ASTM D6758-18e1

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.
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Designation: D6758 − 18
Standard Test Method for
Measuring Stiffness and Apparent Modulus of Soil and Soil-
Aggregate In-Place by Electro-Mechanical Method
This standard is issued under the fixed designation D6758; 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.
ε NOTE—Editorially corrected units of measurement statement in June 2021.
1. Scope 1.4 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 by electro-
responsibility of the user of this standard to establish appro-
mechanical means of the in-place stiffness of soil or soil-
priate safety, health, and environmental practices and deter-
aggregate mixtures so as to determine a Young’s modulus
mine the applicability of regulatory limitations prior to use.
based on certain assumptions. The apparatus and procedure
provide a fairly rapid means of testing so as to minimize NOTE 1—Notwithstanding the statements on precision and bias con-
tained in this test method; the precision of this test method is dependent
interference and delay of construction. The test procedure is
onthecompetenceofthepersonnelperformingit,andthesuitabilityofthe
intended for evaluating the stiffness or modulus of materials
equipment and facilities used. Agencies that meet the criteria of Practice
used in earthworks and roadworks. Rapid in-place stiffness
D3740 are generally considered capable of competent and objective
testing supports U.S. federal and state efforts to specify the
testing. Users of this test method are cautioned that compliance with
in-placeperformanceofconstructionmaterialsbasedonmodu- Practice D3740 does not in itself assure reliable testing. Reliable testing
depends on many factors; Practice D3740 provides a means of evaluating
lus. Results obtained from this method are applicable to the
some of those factors.
evaluation of granular cohesionless materials. They are also
1.5 This international standard was developed in accor-
applicable to the evaluation of silty and clayey materials with
dance with internationally recognized principles on standard-
more than 20 % fines that are not subject to a change in
ization established in the Decision on Principles for the
moisture content. If the silty and clayey material experiences a
Development of International Standards, Guides and Recom-
change in moisture content, then moisture content shall be
mendations issued by the World Trade Organization Technical
taken into account if the results of this method are to be
Barriers to Trade (TBT) Committee.
applicable. The stiffness measured with this method is influ-
enced by boundary conditions, specifically the support offered
2. Referenced Documents
by underlying layers as well as the thickness and modulus of
the layer being tested. Since this method approximates the
2.1 ASTM Standards:
layer(s) being evaluated as a half-space, then the modulus
D653 Terminology Relating to Soil, Rock, and Contained
measured is also approximate.
Fluids
D698 Test Methods for Laboratory Compaction Character-
1.2 The stiffness, in force per unit displacement, is deter-
istics of Soil Using Standard Effort (12,400 ft-lbf/ft (600
mined by imparting a small measured force to the surface of
kN-m/m ))
the ground, measuring the resulting surface velocity and
D1557 Test Methods for Laboratory Compaction Character-
calculating the stiffness. This is done over a frequency range
istics of Soil Using Modified Effort (56,000 ft-lbf/ft
and the results are averaged.
(2,700 kN-m/m ))
1.3 Units—The values stated in SI units are to be regarded
D2216 Test Methods for Laboratory Determination of Water
as standard. The values given in parentheses are provided for
(Moisture) Content of Soil and Rock by Mass
information only and are not considered standard.
D3740 Practice for Minimum Requirements for Agencies
Engaged in Testing and/or Inspection of Soil and Rock as
Used in Engineering Design and Construction
ThistestmethodisunderthejurisdictionofASTMCommitteeD18onSoiland
Rock and is the direct responsibility of Subcommittee D18.08 on Special and
Construction Control Tests.
Current edition approved Feb. 15, 2018. Published February 2018. Originally For referenced ASTM standards, visit the ASTM website, www.astm.org, or
approved in 2002. Last previous edition approved in 2008 as D6758 – 08, which contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
was withdrawn January 2017 and reinstated in February 2018. DOI: 10.1520/ Standards volume information, refer to the standard’s Document Summary page on
D6758-18E01. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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D6758 − 18
D4220 Practices for Preserving and Transporting Soil 4.2 This method is useful as a non-destructive method for
Samples monitoring or controlling compaction so as to avoid under-
D4643 Test Method for Determination of Water Content of
compaction, over-compaction or wasted effort. Through an
Soil and Rock by Microwave Oven Heating understandingofhowstiffnessrelatestodensityforaparticular
D4944 TestMethodforFieldDeterminationofWater(Mois-
material, moisture content and compaction procedure, the
ture)ContentofSoilbytheCalciumCarbideGasPressure
stiffness achieved can be related to % compaction in connec-
Tester
tion with density based compaction control or specifications,
D4959 Test Method for Determination of Water Content of
for example, to meet the requirements of Method D698 using
Soil By Direct Heating
standard effort or Method D1557 using modified effort.
4.2.1 This method applies to silty and clayey materials
3. Terminology
containing greater than 20 % fines. In such cases, the relation-
3.1 Definitions:
ship between stiffness and dry density or dry unit weight is
3.1.1 Forcommondefinitionsoftermsinthisstandard,refer
sensitive to the water content. Water contents should be
to Terminology D653.
determined by use of: Test Method D2216, D4643,or D4959.
3.1.2 stiffness, n—the ratio of change of force to the corre-
If the determination cannot be made immediately at the time of
sponding change in translational deflection of an elastic
the stiffness measurements, then soil samples shall be pre-
element. D653
served and transported in accordance with Practice D4220,
Section 8, Groups B, C, or D soils.
3.1.3 Young’s modulus, n—the ratio of the increase in stress
on a test specimen to the resulting increase in strain under
4.2.2 Thismethodisusefulintheconstructionofroadbases
constant traverse stress limited to materials having a linear
or earthworks, including the installation of buried pipe (2).
stress-strain relationship over a range of loading. Also called
4.2.3 The rapid, non-penetrating nature of this method is
elastic modulus. D653
suited to production testing, for example, it provides a means
3.1.4 Poisson’s ratio, n—the ratio between linear strain of testing that does not necessarily interfere with or delay
changes perpendicular to and in the direction of a given construction.
uniaxial stress change. D653
4.3 This method is suitable for mitigating the risk of
3.2 Definitions of Terms Specific to This Standard:
pavement failure. By assuring the relative uniformity of
3.2.1 shear modulus, (G), n—as equation:
highwaysubbase,subgradeandbasestiffnesses,stressesonthe
pavement is more uniformly distributed. In this way the life of
E
G 5 (1)
a pavement is extended and repairs minimized.
2 11ν
~ !
where: 4.4 This method is suitable for determining when the
surface of a soil or soil-aggregate structure is capable of
G = shear modulus, MPa (kpsi),
supportingdesignloads.Thisisusefulforstabilizedfillswhere
E = Young’s modulus, MPa (kpsi), and
ν = Poisson’s ratio. the material hardens (stiffens) over time without measurable
changes in density or moisture content.
3.2.2 foot, n—that part of the apparatus which contacts the
ground and imparts force to it.
4.5 This test method is suitable for the in-place determina-
tion of a Young’s and a shear modulus of soil and soil-
3.2.3 footprint, n—the annular ring imprint left on the
aggregate mixtures (3, 4). Stiffness, as measured by this
ground by the foot of the apparatus.
method, is related to modulus (5) from an assumption of
3.2.4 non-destructive, adj—a condition that does not impair
Poisson’s ratio and from the radius of the foot of the apparatus
future usefulness and serviceability of a layer of soil or
as follows:
soil-aggregate mixture in order to measure, evaluate or assess
its physical properties.
1.77RE 3.54RG
K ' ' (2)
gr
1 2ν 1 2ν
~ ! ~ !
3.2.5 seating the foot, v—the process of placing the appa-
ratus on the ground such that the desired footprint is achieved.
where:
3.2.6 site, n—thegeneralareawheremeasurementsaretobe
K = stiffness of the ground layer being measured, MN/m
gr
made.
(klbf/in.),
R = outside radius of the apparatus’ foot, m (in.),
3.2.7 test location, n—a specific location on the ground
ν = Poisson’s ratio,
where a measurement is made.
E = Young’s modulus, MPa (kpsi), and
G = Shear modulus, MPa (kpsi).
4. Significance and Use
4.5.1 Thestiffnessandmodulusofsiltyandclayeymaterials
4.1 The apparatus and procedure described provides a
means for measurement of the stiffness of a layer of soil or will change with moisture content and can possibly result in
hydro-compaction collapse, loss of bearing capacity or loss of
soil-aggregate mixture from which aYoung’s modulus may be
determined for an assumed Poisson’s ratio. Low strain cyclic effective shear strength. In addition, for silty and clayey
loading is applied by the apparatus about a static load that is materials with significant fines content, higher stiffness does
consistent with highway applications (1). not necessarily assure adequate compaction (6).
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D6758 − 18
5. Apparatus where:
n = number of test frequencies used in the apparatus,
5.1 Stiffness Gauge—An electro-mechanical instrument,
V = velocity at the flexible plate, m/s (ft/s), and
such as that illustrated in Fig. 1, capable of being seated on the 2
V = velocity at the rigid foot, m/s (ft/s).
surface of the material under test and which provides a
meaningful and measurable stress level and a means of This approach avoids the need for a non-moving reference
determining force and displacement. forgrounddisplacementandpermitstheaccuratemeasurement
of small displacements. It also assumes the following condi-
5.2 Moist Sand—Asupply of clean, fine sand passing a No.
tions.
30 (600-µm) sieve, that is sufficiently moist to clump in the
5.3.1 A significant number of discrete measurement fre-
palm of the hand. This is used to assist the seating of the rigid
quencies (for example, ≥20) should be above the typical
foot on hard and rough ground surfaces or at anytime when
operating frequencies of construction equipment and below the
additional assistance in seating is required.
frequencies where ground impedance is no longer stiffness
5.3 Principle of Operation—Theforceappliedbytheshaker
controlled (for example, 100 to 200 Hz).
and transferred to the ground, as illustrated in Fig. 1,is
5.3.2 So as to not interfere with or delay construction, a
measured and calculated by differential displacement across
sufficiently short period of time should be required for a single
the internal flexible plate as follows:
measurement, for example, <2 min.
F 5 K X 2 X 1ω m X (3) 5.3.3 The depth of measurement is on the order of twice the
~ !
dr flex 2 1 int 1
foot outside diameter. The depth of measurement may be
where:
confirmed by measuring the stiffness of a layer of material in
F = force applied by the shaker, N (lbf),
dr
a confined bin per this method and comparing it to the stiffness
K = stiffness of the flexible plate, MN/m (klbf/in),
flex
of the layer
...