Suitability of Thermocouple Psychrometers for Studying Moisture Movement in Unsaturated Soils

    Published: Jan 1981

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    Interest in moisture movement in partially saturated soils has developed rapidly in recent years mainly as a result of increasing use of sites in arid regions for disposal of toxic industrial and radioactive wastes. In attempting to measure hydraulic properties of soils in arid regions, problems are encountered with measurement of large suctions. Accordingly, we investigated the possibility of using thermocouple psychrometers, which have a broader range than most other suction probes, for studies of moisture movement in unsaturated soils. In this paper, the general features of psychrometers are described, procedures for calibration and use are reviewed, and experimental data are presented and discussed. Psychrometric measurements were found to be reproducible within about ±10 to 30 percent over a range in suction of about 2 to 80 atm. Response times were typically less than an hour. Problems with corrosion of psychrometers were severe with strongly acidic soils but not with a basic soil. Independent measurements of suction provided quantitative evidence that psychrometric measurements are reliable. The conclusion is that psychrometers seem to be the most suitable devices now available for measuring suctions in relatively dry, partially saturated soils.


    permeability, soils, partially saturated soils, unsaturated soils, psychrometers, relative humidity, suction, pore water pressure, thermocouples, groundwater

    Author Information:

    Daniel, DE
    Assistant professor and professor of civil engineering, University of Texas, Austin, Tex.

    Hamilton, JM
    Geotechnical engineer, Law Engineering Testing Co., Houston, Tex.

    Olson, RE
    Assistant professor and professor of civil engineering, University of Texas, Austin, Tex.

    Committee/Subcommittee: D18.14

    DOI: 10.1520/STP28318S

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