Significance and Use
The determination of the water-content, or moisture content, of soil is one of the fundamental needs in the soil physics and hydrology disciplines. The need arises from requirements for defining the optimal time for irrigation, the infiltration rate, the soil-moisture flux, contaminant transport rates, and evaluating the potential for leakage from a waste site or a surface or subsurface barrier.
The TDR application covered in this test method is that used for point measurements of moisture content in soil. The application is either through manual insertion into the soil or by burying a probe in the subsurface to acquire moisture content data at a specific location. In addition, core samples may be tested with TDR at a drill site to acquire real-time soil moisture data.
1.1 This test method covers the determination of water content (or moisture content) in soil by the use of the electromagnetic technique called Time-Domain Reflectometry (TDR).
1.2 This test method was written to detail the procedure for conventional TDR measurements of soil. Other TDR applications exist for the purpose of quantifying water content in soil and are not covered here, such as flat probe technologies and wetting front advance methods.
1.3 Commercial TDR applications exist which automate the TDR methodology and are not detailed in this test method. It is likely that overlap exists in the automated commercial systems versus this applied method, and the user is encouraged to adhere to this test method when applicable.
1.4 This test method is one of a series on vadose zone characterization methods. Other standards have been prepared on vadose zone characterization techniques.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
D653 Terminology Relating to Soil, Rock, and Contained Fluids
D1452 Practice for Soil Exploration and Sampling by Auger Borings
D2216 Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass
D4643 Test Method for Determination of Water (Moisture) Content of Soil by Microwave Oven Heating
D4700 Guide for Soil Sampling from the Vadose Zone
D4944 Test Method for Field Determination of Water (Moisture) Content of Soil by the Calcium Carbide Gas Pressure Tester
D5220 Test Method for Water Mass per Unit Volume of Soil and Rock In-Place by the Neutron Depth Probe Method
Balun transformer; multiplexers; propagation velocity; soil samples; TDR probes; time domain reflectometry (TDR); volumetric water (moisture) content
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Citing ASTM Standards
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