Cyclic Shear Behavior of Co-Extruded Geomembrane–Geotextile Interfaces Under Horizontal Cyclic Loading

The cyclic shear behavior of geomembrane (GM)–geotextile (GT) interfaces is critical to the seismic stability and containment performance of composite bottom liners. This study quantified the cyclic shear behavior of co-extruded textured geomembrane (GMTC)–nonwoven geotextile (NWGT) interfaces through 27 large-scale horizontal cyclic shear tests conducted under normal stresses (σn) of 100, 200, and 400 kPa, displacement amplitudes (A) of 5, 10, and 20 mm, and shear frequencies (f) of 0.5, 1.0, and 2.0 Hz, with 60 loading cycles applied to each test. The results show that the cyclic shear response varied substantially with normal stress. At f = 0.5 Hz, peak cyclic shear resistance increased with normal stress, whereas the 60th-cycle strength-retention ratio generally decreased, indicating a larger relative difference between the maximum measured cyclic shear resistance and the 60th-cycle resistance under higher confinement conditions. The measured peak cyclic shear resistance varied with displacement amplitude in a normal-stress-dependent manner. At 100 kPa, the measured peak resistances at 5 and 10 mm were similar, with a higher value at 20 mm, whereas at 200 and 400 kPa, the values at 5 and 10 mm were similar and were lower at 20 mm. The fitted peak friction angles at 5 and 10 mm were similar and lower at 20 mm. The calculated cyclic secant stiffness decreased by approximately 30–35% after 60 cycles at f = 0.5 Hz. Under a normal stress of 400 kPa and a displacement amplitude of 5 mm, the measured peak cyclic shear resistance differed among the tested coupled frequency–velocity conditions. At σn = 400 kPa and A = 20 mm, post-test photographs showed different surface conditions among the tested coupled frequency–velocity conditions, including surface scratching, detached particles, and more pronounced fiber attachment at 2.0 Hz. The findings suggest that dynamic interface performance should be evaluated using not only peak cyclic shear resistance but also cyclic resistance degradation, stiffness reduction, damping evolution, and surface characteristics.