1、Designation: D 6758 02Standard Test Method forMeasuring Stiffness and Apparent Modulus of Soil and Soil-Aggregate In-Place by an Electro-Mechanical Method1This standard is issued under the fixed designation D 6758; the number immediately following the designation indicates the year oforiginal adopti
2、on or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This method covers the measurement by electro-mechanical means of the in-
3、place 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 o
4、r 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 m
5、aterials. 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-sp
7、ace, 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 resul
8、ts 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
9、establish appro-priate safety and health practices and determine the applica-bility 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 personnel perfo
10、rming it, and the suitability of theequipment and facilities used. Agencies that meet the criteria of PracticeD 3740 are generally considered capable of competent and objectivetesting. Users of this test method are cautioned that compliance withPractice D 3740 does not in itself assure reliable test
11、ing. Reliable testingdepends on many factors; Practice D 3740 provides a means of evaluatingsome of those factors.2. Referenced Documents2.1 ASTM Standards:D 653 Terminology Relating to Soil, Rock and Contained2D 698 Test Method for Laboratory Compaction Character-istics of Soil Using Standard Effor
12、t2D 1557 Test Method for Laboratory Compaction Character-istics of Soil Using Modified Effort2D 2216 Test Method for Laboratory Determination of Water(Moisture) Content of Soil and Rock by Mass2D 3740 Practice for Minimum Requirements for AgenciesEngaged in the Testing and/or Inspection of Soil and
13、Rockas Used in Engineering Design and Construction23. Terminology3.1 Definitions:3.1.1 For common definitions of terms in this standard, referto Terminology D 653.3.1.2 stiffness, nthe ratio of change of force to thecorresponding change in translational deflection of an elasticelement. D 6533.1.3 Yo
14、ungs 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. D 6533.1.4 Poissons ratio, nthe ratio between lin
15、ear strainchanges perpendicular to and in the direction of a givenuniaxial stress change. D 6533.2 Definitions of Terms Specific to This Standard:3.2.1 shear modulus, (G), nas equation:G 5E21 1n!(1)1This test method is under the jurisdiction of ASTM Committee D18 on Soil andRock and is the direct re
16、sponsibility of Subcommittee D18.08 on Special andConstruction Control Tests.Current edition approved Jan. 10, 2002. Published February 2002.2Annual Book of ASTM Standards, Vol 04.08.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.wh
17、ere:G = shear modulus, MPa (kpsi),E = Youngs modulus, MPa (kpsi), andn = Poissons 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 condi
18、tion that does not impairfuture usefulness and serviceability of a layer of soil 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
19、, nthe general area where measurements are tobe made.3.2.7 test location, na specific 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 w
20、hich a Youngs modulus may bedetermined for an assumed Poissons ratio. Low strain 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
21、under-compaction, over-compaction or wasted effort. Through anunderstanding of 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 specificat
22、ions,for example, to meet the requirements of Method D 698 usingstandard effort or Method D 1557 using modified effort.4.2.1 This method applies to silty and clayey materialscontaining significant fines. In such cases, the compactiveeffort and moisture content form a more critical relationshipregard
23、ing the quality of compaction from stiffness and there-fore moisture content should be measured, for example,Method D 2216, at the time of the stiffness measurements.4.2.2 This method is useful in the construction of road basesor earthworks, including the installation of buried pipe (2).4.2.3 The ra
24、pid, 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 the risk ofpavement failure. By assuring the relative uniformity ofhighway su
25、bbase, 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 a soil or soil-aggregate structure is capable ofsupporting design loads. Thi
26、s 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 shear modulus of soil and soil-aggregate mixtures (3,4). Stiffness, as measured
27、by thismethod, is related to modulus (5) from an assumption ofPoissons ratio and from the radius of the foot of the apparatusas follows:Kgr1.77RE1n2!3.54RG1n!(2)where:Kgr= stiffness of the ground layer being measured, MN/m(klbf/in.),R = outside radius of the apparatus foot, m (in.),n = Poissons rati
28、o,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 of bearing capacity or loss ofeffective shear strength. In addition, for silty a
29、nd 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, capable of being seated on thesurface of the material under test and which provid
30、es ameaningful 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 thepalm of the hand. This is used to assist the seating of the rigidfoot on hard and rough grou
31、nd surfaces or at anytime whenadditional assistance in seating is required.5.3 Principle of OperationThe force applied by theshaker and transferred to the ground, as illustrated in Fig. 1, ismeasured and calculated by differential displacement acrossFIG. 1 Possible Apparatus SchematicD 67582the inte
32、rnal flexible plate as follows:Fdr5 KflexX2 X1! 1v2mintX1(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.),v =2pf, where f is frequency, Hz, andmint= ma
33、ss of the internal components attached to therigid foot 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/in).By substituting Eq 3 for Fdrin Eq 4, a
34、veraging over theoperating frequencies and substituting velocity, V, for displace-ment, X, since the units cancel each other, the ground stiffnessis calculated as follows:Kgr5 KflexS1nSX2 X1X1Dn1S1nv2nmint5 KflexS1nSV2 V1V1Dn1S1nv2nmint(5)where:n = number of test frequencies used in the apparatus,V2
35、= 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 condi-tions.5.3.1 A significant number
36、 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 interfere with or delay construction, a
37、sufficiently 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 material ina confined bin per this meth
38、od 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 noise and vibration do not interfere
39、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 measurement should not densify the materialbei
40、ng 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 material.5.3.7 The apparatus should b
41、e 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 absolutereference for stiffness measurements. This ma
42、y 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 measurementof stiffness in this configuration should agree with the follow-ing equation within 61%.Keff5S1nMv!2n(6)where:Ke
43、ff= effective stiffness offered by the moving mass,MN/m (klbf/in.),M = value of the moving mass, kg (lb),v =2pf, where f is frequency, Hz, andn = the number of frequencies used in the apparatus.6.2 Calibration of the apparatus is suggested every 12months.6.3 When any stiffness measurement is in doub
44、t, 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 s
45、oan appropriate tolerance should be assigned to the check (forexample, 65 % relative to the value of stiffness expected).7. Procedure7.1 Guidelines for Seating the Foot:7.1.1 Before seating the foot, lightly brush any loose mate-rial away from the test location. The surface need not beleveled if the
46、 gauge can stand on its own. If leveling isrequired, scraping the surface with a square point shovel issufficient.7.1.2 To provide for consistent stress on the ground for eachmeasurement, at least 60 % of the foots annular ring surfacemust seat or contact the ground. The amount of surface contactis
47、visibly estimated from the footprint left by the foot when theapparatus is lifted off the ground after the measurement istaken.7.1.3 If the footprint cannot be readily seen, assist theseating of the foot as described in 7.1.4.7.1.4 If the requirement of 7.1.2 cannot be met because of arough or irreg
48、ular ground surface or if the surface is hard andsmooth, apply a thin layer of clean, moist sand about 3.0 to 6.0mm (18 to14 in.) thick, on the test location. Pat down firmly.Seat the foot on top of the sand.7.1.5 Practice in seating the foot is suggested as describedD 67583above at each site prior
49、to any actual measurements or eachtime ground surface conditions change. In addition, follow themanufacturers recommendations as appropriate.7.2 Stiffness Measurement:7.2.1 Assure that the foot is clean and free of soil and otherdebris.7.2.2 Turn on the apparatus.7.2.3 Seat the foot per the directions of 7.1.7.2.4 Assure that the external case of the apparatus does notcome into contact with a trench wall, pipe or any other object.7.2.5 Initiate the measurement. The apparatus should dwellat each frequency. The shaker will impart a force to the f
