1、Designation: D 5731 07Standard Test Method forDetermination of the Point Load Strength Index of Rock andApplication to Rock Strength Classifications1This standard is issued under the fixed designation D 5731; the number immediately following the designation indicates the year oforiginal adoption or,
2、 in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This test method covers the guidelines, requirements,and procedures for determ
3、ining the point load strength index ofrock. This is an index test and is intended to be used to classifyrock strength.1.2 Specimens in the form of rock cores, blocks, or irregularlumps with a test diameter from 30 to 85 mm can be tested bythis test method.1.3 This test method can be performed in eit
4、her the field orlaboratory. The test is typically used in the field because thetesting machine is portable, little or minimal specimen prepa-ration is required, and specimens can be tested within a shorttime frame of being collected.1.4 This test method applies to medium strength rock(compressive st
5、rength over 15 MPa (2200 psi).1.5 This test method does not cover which type of specimenshould be tested or whether anisotropic factors should beconsidered. The specifics of the point load test program need tobe developed prior to testing and possibly even before sam-pling. Such specifics would be d
6、ependent on the intended useof the data, as well as possible budgetary constraints andpossible other factors, which are outside the scope of this testmethod.1.6 All observed and calculated values shall conform to theguidelines for significant digits and rounding established inPractice D 6026.1.7 The
7、 method used to specify how data are collected,calculated, or recorded in this standard is not directly related tothe accuracy to which the data can be applied in design or otheruses, or both. How one applies the results obtained using thisstandard is beyond its scope.1.8 The values stated in the SI
8、 units are to be regarded asstandard.1.9 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 lim
9、itations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 653 Terminology Relating to Soil, Rock, and ContainedFluidsD 2216 Test Methods for Laboratory Determination of Wa-ter (Moisture) Content of Soil and Rock by MassD 3740 Practice for Minimum Requirements for AgenciesEngaged in the Test
10、ing and/or Inspection of Soil and Rockas Used in Engineering Design and ConstructionD 5079 Practices for Preserving and Transporting RockCore SamplesD 6026 Practice for Using Significant Digits in Geotechni-cal DataD 7012 Test Method for Compressive Strength and ElasticModuli of Intact Rock Core Spe
11、cimens under VaryingStates of Stress and TemperaturesE18 Test Methods for Rockwell Hardness and RockwellSuperficial Hardness of Metallic MaterialsE 122 Practice for Calculating Sample Size to Estimate,With a Specified Tolerable Error, the Average for aCharacteristic of a Lot or Process2.2 ISRM Stand
12、ard:Suggested Methods for Determining Point Load Strength33. Terminology3.1 For definitions of terms used in this test method refer toTerminology D 653.3.2 Definitions of Terms Specific to This Standard:3.2.1 diameterD, for point load tests, the dimension ofthe specimen between the opposing conical,
13、 test platens whenplaced in the test machine3.2.2 point load strength anisotropy indexIa(D), thestrength anisotropy index is defined as the ratio of mean Is (D)values measured perpendicular and parallel to planes of weak-ness, that is, the ratio of greatest to least point load strength1This test met
14、hod 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 Feb. 1, 2007. Published April 2007. Originallyapproved in 1995. Last previous edition approved in 2005 as D 573105.2For referenced AST
15、M 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.3“Suggested Methods for Determining Point Load Strength”, InternationalSociety f
16、or Rock Mechanics Commission on Testing Methods, Int. J. Rock. Mech.Min. Sci. and Geomechanical Abstr., Vol 22, No. 2, 1985, pp. 5160.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,
17、 United States.indices on different axes that result in the greatest and leastratio of point load strengths values.3.2.3 size-corrected point load strength indexIs (D), theoriginal point load strength index value multiplied by a factorto normalize the value that would have been obtained withdiametra
18、l test of diameter (D).3.2.4 uncorrected point load strength index(Is), an indi-cator of strength (see 10.1) obtained by subjecting a rockspecimen to an increasingly concentrated point load, appliedthrough a pair of truncated, conical platens, until failureoccurs.34. Summary of Test Method4.1 This i
19、ndex test is performed by subjecting a rockspecimen to an increasingly concentrated load until failureoccurs by splitting the specimen. The concentrated load isapplied through coaxial, truncated conical platens. The failureload is used to calculate the point load strength index.4.2 The point load st
20、rength index can be used to classify therocks. A common method used is by estimating the uniaxialcompressive strength.5. Significance and Use5.1 The uniaxial compression test (see Test Method D 7012)is used to determine compressive strength of rock specimens.However, it is a time-consuming and expen
21、sive test thatrequires significant specimen preparation and the results maynot be available for a long time after the samples are collected.When extensive testing and/or timely information is requiredfor preliminary and reconnaissance information, alternativetests such as the point load test can be
22、used to reduce the timeand cost of compressive strength tests, when used in the field.Such data can be used to make timely and more informeddecisions during the exploration phases and more efficient andcost effective selection of samples for more precise andexpensive laboratory tests.5.2 The point l
23、oad strength test is used as an index test forstrength classification of rock materials. The test results shouldnot be used for design or analytical purposes.5.3 This test method is performed to determine the pointload strength index of rock specimens and, if required, thepoint load strength anisotr
24、opy index.5.4 Rock specimens in the form of either core (the diametraland axial tests), cut blocks (the block test), or irregular lumps(the irregular lump test) are tested by application of concen-trated load through a pair of truncated, conical platens. Little orno specimen preparation is required
25、and can therefore be testedshortly after being obtained and any influence of moisturecondition on the test data minimized. However, the results canbe highly influenced by how the specimen is treated from thetime it is obtained until the time it is tested. Therefore, it maybe necessary to handle spec
26、imens in accordance with PracticeD 5079 and to document moisture conditions in some mannerin the data collection.NOTE 1The quality of the result produced by this standard isdependent upon the competence of the personnel performing it, and thesuitability of the equipment and facilities used. Agencies
27、 that meet thecriteria of Practice D 3740 are generally considered capable of competentand objective testing and sampling. Users of this standard are cautionedthat compliance with Practice D 3740 does not in itself assure reliableresults. Reliable results depend on many factors; Practice D 3740 prov
28、idesa means of evaluating some of those factors.6. Apparatus6.1 GeneralA basic point load tester (see Fig. 1) consistsof a loading system typically comprised of a loading frame,platens, a measuring system for indicating load, P, (required tobreak the specimen), and a means for measuring the distance
29、,D, between the two platen contact points at the start of testingand after failure. The equipment shall be resistant to shock andvibration so that the accuracy of readings is not adverselyaffected by repeated testing. Any special operational, mainte-nance or calibrations instructions provided by the
30、 manufacturerfor the particular apparatus being used shall be followed.6.2 Loading System:6.2.1 The loading system shall have a loading frame with aplaten-to-platen clearance that allows testing of rock specimensin the required size range. Typically, this range is between 30to 100 mm, or the maximum
31、 opening size of the load frame, sothat an adjustable distance is available to accommodate bothsmall and large specimens.NOTE 2It is generally accepted that specimens smaller than 42 mm(BX cores) are not recommended because for smaller diameters theloading points can not be considered as theoretical
32、 “points” in relation tospecimen size.46.2.2 The loading capacity shall be sufficient to break thelargest and strongest specimens to be tested. Point loadstrength of rock is usually an order of magnitude lower than thecompressive strength of rock.6.2.3 The load frame shall be designed and constructe
33、d sothat it does not permanently distort during repeated applica-tions of the maximum test load, and so that the platens remaincoaxial within 60.2 mm throughout testing. No spherical seator other nonrigid component is permitted in the loadingsystem. Loading system rigidity is essential to avoid slip
34、pagewhen specimens of irregular geometry are tested.6.2.4 Truncated, conical platens, as shown on Fig. 2, are tobe used. The 60 cone and 5-mm radius spherical platen tipshall meet tangentially. The platens shall be of hard material(Rockwell 58 HRC, as explained in Test Method E18) such astungsten ca
35、rbide or hardened steel so they remain undamagedduring testing.6.3 Load Measuring System:6.3.1 A load measuring system, for example a load cell or ahydraulic pressure gage, that will indicate failure load, P,required to break specimen. The system should conform to therequirements of 6.3.2-6.3.4.6.3.
36、2 Measurements of failure load, P, shall be to a preci-sion of 65 % or better of full-scale load-measuring system,irrespective of the size and strength of specimen that is tested.6.3.3 Failure is often sudden, therefore, and a peak loadindicator is required so the failure load can be recorded aftere
37、ach test.4Bieniawski, Z.T., The Point Load Test in Geotechnical Practice, EngineeringGeology (9), pages 1-11, 1975.D57310726.3.4 If required, the system should be capable of usinginterchangeable, mechanical or electronic gauge, load measur-ing devices in order to be consistent with the estimated str
38、engthof rock and have the desired reading accuracy.6.4 Distance Measuring System:6.4.1 The distance measuring system, an electronic or ver-nier direct reading scale, should connect to the loading framefor measuring the distance, D, between specimen-platen con-tact points at the start of testing and
39、just prior to failure andconform to requirements 6.4.2 and 6.4.3.6.4.2 Measurements of D shall be to an accuracy of 62%or better of distance between contact points, irrespective of thesize and strength of specimen that is tested.6.4.3 The measuring system shall allow a check of the “zerodisplacement
40、” value when the two platens are in contact andshould include a zero adjustment and a means to record ormeasure any penetration of the specimen by the point loadplatens during testing.6.4.4 An instrument such as a caliper or a steel rule isrequired to measure the width, W, (with an accuracy of 65%)o
41、f specimens for all but the diametral test.6.5 Miscellaneous ItemsDepending on the type ofsamples (core or non core) and the type of specimens to betested (diametral, Block, Axial, etc.), the following items maybe needed: diamond saw, chisels, towels, marking pens, andplotting paper.7. Test Samples7
42、.1 Rock samples are grouped on the basis of rock type, testdirection if rock is aniasotropic, and estimated strength.7.2 Sample Size7.2.1 When testing core or block samples at least tenspecimens are selected for the samples.7.2.2 When testing irregular-shaped specimens obtained byother means at leas
43、t 20 specimens are selected for the samples.7.2.3 Sample sizes may need to be larger if the rock isanisotropic or heterogeneous.7.2.4 If needed, Practice E 122 can be used to more pre-cisely determine the sample size.7.3 Samples in the form of core are preferred for a moreprecise classification.7.4
44、For anisotropic rocks the best results for core samples iswhen the core axis is perpendicular to the plane of weakness.8. Test Specimens8.1 Test DiameterThe specimens external test diametershall not be less than 30 mm and not more than 85 mm with thepreferred test diameter of about 50 mm.8.2 Size an
45、d ShapeThe size and shape requirements fordiametral, axial, block, or irregular lump testing shall conformwith the recommendations shown on Fig. 3. The sides of thespecimens shall be free from abrupt irregularities that canNOTELoad frame general information (figure 1)Load is applied to thespecimens
46、through two standard hardened points (1)Two column fixedcrosshead frame (2)Scale (3)Scale pointer (4)Attached by a bolt (5) to thehydraulic pump body (6)Oil filler cap (7)The hydraulic piston assemblyincorporated the oil reservoir, a single acting pump, pressure relief valve(9), and a handle (8)Pump
47、 handle (8)Pressure release valve (9)Caselatched for top cover (10)Digital pressure readout (11)Point load tester topcover(12)FIG. 1 Example of a Light-Weight Point Load Test ApparatusD5731073FIG. 2 Truncated, Conical Platen Dimensions for Point LoadApparatusNOTE 1Legend: L = distance between contac
48、t points and nearest free face, and De= equivalent core diameter (see 10.1).FIG. 3 Load Configurations and Specimen Shape Requirement for (a) the Diametral Test, (b) the Axial Test, (c) the Block Test, and (d)the Irregular Lump Test3D5731074generate stress concentrations. No specimen preparation isr
49、equired, however a rock saw or chisels may be required forblock or irregular specimens. Proper planning of diametraltests on rock cores can produce suitable lengths of core forsubsequent axial testing provided they are not weakened by thediametral test. Otherwise, suitable specimens can be obtainedfrom the cores by saw-cutting, or core splitting.NOTE 3While there are no established specimen guidelines for grainsize versus specimen size this subject is still important and must beincluded in the testing and use of the data. Concrete testing using a pointload tester rec
