1、Designation: D2845 08Standard Test Method forLaboratory Determination of Pulse Velocities and UltrasonicElastic Constants of Rock1This standard is issued under the fixed designation D2845; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revi
2、sion, 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. Scope*1.1 This test method describes equipment and proceduresfor laboratory measurements of the pulse velocit
3、ies of com-pression waves and shear waves in rock (1)2and the determi-nation of ultrasonic elastic constants (Note 1) of an isotropicrock or one exhibiting slight anisotropy.NOTE 1The elastic constants determined by this test method aretermed ultrasonic since the pulse frequencies used are above the
4、 audiblerange. The terms sonic and dynamic are sometimes applied to theseconstants but do not describe them precisely (2). It is possible that theultrasonic elastic constants may differ from those determined by otherdynamic methods.1.2 This test method is valid for wave velocity measure-ments in bot
5、h anisotropic and isotropic rocks although thevelocities obtained in grossly anisotropic rocks may be influ-enced by such factors as direction, travel distance, and diam-eter of transducers.1.3 The ultrasonic elastic constants are calculated from themeasured wave velocities and the bulk density. The
6、 limitingdegree of anisotropy for which calculations of elastic constantsare allowed and procedures for determining the degree ofanisotropy are specified.1.4 The values stated in inch-pound units are to be regardedas standard. The values given in parentheses are mathematicalconversions to SI units t
7、hat are provided for information onlyand are not considered standard.1.5 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 establish appro-priate safety and health practices and determine the
8、applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3D653 Terminology Relating to Soil, Rock, and ContainedFluidsD2216 Test Methods for Laboratory Determination of Water(Moisture) Content of Soil and Rock by MassD3740 Practice for Minimum Requirements for
9、AgenciesEngaged in Testing and/or Inspection of Soil and Rock asUsed in Engineering Design and ConstructionD6026 Practice for Using Significant Digits in GeotechnicalDataE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3. Terminology3.1 For common defin
10、itions of terms in this standard, referto Terminology D653.3.2 Definitions of Terms Specific to This Standard:3.2.1 compression wave velocitythe dilational wave ve-locity which is the propagation velocity of a longitudinal wavein a medium that is effectively infinite in lateral extent. It is notto b
11、e confused with bar or rod velocity.4. Summary of Test Method4.1 Details of essential procedures for the determination ofthe ultrasonic velocity, measured in terms of travel time anddistance, of compression and shear waves in rock specimensinclude requirements of instrumentation, suggested types oft
12、ransducers, methods of preparation, and effects of specimengeometry and grain size. Elastic constants may be calculatedfor isotropic or slightly anisotropic rocks, while anisotropy isreported in terms of the variation of wave velocity withdirection in the rock.1This test method is under the jurisdic
13、tion ofASTM Committee D18 on Soil andRock and is the direct responsibility of Subcommittee D18.12 on Rock Mechanics.Current edition approved July 1, 2008. Published July 2008. Originally approvedin 1969. Last previous edition approved in 2005 as D2845 05. DOI: 10.1520/D2845-08.2The boldface numbers
14、in parentheses refer to the list of references at the end ofthis test method.3For 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 standards Document Summary page ont
15、he ASTM website.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesNOTICE: This standard has either been superseded and replaced by a new version or withdrawn.Contact ASTM I
16、nternational (www.astm.org) for the latest information15. Significance and Use5.1 The primary advantages of ultrasonic testing are that ityields compression and shear wave velocities, and ultrasonicvalues for the elastic constants of intact homogeneous isotropicrock specimens (3). Elastic constants
17、are not to be calculatedfor rocks having pronounced anisotropy by procedures de-scribed in this test method.The values of elastic constants oftendo not agree with those determined by static laboratorymethods or the in situ methods. Measured wave velocitieslikewise may not agree with seismic velociti
18、es, but offer goodapproximations. The ultrasonic evaluation of rock properties isuseful for preliminary prediction of static properties. The testmethod is useful for evaluating the effects of uniaxial stress andwater saturation on pulse velocity. These properties are in turnuseful in engineering des
19、ign.5.2 The test method as described herein is not adequate formeasurement of stress-wave attenuation. Also, while pulsevelocities can be employed to determine the elastic constants ofmaterials having a high degree of anisotropy, these proceduresare not treated herein.NOTE 2The quality of the result
20、 produced by this standard isdependent on the competence of the personnel performing it, and thesuitability of the equipment and facilities used. Agencies that meet thecriteria of Practice D3740 are generally considered capable of competentand objective testing and sampling. Users of this standard a
21、re cautionedthat compliance with Practice D3740 does not in itself assure reliableresults. Reliable results depend on many factors; Practice D3740 providesa means of evaluating some of those factors.6. Apparatus6.1 GeneralThe testing apparatus (Fig. 1) should haveimpedance matched electronic compone
22、nts and shielded leadsto ensure efficient energy transfer. To prevent damage to theapparatus allowable voltage inputs should not be exceeded.6.2 Pulse Generator UnitThis unit shall consist of anelectronic pulse generator and external voltage or poweramplifiers if needed. A voltage output in the form
23、 of eitherrectangular pulse or a gated sine wave is satisfactory. Thegenerator shall have a voltage output with a maximum valueafter amplification of at least 50 V into a 50- impedance load.A variable pulse width, with a range of 1 to 10 s is desirable.The pulse repetition rate may be fixed at 60 re
24、petitions persecond or less although a range of 20 to 100 repetitions persecond is recommended. The pulse generator shall also have atrigger-pulse output to trigger the oscilloscope. There shall bea variable delay of the main-pulse output with respect to thetrigger-pulse output, with a minimum range
25、 of 0 to 20 s.6.3 TransducersThe transducers shall consist of a trans-mitter that converts electrical pulses into mechanical pulsesand a receiver that converts mechanical pulses into electricalpulses. Environmental conditions such as ambient temperature,moisture, humidity, and impact should be consi
26、dered in select-ing the transducer element. Piezoelectric elements are usuallyrecommended, but magnetostrictive elements may be suitable.Thickness-expander piezoelectric elements generate and sensepredominately compression-wave energy; thickness-shearpiezoelectric elements are preferred for shear-wa
27、ve measure-ments. Commonly used piezoelectric materials include ceram-ics such as lead-zirconate-titanate for either compression orshear, and crystals such as a-c cut quartz for shear. To reducescattering and poorly defined first arrivals at the receiver, thetransmitter shall be designed to generate
28、 wavelengths at least3 the average grain size of the rock.NOTE 3Wavelength is the wave velocity in the rock specimen dividedby the resonance frequency of the transducer. Commonly used frequenciesrange from 75 kHz to 3 MHz.6.3.1 In laboratory testing, it may be convenient to useunhoused transducer el
29、ements. But if the output voltage of thereceiver is low, the element should be housed in metal(grounded) to reduce stray electromagnetic pickup. If protec-tion from mechanical damage is necessary, the transmitter aswell as the receiver may be housed in metal. This also allowsNOTE 1Components shown b
30、y dashed lines are optional, depending on method of travel-time measurement and voltage sensitivity of oscilloscope.FIG. 1 Schematic Diagram of Typical ApparatusD2845 082special backings for the transducer element to alter its sensi-tivity or reduce ringing (4). The basic features of a housedelement
31、 are illustrated in Fig. 2. Energy transmission betweenthe transducer element and test specimen can be improved by(1) machining or lapping the surfaces of the face plates to makethem smooth, flat, and parallel, ( 2) making the face plate froma metal such as magnesium whose characteristic impedance i
32、sclose to that of common rock types, (3) making the face plateas thin as practicable, and (4) coupling the transducer elementto the face plate by a thin layer of an electrically conductiveadhesive, an epoxy type being suggested.6.3.2 Pulse velocities may also be determined for specimenssubjected to
33、uniaxial states of stress. The transducer housingsin this case will also serve as loading platens and should bedesigned with thick face plates to assure uniform loading overthe ends of the specimen (5).NOTE 4The state of stress in many rock types has a marked effect onthe wave velocities. Rocks in s
34、itu are usually in a stressed state andtherefore tests under stress have practical significance.6.4 PreamplifierA voltage preamplifier is required if thevoltage output of the receiving transducer is relatively low orif the display and timing units are relatively insensitive. Topreserve fast rise tim
35、es, the frequency response of the pream-plifier shall drop no more than 2 dB over a frequency rangefrom 5 kHz to 4 the resonance frequency of the receiver. Theinternal noise and gain must also be considered in selecting apreamplifier. Oscilloscopes having a vertical-signal output canbe used to ampli
36、fy the signal for an electronic counter.6.5 Display and Timing UnitThe voltage pulse applied tothe transmitting transducer and the voltage output from thereceiving transducer shall be displayed on a cathode-rayoscilloscope for visual observation of the waveforms. Theoscilloscope shall have an essent
37、ially flat response between afrequency of 5 kHz and 4 the resonance frequency of thetransducers. It shall have dual beams or dual traces so that thetwo waveforms may be displayed simultaneously and theiramplitudes separately controlled. The oscilloscope shall betriggered by a triggering pulse from t
38、he pulse generator. Thetiming unit shall be capable of measuring intervals between 2s and 5 ms to an accuracy of 1 part in 100. Two alternativeclasses of timing units are suggested, the respective positionsof each being shown as dotted outlines in the block diagram inFig. 1:(1) an electronic counter
39、 with provisions for timeinterval measurements, or (2) a time-delay circuit such as acontinuously variable-delay generator, or a delayed-sweepfeature on the oscilloscope. The travel-time measuring circuitshall be calibrated periodically with respect to its accuracy andlinearity over the range of the
40、 instrument. The calibration shallbe checked against signals transmitted by the National Instituteof Standards and Technology radio station WWV, or against acrystal controlled time-mark or frequency generator that can bereferenced back to the signals from WWV periodically. It isrecommended that the
41、calibration of the time measuring circuitbe checked at least once a month and after any severe impactthat the instrument may receive.7. Test Specimens7.1 PreparationExercise care in core drilling, handling,sawing, grinding, and lapping the test specimen to minimizethe mechanical damage caused by str
42、ess and heat. It isrecommended that liquids other than water be prevented fromcontacting the specimen, except when necessary as a couplingmedium between specimen and transducer during the test. Thesurface area under each transducer shall be sufficiently planethat a feeler gage 0.001 in. (0.025 mm) t
43、hick will not passunder a straightedge placed on the surface. The two oppositesurfaces on which the transducers will be placed shall beparallel to within 0.005 in./in. (0.1 mm/20 mm) of lateraldimension (Fig. 3). If the pulse velocity measurements are tobe made along a diameter of a core, the above
44、tolerance thenrefers to the parallelism of the lines of contact between thetransducers and curved surface of the rock core. Moisturecontent of the test specimen can affect the measured pulsevelocities. Pulse velocities may be determined on the velocitytest specimen for rocks in the oven-dry state (0
45、 % saturation),in a saturated condition (100 % saturation), or in any interme-diate state. If the pulse velocities are to be determined with therock in the same moisture condition as received or as existsunderground, care must be exercised during the preparationprocedure so that the moisture content
46、 does not change. In thiscase it is suggested that both the sample and test specimen bestored in moisture-proof bags or coated with wax and that drysurface-preparation procedures be employed. If results aredesired for specimens in the oven-dried condition, refer to TestMethod D2216.The specimen shal
47、l remain submerged in waterup to the time of testing when results are desired for thesaturated state.7.2 Limitation on DimensionsIt is recommended that theratio of the pulse-travel distance to the minimum lateraldimension not exceed 5. Reliable pulse velocities may not bemeasurable for high values o
48、f this ratio. The travel distance ofFIG. 2 Basic Features of a Housed Transmitter or ReceiverNOTE 1(A) must be within 0.1 mm of (B) for each 20 mm of width(C).FIG. 3 Specification for ParallelismD2845 083the pulse through the rock shall be at least 10 the averagegrain size so that an accurate averag
49、e propagation velocity maybe determined. The grain size of the rock sample, the naturalresonance frequency of the transducers, and the minimumlateral dimension of the specimen are interrelated factors thataffect test results. The wavelength corresponding to the domi-nant frequency of the pulse train in the rock is approximatelyrelated to the natural resonance frequency of the transducer andthe pulse-propagation velocity, (compression or shear) asfollows:V/f, (1)where: = dominant wavelength of pulse train, in. (or m),V = pulse propagation
