Geology, sedimentation, and arid climate influence the formation of the expansive soil in Ankara, the capital of Turkey. The soil called Ankara clay locally bears carbonate concretions at shallow depths in the western parts of the city. To better understand the swelling properties of the soil, a detailed investigation was conducted at the Beytepe Campus area of Hacettepe University, where Ankara clay with carbonate concretions is typically observed. The principal aims of this investigation were to study the engineering properties, mineralogical composition, and swelling characteristics of the clay; to investigate the effect of carbonate content on the swelling behavior of Ankara clay; to develop empirical relationships for predicting the swelling pressure and swelling percentage of the clay from its index and mineralogical properties to be used when it contains carbonate concretions; and to generate swelling maps of the site for further engineering practice. Test results indicate a strong relationship between the presence of carbonate content and swelling parameters. Statistical assessments suggest that the empirical equations developed in this study exhibit superior prediction performance compared to those based on a data set using Ankara clay samples generally free from carbonate concretions and nodules. One of the prediction equations using only three parameters also was applied to the data set from Turkey and other countries. This equation showed acceptable performance for a cheap first cut, particularly for field engineers who need to make decisions based on limited data. In addition, swelling maps of the study site were generated based on the swelling data derived from the proposed predictive equations.

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