Measurements of the induced pore pressure in packings of glass beads due to an incident airborne acoustic wave

Abstract

The Biot theory predicts the existence of two P waves (referred to here as type I and type II) and one S wave. In a previous experiment where airborne sound was incident upon an air-filled packing of sand, it was postulated that the signal detected by microphones at shallow depths was due to the type II P wave whereas at the deeper depths the signal is associated with the type I P wave [C. J. Hickey and J. M. Sabatier, J. Acoust. Soc. Am. 102, 128–136 (1997)]. In this presentation we discuss the results of measurements obtained in packings of glass beads. Four different packing were respectively made with 304 (30–40 mm), 405 (40–50 mm), 507 (50–70 mm) and 1014 (100–140 mm) size glass beads. A smaller bead size increases the flow resistivity of the packing, thereby increasing the attenuation of the type II P wave. If the previous interpretation is correct then the depth at which the signal is dominated by type I or type II P wave should change with glass bead size.