Ciência e Natura ISSN: 0100-8307 [email protected] Universidade Federal de Santa Maria Brasil Ajam, Mohammad; Reza Sabour, Mohammad; Ali Dezvareh, Gorban Study of water salinity effect on geotechnical behavior of soil structure using response surface method (RSM), (Case study: Gotvand Dam) Ciência e Natura, vol. 37, núm. 6-1, 2015, pp. 350-359 Universidade Federal de Santa Maria Santa Maria, Brasil Available in: http://www.redalyc.org/articulo.oa?id=467547682041 How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative 350 Ciência eNatura, Santa Maria, v. 37 Part 1 2014, p. 350−359 ISSN impressa: 0100-8307 ISSN on-line: 2179-460X Study of water salinity effect on geotechnical behavior of soil structure using response surface method (RSM), (Case study: Gotvand Dam) Mohammad Ajam1, Mohammad Reza Sabour2, Gorban Ali Dezvareh3 1M.Sc. of Civil & Environmental Engineering, K.N.Toosi University of Technology, Tehran, Iran 2Associate Professor of Civil & Environmental Engineering Faculty, K.N.Toosi University of Technology, Tehran, Iran 3 Ph. D. Candidate of Civil & Environmental Engineering, K.N.Toosi University of Technology, Tehran, Iran Abstract Specifying the mechanical characteristics of soil is as one of the major steps in designing the foundation for civil projects, particularly hydraulic structures. This study examines the water salinity effect on engineering characteristics of fine-grained soil in clayey core of Gotvand dam which it is located on the Karun River in Khuzestan province, Iran. For this purpose, three types of salt; sodium chloride, magnesium chloride and calcium sulfate is considered that the last one has the highest concentration in the water of reservoir behind the dam, and then their effect on the mechanical characteristics of clay including density, Atterberg limits, angel of internal friction, adhesion and open inflation have examined. Therefore, treatments required for testing were provided by combining the mentioned salts considering the weight percentage of salt in the water behind the dam and designing a test using response surface methodology (RSM). The results were statistically analyzed by RSM. Results showed that type and amount of soil salinity has no significant impact on the compaction characteristics of soil namely optimum moisture content and the maximum dry density. Results of changes in Atterberg limits showed that presence of salt ions reduces the plasticity of the soil and it was seen a certain decrease in the liquid limit and subsequently a dramatic drop in soil plasticity by increasing the percentage of soil; while the plastic limit remained almost unchanged. Eventually, results of open inflation showed that whatever the salt concentration be higher, the rate of sample's open inflation will be lower. Kew words: Gotvand dam, Water salinity and soil open inflation, Density characteristics, Plasticity properties, RSM. Recebido: dia/mês/ano Aceito: dia/mês/ano 351 distance of 380 km from the outfall of the Karun 1 Introduction river, at the distance of 25 km from north of Shushtar city and at the distance of 10 km from Engineering characteristics of fine-grained soils northeast of Gotvand city in Khuzestan province. especially clayey soils are subject to several It is the last dam which can be constructed on the factors including density, porosity, structure, Karun River. This dam's lake has a reservoir of history of tension, granulation, amount and type 4.5 billion cubic meters which makes it the of clayey minerals, plastic property and amount second largest artificial lake in Iran after karkhe and kind of minerals in the pore water [1]. Any dam. The Gotvand dam is a rock fill dam with change in each of these characteristics will clay core and a height of 182 meters which change the physical and mechanical makes it the largest earthen dam of the country. characteristics of soil, and consequently Executive operations of this project have begun structures which are built on soil will exposed to in 1976. This dam is located more downstream change or threat. Density, shear strength and among the built dams and dams that are plasticity are considered as characteristics of soil currently under construction on the Karun River. engineering which play an important role in The salt domes and veins around the inundation designing foundation of most civil structures [2]. area of dam is one of the major challenges about Basically, theories of soil mechanic are based on the dam which it goes under water after the concept of effective stresses. In these theories inundation and leads to excessive salinity of the pore water and solid particles are both water in downstream of this dam. Experts of assumed to be chemically inert, so no chemical environment and engineering council believe interaction takes place between the different that closeness of salt mine and Gachsaran's salt phases. While, due to the negative charge on the formation to the site of the Upper Gotvand dam surface of clayey mineral particles, electro- is not considered in this research project. This chemical forces exist between the solid, liquid mine is located 5 km away from the dam and its and dissolved phases that they can mainly salt has been estimated hundreds of million tons. change the mechanical behavior of clayey soil During inundation and formation of the lake [3]. The quantity and nature of electro-chemical behind the dam, this mine has gone completely forces and consequently changes in properties of under water and caused that the salinity of soil depends on the amount and type of anion Karun River's water reaches to the highest and cation in exchange phase and their impact possible extent. The passage of time proved that on the cation exchange capacity [4]. inundation of this dam has led to the salinity of Any change in soil engineering properties can Karun River about 10 times. After the cause changes in the parameters used in construction operation and before beginning the designing soil structures, civil and water related inundation, constructors proceed to build a clay constructions and other structures' foundations. blanket on the salt formations. But, signs of So, determining the behavior and reaction of soil cracking were observed on clay blanket just three under the influence of solutions and different days after the edges of these blankets went materials can be effective in designing and under water. Investigating the water behind the making the correct decisions. Type of chemicals dam showed that the blankets had no effect on that are combined with clayey soil and also its reducing the amount of water salinity. Figure 1 constituents are considered as one of the shows an overview of the dam. important issues to understand changes in soil Considering the current situation, it seems that engineering properties [5]. the following problems are predictable in this This study has examined Gotvnd dam as the case dam: study. Upper Gotvand dam is one of Iran's 1. Extreme ruin and change in the quality largest dams which it is built on Karun River, of water in the dam's lake southwest of Iran. This dam is located at the Recebido: dia/mês/ano Aceito: dia/mês/ano 352 2. The instability of Gachsaran's formation strongly change against the sea water [10]. Rao and creating large landslides in the and Thyagaraj (2007) investigated the effect of dam's reservoir sodium chloride solution on inflation behavior of 3. The damaging effects of water salinity on compacted clayey soil by using consolidation test the dam's body in long-term [11]. Baumgartner et al. (2008) suggested that calcium chloride reduces the potential for inflation [12]. Olson and Mitronovas (1960) figured out that the electrolyte concentration has little effect on the Atterberg limits by examining the consolidation characteristics and shear strength of calcium and magnesium illites[13]. The study results from Kenny (1967) and Moore (1991) suggest that the resistance of remaining clays depends on the type of minerals and the chemical properties of pore water [14]. Chatopad haya (1972) measured the shear strength remaining from samples of Montmorillonite Figure 1: a view of Gotvand clays that had been affected by salt water and he showed that the remaining shear strength will This study investigates the damaging effects of rise by increasing the concentration of water [15]. water salinity on the dam's body and the clayey D Maio (1994) also finds similar results. D Maio lands around the lake, to investigate the conducted some tests on the liquid limit of possibility of slippage, by studying the impact of disturbed samples of Bentonite with NaC1 and pore water salinity on the mechanical properties he observed that liquid limit will decrease of clayey soil. rapidly by increasing the salt concentration [16]. Various researches have conducted scattered and Mashkouh (2011) examined the impact of salt diverse researches on investigating and and moisture on mechanical properties of clayey determining the effect of different salts and soil [17]. Abbasi (2013) also investigated the solutions on the engineering properties of clayey effect of pore water salinity on the consolidation soils. Lambe (1985) states that in a certain porous and compaction properties of clayey soil [18]. ratio, any change in the water-soil system that This study also investigates the effect of pore inflates the dual layer will reduce the resistance water salinity on some geotechnical [6]. Mitchell (1993) believes that in addition to characteristics of clayey soil by considering the the type and amount of clay in the soil, its abundant use of clayey soils in the foundations' chemical characteristics such as the amount and structures, due to the high compressibility, and type of anion and the existing cations have a also the main body of embankment dams and substantial impact on the physical and high level of water salinity in the vast areas of mechanical behavior of soil such as construction, the world, including Iran.