1、Designation: D7748/D7748M 141Standard Test Method forFlexural Rigidity of Geogrids, Geotextiles and RelatedProducts1This standard is issued under the fixed designation D7748/D7748M; the number immediately following the designation indicates theyear of original adoption or, in the case of revision, t
2、he year of last revision. A number in parentheses indicates the year of lastreapproval. A superscript epsilon () indicates an editorial change since the last revision or reapproval.1NOTEEquation 4 in Section 11.5 was editorially corrected in June 2016.1. Scope1.1 This test method covers the measurem
3、ent of stiffnessproperties of geogrids, geotextiles and geogrid-geotextile com-posites all of which are referred to as geosynthetics within thistest method. Bending length is measured and flexural rigidity iscalculated through use of the cantilever test procedure.1.1.1 This test method employs the p
4、rinciple of cantileverbending of the geosynthetic under its own mass.1.2 This test method applies to geogrids, geotextiles andgeogrid-geotextile composites.1.3 This test method is for manufacturing quality controlpurposes only, to ensure uniformity and consistency of flexuralrigidity for a specific
5、product from roll to roll and lot to lot.1.4 The values stated in either SI units or inch-pound unitsare to be regarded separately as standard. The values stated ineach system may not be exact equivalents; therefore, eachsystem shall be used independently of the other. Combiningvalues from the two s
6、ystems may result in non-conformancewith the standard.1.5 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
7、of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D123 Terminology Relating to TextilesD1776 Practice for Conditioning and Testing TextilesD4354 Practice for Sampling of Geosynthetics and RolledErosion Control Products(RECPs) for TestingD4439 Terminology for Geosynthe
8、ticsE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3. Terminology3.1 For common definitions of terms in this test method,refer to Terminology D123 and Terminology D4439.3.2 Defin
9、itions of Terms Specific to This Standard:3.2.1 bending length, na measure of the interaction be-tween geosynthetic weight and geosynthetic stiffness as shownby the way in which a geosynthetic bends under its ownweight.3.2.1.1 DiscussionBending length reflects the stiffness ofa geosynthetic when ben
10、t in one plane under the force ofgravity.4. Summary of Test Method4.1 A specimen is slid at a specified rate in a directionparallel to its long dimension, until its leading edge projectsfrom the edge of a horizontal surface. The length of theoverhang is measured when the tip of the specimen is de-pr
11、essed under its own mass to the point where the line joiningthe top to the edge of the platform makes a 0.724 radians41.5 angle with the horizontal. From this measured length,the bending length and flexural rigidity are calculated.5. Significance and Use5.1 This test method is considered satisfactor
12、y for manufac-turing quality control testing of a specific geosynthetic;however, caution is advised since information about between-laboratory precision is incomplete. Comparative tests as di-rected in 5.1.1 may be advisable.5.1.1 In case of a dispute arising from differences inreported test results
13、 when using this test method for acceptancetesting of commercial shipments, the purchaser and the sup-plier should conduct comparative tests to determine if there is1This test method is under the jurisdiction of ASTM Committee D35 onGeosynthetics and is the direct responsibility of Subcommittee D35.
14、01 on Mechani-cal Properties.Current edition approved Jan. 1, 2014. Published January 2014. Originallyapproved in 2012. Last previous edition approved in 2013 as D7748/D7748M13.DOI: 10.1520/D7748_D7748M14E01.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Custome
15、r Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1a statistical bias between their labora
16、tories. Competent statis-tical assistance is recommended for the investigation of bias.As a minimum, the two parties should take a group of testspecimens that are as homogeneous as possible and that arefrom a lot of material of the type in question. Test specimensshould then be randomly assigned in
17、equal numbers to eachlaboratory for testing. The average results from the twolaboratories should be compared using the appropriate statis-tical analysis and an acceptable probability level chosen by thetwo parties before testing is begun. If a bias is found, either itscause must be found and correct
18、ed or the purchaser and thesupplier must agree to interpret future test results with consid-eration to the known bias.5.2 This test method is not suitable for very limp geosyn-thetics or those that show a marked tendency to curl or twist ata cut edge.5.3 The stiffness of a geosynthetic may change wi
19、th storage.5.4 No evidence has been found showing that bendinglength is dependent on specimen width. The tendency forspecimens to curl or twist will affect the result, because of therigidity provided at the edge. Consequently, the edge effect isless of an issue for a wider strip.6. Apparatus6.1 Flex
20、ural Rigidity Tester (Fig. 1).6.1.1 Horizontal Platform, with a minimum area of 100 by900 mm 4 by 36 in. and having a smooth low-friction, flataluminum surface. A leveling bubble shall be incorporated inthe platform.6.1.1.1 Indicator, inclined at an angle of 0.724 6 0.01radians 41.5 6 0.5 below the
21、plane of the platform surface.6.1.1.2 Movable Slide, consisting of a metal plate not lessthan 50 by 200 mm 2 by 8 in. by approximately 3 mm 1/8in. thick and having a mass of 270 6 5 g 0.6 6 0.01 lb.6.1.1.3 Scale and Reference Point, to measure the length ofthe overhang.6.1.1.4 Specimen Feed Unit, mo
22、torized set to 120 mm/min4.75 in./min 6 5 %, or manual equivalent.7. Sampling and Test Specimens7.1 Lot SampleAs a lot sample for acceptance testing,randomly select the number of rolls or pieces of geosyntheticdirected in an applicable material specification or other agree-ment between the purchaser
23、 and the supplier. Consider the rollsor pieces of geosynthetic to be the primary sampling units. Inthe absence of such an agreement, take the number of geosyn-thetic rolls specified in Practice D4354.7.2 For acceptance testing, take a swatch extending thewidth of the geosynthetic and approximately2m
24、6ftalongthe machine direction from each roll or piece in the lot sample.For rolls of geosynthetic, take a sample that will excludegeosynthetic from the outer wrap of the roll or the inner wraparound the core of the roll of geosynthetic, or any end piece.7.3 Direction of TestConsider the long dimensi
25、on of thespecimen as the direction of test.7.4 Number of Test SpecimensFrom each laboratory sam-pling unit, take five specimens from the machine direction andfive specimens from the cross-machine direction as applicableto a material specification or contract order.7.5 Cutting Test SpecimensCut the s
26、pecimens to be usedfor the measurement of machine direction with the longerdimension parallel to the machine direction. Cut the specimensto be used for the measurement of the cross-machine directionwith the longer dimension parallel to the cross-machine direc-tion. Label to maintain specimen identit
27、y.7.5.1 Take specimens, representing a broad distributionacross the width and length, preferably along the diagonal ofthe laboratory sample, and no nearer the edge than one-tenth itsFIG. 1 Example Test Rig SetupD7748/D7748M 1412width. Ensure specimens are free of folds, creases, or wrinkles.Avoid ge
28、tting oil, water, grease, etc. on the specimens whenhandling.7.5.2 For geogrids and geotextile-geogrid composites cutspecimen such that the specimen include two (2) geogridapertures in width or a minimum of 5 by 90 cm 6 0.1 cmminimum of 2 by 36 in. 6 0.04 in.7.5.2.1 It is important to cut the ribs o
29、f the specimens inboth the width and the length direction exactly midwaybetween junctions such that a representative mass per unit areacan be obtained for each specimen.7.5.3 For geotextiles cut test specimens 5 by 90 cm 6 0.1cm 2 by 36 in. 6 0.04 in.8. Preparation of Test Apparatus and Calibration8
30、.1 Set the tester on a table or bench with the horizontalplatform and inclined reference lines. Adjust the platform tohorizontal as indicated by the leveling bubble.8.1.1 Verify that the apparatus bend angle is at the 0.724radians 41.5 angle.9. Conditioning9.1 For Geogrids and Geogrid-geotextile Com
31、positesDonot fold or bend the lab sample. If the lab sample must beobtained from roll inventory, it shall be conditioned by counterrolling and taping the cut specimens in the opposite direction ofthe curl for a minimum of 24 h within a laboratory exhibitingthe proper atmosphere for testing geosynthe
32、tics. Counter rollspecimen to a diameter that is not more than that of thediameter from the original manufactured roll. For most prod-ucts a diameter of 150 mm 6 in. is adequate. Alternately, thesample can be conditioned by placing weights to restrain thespecimen in a flat position for the 24-h peri
33、od.9.2 For GeotextilesPrecondition the specimens by bring-ing them to approximate moisture equilibrium in the standardatmosphere for preconditioning geotextiles as directed inPractice D1776, unless otherwise directed in a material speci-fication or contract order.9.3 After preconditioning, bring the
34、 test specimens to equi-librium for testing in the standard atmosphere as, unlessotherwise directed in a material specification or contract order.directed in Practice D1776 or, if applicable, in the specifiedatmosphere in which the testing is to be performed.10. Procedure10.1 Test the conditioned sp
35、ecimens in the standard atmo-sphere for testing geosynthetics, which is 21 6 2C 70 6 4Fand 50 to 70 % relative humidity, unless otherwise directed ina material specification or contract order.10.2 Remove the movable slide. Place the specimen on thehorizontal platform with the length of the specimen
36、parallel tothe platform edge and the specimen face side up. Align theedge of the specimen with the line scribed on the right-handedge of the horizontal platform.10.2.1 Place the movable slide on the specimen, beingcareful not to change its initial position.10.2.2 For automatic testers, turn the test
37、er switch on andwatch the leading edge of the specimen closely. Turn theswitch off the instant the edge of the specimen touches theinclined portion of the tester.FIG. 2 Test in ProgressD7748/D7748M 141310.2.3 For manual testers, move the clamped specimen byhand in a smooth manner at approximately 12
38、 cm/min 4.75in./min 6 5 % until the edge of the specimen touches theinclined portion of the tester, as shown in Fig. 2 and Fig. 3.10.2.4 Read the overhang length by measuring the lengthstill lying on the horizontal surface after the specimen hastouched the inclined surface and subtracting that measu
39、rementfrom the initial specimen length. Record from the linear scaleto the nearest 0.1 cm 0.1 in.NOTE 1If the specimen has a tendency to twist, take the referencepoint at the center of the leading edge. Do not measure specimens thattwist more than 0.785 radian 45.10.2.5 Test the face and back of bot
40、h ends of each specimenfor a total of four readings per specimen.10.3 Specimen MassDetermine the geosynthetic mass perunit area as directed in 11.2 to the nearest 0.1 mg.10.4 Specimen AreaDetermine the area of the specimensin 10.4 to the nearest 1 cm2.10.5 Number of SpecimensContinue as directed in1
41、0.110.5 as applicable, until five specimens have been testedfor each testing direction for each laboratory sampling unit (Atotal of 20 readings for each direction).11. Calculation11.1 Length of Overhang, Individual SpecimensFor eachspecimen, average the five readings obtained to the nearest 0.1cm as
42、 the length of overhang, unless otherwise agreed uponbetween the purchaser and supplier.NOTE 2In some cases it may be of interest to differentiate between thesides of the geosynthetic by averaging those readings made with thegeosynthetic face side up (out) separately from those with the geosynthetic
43、face side down (in).11.2 Mass per Unit AreaDetermine the mass per unit areato the nearest 0.1 mg/cm2using Eq 1.W = specimen mass/(specimen length 3 specimen width) (1)11.3 Bending Length, Individual SpecimensCalculate thebending length for each testing direction to the nearest 1 mm,using Eq 2.c 5 O2
44、 (2)where:c = bending length, cm, andO = length of overhang (total specimen length minus theremaining horizontal length of specimen at the conclu-sion of the test, Fig. 3), cm.11.4 Flexural Rigidity, Individual SpecimensCalculate theflexural rigidity for each testing direction to three significantdi
45、gits using Eq 3.G 5 W 3 c3(3)where:G = flexural rigidity, mg-cm,W = geosynthetic mass per unit area, mg/cm2, andC = bending length, cm.11.5 Overall Flexural RigidityCalculate the overall flex-ural rigidity using Eq 4.Overall Flexural Rigidity 5Gmachine direction3 Gcross machine direction!12(4)FIG. 3
46、 Conclusion of TestD7748/D7748M 141411.6 Average ValuesCalculate the average bending length,flexural rigidity and overall flexural rigidity as applicable to amaterial specification or contract order for each laboratorysampling unit and for the lot, for each testing direction.11.7 Standard Deviation,
47、 Coeffcient of VariationCalculate when requested.12. Report12.1 Report that the stiffness as bending length, flexuralrigidity and overall flexural rigidity were determined as di-rected in Test Method D7748/D7748M. Describe the materialor product sampled and the method of sampling used.12.2 Report th
48、e following information for each laboratorysampling unit and for the lot as applicable to a materialspecification or contract order.12.2.1 Bending length for each testing direction.12.2.2 Flexural rigidity for each testing direction.12.2.3 Number of specimens tested for each direction.12.2.4 Overall
49、 flexural rigidity.12.2.5 When calculated, the average and standard deviationor the coefficient of variation.12.2.6 Any modification of the test method.13. Precision and Bias313.1 PrecisionThe precision of this test method is basedon an interlaboratory study of ASTM D7748/D7748M Stan-dard Test Method for Flexural Rigidity of Geogrids, Geotex-tiles and Related Products, conducted in 2012. A singlelaboratory participated in this study, testing two differentmaterials. Every “test result” represents an individu
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