ASTM D4945-2008 Standard Test Method for High-Strain Dynamic Testing of Piles《基桩高应变动力检测的标准试验方法》.pdf

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1、Designation: D 4945 08Standard Test Method forHigh-Strain Dynamic Testing of Deep Foundations1This 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

2、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 dynamic test method covers the procedure forapplying an axial impact force with a pile driving hammer ora large drop weight that

3、will cause a relatively high strain at thetop of an individual vertical or inclined deep foundation unit,and for measuring the subsequent force and velocity responseof that deep foundation unit. High-strain dynamic testingapplies to any deep foundation unit, also referred to herein asa “pile,” which

4、 functions in a manner similar to a driven pile ora cast-in-place pile regardless of the method of installation, andwhich conforms with the requirements of this test method.1.2 This standard provides minimum requirements for dy-namic testing of deep foundations. Plans, specifications, orprovisions (

5、or combinations thereof) prepared by a qualifiedengineer may provide additional requirements and proceduresas needed to satisfy the objectives of a particular test program.The engineer in responsible charge of the foundation design,referred to herein as the “Engineer”, shall approve any devia-tions,

6、 deletions, or additions to the requirements of thisstandard.1.3 The proper conduct and evaluation of high-strain dy-namic tests requires special knowledge and experience. Aqualified engineer should directly supervise the acquisition offield data and the interpretation of the test results so as topr

7、edict the actual performance and adequacy of deep founda-tions used in the constructed foundation. A qualified engineershall approve the apparatus used for applying the impact force,driving appurtenances, test rigging, hoist equipment, supportframes, templates, and test procedures.1.4 The text of th

8、is standard references notes and footnoteswhich provide explanatory material. These notes and footnotes(excluding those in tables and figures) shall not be consideredas requirements of the standard. The word “shall” indicates amandatory provision, and the word “should” indicates arecommended or advi

9、sory provision. Imperative sentencesindicate mandatory provisions.1.5 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.6 All observed and calculated values shall conform to theguidelines for significant digits and rounding esta

10、blished inPractice D 6026.1.7 The method used to specify how data are collected,calculated, or recorded in this standard is not directly related tothe accuracy to which the data can be applied in design or otheruses, or both. How one applies the results obtained using thisstandard is beyond its scop

11、e.1.8 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 regulatory limitations prior to use. For a specif

12、icprecautionary statement, see Note 4.2. Referenced Documents2.1 ASTM Standards:2C 469 Test Method for Static Modulus of Elasticity andPoissons Ratio of Concrete in CompressionD 198 Test Methods of Static Tests of Lumber in StructuralSizesD 653 Terminology Relating to Soil, Rock, and ContainedFluids

13、D 1143/D 1143M Test Methods for Deep Foundations Un-der Static Axial Compressive LoadD 3689 Test Methods for Deep Foundations Under StaticAxial Tensile LoadD 3740 Practice for Minimum Requirements for AgenciesEngaged in Testing and/or Inspection of Soil and Rock asUsed in Engineering Design and Cons

14、tructionD 6026 Practice for Using Significant Digits in Geotechni-cal Data3. Terminology3.1 DefinitionsFor common definitions of terms used inthis standard, see Terminology D 653.3.2 Definitions of Terms Specific to This Standard:3.2.1 cast in-place pile, na deep foundation unit made ofcement grout

15、or concrete and constructed in its final location,1This test method is under the jurisdiction ofASTM Committee D18 on Soil andRock and is the direct responsibility of Subcommittee D18.11 on Deep Foundations.Current edition approved Oct. 1, 2008. Published November 2008. Originallyapproved in 1989. L

16、ast previous edition approved in 2000 as D 4945 00.2For 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 onthe ASTM website.1*A Summar

17、y 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.for example, drilled shafts, bored piles, caissons, auger castpiles, pressure-injected footings, etc.3.2.2 deep foundation, na re

18、latively slender structuralelement that transmits some or all of the load it supports to thesoil or rock well below the ground surface, that is, a drivenpile, a cast-in-place pile, or an alternate structural elementhaving a similar function.3.2.3 deep foundation cushion, nthe material insertedbetwee

19、n the helmet on top of the deep foundation and the deepfoundation (usually plywood).3.2.4 deep foundation impedance, na measure of the deepfoundations resistance to motion when subjected to an impactevent. Deep foundation impedance can be calculated bymultiplying the cross-sectional area by the dyna

20、mic modulus ofelasticity and dividing the product by the wave speed. Alter-natively, the impedance can be calculated by multiplying themass density by the wave speed and cross-sectional area.Z 5 EA / c! 5rcA (1)where:Z = impedance,E = dynamic modulus of elasticity,A = cross-sectional area,c = wave s

21、peed, andr = mass density.3.2.5 driven pile, na deep foundation unit made of pre-formed material with a predetermined shape and size andtypically installed by impact hammering, vibrating, or pushing.3.2.6 follower, na structural section placed between theimpact device and the deep foundation during

22、installation ortesting.3.2.7 hammer cushion, nthe material inserted between thehammer striker plate and the helmet on top of the deepfoundation.3.2.8 impact event, nthe period of time during which thedeep foundation is moving due to the impact force application.See Fig. 1.3.2.9 impact force, nin the

23、 case of strain transducers, theimpact force is obtained by multiplying the measured strain ()with the cross-sectional area (A) and the dynamic modulus ofelasticity (E).3.2.10 mandrel, na stiff structural member placed inside athin shell to allow impact installation of the thin section shell.3.2.11

24、moment of impact, nthe first time after the start ofthe impact event when the acceleration is zero. See Fig. 1.3.2.12 particle velocity, nthe instantaneous velocity of aparticle in the deep foundation as a strain wave passes by.3.2.13 restrike, n or vthe redriving of a previously drivenpile, typical

25、ly after a waiting period of 15 min to 30 days ormore, to assess changes in ultimate axial compressive staticcapacity during the time elapsed after the initial installation.3.2.14 wave speed, nthe speed with which a strain wavepropagates through a deep foundation. It is a property of thedeep foundat

26、ion composition and for one-dimensional wavepropagation is equal to the square root of the quotient of theModulus of Elasticity divided by mass density: c =(E/r)1/2.4. Significance and Use4.1 Based on the measurements from strain or force, andacceleration, velocity, or displacement transducers, this

27、 testmethod obtains the force and velocity induced in a pile duringan axial impact event (see Figs. 1 and 2). The Engineer mayanalyze the acquired data using engineering principles andjudgment to evaluate the integrity of the pile, the performanceof the impact system, and the maximum compressive and

28、tensile stresses occurring in the pile.4.2 If sufficient axial movement occurs during the impactevent, and after assessing the resulting dynamic soil responsealong the side and bottom of the pile, the Engineer may analyzeFIG. 1 Typical Force and Velocity Traces Generated by the Apparatus for Obtaini

29、ng Dynamic MeasurementsD4945082the results of a high-strain dynamic test to estimate the ultimateaxial static compression capacity (see Note 1). Factors thatmay affect the axial static capacity estimated from dynamictests include, but are not limited to the: (1) pile installationequipment and proced

30、ures, (2) elapsed time since initialinstallation, (3) pile material properties and dimensions, (4)type, density, strength, stratification, and saturation of the soil,or rock, or both adjacent to and beneath the pile, (5) quality ortype of dynamic test data, (6) foundation settlement, (7)analysis met

31、hod, and (8) engineering judgment and experience.If the Engineer does not have adequate previous experiencewith these factors, and with the analysis of dynamic test data,then a static load test carried out according to Test MethodD 1143 should be used to verify estimates of static capacity andits di

32、stribution along the pile length. Test Method D 1143provides a direct and more reliable measurement of staticcapacity.NOTE 1The analysis of a dynamic test will under predict the ultimateaxial static compression capacity if the pile movement during the impactevent is too small. The Engineer should de

33、termine how the size and shapeof the pile, and the properties of the soil or rock beneath and adjacent tothe pile, affect the amount of movement required to fully mobilize thestatic capacity.Apermanent net penetration of as little as 2 mm per impactmay indicate that sufficient movement has occurred

34、during the impactevent to fully mobilize the capacity. However, high displacement drivenpiles may require greater movement to avoid under predicting the staticcapacity, and cast-in-place piles often require a larger cumulative perma-nent net penetration for a series of test blows to fully mobilize t

35、hecapacity. Static capacity may also decrease or increase over time after thepile installation, and both static and dynamic tests represent the capacityat the time of the respective test. Correlations between measured ultimateaxial static compression capacity and dynamic test estimates generallyimpr

36、ove when using dynamic restrike tests that account for soil strengthchanges with time (see 6.8).NOTE 2Although interpretation of the dynamic test analysis mayprovide an estimate of the piles tension (uplift) capacity, users of thisstandard are cautioned to interpret conservatively the side resistanc

37、eestimated from analysis of a single dynamic measurement location, and toavoid tension capacity estimates altogether for piles with less than 10 membedded length. (Additional transducers embedded near the pile toe mayalso help improve tension capacity estimates.) If the Engineer does nothave adequat

38、e previous experience for the specific site and pile type withthe analysis of dynamic test data for tension capacity, then a static load testcarried out according to Test Method D 3689 should be used to verifytension capacity estimates. Test Method D 3689 provides a direct andmore reliable measureme

39、nt of static tension capacity.NOTE 3The quality of the result produced by this test method isdependent on the competence of the personnel performing it, and thesuitability of the equipment and facilities used. Agencies that meet thecriteria of Practice D 3740 are generally considered capable of comp

40、etentand objective testing/sampling/inspection/etc. Users of this test methodare cautioned that compliance with Practice D 3740 does not in itselfassure reliable results. Reliable results depend on many factors; PracticeD 3740 provides a means of evaluating some of those factors.5. Apparatus5.1 Impa

41、ct DeviceA high-strain dynamic test measuresthe pile response to an impact force applied at the pile head andin concentric alignment with its long axis (see Figs. 2 and 3).The device used to apply the impact force should providesufficient energy to cause pile penetration during the impactevent adequ

42、ate to mobilize the desired capacity, generallyproducing a maximum impact force of the same order ofmagnitude, or greater than, the ultimate pile capacity (staticplus dynamic). The Engineer may approve a conventional piledriving hammer, drop weight, or similar impact device basedon predictive dynami

43、c analysis, experience, or both. Theimpact shall not result in dynamic stresses that will damage thepile, typically less than the yield strength of the pile materialafter reduction for potential bending and non-uniform stresses(commonly 90 % of yield for steel and 85 % for concrete). TheEngineer may

44、 require cushions, variable control of the impactenergy (drop height, stroke, fuel settings, hydraulic pressure,etc.), or both to prevent excessive stress in the pile during allphases of pile testing.5.2 Dynamic MeasurementsThe dynamic measurementapparatus shall include transducers mounted externall

45、y on thepile surface, or embedded within a concrete pile, that arecapable of independently measuring strain and accelerationversus time during the impact event at a minimum of onespecific location along the pile length as described in 5.2.7.5.2.1 External TransducersFor externally mounted trans-duce

46、rs, remove any unsound or deleterious material from thepile surface and firmly attach a minimum of two of each of typeof transducer at a measurement location that will not penetratethe ground using bolts, screws, glue, solder, welds, or similarattachment.5.2.2 Embedded TransducersPosition the embedd

47、edtransducers at each measurement location prior to placing thepile concrete, firmly supported by the pile reinforcement orformwork to maintain the transducer location and orientationFIG. 2 Typical Arrangement for High-Strain Dynamic Testing of aDeep FoundationD4945083during the concrete placement.

48、When located near the pilehead, one of each type of embedded transducer located at thecentroid of the pile cross-section should provide adequatemeasurement accuracy, which may be checked by proportion-ality (see 6.9). Embedded transducers installed along the pilelength and near the pile toe help def

49、ine the distribution of thedynamic load within the pile, but usually require data qualitychecks other than proportionality, such as redundant transduc-ers (see 6.9). Embedded transducers shall provide firm anchor-age to the pile concrete to obtain accurate measurements; theanchorage and sensors should not significantly change the pileimpedance.5.2.3 Transducer AccuracyThe transducers shall be cali-brated prior to installation or mounting to an accuracy of 3 %throughout the applicable measurement range. If damaged orfunctioning improperly, the transducers