AASHTO T 298-2015 Standard Method of Test for High-Strain Dynamic Testing of Piles.pdf

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1、 Standard Method of Test for High-Strain Dynamic Testing of Piles AASHTO Designation: T 298-151 American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-1b T 298-1 AASHTO Standard Method of Test for High-Strain Dynamic Test

2、ing of Piles AASHTO Designation: T 298-1511. 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 metho

3、d 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. These elements can include drilled shafts, micropiles, and continuous flight auger cast piles. 1

4、.2. This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety concerns associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the app

5、licability of regulatory limitations prior to use. For a specific precautionary statement, see Note 7. Note 1High-strain dynamic testing requires a strain at impact that is representative of a force in the pile having the same order of magnitude, or greater, than the ultimate pile-soil resistance. N

6、ote 2This standard method may be applied to the high-strain dynamic testing of piles with the use of either force or strain transducers and either acceleration, velocity, or displacement transducers as long as the test results clearly state how the testing deviates from the standard, i.e., what comb

7、ination of instruments was used. Note 3A suitable follower may be required for testing existing cast-in-place concrete piles. This follower should have an impedance within 50 percent of the impedance of the pile. However, additional caution and analysis may be required if the impedance is not within

8、 10 percent. Note 4For mandrel-driven piles, the mandrel may be instrumented in a similar way to a driven pile. However, results from a mandrel that is more than two pieces, one that has joints, will require additional analysis. 2. REFERENCED DOCUMENTS 2.1. ASTM Standards: C469/C469M, Standard Test

9、Method for Static Modulus of Elasticity and Poissons Ratio of Concrete in Compression2 D198, Standard Test Methods of Static Tests of Lumber in Structural Sizes3 D653, Standard Terminology Relating to Soil, Rock, and Contained Fluids4 D1143/D1143M, Standard Test Methods for Deep Foundations Under St

10、atic Axial Compressive Load4 D3689, Standard Test Methods for Deep Foundations Under Static Axial Tensile Load4 D4945, Standard Test Method for High-Strain Dynamic Testing of Deep Foundations1 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplica

11、tion is a violation of applicable law.TS-1b T 298-2 AASHTO 3. TERMINOLOGY 3.1. For common definitions of terms used in this standard see ASTM D653, Standard Terminology Relating to Soil, Rock, and Contained Fluids. 3.2. Definitions of Terms Specific to This Standard: 3.2.1. hammer cushioncast steel

12、insert between the hammer striker plate and the drive cap or helmet to protect the hammer during driving. 3.2.2. pile cushionthe material inserted between the drive cap or helmet and top of the pile to protect the pile during driving. 3.2.3. impact eventthe period of time during which the pile is mo

13、ving in a positive and/or negative direction of penetration due to a single impact force application. (See Figure 1.) Figure 1Typical Force and Velocity Traces Generated by the Apparatus for Obtaining Dynamic Measurements 3.2.4. moment of impactthe first moment of time after the start of the impact

14、event when the acceleration is zero, i.e., first major velocity peak. (See Figure 1.) 3.2.5. strain wave speed (or wave speed)the speed with which a strain wave propagates through a pile. It is a property of the pile material. 3.2.6. particle velocitythe velocity of a particle in the pile as a strai

15、n wave passes by. 3.2.7. pile impedanceindicates the resistance a pile has to a sudden change in velocity. It can be calculated by multiplying Youngs Modulus of Elasticity by the cross-sectional area and dividing the product by the strain wave speed (proportionality constant): Z = AE/c = cA (1) wher

16、e: Z = impedance, A = cross-sectional area, 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1b T 298-3 AASHTO E = Youngs Modulus of Elasticity, c = wave speed of the pile, and = unit mass density of t

17、he pile material. 3.2.8. restrikingthe redriving of a previously driven pile after a waiting period of from 15 min to 30 days or more, to assess changes in ultimate axial compressive static capacity during the elapsed time from the initial installation. Waiting period shall be determined based upon

18、type of pile, soil, and time constraints. 3.2.9. transducer attachment area (TAA) the minimum distance from the top of the pile to the transducers. The minimum length of the TAA is two element diameters. This length can be achieved by using a buildup to extend the column height and/or by excavation

19、of the soil from around the existing pile. 4. SIGNIFICANCE AND USE 4.1. 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 may be used to estimate the bearing capacity (nominal resistance) and the integrity o

20、f the pile, as well as hammer performance, pile stresses, and soil dynamics characteristics such as soil damping coefficients and quake values. 5. APPARATUS 5.1. Apparatus for Applying Impact Force: 5.1.1. Impact Force ApplicationAny conventional pile-driving hammer or similar device is acceptable f

21、or applying the impact force. The hammer or device should be capable of generating: A net measurable pile penetration; or An estimated mobilized static resistance in the bearing strata that exceeds the nominal resistance assigned to the pile, as judged by the engineer. The device shall be positioned

22、 so that the impact is applied axially to the head of the pile and concentric with the pile. For nondriven piles, the concrete should be level with or above any casing. The top should be fitted with a cushioning material with a thickness of 50 to 150 mm. The final thickness shall be determined from

23、a wave equation study. A steel striker plate, if used, should be greater than the lesser of the 70 to 90 percent of the shaft area or the area of drop weight impact surface. The striker plate should have a minimum thickness of 50 mm. Note 5If protruding reinforcing bars are present, the contractor h

24、as the option to incorporate the reinforcing bars inside the TAA, or use a pedestal follower (see Note 3). 5.2. Apparatus for Obtaining Dynamic Measurements: 5.2.1. Measurement Transducer RequirementsThe apparatus shall include transducers that are capable of independently measuring strain and accel

25、eration versus time at a specific location along the pile axis during the impact event. The transducers should have a natural frequency in excess of 2000 Hz once they are attached to the pile. A minimum of two each of these devices shall be attached securely to the pile so that they do not slip. Bol

26、t-on, glue-on, or weld-on transducers are acceptable. The transducers shall be calibrated to a traceable standard such as the National Institute of Standards and Technology with an accuracy of 3.0 percent and recalibrated as required according to ASTM D4945 to maintain accuracy throughout the applic

27、able measurement range. If damage is suspected during use, the transducers shall be replaced or recalibrated. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1b T 298-4 AASHTO 5.2.2. Location of Trans

28、ducersThe measurement transducers shall be located at equal radial distances on diametrically opposite sides of the pile. They shall be located the same axial distance from the bottom of the pile, so that measurements are not affected by bending of the pile. When near the upper end of the pile, they

29、 shall be attached at least one and one-half pile diameters from the head; where practicable, this distance should be three diameters. When testing large diameter piles or nondriven elements, it is recommended to use four transducers, if practicable. Attach transducers to a TAA created with a casing

30、. This is illustrated in Figures 4 through 7. Figure 2Typical Arrangement for High-Strain Testing Figure 3Schematic Diagram of Apparatus for Dynamic Monitoring of Piles 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of a

31、pplicable law.TS-1b T 298-5 AASHTO Note: All dimensions shown in millimeters unless otherwise noted. Figure 4Instrument Attachment Schemes and Dimensions Figure 5Typical Attachment for H-Piles and Pipe Piles Strain TransducersCableSupportAccelerometer 2015 by the American Association of State Highwa

32、y and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1b T 298-6 AASHTO Figure 6Typical Attachment for Concrete and Timber Piles Figure 7Typical Arrangement for Attaching Transducers to a Nondriven Pile 5.2.3. Force or Strain TransducersThe strain transd

33、ucers shall have a linear output over the range of possible pile strains. The measured strain shall be converted to force using the pile cross-sectional area and dynamic modulus of elasticity at the measuring location. The dynamic modulus of elasticity may be assumed to be 200 to 207 GPa for steel.

34、The dynamic modulus of elasticity for concrete and wood piles may be calculated from the wave speed determined as indicated in Section 6.2. The dynamic modulus of elasticity is equal to the product of the strain wave speed squared and the unit weight of the pile divided by gravity. AccelerometersStr

35、ain TranducersAccelerometersStrain Tranducers 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1b T 298-7 AASHTO 22E=c g=c (2) where: E = dynamic modulus of elasticity, c = wave speed of pile, = unit w

36、eight of pile material, g = gravity, and = unit mass density of the pile material. Alternatively, the dynamic modulus of elasticity may be estimated from the static modulus of elasticity by measurement during a compression test in accordance with ASTM C469 and D198, for concrete and wood, respective

37、ly. 5.2.3.1. Force measurements also can be made by a force transducer, an instrumented unit, placed between the pile head and the driving hammer, although it should be recognized that such a transducer may alter the dynamic characteristics of the driving system. Force transducers shall have an impe

38、dance between 50 and 200 percent of the pile impedance. The output signal must be linearly proportional to the axial force, even under eccentric load application. The connection between the force transducers and the pile shall have the smallest possible mass and least possible cushion necessary to p

39、revent damage. 5.2.4. Acceleration, Velocity, or Displacement TransducersVelocity data shall be obtained with accelerometers, provided the signal can be processed by integration in the apparatus for reducing data. The accelerometers shall be linear to at least 1000 g and 1000 Hz for satisfactory res

40、ults on concrete and timber piles. For steel piles, it is advisable to use accelerometers that are linear up to 2000 g and 2000 Hz. Either piezoelectric or piezoresistive accelerometers can be used. If piezoelectric devices are used, the resonant frequency shall be above 50 000 Hz and the time const

41、ant shall be at least 1.0 s. If piezoresistive accelerometers are used, then they should have a resonant frequency of at least 2500 Hz and a damped mounting. Alternatively, velocity or displacement transducers may be used to obtain velocity data, provided they are equivalent in performance to the sp

42、ecified accelerometers. 5.3. Signal TransmissionThe signals from the transducers shall be transmitted to the apparatus for recording, reducing, and displaying the data (see Section 5.4) by means of a cable or wireless equivalent. The signals arriving at the apparatus shall be linearly proportional t

43、o the measurements at the pile over the frequency range of the equipment. Cables shall be shielded to limit electronic and other transmission interference. If wireless transmission is used, the signals arriving at the apparatus shall accurately represent the continuity and magnitude of the transduce

44、r measurements over the frequency range of the dynamic measurement apparatus. 5.4. Apparatus for Recording, Reducing, and Displaying Data: 5.4.1. GeneralThe signals from the transducers (see Section 5.2) during the impact event shall be transmitted to an apparatus for recording, reducing, and displa

45、ying data to allow determination of the force and velocity versus time. It may be desirable to also determine the acceleration and displacement of the pile head, and the energy transferred to the pile. The apparatus shall include an LCD screen for displaying the force and velocity traces; a nonvolat

46、ile memory for obtaining a record for future analysis; and a means to provide results consistent with the engineers field testing objectives. The apparatus for recording, reducing, and displaying data shall have the capability of making an internal calibration check of strain, acceleration, and time

47、 scales. No error shall exceed 2 percent of the maximum signals expected. A typical schematic arrangement for this apparatus is illustrated in Figure 3. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS

48、-1b T 298-8 AASHTO 5.4.2. Recording ApparatusSignals from the transducers shall be recorded electronically in either analog or digital form so that frequency components below 1500 Hz are retained. When digitizing, the sample frequency shall be at least 5000 Hz for each data channel. The minimum tota

49、l time sampled for each impact event shall be the greater of 100 milliseconds or 3L/c (where L is the pile length and c is the pile material wave speed) with most of this time following the moment of impact as shown in Figure 1. 5.4.3. Apparatus for Reducing DataThe apparatus for reducing signals from transducers shall be a computer capable of at least the following functions: 5.4.3.1. Force MeasurementsThe apparatus shall provide signal conditioning, amplification, and calibration for the force measurements system. If strain t