1、Designation: D7737 11Standard Test Method forIndividual Geogrid Junction Strength1This standard is issued under the fixed designation D7737; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in par
2、entheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method is an index test which provides aprocedure for determining the strength of an individual geogridjunction, also called a node. The t
3、est is configured such that asingle rib is pulled from its junction with a cross-rib to obtainthe maximum force, or strength of the junction. The procedureallows for the use of two different clamps with the appropriateclamp selected to minimize the influence of the clampingmechanism on the specific
4、type of geogrid to be tested.1.2 The values stated in SI units are to be regarded as thestandard.1.3 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
5、practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D4354 Practice for Sampling of Geosynthetics for TestingD4439 Terminology for GeosyntheticsD5262 Test Method for Evaluating the Unconfined TensionCreep and Creep Rupture Behav
6、ior of Geosynthetics3. Terminology3.1 Definitions of other terms applying to this test methodappear in Terminology D4439.3.2 Definitions:3.2.1 atmosphere for testing geosynthetics, nair main-tained at a relative humidity of 50 to 70 % and a temperatureof 21 6 2C (70 6 4F).3.2.2 breaking force, (F),
7、nthe force at failure.3.2.3 geogrid, nthe force at failure.3.2.4 integral, adja geosynthetic formed by a regularnetwork of integrally connected elements with aperturesgreater than 6.35 mm (14 inch) to allow interlocking withsurrounding soil, rock, earth, and other surrounding materialsto primarily f
8、unction as reinforcement. (D5262)3.2.5 index test, na test procedure which may containknown bias, but which may be used to establish an order for aset of specimens with respect to the property of interest.3.2.6 junction, nthe point where geogrid ribs are intercon-nected to provide structure and dime
9、nsional stability.3.2.7 rib, nfor geogrids, the continuous elements of ageogrid which are interconnected to a node or junction.3.2.8 rupture, nfor geogrids, the breaking or tearing apartof ribs.4. Summary of Test Method4.1 This standard proposes a test method for performingtension tests on geogrid j
10、unctions. The procedure provides twoclamping techniques for the junction to be tested including:MethodAin which the clamps firmly grip the ribs transverse tothe test direction on each side of the junction; and, Method Bin which the ribs transverse to the test direction are constrainedin a slot, cons
11、training rotation of the junction, while the rib inthe test direction passes through the slot without the junctionclamp applying confinement to the junction. The junctionclamping technique is selected for the specific type of geogridin order to minimize rotation and corresponding peal of thejunction
12、 during the test. The rib in the test direction goingthrough the junction is then clamped at a distance from thejunction and the system tensioned until junction (or rib) failureoccurs. This forces a tension or shear force to occur within thejunction in the direction of the applied load. The junction
13、 hasno normal pressure on it, i.e., it is horizontally unconfined.1This test method 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 Sept. 15, 2011. Published November 2011. DOI:
14、10.1520/D7731112For referenced ASTM standards, visit the ASTM website, www.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
15、 Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5. Significance and Use5.1 This index test method is to be used to determine thestrength of an individual junction in a geogrid product. The testis performed in isolation, while in service the junction istypically confined. Thus th
16、e results from this test method arenot anticipated to be related to design performance.5.2 The value of junction strength can be used for manu-facturing quality control, development of new products, or ageneral understanding of the in-isolation behavior of a particu-lar geogrids junction (for exampl
17、e., in relation to handlingduring shipment and placement of the geogrid).5.3 This test method is applicable to geogrid products withessentially orthogonal ribs, yarns or straps, that is, geogridswhich are composed of ribs, yarns or straps that are entangledthrough weaving or knitting, welded, bonded
18、 or formedthrough drawing.6. Apparatus6.1 The test apparatus for this method consists of threeparts; the tensile testing machine, the junction clamp and therib clamp.6.2 Tensile Testing Machine - The testing machine shouldoperate under a constant rate of extension. It should have thecapabilities of
19、measuring the tensile force, typically with a loadcell having an adequate load capacity to cover the full range ofproducts to be tested. The test recorder must be able toadequately record the complete force-elongation curve duringthe test.6.3 Method A: Junction Clamp (Rotation is Unconstrained)- The
20、 clamp assembly which holds the geogrid junction shallbe of the same design or equivalent to that shown in Fig. 1. Theclamp must only confine the horizontal rib on each side of thejunction and not the junction itself. The ribs transverse to thetest direction should be placed horizontally level such
21、thatFIG. 1 Typical Junction Strength Test Specimen Test Setup Rotation is not Constrained per Section 6.3D7737 112torsion is not applied to the junction. The clamp cannot hinderor influence the junction. The two movable parts of therestraining clamp should be adjustable to allow the bearingsurfaces
22、to fit snugly without touching the junction of thegeogrid product being tested. The clamp assembly shouldprovide the appropriate clamping power to prevent slipping orcrushing (damage) of the horizontal rib. The entire clampassembly is to be placed in the upper portion of the testingmachine.NOTE 1The
23、se clamps are particularly well suited for homogeneousextruded and woven geogrids with longitudinal ribs concentric withtransverse ribs.6.4 Method B: Junction Clamp (Rotation is Constrained) -The clamps according to Fig. 3 must only confine the horizon-tal rib on each side of the junction and not th
24、e junction itself.The clamps should continuously support the transverse rib tothe test direction such that torsion is not applied. The clampcannot hinder or influence the junction. The insert clamp shallfit snugly into the opening of the restraining clamp. Fig. 3aisfor geogrids with two straps welde
25、d together in one junction,FIG. 2 Typical Junction Strength Specimens for Various Geogrid ProductsD7737 113FIG. 3 Alternative Clamp for Constraining Rotation of the Geogrid Junction per Section 6.4D7737 114Fig. 3b is for geogrids with two horizontal straps welded to onevertical strap. The screws in
26、Fig. 3a and Fig. 3b are not neededif the insert clamp fits snugly into the opening of the restrainingclamp. The entire clamp assembly is to be placed in the upperportion of the testing machine. The dimensions of the insertclamp as stated in Fig. 3a and Fig. 3b should be as follows:a - average width
27、of vertical strap mm (readability 0.1mm) + 0.6 mmb-5-10mmc - average thickness of junction mm (readability 0.1mm) + 0.2 mmd - average thickness of vertical strap mm (readability 0.1mm) + 0.2 mmThe assembled configuration of these clamps is shown inFig. 4.NOTE 2These clamps are particularly well suit
28、ed for welded or strapgeogrids with longitudinal ribs not concentric with transverse ribs. Theyare also better suited than the unconstrained clamps for various woven andknit geogrids with transverse elements (that is, ribs or nodes) that tend torotate when tension is applied.6.5 Rib Clamp - The lowe
29、r portion of the vertical ribpassing through the clamp assembly is placed in a separateclamp at the base of the testing machine. This is typically thelongitudinal rib of the geogrid test specimen. The clamp mustbe sufficiently wide to grip the entire rib and must have theappropriate clamping power t
30、o prevent slipping or crushing(damage). The suggested style of clamp is a wedge action typeas used for a rib tensile strength test.NOTE 3It is also possible to reverse the positioning of the testassembly from that described in Sections 6.3 and 6.4. In such a case, thejunction clamp would be in the b
31、ase of the testing machine and the ribclamp in the crosshead adjacent to the load cell.7. Test Specimens7.1 The test specimen shape is unique to the particulargeogrid being tested. It generally involves specimens to be cutin the shape of a 9T9 with at least one junction remaining oneach side of the
32、junction being tested. See Fig. 2 for illustra-tions of some geogrid test specimens. For woven and knittedgeogrids where nodes may unravel when cut, adjacent ribs canbe cut away from the node as shown in Figure 2d to minimizethe effect of cutting on the structure of the product. Thespecimens should
33、be cut to allow for the maximum amount oftransverse rib on each side of the junction to be tested. Thecenter rib shall be long enough (typically a minimum of threebars or nodes), so as to allow for enough clamping actionwithin the rib clamp. The test specimens should be brought tostandard test condi
34、tions of temperatures 21 6 2C (70 6 4F)and tested under the same conditions. Relative humidity is notan issue for this test method.7.2 Number of test specimens:7.2.1 Reliable Estimate of vWhen there is a reliableestimate of v based upon extensive past records for similarmaterials tested in the users
35、 laboratory as directed in themethod, calculate the required number of specimens using Eq1, as follows:n 5 tv/A!2(1)where:n = number of test specimens (rounded upward to a wholenumber),v = reliable estimate of the coefficient of variation ofindividual observations on similar materials in theusers la
36、boratory under conditions of single-operatorprecision, %t = the value of Students t for one-sided limits, a 95 %probability level, and the degrees of freedom associ-ated with the estimate of v, and;A = 5.0 % of the average, the value of allowable variation.7.2.2 No Reliable Estimate of vWhen there i
37、s no reliableestimate of v for the users laboratory, Eq 1 should not be useddirectly. Instead, there should be ten (10) replicate specimenstested in the direction of concern. . This number of specimensis somewhat larger than usually found using a reliable estimateof v. When a reliable estimate of v
38、for the users laboratorybecomes available, Eq 1 will usually require fewer than thefixed number of specimens.8. Procedure8.1 Calibrate and balance the testing system.8.2 Install testing clamps; the junction clamp is typically theupper fixture and the rib clamp is then the lower fixture.8.3 Adjust th
39、e movable parts of the junction clamp to fit asclosely to the vertical center rib as possible, without touchingit or influencing it (that is, within 1 mm of the edge of thejunction).8.4 Mount the specimen carefully in the upper clamps,tighten it with sufficient force to prevent slipping or damage of
40、the specimen and see that its alignment is proper to mate withthe lower rib clamp.8.5 Mount the rib in the lower clamp so that bending ortorsion is avoided and the rib is positioned so as to beuniaxially tensioned with respect to the upper assembly.NOTE 4If Note 3 is followed, 8.4 and 8.5 would be r
41、eversed.8.6 Set the constant rate of extension of the test machine tobe 50 mm/min (2 in./min)8.7 Rebalance the test system and initiate the test by startingthe testing machine and continue until rupture occurs. Recordand report the maximum force obtained to cause failure.8.8 Repeat the above procedu
42、re for ten (10) representativetest specimens. Calculate the average junction strength per ribas described in the following section.9. Calculations9.1 From the resulting test data, the average junctionstrength per rib 9Javg9 is calculated;Javg5(151nJi/n (2)where:Javg= average junction strength per ri
43、b in kN (lb)Ji= test strength for each junction evaluated in kN (lb)n = number of specimens tested9.2 Using Javg, the average junction strength per unit width“Xjavg9 expressed in N/m (lbf/in.) is calculated;Xjavg5JavgNt(3)D7737 115FIG. 4 Entire Assembly for Constrained Rotation of the Geogrid Juncti
44、on per Section 6.4D7737 116where:Xjavg= average junction strength per unit width in N/m(lbf/in.)Nt= number of tensile elements in the testing directionper unit width, equal to Ncdivided by b in thedirection transverse to the rib being tested (seeNote 5).NOTE 5Ntis determined by taking the average of
45、 three measurementsfrom samples that are 95 % of the manufactured product roll width andsame equivalent length. The b value is determined by measuring thedistance from the central point of the starting aperture (center line tocenter line aperture dimension divided by 2) to the center point of theape
46、rture a distance equal to 95 % of the manufactured product roll widthaway from the starting aperture. As such, this measurement will result ina fractional value. The number of tensile elements, Nc, within thisdistance, b, are counted and Ntis determined by dividing the Ncvalue bythe b value. For mul
47、tiple layer geogrids, “b” should be measured using thesingle layer. The number of tensile elements, Nc, within this distance, “b”,are counted and multiplied by the number of layers found in the testspecimen10. Report10.1 Report the following information:10.1.1 Identification and description of geogr
48、id sample(s),10.1.2 The direction of testing,10.1.3 Any deviation of the specified test procedure,10.1.4 The type of junction clamp (that is., Method A orMethod B),10.1.5 The number of tests performed, and10.1.6 The average and standard deviation for the junctionstrength per width of geogrid (Xjave)
49、, recorded during thetesting program for each type of geogrid and direction ofconcern.10.1.7 If requested, a description of the way the sample wasprepared and the forceelongation curves for each test (with adescription of the type of failure that occurred) should also beincluded.10.1.8 The rib spacing used in the calculation of junctionstrength.11. Precision and Bias11.1 PrecisionNo precision and bias has been establishedfor this test standard.12. Keywords12.1 geogrid; geogrid rib; geogrid junction; geosynthetic;geotextile; index test; ten
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