1、Designation: D6758 18Standard Test Method forMeasuring Stiffness and Apparent Modulus of Soil and Soil-Aggregate In-Place by Electro-Mechanical Method1This standard is issued under the fixed designation D6758; the number immediately following the designation indicates the year oforiginal adoption or
2、, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the measurement by electro-mechanical means of the in-p
3、lace stiffness of soil or soil-aggregate mixtures so as to determine a Youngs modulusbased on certain assumptions. The apparatus and procedureprovide a fairly rapid means of testing so as to minimizeinterference and delay of construction. The test procedure isintended for evaluating the stiffness or
4、 modulus of materialsused in earthworks and roadworks. Rapid in-place stiffnesstesting supports U.S. federal and state efforts to specify thein-place performance of construction materials based on modu-lus. Results obtained from this method are applicable to theevaluation of granular cohesionless ma
5、terials. They are alsoapplicable to the evaluation of silty and clayey materials withmore than 20 % fines that are not subject to a change inmoisture content. If the silty and clayey material experiences achange in moisture content, then moisture content shall betaken into account if the results of
6、this method are to beapplicable. The stiffness measured with this method is influ-enced by boundary conditions, specifically the support offeredby underlying layers as well as the thickness and modulus ofthe layer being tested. Since this method approximates thelayer(s) being evaluated as a half-spa
7、ce, then the modulusmeasured is also approximate.1.2 The stiffness, in force per unit displacement, is deter-mined by imparting a small measured force to the surface ofthe ground, measuring the resulting surface velocity andcalculating the stiffness. This is done over a frequency rangeand the result
8、s are averaged.1.3 The values stated in SI units are to be regarded as thestandard. The inch-pound units equivalents may be approxi-mate.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to e
9、stablish appro-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.NOTE 1Notwithstanding the statements on precision and bias con-tained in this test method; the precision of this test method is dependenton the competence of the
10、personnel performing it, and the suitability of theequipment and facilities used. Agencies that meet the criteria of PracticeD3740 are generally considered capable of competent and objectivetesting. Users of this test method are cautioned that compliance withPractice D3740 does not in itself assure
11、reliable testing. Reliable testingdepends on many factors; Practice D3740 provides a means of evaluatingsome of those factors.1.5 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theD
12、evelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D653 Terminology Relating to Soil, Rock, and ContainedFluidsD698 Test Methods for Laboratory Compaction Char
13、acter-istics of Soil Using Standard Effort (12,400 ft-lbf/ft3(600kN-m/m3)D1557 Test Methods for Laboratory Compaction Character-istics of Soil Using Modified Effort (56,000 ft-lbf/ft3(2,700 kN-m/m3)D2216 Test Methods for Laboratory Determination of Water(Moisture) Content of Soil and Rock by MassD37
14、40 Practice for Minimum Requirements for AgenciesEngaged in Testing and/or Inspection of Soil and Rock asUsed in Engineering Design and ConstructionD4220 Practices for Preserving and Transporting SoilSamplesD4643 Test Method for Determination of Water Content ofSoil and Rock by Microwave Oven Heatin
15、g1This test method is under the jurisdiction ofASTM Committee D18 on Soil andRock and is the direct responsibility of Subcommittee D18.08 on Special andConstruction Control Tests.Current edition approved Feb. 15, 2018. Published February 2018. Originallyapproved in 2002. Last previous edition approv
16、ed in 2008 as D6758 08, whichwas withdrawn January 2017 and reinstated in February 2018. DOI: 10.1520/D6758-18.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the s
17、tandards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the
18、Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1D4944 Test Method for Field Determination of Water (Mois-ture) Content of Soil by the Calcium Carbide Gas PressureTeste
19、rD4959 Test Method for Determination of Water Content ofSoil By Direct Heating3. Terminology3.1 Definitions:3.1.1 For common definitions of terms in this standard, referto Terminology D653.3.1.2 stiffness, nthe ratio of change of force to the corre-sponding change in translational deflection of an e
20、lasticelement. D6533.1.3 Youngs modulus, nthe ratio of the increase in stresson a test specimen to the resulting increase in strain underconstant traverse stress limited to materials having a linearstress-strain relationship over a range of loading. Also calledelastic modulus. D6533.1.4 Poissons rat
21、io, nthe ratio between linear strainchanges perpendicular to and in the direction of a givenuniaxial stress change. D6533.2 Definitions of Terms Specific to This Standard:3.2.1 shear modulus, (G), nas equation:G 5E211!(1)where:G = shear modulus, MPa (kpsi),E = Youngs modulus, MPa (kpsi), and = Poiss
22、ons ratio.3.2.2 foot, nthat part of the apparatus which contacts theground and imparts force to it.3.2.3 footprint, nthe annular ring imprint left on theground by the foot of the apparatus.3.2.4 non-destructive, adja condition that does not impairfuture usefulness and serviceability of a layer of so
23、il orsoil-aggregate mixture in order to measure, evaluate or assessits physical properties.3.2.5 seating the foot, vthe process of placing the appa-ratus on the ground such that the desired footprint is achieved.3.2.6 site, nthe general area where measurements are to bemade.3.2.7 test location, na s
24、pecific location on the groundwhere a measurement is made.4. Significance and Use4.1 The apparatus and procedure described provides ameans for measurement of the stiffness of a layer of soil orsoil-aggregate mixture from which a Youngs modulus may bedetermined for an assumed Poissons ratio. Low stra
25、in cyclicloading is applied by the apparatus about a static load that isconsistent with highway applications (1).4.2 This method is useful as a non-destructive method formonitoring or controlling compaction so as to avoid under-compaction, over-compaction or wasted effort. Through anunderstanding of
26、 how stiffness relates to density for a particularmaterial, moisture content and compaction procedure, thestiffness achieved can be related to % compaction in connec-tion with density based compaction control or specifications,for example, to meet the requirements of Method D698 usingstandard effort
27、 or Method D1557 using modified effort.4.2.1 This method applies to silty and clayey materialscontaining greater than 20 % fines. In such cases, the relation-ship between stiffness and dry density or dry unit weight issensitive to the water content. Water contents should bedetermined by use of: Test
28、 Method D2216, D4643,orD4959.If the determination cannot be made immediately at the time ofthe stiffness measurements, then soil samples shall be pre-served and transported in accordance with Practice D4220,Section 8, Groups B, C, or D soils.4.2.2 This method is useful in the construction of road ba
29、sesor earthworks, including the installation of buried pipe (2).4.2.3 The rapid, non-penetrating nature of this method issuited to production testing, for example, it provides a meansof testing that does not necessarily interfere with or delayconstruction.4.3 This method is suitable for mitigating t
30、he risk ofpavement failure. By assuring the relative uniformity ofhighway subbase, subgrade and base stiffnesses, stresses on thepavement is more uniformly distributed. In this way the life ofa pavement is extended and repairs minimized.4.4 This method is suitable for determining when thesurface of
31、a soil or soil-aggregate structure is capable ofsupporting design loads. This is useful for stabilized fills wherethe material hardens (stiffens) over time without measurablechanges in density or moisture content.4.5 This test method is suitable for the in-place determina-tion of a Youngs and a shea
32、r modulus of soil and soil-aggregate mixtures (3, 4). Stiffness, as measured by thismethod, is related to modulus (5) from an assumption ofPoissons ratio and from the radius of the foot of the apparatusas follows:Kgr1.77RE1 2 2!3.54RG1 2 !(2)where:Kgr= stiffness of the ground layer being measured, M
33、N/m(klbf/in.),R = outside radius of the apparatus foot, m (in.), = Poissons ratio,E = Youngs modulus, MPa (kpsi), andG = Shear modulus, MPa (kpsi).4.5.1 The stiffness and modulus of silty and clayey materialswill change with moisture content and can possibly result inhydro-compaction collapse, loss
34、of bearing capacity or loss ofeffective shear strength. In addition, for silty and clayeymaterials with significant fines content, higher stiffness doesnot necessarily assure adequate compaction (6).5. Apparatus5.1 Stiffness GaugeAn electro-mechanical instrument,such as that illustrated in Fig. 1, c
35、apable of being seated on thesurface of the material under test and which provides aD6758 182meaningful and measurable stress level and a means ofdetermining force and displacement.5.2 Moist SandA supply of clean, fine sand passing a No.30 (600-m) sieve, that is sufficiently moist to clump in thepal
36、m of the hand. This is used to assist the seating of the rigidfoot on hard and rough ground surfaces or at anytime whenadditional assistance in seating is required.5.3 Principle of OperationThe force applied by the shakerand transferred to the ground, as illustrated in Fig. 1,ismeasured and calculat
37、ed by differential displacement acrossthe internal flexible plate as follows:Fdr5 KflexX22 X1!12mintX1(3)where:Fdr= force applied by the shaker, N (lbf),Kflex= stiffness of the flexible plate, MN/m (klbf/in),X2= displacement at the flexible plate, m (in.),X1= displacement at the rigid foot, m (in.),
38、 =2f, where f is frequency, Hz, andmint= mass of the internal components attached to the rigidfoot and the foot itself, kg (lb).At the frequencies of operation, the ground-input impedanceis dominantly stiffness controlled.Kgr5FdrX1(4)where:Kgr= stiffness of the ground layer being measured, MN/m(klbf
39、/in).By substituting Eq 3 for Fdrin Eq 4, averaging over theoperating frequencies and substituting velocity, V, fordisplacement, X, since the units cancel each other, the groundstiffness is calculated as follows:KHgr5 Kflex1nSX22 X1X1Dn11n2nmint5 Kflex1nSV22 V1V1Dn11n2nmint(5)where:n = number of tes
40、t frequencies used in the apparatus,V2= velocity at the flexible plate, m/s (ft/s), andV1= velocity at the rigid foot, m/s (ft/s).This approach avoids the need for a non-moving referencefor ground displacement and permits the accurate measurementof small displacements. It also assumes the following
41、condi-tions.5.3.1 A significant number of discrete measurement fre-quencies (for example, 20) should be above the typicaloperating frequencies of construction equipment and below thefrequencies where ground impedance is no longer stiffnesscontrolled (for example, 100 to 200 Hz).5.3.2 So as to not in
42、terfere with or delay construction, asufficiently short period of time should be required for a singlemeasurement, for example, 2 min.5.3.3 The depth of measurement is on the order of twice thefoot outside diameter. The depth of measurement may beconfirmed by measuring the stiffness of a layer of ma
43、terial ina confined bin per this method and comparing it to the stiffnessof the layer as calculated from the measured void ratio, theestimated mean effective stress under the apparatus foot andthe estimated Poissons ratio (7).5.3.4 The apparatus should be used in a manner such thatconstruction site
44、noise and vibration do not interfere with thetest. The apparatus should be immune to construction noise andvibration as much as is practical.5.3.5 There should be an apparatus weight sufficient toproduce a meaningful stress on the ground, for example, 20.6to 27.6 kPa (3 to 5 psi).5.3.6 The measureme
45、nt should not densify the materialbeing measured or otherwise change its material properties.Periodic, repeated measurements (at least 10) at selectedlocations where individual results are about equally distributedabout the mean of all results will indicate that the measurementhas not densified the
46、material.5.3.7 The apparatus should be of sufficient accuracy toachieve the required precision and bias.6. Calibration6.1 Follow the recommendations of the apparatus manufac-turer. Calibration via the force-to-displacement produced bymoving a mass is suggested, as it will provide an absolutereferenc
47、e for stiffness measurements. This may be done byrigidly attaching a mass of known value to the foot of theapparatus and attaching the mass to isolation mounts with ahigh frequency cut-off of approximately 5 Hz. A measurementFIG. 1 Possible Apparatus SchematicD6758 183of stiffness in this configurat
48、ion should agree with the follow-ing equation within 61%.Keff51nM!2n(6)where:Keff= effective stiffness offered by the moving mass, MN/m(klbf/in.),M = value of the moving mass, kg (lb), =2f, where f is frequency, Hz, andn = the number of frequencies used in the apparatus.6.2 Calibration of the appara
49、tus is suggested every 12months.6.3 When any stiffness measurement is in doubt, a fieldcheck of the calibration may be needed. A check via theforce-to-displacement produced by moving a known mass issuggested, as it will provide an approximate reference forstiffness measurements (see 6.1). Note that field conditionsmay not allow the precision of a laboratory calibration and soan appropriate tolerance should be assigned to the check (forexample, 65 % relative to the value of stiffness expected).7. Procedure7.1 Guidelines for S
