1、Designation: D7864/D7864M 15Standard Test Method forDetermining the Aperture Stability Modulus of Geogrids1This standard is issued under the fixed designation D7864/D7864M; the number immediately following the designation indicates theyear of original adoption or, in the case of revision, the year o
2、f 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. Scope1.1 This test method covers the procedure for measuring the“Aperture Stability Modulus” of a geogrid. (The terms “Secant
3、Aperture Stability Modulus,” “Torsional Rigidity Modulus,”“In-plane Shear Modulus,” and “Torsional Stiffness Modulus”have been used in the literature to describe this same property.)1.2 This test method is intended to determine the in-planestability of a geogrid by clamping a center node and measuri
4、ngthe stiffness over an area of the geogrid. This test method isapplicable for various types of geogrid.1.3 This test method is intended to provide characteristicproperties for design. The test method was developed forpavement and subgrade improvement calibrated design meth-ods requiring input of ap
5、erture stability modulus.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 systems may resul
6、t 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 of regulatory li
7、mitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D4439 Terminology for GeosyntheticsD4354 Practice for Sampling of Geosynthetics and RolledErosion Control Products(RECPs) for Testing2.2 FHWA Document:3FHWA Geosynthetic Design and Construction Guidelines(2008)3. Terminology3.1 Defini
8、tions:3.1.1 For definitions of general terms used in this testmethod, refer to Terminology D4439.3.1.2 geogrid, na geosynthetic formed by a regular net-work of integrally connected elements with apertures greaterthan 6.35 mm 14 in. to allow interlocking with surroundingsoil, rock, earth, and other s
9、urrounding materials to primarilyfunction as reinforcement.3.1.3 index test, na test procedure which may contain aknown bias but which may be used to establish an order for aset of specimens with respect to property of interest.3.2 Definitions of Terms Specific to This Standard:3.2.1 aperturethe ope
10、nings between adjacent ribs formingan angle which enable soil interlocking to occur.3.2.2 aperture stability modulusa measure of the in-planetorsional stiffness of a geogrid. This is defined as torque,divided by the rotation at that torque.3.2.3 geosynthetic, na product manufactured from poly-meric
11、material used with soil, rock, earth, or other geotechnicalengineering material as integral part of a man made project,structure, or system.3.2.4 initial aperture stability modulus, nthe change inmoment at 0.5 and 1.0 N-m 4.4 and 8.8 lbf-in., respectively,divided by the change in angular rotation at
12、 these two momentvalues.3.2.5 junction, nthe point where geogrid ribs are intercon-nected to provide structure and dimensional stability.3.2.6 offset aperture stability modulusthe change in mo-ment at 2.0 and 2.5 N-m 17.7 and 22.1 lbf-in., respectively,divided by the change in angular rotation at th
13、ese two momentvalues.3.2.7 rib, nfor geogrids, the continuous oriented elementsof a geogrid which are interconnected to a node or junction.1This test method is under the jurisdiction of ASTM Committee D35 onGeosynthetics and is the direct responsibility of Subcommittee D35.01 on Mechani-cal Properti
14、es.Current edition approved June 1, 2015. Published July 2015. DOI: 10.1520/D7864_D7864M-152For 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 Su
15、mmary page onthe ASTM website.3Available from U.S. Department of Transportation, Federal HighwayAdministration, 1200 New Jersey Ave., SE, Washington, DC 20590, http:/www.fhwa.dot.gov.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States14.
16、Summary of Test Method4.1 A geogrid sample is placed over a square, horizontalopening and the edges are anchored just outside the opening.Arod is clamped vertically on the single center node or junction.A torque is applied to the rod, which twists the clamped nodeor junction and the geogrid rib matr
17、ix, thereby applying amoment causing bending to each of the ribs that intersects thesingle clamped center node or junction. The torque divided bythe angle of rotation is termed the Aperture Stability Modulusexpressed in units of N-m/degree lbf-in./degree.5. Significance and Use5.1 The Aperture Stabi
18、lity Modulus is a measure of thein-plane shear modulus, which is a function of other geogridcharacteristics, most notably junction stability, flexural ribstiffness, and rib tensile modulus.5.2 The test data can be used in conjunction with interpre-tive methods to evaluate the geogrid aperture stabil
19、ity atvarious traffic loads and base/subgrade conditions.NOTE 1Aperture stability modulus is referenced in the FHWAGeosynthetics Design and Construction Guidelines (2008) as an inputparameter for the design of geogrid-reinforced unpaved roads usingpunched and drawn biaxial geogrids. Geogrids of diff
20、erent manufacturingprocess and material composition may use this property in calibration andvalidation of their material within the associated design.5.3 This test method is not intended for routine acceptancetesting of geogrid. This test method should be used to charac-terize geogrid intended for u
21、se in applications in whichaperture stability is considered relevant.6. Apparatus6.1 The apparatus consists of a table, table clamps for theedges of the geogrid, a rod with a center clamp that attaches tothe ribs around a node or junction, a loading mechanism, anda method of measuring the moment and
22、 the angle of rotation ofthe rod. A cross section of the apparatus used originally todevelop the test method is shown in Figs. 1-4. Other methodsof clamping, applying a moment, loading, and measuring havebeen used by others and are acceptable, subject to the con-straints discussed in the following s
23、ubsections. Details of eachpart follow.6.1.1 TableThe table shall be constructed so that thegeogrid can be laid over a 229-mm 9-in.-square hole andanchored in place. The geogrid must be placed as it would bein the field, flat but not stretched. This requires a supportingplate beneath the geogrid and
24、 a loading plate over the geogridto keep it flat while it is being laid over the table and clampedaround the edges with table clamps. The plate must be largeenough to support every node or junction and any part of thegeogrid that tends to protrude above or below the planes of theFIG. 1 Test Apparatu
25、s during Test (Loading Plates and Weights Not Shown)D7864/D7864M 152tops and bottoms of the nodes or junction. The loading platemust cover the same nodes or junctions and be weighted withnot less than 100 N 22.5 lbf to sufficiently maintain thegeogrid flat during clamping. These plates must be remov
26、edbefore test loads are applied and the sample inspected to insurethat it is completely flat. No additional tensioning of thegeogrid should be done.6.1.2 Table ClampsClamps for the outside edges of thegeogrid. The table clamps should have smooth surfaces and berectangular in shape (Fig. 2). The tabl
27、e clamps hold the geogridribs firmly in place with respect to lateral movement at adistance of 8 mm 0.31 in. 6 6 mm 0.24 in. from the edgeof the hole. If the node or junction is more than 12.7 mm0.5 in. outside the hole then the rib must be clamped betweenthe node or junction and the edge of the hol
28、e. If the node orjunction is within 12.7 mm 0.5 in. of the edge of the hole, thenode or junction must be clamped. Each rib must be held sothat it does not move laterally more than 0.1 mm 0.004 in.during the test. The tension in some ribs may be very high,perhaps on the order of several thousand N se
29、veral hundredlbf for geogrids with high modulus values and large aperturesizes. The higher the Aperture Stability Modulus, the moreimportant it is that the clamps do not allow lateral movement.The direction of maximum movement will be in the generaldirection of the rib. If the clamped point moves mo
30、re than0.1 mm 0.004 in., the test should be discarded. Once confi-dence has been developed in a particular clamping techniquewith a particular geogrid, it will not be necessary to measurethe potential movement in every test. However, while devel-oping the clamping technique for a particular geogrid,
31、 theclamping efficiency must be checked. One method of doingthis is to measure the distance from the edge of the clamp to apoint close to the clamp on the rib. The clamping techniqueused to develop this test method was determined to be adequatefor the geogrids tested and is shown in Figs. 1 and 2. T
32、he tableclamps are made of steel bars with 9.5-mm 3/8-in. bolts with16 threads per 25 mm 1 in. on about 50 mm 2 in. spacing.The bolts were torqued to 13.5 N-m 120 lbf-in.6.1.3 Torqueing RodThe torquing rod must have a clampat one end to attach it to the ribs around the single center nodeor junction
33、of the geogrid. The rod must be supported so thatit does not apply a vertical force on the geogrid. In addition, therod must be held in a vertical orientation to avoid applying anout-of-plane torque to the geogrid structure. The same dis-placement is required on each rib. The clamp that connects the
34、torquing rod to the center node or junction is the center clamp.The center clamp is made of stainless steel and must apply ahorizontal force to each intersecting rib at a uniform distance of12.7 6 1.0 mm 0.5 6 0.04 in. from the center of the centernode or junction. The maximum torque expected is 2.5
35、 N-m22.1 lbf-in. Therefore, each contact point must be able toresist at least 250 N 55 lbf. The clamping method used todevelop the test method consists of two stainless steel metalblocks (center clamp) 35 6 0.5 mm 138 in. in diameter, witha central hole to clear the geogrid node of 15.5 6 0.5mm38 in
36、. and with a clamp bolt circle diameter of 25.4 6 0.5 mmFIG. 2 Details of Table Clamps and Supporting PlatesD7864/D7864M 153FIG. 3 Loading Plates and Weights Applied Prior to Clamping Specimens on Table ClampsFIG. 4 Torqueing Rod with Encoder Being Lock In-PlaceD7864/D7864M 15412 in. The two blocks
37、are held together with four or six sized8-32 socket head cap screws, 4.2 mm 0.164 in. bolts with 32threads per 25.4 mm 1 in. or 4-0.7 metric socket head capscrews, 4.0 mm diameter by 0.7 mm screw thread pitch. Thenumber of bolts shall be equal to the number of ribs that radiatefrom the node or junct
38、ion. The bolts are torqued to 0.5 N-m4.5 lbf-in. This method provides reproducible results with noapparent slippage. If the ribs are of a different thickness,length, special clamping mechanisms may have to be used. Ifinsufficient clamping force is used, or the ribs are not seatedagainst the four or
39、six clamping bolts prior to tightening theclamping bolts, then the ribs may slip in the clamp, which willnegate the test results. Clamps should not slip or damage thesingle center node or junction and the intersecting ribs.NOTE 2The bolts must be placed directly against the intersecting ribsin the d
40、irection that the torque will be applied. The bolts should bearagainst the ribs immediately as the torque is applied. The node or junctionmust be centered within the center clamp.6.1.4 Torqueing MechanismThe torquing mechanismmust be such that it can apply a clockwise torque (as viewedfrom the top o
41、f the device) of at least 2.5 N-m 22.1 lbf-in.The mechanism must be capable of applying the torque inincrements so that the torque can be held and readings taken atseveral torque levels between the minimum and maximumvalues. The torque must be accurate to within 62 % of thereading. The loading metho
42、d used to develop the test is shownin Fig. 4. It consists of attaching a sheave to the torquing rodand running a 0.9 mm 0.035 in. nylon-monofilament linearound the sheave and over pulleys to a dead-load bar under thetable. The total weight of the pulley assembly shall be200 6 5 g 7 oz. The sheave sh
43、all be approximately 100 mm4.00 in. in diameter, and a total of five 10 N 2.25 lbf weightsshall be applied to create the incremental loads.6.1.4.1 If the sheave is not exactly 100 mm in diameter theweights shall be adjusted to give torque increments of 0.5 60.01 N-m 4.4 6 0.09 lbf-in.6.2 Method of M
44、easuring the Angle or RotationThe angleof rotation of the vertical rod must be measured to within60.05 degree. There are many ways to measure the angle,including both mechanical and electrical devices. The mea-surement may be made on the rod or an extension of the rod,or it may be made on the moveme
45、nt of the loading mechanismor an extension of the loading mechanism. The result must bea measurement of the rotation of the rod. If there is significantdeformation between the points where the measurement istaken and the rotation of the rod, that deformation must beaccounted for by calibration and c
46、orrection. One obviousexample of this is that it would be possible to measure themovement of the weights in the loading system shown in Fig.1. If the nylon-monofilament line stretch or creep, there wouldbe an error created that must be considered in the calculation ofthe angle. Several methods of me
47、asuring the angles have beenused in the development of this test; each seemed to giveadequate results.7. Sampling, Test Specimens, and Test Units7.1 The test specimen shall be a representative sample ofgeogrid prepared as follows:7.1.1 Cut a square sample of geogrid with a node or junctionat the cen
48、ter. The size of the sample depends on the clampingmechanism used. It must be large enough to be properlyclamped, and yet not so large that the extra geogrid interfereswith the other parts of the testing apparatus. With the testapparatus used to develop the test, the samples were cut330 mm 13 in. sq
49、uare.7.1.2 Lab or field sampling of geogrid test specimens, orboth, should be performed in accordance with Practice D4354.All samples should be conditioned to standard laboratorytemperature of 20 6 2C 68 6 2F.8. Procedure8.1 Test Setup:8.1.1 Install the supporting plate so that it keeps the geogridflat during clamping.8.1.2 Place the sample over the supporting plate with onenode or junction at the center of the location of the clampingmechanism.8.1.3 Place the 229-mm 9-in. loading pl
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