A knowledge of the mechanical properties of coal measure rocks is essential for strata control in coal mining operations, for example, in the maintenance of roadways and support at the coal face. And these properties are strongly influenced by water and moisture. Therefore, hygroscopicity is a fundamental factor in the experiments for studying the effect of water on the mechanical properties.
In this paper, the equilibrium water content when exposed to moist air and liquid water was measured for samples taken from four coal mines in Kyushu and Hokkaido. Also, specific surfaces and pore size distributions of these samples were measured and their correlation with the equilibrium water content was investigated.
The results of this study are summarized as follows;
1) The moisture adsorption isotherms are of BET type.
2) In some samples, water saturation of pores by water vapour adsorption at higher humidity is so high as to be more than 70% of the maximum saturation by sucking liquid water.
3) The equilibrium water content at lower humidity is proportional to the specific surface and pore volume corresponding to the radius ranging between 37.5 Å and 103 Å.