Shear strength of the geomembrane–subgrade interface in heap leaching applications

A series of large-scale direct shear tests was carried out to examine the effectiveness of smooth, textured and structured surface geomembranes (GMBs) with different soil subgrades for heap leach pad applications. Four different subgrades – namely, sand, two different coarse-grained underliners and a clayey soil representing the layers directly underlying the GMB liner in heap leach pads – were used to examine the shear strength of the GMB–subgrade interfaces at normal stresses between 50 and 1000 kPa. It was found that increasing the normal stresses can change the mechanisms contributing to the shear resistance at the interface. This resulted in a statistically insignificant increase in the interface friction of the GMB–granular soil interfaces when using GMBs with surface roughness relative to the interface friction of the smooth GMB. Furthermore, depending on the type of subgrade, establishing the shear envelopes over a wide range of normal stresses was found to overestimate or underestimate the shear strength at the field stresses even when linear regressions present the best fit for the data.