Effect of Surface Roughness on the Cyclic Shear Behavior of Sand-FRP Interface

Fiber-reinforced polymer (FRP) composites are attractive alternatives to conventional geotechnical structures exposed to aggressive environments, but their relatively low hardness makes the long-term response of sand-FRP interfaces sensitive to wear-induced roughness evolution. This study investigates the monotonic and cyclic shear behavior of dry sand against serrated FRP plates with nominal maximum surface roughness (Rmax) of 0, 0.2, 0.4 and 1.2 mm. Monotonic tests were performed at relative densities of 60% and 90%, while the dense specimens were subjected to 50 displacement-controlled cycles with a semi-amplitude of 2.5 mm under normal stresses of 200 and 400 kPa. A steel plate with Rmax of 0.2 mm provided a reference, and 3D optical scanning quantified surface evolution. Within the tested FRP surface series, configurations with larger nominal Rmax generally exhibited greater peak resistance, dilation and cyclic stiffness. Raising Rmax from 0 to 1.2 mm increased the peak interface friction angle by 76.6% and 88.4% for loose and dense sand, respectively. Rougher interfaces retained greater shear resistance but accumulated greater contraction and exhibited lower damping ratios. At the same nominal groove geometry, sand-FRP interface exhibited greater initial shear resistance than sand-steel interface, but abrasion reduced its retained resistance.