ASTM D7698-21

Standard Test Method for In-Place Estimation of Density and Water Content of Soil and Aggregate by Correlation with Complex Impedance Method

SIGNIFICANCE AND USE
5.1 CIMI measurements as described in this Standard Test Method are applicable to measurements of compacted soils intended for roads and foundations.  
5.2 The test method is used for estimating in-place values of density and water content of soils and soil-aggregates based on electrical measurements.  
5.3 The test method may be used for quality control and acceptance testing of compacted soil and soil aggregate mixtures as used in construction and also for research and development. The minimal disturbance nature of the methodology allows repetitive measurements in a single test location and statistical analysis of the results.  
5.4 Limitations:  
5.4.1 This test method provides an overview of the CIMI measurement procedure using a controlling console connected to a soil sensor unit which applies a 3.0 MHz RF voltage to an in-place soil via metallic probes that are driven into the soil at a prescribed distance apart. This test method does not discuss the details of the CIMI electronics, computer, or software that utilize on-board algorithms for estimating the soil density and water content  
5.4.2 It is difficult to address an infinite variety of soils in this standard. However, data presented in X3.1 provides a list of soil types that are applicable for the CIMI use.  
5.4.3 The procedures used to specify how data are collected, recorded, or calculated in this standard are regarded as the industry standard. In addition, they are representative of the significant digits that generally should be retained. The procedures prescribed in this standard do not consider material variation, purpose for obtaining the data, special purpose studies, or any considerations for the user’s objectives; it is common practice to increase or reduce significant digits of reported data to be commensurate with these considerations. It is beyond the scope of this standard to consider significant digits used in analytical methods for engineering design.
Note 1: Notwithstanding th...
SCOPE
1.1 Purpose and Application—This test method describes the procedure, equipment, and interpretation methods for estimating in-place soil dry density and water content using a Complex-Impedance Measuring Instrument (CIMI).  
1.1.1 The purpose and application of this test method is for testing porous material such as used in roadway base or building foundations that may be deployed in the field at various test sites. The test apparatus includes electrodes that contact the porous material under test and a sensor unit that supplies electromagnetic signals to the porous material. Response signals reveal electrical parameters such as complex impedance which can be equated to material properties such as density and moisture content.  
1.1.2 CIMI measurements as described in this test method are applicable to measurements of compacted soils intended for roads and foundations.  
1.1.3 This test method describes the procedure for estimating in-place density and water content of soils and soil-aggregates by use of a CIMI. The electrical properties of the soil are measured using a radio frequency (RF) voltage source connected to soil electrical probes driven into the soils and soil-aggregates to be tested, in a prescribed pattern and depth. Certain algorithms of these properties are related to wet density and water content. This correlation between electrical measurements, and density and water content is accomplished using a calibration methodology. In the calibration methodology, density and water content are determined by other ASTM Test Standards that measure soil density and water content, thereafter correlating the corresponding measured electrical properties to the soil physical properties.  
1.2 Units—The values stated in SI units are to be regarded as standard. The inch-pound units given in parentheses are mathematical conversions which are provided for information purposes only and are not considered standard.  
1.2.1...

General Information

• Status: Published
• Publication Date: 30-Apr-2021
• ICS: 13.080.20 - Physical properties of soils
• Technical Committee: D18 - Soil and Rock
• Drafting Committee: D18.08 - Special and Construction Control Tests

Relations

• Refers: ASTM D3740-23 - Standard Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction
• Effective Date: 01-Nov-2023
• Refers: ASTM D7382-20 - Standard Test Methods for Determination of Maximum Dry Unit Weight of Granular Soils Using a Vibrating Hammer
• Effective Date: 01-Jul-2020
• Refers: ASTM D3740-19 - Standard Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction
• Effective Date: 01-Oct-2019
• Refers: ASTM D2216-19 - Standard Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass
• Effective Date: 01-Mar-2019
• Refers: ASTM D4944-18 - Standard Test Method for Field Determination of Water (Moisture) Content of Soil by the Calcium Carbide Gas Pressure Tester
• Effective Date: 15-Feb-2018
• Refers: ASTM D4643-17 - Standard Test Method for Determination of Water Content of Soil and Rock by Microwave Oven Heating
• Effective Date: 01-Feb-2017
• Refers: ASTM D4253-16e1 - Standard Test Methods for Maximum Index Density and Unit Weight of Soils Using a Vibratory Table
• Effective Date: 01-Mar-2016
• Refers: ASTM D4253-16 - Standard Test Methods for Maximum Index Density and Unit Weight of Soils Using a Vibratory Table
• Effective Date: 01-Mar-2016
• Refers: ASTM D4253-14 - Standard Test Methods for Maximum Index Density and Unit Weight of Soils Using a Vibratory Table
• Effective Date: 15-Dec-2014
• Refers: ASTM D653-14 - Standard Terminology Relating to Soil, Rock, and Contained Fluids
• Effective Date: 01-Aug-2014
• Refers: ASTM E691-13 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-May-2013
• Refers: ASTM D698-12e1 - Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Standard Effort (12 400 ft-lbf/ft³ (600 kN-m/m³))
• Effective Date: 01-May-2012
• Refers: ASTM D698-12 - Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Standard Effort (12 400 ft-lbf/ft³ (600 kN-m/m³))
• Effective Date: 01-May-2012
• Refers: ASTM D3740-12a - Standard Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction
• Effective Date: 01-May-2012
• Refers: ASTM D1557-12 - Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Modified Effort (56,000 ft-lbf/ft³ (2,700 kN-m/m³))
• Effective Date: 01-May-2012

Overview

ASTM D7698-21 is a standard test method developed by ASTM International for the in-place estimation of density and water content of soil and aggregate using the Complex Impedance Method (CIMI). This method provides a non-destructive, field-applicable approach to measure the physical properties of compacted soils and soil-aggregate mixtures, which are frequently used in road construction and building foundations. By correlating measured electrical properties-specifically, complex impedance-to density and moisture, the method enables rapid, reliable assessment essential for quality control, acceptance testing, and research.

Key Topics

• Complex Impedance Measuring Instrument (CIMI):

  • Utilizes electrodes that apply an RF (radio frequency) voltage to in-place soil or aggregate.
  • Measures key electrical parameters (such as voltage, current, and phase difference) to determine complex impedance.
  • Converts these electrical properties into estimates of soil density and water content using calibration and regression analysis.

• Calibration and Correlation:

  • Requires a soil-specific model developed by correlating electrical readings with traditional density and moisture content tests on representative samples.
  • Calibration ensures accuracy by capturing the variability of the tested material.

• Minimal Disturbance:

  • The method allows for repetitive testing at the same location with little impact on the test area, supporting both spot-checks and statistical analyses.

• Significance in Field Applications:

  • Enables rapid, on-site evaluation of compaction quality, essential for civil engineering and construction projects.
  • Facilitates better process control compared to destructive or sample-based laboratory methods.

• Limitations and Interferences:

  • Performance may be affected by large rocks, construction debris, non-representative soil samples, soil temperature variations, and electrical anomalies.
  • Accuracy depends on soil homogeneity and proper electrode-to-soil contact.

Applications

ASTM D7698-21 is widely applicable within the construction, geotechnical, and civil engineering sectors, including:

• Road Construction: Assessing compaction and verifying water content of subgrades, bases, and embankments.
• Foundation Engineering: Evaluating compaction and moisture in soils underlying building foundations for stability and compliance.
• Quality Control: Non-destructive assessment during project execution to ensure adherence to specified compaction and moisture standards.
• Acceptance Testing: Providing objective criteria for the evaluation and acceptance of completed earthwork before subsequent construction phases.
• Research and Development: Supporting studies on soil behavior, compaction methods, and material performance under various environmental conditions.

The test method is valuable for any application requiring efficient, reliable estimations of dry density and water content of soils and aggregates, especially where repetitive or minimally invasive testing is desired.

Related Standards

The application and calibration of ASTM D7698-21 often involve reference to other established ASTM standards in geotechnical testing, including:

• ASTM D1556 - Density and Unit Weight of Soil by the Sand-Cone Method
• ASTM D2216 - Laboratory Determination of Water Content of Soil and Rock by Mass
• ASTM D698 & D1557 - Laboratory Compaction Characteristics of Soil using Standard or Modified Effort
• ASTM D4253 - Maximum Index Density and Unit Weight of Soils Using a Vibratory Table
• ASTM D4643 & D4944 - Determination of Water Content by Microwave Oven and Calcium Carbide Gas Pressure Tester
• ASTM D653 - Terminology Relating to Soil, Rock, and Contained Fluids

Developing and using a proper calibration for the CIMI device may require performing one or more of these referenced test methods alongside in-field electrical measurements.

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Keywords: ASTM D7698, soil density, water content, complex impedance, in-place testing, CIMI, aggregate, soil compaction, non-destructive testing, construction quality control, road foundation testing, geotechnical standards

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D7698 − 21
Standard Test Method for
In-Place Estimation of Density and Water Content of Soil
and Aggregate by Correlation with Complex Impedance
Method
This standard is issued under the fixed designation D7698; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope* mathematical conversions which are provided for information
purposes only and are not considered standard.
1.1 Purpose and Application—This test method describes
1.2.1 All observed and calculated values shall conform to
the procedure, equipment, and interpretation methods for
the guidelines for significant digits and rounding established in
estimating in-place soil dry density and water content using a
Practice D6026 unless superseded by this standard.
Complex-Impedance Measuring Instrument (CIMI).
1.1.1 The purpose and application of this test method is for
1.3 Generalized Theory:
testing porous material such as used in roadway base or
1.3.1 Two key electrical properties of soil are conductivity
building foundations that may be deployed in the field at
and relative dielectric permittivity which are manifested as a
various test sites. The test apparatus includes electrodes that
value of complex-impedance that can be determined.
contact the porous material under test and a sensor unit that
1.3.2 The soil conductivity contributes primarily to the real
supplies electromagnetic signals to the porous material. Re-
component of the complex-impedance, and the soil relative
sponse signals reveal electrical parameters such as complex
dielectric permittivity contributes primarily to the imaginary
impedance which can be equated to material properties such as
component of the complex-impedance.
density and moisture content.
1.3.3 The complex-impedance of soil can be determined by
1.1.2 CIMI measurements as described in this test method
placing two electrodes in the soil to be tested at a known
areapplicabletomeasurementsofcompactedsoilsintendedfor
distance apart and a known depth. The application of a known
roads and foundations.
frequency of alternating current to the electrodes enables a
1.1.3 This test method describes the procedure for estimat-
measurement of current through the soil, voltage across the
ing in-place density and water content of soils and soil-
electrodes, and the electrical phase difference between the
aggregates by use of a CIMI. The electrical properties of the
voltage and current. Complex-impedance is calculated from
soil are measured using a radio frequency (RF) voltage source
these known and measured parameters.
connected to soil electrical probes driven into the soils and
1.3.4 From the determined complex-impedance, an electri-
soil-aggregates to be tested, in a prescribed pattern and depth.
cal network consisting of a resistor (R) and capacitor (C)
Certainalgorithmsofthesepropertiesarerelatedtowetdensity
connected in parallel are used to represent a model of the soil
and water content. This correlation between electrical
being tested.
measurements, and density and water content is accomplished
1.3.5 Relationships can be made between the soil wet
using a calibration methodology. In the calibration
density and the magnitude of the complex-impedance, and also
methodology, density and water content are determined by
between the soil water mass per unit measured, and the
otherASTMTestStandardsthatmeasuresoildensityandwater
quotient of the values of C and R using a Soil Model process.
content, thereafter correlating the corresponding measured
1.3.6 The Soil Model process results in mathematical rela-
electrical properties to the soil physical properties.
tionships between the physical and electrical characteristics of
1.2 Units—The values stated in SI units are to be regarded
thesoilwhichareusedforsoil-specificcalibrationoftheCIMI.
as standard. The inch-pound units given in parentheses are
1.3.7 Refer to Appendix X1 for a more detailed explanation
of complex-impedance measurement of in-place soil, and its
use in field measurements for the estimation of dry density and
ThistestmethodisunderthejurisdictionofASTMCommitteeD18onSoiland
water content.
Rock and is the direct responsibility of Subcommittee D18.08 on Special and
Construction Control Tests.
1.4 Precautions:
Current edition approved May 1, 2021. Published May 2021. Originally
1.4.1 The low-level RF output power levels of the CIMI
approved in 2011. Last previous edition approved in 2020 as D7698–20. DOI:
10.1520/D7698-21. method are harmless.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7698 − 21
1.4.2 The SI units presented for apparatus are substitutions 3.2 Definitions of Terms Specific to This Standard:
of the inch-pound units, other similar SI units should be 3.2.1 complex impedance, n—the ratio of the phasor equiva-
acceptable providing they meet the technical requirements lent of a steady-state sine-wave or voltage like quantity
established by the inch-pound apparatus. (driving force) to the phasor equivalent of a steady-state
sine-wave current of current like quantity (response).
1.5 This standard does not purport to address all of the
safety concerns, if any, associated with its use. There are no 3.2.2 relative permittivity, n—the permittivity of the mate-
known hazards associated with this standard. It is the respon- rial relative to that of free space.
sibility of the user of this standard to establish appropriate
3.2.3 phase relationship, n—the electrical phase difference
safety, health, and environmental practices and determine the
between the applied probe-to-probe RF voltage, and the
applicability of regulatory limitations prior to use.
resulting soil current.
1.6 This international standard was developed in accor-
3.2.4 probe-to-probe RF voltage, n—the peak value of RF
dance with internationally recognized principles on standard-
voltage measured across two probes that are conducting soil
ization established in the Decision on Principles for the
current.
Development of International Standards, Guides and Recom-
3.2.5 soil capacitance, n—the value of the capacitor in an
mendations issued by the World Trade Organization Technical
equivalent parallel resistor-capacitor circuit that results from
Barriers to Trade (TBT) Committee.
theprobe-to-probeRFvoltage,currentinthesoil,andresulting
phaserelationshipduetotheapplicationofaRFvoltagesource
2. Referenced Documents
applied to the probes.
2.1 ASTM Standards:
3.2.6 soil current, n—the peak value of the RF current
D653 Terminology Relating to Soil, Rock, and Contained
passing through the soil from one probe electrode to another.
Fluids
D698 Test Methods for Laboratory Compaction Character-
3.2.7 Soil Model, n—the result of a calibration procedure
istics of Soil Using Standard Effort (12,400 ft-lbf/ft (600
that establishes a correlating linear function between measured
kN-m/m ))
electrical soil properties and measured physical soil properties.
D1556 Test Method for Density and Unit Weight of Soil in
3.2.8 Soil Model linear correlation function, n—one of the
Place by Sand-Cone Method
two mathematical expressions that are derived from perform-
D1557 Test Methods for Laboratory Compaction Character-
ing linear regressions on two sets of soil test data; measured
istics of Soil Using Modified Effort (56,000 ft-lbf/ft
physical soil characteristics, and a corresponding set of elec-
(2,700 kN-m/m ))
trical measurements made on the soil samples.
D2216 Test Methods for Laboratory Determination of Water
3.2.9 soil resistance, n—the value of the resistor in an
(Moisture) Content of Soil and Rock by Mass
equivalent parallel resistor-capacitor circuit that results from
D3740 Practice for Minimum Requirements for Agencies
theprobe-to-probeRFvoltage,soilcurrent,andresultingphase
Engaged in Testing and/or Inspection of Soil and Rock as
relationshipduetotheapplicationofaRFsourceappliedtothe
Used in Engineering Design and Construction
probes.
D4253 Test Methods for Maximum Index Density and Unit
Weight of Soils Using a Vibratory Table
4. Summary of the Test Method
D4643 Test Method for Determination of Water Content of
4.1 The test method is a two-step process.
Soil and Rock by Microwave Oven Heating
4.1.1 A Soil Model that relates impedance measurement to
D4718 Practice for Correction of Unit Weight and Water
the density and water content of the soil is developed. In this
Content for Soils Containing Oversize Particles
step the electrical measurements are collected at locations that
D4944 TestMethodforFieldDeterminationofWater(Mois-
have various water contents and densities typical of the range
ture)ContentofSoilbytheCalciumCarbideGasPressure
to be expected. Concurrent with collecting the electrical data,
Tester
determinationofdensityandwatercontentareperformedatthe
D6026 Practice for Using Significant Digits in Geotechnical
same locations using one or more of the traditional test
Data
methods,suchasTestMethodsD1556andD2216.Theprocess
D7382 Test Methods for Determination of Maximum Dry
is repeated over the site such that a range of water contents and
Unit Weight of Granular Soils Using a Vibrating Hammer
densities are obtained. The combined data (impedance and
E691 Practice for Conducting an Interlaboratory Study to
density/water content) will generate the correlating linear
Determine the Precision of a Test Method
regression functions of the Soil Model.
4.1.2 Once the Soil Model has been developed the CIMI
3. Terminology
device is used to make electrical measurements of the soil at
3.1 Definitions—For definitions of common technical terms
locationsofunknowndensityandwatercontent.UsingtheSoil
used in this standard, refer to Terminology D653.
Model linear correlation functions, the procedure then esti-
mates the values of soil density and water content based on the
measured electrical properties.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on Institute of Electrical and Electronics Engineers Standards 100, 1972
the ASTM website. Sears & Zemansky, University Physics, 10th Edition
D7698 − 21
5. Significance and Use probes and the soil being tested. Large air voids, relative to the
volume of material being tested, that may be present between
5.1 CIMI measurements as described in this Standard Test
soil probes and the surface of the material being tested may
Method are applicable to measurements of compacted soils
cause incorrect density measurements. The shape of the soil
intended for roads and foundations.
electrical probe is important to the quality of the electrical
5.2 Thetestmethodisusedforestimatingin-placevaluesof
measurements collected by the CIMI.
density and water content of soils and soil-aggregates based on
6.3 When driving the measuring electrical probes, it is
electrical measurements.
critical to the accuracy of the measurement that they make a
5.3 The test method may be used for quality control and
complete and tight contact with the soil over the entire conical
acceptance testing of compacted soil and soil aggregate mix-
part of the probe.
tures as used in construction and also for research and
6.4 If the volume of soil material being tested as defined in
development. The minimal disturbance nature of the method-
X2.10 has oversize particles or large voids in the electrical
ology allows repetitive measurements in a single test location
field, this may cause errors in measurements of electrical
and statistical analysis of the results.
properties.Wherelackofuniformityinthesoilduetolayering,
5.4 Limitations:
aggregate or voids is suspected, the test site shall be excavated
5.4.1 This test method provides an overview of the CIMI
and visually examined to determine if the test material is
measurement procedure using a controlling console connected
representative of the in-situ material in general and if an
to a soil sensor unit which applies a 3.0 MHz RF voltage to an
oversize correction is required in accordance with Practice
in-place soil via metallic probes that are driven into the soil at
D4718. Soils must be homogeneous and practically free of
a prescribed distance apart. This test method does not discuss
rocks that are in excess of five centimeters in diameter (2 in.)
the details of the CIMI electronics, computer, or software that
and construction debris for the most accurate results.
utilize on-board algorithms for estimating the soil density and
6.5 Statistical variance may increase for soil material that is
water content
significantlydrierorwetterthanoptimumwatercontent(2.5 %
5.4.2 It is difficult to address an infinite variety of soils in
over optimum or 6.0 % below optimum) as determined using
this standard. However, data presented in X3.1 provides a list
Test Methods D698 or D1557. Statistical variance may in-
of soil types that are applicable for the CIMI use.
crease for soil material that is compacted to less than 88 % of
5.4.3 Theproceduresusedtospecifyhowdataarecollected,
the maximum dry density as determined using Test Methods
recorded, or calculated in this standard are regarded as the
D698orD1557.TheCIMIisgenerallymoreaccuratewhenthe
industry standard. In addition, they are representative of the
Soil Model range is broader than the range of soil density and
significant digits that generally should be retained. The proce-
water content being tested in the field.
dures prescribed in this standard do not consider material
6.6 If temperature measurements are not used, an error may
variation, purpose for obtaining the data, special purpose
be introduced in the results depending on the value of the
studies, or any considerations for the user’s objectives; it is
difference between the temperature of the soil used for the Soil
common practice to increase or reduce significant digits of
Model and the unknown in-place soil being measured. All
reported data to be commensurate with these considerations. It
electrical values are equilibrated to 15.5 °C (60 °F). The
is beyond the scope of this standard to consider significant
equilibration is necessary because the soil temperature affects
digits used in analytical methods for engineering design.
theelectricalsignalsthataremeasured.Theoperatingtempera-
NOTE 1—Notwithstanding the statements on precision and bias con-
ture range where the CIMI has been used globally is for the
tainedinthistestmethod,theprecisionofthistestmethodisdependenton
CIMI is between 1.1 °C (34 °F) and 50 °C (122 °F).
the competence of the personnel performing it and the suitability of the
equipment and facilities used. Agencies that meet the criteria of Practice 6.7 This test method applies only to non-frozen soil. The
D3740 are generally considered capable of competent and objective
electrical properties of soil change considerably as soil tem-
testing. Users of this test method are cautioned that compliance with
perature approaches the freezing point of the entrained water.
Practice D3740 does not in itself ensure reliable results. Reliable testing
depends on many factors; Practice D3740 provides a means of evaluating 6.8 The use of electrical probes with different length than
some of those factors.
thoseusedtomaketheSoilModelwillintroduceanerrorinthe
interpretation of the data and the estimation of the density of
5.5 All observed and calculated values shall conform to the
water content of the tested soils.
guidelines for significant digits and rounding established in
Practice D6026, unless superseded by this test method.
6.9 The use of a Soil Model that was generated from a
different soil than that selected for unknown in-place measure-
6. Interferences
ments will result in errors in the estimation of the density and
water content of the tested soils.
6.1 Anomalies in the test material with electrical impedance
properties significantly different from construction soils and
6.10 Attempts to measure unknown in-place soils with a
aggregate evaluated during Soil Model development, such as
Soil Model that was generated from a limited range of wet
metal objects or organic material, may affect the accuracy of
density or water content values, or both, may result in density
the test method.
and water content estimation errors.
6.2 The accuracy of the results obtained by this test method 6.11 Variation in pore water salinity, soil chemistry, soil
may be influenced by poor contact between the soil electrical mineralogy or other anomalies that causes field-test electronic
D7698 − 21
measurements to be outside the soil model operational range construction material a shoulder is machined at the end of the
will cause the CIMI to report a warning message. X2.1 conical taper that is undercut. When the conical electrode is
containsadditionalinformationregardingvariationinelectrical driven in the compacted construction material to the level
measurements and CIMI management techniques. where the shoulder is level with the construction material
surface, a repeatable surface area of the electrode is in contact
7. Apparatus
with the construction material. The soil electrode achieves
good contact with the compacted construction material and
7.1 Complex-Impedance Measuring Instrument (See Fig.
1)—Whileexactdetailsofconstructionoftheapparatusandthe allows for consistency in electrical measurements.
7.2.1 The length of soil electrical probes can vary typically
electric circuits therein may vary, the system shall consist of
the following: havingembedmentlengthsbetween102mm(4in.)and31mm
(1.2 in.). The bottom diameter of each soil electrical probe is 5
7.1.1 Soil Sensor Unit—The “Soil Sensor” is a component
of the CIMI which electronically combines the RF voltage mm (0.2 in.).The top diameter of the embedded length of each
soil electrical probe varies between 14 mm (0.56 in.) for the
source and the three RF measurement devices. Cables are used
to connect the Soil Sensor to the electrical probes. 102 mm (4 in.) embedded length probe and 32 mm (1.25 in.)
for the 305 mm (12 in.) embedded length probe. During the
7.1.1.1 RF Source—Typically a 3 MHz RF voltage source is
testing procedure, the soil electrical probe length is selected to
applied to the soil under test by probe type electrodes driven
best match thickness of the compacted material. Since a
into the in-place soil at a prescribed depth and spacing. It
portion of the probe must be above the surface to facilitate
measures the RF voltage applied to the soil electrical probes
and RF current drawn by the soil. Additionally, the electrical electrical clip connector, the desired embedment depth must be
clearly indicated with a scribed mark or change in geometry.
phase relationship between the soil current and the probe-to-
probe RF voltage is determined. The drawing inFig. 2 below shows the size and dimensions for
the 152 mm (6 in.) electrical probe, the other electrical probes
7.1.1.2 Ammeter—Means for measuring the RF soil current.
7.1.1.3 Voltmeter—Means for measuring the probe-to-probe have similar shape and can be reviewed in the manufacturer’s
catalog.
RF voltage.
7.1.1.4 Phase Difference Meter—Means for measuring the
7.3 A template shall be used to place the electrodes as they
phase difference between the probe-to-probe RF voltage and
are driven into the soil. The four probes are driven into the soil
RF soil current.
atthe0°,90°,180°,and270°inclockwisepositionsaroundthe
7.1.1.5 Connecting Cables—For connecting the soil electri-
periphery of the template.
cal probes to the display console meter (that is, ammeter,
7.4 Thermistor temperature probe that connects to the CIMI
voltmeter, and phase difference meter).
for soil temperature measurement, and resulting compensation
7.1.2 Display Console Unit
of calculated electrical soil parameters.
7.2 Soil Electrical Probes (Four Required, Equally
7.5 Hand Tools—Hand tools for driving and retrieving the
Dimensioned)—Of electrical conducting material suitable for
soil electrical probes. A 2.7-kg to 5.4-kg (6-lb to 12-lb) dead
driving into compacted material, typically constructed of
blow or brass-faced hammer is used to avoid damaging the
common water hardened drill steel or stainless steel. The soil
steel probes. The soil electrical probes are removed from the
electrical probes have a conical shape designed to optimize the
soil that has been tested using 30.5 cm (12 in.) channel lock
contact between the electrode and the compacted construction
pliers.
material around the electrode as it is driven in. To further
control the contact area of the electrode with the compacted 7.6 Other components of the system are:
NOTE 1—The wires crossing in the diagram are not touching each other during use to prevent parasitic capacitance.
In the drawing the small probe is the thermistor and the three large probes are three of the four used to collect soil electrical data, the fourth probe
is not seen in the section drawing because it is directly behind the center probe.
FIG. 1 Diagram of a Complex Impedance Measuring Instrument in Use
D7698 − 21
FIG. 2 Drawing of a 152.4 mm (6 in.) Soil Electrical Probe
7.6.1 Safety goggles, and of different densities or water contents should be done the day
7.6.2 Software with which to download and process the before, so as to allow stabilization of the soil water content.
data.
8.7 A matrix of six (6) spots should be used during the
calibration procedure, consisting of two different soil density
8. Calibration and Standardization
conditions and three (3) water content conditions that cover the
8.1 For a soil type that has not yet been modeled, a Soil
range that is expected to be measured. The three calibration
Modelmustbegenerated.RefertoSection9fordetailsonhow
tests that evaluate high density soil will use test locations that
the testing is performed.
ideally will have soil conditions that are close to the maximum
8.2 Determine the test method(s) that will be used in
density as determined byTest Methods D1557 or an equivalent
conjunction with developing the Soil Model through calibra-
method. The range in water content shall include low water
tion. For example, one or more of the test methods cited in 2.1.
content, middle range water content, and high water content
Assemble the equipment required for each test method.
that is near the optimum water content as determined by Test
Methods D1557 and D2216 or equivalent test methods.
8.3 Obtain a representative sample of soil from the site
where in-place testing is conducted or from the borrow area
8.7.1 A four spot Soil Model matrix will result in the
planned as a source of material. The sample shall be of
development of a Soil Model with an accuracy that will
sufficient amount of soil for at least five compaction
typically be less than the six-spot matrixes, and a nine-spot soil
specimens,typicallyabout20kg(44lb).Morematerialmaybe
matrix will only slightly increase the accuracy of the Soil
requiredifancillarytestingisplanned,suchasAtterberglimits,
Model over that of the six-spot Soil Model matrixes. The
particle size analysis, etc.
four-spot Soil Model matrixes shall have variation of two
density conditions and two water content conditions, wherein
8.4 Determine the laboratory compaction characteristics of
the material to be tested. Test Methods D698 or D1557 for fine the high density and high water content shall be performed in
soil that is near the maximum density and optimum water
grained soils and soil rock mixtures that exhibit a clear
maximum dry density or Test Methods D4253 or D7382 for contentasdeterminedbyTestMethodsD1557oranequivalent
predominately granular material. test method. The nine-spot Soil Model shall have variation of
three density conditions and three water contents, wherein the
8.5 Determinethedepthofinvestigationrequiredforthejob
high density-high water content shall be performed in soil that
and select the electrical probes with length equal to the depth
is near the maximum density and optimum water content as
of investigation. Th
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D7698 − 20 D7698 − 21
Standard Test Method for
In-Place Estimation of Density and Water Content of Soil
and Aggregate by Correlation with Complex Impedance
Method
This standard is issued under the fixed designation D7698; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope Scope*
1.1 Purpose and Application—This test method describes the procedure, equipment, and interpretation methods for estimating
in-place soil dry density and water content using a Complex-Impedance Measuring Instrument (CIMI).
1.1.1 The purpose and application of this test method is for testing porous material such as used in roadway base or building
foundations that may be deployed in the field at various test sites. The test apparatus includes electrodes that contact the porous
material under test and a sensor unit that supplies electromagnetic signals to the porous material. Response signals reveal electrical
parameters such as complex impedance which can be equated to material properties such as density and moisture content.
1.1.2 CIMI measurements as described in this test method are applicable to measurements of compacted soils intended for roads
and foundations.
1.1.3 This test method describes the procedure for estimating in-place density and water content of soils and soil-aggregates by
use of a CIMI. The electrical properties of the soil are measured using a radio frequency (RF) voltage source connected to soil
electrical probes driven into the soils and soil-aggregates to be tested, in a prescribed pattern and depth. Certain algorithms of these
properties are related to wet density and water content. This correlation between electrical measurements, and density and water
content is accomplished using a calibration methodology. In the calibration methodology, density and water content are determined
by other ASTM Test Standards that measure soil density and water content, thereafter correlating the corresponding measured
electrical properties to the soil physical properties.
1.2 Units—The values stated in SI units are to be regarded as standard. The inch-pound units given in parentheses are
mathematical conversions which are provided for information purposes only and are not considered standard.
1.2.1 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice
D6026 unless superseded by this standard.
1.3 Generalized Theory:
1.3.1 Two key electrical properties of soil are conductivity and relative dielectric permittivity which are manifested as a value of
complex-impedance that can be determined.
This test method is under the jurisdiction of ASTM Committee D18 on Soil and Rock and is the direct responsibility of Subcommittee D18.08 on Special and Construction
Control Tests.
Current edition approved June 1, 2020May 1, 2021. Published June 2020May 2021. Originally approved in 2011. Last previous edition approved in 20192020 as
D7698–19.–20. DOI: 10.1520/D7698-20.10.1520/D7698-21.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7698 − 21
1.3.2 The soil conductivity contributes primarily to the real component of the complex-impedance, and the soil relative dielectric
permittivity contributes primarily to the imaginary component of the complex-impedance.
1.3.3 The complex-impedance of soil can be determined by placing two electrodes in the soil to be tested at a known distance apart
and a known depth. The application of a known frequency of alternating current to the electrodes enables a measurement of current
through the soil, voltage across the electrodes, and the electrical phase difference between the voltage and current.
Complex-impedance is calculated from these known and measured parameters.
1.3.4 From the determined complex-impedance, an electrical network consisting of a resistor (R) and capacitor (C) connected in
parallel are used to represent a model of the soil being tested.
1.3.5 Relationships can be made between the soil wet density and the magnitude of the complex-impedance, and also between the
soil water mass per unit measured, and the quotient of the values of C and R using a Soil Model process.
1.3.6 The Soil Model process results in mathematical relationships between the physical and electrical characteristics of the soil
which are used for soil-specific calibration of the CIMI.
1.3.7 Refer to Appendix X1 for a more detailed explanation of complex-impedance measurement of in-place soil, and its use in
field measurements for the estimation of dry density and water content.
1.4 Precautions:
1.4.1 The low-level RF output power levels of the CIMI method are harmless.
1.4.2 The SI units presented for apparatus are substitutions of the inch-pound units, other similar SI units should be acceptable
providing they meet the technical requirements established by the inch-pound apparatus.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. There are no known
hazards associated with this standard. It is the responsibility of the user of this standard to establish appropriate safety, health,
and environmental practices and determine the applicability of regulatory limitations prior to use.
1.6 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D653 Terminology Relating to Soil, Rock, and Contained Fluids
3 3
D698 Test Methods for Laboratory Compaction Characteristics of Soil Using Standard Effort (12,400 ft-lbf/ft (600 kN-m/m ))
D1556 Test Method for Density and Unit Weight of Soil in Place by Sand-Cone Method
D1557 Test Methods for Laboratory Compaction Characteristics of Soil Using Modified Effort (56,000 ft-lbf/ft (2,700
kN-m/m ))
D2216 Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass
D3740 Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in
Engineering Design and Construction
D4253 Test Methods for Maximum Index Density and Unit Weight of Soils Using a Vibratory Table
D4643 Test Method for Determination of Water Content of Soil and Rock by Microwave Oven Heating
D4718 Practice for Correction of Unit Weight and Water Content for Soils Containing Oversize Particles
D4944 Test Method for Field Determination of Water (Moisture) Content of Soil by the Calcium Carbide Gas Pressure Tester
D6026 Practice for Using Significant Digits in Geotechnical Data
D7382 Test Methods for Determination of Maximum Dry Unit Weight of Granular Soils Using a Vibrating Hammer
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
D7698 − 21
3. Terminology
3.1 Definitions—For definitions of common technical terms used in this standard, refer to Terminology D653.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 complex impedance, n—the ratio of the phasor equivalent of a steady-state sine-wave or voltage like quantity (driving force)
to the phasor equivalent of a steady-state sine-wave current of current like quantity (response).
3.2.2 relative permittivity, n—the permittivity of the material relative to that of free space.
3.2.3 phase relationship, n—the electrical phase difference between the applied probe-to-probe RF voltage, and the resulting soil
current.
3.2.4 probe-to-probe RF voltage, n—the peak value of RF voltage measured across two probes that are conducting soil current.
3.2.5 soil capacitance, n—the value of the capacitor in an equivalent parallel resistor-capacitor circuit that results from the
probe-to-probe RF voltage, current in the soil, and resulting phase relationship due to the application of a RF voltage source applied
to the probes.
3.2.6 soil current, n—the peak value of the RF current passing through the soil from one probe electrode to another.
3.2.7 Soil Model, n—the result of a calibration procedure that establishes a correlating linear function between measured electrical
soil properties and measured physical soil properties.
3.2.8 Soil Model linear correlation function, n—one of the two mathematical expressions that are derived from performing linear
regressions on two sets of soil test data; measured physical soil characteristics, and a corresponding set of electrical measurements
made on the soil samples.
3.2.9 soil resistance, n—the value of the resistor in an equivalent parallel resistor-capacitor circuit that results from the
probe-to-probe RF voltage, soil current, and resulting phase relationship due to the application of a RF source applied to the probes.
4. Summary of the Test Method
4.1 The test method is a two-step process.
4.1.1 A Soil Model that relates impedance measurement to the density and water content of the soil is developed. In this step the
electrical measurements are collected at locations that have various water contents and densities typical of the range to be expected.
Concurrent with collecting the electrical data, determination of density and water content are performed at the same locations using
one or more of the traditional test methods, such as Test Methods D1556 and D2216. The process is repeated over the site such
that a range of water contents and densities are obtained. The combined data (impedance and density/water content) will generate
the correlating linear regression functions of the Soil Model.
4.1.2 Once the Soil Model has been developed the CIMI device is used to make electrical measurements of the soil at locations
of unknown density and water content. Using the Soil Model linear correlation functions, the procedure then estimates the values
of soil density and water content based on the measured electrical properties.
5. Significance and Use
5.1 CIMI measurements as described in this Standard Test Method are applicable to measurements of compacted soils intended
for roads and foundations.
5.2 The test method is used for estimating in-place values of density and water content of soils and soil-aggregates based on
electrical measurements.
Institute of Electrical and Electronics Engineers Standards 100, 1972
Sears & Zemansky, University Physics, 10th Edition
D7698 − 21
5.3 The test method may be used for quality control and acceptance testing of compacted soil and soil aggregate mixtures as used
in construction and also for research and development. The minimal disturbance nature of the methodology allows repetitive
measurements in a single test location and statistical analysis of the results.
5.4 Limitations:
5.4.1 This test method provides an overview of the CIMI measurement procedure using a controlling console connected to a soil
sensor unit which applies a 3.0 MHz RF voltage to an in-place soil via metallic probes that are driven into the soil at a prescribed
distance apart. This test method does not discuss the details of the CIMI electronics, computer, or software that utilize on-board
algorithms for estimating the soil density and water content
5.4.2 It is difficult to address an infinite variety of soils in this standard. However, data presented in X3.1 provides a list of soil
types that are applicable for the CIMI use.
5.4.3 The procedures used to specify how data are collected, recorded, or calculated in this standard are regarded as the industry
standard. In addition, they are representative of the significant digits that generally should be retained. The procedures prescribed
in this standard do not consider material variation, purpose for obtaining the data, special purpose studies, or any considerations
for the user’s objectives; it is common practice to increase or reduce significant digits of reported data to be commensurate with
these considerations. It is beyond the scope of this standard to consider significant digits used in analytical methods for engineering
design.
NOTE 1—Notwithstanding the statements on precision and bias contained in this test method, the precision of this test method is dependent on the
competence of the personnel performing it and the suitability of the equipment and facilities used. Agencies that meet the criteria of Practice D3740 are
generally considered capable of competent and objective testing. Users of this test method are cautioned that compliance with Practice D3740 does not
in itself ensure reliable results. Reliable testing depends on many factors; Practice D3740 provides a means of evaluating some of those factors.
5.5 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice
D6026, unless superseded by this test method.
6. Interferences
6.1 Anomalies in the test material with electrical impedance properties significantly different from construction soils and aggregate
evaluated during Soil Model development, such as metal objects or organic material, may affect the accuracy of the test method.
6.2 The accuracy of the results obtained by this test method may be influenced by poor contact between the soil electrical probes
and the soil being tested. Large air voids, relative to the volume of material being tested, that may be present between soil probes
and the surface of the material being tested may cause incorrect density measurements. The shape of the soil electrical probe is
important to the quality of the electrical measurements collected by the CIMI.
6.3 When driving the measuring electrical probes, it is critical to the accuracy of the measurement that they make a complete and
tight contact with the soil over the entire conical part of the probe.
6.4 If the volume of soil material being tested as defined in X2.10 has oversize particles or large voids in the electrical field, this
may cause errors in measurements of electrical properties. Where lack of uniformity in the soil due to layering, aggregate or voids
is suspected, the test site shall be excavated and visually examined to determine if the test material is representative of the in-situ
material in general and if an oversize correction is required in accordance with Practice D4718. Soils must be homogeneous and
practically free of rocks that are in excess of five centimeters in diameter (2 in.) and construction debris for the most accurate
results.
6.5 Statistical variance may increase for soil material that is significantly drier or wetter than optimum water content (2.5 % over
optimum or 6.0 % below optimum) as determined using Test Methods D698 or D1557. Statistical variance may increase for soil
material that is compacted to less than 88 % of the maximum dry density as determined using Test Methods D698 or D1557. The
CIMI is generally more accurate when the Soil Model range is broader than the range of soil density and water content being tested
in the field.
D7698 − 21
6.6 If temperature measurements are not used, an error may be introduced in the results depending on the value of the difference
between the temperature of the soil used for the Soil Model and the unknown in-place soil being measured. All electrical values
are equilibrated to 15.5 °C (60 °F). The equilibration is necessary because the soil temperature affects the electrical signals that
are measured. The operating temperature range where the CIMI has been used globally is for the CIMI is between 1.1 °C (34 °F)
and 50 °C (122 °F).
6.7 This test method applies only to non-frozen soil. The electrical properties of soil change considerably as soil temperature
approaches the freezing point of the entrained water.
6.8 The use of electrical probes with different length than those used to make the Soil Model will introduce an error in the
interpretation of the data and the estimation of the density of water content of the tested soils.
6.9 The use of a Soil Model that was generated from a different soil than that selected for unknown in-place measurements will
result in errors in the estimation of the density and water content of the tested soils.
6.10 Attempts to measure unknown in-place soils with a Soil Model that was generated from a limited range of wet density or
water content values, or both, may result in density and water content estimation errors.
6.11 Variation in pore water salinity, soil chemistry, soil mineralogy or other anomalies that causes field-test electronic
measurements to be outside the soil model operational range will cause the CIMI to report a warning message. X2.1 contains
additional information regarding variation in electrical measurements and CIMI management techniques.
7. Apparatus
7.1 Complex-Impedance Measuring Instrument (See Fig. 1)—While exact details of construction of the apparatus and the electric
circuits therein may vary, the system shall consist of the following:
7.1.1 Soil Sensor Unit—The “Soil Sensor” is a component of the CIMI which electronically combines the RF voltage source and
the three RF measurement devices. Cables are used to connect the Soil Sensor to the electrical probes.
7.1.1.1 RF Source—Typically a 3 MHz RF voltage source is applied to the soil under test by probe type electrodes driven into the
in-place soil at a prescribed depth and spacing. It measures the RF voltage applied to the soil electrical probes and RF current
drawn by the soil. Additionally, the electrical phase relationship between the soil current and the probe-to-probe RF voltage is
determined.
7.1.1.2 Ammeter—Means for measuring the RF soil current.
NOTE 1—The wires crossing in the diagram are not touching each other during use to prevent parasitic capacitance.
In the drawing the small probe is the thermistor and the three large probes are three of the four used to collect soil electrical data, the fourth probe
is not seen in the section drawing because it is directly behind the center probe.
FIG. 1 Diagram of a Complex Impedance Measuring Instrument in Use
D7698 − 21
7.1.1.3 Voltmeter—Means for measuring the probe-to-probe RF voltage.
7.1.1.4 Phase Difference Meter—Means for measuring the phase difference between the probe-to-probe RF voltage and RF soil
current.
7.1.1.5 Connecting Cables—For connecting the soil electrical probes to the display console meter (that is, ammeter, voltmeter, and
phase difference meter).
7.1.2 Display Console Unit
7.2 Soil Electrical Probes (Four Required, Equally Dimensioned)—Of electrical conducting material suitable for driving into
compacted material, typically constructed of common water hardened drill steel or stainless steel. The soil electrical probes have
a conical shape designed to optimize the contact between the electrode and the compacted construction material around the
electrode as it is driven in. To further control the contact area of the electrode with the compacted construction material a shoulder
is machined at the end of the conical taper that is undercut. When the conical electrode is driven in the compacted construction
material to the level where the shoulder is level with the construction material surface, a repeatable surface area of the electrode
is in contact with the construction material. The soil electrode achieves good contact with the compacted construction material and
allows for consistency in electrical measurements.
7.2.1 The length of soil electrical probes can vary typically having embedment lengths between 102 mm (4 in.) and 31 mm (1.2
in.). The bottom diameter of each soil electrical probe is 5 mm (0.2 in.). The top diameter of the embedded length of each soil
electrical probe varies between 14 mm (0.56 in.) for the 102 mm (4 in.) embedded length probe and 32 mm (1.25 in.) for the 305
mm (12 in.) embedded length probe. During the testing procedure, the soil electrical probe length is selected to best match
thickness of the compacted material. Since a portion of the probe must be above the surface to facilitate electrical clip connector,
the desired embedment depth must be clearly indicated with a scribed mark or change in geometry. The drawing in Fig. 2 below
shows the size and dimensions for the 152 mm (6 in.) electrical probe, the other electrical probes have similar shape and can be
reviewed in the manufacturer’s catalog.
7.3 A template shall be used to place the electrodes as they are driven into the soil. The four probes are driven into the soil at the
0°, 90°, 180°, and 270° in clockwise positions around the periphery of the template.
FIG. 2 Drawing of a 152.4 mm (6 in.) Soil Electrical Probe
D7698 − 21
7.4 Thermistor temperature probe that connects to the CIMI for soil temperature measurement, and resulting compensation of
calculated electrical soil parameters.
7.5 Hand Tools—Hand tools for driving and retrieving the soil electrical probes. A 2.7-kg to 5.4-kg (6-lb to 12-lb) dead blow or
brass-faced hammer is used to avoid damaging the steel probes. The soil electrical probes are removed from the soil that has been
tested using 30.5 cm (12 in.) channel lock pliers.
7.6 Other components of the system are:
7.6.1 Safety goggles, and
7.6.2 Software with which to download and process the data.
8. Calibration and Standardization
8.1 For a soil type that has not yet been modeled, a Soil Model must be generated. Refer to Section 9 for details on how the testing
is performed.
8.2 Determine the test method(s) that will be used in conjunction with developing the Soil Model through calibration. For
example, one or more of the test methods cited in 2.1. Assemble the equipment required for each test method.
8.3 Obtain a representative sample of soil from the site where in-place testing is conducted or from the borrow area planned as
a source of material. The sample shall be of sufficient amount of soil for at least five compaction specimens, typically about 20
kg (44 lb). More material may be required if ancillary testing is planned, such as Atterberg limits, particle size analysis, etc.
8.4 Determine the laboratory compaction characteristics of the material to be tested. Test Methods D698 or D1557 for fine grained
soils and soil rock mixtures that exhibit a clear maximum dry density or Test Methods D4253 or D7382 for predominately granular
material.
8.5 Determine the depth of investigation required for the job and select the electrical probes with length equal to the depth of
investigation. These same length probes must be used for both creating the Soil Model and for testing at the Job Site.
8.6 Select areas on the Job Site where the type of soil is consistent from place to place, and where there are differences in water
content and compaction. Special preparation of spots of different densities or water contents should be done the day before, so as
to allow stabilization of the soil water content.
8.7 A matrix of six (6) spots should be used during the calibration procedure, consisting of two different soil density conditions
and three (3) water content conditions that cover the range that is expected to be measured. The three calibration tests that evaluate
high density soil will use test locations that ideally will have soil conditions that are close to the maximum density as determined
by Test Methods D1557 or an equivalent method. The range in water content shall include low water content, middle range water
content, and high water content that is near the optimum water content as determined by Test Methods D1557 and D2216 or
equivalent test methods.
8.7.1 A four spot Soil Model matrix will result in the development of a Soil Model with an accuracy that will typically be less
than the six-spot matrixes, and a nine-spot soil matrix will only slightly increase the accuracy of the Soil Model over that of the
six-spot Soil Model matrixes. The four-spot Soil Model matrixes shall have variation of two density conditions and two water
content conditions, wherein the high density and
...