1、Designation: D 4694 96 (Reapproved 2003)Standard Test Method forDeflections with a Falling-Weight-Type Impulse LoadDevice1This standard is issued under the fixed designation D 4694; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, t
2、he year of last revision. A number in parentheses 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 measurement of deflectionsof paved and unpaved surfaces with a falling-weight-
3、typeimpulse load device. These devices are commonly referred toas falling-weight deflectometers or FWDs.1.2 This test method describes the measurement of verticaldeflection response of the surface to an impulse load applied tothe pavement surface. Vertical deflections are measured on theload axis an
4、d at points spaced radially outward from the loadaxis.NOTE 1Subcommittee D04.39 is currently working on the develop-ment of a Precision and Bias statement. Therefore, the committeerecommends that the results from this test method should not be used ina buying or selling relationship for construction
5、 materials or constructionmaterials acceptance.1.3 The values stated in SI units are to be regarded as thestandard.1.4 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
6、safety and health practices and determine the applica-bility of regulatory limitations prior to use. A specific hazardstatement is given in Section 6.2. Referenced Documents2.1 ASTM Standards:2D 4695 Guide for General Pavement Deflection Measure-ments2.2 Strategic Highway Research Program:Manual for
7、 FWD Testing in the Long Term PavementPerformance Study, Operational Field Guidelines, Version2.0, February 19933. Summary of Test Method3.1 This test method is a type of plate-bearing test. The loadis a force pulse generated by a weight dropped on a buffersystem and is transmitted through a plate r
8、esting on thepavement surface. The test apparatus may be mounted in avehicle or on a suitable trailer towed by a vehicle.3.2 The vehicle is brought to a stop with the loading platepositioned over the desired test location. The plate and deflec-tion sensors are lowered to the pavement surface. The we
9、ightis raised to the height that, when dropped, will impart thedesired force to the pavement. The weight is dropped and theresulting vertical movement or deflection of the pavementsurface is measured using suitable instrumentation. Multipletests at the same or different heights of drop may be perfor
10、medbefore the apparatus is then raised and moved to the next testsite.3.3 Peak pavement deflections at each measured locationresulting from the force pulse are recorded in micrometres,millimetres, mils, or inches, as appropriate.3.4 The peak force imparted by the falling weight ismeasured by a load
11、cell and recorded, as the force in kN or lbfor mean stress (the load divided by the plate area) in kN/m2orpsi as appropriate.4. Significance and Use4.1 This test method covers the determination of pavementsurface deflections as a result of the application of an impulseload to the pavement surface. T
12、he resulting deflections aremeasured at the center of the applied load and at variousdistances away from the load. Deflections may be eithercorrelated directly to pavement performance or used to deter-mine the in-situ material characteristics of the pavement layers.Some uses of data include structur
13、al evaluation of loadcarrying capacity and determination of overlay thicknessrequirements for highway and airfield pavements.1This test method is under the jurisdiction of ASTM Committee E17 onVehicle-Pavement Systems and is the direct responsibility of Subcommittee E17.41on Pavement Management.Curr
14、ent edition approved Dec. 1, 2003. Published December 2003. Originallyapproved in 1987. Last previous edition approved in 1996 as D 4694 96.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volum
15、e information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5. Apparatus5.1 Instrumentation System, conforming to the followinggeneral requirements:5.1.1 Instruments
16、Exposed to the Elements (outside thevehicle), shall be operable in the temperature range of 10 to50C (10 to 120F) and shall tolerate relatively high humidity,rain or spray, and all other adverse conditions such as dust,shock, or vibrations that may normally be encountered.5.1.2 Instruments Not Expos
17、ed to the Elements (inside thevehicle), shall be operable in the temperature range of 5 to40C (40 to 105F).5.2 Force-Generating Device (falling “weight”), with aguide system. The force-generating device shall be capable ofbeing raised to one or more predetermined heights anddropped. The resulting fo
18、rce pulse transmitted to the pavementshall be reproducible within the requirements of 7.1. The forcepulse shall approximate the shape of a haversine or half-sinewave, and a peak force of approximately 50 kN (11 000 lbf)shall be achievable.NOTE 2It is common practice to use a force-pulse duration of
19、20 to 60ms or a rise time of 10 to 30 ms.5.2.1 Guide System, designed to operate with negligiblefriction or resistance and designed so the weight falls perpen-dicular to the pavement surface.5.3 Loading Plate, capable of an approximate uniformdistribution of the load on the pavement surface. Typical
20、loading plates are 300 and 450 mm (12 and 18 in.) in diameterfor measurements on conventional roads and airfields orsimilar stiff pavements. The plate shall be suitably constructedto allow pavement deflection measurements at the center of theplate.5.4 Deflection Sensor, capable of measuring the maxi
21、mumvertical movement of the pavement and mounted in such amanner as to minimize angular rotation with respect to itsmeasuring plane at the maximum expected movement. Thenumber and spacing of the sensors is optional and will dependupon the purpose of the test and the pavement layer character-istics.
22、A sensor spacing of 300 mm (12 in.) is frequently used.Sensors may be of several types such as displacement trans-ducers, velocity transducers, or accelerometers.5.5 Data Processing and Storage SystemLoad and deflec-tion data shall be recorded on either or both a magnetic storagedevice or paper stri
23、p recorder. Supporting information such asair temperature, pavement surface temperature, distance mea-surements, and identification data for each test point can berecorded either automatically or manually.5.6 Load Cell, to measure the applied load on each impactshall be placed in a position to minim
24、ize the mass between theload cell and the pavement. The load cell shall be positioned insuch a way that it does not restrict the ability to obtaindeflection measurements under the center of the load plate. Theload cell shall be water resistant, and shall be resistant tomechanical shocks from road im
25、pacts during testing or travel-ling, or both.6. Hazards6.1 The test vehicle, as well as all attachments to it, shallcomply with all applicable state and federal laws. Precautionsshall be taken beyond those imposed by laws and regulations toensure maximum safety of operating personnel and othertraffi
26、c.7. Calibration7.1 Force-Generating DevicePrior to load and deflectionsensor calibration, pre-condition the device by dropping theweight at least five times and checking the relative differencein each loading. Loadings shall not vary from each other morethan 3 %. If the variations exceed this toler
27、ance, the height ofthe drop, cleanliness of the track, as well as any springs orrubber pads that are used to condition the load shall bechecked. Improperly operating parts shall be replaced orrepaired prior to calibration to ensure that the horizontal forcesare minimized.7.2 Load Calibration Platfor
28、mFollow the manufacturersrecommendations for calibration since several types of thesedevices are commercially available.7.3 Deflection SensorsCalibrate sensors at least once amonth or in accordance with the manufacturers recommenda-tions.7.3.1 Relative Deflection CalibrationThe relative deflec-tion
29、calibration procedure shall be used to adjust the deflectionmeasurements from each deflection sensor so that they willproduce the same deflection measurement (within the precisionlimits specified in 8.2). The relative deflection calibrationrequires a sensor holding tower available from the manufac-t
30、urer. The tower must have sufficient sensor positions toaccommodate all of the sensors used during testing. The towershall position the sensors one above the other along a verticalaxis. The base of the tower shall have a single support post onthe same vertical axis. The tower shall have sufficient s
31、tiffnessto allow each sensor to experience the same deflection gener-ated by the Force-Generating Device. Mount the sensors in thetower and position as near the load plate as possible. The towerposition shall be fixed by making a small divot in the pavementor by cementing a washer on the pavement to
32、 provide a solidcontact point for the support post. The load plate shall stay incontinuous contact with the pavement surface while gatheringcalibration data. During calibration, rotate the sensors so thateach sensor occupies every level in the tower. At each towerposition, record five deflections fo
33、r each sensor. The towershall be manually held in a vertical position with a moderatedownward pressure while measuring the deflections. Deflec-tion magnitudes of about 400 m (15 mils) are desired. Thesame load setting shall be maintained throughout the calibra-tion. Determine deflection ratios for e
34、ach sensor by dividingthe average for all the sensors by the average of that sensor. Ifany of the resulting ratios are greater than 1.003 or less than0.997, all of the sensor calibration factors shall be replaced bythe existing calibration factor multiplied by the ratio. If any ofthe calibration fac
35、tors exceed the limits established by themanufacturer, the device should be repaired and recalibratedaccording to the manufacturers recommendations.7.3.2 To ensure that small deflections (as typically encoun-tered near the outer edge of the deflection basin) are monitoredto a reasonable degree of ac
36、curacy, repeat the above procedureat a distance of 1 to 1.5 m (3 to 5 ft) from the load plate.Deflection magnitudes of between 50 m and 100 m (2 to 4D 4694 96 (2003)2mils) are desired. Ensure that the average difference betweenany two sensor readings is 2 m (0.08 mils) or less; the sensorcalibration
37、 factors should not be altered. If any differences inaverage deflection greater than 2 m (0.08 mils) are found, thedevice should be repaired and recalibrated according to themanufacturers recommendations.NOTE 3Several methods have been developed by agencies other thanthe manufacturers to calibrate f
38、alling-weight-type impulse load devicesusing independent load cells and deflection sensors. One such method isthe Reference Calibration procedure developed by the Strategic HighwayResearch Program (SHRP), presently under the direction of the LongTerm Pavement Performance (LTPP) Office of the Federal
39、 HighwayAdministration (FHWA). For the purpose of using this reference methodto calibrate the FallingWeight Deflectometers used in the LTPPstudy, fourregional calibration centers have been established, one in each LTPPregion. These centers are in Pennsylvania, Minnesota, Texas, and Nevada,operated b
40、y their respective State Departments of Transportation.Anothermethod is a transportable calibration verification system developed at theUniversity of Texas at El Paso (UTEP) for the Texas DOT. This also usesindependent load cells and deflection sensors to measure the load anddeflections created by a
41、 falling-weight-type device. Both SHRP and theUTEPmethod can use the same point on the pavement surface to calibratethe deflection readings by removing the “sensor under test” from its holderand placing it in a reference holder, while the UTEP method can alsoretain the use of the sensor holders prov
42、ided by the manufacturer, with theverification deflection sensor(s) placed as close as possible to the sensorunder test. These two calibration methods are more complementary thaninterchangeable, with the stationary method used to make adjustments of2 % or less to the deflection sensor gains and the
43、portable UTEP methodused as a verification of the deflection sensor/sensor holder combination asused in the field, under actual field conditions.8. Signal Conditioning and Recorder System8.1 All signal conditioning and recording equipment shallallow data reading resolution to meet the following requ
44、ire-ments:8.1.1 Load measurements shall be displayed and stored witha resolution of 200 N (50 lbf) or less.8.1.2 Deflection measurements shall be displayed andstored with a resolution of 61 m (0.04 mils) or less.8.2 The load and deflection measurements shall be recordedas specified under 8.1.1 and 8
45、.1.2, respectively, within a timeperiod or measurement window of at least 60 ms, to anaccuracy at the time of peak load and deflection of 62 %, anda precision for deflections of 62 m (0.08 mils).9. Procedure9.1 Transport the device to the test location and position theloading plate over the desired
46、test point. The test location shallbe as clean as possible of rocks and debris to ensure that theloading plate will be properly seated. Gravel or soil surfacesshall be as smooth as possible and all loose material removed.(See Guide D 4695.)9.2 Lower the loading plate and the sensors to ensure theyar
47、e resting on a firm and stable surface.9.3 Raise the force generator to the desired height and dropthe “weight.” Record the resulting peak surface deflections andpeak load.NOTE 4If significant permanent deformation under the loading plateoccurs, move the apparatus and reduce the applied force until
48、thepermanent deformation is of no significance to the first test at a testlocation.9.4 Perform at least two loading sequences (9.3) and com-pare the results. If the difference is greater than 3 % for anysensor, note the variability in the report. Additional tests maybe run at the same or different l
49、oads.10. Precision and Bias10.1 PrecisionAt this time, no precision from a statisti-cally designed series of tests with different devices has beenobtained. Test results from the same device or from differentdevices may vary due to variations in buffer stiffness orpavement stiffness. Each device, however, should be able tomeet the accuracy requirements of 8.2 and the calibrationrequirements established by the manufacturer and SHRP.10.2 BiasNo statement is being made as to the bias of thistest method at the present time.11. Keywords11.1 deflection surveys; de
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