1、Designation: D 4535 85 (Reapproved 2004)Standard Test Methods forMeasurement of Thermal Expansion of Rock Using aDilatometer1This standard is issued under the fixed designation D 4535; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision
2、, 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 These test methods cover the laboratory measurement ofthe linear (one-dimensional) thermal expansion of
3、 rocks usinga dilatometer.1.2 These test methods are applicable between temperaturesof 25C to 300C. Both bench top and confined measurementtechniques are presented. Rocks of varying moisture contentcan be tested.1.3 For satisfactory results in conformance with these testmethods, the principles gover
4、ning the size, construction, anduse of the apparatus described in these methods should befollowed. If the results are to be reported as having beenobtained by this method, then all pertinent requirementsprescribed in this method shall be met.1.4 These test methods do not establish details of constru
5、c-tion and procedure to cover all test situations that might offerdifficulties to a person without technical knowledge concerningthe theory of heat flow, temperature measurement, and generaltesting practices. Standardization of these test methods doesnot reduce the need for such technical knowledge.
6、 It isrecognized also that it would be unwise, because of thestandardization of this method, to resist in any way the furtherdevelopment of improved or new methods or procedures byresearch workers.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its us
7、e. 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:2E83 Practice for Verification and Classification of Exten-sometersE 228 Tes
8、t Method for Linear Thermal Expansion of SolidMaterials with Vitreous a Silica Dilatometer3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 sample thermal strain, et change in length of a unitlength of sample when the sample is subjected to heat. Themathematical expression is:et
9、5 L22 L1!/L0(1)where:L1and L2= specimen lengths corresponding to tempera-tures T1and T2, andL0= the original specimen length at some refer-ence temperature T0.Thermal strain is also equal to the specimen thermal dis-placement, dt, divided by the original sample length:et5dt/L0(2)3.1.2 mean coeffcien
10、t of linear expression, ambetweentwo temperatures, T1and T2, is defined as follows:am5 L22 L1!/L0T22 T1!# (3)where:L1and L2= specimen lengths at temperatures T1and T2,respectively. Therefore, amis obtained bydividing the linear thermal strain, (L1 L2)/L0, by the change in temperature units areinch/i
11、nch or centimetre/centimetre per tem-perature change in F or C, respectively. amis often expressed in parts per million perdegree.3.1.3 Upon heating ( T2 T1), an increase in the length of therock sample will give a positive value of am. If a decrease inlength (contraction) is observed, amwill become
12、 negative.4. Summary of Test Methods4.1 The application of heat to a rock causes it to expand.This expansion divided by the original length of the rockspecimens is the thermal strain from which coefficients ofexpansion can be calculated. This standard covers two methods1These test methods are under
13、the jurisdiction ofASTM Committee D18 on Soiland Rock and are the direct responsibility of Subcommittee D18.12 on RockMechanics.Current edition approved Nov. 1, 2004. Published December 2004. Originallyapproved in 1985. Last previous edition approved in 2000 as D 453585(2000)2For referenced ASTM sta
14、ndards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandardsvolume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken,
15、PA 19428-2959, United States.for measuring rock expansion. The primary difference betweenthe two methods is in the type of dilatometer used.4.1.1 Test Method ITest Method I is the procedure usedwhen making unconfined or bench top measurements. Themethod and apparatus are similar to that described in
16、 TestMethod E 228. The rock specimen thermal displacement ismeasured using a dilatometer as shown in Fig. 1. The sampledisplacement is measured by a transducer located outside theheated area of the sample; therefore, apparent strain due toapparatus expansion and contraction is minimized.4.1.2 Test M
17、ethod IITest Method II employs a dilatomet-ric device which is located inside the heated zone, as shown inFig. 2. This test method is most suited for the measurement ofrock thermal strain under confined conditions.4.2 In both test methods, sample expansion is measuredcontinuously as temperature is g
18、radually increased or allowedto stabilize at discrete temperature points.5. Significance and Use5.1 Information concerning the thermal expansion charac-teristics of rocks is important in the design of any undergroundexcavation where the surrounding rock may be heated. Ther-mal strain causes thermal
19、stresses which ultimately affectexcavation stability. Examples of applications where rockthermal strain is important include: nuclear waste repositories,underground power stations, compressed air energy storagefacilities, and geothermal energy facilities.5.2 The coefficient of thermal expansion or “
20、alpha” or rockis known to vary as the temperature changes. These methodsprovide continuous thermal strain values as a function oftemperature, and therefore provide information on how alphachanges with temperature.5.3 Rocks are also often anisotropic, thus displaying differ-ent thermal strains depend
21、ing on the orientation of strainmeasurement. These methods allow for measuring strain in onedirection only. If anisotropy is expected, samples with differentorientations should be prepared and tested.5.4 Care should be exercised in the interpretation of thermalstrain data of rocks with significant m
22、oisture content. Undercertain temperature and pressure conditions, steam may beproduced in the pore space. Steam may cause errors because ofmicrocrack production or changes in the pore pressure. Thephase change from water to steam in the pore space can resultin several phenomena which complicate dat
23、a analysis, asfollows:5.4.1 Evolved steam may change the pore pressure and thusthe effective stress in the rock, resulting in anomalous strainreadings.5.4.2 Losing all the moisture may dehydrate clays in thepore space and thus change expansion characteristics, espe-cially in layered rocks.5.5 The re
24、searcher using this standard must use best judg-ment as to how to make the thermal expansion measurement sothat it accurately represents the conditions in the field.5.6 Method II is amenable to confined thermal strain deter-minations. Confined tests may be most appropriate when:5.6.1 Pore pressure m
25、ust be imposed in the pore space tomaintain the liquid phase of water through the desired tem-perature range.5.6.2 The thermal strain of the rock is sensitive to confiningstress.5.6.3 The sample is fragile or friable, or both, and cannot bemachined into the shapes required for Method I.6. Apparatus6
26、.1 Dilatometer:6.1.1 Method IThe dilatometer used for bench measure-ments may be of the tube or rod type, as shown in Fig. 1. Thosecomponents of the dilatometer exposed to elevated tempera-tures should be fabricated of materials with coefficients oflinear expansion that are as small as practicable.6
27、.1.2 Method IIIn Method II the entire dilatometer isexposed to elevated temperature. Therefore, transducers, rods,and other components should be fabricated of materials withlow thermal expansions (for example, fused silica, superinvar). When the apparatus is tested with a quartz calibrationspecimen,
28、 the apparatus strain should be less than 20 % of theanticipated rock strain (refer to Fig. 2).6.2 ExtensometerExtensometers measure length change.In principle, any accurate length measuring device with goodlong-term stability may be used; this includes dial gages, linearvariable differential transd
29、ucers, or capacitive transducers.Whichever device is selected, it must have sufficient resolutionto measure 0.01 % sample strain (Refer to Practice E83).6.2.1 Those devices used in Method II must be fabricated ofmaterials that allow direct exposure of the device to theanticipated temperature. Also,
30、transducer bodies should bevented for operation in a pressure environment. At least twotransducers are used, as shown in Fig. 2, and their outputsaveraged.FIG. 1 Apparatus Commonly Used to Perform Bench Top (MethodI) Thermal Expansion MeasurementsD 4535 85 (2004)26.3 FurnaceThe furnace shall be larg
31、e enough to containthe specimen and apparatus and maintain uniform temperaturealong the axis of the specimen with variations no greater than61C. The mean sample temperature shall be controlled within61C. The use of a programmable temperature controller thatcan slowly increase or decrease sample temp
32、eratures at rates atleast as low as 0.1C/min is recommended.6.4 Temperature Measuring Instruments Thermocouplesor platinum resistant thermometers are recommended. Theexact type will depend on the temperature range of interest. Ingeneral, the temperature should be measured to within 60.5Cwith a resol
33、ution of at least6 0.2C. Make measurements atthree locations on the axis of the sample, one near each end andone at the sample midpoint.6.5 MicrometerCalipers should have an index permittingdirect reading of 0.025 mm for measuring the initial length ofthe specimen.Ahigh grade screw micrometer custom
34、arily usedin machine shop practice is satisfactory.7. Sampling7.1 The number and types of rock cores tested depend partlyon the intended application of the test results. For example, aninitial mechanical characterization of a site might requireseveral samples from a variety of formations, while a de
35、tailedthermo-mechanical investigation of a particular location mayrequire many rock tests from a single formation. The finaltesting program will depend on the technical judgment and theexperience of project personnel.7.2 Statistical RequirementsIt is recommended that thenumber of samples tested be s
36、ufficient to provide an adequatestatistical basis for evaluation of the results. Rock types whichare highly variable would require more tests than relativelyuniform rocks, in order to evaluate the results with equalcertainty.FIG. 2 Apparatus Commonly Used to Perform Confined (Method II) Thermal Expa
37、nsion MeasurementsD 4535 85 (2004)37.3 Moisture Condition of Samples The moisture condi-tion of the rock can influence the measured thermal expansion.Test the specimens in a manner that best simulates the in situconditions of interest. For natural conditions, the moisturecontent of the rock core and
38、 the chemical characteristics of thepore fluid shall be preserved between the time of recovery andtesting; then determine the moisture content of core materialcontiguous to the test specimen.7.4 AnisotropyThe thermal expansion coefficient of manyrocks is different along various axes of the rock. Mea
39、sure thethermal expansion in several directions in order to assess thedegree of anisotropy.7.5 DocumentationSince the thermal expansion of mostrock is anisotropic, it is important that the field orientation ofeach sample is recorded. Note the orientation of each sampleon the sample and carry suitabl
40、e markings through each cuttinguntil the final specimen is ready for testing. These markingsshould indicate compass direction and up/down directions, andother orientation with respect to geologic structures.8. Test Specimens8.1 Dimension and GeometryIn general, the proper ge-ometry is a right circul
41、ar cylinder. The specific recommendeddimensions for Method I are given in Test Method E 228. ForMethod II, the sample should be a right circular cylinder witha length to diameter ratio of 2 to 1. For both methods theminimum dimension should be 10 times the largest grain size.9. Preparation9.1 Do not
42、 degrade the rock during machining. Preventmechanical and fracture damage to the rock fabric by appro-priately slow machining processes and the use of propercoolant. Select coolant fluids based upon chemical compatibil-ity with the rock; for example, tap water may be adequate forgranite, whereas a s
43、aturated brine or mineral oil may be bestfor salt.9.2 DryingIf the sample is to be tested dry, dry at 80C ina vacuum oven for 24 h. At no time during the drying processshall the sample be subjected to heating or cooling rates greaterthan 1C/min.9.2.1 An alternative drying schedule may be used in tho
44、seinstances where a vacuum oven is not available and it is not ofinterest to know the test specimen response to the firstapplication of heat. In such a case, heat the specimen to 105 62C at a rate not greater than 1C/min. Maintain this tempera-ture for at least 24 h. Cool the sample to ambient tempe
45、ratureat a rate no greater than 1C/min.10. Standardization10.1 Calibration SpecimenPrepare a calibration specimenof known thermal expansion from fused silica or other materialof known low (;0.55 3 106 cm/cm/C) thermal expansion.The specimen shall have the same geometry and dimensions asthe rock spec
46、imens to be tested.10.2 Test the calibration specimen using the same procedure(see the procedure section) and the same apparatus to be usedto test the rock samples. The resulting data set thus representsthe thermal expansion of the test apparatus and will besubtracted from the rock test data.10.3 Re
47、peat the standardization test procedure three times,starting from the same initial condition, to verify the repeat-ability of the dilatometer. Variation from run to run should beno greater than 5 %.10.4 The calculated expansion of the calibration specimen issubtracted from the calibration expansion
48、results as follows:d25d12ds; (4)where:ds5alDT (5)where:d2= thermal expansion of the test apparatus, cm,d1= apparent thermal expansion measured by the appa-ratus, cmds= thermal expansion of the calibration specimen, cma = coefficient of linear expansion for the calibrationspecimen,l = gage length of
49、the calibration specimen, cm, andDT = temperature difference between a reference tempera-ture (room temperature or slightly elevated aboveroom temperature) and an elevated temperature, C.10.5 The thermal expansion of the apparatus should be lessthan 20 % of the measured thermal expansion of the rock. Themeasured thermal expansion of the apparatus shall be reportedas specified in Section 14.11. Preconditioning11.1 Rock samples shall not be thermally cycled before theactual testing unless drying is specified, in which case dryingshall be perfo
