Browsing by Author "Yukselen-Aksoy, Y"

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    Seawater effect on consistency limits and compressibility characteristics of clays
    Yukselen-Aksoy, Y; Kaya, A; Ören, AH
    The reported results in the literature indicate that there is a discrepancy regarding seawater effect on the consistency limits and compressibility properties of clayey soils having relatively low and high plasticity. To clarify this discrepancy, consistency limits including liquid, plastic and shrinkage limits, sediment volume and compressibility characteristics of ten soils were tested using distilled water and natural seawater from the Aegean Sea. The results indicate that the effect of seawater is negligible on the tested consistency limits and compressibility characteristics of soils when they have liquid limits up to 110%. The seawater effect is most noticed on the consistency limits and compressibility of Na-bentonites. The results of previous research were compiled and compared with those obtained in this study. All reported data were normalized by dividing the index values obtained using seawater by those obtained using distilled water. The comparison of data indicate that the compiled data and present study data are in good agreement, i.e. when the normalized values are plotted as function of liquid limit, all index properties plot along the unity line until the liquid limit of soils is about 110%; then, the normalized index values decrease almost linearly with liquid limit. (C) 2008 Elsevier B.V. All rights reserved.
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    The Use of Neural Networks for the Prediction of Zeta Potential of Kaolinite
    Erzin, Y; Yukselen-Aksoy, Y
    The sign and the magnitude of the zeta potential must be known for many engineering applications. For clay soils, it is usually negative, but it is strongly dependent on the pore fluid chemistry. However, measurement of zeta potential time is time-consuming and requires special and expensive equipment. In this study, the prediction of zeta potential of kaolinite has been investigated by artificial neural networks (ANNs) and multiple regression analyses (MRAs). To achieve this, ANN and MRA models based on zeta potential measurements of kaolinite in the presence of salt and heavy metal cations at different pH values have been developed. The results of the models were compared with the experimental results. The performance indices, including coefficient of determination, root mean square error, mean absolute error, and variance, were used to assess the performance of the prediction capacity of the models developed in this study. The obtained indices make it clear that the constructed ANN models were able to predict zeta potential of kaolinite quite efficiently and outperformed the MRA models. Results showed that ANN models can be used satisfactorily to predict zeta potential of kaolinite as a rapid inexpensive substitute for laboratory techniques.
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    Artificial neural networks approach for ζ potential of Montmorillonite in the presence of different cations
    Yukselen-Aksoy, Y; Erzin, Y
    In this study, the zeta potential of montmorillonite in the presence of different chemical solutions was modeled by means of artificial neural networks (ANNs). Zeta potential of the montmorillonite was measured in the presence of salt cations, Na+, Li+ and Ca2+ and metals Zn2+, Pb2+, Cu2+, and Al3+ at different pH values, and observed values pointed to a different behavior for this mineral in the presence of salt and heavy metal cations. Artificial neural networks were successfully developed for the prediction of the zeta potential of montmorillonite in the presence of salt and heavy metal cations at different pH values and ionic strengths. Resulting zeta potential of montmorillonite shows different behavior in the presence of salt and heavy metal cations, and two ANN models were developed in order to be compared with experimental results. The ANNs results were found to be close to experimentally measured zeta potential values. The performance indices such as coefficient of determination, root mean square error, mean absolute error, and variance account for were used to control the performance of the prediction capacity of the models developed in this study. These indices obtained make it clear that the predictive models constructed are quite powerful. The constructed ANN models exhibited a high performance according to the performance indices. This performance has also shown that the ANNs seem to be a useful tool to minimize the uncertainties encountered during the soil engineering projects. For this reason, the use of ANNs may provide new approaches and methodologies.
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    The effect of soil mineralogy and pore fluid chemistry on the suction and swelling behavior of soils
    Pulat, HF; Yukselen-Aksoy, Y; Egeli, I
    Soil suction is one of the most important parameters for describing the moisture condition and engineering behavior of unsaturated soils. Therefore, changes in suction behavior of soils in the presence of saline waters are important for engineered barriers. The aim of this study was to determine the change in suction and swelling behavior of soils, which were exposed to salt solutions (NaCl, CaCl2, natural seawater) with respect to distilled water. The three soil samples were gathered with different mineralogy and plasticity characteristics and tested for determining matric and total suction values and for obtaining free swelling characteristics in the presence of salt solutions. The bentonitic soil sample had the highest total suction value in the presence of seawater. Kaolinitic and zeolitic soil samples had the highest total suction values in the presence of NaCl solution. The highest modified free swell index value of the samples was obtained in the presence of NaCl solution for all the soil samples. No relationship was found between the total suction, matric suction and the modified free swell index value of the tested soils.
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    Developing cation exchange capacity and soil index properties relationships using a neuro-fuzzy approach
    Pulat, HF; Tayfur, G; Yukselen-Aksoy, Y
    Artificial intelligence methods are employed to predict cation exchange capacity (CEC) from five different soil index properties, namely specific surface area (SSA), liquid limit, plasticity index, activity (ACT), and clay fraction (CF). Artificial neural networks (ANNs) analyses were first employed to determine the most related index parameters with cation exchange capacity. For this purpose, 40 datasets were employed to train the network and 10 datasets were used to test it. The ANN analyses were conducted with 15 different input vector combinations using same datasets. As a result of this investigation, the ANN analyses revealed that SSA and ACT are the most effective parameters on the CEC. Next, based upon these most effective input parameters, the fuzzy logic (FL) model was developed for the CEC. In the developed FL model, triangular membership functions were employed for both the input (SSA and ACT) variables and the output variable (CEC). A total of nine Mamdani fuzzy rules were deduced from the datasets, used for the training of the ANN model. Minimization (min) inferencing, maximum (max) composition, and centroid defuzzification methods are employed for the constructed FL model. The developed FL model was then tested against the remaining datasets, which were also used for testing the ANN model. The prediction results are satisfactory with a determination coefficient, R (2) = 0.94 and mean absolute error, (MAE) = 7.1.
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    Influence of Seawater on the Suction and Swelling Behavior of Clayey Soils
    Pulat, HF; Yukselen-Aksoy, Y
    The present study examines the suction characteristics and swelling behavior of clayey soils when exposed to natural seawater with respect to distilled water. The effects of saline waters on the engineering behavior of soils need to be determined since the salinity of the pore fluid of soils near coastal areas increases continuously. Six clayey soil samples with different mineralogy and characteristics were gathered and tested to determine the suction and swelling characteristics in the presence of natural seawater and distilled water. The results show that the total suction values of the samples are higher in the presence of seawater than in distilled water. The samples with high swelling potential have lower matric suction values than nonswelling soils. Moreover, in contrast to swelling-type soils, the matric suction values of the nonswelling soils remain similar in the presence both distilled water and seawater. The modified free swell index (MFSI) of the samples is well correlated with the liquid limit (LL), plasticity index (PI), and cation exchange capacity (CEC) in distilled water. However, coefficients of determination decreased in the presence of seawater. Also, there is no significant correlation existing between total and matric suction values and the MFSI values of the samples.
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    Electrokinetic Delivery and Activation of Persulfate for Oxidation of PCBs in Clayey Soils
    Yukselen-Aksoy, Y; Reddy, KR
    Contamination of soils by polychlorobiphenyls (PCBs) is of environmental concern because of their toxicity, persistence, hydrophobic nature, and slow biodegradation potential. Among the PCB remedial technologies, direct oxidation by persulfate is considered to have great potential to be both simple and rapid. However, to produce faster reaction rates, persulfate is often activated using heat, metal chelates, hydrogen peroxide, or high pH. Furthermore, delivery of persulfate in low permeability clayey soils is difficult. Integrating electrokinetic remediation with persulfate has the potential to overcome such difficulties because the applied electric potential can facilitate the delivery of persulfate in low permeability soils as well as activate oxidizing radicals and simultaneously induce oxidative/reductive reactions directly in the soil. This study investigates the potential for in situ oxidation of PCBs in low permeability soils using persulfate as an oxidant and also evaluates the benefits of integrating oxidation with electrokinetic remediation. Several series of laboratory batch and bench-scale electrokinetic experiments were conducted using kaolin, a representative clayey soil, spiked with 50 mg/kg of 2,2',3,5' tetrachlorobiphenyl (PCB 44), a representative PCB. Persulfate oxidation activators [elevated temperature (45 degrees C) and high pH (at the cathode)] were investigated to maximize the PCB degradation. In addition, the effect of oxidant dosage on PCB degradation was investigated. The electrokinetically enhanced temperature-only activated persulfate oxidation test resulted in better PCB 44 remediation (77.9%) than the temperature and high-pH activated persulfate oxidation (76.2%) in a 7-day period. The optimal dosage for effective remediation was 30% Na-persulfate (76.2%) because a 20% concentration of the oxidant yielded a lower rate of degradation (55.2%) of PCB 44. The results are encouraging for the use of electrokinetically enhanced persulfate oxidation for the effective remediation of PCBs in soils. DOI: 10.1061/(ASCE)GT.1943-5606.0000744. (C) 2013 American Society of Civil Engineers.
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    Destruction of PCB 44 in Spiked Subsurface Soils Using Activated Persulfate Oxidation
    Yukselen-Aksoy, Y; Khodadoust, AP; Reddy, KR
    The effectiveness of persulfate oxidation for the destruction of tetrachlorobiphenyl a representative polychlorobiphenyl (PCB), in spiked subsurface soils was evaluated in this study. Kaolin and glacial till soils were selected as representative low permeability soils; both soils were spiked with 50 mg PCB per dry kilogram of soil. Activation of persulfate oxidation was necessary to achieve effective destruction of PCBs in soils. As persulfate oxidation activators, temperature and high pH were used in order to maximize PCB destruction. In addition, the effect of oxidant dose and reaction time was investigated. The optimal dose for persulfate was found to be 30% for maximum oxidation. The persulfate activation with temperature of 45A degrees C was superior to persulfate activation with high pH (pH 12), where higher PCB destructions were observed for kaolin and glacial till soils. PCB destruction increased with reaction time, where maximum degradation was achieved after 7 days. The highest PCB destruction was achieved with temperature activation at 45A degrees C using a dosage of 30% persulfate at pH 12 for kaolin and glacial till soils after 7 days.
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    Investigation of the biopolymer additives effect on permeability and shear strength of clayey and sandy soils
    Pulat, HF; Taytak, B; Yukselen-Aksoy, Y
    Many methods are used to improve the engineering properties of the soils. While the some of the developed methods cannot produce an effective solution, some of them are not economical for practical solution. In this study, permeability and shear strength behaviors of natural kaolin, bentonite and sand mixtures have been investigated in the presence of three different biopolymers (xanthan gum, chitosan and chitin) and different concentrations (0.25-0.50-0.75 and 1%). The results have shown that, the xanthan gum and chitosan addition decreased the permeability coefficient almost 30 hold. While the biopolymer effect on shear strength behavior is investigated, 1% xanthan gum and chitosan concentration addition provided 15-10% increase in angle of internal friction. The obtained test results have shown that, biopolymers can be used in dams and landfills at impermeable clay liner applications.
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    Specific surface area effect on compressibility behaviour of clayey soils
    Yukselen-Aksoy, Y; Kaya, A
    In this study, the effect of specific surface area on compressibility and permeability characteristics of remoulded and intact clayey soils was investigated. Fifteen remoulded and 15 intact soils with a wide range of physicochemical properties were tested. The results indicate that specific surface area has a significant effect on compressibility and permeability behaviour of clayey soils. In addition to other soil index properties, specific surface area can be used for estimating these engineering properties. Significantly high correlation coefficient (r = 0.97) between compression index (C-c) and the specific surface area is observed for remoulded clayey soils with only methylene blue-spot specific surface area. There is no significant correlation between the BET-N-2 specific surface area and C-c: The effect of the remoulded water content on proposed specific surface area and C-c relationship is also investigated. The results show that as specific surface area of soils increases, c(v) decreases, indicating the importance of the diffuse double layer on the consolidation process. The results also reveal that permeability is controlled by the specific surface area of soils. In addition, the data obtained in this study indicate that there is a linear correlation between C-c/n(0) and C-c, which indicates the significance of initial void ratio on the compressibility characteristics of soils.
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    A study of factors affecting on the zeta potential of kaolinite and quartz powder
    Yukselen-Aksoy, Y; Kaya, A
    The purpose of this study was to determine the effects of pH, ion type (salt and metal cations), ionic strength, cation valence, hydrated ionic radius, and solid concentration on the zeta potential of kaolinite and quartz powder in the presence of NaCl, KCl, CaCl2, CuCl2, BaCl2, and AlCl3 solutions. The kaolinite and quartz powder have no isoelectric point (iep) within the entire pH range (3 < pH < 11). In the presence of hydrolysable metal ions, kaolinite and quartz powder have two ieps. As the cationic valence increases, the zeta potential of kaolinite and quartz powder becomes less negative. Monovalent cation, K+, yields more negative zeta potential values than the divalent cation Ba2+. As concentration of solid increases, the zeta potential of the minerals becomes more positive under acidic conditions; however, under alkaline conditions as solid concentration increases the zeta potential becomes more negative. Hydrated ionic radius also affects the zeta potential; the larger the ion, the thicker the layer and the more negative zeta potential for both kaolinite and quartz powder.
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    Ageing effect on compressibility, permeability and shear strength of clayey soils exposed to salt solutions
    Çakar, E; Yukselen-Aksoy, Y
    The present study investigated the ageing effect on compressibility, permeability and shear strength behavior of kaolin and bentonite samples in the presence of NaCl and CaCl2 solutions. The compressibility, permeability and shear strength parameters were determined on the 60, 190, and 250 days cured samples. The results have shown that, the kaolin sample becomes more compressible in the presence Ca2+ ions with ageing. Generally, the normalized compression index values of bentonite samples increased at the end of 60 days and 250 days curing time periods. The normalized permeability value of kaolin decreased by ageing in the presence of Na+ ions almost twofold. The permeability values of bentonite increased both in NaCl and CaCl2 solutions during ageing. In the presence of Na+ ions kaolin had higher max. shear stress value than Ca2+ ions. When the max. shear stress values of 0, 60 and 190 days samples were compared, it was seen that NaCl solution had no significant effect on the shear strength of kaolin sample. However, the shear strength of kaolin increased in the CaCl2 solution during ageing. In the presence of Ca2+ ions the max. shear stress value of bentonite was higher. The results of this study have shown that ageing has significant effects on the compressibility, permeability and shear strength of kaolinitic and bentonitic clayey soils.
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    Suitability of the methylene blue test for surface area, cation exchange capacity and swell potential determination of clayey soils
    Yukselen-Aksoy, Y; Kaya, A
    Application of the methylene blue test methods in determining soil properties, including specific surface area (SSA), cation exchange capacity (CEC), swell index, and swell potential are investigated on clayey soil samples with widely different mineralogy. The results indicate that the MB methods yield accurate prediction of some soil index properties, and they are easy to apply with simple test equipment. The results also show that the testing methods can be applied for soils that have widely different mineralogy. External and internal surface areas of soils can be measured by the MB adsorption methods. Effect of particle size on the MB surface area measurement accuracy was also studied using samples passing 0.425 mm (No. 40) and 0.075 mm (No. 200) sieves. The results show that there is no significant difference in the amount of absorbed methylene blue of the soil samples passing the No. 40 and No. 200 sieves. The test results also indicate that the MB-CEC values are generally lower than those obtained by the ammonium acetate method. The correlation coefficient between the MB-CEC and NH4-Na results is 0.88 indicating that MB can be used effectively to measure CEC of soils. The results also show that swell index and swell potential of the soils can be estimated with MB methods accurately, economically and readily. Significant relationship is observed between the swelling potential and MBV (methylene blue value) for a wide range of soils. A new classification for swelling soils is proposed using MBV. (C) 2008 Elsevier B.V. All rights reserved.
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    Method dependency of relationships between specific surface area and soil physicochemical properties
    Yukselen-Aksoy, Y; Kaya, A
    It is postulated that the behavior of fine-grained soils may be explained by the relationship between surface area and other geotechnical properties. To this end, there are several studies correlating geotechnical indexes with specific surface area (SSA). However, there is no universally accepted specific surface area determining method as several methods are available. Depending on the method employed, the measured specific surface area may show variations for a given soil. This is because the predictive power of each method depends on the type of minerals and organic matter that are present in the soil. Thus, different SSA determination methods yield widely different estimates of index properties and regression equations. To examine the role of method on SSA of soils, the SSAs of 32 soils with different mineralogies were determined using BET-N-2, EGME, MB-titration, and MB-spot test methods. The measured SSA of soils was correlated with their respective geotechnical index properties. Further, the data obtained in this study and those reported by previous researchers were compared. The results suggest that correlations between geotechnical index properties and SSA using different methods may not be comparable. Accurate prediction, however, is provided only if the relationship is calibrated using soils having similar physical and chemical characters. (c) 2010 Elsevier B.V. All rights reserved.
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    Predicting soil swelling behaviour from specific surface area
    Yukselen-Aksoy, Y; Kaya, A
    Some geotechnical index properties, such as the liquid limit, plasticity index, clay content and cation exchange capacity, have been used to predict the swelling potential of soils. However, a literature review indicates that prediction of the swelling potential of soils using these index properties is not completely successful. At the same time, the methods used to determine swelling potential are time-consuming. Thus researchers have been investigating other methods that can predict the swelling potential of soils readily and accurately. To this end, in this study the BET (Brunauer, Emmett and Teller equation)-N-2 adsorption, ethylene glycol monoethyl ether (EGME) and methylene blue (MB) measured specific surface areas (SSA) are correlated with the swell index and modified free swell index of soils. The SSA and swell index of 16 remoulded and 15 undisturbed soils consisting of a wide range of mineralogy were determined. Results indicate that the correlation between the SSA and the swelling behaviour of the clayey soils examined is significant. A linear relationship is observed between the swell index, C-s, and the MB SSA: the swell index of the soils increases as the SSA increases. The correlation coefficient between the SSA and the modified free swell index (MFSI) is 0.93, indicating that the MB SSA does exert a significant influence on the swelling behaviour of clayey soils. Based on the test results obtained, a new swelling potential classification is proposed.
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    Composition and degradation effects on the compaction characteristics of municipal solid wastes
    Pulat, HF; Yukselen-Aksoy, Y
    In order to protect environment and human health, MSW must be stored regularly and confidently. For safe and economic MSW storage, significant processes are initialized (dumping, spread out, burying and compacting). Compaction is the one of the most important stages of the storage process. Well compacted MSW renders less volume than the same weighted uncompacted MSW. Furthermore, well compaction provides safer storage area. In this study, the effect of composition, degradation, and energy on the compaction behavior of artificially prepared and natural fresh and aged MSW samples were determined. The standard and modified proctor tests were performed on the fresh and aged samples. Artificial samples were prepared in different compositions to examine the effect of composition. In addition to the synthetic MSW samples, natural MSW samples were provided from municipal landfill area of Manisa city.
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    Suction characteristics of compacted zeolite-bentonite and sand-bentonite mixtures
    Durukan, S; Pulat, HF; 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.
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    Characterization of two natural zeolites for geotechnical and geoenvironmental applications
    Yukselen-Aksoy, Y
    This paper reports the findings of experimental studies on two natural zeolitic soils. Engineering properties (e.g., grain size, specific gravity, compressibility, hydraulic conductivity, swelling behavior and shear strength) were determined in order to assess their suitability for geotechnical and geoenvironmental applications. The two zeolite-rich tuff samples investigated were mainly composed of clinoptilolite. The results show that the cation exchange capacities are 60.5 and 57.2 mEq/100 g, which are below the theoretical reported values. Compression index values obtained reveal that the zeolitic soils are not highly compressible. The modified free swell indexes of the zeolitic samples are around 2.0, suggesting that they have low swelling potential. The drained residual friction angles indicate that the zeolitic soils have relatively high internal friction angles (34 degrees and 36.5 degrees for Z-1 and Z-2, respectively). Based on the results obtained, it was concluded that zeolites are mechanically stable materials that are suitable for embankment materials and landfill liner applications. (C) 2010 Elsevier B.V. All rights reserved.
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    Compaction behavior of synthetic and natural MSW samples in different compositions
    Pulat, HF; Yukselen-Aksoy, Y
    Compaction is the one of the most important stages of the storage process in landfills. Well-compacted municipal solid waste (MSW) occupies less volume than an uncompacted MSW sample of the same weight and provides a safer storage area. The composition of MSW changes in between countries and even cities. For that reason, for effective compaction, the composition effect should be investigated. In this study, effects of composition, degradation and energy on the compaction behavior of artificially-prepared and natural fresh and aged MSW samples were determined. Artificial samples were prepared in representative different compositions Europe (E-1), Turkey (T-1) and the USA (U-1) to examine the effect of the composition. In addition to the synthetic MSW samples, natural MSW samples were obtained from the municipal landfill area of Manisa, Turkey. The standard Proctor test results have shown that the highest maximum dry unit weight was observed with the U-1 composition, which has the lowest organic content and the highest metal content. The degradation effect was investigated on the natural samples. The degraded MSW sample (3-4 years) has significantly higher maximum dry unit weight than the fresh natural MSW sample because of its low organic content. According to the results of this study, with respect to the composition effect, the percentage of organic waste is the most important factor on the compaction behavior of MSWs. As paper, organic and plastic contents increase in the MSW composition the (dry-max) value decreases and w(opt) increases. The ash content does it reversely, as such that any increase in (dry-max) decreases the w(opt) value of the MSW.