Water content is recognized as one of the most significant factors influencing rock mechanical properties, particularly ground water always presents a challenge to mining activities. To quantify such an effect, laboratory tests are commonly conducted by measuring the strength and stiffness of rocks, which have been immersed in water for various time durations. The results are typically reported in terms of the water content (mass of water divided by mass of solid) and saturated density as well as water absorption. The use of "water content", which represents the total amount of water absorbed by the rock specimen, is however difficult to assess and compare the water effect on various rock types associated with different water absorbing capabilities. Such representation is however less popular since a porosity measurement is also required. In addition, "water absorption" which is closely related to such two terms, is also usually given in laboratory studies. This article reviews the relevant terminologies and compiles some representative data sets available in the literature, attempting to address the relationship between the degree of saturation, water content, dry density, water absorption and effective porosity. The importance of properly defining the relevant terminologies is highlighted in this paper.
The water weakening effect on rock strength has been a hot research topic for decades (Obert et al. 1946; Colback & Wiid 1965; Simpson & Fergus 1968; Burshtein 1969; Hawkes & Mellor 1970; Bell et al. 1986; Ojo & Brook 1990; Koji 2001; Erguler & Ulusay 2009; Işık 2010). Although various empirical relations have been established to relate rock strength to the amount of water stored in the rock, no well-proven explanations are universally acceptable to account for such an influence of water on the strength of rock (Van Eeckhout 1976).