Electromagnetic signal velocity measurements are common in soil disciplines, often involving Time-Domain Reflectometry. However, Time-Domain Reflectometry measurements are of limited use where velocity is frequency dependent, such as in finegrained soils. Therefore, Quarter-Wavelength Analysis was developed for measurements of velocities in fine-grained soils. The developed measurement cell was used to undertake velocity measurements in parallel with geotechnical index tests, in order to develop cross-disciplinary relationships. It was found that relationships exist between velocities and geotechnical properties, both for a wide range of soils at their Liquid Limits and for two fine-grained soils over their full saturated water content ranges. Also, it was found that Atterberg Limits can be used to define water content ranges over which different mixing models are required to relate velocity and water content. This led to initial development of mixing models specifically for the saturated state to allow more accurate use of laboratory velocity measurements in determining fine-grained soil water contents. Furthermore, it was found that variations in velocities between low and high frequencies relate to linear shrinkage. These relationships have wide-ranging uses in engineering, including rapid index testing, geo-hazard monitoring, improved electromagnetic field surveys, and researching the properties of soil porewater.
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