ASTM D4945-00
(Test Method)Standard Test Method for High-Strain Dynamic Testing of Piles
Standard Test Method for High-Strain Dynamic Testing of Piles
SIGNIFICANCE AND USE
This test method is used to provide data on strain or force and acceleration, velocity or displacement of a pile under impact force. The data are used to estimate the bearing capacity and the integrity of the pile, as well as hammer performance, pile stresses, and soil dynamics characteristics, such as soil damping coefficients and quake values. This test method is not intended to replace Test Method D 1143.
SCOPE
1.1 This test method covers the procedure for testing vertical or batter piles individually to determine the force and velocity response of the pile to an impact force applied axially by a pile driving hammer to the top of the pile. This test method is applicable to deep foundation units that function in a manner similar to foundation piles, regardless of their method of installation provided that they are receptive to high strain impact testing.
1.2 This standard does not purport to address all of the safety problems 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. For a specific precautionary statement, see Note 5.
Note 1--High-strain dynamic testing requires a strain at impact which is representative of a force in the pile having the same order of magnitude, or greater, than the ultimate capacity of the pile.
Note 2--This standard method may be applied for high-strain dynamic testing of piles with the use of only force or strain transducers and/or acceleration, velocity or displacement transducers as long as the test results clearly state how the testing deviates from the standard.
Note 3--A suitable follower may be required for testing cast-in-place concrete piles. This follower should have an impedance within 80 and 150% of that of the pile. However, additional caution and analysis may be required if the impedance is not within 10%. For mandrel driven piles, the mandrel may be instrumented in a similar way to a driven pile provided that the mandrel is constructed of a single member with no joints.
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Designation:D4945–00
Standard Test Method for
High-Strain Dynamic Testing of Piles
This standard is issued under the fixed designation D4945; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope D653 Terminology Relating to Soil, Rock, and Contained
Fluids
1.1 This test method covers the procedure for testing verti-
D1143 Test Method for Piles Under StaticAxial Compres-
cal or batter piles individually to determine the force and
sive Load
velocity response of the pile to an impact force applied axially
by a pile driving hammer or similar device that will cause a
3. Terminology
large strain impact to the top of the pile. This test method is
3.1 Except as defined in 3.2, the terminology used in this
applicable to deep foundation units that function in a manner
test method conforms with Terminology D653.
similar to foundation piles, regardless of their method of
3.2 Definitions of Terms Specific to This Standard:
installation provided that they are receptive to high strain
3.2.1 capblock—the material inserted between the hammer
impact testing.
striker plate and the drive cap on top of the pile (also called
1.2 This standard does not purport to address all of the
hammer cushion).
safety concerns, if any, associated with its use. It is the
3.2.2 cushion—the material inserted between the drive cap
responsibility of the user of this standard to establish appro-
on top of the pile and the pile (also called pile cushion).
priate safety and health practices and determine the applica-
3.2.3 impact event—the period of time during which the
bility of regulatory limitations prior to use. For a specific
pile is moving in a positive and/or negative direction of
precautionary statement, see Note 5.
penetration due to the impact force application. See Fig. 1.
NOTE 1—High-strain dynamic testing requires a strain at impact which
3.2.4 moment of impact—the first moment of time after the
isrepresentativeofaforceinthepilehavingthesameorderofmagnitude,
startoftheimpacteventwhentheaccelerationiszero.SeeFig.
or greater, than the ultimate capacity of the pile.
1.
NOTE 2—Thisstandardmethodmaybeappliedforhigh-straindynamic
3.2.5 pile impedance—indicates the resistance a pile has to
testing of piles with the use of only force or strain transducers and/or
a sudden impact change in velocity.
acceleration, velocity or displacement transducers as long as the test
results clearly state how the testing deviates from the standard.
3.2.5.1 Discussion—It can be calculated by multiplying the
NOTE 3—A suitable follower may be required for testing cast-in-place
cross-sectional area by Young’s Modulus of Elasticity and
concrete piles. This follower should have an impedance between 80 and
dividing the product by the strain wave speed. Alternatively,
150%ofthatofthepile.However,additionalcautionandanalysismaybe
the impedance can be calculated by multiplying the unit
required if the impedance is not within 10%. For mandrel-driven piles,
specific density by the wave speed and cross-sectional area.
the mandrel may be instrumented in a similar way to a driven pile
provided that the mandrel is constructed of a single member with no
Z 5 AE/c5r CA (1)
joints.
where:
2. Referenced Documents
Z = Impedance,
A = Cross-sectional area,
2.1 ASTM Standards:
E = Young’s Modulus of Elasticity,
C469 Test Method for Static Modulus of Elasticity and
2 C = Wave speed of pile, and
Poisson’s Ratio of Concrete in Compression
r = Unit specific density.
D198 Methods of Static Tests of Timbers in Structural
3 3.2.6 strain wave speed (or wave speed)—the speed with
Sizes
which a strain wave propagates through a pile; it is a property
of the pile composition.
3.2.7 particle velocity—the instantaneous velocity of a par-
ThistestmethodisunderthejurisdictionofASTMCommitteeD18onSoiland
RockandisthedirectresponsibilityofSubcommitteeD18.11onDeepFoundations.
ticle in the pile as a strain wave passes by.
Current edition approved Nov. 10, 2000. Published November 2000. Originally
published as D4945–89. Last previous edition D4945–96.
Annual Book of ASTM Standards, Vol 04.02.
3 4
Annual Book of ASTM Standards, Vol 04.10. Annual Book of ASTM Standards, Vol 04.08.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D4945
accordance with Test Method C469 and Methods D198.
Alternatively,themodulusofelasticityforconcrete,wood,and
steel piles can be calculated from the square of the wave speed
(determined as indicated in 6.2) times the specific unit density
( E =pc ).
5.2.1.1 Force measurements also are made by force trans-
ducers placed between the pile head and the driving hammer,
although it should be recognized that such a transducer is
capable of altering the dynamic characteristics of the driving
system. Force transducers shall have an impedance between
50%and200%ofthepileimpedance.Theoutputsignalmust
belinearlyproportionaltotheaxialforce,evenundereccentric
FIG. 1 Typical Force and Velocity Traces Generated by the
loadapplication.Theconnectionbetweentheforcetransducers
Apparatus for Obtaining Dynamic Measurements
and the pile shall have the smallest possible mass and least
possible cushion necessary to prevent damage.
3.2.8 restriking—the redriving of a previously driven pile
5.2.2 Acceleration, Velocity or Displacement Transducers—
after a waiting period of from 15 min to 30 days or more.
Velocity data shall be obtained with accelerometers, provided
3.2.8.1 Discussion—The length of the waiting period is
the signal is capable of being processed by integration in the
dependent upon the type of pile and the soil conditions along
apparatusforreducingdata.Aminimumoftwoaccelerometers
the shaft and at the toe of the pile.
with a resonant frequency above 2500 Hz shall be at equal
radialdistancesondiametricallyoppositesidesofthepile.The
4. Significance and Use
accelerometers shall be linear to at least 1000 g and 1000 Hz
4.1 This test method is used to provide data on strain or
for satisfactory results on concrete piles. For steel piles, it is
forceandacceleration,velocityordisplacementofapileunder
advisable to use accelerometers that are linear to at least 2000
impactforce.Thedataareusedtoestimatethebearingcapacity
g and 2000 Hz. Either ac or dc accelerometers can be used. If
and the integrity of the pile, as well as hammer performance,
AC devices are used, the resonant frequency shall be above
pile stresses, and soil dynamics characteristics, such as soil
30000 Hz and the time constant shall be at least 1.0 s. If DC
damping coefficients and quake values.This test method is not
devices are used, then they should be damped with low pass
intended to replace Test Method D1143.
filters having a minimum frequency of 1500 Hz (−3dB).
Alternatively, velocity or displacement transducers may be
5. Apparatus
used to obtain velocity data, provided they are equivalent in
5.1 Apparatus for Applying Impact Force:
performance to the specified accelerometers.
5.1.1 Impact Force Application—Any conventional pile
5.2.3 Placement of Transducers—The transducers shall be
drivinghammerorsimilardeviceisacceptableforapplyingthe
placed, diametrically opposed and on equal radial distances, at
impact force provided it is capable of generating a net
the same axial distance from the bottom of the pile so that the
measurable pile penetration, or an estimated mobilized static
measurements compensate for bending of the pile. When near
resistanceinthebearingstratawhich,foraminimumperiodof
the upper end, they shall be attached at least one and one-half
3 ms, exceeds to a sufficient degree the working load assigned
pile diameters from the pile head. This is illustrated in Figs.
to the pile, as judged by the engineer in charge. The device
2-7.Careshallbetakentoensurethattheapparatusissecurely
shall be positioned so that the impact is applied axially to the
attached to the pile so that slippage is prevented. The trans-
head of the pile and concentric with the pile.
ducers shall have been calibrated to an accuracy of 3%
5.2 Apparatus for Obtaining Dynamic Measurements—The
throughout the applicable measurement range. If damage is
apparatus shall include transducers, which are capable of
suspected during use, the transducers shall be re-calibrated (or
independently measuring strain and acceleration versus time at
replaced).
a specific location along the pile axis during the impact event.
5.3 Signal Transmission—The signals from the transducers
A minimum of two of each of these devices, one of each on
shall be transmitted to the apparatus for recording, reducing,
opposing sides of the pile, shall be securely attached so that
and displaying the data (see 5.4) by means of a cable or
they do not slip. Bolt-on, glue-on, or weld-on transducers are
equivalent. This cable shall be shielded to limit electronic or
acceptable.
other interferences. The signals arriving at the apparatus shall
5.2.1 Force or Strain Transducers—The strain transducers
be linearly proportional to the measurements at the pile over
shall have a linear output over the entire range of possible
the frequency range of the equipment.
strains.When attached to the pile, their natural frequency shall
5.4 Apparatus for Recording, Reducing and Displaying
be in excess of 2000 Hz. The measured strain shall be
Data:
converted to force using the pile cross-section area and
dynamic modulus of elasticity at the measured location. The 5.4.1 General—The signals from the transducers (see 5.2)
dynamic modulus of elasticity may be assumed to be 200 to duringtheimpacteventshallbetransmittedtoanapparatusfor
207 310 kPa (29 to 30 310 psi) for steel. The dynamic recording,reducing,anddisplayingdatatoallowdetermination
modulus of elasticity for concrete and wood piles may be of the force and velocity versus time. It may be desirable to
estimated by measurement during the compression test in also determine the acceleration and displacement of the pile
D4945
FIG. 2 Typical Arrangement for High Strain Dynamic Testing of
Piles
FIG. 3 Schematic Diagram for Apparatus for Dynamic Monitoring
of Piles
velocity between impact events and shall adjust the velocity
head,andtheenergytransferredtothepile.Theapparatusshall
record to account for transducer zero drift during the impact
include an oscilloscope, oscillograph, or LCD graphics screen.
event.
For displaying the force and velocity traces, a tape recorder,
5.4.3.3 Signal Conditioning—The signal conditioning for
digital disk or equivalent for obtaining a record for future
force and velocity shall have equal frequency response curves
analysis, and a means to reduce the data. The apparatus for
to avoid relative phase shifts and relative amplitude differ-
recording, reducing, and displaying data shall have the capa-
ences.
bility of making an internal calibration check of strain, accel-
5.4.4 Display Apparatus—Signals from the transducers
eration, and time scales. No error shall exceed 2% of the
specified in 4.2.1 and 4.2.2 shall be displayed by means of an
maximum signal expected. A typical schematic arrangement
apparatus, such as an oscilloscope, oscillograph, or LCD
for this apparatus is illustrated in Fig. 3.
graphics screen on which the force and velocity versus time
5.4.2 Recording Apparatus—Signals from the transducers
can be observed for each hammer blow. This apparatus may
shall be recorded electronically in either analog or digital form
receive the signals from the transducers directly or after they
so that frequency components have a low pass cut-off fre-
have been processed by the apparatus for reducing the data.
quency of 1500 Hz (−3 dB). When digitizing, the sample
The apparatus shall be adjustable to reproduce a signal having
frequency shall be at least 5000 Hz for each data channel.
a range of duration of between 5 and 160 ms. Both the force
5.4.3 Apparatus for Reducing Data—The apparatus for
and velocity data can be reproduced for each blow and the
reducing signals from the transducers shall be an analog or
apparatus shall be capable of holding and displaying the signal
digital computer capable of at least the following functions:
from each selected blow for a minimum period of 30 s.
5.4.3.1 Force Measurements—The apparatus shall provide
6. Procedure
signal conditioning, amplification and calibration for the force
measurement system. If strain transducers are used (see 5.2.1),
6.1 General—Record applicable project information (Sec-
the apparatus shall be able to compute the force. The force
tion7).Attachthetransducers(see5.2)tothepile,performthe
outputshallbecontinuouslybalancedtozeroexceptduringthe
internalcalibrationcheck,andtakethedynamicmeasurements
impact event.
for the impacts during the interval to be monitored together
5.4.3.2 Velocity Data—If accelerometers are used (see with routine observations of penetration resistance. Determine
5.2.2), the apparatus shall integrate the acceleration over time propertiesfromaminimumoftenimpactrecordsduringinitial
to obtain velocity. If displacement transducers are used, the driving and, when used for soil resistance computations,
apparatus shall differentiate the displacement over time to normally from one or two representative blows at the begin-
obtain velocity. If required, the apparatus shall zero the ning of restriking. The force and velocity versus time signals
D4945
FIG. 4 Typical Arrangement for Attaching Transducers to Pipe
Piles
FIG. 5 Typical Arrangement for Attaching Transducers to
Concrete Piles
shall be reduced by the apparatus for reducing data, computer,
or manually to calculate the developed force, velocity, accel-
eration, displacement, and energy over the impact event. 6.3 Preparation—Mark the piles clearly at appropriate in-
6.2 Determination of Strain Wave Speed for Concrete or tervals.Attach the transducers securely to the piles by bolting,
Wood Piles—The wave speed should be determined from the gluing, or welding. For pile materials other than steel, deter-
impact event if a tensile reflection wave from the pile toe is mine the wave speed (see 6.2). Position the apparatus for
clearly identified. Alternatively, place the pile on supports or applying the impact force so that the force is applied axially
levelgroundfreeandclearfromneighboringpilesandobstruc- and concentrically with the pile. Set up the apparatus for
tions.Attachaccelerometertooneendofthepileandstrikethe recording,reducing,anddisplayingdatasothatitisoperational
other
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