ASTM D2845-00
(Test Method)Standard Test Method for Laboratory Determination of Pulse Velocities and Ultrasonic Elastic Constants of Rock
Standard Test Method for Laboratory Determination of Pulse Velocities and Ultrasonic Elastic Constants of Rock
SCOPE
1.1 This test method describes equipment and procedures for laboratory measurements of the pulse velocities of compression waves and shear waves in rock (1) (Note 2) and the determination of ultrasonic elastic constants (Note 1) of an isotropic rock or one exhibiting slight anisotropy.
Note 2--The elastic constants determined by this test method are termed ultrasonic since the pulse frequencies used are above the audible range. The terms sonic and dynamic are sometimes applied to these constants but do not describe them precisely (2). It is possible that the ultrasonic elastic constants may differ from those determined by other dynamic methods.
1.2 This test method is valid for wave velocity measurements in both anisotropic and isotropic rocks although the velocities obtained in grossly anisotropic rocks may be influenced by such factors as direction, travel distance, and diameter of transducers.
1.3 The ultrasonic elastic constants are calculated from the measured wave velocities and the bulk density. The limiting degree of anisotropy for which calculations of elastic constants are allowed and procedures for determining the degree of anisotrophy are specified.
1.4 The values stated in U.S. customary units are to be regarded as the standard. The metric equivalents of U.S. customary units are rationalized.
1.5 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.
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Designation: D 2845 – 00
Standard Test Method for
Laboratory Determination of Pulse Velocities and Ultrasonic
Elastic Constants of Rock
This standard is issued under the fixed designation D 2845; 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.
1. Scope * D 3740 Practice for Minimum Requirements for Agencies
Engaged in the Testing and/or Inspection of Soil and Rock
1.1 This test method describes equipment and procedures
as Used in Engineering Design and Construction
for laboratory measurements of the pulse velocities of com-
E 691 Practice for Conducting an Interlaboratory Study to
pression waves and shear waves in rock (1) (Note 2) and the
Determine the Precision of a Test Method
determination of ultrasonic elastic constants (Note 1) of an
isotropic rock or one exhibiting slight anisotropy.
3. Terminology
NOTE 1—The elastic constants determined by this test method are
3.1 For common definitions of terms in this standard, refer
termed ultrasonic since the pulse frequencies used are above the audible
to Terminology D 653.
range. The terms sonic and dynamic are sometimes applied to these
3.2 Definitions of Terms Specific to This Standard:
constants but do not describe them precisely (2). It is possible that the
3.2.1 compression wave velocity—the dilational wave ve-
ultrasonic elastic constants may differ from those determined by other
dynamic methods. locity which is the propagation velocity of a longitudinal wave
in a medium that is effectively infinite in lateral extent. It is not
1.2 This test method is valid for wave velocity measure-
to be confused with bar or rod velocity.
ments in both anisotropic and isotropic rocks although the
velocities obtained in grossly anisotropic rocks may be influ-
NOTE 2—The compression wave velocity as defined here is the dilata-
enced by such factors as direction, travel distance, and diam- tional wave velocity. It is the propagation velocity of a longitudinal wave
in a medium which is effectively infinite in lateral extent. It should not be
eter of transducers.
confused with the bar or rod velocity.
1.3 The ultrasonic elastic constants are calculated from the
measured wave velocities and the bulk density. The limiting
4. Summary of Test Method
degree of anisotropy for which calculations of elastic constants
4.1 Details of essential procedures for the determination of
are allowed and procedures for determining the degree of
the ultrasonic velocity, measured in terms of travel time and
anisotrophy are specified.
distance, of compression and shear waves in rock specimens
1.4 The values stated in U.S. customary units are to be
include requirements of instrumentation, suggested types of
regarded as the standard. The metric equivalents of U.S.
transducers, methods of preparation, and effects of specimen
customary units are rationalized.
geometry and grain size. Elastic constants may be calculated
1.5 This standard does not purport to address all of the
for isotropic or slightly anisotropic rocks, while anisotropy is
safety concerns, if any, associated with its use. It is the
reported in terms of the variation of wave velocity with
responsibility of the user of this standard to establish appro-
direction in the rock.
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
5. Significance and Use
5.1 The primary advantages of ultrasonic testing are that it
2. Referenced Documents
yields compression and shear wave velocities, and ultrasonic
2.1 ASTM Standards:
valuesfortheelasticconstantsofintacthomogeneousisotropic
D 653 Terminology Relating to Rock, Soil, and Contained
3 rock specimens (3). Elastic constants are not to be calculated
Fluids
for rocks having pronounced anisotropy by procedures de-
scribedinthistestmethod.Thevaluesofelasticconstantsoften
do not agree with those determined by static laboratory
ThistestmethodisunderthejurisdictionofASTMCommitteeD18onSoiland
methods or the in situ methods. Measured wave velocities
Rock and is the direct responsibility of Subcommittee D18.12 on Rock Mechanics.
Current edition approved June 10, 2000. Published August 2000. Originally
likewise may not agree with seismic velocities, but offer good
published as D 2845 – 69. Last previous edition D 2845 – 95e .
approximations. The ultrasonic evaluation of rock properties is
The boldface numbers in parentheses refer to the list of references at the end of
useful for preliminary prediction of static properties. The test
this test method.
methodisusefulforevaluatingtheeffectsofuniaxialstressand
Annual Book of ASTM Standards, Vol 14.02.
*A Summary of Changes section appears at the end of this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 2845
water saturation on pulse velocity. These properties are in turn pulses. Environmental conditions such as ambient temperature,
useful in engineering design. moisture, humidity, and impact should be considered in select-
5.2 The test method as described herein is not adequate for ing the transducer element. Piezoelectric elements are usually
measurement of stress-wave attenuation. Also, while pulse recommended, but magnetostrictive elements may be suitable.
velocitiescanbeemployedtodeterminetheelasticconstantsof Thickness-expander piezoelectric elements generate and sense
materials having a high degree of anisotropy, these procedures predominately compression-wave energy; thickness-shear pi-
are not treated herein. ezoelectric elements are preferred for shear-wave measure-
ments. Commonly used piezoelectric materials include ceram-
NOTE 3—The quality of the result produced by this standard is
ics such as lead-zirconate-titanate for either compression or
dependent on the competence of the personnel performing it, and the
shear, and crystals such as a-c cut quartz for shear. To reduce
suitability of the equipment and facilities used. Agencies that meet the
scattering and poorly defined first arrivals at the receiver, the
criteria of Practice D 3740 are generally considered capable of competent
and objective testing and sampling. Users of this standard are cautioned
transmitter shall be designed to generate wavelengths at least
that compliance with Practice D 3740 does not in itself assure reliable
3 3 the average grain size of the rock.
results.Reliableresultsdependonmanyfactors;PracticeD 3740provides
NOTE 4—Wavelength is the wave velocity in the rock specimen divided
a means of evaluating some of those factors.
bytheresonancefrequencyofthetransducer.Commonlyusedfrequencies
6. Apparatus range from 75 kHz to 3 MHz.
6.1 General—The testing apparatus (Fig. 1) should have 6.3.1 In laboratory testing, it may be convenient to use
impedance matched electronic components and shielded leads unhoused transducer elements. But if the output voltage of the
to ensure efficient energy transfer. To prevent damage to the receiver is low, the element should be housed in metal
apparatus allowable voltage inputs should not be exceeded. (grounded) to reduce stray electromagnetic pickup. If protec-
6.2 Pulse Generator Unit—This unit shall consist of an tion from mechanical damage is necessary, the transmitter as
electronic pulse generator and external voltage or power well as the receiver may be housed in metal. This also allows
amplifiers if needed. A voltage output in the form of either special backings for the transducer element to alter its sensi-
rectangular pulse or a gated sine wave is satisfactory. The tivity or reduce ringing (4). The basic features of a housed
generator shall have a voltage output with a maximum value element are illustrated in Fig. 2. Energy transmission between
afteramplificationofatleast50Vintoa50-Vimpedanceload. the transducer element and test specimen can be improved by
Avariable pulse width, with a range of 1 to 10µ s is desirable. ( 1) machining or lapping the surfaces of the face plates to
The pulse repetition rate may be fixed at 60 repetitions per make them smooth, flat, and parallel, (2) making the face plate
second or less although a range of 20 to 100 repetitions per from a metal such as magnesium whose characteristic imped-
second is recommended. The pulse generator shall also have a ance is close to that of common rock types, (3) making the face
trigger-pulse output to trigger the oscilloscope. There shall be plate as thin as practicable, and (4) coupling the transducer
a variable delay of the main-pulse output with respect to the element to the face plate by a thin layer of an electrically
trigger-pulse output, with a minimum range of 0 to 20 µs. conductive adhesive, an epoxy type being suggested.
6.3 Transducers—The transducers shall consist of a trans- 6.3.2 Pulsevelocitiesmayalsobedeterminedforspecimens
mitter that converts electrical pulses into mechanical pulses
subjected to uniaxial states of stress. The transducer housings
and a receiver that converts mechanical pulses into electrical in this case will also serve as loading platens and should be
NOTE 1—Components shown by dashed lines are optional, depending on method of travel-time measurement and voltage sensitivity of oscilloscope.
FIG. 1 Schematic Diagram of Typical Apparatus
D 2845
medium between specimen and transducer during the test. The
surface area under each transducer shall be sufficiently plane
that a feeler gage 0.001 in. (0.025 mm) thick will not pass
under a straightedge placed on the surface. The two opposite
surfaces on which the transducers will be placed shall be
parallel to within 0.005 in./in. (0.1 mm/20 mm) of lateral
dimension (Fig. 3). If the pulse velocity measurements are to
be made along a diameter of a core, the above tolerance then
FIG. 2 Basic Features of a Housed Transmitter or Receiver
refers to the parallelism of the lines of contact between the
transducers and curved surface of the rock core. Moisture
designed with thick face plates to assure uniform loading over
content of the test specimen can affect the measured pulse
the ends of the specimen (5).
velocities (see 7.2). Pulse velocities may be determined on the
velocity test specimen for rocks in the oven-dry state (0 %
NOTE 5—The state of stress in many rock types has a marked effect on
the wave velocities. Rocks in situ are usually in a stressed state and
saturation), in a saturated condition (100 % saturation), or in
therefore tests under stress have practical significance.
any intermediate state. If the pulse velocities are to be
6.4 Preamplifier—A voltage preamplifier is required if the determined with the rock in the same moisture condition as
voltage output of the receiving transducer is relatively low or received or as exists underground, care must be exercised
if the display and timing units are relatively insensitive. To
during the preparation procedure so that the moisture content
preserve fast rise times, the frequency response of the pream-
does not change. In this case it is suggested that both the
plifier shall drop no more than 2 dB over a frequency range
sample and test specimen be stored in moisture-proof bags or
from5kHzto4 3 theresonancefrequencyofthereceiver.The
coatedwithwaxandthatdrysurface-preparationproceduresbe
internal noise and gain must also be considered in selecting a
employed. If results are desired for specimens in the oven-
preamplifier. Oscilloscopes having a vertical-signal output can
dried condition, the oven temperature shall not exceed 150°F
be used to amplify the signal for an electronic counter.
(66°C). The specimen shall remain submerged in water up to
6.5 Display and Timing Unit—The voltage pulse applied to
the time of testing when results are desired for the saturated
the transmitting transducer and the voltage output from the
state.
receiving transducer shall be displayed on a cathode-ray
7.2 Limitation on Dimensions—It is recommended that the
oscilloscope for visual observation of the waveforms. The
ratio of the pulse-travel distance to the minimum lateral
oscilloscope shall have an essentially flat response between a
dimension not exceed 5. Reliable pulse velocities may not be
frequency of 5 kHz and 4 3 the resonance frequency of the
measurable for high values of this ratio. The travel distance of
transducers. It shall have dual beams or dual traces so that the
the pulse through the rock shall be at least 10 3 the average
two waveforms may be displayed simultaneously and their
amplitudes separately controlled. The oscilloscope shall be
grainsizesothatanaccurateaveragepropagationvelocitymay
triggered by a triggering pulse from the pulse generator. The
be determined. The grain size of the rock sample, the natural
timing unit shall be capable of measuring intervals between 2
resonance frequency of the transducers, and the minimum
µs and 5 ms to an accuracy of 1 part in 100. Two alternative
lateral dimension of the specimen are interrelated factors that
classes of timing units are suggested, the respective positions
affect test results. The wavelength corresponding to the domi-
of each being shown as dotted outlines in the block diagram in
nant frequency of the pulse train in the rock is approximately
Fig. 1: (1) an electronic counter with provisions for time
relatedtothenaturalresonancefrequencyofthetransducerand
interval measurements, or (2) a time-delay circuit such as a
the pulse-propagation velocity, (compression or shear) as
continuously variable-delay generator, or a delayed-sweep
follows:
feature on the oscilloscope. The travel-time measuring circuit
L' V/f, (1)
shall be calibrated periodically with respect to its accuracy and
linearity over the range of the instrument. The calibration shall
be checked against signals transmitted by the National Institute
of Standards and Technology radio station WWV, or against a
crystalcontrolledtime-markorfrequencygeneratorthatcanbe
referenced back to the signals from WWV periodically. It is
recommended that the calibration of the time measuring circuit
be checked at least once a month and after any severe impact
that the instrument may receive.
7. Test Specimens
7.1 Preparation—Exercise care in core drilling, handling,
sawing, grinding, and lapping the test specimen to minimize
the mechanical damage caused by stress and heat. It is
NOTE 1—(A) must be within 0.1 mm of (B) for each 20 mm of width
recommended that liquids other than water be prevented from
(C).
contacting the specimen, except when necessary as a coupling FIG. 3 Specification for Parallelism
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