Abstract:

The addition of small amounts of gas into a fully saturated sand drastically reduces the sound velocities in that material. The technique used to wet the sand in a series of experiments was to allow the water to be pulled into the granular material by capillary action. This process can entrap various amounts of air, depending on the grain size and the negative tension under which the water is allowed into the sand. The moisture content was measured using the time domain reflectometry method. Compressional and shear-wave velocities were measured as a function of water content in the sand. An average of 15% decrease in velocity was observed as the water content was increased from room dry state to 97% saturation. The change in velocities over this saturation range can be largely attributed to the change in bulk material density. The saturating technique used in these experiments did not achieve a high enough saturation range where a significant increase in compressional velocity has been observed. [Work supported by ONR.]