Characterization and modeling of long-term stress-strain behavior of water confined pre-saturated gypsum rock in Kurdistan Region, Iraq

In order to understand the effects of soaking time and confined water pressure on the strength of rock due to dissolution of gypsum, rock samples with 96% of gypsum content collected from Kurdistan Region in northern Iraq were investigated. Laboratory tests were then performed on the normal gypsum rock samples under pre-saturated condition to obtain their uniaxial compressive strength (UCS) values. The pre-saturated samples were submerged in distilled water for 35 d, 70 d and 105 d, respectively, under confined water pressures of 0-0.5 MPa. The gypsum content decreased by 11% after 105 d of soaking under confined water pressure of 0.5 MPa. The UCS of the normal gypsum rock was 19.6 MPa and it decreased to 6.3 MPa and 2 MPa after 105 d of soaking under confined water pressures of 0 and 0.5 MPa, respectively. A nonlinear constitutive model was used to simulate the experimental stress-strain relationships of rock samples under various conditions. The constitutive model parameters were sensitive to the gypsum content.