Grain size effect on the anisotropic shear behavior of sand–textured geomembrane interface

A set of direct shear tests was conducted to investigate the effects of sand mean grain size and geomembrane surface roughness on the shear behaviour of the sand–geomembrane interface. Four types of sands with different mean grain sizes were used and the interfaces included a smooth geomembrane (SGM) and four textured ones with different asperity characteristics. The samples were prepared in a direct shear box at five sedimentation angles. The experimental results showed that the peak friction angle of the soil–textured geomembrane interface was dependent on the mean grain size, inherent anisotropy and surface roughness of the geomembrane. The shear strength of sand–textured geomembranes was two to three times larger than that of the sand–SGM interface. The peak and residual friction angles of sand-SGM interface occurred at sedimentation angle of 72° while it was 108° for sand-TGM interfaces. An increase in mean grain size increased the shear strength of the sand–textured geomembrane interface; while a reverse condition occurred for the sand–SGM interface. The shear strength occurred at larger horizontal displacement as mean particle size increased and the effect of relative roughness on peak friction angle increased with increase in mean grain size.