UNPAVED GEOSYNTHETIC-BUILT RESOURCE ACCESS ROADS - STIFFNESS RATHER THAN RUT DEPTH AS THE KEY DESIGN CRITERION

The economic significance of unpaved, resource access roads is enormous, contrary to widespread opinion, and their unique behaviour and requirements are in need of further study. It is pointed out that overall transportation costs and efficiencies are inextricably linked to the relationships between roads and vehicles. Because of the impact that road stiffness has on fuel consumption and therefore vehicle operating costs, it is contended that stiffness rather than permanent rut depth should be adopted as the key design criterion for resource access roads. In addition, carrying the rut depth criterion used in the design of sealed roads into the design of unsealed access roads is inappropriate, because for these roads, ruts can be eradicated by periodic maintenance operations. Because it is reasonable to expect that the stiffness of a low-standard access road structure could be significantly increased by the inclusion of a geogrid or geotextile, the range of road stiffness to be expected, and how it is affected by geosynthetic inclusions, was investigated by cycled-load testing of large-scale, model pavement structures, consisting of granular bases provided with various geosynthetics placed on peat subgrades. Surprisingly, the improvement in model pavement stiffness over that for the subgrade itself was not great.