Electrical imaging of the geoenvironment around water infrastructures in Istanbul city

Abstract

Subsurface structures from two different districts of Istanbul, hosting waste and freshwater transmission lines, were imaged by geoelectrical method. The environmental impact on Kağıthane-Terkos freshwater transmission line is one of the issues. That waterline underwent a substantial landslide damage. The previous site selection of Kağıthane-Terkos line was only based on surface geological observations. Even though the pipeline was positioned away from the surface scarps of landslides, the pipes were damaged. To find out the reason, we made some vertical electrical sounding measurements using Schlumberger array in the region. We inverted the electrical sounding data using 2D inversion technique. The final geoelectrical images show main landslide failures, at about 10–30 m depth, which are overlain by debris with a resistivity value of with <6 Ω m. The geoelectrical findings reveal that a buried major failure surrounds the surface landslides behind. Consequently, the water infrastructure remains under the influence of landslide. Our second application site was the area of the Sazlıdere tunnel, which will transfer wastewater, polluting Sazlıdere dam, to the treatment plant. The geoelectrical images along Sazlıdere tunnel route show resistive (<100 Ω m) and moderately conductive (≤50 Ω m) structures along the tunnel axis, representing unaltered to highly weathered rocks, respectively. Furthermore, consecutive hidden fault zones which severely affect the construction process of the tunnel are detected and located.