Influence of water content on the strength and deformability of gypsum

Abstract

Strength and deformability characteristics of rock are very important parameters for rock classification and design of structures either upon or inside rock. In addition they are essential for judgment about their suitability for various construction purposes. Numerical and analytical methods in design approaches mainly require elastic and failure properties. Modulus of elasticity is vital because this parameter represents the pre-failure mechanical behavior of rock. Some rock is weakened by the addition of water, the effect being a chemical deterioration of the cement or clay binder. The harmful effect of water on different types of rock has been observed by many researchers [1–6]. Previous results have shown that up to 90% of the unconfined compressive strength can be lost at approximately one third of the saturation moisture content [3,8]. However, most of the analyses are qualitative descriptions based on laboratory observations rather than quantitative expressions. Meanwhile, although various hypotheses have been put forward such as fracture energy reduction, capillary tension decrease, frictional reduction, chemical and corrosive deterioration and effective stress decrease due to the pore pressure increase [7] in attempts to interpret the water effects, none of them provides a reliable and general quantitative measure of the problem [9]. Colback and Wild [3] reported 50% loss in unconfined compressive strength (UCS) from dry to saturated condition. Burshtein’s [10] study on the effect of water content on the strength and deformability characteristics of Russian sedimentary rocks such as quartz arenite and clay-rich sandstone indicated that a 50% loss in UCS of quartz arenite for water content change from 0 to 4%. However, approximately 1.5% change in water content caused a