ASTM D5220-92(1997)
(Test Method)Standard Test Method for Water Content of Soil and Rock In-Place by the Neutron Depth Probe Method
Standard Test Method for Water Content of Soil and Rock In-Place by the Neutron Depth Probe Method
SCOPE
1.1 This test method covers the calculation of the water content 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 (see Note 1).
1.2 The water content, in mass per unit volume of the material under test, is calculated 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.
1.4 The values expressed in SI units are regarded as the standard. The inch-pound units given in parentheses may be approximate and are provided for information only.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Specific hazards are given in Section 7.
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Designation: D 5220 – 92 (Reapproved 1997)
Standard Test Method for
Water Content of Soil and Rock In-Place by the Neutron
Depth Probe Method
This standard is issued under the fixed designation D 5220; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope D 4428/D 4228M Test Method for Crosshole Seismic Test-
ing
1.1 This test method covers the calculation of the water
D 5195 Test Method for Density of Soil and Rock in Place
content of soil and rock by thermalization or slowing of fast
at Depths Below the Surface by Nuclear Methods
neutrons where the neutron source and the thermal neutron
detector are placed at the desired depth in the bored hole lined
3. Summary of Test Method
by an access tube (see Note 1).
3.1 This test method uses thermalization of neutron radia-
1.2 The water content, in mass per unit volume of the
tion to calculate the in-place water content of soil and rock at
material under test, is calculated by comparing the thermal
various depths by placing a probe containing a neutron source
neutron count rate with previously established calibration data
and a thermal neutron detector at desired depths in a bored hole
(see Annex A1).
lined by an access tube as opposed to surface measurements in
1.3 The values expressed in SI units are regarded as the
accordance with Test Method D 3017.
standard. The inch-pound units given in parentheses may be
3.2 Neutrons emitted by the source are thermalized (slowed)
approximate and are provided for information only.
by collisions with materials of low atomic numbers. Hydrog-
1.4 This standard does not purport to address all of the
enous materials, such as water and other compounds contain-
safety concerns, if any, associated with its use. It is the
ing hydrogen, are most effective in thermalizing neutrons. In
responsibility of the user of this standard to establish appro-
this apparatus the neutrons thermalized by the material under
priate safety and health practices and determine the applica-
test are detected by the thermal neutron detector.
bility of regulatory limitations prior to use. Specific hazards are
3.3 In the absence of interference elements as discussed in
given in Section 7.
Section 5, the number of thermalized neutrons is a function of
2. Referenced Documents the hydrogen content of the material under test and the water
content is proportional to the hydrogen content.
2.1 ASTM Standards:
3.4 By the use of a calibration process the water content is
D 1452 Practice for Soil Investigation and Sampling by
calculated by correlating the count rate to known water
Auger Borings
contents.
D 1586 Method for Penetration Test and Split-Barrel Sam-
pling of Soils
4. Significance and Use
D 1587 Practice for Thin Walled Tube Sampling of Soils
4.1 This test method is useful as a rapid, nondestructive
D 2113 Practice for Diamond Core Drilling for Site Inves-
2 technique for the calculation of the in-place water content of
tigation
soil and rock at desired depths below the surface.
D 2216 Test Method for Laboratory Determination of Water
4.2 With proper calibration in accordance with Annex A1,
(Moisture) Content of Soil, Rock, and Soil-Aggregate
2 this test method can be used for quality control and acceptance
Mixtures
testing for construction and for research and development
D 2937 Test Method for Density of Soil in Place by the
2 applications.
Drive-Cylinder Method
4.3 The non-destructive nature of this test method allows
D 3017 Test Method for Moisture Content of Soil and
repetitive measurements to be made at a single test location for
Soil-Aggregate in Place by Nuclear Methods (Shallow
2 statistical analysis and to monitor changes over time.
Depth)
2 4.4 The fundamental assumptions inherent in this test
D 3550 Practice for Ring-Lined Barrel Sampling of Soils
method are that the material under test is homogeneous and
hydrogen present is in the form of water as defined by Test
Method D 2216.
This test method is under the jurisdiction of ASTM Committee D-18 on Soil
and Rock and is the direct responsibility of Subcommittee D18.02 on Sampling and
Related Field Testing for Soil Investigations.
Current edition approved Jan. 15, 1992. Published March 1992.
2 3
Annual Book of ASTM Standards, Vol 04.08. Annual Book of ASTM Standards, Vol 04.09.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
D 5220
5. Interferences 6.1.2 A suitable timed scaler and power source.
6.2 The apparatus shall be equipped with a cylindrical probe
5.1 The sample heterogeneity, density, and chemical com-
containing the neutron source and detector, connected by a
position of the material under test will affect the measurements.
cable of sufficient design and length, that is capable of being
The apparatus must be calibrated to the material under test or
lowered down the cased hole to desired test depths.
adjustments made in accordance with Annex A2.
6.3 The apparatus shall be equipped with a reference stan-
5.1.1 Hydrogen, in forms other than water, as defined by
dard, a fixed shape of hydrogenous material used for checking
Test Method D 2216 and carbon, present in organic soils, will
apparatus operation and to establish conditions for a reproduc-
cause measurements in excess of the true water value. Some
ible reference count rate. It may also serve as a radiation shield.
elements such as boron, chlorine, and minute quantities of
6.4 Apparatus Precision—See Annex A3 for the precision
cadmium, if present in the material under test, will cause
of the apparatus.
measurements lower than the true water value.
6.5 Accessories:
5.2 This test method exhibits spatial bias in that it is more
6.5.1 Access Tubing—The access tubing (casing) is required
sensitive to water contained in the material closest to the access
for all access holes in nonlithified materials (soils and poorly
tube. The measurement is not necessarily an average water
consolidated rock) that cannot maintain constant borehole
content of the total sample involved.
diameter with repeated measurements. If access tubing is
5.2.1 Voids around the access tube can affect the measure-
required the tubing shall be of a material such as aluminum,
ment (see 11.1.2).
3 3
steel, or polyvinyl chloride, having an interior diameter large
5.3 The sample volume is approximately 0.048 m (1.7 ft )
3 3
enough to permit probe access without binding. The tubing
with a water content of 200 kg/m (12.5 lbf/ft ). The actual
shall be as thin-walled as possible to provide close proximity of
sample volume is indeterminate and varies with the apparatus
the probe to the material under test. The same type of tubing
and the water content of the material. In general, the greater the
shall be used in the field as is used in calibration.
water content of the material, the smaller the volume involved
6.5.2 Hand auger or power drilling equipment that can be
in the measurement.
used to establish the access hole. Any drilling equipment that
6. Apparatus (See Fig. 1)
provides a suitable clean open hole for installation of access
6.1 The apparatus shall consist of a nuclear instrument
tubing and insertion of the probe shall be acceptable. The
capable of measuring water content at various depths below the
equipment used shall be capable of maintaining constant
surface containing the following:
borehole diameter to ensure that the measurements are per-
6.1.1 A sealed mixture of a radioactive material such as
formed on undisturbed soil and rock. The type of equipment
americium or radium with a target element such as beryllium,
and methods of advancing the access hole should be reported.
and a suitable thermal neutron detector, and
6.5.3 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.
7. Hazards
7.1 This equipment utilizes radioactive materials that may
be hazardous to the health of the users unless proper precau-
tions are taken. Users of this equipment must become com-
pletely familiar with possible safety hazards and with all
applicable regulations concerning the handling and use of
radioactive materials. Effective user instructions together with
routine safety procedures are a recommended part of the
operation of this apparatus.
8. Calibration, Standardization, and Reference Check
8.1 Calibrate the instrument in accordance with Annex A1.
8.2 Adjust the calibration in accordance with Annex A2 if
adjustments are necessary.
8.3 Standardization and Reference Check:
8.3.1 Nuclear apparatus are subject to the long-term decay
of the radioactive source and aging of detectors and electronic
system, that may change the relationship between count rate
and water content. To offset these changes, the apparatus may
be calibrated as the ratio of the measurement count rate to a
count rate made on a reference standard. The reference count
rate should be in the same or a higher order of magnitude than
the range of measurement count rates over the useful water
FIG. 1 Schematic Diagram; Water Content by Neutron Depth
Probe Method content range of the apparatus.
D 5220
8.3.2 Standardization of equipment should be performed at 9.1.2.1 If voids are suspected to be caused by the drilling
the start of each day’s work and a permanent record of these process they can be grouted using procedures in Test Method
data retained. Perform the standardization with the apparatus D 4428.
located at least 10 m (30 ft) away from other apparatus 9.1.2.2 The only method to determine the presence of voids
containing neutron emitting radioactive sources and clear of is to perform field calibrations provided in Annex A2.2.3.
large masses of water or other items which may affect the 9.1.3 Record and note the position of the ground water
reference count rate. table, perched water tables, and changes in strata as drilling
8.3.2.1 If recommended by the apparatus manufacturer to progresses.
provide more stable and consistent results: turn on the appa- 9.1.3.1 If ground water is encountered or saturated condi-
ratus prior to use to allow it to stabilize; and leave the power tions are expected to develop, seal the tube at the bottom to
on during the day’s testing. prevent water seepage into the tube using procedures given in
8.3.2.2 Using the reference standard, take at least four Test Method D 4428 or the manufacturer’s recommended
repetitive readings at the manufacturer’s recommended mea- procedures. This will prevent erroneous readings and possible
surement period and determine the mean. If available on the damage to the probe.
apparatus, one measurement at a period of four or more times 9.1.4 The tubing should project above the ground and be
the recommended period is acceptable. These measurements capped to prevent foreign material from entering. The access
constitute one standardization check. tube should not project above the ground so high that it might
8.3.2.3 If the value obtained above is within the limits stated be damaged by equipment passing over it.
below, the equipment is considered to be in satisfactory 9.1.4.1 Install all tubes at the same height above the ground
condition and the value may be used to determine the count as this enables marking the cable to indicate the measured
ratios for the day of use. If the value is outside these limits, depth to be used for all tubes.
allow additional time for the apparatus to stabilize, make sure 9.2 Lower a dummy probe down the access tube to verify
the area is clear of sources of interference and then conduct proper clearance before lowering the probe containing the
another standardization check. If the second standardization radioactive source.
check is within the limits, the apparatus may be used, but if it 9.3 Standardize the apparatus.
also fails the test, the apparatus shall be adjusted or repaired as 9.4 Proceed with the test as follows:
recommended by the manufacturer. The limits are as follows: 9.4.1 Seat the apparatus firmly over the access tube, then
lower the probe into the tube to the desired depth. Secure the
2.0=N
o
N ,5 N 1
probe by cable clamps (usually provided by the apparatus
s o
F
=
manufacturer).
and
9.4.2 Take a measurement count at the selected timing
period.
2.0=N
o
N .5 N 2
s o
F
=
NOTE 2—The above procedure is performed in an installed access tube
that will allow repeated in-place measurements. In some field situations it
where:
may be more appropriate to use a drilling technique involving alternating
N 5 value of current standardization check,
s
before access tubing and one of the following: a large diameter hollow
N 5 average of the past four values of N taken previously,
o s
stem auger, a split-spoon sampler, or a thin-walled volumetric sampler.
and
This technique is destructive and only one measurement can be made at
F 5 value of prescale.
each depth per hole.
NOTE 1—Some instruments have built-in provisions to compute and
10. Interpretation
display the results of a statistical test of the standardization counts and to
10.1 Determine the ratio of the reading obtained compared
indicate if the apparatus is in satisfactory condition.
to the standard count. Then using the calibration data combined
8.3.3 Use the value of N to determine the count ratios for
s
with appropriate calibration adjustments, or apparatus direct
the current day’s use of the apparatus. If, for any reason, the
readout features, calculate the water content in mass per unit
measured water content becomes suspect during the day’s use,
volume of the material under test.
perform another standardization check.
NOTE 3—Some instruments have built-in provisions to compute and
8.3.4 If the instrument was calibrated in the field using
display the ratio and corrected water content per unit volume.
methods described in Annex A1.2.3 the count rate on any trial
reading may be adjusted by a correction factor determined in 10.2 If water content as a percentage of dry density is
initial calibration.
required, the in-place density may be determined by using
either the same apparatus or a different apparatus that deter-
9. Procedure
mines density at depths below the surface by the nuclear
9.1 Installation of Access Tubing (Casing):
method (see Test Method D 5195) or by a method such as
9.1.1 Drill the access tube hole and install access tubing in
density determination of soil in-place by the drive-cylinder
a manner dependent upon the material to be test
...
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