| The objective of this study is to investigate the behavior of reinforced unpaved structure under cyclic load through laboratory testing, finite element and theoretical analyses. Main focus of research was on such behavior with degradation of aggregate base layer. Fourteen laboratory large-scale cyclic load plate tests were conducted on unpaved structure sections with two base course thicknesses and several geosynthetic reinforcements placed between base layer and subgrade. Results indicated that reinforcement improved stress distribution transferred to the subgrade, and decreased degradation of base course and surface deformation accumulation. Stiffer geogrids showed better stress attenuation effect and reduced plastic surface deformation as compared with lower modulus geogrids. Degradation was related to base layer thickness and base layer/geogrid interaction. The degradation and permanent surface deformation were correlated to geogrid torsional stiffness. Performance of geogrid-reinforced test sections was simulated using the FEM program ABAQUS. FEM results indicated that geogrid reinforcement can provide lateral confinement at the bottom of the base layer by improving interface shear resistance and increasing mean stress at the bottom of the base layer. The effect of geogrid reinforcement was also shown to reduce surface deformation, improve stress distribution on subgrade layer, and reduce strain induced at the bottom of the base layer due to lateral spread. As ABC thickness decreased, or the elastic modulus ratio decreased, the benefit due to geogrid reinforcement becomes more apparent. In general, geogrid with higher tensile modulus and better interface friction coefficient enhanced the reinforcement effects. A new unpaved road design model was developed on the basis of geogrid reinforcement mechanisms, degradation of base course, and mobilization of subgrade bearing capacity. Required base course thicknesses calculated using the proposed method compared favorably with results of the field tests reported by Fannin and Sigurdsson (1996). |
