1、Designation: D7748/D7748M13D7748/D7748M14 Standard Test Method for Flexural Rigidity of Geogrids, Geotextiles and Related Products 1 This standard is issued under the xed designation D7748/D7748M; the number immediately following the designation indicates the year of original adoption or, in the cas
2、e of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript epsilon () indicates an editorial change since the last revision or reapproval. 1. Scope 1.1 This test method covers the measurement of stiffness properties of geogrids, geotextiles
3、 and geogrid-geotextile composites all of which are referred to as geosynthetics within this test method. Bending length is measured and exural rigidity is calculated through use of the cantilever test procedure. 1.1.1 This test method employs the principle of cantilever bending of the geosynthetic
4、under its own mass. 1.2 This test method applies to geogrids, geotextiles and geogrid-geotextile composites. 1.3 Thistestmethodisformanufacturingqualitycontrolpurposesonly,toensureuniformityandconsistencyofexuralrigidity for a specic product from roll to roll and lot to lot. 1.4 The values stated in
5、 either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard. 1.5 T
6、his standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. 2. Referenced Docum
7、ents 2.1 ASTM Standards: 2 D123Terminology Relating to Textiles D1776Practice for Conditioning and Testing Textiles D4354Practice for Sampling of Geosynthetics and Rolled Erosion Control Products(RECPs) for Testing D4439Terminology for Geosynthetics E177Practice for Use of the Terms Precision and Bi
8、as in ASTM Test Methods E691Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method 3. Terminology 3.1 For common denitions of terms in this test method, refer to Terminology D123 and Terminology D4439. 3.2 Denitions of Terms Specic to This Standard: 3.2.1 bendin
9、g length, na measure of the interaction between geosynthetic weight and geosynthetic stiffness as shown by the way in which a geosynthetic bends under its own weight. 3.2.1.1 Discussion Bending length reects the stiffness of a geosynthetic when bent in one plane under the force of gravity. 1 Thistes
10、tmethodisunderthejurisdictionofASTMCommitteeD35onGeosyntheticsandisthedirectresponsibilityofSubcommitteeD35.01onMechanicalProperties. Current edition approved May 1, 2013Jan. 1, 2014. Published May 2013January 2014. Originally approved in 2012. Last previous edition approved in 20122013 as D774812D7
11、748/D7748M13. e1 . DOI: 10.1520/D7748_D7748M13.10.1520/D7748_D7748M14. 2 ForreferencedASTMstandards,visittheASTMwebsite,www.astm.org,orcontactASTMCustomerServiceatserviceastm.org.ForAnnualBookofASTMStandards volume information, refer to the standards Document Summary page on the ASTM website. This d
12、ocument is not anASTM standard and is intended only to provide the user of anASTM standard an indication of what changes have been made to the previous version. Because it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions a
13、s appropriate. In all cases only the current version of the standard as published by ASTM is to be considered the official document. Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States 14. Summary of Test Method 4.1 A specimen is slid at
14、a specied rate in a direction parallel to its long dimension, until its leading edge projects from the edgeofahorizontalsurface.Thelengthoftheoverhangismeasuredwhenthetipofthespecimenisdepressedunderitsownmass tothepointwherethelinejoiningthetoptotheedgeoftheplatformmakesa0.724radians41.5anglewithth
15、ehorizontal.From this measured length, the bending length and exural rigidity are calculated. 5. Signicance and Use 5.1 This test method is considered satisfactory for manufacturing quality control testing of a specic geosynthetic; however, caution is advised since information about between-laborato
16、ry precision is incomplete. Comparative tests as directed in 5.1.1 may be advisable. 5.1.1 In case of a dispute arising from differences in reported test results when using this test method for acceptance testing of commercial shipments, the purchaser and the supplier should conduct comparative test
17、s to determine if there is a statistical bias between their laboratories. Competent statistical assistance is recommended for the investigation of bias.As a minimum, the two parties should take a group of test specimens that are as homogeneous as possible and that are from a lot of material of the t
18、ype in question.Test specimens should then be randomly assigned in equal numbers to each laboratory for testing.The average results from the two laboratories should be compared using the appropriate statistical analysis and an acceptable probability level chosen by the two parties before testing is
19、begun. If a bias is found, either its cause must be found and corrected or the purchaser and the supplier must agree to interpret future test results with consideration 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
20、 twist at a cut edge. 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 specimen width. The tendency for specimens to curl or twist will affect the result, because of the rigidity provided at the edge. Consequently
21、, the edge effect is less of an issue for a wider strip. 6. Apparatus 6.1 Flexural Rigidity Tester (Fig. 1). 6.1.1 Horizontal Platform, with a minimum area of 100 by 900 mm 4 by 36 in. and having a smooth low-friction, at aluminum surface. A leveling bubble shall be incorporated in the platform. 6.1
22、.1.1 Indicator, inclined at an angle of 0.724 6 0.01 radians 41.5 6 0.5 below the plane of the platform surface. 6.1.1.2 MovableSlide,consistingofametalplatenotlessthan50by200mm2by8in.byapproximately3mm1/8in.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 me
23、asure the length of the overhangoverhang. 6.1.1.4 Specimen Feed Unit, motorized set to 120 mm/min 4.75 in./min 6 5 %, or manual equivalent. FIG. 1 Example Test Rig Setup D7748/D7748M 14 27. Sampling and Test Specimens 7.1 Lot SampleAs a lot sample for acceptance testing, randomly select the number o
24、f rolls or pieces of geosynthetic directed in an applicable material specication or other agreement between the purchaser and the supplier. Consider the rolls or pieces of geosynthetictobetheprimarysamplingunits.Intheabsenceofsuchanagreement,takethenumberofgeosyntheticrollsspecied in Practice D4354.
25、 7.2 For acceptance testing, take a swatch extending the width of the geosynthetic and approximately 2 m 6 ft along the machine direction from each roll or piece in the lot sample. For rolls of geosynthetic, take a sample that will exclude geosynthetic from the outer wrap of the roll or the inner wr
26、ap around the core of the roll of geosynthetic, or any end piece. 7.3 Direction of TestConsider the long dimension of the specimen as the direction of test. 7.4 Number of Test SpecimensFrom each laboratory sampling unit, take ve specimens from the machine direction and ve specimens from the cross-ma
27、chine direction as applicable to a material specication or contract order. 7.5 CuttingTestSpecimensCutthespecimenstobeusedforthemeasurementofmachinedirectionwiththelongerdimension paralleltothemachinedirection.Cutthespecimenstobeusedforthemeasurementofthecross-machinedirectionwiththelonger dimension
28、 parallel to the cross-machine direction. Label to maintain specimen identity. 7.5.1 Take specimens, representing a broad distribution across the width and length, preferably along the diagonal of the laboratory sample, and no nearer the edge than one-tenth its width. Ensure specimens are free of fo
29、lds, creases, or wrinkles.Avoid getting oil, water, 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 apertures in width or a minimum of 5 by 90 cm 6 0.1 cm minimum of 2 by 36 in. 6 0.04 in. 7
30、.5.2.1 It is important to cut the ribs of the specimens in both the width and the length direction exactly midway between junctions 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 6 0.1 cm 2 by 36 in. 6 0.04 in. 8.
31、Preparation of Test Apparatus and Calibration 8.1 Setthetesteronatableorbenchwiththehorizontalplatformandinclinedreferencelines.Adjusttheplatformtohorizontal as indicated by the leveling bubble. 8.1.1 Verify that the apparatus bend angle is at the 0.724 radians 41.5 angle. 9. Conditioning 9.1 For Ge
32、ogrids and Geogrid-geotextile CompositesDo not fold or bend the lab sample. If the lab sample must be obtained from roll inventory, it shall be conditioned by counter rolling and taping the cut specimens in the opposite direction of the curl for a minimum of 24 h within a laboratory exhibiting the p
33、roper atmosphere for testing geosynthetics. Counter roll specimen to a diameter that is not more than that of the diameter from the original manufactured roll. For most products a diameter of 150 mm 6 in. is adequate.Alternately, the sample can be conditioned by placing weights to restrain the speci
34、men in a at position for the 24-h period. 9.2 For GeotextilesPrecondition the specimens by bringing them to approximate moisture equilibrium in the standard atmosphere for preconditioning geotextiles as directed in Practice D1776, unless otherwise directed in a material specication or contract order
35、. 9.3 After preconditioning, bring the test specimens to equilibrium for testing in the standard atmosphere as, unless otherwise directed in a material specication or contract order. directed in Practice D1776 or, if applicable, in the specied atmosphere in which the testing is to be performed. 10.
36、Procedure 10.1 Test the conditioned specimens in the standard atmosphere for testing geosynthetics, which is 21 6 2C 70 6 4F and 50 to 70% 70 % relative humidity, unless otherwise directed in a material specication or contract order. 10.2 Remove the movable slide. Place the specimen on the horizonta
37、l platform with the length of the specimen parallel to the platform edge and the specimen face side up.Align the edge of the specimen with the line scribed on the right-hand edge of the horizontal platform. 10.2.1 Place the movable slide on the specimen, being careful not to change its initial posit
38、ion. 10.2.2 For automatic testers, turn the tester switch on and watch the leading edge of the specimen closely. Turn the switch off the instant the edge of the specimen touches the inclined portion of the tester. 10.2.3 Formanualtesters,movetheclampedspecimenbyhandinasmoothmanneratapproximately12cm
39、/min4.75in./min 6 5 % until the edge of the specimen touches the inclined portion of the tester, as shown in Fig. 2 and Fig. 3. 10.2.4 Read the overhang length by measuring the length still lying on the horizontal surface after the specimen has touched the inclined surface and subtracting that measu
40、rement from the initial specimen length. Record from the linear scale to the nearest 0.1 cm 0.1 in. D7748/D7748M 14 3NOTE 1If the specimen has a tendency to twist, take the reference point at the center of the leading edge. Do not measure specimens that twist more than 0.785 radian 45. 10.2.5 Test t
41、he face and back of both ends of each specimen for a total of four readings per specimen. 10.3 Specimen MassDetermine the geosynthetic mass per unit 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 cm 2 . FIG. 2 Test in Pr
42、ogress FIG. 3 Conclusion of Test D7748/D7748M 14 410.5 Number of SpecimensContinue as directed in 10.110.5 as applicable, until ve specimens have been tested for each testing direction for each laboratory sampling unit (A total of 20 readings for each direction). 11. Calculation 11.1 Length of Overh
43、ang, Individual SpecimensFor each specimen, average the ve readings obtained to the nearest 0.1 cm as the length of overhang, unless otherwise agreed upon between the purchaser and supplier. NOTE 2In some cases it may be of interest to differentiate between the sides of the geosynthetic by averaging
44、 those readings made with the geosynthetic 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/cm 2 using Eq 1. W=specimenmass/(specimenlength3specimenwidth) (1) 11.3 Bending Length, Individ
45、ual SpecimensCalculate the bending length for each testing direction to the nearest 1 mm, using Eq 2. c5O2 (2) where: c = bending length, cm, and 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
46、Rigidity, Individual SpecimensCalculate the exural rigidity for each testing direction to three signicant digits using Eq 3. G5W3c 3 (3) where: G = exural rigidity, mg-cm, W = geosynthetic mass per unit area, mg/cm 2 , and C = bending length, cm. 11.5 Overall Flexural RigidityCalculate the overall e
47、xural rigidity using Eq 4. OverallFlexuralRigidity 5 G machinedirection 3G crossmachinedirection !2 (4) 11.6 Average ValuesCalculate the average bending length, exural rigidity and overall exural rigidity as applicable to a material specication or contract order for each laboratory sampling unit and
48、 for the lot, for each testing direction. 11.7 Standard Deviation, Coeffcient of VariationCalculate when requested. 12. Report 12.1 Reportthatthestiffnessasbendinglength,exuralrigidityandoverallexuralrigidityweredeterminedasdirectedinTest Method D7748D7748/D7748M. Describe the material or product sa
49、mpled and the method of sampling used. 12.2 Report the following information for each laboratory sampling unit and for the lot as applicable to a material specication 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 exural rigidity. 12.2.5 When calculated, the average and standard deviation or the coefficient of variation. 12.2.6 Any mod
