Characterization of Spectral Analysis of Surface Waves Shear Wave Velocity Measurement Uncertainty

The spectral analysis of surface waves (SASW) method is a nondestructive test for characterization of the variation with depth of the shear modulus 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. Phase angle, inverse phase angle, and phase velocity data typically display a coefficient of variation (COV) of 2%, and the COV for combined phase velocity data is typically 1.5%. The COV for shear wave velocity is typically between $5$ and 10%, and thus the inversion appears to magnify measurement uncertainty. Phase angle, inverse phase angle, phase velocity, and combined phase velocity data are normally distributed. Shear wave velocity samples at a given depth are generally normally distributed. Using a small sample of experimental data and the analytically based process developed in this study, the measurement uncertainty of SASW test results can be assessed as part of routine testing.