ASTM_D_7698_-_21.pdf

Designation:D769821Standard Test Method forIn-Place Estimation of Density and Water Content of Soiland Aggregate by Correlation with Complex ImpedanceMethod1This standard is issued under the fixed designation D7698;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope*1.1 Purpose and ApplicationThis test method describesthe procedure,equipment,and interpretation methods forestimating in-place soil dry density and water content using aComplex-Impedance Measuring Instrument(CIMI).1.1.1 The purpose and application of this test method is fortesting porous material such as used in roadway base orbuilding foundations that may be deployed in the field atvarious test sites.The test apparatus includes electrodes thatcontact the porous material under test and a sensor unit thatsupplies electromagnetic signals to the porous material.Re-sponse signals reveal electrical parameters such as compleximpedance which can be equated to material properties such asdensity and moisture content.1.1.2 CIMI measurements as described in this test methodare applicable to measurements of compacted soils intended forroads and foundations.1.1.3 This test method describes the procedure for estimat-ing in-place density and water content of soils and soil-aggregates by use of a CIMI.The electrical properties of thesoil are measured using a radio frequency(RF)voltage sourceconnected to soil electrical probes driven into the soils andsoil-aggregates to be tested,in a prescribed pattern and depth.Certain algorithms of these properties are related to wet densityand water content.This correlation between electricalmeasurements,and density and water content is accomplishedusingacalibrationmethodology.Inthecalibrationmethodology,density and water content are determined byotherASTM Test Standards that measure soil density and watercontent,thereafter correlating the corresponding measuredelectrical properties to the soil physical properties.1.2 UnitsThe values stated in SI units are to be regardedas standard.The inch-pound units given in parentheses aremathematical conversions which are provided for informationpurposes only and are not considered standard.1.2.1 All observed and calculated values shall conform tothe guidelines for significant digits and rounding established inPractice D6026 unless superseded by this standard.1.3 Generalized Theory:1.3.1 Two key electrical properties of soil are conductivityand relative dielectric permittivity which are manifested as avalue of complex-impedance that can be determined.1.3.2 The soil conductivity contributes primarily to the realcomponent of the complex-impedance,and the soil relativedielectric permittivity contributes primarily to the imaginarycomponent of the complex-impedance.1.3.3 The complex-impedance of soil can be determined byplacing two electrodes in the soil to be tested at a knowndistance apart and a known depth.The application of a knownfrequency of alternating current to the electrodes enables ameasurement of current through the soil,voltage across theelectrodes,and the electrical phase difference between thevoltage and current.Complex-impedance is calculated fromthese known and measured parameters.1.3.4 From the determined complex-impedance,an electri-cal network consisting of a resistor(R)and capacitor(C)connected in parallel are used to represent a model of the soilbeing tested.1.3.5 Relationships can be made between the soil wetdensity and the magnitude of the complex-impedance,and alsobetween the soil water mass per unit measured,and thequotient of the values of C and R using a Soil Model process.1.3.6 The Soil Model process results in mathematical rela-tionships between the physical and electrical characteristics ofthe soil which are used for soil-specific calibration of the CIMI.1.3.7 Refer to Appendix X1 for a more detailed explanationof complex-impedance measurement of in-place soil,and itsuse in field measurements for the estimation of dry density andwater content.1.4 Precautions:1.4.1 The low-level RF output power levels of the CIMImethod are harmless.1This test method is under the jurisdiction ofASTM Committee D18 on Soil andRock and is the direct responsibility of Subcommittee D18.08 on Special andConstruction Control Tests.Current edition approved May 1,2021.Published May 2021.Originallyapproved in 2011.Last previous edition approved in 2020 as D769820.DOI:10.1520/D7698-21.*A Summary of Changes section appears at the end of this standardCopyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International