ASTM D7698-11

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:D7698–11
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 dielectric permittivity contributes primarily to the imaginary
component of the complex-impedance.
1.1 Purpose and Application
1.2.3 The complex-impedance of soil can be determined by
1.1.1 This test method describes the procedure, equipment,
placing two electrodes in the soil to be tested at a known
and interpretation methods for estimating in-place soil dry
distance apart and a known depth. The application of a known
density and water content using a Complex-Impedance Mea-
frequency of alternating current to the electrodes enables a
suring Instrument (CIMI).
measurement of current through the soil, voltage across the
1.1.2 CIMI measurements as described in this StandardTest
electrodes, and the electrical phase difference between the
Method are applicable to measurements of compacted soils
voltage and current waves. Complex-impedance is calculated
intended for roads and foundations.
from these known and measured parameters.
1.1.3 This test method describes the procedure for estimat-
1.2.4 From the determined complex-impedance, an electri-
ing in-place density and water content of soils and soil-
cal network consisting of a resistor (R) and capacitor (C)
aggregates by use of a CIMI. The electrical properties of soil
connected in parallel are used to represent a model of the soil
are measured using a radio frequency voltage applied to soil
being tested.
electrical probes driven into the soils and soil-aggregates to be
1.2.5 Relationships can be made between the soil wet
tested, in a prescribed pattern and depth. Certain algorithms of
density and the magnitude of the complex-impedance, and also
these properties are related to wet density and water content.
between the soil water mass per unit measured, and the
This correlation between electrical measurements, and density
quotient of the values of C and R using a Soil Model process.
and water content is accomplished using a calibration method-
1.2.6 The Soil Model process results in mathematical rela-
ology. In the calibration methodology, density and water
tionships between the physical and electrical characteristics of
content are determined by other ASTM Test Standards that
thesoilwhichareusedforsoil-specificcalibrationoftheCIMI.
measure soil density and water content, thereafter correlating
1.2.7 Refer toAppendix X1 for a more detailed explanation
the corresponding measured electrical properties to the soil
of complex-impedance measurement of in-place soil, and its
physical properties.
use in field measurements for the estimation of dry density and
1.1.4 The values stated in SI units are to be regarded as
water content.
standard. The inch-pound units given in parentheses are
1.3 Precautions
mathematical conversions which are provided for information
1.3.1 The radio frequencies and output power levels of the
purposes only and are not considered standard.
CIMI method are such that they are harmless according to the
1.1.5 Allobservedandcalculatedvaluesshallconfirmtothe
Federal Communications Commission (FCC).
guidelines for significant digits and rounding established in
1.3.2 This standard does not purport to address all of the
Practice D6026 unless superseded by this standard.
safety concerns, if any, associated with its use. It is the
1.2 Generalized Theory
responsibility of the user of this standard to establish appro-
1.2.1 Two key electrical properties of soil are conductivity
priate safety and health practices and determine the applica-
and relative dielectric permittivity which are manifested as a
bility of regulatory limitations prior to use.
value of complex-impedance that can be determined.
1.2.2 The soil conductivity contributes primarily to the real
2. Referenced Documents
component of the complex-impedance, and the soil relative
2.1 ASTM Standards:
ThistestmethodisunderthejurisdictionofASTMCommitteeD18onSoiland
Rock and is the direct responsibility of Subcommittee D18.08 on Special and For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Construction Control Tests. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Current edition approved Feb. 1, 2011. Published March 2011. DOI: 10.1520/ Standards volume information, refer to the standard’s Document Summary page on
D7698-11. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D7698–11
D653 Terminology Relating to Soil, Rock, and Contained 3.2.5 radio frequency, n—a frequency useful for radio
Fluids transmission (1).
3.2.6 soil capacitance, n—the value of the capacitor in an
D698 Test Methods for Laboratory Compaction Character-
equivalent parallel resistor – capacitor circuit that results from
istics of Soil Using Standard Effort (12 400 ft-lbf/ft (600
the probe to probe voltage, soil current, and resulting phase
kN-m/m ))
relationship due to the application of a radio frequency
D1556 Test Method for Density and Unit Weight of Soil in
alternating voltage source applied to the probes.
Place by Sand-Cone Method
3.2.7 soil current , n—the peak value of the radio frequency
D1557 Test Methods for Laboratory Compaction Charac-
current passing through the soil from one probe electrode to
teristics of Soil Using Modified Effort (56,000 ft-lbf/
3 3 another.
ft (2,700 kN-m/m ))
3.2.8 Soil Model, n—the result of a calibration procedure
D2216 Test Methods for Laboratory Determination of Wa-
that establishes a correlating linear function between measured
ter (Moisture) Content of Soil and Rock by Mass
electrical soil properties and measured physical soil properties.
D3740 Practice for Minimum Requirements for Agencies
3.2.9 Soil Model linear correlation function, n—one of the
Engaged in Testing and/or Inspection of Soil and Rock as
two mathematical expressions that are derived from perform-
Used in Engineering Design and Construction
ing linear regressions on two sets of soil test data; measured
D4253 Test Methods for Maximum Index Density and Unit
physical soil characteristics, and a corresponding set of elec-
Weight of Soils Using a Vibratory Table
trical measurements made on the same soil samples.
D4643 Test Method for Determination of Water (Moisture)
3.2.10 soil resistance, n—the value of the resistor in an
Content of Soil by Microwave Oven Heating
equivalent parallel resistor-capacitor circuit that results from
D4718 Practice for Correction of Unit Weight and Water the probe to probe voltage, soil current, and resulting phase
relationship due to the application of a radio frequency
Content for Soils Containing Oversize Particles
alternating voltage source applied to the probes.
D4944 Test Method for Field Determination of Water
3.2.11 water mass per unit volume, n—the mass of water
(Moisture) Content of Soil by the Calcium Carbide Gas
contained in a volume of soil being measured, and is expressed
Pressure Tester
dimensionally as kg/m.
D6026 PracticeforUsingSignificantDigitsinGeotechnical
Data
4. Summary of the Test Method
D7382 Test Methods for Determination of Maximum Dry
4.1 The test method is a two step process.
Unit Weight and Water Content Range for Effective
4.1.1 A Soil Model that relates impedance measurement to
Compaction of Granular Soils Using a Vibrating Hammer
the density and water content of the soil is developed. In this
step the electrical measurements are collected at locations that
3. Terminology
have various water contents and densities typical of the range
3.1 Definitions shall be in accordance with the terms and
to be expected. Concurrent with collecting the electrical data,
symbols given in Terminology D653.
determinationofdensityandwatercontentareperformedatthe
3.2 Definitions of Terms Specific to This Standard:
same locations using one or more of the traditional test
methods,suchasTestMethodsD1556andD2216.Theprocess
3.2.1 compleximpedance,n—theratioofthephasorequiva-
is repeated over the site sufficiently that a range of water
lent of a steady-state sine-wave or voltage like quantity
contents and densities are obtained. The combined data (im-
(driving force) to the phasor equivalent of a steady-state
pedance and density/water content) will generate the correlat-
sine-wave current of current like quantity (response) (1).In
ing linear regression functions of the Soil Model.
practice, the instrument uses the magnitude of the impedance
4.1.2 Once the Soil Model has been developed the CIMI
ratio (|Z|) in its calculations.
device is used to make electrical measurements of the soil at
3.2.2 dielectricproperties,n—seerelativedielectricpermit-
locationsofunknowndensityandwatercontent.UsingtheSoil
tivity and dielectric phase angle
Model linear correlation functions, the procedure then esti-
3.2.2.1 dielectric phase angle, n—the angular difference in
mates the values of soil density and water content based on the
phase between the sinusoidal alternating voltage applied to a
measured electrical properties.
dielectric and the component of the resulting alternating
current having the same period as the voltage.
5. Significance and Use
3.2.2.2 relative dielectric permittivity, n—the property that
5.1 The test method is a procedure for estimating in-place
determines the electrostatic energy stored per unit volume for
values of density and water content of soils and soil-aggregate
unit potential gradient multiplied by the permittivity of free
based on electrical measurements.
space (2).
5.2 The test method may be used for quality control and
3.2.3 phase relationship, n—the electrical phase difference
acceptance testing of compacted soil and soil aggregate mix-
between the applied probe to probe radio frequency voltage,
tures as used in construction and also for research and
and the resulting soil current.
3.2.4 probe to probe voltage, n—the peak value of radio
frequency voltage measured across two probes that are con-
The boldface numbers in parentheses refer to a list of references at the end of
ducting soil current. this standard.
D7698–11
development. The minimal disturbance nature of the method- properties.Wherelackofuniformityinthesoilduetolayering,
ology allows repetitive measurements in a single test location aggregate or voids is suspected, the test site should be
and statistical analysis of the results. excavated and visually examined to determine if the test
5.3 Limitations: material is representative of the in-situ material in general and
5.3.1 This test method provides an overview of the CIMI ifanoversizecorrectionisrequiredinaccordancewithPractice
measurement procedure, using a controlling console, con- D4718. Soils must be homogeneous and practically free of
nected to a soil sensor unit which applies 3.0 MHz radio rocks that are in excess of five centimeters in diameter and
frequency to an in-place soil in which metallic probes are construction debris for the most accurate results.
driven at a prescribed distance apart.This test method does not
6.5 Statistical variance may increase for soil material that is
discuss the details of the CIMI electronics, computer, or significantlydrierorwetterthanoptimumwatercontent(2.5 %
software that utilized on-board algorithms for estimating the
over optimum or 6.0 % below optimum) as determined using
soil density and water content Test Methods D698 or D1557. Statistical variance may in-
5.3.2 It is difficult to address an infinite variety of soils in
crease for soil material that is compacted to less than 88 % of
this standard. This test method does not address the various the maximum dry density as determined using Test Methods
types of soils on which the CIMI method may or may not be
D698orD1557.TheCIMIisgenerallymoreaccuratewhenthe
applicable. However, data presented in 12.1.1 provides a list of
Soil Model range is broader than the range of soil density and
soil types that are applicable for the CIMI use.
water content being tested in the field.
5.3.3 Theproceduresusedtospecifyhowdataarecollected,
6.6 If temperature measurements are not used, an error may
recorded, or calculated in this standard are regarded as the
be introduced in the results depending on the value of the
industry standard. In addition, they are representative of the
difference between the temperature of the soil used for the Soil
significant digits that generally should be retained. The proce-
Model and the unknown in-place soil being measured. All
dures prescribed in this standard do not consider material
electrical values are equilibrated to 15.55 °C.The equilibration
variation, purpose for obtaining the data, special purpose
is necessary because the soil temperature affects the electrical
studies, or any considerations for the user’s objectives; it is
signals that are measured.
common practice to increase or reduce significant digits of
6.7 This test method applies only to non-frozen soil. The
reported data to be commensurate with these considerations. It
electrical properties of soil change considerably as soil tem-
is beyond the scope of this standard to consider significant
perature approaches the freezing point of the entrained water.
digits used in analytical methods for engineering design.
6.8 The use of electrical probes with different length than
those used to make the soil mode will introduce an error in the
6. Interferences
interpretation of the data and the estimation of the density of
6.1 Anomalies in the test material with electrical impedance water content of the tested soils.
properties significantly different from construction soils and
6.9 The use of a Soil Model that was generated from a
aggregate evaluated during Soil Model development, such as
different soil than that selected for unknown in-place measure-
metal objects or organic material, may affect the accuracy of
ments will result in errors in the estimation of the density of
the test method.
water content of the tested soils.
6.2 The accuracy of the results obtained by this test method
6.10 Attempts to measure unknown in-place soils with a
may be influenced by poor contact between the soil electrical
Soil Model that was generated from a limited range of wet
probes and the soil being tested. Large air voids, relative to the
density or water content values, or both, may result in
...