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Dispersive and expansive soils are considered problematic, and these soil properties cause serious problems for many engineering structures. For many years, comprehensive studies have been carried out with the aim of improving the swelling and dispersive qualities of soils by using additives. Each feature in the literature associated with the improvement of the dispersive and swell properties of clay soil with additives was separately evaluated. In this study, the effect of cement and natural zeolite additives on the characteristics of dispersibility and swelling potential of clay soils were investigated. A fixed percentage of cement (3%) plus different percentages of natural zeolite (1%, 3%, 6%, 10%, 15%, and 20%) were mixed with four different clay soil samples. In this context, first, the physical and chemical properties of the soil samples were determined. Next, the swell percentage, swell pressure, crumb, pinhole and unconfined compressive strength tests at different curing times were performed on samples with and without the additive by compressing the sample to achieve particular compaction characteristics. Significant strength value increases depended on curing time, and the properties were improved with the mixture of cement and zeolite additives, depending on the sodium adsorption ratio (SAR) and exchangeable sodium percentage (ESP) values of clay soil samples with different plasticity characteristics that exhibit dispersive and swell properties. This study not only showed that a mixture of cement and zeolite additives improved the dispersive and swell properties of clay soil samples with four different plasticity characteristics, depending on their SAR and ESP values, but also significant increases in strength values were observed.

Abstract. Liquefaction is one of the critical problems in geotechnical engineering. High ground water levels and alluvial soils have a high potential risk for damage due to liquefaction, especially in seismically active regions. Eskişehir urban area, studied in this article, is situated within the second degree earthquake region on the seismic hazard zonation map of Turkey and is surrounded by Eskişehir, North Anatolian, Kütahya and Simav Fault Zones. Geotechnical investigations are carried out in two stages: field and laboratory. In the first stage, 232 boreholes in different locations were drilled and Standard Penetration Test (SPT) was performed. Test pits at 106 different locations were also excavated to support geotechnical data obtained from field tests. In the second stage, experimental studies were performed to determine the Atterberg limits and physical properties of soils. Liquefaction potential was investigated by a simplified method based on SPT. A scenario earthquake of magnitude M = 6.4, produced by Eskişehir Fault Zone, was used in the calculations. Analyses were carried out for PGA levels at 0.19, 0.30 and 0.47 g. The results of the analyses indicate that presence of high ground water level and alluvial soil increase the liquefaction potential with the seismic features of the region. Following the analyses, liquefaction potential maps were produced for different depth intervals and can be used effectively for development plans and risk management practices in Eskişehir.

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The use of dispersive soils, which are common in many parts of the world, in engineering applications such as water structures, earthen dams and road embankments is possible with their improvement. Recently, the effects of different chemicals on the stabilization of dispersive soils have been investigated. The use of waste materials in stabilization is preferred both because of the more sustainable environment and the economic advantages it provides. The use of silica fume (SF) as a waste material in different engineering applications provides an important advantage in environmentally and economically sustainable ways. Many studies have been carried out regarding silica fume, especially in the construction industry. Although SF is used in many industries, there is no study about its potential impact on the stabilization and dynamic properties of dispersive soils. In this study, first, Atterberg limits and standard Proctor compaction tests were performed on the mixtures prepared by adding different SF percentages (0, 5, 10, 15, 20, 25 and 30%). Afterward, pinhole tests and resonant column tests were performed to determine dispersibility and dynamic properties on the samples prepared by compaction characteristics for each SF percentage reached. In general, it was determined that SF contributed to a change in soil class, and improvement in dispersibility and dynamic properties of the soil sample, depending on SF content; positive effects of SF were observed in terms of shallow soil improvement.

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