Laboratory simulation of gypsum rock dissolution at different pressures, water-flow velocities and pH ranges

Abstract

Sulfate rocks, particularly gypsum rock as its most common near-surface form in the Earth's crust, are among the evaporitic rocks that due to their solubility can cause serious problems if they are present in the foundations and abutments of reservoir dams. To investigate the solubility of gypsum, gypsum blocks were taken from Gachsaran Formation outcrops located at a reservoir dam construction site in Iran. To perform the rock-dissolution experiments under pressure and water-flow conditions, a pneumatic–hydraulic pressure vessel with internal water circulation was designed and manufactured. Dissolution simulation experiments were performed at a constant temperature (25°C) and for a range of pressures, water-flow velocities and water acidities, the solution-rate constants for the experimental conditions considered. The results confirmed, first, that there are strong direct increasing relationships between pressure and the water-flow velocity with the solution-rate constant, while these relationships with increasing pH are reversed. Secondly, the values obtained from the rock-dissolution experiments under atmospheric conditions cannot be trusted as design parameters for dam foundation or abutments because the solution-rate constant values at the affected depth below reservoir dams can be several times higher than the surface value.