Investigation of Soil Behavior of Ankara Clay Based on Geotechnical Field and Laboratory Experiments

Abstract

This study aims to evaluate the geotechnical characteristics of clayey soils in the west of Ankara and, accordingly, the depositional environments, depending on the laboratory and the in-situ tests. The clayey soils mentioned are Plio-Quaternary fluvial sediments, also known as “Ankara Clay” in the literature. Plio-Pleistocene fluvial deposits are mostly old terrace formations in flood plains. Quaternary lithologies, which differentiate as the young terrace and recent alluvial deposits, are observed along the Ankara River and its tributaries. These deposits are encountered at low land topography as they are formed by the river terraces and in the form of steps on the main routes of the rivers formed by their tributaries and floods. Ankara Clay is a unique soil type distinguished by its proconsolidated, active, highly plastic, and stiff consistency properties. As a consequence of the challenging characteristics of Ankara Clay, it is difficult to obtain undisturbed samples due to volumetric behavior, which has an unfavorable effect on the dependability of regional studies. In most previous research studies, geotechnical characteristics of the clayey sediments have been assessed at shallow depths in the Ankara basin due to such obstacles. Thus, the variations of the geotechnical parameters along with the consolidation characteristics depending on the depth were emphasized explicitly in this thesis. Additionally, laboratory test results were compared with existing literature to assess the effects of sample disturbance and verify that the correlations established between soil characteristics due to statistical analyses are as accurate as possible. Furthermore, with the guidance of those researches, a newly developed approach for detecting disturbance characteristics in soil samples has been presented here. In doing this, the precipitation environments and geotechnical properties of clayey soils were evaluated comparatively by determining the frequency distributions associated with each soil index mentioned below. Regarding these clayey soils in the west of Ankara, it is aimed to perform soil characterization with the geotechnical data gathered from the study area by using geo-engineering applications, in-situ field, and laboratory test results and studies depending on the depositional environments of the region. The behavior of these sediments and the frequency distributions of the geotechnical characteristics of the Ankara Clay were analyzed statistically using an extensive database of laboratory test results (i.e., soil class, index properties, swelling potential, volume change behavior, consolidation parameters, undrained shear strength, and strength properties) and in-situ geotechnical reports (i.e., SPT-N, pressuremeter testing results). The results were integrated into the prepared geo-statistical database, and empirical formulas were developed with multivariate linear approach analyses to systematically interrogate and predict the clayey soils formed in different deposition environments in the west of Ankara in terms of different soil parameters.