Measuring Dielectric Constant in Highly Conductive Soils Based on Surface Reflection Coefficients
Publication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 135, Issue 12
Abstract
In soils with high electrical conductivities, time domain reflectometry (TDR) principles fail to measure the apparent dielectric constant by travel time analysis. This limits the application of water content measurement of existing TDR technologies on those materials. This paper describes a new approach for determining the dielectric constants in highly conductive soils from surface reflections of TDR signals. The multiple reflections at the interfaces of impedance mismatches in the ASTM standard probe were studied. Extension rods were used to avoid the overlap of the reflections along the probe. A relationship between the reflection coefficient at the soil surface and the apparent dielectric constant of the soil was established theoretically and validated by laboratory experiments. Results indicate that the dielectric constant can be determined with reasonable accuracy from the surface reflection coefficient even for soils with high electrical conductivities, where the conventional travel time analysis fails. Compared with alternative approaches, such as based on inversion model, this new method offers high time efficiency in extending TDR applications in highly conductive soils.
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Acknowledgments
The writers thank the National Natural Science Foundation of China for financial support (Grant Nos. NNSFC50538080 and NNSFC50878193), program for New Century Excellent Talents in university (NCET), and the National Basic Research Program of China (Grant No. UNSPECIFIED2007CB714001). The suggestions provided by Dr. D. G. Fredlund are also greatly appreciated. The discussion with Professor V. P. Drnevich helped improve significantly the manuscript. The work of master candidate Wei Chen is gratefully acknowledged.
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Information
Published In
Journal of Geotechnical and Geoenvironmental Engineering
Volume 135 • Issue 12 • December 2009
Pages: 1883 - 1891
Copyright
© 2009 ASCE.
History
Received: Oct 13, 2008
Accepted: Jun 5, 2009
Published online: Jun 10, 2009
Published in print: Dec 2009
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