Improving Gravel Material Specifications for Unpaved Roads: Australian Case Study

Abstract Gravel surfacing is a cost-effective approach for constructing roads in sparsely populated regions. However, maintaining the shape and usability of gravel roads requires regular upkeep to ensure road user safety. This study focuses on the significant gravel material specifications for wearing courses and highlights the findings of the Department of Transport and Main Roads (TMR) in Australia regarding the crucial role of material specifications in road maintenance routines. The Goondiwindi area in Queensland, featuring approximately 2000 km of gravel roads, serves as a case study for investigating the viability of granular stabilization techniques in enhancing re-sheeting materials for this network. In this research, gravel samples from ten gravel pits in the region were characterized through a range of tests, including particle-size distribution, Atterberg limit, California bearing ratio (CBR), and capillary rise. These laboratory investigations facilitated the development of a desktop analysis tool that predicts the engineering properties of gravel blends obtained from different pits. The validity of this analysis tool was assessed by comparing its results with comprehensive laboratory investigations of gravel samples and their blends. The verification process demonstrated that the results obtained from the desktop analysis tool aligned well with the test results. The study concludes that the analysis tool can effectively identify suitable gravel blends that meet target specifications, provided that the shrinkage product and CBR values of the parent pits are acceptable. The findings of this research can enhance confidence in designing gravel blends for wearing courses based on the properties of individual gravel pits, eliminating the need for additional testing on the gravel blends, and thus reducing costs.