Browsing by Author "Durukan S."
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Item Determining the engineering properties of bentonite - Zeolite mixtures; [Bentonit - Zeolit karişimlarinin mühendislik özelliklerinin belirlenmesi](2006) Kaya A.; Durukan S.; Ören A.H.; Yükselen Y.In this study, bentonite-embedded zeolites with different bentonite content were developed for possible use as barrier material, as an alternative to bentonite-embedded sand. Cation exchange capacity (CEC) of Na-bentonite and zeolite; volumetric shrinkage, compaction characteristics; and hydraulic conductivity of the mixtures were investigated. Considering the zero adsorption capacity of sand, the practical implication of high CEC of zeolite is remarkable. Hydraulic conductivity tests on bentonite embedded zeolite with 10% and 20% bentonite content show that the hydraulic conductivity of both mixtures are less than 1*10 -9 m/s, which meets the common regulatory requirements. Moreover, the test results reveal that variations in hydraulic conductivity of the mixtures with different stress conditions are negligible for practical purposes.Item Suction characteristics of compacted zeolite-bentonite and sand-bentonite mixtures(2014) Durukan S.; Pulat H.F.; Yukselen-Aksoy Y.Soil suction is one of the most important parameters describing soil moisture conditions for unsaturated soils used in landfill liners. However, few studies have been conducted on the suction characteristics of compacted zeolite-bentonite mixtures (ZBMs) and sand-bentonite mixtures (SBMs), which are proposed for use as liner materials. Nevertheless, zeolite is known for its microporous skeleton containing cages and tunnels and it has a great physical affiliation to water uptake. Zeolite and bentonite, in a mixture, are thought to be in competition for water uptake and this may alter the distribution of water content for each soil in the mixture. The present study investigated the suction properties of compacted ZBMs and SBMs for varying mixing ratios and compaction water contents. The soil suction measurement technique chosen was the filter-paper method. The suction characteristics of powdered, granular, and block zeolites, as well as 0, 10, and 20% bentonite in ZBMs and SBMs were measured and compared with each other. Contaminated compacted ZBMs are compared with those of uncontaminated compacted ones at the optimum water content for the 10% and 20% mixtures. The results show that suction capacity of zeolite increases with grain size. As bentonite content increases, both matric and total suction increase for both mixtures. ZBMs have higher matric suction values than SBMs, but not total suction values. Contaminated total suction values are found to be higher than those of uncontaminated samples due to an increase in dissolved ion concentration. © The Author(s) 2014.Item Influence of compaction water content on the hydraulic conductivity of sandbentonite and zeolite-bentonite mixtures(Mineralogical Society, 2014) Ören A.H.; Durukan S.; Kayalar A.S.Although investigation of the hydraulic conductivity behaviour of zeolite-bentonite mixtures (ZBMs) has been a topic of interest for researchers recently, the influence of compaction water content on the hydraulic conductivity of ZBMs has not been studied so far. This study discusses the hydraulic conductivities of ZBMs and compares the results with those of sand-bentonite mixtures (SBMs). The hydraulic conductivities of SBMs were unaffected by compaction water content and bentonite content, but the hydraulic conductivities of ZBMs were substantially different in mixtures containing 10% and 20% bentonite. The hydraulic conductivity of 10% ZBM (i.e. containing 10% bentonite and 90% wt. zeolite) gradually decreased as the water content increased to optimum water content and then it tended to decrease rapidly when the water content exceeded the optimum. In contrast, the hydraulic conductivity of 20% ZBM sharply decreased at the early stages of compaction water content (i.e. on the dry side of optimum water content) and levelled off when the water content was at the optimum water content. However, there is at least one order of magnitude difference between the hydraulic conductivities of ZBMs and SBMs, supporting the zeolite network model as suggested in previous works. © 2014 The Mineralogical Society.Item Assessment and statistical evaluation of suction characteristics obtained via filter paper technique on zeolite–bentonite mixtures(Springer Verlag, 2017) Durukan S.; Akıncı G.Filter paper technique (FPT) is known to measure both matric and total suctions in a wide measurement range. However, it has many individual errors due to the uncertainty of calibration curve and sensitivity of the measurements to the temperature and relative humidity variations. Besides, the ASTM procedure for FPT does not specify any sample preparation and repetition for experiments. In this regard, this study covers the reliability of suction measurements using the FPT and its application on zeolite–bentonite mixtures (ZBMs), which were proposed for use of liner material in the literature. A calibration curve for Whatman No. 42 filter paper was constructed and compared to the other calibration curves given in the literature. Due to large scatter of calibration curves, total suction measurement is found to be inconvenient for suction values under 1000 kPa. An improvement in sample preparation and necessary minimum numbers of tests are also suggested. When preparing the test specimen, the compacted sample is recommended not to be cut but to be compacted separately as upper and lower parts where the contact filter paper to be placed in between in order to obtain good contact area to measure the matric suction accurately. The necessary minimum numbers of tests for ± 10% accuracy band in a confidence level of 95% for ASTM procedure on ZBMs are suggested. Repetitions were found to vary depending on the suction type and bentonite content. Repetitions of six and eight times are recommended for 10% ZBMs for matric and total suction measurements, respectively. Similarly, for 20% ZBMs the repetitions of six and ten times are found for matric and total suction measurements, respectively. In addition, the influence of index properties and compaction states on suction was also investigated. Matric suction values decrease from dry of optimum water content to the wet of optimum water content and approach to zero for higher water contents. The suction values are found to increase with decreasing water contents where the dry density and the void ratio were constant. On the other hand, for a given water content, matric suction values are found to be increasing with increasing dry densities, while the void ratio was decreasing being more evident at relatively higher saturation degrees. © 2017, Springer-Verlag GmbH Germany.Item Groundwater recharge estimation using HYDRUS 1D model in Alaşehir sub-basin of Gediz Basin in Turkey(Springer International Publishing, 2019) Tonkul S.; Baba A.; Şimşek C.; Durukan S.; Demirkesen A.C.; Tayfur G.Gediz Basin, located in the western part of Turkey constituting 2% land of the country, has an important groundwater potential in the area. Alasehir sub-basin, located in the southeast of the Gediz Basin and subject to the extensive withdrawal for the irrigation, constitutes the study area. Natural recharge to the sub-basin due to precipitation is numerically investigated in this study. For this purpose, 25 research wells, whose depths range from 20 to 50 m, were drilled to observe the recharge and collect the necessary field data for the numerical model. Meteorological data were collected from 3 weather stations installed in the study area. The numerical model HYDRUS was calibrated using the field water content data. Soil characterization was done on the core samples; the aquifer characterization was performed, and the alluvial aquifer recharge due to precipitation was calculated. As a result, the computed recharge value ranges from 21.78 to 68.52 mm, with an average value of 43.09 mm. According to the numerical model, this amount of recharge corresponds to 10% of the amount of annual rainfall. © 2019, Springer Nature Switzerland AG.Item Estimation groundwater total recharge and discharge using GIS-integrated water level fluctuation method: a case study from the Alaşehir alluvial aquifer Western Anatolia, Turkey(Springer, 2020) Şimşek C.; Demirkesen A.C.; Baba A.; Kumanlıoğlu A.; Durukan S.; Aksoy N.; Demirkıran Z.; Hasözbek A.; Murathan A.; Tayfur G.The estimation of groundwater recharge is an essential process for hydrogeological study. Realistic determination approach is crucial for assessing groundwater potential in an aquifer system and estimating of groundwater levels and/or changes in dry periods. Based on these matters, we employ a GIS-integrated groundwater level fluctuation method to determine the groundwater recharge for a hydrological period in the Alaşehir alluvial aquifer (W. Anatolia). The method basically takes into account both increasing and decreasing of the groundwater levels due to the recharge and discharge mechanisms in the aquifer. In this study, 16 pumping and monitoring wells were drilled with a total depth of 1300 m, and water level data loggers were installed into the monitoring wells to determine the groundwater level changes. The spatial distribution of the monthly groundwater level change map was multiplied by the aquifer storage distribution map and then the accurate water volume is calculated by using the 3-D spatial analysis. According to our evaluation in the aquifer, positive volume change of the groundwater is 187 hm3 in a year, which is considered as a recharge value of groundwater. It is concluded that the GIS-integrated water table fluctuation method gave rise to estimate the total recharge amount of the groundwater in the Alaşehir aquifer. The total groundwater recharge indicates that total inflow in the aquifer from precipitation, leakage from surface water and irrigation waters. It can be stated that the recharge estimation of groundwater in a surficial aquifer, like the Alaşehir aquifer, is fairly easy using the GIS-integrated water table fluctuation method. © 2020, Saudi Society for Geosciences.Item Influence of leachate percolation on two bentonitic mixtures(Springer Science and Business Media Deutschland GmbH, 2021) Durukan S.; Başarı E.This study investigates the response of leachate percolation in sand-bentonite and zeolite-bentonite mixtures for use of a liner. For this purpose, leachate sample was collected from Manisa Uzunburun landfill site, and flexible wall hydraulic conductivity tests were performed on these binary mixtures. During the study, the characterization of the leachate was done, pH and electrical conductivity values were measured, and chemical change in inlet and outlet samples was determined for varying pore volumes of flow. The hydraulic conductivity values were determined as 3 × 10−10 m/s and 7 × 10−11 m/s for sand-bentonite and zeolite-bentonite mixtures, respectively. The Ca+2 element showed a decrease in the outlet samples of sand-bentonite mixture test where an increase in zeolite-bentonite mixture outlet samples were measured showing that Ca+2 element was taken by sand-bentonite mixture and released by zeolite-bentonite mixture. Regarding the preliminary results, sand-bentonite mixture was found to be more successful to uptake Ca, Mg, Fe, and Mn where zeolite-bentonite mixture was more successful to uptake Ba, Ti, Cr, As, S, and Na when the permeant was Manisa Uzunburun leachate. Both soil mixtures hydraulic conductivities were found to be low enough to act as a liner; however, zeolite-bentonite mixture was found to be more successful when regarding the hydraulic conductivity and chemical stability. © 2021, Saudi Society for Geosciences.Item Performance of Sand Bentonite Mixtures Under Leachate Percolation(Springer Science and Business Media Deutschland GmbH, 2023) Ayvalık K.F.; Başarı E.; Durukan S.The permeability behavior of sand bentonite mixtures which were proposed for use of liner was investigated by using original leachate. In this regard, the 3-axial hydraulic conductivity tests were run while the chemical composition of the inlet and outlet leachate samples were identified. In addition, the adsorbed contaminants and the soil fabric of the mixtures were pictured via microscopic image technics. In literature, the conventional test procedures generally comprise the permeability values of the liner and/or filter materials which were determined by using tap water, this study suggested determining the hydraulic conductivities under the effect of leachate. Thus, leachate samples were taken from landfill sites located in Manisa Uzunburun municipal solid waste site. The pH of the environment for each test was found to be basic. The electrical conductivity values for each test were found to be under 1. This situation implies that the cation exchange process was not completed when the tests were ended. The hydraulic conductivity value of 10% sand-bentonite mixture sample was found to be higher when the inlet fluid was original leachate. When the inlet and outlet samples of leachates were investigated, it is found that sand-bentonite mixtures held Ca+2 while releasing Na+ which may be one of the main causes of the increase in hydraulic conductivity. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd 2023.Item Slope Stability Under Extreme Rainfall Conditions(Springer Science and Business Media Deutschland GmbH, 2023) Ayvalik K.F.; Durukan S.It is known that natural or cut slopes are usually unsaturated soils. A slope may lose its current stability because of the decrease in matric suction due to the increase in water content. One of the reasons that can cause an increase in water content is rainfall, which is an environmental issue. The failure of a natural and/or cut slope triggered by a rainfall may cause environmental disasters resulting in fatal loses and injuries as well as economic damages. This study covers the stability of natural slopes under extreme rainfall conditions. During the stability analysis, a numerical analysis program was used which utilizes finite difference formulations. The slope model used in the study was designed to represent a classical natural slope dimensions and two different soil types were selected to compare; both are silty soils but having different suction characteristics and hydraulic conductivities. Three rainfall intensities have been selected and the two were from the recorded past events. The first is a long-term precipitation with low intensity, and the second and the third ones are short-term intensive precipitations, and all the rainfall models were acted individually with the same antecedent saturation degree. The factor of safety values was calculated for each situation and compared as well. As a result of the analysis, it has been seen that slope stability analysis of the unsaturated soils are very depended on their suction characteristics and hydraulic conductivities even though they have similar mechanical properties. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd 2023.Item Evaluation of the Antecedent Saturation and Rainfall Conditions on the Slope Failure Mechanism Triggered by Rainfalls(Multidisciplinary Digital Publishing Institute (MDPI), 2024) Durukan S.The stability analysis of rainfall-induced slope failures considers a number of factors including the characteristics of the rainfall, vegetation, geometry of the slope, unsaturated soil characteristics, infiltration capacity, and saturation degree variations. Amongst all these factors, this study aims to investigate the effects of the antecedent rainfall and saturation conditions. A numerical modeling study was conducted using finite difference code software on a representative slope geometry with two different soil types. Two scenarios were followed: The first involved the application of three different rainfall intensities for varying initial saturation levels between 40% and 60%, representing the antecedent saturation conditions. The second scenario involved modeling successive rainfalls for a typical initial saturation degree of 50%. The impact of antecedent rainfall was assessed by determining the time required for failure during the application of a main extreme rainfall after a preceding rainfall of varying durations. Consequently, a zone of susceptible time for failure was suggested for use as a criterion in hazard management, allowing for the tracking of rainfall and its duration through the proposed chart for potential failures. Once the anticipated critical rainfall intensities have been determined through a meteorological analysis, a risk assessment for a specific slope can be conducted using the proposed practical procedure. Accordingly, a control mechanism may be established to detect the potential for a natural hazard. Furthermore, the proposed procedure was applied to a case study, whose modeling insights were in harmony with the real conditions of the slope failure. Thus, this demonstrated the significance of the antecedent conditions in modeling landslides triggered by rainfalls. © 2024 by the author.