Abstract:

An investigation of sound waves propagating in an unconsolidated water-saturated porous medium has been conducted in the NRL shallow-water laboratory. To minimize the interaction of the water--sand interface, a transducer was buried approximately 1.5 m facing up toward the sand--water interface. The unconsolidated water-saturated porous medium is a 3.0-m deep bed of a manufactured 212-(mu)m mean diameter sand. To obtain a short pulse that provides better temporal resolution of the acoustical waves propagating in the media, a 1-3 composite transducer was used. The sound field is measured with a single hydrophone that is initially buried just above the source and then incrementally pulled up through the sand toward the sand--water interface. This provide a synthetic array meaurement of the sound field directly above the transducer. A 1680-m/s fast compressional wave and a 550-m/s slower wave are easily observed using both temporal and spatial analysis techniques. Comparisons of these wave speeds with predictions from a Biot model are discussed. [Work supported by ONR.]