Stress-Displacement Response of Sand-Geosynthetic Interfaces under Different Volume Change Boundary Conditions

Volume change boundary conditions might dictate significant changes in normal stress and, accordingly, dramatically affect the stress-displacement response of soil-structure interfaces. Using a Norwegian Geotechnical Institute-type direct simple shear (NGI-DSS) apparatus, a series of tests covering a wide range for normal stiffness, initial normal stress, and sand relative density values was performed on interfaces between sand and two different types of geosynthetics. The experimental data presented indicate that the peak and ultimate shear strengths of the dense and medium-dense sand-geosynthetic interfaces increase as the initial normal stress and constant normal stiffness are increased. In contrast, the loose sand-geosynthetic interfaces exhibit a decrease in the peak and residual post-peak shear strengths with increasing normal stiffness because of the sand contraction. A state-dependent elastic-plastic constitutive model is found to capture the influence of various volume change boundary conditions on the mechanical behavior of sand-geosynthetic interfaces.