Researchers performed laboratory experiments on soil-fabric-aggregate systems to evaluate the effect of a geotextile on unpaved road performance. Direct shear tests performed on gravel indicated a 42-degree friction angle. Similar tests performed on soil-fabric-aggregate systems resulted in an interface friction value for the nonwoven geotextile system similar to that of the gravel alone. The slit film and heavy weight woven systems generated friction angles about 20 percent lower.
Observations of model tests showed that in terms of rut depths, the nonwoven performed better than the slit film woven geotextile for all gravel thickness', most likely because of the nonwoven's higher frictional characteristics. The rut diameters for the slit film and nonwoven reinforced systems tended to be larger than those observed for the unreinforced systems indicating an increased load-spread angle through the gravel. Based on rutting alone, the unreinforced model with 200 mm (8 in.) gravel was equivalent to that of the slit film in reinforced model with 150 mm (6 in.) gravel and the nonwoven model with 100 mm (4 in.) gravel. A so-called bearing capacity factor for the unreinforced models was approximately 50 percent less than the nonwoven reinforced models, in reasonable agreement with theory.