Mechanistic Analysis and Design Framework for Geosynthetic Stabilized Unpaved Roads

Geosynthetics provide mechanical stabilization benefits to paved or unpaved roads through lateral restraint of unbound aggregate particles and bearing capacity improvement over weak subgrades. The current state of the art incorporating geosynthetics into paved or unpaved road design involves conducting proper elastic layered system mechanistic analysis to determine the improvement of aggregate layer stiffness for increased traffic capacity or reduction in aggregate layer thickness. This paper presents a mechanistic analysis and design pipeline for determining the required aggregate thickness via the finite element (FE) modeling approach. An advanced FE analysis tool, C-FLEX, was employed to analyze axisymmetric multilayered unpaved road structures, accounting for the nonlinear stress-dependent behavior of unbound aggregates. The modulus enhancements were quantified for 10 different geosynthetics using the latest Bender Element sensor technology in both triaxial and large-scale tests conducted on typical dense-graded base aggregates. They were then incorporated into base course stiffness characterization via a sublayering approach for the unpaved road comprising aggregate base placed over soft subgrade. Both the measured enhanced moduli and the the extent of geosynthetic influence zones were adequately established in the sublayering approach. Further, sensitivity analysis was conducted for different aggregate modulus models and different sublayer structures, which verified the proposed design pipeline to provide satisfactory results. The method was also compared with the Giroud and Han method, which revealed the inherent difference in the two methods, given that the design here is based on the critical pavement responses and subgrade strength, while the Giroud and Han method also incorporated the field data with performance evaluation.