventional 1.5-mm HDPE GMB were also compared and the vulnerability of BGMs to static gravel puncture (despite being much thicker than HDPE GMBs) is shown. However, it was also observed that the puncturing gravel particles became embedded in the BGM raising the question of hydraulic significance. To investigate this, a series of leakage tests were conducted to examine this “plugging effect” and its relation to vertical stress magnitude, stress history, and liner head. Despite the plug effect retarding leakage through BGM punctures, two different failure mechanisms were identified.