Shear behavior of sand-smooth geomembrane interfaces through micro-topographical analysis

Quantitative measurement of induced surface changes in the geomembranes by sliding and plowing of sand particles during shear is highly beneficial for understanding the macro stress–strain response of non-dilative interface systems. This paper presents large scale direct shear and interface shear tests with a smooth geomembrane performed on sands of varying particle sizes and morphology at different normal stresses. Three sands of different particle sizes and same morphology and two sands of same size but dissimilar morphologies were used in the experiments to understand the individual effects of particle size and morphology on the interface shear behavior. The morphological properties of sands including roundness, sphericity and regularity were determined by image analysis. An advanced 3D optical profilometer was used for micro-topographical analysis of geomembrane surfaces before and after the test. Results from interface shear tests supported by surface roughness studies revealed that interface friction angle depends on the effective contacts formed on the surface of the geomembrane. Morphology of the sands was found to have major influence on the interface shear strength among all the parameters investigated. Increase in angularity of sand particles caused deeper grooves on the surface of the geomembrane, resulting in higher shear resistance at the interface. The shearing mechanism at the interface changed from sliding to sliding plus plowing beyond the critical normal stress of 53 kPa.