1、Designation: D4694 09Standard Test Method forDeflections with a Falling-Weight-Type Impulse LoadDevice1This standard is issued under the fixed designation D4694; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revi
2、sion. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () 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-typeimpulse load devi
3、ce. 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 and at points spaced ra
4、dially outward from the loadaxis.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 safety and hea
5、lth 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:2D4695 Guide for General Pavement Deflection Measure-ments2.2 Strategic Highway Research Program:Long Term Pavement Perfor
6、mance Program Manual forFalling Weight Deflectometer Measurements, Version4.1, December 20063. 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 resting on thepavemen
7、t 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 weightis raised to the
8、 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 performedbefore the appara
9、tus 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 cell and recorded, a
10、s 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. The resulting deflect
11、ions 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 structural evaluation of loa
12、dcarrying capacity and determination of overlay thicknessrequirements for highway and airfield pavements.5. Apparatus5.1 Instrumentation System conforming to the followinggeneral requirements:5.1.1 Instruments Exposed to the Elements (outside thevehicle) shall be operable in the temperature range of
13、 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.1This test method is under the jurisdiction of ASTM Committee E17 on Vehicle- Pavement Systems and is the direct respo
14、nsibility of Subcommittee E17.41 onPavement Management and Data Needs.Current edition approved Nov. 1, 2009. Published December 2009. Originallyapproved in 1987. Last previous edition approved in 2003 as D4694 96 (2003).DOI: 10.1520/D4694-09.2For referenced ASTM standards, visit the ASTM website, ww
15、w.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 Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5.1.
16、2 Instruments Not Exposed to the Elements (inside thevehicle) shall be operable in the temperature range of 5 to 40C(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 anddrop
17、ped. The resulting force 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 1It is common practice to use a for
18、ce-pulse duration of 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 uniform dis-tribution of the load on the pave
19、ment surface. Typical loadingplates are 300 and 450 mm (12 and 18 in.) in diameter formeasurements on conventional roads and airfields or similarstiff pavements. The plate shall be suitably constructed to allowpavement deflection measurements at the center of the plate.5.4 Deflection Sensor capable
20、of measuring the maximumvertical 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 lay
21、er character-istics. 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 a personal computer. Supportingi
22、nformation such as air temperature, pavement surface tem-perature, distance measurements, and identification data foreach test point can be recorded either automatically or manu-ally.5.6 Load Cell to measure the applied load on each impactshall be placed in a position to minimize the mass between th
23、eload 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 impacts during testing or
24、 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 othertraffic.7. Calibration7.1 For
25、ce-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 tolerance, the height ofthe
26、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 PlatformFollow the manufacture
27、rsrecommendations 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 calibration procedure s
28、hall 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-turer. The tower must ha
29、ve 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 stiffnessto allow each s
30、ensor 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 provide a solidcontact
31、 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 for each sensor. The towe
32、rshall 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 each sensor by dividingt
33、he 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 factors exceed the limits
34、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 accuracy, repeat the abov
35、e 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 4mils) are desired. Ensure that the average difference betweenany two sensor readings is 2 m (0.08 mils) or less; the sensorcalibration factors should not be altered. If any d
36、ifferences inaverage deflection greater than 2 m (0.08 mils) are found, thedevice should be repaired and recalibrated according to themanufacturers recommendations.NOTE 2Several methods have been developed by agencies other thanthe manufacturers to calibrate falling-weight-type impulse load devicesD
37、4694 092using 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 HighwayAdministration (FHWA).
38、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 by their respective State Depart
39、ments 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 falling-weight-type device. Bo
40、th 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 provided by the manufacturer, with
41、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 portable UTEP methodused as a v
42、erification 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 require-ments:8.1.1 Load measuremen
43、ts 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 8.1.2, respectively, within a ti
44、meperiod 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 test point. The test location s
45、hallbe 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 D4695.)9.2 Lower the loading plate and the sensors to ensure theyare resting on a firm and stable s
46、urface.9.3 Raise the force generator to the desired height and dropthe “weight.” Record the resulting peak surface deflections andpeak load.NOTE 3If significant permanent deformation under the loading plateoccurs, move the apparatus and reduce the applied force until thepermanent deformation is of n
47、o 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 loads.10. Precision and Bias10.1
48、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
49、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; deflection testing; falling weightdeflectometer (FWD); impulse deflection testing device; load/deflection testing; nondestructive testing (NDT); pavementdeflection; pavement testingASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users o
