1、Designation: D 5334 08Standard Test Method forDetermination of Thermal Conductivity of Soil and SoftRock by Thermal Needle Probe Procedure1This standard is issued under the fixed designation D 5334; the number immediately following the designation indicates the year oforiginal adoption or, in the ca
2、se 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 presents a procedure for determiningthe thermal conductivity of soil and
3、 soft rock using a transientheat method. This test method is applicable for both undis-turbed and remolded soil specimens and soft rock specimens.This test method is suitable only for isotropic materials.1.2 This test method is applicable to dry materials over awide temperature range from 100C, depe
4、nding on thesuitability of the thermal needle probe construction to tempera-ture extremes. This method may also be used for specimenscontaining moisture. However, care must be taken to preventsignificant error from: (1) redistribution of water due to thermalgradients resulting from heating of the ne
5、edle probe, and (2)phase change (melting) of ice in specimens with temperatures4 W/(mk).3.2.3 thermal greaseany thermally conductivity greasehaving a value of l 4 W/(mk).4. Summary of Test Method4.1 The thermal conductivity is determined by a variation ofthe line source test method using a needle pr
6、obe having a large1This test method is under the jurisdiction ofASTM Committee D18 on Soil andRock and is the direct responsibility of Subcommittee D18.12 on Rock Mechanics.Current edition approved July 1, 2008. Published July 2008. Originally approvedin 1992. Last previous edition approved in 2005
7、as D 5334 05.2For referenced ASTM 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.1*A Summary of Changes section appears at the en
8、d of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.length to diameter ratio to simulate conditions for an infinitelylong, infinitely thin heating source. The probe consists of aheating element and a temperature measuri
9、ng element and isinserted into the specimen. A known current and voltage areapplied to the probe and the temperature rise with time isrecorded over a period of time. The temperature decay withtime after the cessation of heating can also be included in theanalysis to minimize effects of temperature d
10、rift during mea-surement. The thermal conductivity is obtained from an analy-sis of the time series temperature data during the heating cycleand cooling cycle if applicable.5. Significance and Use5.1 The thermal conductivity of both undisturbed and re-molded soil specimens as well as soft rock speci
11、mens is usedto analyze and design systems used, for example, in under-ground transmission lines, oil and gas pipelines, radioactivewaste disposal, and solar thermal storage facilities.NOTE 1Notwithstanding the statements on precision and bias con-tained in this test method; the precision of this tes
12、t method is dependenton the competence of the personnel performing it, and the suitability of theequipment and facilities used. Agencies that meet the criteria of PracticeD 3740 are generally considered capable of competent and objectivetesting. Users of this test method are cautioned that complianc
13、e withPractice D 3740 does not in itself assure reliable testing. Reliable testingdepends on many factors; Practice D 3740 provides a means of evaluatingsome of those factors.6. Apparatus6.1 Thermal Needle ProbeA device that creates a linearheat source and incorporates a temperature measuring elemen
14、t(thermocouple or thermistor) to measure the variation oftemperature at a point along the line. The construction of asuitable device is described in Annex A1.6.2 Constant Current SourceA device to produce a con-stant current.6.3 Temperature Readout Unit or RecorderA device torecord or produce a digi
15、tal readout of temperature in degreesCelsius with enough resolution to resolve changes in tempera-ture induced by heating of the needle (typically 0.1 to 0.01 K).6.4 Voltage-Ohm-Meter (VOM)A device to read voltageand current to the nearest 0.01 V and ampere.6.5 Timer, stopwatch or integrated electro
16、nic timer capableof measuring to the nearest 0.1 s for the duration of themeasurement.6.6 Equipment, capable of drilling a straight vertical holehaving a diameter as close as possible to that of the needle andto a depth at least equal to the length of the needle.7. Specimen Preparation7.1 Undisturbe
17、d Soil Specimens:7.1.1 Thin-Walled Tube or Drive SpecimensCut a 200 630-mm (8.0 6 1-in.) long section of a sampling tube containingan undisturbed soil specimen. The tube section should have aminimum diameter of 51 mm (2 in.).7.1.2 Weigh the specimen in a sampling tube or brass rings.7.1.3 Insert the
18、 thermal needle probe down the axis of thespecimen by either pushing the probe into a predrilled hole(dense specimen) to a depth equal to the length of the probe orpushing the probe into the specimen (loose specimen). Careshould be taken to ensure that the thermal probe shaft is fullyembedded in the
19、 specimen and not left partially exposed. (SeeNote 2.)NOTE 2To provide better thermal contact between the specimen andthe probe, the probe may be coated with a thin layer of thermal grease. Ifa hole is predrilled for the needle probe, the diameter of the hole shouldbe equal to the diameter of the ne
20、edle probe to ensure a tight fit. A device,such as a drill press, may be used to insert the probe to ensure that theprobe is inserted vertically and that no void spaces are formed between thespecimen and the probe.7.2 Remolded Soil Specimens:7.2.1 Compact the specimen to the desired density andwater
21、 content (in a thin-walled metal or plastic tube) using anappropriate compaction technique. For further guidance on theeffect of the various compaction techniques on thermal con-ductivity, refer to Mitchell et al (1).3The tube should have aminimum diameter of 51 mm (2 in.) and a length of 200 6 30mm
22、 (8.0 6 1 in.).7.2.2 Perform 7.1.2 and 7.1.3.7.3 Soft Rock Specimens:7.3.1 Specimen dimensions shall be no less than those of thecalibration standard (8.3).7.3.2 Insert the thermal needle probe into the specimen bypredrilling a hole to a depth equal to the length of the probe.Care should be taken to
23、 ensure that the thermal probe shaft isfully embedded in the specimen and not left partially exposed.(See Note 2.)8. Calibration8.1 The thermal needle probe apparatus should be calibratedbefore its use. Perform calibration by comparing the experi-mental determination of the thermal conductivity of a
24、 standardmaterial to its known value. A calibration factor, C, should becalculated where:C 5lmateriallmeasured(1)where:lmaterial= the known thermal conductivity of the cali-bration material, and3The boldface numbers given in parentheses refer to the list of references at theend of this standard.FIG.
25、 1 Thermal Probe Experimental SetupD5334082lmeasured= the thermal conductivity of that material mea-sured with the thermal needle probe appara-tus.8.1.1 All subsequent measurements with the thermal needleprobe apparatus should be multiplied by C before beingreported. This is especially important wit
26、h large diameterneedle probes (that is, d 2.5 mm) where departures from theassumption of an infinitely thin probe cause potentially signifi-cant differences in estimation of the thermal conductivity dueto non-negligible heat storage and transmission in the needleprobe itself.8.1.2 The calibration fa
27、ctor, C, has been shown to be afunction of thermal conductivity when using a large diameterneedle probe (see Hanson et al, 2004) (2). For users of largediameter probes, it may be necessary to determine C at severalthermal conductivities in the range of measurement and con-struct a calibration functi
28、on which is then applied to subse-quent data collected with the thermal needle probe.8.2 Conduct the test specified in Section 9 using a calibra-tion standard as specified in 8.3.8.3 Calibration StandardOne or more materials withknown values of thermal conductivity in the range of thematerials being
29、 measured (typically 0.2 Q4pllnt! 0 , t#t1(4)DT Q4pllnStt t1Dt . t1(5)10.2 Simplified Method:10.2.1 For thermal needle probes with diameter of 2.5 mmor less, exclude from the analysis the first 10 to 30 seconds ofdata from both the heating and, if used, cooling data. For largerdiameter thermal needl
30、e probes it will be necessary to plot thedata on a semi-log plot as described in 10.2.2 and identify theduration of the non-linear portion of initial data that should beexcluded. These data are most strongly affected by termsignored in Eq 4 and 5, and will result in decreased accuracy ifthey are inc
31、luded in the subsequent analysis. The total timeduration of the data included in the analysis, and duration ofinitial values excluded from the analysis, should be fixed forany thermal needle probe configuration and used duringcalibration and all subsequent thermal conductivity measure-ments with tha
32、t probe type to avoid biasing results due tosubjective selection of the time range for analysis.10.2.2 Using the remaining data, determine the slope, Shofa straight line representing temperature versus ln t for theheating phase, and, if used, the slope, Scof a straight linerepresenting temperature v
33、ersus lnt/(tt1) for the coolingphase (see Fig. 4). The early and late portions of the testFIG. 3 Typical Record of Data (Idealized Curve)D5334084(representing transient conditions and boundary effects, respec-tively) should not be used for the curve fitting. These slopescan be determined using linea
34、r regression with any standardspreadsheet or data analysis software, or manually, by plottingthe data and fitting a straight line to the data by eye. If manualmethods are used to determine the slope, it may be convenientto use semi-log graph paper with log10time. If the slope oftemperature versus lo
35、g10t is used in the analysis, the slopes ofthe plots should be termed (Sh10) for the heating phase, and(Sc10) for the cooling phase.10.2.3 The data included in the analysis should be evenlyspaced with the logarithm of time (X-axis). If data are collectedin even time increments and subsequently plott
36、ed on a log timescale, then the distribution becomes uneven biasing the analy-sis too heavily toward the long-term of the testing period. Fig.4 shows a data set that has been properly filtered to provide aneven data distribution along the log time axis.10.2.4 Compute thermal conductivity using Eq 6,
37、 where S isthe average of Shand Scand S10is the average of Sh10and Sc10if both heating and cooling data are used for the analysis or justSh(or Sh10) if only heating data are used. Typically Shand Scdiffer because of specimen temperature drift during the mea-surement. Averaging the two values minimiz
38、es the effects ofthe drift, which can cause large errors in determination of l.Note that C is the calibration coefficient determined in Section8.l5CQ4pS52.3CQ4pS10(6)where:Q =I2RL5EILQ = heat input (W/m),C = calibration constant from Section 8,l = thermal conductivity W/(mK),S = slope used to comput
39、e thermal conductivity if ln(t)isused in analysis,S10= slope used to compute thermal conductivity iflog10(t) is used in analysis,t = time (s),I = current flowing through heater wire (A),R = total resistance of heater wire (V),L = length of heated needle (m), andE = measured voltage (V).10.3 Derivati
40、on of the basis for Eq 2 and 3 are presented byCarslaw and Jaeger (5), and adapted to soils by VanRooyen andWinterkorn (6); VanHerzen and Maxwell (7); and Winterkorn(8).11. Report11.1 For each thermal conductivity test, fill out a data sheetsimilar to that shown in Fig. 2, reporting the following:11
41、.1.1 Date of the test and project name or number,11.1.2 Boring number, sample or tube number, sampledepth, and data recorded in 9.5.11.1.3 Initial moisture content and dry density,11.1.4 Time versus temperature plot (see Fig. 3),11.1.5 Thermal conductivity, and11.1.6 Physical description of sample i
42、ncluding soil or rocktype. If rock, describe location and orientation of apparentweakness planes, bedding planes, and any large inclusions orinhomogeneities.12. Precision and Bias12.1 An interlaboratory study involving line-source meth-ods, including needle probes used for rock and soils, wasunderta
43、ken by ASTM Committee C16 (9). The materials ofknown thermal conductivity that were evaluated includedOttawa sand and paraffin wax (having a thermal conductivitysimilar to certain soil and soft rock types). The results indicateda measurement precision of between 610 and 615 %, respec-tively, with a
44、tendency to a positive bias (higher value) over theknown values for the materials studied. With careful calibra-tion of thermal needle probes in materials of known thermalNOTE 14a shows data from the heating portion of the cycle and 4b shows data from the cooling portion of the cycle.NOTE 2The slope
45、s (Shand Sc) are shown in bold.NOTE 3The data are approximately evenly spaced on the X-axis to avoid bias as discussed in 10.2.2.FIG. 4 (a temperature; thermal conductivity; thermalprobe; thermal propertiesANNEXES(Mandatory Information)A1. COMPONENTS AND ASSEMBLY OF THERMAL NEEDLEA1.1 The thermal ne
46、edle consists of a stainless steelhypodermic tubing containing a heater element and a thermo-couple as shown in Fig.A1.1. Its components and assembly aresimilar to the one described by Mitchell et al (1) and Footnote5.4To construct a thermal needle, hypodermic tubing is cut to115mm(412 in.) in lengt
47、h. The end to be inserted into thebakelite head of a thermocouple jack is roughened for a lengthof 15 mm (0.5 in.). A copper-constantan thermocouple wirejunction previously coated with an insulating varnish isthreaded into the hypodermic needle with the junction 50 mm(2 in.) from the end of the need
48、le (see Note A1.1). At the sametime, a manganin heater element is inserted with approximately75-mm (3-in.) pigtails extending from the top of the needle asshown in Fig.A1.2. The uncut end of the needle is then insertedinto an evacuating flask through a rubber stopper and the otherend is placed in a
49、reservoir of thermal epoxy primer as shownin Fig.A1.2.Avacuum pump connected to the evacuating flaskis used to draw the thermal epoxy up through the needle. Theneedle is removed from the reservoir and flask, and a blob ofputty is placed at the end of the needle to hold the thermalepoxy in place for hardening. After the thermal epoxy hardens,the thermocouple wires are soldered to the pins of a polarized4Mitchell, J. K., (Personal Communication), 1978 b.FIG. A1.1 Typical Probe ComponentsD5334086thermocouple jack and the roughened end of the needle isplaced in
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