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| | Abstract | | In step with growing of Japan's offshore wind farm market, the demand for offshore geotechnical investigation is increasing. Suspension PS logging is the most commonly used method to measure S wave velocity (Vs) required for seismic design. Since long-term investigation at an offshore site have high risk, more efficient geophysical methods are required. As an effective technique, we propose "Offshore inverse PS logging", which is an uphole type PS logging using vibration generated in the standard penetration test. The inverse analysis based on ray tracing was introduced in order to define Vs with high accuracy from shallow to deep. To verify feasibility of this method, a field application test was conducted at an offshore site. As a result, clear waveform records were acquired, and the obtained Vs profiles matched with the result of suspension PS logging carried out in the same borehole. The agreement between two Vs profiles shows that the Offshore inverse PS logging works properly and effectively. This method makes it possible to conduct geotechnical investigation efficiently even in offshore harsh environments. |
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