1、Designation: D 4436 08Standard Test Method forRock Bolt Long-Term Load Retention Test1This standard is issued under the fixed designation D 4436; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number i
2、n parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 The objective of this test method is to determine thetime over which rock bolt tension decreases from the installedvalue to a designated minim
3、um value.1.2 This test method is applicable to any anchor systemwhich is not fully encapsulated immediately upon installation,including mechanical, cement grout, resin (epoxy, polyester,and the like) or other similar systems.1.3 The values stated in inch-pound units are to be regardedas standard. Th
4、e values given in parentheses are mathematicalconversions to SI units that are provided for information onlyand are not considered standard.1.4 All observed and calculated values shall conform to theguidelines for significant digits and rounding established inPractice D 6026.1.4.1 The method used to
5、 specify 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.1.5 This standard does not purport to address
6、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 determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 653 Terminology
7、Relating to Soil, Rock, and ContainedFluidsD 3740 Practice for Minimum Requirements for AgenciesEngaged in Testing and/or Inspection of Soil and Rock asUsed in Engineering Design and ConstructionD 4435 Test Method for Rock Bolt Anchor Pull TestD 6026 Practice for Using Significant Digits in Geotechn
8、i-cal DataD 6167 Guide for Conducting Borehole Geophysical Log-ging: Mechanical Caliper3. Terminology3.1 See Terminology D 653 for general definitions.3.2 Definitions of Terms Specific to This Standard:3.2.1 loadthe total axial force on the rock bolt.3.2.2 design loadthe load specified for the rock
9、boltduring the life of the project.3.2.3 installation loadthe load on the bolt immediatelyafter installation.3.2.4 stand timethe time required for the bolt load todecrease from the installation load to the design load.4. Summary of Test Method4.1 A rock bolt is installed in the same manner and in th
10、esame material as its intended support use. The load on the boltis monitored over a period of time, usually several weeks.5. Significance and Use5.1 Rock bolts are used for support in a variety of miningand civil engineering situations.3After a bolt is installed, theload generally decreases over tim
11、e due to deterioration of theborehole wall, creep, and other factors. This process may bearrested by fully encapsulating the bolt shortly after installa-tion. This is generally done by pumping the bolt hole full ofcement grout, though synthetic resins may also be used. Therate of load loss determine
12、s the interval during which the boltmust be encapsulated during construction.5.2 The local characteristics of the rock, such as roughnessof the borehole and induced fractures, are significant factors inthe load loss characteristics of the bolt. To obtain realisticvalues, the test holes should be dri
13、lled using the same methodsas those used for the construction boreholes.5.3 In establishing a testing program, the following factorsshould be considered:5.3.1 Load retention tests should be conducted in all rocktypes where construction bolts will be installed. If the rock isanisotropic, for example,
14、 bedded or schistose, the tests should1This 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 1984. Last previous editi
15、on approved in 2004 as D 4436 04.2For 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.3For additional information
16、see, “Suggested Method for Monitoring Rock BoltTension Using Load Cells,” Suggested Methods for Rock Bolt Testing, InternationalSociety for Rock Mechanics Commission on Standardization of Laboratory andField Tests, 1974.1*A Summary of Changes section appears at the end of this standard.Copyright AST
17、M International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.be conducted in the same orientations relative to the anisotropyas the construction bolts will be installed.5.3.2 In each rock type, at each orientation, and for eachanchor system, a sufficient numbe
18、r of tests should be con-ducted to determine the average and minimum long-termcapacities within a fixed uncertainty band at the 95 % confi-dence level. The allowable uncertainty band depends on theproject and involves such factors as rock quality, expectedproject lifetime, and importance of the area
19、s to be bolted. Theuncertainty band determination will require considerable engi-neering judgment. As a rough guideline, at least six long-termtests for a single set of variables have been found necessary tosatisfy the statistical requirements.5.3.3 The design load and installation load on the rock
20、boltsystem should be predetermined. The installation load is lessthan the anchor capacity, as determined by Method D 4435.The design load is less than the installation load; the amountdepends on rock properties and the minimum time required toencapsulate the bolts. Alternatively, this method can be
21、run fora predetermined time interval based on construction require-ments, and a realistic design load can be determined from thedata.NOTE 1The quality of the result produced by this standard isdependent on the competence of personnel performing it, and thesuitability of the equipment and facilities
22、used. Agencies that meet thecriteria of Practice D 3740 are generally considered capable of competentand objective testing/sampling/inspection/etc. Users of this standard arecautioned that compliance with Practice D 3740 does not in itself assurereliable results. Reliable results depend on many fact
23、ors; Practice D 3740provides a means of evaluating some of those factors.6. Apparatus6.1 Load CellA load cell shall be used to measure thetension in the rock bolt. The cell may be of the mechanical,photoelastic, hydraulic, rubber compression pad, or electronictype. The electronic type is recommended
24、. The cell shall havean accuracy of at least 6200 lbf (6890 N), including errorsintroduced by the excitation and read-out system, and aresolution of least 100 lbf (445 N).6.2 Anchor SystemsThe anchors used for testing shall befrom the manufacturers standard production stock. Mechani-cal anchors shal
25、l be inspected to ensure that no defectiveanchors are tested. Grout or resin shall be fresh (within theshelf life) and obtained from unopened containers. If groutedanchors are to be tested, ensure resin cartridge sizes arecompatible with hole diameter, rock bolt bar diameter andlength of anchorage r
26、equired. For anchorages utilizing injectedgrout, ensure mixing and injection equipment and systems arecompatible with manufacturers recommendations.6.3 Rock Bolt and AccessoriesThe rock bolt shall be ofsufficient diameter and strength so that its elastic range is notexceeded during the tests. Standa
27、rd bearing plates, washers,and the like may be used as required to align the load cell. Aspherical bearing is desirable on very uneven surfaces. Rockbolts used with grout or resin anchors shall have identicalungrouted bolt lengths.6.4 Drilling EquipmentThe same type of drilling equip-ment and drill
28、bits that will be used for installing rock boltsduring the construction phase of the project shall be used todrill the test holes.6.5 Torque WrenchIf expandable shell mechanical an-chors are used, a torque wrench shall be used to set them. Thetorque wrench shall also be used to load the bolts. It sh
29、all havea capacity at least 20 % greater than the manufacturersrecommended anchor-setting torque. The torque wrench shallhave an accuracy of at least 62 % of the full-scale reading anda resolution of at least 1 % of the full-scale reading.6.6 Hydraulic Pulling SystemAs an alternative to thetorque wr
30、ench, a hydraulic ram and reaction frame may beused to tension the bolts.6.7 Borehole Diameter Measuring Gauge A gauge shallbe used to measure the diameter of the borehole at the anchorlocation. It shall have an accuracy of at least 60.02 in. (0.5mm) and resolution of at least 0.01 in. (0.25 mm).6.8
31、 ThermometerA thermometer shall be used to measuretemperature in the borehole, within the anchor zone if resin orcement grout anchorages are being tested. The temperature ofthe resin or grout shall also be measured at the time ofinjection. The thermometer should have an accuracy of at least+ 0.5F (0
32、.28C) and a resolution of at least 1F (0.56C).7. Procedure7.1 LocationDo not locate the test area in a zone that willbe affected by future excavations, as rock response to stresschanges can produce load changes in the bolt.7.2 Drilling the Test Hole:7.2.1 Drill the test hole using the same procedure
33、 that willbe used during construction. Wash or blow the borehole cleanof all cuttings.7.2.2 The hole need not be as deep as the proposed length ofthe construction rock bolts. It shall, however, be deep enoughto set the anchor past the zone of disturbance caused by theexcavation and conform to the ma
34、nufacturers specificationsfor optimum performance, considering also compatibility withactual field conditions. For mechanical shell anchors, drill thehole 1 ft (300 mm) past the end of the anchor. A holeapproximately 6 ft (1.8 m) in length has generally been foundto be adequate.7.2.3 Inspect the tes
35、t hole visually using a flashlight, ormirror to reflect sunlight down the hole. If more than one-halfof the bottom of the hole cannot be seen, the hole is notsufficiently straight for the test and shall not be used.7.2.4 Measure the test hole diameter in two perpendiculardirections at the top and bo
36、ttom of the anchor location, usingthe borehole diameter measuring gauge, for a total of fourmeasurements.7.3 Preparation of AnchorsIf any anchor preparations,such as degreasing or rust removal, will be done duringconstruction, prepare the test anchors in the same way. If nospecial preparation is don
37、e during construction, do not preparethe anchors.7.4 Setting the Anchor:7.4.1 If mechanical anchors are used, lightly lubricate thedownhole end of the rock bolt and screw on the anchor. WhenD4436082in position, torque the bolt to the manufacturers recommen-dations to set the anchor. A pair of jam-nu
38、ts on the upper endof the rod may be used to apply torque without producing axialload in the bolt. If the manufacturers torque cannot beachieved because of anchor slippage due to shear failure in therock, note the maximum torque reading and install subsequentanchors to 80 % of this value. Do not tes
39、t anchors whererotation occurs between rock bore hole surface and anchor. Inall cases, record any slipping or other anomalous behavior asshown in Fig. 1.7.4.2 Install grout or resin anchors according to the manu-facturers recommendations. Record the temperature in theborehole within the anchor zone;
40、 the temperature of the resin orgrout at the time of injection and the ambient air temperature.Ideally the test anchorages should be installed under the sametemperature conditions as expected during construction. Thetime required for resin or grout anchorages to reach theirdesign strengths is temper
41、ature dependent and may varysignificantly. Consult the resin or grout manufacturers litera-ture for recommended curing times under various temperatureconditions. Curing times may be varied between 1 to 5 daysunder similar temperature conditions to assess the effects ofcuring time on strength. To eva
42、luate the influence of groutedbond length on anchor strength, several anchorage lengthsshould be tested, ideally under similar temperature conditionsand curing times.7.5 Loading the Bolt:7.5.1 The torque wrench is recommended for tensioning thebolt.Alternatively, the hydraulic pulling system may be
43、used toapply load. In this case, attach a pulling rod to the rock boltabove the nut. Apply the load hydraulically, then tighten thenut. As the nut is tightened, the hydraulic pressure decreasesbecause the load is transferred from the ram to the nut.7.5.2 Tension the bolt until the load cell indicate
44、s that theinstallation load has been achieved.7.6 Reading IntervalsMonitor the load on the bolt at leasttwice daily for a period of 2 weeks after installation, and oncedaily thereafter. Bolts in rapidly yielding material may requiremore frequent readings.FIG. 1 Rock Bolt Long Term Load Retention Tes
45、t Sample FormD44360837.7 Data RecordingAs a minimum for this method,record all the data shown in Fig. 1.8. Calculation8.1 For each test, plot the load on the rock bolt as a functionof time, as shown in Fig. 2. If either design load or stand timeis specified, the other may be determined from the grap
46、h.8.2 For each group of tests in a similar rock type, with thesame anchor type and orientation (if applicable), calculate themean and uncertainty of the loads at the 95 % confidencelevel.49. Report9.1 The report shall include the following:9.1.1 Describe the rock materials in which the anchors weret
47、ested, including the composition, texture, and any structuralfeatures which could affect anchor behavior, such as joints,weathering, and the like,9.1.2 Briefly describe the types of anchors tested,9.1.3 Prepare a summary table of the test program, includ-ing test number, anchor type, orientation, an
48、d test depth,9.1.4 List the equipment, other than anchors, with modelnumbers or dimensions as appropriate. Include the range,accuracy, and resolution of any devices used to make measure-ments,9.1.5 Present the equations used to convert transduceroutput into engineering units,9.1.6 Prepare a summary
49、table of the results in each rocktype, including anchor type, number of tests, mean stand timeor design load, range, and uncertainty of the mean. If resin orgrouted anchorages were tested, record the measurementsmade during installation of borehole, grout and ambienttemperatures,9.1.7 Include a plot of load versus time for each test, and adescription of the nature of any failures or any other observa-tions pertinent to the test.9.1.8 Append the data sheet for each test.9.1.9 For the evaluation of grouted rock bolts, the results ofseveral tests should be
