12

2 T ~T T T T T T T T T T T T T T
ne 4
10h ° 4
° e@ 8
3 ob ° ° 4
* °
2 . °
8 ce a 8 °
=
Book . 4
e HOLE |
A 2 4
a © Vertical ground stress
© Horizontal ground stress
sk
a
al 1 Ll L 1 i n Ll L 1 L Ll 1 L L Vertical —L L
| ° |
Ss
Ss Ss
Ss \ =
+ —\ A xi N s “ee
a

HOLE DEPTH, feet

FIGURE 7. = Stress Versus Depth, Hole 1.
Stress Estimates

A computer program based upon equations reported by the Bureau of Mines
previously (6) was prepared to calculate the secondary principal stresses and
the vertical and horizontal components of stress. The data from overcoring
stress-relief work were programed for the computer. In all calculations, a
value of 6.36 x 10° psi was used for the modulus of elasticity of the quartz-
ite. On the basis of data obtained using strain gages on the uniaxial com-
pression specimens, Poisson's ratio was determined to be 0.26. Graphs of the
stress determinations obtained are shown in figures 7 and 8.

A significant difference between the data obtained from hole 1 and those
obtained from hole 2 is the stress concentrations indicated near the "skin" of

the opening at hole 2; there are no apparent concentrations around the open-
ing at hole 1.

The vertical down hole, hole 3, was difficult to drill, because the
stress-relief cores broke frequently, yielding disks with concave -convex
fracture planes which indicated a high lateral stress compared with the axial
(vertical) stress. Only three borehole deformation readings were obtained in
18 feet of overcoring: The u, reading taken at 4.7 feet; the u, at 11.3 feet;
and the u,, at 12.8 feet. Consequently, the data from hole 3 were used only
in calculating the average ground stress components, which was done by the
method Panek developed (12). Panek used a borehole deformation stress -relief
arrangement nearly identical to that of hole 3 as an example.


FIGURE 3. - Cuttings Catcher for Down Holes.
Data

The technique of stress-relief drilling had been established previously,
at the Star mine (1); it was possible, therefore to perform the mechanical
function of the job a little more efficiently at the Galena mine. Table 1
shows the drilling rate and the number of deformation readings per hole.

TABLE 1. - Overcore stress-relief drilling data

Hole Total |Feet per Total EX |6-inch

No. Direction Shifts|footage!] shift |deformation|bits] bits

readings? |used| used
1.. Horizontal (E-W) 13 27.3 2.1 24 1 2
2. Horizontal (N-S) 8 19.0 2.4 15 1 2
3 Vertical (down) | 12 18.4 | 1.5 3 4 2

16-inch-diameter stress-relief hole.
2Using Bureau of Mines single-component borehole deformation gage.
8Necessary to collar hole and concrete 2 zones of the hole to prevent

ravelling.


16

tester and standard laboratory static tests of l-inch-diameter oriented cores.
The average of 140 laboratory static tests for modulus of elasticity appeared
to be the best estimate to use, because the large standard deviation obscures
any difference that may exist in different directions.

The borehole deformation data obtained from hole 3 generally confirmed
the information from hole 1, that is, the deformation in the direction of the
stoped area was least. Borehole deformation data taken alone, however, are
not conclusive. Using the method described by Panek (12, p. 41), the standard
deviation of the U measurements (borehole deformation) was calculated to be
1,000 x 10-® inch, which is large but consistent with the magnitude and scat-
ter of the original values given in table A-1 (appendix). Deformation meas -
urements of hole 3 coupled with the data from holes 1 and 2 gave some evidence
that the direction of greatest stress was toward winze and nearly parallel
with the bedding of this zone. Subsequent to the overcoring stress-relief
work, a rock burst took place in the vicinity of 88 winze.

The equipment used was satisfactory for the work, but with the three-
component borehole deformation gage which the Bureau of Mines is developing ,+
it may be possible to make more stress estimates per foot of hole and to make
them much more rapidly than we can now. This potential capability for rapid
stress determinations coupled with Panek's method of absolute stress-ellipsoid
determinations by measurements in only two drill holes (12) should be of great
practical assistance to mining operators. ~~

Private communication with Robert H. Merrill, Research Physicist, Bureau of
Mines, Denver Mining Research Center, Denver, Colorado.


STRESS ELLIPSOID DETERMINATION
IN A ROCK-BURST-PRONE AREA

AT A 4,000-FOOT DEPTH,

GALENA MINE, WALLACE, IDAHO

By Robert W. Ageton

* # * # © © * » & » «© report of investigations 6997

UNITED STATES DEPARTMENT OF THE INTERIOR
Stewart L. Udall, Secretary

BUREAU OF MINES
Walter R. Hibbard, Jr., Director


13

2 T T T T T T T T T T T T
We ° 4
° °

tor 4
a
% 9h ° . 4
G cy
@ ak ° . 4
© °
ra
° a

Th a S 4

8 HOLE 2
e
6 @ Vertical ground stress —
© Horizontal ground stress
5 1 L 1 L 1 1 i 1 L L 1 i
Vertical
S | ax 10,000 psi
Ss | Ss aps
A S_4 A 1 4 4 1 r
) 2 4 6 8 10 12 14 16 18

HOLE DEPTH, feet

FIGURE 8. - Stress Versus Depth, Hole 2.

The procedure described in Panek's report was faithfully followed, and
furthermore, all measurements made 80 inches or more from the collars of drill
holes 1 and 2 were pooled with the three measurements obtained at drill hole

3 and a single stress system was calculated.

Calculating stress using an

office calculator is time consuming, but the technique can be used by any
mining office without an available computer facility.
to the calculation of the stresses are given in the appendix with some aids
to understanding the method.

Two tables essential

The stresses calculated in this investigation follow:

Oo, (east).....
gy (north)
oy (up)..

Existing
lithostatic

stress, psi

-11,200
-11,000
-8 900

+2 600

+1,200

+500

Standard
deviation,
psi
800
700
600
700
500
50u


19

After determining the x, y, z coordinate system and the matter of the
angle of orientation of the drill hole diameter, one must find the direction
cosines for the positive h,, h,, and hy axes of each drill hole with respect
to the x, y, z axes. These values are found in Panek's table A-1:

For hole 1,

and from Panek's equation 19,

30° 90° 150°
J, = = -0.500/E -0,500/E -0.500/E
Jp =f, = 2.833/E -1.167/E 2.833/E
J, =f, = 0.167/E 4.167/E 0.167/E
J, =0 0 0 0
J, = fy -4,619/E 0 4.619/E
J, = 0 C) 0 0

For hole 2,

and from equation 19,

30° 90° 150°
J, =f, = 2.833/E -1.167/E 2.833/E
Jp = fy = -0,500/E -0.500/E -0.500/E
Js = £, = 0.167/E 4.167/E 0.167/E
J, = 0 0 0 0
J, = 0 0 0 0
J, = -fy = ~4.619/E 0 4.619/E

Hole 3 was arbitrarily assigned a north bearing; then as shown in figure
10, 9 is measured from east (+h,) toward the south (+ h,). The @ values are
0°, 60°, and 120° for u,, u,, and u, respectively. From Panek's table A-1,


Lever
2400

2600

Unmined
Mined

Mined during
drill hole tests

Rock burst zone

Idealized stoirstep
mining progress

Vertical

Longitudinal Projection
Looking North

FIGURE 9. - View of 3400-Level Test Site.

Pr

Cees

88 WINZE

pete,

B

Isometric View of Test Site

Looking North

,

US RAISE

15

S37l1,000 psi

Orit hole 4 (E-W)
aX

'S3j-11,000 pst

LEGEND FOR PART ©

X,Y, Z: Right-hand
rectangular coordinates

S,, Se Ss, 3 Principal stresses

Cc

Stress Ellipsoid

A, Vertical longitudinal section looking north; B, isometric view of test site; and C, stress ellipsoid.


10

core samples were obtained at the point where the deformation readings were taken when
possible, and additional samples were cut along the same plane or orientation. Not all
of the stress-relief cores sent to the station were satisfactory for laboratory testing.
This situation was anticipated since the quartzite was intruded with irregular veins and
veinlets of siderite. The quartzite showed moderate alteration at the contact with the
siderite. Table 3 gives an analysis of all moduli determined. The elastic constants
were determined by uniaxial static loading of 1-inch-diameter cores having an length-
diameter ratio of 2. With uniaxial static loading, the orientation of the core did not
appear to have a statistical significance for modulus of elasticity determinations.

The large standard deviations might be expected from a rock consisting of a mixture of
quartzite and siderite.

TABLE 3. - Young's modulus of elasticity (E) values for 6-inch-diameter
stress-relief cores from laboratory tests

Orientation
4 Ye
Core samples umber | Average] Standard | Number [Average| Standard
of E, deviation,| of E, deviation,
lsamples| 10° psi psi samples|10° psi psi
Hole 1, El at deformation reading
point......... see eeeceeeccees . 8 5.56 0.67 8 6.64 1.68
Hole 1, Et along u,, u,, and u,.. 33 6.04 1.90 31 6.87 1.97
Hole 2, E along u,, u,, and u,. 6 6.43 1.04 14 5.84 2.17

Hole 1, biaxial tester determina -
tions at point of deformation
TEAGING. . cece cece eee e cence ner en ener 3 5.50 - 4 7.65 -

E laboratory results of all deter — .
minations of cores at 3400-level
Station? .......e cee cece eee ee cence = - : - - -

Orientation
u, Total or average
lumber | Average} Standard | Number |Average| Standard
of E, deviation,| of E, deviation,
bamples| 10° psi psi samples|10° psi psi
Hole 1, Et at deformation reading
point.... seeee 8 6.14 1.24 24 6.11 1.27
Hole 1, EY along uy, u,, and u, 21 5.92 2.41 85 6.31 2.08
Hole 2, Et along u,, u,, and eneeet 14 7.44 2.22 34 6.60 2.15
Hole 1. biaxial tester determina -
tions at points of deformation
reading. se eeee ee 1 6.76 - 8 6.73 -
E laboratory results of all deter-
minations of cores at 3400-level
Station.... nee eee = - - 140 6.36 2.01

1fwin Cities Mining Research Center laboratory uniaxial test of 1-inch-diameter
laboratory-sample cores with length-diameter ratio of 2. Laboratory sample cores cut
along orientation directions.

2E of all samples including some that were drilled parallel to the axis of the EX hole and
excluding the biaxial test results.

Laboratory tests for tensile and compressive strength and for density were made on
most of the core samples. The test results appear in table 4. The average values appear
to be as good as the selected orientation average values. The average compressive
strength of all laboratory core tests was 16,500 psi with a standard deviation of 6,000
psi which means that 68 percent of the test values lie between about 10,000 to 22,000 psi.


established the overcoring stress-relief technique as a valid engineering tool
to use more than a mile underground in the fractured quartzites of the Star
mine, Burke, Idaho, in a zone apparently not affected by mining-induced stress
concentrations (1).

The study described in this report concerns stress determinations in an
area known to be under high stress concentration induced by prior mining oper-
ations. The objective was to obtain a stress ellipsoid in a test location by
drilling three mutually perpendicular holes.? This report contains a descrip-
tion of the overcoring stress-relief technique used, the rate at which the
work was done, the final results of the stress determination, and a brief
description of the tools used to overcore a vertical down hole to a depth of
18 feet. The appendix presents a tabulation of the data used to determine
the stress ellipsoid based on the method reported by Panek (12).

ACKNOWLEDGMENT

The cooperation of the American Smelting and Refining Company in provid-
ing the test site facilities at the Galena mine, Wallace, Idaho, is grate-
fully acknowledged.

THE GALENA MINE
Geology

The silver vein of the Galena mine does not crop out; it has an irregular
strike trending east-west (3). The vein dips about 70° S and is slightly
offset on the east and west ends by north-striking faults. The ore is typical
of the siderite-tetrahedrite veins of the Page-Galena mineral belt. Minor
amounts of unreplaced country rock and white quartz may be found in both lean
and rich silver-lead ore. The country rock is Revett Quartzite.

Mining

The method of mining is horizontal-slice cut and fill. The mine is
developed by vertical shafts, crosscuts, drifts, and raises on the veins.
Mill tailings are used for the fill. The unique feature employed at the
Galena mine is the "stairstep" manner in which the mining is carried from east
to west. (This is discussed at the end of the report.) To mine the vein in
this fashion, intermediate levels are driven between the main levels, which
are 300 feet apart in the lower part of the mine. Raises are driven at 200-
foot intervals so that the maximum slushing distance is 100 feet.

Test Site
The test site was on the 3400 level at the tail end of the main haulage

erosscut, about 50 feet south of the vein. Figure 1 is a plan of the imme-
diate area of the test site, showing the location of the three mutually

3This work was completed in May 1965 prior to the conception and publication
of Bureau of Mines Report of Investigations 6732 by Panek (12); otherwise
it is possible that only two holes would have been drilled.


22 TABLE A-2. - Solution for
Operation | Row 1 2 3 4 5 6
I | 0.90826 -0.24167 -0.29170 (0) 0 0
II | -.24167 1.07484 -.30838 0 0 0
III | -.29170 --30838 1.57530 0 0 0
Iv 0 te) 0 0.42670 0 0
Vv 0 0 to) 0 2.13352 0
VI 0 0 (0) 0 0 1.70681)
I «90826 -.24167 -.29170 0 0 0
-I/1, D -1 «26608 -32116 10) 0 ie)
IL 1.07484 -.30838 0 0 0
Ix D, -.06430 -.07762 0} 0 0
Add E! T.01054 | -.38600 0 0 0
-E'/E,’ E -1 38197 0 0 0 |
TIT | ...-..- 1.57530 i} 0 1)
Ix D, -.09368 0 0 0
E' x E -.14744 i) 0 (e)
Add F! 1.33418 0 0 0
-F'/F,' F rn ene -1 0 0 0
|
Iv +42670 0 0
1x D, 0 0 0
E' x E, 0 0 0
FI x F, i} i) i)
Add G' 42670 0 0
-G! /G, ' G -1 0 0
Vi cece ene foweecece [ooceeces  fevceeee 2.13352 0
I x D, 0 0
E' x E, ) 0
F'x Fy . 0 0
G' x G, 0 0
Add H! o 2.13352 0
-H' /H,! H . -1 0
VI + 70681
Ix D, ie)
E' x E, 0
F'x F, (e)
G' x G, 0
H' x Hy 0
Add K' 1.70681
-K'/K,! K -1

TThis table is similar to Panek's table A-7, R.I.

732 (12).


CONTENTS

Abstract
Introduction
Acknowledgments
The Galena mine
Geology...
Mining.
Test site...
Instrumentation and procedure
Borehole stress relief..
General description..
Equipment and instrumentation..
Datarrcccsccssscvcseseceeee
Physical property determinations.
Biaxial tester..
Laboratory determinations
Stress estimates..

Summary.....
References........
Appendix...... tees
ILLUSTRATIONS
Fig.
1. Plan of 3400-level area near test site............005
2. Test site and diamond drill with hydraulic props......
3. Cuttings catcher for down holes...... bee e eee eee eee eeee
4. Borehole deformation readings versus depth, hole 1.
5. Borehole deformation readings versus depth, hole 2.
6. Vertical down hole--Hole 3 stress-relief core showing concave
disking............. bea eeneneees
7. Stress versus depth, hole 1.
8. Stress versus depth, hole 2. sees .
9. View of 3400-level test site. .
10. Diametral orientations using single - -component borehole deformation
Bage.....e- Cee merece nee ee nsec essscereeeeeeeeees Sede eeeeeeeens
TABLES
1. Overcore stress-relief drilling data....... ccc eee cece eee eee eee

2. Young's modulus of elasticity values for 6-inch-diameter stress-
relief cores from hole 1 using biaxial tester..........eeeeevees
3. Young's modulus of elasticity values for 6-inch-diameter stress-
relief cores from laboratory tests....... seen
4. Average tensile and compressive strength and density values of
6-inch-diameter stress-relief COreS........eeeeeeeee eae e ee eeeeee
A-1. Primary data for calculation of lithostatic stress field..... sees
A-2. Solution for the stress componentS.........e.eeeeeeeeee dee eee eee

Page

WDADHWWWNNNNNEHE

10

11

22


This publication has been cataloged as follows:

Ageton, Robert W
Stress ellipsoid determination in a rock-burst-prone area at
a 4,000-foot depth, Galena mine, Wallace, Idaho. [Washing-
ton] U. S. Dept. of the Interior, Bureau of Mines [1967]

23 p. illus., tables. (U.S. Bureau of Mines. Report of investi+
gations 6997)
Includes bibliography.

1. Rock pressure. 2. Mining engineering. I. Title. (Series)

TN23.U7 no. 6997 622.06173

U. S. Dept. of the Int. Library



1

These data are, of course, only strengths obtained from uniaxial testing and may not be
indicative of failure under triaxial conditions. Failure under triaxial conditions is
due to stress differentials. Failure under uniaxial conditions (as these samples were
tested) is only one particular case of the triaxial condition.

TABLE 4, - Average tensile and compressive strength and density values
of 6-inch-diameter stress -relief cores

Tensile strength|Compressive strength Density
Number Standard Standard Standard
Orientation of Psi devia - Psi devia- |G/cu cm} devia-
samples tion, tion, tion,
psi psi g/cu cm
uy :
10 1,100 450 15,900 - - -
Hole 36 - - - 5,700 - -
37 - - - - 2.84 0.09
7 1,700 160 - - - -
Hole 6 - - 16,700 5,700 - -
6 - - - - 2.88 -07
uz:
5 1,500 240 - - - -
Hole 31 - - 16,900 5,200 - -
20 - - - - 2.87 13
10 1,700 1,100 - - - -
Hole 15 - - 16,200 6,200 - -
15 - - - - 2.96 -ll
Ugt
10 1,400 640 - - - -
Hole 22 - - 15,200 6,200 - -
18 - - - - 2.86 .09
6 1,800 720 - - - -
Hole 10 - - 20,800 8,500 - -
14 - - - - 2.95 .16
Subtotal or average:
Hole 1:
lst replicate....... 25 1,300 510 - - - -
2d replicate. 89 - - 16,100 5,600 - -
3d replicate. 75 - - - - 2.85 ll
Hole 2:
1st replicate... 23 1,700 810 - - - -
2d replicate. 31 - - 17,800 7,000 - -
3d replicate. 35 - - - - 2.91 13
Hole 3:*
lst replicate....... 2 2,500 550 - - - -
2d replicate........ 3 - - 15,300 2,100 - -
3d replicate. sees 3 - - - - 3.04 17
Overall total or average:
Ist replicate.... . 50 1,500 720 - - - -
2d replicate.......... 123 - - 16,500 6,000 - -
3d replicate..........] 113 - - - - 2.88 ~12

ToOnly two 6-inch-diameter cores from hole 3 were satisfactory for these laboratory tests.


STRESS ELLIPSOID DETERMINATION IN A ROCK-BURST-PRONE AREA
AT A 4,000-FOOT DEPTH, GALENA MINE, WALLACE, IDAHO

by

Robert W. Ageton !

ABSTRACT

Optimal planning for mining the deep, lead-zinc-silver deposits of the
Coeur d'Alene mining district, Shoshone County, Idaho, could be facilitated
by a knowledge of the magnitude and direction of the pressure acting in the
virgin rock. The distribution of primary stresses should be considered in
order to prevent possibly destructive mining-induced stress concentrations.
This particular investigation was concerned with determining stress in a zone
4,000 feet below the surface and known to be under stress concentrations due
to mining operations. Disking of the stress-relief cores obtained in a
vertical down hole permitted qualitative evaluation from visual observations;
the results indicate that a high lateral stress existed at the time the
measurements were made.

Stress-ellipsoid determinations gave a compressive principal stress of
-13,000 psi oriented about N 45° W and nearly horizontal, a compressive
principal stress of -11,000 psi oriented about S 45° W and about 60° off the
vertical pointing away from the vein, and a compressive principal stress of
-7,000 psi oriented N 45° E and about 60° off the vertical, pointing toward
the vein.

Subsequent to the overcoring stress-relief drilling, a rock burst
occurred about 100 feet northwest of the test site.

INTRODUCTION

Knowledge of the original stresses in the earth and how they are redis-
tributed with mining activity is useful in developing sound engineering judg-
ment in mine design and operating practice (4, p. 90; 9, p. 4; 12, p. 11-15;

13; 14) .? Previous Bureau of Mines work in the Coeur d'Alene mining district

Tgupervisory mining engineer, Area VII Mineral Resource Office, Field office,
Bureau of Mines, Spokane, Wash.

2Underlined numbers in parentheses refer to items in the list of references
at the end of this report.


te

10.

ll.

12.

13.

14.

15.

7

REFERENCES®

Ageton, Robert W. Deep Mine Stress Determinations Using Flatjack and
Borehole Deformation Methods. BuMines Rept. of Inv. 6887, 1967, 25 pp.

Fitzpatrick, John. Biaxial Device for Determining the Modulus of Elas-
ticity of Stress-Relief Cores. BuMines Rept. of Inv. 6128, 1962, 13 pp.

Fryklund, V. C., Jr. Ore Deposits of the Coeur d'Alene District, Shoshone
County, Idaho, with a section on The Bleached Rock in the Coeur d'Alene
District by L. Weis. U.S. Geol. Survey Prof. Paper 445, 1964,
pp. 80-81.

Griswold, George B. How To Measure Rock Pressures: New Tools and Proved
Techniques Aid Mine Design. Eng. and Min. J., v. 164, No. 10, October
1963, pp. 90-95.

Hast, Nils. (The Measurement of Rock Pressure in Mines.) Sverige's
Geologiska Undersokning, Arsbok 52 (Sweden's Geological Survey,
Yearbook 52) Ser. C, No. 3, P. A. Norstedt, Stockholm, Sweden,
1958, pp. 12-160.

Merrill, Robert H., and Jon R. Peterson. Deformation of a Borehole in
Rock. BuMines Rept. of Inv. 5881, 1961, p. 2.

Merrill, Robert H., James V. Williamson, David M. Rapchan, and George H.
Kruse. Stress Determinations by Flatjack and Borehole-Defomation
Methods. BuMines Rept. of Inv. 6400, 1964, 39 pp.

Obert, Leonard. In Situ Determination of Stress in Rock. Min. Eng.,
v. 14, No. 8, August 1962, pp. 51-58.

Obert, Leonard, Wilbur I. Duvall, and Robert H. Merrill. Design of
Underground Openings in Competent Rock, BuMines Bull. 587, 1960, 36 pp.

Obert, Leonard, Robert H. Merrill, and Thomas A. Morgan. Borehole
Deformation Gage for Determining the Stress in Mine Rock. BuMines
Rept. of Inv. 5978, 1962, 11 pp.

Obert, Leonard, and D. E. Stephenson. Stress Conditions Under Which Core
Disking Occurs. Trans., AIME, V. 235, 1966, pp. 227-234.

Panek, Louis A. Calculation of the Average Ground Stress Components From
Measurements of the Diametral Deformation of a Drill Hole. BuMines
Rept. of Inv. 6732, 1966, 41 pp.

Potts, L. J. The "In Situ'' Measurement of Rock Stress Based on Deforma-
tion Measurements. The Rand Corp., Memorandum RM-3583, May 1963, 12 pp.

Stefanko, Robert. Technical Problems of Underground Stress Instrumenta-
tion. Soc. of Min. Eng., AIME, Preprint 63F319, 1963, p. 1.

Wisecarver, David W. A Device for Placing a Borehole Deformation Gage in
a Horizontal Hole. BuMines Rept. of Inv. 6544, 1964, 13 pp.

Titles enclosed in parentheses are translations from the language in which

the item was published.


Stack-
pembox

&
b f mi
p | report of peels 6997 A

STRESS ELLIPSOID DETERMINATION
IN A ROCK-BURST-PRONE AREA

AT A 4,000-FOOT DEPTH,

GALENA MINE, WALLACE, IDAHO

By Robert W. Ageton

UNITED STATES DEPARTMENT OF THE INTERIOR
BUREAU OF MINES

August 1967


Overcoring at the Galena mine followed the method described previously
(1); however, some modifications were made to improve measurement results.
Each day, routinely, the deformation gage was calibrated. The stress-relief
work was started by drilling an EX hole to a depth of only 3 to 5 feet. This
was done for two reasons. First, only a short length of EX hole would be
exposed to the humid air and high stress concentrations of the mine, which
might cause accelerated deformation of the hole and give rise to false
deformation readings (5, p. 52). Second, a short EX hole would tend to remain
concentric with respect to the 6-inch-diameter overcoring hole; this was
essential to the subsequent determination of the modulus of elasticity by
the biaxial tester (2).

After the EX hole was drilled it was marked so that the 6-inch cores
could be properly oriented, at the location of the deformation readings, for
modulus of elasticity determinations using the biaxial tester. The EX hole
was marked by a special anvil inserted on the gage and oriented to give a
trace on the bottom of the hole. (It was also observed that the very act of
inserting the deformation gage into the hole, as a general rule, left trace
lines that were visible in the EX hole of the stress-relief cores and gave a
positive indication of orientation.) To start a series of stress-relief read-
ings, the deformation gage was placed in the EX hole and oriented to measure
change of hole diameter in the u, direction, 90° from the horizontal. A 6-
inch masonry-type coring bit was used to cut an annular space concentrically
around the 1-1/2-inch EX hole, thereby relieving stress in the zone of the
gage. Change in hole diameter usually ceased when the overcoring reached a
depth about 2 to 3 inches beyond the point of measurement. Then, the 6-inch
overcoring was stopped. The borehole deformation gage was moved to the next
deeper point of measurement and oriented to measure the change of hole diam-
eter in the direction 60° counterclockwise from the vertical (uj). Then
overcoring operations were repeated. At the third point of measurement, the
gage was oriented 60° clockwise from the u, direction (u,) and so on.

Equipment and Instrumentation

Borehole deformation measurements were made with a Bureau of Mines
single-component borehole deformation gage (10). The gage was inserted into
the EX hole with an inserting tool similar to the one described by Wisecarver
(15). This inserting equipment permits the placement of the single-component
deformation gage in a horizontal hole at the proper orientation for deforma-
tion measurements at 30°, 90°, and 150° from the horizontal. Overcoring
stress-relief diamond drilling was done with a hydraulic, instrumented diamond
drill developed by the Bureau of Mines (1); it is shown in figure 2. Note the
hydraulic props used to brace the drill. Each prop is fitted with a pressure

gage that is monitored throughout a shift so that more pressure can be applied
to a unit to prevent movement of the drill.

To drill a vertical down hole it was necessary to construct a drill-
cutting catcher (fig. 3) and a water jet pump. The cuttings catcher was made
from a section of 6-inch masonry bit and is attached immediately behind the
bit. The cuttings catcher retained some of the fines; the jet pump was used
to clean out fine and coarse cuttings from the bottom of the hole. The jet
pump was put down the hole after the drill string had been removed.


EE «(Mineralized zone
x7 Bedding

wo Vein dip

DH Drill’ hole

50 ° 50

‘Scale, feet

FIGURE 1. - Plan of 3400-Level Area Near Test Site.

perpendicular stress-relief holes. The objective was to determine the maximum
and minimum secondary principal stresses in planes normal to the axis of the
holes and to utilize all the data obtained in the calculation of a principal
stress ellipsoid.

The site was selected because it was in a zone known to be under stress
concentrations induced by prior mining. The direction of the stress-relief
holes was chosen to yield stress profiles parallel and normal to the strike
of the vein. The station was approximately 4,000 feet below the surface.

INSTRUMENTATION AND PROCEDURE

There are a number of methods to determine in-situ stress in rock by
relief techniques (4, 7). The overcore stress-relief technique was used for
this investigation, instead of the restricted-depth flatslot annulment tech-
nique, in order to determine stresses at depths more than 2 radii from the
drift walls and floor. The stress-relief method used in this investigation
was the borehole deformation technique developed by the Bureau of Mines and
described by Obert (8). The Bureau's single-component deformation gage, used
in this investigation, has been reported by Obert, Merrill, and Morgan (10).
The overcore stress-relief technique applied in the Coeur d'Alene mining
district at the Star mine and reported by the Bureau (1) was followed at the
Galena mine. ~

Borehole Stress -Relief

General Description

The Bureau of Mines' procedure for in-situ determinations of stress in
rock using its single-component borehole deformation gage has been adequately
reported previously (1, 7-8).




the stress components!

23

7 11 12 13 14 15 16 17
7.72202 1 0 ce) 0 i) 0 9.09691
10.07182 0 1 ce) 0 0 0 11.59661
11.56415 ie} e) 1 te) 0 0 13.53937
-1.72612 0 0 te) 1 0 0 -.29942
-3.89059 0 0 0 0 1 1) -.75707
-1.28593 0 10) 0 ie) 0 1 1.42088
7.72202 1 0 0 0 0 9.09691
-8.50199 -1.10101 Oo 0 1) 0 0 -10.01576

Check -10.01576

10.07182 0 1 0 0) 0 i} 11.83828
2.05468 +26608 ) ie) 0 ie) 0 2.17884
12.12650 + 26608 1 0 [) 0 0 14.01712
|-12 .00002 -.26330 | -.98957 0 te) 0 0 13.87092
Check 13.87092

11.56415 i) 0 1 0 i?) 0 14.13945
2.48003 -32116 0 1) 0 0 0 2.70748
4.58365 -10163 | .38197 0 0 i) 0 4.91981
18 .62783 +42279 | .38197 T 0 0 0 21.76674
-13.96201 -.31689 | -.28631 | -.74952 0 i) 0 -16.31470
a oa Check -16.31473
-1.72612 0 0 0 1 0 i) -.29942

0 0 0 0 0 i) 0 0

0 (0) 0 (0) 0 (0) 0 i)

0 i) 0) i) i?) i} i‘) 0
-1.72612 0 0 0 1 10) 0 -.29942
4.04528 0) 0 0 -2.34357 10) 0 70171

Check 70171
-3.89059 te) e) 0 10) 1 te) -.75707

0 0 0 0 0 0 0 0

0 0 i) 0 0 0 0 0

(0) (0) (0) 0 0 te) 0 0

i) i) 0 i) 0 9} 0 i)
-3.89059 0 0 0 0 1 0 «15107
1.82355 0 0 0 0 -.46871 0 35484

Check 35484
-1,28593 0) ie) 0 0 te) 1 1.42088

0 0 0 0 ie) 0 (0) 0

0 0 0 0 0) 0 0 0

0 o) ie} 0 ie) ie) (0) 0

0) 0 i) 0) i) 0 0 0

it} 0 0 ) i) ie} i) 0
-1.28593 () (0) (0) 0 0 1 1.42088

75341 0 ie) 0 0 oO -.58589 -.83248

Check: ~ 83248

INT.*BU.OF MINES,PGH.,PA. 11077




14

Principal stresses Direction cosines
Cos (n, ,x) = 0.60419 = cos 52°-49'
8, = -13,000 psi.........000, Cos (n, ,y) = -0.78393 = cos 141°-37'
Cos (m ,z) = 0.14282 = cos 81°-47'
Cos (n,,x) = 0.64827 = cos 49°-35'
8S, = -7,000 psi.... Cos (n,,y) = 0.56288 = cos 55°-45'
Cos (ng,z) = 0.51295 = cos 59°-08'
Cos (a, »Xx) = -0.28524 = cos 106°-35'
s, = -11,000 psi............ - {Cos (n,,y) = -0.79749 = cos 142°-53'
Cos (n,,z) = 0.53163 = cos 57°-53'

Figure 9 is a composite; part A shows the test site in relation to the
Silver fault and the B branch of thé Galena fault. Also shown is an idealized
stoping sequence designed to minimize mining-induced stress concentrations and,
consequently, lower the severity and frequency of rock bursts. The mining
method is cut and fill with stoping advancing in a longwall from the east
boundary, the B branch of the Galena fault, proceeding in a stairstep fashion
toward the west boundary with two stopes developed per level.

Part B of figure 9 is an isometric view of the test site, which is about
50 feet south of the vein. The location of the drill holes and the stoping
completed during the drilling operation are shown. Note the zone affected
by a rock burst that occurred 3 months after the drilling was completed. The
burst occurred near a pillar (the ground above the 3400 level and between 88
winze and 98 raise). Later, the pillar was stoped without changes in the
mining method and without further rock bursts.

Part C of figure 9 is a stress ellipsoid showing the principal stresses
and their magnitude, orientation, and relationship to the three overcore
stress-relief holes. A compressive principal stress, -13,000 psi is oriented
about N 45° W and is nearly horizontal; a compressive principal stress,
-11,000 psi is oriented about S 45° W and is about 60° off the vertical
pointing away from the vein; and a compressive principal and stress, -7,000
psi, is oriented N 45° E and is about 60° off the vertical, pointing toward
the vein.

SUMMARY

Stress determinations in a zone known to be under high stress concentra-
tions were made using the Bureau of Mines single-component borehole deforma-
tion gage. One important assumption required for stress calculations was that
a reasonable engineering value for the modulus of elasticity of the rock was
possible. The quartzite at the test site on the 3400 level of the Galena mine
was intruded with siderite forming irregular veins and veinlets (fig. 6). The
quartzite showed a moderate amount of alteration at the contact with the
siderite. Estimates of the elastic constant were obtained using a biaxial


20

4 mg = -—m,=1

m =n =1, =m =1, =n, =0

Then from his equations 8 and 19 (or his table A-2, for bearing north,
inclination 90°),

60° 0° 120°
ho =f, 0.167/E 4,167/E 0.167/E
Jz = f, 2.833/E -1.167/E 2.833/E
J, = fp -0.500/E -0.500/E -0.500/E
J, =%& -4,619/E ) 4.619/E
J, =0 0 ) 0

J, = 0 0 0 )

Hole 3 borehole deformations were recorded as shown in figure 10. The
10-1EJ, values for this hole are based on the fact that field data recorded as
u, go with coefficients for 120° and u, field data go with coefficients for
60°; finally, u, field data go with 0° coefficients. The 10-2 EJ, values for
the three holes are tabulated in table A-1 of this publication.

Referring to table A-2 of this publication, row I, column 1 is simply the
coefficients of -10"7 EJ, multiplied by themselves and accumulated. Row II,
column 1 is simply 10-1 EJ, values multiplied by 10-1EJ, value and accumulated,
and so on to row VI and column 6. The remainder of the table is self-
explanatory.

The calculation of the b, as well as the other important parameters of
the calculation follows from Panek. The greatest problem may arise in estab-
lishing the proper coordinate system to use and the initial entrance into
table A-2 of this report. For these reasons this brief summary of the pro-
cedure may be of assistance to anyone planning a program of stress determina-
tions based upon the method developed and described by Panek.




BOREHOLE DEFORMATION, 102 y inch
&

1F Borehole gage orientation
©-30"
wr 4-90"
s 3-150)
o-t2s 46 6 7 6 ® 10 W 12 18 16 16 17 l@ 19 20 21 22 23 24 25 26 87 20

GAGE DEPTH, feet

FIGURE 4. - Borehole Deformation Readings Versus Depth, Hole 1.

As shown in figure 1, the strike of the quartzite beds at the test site
intersected the direction of holes 1 and 2 at an angle of about 45°. This
persistent plane of fracture was an aid to a minor degree in orienting the
stress-relief core from those holes. In figure 4 are plotted borehole
deformation readings and depth for hole 1. Consistently the readings taken
30° counterclockwise from the horizontal were greater than those for the
other two directions. A trend toward a greater deformation change at all
orientations with depth of hole was also indicated.

Borehole deformation and depth for hole 2 are shown in figure 5. The
data from hole 2 show a possible stress concentration within 1 radius of the
opening. This condition differs from that observed at hole 1.

Only three borehole deformation readings were obtained from drilling
18-1/2 feet of stress-relief hole vertically down at hole 3. Deformation
readings in this vertical down hole were so oriented that the u, direction in
the vertical hole was parallel to the axis of hole 1. The orientation proce-
dure was similar to the system reported by Obert (8, p. 57). The deformation
reading obtained from vertical down hole 3 at the ug orientation (150°
counterclockwise from south) was the least of the three readings. The ug
readings for hole 1 were consistently below those made at other two orienta-
tions. In other words, sampling the deformation in holes 1 and 3 in the same
general direction yielded the same qualitative indicators; namely, deforma-
tions in the northeast quadrant were less than deformations in the southeast
quadrant.

While drilling hole 3, the vertical down hole, it was considered neces -
sary to overcore through zones that yielded thin disks. Occasionally the
overcoring with the 6-inch bit was performed when there was no EX hole. Most
frequently the 5-5/8-inch-diameter core without a center EX hole was obtained
in long segments. Cores with center holes disked most frequently. This


FIGURE 6. - Vertical Down Hole—Hole 3 Stress-Relief Core Showing Concave Disking.

TABLE 2. - Young's modulus of elasticity (E) values for 6-inch-diameter

stress-relief cores from hole 1 using biaxial tester

Depth, Orientation, E,
feet degrees 10° psi
90, uz 10.10
30, u, 5.70
90, uy 7.57
150, ug 6.76
30, u, 5.20
90, uy 5.90
30 u, 5.61
weeee 90, up 7.12
AVETAGE...- sees eee ee eee eee eee eee - 6.73

Laboratory Determinations

All of the cores were sent to the Bureau of Mines Twin Cities Mining

Research Center, Minneapolis, Minn., for physical property tests.

Laboratory


Bureau of Mines
Report of Investigations 6997

STRESS ELLIPSOID DETERMINATION IN A ROCK-BURST-PRONE
AREA AT A 4,000-FOOT DEPTH, GALENA MINE,

WALLACE, IDAHO
by

Robert W. Ageton

Page

Page

Page

Page
Page

Page

10,

ll,

16,

18,
20,

23,

table 3. -

table 4, -

line 13. -

line 2. -

line 8. -

table A-2.

ERRATA

The four standard deviation boxheads should be
corrected to read as follows:

Standard
deviation,
10° psi

Under the fifth boxhead (Psi), 15,900 should be
on the second line with 36 samples and opposite
5,700.

Correct to read as follows: +.-greatest stress
was toward 88 winze...

The word "contentions" should be "conventions."
Correct to read as follows: J4 = -f4

- Under column 17 on line H', the figure should
corrected to read as follows: -.75707.

be

11888


18

APPENDIX

To make maximum use of the numerical values given by L. A. Panek (12), it
is convenient to adopt his contentions of x, y, and z axes and the hole number-
ing system he used. Important, also, is the method of recording and determin-
ing the diametral deformation (u) and the various 9 orientations of the drill
holes. The angle 9 specifying the orientation of a particular drill hole diam-
eter is measured from the positive h, axis (fig. 10); each drill hole is
assigned a right-hand rectangular coordinate system, h,, h,, and h, (12, p. 4).
Positive h, axis is horizontal and to the right for an observer facing the
positive h, direction of any drill hole. Following the procedure outlined by
Panek, positive x is east, positive y is north, and positive z is vertically
up. The positive h, direction was taken to be east for drill hole 1, south
for drill hole 2, and up for drill hole 3.

Z(Up)

(North)

|
|
|
|
| 7
|
|
|
|
|

-X (West) — — — — — — —~ — — X(East)
Drill hole 1

Note: Each hole has its own separate

~Y (South) hy ,haand hs coordinate system

Drill hole 2

Ur
-Z (Down)
Drill hole 3

FIGURE 10. - Diametral Orientations Using SingleeComponent Borehole Deformation Gage.


This document is released by the Bureau of Mines
in recognition of the necessity for prompt and
timely reporting. It is understood that the informa-
tion contained herein may be superseded by sub-
sequent publications. Some concessions in form
and style are made in the interest of timeliness.

Director


21

TABLE A-1. - Primary data for calculation of lithostatic stress field?

@ |-10° u | lo-? Eg, | 10-7 EJ, | 10-* EJ, | 10-2 EJ, | 10-* EJ, | 107? Eg,
Drill Hole 1
4.288 | -0.0500 0.2833 0.0167 0 -0.4619 0
4.145 -.0500 -2833 +0167 0 4619 0
30 |{ 4.334 -.0500 -2833 +0167 0 - 4619 t)
6.133 -.0500 +2833 +0167 0 4619 0
6.295 -.0500 +2833 +0167 0 -.4619 0
2.265 -.0500 -.1167 -4167 0 0 0
2.520 --0500 -. 1167 4167 ty) ty) 0
90 |) 3.645 -.0500 -.1167 -4167 0 ty) 0
3.147 -.0500 -.1167 -4167 0 0 0
4.843 -.0500 -.1167 -4167 0 0 0
4.207 -.0500 .2833 -0167 Cy) 0.4619 0
3.120 --0500 +2833 +0167 0 4619 0
150 }{ 3.807 -.0500 -2833 +0167 0 4619 0
2.502 --0500 +2833 +0167 0 -4619 0
3.136 --0500 +2833 -0167 0 +4619 )
Drill hole 2
3.328 0.2833 | -0.0500 0.0167 0 0 -0.4619
30 |) 6-225 -2833 -.0500 -0167 0 0 --4619
3.758 +2833 -.0500 -0167 0 0) -.4619
3.925 +2833 -.0500 +0167 0 0 --4619
2.090 --1167 --0500 4167 0 0 0
90 |) 2-584 -.1167 -.0500 -4167 0 0 0
3.069 -.1167 -.0500 -4167 0 0 0
2.670 -.1167 -.0500 -4167 0 0 0
3.638 +2833 -.0500 +0167 0 0 4619
150 |) 4-620 +2833 -.0500 -0167 0 0 4619
3.289 -2833 -.0500 -0167 0 0 4619
2.905 +2833 --0500 +0167 0 ) 4619
Drill Hole 3
60 | 7.095 0.0167 0.2833 -.0500 | -0.4619 0 0
0} 6.491 -4167 -.1167 --0500 0 ty) 0
120 | 3.358 +0167 +2833 -.0500 -4619 Y) 0

iThis table

is similar

to Panek's table A-6, R.I. 6732 (12).


FIGURE 2. - Test Site and Diamond Drill With Hydraulic Props. Props are fitted with
pressure gages which permit monitoring of prop pressure changes so that
pressure can be regulated to prevent movement of the drill.



65 T

60r

55-

50F

45

35h

25

BOREHOLE DEFORMATION, 102 p inch

Borehole gage orientation
1OF e— 30° 7
4- 30°

Sh 0-150" 4

o 8 2@ 3 4 5 6 7 8 9 0 Wo 1 13 14 15 16 17 18 19
GAGE DEPTH, feet

FIGURE 5. - Borehole Deformation Readings Versus Depth, Hole 2.

phenomenon has been studied (11, p. 231) and Obert and Stephenson presented
graphs showing that the radial and axial stresses required for disking are
lower when the core has a center hole. Only in the vertical down hole did
the disking of the stress-relief core approach the classical concave -convex
pattern as shown in figure 6.

Physical Property Determinations

Biaxial Tester

Cores, approximately 6 inches in diameter, obtained from overcoring
stress-relief work at the station on the 3400 level of the Galena mine were
marked where the deformation readings were made. All the samples suitable
for testing in the biaxial tester came from hole 1. Table 2 gives the
results. The sample at 7.85 feet indicated that the elastic constant might
vary with direction. The tendency did not persist, however, and although
directional differences do exist, they were not of the magnitude indicated
in this single sample. (The average of the last six determinations is
6.36 x 10° psi.)