Engineers Australia

Equilibrium moisture content of volumetrically active clay earthworks in Queensland

B. G. Look


The water changes of volumetrically active clays result in movement of the overlying pavements and in a change in the subgrade strength. This adverse effect results in damage to roads and buildings, with over one-third of Queensland covered with such clays.

This paper discusses the equilibrium moisture content (EMC) operating range in southeast Queensland, and the philosophy behind the procedures for assessment and design on reactive clay earthworks. Two important considerations for wet environments with highly reactive clays are 1) the EMC is wet of the Optimum Moisture Content (OMC), and 2) the long-term density is below the Maximum Dry Density (MDD). If this placement condition is not targeted, then movements can be expected in the early years. This may result in damage to overlying structures irrespective of the design subgrade strength adopted. Targeting the OMC and MDD in such cases is building in future long term movement.

This EMC condition must be considered together with construction issues.