Measurement of the Unfrozen Water Content of Soils. Comparison of NMR (Nuclear Magnetic Resonance) and TDR (Time Domain Reflectometry) Methods

• Main Authors: Smith, Michael W., Tice, Allen R.
• Other Authors: COLD REGIONS RESEARCH AND ENGINEERING LAB HANOVER NH
• Format: Text
• Language: English
• Published: 1988
• Subjects: Soil Mechanics; Snow; Ice and Permafrost; *SOIL TESTS; *MOISTURE CONTENT; *SOILS; LABORATORY TESTS; NUCLEAR MAGNETIC RESONANCE; WATER; COMPARISON; TEST METHODS; ESTIMATES; DIELECTRIC PROPERTIES; FREEZING; CONSTANTS; ERRORS; PRECISION; CALIBRATION; ABSORPTION; EQUATIONS; RANGE(EXTREMES); REFLECTOMETERS; TEXTURE; TIME DOMAIN; VOLUME; CURVED PROFILES; PROBES; TEMPERATURE; TIME DOMAIN REFLECTOMETRY; DIELECTRIC CONSTANT; FROZEN SOILS; PE62730A; WU002; Ice; permafrost
• Online Access: http://www.dtic.mil/docs/citations/ADA203082; http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA203082

The results of a laboratory testing program, carried out to compare two independent methods for determining the unfrozen water content of soils, are described. With the time domain reflectometry method, the unfrozen water content is inferred from a calibration curve of apparent dielectric constant vs volumetric water content, determined by experiment. Previously, precise calibration of the TDR technique was hindered by the lack of a reference comparison method, which nuclear magnetic resonance now offers. This has provided a much greater scope for calibration, including a wide range of soil types and temperature (unfrozen water content). The results of the testing program yielded a relationship between dielectric constant and volumetric unfrozen water content that is largely unaffected by soil type, although a subtle but apparent dependency on the texture of the soil was noted. It is suggested that this effect originates from the lower valued dielectric constant for absorbed soil water. In spite of this, the general equation presented may be considered adequate for most practical purposes. The standard error of estimate is 0.015 cc/cc, although this may be reduced by calibrating for individual soils. Brief guidelines on system and probe design are offered to help ensure that use of the TDR method will give results consistent with the relationship presented. Keywords: Dielectric constant; Frozen soils; Soils tests; Time domain reflectometry.