LAUSR

Abstract 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.