DEVELOPMENT OF PROTOTYPE SOIL MOISTURE SENSORS

In an effort to develop innovative sensors for the in situ measurement of moisture in aggregate base and soil subgrade layers of pavements, two prototypes have been developed and laboratory evaluated: a sensor based on nuclear magnetic resonance (NMR) technology and a sensor using dielectric constant technology. Both sensor types are potentially applicable to highway soil moisture measurement problems. Each sensor measures the amount of water in the effective volume of a soil sample and is somewhat influenced by soil type. For a particular soil of known dry density, the percentage water on a dry weight basis can be determined by empirical calibration. Under an extension of this study, the sensors are undergoing (1) refinement and development of ancillary readout equipment; (2) simulated field evaluation over a range of soil, compaction, moisture, and contamination conditions; and (3) field installation and practical evaluation in two different climatic regions. The NMR sensor based on the spin echo approach was tested with bentonite clay, silica flour, and an organic silty clay. The influences of soil density, organic matter and dissolved salts were investigated. In the prototype dielectric model, the sensor electrodes are incorporated as part of a resonance circuit whose frequency of oscillation circuit is contained within the buried sensor; a coaxial cable connects the sensor to the external power supply and readout instrument. It is hoped that in addition to the original objectives, the technology developed in the study may be applied to the development of laboratory instruments for instantaneous measurement of moisture in soil samples without the need for drying.

• Record URL:
  • http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rrd_75.pdf
• Supplemental Notes:
  • An NCHRP staff digest of the essential findings from the final reports on the sensor development phases of NCHRP Projects 21-2 and 21-2(2), "Instrumentation for Moisture Measurement--Bases, Subgrades, and Earth Materials," by C.G. Gardner, G.A. Matzkanin, and J.R. Birchak, Southwest Research Institute, San Antonio, Texas (Project 21-2); and E.T. Selig, D.C. Wobschall, S. Mansukhami, and A. Motiwala, State University of New York, Buffalo, New York (Project 21-2(2)). Distribution, posting, or copying of this PDF is strictly prohibited without written permission of the Transportation Research Board of the National Academy of Sciences. Unless otherwise indicated, all materials in this PDF are copyrighted by the National Academy of Sciences. Copyright © National Academy of Sciences. All rights reserved.
• Corporate Authors:

  Transportation Research Board

  500 Fifth Street, NW
  Washington, DC  United States  20001
• Publication Date: 1975-7

Media Info

• Media Type: Digital/other
• Pagination: 2 p.
• Serial:
  • NCHRP Research Results Digest
  • Issue Number: 75
  • Publisher: Transportation Research Board

Subject/Index Terms

• TRT Terms: Bend tests; Calibration; Clay; Climate; Dielectric properties; Dry density; Equipment; Laboratory studies; Measurement; Nuclear magnetic resonance; Organic soils; Pavement base course; Pavement subgrade; Performance; Sensors; Silica; Soil water
• Uncontrolled Terms: Field performance
• Subject Areas: Geotechnology; Highways;

Filing Info

• Accession Number: 00099751
• Record Type: Publication
• Files: TRIS, TRB
• Created Date: Oct 18 1975 12:00AM