The effect of moisture on compressional and shear wave speeds in unconsolidated granular material

Abstract

The effect of water vapor on the shear and compressional wave speeds in two different kinds of glass beads and in Ottawa sand has been measured. The nominal diameter of the glass beads was 125 microm and of the sand, 500 microm. Measurements were made as the water vapor was introduced slowly into the evacuated material. The vapor pressure isotherm for the beads made of glass with a high concentration of titanium and barium oxides was fit reasonably well by the simple Brunauer-Emmett-Teller (BET) theory. For the Ottawa sand, the BET theory fit the vapor pressure isotherm if the surface area of the grains was assumed to be three times the area calculated, assuming all of the grains were spheres with a diameter of 500 microm. In these two materials, the vapor had little effect on the wave speeds. For beads made of glass containing sodium oxide, however, the wave speeds approximately double with the introduction of water vapor, and the vapor pressure isotherm had the BET shape only if the saturated vapor pressure was assumed to be lowered by 20%. These results have been explained by assuming that a chemical reaction occurred between the lime glass and the water to form a gel.