ASTM_D_2936_-_08.pdf

Designation:D293608Standard Test Method forDirect Tensile Strength of Intact Rock Core Specimens1This standard is issued under the fixed designation D2936;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 parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope*1.1 This test method covers the determination of the directtensile strength of intact cylindrical rock specimens.1.2 The values stated in SI units are to be regarded asstandard.The values provided in parenthesis are for informa-tion only.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 practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2D2216 Test Methods for Laboratory Determination of Water(Moisture)Content of Soil and Rock by MassD3740 Practice for Minimum Requirements for AgenciesEngaged in Testing and/or Inspection of Soil and Rock asUsed in Engineering Design and ConstructionD4543 Practices for Preparing Rock Core as Cylindrical TestSpecimens and Verifying Conformance to Dimensionaland Shape TolerancesE4 Practices for Force Verification of Testing MachinesE122 Practice for Calculating Sample Size to Estimate,WithSpecified Precision,the Average for a Characteristic of aLot or Process3.Summary of Test Method3.1 A rock core sample is cut to length and its ends arecemented to metal caps.The metal caps are attached to atesting machine and the specimen is loaded in tension until itfails.4.Significance and Use4.1 Rock is much weaker in tension than in compression.Thus,in determining the failure condition for a rock structure,many investigators employ tensile strength of the componentrock as the failure strength for the structure.Direct tensilestressing of rock is the most basic test for determining thetensile strength of rock.5.Apparatus5.1 Loading Device,to apply and measure axial load on thespecimen,of sufficient capacity to apply the load at a rateconforming to the requirements of 8.2.The device shall beverified at suitable time intervals in accordance with theprocedures given in Practices E4 and shall comply with therequirements prescribed therein.5.2 CapsCylindrical metal caps that,when cemented tothe specimen ends,provide a means through which the directtensile load can be applied.The diameter of the metal capsshall not be less than that of the test specimen,nor shall itexceed the test specimen diameter by more than 1.10 times.Caps shall have a thickness of at least 30 mm(114in.).Capsshall be provided with a suitable linkage system for loadtransfer from the loading device to the test specimen.Thelinkage system shall be so designed that the load will betransmitted through the axis of the test specimen without theapplication of bending or torsional stresses.The length of thelinkages at each end shall be at least two times the diameter ofthe metal end caps.One such system is shown in Fig.1.NOTE1Roller of link chain of suitable capacity has been found toperform quite well in this application.Because roller chain flexes in oneplane only,the upper and lower segments should be positioned at rightangles to each other to effectively reduce bending in the specimen.Ball-and-socket,cable,or similar arrangements have been found to begenerally unsuitable as their tendency for bending and twisting makes theassembly unable to transmit a purely direct tensile stress to the testspecimen.6.Sampling6.1 Select the specimen from the cores to represent a validaverage of the type of rock under consideration.This can beachieved by visual observations of mineral constituents,grainsizes and shape,partings,and defects such as pores andfissures,or by other methods such as ultrasonic velocitymeasurements.1This test method is under the jurisdiction ofASTM Committee D18 on Soil andRock and is the direct responsibility of Subcommittee D18.12 on Rock Mechanics.Current edition approved July 1,2008.Published July 2008.Originally approvedin 1971.Last previous edition approved in 2004 as D2936 95(2004)1.DOI:10.1520/D2936-08.2For 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.*A Summary of Changes section appears at the end of this standardCopyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 7.Test Specimens7.1 PreparationPrepare test specimens in accordance withPractice D4543,except that the degree of flatness and smooth-ness of the specimen ends is not critical.End surfaces,such asresult from sawing with a diamond cutoff wheel,are entirel