A comparison of two design methods for unpaved roads reinforced with geogrids

Abstract

The design of geosynthetic-reinforced unpaved roads is based on a limit equilibrium analysis of bearing capacity at the ultimate limit state. Two semiempirical design methods are shown to be predicated on a common fundamental relation, but differ in the parameterization of input groups. Degradation of subgrade strength with repeated loading is well characterized by each design method and is believed to be of primary importance in obtaining good agreement between the result from analysis and the observed response to field trafficking. The two design methods were found to require different values for the undrained shear strength of the subgrade, which is partly attributed to the significantly different load spread angles used to model the effect of the base course. Selection of the initial undrained shear strength deserves careful consideration in sensitive soils. In order to use one of the design methods, it is important to select this value so that it is consistent with the other parameter groups being used.Key words: bearing capacity, geogrid, unpaved road.