Geotechnical and Geological Aspects of Differential Subsidence in the Skaw Spit, Denmark

Local differential subsidence has been observed by means of repeated precise levellings in the township of Skagen at the northernmost tip of the Skaw Spit in Jutland. We have l studied the possible causes of the subsidence. Oedometer tests have been carried out on undisturbed clayey samples from the Holocene in a boring at the depth interval 30-114 m. Seismic profiles were acquired in Kattegat along the coast and on land. The geotechnical investigations indicate that the consolidation process in the Holocene sediments is completed. Other possible causes: lowering of the groundwater table in water supply wells, and filling in the harbour area seem to be insufficient to account for the subsidence. In the Quaternary the seismic profiles indicate dislocations that may be related to faults in the pre-Quaternary substratum. A relationship between the subsidence and active faulting is considered a possibility.