Preliminary observations on soil moisture and 'dry' compaction in pavement design on the darling downs, Queensland

This paper describes the first stage of a long term investigation into the effects of pavement configuration and subgrade compaction and moisture on performance at a test site on the expansive clay soil on the darling downs, Queensland. Results suggest that the subgrade equilibrium moisture content will be considerably dryer than optimum moisture content for standard compaction. Where pavements are constructed on soil with a moisture content significantly higher than or lower than this equilibrium condition, distress due to volume change in the subgrade can be expected as moisture conditions move towards the equilibrium. Construction procedures which ensure that the soil is at its equilibrium condition will minimize this volume change provided precautions are taken to ensure the stability of the subgrade. The compactive effort, the type of construction adopted, and the maintenance of the sealed pavement and the shoulders have a large bearing on subgrade stability and therefore pavement performance (a).