1、Designation: D7748 121D7748/D7748M 13Standard Test Method forFlexural Rigidity of Geogrids, Geotextiles and RelatedProducts1This standard is issued under the fixed designation D7748;D7748/D7748M; the number immediately following the designation indicatesthe year of original adoption or, in the case
2、of revision, the 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.1 NOTEThis test method was editorially corrected in May 2012.1. Scope1.1 This test method covers the meas
3、urement of stiffness properties of geogrids, geotextiles and geogrid-geotextile compositesall of which are referred to as geosynthetics within this standard. test method. Bending length is measured and flexural rigidity iscalculated through use of the cantilever test procedure.1.1.1 This test method
4、 employs the principle of cantilever bending of the geosynthetic under its own mass.1.2 This test method applies to geogrids, geotextiles and geogrid-geotextile composites.1.3 This test method is for manufacturing quality control purposes only, to ensure uniformity and consistency of flexural rigidi
5、tyfor a specific product from roll to roll and lot to lot.1.4 The values stated in either SI units or inch-pound units are to be regarded separately as the standard. The U.S. customaryunits may be approximate.values stated in each system may not be exact equivalents; therefore, each system shall be
6、usedindependently of the other. Combining values from the two systems may result in non-conformance with the standard.1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropria
7、te safety and health practices and determine the applicability of regulatorylimitations 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 Rolled Erosion Con
8、trol Products(RECPs) for TestingD4439 Terminology for GeosyntheticsD4759 Practice for Determining the Specification Conformance of GeosyntheticsD5261 Test Method for Measuring Mass per Unit Area of Geotextiles3. Terminology3.1 For common definitions of terms in this test method, refer to Terminology
9、 D123 and Terminology D4439.3.2 Definitions of Terms Specific to This Standard:3.2.1 bending length, na measure of the interaction between geosynthetic weight and geosynthetic stiffness as shown by theway in which a geosynthetic bends under its own weight.3.2.1.1 DiscussionBending length reflects th
10、e stiffness of a geosynthetic when bent in one plane under the force of gravity.1 This test method is under the jurisdiction ofASTM Committee D35 on Geosynthetics and is the direct responsibility of Subcommittee D35.01 on Mechanical Properties.Current edition approved Feb. 1, 2012May 1, 2013. Publis
11、hed March 2012May 2013. Originally approved in 2012. Last previous edition approved in 2012 as D7748121.DOI: 10.1520/D774812E0110.1520/D7748_D7748M13.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Stand
12、ardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible
13、to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Co
14、nshohocken, PA 19428-2959. United States14. Summary of Test Method4.1 A specimen is slid at a specified rate in a direction parallel to its long dimension, until its leading edge projects from theedge of a horizontal surface. The length of the overhang is measured when the tip of the specimen is dep
15、ressed under its own massto the point where the line joining the top to the edge of the platform makes a 0.724 radians (41.5)41.5 angle with thehorizontal. From this measured length, the bending length and flexural rigidity are calculated.5. Significance and Use5.1 This test method is considered sat
16、isfactory for manufacturing quality control testing of a specific geosynthetic; however,caution is advised since information about between-laboratory precision is incomplete. Comparative tests as directed in 5.1.1 maybe advisable.5.1.1 In case of a dispute arising from differences in reported test r
17、esults when using this test method for acceptance testing ofcommercial shipments, the purchaser and the supplier should conduct comparative tests to determine if there is a statistical biasbetween their laboratories. Competent statistical assistance is recommended for the investigation of bias. As a
18、 minimum, the twoparties should take a group of test specimens that are as homogeneous as possible and that are from a lot of material of the typein question. Test specimens should then be randomly assigned in equal numbers to each laboratory for testing. The average resultsfrom the two laboratories
19、 should be compared using the appropriate statistical analysis and an acceptable probability level chosenby the two parties before testing is begun. If a bias is found, either its cause must be found and corrected or the purchaser and thesupplier must agree to interpret future test results with cons
20、ideration to the known bias.5.2 This test method is not suitable for very limp geosynthetics or those that show a marked tendency to curl or twist at a cutedge.5.3 The stiffness of a geosynthetic may change with storage.5.4 No evidence has been found showing that bending length is dependent on speci
21、men width. The tendency for specimens tocurl or twist will affect the result, because of the rigidity provided at the edge. Consequently, the edge effect is less of an issue fora wider strip.6. Apparatus6.1 Flexural Rigidity Tester (Fig. 1).6.1.1 Horizontal Platform, with a minimum area of 100 by 90
22、0 mm (44 by 36 in.)in. and having a smooth low-friction, flataluminum surface. A leveling bubble shall be incorporated in the platform.6.1.1.1 Indicator, inclined at an angle of 0.724 6 0.01 radians (41.541.5 6 0.5)0.5 below the plane of the platform surface.6.1.1.2 Movable Slide, consisting of a me
23、tal plate not less than 50 by 200 mm (22 by 8 in.)in. by approximately 3 mm (1/8in.)1/8 in. thick and having a mass of 270 6 5 g (0.60.6 6 0.01 lb).lb.6.1.1.3 Scale and Reference Point, to measure the length of the overhang6.1.1.4 Specimen Feed Unit, motorized set to 120 mm/min (4.75 in./min) 65 4.7
24、5 in./min 6 5 %, or manual equivalent.FIG. 1 Example Test Rig SetupD7748/D7748M 1327. Sampling and Test Specimens7.1 Lot SampleAs a lot sample for acceptance testing, randomly select the number of rolls or pieces of geosynthetic directedin an applicable material specification or other agreement betw
25、een the purchaser and the supplier. Consider the rolls or pieces ofgeosynthetic to be the primary sampling units. In the absence of such an agreement, take the number of geosynthetic rolls specifiedin Practice D4354.7.2 For acceptance testing, take a swatch extending the width of the geosynthetic an
26、d approximately 2 m (6 ft)6 ft alongthe 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 wrap around the core of the roll of geosynthetic, or any end piece.7.3 Direction of
27、 TestConsider the long dimension of the specimen as the direction of test.7.4 Number of Test SpecimensFrom each laboratory sampling unit, take five specimens from the machine direction and fivespecimens from the cross-machine direction as applicable to a material specification or contract order.7.5
28、Cutting Test SpecimensCut the specimens to be used for the measurement of machine direction with the longer dimensionparallel to the machine direction. Cut the specimens to be used for the measurement of the cross-machine direction with the longerdimension parallel to the cross-machine direction. La
29、bel to maintain specimen identity.7.5.1 Take specimens, representing a broad distribution across the width and length, preferably along the diagonal of thelaboratory sample, and no nearer the edge than one-tenth its width. Ensure specimens are free of folds, creases, or wrinkles.Avoidgetting oil, wa
30、ter, grease, etc. on the specimens when handling.7.5.2 For geogrids and geotextile-geogrid composites cut specimen such that the specimen include two (2) geogrid aperturesin width or a minimum of 5 by 90 cm 60.1 6 0.1 cm (minimumminimum of 2 by 36 in. 6 0.04 in.).in.7.5.2.1 It is important to cut th
31、e ribs of the specimens in both the width and the length direction exactly midway betweenjunctions such that a representative mass per unit area can be obtained for each specimen.7.5.3 For geotextiles cut test specimens 5 by 90 cm, 60.1 cm (2 cm 6 0.1 cm 2 by 36 in. 6 0.04 in.).in.8. Preparation of
32、Test Apparatus and Calibration8.1 Set the tester on a table or bench with the horizontal platform and inclined reference lines.Adjust the platform to horizontalas indicated by the leveling bubble.8.1.1 Verify that the apparatus bend angle is at the 0.724 radians (41.5)41.5 angle.9. Conditioning9.1 F
33、or Geogrids and Geogrid-geotextile compositesCompositesDo not fold or bend the lab sample. If the lab sample mustbe obtained from roll inventory, it shall be conditioned by counter rolling and taping the cut specimens in the opposite directionof the curl for a minimum of 24 hoursh within a laborator
34、y exhibiting the proper atmosphere for testing geosynthetics. Counterroll specimen to a diameter that is not more than that of the diameter from the original manufactured roll. For most products adiameter of (150 mm) 6 inches150 mm 6 in. is adequate.Alternately, the sample can be conditioned by plac
35、ing weights to restrainthe specimen in a flat position for the 24 hour 24-h period.9.2 For GeotextilesPrecondition the specimens by bringing them to approximate moisture equilibrium in the standardatmosphere for preconditioning geotextiles as directed in Practice D1776, unless otherwise directed in
36、a material specification orcontract order.9.3 After preconditioning, bring the test specimens to equilibrium for testing in the standard atmosphere as, unless otherwisedirected in a material specification or contract order. directed in Practice DD1776 1776 or, if applicable, in the specified atmosph
37、erein which the testing is to be performedperformed.10. Procedure10.1 Test the conditioned specimens in the standard atmosphere for testing geosynthetics, which is 21 6 2C (7070 6 4F)4Fand 50 to 70% relative humidity, unless otherwise directed in a material specification or contract order.10.2 Remov
38、e the movable slide. Place the specimen on the horizontal platform with the length of the specimen parallel to theplatform edge and the specimen face side up. Align the edge of the specimen with the line scribed on the right-hand edge of thehorizontal platform.10.2.1 Place the movable slide on the s
39、pecimen, being careful not to change its initial position.10.2.2 For automatic testers, turn the tester switch on and watch the leading edge of the specimen closely. Turn the switch offthe instant the edge of the specimen touches the inclined portion of the tester.10.2.3 For manual testers, move the
40、 clamped specimen by hand in a smooth manner at approximately 12 cm/min (4.75in./min)6 4.75 in./min 6 5 % until the edge of the specimen touches the inclined portion of the tester, as shown in Fig. 2 andFig. 3.D7748/D7748M 13310.2.4 Read the overhang length by measuring the length still lying on the
41、 horizontal surface after the specimen has touchedthe inclined surface and subtracting that measurement from the initial specimen length. Record from the linear scale to the nearest0.1 cm (0.1 in.).0.1 in.NOTE 1If the specimen has a tendency to twist, take the reference point at the center of the le
42、ading edge. Do not measure specimens that twist morethan 0.785 radian (45).45.10.2.5 Test the face and back of both ends of each specimen for a total of four readings per specimen.FIG. 2 Test in ProgressFIG. 3 Conclusion of TestD7748/D7748M 13410.3 Specimen MassDetermine the geosynthetic mass per un
43、it area as directed in 11.2 to the nearest 0.1 mg.10.4 Specimen AreaDetermine the area of the specimens in 10.4 to the nearest 1 cm2.10.5 Number of SpecimensContinue as directed in 10.110.5 as applicable, until five specimens have been tested for eachtesting direction for each laboratory sampling un
44、it (A total of 20 readings for each direction).11. Calculation11.1 Length of Overhang, Individual SpecimensFor each specimen, average the five readings obtained to the nearest 0.1 cmas the Lengthlength of Overhang,overhang, unless otherwise agreed upon between the purchaser and supplier.NOTE 2In som
45、e cases it may be of interest to differentiate between the sides of the geosynthetic by averaging those readings made with thegeosynthetic face side up (out) separately from those with the geosynthetic face side down (in).11.2 Mass per Unit AreaDetermine the mass per unit area to the nearest 0.1 mg/
46、cm2mg/cm2 using Eq 1.W5specimen massspecimen length 3specimen width! (1)W = specimen mass/(specimen length3specimen width) (1)11.3 Bending Length, Individual SpecimensCalculate the bending length for each testing direction to the nearest 1 mm, usingEq 2.c 5O2 (2)where:c = bending length, cm, andO =
47、length of overhang (Total specimen length minus the remaining horizontal length of specimen at the conclusion of thetest,Fig. 3), cm.O = length of overhang (total specimen length minus the remaining horizontal length of specimen at the conclusion of the test,Fig. 3), cm.11.4 Flexural Rigidity, Indiv
48、idual SpecimensCalculate the flexural rigidity for each testing direction to three significant digitsusing Eq 3.G5W3c3 (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 flexural rigidity us
49、ing Eq 4.Overall Flexural Rigidity 5(Gmachine direction 3Gcross machine direction)12 (4)Overall Flexural Rigidity 5Gmachine direction3Gcross machine direction!2 (4)11.6 Average ValuesCalculate the average bending length, flexural rigidity and overall flexural rigidity as applicable to amaterial specification or contract order for each laboratory sampling unit and for the lot, for each testing direction.11.7 Standard Deviation, Coeffcient of VariationCalculate when requested.12. Report12.1 Report t
