Integration of electrical resistivity imaging (ERI) and ground-penetrating radar (GPR) methods to identify soil profile around Necatibey Subway Station, Ankara, Turkey

Electrical Resistivity Imaging (ERI) and Ground-Penetrating Radar (GPR) methods were utilized in this study to identify soil profiles around Necatibey Subway Station of Kızılay–Çayyolu metro line, Ankara, Turkey. The Necatibey Metro Station is located within the alluvial deposits of Dikmen stream and the so-called Ankara clay. At the metro station, a number of boreholes were drilled. However, due to the spacing of the boreholes the boundary between alluvium and Ankara clay deposits could not be separated precisely. Thus, in this study, ERI and GPR methods were utilized to distinguish soil types at the study area. GPR measurements were taken from a total of 14 profiles and total length of the profiles was about 320 m. For every ERI measurement section, Schlumberger Dipole–Dipole, Dipole–Dipole, Schlumberger and Wenner arrays were used. Results from the geophysical measurements identified that the fill materials are underlain by the Dikmen stream channel deposits, which consist of silty clay and gravelly sand units. The study also shows that the Dikmen stream channel deposits are underlain by the Ankara clay unit. The meaningful range of resistivity values was between 1 and 15 Ωm, and the GPR signals were strong in sandy units while they attenuated in clayey environments. Based on borehole logs, ERI and GPR data, three-dimensional lithological subsurface model of the survey area was constructed. The resultant three-dimensional diagrams may serve engineers as a practical tool during different construction stages, groundwater–surface water interactions within short and long term, and probable remedial measures.