New Methodology for Density and Water Content by Time Domain Reflectometry

Abstract

This paper provides a new methodology for determining soil water content and density under different compaction energies. A new calibration equation was introduced making use of the voltage drop associated with the first passage of the electromagnetic wave through the soil specimen, the final voltage level after wave propagation ceases, and dry density normalized by the density of water. The new calibration equation allows for the direct calculation of dry density. Values of dry density are then used in the normalized apparent dielectric constant equation to determine the water content. Results of numerous laboratory tests on a wide variety of soils (including coarse-grained soils) showed that the proposed method accommodates different levels of compaction energy. The method also was validated with different field tests at sites commonly used in geotechnical earthwork construction, using soil-specific model coefficients determined from laboratory compaction tests. The results of this study indicate that the new calibration relationships appear relatively independent of the effects of compaction energy and of probe configuration in time domain reflectometry (TDR) testing. The proposed method presents an improvement to the one-step TDR method.