ASTM D6758-02
(Test Method)Standard Test Method for Measuring Stiffness and Apparent Modulus of Soil and Soil-Aggregate In-Place by an Electro-Mechanical Method
Standard Test Method for Measuring Stiffness and Apparent Modulus of Soil and Soil-Aggregate In-Place by an Electro-Mechanical Method
SCOPE
1.1 This method covers the measurement by electro-mechanical means of the in-place stiffness of soil or soil-aggregate mixtures so as to determine a Young's modulus based on certain assumptions. The apparatus and procedure provide a fairly rapid means of testing so as to minimize interference and delay of construction. The test procedure is intended for evaluating the stiffness or modulus of materials used in earthworks and roadworks. Rapid in-place stiffness testing supports U.S. federal and state efforts to specify the in-place performance of construction materials based on modulus. Results obtained from this method are applicable to the evaluation of granular cohesionless materials. They are also applicable to the evaluation of silty and clayey materials with more than 20 % fines that are not subject to a change in moisture content. If the silty and clayey material experiences a change in moisture content, then moisture content shall be taken into account if the results of this method are to be applicable. The stiffness measured with this method is influenced by boundary conditions, specifically the support offered by underlying layers as well as the thickness and modulus of the layer being tested. Since this method approximates the layer(s) being evaluated as a half-space, then the modulus measured is also approximate.
1.2 The stiffness, in force per unit displacement, is determined by imparting a small measured force to the surface of the ground, measuring the resulting surface velocity and calculating the stiffness. This is done over a frequency range and the results are averaged.
1.3 The values stated in SI units are to be regarded as the standard. The inch-pound units equivalents may be approximate.
1.4 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.
Note 1—Notwithstanding the statements on precision and bias contained in this test method; the precision of this test method is dependent on the competence of the personnel performing it, and the suitability of the equipment and facilities used. Agencies that meet the criteria of Practice D 3740 are generally considered capable of competent and objective testing. Users of this test method are cautioned that compliance with Practice D 3740 does not in itself assure reliable testing. Reliable testing depends on many factors; Practice D 3740 provides a means of evaluating some of those factors.
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Designation:D6758–02
Standard Test Method for
Measuring Stiffness and Apparent Modulus of Soil and Soil-
Aggregate In-Place by an Electro-Mechanical Method
This standard is issued under the fixed designation D 6758; 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.
tained in this test method; the precision of this test method is dependent
1. Scope
onthecompetenceofthepersonnelperformingit,andthesuitabilityofthe
1.1 This method covers the measurement by electro-
equipment and facilities used. Agencies that meet the criteria of Practice
mechanical means of the in-place stiffness of soil or soil-
D 3740 are generally considered capable of competent and objective
aggregate mixtures so as to determine a Young’s modulus
testing. Users of this test method are cautioned that compliance with
based on certain assumptions. The apparatus and procedure Practice D 3740 does not in itself assure reliable testing. Reliable testing
depends on many factors; Practice D 3740 provides a means of evaluating
provide a fairly rapid means of testing so as to minimize
some of those factors.
interference and delay of construction. The test procedure is
intended for evaluating the stiffness or modulus of materials
2. Referenced Documents
used in earthworks and roadworks. Rapid in-place stiffness
2.1 ASTM Standards:
testing supports U.S. federal and state efforts to specify the
D 653 Terminology Relating to Soil, Rock and Contained
in-placeperformanceofconstructionmaterialsbasedonmodu-
D 698 Test Method for Laboratory Compaction Character-
lus. Results obtained from this method are applicable to the
istics of Soil Using Standard Effort
evaluation of granular cohesionless materials. They are also
D 1557 Test Method for Laboratory Compaction Character-
applicable to the evaluation of silty and clayey materials with
istics of Soil Using Modified Effort
more than 20 % fines that are not subject to a change in
D 2216 TestMethodforLaboratoryDeterminationofWater
moisture content. If the silty and clayey material experiences a
(Moisture) Content of Soil and Rock by Mass
change in moisture content, then moisture content shall be
D 3740 Practice for Minimum Requirements for Agencies
taken into account if the results of this method are to be
Engaged in the Testing and/or Inspection of Soil and Rock
applicable. The stiffness measured with this method is influ-
as Used in Engineering Design and Construction
enced by boundary conditions, specifically the support offered
by underlying layers as well as the thickness and modulus of
3. Terminology
the layer being tested. Since this method approximates the
3.1 Definitions:
layer(s) being evaluated as a half-space, then the modulus
3.1.1 Forcommondefinitionsoftermsinthisstandard,refer
measured is also approximate.
to Terminology D 653.
1.2 The stiffness, in force per unit displacement, is deter-
3.1.2 stiffness, n—the ratio of change of force to the
mined by imparting a small measured force to the surface of
corresponding change in translational deflection of an elastic
the ground, measuring the resulting surface velocity and
element. D 653
calculating the stiffness. This is done over a frequency range
3.1.3 Young’s modulus, n—the ratio of the increase in stress
and the results are averaged.
on a test specimen to the resulting increase in strain under
1.3 The values stated in SI units are to be regarded as the
constant traverse stress limited to materials having a linear
standard. The inch-pound units equivalents may be approxi-
stress-strain relationship over a range of loading. Also called
mate.
elastic modulus. D 653
1.4 This standard does not purport to address all of the
3.1.4 Poisson’s ratio, n—the ratio between linear strain
safety concerns, if any, associated with its use. It is the
changes perpendicular to and in the direction of a given
responsibility of the user of this standard to establish appro-
uniaxial stress change. D 653
priate safety and health practices and determine the applica-
3.2 Definitions of Terms Specific to This Standard:
bility of regulatory limitations prior to use.
3.2.1 shear modulus, (G), n—as equation:
NOTE 1—Notwithstanding the statements on precision and bias con-
E
G 5 (1)
2~11n!
ThistestmethodisunderthejurisdictionofASTMCommitteeD18onSoiland
Rock and is the direct responsibility of Subcommittee D18.08 on Special and
Construction Control Tests.
Current edition approved Jan. 10, 2002. Published February 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.
D6758
4.2.3 The rapid, non-penetrating nature of this method is
where:
suited to production testing, for example, it provides a means
G = shear modulus, MPa (kpsi),
of testing that does not necessarily interfere with or delay
E = Young’s modulus, MPa (kpsi), and
n = Poisson’s ratio. construction.
4.3 This method is suitable for mitigating the risk of
3.2.2 foot, n—that part of the apparatus which contacts the
pavement failure. By assuring the relative uniformity of
ground and imparts force to it.
highwaysubbase,subgradeandbasestiffnesses,stressesonthe
3.2.3 footprint, n—the annular ring imprint left on the
pavement is more uniformly distributed. In this way the life of
ground by the foot of the apparatus.
a pavement is extended and repairs minimized.
3.2.4 non-destructive, adj—a condition that does not impair
4.4 This method is suitable for determining when the
future usefulness and serviceability of a layer of soil or
surface of a soil or soil-aggregate structure is capable of
soil-aggregate mixture in order to measure, evaluate or assess
supporting design loads.This is useful for stabilized fills where
its physical properties.
the material hardens (stiffens) over time without measurable
3.2.5 seating the foot, v—the process of placing the appa-
changes in density or moisture content.
ratus on the ground such that the desired footprint is achieved.
4.5 This test method is suitable for the in-place determina-
3.2.6 site, n—the general area where measurements are to
tion of a Young’s and a shear modulus of soil and soil-
be made.
aggregate mixtures (3,4). Stiffness, as measured by this
3.2.7 test location, n—a specific location on the ground method, is related to modulus (5) from an assumption of
Poisson’s ratio and from the radius of the foot of the apparatus
where a measurement is made.
as follows:
4. Significance and Use
1.77RE 3.54RG
K ' ' (2)
gr 2
~1– n!
~1– n !
4.1 The apparatus and procedure described provides a
means for measurement of the stiffness of a layer of soil or
where:
soil-aggregate mixture from which aYoung’s modulus may be
K = stiffness of the ground layer being measured, MN/m
gr
determined for an assumed Poisson’s ratio. Low strain cyclic
(klbf/in.),
loading is applied by the apparatus about a static load that is
R = outside radius of the apparatus’ foot, m (in.),
consistent with highway applications (1).
n = Poisson’s ratio,
4.2 This method is useful as a non-destructive method for E = Young’s modulus, MPa (kpsi), and
G = Shear modulus, MPa (kpsi).
monitoring or controlling compaction so as to avoid under-
compaction, over-compaction or wasted effort. Through an 4.5.1 Thestiffnessandmodulusofsiltyandclayeymaterials
understandingofhowstiffnessrelatestodensityforaparticular will change with moisture content and can possibly result in
material, moisture content and compaction procedure, the hydro-compaction collapse, loss of bearing capacity or loss of
stiffness achieved can be related to % compaction in connec- effective shear strength. In addition, for silty and clayey
materials with significant fines content, higher stiffness does
tion with density based compaction control or specifications,
for example, to meet the requirements of Method D 698 using not necessarily assure adequate compaction (6).
standard effort or Method D 1557 using modified effort.
5. Apparatus
4.2.1 This method applies to silty and clayey materials
containing significant fines. In such cases, the compactive
5.1 Stiffness Gauge—An electro-mechanical instrument,
effort and moisture content form a more critical relationship
such as that illustrated in Fig. 1, capable of being seated on the
regarding the quality of compaction from stiffness and there-
surface of the material under test and which provides a
fore moisture content should be measured, for example,
meaningful and measurable stress level and a means of
Method D 2216, at the time of the stiffness measurements.
determining force and displacement.
4.2.2 This method is useful in the construction of road bases 5.2 Moist Sand—Asupply of clean, fine sand passing a No.
or earthworks, including the installation of buried pipe (2). 30 (600-µm) sieve, that is sufficiently moist to clump in the
FIG. 1 Possible Apparatus Schematic
D6758
palm of the hand. This is used to assist the seating of the rigid test.Theapparatusshouldbeimmunetoconstructionnoiseand
foot on hard and rough ground surfaces or at anytime when vibration as much as is practical.
additional assistance in seating is required. 5.3.5 There should be an apparatus weight sufficient to
produce a meaningful stress on the ground, for example, 20.6
5.3 Principle of Operation—The force applied by the
to 27.6 kPa (3 to 5 psi).
shaker and transferred to the ground, as illustrated in Fig. 1, is
5.3.6 The measurement should not densify the material
measured and calculated by differential displacement across
being measured or otherwise change its material properties.
the internal flexible plate as follows:
Periodic, repeated measurements (at least 10) at selected
F 5 K ~X – X !1v m X (3)
dr flex 2 1 int 1
locations where individual results are about equally distributed
about the mean of all results will indicate that the measurement
where:
has not densified the material.
F = force applied by the shaker, N (lbf),
dr
K = stiffness of the flexible plate, MN/m (klbf/in), 5.3.7 The apparatus should be of sufficient accuracy to
flex
X = displacement at the flexible plate, m (in.), achieve the required precision and bias.
X = displacement at the rigid foot, m (in.),
6. Calibration
v =2pf, where f is frequency, Hz, and
m = mass of the internal components attached to the
int
6.1 Follow the recommendations of the apparatus manufac-
rigid foot and the foot itself, kg (lb).
turer. Calibration via the force-to-displacement produced by
At the frequencies of operation, the grou
...
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