Determining Soil Volumetric Moisture Content Using Time Domain Reflectometry

007580281998PDFResearch PaperFHWA-RD-97-I 39SoilsMoisture contentVolumetric analysisDielectric propertiesTime domain reflectometersdielectric constantinsitu methodstime domain reflectometry (TDR)United StatesUnited States. Federal Highway AdministrationUnited States. Federal Highway AdministrationNTL-HIGHWAY/ROAD TRANSPORTATION-Soils and GeologyFederal Highway AdministrationTime domain reflectometry (TDR) is a technique used to measure indirectly the in situ volumetric moisture content of soil. Current research provides a variety of prediction equations that estimate the volumetric moisture content using the dielectric constant calculated from the apparent length obtained from the TDR reader. However, very limited research exists regarding which of several available procedures should be used to obtain the apparent length of the TDR response for use in calculating the dielectric constant. The purpose of this study is to enhance the predictive accuracy of in situ volumetric moisture content estimation from TDR measurements. The study is divided into two phases. The initial phase evaluates the five known methods of analyzing the apparent length of TDR responses to determine which provides the most accurate method for estimating the volumetric moisture content. Phase II, through a mixing model form, regresses the volumetric properties of the soil and the apparent length of the TDR response to obtain a predicted volumetric moisture content.93