Urban Geoelectrical Survey and Spatially Constrained Interpretation for a New Metro in Copenhagen

Geophysical methods are prone to fail in an urban environment as all sources of noise are present in cities. The Fælledparken Park, a large open space area in Copenhagen, Denmark is not an exception. However, an extension of the metro along sections of high variability on the surface of a limestone surface motivated the use of geoelectrics as complement to seismic methods. The site conditions have implications for hydrogeological understanding and groundwater modelling validation needed for dewatering design during construction. The geo-electrical survey aim was the mapping of sediment layers in open areas where the recharge through Quaternary layers to the limestone aquifer is important for reliable groundwater modelling of dewatering scenarios. The main objectives of the surveys were to; a) Produce information that can be used to refine or update the site specific hydrogeological model for Cityringen tunnel and station locations. b) Map the sediment layers in the area, including an assessment of their areal distribution. c) Map the top of the limestone. The main outcome was that the area had heterogeneous conditions, where the west part was comprised of both sands and tills and a buried valley structure, and in the east a continuous sequence of sands.