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聽kPa for a minimum of 100 years under a normal stress of 50聽kPa at a field temperature of 30聽掳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.