Damages and economical losses due to problematic soils have caused researchers to conduct many studies for the stabilization of these soils within years. Especially, the use of fly ashes in soil stabilization provides great benefits in contributing to the economy, as well as decreasing the environmental pollution. In the present study, the stabilization characteristics of soil-fly ash mixtures were evaluated in terms of Atterberg limits, compaction characteristics, swell potential and unconfined compressive strength with curing effect. To determine these effects, Catalagzi and Soma fly ashes obtained from Turkey were used in different proportions by weight for stabilization of clay soil samples. It was found that the plasticity index of the soils decreased considerably with the addition of fly ashes, while the strength improved and swell potential decreased. The decreasing trend in the swell percentage and swell pressure values decelerated especially after 25% fly ash additive content and negligible changes occurred. Similar behavior was observed in strength tests. Experimental results show that swelling and strength properties of the soils could be improved by using fly ash and Soma fly ash is far more effective than Catalagzi fly ash.

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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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Abstract. The city of Eskişehir in inner-western Turkey has experienced a destructive earthquake with M s =6.4 in 1956 in addition to many events with magnitudes greater than 5. It is located in a wide basin having young sedimentary units and thick alluvium soils which also include liquefiable sand materials. There is also an active fault passing beneath the city center and the groundwater level is very close to the ground surface. Approximately 600 thousand people are living in the province of Eskişehir. Therefore, the city and its vicinity have a high risk, when earthquake hazard is considered. This paper summarizes the probabilistic seismic hazard analysis (PSHA) which was performed for the province of Eskişehir and introduces seismic hazard maps produced by considering earthquakes with magnitude M s ≥4.0 occurred during the last 100-years and a seismic model composed of four seismic sources. The results of PSHA show that the average peak ground acceleration (PGA) for the city center is 0.40 g for 10 percent probability of exceedance in 50 years, for rock site. The seismic hazard maps were obtained by means of a program of Geographic Information System.