MEASUREMENTS OF 2 TYPES OF DILATATIONAL WAVES IN AN AIR-FILLED UNCONSOLIDATED SAND

This study consists of laboratory measurements of dilatational waves p ropagating through an air-filled unconsolidated sand. One excitation t echnique consists of a loudspeaker suspended in the air above the pack ing of sand. A second excitation technique uses a mechanical shaker in contact with the sand. The transmitted signals are received sung micr ophones and geophones located at various depths within the sand. An in terpretation based on measured phase speeds indicates that the transmi tted energy from the suspended loudspeaker source is partitioned prima rily but not exclusively into the type-II dilatational wave. This wave attenuates rapidly and is only detected at depths of less than about 15 cm for this particular sample. At the deeper depths the detected si gnal is associated with the type-I dilatational wave. The mechanical s haker produces only type-I dilatational wave. Both the geophone and mi crophone sensors can detect both types of dilatational waves. (C) 1997 Acoustical Society of America.