Effects of homogeneous/heterogeneous water distribution on GPR wave velocity in a soil's wetting and drying process

This paper studies the effects of relatively homogeneous (RHWD) and relatively inhomogeneous water distributions (RIWD) in soil compared by varying the water content through a wetting and drying cycle in a tank (1.85m long × 1.55m wide × 1m deep) filled with 750mm thick plant soil. During the cycle, a 900MHz antenna was regularly used to capture GPR radargrams on a buried steel pipe. Hyperbolic reflections of a buried pipe at a fixed position were extracted to measure wave velocities/dielectric constants at different RHWD and RIWD in the wetting and drying cycle. A vertical coaxial-based water content sensor was also installed in a vertical standpipe in the middle of the tank to obtain the vertical water content profile, synchronized with and correlated to the GPR wave velocity/dielectric constant of the soil. The result of cross plotting between the dielectric constant and soil water content shows that the volumetric fraction of water in a porous medium is the sole important factor affecting dielectric properties of soil.