The paper presents experimental results of investigations of offshore deposits from the Gulf of Finland in the Baltic Sea. Firstly, it briefly reviews the sedimentary history of the studied site. Then, it presents results from marine geological investigations, including seismoacoustic reflection sub-bottom profiles and long sediment cores collected by piston coring. Finally, the paper presents the physical and mechanical properties of the intact soil samples through geotechnical laboratory tests. The data show the distribution of water content, bulk density, undrained shear strength, sensitivity, and organic content of the samples at various depths up to approximately 4 meters. The undrained shear strengths, obtained by fall cone tests, are scattered and the variations are ±35% for the studied specimens. A quantitative correlation between geotechnical data and local sedimentary units and depositional history was not possible in this study. Further efforts are needed to reduce the uncertainties and measurement errors in determining the undrained shear strengths in geotechnical laboratory.@en

In situ free-fall cone penetrometers (FF-CPTs) allow for rapid investigations of undrained shear strength of soft shallow water deposits. Often samples are also studied in geotechnical laboratory by fall cone tests. This study presents in situ FF-CPT and laboratory fall cone testing results of an offshore site in the northern part of the Gulf of Finland, Baltic Sea. Site investigations included seismoacoustic surveys and sediment coring. Based on seismoacoustic reflection profiles and long sediment cores, the local deposits were classified and divided into glaciolacustrine, post-glacial lacustrine and brackish-water stratigraphic units. FFCPT measurements provided in situ undrained shear strength and dynamic cone resistance of the seabed geological units. Laboratory fall cone tests were performed on the vertical core samples at every 0.5m. Comparisons were established between undrained shear strength from FF-CPT tests and from fall cone tests.@en