Geotextile-reinforced unpaved roads: Model tests

Laboratory experiments were performed on soil-fabric-aggregate systems to evaluate the performance of an unpaved road reinforced with a geotextile. Because shear stress develops at the base of a gravel layer under a wheel load, interface characteristics (friction and stiffness) of the soil-fabric-aggregate system become important design parameters. Direct shear tests indicated that a nonwoven geotextile could develop an interface friction value similar to the gravel alone (42-45 degrees), while a slit film can show a friction angle 20% lower (about 34 degrees). Stiffness (k) in terms of shear stress/displacement response of the two geotextiles systems showed a contrasting behavior, with the slit film being stiffer (k(slit) ~ 6 kPa/mm and k(non) ~ 4 kPa/mm). From model tests on three gravel thicknesses (100 mm, 150mm and 200 mm), it was observed that both geotextiles provided some degree of reinforcement. In terms of rut depths, the nonwoven reinforced system with 100 mm (4 in.) of gravel was equivalent to the slit-film reinforced system with 150 mm (6 in.) of gravel and the unreinforced system with 200 mm (8 in.) of gravel. The bearing capacity factor (the ratio of maximum applied stress and shear strength) for the nonwoven reinforced models was approximately 1.5-2 times greater than the unreinforced models, in reasonable agreement with theory.