ASTM D6780-02

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Designation: D 6780 – 02
Standard Test Method for
Water Content and Density of Soil in Place by Time Domain
Reflectometry (TDR)
This standard is issued under the fixed designation D6780; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope D698 Test Methods for Moisture-Density Relations of
Soils and Soil-Aggregate Mixtures, Using 5.5 lb (2.49 kg)
1.1 This test method may be used to determine the water
Rammer and 12-in. (305-mm) Drop
content of soils and the in-place density of soils using a TDR
D1556 Test Method for Moisture-Density of Soil In-Place
apparatus.
by the Sand-Cone Method
1.2 This test method applies to soils that have 30% or less
D1557 Test Methods for Moisture-Density Relations of
by weight of their particles retained on the 19.0-mm ( ⁄4-in.)
Soils and Soil-Aggregate Mixtures, Using 10 lb (4.54 kg)
sieve.
Rammer and 18-in. (457-mm) Drop
1.3 This test method is suitable for use as a means of
D2167 Test Method for Density of Soil In-Place by the
acceptance for compacted fill or embankments.
Rubber-Balloon Method
1.4 This test method may not be suitable for organic and
D2216 Method for Laboratory Determination of Water
highly plastic soils.
(Moisture) Content of Soil, Rock, and Soil-Aggregate
1.5 All observed and calculated values shall conform to the
Mixtures
guidelines for significant digits and rounding established in
D2922 Test Methods for Density of Soil and Soil Aggre-
Practice D6026.
gate and Rock in Place by Nuclear Methods (Shallow
1.5.1 The method used to specify how data are collected,
Depth)
calculated,orrecordedinthisstandardisnotdirectlyrelatedto
D2937 Test Method for Density of Soil In-Place by the
theaccuracytowhichthedatacanbeappliedindesignorother
Drive-Cylinder Method
uses, or both. How one applies the results obtained using this
D3017 Test Method for Water Content of Soil and Rock
standard is beyond its scope.
In-Place by Nuclear Methods (Shallow Depth)
1.6 The values stated in either SI units or inch-pound units
D3740 Practice for Minimum Requirements for Agencies
are to be regarded separately as standard. The values stated in
Engaged in theTesting and/or Inspection of Soil and Rock
each system may not be exact equivalents; therefore, each
as Used in Engineering Design and Construction
system shall be used independently of the other. Combining
D4643 Method for Determination of Water (Moisture)
values from the two systems may result in non-conformance
Content of Soil by the Microwave Oven Method
with the standard.
D4718 Practice for Correction of Unit Weight and Water
1.7 This standard does not purport to address all of the
Content for Soils Containing Oversize Particles
safety concerns, if any, associated with its use. It is the
D4753 Specification for Evaluating, Selecting, and Speci-
responsibility of the user of this standard to establish appro-
fying Balances and Scales for Use in Soil and Rock
priate safety and health practices and determine the applica-
Testing
bility of regulatory limitations prior to use.
D4914 Test Method for Density and Unit Weight of Soil
2. Referenced Documents
and Rock in Place by the Sand Replacement Method
D4944 Test Method for Field Determination of Water
2.1 ASTM Standards:
(Moisture) Content of Soil by the Calcium Carbide Gas
D653 Terminology Relating to Soil, Rock, and Contained
Pressure Tester Method
Fluids
D4959 Test Method for Determination ofWater (Moisture)
Content of Soil by Direct Heating Method
D5030 Test Methods for Density and Unit Weight of Soil
1 2
ThistestmethodisunderthejurisdictionofASTMCommitteeD18onSoiland
and Rock in Place by the Water Replacement Method
Rock and is the direct responsibility of Subcommittee D18.08 on Special and
D5080 Test Method for Rapid Determination of Percent
Construction Control Tests.
Compaction
Current edition approved April 10, 2002. Published August 2002.
Annual Book of ASTM Standards, Vol 04.08.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D6780–02
D6026 Practice for Using Significant Digits in Geotechni- metallicendplate,filledwithcompactedsoil,andwithaninner
cal Data conductorconsistingofaroddrivenintothesoilalongtheaxis
D6565 Test Method for Determination ofWater (Moisture) of the mold.
Content of Soil by the Time Domain Reflectometry 3.2.5 multiple rod probe, MRP —aprobeformedbydriving
Method four rods of equal length into the soil in a pattern where three
E1 Specification for ASTM Thermometers of the rods define the outer conductor of a “coaxial cable” and
E11 Specification for Wire-Cloth Sieves for Testing Pur- one of the rods is the inner conductor.
poses 3.2.6 probe length, L—the length of the TDR probe that is
SI10 Standard for Use of the International System of Units below the surface of the soil.
(SI): The Modern Metric System 3.2.7 scaled distance, l—the product of the velocity of light
in air and electromagnetic wave travel time in the soil divided
3. Terminology
by two.
3.1 Definitions—Refer to Terminology D653 for standard
4. Summary of Test Method
definitions of terms.
4.1 Thedielectricconstantofthesoilin-placeisdetermined
3.2 Definitions of Terms Specific to This Standard:
using a multiple rod probe (MRP), a coaxial head (CH), and
3.2.1 apparent dielectric constant, K , K —the
insitu mold
TDR apparatus.The soil at the location of the in-situ measure-
squared ratio of the velocity of light in air to the apparent
ment is then excavated and compacted in a mold. By measure-
velocity of electromagnetic wave propagation in the soil
ment of the mass of the mold and soil and with the mass and
measured by a TDR apparatus in place and in the cylindrical
volume of the mold known, the wet density of the soil in the
mold, respectively.
mold is determined.Arod driven into the soil along the axis of
3.2.2 apparent length, l —on a plot of electromagnetic
a
the mold creates a cylindrical mold probe (CMP). Using the
wave signal versus scaled distance measured by a TDR
same coaxial head (CH), an adapter ring, and the TDR
apparatus as shown in Fig. 1, it is the horizontal distance
apparatus the dielectric constant of the soil in the mold is
between the point on the waveform due to the reflection from
measured. The water content of the soil in the mold is
the surface of the soil where the probe is inserted into the soil
determined using a correlation between the dielectric constant,
tothepointonthewaveformduetothereflectionfromtheend
moisture content and soil density.The correlation requires two
of the probe.
constantsthataresomewhatsoilspecific.Itisassumedthatthe
3.2.3 coaxial head, CH —a device that forms a transition
water content of the soil in place is the same as the water
from the coaxial cable connected to the TDR apparatus to the
content in the mold. The density of the soil in place is
Multiple Rod Probe or to a Cylindrical Mold Probe.
determined from the density of the soil in the mold and the
3.2.4 cylindrical mold probe, CMP —a probe formed by a
dielectric constants measured in the mold and in place.
cylindrical metal mold as the outer conductor having a non-
5. Significance and Use
5.1 This test method can be used to determine the density
Annual Book of ASTM Standards, Vol 04.08.
and water content of naturally occurring soils and of soils
Annual Book of ASTM Standards, Vol 14.02.
placed during the construction of earth embankments, road
Annual Book of ASTM Standards, Vol 14.04.
fills, and structural backfills.
The apparatus is covered by patents. Interested parties are invited to submit
information regarding the identification of alternative(s) to this patented item to the
5.2 Time domain reflectometry (TDR) measures the appar-
ASTMHeadquarters.Yourcommentswillreceivecarefulconsiderationatameeting
entdielectricconstantofsoil.Thedielectricconstantisaffected
of the responsible technical committee, which you may attend.
FIG. 1 Typical TDR Curve Showing Reflection Points and Apparent Length, l
a
D6780–02
significantly by the water content and density of soil, and to a 9.5-mm ( ⁄8-in.). (Other length spikes, but with the same
lesser extent by the chemical composition of soil and pore diameter, may be used but in no case should they have lengths
waterandbytemperature.Thewatercontentdeterminedinthis less than 150-mm (6-in.). For lengths longer than 250-mm
standardmakesuseofadifferentrelationshipbetweenapparent (10-in.), drift in the alignment of the spikes and loss of
dielectric constant and water content from that used in Test reflected signal from the end of the MRP may occur.)
Method D6565. 7.2.2 AMRPguidetemplate(seeFig.2)isusedtoguidethe
5.3 Soil and porewater characteristics are accounted for in spikesastheyaredrivenintothesoil.Thetemplatemustallow
this method with two calibration constants that are determined for its removal after the spikes are driven and before a TDR
foragivensoilbyperformingcompactiontestsasdescribedin measurementismade.(Theradiusfromthecentralspiketothe
Annex A2 where water content also is measured by use of outer spikes must be within the range of 5 to 7.5 times the
Method D2216. diameter of the central spike.)
5.4 Thewatercontentistheaveragevalueoverthelengthof 7.2.3 The Coaxial Head (CH) (see Fig. 3) forms a transi-
the cylindrical mold and the density is the average value over tion from the coaxial cable coming from theTDR apparatus to
the length of the multiple-rod probe embedded in the soil. the MRP.
7.3 Cylindrical Mold Probe (CMP) , the CMPconsists of a
NOTE 1—The quality of the result produced by this standard is
cylindrical mold, a guide template, a central rod, and a ring
dependent on the competence of the personnel performing it, and the
collar. Details for these items are shown in Fig. 4.
suitability of the equipment and facilities used. Agencies that meet the
criteria of Practice D3740 are generally considered capable of competent 7.3.1 The central rod is a stainless steel rod with a diameter
and objective testing/sampling/inspection/etc. Users of this standard are
of 8.0-mm ( ⁄16-in.) and a length of 264-mm (10.4-in.) in
cautioned that compliance with Practice D3740 does not in itself assure
length.
reliable results. Reliable results depend on many factors; Practice D3740
7.4 Balances or Scales, meeting Specification GP10 of
provides a means of evaluating some of those factors.
Specification D4753 to determine the mass of the soil and the
cylindrical mold.Abattery-operated balance or scale having a
6. Interferences
minimum capacity of 10 kg is suitable when an apparatus with
6.1 Quality and accuracy of the test results significantly
the dimension given in Fig. 3 is used.
depend on soil having contact with the inner conductor of the
7.5 Driving Tools, a brass-headed hammer for driving
probes.To assist this, when installing the rods of the MRP, the
spikes for the MRP and the central rod into the cylindrical
rod that forms the inner conductor must be the last rod
mold.Aresin-headedhammeralsomaybeusedfordrivingthe
installed.Ifintheinstallationprocess,therodhitsuponalarge
central rod into the cylindrical mold. (Use of these hammers
particle that causes it to drift from vertical alignment, all rods
prevents peening of the driving end of the steel rods from
should be removed and the test conducted in a new location at
repeated use.)
least 0.2-m (8-in.) from the previous test location.
7.6 Tamping Rod, an aluminum rod with flat ends, a
6.2 The quality of the signal read by the TDR apparatus
diameter of 37-mm (1.5-in.), and a length of 380-mm (15-in.).
depends on having clean contacts between the CH and the
7.7 Thermometer, 0 to 50°C range, 0.5°C graduations,
MRP and the CMP. The contacting surfaces should be wiped
conforming to requirements of Specification E1.
with a clean cloth prior to placing the CH on the MRPand the
7.8 Vernier or Dial Caliper, having a measuring range of at
CMP. Once placed, observe the signal on the TDR apparatus.
least 0 to 250-mm (0 to 10-in.) and readable to at least
If the characteristic signal is not present, the CH may have to
0.02-mm (0.001-in.).
be slightly rotated about its axis to make better contact.
7.9 Miscellaneous Tools, a battery-powered hand drill with
6.3 This test method only applies to non-frozen soil. The
a spare battery and charger and with a 25-mm (1-in.) diameter
apparent dielectric constant is slightly temperature dependent
auger bit (alternatively, a small pick will work), straight edge
for soils and depends on soil type. For soil temperatures
for smoothing the surface of the soil for the in-place test and
between 15°C and 25°C (59°F and 77°F), no temperature
for smoothing the surface of the soil in the cylindrical mold,
corrections are needed for most soils. A simple temperature
pliers for removing the spikes and central rod, small scoop or
adjustment for water content determination is part of the test
spoonforremovaloftheloosenedsoilandforplacementinthe
method.
cylindrical mold, and a brush for removing excess soil from
aroundthebaseofthecylindricalmoldpriortodeterminingits
7. Apparatus
mass.
7.1 TDR Apparatus,aMetallicTimeDomainReflectometer
with a scaled length resolution of at least 2.4-mm (0.10-in.)
8. Preparation of Apparatus
(this corresponds approximately to a time between data points
-12
8.1 Charge or replace, as appropriate batteries in the TDR
less than or equal to sixteen picoseconds (16 310 s). A
apparatus, the hand drill, and the balance.
portable computer with a serial communication port to the
TDR is suggested for controlling the apparatus, acquiring and
9. Calibration and Standardization
saving the data, and for making the calculations as the test
proceeds. 9.1 Determine the average length of the spikes that will
6 3
7.2 Multiple Rod Probe (MRP) with Coaxial Head (CH) penetrate into the soil surface in the in-place test, L ,m
insitu
7.2.1 The MRP consists of four common steel spikes, (in.), by inserting each spike into the MRPguide template and
typically 250-mm (10-in.) in length and uniform diameters of measuring the length that each spike protrudes from the
D6780–02
FIG. 2 MRP Guide Template
TABLE 1 Metric Equivalents for Dimensions in Fig. 2
9.5 Determinethevaluesof aand bforthesoilstobetested
(in.) Tol. (in.) (mm) Tol. (mm)
in the field by procedures in Annex A2.
0.391 6 0.002 10.00 6 0.05
1.000 6 0.005 25.00 6 0.15
10. Procedure
1.350 6 0.015 34.30 6 0.40
1.500 6 0.015 38.00 6 0.40
10.1 Measure t
...