Water Retention Characteristics of Unsaturated Coal

This paper presents data on the water retention characteristic properties of some typical eastern Australian bituminous coals. "Soil water" characteristic curves, comprising wetting and drying paths, derived using filter-paper methods are presented and compared. The water retention properties of processed coal differ considerably from those of most soils, due primarily to the significant number of hydrophobic sites on coal particle surfaces. The properties of different coals are also found to vary widely, according to the rank or carbon content of the coal. In general, matric suctions in coal are very low for a large range in water content below saturation, and become significant only at water contents below about 50–70 percent of the saturated value. The difference between total and matric suctions is significant at all water contents, and it increases with reducing moisture content.