Application of electrical resistivity imaging and land surveying in the analysis of underground construction impact on the Warsaw Scarp

The paper presents the analysis of the II Underground Line construction’s impact on the Warsaw Scarp with the use of the electrical resistivity imaging (ERI, also known as the electrical resistivity tomography) and further total station position measurements. The underground passes under the scarp perpendicular in the area of Dynasy Street 6, in Downtown district. The electrical resistivity imaging was performed for recognition of the geological structure and a potential landslide surface or zone. The gradient system was used during the prospection. In these analyses, the longitudinal section was 40 m long, and the depth of survey amounted to 6 m. In the case of the 200 m long transverse section, the resulted depth of survey was 30 m. The geophysical image of the longitudinal section, does not contain loosening soil zones, which could indicate slip surface. Next, total station measurements, which were tied to the archival geodetic observations’ results, were carried out. The aim of the measurements was to verify the activity of the horizontal and vertical displacements. The TBM excavation process led to summary vertical displacements up to approx. 24 mm and horizontal displacements amounting to approx. 13 mm. To sum up, the current land surveys reveals minor underground line’s construction impact on the scarp displacement. Nevertheless, the sensitive urban environment requires further monitoring, especially that the operation loads can result in displacement rate change.