1、Designation: D 5335 08Standard Test Method forLinear Coefficient of Thermal Expansion of Rock UsingBonded Electric Resistance Strain Gauges1This standard is issued under the fixed designation D 5335; the number immediately following the designation indicates the year oforiginal adoption or, in the c
2、ase 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 laboratory determination ofthe linear (one-dimensional) coef
3、ficient of thermal expansionof rock using bonded electric resistance strain gauges.1.2 This test method is applicable for unconfined pressureconditions over the temperature range from 20 to 260C (68 to500F).NOTE 1Unconfined tests performed at elevated temperatures mayalter the mineralogy or grain st
4、ructure of the test specimen. This alterationmay change the physical and thermal properties of the test specimen.NOTE 2The strain gauges are mounted with epoxy. Most commer-cially available high temperature epoxies require elevated temperaturecuring. The elevated temperature required for this curing
5、 may alter thephysical and thermal properties of the test specimen. Epoxy should beselected based upon the maximum expected test temperature. Roomtemperature curing epoxy should be used whenever possible.1.3 The test specimens may be either saturated or dry. Ifsaturated specimens are used, then the
6、test temperature shall beat least 10C (18F) less than the boiling point of the saturatingfluid in order to minimize the effects of evaporation of thefluid.NOTE 3When testing a saturated specimen, the moisture content ofthe specimen may change unless special precautions are taken to encap-sulate the
7、test specimen. Refer to 7.4.1.4 For satisfactory results in conformance with this testmethod, the principles governing the size, construction, anduse of the apparatus described in this test method should befollowed. If the results are to be reported as having beenobtained by this test method, then a
8、ll pertinent requirementsprescribed in this test method shall be met.1.5 It is not practicable in a test method of this type to aimto establish details of construction and procedure to cover allcontingencies that might offer difficulties to a person withouttechnical knowledge concerning the theory o
9、f heat flow,temperature measurement, and general testing practices. Stan-dardization of this test method does not reduce the need forsuch technical knowledge. It is recognized also that it would beunwise, because of the standardization of this test method, toresist in any way the further development
10、 of improved or newmethods or procedures by research workers.1.6 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are mathematicalconversions to inch-pound units that are provided for informa-tion only and are not considered standard.1.7 All observed a
11、nd calculated values shall conform to theguidelines for significant digits and rounding established inPractice D 6026.1.7.1 The method used to specifiy 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
12、 otheruses, or both. How one applies the results obtained using thisstandard is beyond its scope.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
13、practices and determine the applica-bility of regulatory requirements prior to use.2. Referenced Documents2.1 ASTM Standards:2D 653 Terminology Relating to Soil, Rock, and ContainedFluidsD2113 Practice for Rock Core Drilling and Sampling ofRock for Site InvestigationD 2216 Test Methods for Laborator
14、y Determination of Wa-ter (Moisture) Content of Soil and Rock by MassD 3740 Practice for Minimum Requirements for AgenciesEngaged in Testing and/or Inspection of Soil and Rock asUsed in Engineering Design and ConstructionD 6026 Practice for Using Significant Digits in Geotechni-cal DataE83 Practice
15、for Verification and Classification of Exten-someter SystemsE 122 Practice for Calculating Sample Size to Estimate,With Specified Precision, the Average for a Characteristicof a Lot or Process1This test method is under the jurisdiction ofASTM Committee D18 on Soil andRock and is the direct responsib
16、ility of Subcommittee D18.12 on Rock Mechanics.Current edition approved July 1, 2008. Published July 2008. Originally approvedin 1992. Last previous edition approved in 2004 as D 5335 04.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at servicea
17、stm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United
18、States.E 228 Test Method for Linear Thermal Expansion of SolidMaterials With a Push-Rod DilatometerE 289 Test Method for Linear Thermal Expansion of RigidSolids with Interferometry3. Terminology3.1 See Terminology D 653 for general definitions.3.2 Definitions of Terms Specific to This Standard:3.2.1
19、 linear coeffcient of thermal expansionthe change inlength of a unit length for a temperature change of 1. Themathematical expression is:a 5 L22 L1!/L0# 3 1/T22 T1!# (1)In terms of thermal strains:a 5 T22T1!/T22 T1! 5DT/DT (2)where T1and T2are the thermal strains of the specimen asa result of a temp
20、erature change from T0to T1and from T0toT2respectively, a is obtained by dividing the change in thermalstrain (DT) by the change in temperature (DT). The units of aare millimetres/millimetre per degree Celsius (inches/inch perdegree Fahrenheit).3.2.2 thermal strainthe change in length of a unit leng
21、thof a sample due to a change in temperature. The mathematicalexpression is:T5L22 L1L0(3)where L1and L2are the specimen lengths at temperatures T1and T2, respectively, and L0is the specimen length at thereference temperature T0.4. Summary of Test Method4.1 The application of heat to rock causes it t
22、o expand. Thischange in dimension of the rock when divided by the length ofrock is the strain developed in the rock. A wire or foil gridsuitably bonded to the rock will be strained precisely the sameamount as the rock. This straining, or stretching, of the gridresults in a change in the electrical r
23、esistance of the grid.Measurement of the change in the electrical resistance of thegrid is thus a measure of the change in dimension of the rock.4.2 The application of heat to the grid may cause a changein the electrical resistance of the grid. To eliminate errors dueto gauge heating, a second grid
24、is attached to a referencespecimen and the output of the gauge attached to the referencespecimen is subtracted from the output of the gauge attached tothe test specimen.5. Significance and Use5.1 Information concerning the thermal expansion charac-teristics of rocks is important in the design of any
25、 undergroundexcavation where the temperature of the surrounding rock maybe altered. Thermal strain causes thermal stress that ultimatelyaffects the stability of underground excavations. Examples ofapplications where rock thermal strain is important include:nuclear waste repositories, underground pow
26、er stations, com-pressed air energy storage facilities, and geothermal energyfacilities.5.2 The linear coefficient of thermal expansion, a, of rock isknown to vary as the temperature changes. Rock thermal strainis normally not a linear function of temperature. This testmethod provides a procedure fo
27、r continuously monitoringthermal strain as a function of temperature. Therefore, infor-mation on how a changes with temperature is obtained.5.3 Other methods of measuring the expansion coefficient ofrock by averaging the thermal strain of a large specimen overa temperature range of many degrees may
28、result in failure todetermine the variation in a of that rock for one or more of thefollowing reasons:5.3.1 Alpha is not always linear with temperature,5.3.2 Some rocks are anisotropic having directional charac-teristics which can vary by more than a factor of two.5.3.3 Alpha may have a negative val
29、ue in one direction and,at the same time, a positive value in the others.5.4 Strain gauges, both wire and foil types, have beensuccessfully employed to measure the thermal expansioncoefficients of rock. These coefficients are frequently verysmall, being on the order of millionths of a millimetre per
30、millimetre for each degree Celsius (millionths of an inch perinch for each degree Fahrenheit). The thermal strain of rocks isabout one tenth that of plastics and one half or one quarter thatof many metals. Therefore, measurement methods for rocksrequire greater precision than methods that are routin
31、ely usedon plastics and metals.NOTE 4Notwithstanding 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 cr
32、iteria 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 evaluating
33、some of those factors.6. Apparatus6.1 Bonded Strain Gauges, corresponding toASTM ClassAresistance strain gauge extensometer (see Practice E83). Thegauge length shall be at least ten times the largest grain in therock. Care shall be exercised to have the same length and typeof connecting wires on all
34、 specimens.6.2 Strain-Measuring System, having sensitivity of at least 5m/m (5 in./in.) with an accuracy of at least 60.1 % of thereading and a linearity of at least 60.1 % of the interval.6.3 Reference Specimen, having minimum dimensions atleast twice the length of the strain gauge. The referencesp
35、ecimen shall have a maximum linear coefficient of thermalexpansion of 0.5 3 106cm/cmC (0.9 3 106in./in.F).NOTE 5Suitable reference materials include titanium silicate, Zero-dur, and ultra-low expansion glass, all having expansion coefficients ofless than 0.5 3 106/C (0.9 3 106/F) over the temperatur
36、e range from 0to 200C (32 to 400F)6.4 Temperature Measurement SystemThe system chosento monitor and record temperature depends primarily on thetest apparatus and the maximum test temperature. Speciallimits of error thermocouples or platinum resistance thermom-eters (RTDs) are recommended. The temper
37、ature sensor (trans-ducer) shall be accurate to better than 0.2C (0.5F) with aresolution of better than 0.05C (0.1F).D53350826.5 Heating SystemThe heating unit (furnace) shall belarge enough to contain the test calibration, and referencespecimens such that the gauge length specified in 6.1 can bemai
38、ntained at a constant temperature over its length to 0.1C(0.2F). It shall also incorporate controls so that specimensmay be heated or cooled at a rate not greater than 1C(1.8F)/min while still maintaining the constant temperaturealong the gauge length. If the heating unit consists of a liquidbath, t
39、hen the specimens shall be encapsulated to preventpenetration of the fluid into the specimens.7. Sampling7.1 ScopeRock samples can be in the form of blocksamples or core samples. The number and types of rocksamples needed depends partly on the intended application ofthe test results. For example, an
40、 initial mechanical character-ization of the site might require several samples from a varietyof formations, while a detailed thermomechanical investigationof a specific rock type may require many tests from a singleformation. The final testing program will depend heavily on thetechnical judgment an
41、d experience of project personnel. Addi-tional information may be found in Practice D 2113, whichdescribes rock core drilling and sampling of rock for siteinvestigations.7.2 Statistical RequirementsThe number of samples andspecimens tested shall be sufficient to provide an adequatestatistical basis
42、for evaluation of the results. Rock types that arehighly variable will require more tests than relatively uniformrocks in order to evaluate the results with equal uncertainty.7.2.1 The number of samples and specimens required toobtain a specific level of statistically valid results may bedetermined
43、using test method E 122. However, it may not beeconomically possible to achieve specific confidence levels andprofessional judgment may be required.7.3 NonhomogenitiesDiscontinuities in the rock mass,such as joints, inclusions, voids, veins, bedding, etc., caninfluence the thermal expansion of the r
44、ock. Microcracks maybe produced during sampling or test preparation.7.4 Moisture Condition of SamplesThe moisture condi-tion of the rock can influence the measured thermal expansion.It is recommended that specimens be tested in both natural anddry conditions. For natural conditions, preserve the moi
45、sturecontent of the rock between the time of recovery and testing.7.5 AnisotropyThe thermal expansion coefficient of manyrocks is dependent on direction. Therefore, thermal expansionshould be measured in several directions in order to assess thedegree of anisotropy.7.6 DocumentationSince the thermal
46、 expansion of mostrocks is anisotropic, it is important that the field orientation ofeach sample is recorded. The orientation of each sample shallbe noted on the sample and suitable markings shall be carriedthrough each cutting to the final specimen ready for testing.These markings should indicate c
47、ompass direction, up/downdirections, and orientation with respect to geologic structure.8. Test Specimens8.1 DimensionsTest specimens shall be right circularcylinders or right prisms. The minimum dimensions shall beadequate to accommodate the strain gauges as specified in 6.1.8.2 Preparation:8.2.1 U
48、se a segmented diamond saw for cutting core orblock samples into right circular cylinders or right prisms.Right circular cylinders are easily produced by cutting a coresample at two locations as required by 8.1, parallel to eachother and at right angles to the longitudinal axis.Apply coolingfluid co
49、ntinuously to cool the blade and flush cuttings from thecut. If required, laboratory core drilling of the rock blocksamples can be done to obtain drill cores.8.2.2 The areas on the specimen where the strain gauges areto be mounted shall be smooth to within 0.025 mm (0.001 in.).8.2.3 Do not degrade the rock during the machining process.Prevent thermal fracturing by cooling with an appropriate fluidas required. Generally, water is used for hard rock, but somematerials require special fluids, such as saturated brine for saltor gl
