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~~ Designation: D 2938 - 86E' <br />• I, <br />Standard Test Method for <br />Unconfined Compressive Strength of Intact Rock Core <br />Specimens' <br />This standard is issued undo the fucd dmgnation D 2938; the numbs immediately fo8owio6 Ibe desigoauon iudinta the ynr of <br />arigrioal adoption or, io the tax of revision, the year of last rerision. A number in parnthera indintes the yev of lan rmpDroval. A <br />superscript epsilon (r) iodintes au edimrial change sins the last reridoo or rcapDroval. <br />e1 Nmr~ectiou 9 was addad cdimriaBY io Deermba 1991. <br />1. Scope <br />1.1 This tat method covets the determination of the <br />unconfined compressive strength of intact cylindrical rock <br />specimens. <br />1.2. The values stated in inch-pound units arc to be <br />regarded az the standazd. <br />1.3 This standard may involve hazardous materials, oper- <br />ations, and equipment. Thrs standard does not purpoK to <br />address all ojthe sajety problems associated with its use. It is <br />the responsibility of the user of this standard to establish <br />appropriate sajety and health practices and determine the <br />applicability ojregulatory limitations prior to use. <br />.Referenced Ilbcumeots <br />!.1 ASTM Standards <br />D 4543 Practice for Preparing Rock Core Specimens and <br />Determining Dimensional and Shape Toleranoes2 <br />E 4 Practices for Load Verification of Testing Machines3 <br />E 122 Practice for Choice of Sample Siff to Estimate the <br />Average Quality of a Lot or Process` <br />3. Apparatus <br />3.1 Loading Device, to apply and measure axial load on <br />the specimens, of su@icient capacity to apply load at a rate <br />conforming to the requirements set forth in 5.3. It shall be <br />verified at suitable time intervals in accordance with the <br />procedures given in Practices E 4, and comply with the <br />requirements prescribed therein. <br />3.2 Bearing Surfaces-The testing machine shall be <br />equipped with two steel beazing blocks having a Rockwell <br />hazdness of not less than IiRC 58 (Note l). One of the blocks <br />shall be spherically seated and the other a plain rigid block. <br />The bearing faces shall not depart from a plane by mote than <br />0.0005 in. (O.Ol3 mm) when the blocks are new and shall be <br />maintained within a permissible vaziation of 0.001 in. (0.025 <br />mm). The diameter of the spheritxlly seated bearing face <br />shall be at least as large az that of the tut specimen but shall <br />not exceed twice the diameter of the test specimen. The <br />center of the sphere for the spherically seated block shall <br />method is uada thcJm>sdictioo of ASTM Committer D-18 on Soil and <br />~ ;k and u the direct roponsilritiry of Suboommitter D18.I2 0o RorJ< MerLaoie <br />Qutem edition approved Oct 31, 1986. Published Deermber 1986. aigiaauy <br />published u D 2978 - 71. Isst previous ediuoo D 2938 - 79. <br />' Mnual Book ofASTM Srandardr, Vol 04.08. <br />s Annaaf Book of ASTM Srardardr, Vol 03.01. <br />• Annul Back of ASTM Srandardr. Vol 14.02. <br />coincide with the beazing face of the specimen. The movable <br />portion of the bearing block shall be held closely in the <br />spherical seat, but the design shall be such that the bearing <br />face can be rotated and tilted through small angles in any <br />rfirection. <br />Noce I-Parse platens, with plane bearing fear conforming to. the <br />requirements of this method may be usaL These shall consitt of disks <br />about th to ~/. in. (12.7 to 19.05 mm) thick, oil-hardened m mote than <br />HRC Sg, and sutfarx ground With abruive rocks, these platen tend to <br />roughen after a number of spaimens Gave been testa!, and 6ena need <br />m be resurfaced from time to time. <br />4. Tat Specimens <br />4.1 Prepare tat specimens in accordance with Practice <br />D 4543. <br />4.2 The moisture condition of the specimen at time of test <br />can have a significant effect upon the indicated strength of <br />the rock. Good practice generally dictates that laboratory <br />tests be made upon specimens representative of field condi- <br />tions. Thus it follows that the field moisture condition of the <br />specimen should be prtserved until time of test. On the other <br />hand, there may be reasons for testing spaamens at other <br />moisture contents including zero. In any case, .tailor the <br />moisture content of the test specimen to the problem at hand <br />and report it is accordance with 7.1.7. <br />5. Procedure <br />5.1 Check the ability of the spherical seat to rotate freely <br />in its socket before each test <br />5.2 Wipe clean the bearing faces of the upper and lower <br />bearing blocks and of the test specimen and place the test <br />specimen on the lower beating block. As the load is gradually <br />brought to beaz on the specimen, adjust the movable portion <br />of the spherically seated block so that uniform seating is <br />obtained. <br />5.3 Many rack types fail in a violent manner when loaded <br />to failure in compression. A protective shield should be <br />placed azound the test specimen ~to prevent injury from <br />flying rock Ctagments. <br />5.4 Apply the load continuously and without shock to <br />produce an approximately constant rate of load or deforma- <br />tion such that Cailure will occur within 5 to 15 min of <br />loading. <br />No7E 2-Results oC fists by several investigamts have shown that <br />strain rates wiWin this range will Drovide strength values that are <br />reasonably free of rapid loading elrects and reptoduable within accept- <br />able toleranar. <br />z7n <br />6. <br />spe <br />spe <br />lau <br />~. <br />h0: <br />fm <br />del <br />loc <br />din <br />get <br />din <br />at <br />dr} <br />COt <br />reE <br />az~ <br />5pe <br />tin <br />c <br />