Abstract
In this study, the effects of soaking time and confining water pressure on the compressive and flexural strengths of rock due to the dissolution of gypsum content in rock samples with 96% gypsum (CaSO4·2H2O) content collected from northern Iraq (Kurdistan Region) were investigated. Experiments on compressive strength and flexural strength were performed on gypsum rock samples in normal and pre-saturated conditions. The pre-saturated samples were submerged in distilled water for 35, 70 and 105 d and subjected to confined pressures of 0–0·5 MPa. Thermogravimetric analyses showed a notable reduction in the weight of gypsum rock between 25 and 120°C. Also, the total weight loss at 800°C for the field rock sample was 7·53%. The weight loss of the gypsum rock increased with increasing soaking time and confining water pressure. The gypsum content decreased by 11% under a soaking time of 105 d and a confining water pressure of 0·5 MPa with respect to the natural samples. The compressive strength of the normal gypsum rock was 19·6 MPa, and it decreased by 68 and 90% after 105 d of soaking under confining water pressures of 0 and 0·5 MPa, respectively. The flexural strength of the normal gypsum rock was 10·8 MPa, and it decreased by 65 and 91% after 105 d of soaking under confining water pressures of 0 and 0·5 MPa, respectively. Two non-linear constitutive models were used to simulate the experimental stress–strain relationships in various conditions. The constitutive model parameters were sensitive to the gypsum content. Based on the methods of the coefficients of determination (R2) and root mean square errors, the non-linear constitutive model (Vipulanandan p–q model) predicted the stress–strain behaviour for the gypsum rock very well.
Highlights
Gypsum (CaSO4·2H2O) rocks cover more than 20% of the earth’s surface, with 7 million km2 covered by highly soluble gypsumbearing rocks (Dreybrodt et al, 2002)
■ GC decreased with increasing soaking time and confined water pressure
■ The compressive strength of gypsum rock decreased by 50 and 68% when the samples were subjected to 0·5 MPa of confined water pressure for 35 and 105 d, respectively
Summary
Gypsum (CaSO4·2H2O) rocks cover more than 20% of the earth’s surface, with 7 million km covered by highly soluble gypsumbearing rocks (Dreybrodt et al, 2002). Gypsum is a soluble mineral deposit resulting from evaporation of natural water. The influence of saturation on the compressive properties of gypsum rock has been considered by several research studies; usually with increasing soaking time (i.e. increasing degree of saturation), the strength of gypsum rock decreases (Heidari et al, 2012; Salih et al, 2015; Vásárhelyi and Ván, 2006). Water is suggested to be a significant factor influencing the stability and mechanical properties of gypsum rock (Dusseault, 2011; Mohammed and Mahmood, 2018a, 2018b; Salih et al, 2015). Among the various notable problems investigated by various research studies, gypsum rock can experience formation of karst features
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