Relating wave frequency and pore fluid homogeneity in quasi-saturated sands

P-wave velocity is regularly proposed as a proxy for water saturation when studying quasisaturated soils. However, several authors have underlined that this velocity can only be reliably correlated to water saturation if the pore fluid is "homogeneous". Using bender elements to measure compression wave velocity in quasi-saturated Fontainebleau sand, we show it is highly sensitive to both saturation and frequency. The characteristic length of pore pressure diffusion is used to explain the link between frequency, gas distribution and P-wave velocity. This criterion is shown to be fairly reliable for assessing the homogeneity of a pore fluid distribution in quasi-saturated Fontainebleau sand.