Untersuchung der Effektivität einer inversen Wenner-Schlumberger-Konfiguration

Testing the effectiveness of an inverse Wenner-Schlumberger array. On the Swabian Alb high plain, southwestern Germany, the new high-speed railway line Wendlingen–Ulm of the German Railway Company (Deutsche Bahn AG) is under construction. 2.5D electrical resistivity tomography (ERT) measurements (meaning the use of parallel 2D lines) were performed at the excavation bottom level in addition to the investigation program of the construction company including microgravimetric and seismic methods. The aim was to test the effectiveness of an inverse Wenner-Schlumberger array for exploring geological defective karst voids and other karstic features in a highly heterogeneous karstic environment. The 2.5D ERT survey provided resistivity values of marls and marlstones, a limestone bedrock, a collapse doline and of an air-filled cavity. A clear demarcation between the marls and marlstones and the limestone bedrock was only possible outside the area of influence of the collapse doline; the latter could not be exactly delineated from the adjoining geological units. In addition, one of three air-filled voids (open fractures, cavities) could be derived accurately in location and roughly in size and shape from the 2.5D ERT survey; the other two were not detected by means of ERT because of (i) its location beneath a high-resistive anomaly and (ii) its comparatively small maximum horizontal opening width of only 1 time the used inter-electrode spacing.