ASTM D4945-2000 Standard Test Method for High-Strain Dynamic Testing of Piles《桩的高应力动态试验的标准试验方法》.pdf

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1、Designation: D 4945 00Standard Test Method forHigh-Strain Dynamic Testing of Piles1This standard is issued under the fixed designation D 4945; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in p

2、arentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the procedure for testing verti-cal or batter piles individually to determine the force andvelocity response of the pile

3、to an impact force applied axiallyby a pile driving hammer or similar device that will cause alarge strain impact to the top of the pile. This test method isapplicable to deep foundation units that function in a mannersimilar to foundation piles, regardless of their method ofinstallation provided th

4、at they are receptive to high strainimpact testing.1.2 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 applica-bility of

5、regulatory limitations prior to use. For a specificprecautionary statement, see Note 5.NOTE 1High-strain dynamic testing requires a strain at impact whichis representative of a force in the pile having the same order of magnitude,or greater, than the ultimate capacity of the pile.NOTE 2This standard

6、 method may be applied for high-strain dynamictesting of piles with the use of only force or strain transducers and/oracceleration, velocity or displacement transducers as long as the testresults clearly state how the testing deviates from the standard.NOTE 3A suitable follower may be required for t

7、esting cast-in-placeconcrete piles. This follower should have an impedance between 80 and150 % of that of the pile. However, additional caution and analysis may berequired if the impedance is not within 10 %. For mandrel-driven piles,the mandrel may be instrumented in a similar way to a driven pilep

8、rovided that the mandrel is constructed of a single member with nojoints.2. Referenced Documents2.1 ASTM Standards:C 469 Test Method for Static Modulus of Elasticity andPoissons Ratio of Concrete in Compression2D 198 Methods of Static Tests of Timbers in StructuralSizes3D 653 Terminology Relating to

9、 Soil, Rock, and ContainedFluids4D 1143 Test Method for Piles Under Static Axial Compres-sive Load43. Terminology3.1 Except as defined in 3.2, the terminology used in thistest method conforms with Terminology D 653.3.2 Definitions of Terms Specific to This Standard:3.2.1 capblockthe material inserte

10、d between the hammerstriker plate and the drive cap on top of the pile (also calledhammer cushion).3.2.2 cushionthe material inserted between the drive capon top of the pile and the pile (also called pile cushion).3.2.3 impact eventthe period of time during which thepile is moving in a positive and/

11、or negative direction ofpenetration due to the impact force application. See Fig. 1.3.2.4 moment of impactthe first moment of time after thestart of the impact event when the acceleration is zero. See Fig.1.3.2.5 pile impedanceindicates the resistance a pile has toa sudden impact change in velocity.

12、3.2.5.1 DiscussionIt can be calculated by multiplying thecross-sectional area by Youngs Modulus of Elasticity anddividing the product by the strain wave speed. Alternatively,the impedance can be calculated by multiplying the unitspecific density by the wave speed and cross-sectional area.Z 5 AE/c 5r

13、CA (1)where:Z = Impedance,A = Cross-sectional area,E = Youngs Modulus of Elasticity,C = Wave speed of pile, andr = Unit specific density.3.2.6 strain wave speed (or wave speed)the speed withwhich a strain wave propagates through a pile; it is a propertyof the pile composition.3.2.7 particle velocity

14、the instantaneous velocity of a par-ticle in the pile as a strain wave passes by.3.2.8 restrikingthe redriving of a previously driven pileafter a waiting period of from 15 min to 30 days or more.3.2.8.1 DiscussionThe length of the waiting period isdependent upon the type of pile and the soil conditi

15、ons alongthe shaft and at the toe of the pile.1This test method is under the jurisdiction of ASTM Committee D18 on Soil andRock and is the direct responsibility of Subcommittee D18.11 on Deep Foundations.Current edition approved Nov. 10, 2000. Published November 2000. Originallypublished as D 4945 8

16、9. Last previous edition D 4945 96.2Annual Book of ASTM Standards, Vol 04.02.3Annual Book of ASTM Standards, Vol 04.10.4Annual Book of ASTM Standards, Vol 04.08.1Copyright ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.4. Significance and Use4.1 This test method is used

17、 to provide data on strain orforce and acceleration, velocity or displacement of a pile underimpact force. The data are used to estimate the bearing capacityand the integrity of the pile, as well as hammer performance,pile stresses, and soil dynamics characteristics, such as soildamping coefficients

18、 and quake values. This test method is notintended to replace Test Method D 1143.5. Apparatus5.1 Apparatus for Applying Impact Force:5.1.1 Impact Force ApplicationAny conventional piledriving hammer or similar device is acceptable for applying theimpact force provided it is capable of generating a n

19、etmeasurable pile penetration, or an estimated mobilized staticresistance in the bearing strata which, for a minimum period of3 ms, exceeds to a sufficient degree the working load assignedto the pile, as judged by the engineer in charge. The deviceshall be positioned so that the impact is applied ax

20、ially to thehead of the pile and concentric with the pile.5.2 Apparatus for Obtaining Dynamic MeasurementsTheapparatus shall include transducers, which are capable ofindependently measuring strain and acceleration versus time ata specific location along the pile axis during the impact event.A minimu

21、m of two of each of these devices, one of each onopposing sides of the pile, shall be securely attached so thatthey do not slip. Bolt-on, glue-on, or weld-on transducers areacceptable.5.2.1 Force or Strain TransducersThe strain transducersshall have a linear output over the entire range of possibles

22、trains. When attached to the pile, their natural frequency shallbe in excess of 2000 Hz. The measured strain shall beconverted to force using the pile cross-section area anddynamic modulus of elasticity at the measured location. Thedynamic modulus of elasticity may be assumed to be 200 to207 3 106kP

23、a (29 to 30 3 106psi) for steel. The dynamicmodulus of elasticity for concrete and wood piles may beestimated by measurement during the compression test inaccordance with Test Method C 469 and Methods D 198.Alternatively, the modulus of elasticity for concrete, wood, andsteel piles can be calculated

24、 from the square of the wave speed(determined as indicated in 6.2) times the specific unit density( E =pc2).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 iscapable of altering

25、 the dynamic characteristics of the drivingsystem. Force transducers shall have an impedance between50 % and 200 % of the pile impedance. The output signal mustbe linearly proportional to the axial force, even under eccentricload application. The connection between the force transducersand the pile

26、shall have the smallest possible mass and leastpossible cushion necessary to prevent damage.5.2.2 Acceleration, Velocity or Displacement TransducersVelocity data shall be obtained with accelerometers, providedthe signal is capable of being processed by integration in theapparatus for reducing data.

27、A minimum of two accelerometerswith a resonant frequency above 2500 Hz shall be at equalradial distances on diametrically opposite sides of the pile. Theaccelerometers shall be linear to at least 1000 g and 1000 Hzfor satisfactory results on concrete piles. For steel piles, it isadvisable to use acc

28、elerometers that are linear to at least 2000g and 2000 Hz. Either ac or dc accelerometers can be used. IfAC devices are used, the resonant frequency shall be above30 000 Hz and the time constant shall be at least 1.0 s. If DCdevices are used, then they should be damped with low passfilters having a

29、minimum frequency of 1500 Hz (3dB).Alternatively, velocity or displacement transducers may beused to obtain velocity data, provided they are equivalent inperformance to the specified accelerometers.5.2.3 Placement of TransducersThe transducers shall beplaced, diametrically opposed and on equal radia

30、l distances, atthe same axial distance from the bottom of the pile so that themeasurements compensate for bending of the pile. When nearthe upper end, they shall be attached at least one and one-halfpile diameters from the pile head. This is illustrated in Figs.2-7. Care shall be taken to ensure tha

31、t the apparatus is securelyattached to the pile so that slippage is prevented. The trans-ducers shall have been calibrated to an accuracy of 3 %throughout the applicable measurement range. If damage issuspected during use, the transducers shall be re-calibrated (orreplaced).5.3 Signal TransmissionTh

32、e signals from the transducersshall be transmitted to the apparatus for recording, reducing,and displaying the data (see 5.4) by means of a cable orequivalent. This cable shall be shielded to limit electronic orother interferences. The signals arriving at the apparatus shallbe linearly proportional

33、to the measurements at the pile overthe frequency range of the equipment.5.4 Apparatus for Recording, Reducing and DisplayingData:5.4.1 GeneralThe signals from the transducers (see 5.2)during the impact event shall be transmitted to an apparatus forrecording, reducing, and displaying data to allow d

34、eterminationof the force and velocity versus time. It may be desirable toalso determine the acceleration and displacement of the pilehead, and the energy transferred to the pile. The apparatus shallinclude an oscilloscope, oscillograph, or LCD graphics screen.For displaying the force and velocity tr

35、aces, a tape recorder,digital disk or equivalent for obtaining a record for futureanalysis, and a means to reduce the data. The apparatus forFIG. 1 Typical Force and Velocity Traces Generated by theApparatus for Obtaining Dynamic MeasurementsD 49452recording, reducing, and displaying data shall have

36、 the capa-bility of making an internal calibration check of strain, accel-eration, and time scales. No error shall exceed 2 % of themaximum signal expected. A typical schematic arrangementfor this apparatus is illustrated in Fig. 3.5.4.2 Recording ApparatusSignals from the transducersshall be record

37、ed electronically in either analog or digital formso that frequency components have a low pass cut-off fre-quency of 1500 Hz (3 dB). When digitizing, the samplefrequency shall be at least 5000 Hz for each data channel.5.4.3 Apparatus for Reducing DataThe apparatus forreducing signals from the transd

38、ucers shall be an analog ordigital computer capable of at least the following functions:5.4.3.1 Force MeasurementsThe apparatus shall providesignal conditioning, amplification and calibration for the forcemeasurement system. If strain transducers are used (see 5.2.1),the apparatus shall be able to c

39、ompute the force. The forceoutput shall be continuously balanced to zero except during theimpact event.5.4.3.2 Velocity DataIf accelerometers are used (see5.2.2), the apparatus shall integrate the acceleration over timeto obtain velocity. If displacement transducers are used, theapparatus shall diff

40、erentiate the displacement over time toobtain velocity. If required, the apparatus shall zero thevelocity between impact events and shall adjust the velocityrecord to account for transducer zero drift during the impactevent.5.4.3.3 Signal ConditioningThe signal conditioning forforce and velocity sha

41、ll have equal frequency response curvesto avoid relative phase shifts and relative amplitude differ-ences.5.4.4 Display ApparatusSignals from the transducersspecified in 4.2.1 and 4.2.2 shall be displayed by means of anapparatus, such as an oscilloscope, oscillograph, or LCDgraphics screen on which

42、the force and velocity versus timecan be observed for each hammer blow. This apparatus mayreceive the signals from the transducers directly or after theyhave been processed by the apparatus for reducing the data.The apparatus shall be adjustable to reproduce a signal havinga range of duration of bet

43、ween 5 and 160 ms. Both the forceand velocity data can be reproduced for each blow and theapparatus shall be capable of holding and displaying the signalfrom each selected blow for a minimum period of 30 s.6. Procedure6.1 GeneralRecord applicable project information (Sec-tion 7). Attach the transduc

44、ers (see 5.2) to the pile, perform theinternal calibration check, and take the dynamic measurementsfor the impacts during the interval to be monitored togetherwith routine observations of penetration resistance. Determineproperties from a minimum of ten impact records during initialdriving and, when

45、 used for soil resistance computations,normally from one or two representative blows at the begin-ning of restriking. The force and velocity versus time signalsshall be reduced by the apparatus for reducing data, computer,or manually to calculate the developed force, velocity, accel-eration, displac

46、ement, and energy over the impact event.6.2 Determination of Strain Wave Speed for Concrete orWood PilesThe wave speed should be determined from theimpact event if a tensile reflection wave from the pile toe isFIG. 2 Typical Arrangement for High Strain Dynamic Testing ofPilesFIG. 3 Schematic Diagram

47、 for Apparatus for Dynamic Monitoringof PilesD 49453clearly identified. Alternatively, place the pile on supports orlevel ground free and clear from neighboring piles and obstruc-tions. Attach accelerometer to one end of the pile and strike theother end of the pile with a sledge hammer of suitable w

48、eight.Take care not to damage or dent the pile. Record (see 5.4.2) anddisplay (see 5.4.4) the accelerometer signal. Measure the timebetween acceleration peaks for as many cycles of reflection aspossible. Divide this time by the appropriate travel length ofthe strain waves during this interval to det

49、ermine the wavespeed.6.3 PreparationMark the piles clearly at appropriate in-tervals. Attach the transducers securely to the piles by bolting,gluing, or welding. For pile materials other than steel, deter-mine the wave speed (see 6.2). Position the apparatus forapplying the impact force so that the force is applied axiallyand concentrically with the pile. Set up the apparatus forrecording, reducing, and displaying data so that it is operationaland the force and velocity signals are zeroed.6.4 Taking MeasurementsRecord the number of impactsfor a specif