1、Designation: D4623 16Standard Test Method forDetermination of In Situ Stress in Rock Mass by OvercoringMethodThree Component Borehole Deformation Gauge1This standard is issued under the fixed designation D4623; the number immediately following the designation indicates the year oforiginal adoption o
2、r, in the case 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 determination of the ambi-ent local stresses (pri
3、ncipal and secondary) in a rock mass andthe equipment required to perform in situ stress tests using athree-component borehole deformation gauge (BDG) that wasdeveloped by the U.S. Bureau of Mines (USBM); see Note 1.1.2 The test procedure and method of data reduction aredescribed, including the theo
4、retical basis and assumptionsinvolved in the calculations.1.3 A section is included on troubleshooting equipmentmalfunctions.NOTE 1The gauge used in this test method is commonly referred to byusers as a USBM gauge (U.S. Bureau of Mines three-component boreholedeformation gauge).21.4 The values state
5、d in inch-pound units are to be regardedas standard, except as noted below. The values given inparentheses are mathematical conversions to SI units, whichare provided for information only and are not consideredstandard. Reporting of test results in units other than SI shallnot be regarded as nonconf
6、ormance with this test method.1.5 This standard does not purport to address all of thesafety problems, 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 limitation
7、s prior to use.2. Referenced Documents2.1 ASTM Standards:3D653 Terminology Relating to Soil, Rock, and ContainedFluidsD3740 Practice for Minimum Requirements for AgenciesEngaged in Testing and/or Inspection of Soil and Rock asUsed in Engineering Design and ConstructionD4394 Test Method for Determini
8、ng In Situ Modulus ofDeformation of Rock Mass Using Rigid Plate LoadingMethodD4395 Test Method for Determining In Situ Modulus ofDeformation of Rock Mass Using Flexible Plate LoadingMethodD4971 Test Method for Determining In Situ Modulus ofDeformation of Rock Using Diametrically Loaded 76-mm(3-in.)
9、Borehole JackD6026 Practice for Using Significant Digits in GeotechnicalDataD7012 Test Methods for Compressive Strength and ElasticModuli of Intact Rock Core Specimens under VaryingStates of Stress and Temperatures3. Terminology3.1 Definitions:3.1.1 For terminology used in this test method, refer to
10、Terminology D653.3.2 Definitions of Terms Specific to This Standard:3.2.1 deformation, ndisplacement change in dimension ofthe borehole due to changes in stress.3.2.2 in situ stress, nthe stress levels and orientationsexisting in the rock mass before excavation.3.2.3 principal plane, nany plane in w
11、hich the shearstresses are zero.3.2.4 principal stresses, nthe normal stresses acting on thethree principal planes and which are perpendicular to eachother.3.2.4.1 DiscussionThe major, intermediate or minor nor-mal or principal stresses refers to the maximum, intermediateand minor normal stresses oc
12、curring in the rock element.3.2.5 reverse case, nin rock which tends to fracture easily,“disc” or “poker chip” during overcoring, the borehole gaugecan be modified by replacing the standard housing with a“reverse case” housing which allows the cantilever plungers tobe positioned very close to the st
13、art of the EX hole.1This 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 Dec. 1, 2016. Published January 2017. Originallyapproved in 1986. Last previous edition approved in 2
14、005 as D4623 05. DOI:10.1520/D4623-08.2Considerable information presented in this test method was taken from Bureauof Mines Information Circular No. 8618, and Hooker, V.E., and Bickel, D.L.,“Overcoring Equipment and Techniques Used in Rock Stress Determination,”Denver Mining Research Center, Denver,
15、 CO, 1974.3For 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.*A Summary of Changes section appears at the end of
16、 this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelo
17、pment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.13.2.6 secondary principal stresses, nthe maximum, inter-mediate and minimum stresses for stress ellipsoids other thanthe stress ellipsoid that contains the
18、 three maximum principalstresses.4. Summary of Test Method4.1 The overcore test measures the diametral deformation ofa small-diameter borehole as it is removed from the surround-ing stress field by coaxially coring a larger diameter hole.Deformation is measured across three diameters of the smallhol
19、e, spaced 60 apart, using a deformation gauge developedby the U.S. Bureau of Mines. With knowledge of the rockdeformation moduli, the measured borehole deformation canbe related to the change in stress in a plane perpendicular to theborehole. This change in stress is assumed to be numericallyequal,
20、although opposite in sense to the stresses existing in theparent rock mass. Deformation measurements from threenonparallel boreholes, together with rock deformation moduli,allow calculation of an estimate of the complete three-dimensional state of stress in the rock mass. Deformationmeasurements in
21、only one drill hole direction will only give thesecondary principal stresses unless something is known aboutone of the principal stress directions and the drill hole axis isaligned with that principal stress direction.5. Significance and Use5.1 Either the in situ stresses or the stresses as influenc
22、ed byan excavation may be determined. This test method is writtenassuming testing will be done from an underground opening;however, the same principles may be applied to testing in arock outcrop at the surface.5.2 This test method is generally performed at depths within50 ft (15 m) of the working fa
23、ce because of drilling difficultiesat greater depths. Some deeper testing with this gauge has beendone, but should be considered developmental. This testmethod has a long and proven record and considered veryaccurate relative to many other techniques, both new and old,out there. Other overcoring met
24、hods that use instruments thatare different, but follow much of the same basic concepts arenow available and can go deeper; however, the pros and consof each method need to be carefully compared to this testmethod.5.3 It is also useful for obtaining stress characteristics ofexisting concrete and roc
25、k structures, such as mass concretedams, for safety (such as alkali aggregate issues), vetting ofcomputer models, and modification investigations.5.4 This test method is difficult in rock with fracturespacings of less than 5 in. (130 mm). A large number of testsmay be required in order to obtain dat
26、a.5.5 The rock tested is assumed to be homogeneous andlinearly elastic. The moduli of deformation and Poissons ratioof the rock overcore are required for data reduction. Thepreferred method for determining modulus of deformationvalues involves biaxially testing the recovered overcores, asdescribed i
27、n Section 8. If this is not possible, values may bedetermined from uniaxial testing of smaller cores in accor-dance with Test Method D7012. However, this generallydecreases the accuracy of the stress determination in all but themost homogeneous and isotropic rock. Modulus of deforma-tion results may
28、 be used from other in situ tests, such as TestMethods D4394 and Test Method D4395, D4971 or other testmethods that can determine the modulus of deformation inspecific directions.5.6 The physical conditions present in three separate drillholes are assumed to prevail at one point in space to allow th
29、ethree-dimensional stress field to be estimated. This assumptionis difficult to verify, as rock material properties and the localstress field can vary significantly over short distances. Confi-dence in this assumption increases with careful selection of thetest site.5.7 Local geologic features with
30、mechanical propertiesdifferent from those of the surrounding rock can influencesignificantly the local stress field. In general, these features, ifknown to be present, should be avoided when selecting a testsite location. It is often important, however, to measure theFIG. 1 Three-Component Borehole
31、Deformation Gauge Showing Outer Housing Pulled Apart with Cable Assembly on Top Right; Three-Component Pistom Assembly in Center and Outer Protective Cover on Left. Special Pliers for Working on Gauge at the Top, a Piston,Dissassembled Piston and Washer (lower left), and a Transducer with Nut (lower
32、 right)D4623 162stress level on each side of a large fault. All boreholes at asingle test station should be in the same formation or rockmass.5.8 Since most overcoring is performed to measure in situstress levels, the boreholes should be drilled from a portion ofthe test opening and the testing perf
33、ormed at least threeexcavation diameters from any free surface. The smallestopening that will accommodate the drilling equipment isrecommended; openings from 8 to 12 ft (2.4 to 3.6 m) indiameter have been found satisfactory.5.9 Aminimum of three nonparallel boreholes is required todetermine the comp
34、lete stress tensor. The optimum angle eachhole makes with the other two (trihedral arrangement) is 90.However, angles of 45 provide satisfactory results for deter-mining all three principal stresses. Boreholes inclined upwardare generally easier to work in than holes inclined downward,particularly i
35、n fractured rock.NOTE 2The quality of the result produced by this standard isdependent on the competence of the personnel performing it, and thesuitability of the equipment and facilities used. Agencies that meet thecriteria of Practice D3740 are generally considered capable of competentand objectiv
36、e testing/sampling/inspection/ and the like. Users of thisstandard are cautioned that compliance with Practice D3740 does not initself assure reliable results. Reliable results depend on many factors;Practice D3740 provides a means of evaluating some of those factors.6. Apparatus6.1 Instrumentation:
37、6.1.1 Borehole Deformation GaugeThe borehole defor-mation gauge is shown in Fig. 1 (in fractured rock, thereverse-case modification of the gauge is recommended). Thegauge is designed to measure diametral deformations duringovercoring along three diameters, 60 apart in a plane perpen-dicular to the w
38、alls of an EX (112-in. (38-mm) diameter)borehole.4Required accessories are special pliers, 0.005 and0.015 in. (0.127 and 0.381 mm) thick, brass piston washers,and silicone grease.6.1.2 Strain Readout IndicatorsThree strain readout indi-cators are normally used to read the deformations.(Alternatively
39、, one indicator with a switch and balance unitmay be used (see Fig. 2) or one indicator may be used inconjunction with a manual wire changing to obtain readingsfrom the three axes.) These units need a full range digitalreadout limit of 40,000 indicator units. Indicators need to becapable of measurin
40、g to an accuracy of 65106in.(13105mm) with a resolution of 1 106in. (25 106mm). A calibration factor must be obtained for each axis torelate indicator units to microinches deflection. The calibrationfactor for each axis will change proportionally with the gaugefactor used. Normally, a gauge factor o
41、f 0.40 gives a goodbalance between range and sensitivity. Fig. 2 shows a typicalstrain indicator, calibration jig, and a switching unit. Newerdata acquisition systems and microcomputer may be substi-tuted for the indicators.6.1.3 CableA shielded eight-wire conductor cable trans-mits the strain measu
42、rements from the gauge to the strainindicators. The length of cable required is the depth to the testposition from the surface plus about 30 ft (10 m) to reach thestrain indicators. A spare cable or an entire spare gauge andcable should be considered if many tests are planned.6.1.4 Calibration JigA
43、jig (Fig. 2) used to calibrate theBDG before and after testing with the use of two micrometerheads.4More details of the gauge are described in: Hooker, V.E., Aggson, J.R., andBickel, D.L., Improvements in the Three-Component Borehole Deformation Gaugeand Overcoring Techniques, Report of Investigatio
44、n 7894, U.S. Bureau of Mines,Washington, DC, 1984.FIG. 2 The Calibration Jig (Left Side), with the BDG Inserted, Strain Readout Unit in Middle and a Switching and Balancing Unit (RightSide)D4623 1636.1.5 Biaxial Modulus Chamber ApparatusA steel cham-ber incorporating an internal neoprene membrane wh
45、ich issized to hold the rock overcore internally and which inconjunction with a hand hydraulic pump and pressure gaugeand permits a known and sufficient biaxial pressure to beapplied hydraulically to the overcore sample while the BDG isinserted and deformation readings are taken. Ideally the maxi-mu
46、m pressure should be similar to the best estimates of the insitu rock stress, but usually should not exceed 3000 psi(20MPa). The biaxial chamber is used to obtain data that isthen used for determining the deformation modulus of theretrieved rock core. A schematic of the entire apparatus isshown in F
47、ig. 3.6.2 Orientation, Placement, and Retrieval Tools6.2.1 Placement and retrieval tool or “J slot tool” as shownin Fig. 4.6.2.2 Placement or retrieval rod extensions as shown in Fig.4.6.2.3 Orientation tool or “T” handle, also shown in Fig. 4.6.2.4 Ascribing tool, for making an orientation mark on
48、thecore for later biaxial testing, is optional. It consists of abullet-shaped stainless steel head attached to a 3-ft (1-m) rodextension. Projecting perpendicularly from the stainless steelhead is a diamond stud. The stud is adjusted outward until asnug fit is achieved in the EX hole, so that a line
49、 is scratchedalong the borehole wall as the scribing tool is pushed inward.6.2.5 Pajari alignment device for inserting into the hole todetermine the inclination. It consists of a floating compass andan automatic locking device which locks the compass inposition before retrieving it.6.3 Drilling EquipmentA detailed description of the drill-ing apparatus required is included in Annex A1.6.4 Miscellaneous EquipmentThis field operation requiresa good set of assorted hand tools which should include asoldering iron, solder and flux, heat gun, pliers, pi
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