Deformation–Resistance Model for Geogrid-Reinforced Unpaved Road

Abstract

Unpaved road sections experience degradation and accumulation of plastic deformation under repeated loading. Geogrid placed between subgrade and aggregate base course (ABC) can improve section performance through several mechanisms and lead to reduction in stresses and plastic deformation. An unpaved road design model that includes provisions for mobilization of subgrade bearing capacity under axisymmetric condition is proposed. The model incorporates base course property, mobilization of subgrade bearing capacity with rutting, degradation of base course stress attenuation with cyclic load, and the effect of reinforcement inclusion. An elastic layer method has been used to back-analyze the vertical stresses on subgrade with data from previous cyclic plate load tests performed in the laboratory. The degradation of unpaved sections was expressed as a reduction in base course–subgrade elastic modulus ratio (E₁/E₂) with an increasing number of cycles or a decrease in stress distribution angle of base course. The proposed model has been validated by data from a field study. Computed base course thickness matched well with the test results, but further verification of the method based on field testing is needed before it is accepted as a viable design tool.