1、Designation: D7748 121Standard Test Method forFlexural Rigidity of Geogrids, Geotextiles and RelatedProducts1This standard is issued under the fixed designation D7748; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of las
2、t revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1NOTEThis test method was editorially corrected in May 2012.1. Scope1.1 This test method covers the measurement of stiffnesspropertie
3、s of geogrids, geotextiles and geogrid-geotextile com-posites all of which are referred to as geosynthetics within thisstandard. Bending length is measured and flexural rigidity iscalculated through use of the cantilever test procedure.1.1.1 This test method employs the principle of cantileverbendin
4、g 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 product from roll to roll an
5、d lot to lot.1.4 The values stated in SI units are to be regarded as thestandard. The U.S. customary units may be approximate.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 ap
6、pro-priate safety and health practices and determine the applica-bility 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 for TestingD
7、4439 Terminology for GeosyntheticsD4759 Practice for Determining the Specification Confor-mance of GeosyntheticsD5261 Test Method for Measuring Mass per Unit Area ofGeotextiles3. Terminology3.1 For common definitions of terms in this test method,refer to Terminology D123 and Terminology D44393.2 Def
8、initions 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 b
9、ent 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-
10、pressed under its own mass to the point where the line joiningthe top to the edge of the platform makes a 0.724 radians(41.5) 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 satisfa
11、ctory 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 res
12、ults when using this test method for acceptancetesting of commercial shipments, the purchaser and the sup-plier should conduct comparative tests to determine if there isa statistical bias between their laboratories. Competent statis-tical assistance is recommended for the investigation of bias.As a
13、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 equal numbers to eachlaboratory for testing. The average results from the two1This test meth
14、od is under the jurisdiction of ASTM Committee D35 onGeosynthetics and is the direct responsibility of Subcommittee D35.01 on Mechani-cal Properties.Current edition approved Feb. 1, 2012. Published March 2012. DOI: 10.1520/D774812E012For referenced ASTM standards, visit the ASTM website, www.astm.or
15、g, orcontact ASTM Customer 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 States1laboratories s
16、hould 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 corrected or the purchaser and thesupplier must agree to interpret future test results with consid
17、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 with storage.5.4 No evidence has been found showing that bendinglength is dependent on specim
18、en 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 Flexural Rigidity Tester (Fig. 1).6.1.1 Horizontal Platform, with a minimum area of 100 by900 m
19、m (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 plane of the platform surface.6.1.1.2 Movable Slide, consisting of a metal plate not le
20、ssthan 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 overhang6.1.1.4 Specimen Feed Unit, motorized set to 120 mm/min(4.75 in./min) 65 %, or manual equivalent.7. Sampling and
21、 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 and the supplier. Consider the rollsor pieces of geosynthetic to be the primary
22、sampling units. Inthe absence of such an agreement, take the number of geosyn-thetic rolls specified in D4354.7.2 For acceptance testing, take a swatch extending thewidth of the geosynthetic and approximately2m(6ft)alongthe machine direction from each roll or piece in the lot sample.For rolls of geo
23、synthetic, 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 dimension of thespecimen as the direction of test.7.4 Number of Test SpecimensFrom each laborat
24、ory 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 specimens to be usedfor the measurement of machine direction with the longerdimension par
25、allel 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 identity.7.5.1 Take specimens, representing a broad distributionacross the width and length, pr
26、eferably along the diagonal ofthe laboratory sample, and no nearer the edge than one-tenth itsFIG. 1 Example Test Rig SetupD7748 1212width. Ensure specimens are free of folds, creases, or wrinkles.Avoid getting oil, water, grease, etc. on the specimens whenhandling.7.5.2 For geogrids and geotextile-
27、geogrid composites cutspecimen such that the specimen include two (2) geogridapertures in width or a minimum of 5 by 90 cm 60.1 cm(minimum of 2 by 36 in. 6 0.04 in.).7.5.2.1 It is important to cut the ribs of the specimens inboth the width and the length direction exactly midwaybetween junctions suc
28、h that a representative mass per unit areacan be obtained for each specimen.7.5.3 For geotextiles cut test specimens 5 by 90 cm, 60.1cm (2 by 36 in. 6 0.04 in.).8. Preparation of Test Apparatus and Calibration8.1 Set the tester on a table or bench with the horizontalplatform and inclined reference l
29、ines. 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 compositesDonot fold or bend the lab sample. If the lab sample must beobtained from roll in
30、ventory, it shall be conditioned by counterrolling and taping the cut specimens in the opposite direction ofthe curl for a minimum of 24 hours within a laboratoryexhibiting the proper atmosphere for testing geosynthetics.Counter roll specimen to a diameter that is not more than thatof the diameter f
31、rom the original manufactured roll. For mostproducts a diameter of (150 mm) 6 inches is adequate.Alternately, the sample can be conditioned by placing weightsto restrain the specimen in a flat position for the 24 hour period.9.2 For GeotextilesPrecondition the specimens by bring-ing them to approxim
32、ate 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 test specimens to equi-librium for testing in the standard atmosphere as, unl
33、essotherwise directed in a material specification or contract order.directed in Practice D 1776 or, if applicable, in the specifiedatmosphere in which the testing is to be performed10. Procedure10.1 Test the conditioned specimens in the standard atmo-sphere for testing geosynthetics, which is 21 6 2
34、C (70 6 4F)and 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 parallel tothe platform edge and the specimen face side up. Align theedge of
35、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 tester switch on andwatch the leading edge of the specimen closely. Turn theswitc
36、h off the instant the edge of the specimen touches theinclined portion of the tester.10.2.3 For manual testers, move the clamped specimen byhand in a smooth manner at approximately 12 cm/min (4.75in./min)6 5 % until the edge of the specimen touches theinclined portion of the tester, as shown in Fig.
37、 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 measurementfrom the initial specimen length. Record from the linear scaleto the nearest 0.1 cm (0.1 in.).NOTE 1If the specimen has a
38、 tendency to twist, take the referencepoint at the center of the leading edge. Do not measure specimens thattwist more than 0.785 radian (45).FIG. 2 Test in ProgressD7748 121310.2.5 Test the face and back of both ends of each specimenfor a total of four readings per specimen.10.3 Specimen MassDeterm
39、ine 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 in10.110.5 as applicable, until five specimens have been testedfor each testing direction fo
40、r 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 the Length of Overhang, unless otherwise agreed uponbetween the purchaser and supplier.N
41、OTE 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 geosyntheticface side down (in).11.2 Mass per Unit AreaDetermine the mass per unit areato the nearest
42、 0.1 mg/cm2 using Eq 1.W 5 specimen massspecimen length 3 specimen width!(1)11.3 Bending Length, Individual SpecimensCalculate thebending length for each testing direction to the nearest 1 mm,usingEq 2.c 5 O2 (2)where:c = bending length, cm, andO = length of overhang (Total specimen length minus the
43、remaining 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 significantdigits using Eq 3.G 5 W 3 c3(3)where:G = flexural rigidity, mg-cm,W = geosynthetic mass per uni
44、t area, mg/cm2, andC = bending length, cm.11.5 Overall Flexural RigidityCalculate the overall flex-ural rigidity using Eq 4.Overall Flexural Rigidity 5 (Gmachine direction3 Gcross machine direction)12(4)11.6 Average Values11.7 Standard Deviation, Coeffcient of VariationCalculate when requested.12. R
45、eport12.1 Report that the stiffness as bending length, flexuralrigidity and overall flexural rigidity were determined as di-rected in Test Method D7748. Describe the material or productsampled and the method of sampling used.12.2 Report the following information for each laboratorysampling unit and
46、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.FIG. 3 Conclusion of TestD7748 121412.2.4 Overall flexural rigidity12.2.5 W
47、hen calculated, the average and standard deviationor the coefficient of variation.12.2.6 Any modification of the test method.13. Precision and Bias13.1 PrecisionThe precision of the procedure in TestMethod D7748 is being established13.2 BiasThe procedure in Test Method D7748 for deter-mining the fle
48、xural rigidity of geogrids and geotextiles canonly be defined in terms of a specific test method. Within thislimitation, the procedures in Test Method D7748 has no knownbias.14. Keywords14.1 bending length; flexural rigidity; geogrid; geogrid-geotextile composite; geosynthetic; geotextile; stiffness
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