The shear strength of the soil-low permeability geomembrane interface, commonly used in the stability analysis of heap leach pads, is obtained based on large-scale direct shear laboratory tests, using rigid substrates in the lower box of the direct shear device. This paper presents a review of a large database of large-scale direct shear tests, performed on low permeability soils, from different mining projects in Peru, and LLDPE and HDPE geomembranes, of different thickness and texture, in most of which a clear non-linear trend of the shear strength envelope has been observed. This study compares the influence of the use of linear and non-linear envelopes on the stability of the heap leach pad, considering two real cases of shear strength envelopes and cases of different heap height. In addition, a discussion of the influence of high and low normal stresses on the shear strength of the interface is included, where the difference in this resistance is important when using a linear or non-linear envelope. The linear envelope could overestimate the interface strength and therefore the factor of safety in the stability analysis, especially when analyzing very high leach heaps (more than 150 m high), increasingly common in mining, where the vertical stress could be very high, much higher than the capacity of large-scale direct shear equipment. The shear strength of the low permeability soil-geomembrane interface, commonly used in stability analysis of leaching piles, is obtained from large-scale direct shear laboratory tests, using a rigid substrate in the lower box of the direct shear equipment. This study presents a review of the results of a large number of large-scale direct shear tests, performed on low permeability soil interfaces, from different mining projects in Peru, and LLDPE and HDPE geomembranes of different thickness and texture, in most of which a clear non-linear trend of the shear strength envelope has been observed.