1、Designation: D2936 08Standard 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
2、. 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
3、 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
4、 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 Testi
5、ng 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 Sam
6、ple 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 itfai
7、ls.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 basi
8、c 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 thepro
9、cedures 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 sp
10、ecimen, nor shall itexceed the test specimen diameter by more than 1.10 times.Caps shall have a thickness of at least 30 mm (114 in.). 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 l
11、oad 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.NOTE 1Roller of link chain of suitable capacit
12、y 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 beg
13、enerally 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
14、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 D
15、18.12 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 se
16、rviceastm.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. Uni
17、ted StatesNOTICE: This standard has either been superseded and replaced by a new version or withdrawn.Contact ASTM International (www.astm.org) for the latest information17. Test Specimens7.1 PreparationPrepare test specimens in accordance withPractice D4543, except that the degree of flatness and s
18、mooth-ness of the specimen ends is not critical. End surfaces, such asresult from sawing with a diamond cutoff wheel, are entirelyadequate. Grinding, lapping, or polishing beyond this pointserves no useful purpose, and in fact, may adversely affect theadhesion of the cementing medium.7.2 Water conte
19、nt of the specimen at the time of test canhave a significant effect upon the deformation of the rock.Good practice generally dictates that laboratory tests be madeupon specimens representative of field conditions. Thus, itfollows that the field water content of the specimen should bepreserved until
20、the time of test. On the other hand, there maybe reasons for testing specimens at other water contents,including zero. In any case, the water content of the testspecimen should be tailored to the problem at hand andreported in accordance with 10.1.6. If the water content of thespecimen is to be dete
21、rmined, follow the procedures given inTest Method D2216.7.3 If water content is to be maintained, and the elevatedtemperature enclosure is not equipped with humidity control,seal the specimen using a flexible membrane or apply a plasticor silicone rubber coating to the specimen sides.8. Procedure8.1
22、 Cement the metal caps to the test specimen to ensurealignment of the cap axes with the longitudinal axis of thespecimen (see Note 2). The thickness of the cement layershould not exceed 1.5 mm (116 in.) at each end. The cementlayer must be of uniform thickness to ensure parallelismbetween the top su
23、rfaces of the metal caps attached to bothends of the specimens. This should be checked before thecement is hardened (see Note 1) by measuring the length of theend-cap assembly at three locations 120 apart and near theedge. The maximum difference between these measurementsshould be less than 0.10 mm
24、(0.005 in.) for each 25.0 mm (1.0in.) of specimen diameter. After the cement has hardenedsufficiently to exceed the tensile strength of the rock, place thespecimen in the testing machine, making certain that the loadtransfer system is properly aligned.NOTE 2In cementing the metal caps to the test sp
25、ecimens, use jigs andfixtures of suitable design to hold the caps and specimens in properalignment until the cement has hardened. The chucking arrangement of amachine lathe or drill press is also suitable. Epoxy resin formulations ofrather stiff consistency and similar to those used as a patching an
26、d fillingcompound in automobile body repair work have been found to be asuitable cementing medium.8.2 Apply the tensile load continuously and without shockto failure. Apply the load or deformation at an approximatelyconstant rate such that failure will occur in not less than fivenor more than 15 min
27、. Note and record the maximum loadcarried by the specimen during the test.NOTE 3In this test arrangement failure often occurs near one of thecapped ends. Discard the results for those tests in which failure occurseither partly or wholly within the cementing medium.9. Calculation9.1 Calculate the ten
28、sile strength of the rock by dividing themaximum load carried by the specimen during the test by thecross-sectional area; express the result to the nearest 35.0 kPa(5 psi).10. Report10.1 Report the following information:10.1.1 Source of sample including project name and loca-tion, and if known, stor
29、age environment (often location isfrequently specified in terms of the borehole number and depthof specimen from the collar of the hole),10.1.2 Physical description of the sample including: rocktype, location and orientation of apparent planes, beddingplanes, and schistosity; and large inclusions or
30、 inhomogene-ities, if any,10.1.3 Date of sampling and testing,10.1.4 Specimen length and diameter, also conformancewith dimensional requirements,10.1.5 Rate of loading or deformation rate,10.1.6 General indication of water condition of sample attime of test, such as, as-received, saturated, laborato
31、ry air dry,or oven dry (it is recommended that the moisture condition bemore precisely determined when possible and reported aseither water content or degree of saturation,10.1.7 Direct tensile strength for each specimen as calcu-lated, average direct tensile strength of all specimens, standarddevia
32、tion, or coefficient of variation,10.1.8 Type and location of failure (a sketch of the fracturedspecimen is recommended), andFIG. 1 Direct Tensile-Strength Test AssemblyD2936 08210.1.9 Other available physical data.NOTE 4The number of specimens tested may depend upon theavailability of specimens, bu
33、t normally a minimum of ten is preferred. Thenumber of specimens tested should be indicated. The statistical basis forrelating the number of specimens to the variability of measurements isgiven in Practice E122.11. Precision and Bias11.1 PrecisionDue to the nature of the rock materialstested by this
34、 test method, it is, at this time, either not feasibleor too costly at this time to produce multiple specimens whichhave uniform mechanical properties. Therefore, since speci-mens which would yield the same test results cannot be tested,Subcommittee D18.12 cannot determine the variation betweentests
35、 since any variation observed is just as likely to be due tospecimen variation as to operator or laboratory testing varia-tion. Subcommittee D18.12 welcomes proposals to resolve thisproblem that would allow for development of a valid precisionstatement.11.2 BiasThere is no accepted reference value f
36、or this testmethod; therefore, bias cannot be determined.NOTE 5The quality of the result produced by this standard isdependent on the competence of the personnel performing it, and thesuitability of the equipment and facilities used. Agencies that meet thecriteria of Practice D3740 are generally con
37、sidered capable of competentand objective testing and sampling. Users of this standard are cautionedthat compliance with Practice D3740 does not in itself assure reliableresults. Reliable results depend on many factors; Practice D3740 providesa means of evaluating some of those factors.12. Keywords1
38、2.1 loading tests; rock; tension (tensile) properties/tests;tensile strengthSUMMARY OF CHANGESCommittee D18 has identified the location of selected changes to this standard since the last issue (D2936 95(2004)1) that may impact the use of this standard. (Approved July 1, 2008.)(1) Changed units stat
39、ement in 1.2.(2) Inserted reference to Practice D3740.(3) Changed jugs to jigs in Note 2.(4) Inserted Note 5.(5) Inserted Fig. 1.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard ar
40、e expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not
41、revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which yo
42、u may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United
43、 States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).D2936 083
