Estimation of drainability and its effect on the design moisture content of base course material

Climate, groundwater level, permeability and drainage conditions play a key role in the determination of the design moisture content of base course material in pavement design. Most of Western Australia (WA) has an arid or semi-arid climate. Therefore, moisture content close to the Optimum Moisture Content (OMC) is usually used for the Design Moisture Content (DMC) for sealed roads. In fact, moisture content is unlikely to be constant due to water penetration from surface failures or unusual water precipitation. Thus the material should have suitable drainability to be able to dissipate possible excess moisture content. The natural material for base course in WA can have a relatively high percentage of cohesive fines content (fraction smaller than 0.075 mm size) that limits drainability. In order to improve estimations of DMC, this paper presents a review of the drainability potential concept and its empirical estimation method. This is followed by the development of an analytical method of drainability potential estimation. The results of the drainability potential using the two methods, applied to common base course materials, are compared with their corresponding design moisture content, as required by material specifications in WA. This comparison provides information to allow a more accurate determination of DMC for the base course material.