Journal of the Korean Geotechnical Society ISSN:1229-2427(Print) 2288-646X(Online) 한국지반공학회 논문집

Dielectric constant depends on the variation of soil water content, and the estimation of soil water content using time domain reflectometry (TDR) has been studied by many researchers. The purpose of this study is the development and application of TDR penetrometer (TDRP) in order to evaluate the soil water content according to the penetration depth. The TDRP consists of cone, sleeve, driving rod, hammer, and guide. Three electrodes, which are used to measure the dielectric constant of soils, are mounted on the surface of sleeve and, in turn, connected with coaxial cable and time domain reflectometer. To establish the relationship between the volumetric water content and dielectric constant, several laboratory tests by using the TDRP are performed in the specimens with a variety of volumetric water content. The experimental results show that the dielectric constant is strongly correlated to volumetric water content as polynomial equations with an order of 3. In addition, the volumetric water content calculated from the dielectric constant is similar to that obtained from the sample weight. In the field, a small sampler is used to compare the volumetric water content calculated from the dielectric constant with the volumetric water content obtained from the sample. The results of field application demonstrate that the volumetric water content estimated by the TDRP shows similar trend to the gravimetric water content of sample. This study suggests that the TDRP is effectively used to evaluate the volumetric water content of unsaturated soils according to the penetration depth.