Shear Behavior of GMTC/BPC-GCL Interface Under Dry and Hydrated Conditions with Varying Polymer Content

Polymeric geosynthetics serve as fundamental components of engineered composite liners in waste containment facilities. The interface shear behavior between a coextruded textured geomembrane (GMTC) and a bentonite-polymer composite geosynthetic clay liner (BPC-GCL) was investigated under both dry and hydrated conditions, with varying polymer content (0%, 3.5%, and 5.5%), using large-scale direct shear tests. Hydration of BPC-GCL was found to significantly reduce GMTC/BPC-GCL interface shear strengths, with the magnitude of reduction increasing with normal stress. For the BPC-GCL with 3.5% polymer content, the peak strength at 400 kPa decreased by 36% from 272 kPa (dry) to 175 kPa (hydrated), which was attributed to bentonite softening and reduced frictional resistance. Polymer content non-linearly influenced shear behavior. At 400 kPa, the 3.5% BPC-GCL exhibited an 18% higher peak strength than the conventional GCL, while the 5.5% BPC-GCL showed a 9% reduction compared to the 3.5% specimen, attributed to internal structural damage and interfacial lubrication. Visual post-shear inspections revealed that dry conditions promoted interfacial friction-dominated failure, while hydration induced significant internal BPC-GCL damage, including fiber break and bentonite extrusion. The failure mode shifted with polymer content, and conventional GCL failed through internal bentonite deformation, while BPC-GCL exhibited a composite mechanism combining internal reinforcement and interfacial friction, with the 3.5% BPC-GCL demonstrating a more favorable composite effect than the 5.5% BPC-GCL. The study underscored the critical roles of hydration conditions and polymer modification in governing the shear mechanisms and strength at the GMTC/BPC-GCL interface.