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

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 n ominal diameter of the glass beads was 125 mum and of the sand, 500 mum. Me asurements were made as the water vapor was introduced slowly into the evac uated material. The vapor pressure isotherm for the beads made of glass wit h a high concentration of titanium and barium oxides was fit reasonably wel l by the simple Brunauer-Emmett-Teller (BET) theory. For the Ottawa sand, t he BET theory fit the vapor pressure isotherm if the surface ai-ea of the g rains was assumed to be three times the area calculated, assuming all of th e grains were spheres with a diameter of 500 mum. In these two materials, t he vapor had little effect on the wave speeds. For beads made of glass cont aining sodium oxide, however, the wave speeds approximately double with the introduction of water vapor, and the vapor pressure isotherm had the BET s hape only if the saturated vapor pressure was assumed to be lowered by 20%. These results have been explained by assuming that a chemical reaction occ urred between the lime glass and the water to form a gel. (C) 2000 Acoustic al Society of America.