■ u' 
 
 
 *• "% V 
 ^ ^ 
 
 < o 
 
 > ^ -3 
 
 
 
 vv 
 
 
 
 A . I. ' • „ ^ 
 
 ,6 V c>. 
 
 * a v ^ 
 
 
 
 
 V, * o „ o ° 
 
 a0 
 
 
 
 * a7 v 
 
 V 
 
 ^ 9m^^ ++# o 
 
 »b K 
 
 A "7j 
 
 , r ^^ 
 
 * V •*>■ • SIB * <v <«> * 
 
 , -^ V -?!fwa* a* % * - 
 
 
 fV , o " 5 
 
 * 
 
 '- 
 
 
 
 
 8 ^ v *v 
 
 v^ 
 
 
 
 **. a ' .^v>»:« '^ jf 
 
 
 A < 
 
 A" .."«. 
 
 «^q* 
 
 <?-. 
 
 :>;:^>,^>;:->:^x- T; :v<ti-i:X 
 
 % S11 *o* 
 
 /^ 
 
 
 
 %/ : 
 
 
 
 V 7 ^' -^ 
 
 A. v ^J. 
 
 
 ^•0* 
 
 
 A ^ *..»• .6' 
 
 
 
 'bV 
 
 
 1 rt- 1 
 
 r. ^ j ' /^V/jl'-. % >' 
 
 .Asia*.^ .. v ^:^i:.X J>s*ri:~* 
 
 
 » A^ %« 
 
 
 C^_ *• 
 
 %> 
 ^ 
 
 
 
 ♦bv" 
 
 
 
 
 A^ ^ 
 
 ^0^ 
 
 % 
 
 *bV" 
 
 a0^ »1^L'. *> 
 
 *«-•. ^ .<^ ^aR" "^ ^ SA%fA°„ V t s*' 
 
 ; a^ v ^ 
 
 ^^ v 
 6 ^v 
 
 * A* <*> •> 
 
 
 v'o "V A* ,^ 
 
 
 '*^* v 
 
 ... ** \-s^/ \--^-\^ *<.*--ft--*X X'^Sf'V V--.^->* ^ 
 
 ^ \. ^ /ifitei-. ^ ^ ^V^. V>* /^te\ %^ :Mk\ \«& 
 
 .0 C° " ° ". o 
 
 
 
 
 * A v > 
 
 ^°^ 
 
 o -5 Oft 
 
 A 
 
 „ ^ 
 
 ^o« 
 
 4 ^ 
 .A 
 
 a V 
 
 -*. --•-/... v-^y\./v--'„*°^../<--\>^.. "^••"''•;,^^.:%'- 
 
 
 
* o. 
 
 o_ * 
 
 jP<*. 
 
 > ^ 
 
 
 P-*. tMK.' vlq. 
 
 
 mi ^ 
 
 '• ** A* ^ 
 
 4* &+ "%1^^\ A* "^ 
 
 *bv* 
 
 
 • * A <► *^.> A*" V **T7T»* A <* "*o.1 
 
 o V 
 
 ^ * 
 
 W 
 
 
 fc. ^«^\° &~* v^ns^ _r*+ A °- 
 
 jpv\ : 
 
 * -t. 
 
 
 
 
 > -^ 
 
 *• vj&V 
 
 ? 
 
 - 
 
 
 a* V ^ °. 
 
 
 • % ^ 
 
 
 
 ': *^* 
 
 
 
 
 VV 
 
 
 
 
 
 
 .* ^ v 
 
 I. V A *°c!Atfk:-^ ^..i-i-V .*°.!Aa^%^ ^ t :^'. e . 
 
 • .o 
 
 
 1 ^o ^' 
 
 
 <>. c^ 
 
 c ^- ^' 
 
 
 
 g f , . . , <^ * • » » - 
 
 
 'k./'WJ? 
 
 
 
 
 
 r%= s A 
 
 »bV* 
 
 >°^ 
 
 
 0^ 
 
 
 v-o* 
 
 /°- 
 
 
 £*<* \ 
 
 J ^^ 
 
 
 >^ .^ U ^ 
 
 
 
 c% * 
 
 -ov* :m%&* ^o 4 ;^M". "bv* 
 
 
 
 - --_ 
 
 
 °o J 
 
 ,V . . o . -*•„ 
 
 
 »P^.. 
 
 * "^ . 
 
 
 
 & v 
 
 
 
 ^^ 
 
 
 ,1' , -^» » • » aw *^, " • • s " v 
 
 ;- '^o< f 
 
 o N ° * ' n 
 
 A v 
 
 <^ ^ 
 
 
 jP^. 
 
 t'? 1 ^^ 
 
 
 ^^ 
 
 
 A v 
 
 4 o 
 
 
 
 ,/\. 
 
 
 
 
 V* V 
 
 
 
 < o 
 
 
 
 ^ ^ ^*. --SBV . * 
 
 * A 1 *Xs 
 
 ' «*' 
 
 
 A 9. 
 
 o k 
 
 '",^0 
 
 ■<<•. A » 
 f i0h\ *<? 
 
 54 aV^ . ^ ' 
 
 rt- A v *- 
 
 if CI 
 
 
 o^ 
 
 <> *^.^* .A^ 'b, *^vT*' A < 
 
 ^b. 
 
 
 
 
 ^. -^ 
 
 
 <u 
 
 
 
 
 *bv* 
 
 ♦ J s55tt^*.. v> 
 
 ^ A 
 
 ^tff 
 
 > w ^ «^° A s "- 
 
 A v ..- 
 
 
 
IC 9 ° 13 
 
 Bureau of Mines Information Circular/1985 
 
 Overcoring Equipment and Techniques 
 Used in Rock Stress Determination 
 (An Update of IC 8618) 
 
 By David L. Bickel 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 
 75! 
 
 AMINES 75TH A^ 
 
Information Circular 9013 
 
 Overcoring Equipment and Techniques 
 Used in Rock Stress Determination 
 (An Update of IC 8618) 
 
 By David L. Bickel 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 Donald Paul Hodel, Secretary 
 
 BUREAU OF MINES 
 Robert C. Horton, Director 
 

 Library of Congress Cataloging in Publication Data: 
 
 Bickel, David L 
 
 Overcoring equipment and techniques used in rock stress determina- 
 tion (an update of IC 8618). 
 
 (Information circular / United States Department of the Interior, Bu- 
 reau of Mines ; 9013) 
 
 Bibliography: p. 21. 
 Supt. of Docs, no.: I 28.27:9013. 
 
 1. Rocks— Testing— Equipment and supplies. 2. Rock mechanics. I. 
 Title. II. Series: Information circular (United States. Bureau of Mines) ; 
 
 9013. 
 
 TN295.U4 [TA706.5] 622s [624. 1*5132] 84-600280 
 
CONTENTS 
 
 Page 
 
 \^Abstract 1 
 
 Introduction 2 
 
 KJ Acknowledgment 2 
 
 Drilling equipment 2 
 
 Instrumentation 7 
 
 Site selection 9 
 
 Overcoring procedure 11 
 
 Procedure for operating the three-component borehole gauge 16 
 
 Procedure for biaxial testing of the overcore to determine its anisotropic 
 
 parameters 17 
 
 Borehole gauge calibration 18 
 
 Calibration data analysis 19 
 
 Identification of source of borehole gauge malfunction 20 
 
 Lack, of balance on one or more indicators 20 
 
 Insensitivity of one or more elements on indicator 20 
 
 Lack of component balance 20 
 
 Sensitivity of indicators when touched 20 
 
 References 21 
 
 Appendix. — Equipment diagrams 22 
 
 ILLUSTRATIONS 
 
 1. Type CP-65 air drill 3 
 
 2. EX-size bit with core spring, reamer, and 2-ft EWX core barrel 3 
 
 3. Stabilizer on 2-ft section of EW drill rod, stabilizer on 1-ft section 
 
 of BX wire line drill rod, and 2-ft piece of BX wire line drill rod.... 4 
 
 4. Water swivel with solid plug and plug used during overcoring 4 
 
 5. Core barrel, 6 in. in diam by 27 in long (referred to as a 2-ft core 
 
 barrel), and disassembled expander head 5 
 
 6. Expander head assembled (adapted for BX wire line drill rod) and 6-in- 
 
 diam core barrel 5 
 
 7. Starting the 6-in-diam overcoring hole 5 
 
 8. Starter barrel, 6 in. in diam by 1 ft long, with pilot and expander 
 
 head adapted for EW drill rod 6 
 
 9 . Centering stabilizer 6 
 
 10. Starting the EX hole in the bottom of the 6-in-diam hole 6 
 
 11. Core breaker, core shovel, and core puller 7 
 
 12. Retrieval tool used in place of core puller to retrieve 6-in-diam core 
 
 from a vertical hole that has an EX hole through the core 7 
 
 13. Special pliers, Bureau of Mines three-component borehole gauge, piston, 
 
 disassembled piston and washer, and transducer with nut 8 
 
 14. Strain indicator with calibration device and switching unit 8 
 
 15. Placement and retrieval tool 9 
 
 16. Biaxial chamber and pump 10 
 
 17. Drill hole configurations 10 
 
 18. Setup for three-component (3-D) borehole gauge emplacement 11 
 
 19. Wire hookup to strain indicators 12 
 
 20. Field data sheet 13 
 
 21. Positioning three-component (3-D) borehole gauge with placement rod 
 
 through the 6-in-diam core barrel and drill rod 14 
 
 k A-l . Three-component (3-D) borehole gauge 22 
 
 l v A-2. Borehole gauge placing and retrieving tool 23 
 
ILLUSTRATIONS— Continued 
 
 Page 
 
 A-3. Calibration jig and transducer testing jig 24 
 
 A-4. Biaxial pressure chamber 25 
 
 A-5. Borehole gauge placement tool for biaxial chamber 26 
 
 A-6. Triaxial pressure chamber 27 
 
 
 UNIT OF MEASURE ABBREVIATIONS 
 
 USED IN 
 
 THIS REPORT 
 
 ft 
 
 foot 
 
 
 pet 
 
 percent 
 
 hp 
 
 horsepower 
 
 
 psi 
 
 pound per square inch 
 
 in 
 
 inch 
 
 
 rpi 
 
 revolution per inch 
 
 min 
 
 minute 
 
 
 rpm 
 
 revolution per minute 
 
 pin 
 
 microinch 
 
 
 s 
 
 second 
 
 yin/in 
 
 microinch per 
 
 inch 
 
 
 
OVERCORING EQUIPMENT AND TECHNIQUES USED 
 
 IN ROCK STRESS DETERMINATION 
 
 (AN UPDATE OF IC 8618) 
 
 By David L. Bickel 1 
 
 ABSTRACT 
 
 Stress-relief techniques and instrumentation have been developed 
 through many years of research in the Bureau of Mines and successfully 
 used to determine the in situ state of stress in rock. This report de- 
 scribes the Bureau's three-component borehole deformation gauge and the 
 drilling equipment and accessories used with it. Operation and calibra- 
 tion procedures for the deformation gauge are discussed in detail, along 
 with site selection and overcoring procedures. Information and refer- 
 ences included in this publication provide a guide to the Bureau's over- 
 coring method for determining rock stress. 
 
 'Physical scientist, Denver Research Center, Bureau of Mines, Denver, CO. 
 
INTRODUCTION 
 
 This publication updates some of the 
 overcoring procedures described in IC 
 8618 06). 2 It also includes the field 
 biaxial testing procedure used for deter- 
 mining the modulus of elasticity, as well 
 as additional references not previously 
 available. 
 
 The Bureau of Mines three-component 
 borehole deformation gauge (9^, which 
 measures three diameters 60° apart and 
 has all sensing elements in the same 
 plane, is designed to measure diametral 
 deformations of a 1-1/2-in borehole dur- 
 ing stress relief by overcoring. The 
 process essentially consists of (1) 
 drilling a 1-1/2-in-diam gauge hole 
 (pilot hole) with a diamond bit and ream- 
 er, (2) positioning the gauge in the 
 gauge hole, and (3) drilling over the 
 gauge with a 6-in-diam thin-walled dia- 
 mond masonry bit. The 6-in core is cut 
 in one continuous run, and the deforma- 
 tion readings are taken at the start, 
 during, and at the end of the run. After 
 overcoring is completed, the gauge is re- 
 moved and the core is freed from the 
 bottom of the hole and retrieved. The 
 
 core orientation and the position of the 
 gauge are marked on the core. 
 
 The marked core is then tested in a bi- 
 axial chamber (4) to determine the physi- 
 cal properties of the rock. The physical 
 properties and the deformation measure- 
 ments from each overcore are used to cal- 
 culate the stress distribution in the 
 plane normal to the axis of the borehole. 
 The core can then be prepared and tested 
 in a triaxial chamber (10) at the same 
 stress level it experienced in situ 
 (which is not always possible during bi- 
 axial testing) to determine Poisson's ra- 
 tio and a more accurate modulus of elas- 
 ticity. The effects of anisotropy can be 
 included in these calculations (1). If 
 borehole deformation measurements are ob- 
 tained from at least three nonparallel 
 holes, the three-dimensional representa- 
 tion of the average ground stress compo- 
 nents can be determined (11) . A least 
 squares method of calculating the average 
 rock stress components, from more than 
 three diametral deformation measurements 
 in a borehole has been developed (3). 
 
 ACKNOWLEDGMENT 
 
 Acknowledgment is extended to Verne E. 
 Hooker, senior author of the previous 
 edition of this report. Mr. Hooker was 
 
 with the Bureau's Denver 
 before his retirement. 
 
 Research Center 
 
 DRILLING EQUIPMENT 
 
 The following drilling equipment should 
 be employed for in situ stress measure- 
 ments: 
 
 1. A drill with a chuck speed ranging 
 down to 120 rpm and a penetration rate of 
 1/2 in per 30 to 50 s using a 6-in-diam 
 overcoring bit; the chuck and quill must 
 be large enough to accomodate EW 3 drill 
 rod (fig. 1). Since drills do not 
 
 — 
 Underlined numbers in parentheses re- 
 fer to items in the list of references 
 preceding the appendix. 
 
 J E, EW, B, and N denote diameter or 
 size. 
 
 normally have chuck speeds as low as 120 
 rpm, a change in gear ratio may be neces- 
 sary. For a typical 20-hp air drill, the 
 recommended rotation speed is to 1,000 
 rpm and the feed ratios are 200, 300, 
 500, and 800 rpi. 
 
 2. Two EWX 4 double-tube swivel-type 
 core barrels, one 5 ft and one 7 ft in 
 length, and an EWX single-tube core bar- 
 rel 2 ft in length (fig. 2). 
 
 3. EX (1-1/2-in diam) diamond bits. 
 
 4 X denotes manufacturer's series of 
 equipment. 
 
FIGURE 1. - Type CP-65 air dri 
 
 FIGURE 2. - EX-size bit with core spring, reamer, and 2-ft EWX core barrel 
 
 4. A reamer for use with the EX bit 
 in the EX pilot gauge hole. 
 
 5. EW drill rod in the following 
 lengths: six 5-ft pieces, four 2-ft 
 pieces, and two 1-ft pieces. 
 
 6. Two stabilizers (5-7/8 in. in diam 
 by 8 in long) on a 2-ft length of EW 
 drill rod (fig. 3). (Note. — The stabi- 
 lizer can be made from a used 6-in-diam 
 core barrel cut 8 in long.) 
 
 7. BX wire line drill rod (fig. 3) in 
 the following lengths: three 5-ft pieces, 
 
 four 2-ft pieces, and two 1-ft pieces. 
 BX wire line drill rod has been found 
 best for overcore drilling. The inside 
 diameter of this drill rod is large 
 enough for the borehole gauge and place- 
 ment tool to pass through. Also, the 
 wire line drill rod is lightweight yet 
 has the necessary strength for overcore 
 drilling requirements. The rod has four 
 threads per inch, which is desirable to 
 provide fast coupling. 
 
 8. Two stabilizers (5-7/8 in. in 
 diam by 8 in long) on a 2-ft length of BX 
 wire line drill rod. 
 
FIGURE 3. - Stabilizer on 2-ft section of EW drill rod (upper left), stabilizer on 1-ft section of BX 
 wire line drill rod (upper right), and 2-ft piece of BX wire line drill rod (foreground). 
 
 9. An adapter sub (EW box to BX wire 
 line pin) for connecting the EW drill rod 
 in the chuck, and quill to the BX wire 
 line drill rod. 
 
 10. A water swivel having a plug with 
 a 1/2-in hole to allow threading of the 
 gauge cable when it is in use and an add- 
 itional solid plug to fit when the cable 
 is not in use (fig. 4). The water swivel 
 connects to the EW drill rod in the 
 drill. (Note. — The EW pins at the water 
 swivel and at the chuck must be drilled 
 out to at least 9/16 in ID to allow cable 
 and drilling water to pass through.) 
 
 11. An expander head for connecting 
 the BX wire line drill rod to the 6-in-OD 
 diamond overcoring bit (figs. 5-6). 
 
 12. Thin-wall masonry overcoring bits 
 6 in. in diam and long enough to obtain 
 18 in of overcore 5-5/8 in. in diam (fig. 
 6). 
 
 13. A 6-in-diam starter barrel 1 ft 
 in length, equipped with a detachable 1- 
 1/2-in-diam pilot shaft in the center 
 that extends approximately 5 in beyond 
 the diamonds of the starter barrel. This 
 barrel is used to center the 6-in-diam 
 hole over the initial EX hole (figs. 7- 
 8). 
 
 FIGURE 4. - Water swivel with solid plug and plug 
 (right) used during overcoring. 
 
 14. An EW core barrel to replace the 
 detachable pilot shaft, sized to extend 1 
 in beyond the starter barrel. With the 
 bit and reamer attached, this unit is 
 used to drill an EX starter hole 4 in 
 deep in the bottom of the 6-in-diam hori- 
 zontal or vertical hole. 
 
 15. A 6-in-diam centering stabilizer 
 for starting the 5- or 7-ft EWX core bar- 
 rel into the 4-in-deep horizontal starter 
 hole or for centering the EWX core barrel 
 in the bottom of a 6-in-diam vertical 
 hole (fig. 9). 
 
FIGURE 5. - Core barrel, 6 in. in diam by 27 in long (referred to as a 2-ft core barrel), and 
 disassembled expander head. 
 
 FIGURE 6. - Expander head assembled (adapted for BX wire line drill rod) and 6-in-diam core barrel 
 
 t . 
 
 <- EX (IVin diam) hole 
 Drill7ftdeep. 
 
 ^Expander head 
 
 Chuck 
 
 iV 
 
 ^-EW rod 
 
 0_ 
 
 FIGURE 7. - Starting the 6-in-diam overcoring hole. 
 
FIGURE 8. - Starter barrel, 6 in. in diam by 1ft long, 
 with pilot and expander head adapted for EW drill rod. 
 
 FIGURE 9. - Centering stabilizer. 
 
 Diameter of mine opening 
 
 EX bit-^ \J\ rDiamonds 
 
 ^L 
 
 *-„ — "5* 
 
 Reamer-^ ^ 
 
 ^Core barrel 
 
 Steel ring-' vr on t»rinn c+nhiliTor 
 
 EW rod -' 
 
 Chuck. 
 
 ~J 
 
 Centering stabilizer 
 
 .-Face 
 
 NOTE.-- ID of steel ring must be less 
 than OD of diamonds of reamer. 
 
 FIGURE 10. - Starting the EX hole in the bottom of the 6-in-diam hole. 
 
 16. A steel retriever ring 2 in. in 
 OD, 1.448 in. in ID, and 3/4 in wide 
 placed on the EWX core barrel in front of 
 the centering stabilizer for retrieving 
 the centering stabilizer (fig. 10). 
 
 17. A core breaker to fit the EW rod. 
 The core breaker, constructed of steel, 
 should be at least 2-1/2 in wide and 
 hardened (fig. 11). 
 
 18. A 6-in core shovel to fit an EW 
 rod for retrieving the core from a hori- 
 zontal hole (fig. 11). 
 
 19. A 6-in core puller approximately 
 18 in long to fit an EW drill rod for re- 
 trieving the core from a vertical hole 
 (fig. 11). The attachment end of the 
 barrel should have an approximately 5/8- 
 in-thick steel plate welded around its 
 circumference to the barrel, with an EW 
 box welded in the center of the plate. 
 
 Three 1-1/2-in-diam holes on 120° centers 
 are drilled through the plate to allow 
 water to pass when the core puller is 
 lowered into the 6-in-diam hole. The 
 downhole end of the barrel has four U- 
 cuts 90° apart. The remaining rectang- 
 ular sections of metal are bent in toward 
 the center slightly to hold the 6-in core 
 in the barrel when lifting it out of the 
 vertical hole. The core puller must be 
 marked and kept from rotating as it is 
 lowered into the 6-in-diam hole, to en- 
 sure orientation of the core. (Note. — 
 The shovel and core puller should be 
 made from a used 6-in-diam core barrel.) 
 
 An alternate means of retrieving an in- 
 tact 6-in core having an EX-size hole in 
 it from a vertical hole is by means of a 
 roof bolt anchor. A diamond shaped steel 
 point must be welded on the front of the 
 anchor (fig. 12). A section of threaded 
 
FIGURE 11. - Core breaker (lower right), core shovel (lower left), and core puller (center) 
 
 ■To 
 
 i i i i 
 
 - . 
 
 5 6 
 
 I 1 
 
 
 ■■' ■ *J 
 
 ■■' 
 
 
 Scale, in 
 
 
 
 
 FIGURE 12. - Retrieval tool used in place of core puller to retrieve 6-in-diam core from a vertical 
 hole that has an EX hole through the core. 
 
 rod is then screwed into the anchor, and are used to extend this tool into the 
 sections of 3/8-in pipe, 5 ft in length, hole. 
 
 INSTRUMENTATION 
 
 The following instruments are required 
 for calibrating, testing the drilled 
 core, and measuring the deformations dur- 
 ing the overcoring: 
 
 1. Three-component (3-D) borehole 
 gauge and accessories (including special 
 pliers, 0.005- and 0.015-in-thick. brass 
 washers, and silicone grease) (fig. 13). 
 A report on the assembly and wiring of 
 the gauge is available (2) . This inform- 
 ation is useful when minor repairs on the 
 gauge are required. 
 
 2. Three Vishay model P-350 5 or 
 equivalent strain indicators (fig. 14). 
 
 -"Reference to specific products does 
 not imply endorsement by the Bureau of 
 Mines. 
 
 (Note. — Normally, a gauge factor (G.F.) 
 of 0.40 is used so that an indicator unit 
 (1 yin/in) represents approximately 1 uin 
 displacement. If other indicators are 
 used and a G.F. of 0.40 cannot be obtain- 
 ed, then calibration at a G.F. suitable 
 to the indicator used is necessary.) If 
 only one indicator is available, a 
 switching and balancing unit or a switch- 
 ing unit must be used. 
 
 3. Orientation and placement tool for 
 the gauge (fig. 15). 
 
 4. A calibration device for 
 (fig. 14). 
 
 the gauge 
 
 5. A biaxial chamber for determining 
 the modulus of elasticity of the rock 
 (fig. 16). 
 
O I 2 3 4 5 6 
 
 iill I 1 I 
 
 Scale, in 
 
 I t o i 
 
 p 
 
 FIGURE 13. - Special pliers, Bureau of Mines three-component borehole gauge, piston, disassembled 
 piston and washer, and transducer with nut. 
 
 Scale, in 
 
 FIGURE 14. - Strain indicator with calibration device (left) and switching unit (right). 
 
FIGURE 15. - Placement and retrieval tool. 
 
 SITE SELECTION 
 
 To calculate the complete stress ellip- 
 soid, deformation measurements must be 
 obtained in at least three nonparallel 
 holes. Typical layouts of boreholes and 
 directions of measurement are shown in 
 figure 17. Three orthogonal boreholes 
 provide the best configuration of three 
 boreholes for determining all six stress 
 components with uniform precision 
 (fig. 17 A). It is possible to obtain 
 very good results from configurations 
 175, C, and D, where the angle between 
 the horizontal holes has been decreased 
 from 90° to not less than 60°. Deform- 
 ation measurements should be made outside 
 the zone of influence of the mined 
 
 opening. This distance is usually taken 
 to be one diameter of the mine opening. 
 Borehole configurations 17^4, B, and C re- 
 quire only one drill setup. Geologic or 
 structural conditions may require that 
 the zone of stress measurement be confin- 
 ed to a small area. The configuration 
 17D will provide good engineering esti- 
 mates of the stress components, but a 
 high standard deviation will exist for 
 any calculated principal stress component 
 with an orientation parallel or subparal- 
 lel to the axis of any of the boreholes. 
 This configuration also requires three 
 drill setups. 
 
10 
 
 
 
 12 3 4 
 
 III! 
 
 
 
 
 
 L_ 
 
 5 6 1 
 1 1 I 
 
 Scale, in 
 
 FIGURE T6. - Biaxial chamber and pump. 
 
 .e,o°-?o° 
 
 ^j/^j&M^s/hakMM. 
 
 D 
 
 °Vertical downhole 
 
 FIGURE 17. - Drill hole configurations 
 diameter of mine opening.) 
 
 (D ind icates 
 
 Horizontal holes should be started 3° 
 upward from horizontal to facilitate re- 
 moval of water and drill cuttings from 
 the hole. For holes longer than 25 ft, a 
 5° up-angle is necessary. The drill site 
 should be located in competent rock where 
 core lengths of at least 1 ft can be 
 obtained. Sometimes it may be advisable 
 to drill NX holes at the proposed over- 
 coring location prior to beginning the 
 actual overcoring operation to determine 
 if cores of sufficient length can be 
 obtained. 
 
 Recent improvements (5) to the borehole 
 gauge now allow for a complete stress re- 
 lief in cores of 6-in length. At the 
 present time, the minimum length of core 
 required to perform a biaxial test in the 
 field for the modulus of elasticity is 6 
 in. 
 
OVERCORING PROCEDURE 
 
 11 
 
 For determining stress distribution 
 near the mine opening, overcoring is 
 started at the face and the following 
 procedures apply: 
 
 1. Drill 7 ft of EX pilot hole. This 
 distance is the usual limit of pilot-hole 
 depth because overcoring in longer holes 
 off-centers the pilot hole to such a de- 
 gree that the cores cannot be tested for 
 Young's modulus. However, the deform- 
 ation readings will not be affected if 
 the pilot hole becomes nonconcentric with 
 the 6-in-diam hole. For the test to de- 
 termine Young's modulus, the pilot hole 
 must be at least 1-1/4 in from the cir- 
 cumference of the 5-5/8-in-diam core cut 
 by the 6-in-diam thin-wall diamond bit. 
 
 2. Use the 6-in-diam starter barrel 
 to drill approximately 1/4 in of kerf so 
 that the overcoring barrel can be started 
 (fig. 7). 
 
 3. Uncouple the starter barrel from 
 the drill rod near the chuck and remove 
 the starter barrel. 
 
 4. Open the drill to provide clear- 
 ance for the borehole gauge placement and 
 retrieval tool. 
 
 5. String the taped end of the gauge 
 cable through the adapter sub, EW drill 
 rod, and water swivel (fig. 18). 
 
 6. Remove the tape from the gauge 
 cable and connect the cable to the three 
 strain indicators as shown in figure 19. 
 Then remove the pistons with the special 
 pliers, grease with silicone grease, and 
 replace in their proper place in the 
 gauge. (If a piston is accidentally 
 dropped, foreign materials can be removed 
 from the O-ring with a toothbrush and the 
 piston wiped clean with a cloth. The 0- 
 ring is then greased and the piston re- 
 placed into the gauge.) To assure that 
 the transducers across the diameters are 
 properly connected to the strain indica- 
 tors, apply a slight pressure with the 
 thumb on each piston in turn while watch- 
 ing the indicator. The respective indi- 
 cator needles will move as the pressure 
 is applied to the piston. 
 
 Examine the case screws of 
 and tighten them if necessary. 
 
 the gauge 
 
 Then pull the six pistons about halfway 
 out of the gauge using the special pli- 
 ers, to ensure they are not touching the 
 transducers. Take a zero reading for 
 each diametral component and record them 
 on the field data sheet (fig. 20) in the 
 row labeled "Zero," in the three columns 
 labeled "U,," "U 2 ," and "U 3 ." Push the 
 pistons back to their original position. 
 
 If only one indicator is available, 
 a switching and balancing unit or a 
 
 m i. 
 
 6-in-diam diamond bit 27 in long 
 
 r BX wire line drill rod 
 
 "3-D borehole gouge 
 
 ,EW rod 
 
 o 
 
 -Column (for mounting drill) 
 ^Drill (open position) 
 
 Cable going to 
 strain indicator, 
 
 "-Qui 1 1 
 
 Water swive 
 Water hose- 
 
 FIGURE T8. - Setup for three-component (3-D) borehole gauge emplacement. 
 
12 
 
 Sensitivity knob: turn full clockwise. 
 
 Balance knob: put in midrange (5 turns of the IO-turn potentiometer). 
 
 Bridge switch: to full. 
 
 GALV SENSI 
 
 ° O 
 
 SCOPE 
 
 o obat. test 
 
 BALANCE 
 
 Brown 
 8-conductor cable No. 18 
 
 NOTE. — Hook black and green wires to indicator 2 and use 2 other wires (No. 18 or No. 20) 
 to common P+ and P-(or ^ and P„ ) of all 3 indicators. 
 
 FIGURE 19. - Wire hookup to strain indicators. 
 
 switching unit must be used. If no 
 switching unit is available, proceed as 
 follows: (1) Hook up the indicator as 
 shown in figure 19, first indicator, (2) 
 take a reading U], (3) replace the white 
 and red wires with the yellow and orange 
 wires, (4) take another reading TJ 2 , (5) 
 replace the yellow and orange wires with 
 the brown and blue wires, and (6) read 
 U 3 . 
 
 It is strongly recommended that three 
 strain indicators be used when overcor- 
 ing. This allows the indicator reader to 
 monitor all three components of the gauge 
 simultaneously, and if a fracture or min- 
 eralized vein separates, it can be de- 
 tected and noted on the field data sheet 
 (fig. 20) so that the deformation reading 
 can be corrected. Also, a breaking core 
 will be immediately detected and the 
 drill operator notified so that the drill 
 can be stopped before the gauge is damag- 
 ed. When a switching unit is used and 
 
 the core happens to break while the unit 
 is being switched from one channel to an- 
 other, the gauge will spin with the 6-in- 
 diam barrel. This will twist the cable 
 and tear the wires from the connecting 
 plug, resulting in a major gauge repair. 
 Also, if a fracture or mineralized vein 
 opens but does not completely separate 
 during channel switching, it will not be 
 detected. Thus, without anyone's know- 
 ing, the deformation reading(s) would be 
 erroneous. 
 
 7. Place the 6-in-diam core barrel in- 
 to the kerf cut by the starter barrel. 
 
 8. Holding the gauge with the notch 
 indicating Uj (component 1) up, engage 
 the orientation pins of the gauge with 
 the placement and retrieval tool using a 
 clockwise rotation. The notch is filed 
 in front of the piston hole in the gauge 
 case. 
 
13 
 
 Hole No. 
 Gouge No. 
 
 Dote. 
 
 Gauge factor 
 
 True bearing of hole. 
 
 Orientation ! U| 
 
 Calibration factor U| 
 
 U 2 
 
 u, 
 
 DEPTH 
 
 
 DEFORMATION 
 
 TIME 
 
 TEMP. 
 
 REMARKS 
 
 Gauge 
 
 Hole 
 
 ( + ) 
 
 INDICATOR READING 
 
 Gauge 
 Set 
 
 Overcore 
 Start 
 
 Deformation 
 Read 
 
 Rock 
 
 Water 
 
 U| 
 
 U 2 
 
 u 3 
 
 
 
 
 Zer o 
 
 
 
 
 
 
 
 
 
 
 9" 
 
 Face 
 
 Bias 
 
 
 
 
 
 
 
 
 
 
 
 1/2 
 
 
 
 
 
 
 
 
 
 
 
 
 l" 
 
 
 
 
 
 
 
 
 
 
 
 
 1 1/2 
 
 
 
 
 
 
 
 
 
 
 
 
 2" 
 
 
 
 
 
 
 
 
 
 
 
 
 oj^jj 
 
 
 
 
 
 
 
 
 
 
 
 7^2 
 
 8^2 
 
 Plstoni 
 
 9" 
 
 9/2 
 
 10" 
 
 10/2 
 
 
 13 
 
 
 
 
 
 
 
 
 
 
 
 l3j/ 2 " 
 
 
 
 
 
 
 
 
 
 
 
 14" 
 
 
 
 
 
 
 
 
 
 
 
 14^ 
 
 
 
 
 
 
 
 
 
 
 
 15" 
 
 
 
 
 
 
 
 
 
 
 
 1 5 Yi 
 
 
 
 
 
 
 
 
 
 
 
 16" 
 
 
 
 
 
 
 
 
 
 
 
 l6'/2 
 
 
 
 
 
 
 
 
 
 
 
 17 
 
 
 
 
 
 
 
 
 
 
 
 17^' 
 
 
 
 
 
 
 
 
 
 
 
 16 
 
 
 
 
 
 
 
 
 
 
 NOTE.-- Next relief would start at 18 in and go to 36in; gauge 
 would be orientated at a depth of 27 in. 
 
 FIGURE 20. - Field data sheet. 
 
14 
 
 POSITION OF COMPONENTS 
 
 u, 
 
 U 2 ^--v-\ U 3 Notch in gauge (at U |) 
 
 Viewed from cable end of gauge. 
 
 The clockwise rotation sets and orients 
 the gauge. Since U] (the notch in the 
 gauge) is perpendicular to the orienta- 
 tion handle, a small level can be used on 
 the handle for orientation in horizontal 
 holes. (Note. — If the gauge is oriented 
 too far clockwise, a counterclockwise 
 motion of more than 120° will allow the 
 gauge to be moved counterclockwise, then 
 reoriented correctly with the clockwise 
 rotation. ) 
 
 9. With the placement rod, put the 
 gauge through the 6-in-diam core barrel 
 and into the EX hole 9 in past the 6- 
 in-diam kerf, and orient the gauge (fig. 
 21). (Note. — The 9-in gauge placement 
 can be reduced to 6 in, thereby reducing 
 the total length of the overcore from 18 
 to 12 in, and good results will still be 
 obtainable. A further reduction in core 
 length can be obtained using the reversed 
 gauge case (_5_) in rock that consistently 
 breaks prematurely.) 
 
 10. Check the bias of the gauge on 
 the strain indicators. (See the next 
 section, "Procedure for Operating the 
 Three-Component Borehole Gauge," for 
 amount of bias needed and for changing 
 bias. ) 
 
 11. Turn the placement tool counter- 
 clockwise (approximately 60°) to free it 
 from the gauge. 
 
 12. Remove the tool from the hole. 
 
 13. Close the drill. 
 
 14. Pull all excess cable through the 
 drill. 
 
 15. Couple the EW drill rod in the 
 chuck to the BX wire line drill rod ex- 
 tending out of the drill hole. 
 
 16. Hold or tie the cable behind the 
 water swivel. 
 
 , EX hole 
 
 f Borehole gauge cable 
 
 BX wire line drill rod -\ 
 i i 
 
 ( Placement and retrieval 
 * tool 
 
 /Level 
 
 Wood taped to placement 
 rod to hold placement 
 rod in center. 
 
 ^-Face 
 
 Orientation 
 handle 
 
 FIGURE 21. - Positioning three-component (3-D) borehole gauge with placement rod through the 6-in- 
 diam core barrel and drill rod. 
 
15 
 
 17. Turn on water. Allow approxi- 
 mately 10 min from the time the gauge is 
 set for the gauge, drill water, and rock 
 to come to temperature equilibrium. 
 
 18. Start the overcore with a chuck 
 speed of approximately 120 rpm and a pen- 
 etration rate of 1/2 in per 40 s; 120 rpm 
 gives very satisfactory bit life and will 
 lessen the chance of damaging the gauge 
 if the core should break during over- 
 coring. (Note. — If the core breaks dur- 
 ing overcoring, this breakage will be 
 shown by the indicators fluctuating or 
 the cable twisting through the drill rod. 
 If this happens, the drill should be shut 
 down immediately and the gauge and broken 
 core retrieved.) 
 
 Each 1/2-in penetration should be sig- 
 naled to the indicator reader, and the 
 indicator readings (deformation measure- 
 ments) should be recorded on the field 
 data sheet (fig. 20). The rate of pene- 
 tration of 1/2 in every 40 s allows just 
 enough time for recording three diametral 
 readings. Overcoring should proceed for 
 a total of 18 in, which is 9 in beyond 
 the plane of measurement. This will re- 
 sult in 36 sets of readings. (See note 
 in step 9.) 
 
 19. Upon completion of overcoring or 
 if the core breaks prematurely, uncouple 
 the BX wire line drill rod at the adapter 
 sub. 
 
 20. Pull a little slack in the cable 
 so the drill can be opened. 
 
 21. Hook the retrieval tool onto the 
 gauge cable with the wire clip and insert 
 it through the BX wire line drill rod 
 while holding the handle of the tool 
 counterclockwise approximately 60° from 
 horizontal. Then push the retrieval tool 
 into the borehole until the tool slips 
 onto the gauge. Rotate the handle clock- 
 wise until the tool stops against the 
 orientation pins on the gauge. Remove 
 the gauge from the borehole. 
 
 22. Remove the core barrel and drill 
 rod from the hole. 
 
 23. Use the core breaker to break 
 core. 
 
 24. Retrieve the core with the core 
 shovel in a horizontal hole or with the 
 core puller in a vertical hole. Exercise 
 great care not to rotate the core puller 
 as it is lowered into the 6-in-diam hole, 
 to ensure orientation of the core. Mark 
 the orientation, depth, and plane of mea- 
 surement on the core. 
 
 25. Place the 6-in-diam core barrel 
 and drill rod back into the hole. 
 
 26. Repeat steps 8 through 25 for 
 each additional set of readings in the 
 remaining EX pilot hole. Do not position 
 the gauge pistons closer than 12 in to 
 the bottom of the pilot hole. 
 
 Overcores should be tested in a biaxial 
 chamber as soon as conveniently possible 
 after recovery to determine the modulus 
 of elasticity. 
 
 The 7-ft EX hole allows for approxi- 
 mately five complete overcores. After 
 they are completed, the remaining EX hole 
 is drilled out, a new pilot hole is 
 drilled, and additional overcores are 
 performed. Stabilizers are inserted in 
 the drill stem at 10-ft intervals or when 
 drill rod vibration occurs. 
 
 In all drilling, the EX pilot hole 
 should be cored with a double-tube barrel 
 so that the core can be obtained for ob- 
 servations. This core indicates the 
 fractures and/or if core disking is oc- 
 curring so that the gauge can be placed 
 in the competent zones. Disking areas or 
 highly fractured areas should be drilled 
 out. 
 
 If the only interest is to determine 
 the stress field outside the influence of 
 the mine opening, time can be saved by 
 first drilling a 6-in-diam hole without 
 instrumentation to a depth of one diame- 
 ter of the mine opening. Then, centered 
 in the bottom of the 6-in-diam hole, 
 approximately 7 ft of EX hole is drilled 
 for gauge emplacement and subsequent 
 
16 
 
 overcore determinations (fig. 10) . At a 
 distance of one diameter from the mine 
 opening, at least three good sets of 
 readings are required from each hole in 
 order to obtain a good statistical de- 
 termination of the average ground stress 
 components. 
 
 Surface topography influences the grav- 
 itational stress in underground openings. 
 The loading values attributable to to- 
 pography should be calculated (7) and 
 compared with the calculated stresses de- 
 termined from the overcoring. 
 
 PROCEDURE FOR OPERATING THE THREE-COMPONENT BOREHOLE GAUGE 
 
 The procedures described in this sec- 
 tion have been developed through use of 
 the borehole gauge over a long period of 
 time. It is important that the details 
 be followed closely in order to minimize 
 any chance of damage to the gauge and 
 to provide the most reliable data 
 acquisition. 
 
 1. Hook the gauge to the indicators, 
 as shown in figure 19, or to a switching 
 unit and one indicator. 
 
 2. Remove all the pistons from the 
 gauge with special pliers (fig. 13). The 
 special pliers are made by brazing a 1/2- 
 in-diam by 3/8-in-long brass rod to the 
 jaws of a standard pair of pliers. The 
 cylindrical axis of the rod is parallel 
 to the handles of the pliers. ^ An 11/32- 
 in-diam hole is drilled axially through 
 the center of the brass. The pliers are 
 opened by sawing through the brass along 
 the diameter perpendicular to the handles 
 of the pliers leaving a half-round piece 
 of brass attached to each jaw. The out- 
 side edges are then filed to fit inside 
 the 1/2-in-wide milled flats of the gauge 
 case. 
 
 3. Record the zero reading for each 
 of the three diametral components. Label 
 them U lf U 2 , and U 3 zero reading. 
 
 4. Grease the 0-ring on each piston 
 and insert the pistons into their proper 
 place in the gauge. 
 
 5. Place the gauge into the EX hole 
 or into a test specimen if the work is 
 being done in the laboratory. Caution. — 
 Do not force the gauge into the EX hole. 
 
 "See the appendix, figure A-1 . 
 
 If it fits very tightly, remove washers 
 from the pistons as follows: 
 
 a. Remove one piston of a diame- 
 tral pair with the special pliers. 
 
 b. Hold the piston with both pli- 
 ers and screw it apart, being careful 
 not to grasp the 0-ring with the 
 pliers. 
 
 c. Remove a washer and screw the 
 piston firmly back together. 
 
 d. Grease the 0-ring and insert 
 the piston into the gauge. 
 
 e. Repeat steps a through d for 
 the remaining two diametral pairs. Re- 
 set the gauge in the EX hole. If the 
 gauge is still too tight, remove a 
 washer from the remaining three pistons 
 as stated in steps a through d. If up- 
 on the initial insertion the gauge is 
 very loose inside the EX hole, remove 
 the pistons one at a time and add a 
 washer using steps a through d. 
 
 6. When the gauge is properly sized, 
 it should offer minimal to moderate re- 
 sistance as it is placed into the EX 
 hole. After the gauge is inserted to the 
 proper depth, position it in the desired 
 orientation. 
 
 7. Read all three components (U 1 , U 2 , 
 and U 3 ). 
 
 When relieving stress, as in field 
 overcoring, the bias set on each compo- 
 nent should be between 13,000 and 20,000 
 indicator units (microinches per inch) , 
 with a G.F. of 0.40. When stress is 
 applied to a specimen, as in the 
 
17 
 
 laboratory or in the biaxial chamber, the 
 bias set on each of the components should 
 be between 8,000 and 15,000 indicator 
 units for the same G.F. 
 
 The following tabulation shows typical 
 zero readings and calibration factors for 
 a G.F. of 0.40: 
 
 Zero readings (pistons out), uin/in: 
 
 U, = -4,000 
 
 U 2 « +3,100 
 
 U 3 a +4,100 
 Calibration factors, uin per pin/in: 
 
 U, = 1.00 
 
 U 2 = 1.00 
 
 U 3 = 1.04 
 
 Care must be exercised not to overload 
 the transducers, since not all borehole 
 gauges have the element safety plug in- 
 stalled in the gauge case. Maximum load 
 on any component must not exceed 50,000 
 indicator units with a G.F. of 0.40. 
 The purpose of the element safety plug is 
 to restrict the end displacement of the 
 transducer to less than 0.025 in. 
 
 Lowering the G.F. increases sensitiv- 
 ity. A G.F. of 0.40 provides a reading 
 of one indicator unit for 1 uin of 
 deformation. 
 
 When a G.F. other than 0.40 is used, 
 
 the working range and calibration factor 
 
 must be determined in advance of 
 operating. 
 
 PROCEDURE FOR BIAXIAL TESTING OF THE OVERCORE TO DETERMINE 
 ITS ANISOTROPIC PARAMETERS 
 
 The cores recovered from the overcoring 
 stress relief should be biaxially tested 
 (4^) as soon as possible to determine the 
 modulus of elasticity (E). Generally, 
 the cores recovered from an overcoring 
 hole are tested while the setup is made 
 on the second hole and preliminary drill- 
 ing performed. The core to be tested 
 must be intact for at least 6 in. Cores 
 cut with a used bit will fit the testing 
 apparatus properly. Those cut with a new 
 bit may require one wrap of 0.015- 
 in-thick plastic to fit properly. The 
 core, either wrapped or unwrapped, is in- 
 serted into the biaxial chamber with the 
 plane of measurement centered in the 
 chamber and with the orientation mark 
 (position U ( ) at the 12-o'clock position. 
 If it is not possible to center the plane 
 of measurement, it should be positioned 
 in the center third of the chamber keep- 
 ing U] in the 12-o'clock position. The 
 clearance is checked between the circum- 
 ference of the core and the biaxial 
 chamber at the 12-o'clock position. If 
 there is more than approximately 1/16 in 
 (0.06 in) clearance, then the core must 
 be centered in the chamber with wooden 
 wedges to prevent the liner from "popping 
 out" and releasing oil when pressure is 
 applied. This would also require repair- 
 ing the liner and chamber. The core is 
 
 centered by using four pieces of wood 
 approximately 1/32 in thick, 1/8 in wide, 
 and 3 to 4 in long with the last inch 
 beveled to an edge. Place two wedges at 
 each end between the core and the chamber 
 at the 4:30 and 7:30 positions, inserting 
 the wood about 3/4 in. Then apply about 
 100 psi to the core while the valve is 
 slowly opened to remove any entrapped air 
 in the system. Repressure the core 
 (about 50 psi) to hold it rigid, then em- 
 place the borehole gauge. 
 
 The borehole gauge is positioned and 
 oriented at the same position in the core 
 as it was during the overcoring stress 
 relief, if possible. The core is pre- 
 loaded three times to a selected stress 
 level and then a set of data is recorded. 
 (Note. — Care must be taken not to select 
 a stress level that exceeds the tensile 
 strength of the rock in the axial direc- 
 tion: otherwise, the core will fail in 
 tension and the test for the modulus of 
 elasticity will be lost. Values for the 
 stress level should range from 1,500 psi 
 for granites down to 250 psi for tuff or 
 fractured rock.) A run consists of (1) 
 recording a no-load reading for each com- 
 ponent (Uj, U 2 , and U 3 ), (2) pressuring 
 the core to the selected stress level and 
 reading each component, and (3) releasing 
 
the pressure and recording 
 readings after unloading. 
 
 the component 
 
 The gauge is rotated counterclockwise 
 within the core 15°, preloaded twice, and 
 another run made. These three sets of 
 readings are labeled U]+15, U 2 +15, and 
 U3+I5. This procedure is followed three 
 more times. The last run is a repetition 
 of the first run, except U 3 is now posi- 
 tioned at Uj, U| at U 2 , and U 2 at U 3 . 
 The three sets of readings from the third 
 
 run are labeled U,+30, U 2 +30, and U 3 +30. 
 The fourth run is labeled U,+45, U 2 +45 , 
 and U3+45. The fifth or redundant read- 
 ings are U,+60, U 2 +60, and U3+6O. 
 
 Root reciprocals [U]"' /2 of these 12 
 readings are plotted, and a least squares 
 fit (8^) is performed to determine the 
 maximum and minimum axes of the defor- 
 mations. From these data, the maximum 
 and minimum E values or anisotropic par- 
 ameters of the core are obtained. 
 
 BOREHOLE GAUGE CALIBRATION 
 
 The following describes the procedure 
 for calibrating the three-component bore- 
 hole gauge. The gauge should be cali- 
 brated before it is used. It is a good 
 practice to recalibrate the gauge after 
 use, also, to assure that no damage has 
 occurred to it. 
 
 1. Grease all pistons. 
 
 2. Put them into the gauge. 
 
 3. Place the gauge into the calibra- 
 tion jig. 
 
 4. Position the gauge so that the 
 pistons for component 1 (U j) are visible 
 through the micrometer holes. 
 
 5. Tighten the three wingnuts. 
 
 6. Install the two micrometer heads 
 and lightly tighten the set screws. 
 
 7. Set the strain indicator on "Full 
 Bridge," center the balance knob if there 
 is one, and set the G.F. at 0.40 or the 
 factor desired. (Note. — The G.F. set- 
 ting for calibration must be the same as 
 that used in the field for overcoring and 
 biaxial testing.) 
 
 8. Hook the wires for component 1 
 (Ui) (black, green, white, and red) to 
 the indicator as shown in figure 19 and 
 balance it. 
 
 9. Turn one micrometer in, until the 
 needle of the indicator just starts to 
 
 move. The micrometer is now in contact 
 with the pistons. 
 
 10. Do the same with the opposite 
 micrometer. 
 
 11. Rebalance 
 necessary. 
 
 the indicator if 
 
 12. Record this no-load reading (zero 
 displacement). 
 
 13. Turn each micrometer in 0.0160 in 
 (a total of 0.0320 in displacement for 
 component 1). (Note. — The micrometer 
 reads to ten-thousandths of an inch. ) 
 
 14. Balance the indicator. 
 
 15. Record the reading. 
 
 16. Wait 2 min and check the combined 
 creep for the two transducers. Creep for 
 2 min should not exceed 20 yin/in. 
 
 17. Record the new reading. 
 
 18. Back off each micrometer 0.0040 
 in (a total of 0.0080 in for the 
 component) . 
 
 19. Balance and record. 
 
 20. Continue this procedure until the 
 micrometers are back to the zero posi- 
 tion. This reading is also the zero dis- 
 placement reading for the second run. 
 
19 
 
 21. Repeat steps 13 through 20 for 
 the second cycle. 
 
 22. Loosen the wingnuts and rotate 
 the gauge clockwise to line up component 
 2 (U 2 ) with the micrometers. 
 
 23. Retighten the wingnuts. 
 
 24. Hook up the wires for component 2 
 (U 2 ) (black, green, yellow, and orange) 
 to the strain indicator. 
 
 25. Repeat steps 9 through 21 for com- 
 ponent 2. 
 
 26. Calibrate component 3 (U 3 ) in a 
 similar manner. 
 
 CALIBRATION DATA ANALYSIS 
 
 The following is an example using two runs for one 
 of 0.40: 
 
 component, calibrated at a G.F. 
 
 Displacement, in 
 
 Indicator reading, uin/in Difference, pin/in 
 
 
 RUN 1 
 
 
 
 -693 
 
 NAp 
 
 .0320 
 
 +30,140 
 
 ( 2 ) 
 
 .0320 
 
 30,055 
 
 30,535 
 
 .0240 
 
 21,920 
 
 22,400 
 
 .0160 
 
 14,040 
 
 14,520 
 
 .0080 
 
 6,380 
 
 6,860 
 
 
 
 -480 
 
 NAp 
 
 RUN 2 
 
 
 
 -480 
 
 NAp 
 
 .0320 
 
 +30,034 
 
 ( 2 ) 
 
 .0320 
 
 29,980 
 
 30,430 
 
 .0240 
 
 21,914 
 
 22,364 
 
 .0160 
 
 13,975 
 
 14,425 
 
 .0080 
 
 6,335 
 
 6,785 
 
 
 
 -450 
 
 NAp 
 
 NAp Not applicable. 
 
 i„ , ., . ,. Known displacement (uin) 
 
 Calibration factor: — 
 
 2 Wait 2 min. 
 
 Indicator units 
 
 uin/indicator unit. 
 
 Subtract the zero displacement reading 
 (last reading of each run) from all the 
 other indicator readings to determine the 
 differences. These values are in micro- 
 inches per inch. Because of friction be- 
 tween the piston 0-ring and the wall of 
 the hole in the gauge case, the least 
 difference value (in run 1, 6,860 uin/in 
 at 0.0080-in displacement) is subtracted 
 from the largest difference value (30,535 
 uin/in at 0.0320 in). This difference 
 (23,675), in microinches per inch, is 
 divided into the deformation difference 
 for the given range; in this case 0.0240 
 in or 24,000 yin. The result is the cal- 
 ibration factor. Repeat these calcula- 
 tions for the second run and average them 
 
 to obtain 
 ponent 1. 
 
 the calibration factor for corn- 
 
 Thus , for run 1 , 
 
 and for run 2, 
 
 24,000 
 23,675 
 
 = 1.014, 
 
 24,000 . 
 23,645 
 
 Use a calibration factor 
 the component. 
 
 Repeat the above procedure 
 the calibration factors for 
 and 3. 
 
 1.015. 
 
 of 1.01 for 
 
 to determine 
 components 2 
 
20 
 
 The above method is a faster means of 
 calculation and yields results accurate 
 to within 1 pet of the least squares 
 method. However, if desired, a least 
 
 squares determination can be made using a 
 plot of micrometer displacement versus 
 indicator units. 
 
 IDENTIFICATION OF SOURCE OF BOREHOLE GAUGE MALFUNCTION 
 
 LACK OF BALANCE ON ONE 
 OR MORE INDICATORS 
 
 If balance on one or more of the indi- 
 cators is not achieved, recheck the wir- 
 ing hookup to see that it is in accord- 
 ance with the wiring diagrams in figure 
 19 and that all connections are tight. 
 If balancing is still not achieved, the 
 problem may be in the plug-in cable con- 
 nection to the borehole gauge. This is 
 checked by removing all of the screws 
 from the placement end of the gauge, re- 
 moving the end, turning off the knurled 
 clamping nut, and pushing in the cable to 
 ensure good connection. With the indi- 
 cators set to their respective zero read- 
 ings, each component will provide indi- 
 cator balance when a good connection is 
 made. Screw the knurled clamping nut 
 very tightly into place and replace the 
 end. (Note. — Nonbalance may occur when 
 too much pull has been exerted on the 
 cable accidentally or intentionally dur- 
 ing gauge retrieval after overcoring. 
 Sometimes in a vertical hole, cuttings or 
 broken rock drop into the EX hole, imped- 
 ing the gauge retrieval tool from hooking 
 onto the orientation pins of the gauge. 
 Do not attempt to retrieve the gauge by 
 pulling the cable. Instead, remove the 
 drilling rod and the 6-in-diam core bar- 
 rel and break off the core with the gauge 
 still in place. Remove the gauge cable 
 from the drill, the 6-in-diam core bar- 
 rel, and the drill rod. String the cable 
 through one of the holes in the end of 
 the core puller and then retrieve both 
 core and gauge with the core puller. ) 
 
 INSENSITIVITY OF ONE OR MORE ELEMENTS 
 ON INDICATOR 
 
 If elements become insensitive to de- 
 flection of the pistons or nonresponsive 
 
 to the turning of the indicator dial, the 
 probability exists that moisture has en- 
 tered the connecting plug or cable. In 
 this case, do the following: 
 
 1. Remove the pistons and the bore- 
 hole gauge case to check for water. If 
 water is present, check the piston 0- 
 rings for a possible cut that may have 
 occurred from gripping the 0-ring with 
 pliers. Grease the 0-rings and replace 
 the case. 
 
 2. Remove the placement end as de- 
 scribed previously. Check the grommet 
 seal. If water is found inside the gauge 
 or in the cable connecting plug, dry out 
 completely, regrease the cable where it 
 passes through the grommet, and tighten 
 the knurled nut firmly. Replace the 
 placement end. 
 
 LACK OF COMPONENT BALANCE 
 
 If one component does not balance any- 
 where on the indicator dials or balances 
 intermittently, this situation indicates 
 a disconnected wire or possibly a cold 
 solder joint. Remove the borehole gauge 
 case and check all wires going to this 
 component including the plug-in cable 
 connector. Solder where needed and re- 
 place the gauge case. 
 
 SENSITIVITY OF INDICATORS WHEN TOUCHED 
 
 If indicators are sensitive when being 
 touched, this sensitivity generally oc- 
 curs after the instruments are used for a 
 period of time in very humid conditions. 
 Use plastic or other insulating material 
 underneath the indicators during the 
 working day. Each night the indicators 
 should be brought out of the mine and 
 allowed to dry. 
 
REFERENCES 
 
 21 
 
 1. Becker, R. M. , and V. E. Hooker. 
 Some Anisotropic Considerations in Rock 
 Stress Determinations. BuMines RI 6965, 
 1967, 23 pp. 
 
 2. Bickel, D. L. Transducer Prepara- 
 tion and Gage Assembly of the Bureau of 
 Mines Three-Component Borehole Deforma- 
 tion Gage. BuMines IC 8764, 1978, 19 pp. 
 
 3. Duvall, W. I., and J. R. Aggson. 
 Least Squares Calculation of Horizontal 
 Stresses From More Than Three Diametral 
 Deformations in Vertical Boreholes. Bu- 
 Mines RI 8414, 1980, 12 pp. 
 
 4. Fitzpatrick, J. Biaxial Device 
 for Determining the Modulus of Elasticity 
 of Stress-Relief Cores. BuMines RI 6128, 
 1962, 13 pp. 
 
 5. Hooker, V. E., J. R. Aggson, and 
 D. L. Bickel. Improvements in the Three- 
 Component Borehole Deformation Gage and 
 Overcoring Techniques. BuMines RI 7894, 
 1974, 29 pp. 
 
 6. Hooker, V. E., and D. L. Bickel. 
 Overcoring Equipment and Techniques Used 
 
 in Rock Stress Determination. 
 8618, 1974, 32 pp. 
 
 BuMines IC 
 
 7. Hooker, V. E., D. L. Bickel, and 
 J. R. Aggson. In Situ Determination of 
 Stresses in Mountainous Topography. Bu- 
 Mines RI 7654, 1972, 19 pp. 
 
 8. Hooker, V. E., and C. F. Johnson. 
 Near-Surface Horizontal Stresses Includ- 
 ing the Effects of Rock Anisotropy. Bu- 
 Mines RI 7224, 1969, 29 pp. 
 
 9. Merrill, R. H. Three-Component 
 Borehole Deformation Gage for Determining 
 the Stress in Rock. BuMines RI 7015, 
 1967, 38 pp. 
 
 10. Obert, L. Triaxial Method for 
 Determining the Elastic Constants of 
 Stress Relief Cores. BuMines RI 6490, 
 1964, 22 pp. 
 
 11. Panek, L. A. Calculation of the 
 Average Ground Stress Components From 
 Measurements of the Diametral Deformation 
 of a Drill Hole. BuMines RI 6732, 1966, 
 41 pp. 
 
22 
 
 APPENDIX.— EQUIPMENT DIAGRAMS 
 
 Working drawings of this equipment are Bureau of Mines, Building 20, Denver Fed- 
 available from Denver Research Center, eral Center, Denver, CO 80225. 
 
 fj 
 
 11 /16" 
 
 Element safety plug 
 
 No 303 stainless 
 1 required 
 
 »J 
 
 Gauge case 
 
 No 303 stainless 
 1 required 
 
 Section A-A 
 
 216" 
 
 336" 109" 
 
 Wear 
 
 button Piston assembly 
 
 Kennametal 6 No. 303 stainless 
 6 required 6 required 
 
 T 
 
 i 
 
 9/32" 
 
 A 
 
 Piston 
 washer 
 
 Brass 
 
 Reverse case 
 
 No 303 stainless 
 1 required 
 
 End view 
 
 U 2" »J 
 
 Locking nut wrench 
 Tool steel 
 
 Connector emplacement tool 
 
 Brass 
 1 required 
 
 13/32" 
 
 Pin 
 
 Brass 
 
 9 required 
 
 'Special' pliers 
 
 13/32" 
 
 Orientation pin 
 
 No 303 stainless 
 2 required 
 
 1-1/8 
 
 Section A-A 
 
 -Jul 
 
 ~v 
 
 -5-1/2" (7-1/2") - 
 «J 
 
 Placement end 
 
 No 303 stainless 
 1 required 
 
 Section B-B 
 
 U J 
 
 3/4" 
 
 Clamping 
 nut 
 
 No 303 stainless 
 1 required 
 
 Grommet 5/8 " 
 washer _ 
 Aluminum Grommet 
 
 Rubber 
 1 required 
 
 1 required 
 
 3-3/8" - 
 
 Gauge body 
 
 No 303 stainless 
 1 required 
 
 End view 
 
 1 /4" 
 
 Locking nut 
 
 No 303 stainless 
 6 required 
 
 U 2-7/16" »-t 
 
 Transducer 
 
 Beryllium copper 
 6 required 
 
 FIGURE A-l. - Three-component (3-D) borehole gauge. 
 
23 
 
 O -o ® 
 
 - 2 5 
 
 tr = CT 
 
 H 
 
 ^ 
 
 c 23 
 
 
 -r 
 
 /£ 
 
 |i 
 
 MT 
 
 as 
 
 _ r __ 
 
 LciJ 
 
 o 
 
 o 
 
 CD 
 
 < 
 
 LL1 
 
 O 
 
 00 h^ CO 
 
 V 
 
24 
 
 
 
 
 Al 
 
 i i 
 
 
 
 H 1" H 
 ignment pin 
 
 Steel 
 2 required 
 
 
 > 
 
 H 
 
 5/8 
 
 ^ 
 
 © 
 
 
 
 
 :S; 
 
 ^ 
 
 
 
 
 
 -« 2-3/4" ». 
 
 Top 
 
 Steel 
 1 required 
 
 
 ««— 2" »• 
 
 Side 
 
 Steel 
 1 required 
 
 1" 
 
 Bottom 
 
 Steel 
 1 required 
 
 Transducer testing jig 
 
 Section A-A 
 
 6" (8") 
 
 1/4-in stud 
 
 Part 3 
 
 Steel 
 
 3 required 
 
 
 r 
 
 FIGURE A-3. - Calibration jig and transducer testing jig. 
 
25 
 
 
 E 
 o 
 
 CO 
 
 O 
 
26 
 
 I 
 
 --©H44 
 
 1 
 
 ffi 
 
 1 
 
 i 
 
 — l 
 
 A 
 
 i 
 
 f£Ll 
 
 ---1 
 
 r- 1 
 
 ~~ I i 
 
 _J 
 -J3 
 
 T 
 
 FJZ 
 
 - + 
 
 1 
 
 1 
 1 
 
 1 
 
 fTf 
 
 Q. i 
 CO 1 
 O 
 
 CO 
 
 -Q 
 
 E 
 a 
 
 <B E 
 
 D 
 
 o 
 
 o 
 
 CD 
 
 < 
 
 LU 
 
 O 
 
27 
 
 
 SO 
 
 i 
 
 < 
 
 LLi 
 O 
 
 ttU.S. CPO: 1985-505-019/20,022 
 
 INT.-BU.OF MINES, PGH..P A. 27932 
 

D DD 
 
 Q- O 
 
 a- 3 
 
 3 O XI 
 
 a. i - 
 
 =" 3 -a 
 
 2 -n — - r 
 
 3Q 
 
 3 > 
 
 n 
 
 03 
 
 II 
 
 m z 
 S en 
 
 m 
 
 CO 
 
 5§0B 
 
 no c 
 - rim 
 
 5mO 
 
 -<1 
 
 < m Z 
 
 > z m 
 
 zcoi 
 
 O 
 m 
 ■d 
 > 
 
 li 
 
 ~n co 
 z co 
 
 m 
 O 
 
 33 
 
 > 
 
 z 
 m 
 D 
 c 
 > 
 r- 
 
 o 
 
 TJ 
 
 o 
 
 aa 
 
 H 
 C 
 Z 
 H 
 -< 
 
 m 
 
 -o 
 
 r - 
 O 
 -< 
 m 
 
 J3 
 
 go 
 
 Z 2 > 
 
 7 1 - 1 z 
 h o o 
 
 a> 
 
 ■n 
 
 -i m 
 I ni 
 m <" 
 
 M 
 
 m O 
 
 6 
 
 3) 
 
,-Cr 
 
 ... % 
 
 °- ^ 
 
 *^ .t'. 
 
 "of 
 
 
 -?- 
 *^ &> 
 
 
 ^°- 
 
 
 9 .v!//^'* ^ vV.Vf». A .4.9 .vL^JV *> 
 
 *^ 
 
 
 *b^ 
 iP-*,. 
 
 «^/- ^.^ 
 
 6? <&. • ' 
 
 
 
 AWAWA 
 
 
 1 ■ • * ^ 
 
 >k 
 
 
 •rfS^*.*'- <3 
 
 A . s. < e . <i?> 
 
 
 
 
 
 
 
 -■ss^V s*5?st-y v^ 5 '/ V-^ - "/ V^ f -* 
 
 • » |W I-' « e o S - " V r 
 
 •o^ 
 
 °" *. ~o_. 
 
 ^ A 
 
 
 :•* .o 
 
 
 ,0* ^b. "*<'T. , T 5 * A 
 
 ^. i# ' »*jA^^/J.*« "^f A*' 
 
 
 
 
 
 
 
 ■o ^^t. 
 
 
 - ^-o^ • 
 
 x* ..»••• 
 
 *bV' 
 
 V^ v 
 
 
 y * 
 
 ate-. V^ .-a 
 
 
 
 
 W^ 
 
 
 
 • ,* v % 
 
 *rt* v 
 
 
 
 
 V *I*°» CVs 
 
 
 <*' w ^ 
 
 vV^, 
 
 
 
 *, v 
 
 ^v^ 
 
 ' .** > ' 
 
 Ai»/% 0^.^i>o ./\>^\ ^° »^<A ,/^^ 
 
 4 
 
 AT, °J 
 
 * r>9 
 
 
 
 
 im?* ^o^ •. 
 
 
 
 
 <U* V 
 
 *.»* ,0 
 
 
 
 
 ..-.- ^O 
 
 o, ♦/^T* A 
 
 
 *P«*. 
 
 A. ^ * 
 
 9 *1,!^L'* ■? 
 
 \^ MMi \«* :sB£z V* 
 
 * v ..^'^ ^e 
 
 ^/—•^ 
 
 
 
 ^ yj 
 
 
 
 
 o, */^T»' A 
 
 .,.• ^\ •.; 
 
 >""%l 
 
 r Ao v 
 
 
 ...''/ °^^ f '/ ^^^\/ %.^-v . v 
 
 
 
 r *^T* a 
 
 
 
 *bv^ 
 
 «p^ 
 
 :- ^o* :■ 
 
 
 
 
 r.T^ .A 
 
 V> A 
 
 A^*^f o 
 
 
 
 C 
 
 - 4.7^,' A, 
 
 •fc 
 
 •_cSS\V^v4, .. O 
 
 
 ^ .<■'•. 
 
 *bv" 
 *p^. 
 
 
 \>f 
 
 *••"-'■:%. 
 
 
 /%. 
 
 o, *^^T»' A 
 
 l^ 7 " A V "^ 
 »/ A^ ^ 
 
 1 <v c* 
 
 a*' »>Va' %•« 4? * v 
 
 9*" »**• 
 
 
 
 °* •••^ , .*° 
 
 bv* 
 
 h ^ ..-••>- 
 
 
 
 
 ^q* 
 
 
 °o. '^.^.0° 
 
 
 •4- 
 
 '* -^ 
 
 0°^ 
 
 
 

 
 • <A l 
 
 <s>. *»«"° a 
 
 >_ *> 
 
 <V^\a 9 
 
 *bP 
 
 ^UT^ 
 
 >°V 
 
 
 a9 .*L^'* *> 
 
 0^ s'VL'* *> 
 
 
 
 <i, * 
 
 Tfe. 
 
 
 
 <> *-..• a 6 °^ ^ s * A^ 
 
 A -S- 
 
 ;v 
 
 * v .. 
 
 *bv p 
 
 ,- » ^ 
 
 
 7 
 
 <v^ o . * » , i * A> <y> * o h o Q • n - v 
 
 
 
 ^ A* / A %- *«« C* 'I 
 
 
 *v<* 
 
 
 **o« 
 
 <J*°* 
 
 A* 
 
 ,* v 
 
 Wmff' ' 
 
 & .- 
 
 
 
 <?%. 
 
 ** ■& »!h 
 
 i^*- %-^ • 
 
 "ft 
 
 ■•^ ; /\-!«? 
 
 
 ne;/ ^ v % 
 
 
 <S> * o . o .^ 
 
 i*« t^ J& «* 
 
 
 A- 
 
 
 
 " ^ 
 
 Asp A 
 
 0^ V '• 
 
 »i 
 
 
 - ^o« 
 
 „C^»' 
 
 .Hq 
 
 --;. 
 
 a0 V sLVL'* V- V" A*°- 
 
 
 ' ^* 
 
 ^ 
 
 /; 
 
 
 
 
 . C 
 
 X 
 
 
 o. *^T 5 A 
 
 
 
 o V 
 
 ■r^Qf 
 
 
 ^ A° 
 
 
 
 
 
 ^' A 
 
 4> 
 
 ^ /i 
 
 
 N*_ A ♦ 
 
 ^•^. 
 
 
 
 
 ^„ c^ .*i?gEsj'. ^* ^ ;, 
 
 AaM'.A 
 
 
 
 
 V'>^« A^ 
 ^ * o . o ^<y 
 
 o > 
 
 A * 
 
 
 o. *^.T^ A 
 
 A 4 °^ 
 
 ^ 
 
 
 
 
 o. * . , , • A 
 
 "^^ 
 
 
 *o. 
 
 
 ' 5> °o %TT,v a 
 
 ,'v 
 
 •r 
 
 . '^ a* v ,*iefi&i'. "^ .^ v *>v^ **«„ _^ sy^'« ^ ^ *^ 
 
 ^^ v 
 
 
 ^V. 
 
 
 ^ *?f^-\o'> 
 
 »°rk 
 
 
 * %1^ a 
 
 .^ 
 
 * A^ ^ 
 
 > A^ 
 
 
 >' > ^. • 
 
 "fey 
 
 V-> « n - xv »7. ' ^ '_<• " \V «£» ~V 
 
 *xi. 
 
 
 ♦° .. * 
 
 HIS. ^ -^ 
 
 
 
 V-^"-"^ 
 
 *> v 4 
 
 
 ^ ..i^"/V 
 
 
 
 ^0« 
 
 > ^ 
 
 
 ^ a^ .: 
 
 
 *» A N ■ 
 
 A^ ^ 
 
 
 o v - ° 
 
 V*^\/ V^ f ^/ V"^^ %*^^%o° V T ^V c 
 
 o "'*^»% , a ^ **f.T* 4 a'' 5 " "V ''♦-^7^''' A < 
 
 % a-^° ' 
 
 ' A^"V 
 
 * A 1 V< 
 
 Vi. »" ""•a^**" * ■ay cv » 
 
 'bV 
 
 '^c^ .**J»fe\ ^^ ;- 
 
 A^.tV- 
 
 ^ * 
 
 •• A V 
 
 a^ v .^^^^ ^ ,a v /AVa!^. "^ >*' 
 
 ^o A^ « * ' - 
 
 >» c^ 
 
 ^■^ 
 
 V ^aSZ 
 
 < -