Assessing the Potential of AEM in Shallow Offshore Geotechnical Investigation for a Railway Tunnel Design Project

The mapping of soft and gaseous sediments in the Danish glacial tunnel valleys by seismic methods is often a challenging task. This mainly due to a high content of gas in the sediments. Alternative methods or indirect measurements of the depth to a geotechnical competent base is often required to minimize drilling cost. An airborne electromagnetic (AEM) survey, SkyTEM, was carried at Vejle Fjord, in eastern Jutland, Denmark, to provide support to geological modelling. This study showed that in favourable conditions, applying proper processing and inversions, and data integration, AEM can be used over shallow waters to map sub-bottom geological layers with fair accuracy. The results are in good agreement with ancillary information available, derived from seismic and boreholes. In particular, AEM inversion models showed to have high correlation with bathymetry, thicknesses of the organic rich Gyttja and depth to the underlying sands.