ASTM D5220/D5220M-21

Standard Test Method for Water Mass per Unit Volume of Soil and Rock In-Place by the Neutron Depth Probe Method

SIGNIFICANCE AND USE
5.1 This test method is useful as a rapid, nondestructive technique for the measurement of the in-place water mass per unit volume of soil and rock at desired depths below the surface.  
5.2 This test method is useful for informational and research purposes. The information acquired from this test method is best used for quality control and acceptance testing when correlated to actual water mass per unit volume using procedures and methods described in A1.2.3.  
5.3 The non-destructive nature of this test method allows repetitive measurements to be made at a single test location for statistical analysis and to monitor changes over time.  
5.4 The fundamental assumptions inherent in this test method are that the material under test is homogeneous and hydrogen present is in the form of water as defined by Test Method D2216.
Note 1: The quality of the result produced by this standard 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/sampling/inspection, and the like. Users of this standard are cautioned that compliance with Practice D3740 does not in itself assure reliable results. Reliable results depend on many factors; Practice D3740 provides a means of evaluating some of those factors.
SCOPE
1.1 This test method covers the measurement of the water mass per unit volume of soil and rock by thermalization or slowing of fast neutrons, where the neutron source and the thermal neutron detector are placed at the desired depth in the bored hole lined by an access tube.  
1.1.1 For limitations see Section 6 on Interferences.  
1.2 The water mass per unit volume, expressed as mass per unit volume of the material under test, is determined by comparing the thermal neutron count rate with previously established calibration data (see Annex A1).  
1.3 Units—The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system are not necessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall be used independently of the other, and values from the two systems shall not be combined. Within the text of this standard, SI units appear first followed by the inch-pound (or other non-SI) units in brackets.  
1.3.1 Reporting of test results in units other than SI shall not be regarded as nonconformance with this standard.  
1.4 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026.  
1.4.1 The procedures used to specify how data are collected, recorded, and calculated in this standard are regarded as the industry standard. In addition, they are representative of the significant digits that should generally be retained. The procedures used do not consider material variation, purpose for obtaining the data, special purpose studies, or any considerations for the user’s objectives; and 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 analysis methods for engineering design.  
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, health, and environmental practices and determine the applicability of regulatory limitations prior to use. Specific hazards are given in Section 8.  
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 ...

General Information

• Status: Published
• Publication Date: 30-Apr-2021
• ICS: 13.080.40 - Hydrological 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 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 D7263-09(2018) - Standard Test Methods for Laboratory Determination of Density (Unit Weight) of Soil Specimens
• Effective Date: 15-Feb-2018
• Refers: ASTM D7263-09(2018)e1 - Standard Test Methods for Laboratory Determination of Density (Unit Weight) of Soil Specimens
• Effective Date: 15-Feb-2018
• Refers: ASTM D6938-17 - Standard Test Methods for In-Place Density and Water Content of Soil and Soil-Aggregate by Nuclear Methods (Shallow Depth)
• Effective Date: 01-Mar-2017
• Refers: ASTM D2937-17 - Standard Test Method for Density of Soil in Place by the Drive-Cylinder Method
• Effective Date: 01-Feb-2017
• Refers: ASTM D2937-17e2 - Standard Test Method for Density of Soil in Place by the Drive-Cylinder Method
• Effective Date: 01-Feb-2017
• Refers: ASTM D2937-17e1 - Standard Test Method for Density of Soil in Place by the Drive-Cylinder Method
• Effective Date: 01-Feb-2017
• Refers: ASTM D6938-15 - Standard Test Methods for In-Place Density and Water Content of Soil and Soil-Aggregate by Nuclear Methods (Shallow Depth)
• Effective Date: 01-Aug-2015
• Refers: ASTM D653-14 - Standard Terminology Relating to Soil, Rock, and Contained Fluids
• Effective Date: 01-Aug-2014
• Refers: ASTM D1587-08(2012)e1 - Standard Practice for Thin-Walled Tube Sampling of Soils for Geotechnical Purposes
• Effective Date: 15-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 D3740-12 - 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-Mar-2012
• Refers: ASTM D1586-11 - Standard Test Method for Standard Penetration Test (SPT) and Split-Barrel Sampling of Soils
• Effective Date: 01-Nov-2011

Overview

ASTM D5220/D5220M-21 is the globally recognized standard test method for determining the water mass per unit volume of soil and rock in-place using the neutron depth probe method. Issued by ASTM International, this standard provides a rapid, non-destructive approach for measuring soil and rock moisture profiles at various depths below the surface. It is widely utilized in geotechnical, construction, and environmental investigations, supporting quality control, acceptance testing, and research activities.

Key Topics

• Non-Destructive Measurement: Utilizes a neutron depth probe, a specialized nuclear instrument, to detect in-situ water content without disturbing the sample, making it ideal for repeated measurements over time.
• In-Place Determination: The method measures water mass per unit volume directly at specified depths, providing accurate in-field moisture data for diverse soil and rock materials.
• Neutron Depth Probe Principle: Involves thermalization (slowing) of fast neutrons; the count rate of thermalized neutrons, proportional to the hydrogen content (primarily from water), is compared to calibration data to determine moisture levels.
• Calibration and Standardization: Emphasizes the importance of establishing calibration curves and performing regular standardization to ensure reliable results, with reference checks required daily.
• Quality Control and Acceptance Testing: Particularly useful when measurements are correlated with laboratory-derived water content values, supporting informed site assessment and decision-making.
• Assumptions and Limitations: Assumes the tested material is homogeneous and the detected hydrogen is in the form of water; recognizes possible interferences from organic content, certain elements, and sample heterogeneity.
• Safety Considerations: Requires handling of equipment containing sealed radioactive sources, necessitating strict adherence to safety and regulatory protocols.

Applications

• Geotechnical Engineering: Commonly used for site characterization, subgrade evaluation, and monitoring changes in soil moisture relevant to foundations, earthworks, and embankments.
• Construction Quality Assurance: Helps verify compaction and moisture conditions for earthworks, road construction, and structural fills, ensuring compliance with project specifications.
• Environmental Monitoring: Useful for tracking soil water movement, groundwater recharge, and managing conditions affecting slope stability and soil erosion.
• Hydrological Studies: Provides precise, repeated measurements for soil moisture dynamics, supporting research into watershed management, agriculture, and climate impact assessments.
• Long-term Site Monitoring: Enables efficient, repeatable monitoring of soil and rock moisture at fixed locations, aiding in the statistical analysis of moisture changes over seasons or project durations.

Related Standards

This standard references several other ASTM standards for terminology, sampling, calibration, and nuclear measurement methods, including:

• ASTM D653: Terminology for Soil, Rock, and Contained Fluids
• ASTM D2216: Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass
• ASTM D2937: Density of Soil in Place by the Drive-Cylinder Method
• ASTM D3740: Minimum Requirements for Agencies Engaged in Testing/Inspection of Soil and Rock
• ASTM D5195: Density of Soil and Rock In-Place by Nuclear Methods
• ASTM D6026: Significant Digits in Geotechnical Data

These related standards provide essential guidance for sample collection, calibration procedures, and best practices in reporting and analysis of geotechnical data.

---

By ensuring accurate, repeatable, and non-invasive measurement of in-place water mass per unit volume, ASTM D5220/D5220M-21 supports informed decision-making in civil engineering, environmental monitoring, and construction quality control. This test method is essential for professionals seeking efficient moisture measurement solutions that prioritize safety, reliability, and data quality.

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: D5220/D5220M − 21
Standard Test Method for
Water Mass per Unit Volume of Soil and Rock In-Place by
the Neutron Depth Probe Method
This standard is issued under the fixed designation D5220/D5220M; 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* 1.5 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 This test method covers the measurement of the water
responsibility of the user of this standard to establish appro-
mass per unit volume of soil and rock by thermalization or
priate safety, health, and environmental practices and deter-
slowing of fast neutrons, where the neutron source and the
mine the applicability of regulatory limitations prior to use.
thermal neutron detector are placed at the desired depth in the
Specific hazards are given in Section 8.
bored hole lined by an access tube.
1.6 This international standard was developed in accor-
1.1.1 For limitations see Section 6 on Interferences.
dance with internationally recognized principles on standard-
1.2 The water mass per unit volume, expressed as mass per
ization established in the Decision on Principles for the
unit volume of the material under test, is determined by
Development of International Standards, Guides and Recom-
comparing the thermal neutron count rate with previously
mendations issued by the World Trade Organization Technical
established calibration data (see Annex A1).
Barriers to Trade (TBT) Committee.
1.3 Units—The values stated in either SI units or inch-
2. Referenced Documents
pound units are to be regarded separately as standard. The
values stated in each system are not necessarily exact equiva-
2.1 ASTM Standards:
lents; therefore, to ensure conformance with the standard, each D653 Terminology Relating to Soil, Rock, and Contained
system shall be used independently of the other, and values
Fluids
from the two systems shall not be combined.Within the text of D1452 Practice for Soil Exploration and Sampling byAuger
this standard, SI units appear first followed by the inch-pound
Borings
(or other non-SI) units in brackets. D1586 Test Method for Standard PenetrationTest (SPT) and
1.3.1 ReportingoftestresultsinunitsotherthanSIshallnot
Split-Barrel Sampling of Soils
be regarded as nonconformance with this standard.
D1587 Practice for Thin-Walled Tube Sampling of Fine-
Grained Soils for Geotechnical Purposes
1.4 All observed and calculated values shall conform to the
D2113 Practice for Rock Core Drilling and Sampling of
guidelines for significant digits and rounding established in
Rock for Site Exploration
Practice D6026.
D2216 Test Methods for Laboratory Determination of Water
1.4.1 Theproceduresusedtospecifyhowdataarecollected,
(Moisture) Content of Soil and Rock by Mass
recorded, and calculated in this standard are regarded as the
D2937 Test Method for Density of Soil in Place by the
industry standard. In addition, they are representative of the
Drive-Cylinder Method
significant digits that should generally be retained. The proce-
D3740 Practice for Minimum Requirements for Agencies
dures used do not consider material variation, purpose for
Engaged in Testing and/or Inspection of Soil and Rock as
obtaining the data, special purpose studies, or any consider-
Used in Engineering Design and Construction
ations for the user’s objectives; and it is common practice to
D4428/D4428M Test Methods for Crosshole Seismic Test-
increase or reduce significant digits of reported data to be
ing
commensuratewiththeseconsiderations.Itisbeyondthescope
D5195 Test Method for Density of Soil and Rock In-Place at
of this standard to consider significant digits used in analysis
Depths Below Surface by Nuclear Methods
methods for engineering design.
D6026 Practice for Using Significant Digits in Geotechnical
Data
ThistestmethodisunderthejurisdictionofASTMCommitteeD18onSoiland
Rock and is the direct responsibility of Subcommittee D18.08 on Special and
Construction Control Tests. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved May 1, 2021. Published May 2021. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 1992. Last previous edition approved in 2014 as D5220 – 14. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/D5220_D5220M-21. the ASTM website.
*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
D5220/D5220M − 21
standard are cautioned that compliance with Practice D3740 does not in
D6938 TestMethodsforIn-PlaceDensityandWaterContent
itself assure reliable results. Reliable results depend on many factors;
of Soil and Soil-Aggregate by Nuclear Methods (Shallow
Practice D3740 provides a means of evaluating some of those factors.
Depth)
D7263 Test Methods for Laboratory Determination of Den-
6. Interferences
sity and Unit Weight of Soil Specimens
6.1 The sample heterogeneity, density, and chemical com-
positionofthematerialundertestwillaffectthemeasurements.
3. Terminology
The apparatus must be calibrated to the material under test or
3.1 Definitions—For definitions of common technical terms
adjustments made in accordance with Annex A2.
in this standard, refer to Terminology D653.
6.1.1 Hydrogen, in forms other than water, as defined by
3.2 Definitions of Terms Specific to This Standard: Test Method D6938 and carbon, present in organic soils, will
cause measurements in excess of the true water value. Some
3.2.1 neutron probe—a cylindrical device containing a fast
neutron source and a thermal neutron detector. elements such as boron, chlorine, and minute quantities of
cadmium, if present in the material under test, will cause
4. Summary of Test Method measurements lower than the true water value.
4.1 This test method uses thermalization of neutron radia-
6.2 This test method exhibits spatial bias in that it is more
tion to determine the in-place water mass per unit volume of sensitivetowatercontainedinthematerialclosesttotheaccess
soil and rock at various depths by placing a probe containing a
tube. The measurement is not necessarily an average water
neutronsourceandathermalneutrondetectoratdesireddepths
content of the total sample involved.
in a bored hole lined by an access tube as opposed to surface
6.2.1 Voids around the access tube can affect the measure-
measurements in accordance with Test Method D6938.
ment (see 10.1.2).
4.2 Neutronsemittedbythesourcearethermalized(slowed)
6.3 The actual sample volume that the instrument measures
by collisions with materials of low atomic numbers. Hydrog-
is indeterminate and varies with the apparatus and the water
enous materials, such as water and other compounds contain-
contentofthematerial.Ingeneral,thegreaterthewatercontent
ing hydrogen, are most effective in thermalizing neutrons. In
of the material, the smaller the volume involved in the
this apparatus the neutrons thermalized by the material under
measurement. For example, the sample volume is approxi-
3 3
test are detected by the thermal neutron detector.
mately 0.048 m [1.7 ft ] for a soil with a water content of 200
3 3
kg/m [12.5 lbm/ft ].
4.3 In the absence of interference elements as discussed in
Section 6, the number of thermalized neutrons is a function of
7. Apparatus (See Fig. 1)
the hydrogen content of the material under test and the water
content is proportional to the hydrogen content.
4.4 By the use of a calibration process the water mass per
unit volume is determined by correlating the count rate to
known water mass per unit volume values.
5. Significance and Use
5.1 This test method is useful as a rapid, nondestructive
technique for the measurement of the in-place water mass per
unit volume of soil and rock at desired depths below the
surface.
5.2 Thistestmethodisusefulforinformationalandresearch
purposes. The information acquired from this test method is
best used for quality control and acceptance testing when
correlated to actual water mass per unit volume using proce-
dures and methods described in A1.2.3.
5.3 The non-destructive nature of this test method allows
repetitive measurements to be made at a single test location for
statistical analysis and to monitor changes over time.
5.4 The fundamental assumptions inherent in this test
method are that the material under test is homogeneous and
hydrogen present is in the form of water as defined by Test
Method D2216.
NOTE1—Thequalityoftheresultproducedbythisstandardtestmethod
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 FIG. 1 Schematic Diagram; Water Content by Neutron Depth
and objective testing/sampling/inspection, and the like. Users of this Probe Method
D5220/D5220M − 21
7.1 The apparatus shall consist of a nuclear instrument Requirements, are a mandatory part of the operation and
capable of measuring water mass per unit volume at various storage of these instruments.
depths below the surface containing the following:
7.1.1 A sealed mixture of a radioactive material such as 9. Calibration, Standardization, and Reference Check
americium or radium with a target element such as beryllium,
9.1 Calibrate the instrument in accordance with Annex A1.
and a suitable thermal neutron detector, and
9.2 Adjust the calibration in accordance with Annex A2 if
7.1.2 A suitable timed scaler and power source.
adjustments are necessary.
7.2 Theapparatusshallbeequippedwithacylindricalprobe
9.3 Perform and evaluate standardization and reference
containing the neutron source and detector, connected by a
check on a daily basis, prior to taking field measurements, in
cable of sufficient design and length, that is capable of being
accordance with Annex A4.
lowered down the cased hole to desired test depths.
7.2.1 The dimensions of the probe vary among manufactur-
10. Procedure
ersandmodels,butaregenerallybetween25mm[1in.]and75
mm [3 in.] in diameter and 20 mm [8 in.] and 1 m [39 in.] in
10.1 Installation of Access Tubing (Casing):
length. Probe diameters are generally designed by the manu-
10.1.1 Drill the access tube hole and install the access
facturer to be commensurate with the internal diameter of
tubing in a manner dependent upon the material to be tested,
commonly used access tubing, or drill hole sizes.
the depth to be tested, and the available drilling equipment.
10.1.2 The access hole shall be clear enough to allow
7.3 The apparatus shall be equipped with a reference
installingthetubingwhilestillprovidingasnugfit.Voidsalong
standard, a fixed shape of hydrogenous material used for
the sides of the tubing may cause erroneous readings.
checking apparatus operation and to establish conditions for a
10.1.2.1 If voids are suspected to be caused by the drilling
reproducible reference count rate. It may also serve as a
process they may be grouted using procedures in Test Method
radiation shield.
D4428/D4428M.
7.4 Apparatus Precision—See Annex A3 for the precision
10.1.2.2 The only method to determine the presence of
of the apparatus.
voids is to perform field calibrations provided in A1.2.3.
7.5 Accessories:
10.1.3 Record and note the position of the ground water
7.5.1 Access Tubing—Theaccesstubing(casing)isrequired
table, perched water tables, and changes in strata as drilling
for all access holes in nonlithified materials (soils and poorly
progresses.
consolidated rock) that cannot maintain constant borehole
10.1.3.1 If ground water is encountered or saturated condi-
diameter with repeated measurements. If access tubing is
tions are expected to develop, seal the tube at the bottom to
required, the tubing shall be of a material such as aluminum,
prevent water seepage into the tube using procedures given in
steel, or polyvinyl chloride, having an interior diameter large
Test Method D4428/D4428M or the manufacturer’s recom-
enough to permit probe access without binding. The tubing
mended procedures. This will prevent erroneous readings and
shallbeasthin-walledaspossibletoprovidecloseproximityof
possible damage to the probe.
the probe to the material under test. The same type of tubing
10.1.4 The tubing shall project above the ground and be
shall be used in the field as is used in calibration.
capped to prevent foreign material from entering. The access
7.5.2 Drilling Tool(s)—Hand auger or power drilling equip-
tube shall not project above the ground so high that it might be
ment that can be used to establish the access hole.Any drilling
damaged by equipment passing over it.
equipment that provides a suitable clean open hole for instal-
10.1.4.1 Install all tubes at the same height above the
lation of access tubing and insertion of the probe shall be
ground as this enables marking the cable to indicate the
acceptable. The equipment used shall be capable of maintain-
measured depth to be used for all tubes.
ingconstantboreholediametertoensurethatthemeasurements
10.2 Lower a dummy probe down the access tube to verify
are performed on undisturbed soil and rock. The type of
proper clearance before lowering the probe containing the
equipment and methods of advancing the access hole shall be
radioactive source.
reported.
7.5.3 Dummy Probe—A cylindrical probe the same size as 10.3 Standardize the apparatus (see Annex A4).
the probe containing the neutron source and a chain or cable of
10.4 Proceed with the test as follows:
sufficient design and length to permit lowering the dummy
10.4.1 Seat the apparatus firmly over the access tube, then
probe down the cased hole to desired test depths.
lower the probe into the tube to the desired depth. Secure the
probe by cable clamps (usually provided by the apparatus
8. Hazards
manufacturer).
8.1 These instruments utilize radioactive materials that may
10.4.2 Take a measurement count at the selected timing
be hazardous to the health of the users unless proper precau-
period.
tions are taken. Users of these instruments must become
10.4.3 If the water content as a percentage of dry density is
familiar with applicable safety procedures and government
required, the in-place density may be determined by using a
regulations.
different apparatus that determines density at depths below the
8.2 Effective user instructions, together with routine safety surface by the nuclear method. Such methods include, but are
procedures and knowledge of and compliance with Regulatory not limited to, Test Method D5195, Test Method D2937
D5220/D5220M − 21
(depths not more than1m[3 ft]), or Test Method D1587 11.2.12 Depth, measurement count data, and water mass per
(fine-grained soils only.) unit volume of each measurement.
12. Precision and Bias
11. Report: Test Data Sheet(s)/Form(s)
12.1 Precision—It is not possible to specify the precision of
11.1 The methodology used to specify how data are re-
the procedure in Test Method D5220/D5220M for measuring
corded on the test data sheet(s)/form(s) as given below is
water mass per unit volume of soil and rock in-place at depths
covered in 1.3 through 1.5 and in Practice D6026.
below the surface by nuclear method because it is not feasible
and too costly at this time to have ten or more agencies
11.2 Record at a minimum the following general informa-
participate in an in situ testing program at a given site.
tion (data):
12.1.1 Subcommittee D18.08 is seeking any data from the
11.2.1 Make, model, and serial number of the apparatus,
users of this test method that might be used to make a limited
11.2.2 Date of calibration,
statement on precision.
11.2.3 Name of operator/test technician,
12.2 Bias—No information can be presented on the bias of
11.2.4 Method of calibration, such as field, factory, etc.,
the procedure in Test Method D5220/D5220M for measuring
11.2.5 Calibration adjustments,
water mass per unit volume of soil and rock in-place at depths
11.2.6 Date of test,
below the surface by nuclear method because it is not feasible
11.2.7 Standard count(s) for the day of the test,
and too costly at this time to have ten or more agencies
11.2.8 Any adjustment data for the day of the test,
participate in an in situ testing program at a given site.
11.2.9 Test site identification including tube location(s),
13. Keywords
tube number(s),
11.2.10 Tube type and tube installation methods (method of
13.1 depth probe; in-place water content; in situ water
drilling, installing and any initial gravimetric and count data),
content; neutron probe; nuclear methods; water mass per unit
11.2.11 Geologic log of the borehole, and volume
ANNEXES
(Mandatory Information)
A1. CALIBRATION
A1.1 At least once each year, establish or verify calibration known or can be calculated from the specific gravity and
curves, tables, or equations by determining the count rate of at chemical composition. A zero water content standard can be
least three samples of different known
...

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: D5220 − 14 D5220/D5220M − 21
Standard Test Method for
Water Mass per Unit Volume of Soil and Rock In-Place by
the Neutron Depth Probe Method
This standard is issued under the fixed designation D5220;D5220/D5220M; 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*
1.1 This test method covers the calculationmeasurement of the water mass per unit volume of soil and rock by thermalization or
slowing of fast neutrons, where the neutron source and the thermal neutron detector are placed at the desired depth in the bored
hole lined by an access tube.
1.1.1 For limitations see Section 6 on Interferences.
1.2 The water mass per unit volume, expressed as mass per unit volume of the material under test, is calculateddetermined by
comparing the thermal neutron count rate with previously established calibration data (see Annex A1).
1.3 A precision statement has not been developed for this standard at this time. Therefore, this standard should not be used for
acceptance or rejection of a material for purchasing purposes unless correlated to other accepted ASTM methods.
1.3 Units—The values expressedstated in either SI units are regarded as the standard. The inch-pound units given in parentheses
may be approximate and are provided for information only. or inch-pound units are to be regarded separately as standard. The
values stated in each system are not necessarily exact equivalents; therefore, to ensure conformance with the standard, each system
shall be used independently of the other, and values from the two systems shall not be combined. Within the text of this standard,
SI units appear first followed by the inch-pound (or other non-SI) units in brackets.
1.3.1 Reporting of test results in units other than SI shall not be regarded as nonconformance with this standard.
1.4 All observed and calculated values shall conform to the guideguidelines for significant digits and rounding established in
Practice D6026.
1.4.1 The procedures used to specify how data are collected, recorded, and calculated in this standard are regarded as the industry
standard. In addition, they are representative of the significant digits that should generally be retained. The procedures used do not
consider material variation, purpose for obtaining the data, special purpose studies, or any considerations for the user’s objectives;
and 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 analysis methods for engineering design.
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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use. Specific hazards are given in Section 8.
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 15, 2014May 1, 2021. Published June 2014May 2021. Originally approved in 1992. Last previous edition approved in 20082014 as
D5220 – 08.D5220 – 14. DOI: 10.1520/D5220-14.10.1520/D5220_D5220M-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
D5220/D5220M − 21
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
D1452 Practice for Soil Exploration and Sampling by Auger Borings
D1586 Test Method for Standard Penetration Test (SPT) and Split-Barrel Sampling of Soils
D1587 Practice for Thin-Walled Tube Sampling of Fine-Grained Soils for Geotechnical Purposes
D2113 Practice for Rock Core Drilling and Sampling of Rock for Site Exploration
D2216 Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass
D2937 Test Method for Density of Soil in Place by the Drive-Cylinder Method
D3550 Practice for Thick Wall, Ring-Lined, Split Barrel, Drive Sampling of Soils
D3740 Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in
Engineering Design and Construction
D4428/D4428M Test Methods for Crosshole Seismic Testing
D5195 Test Method for Density of Soil and Rock In-Place at Depths Below Surface by Nuclear Methods
D6026 Practice for Using Significant Digits in Geotechnical Data
D6938 Test Methods for In-Place Density and Water Content of Soil and Soil-Aggregate by Nuclear Methods (Shallow Depth)
D7263 Test Methods for Laboratory Determination of Density and Unit Weight of Soil Specimens
3. Terminology
3.1 Definitions—For definitions of common technical terms in this standard, refer to Terminology D653.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 detector—a device to observe and measure radiation.
3.2.2 dry density—same as density of dry soil or rock (as defined in Terminology D653); the mass of solid particles per the total
volume of soil or rock.
3.2.1 neutron probe—a cylindrical device containing a fast neutron source and a thermal neutron detector.
3.2.4 neutron (radiation) source—a sealed radioactive material that emits neutron radiation as it decays.
3.2.5 thermalization—the process of “slowing down” fast neutrons by collisions with light-weight atoms, such as hydrogen.
3.2.6 volumetric water content—the volume of water as a percent of the total volume of soil or rock material.
3.2.7 wet density—same as bulk density (as defined in Terminology D653); the total mass (solids plus water) per total volume.
4. Summary of Test Method
4.1 This test method uses thermalization of neutron radiation to calculatedetermine the in-place water mass per unit volume of soil
and rock at various depths by placing a probe containing a neutron source and a thermal neutron detector at desired depths in a
bored hole lined by an access tube as opposed to surface measurements in accordance with Test Method D6938.
4.2 Neutrons emitted by the source are thermalized (slowed) by collisions with materials of low atomic numbers. Hydrogenous
materials, such as water and other compounds containing hydrogen, are most effective in thermalizing neutrons. In this apparatus
the neutrons thermalized by the material under test are detected by the thermal neutron detector.
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.
D5220/D5220M − 21
4.3 In the absence of interference elements as discussed in Section 6, the number of thermalized neutrons is a function of the
hydrogen content of the material under test and the water content is proportional to the hydrogen content.
4.4 By the use of a calibration process the water mass per unit volume is calculateddetermined by correlating the count rate to
known water mass per unit volume values.
5. Significance and Use
5.1 This test method is useful as a rapid, nondestructive technique for the calculationmeasurement of the in-place water mass per
unit volume of soil and rock at desired depths below the surface.
5.2 This test method is useful for informational and research purposes. It should only be The information acquired from this test
method is best used for quality control and acceptance testing when correlated to actual water mass per unit volume using
procedures and methods described in A1.2.3.
5.3 The non-destructive nature of this test method allows repetitive measurements to be made at a single test location for statistical
analysis and to monitor changes over time.
5.4 The fundamental assumptions inherent in this test method are that the material under test is homogeneous and hydrogen
present is in the form of water as defined by Test Method D2216.
NOTE 1—The quality of the result produced by this standard 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/sampling/inspection, and the like. Users of this standard are cautioned that compliance with Practice D3740 does not in itself assure reliable results.
Reliable results depend on many factors; Practice D3740 provides a means of evaluating some of those factors.
6. Interferences
6.1 The sample heterogeneity, density, and chemical composition of the material under test will affect the measurements. The
apparatus must be calibrated to the material under test or adjustments made in accordance with Annex A2.
6.1.1 Hydrogen, in forms other than water, as defined by Test Method D6938 and carbon, present in organic soils, will cause
measurements in excess of the true water value. Some elements such as boron, chlorine, and minute quantities of cadmium, if
present in the material under test, will cause measurements lower than the true water value.
6.2 This test method exhibits spatial bias in that it is more sensitive to water contained in the material closest to the access tube.
The measurement is not necessarily an average water content of the total sample involved.
6.2.1 Voids around the access tube can affect the measurement (see 10.1.2).
6.3 The actual sample volume that the instrument measures is indeterminate and varies with the apparatus and the water content
of the material. In general, the greater the water content of the material, the smaller the volume involved in the measurement. For
3 3 3
example, the sample volume is approximately 0.048 m (1.7[1.7 ft )] for a soil with a water content of 200 kg/m (12.5[12.5
lbm/ft ).].
7. Apparatus (See Fig. 1)
7.1 The apparatus shall consist of a nuclear instrument capable of measuring water mass per unit volume at various depths below
the surface containing the following:
7.1.1 A sealed mixture of a radioactive material such as americium or radium with a target element such as beryllium, and a
suitable thermal neutron detector, and
7.1.2 A suitable timed scaler and power source.
D5220/D5220M − 21
FIG. 1 Schematic Diagram; Water Content by Neutron Depth Probe Method
7.2 The apparatus shall be equipped with a cylindrical probe containing the neutron source and detector, connected by a cable of
sufficient design and length, that is capable of being lowered down the cased hole to desired test depths.
7.2.1 The dimensions of the probe vary among manufacturers and models, but are generally between 25 mm [1 in.] and 75 mm
[3 in.] in diameter and 20 mm [8 in.] and 1 m [39 in.] in length. Probe diameters are generally designed by the manufacturer to
be commensurate with the internal diameter of commonly used access tubing, or drill hole sizes.
7.3 The apparatus shall be equipped with a reference standard, a fixed shape of hydrogenous material used for checking apparatus
operation and to establish conditions for a reproducible reference count rate. It may also serve as a radiation shield.
7.4 Apparatus Precision—See Annex A3 for the precision of the apparatus.
7.5 Accessories:
7.5.1 Access Tubing—The access tubing (casing) is required for all access holes in nonlithified materials (soils and poorly
consolidated rock) that cannot maintain constant borehole diameter with repeated measurements. If access tubing is required, the
tubing shall be of a material such as aluminum, steel, or polyvinyl chloride, having an interior diameter large enough to permit
probe access without binding. The tubing shall be as thin-walled as possible to provide close proximity of the probe to the material
under test. The same type of tubing shall be used in the field as is used in calibration.
7.5.2 Drilling Tool(s)—Hand auger or power drilling equipment that can be used to establish the access hole. Any drilling
equipment that provides a suitable clean open hole for installation of access tubing and insertion of the probe shall be acceptable.
The equipment used shall be capable of maintaining constant borehole diameter to ensure that the measurements are performed
on undisturbed soil and rock. The type of equipment and methods of advancing the access hole shouldshall be reported.
7.5.3 Dummy Probe—A cylindrical probe the same size as the probe containing the neutron source and a chain or cable of
sufficient design and length to permit lowering the dummy probe down the cased hole to desired test depths.
D5220/D5220M − 21
8. Hazards
8.1 These instruments utilize radioactive materials that may be hazardous to the health of the users unless proper precautions are
taken. Users of these instruments must become familiar with applicable safety procedures and government regulations.
8.2 Effective user instructions, together with routine safety procedures and knowledge of and compliance with Regulatory
Requirements, are a mandatory part of the operation and storage of these instruments.
9. Calibration, Standardization, and Reference Check
9.1 Calibrate the instrument in accordance with Annex A1.
9.2 Adjust the calibration in accordance with Annex A2 if adjustments are necessary.
9.3 Standardization and Reference Check: Perform and evaluate standardization and reference check on a daily basis, prior to
taking field measurements, in accordance with Annex A4.
9.3.1 Nuclear density gauges are subject to long-term aging of the radioactive sources, which may change the relationship between
count rates and the material density. To correct for this aging effect, gauges are calibrated as a ratio of the measurement count rate
to a count rate made on a reference standard.
9.3.2 Standardization of the gauge shall be performed at the start of each day’s use, and a record of these data should be retained
for the amount of time required to ensure compliance with either Section 9.3.4 or 9.3.5, whichever is applicable. Perform the
standardization with the gauge far enough away from other apparatus containing radioactive sources to prevent interference due
to radiation from the other apparatus. In addition, perform the standardization far enough away from large masses or other items
which can affect the reference count rates due to reflections from these masses or items.
NOTE 2—Separation of nuclear gauges by a distance of 9 m (30 ft) from one another has typically proven sufficient in preventing radiation from one gauge
from being detected by another gauge and potentially causing an incorrect standardization count. This separation can be reduced by the proper use of
shielding. With regards to reflections from large masses or other items potentially causing incorrect standardization counts, a separation of 1 m (3 ft)
between the gauge and the mass or item in question has typically proven sufficient to prevent such reflections from influencing the standardization counts.
9.3.3 Turn on the gauge and allow for stabilization according to the manufacturer’s recommendations.
9.3.4 Using the reference standard, take at least four repetitive readings at the normal measurement period and obtain the mean.
If available on the gauge, one measurement at four or more times the normal measurement period is acceptable. This constitutes
one standardization check. Use the procedure recommended by the gauge manufacturer to establish the compliance of the standard
measurement to the accepted range. Without specific recommendations from the gauge manufacturer, use the procedure in 9.3.5.
9.3.5 If the value of the current standardization count is outside the limits set by Eq 1, repeat the standardization check. If the
second standardization check satisfies Eq 1, the gauge is considered in satisfactory operating condition.
~ ! ~ !
2ln 2 t 2ln 2 t
T T
0.98N e # N # 1.02N e (1)
1/2 1/2
c 0 c
where:
T = the half-life of the isotope that is used for the density or moisture determination in the gauge. For example, Am:Be,
1/2
the isotope most commonly used for density determination in these gauges, T is 157 788 days,
1/2
N = the standardization count acquired at the time of the last calibration or verification,
c
N = the current standardization count,
t = the time that has elapsed between the current standardization test and the date of the last calibration or verification. The
units selected for t and T should be consistent, that is, if T is expressed in days, then t should also be expressed in
1/2 1/2
days,
ln( ) = the natural logarithm function, and
e = the positive real number for which the natural logarithm value is equal to one. e itself is equal to 2.71828182845904.
9.3.6 Example—A nuclear gauge containing a Am:Be source for density determination (half-life = 157 788 days) is calibrated
on March 1 of a specific year. At the time of calibration, the density standard count was 720 counts per minute (prescaled).
D5220/D5220M − 21
According to Eq 1, what is the allowed range of standard counts for November 1 of the same year? For this example, a total of
245 days have elapsed between the date of calibration or verification (March 1) and the date of the gauge standardization
(November 1).
Therefore:
t = 245 days
T = 157 788 days
1/2
N = 720 counts
c
According to Eq 1, therefore, the lower limit for the density standard count taken on November 1, denoted by N , is
~ ~ !! ~ ~ !!
2 ln 2 t 2 ln 2 ·245
20.00108
0.98 N e T 5 0.98 720 e 157 788 5 706e 5 705 counts
~ ! ~ !
1/2
c
Likewise, the upper limit for the density standard count taken on November 1, denoted by N , is
~ ~ !! ~ ~ !!
2 ln 2 t 2 ln 2 ·245
20.00108
1.02~N !e T 5 1.02~720!e 157 788 5 734e 5 733 counts
1/2
c
Therefore, the density standard count acquired on November 1 should lie somewhere between 705 and 733 counts, or 705 ≤
N ≤ 733.
9.3.7 If for any reason the measured density becomes suspect during the day’s use, perform another standardization check.
10. Procedure
10.1 Installation of Access Tubing (Casing):
10.1.1 Drill the access tube hole and install the access tubing in a manner dependent upon the material to be tested, the depth to
be tested, and the available drilling equipment.
10.1.2 The access hole mustshall be clear enough to allow installing the tubing yet must providewhile still providing a snug fit.
Voids along the sides of the tubing may cause erroneous readings.
10.1.2.1 If voids are suspected to be caused by the drilling process they canmay be grouted using procedures in Test Method
D4428/D4428M.
10.1.2.2 The only method to determine the presence of voids is to perform field calibrations provided in A1.2.3.
10.1.3 Record and note the position of the ground water table, perched water tables, and changes in strata as drilling progresses.
10.1.3.1 If ground water is encountered or saturated conditions are expected to develop, seal the tube at the bottom to prevent
water seepage into the tube using procedures given in Test Method D4428/D4428M or the manufacturer’s recommended
procedures. This will prevent erroneous readings and possible damage to the probe.
10.1.4 The tubing shouldshall project above the ground and be capped to prevent foreign material from entering. The access tube
shouldshall not project above the ground so high that it might be damaged by equipment passing over it.
10.1.4.1 Install all tubes at the same height above the ground as this enables marking the cable to indicate the measured depth to
be used for all tubes.
10.2 Lower a dummy probe down the access tube to verify proper clearance before lowering the probe containing the radioactive
source.
10.3 Standardize the apparatus. apparatus (see Annex A4).
10.4 Proceed with the test as follows:
10.4.1 Seat the apparatus firmly over the access tube, then lower the probe into the tube to the desired depth. Secure the probe
by cable clamps (usually provided by the apparatus manufacturer).
10.4.2 Take a measurement count at the selected timing period.
D5220/D5220M − 21
10.4.3 If the water content as a percentage of dry density is required, the in-place density may be determined by using a different
apparatus that determines density at depths below the surface by the nuclear method. Such methods include, but are not limited
to, Test Method D5195, Test Method D2937 (depths not more than 1 m [3 ft]), or Test Method D1587 (fine-grained soils only.)
11. Interpretation
11.1 Determine the ratio of the reading obtained compared to the standard count. Then using the calibration data combined with
appropriate calibration adjustments, or apparatus direct readout features, calculate the water mass per unit volume of the material
under test.
NOTE 3—Some instruments have built-in provisions to compute and display the ratio and corrected water mass per unit volume. The functional
relationship between the gauge count response and the water mass per unit volume of the soil or rock being measured is typically linear over short ranges
of moisture, quadratic or exponential for larger moisture ranges, or third order polynomial for large ranges of moistures. The functional relationship is
highly dependent on the soil type.
11.2 If water content as a percentage of dry density is required, the in-place density may be determined by using either the same
apparatus or a different apparatus that determines density at depths below the surface by the nuclear method (see Test Method
D5195) or by a method such as density determination of soil in-place by the drive-cylinder method (see Test Method D2937).
11. Report: Test Data Sheet(s)/Form(s)
11.1 The methodology used to specify how data are recorded on the test data sheet(s)/form(s) as given below is covered in
...