1、Designation: D7070 08D7070 16Standard Test Methods forCreep of Rock Core Under Constant Stress andTemperature1This standard is issued under the fixed designation D7070; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of la
2、st 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 These test methods cover the creep behavior of intact softweak and hard rock core in fixed states of stress and tempera
3、ture.They at ambient (room) or elevated temperatures. For creep behavior at lower temperatures refer to Test Method D5520. Themethods specify the apparatus, instrumentation, and procedures for determining necessary to determine the strain as a function oftime under sustained load. Hard rocks are tho
4、se with a maximum axial strain at failure of less than 2 %. Soft rocks include suchmaterials as salt and potash, which often exhibit very large strain at failure.load at constant temperature and when applicable,constant humidity.1.1.1 Hard rocks are considered those with a maximum axial strain at fa
5、ilure of less than 2 %.Weak rocks include such materialsas salt, potash, shale, and weathered rock, which often exhibit very large strain at failure.1.2 This standard replaces and combines the following Standard Test Methods now to be referred to as Methods: consists ofthree methods that cover the c
6、reep capacity of core specimens.Method A (D5341 Creep of Hard Rock Core Specimens in Uniaxial Compression at Ambient/Elevated Temperatures);Method B (D4405 Creep of Soft Rock Core Specimens in Uniaxial Compression at Ambient or Elevated Temperature); andMethod C (D4406 Creep of Rock Core Specimens i
7、n Triaxial Compression at Ambient or Elevated Temperature).1.2.1 Method ACreep of Hard Rock Core Specimens in Uniaxial Compression at Ambient or Elevated Temperature.1.2.2 Method BCreep of Weak Rock Core Specimens in Uniaxial Compression at Ambient or Elevated Temperature.1.2.3 Method CCreep of Rock
8、 Core Specimens in Triaxial Compression at Ambient or Elevated Temperature.1.3 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in PracticeD6026.1.3.1 The method used to specify how data are collected, calculated, or recorded in this
9、standard is not directly related to theaccuracy to which the data can be applied in design or other uses, or both. How one applies the results obtained using this standardis beyond its scope.1.4 The procedures used to specify how data are collected/recorded and calculated in this standard are regard
10、ed as the industrystandard. In addition, they are representative of the significant digits that generally should be retained. The procedures used do notconsider material variation, purpose for obtaining data, special purpose studies, or any considerations for the users objectives; andit is common pr
11、actice to increase or reduce significant digits of reported data to commensurate with these considerations. It isbeyond the scope of these test methods to consider significant digits used in analysis methods for engineering design.1.5 UnitsThe values stated in SI units are to be regarded as the stan
12、dard. The values given in parentheses are mathematicalconversions to inch-pound units that are provided for information only and are not considered standard.1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user
13、of this standard to establish appropriate safety and health practices and to determine the applicability of regulatorylimitations prior to use. For specific precautionary statements, see Section 7.2. Referenced Documents2.1 ASTM Standards:2D653 Terminology Relating to Soil, Rock, and Contained Fluid
14、s1 This test method is under the jurisdiction of ASTM Committee D18 and is the direct responsibility of Subcommittee D18.12 on Rock Mechanics.Current edition approved July 1, 2008Nov. 1, 2016. Published August 2008November 2016. Originally approved in 2004. Last previous edition approved in 20042008
15、as D7070 04.D7070 - 08. DOI: 10.1520/D7070-08.10.1520/D7070-16.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM websit
16、e.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior e
17、ditions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2
18、959. United States1D2113 Practice for Rock Core Drilling and Sampling of Rock for Site ExplorationD2216 Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by MassD2845 Test Method for Laboratory Determination of Pulse Velocities and Ultrasonic Elastic Constants of
19、 RockD3740 Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used inEngineering Design and ConstructionD4543 Practices for Preparing Rock Core as Cylindrical Test Specimens and Verifying Conformance to Dimensional and ShapeTolerancesD5079 Practic
20、es for Preserving and Transporting Rock Core SamplesD5520 Test Method for Laboratory Determination of Creep Properties of Frozen Soil Samples by Uniaxial CompressionD6026 Practice for Using Significant Digits in Geotechnical DataE4 Practices for Force Verification of Testing MachinesE122 Practice fo
21、r Calculating Sample Size to Estimate, With Specified Precision, the Average for a Characteristic of a Lot orProcess3. Terminology3.1 Refer to Terminology D653 for specific definitions.Definitions:3.1.1 For definitions of common technical terms used in this standard, refer to Terminology D653.3.2 De
22、finitions of Terms Specific to This Standard:3.2.1 hard rockrock core exhibiting less than 2 % strain at failure when tested in uniaxial compression.3.2.2 weak rockrock core exhibiting 2 % or greater strain at failure when tested in uniaxial compression.3.2.3 true stressa constant stress applied to
23、a specimen as a result of a varying vertical load based upon changes in thespecimen diameter.4. Summary of Test Method4.1 A section of rock core is cut to length, and the ends are machined flat or are capped in a manner to produce a cylindricaltest specimen.4.2 For Methods A and B, (Uniaxial Compres
24、sion Method) the specimen is positioned onto a loading frame. A specified axialload is applied rapidly to the specimen and sustained throughout the test duration. The specimen may be subjected to an elevatedtemperature and/or constant humidity environment if so desired. The axial deformation is moni
25、tored as a function of elapsed time.The lateral deformation may also be monitored as a function of elapsed time if so desired.4.3 A section of rock core specimen is cut to length, and the ends are machined flat to produce a cylindrical test specimen. Forthe Uniaxial Compression Method,For Method C (
26、Triaxial Compression Method), the specimen is placed in a loading frame. ForTriaxial Compression Method, the specimen is placed in a triaxial loading chamber and subjected to confining pressure. If required,the specimen is heated to the desired test temperature.Axial load is applied rapidly into a t
27、riaxial chamber and then positioned ontoa loading frame. The specimen is subjected to a constant confining pressure. A specified axial load is rapidly applied to thespecimen and sustained. Deformation maintained throughout the test duration. If desired, the specimen, while positioned in thetriaxial
28、cell, can be subjected to elevated temperature. The axial deformation is monitored as a function of elapsed time. The lateraldeformation may also be monitored as a function of elapsed time if so desired.5. Significance and Use5.1 There are many underground structures that are createdconstructed for
29、permanent or long-term use. Often, these structuresare subjected to an approximatelya relatively constant load. Creep tests provide quantitative parameters for stability analysis ofthese structures.5.2 The deformation and strength properties of rock cores measured in the laboratory usually do not ac
30、curately reflectlarge-scale in situ properties, because the latter are strongly influenced by joints, faults, inhomogeneities, weakness planes, andother factors. Therefore, laboratory values for test results of intact specimens mustshall be employedutilized with proper judgmentin engineering applica
31、tions.NOTE 1Notwithstanding the The statements on precision and bias contained in this test method; the precision of this test method is dependent onthe competence of the personnel performing it, and the suitability of the equipment and facilities used. Agencies that meet the criteria of Practice D3
32、740are generally considered capable of competent and objective testing. Users of this test method are cautioned that compliance with Practice D3740 doesnot in itself assure reliable testing. Reliable testing depends on many factors; Practice D3740 provides a means of evaluating some of these factors
33、.6. Apparatus6.1 Loading DeviceThe loading device shall be of sufficient capacity to apply meet the requirements of the testing programand capable of applying the test load at a rate conforming to the requirements specified in 10.69.5 and . The device shall be ableto maintaincapable of maintaining t
34、he specified test load within 2 %. It shall be verified at suitable time intervals to within 62 %.D7070 162The force measurement device or load cell shall be calibrated in accordance with the procedures givenoutlined in PracticesPracticeE4 and comply with the requirements prescribed in thisfollowing
35、 the schedule provided in Practice D3740test method. .NOTE 2By definition, creep is the time-dependent deformation under constant stress. The loading device is specified to maintain constant axial loadand therefore, constant engineering stress. The true stress, however, decreases as the specimen def
36、orms and the cross-sectional area increases. Becauseof the associated experimental ease, constant load testing is recommended. However, the procedure permits constant true-stress testing, provided that theapplied load is increased with specimen deformation so that true stress is constant within 2 %.
37、62 %.6.2 Triaxial ApparatusThe triaxial apparatus shall consist of a chamber in which the test specimen may be is subjected to aconstant lateral fluidhydraulic pressure and the required axial load. The triaxial apparatus shall have safety valves, a workingpressure that exceeds the specified confinin
38、g stress. The triaxial apparatus shall have safety valves where applicable, suitable entryports for filling the chamber, and associated hoses, pressure gauges, and shutoff valves as needed.required. Fig. 1 shows a typicaltest apparatus and associated equipment.6.3 Triaxial Flexible MembraneThisThe m
39、embrane enclosesencases the rock specimen and extends over the platens toprevent penetration byinfiltration of the confining fluid. A sleeve of natural or synthetic rubber or plastic is satisfactory for roomtemperature tests; however, metal ambient (room) temperature tests. Metal or high-temperature
40、 rubber jackets such as viton areusuallynormally required for elevated temperature tests. The membrane shall be inert relative to the confining fluid and shall coversmall pores in the sample without rupturing when the confining pressure is applied. Plastic or silicone rubber coatings may beapplied d
41、irectly to the sample, provided these materials do not penetrate andor strengthen the specimen. Care must betakenexercised to form an effective seal where the platen and specimen meet. Membranes formed by coatings shall be subject tothe same performance requirements as elastic sleeve membranes.6.4 T
42、riaxial Pressure-Maintaining DeviceA hydraulic pump, pressure intensifier, or other system of sufficient capacity tomaintain constant the desired lateral pressure. The pressurization system shall be capable of maintaining the confining pressureconstant to within 61 % throughout the test. test durati
43、on. The confining pressure shall be measured with a hydraulic pressuregauge or electronic transducer and readout having an accuracy of at least 61 % of the confining pressure, including errors due toreadout equipment, pressure and a resolution of at least 0.5 % of the confining pressure.FIG. 1 Typic
44、al Triaxial Test ApparatusD7070 1636.5 Confining-Pressure FluidsFor room ambient (room) temperature tests, hydraulic fluids compatible with the pressure-maintaining device shouldshall be used. For elevated temperature tests the fluid mustshall remain stable at the temperature andpressure levels desi
45、gnated for the test.6.6 Elevated-Temperature EnclosureDeviceThe elevated temperature enclosuredevice may be either an enclosure that fitsin or over the loading apparatus, for Method A and B tests. For Method C (triaxial) tests an internal system that fits in the triaxialapparatus, or an external sys
46、tem encompassing the complete test apparatus. The enclosure triaxial cell or an enclosure thatcompletely encompasses the entire test apparatus may be used. The enclosure, used for Methods A and B, may be equipped withhumidity control for testing specimens in which the moisture content is to be contr
47、olled. For high temperatures, a system of heaters,insulation, and temperature measuring devices are normally required to maintain the specified temperature. Temperature shall bemeasured at three locations, with one sensor near the top, one at midheight, and one near the bottom of the specimen. The a
48、veragespecimen temperature based on the midheight sensor shall be maintained to within 61C of the required test temperature. Themaximum temperature difference between the midheight sensor and either end sensor shall not exceed 3C when measured understeady state temperature conditions as defined in S
49、ection 6.6.NOTE 3An alternative to measuring the temperature at three locations along the specimen during the test is to determine the temperature distributionin a substitute specimen that has temperature sensors located in drill holes at a minimum of six positions: along both the centerline and specimen peripheryat midheight and at each end of the specimen. The temperature controller set point shall be adjusted to obtain steady-state temperatures (see Section 10.5)in the substitute specimen that meet the temperature requirements at each test temperatur
