APPLICATION OF SASW METHOD UNDERWATER

The spectral analysis of surface waves (SASW) method is a nonintrusive testing technique for determining shear wave velocity (V-S) profiles of geotechnical sites using seismic interface waves (also called surfa ce waves). Both small-scale and full-scale experiments have been condu cted to develop the SASW technique for use underwater The small-scale tests were performed to validate theoretical predictions regarding dom inant types of seismic waves at the water/substrate interface. The tes ts clearly show a difference between soft and stiff substrates, where the definition of substrate stiffness is based on the value of the vel ocity of the Rayleigh-type interface wave (V-R) relative to the veloci ty of compression waves in water (V-W). In the simplest case, where th e substrate is soft (V-R < V-W), the dominant wave was found to be the Scholte wave, whose behavior is similar to that of the Rayleigh wave on land. When the substrate is stiff (V-R > V-W), the dominant wave wa s found to be a generalized Rayleigh wave, the measurement of which is less straightforward. Two full-scale field trials were conducted on s oft seafloors: one in the shallow water of a harbor and another as a s hip-based experiment at sea These trials demonstrated that the SASW me thod is a viable technique for characterizing underwater geotechnical sites, and that it shows promise for further development for remote op eration in deep water.