Sustainable and Accurate Seismic Tests to Investigate Small Strain Stiffness Properties to Complement the CPT.

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ABSTRACT: An accurate quantification of shear wave velocity, V_s, is an important consideration in geotechnical design applications, particularly in the field of offshore wind turbine design, where increasing focus is placed on reliable small strain shear modulus G_max profiles. Seismic Cone Penetration Testing (SCPT) is a commonly utilised method to calculate V_s through measurement of shear wave travel times from a source to in situ receivers.

The Icone, a digital Cone Penetration Test (CPT), is easily extendable through addition of click-on modules to measure additional in-situ parameters. The Icone Seismic Module is an instrument utilised to investigate V_s and derive G_max of soils. This click-on module is automatically recognised, creating a true plug & play system. It contains three accelerometers to receive left and right shear waves as well as compression waves. The Icone Seismic Module can be applied both onshore and offshore and has a 1,000m water depth rating.

Through incorporation of a seismic source within a ROSON seabed CPT system, seismic tests can be performed autonomously. The integrated seismic source described within this study contains a low energy impact source, and when coupled with high accuracy accelerometers within a seismic array an optimal configuration in terms of low noise is created.

Ocean Infinity, owner of several ROSON-ST systems with seismic modules, has already utilised the described system to acquire V_s measurements across various projects. Within this context, the paper describes the system advantages and operational advantages of the proposed system in practice.

5th International Symposium on Frontiers in Offshore Geotechnics (ISFOG2025)

2 - Site characterization, in-situ and laboratory testing, measurement