Long-term internal shear strength of a reinforced GCL based on shear creep rupture tests

Abstract Clay geosynthetic barriers (GBR-C) – a synonym for geosynthetic clay liners (GCL) – used on steep slopes, e.g. landfill capping systems, have to withstand permanent shear forces over the long-term. Thermoplastic materials deform under static load. Creep and chemical ageing processes (e.g. oxidation) also influence the strength of the synthetic fibres over the long-term. The lifetime of these geosynthetics (GSY) is a very important issue as GBR-Cs have to demonstrate their long-term durability for more than 100 years in cases such as e.g. landfill capping systems in Germany. The long-term shear strength will be modelled by applying shear stress for long durations at elevated temperature (i.e. to accelerate ageing). In laboratory tests running up to 2 years on a stitch-bonded GBR-C in deionised (DI) water, specimens experienced internal rupture (i.e. rupture of fibres) at higher shear stress. Results showed the times to shear failure directly depend on the applied shear stress. Using the extrapolation of the regression line of times to shear creep rupture together with a lifetime prediction the applicable shear stress was found to 28 kPa for a minimum of 100 years under a normal stress of 50 kPa at a field temperature of 30 °C. Short-term tests cannot give the answer for any long-term behaviour of GBR-Cs. There is always the need for shear creep rupture tests. This new method determines the long-term shear strength of GBR-Cs for any lifetime.