New Approach to Interpretation of Noninvasive Surface Wave Measurements for Soil Profiling

Abstract

Noninvasive shear wave velocity (SWV) profiling of soil deposits has long been recognized as a cost-effective approach to obtain SWV data essential for seismic response analysis including site amplification and liquefaction. The controlled-source measurement of surface wave dispersion (CXW) is a relatively new noninvasive method that is used for site characterization in the United States, Japan, and other countries. The CXW method uses harmonic-controlled sources to produce steady state Rayleigh waves in order to measure the dispersion characteristics of soil and rock. Several interpretation techniques may be used to obtain SWV structure from Rayleigh wave dispersion data (in a process that is referred to as the Vf-VS method). CXW measurement data from more than 200 soil and rock sites were analyzed. These results were used to formulate a new approach for the Vf-VS interpretation method based on the new concept of reference profiles that describes the average dispersion curve and SWV structure. The reference profile is based on SWV dependency on confining pressure (depth) in soils. Simple equations were developed for direct inversion of the reference profile. The new procedure is completed by considering the effects of single layers with properties that are different from the reference profile. This new interpretation procedure is rapid and computationally efficient, and its results are more representative of actual soil structure than results obtained from other noninvasive methods. This study indicates inversion that is based on surface waves dispersion can provide a good estimate of average SWV variation.