Cone penetration testing (CPT) is one of the principal methods for the offshore geotechnical investigations worldwide and can rival drilling and coring in scope of field work. But, in the same time, CPT is not that widespread in Russian practice of the offshore geotechnical researches. Experience of execution of quite large amount of the offshore CPT in seabed mode is described in this article. Distinctive feature of the conducted field investigation is execution of the testing with heavy CPT rig from the vessel of opportunity. Aspects of vessel mobilization and field operations workflow considered in this article. Description of the data processing and interpretation is given. Typical geological cross section for investigated area is shown. Stratification of the soil profile was done using soil behavior types diagrams. Layers of soil are defined and characterized based on CPT data.
Emphasis is given to determination of undrained shear strength based on cone resistance data. Correlation is found between undrained shear strength measured in onboard laboratory with shear vane and in-situ measured cone resistance. Achieved results were compared to materials of other studies on same subject and recommendations of the Russian regulatory document. Generally good correlation was found.
Described approach to the offshore geotechnical investigation and technical solutions can be utilized for Arctic oil and gas fields development, where data for stratification and properties of soils are required. Derived correlations between undrained shear strength and cone resistance can be used for interpretation of CPT data of the future projects in Arctic regions.