ASTM D4945-2012 Standard Test Method for High-Strain Dynamic Testing of Deep Foundations《深层地基高应变动力测试的标准试验方法》.pdf

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1、Designation: D4945 12Standard Test Method forHigh-Strain Dynamic Testing of Deep Foundations1This standard is issued under the fixed designation D4945; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A nu

2、mber in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This dynamic test method covers the procedure forapplying an axial impact force with a pile driving hammer ora large drop weight that wil

3、l 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 fu

4、nctions 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 (or

5、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, de

6、letions, 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 topredi

7、ct 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 this

8、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 advisor

9、y 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 establi

10、shed inPractice D6026.1.7 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 scope.1.

11、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 specificpr

12、ecautionary statement, see Note 4.2. Referenced Documents2.1 ASTM Standards:2C469 Test Method for Static Modulus of Elasticity andPoissons Ratio of Concrete in CompressionD198 Test Methods of Static Tests of Lumber in StructuralSizesD653 Terminology Relating to Soil, Rock, and ContainedFluidsD1143/D

13、1143M Test Methods for Deep Foundations UnderStatic Axial Compressive LoadD3689 Test Methods for Deep Foundations Under StaticAxial Tensile LoadD3740 Practice for Minimum Requirements for AgenciesEngaged in Testing and/or Inspection of Soil and Rock asUsed in Engineering Design and Construction1This

14、 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 May 1, 2012. Published June 2012. Originallyapproved in 1989. Last previous edition approved in 2008 as D494508. DOI:10.152

15、0/D4945-12.2For 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.1Copyright ASTM International, 100 Barr Harbor Dri

16、ve, PO Box C700, West Conshohocken, PA 19428-2959, United States.D6026 Practice for Using Significant Digits in GeotechnicalData3. Terminology3.1 DefinitionsFor common definitions of terms used inthis standard, see Terminology D653.3.2 Definitions of Terms Specific to This Standard:3.2.1 cast in-pla

17、ce pile, na deep foundation unit made ofcement grout or concrete and constructed in its final location,for example, drilled shafts, bored piles, caissons, auger castpiles, pressure-injected footings, etc.3.2.2 deep foundation, na relatively slender structuralelement that transmits some or all of the

18、 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 insertedbetween the helmet on top of the deep foundation and the deepfoundation (u

19、sually 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 dynamic modulus ofelasticity and dividing the product by the wave speed.

20、 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 speed, andr = mass density.3.2.5 driven pile, na deep foundation unit

21、 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 installation ortesting.3.2.7 hammer cushion, nthe material inserted

22、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 case of strain transducers, theimpact force is obtained by multiply

23、ing 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 moment of impact, nthe first time after the start ofthe impact event

24、 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, typically after a waiting period of 15 min to 30 days ormore, to assess cha

25、nges 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 foundation composition and for one-dimensional wavepropagation is equal to

26、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 testFIG. 1 Typical Force and Velocity Traces Generated by the Appar

27、atus for Obtaining Dynamic MeasurementsD4945 122method 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 imp

28、act system, and the maximum compressive andtensile 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 analyzethe results of a high-strain dynamic

29、 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 procedures, (2) elapsed time since initialinstallation, (3) pile material

30、 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 method, and (8) engineering judgment and experience.If the Engineer do

31、es 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 MethodD1143/D1143M should be used to verify estimates of staticcapacity and its distribution along the pile length. Test MethodD1143/D1143M pro

32、vides a direct and more reliable measure-ment of static capacity.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 determine how the size and shapeof the pile, and the pr

33、operties 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 during the impactevent to fully mobilize the capacity

34、. 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 thecapacity. Static capacity may also decrease or incr

35、ease 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 generallyimprove when using dynamic restrike tests that account fo

36、r 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 resistanceestimated from analysis of a single dynamic measurem

37、ent 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 adequate previous experience for the specific site and pile

38、type withthe analysis of dynamic test data for tension capacity, then a static load testcarried out according to Test Method D3689 should be used to verifytension capacity estimates. Test Method D3689 provides a direct and morereliable measurement of static tension capacity.NOTE 3The quality of the

39、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 D3740 are generally considered capable of competentand objective testing/sampling/inspection/etc. User

40、s of this test methodare cautioned that compliance with Practice D3740 does not in itselfassure reliable results. Reliable results depend on many factors; PracticeD3740 provides a means of evaluating some of those factors.5. Apparatus5.1 Impact DeviceA high-strain dynamic test measuresthe pile respo

41、nse 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 adequate to mobilize the desired capacity, generallyproducing a

42、 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 dynamic analysis, experience, or both. Theimpact shall not resul

43、t 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 require cushions, variable control of the impactenergy (d

44、rop 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 externally on thepile surface, or embedded within a concrete pile,

45、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.FIG. 2 Typical Arrangement for High-Strain Dynamic Testing of aDeep FoundationD4945 1235.2.1 External TransducersFor

46、externally mounted trans-ducers, 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 T

47、ransducersPosition the embeddedtransducers at each measurement location prior to placing thepile concrete, firmly supported by the pile reinforcement orformwork to maintain the transducer location and orientationduring the concrete placement. When located near the pilehead, one of each type of embed

48、ded 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 define the distribution of thedynamic load within the pile,

49、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 shall be replaced,repaired and recalibrated, or rejected