Volume 27, Issue 2 (March 2004)
Characterization of SASW Phase Angle and Phase Velocity Measurement Uncertainty
The spectra-analysis-of-surface-waves (SASW) method is a nondestructive test for characterization of the variation with depth of the shear wave velocity of soils. While the testing procedure is well developed, only one preliminary study has investigated measurement uncertainty associated with SASW, and the methods utilized to quantify measurement uncertainty were prohibitive to routine assessment. Knowledge of this uncertainty, and ability to include its assessment in routine testing, would allow for inclusion of SASW results in reliability based design and in assessment of the spatial variability of shear modulus.
In this study, a large sample of test data was collected from two test sites. Characteristic statistics, statistical distribution, and measurement uncertainty were determined for each phase of SASW. Using the empirical statistical properties and measurement uncertainty results as validation criteria, an analytically based uncertainty assessment system was developed.
Specifically, it was shown that SASW phase angle and inverse phase angle typically display a coefficient of variation (COV) of 2 %, and samples appear normally distributed. Further, SASW phase velocity data typically display a coefficient of variation (COV) of 2 %, and the COV for combined phase velocity data is typically 1.5 %. Both phase velocity and combined phase velocity samples appear normally distributed. In addition, it was found that by using a small sample of experimental data and the analytically based process developed in this study, measurement uncertainty of SASW phase angle and phase velocity could be assessed as part of routine testing.