Digital image-based Performance evaluation of GCL-sand interfaces under repeated shearing

Inadequate shear strength mobilization at the interfaces results in translational failures in Geosynthetic Clay Liners (GCL). Periodic addition of solid waste into the landfill causes additional normal and shear stresses in GCLs. The mechanical response of GCLs is highly time dependent and over the time, the quality and strength of fibres of GCL deteriorate. Hence the interface shear resistance reduces under the application of repeated shear cycles. To simulate these conditions, a repeated interface shearing test was conceptualized in this study. A natural river sand and a manufactured sand of identical gradation were used in experiments to understand the effects of particle shape on interface shear strength variation under repeated shearing. Each GCL-sand interface was subjected to eight cycles of shearing in dry and hydrated conditions under three different static normal stresses. Results showed that the variation of the peak interface shear stress has different phases, governed by different mechanisms. Digital image analysis of tested GCL surfaces after each shearing cycle provided important clues for this response. Entrapment of sand particles into GCL surface is beneficial initially because of increased friction at the interface and this benefit is more pronounced in case of manufactured sand, due to the irregular shape of particles. After a few shearing cycles, the fibres of the GCL got ruptured due to repeated rubbing of sand particles, which reduced the shearing resistance. Quantification of sand particle entrapment and surface changes to GCL helped in understanding these micro-level interaction mechanisms.