A Comparison of SASW Survey Results with In-Situ Field Investigation Methods

A geotechnical investigation of a site for two large buried water storage reservoirs was recently conducted. The geotechnical investigation used multiple insitu field methods to characterize the recent alluvial and fluvial deposits overlying bedrock that underlie the reservoir site. The recent deposits had a gravel, cobble and boulder content which made characterization of these deposits by the usual in-situ methods, such as the standard penetration test (SPT), more difficult. Because of the coarser grained materials, Becker Penetration Tests (BPTs) were performed to provide continuous penetration resistance at several locations throughout the large site. To provide additional information, Spectral Analysis of Surface Waves (SASW) testing was performed to characterize the thicknesses and shear wave velocity (Vs) profiles of the alluvial and fluvial deposits and the underlying bedrock. The SASW results were compared with the results of shear wave velocity profiling using the suspension logging technique performed in several rotary wash borings at the site. The SASW shear wave velocity profiles, in combination with the other investigation methods, were useful in determining the nature of the subsurface materials and refinement of the soil and bedrock profiles for liquefaction and soil-structure interaction analyses required in the design of the reservoir structures.