1、Designation: D 4623 08Standard Test Method forDetermination of In Situ Stress in Rock Mass by OvercoringMethodUSBM Borehole Deformation Gauge1This standard is issued under the fixed designation D 4623; the number immediately following the designation indicates the year oforiginal adoption or, in the
2、 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 in a rock mas
3、s and the equipment required toperform in situ stress tests using a three-component boreholedeformation gauge (BDG). The test procedure and method ofdata reduction are described, including the theoretical basis andassumptions involved in the calculations. A section is includedon troubleshooting equi
4、pment malfunctions.NOTE 1The gauge used in this test method is commonly referred to asa USBM gauge (U.S. Bureau of Mines three-component borehole defor-mation gauge).21.2 The values stated in inch-pound units are to be regardedas standard. No other units of measurement are included in thisstandard.1
5、.3 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 limitations prior to use.2. Referenced Do
6、cuments2.1 ASTM Standards:3D 653 Terminology 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 4394 Test Method for Determining the In Situ Modulusof Def
7、ormation of Rock Mass Using the Rigid PlateLoading MethodD 4395 Test Method for Determining In Situ Modulus ofDeformation of Rock Mass Using Flexible Plate LoadingMethodD 6026 Practice for Using Significant Digits in Geotechni-cal DataD 7012 Test Method for Compressive Strength and ElasticModuli of
8、Intact Rock Core Specimens under VaryingStates of Stress and Temperatures3. Terminology3.1 Definitions: See Terminology D 653 for general defini-tions.3.2 Definitions:3.2.1 deformationdisplacement change in dimension ofthe borehole due to changes in stress.3.2.2 in situ stressthe stress levels and o
9、rientations exist-ing in the rock mass before excavation.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 d
10、iameters of the smallhole, 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
11、to be numericallyequal, 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.5. S
12、ignificance and Use5.1 Either virgin stresses or the stresses as influenced by anexcavation 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 met
13、hod is generally performed at depths within50 ft (15 m) of the working face because of drilling difficultiesat greater depths. Some deeper testing has been done, but1This test method is under the jurisdiction ofASTM Committee D18 on Soil andRock and is the direct responsibility of Subcommittee D18.1
14、2 on Rock Mechanics.Current edition approved July 1, 2008. Published July 2008. Originally approvedin 1986. Last previous edition approved in 2005 as D 4623 05.2Considerable information presented in this test method was taken from Bureauof Mines Information Circular No. 8618, and Hooker, V.E., and B
15、ickel, D.L.,“Overcoring Equipment and Techniques Used in Rock Stress Determination,”Denver Mining Research Center, Denver, 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 inform
16、ation, refer to the standards Document Summary page onthe ASTM website.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.should be considered developmental. It is also u
17、seful forobtaining stress characteristics of existing concrete and rockstructures for safety and modification investigations.5.3 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 data.5.4 The rock tested
18、 is assumed to be homogeneous andlinearly elastic. The moduli of deformation and Poissons ratioof the rock are required for data reduction. The preferredmethod for determining modulus of deformation values in-volves biaxially testing the recovered overcores, as describedin Section 8. If this is not
19、possible, values may be determinedfrom uniaxial testing of smaller cores in accordance with TestMethod D 7012. However, this generally decreases the accu-racy of the stress determination in all but the most homoge-neous rock. Results may be used from other in situ tests, suchas Test Method D 4394 an
20、d Test Method D 4395.5.5 The physical conditions present in three separate drillholes are assumed to prevail at one point in space to allow thethree-dimensional stress field to be estimated. This assumptionis difficult to verify, as rock material properties and the localstress field can vary signifi
21、cantly over short distances. Confi-dence in this assumption increases with careful selection of thetest site.5.6 Local geologic features with mechanical propertiesdifferent from those of the surrounding rock can influencesignificantly the local stress field. In general, these features, ifknown to be
22、 present, should be avoided when selecting a testsite location. It is often important, however, to measure thestress level on each side of a large fault. All boreholes at asingle test station should be in the same formation.5.7 Since most overcoring is performed to measure undis-turbed stress levels
23、, the boreholes should be drilled from aportion of the test opening at least three excavation diametersfrom any free surface. The smallest opening that will accom-modate the drilling equipment is recommended; openings from8 to 12 ft (2.4 to 3.6 m) in diameter have been foundsatisfactory.5.8 Aminimum
24、 of three nonparallel boreholes is required todetermine the complete 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 general
25、ly easier to work in than holes inclined downward,particularly in 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
26、 D 3740 are generally considered capable of competentand objective testing/sampling/inspection/ and the like. Users of thisstandard are cautioned that compliance with Practice D 3740 does not initself assure reliable results. Reliable results depend on many factors;Practice D 3740 provides a means o
27、f evaluating some of those factors.6. Apparatus6.1 Instrumentation:6.1.1 Borehole Deformation GaugeThe USBM boreholedeformation gauge is shown in Fig. 1 (in fractured rock, thereverse-case modification of the gauge is recommended). Thegauge is designed to measure diametral deformations duringovercor
28、ing along three diameters, 60 apart in a plane perpen-dicular to the walls 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 indicat
29、orsnormally are used to read the deformations. (Alternatively, oneindicator with a switch and balance unit may be used or oneindicator may be used in conjunction with a manual wirechanging to obtain readings from the three axes.) These unitsneed a full range digital readout limit of 40 000 indicator
30、 units.Indicators need to be capable of measuring to an accuracy of65 3 106in. (13 3 105mm) with a resolution of 1 3 106in.(25 3 106mm).Acalibration factor must be obtained for eachaxis to relate indicator units to microinches deflection. The4More details of the gauge are described in: Hooker, V.E.,
31、 Aggson, J.R., andBickel, D.L., Improvements in the Three-Component Borehole Deformation Gaugeand Overcoring Techniques, Report of Investigation 7894, U.S. Bureau of Mines,Washington, DC, 1984.FIG. 1 Special Pliers, the Bureau of Mines Three-Component Borehole Gauge, a Piston, Disassembled Piston an
32、d Washer, and aTransducer with NutD4623082calibration factor for each axis will change proportionally withthe gauge factor used. Normally, a gauge factor of 0.40 givesa good balance between range and sensitivity. Fig. 2 shows atypical strain indicator, calibration jig, and a switching unit.Newer dat
33、a acquisition systems and microcomputer may besubstituted for the indicators.6.1.3 CableA shielded eight-wire conductor cable trans-mits the strain measurements 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
34、 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 Orientation and Placement Tools The orientationand placement tools consist of:6.1.4.1 Placement tool or “J slot tool” as shown in Fig. 3.6.1.4.2 Placement rod exten
35、sions as shown in Fig. 3.6.1.4.3 Orientation tool or “T handle,” also shown in Fig. 3.6.1.4.4 A scribing tool, for making an orientation mark onthe core for later biaxial testing, is optional. It consists of abullet-shaped stainless steel head attached to a 3-ft (1-m) rodextension. Projecting perpen
36、dicularly 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 is scratchedalong the borehole wall as the scribing tool is pushed inward.6.1.4.5 Pajari alignment device for inserting into the hole todetermine the incl
37、ination. It consists of a floating compass andan automatic locking device which locks the compass inposition before retrieving it.6.1.5 Calibration JigA calibration jig (Fig. 2) is used tocalibrate the BDG before and after testing.6.1.6 Biaxial ChamberA biaxial chamber with hand hy-draulic pump and
38、pressure gauge is used to determine thedeformation modulus of the retrieved rock core.Aschematic ofthe apparatus is shown in Fig. 4.6.2 Drilling EquipmentA detailed description of the drill-ing apparatus is included in Annex A1.6.3 Miscellaneous EquipmentThis field operation re-quires a good set of
39、assorted hand tools which should includea soldering iron, solder and flux, heat gun, pliers, pipewrenches, adjustable wrenches, end wrenches, screwdrivers,allen wrenches, a hammer, electrical tape, a yardstick, carpen-ters rule, chalk, stopwatch, and a thermometer.7. Calibration and Standardization7
40、.1 Gauge CalibationCalibrate the BDG prior to begin-ning and end of the test program, or more frequently ifconditions require. Also recalibrate the BDG if it has under-gone severe vibration (especially to the signal cable), or if thereare any other reasons that exist to suspect that the gaugeperform
41、ance has changed. The recommended calibration pro-cedure is as follows:7.1.1 Grease all gauge pistons with a light coat of siliconegrease and install them in the gauge.7.1.2 Place the gauge in the calibration jig as shown in Fig.2, with the pistons of the U axis visible through the micrometerholes o
42、f the jig. Tighten the wing nuts.7.1.3 Install the two micrometer heads, and lightly tightenthe set screws.7.1.4 Set the strain indicators on “Full Bridge,” and thencenter the balance knob and set the gauge factor to correspondto the respective anticipated in-situ range and sensitivityFIG. 2 The Cal
43、ibration Device (Left Side) and a Switching Unit (Right Side)D4623083requirements.Alower gauge factor results in higher sensitivity.The gauge factor used should be the same for calibration,in-situ testing, and modulus tests.7.1.5 Wire the gauge to the indicators as shown in Fig. 5 orto a switching a
44、nd balance unit and one indicator.7.1.6 Balance the indicator using the “Balance” knob (ifusing three indicators).7.1.7 Turn one micrometer in until the needle of theindicator just starts to move. The micrometer is now in contactwith the piston. Repeat with the other micrometer.7.1.8 Rebalance the i
45、ndicator.7.1.9 Record this no load indicator reading for the U axis.7.1.10 Turn in each micrometer 0.0160 in. (0.406 mm), or atotal of 0.0320 in. (0.813 mm) displacement.7.1.11 Balance the indicator and record the reading and thedeflection.7.1.12 Wait 2 min to check the combined creep of the twotran
46、sducers. Creep should not exceed 20 in./in. (20 mm/mm)in 2 min.7.1.13 Record the new reading.7.1.14 Back out each micrometer 0.0040 in. (0.102 mm) atotal of 0.0080 in. (0.203 mm).7.1.15 Balance and record.7.1.16 Continue this procedure with the same incrementsuntil the initial point on the micromete
47、r is reached. This zerodisplacement will be the zero displacement reading for thesecond run.7.1.17 Repeat the operations described in 7.1.10-7.1.16.FIG. 3 Placement and Retrieval ToolFIG. 4 Schematic: Biaxial Test ApparatusD46230847.1.18 Loosen the wing nuts, and rotate the gauge to alignthe piston
48、of the U2axis with the micrometer holes.7.1.19 Retighten the wing nuts.7.1.20 Repeat the operations described in 7.1.6-7.1.17.7.1.21 Loosen wing nuts, and align pistons of U3axis withmicrometer holes. Repeat the calibration procedure followedfor the U1and U2axis.7.1.22 Determine the calibration fact
49、or for each axis asfollows:7.1.22.1 Subtract the zero displacement strain indicatorreadings (last reading of each run) from the indicator readingfor each deflection to establish the differences.7.1.22.2 Subtract the difference in indicator units at 0.0080-in. (0.203-mm) deflection from the difference in indicator unitsat 0.0320-in. (0.813-mm) deflection.7.1.22.3 Divide the difference in deflection 0.0240 in.(0.610 mm) by the corresponding difference in indicator unitsjust calculated to obtain the calibration factor for that axis.7.1.22.4 Repeat for the s
