Depth-dependent engineering geological and geotechnical characterization of ankara clay: a study on the effect of consolidation on soil variability

Ankara Clay is characterized by overconsolidated, highly swelling, active, medium to high plastic and stiff consistency properties. Despite a wide array of research about the Ankara Clay available, a comprehensive and systematic evaluation of the soil properties, especially in terms of consolidation conditions through depth, is limited in the literature. In this context, a large data set of 5,500 borehole samples was collected across the Ankara Basin, and the variations of 20 different soil parameters from the surface up to 25–30 m in-depth were statistically determined. The correlations between soil parameters were investigated, and the predictive equations were developed for the preconsolidation pressure ( P c ), compression index ( c c ), swelling index ( c s ), and volumetric compression coefficient ( m v ). Investigations also revealed that the normally/lightly overconsolidated (NC-LOC) and moderately/highly overconsolidated (MOC-HOC) samples were frequently observed in specific strata based on depth. Accordingly, a detailed examination was carried out to investigate the influence of consolidation on the variability of the soil parameters. T-tests were performed between NC-LOC/MOC-HOC samples, and a significant difference ( p < 0.05) in the mean values of 6 distinct soil parameters, particularly in the undrained shear strength ( C u ) parameter, was identified. Correspondingly, four novel equations were proposed to predict the C u under normally-consolidated and overconsolidated conditions. Furthermore, the accuracy of C u predictions was validated using two alternative datasets. The results demonstrated that considering the consolidation condition as a criterion notably improved (%35–40) the C u predictions.