ASTM_D_2938_-_95_2002.pdf

Designation:D 2938 95(Reapproved 2002)Standard Test Method forUnconfined Compressive Strength of Intact Rock CoreSpecimens1This standard is issued under the fixed designation D 2938;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(e)indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method specifies the apparatus,instrumenta-tion,and procedures for determining unconfined compressivestrength of intact rock core specimens.1.2 The values stated in inch-pound units are to be regardedas the standard.The SI values given in parentheses are forinformation 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:D 2216 Test Method for Laboratory Determination of Water(Moisture)Content of Soil and Rock2D 4543 Practice for Preparing Rock Core Specimens andDetermining Dimensional and Shape Tolerances2E 4 Practices for Load Verification of Testing Machines3E 122 Practice for Choice of Sample Size to Estimate theAverage Quality of a Lot or Process43.Summary of Test Method3.1 A rock core sample is cut to length and the ends aremachined flat.The specimen is placed in a loading frame and,if required,heated to the desired test temperature.Axial load iscontinuously increased on the specimen until peak load andfailure are obtained.4.Significance and Use4.1 Unconfined compressive strength of rock is used inmany design formulas and is sometimes used as an indexproperty to select the appropriate excavation technique.4.2 The strength of rock cores measured in the laboratoryusually do not accurately reflect large-scale in situ propertiesbecause the latter are strongly influenced by joints,faults,inhomogeneities,weakness planes,and other factors.There-fore,laboratory values for intact specimens must be employedwith proper judgement in engineering applications.5.Apparatus5.1 Loading Device,of sufficient capacity to apply load at arate conforming to the requirements set forth in 9.5.It shall beverified at suitable time intervals in accordance with theprocedures given in Practices E 4,and comply with therequirements prescribed therein.The loading device may beequipped with a displacement transducer that can be used toadvance the loading ram at a specified rate.5.2 Elevated-Temperature EnclosureThe elevated tem-perature enclosure may be either an enclosure that fits in theloading apparatus or an external system encompassing thecomplete test apparatus.The enclosure may be equipped withhumidity control for testing specimens in which the moisturecontent is to be controlled.For high temperatures,a system ofheaters,insulation,and temperature measuring devices arenormally required to maintain the specified temperature.Tem-perature shall be measured at three locations,with one sensornear the top,one at midheight,and one near the bottom of thespecimen.The average specimen temperature based on themidheight sensor shall be maintained to within 61C of therequired test temperature.The maximum temperature differ-ence between the midheight sensor and either end sensor shallnot exceed 3C.NOTE1An Alternative to measuring the temperature at three loca-tions along the specimen during the test is to determine the temperaturedistribution in a dummy specimen that has temperature sensors located indrill holes at a minimum of six positions:along both the centerline andspecimen periphery at midheight and each end of the specimen.Thetemperature controller set point shall be adjusted to obtain steady-statetemperatures in the dummy specimen that meet the temperature require-ments at each test temperature(the centerline temperature at midheightshall be within 61C of the required test temperature,and all otherspecimen temperatures shall not deviate from this temperatures by morethan 3C).The relationship between controller set point and dummyspecimen temperature can be used to determine the specimen temperatureduring testing provided that the output of the temperature feedback sensor1This method is under the jurisdiction of ASTM Committee D18 on Soil andRock and is the direct responsibility of Subcommittee D18.12 on Rock Mechanics.Current edition approved June 15,1995.Published July 1995.Originallypublished as D 2938 71.Last previous edition D 2938 86e1.2Annual Book of ASTM Standards,Vol 04.08.3Annual Book of ASTM Standards,Vol 03.01.4Annual Book of ASTM Standards,Vol 14.02.1Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959,United States.(or other fixed-location temperature sensor in the triaxial apparatus)ismaintained constant within 61C of the r