ASTM_D_7864_-_D_7864M_-_15.pdf

Designation:D7864/D7864M15Standard 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 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.Scope1.1 This test method covers the procedure for measuring the“Aperture Stability Modulus”of a geogrid.(The terms“SecantAperture 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 measuringthe 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 aperture 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 result 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 limitations 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 Definitions: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 14in.to allow interlocking with surroundingsoil,rock,earth,and other surrounding 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 openings 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 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 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 these 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 Properties.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 Summary 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 States1 4.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 matrix,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