Experimental study of mechanical properties of gypsum soaked in brine

Gypsum, glauberite and mudstone are common interlayers in bedded salt deposits. During subterranean cavern development by leaching methods, they will be exposed to saline brines of different concentrations and temperatures over periods of time of at least 18–36 months. To investigate the relevant mechanical properties of gypsum under these conditions, a series of laboratory tests including uniaxial compression, tensile and shear strength was carried out. The soak time for gypsum in different brines was as long as 80 days, and its UCS strength is reduced to different extents with increases in brine concentration and temperature. The strength-weakening coefficient of wet gypsum can be as low as 0.1 after being soaked in saturated brine for 60 days. With increase of temperature and concentration of the soaking brine, the elastic modulus of the gypsum and the tensile strength decrease. The time-dependent mechanical weakening of wet gypsum is also documented. A damage parameter based on rigidity is defined to quantify gypsum deterioration; it drops from 704.4 GPa for dry gypsum to 19.5 GPa for wet gypsum soaked in saturated brine at 70 °C, and the failure style also changes from brittle to ductile. The mechanical properties of gypsum can be severely degraded by exposure to warm brine for long times, and consequently the study has significance for evaluation of interlayer stability and leakage security of storage caverns in bedded salt deposits.