1、Designation:D440384(Reapproved2005)D440312 Standard Practice for Extensometers Used in Rock 1 This standard is issued under the xed designation D4403; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision.Anumb
2、er in parentheses indicates the year of last reapproval.A superscript epsilon () indicates an editorial change since the last revision or reapproval. 1. Scope* 1.1 This practice covers the description, application, selection, installation, data collecting, and data reduction of the various types of
3、extensometers used in the eld of rock mechanics. 1.2 Limitations of each type of extensometer system are covered in Section 35. 1.3 The values stated in inch-pound units are to be regarded as the standard. The SI values given in parentheses are provided for information purposes only. 1.4 The text of
4、 this standard references notes and footnotes which provide explanatory material. These notes and footnotes (excluding those in tables and gures) shall not be considered as requirements of the standard. 1.5 This practice offers a set of instructions for performing one or more specic operations. This
5、 document cannot replace education or experience and should be used in conjunction with professional judgement. Not all aspects of this guide may be applicable in all circumstances. This ASTM standard is not intended to represent or replace the standard of care by which the adequacyofagivenprofessio
6、nalservicemustbejudged,norshouldthisdocumentbeappliedwithoutconsiderationofaprojects many unique aspects. The word Standard in the title of this document means only that the document has been approved through the ASTM consensus process. 1.6 This standard does not purport to address all of the safety
7、 concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. 2. Referenced Documents 2.1 ASTM Standards: 2 D653Terminology Relating to Soi
8、l, Rock, and Contained Fluids D3740Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction 3. Terminology 3.1 DenitionsTerms not dened below may appear in Terminology D653. 3.2 Denitions of terms specic to th
9、is standard are included in Section 5. 4. Signicance and Use 4.1 Extensometers are widely used in the eld of engineering and include most devices used to measure displacements, separation, settlements, convergence, and the like. 4.2 For tunnel instrumentation, extensometers are generally used to mea
10、sure roof and sidewall movements and to locate the tension arch zone surrounding the tunnel opening. 4.3 Extensometers are also used extensively as safety monitoring devices in tunnels, in underground cavities, on potentially unstable slopes, and in monitoring the performance of rock support systems
11、. 1 This practice is under the jurisdiction of ASTM Committee D18 on Soil and Rock and is the direct responsibility of Subcommittee D18.23 on Field Instrumentation. Current edition approved May 1, 2005Aug. 15, 2012. Published June 2005November 2012. Originally approved in 1984. Last previous edition
12、 approved in 20002005 as D440384(2005). DOI: 10.1520/D4403-84R05.10.1520/D4403-12. 2 ForreferencedASTMstandards,visittheASTMwebsite,www.astm.org,orcontactASTMCustomerServiceatserviceastm.org.ForAnnualBookofASTMStandards volume information, refer to the standards Document Summary page on the ASTM web
13、site. This document is not anASTM standard and is intended only to provide the user of anASTM standard an indication of what changes have been made to the previous version. Because it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prio
14、r editions as appropriate. In all cases only the current version of the standard as published by ASTM is to be considered the official document. *ASummary of Changes section appears at the end of this standard Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19
15、428-2959. United States 14.4 An extensometer should be selected on the basis of its intended use, the preciseness of the measurement required, the anticipated range of deformation, and the details accompanying installation. No single instrument is suitable for all applications. NOTE 1Notwithstanding
16、 the statements on precision and bias contained in this test method, the precision of this test method is dependent on the competence of the personnel performing it and the suitability of the equipment and facilities used.Agencies that meet the criteria of Practice D3740 are generally considered cap
17、able of competent and objective testing. Users of these test methods are cautioned that compliance with Practice D3740 does not in itself ensure reliable results. Reliable testing depends on many factors; Practice D3740 provides a means of evaluating some of those factors. 5. Apparatus 5.1 GeneralEx
18、perienceandengineeringjudgmentarerequiredtomatchthepropertypeofextensometersystemstothenature of investigation for a given project. 5.1.1 Inapplicationsforconstructioninrock,precisemeasurementswillusuallyallowtheidenticationofsignicant,possibly dangerous, trends in rock movement; however, precise me
19、asurement is much less important than the overall pattern of movement. Where measurements are used to determine rock properties (such as in plate-jack tests), accurate measurements involving a high degree of precision are required. For in-situ rock testing, instrument sensitivity better than 0.0012
20、in. (0.02 mm) is necessary for proper interpretation. 5.1.2 Most eld measurements related to construction in rock do not require the precision of in-situ testing. Precision in the range of 0.001 to 0.01 in. (0.025 to 0.25 mm) is typically required and is readily obtainable by several instruments. 5.
21、1.3 Asthephysicalsizeofanundergroundstructureorslopeincreases,theneedforhighlyprecisemeasurementsdiminishes. Aprecisionof0.01to0.04in.(0.25to1.0mm)isoftensufficient.Thisrangeofprecisionisapplicabletoundergroundconstruction in soil or weak rock. In most hard rock applications, however, an instrument
22、sensitivity on the order of 0.001 in. (0.025 mm) is preferred. 5.1.4 The least precision is required for very large excavations, such as open pit mines and large moving landslides. In such cases, the deformations are large before failure and, thus, relatively coarse precision is required, on the ord
23、er of 1% of the range where the range may be 3 ft. (1 m) or more. 5.1.5 Forlong-termmonitoring,displacementsaretypicallysmallerthanthosethatoccurduringconstruction.Therefore,greater precision may be required for the long-term measurements. 5.2 Extensometers: 5.2.1 Rod ExtensometersA large variety of
24、 rod extensometers are manufactured. They range from simple single-point units tocomplicatedmultipointsystemswithelectricalreadout.Thesingle-pointextensometerisgenerallyusedtodetectsupportsystem failures. The rod can also serve as a safety warning device in hazardous areas. Generally, the rod extens
25、ometer is read with a depth-measuringinstrumentsuchasadialgageordepthmicrometer,however,variouselectricaltransducerssuchasLVDTs(linear variable differential transformers), linear potentiometers, and microswitches have been used where remote or continuous readings arerequired(asshowninFig.1).Anothert
26、ypeofreadoutrecentlydevelopedisanoncontactremovablesonicprobedigitalreadout systemwhichisinterchangeablewiththedepthmicrometertype.Multipointrodextensometershaveuptoeightmeasuringpoints. Reduced rod diameters are required for multipoint instruments and have been used effectively to depths of at leas
27、t 150 ft (45 m). FIG. 1 Rod Extensometer D440312 2The rod acts as a rigid member and must react in both tension and compression. When used in deep applications, friction caused by drill hole misalignment and rod interference can cause erroneous readings. 5.2.2 Bar ExtensometersBar extensometers are
28、generally used to measure diametric changes in tunnels. Most bar extensometersconsistofspring-loaded,telescopictubesthathavexedadjustmentpointstocoverarangeofseveralfeet.Thexed points are generally spaced at 1 to 4-in. (25 to 100-mm) increments. A dial gage is used to measure the displacements betwe
29、en the anchor points in the rock (as shown in Fig. 2). If the device is not constructed from invar steel, ambient temperature should berecordedandthenecessarycorrectionsappliedtotheresults.Barextensometersareprimarilyusedforsafetymonitoringdevices in mines and tunnels. 5.2.3 TapeExtensometersSuchdev
30、icesaredesignedtobeusedinmuchthesamemannerasbarextensometers,however,tape extensometers allow the user to measure much greater distances, such as found in large tunnels or powerhouse openings. Tape extensometers consist of a steel tape (preferably invar steel), a tensioning device to maintain consta
31、nt tension, and a readout head. Lengths of tape may be pulled out from the tape spool according to the need. The readout may be a dial gage or a vernier, and the tensioning mechanism may be a spring-loading device or a dead-weight (as shown in Fig. 3 and Fig. 4).The tape and readout head are fastene
32、d, or stretched in tension, between the points to be measured.Accuracies of 0.010 to 0.002 in. (0.25 to 0.05 mm) can be expected, depending on the length of the tape and the ability to tension the tape to the same value on subsequent readings, and provided that temperature corrections are made when
33、necessary. 5.2.4 Joint MetersNormally, joint meters consist of an extensometer xed across the exposed surface of a joint (as demonstrated in Fig. 5), and are used to measure displacements along or across joints. The joint movements to be measured may be the opening or closing of the joint or slippag
34、e along the joint. Rod-type extensometers are generally used as joint meters with bothendsxedacrossthejoint.Presetlimitswitchesareoftenmountedonthejointmetertoserveasawarningdeviceinproblem areas such as slopes and foundations. 5.2.5 WireExtensometersSuchdevicesutilizeathinstainlesssteelwiretoconnec
35、tthereferencepointandthemeasuringpoint of the instrument (as shown in Fig. 6). This allows a greater number of measuring points to be placed in a single drill hole. The wireorwiresaretensionedbyspringsorweights.Thewireisextendedoverarollershivandconnectedtoahangingweight.Wire extensometers tensioned
36、 by springs have the advantage of variable spring tension caused by anchor movements. This error must be accounted for when reducing the data. Wire-tensioned extensometers have been used to measure large displacements at drill holedepthsuptoapproximately500ft(150m).Theinstrumentsusedfordeepmeasureme
37、ntsgenerallyrequiremuchheavierwire and greater spring tensions.Although wire extensometers are often used in open drill holes for short-term measurements, in areas of poor ground or unstable holes it is necessary to run a protective sleeve or tube over the measuring wires between the anchors. 5.3 An
38、chor Systems: FIG. 2 Bar Extensometer D440312 35.3.1 GroutableAnchorsThese were one of the rst anchoring systems used to secure wire extensometer measuring points in the drill hole. Groutable anchors are also used for rod type extensometers. Initially PVC (poly(vinyl chloride) pipes clamped FIG. 3 T
39、ape Extensometer with Vernier Readout and Deadweight FIG. 4 Tape Extensometer with Dial Gage and Tension Spring FIG. 5 Joint Meters D440312 4between the anchor points were employed to isolate the measuring wires from the grout column (as shown in Fig. 7), however, thisarrangementwasunreliableatdepth
40、sgreaterthan25ft(7.5m)becausethehydrostaticheadpressureofthegroutcolumnoften collapsed the PVC tubing. To counteract this condition, oil-lled PVC tubes were tried. The use of oil enabled this method to be used to depths of over 50 ft (15 m).As an alternative to this system, liquid-tight exible steel
41、 conduit is used to replace the PVC pipe.This alternative system seems to work well and can be used in most applications. Resin anchors fall in this category and are very successful. 5.3.2 Wedge-Type AnchorsThese consist of a mechanical anchor that has been widely used for short-term anchoring appli
42、cations in hard rock. Fig. 8 shows the two basic types of wedge anchors: (1) the self-locking spring-loaded anchor, and (2) the mechanical-locking anchor. Self-locking anchors, when used in areas subject to shock load vibrations caused by blasting or other construction disturbances, may tend to slip
43、 in the drill holes or become more deeply-seated, causing the center wedge to move.Another disadvantage of the wedge anchor is that no protection is offered, if using wires, to the measuring wires in the drill hole against damage that might be caused by water or loose rock. 5.3.3 Hydraulic AnchorsTh
44、ese anchors have proven to be successful in most types of rock and soil conditions. Fig. 9 shows the two basic types of hydraulic anchors manufactured for use with extensometer systems: (1) the uncoiling Bourdon tube anchor, and (2) the hydraulic piston of grappling hook anchor, which is limited to
45、soft rock and soils. Both anchors have the disadvantage of being rather costly. The Bourdon tube anchor works well in most rock and soil conditions and the complete anchor system can be fabricated before installing it in the drill hole. There have been other specialized anchor systems developed, how
46、ever, these systems have proven to be too costly and unsuccesful for most applications. FIG. 6 Wire Extensometers FIG. 7 Grouted Anchor System D440312 55.4 Extensometer TransducersThese extensometers convert displacements occurring in in-situ materials between two anchored points to mechanical movem
47、ents that can be measured with conventional measuring devices such as dial gages, LVDTs, strain gages, and the like. 5.4.1 Depth-Measuring InstrumentsAdialgage,oradepthmicrometerarethesimplestandmostcommonlyusedmechanical measuringinstruments.Usedinconjunctionwithextensometers,theyprovidethecheapest
48、andsurestmethodsofmakingaccurate measurements. When using the dial gage or depth micrometer, the operator is required to take readings at the instrument head, however, local readings may not be practical or possible due to the instrument location or area conditions. 5.4.2 Electrical TransducersFor r
49、emote or continuous readings, electrical transducers are used rather than dial gages. LVDTs are often used because of their accuracy, small size, and availability. LVDTs require electrical readout equipment consisting of an a-c regulated voltage source and an accurate voltmeter, such as a digital voltmeter or bridge circuit. The use of linear potentiometers or strain gages is often desirable because of the simplicity of the circuitry involved. The disadvantage of using linear potentiometers is their inherently poor linearity and resolution. 5.4
