Abstract:

Shear and compressional wave velocities have been measured in glass beads and Ottawa sand as a function of the percent of the void filled with water. Air-dry glass beads and Ottawa sand were evacuated to a pressure of about 10 mTorr and then exposed to dry nitrogen and water vapor, respectively. The results show that the water vapor increased the compressional wave velocity by a factor of 2 and shear wave velocity by a factor of 3 in glass beads at the water saturation of 0.15%. For Ottawa sand, however, the change in velocities was only a few percent for the same water saturation. At present, it is proposed that vapor condenses to form a ``water lens'' at the points of grain contact. This condensation results from surface tension lowering the vapor pressure above a curved meniscus. As yet there is no satisfactory explanation of the difference in the effect of the condensed water in the beads and sand. [Work supported by the Office of Naval Research.]