1、Designation: D5731 16Standard Test Method forDetermination of the Point Load Strength Index of Rock andApplication to Rock Strength Classifications1This standard is issued under the fixed designation D5731; the number immediately following the designation indicates the year oforiginal adoption or, i
2、n 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 guidelines, requirements,and procedures for determini
3、ng 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 either
4、 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 stren
5、gth over 15 MPa).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 dependent on t
6、he 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 D6026.1.6.1 The procedures
7、used to specify how data are collected/recorded and calculated in this standard are regarded as theindustry standard. In addition, they are representative of thesignificant digits that generally should be retained. The proce-dures used do not consider material variation, purpose forobtaining data, s
8、pecial purpose studies, or any considerationsfor the users objectives; and it is common practice to increaseor reduce significant digits of reported data to commensuratewith these considerations. It is beyond the scope of these testmethods to consider significant digits used in analysis methodsfor e
9、ngineering design1.7 The values stated in the SI units are to be regarded asstandard.1.8 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 an
10、d determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D653 Terminology Relating to Soil, Rock, and ContainedFluidsD2216 Test Methods for Laboratory Determination of Water(Moisture) Content of Soil and Rock by MassD3740 Practice for Minimum R
11、equirements for AgenciesEngaged in Testing and/or Inspection of Soil and Rock asUsed in Engineering Design and ConstructionD5079 Practices for Preserving and Transporting Rock CoreSamplesD6026 Practice for Using Significant Digits in GeotechnicalDataD7012 Test Methods for Compressive Strength and El
12、asticModuli of Intact Rock Core Specimens under VaryingStates of Stress and TemperaturesE18 Test Methods for Rockwell Hardness of Metallic Ma-terialsE122 Practice for Calculating Sample Size to Estimate, WithSpecified Precision, the Average for a Characteristic of aLot or Process2.2 ISRM Standard:Su
13、ggested Methods for Determining Point Load Strength31This 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 Dec. 1, 2016. Published January 2017. Originallyapproved in 1995. La
14、st previous edition approved in 2008 as D5731 08. DOI:10.1520/D5731-16.2For 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 AST
15、M website.3“Suggested Methods for Determining Point Load Strength”, InternationalSociety for Rock Mechanics Commission on Testing Methods, Int. J. Rock. Mech.Min. Sci. and Geomechanical Abstr., Vol 22, No. 2, 1985, pp. 5160.*A Summary of Changes section appears at the end of this standardCopyright A
16、STM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International St
17、andards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.13. Terminology3.1 DefinitionsFor definitions of common technical termsused in this standard refer to Terminology D653.3.2 Definitions of Terms Specific to This Standard:3.2.1 diame
18、ter, nD, for point load tests, the measureddimension of the specimen between the opposing conical testplatens when placed in the test machine3.2.2 point load strength anisotropy index, nIa(D), thestrength anisotropy index is defined as the ratio of mean Is(D)values measured perpendicular and paralle
19、l to planes of weak-ness. That is, the ratio of greatest to least point load strengthindices on different axes that result in the greatest and leastratio of point load strengths values.3.2.3 size-corrected point load strength index, nIs(D), theoriginal point load strength index value multiplied by a
20、 factorto normalize the value that would have been obtained withdiametral test of diameter (D).3.2.4 uncorrected point load strength index, n(Is), anindicator of strength (see 10.1) obtained by subjecting a rockspecimen to an increasingly concentrated point load, appliedthrough a pair of truncated,
21、conical platens, until failureoccurs.34. Summary of Test Method4.1 This index 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
22、 is used to calculate the point load strength index.4.2 The point load strength index can be used to classify therocks and provide a preliminary or reconnaissance-level evalu-ation of spatial variability in rock strength. A common methodused is by estimating the uniaxial compressive strength.5. Sign
23、ificance and Use5.1 The uniaxial compression test (see Test Method D7012)is used to determine compressive strength of rock specimens.However, it is a time-consuming and expensive test thatrequires significant specimen preparation and the results maynot be available for a long time after the samples
24、are collected.When extensive testing and/or timely information is needed forpreliminary and reconnaissance information, alternative testssuch as the point load test can be used to reduce the time andcost of compressive strength tests, when used in the field. Suchdata can be used to make timely and m
25、ore informed decisionsduring the exploration phases and more efficient and costeffective selection of samples for more precise and expensivelaboratory tests.5.2 The point load strength test is used as an index test forstrength classification of rock materials. The test results shouldnot be used for
26、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 anisotropy index.5.4 Rock specimens in the form of either core (the diametraland axial tests), cut blocks (the block test), or irregula
27、r 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 needed and can therefore be testedshortly after being obtained and any influence of moisturecondition on the test data minimized. However
28、, 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 specimens in accordance with PracticeD5079 and to document moisture conditions in some manner inthe data collection.NOTE 1The quality
29、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 that meet thecriteria of Practice D3740 are generally considered capable of competentand objective testing and sampling. Users of
30、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.6. Apparatus6.1 GeneralA basic point load tester (see Fig. 1) consistsof a loading sys
31、tem 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,D, between the two platen contact points at the start of testingand after failure. The equipment shall be resistant to shock andvibra
32、tion so that the accuracy of readings is not adverselyaffected by repeated testing. Any special operational, mainte-nance or calibrations instructions provided by the manufacturerfor the particular apparatus being used shall be followed.6.2 Loading System:6.2.1 The loading system shall have a loadin
33、g 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 opening size of the load frame, sothat an adjustable distance is available to accommodate bothsmall and large specimens.6.2.2 The loa
34、ding 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 constructed sothat it does not permanently distort during repe
35、ated 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 advised to avoid slippagewhen specimens of irregular geometry are tested.6.
36、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 carbide or hardened steel so they remain undamagedduring
37、 testing.NOTE 2It is generally accepted that specimens smaller than 42 mm(BX cores) are not recommended because for smaller diameters theD5731 162loading points cannot be considered as theoretical “points” in relation tospecimen size.46.3 Load Measuring System:6.3.1 A load measuring system, for exam
38、ple a load cell or ahydraulic pressure gage, that will indicate failure load, P,required to break specimen.6.3.2 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 Fail
39、ure is often sudden, therefore, and a peak loadindicator is needed so the failure load can be recorded aftereach test.6.3.4 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 strength
40、of 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 just
41、prior to failure.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” value when the two platens are in contact ands
42、hould 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 isneeded to measure the width, W, (with an accuracy of 65%)of specimens for all but the diametral test.6.5 Mis
43、cellaneous ItemsDepending on the type ofsamples (core or non-core) and the type of specimens to betested (diametral, Block, Axial, and alike), the following itemsmay be needed: diamond saw, chisels, towels, marking pens,and plotting paper.4Bieniawski, Z.T., The Point Load Test in Geotechnical Practi
44、ce, EngineeringGeology (9), pages 1-11, 1975.NOTE 1Load frame general information (Fig. 1):(1) Load is applied to the specimens through two standard hardened points(2) Two column fixed crosshead frame(3) Scale(4) Scale pointer(5) Bolt(6) Hydraulic pump body(7) Oil filler cap(8) Pump handle for hydra
45、ulic piston(9) Pressure release valve for hydraulic piston(10) Case latched for top cover(11) Digital pressure readout(12) Point load tester top coverFIG. 1 Example of a Light-Weight Point Load Test ApparatusD5731 1637. Samples7.1 Rock samples are grouped on the basis of rock type, testdirection if
46、rock is anisotropic, and estimated strength. Speci-mens are selected from each rock sample for testing. Given theinherent variability in test results, the quantity of specimenstested per sample should follow the guidance provided in 7.2.7.2 Sample Size:7.2.1 When testing core or block samples at lea
47、st tenspecimens are selected for each sample.7.2.2 When testing irregular-shaped specimens obtained byother means at least 20 specimens are selected for each sample.7.2.3 Sample sizes (number of specimens per sample) mayneed to be larger if the rock is anisotropic or heterogeneous.7.2.4 If needed, P
48、ractice E122 can be used to more preciselydetermine the sample size.7.3 Samples in the form of core are preferred for a moreprecise classification.7.4 For anisotropic rocks, better results are obtained for coresamples when the core axis is perpendicular to the plane ofweakness.8. Test Specimens8.1 T
49、est 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 and 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 cangenerate stress concentrations. No specimen preparation isneeded, however a rock saw or chisels may be advised forblock or irregular specimens. Proper planning of diametraltests on rock cor
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