Effect of underliner on the strain and puncture response of a bituminous geomembrane in heap leach applications

Experiments simulating a bituminous geomembrane (BGM)-lined heap leach pad were conducted to quantify the short-term punctures and gravel-induced tensile strains that could become locations of puncture in the long term. Vertical pressures ranging from 500 to 2000 kPa were examined with attention focused on the effect of the underliner soil type (i.e., subgrade) on the punctures and tensile strains induced in a 4.1 mm thick BGM by a given coarse overlying drainage layer. The examined underliners included predominately gravel, gravel-sand-silt mixtures (tills), silty sand, and compacted clay. It was found that gravel in the underliner and its gradation were the primary drivers of puncture and high strains with underliner gravel fractions as low as 30% (by weight) resulting in BGM puncture. It was also found that the 4.1 mm thick BGM developed substantially (10-fold) more punctures than a conventional 1.5 mm thick HDPE GMB under nominally identical test conditions. Using a stronger 4.8 mm thick BGM resulted in better performance; however, it still developed more holes than a 1.5 mm thick HDPE GMB signaling that BGMs can be more susceptible to static gravel puncture (despite being much thicker and heavier than HDPE GMBs). The importance of conducting cylinder performance tests using site-specific materials and anticipated stresses is demonstrated. The findings in this study, which represents the first extensive study into BGM puncture resistance, may have relevance to BGMs used in other bottom liner applications (not just heap leach pads).