Effects of chemical composition on the solubility and geomechanical characteristics of gypsum rocks from Gachsaran Forma
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ORIGINAL PAPER
Effects of chemical composition on the solubility and geomechanical characteristics of gypsum rocks from Gachsaran Formation, Iran Morteza Hashemi 1 & Ali Saki 1 & Mohammad Reza Nikudel 2 Received: 26 September 2019 / Accepted: 27 March 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Evaporite rocks of the Gachsaran Formation make the reservoirs and foundations of several important dam site in southwest Iran. The solubility of these rocks is the main cause of instability and leakage problems usually observed in these dam sites. Therefore, investigation and consideration of engineering geological characteristics of these rocks, including their solubility, is crucial. In the present study, 10 gypsum rocks of the Gachsaran Formation were selected from Masjed-Soleyman, Haftkel, and Ramhormoz areas in southwest Iran. The chemical and mineralogical compositions of the samples were determined through optical microscopy, XRD, and XRF analyses. Different characteristics of samples including physical and mechanical properties, solubility, and solution rate were determined. Then, the effects of the chemical composition of gypsum rocks on geomechanical characteristics, solubility, and solution rate were assessed. Results showed that the proportion of two main gypsum components of CaO and SO3 and the CaO/SO3 ratio has a significant effect on gypsum strength and solubility. Also, an increase in the abundance of minor oxides of Al2O3, Fe2O3, SiO2, and K2O leads to a decrease in the solution rate. Keywords Gypsum rocks . Chemical composition . Solution rate constant . Gachsaran Formation
Introduction The Gachsaran Formation (hereafter GF), with an evaporitic lithology and Miocene age, is exposed extensively in southwest Iran (Gill and Ala 1972) (Fig. 1). In this region, GF forms the caprock of numerous oil fields (Bahadori et al. 2011; Mehrgini et al. 2016) and outcrops at the foundation and reservoir of many important dams including Gotvand (Barjasteh 2019), Seymareh (Koleini et al. 2012), Chamshir (TorabiKaveh et al. 2012), Khersan (Mehrgini et al. 2016), Marun (Fig. 2a), and Jarreh (Fig. 2b; Barjasteh and Rajabpoor 2000) dams. The occurrence of evaporite rocks in dam sites leads to some major problems such as leakage and instability problems. Furthermore, the dissolution of soluble rocks in the dam reservoir increases the salinity of the water, which imposes negative effects on the environment at downstream * Morteza Hashemi [email protected] 1
Department of Geology, Faculty of Sciences, University of Isfahan, Isfahan, Iran
2
Department of Engineering Geology, Faculty of Basic Sciences, Tarbiat Modares University, Tehran, Iran
(Chitsazan et al. 2012). Instabilities mainly include landslides, and mass movements occur in dam reservoirs upon impoundment due to the high plasticity and solubility of GF evaporite rocks (Fig. 2a; Bagha Dashtaki et al. 2010; Koleini et al. 2012). To avoid these problems, the evaporite rocks of GF have been widely studied from engineering geological,
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