GYPSUM AND LIMESTONE DISSOLUTION WITHIN FATHA FORMATION (MIDDLE MIOCENE) AT VARIOUS pH SOLUTIONS: A LABORATORY STUDY

The studied rocks (gypsum, limestone, & marl) of Middle Miocene Fatha Formation situated beneath the foundations of the study site in Mosul city. These rocks were obtained from four boreholes, at various depths up to 30 meters. The aim of work is to study the dissolution of rocks at various conditions, and then obtain the effect of the dissolution on their physio-mechanical properties, in addition, to amelioration our understanding of the consequences of the dissolution by acid-sulphate solution which is indisputably linked to sulphur oxidation. Gypsum and limestone rocks (10 samples of each type of rocks) and immersed in three solutions at various pH environmental conditions; acidic (0.0001N H2SO4), neutral (tap water), and alkaline (0.0001N NaOH) solutions. Chemical analysis results of specific elements (Ca2+, Mg2+, Na+, K+, S2-, Cl-) at the acidic, neutral, & alkaline solutions show that: The dissolution (concentration of Ca2+ & S2-) was higher in alkaline solution of gypsum rocks, while the dissolution (concentration of Ca2+) of the limestone rocks was higher in neutral (tap water) solution than other solutions. The physio-mechanical properties of gypsum and limestone rocks samples such as, bulk specific gravity, indirect tensile strength, and unconfined compressive strength were determined. The compressive strength of water-saturated samples of gypsum rocks decreased by 25.56% and of limestone by 23.97% when compared with the dry samples, but the indirect tensile strength of water-saturated samples of gypsum rocks decreased by 36.62% and of limestone by 36.34% compared with the dry samples.