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.orehole shear tester head 4
3. Pulling assembly including hollow jack, half-nut, clamp, and dial gage 5
4. Closeup view of the console 6
5. Schematic of BST in the hole 7
6. BST assembly, step 1 9
7. BST assembly, step 2 9
8. BST assembly, steps 3 and 4 10
9. BST assembly, steps 5 and 6 10
10. BST assembly, step 7 11
11. BST assembly, step 8a 11
12. BST assembly, step 8b 12
13. BST assembly, step 8c-1 12
14. BST assembly, step 8c-2 13
15. BST assembly, step 8c-3 13
16. BST assembly, step 8c-4 14
17. BST assembly, step 9 14
18. Normal stress calibration curve 17
19. Shear stress calibration curve '. 17
20. Example of BST plot 18
A-1. Angle of plate inclination 19
TABLES
1. Types of shear plates available for various rock types 2
2. Sample BST data sheet 15
3. Completed BST data sheet 16
4. Weights of BST components 18
BOREHOLE SHEAR TESTER:
EQUIPMENT AND TECHNIQUE
By Khamis Y. Haramy^
ABSTRACT
This Bureau of Mines paper describes the use of the borehole shear tester (BST) in
mines. Assembly and procedure sections explain how the equipment is assembled and
used properly. Schematics of the BST, limitations, test hole specifications, data record-
ing, and calculations are all explained briefly, and an example of the data collecting and
calculations is given to assist understanding.
INTRODUCTION
The borehole shear tester (BST) was developed by Dr. Richard L. Handy of Iowa
State University in 1976 under Bureau of Mines Contract G0144021. The purpose of the
work was to obtain a device for rapid, in situ measurement of rock shearing strength
as a function of the normal stress acting on the plane of failure. The device is light in
weight, mechanically simple, and easily transported. It is sufficiently durable to with-
stand repeated use in adverse environmental conditions and can be used in the rib,
roof, or floor of the mine. It requires an NX-size borehole.
The data obtained from BST tests support well-known theories such as Mohr's
theory of failure. This theory is based on a relationship between shearing stresses and
normal stress at every point within the specimen body. The Coloumb theory, which is
considered to be a special case of Mohr's theory, and the 1921 Griffith theory, which
deals with material failure on a microscopic basis, are also supported by the BST
results.
Owing to the difficulty in obtaining large samples of coal and rock for laboratory
testing and the bias that is introduced in large samples, the borehole shear tester
promises to be of significant value to the mining engineer and researcher in determin-
ing physical properties of in situ rock formations.
'Mining engineer, Denver Research Center, Bureau of Mines, Denver, Colo.
USING THE BOREHOLE SHEAR TESTER
The BST is a device for making in situ tests to determine
the shear strength of coal and rock using a 76-mm-
diameter borehole (NX-size) up to 12 m long determines
the shear strength as a function of the normal stress act-
ing on a plane of failure.
LIMITATIONS
1. Do not use the BST in unsupported roof rock or
within 1 foot of the borehole collar because it may cause
spalling and buckling.
2. Do not exceed a shearing stress of 6,500 psig.
3. Do not fully extend the shear plates unless the BST
body is in place inside the borehole.
4. Use the right type of shear plates depending on the
type of rock tested, as described in table 1.
TABLE 1.— Types of shear plates available for various rock
types
Type
desig-
nation
Configur-
ation
Tooth
spacing,
inch
Number
of
teeth
Tooth
depth,
inch
Shear
area per
plate,
sq in
Remarks
steel . . .
Carbide
insert.
Flat full
wedge.
. . do . .
0.4
.8
3
2
0.040
.040
0.8
.7
Used for
softer
rocks only.
Used for
coal and
all other
rocks.'
'The upper limit of rock strength has not been decided. However, the
device has been used in hard rock such as granite.
TEST HOLE SPECIFICATIONS
1. Diameter of test hole should be 76 mm (NX-size).
2. Length of test hole should not be less than 1 meter.
3. Hole should be dry to prevent rock dust penetrating
behind the shear plates and thus preventing their free rota-
tion. If water exists, the shear head swivel should be cov-
ered with a heavy grease.
4. Hole must be freshly drilled and clear of dust and
cuttings, especially in rapidly deteriorating material such
as coal and shale.
5. Drilling may be done by diamond bit, pneumatic per-
cussion drill, or others, provided the borehole is smooth,
straight, and free of ridges.
BST COMPONENTS
The unassembled BST components are shown in figure
1.
Shear Head (fig. 2)
1 . Two shear plates, each with two or three teeth which
penetrate into ttie rock when normal pressure is applied,
are mounted at the end of a double-acting hydraulic cylin-
der. The plates are fixed in place and linked to individual
push plates, which apply the normal force. Two types of
shear plates are available for use with different ranges of
rock strength (table 1). The steel plates are adequate for
coal and softer rocks. If the teeth chip or wear, the carbide
insert shoes should be used.
2. The two push plates are connected to a locking
mechanism and stay parallel during initial shear head
expansion.
3. Two short hydraulic hoses of different lengths are
provided, which connect onto the BST body. One is used
for shear plates expansion, the other for retraction.
Pulling Assembly (fig. 3)
1. A 12-ton center hole, hydraulic jack fits over thd
threaded pull rod for pulling.
2. An adjustable tripod is used to assure axial aiine*
ment of jack and threaded rod.
3. Jack base plate.
4. A lock grip half-nut clamp provides a quick-acting
stop nut on the threaded rod.
5. A dial gage reads displacement of BST in the hole, if
required.
Console (fig. 4)
1. Hand pump.
2. Lever-type pump valve for "open-close" operating
modes.
3. Normal pressure valve and gage to read the applied
pressure for normal forces against the shear plates.
4. Shear pressure valve and gage to read the applied
pressure for shearing forces between the shear plates and
the rock.
5. Manifold valve (expand-neutral-retract) used for the
expansion and retraction of the shear plates.
6. Three hydraulic ports (shear, retract, and normal)-
onto which the hydraulic hoses connect.
7. Two unmarked terminals for possible addition of
shear and normal pressure transducers. (Otherwise these
are left capped.)
8. An aluminum case to protect the console.
Miscellaneous
Other BST assembly components include hydraulic ex-
tension lines, threaded rods, RW adapters, and RW-size
rods in 5-foot sections. Figure 5 shows a schematic of the
BST and the way it should appear when placed in the hole.
■m
A. Console
B. Hydraulic hoses
C. Shear head (BST body)
D. RW rod connector
E. Half-nut clamp
F. RW rod adapters
G. Adjustable tripod
H. RW rod
I. Threaded rod
J. Jack base plate
K. Dial gage
L. Hollow jack
FIGURE 1.— Borehole shear tester components.
FIGURE 2.— Cioseup view of the borehole shear tester head.
Adjustable tripod"' ,
Jack base plate''
FIGURE 3.— Pulling assembly including hollow jack, half-nut, clamp and dial gage.
FIGURE 4.— Closeup view of the console.
Threaded rod — ~.
Half-nut clamp
Hollow jack
^-Olal gage
-Tripod
^Jack baie plate
Shear plates- «
• ' •••■.-.•/ hqsj connector
NX hole
^>--BST body
FIGURE 5.— Schematic of the BST in the hole.
BST ASSEMBLY
In assembling the borehole shear tester, refer to the se-
quence of photographs 6 through 17 to help understand
each step In the process. At least a 12-Inch pipe wrench,
several screwdrivers, an 8-inch crescent wrench, shear
plates, and hydraulic fluid are tools needed for the BST
setup.
1. Screw the RW rod adapter into the end of the BST
body. This adapter adapts the thread in the BST body to
the RW rod thread (fig. 6).
2. Couple the hydraulic extension hoses to the hoses
attached to the BST body (fig. 7).
3. Mark the extension hose that is connected to the
shorter hose from the BST body (fig. 8). (The BST has a
long hose section and a short hose section attached to it.)
4. Attach the RW rods in 5-foot sections to the rod
adapter (fig. 8).
5. Place the BST body in the hole with the shear plates
at a known orientation, such as N-S or E-W, and a known
depth (fig. 9). Record both orientation and depth on the
data sheet.
6. When the BST body is at the required depth, attach
another RW adapter, to the RW rod (fig. 9). The reason RW
rods are used is that they are much stiffer than threaded
rods, which eliminates bending or stretching while the
BST Is under shearing load.
7. Screw in a 3-foot threaded bar to the RW adapter at-
tached to the end of the RW drill rod (fig. 10).
8. Mount the pulling assembly at the hole collar as
follows:
a. Place the jack base plate over the threaded bar
and the hoses at the collar of the hole. Allow the hoses
and the threaded bar to pass through the slot in the plate
(fig. 11).
b. Place the tripod with the adjustable screws
against the jack base plate (fig. 12). These screws are used
to aline the jack along the centerline of the hole.
c. Slide the hollow jack over the threaded bar and
against the tripod (fig. 13). Hold it in place, and after
pushing everything tight together, secure the visegrip-type,
half-nut clamp on the threaded bar tight behind the jack
(fig. 14). The pulling assembly should look like figure 15
before testing begins. The dial gage, shown in figures 13-
16, is included in the assembly only if axial displacements
of the BST are to be measured, see "Procedure" section.
Caution:— \i the testing is in a vertical hole, the BST
pulling rods and tripod assembly should be held in the
center of the hole at the collar at all times until the normal
seating pressure is applied. It is recommended that, for
safety purposes, a safety chain and rod hook be used to
hold the assembly in the vertical hole (fig. 16).
9. Connect the hydraulic hoses to connectors, which
are in the upper right-hand corner of the console (fig. 17),
as follows:
a. The marked hose (from step 3 of this section) to
the port on console marked Normal.
b. The other hose from the BST body to the port on
console marked Retract.
c. The hose from the jack to the port on console
marked Shear.
PROCEDURE
The following procedure is for the BST in a vertical up-
ward hole. In a downward vertical hole, the procedure is
similar, except that when placing the BST body in the bore-
hole, one should restrain it or it may be lost in the hole.
Remember to record the orientation and depth of the shear
plates before every test.
1. Assemble the BST body, snap hoses on, connect
rods, and place it in the hole as mentioned in the previous
section, steps 1 through 7 and steps 9a and 9b.
2. Place the pump valve and the valve labeled "shear"
on CLOSE.
3. Open the normal valve, and place the manifold valve
on NORMAL EXPAND.
4. Pump up normal gage pressure to a certain level
which depends on rock type as follows:
400 psig. . . Soft rock.
1,600 psig. . . Medium rock.
3,200 psig. . . Hard rock.
Enough seating pressure must be exerted to achieve full
penetration of the teeth into the rock or coal prior to the
test, to insure that the teeth will shear off a coupon of rock
or coal and not simply scrape the surface. Excessive dis-
placement during the test or low apparent shear strength
may indicate the need to apply a higher seating pressure.
The seating pressures given above are typical and may be
used as a guide. The appendix gives more details on seat-
ing pressure calculations.
5. CLOSE normal valve.
6. Wait 5 minutes for the teeth on the shear head to
penetrate into the rock. Remember to keep holding the
BST in the hole until normal pressure is applied.
7. Mount pulling assembly at the borehole collar as ex-
plained in steps 8a through 8c in the previous section.
8. Snap on the jack hose according to step 9c.
9. Adjust the dial gage for a zero reading and record it
on the data sheet if BST axial displacements are to be
made.
10. OPEN normal valve.
11. Readjust normal pressure to the chosen setting
pressure (if any change in pressure has occurred) by either
pumping (to increase pressure) or opening pump valve
slowly (to reduce pressure).
12. CLOSE normal valve.
13. OPEN shear valve.
14. Pump at a slow rate until shear gage reads 100 psig,
then record the following data on the data sheet (see ex-
ample in appendix):
Normal pressure
Shear pressure .
Displacement . .
From normal gage on console.
From shear gage on console.
From dial gage if desired.
15. Pump the shear pressure in steps to 200 psig, 400
psig, 600 psig, and so on until the peak shear has been de-
termined. Record shear pressure and displacement for
each pressure. If the pulling rod bends as the shear
pressure is increased, the load should be released and the
tripod adjusted so that the pulling action is parallel to the
axis of the hole; otherwise the displacement measure-
ments will be meaningless and the pulling rods may be
damaged.
16. Continue to pump until shearing pressure changes
are relatively slow or a predetermined maximum displace-
ment is reached.
17. Upon each completion of each test, OPEN pump
valve, CLOSE shear valve, OPEN normal valve, and switch
manifold valve to retract.
1 8. Before removing BST from hole, CLOSE pump valve,
CLOSE shear valve, keep normal valve OPEN, and pump
until the shear plates retract and the BST head apparatus
pulls loose from the hole.
19. For the next sequential test, reinsert the device in
the hole either rotated 45° at the same depth, or at a differ-
ent depth. Repeat all above procedures.
A/ofe.— When the BST is used in harder rocks, the shear
plate teeth may wear enough during a series of tests to
begin to affect the results. The effect of this wear should
be distributed over the length of a test hole by randomizing
the depths and orientations of the shear tests.
CLEANING THE BST
After every test, clean off shear plates and make sure
they swivel freely. After the completion of all testing, clean
the BST body very well and lubricate it by using a WD-40
lubricant spray (or equivalent) to prevent rusting.
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DATA AND CALCULATION
A blank data sheet for the borehole shear tester data ap-
pears as table 2; each sheet should be filled in completely
as shown in table 3, including the name and location of
the mine, the type of rock tested, the hole specifications,
the date of testing, and the name of the person(s) doing
the testing.
Every BST has two calibration curves, similar to the
ones shown in figures 18 and 19. One is a normal stress
calibration curve; the other is a shear stress calibration
cun/e. The normal gage pressure Pn and the shear gage
pressure Ps (in psig) are read from the normal and shear
gages respectively on the console. The normal stress on
and the shear stress Ts (in psi) are calculated from for-
mulas such as the following:
Normal stress (on) = 2.604 Pn- 85.135 (1)
Shear stress (Ts) = 1 .744 Pn - 81 .035 (2)
Formulas 1 and 2 were obtained from the calibration
curves. Both curves have a small negative intercept. (One
may also use the curves in figures 18 and 19 to obtain on
and Ts).
The calculated normal stress on is plotted on the X-axis
versus the calculated shear stress Ts on the Y-axis on
linear-linear graph paper. The best-fitting straight line is
drawn through the plotted points. The cohesion (in psi) for
a particular rock is indicated by the intercept of this fitted
line with the Y-axis. Provided that the scales are the same,
the angle of internal friction is the angle between the
X-axis and the plotted line as shown in figure 20. The angle
of internal friction can also be calculated as the arc tan-
gent of the slope of the plotted line.
<|> = arc tan p<
where ^ = the slope of the line (coefficient of friction).
The calculation of the BST tests made in a Utah coal
mine given in table 3 should help clarify the calculations.
A Bureau of Mines computer program can be used to
analyze the BST data; a copy may be obtained from the
author of this paper at the Bureau of Mines, Denver, Colo.
In calculating the shear stress, the weight of the BST
assembly (see table 4) should be taken into consideration
as follows:
1. In an uphole, the shear stress caused by the weight
of the BST body and the hoses used in the hole. The
weights of the RW-size drill rods, threaded rods, plates and
tripod, and hollow jack should all be added to the maxi-
mum shearing force required. If a dial gage is used, its
weight should be added.
2. In a downhole, the shear stress caused by the weight
of the BST body, hoses used in the hole, and RW rods
should be subtracted from the maximum shearing force
required.
3. In a horizontal hole, the shear stress caused by the
weight of the BST assembly has a very small effect. There-
fore it does not have to be included in the shearing force
calculations, and no adjustments are required.
Mine
Type of rock
Hole No
Roof
.Hole location.
TABLE 2.— Sample BST data sheet
DATA SHEET FOR BOREHOLE SHEAR TESTER
Date
Tested by
Floor
Hole depth
Test
Normal
Shear
Orientation
of teeth
Depth
into hole
Displacement
Po
On
Ps
Ts
'n = Normal gage pressure (psig)
On = Normal stress (psi) (calculated).
Pn = Maximum shearing gage pressure.
Ts = Shearing stress (psi) (calculated).
16
TABLE 3.— Completed BST data sheet
DATA SHEET FOR BOREHOLE SHEAR TESTER
Date
OCTOBER 1, 1980
Mine
Type of rock
Hole No. W-25
COAL MINE "X", UTAH
COAL
SANDSTONE
Hole location
Roof
HOLE IN ROOF, CROSSCUT
#25, 3d Rt.
Tested by
Floor
Hole depth
HARAMY AND DeWAELE
30'(NX-HOLE)
Test
Normal
Shear
Orientation
of teeth
Depth*
into hole
Displacement
Pn
On
Ps
Ts
1
1000
2392
1350
1841
NS
12'5" + H**
— —
2
1250
2990
1700
2318
NS
107.5" + H
— —
250
ZERO READING
ON DIAL GAGE = 6.0
5.95 0.05
500
5.61 0.39
750
5.25 0.75
1000
4.85 1.15
1250
4.20 1.80
1500
3.56 2.44
1700
PEAK
2.43 3.57
3
1500
3588
1760
2400
NS
8'4.5' + H
— —
250
5.00 0.00
500
4.90 0.10
750
ZERO DISPL. = 5.0
4.79 0.21
1000
4.44 0.56
1250
2.77 2.23
1500
.16 4.84
1760
PEAK
- -
4
1750
4186
2200
3000
EW
8'11" + H
— —
250
5.80 0.20
500
ZERO DISP = 6.0
5.27 0.73
750
5.09 0.91
1000
4.84 1.16
1250
4.60 1.40
1500
4.21 1.79
1750
3.68 2.32
2000
2.88 3.12
2200
PEAK
1.30 4.70
5
2000
4784
2350
3205
EW
11'0" + H
— —
500
6.55 0.45
750
ZERO DISPL. = 7.0
6.14 0.86
1000
5.72 1.23
1250
5.40 1.60
1500
5.09 1.91
1750
4.70 2.30
5
2000
3.50 3.50
2250
2.00 5.00
2350
1.92 4.08
6
2250
5380
3010
4106
12'6" + H
- -
500
7.09 0.91
1000
6.05 1.95
1500
5.49 2.51
2000
4.90 3.10
2500
3.92 4.08
3000
2.15
3010
- -
'Distance from collar ot borenoie to the
center of loading plates
•H = Length of BST head 1.5'
Pn = Normal gage pressure (psig)
On = Normal stress (psi) (calculated)
Ps = Maximum shearing gage pressure
Ts = Shearing stress (psi) (calculated)
17
14,000
12,000 -
1 0,000 -
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CO
LiJ
CC
t-
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4,000
CO
2,000
Ts= 1.744 P5-8I.O35
r =0.9998(coeff. of correlation)
n= 18 (number of tesfs)
BST serial number 1104
-L
1,000 2P00 3^P00
SHEAR GAGE READING (Pjj.pslg
FIGURE 19.— Shear stress calibration curve.
4p00
5.000
18
4.000
3,000
I 1 r
Mine; Utah cool mine
Type of rock : Sondstone
Dote of test : Oct. 1, 1980
-
Tested by Haramy and DeWoele
to
w
^ 2,000
►-
V)
a:
<
UJ
X
CO
1,000
.NOV*
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^>-Ts = 800 + o-n ton 2 6.56*
Slope = 0.5
i> (angle of internal friction) = 26.56°
SO
ooo
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1,000
J.
X
2,000 3,000 4,000
NORMAL STRESS {a-n),psi
FIGURE 20.— Example of BST plot.
X
5,000
6,000
TABLE 4.— Weights of BST components
Component
RW rod
BST body and 2 attached short hoses .
Hydraulic hoses and fluid
Tripod and base plate
Dial gage
Threaded rods
Hollow jack
Half-nut clamp
Weight
1.8 'bf/ft
9.5 lt>,
0.1 lb/ft
7.0 1b
1.0 1b
1.5 lb/ft
11.01b
.81b
'Stress :
weight
2 (cross-sectional area of plates)
Stress'
0.45 psi/ft
2.375 psi
0.025 psi/ft
1.750 psi
0.250 psi
0.375 psi/ft
2.750 psi/ft
0.200 psi
NOTE.— This table also allows the operator to decide whether a winch is
needed to hold the BST assembly as opposed to the operator handling
the weight.
BIBLIOGRAPHY
1. Handy, R. L, J. M. Pitt, L. E. Engle, and D. E. Klockow. Rock
Borehole Shear Test. Proc. 17th U.S. Symp. on Rock Mech.,
Snowbird, Utah, Aug. 25-27, 1976, pp. 4B6-1-4B6-11.
2. Panek, L A. Criterion of Failure for Design of Rock Mass
Structures as Determined by Borehole Shear Tests. Proc. 4th
Cong., Internat. Soc. for Rock Mechanics, Montreux, Switzerland,
Sept. 2-8, 1979, v. 2, pp. 509-515.
19
APPENDIX— SEATING PRESSURE CALCULATIONS FOR COAL
The coefficient of sliding friction can be calculated as
follows:
/i = tan/?
where ^ = coefficient of friction
and p = angle of friction between the shear
plates and the material being
tested.
In laboratory testing by the Bureau, the coefficient of
friction between coal and steel was found to be 0.3 ± 0.04.
From equation 1
p = arc tan (0.3) = 16.7°.
The minimum normal stress to cause material failure
can be calculated using the following formula:
^o < tan(0 + /3)-tan > 400 psi.
2.5
The normal stress will vary depending on Cg and ^ of
coal. This method of estimating o„ is a good approxima-
tion and may be used for any type of rock.
*U.S. Government Printing Office : 1982 -364-576/7289
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