1、Designation: D 7070 04Standard Test Method forCreep of Rock Core Under Constant Stress andTemperature1This standard is issued under the fixed designation D 7070; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revi
2、sion. 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 covers the creep behavior of intact softand hard rock core in fixed states of stress and temperature. Itspeci
3、fies the apparatus, instrumentation, and procedures fordetermining the strain as a function of time under sustainedload. Hard rocks are those with a maximum axial strain atfailure of less than 2 %. Soft rocks include such materials assalt and potash, which often exhibit very large strain at failure.
4、1.2 This standard replaces and combines the followingStandard Test Methods now to be referred to as Methods:Method A (D 5341 Creep of Hard Rock Core Specimensin Uniaxial Compression at Ambient/Elevated Temperatures);Method B (D 4405 Creep of Soft Rock Core Specimensin Uniaxial Compression at Ambient
5、 or Elevated Temperature);andMethod C (D 4406 Creep of Rock Core Specimens inTriaxial Compression at Ambient or Elevated Temperature).1.3 All observed and calculated values shall conform to theguidelines for significant digits and rounding established inPractice D 6026.1.3.1 The method used to speci
6、fy 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.1.3.2 The values stated in SI units are to be regard
7、ed as thestandard.1.4 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 to determine theapplicability of regulatory limitations prior to
8、use. For specificprecautionary statements, see Section 7.2. Referenced Documents2.1 ASTM Standards:2D 653 Standard Terminology Relating to Soil, Rock, andContained FluidsD 2113 Practice for Diamond Core Drilling for Site Inves-tigationD 2216 Test Method for Laboratory Determination of Water(Moisture
9、) Content of Soil and RockD 4543 Practice for Preparing Rock Core Specimens andDetermining Dimensional and Shape TolerancesD 5079 Practices for Preserving and Transporting RockCore SamplesD 6026 Practice for Using Significant Digits in Geotechni-cal DataE 4 Practices for Load Verification of Testing
10、 MachinesE 122 Practice for Choice of Sample Size to Estimate aMeasure of Quality for a Lot or Process3. Terminology3.1 Refer to Terminology D 653 for specific definitions.4. Summary of Test Method4.1 A section of rock is cut to length, and the ends aremachined flat to produce a cylindrical test spe
11、cimen. A uniaxialspecimen is placed in a loading frame. A triaxial specimen isplaced in a triaxial loading chamber and subjected to confiningpressure. If required, the specimen is heated to the desired testtemperature. Axial load is applied rapidly to the specimen andsustained. Deformation is monito
12、red as a function of elapsedtime.5. Significance and Use5.1 There are many underground structures that are createdfor permanent or long-term use. Often, these structures aresubjected to an approximately constant load. Creep testsprovide quantitative parameters for stability analysis of thesestructur
13、es.5.2 The deformation and strength properties of rock coresmeasured in the laboratory usually do not accurately reflectlarge-scale in situ properties, because the latter are stronglyinfluenced by joints, faults, inhomogeneities, weakness planes,and other factors. Therefore, laboratory values for in
14、tactspecimens must be employed with proper judgment in engi-neering applications.1This test method is under the jurisdiction of ASTM Committee and is the directresponsibility of Subcommittee D18.12 on Rock MechanicsCurrent edition approved Sept. 1, 2004. Published September 2004.2For referenced ASTM
15、 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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohoc
16、ken, PA 19428-2959, United States.NOTE 1Notwithstanding the statements on precision and bias con-tained in this test method; the precision of this test method is dependenton the competence of the personnel performing it, and the suitability of theequipment and facilities used. Agencies that meet the
17、 criteria of PracticeD 3740 are generally considered capable of competent and objectivetesting. Users of this test method are cautioned that compliance withPractice D 3740 does not in itself assure reliable testing. Reliable testingdepends on many factors; Practice D 3740 provides a means of evaluat
18、ingsome of these factors.6. Apparatus6.1 Loading DeviceThe loading device shall be of suffi-cient capacity to apply load at a rate conforming to therequirements specified in 10.6 and shall be able to maintain thespecified load within 2 %. It shall be verified at suitable timeintervals in accordance
19、with the procedures given in PracticesE 4 and comply with the requirements prescribed in this testmethod.NOTE 2By definition, creep is the time-dependent deformation underconstant stress. The loading device is specified to maintain constant axialload and therefore, constant engineering stress. The t
20、rue stress, however,decreases as the specimen deforms and the cross-sectional area increases.Because of the associated experimental ease, constant load testing isrecommended. However, the procedure permits constant true-stress test-ing, provided that the applied load is increased with specimen defor
21、mationso that true stress is constant within 2 %.6.2 Triaxial ApparatusThe triaxial apparatus shall consistof a chamber in which the test specimen may be subjected toa constant lateral fluid pressure and the required axial load. Theapparatus shall have safety valves, suitable entry ports forfilling
22、the chamber, and associated hoses, gages, and valves asneeded. Fig. 1 shows a typical test apparatus and associatedequipment.6.3 Triaxial Flexible MembraneThis membrane enclosesthe rock specimen and extends over the platens to preventpenetration by the confining fluid. A sleeve of natural orsyntheti
23、c rubber or plastic is satisfactory for room temperaturetests; however, metal or high-temperature rubber jackets suchas viton are usually required for elevated temperature tests. Themembrane shall be inert relative to the confining fluid and shallcover small pores in the sample without rupturing whe
24、nconfining pressure is applied. Plastic or silicone rubber coat-ings may be applied directly to the sample, provided thesematerials do not penetrate and strengthen the specimen. Caremust be taken to form an effective seal where the platen andFIG. 1 Test ApparatusD7070042specimen meet. Membranes form
25、ed by coatings shall besubject to the same performance requirements as elastic sleevemembranes.6.4 Triaxial Pressure-Maintaining DeviceA hydraulicpump, pressure intensifier, or other system of sufficient capac-ity to maintain constant the desired lateral pressure. Thepressurization system shall be c
26、apable of maintaining theconfining pressure constant to within 6 1 % throughout thetest. The confining pressure shall be measured with a hydraulicpressure gage or electronic transducer having an accuracy of atleast 61 % of the confining pressure, including errors due toreadout equipment, and a resol
27、ution of at least 0.5 % of theconfining pressure.6.5 Confining-Pressure FluidsFor room temperature tests,hydraulic fluids compatible with the pressure-maintainingdevice should be used. For elevated temperature tests the fluidmust remain stable at the temperature and pressure levelsdesignated for the
28、 test.6.6 Elevated-Temperature EnclosureThe elevated tem-perature enclosure may be either an enclosure that fits in theloading apparatus, an internal system that fits in the triaxialapparatus, or an external system encompassing the completetest apparatus. The enclosure may be equipped with humidityc
29、ontrol for testing specimens in which the moisture content isto be controlled. For high temperatures, a system of heaters,insulation, and temperature measuring devices are normallyrequired to maintain the specified temperature. Temperatureshall be measured at three locations, with one sensor near th
30、etop, one at midheight, and one near the bottom of the specimen.The average specimen temperature based on the midheightsensor shall be maintained to within 61C of the required testtemperature. The maximum temperature difference betweenthe midheight sensor and either end sensor shall not exceed3C whe
31、n measured under steady state temperature conditionsas defined in Section 6.6.NOTE 3An alternative to measuring the temperature at three locationsalong the specimen during the test is to determine the temperaturedistribution in a substitute specimen that has temperature sensors locatedin drill holes
32、 at a minimum of six positions: along both the centerline andspecimen periphery at midheight and at each end of the specimen. Thetemperature controller set point shall be adjusted to obtain steady-statetemperatures (see Section 10.5) in the substitute specimen that meet thetemperature requirements a
33、t each test temperature (the centerline tempera-ture at midheight shall be within 61C of the required test temperature,and all other specimen temperatures shall not deviate from this tempera-ture by more than 3C). The relationship between controller set point andsubstitute specimen temperature can b
34、e used to determine the specimentemperature during testing, provided that the output of the temperaturefeedback sensor (or other fixed-location temperature sensor in the triaxialapparatus) is maintained constant within 6 1C of the required testtemperature. The relationship between temperature contro
35、ller set point andsteady-state specimen temperature shall be verified periodically. Thesubstitute specimen is used solely to determine the temperature distribu-tion in a specimen in the triaxial apparatus; it is not to be used to determinecreep behavior.6.7 Temperature Measuring DeviceSpecial limits
36、-of-errorthermocouples or platinum resistance thermometers (RTDs)having accuracies of at least 61C with a resolution of 0.1C.6.8 PlatensTwo steel platens are used to transmit the axialload to the ends of the specimen. They shall have a hardness ofnot less than 58 HRC. One of the platens should be sp
37、hericallyseated and the other a plain rigid platen. The bearing faces shallnot depart from a plane by more than 0.015 mm when theplatens are new and shall be maintained within a permissiblevariation of 0.025 mm. The diameter of the spherical seat shallbe at least as large as that of the test specime
38、n but shall notexceed twice the diameter of the test specimen. The center ofthe sphere in the spherical seat shall coincide with that of thebearing face of the specimen. The spherical seat shall beproperly lubricated to ensure free movement. The movableportion of the platen shall be held closely in
39、the spherical seat,but the design shall be such that the bearing face can be rotatedand tilted through small angles in any direction. If a sphericalseat is not used, the bearing faces of the platens shall beparallel to 0.0005 mm/mm of platen diameter.6.8.1 Hard Rock SpecimensThe platen diameter shal
40、l beat least as great as the specimen but shall not exceed thespecimen diameter by more than 1.50 mm. This platen diam-eter shall be retained for a length of at least one-half thespecimen diameter.6.8.2 Soft Rock SpecimensThe platen diameter shall be atleast as great as the specimen but shall not ex
41、ceed the specimendiameter by more than 10 % of the specimen diameter. Becausesoft rocks can deform significantly in creep tests, it is importantto reduce friction in the platen-specimen interfaces to facilitaterelative slip between the specimen ends and the platens.Effective friction-reducing precau
42、tions include polishing theplaten surfaces to a mirror finish and attaching a thin, 0.15mmthick teflon sheet to the platen surfaces.6.9 Strain/Deformation Measuring DevicesThe strain/deformation measuring system shall measure the strain with aresolution of at least 25 3 10-6strain and an accuracy wi
43、thin2 % of the value of readings above 250 3 10-6strain andaccuracy and resolution within 5 3 10-6for readings lowerthan 250 3 10-6strain, including errors introduced by excita-tion and readout equipment. The system shall be free fromnoncharacterizable long-term instability (drift) that results inan
44、 apparent strain rate of 10-8/s.NOTE 4The user is cautioned about the influence of pressure andtemperature on the output of strain and deformation sensors located withinthe triaxial environment.6.9.1 Axial Strain DeterminationThe axial deformationsor strains may be determined from data obtained by e
45、lectricalresistance strain gages, compressometers, linear variable dif-ferential transformers (LVDTs), or other suitable means. Thedesign of the measuring device shall be such that the averageof at least two axial strain measurements can be determined.Measuring positions shall be equally spaced arou
46、nd the cir-cumference of the specimen close to midheight. The gagelength over which the axial strains are determined shall be atleast 10 grain diameters in magnitude.6.9.2 Lateral Strain DeterminationThe lateral deforma-tions or strains may be measured by any of the methodsmentioned in 6.9.1. Either
47、 circumferential or diametric defor-mations (or strains) may be measured. A single transducer thatwraps around the specimen can be used to measure the changein circumference. At least two diametric deformation sensorsshall be used if diametric deformations are measured. TheseD7070043sensors shall be
48、 equally spaced around the circumference of thespecimen close to midheight. The average deformation (orstrain) from the diametric sensors shall be recorded. Theaverage lateral strain may also be determined from dilatometricmeasurements of volumetric strain after accounting for theaxial strain compon
49、ent.NOTE 5The use of strain gage adhesives requiring cure temperaturesabove 65C is not allowed unless it is known that microfractures do notdevelop at the cure temperature.7. Hazards7.1 Danger exists near loading and triaxial testing equip-ment because of the high pressures and loads developed withinthe system. Elevated temperatures increase the risks of electri-cal shorts and fire. Test systems must be designed andconstructed with adequate safety factors, assembled withproperly rated fittings, and provided with protective shields toprotect people in the
