Measurement and interpretation of downhole seismic probe data for estimating shear wave velocity in deep-water environments

摘要

Shear wave velocity (V_s) and the related small strain shear modulus (G_(max)) are essential soil parameters for static and dynamic analysis of soil deformation. They can also be used as a basis for non-destructive assessment of sample quality. While the benefit of in-situ measurement of V_s is apparent, only few methods such as seismic cone (SCPTU) and surface wave inversion are available. However, in deep-water environments, there are a number of challenges in obtaining in-situ V_s. This paper describes the engineering and operational aspects of a downhole seismic probe deployed from a seafloor-based portable remotely operated drill system. The waveform, frequency, and noise characteristics of the shear waves generated by seismic hammers, and measured by the seismic cone are described. The paper concludes with a recommendation for conducting downhole SCPTU and data interpretation, which are in line with the new ISO standard on Marine Soil Investigations.