Offshore Technology Research Center

 

OTRC Project Summary

Project Title:

Advances in Interpretation and Analysis Techniques for Spectral-Analysis-of-Surface-Waves (SASW) Measurements

Prinicipal Investigators:

Kenneth Stokoe

Sponsor:

National Science Foundation

Completion Date:

January, 1997

Final Report ID#

B89(Click to view final report abstract)

As with other seismic testing techniques, the SASW method requires the expertise of an experienced personal.  The objectives of this research are to develop improved data interpretation and analysis procedures which could be used for offshore as well as on-land applications.

Data interpretation of SASW measurements involves interpreting a phase spectrum determined in the field.  This process, called masking, involves elimination undesirable portions of the phase spectrum and evaluating the number of cycles of wrapped angles in the phase spectrum.  Interpretation of the umber of cycles is critical for accurate calculation of phase velocities.  At simple sites with increasing stiffness with depth, there is no difficulty in interpreting the phase spectrum.  However, at some sites, correctly counting the number of cycles in the phase spectrum can not be easily done.  There is, therefore, a need for data interpretation schemes to simplify this process.

The analysis of SASW measurements involves the evaluation of a shear stiffness profile from the phase velocity dispersion data.  Presently, the common practice is to evaluate the stiffness profile using an iterative procedure based on forward modeling.  The iterative procedure is often not efficient, because the iteration incorporates heuristic judgment and, therefore, requires a lot of personnel time to complete.  There is, therefore, a strong need for development of a robust inversion algorithm to analyze SASW data and efficiently develop stiffness profiles.

In summary, then, the overall objectives of this study are to reduce the difficulties involved in the data interpretation and analysis of SASW measurements by providing useful tools to interpret and analyze SASW test results more efficiently.

Related Publications: Joh, S.-H., Rosenblad, B.L. and Stokoe, K.H., “Improved Data Interpretation Method for SASW Tests at Complex Geotechnical Sites,” Proceedings, 7th ISOPE Conference, 1997.

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