Application of SASW method underwater

The spectral analysis of surface waves (SASW) method is a nonintrusive testing technique for determining shear wave velocity (V) profiles of geotechnical sites using seismic interface waves (also called surface waves). Both small-scale and full-scale experiments have been conducted to develop the SASW technique for use underwater. The small-scale tests were performed to validate theoretical predictions regarding dominant types of seismic waves at the water/substrate interface. The tests clearly show a difference between soft and stiff substrates, where the definition of substrate stiffness is based on the value of the velocity of the Rayleigh-type interface wave (V) relative to the velocity of compression waves in water (V). In the simplest case, where the substrate is soft (V 9T V), 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 (V9U V), the dominant wave was found to be a generalized Rayleigh wave, the measurement of which is less straightforward. Two full-scale field trials were conducted on soft seafloors: one in the shallow water of a harbor and another as a ship-based experiment at sea. These trials demonstrated that the SASW method is a viable technique for characterizing underwater geotechnical sites, and that it shows promise for further development for remote operation in deep water. The spectral analysis of surface waves (SASW) method is a nonintrusive testing technique for determining shear wave velocity (V) profiles of geotechnical sites using seismic interface waves (also called surface waves). Both small-scale and full-scale experiments have been conducted to develop the SASW technique for use underwater. The small-scale tests were performed to validate theoretical predictions regarding dominant types of seismic waves at the water/substrate interface. The tests clearly show a difference between soft and stiff substrates, where the definition of substrate stiffness is based on the value of the velocity of the Rayleigh-type interface wave (V) relative to the velocity of compression waves in water (V). In the simplest case, where the substrate is soft (VV), the dominant wave was found to be a generalized Rayleigh wave, the measurement of which is less straightforward. Two full-scale field trials were conducted on soft seafloors: one in the shallow water of a harbor and another as a ship-based experiment at sea. These trials demonstrated that the SASW method is a viable technique for characterizing underwater geotechnical sites, and that it shows promise for further development for remote operation in deep water.