Is the soil dry density important when using TDR?

Abstract

Abstract The use of Time Domain Reflectometry (TDR) to monitor soil water content at either field or laboratory scales is highly common. Regarding the soil bulk density effect on the TDR application, three main approaches are found in the literature: [1] Ignore the density issue and use calibration to a evaluate the water content regardless of the density. This approach is early and basic - yet common. [2] Include soil density in the calibration equation and use empirical calibration for the water content as a function of both the TDR output and soil density. In this approach, the soil density should be provided from a outsource. [3] Calibrate the soil dry density from the TDR waveform. In this case both water content and dry density are determined from the TDR analysis. In cases where the dry density is not available, in order to use TDR for water content measurement, a decision has to be made whether to address the density issue, despite it is requires resources, or not. This paper reviews this issue and validates the density effect using an efficient TDR calibration methodology. A calibration scheme which controls dry density of the specimen has been developed and applied. The methodology creates continuous calibration curves over a range of volumetric water content from a single test specimen. This paper presents a unique examination of the ASTM D6780 standard.