Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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MINE ROOF BOLT
RELATED APPLICATION
This application corresponds to U.S. Patent No.
5,259,703, issued November 9, 1993, entitled Mine Roof
Bolt.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to mine roof bolts,
and more particularly relates to mine roof bolts
constructed of multi-strand steel cable.
2. Description of the Prior Art
In the art of mine tunnel roof support, there are
two major categories of bolting systems wherein mine roof
bolts are anchored in bore holes drilled in the mine
roof, the bolts' purpose being to reinforce and stabilize
the unsupported rock formation above the mine tunnel.
These two categories of mine roof bolting systems are:
(1) tension-type systems, and (2) passive-type systems.
In each system, it is common practice to, first, drill a
hole through the mine tunnel ceiling into the rock
formation above to a depth appropriate for the type of
rock formation to be supported. A mine roof bolt and
roof plate are then anchored in the bore hole to support
the mine roof and maintain the rock formation in place.
B
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In a common tension-type mine roof bolt
system, an expansion shell type anchor is installed
on the threaded end of the bolt. The bolt and
expansion shell anchor are inserted up into the bore
hole until the roof plate is against the mine roof.
The bolt is then rotated to thread a tapered plug
section of the expansion shell down toward the bolt
head, in order to expand the jaws of the expansion
shell against the interior wall of the bore hole to
thereby hold the mine roof bolt in place within the
bore hole, the mine roof bolt functioning to support
and stabilize the rock formation above the mine
tunnel.
In passive-type mine roof bolt systems, the
passive-type bolt is not attached to an expansion
shell or similar anchor at the free (upper) end of
the bolt, but rather is retained in place within the
rock formation by a rapid-curing resin adhesive
material that is mixed in the bore hole as the bolt
is rotated and positioned within the bore hole. In
theory, the resin adhesive bonds the bolt to the rock
formation along the total length of the bolt within
the bore hole in the rock formation. It is also
common practice to use resin adhesive with a
tension-type mine roof bolt to retain the bolt within
the mine roof bore hole, at least along the upper
portion of the bolt.
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In passive-type and some tension-type mine
roof bolt systems, one or more resin cartridges are
inserted into the bore hole prior to (ahead of) the
mine roof bolt. Forcing the mine roof bolt into the
bore hole while simultaneously rotating the bolt
ruptures the resin cartridge(s) and mixes the Lesin
components within the annulus between the bolt shank
and bore hole wall. Ideally, the resin adhesive
mixture totally fills the annulus between the bolt
shank and bore hole wall at least along the upper
portion of tension-type bolting systems, and along
the total length of the bolt shank and bore hole wall
in passive-type systems. The resin mixture is forced
into cracks and crevices in the bore hole wall and
into the surrounding rock formation to adhere the
bolt to the rock formation.
When extremely long mine roof bolts are
necessary, it is common practice to att.ach two or
more bolt shank sections together by couplers to
result in a "roof bolt" of sufficient length
appropriate for the particular type of rock
formation. These couplers between bolt sections,
being of a larger diameter than the bolt shanks,
prevent the mixed resin adhesive from flowing
downwardly (resin return) within the bore hole
annulus from the first (upper) bolt section to the
lower section(s). Therefore, the effective anchoring
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of the bolt to the bore hole wall within the rock
formation is, essentially, only along the length of
the first ~upper~ bolt section where-in the resin --
adhesiveltotally fills-th@ ~annulus-b~tween the bolt
section and the bore hole wall.
To alleviate this problem, it has been
c~mmon practice simply to drill a larger bore hole in
the rock formation that will enable the resin
adhesive to flow around the coupler(s) as the bolt is
being inserted into-and-rotated within the-bore hole
to mix the resin. Although this does effect the
desired result ~resin return around the coupler(s)
within the annulus between the bolt shank and bore
hole wall), it creates another problem that,
depending on the type of rock formation, may be more
dangerous than the problem that is corrected by a
larger bore hole. Specifically, the bonding
effectiveness of the resin adhesive material to hold
the mine roof bolt in place within the bore hole is
considerably weakened by virtue of the increased
distance between the bolt shank and bore hole wall,
and the sheer volume of resin adhesive material
necessary to totally fill the annulus. Additionally,
by virtue of their specific makeups, mine roof rock
formations that actually require long (fifteen feet
or longer) mine roof bolts are more susceptible to
movement and shifting within the rock formation, than
are more solid rock formations that require only
shorter mine roof bolts.
; Another common problem with using mine roof
bolt sections coupled toge-ther;in such rock
formations that require longer (coupled) mine roof
bolts, this shifting of the rock formation (shear)
causes the bolt couplers to fracture. When this
happens, of course, the effective holding length of
the mine roof bolt is instantly decreased. -In-many
instances~there is-n~-or very little-resin adhesive
material arou~d the broken bolt-shank- to~help
stabilize the rock formation. There~ore, in almost
all instances, this shortened mine roof bolt is
ineffective to safely prevent the mine roof rock
formation from further shifting and potential
collapse.
It is therefore an object of the present
invention to provide an improved mine roof bolt that
does not require an oversized mine roof bore hole in
order to effect full and complete resin return within
the annulus between the bolt shank and bore hole wall
along the total length of the bolt shank.
It is another object of the present
invention to provide an improved mine roof bolt that
is available in various lengths without the use of
bolt shank couplers that are susceptible to fracture
when the mine roof rock formation shifts.
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It is a further object of the present
invention to provide an improved mine roof bolt
having an outer surface that aids in effecting
complete mixture,o~ the resin adh-esive ma-terial, and
also includes crevices within the mine roof bolt
shank that permit penetration of the resin bonding
material- into the-bo-lt shank for more effective resin
bonding thereto.
It is-a,still further,object o~ the present
invention to provide an improved-mine roof bolt that-
will easily bend for insta-llation into a bore hole
that is considerably deeper than the he ght o~ the-
mine tunnel at the installation location, and will
also bend with a shifting rock formation, and fully
retain its bonding within the rock formation along
the total length of the mine roof bolt without
breaking when the rock formation shifts.
It is yet another object of the present
invention to provide an improved mine roof bolt that
includes means for preventing voids in the mixture of
resin adhesive material in the annulus surrounding
the bolt shank.
It is a further object of the present
invention to provide an improved mine roof bolt that
includes means for preventing premature rupture of
resin cartridges while positioning the cartridges
into the bore hole.
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It is yet a further object of the present
invention to provide an improved mine roof bolt that
includes means on the bolt shank for preventing voids
in the resin adhesive material, such means also
permitting the resin adhesive to flow around and
under the means to further support the mine roof bolt
and the rock formation.
It is a still further object of the prevent
invention to provide an improved mine roof bolt
having means for protecting the bolt shank from
abrasive wear from the roof plate as the bolt is
being spun into the bore hole.
It is another object of the present
invention to provide an improved mine roof bolt
having means for permitting the bolt to UyieldN
within the bore hole at a consistent yielding force
as shifting of the rock formation tends to cause the
bolt shank to ~slip" relative to the resin adhesive.
It is still another object of the present
invention to provide an improved mine roof bolt
having means for preventing the bolt heads from
falling from the bore hole, in the event the bolt
fails under extreme load.
SUMMARY OF THE INVENTION
The improved mine roof bolt of the present
invention is constructed of a length of
pre-tensioned, multi-strand steel cable, commonly
formed of six individual pre-tensioned steel strands
spirally wrapped around a seventh steel strand. The
head of the bolt is formed by positioning a two-piece
tapered plug around the stranded steel cable at one
end, and then slipping a hexagonal- or other
drive-headed internally tapered collar around the
tapered plug. Pressing the internally tapered
hexagonal head collar down around and against the
two-piece tapered plug urges serrations on the
interior circumference of the plug sections to "bite"
into the stranded steel cable to form a rigid
hexagonal bolt head on the cable that further
tightens against the steel strands as tension is
applied to the mine roof bolt.
The mine roof bolt includes a number of
embodiments that enhance its ability to be retained
within the bore hole, and therefore, to stabilize the
rock formation~ "Buttons" or sleeves swaged on the
shank cable effect improved bonding of the resin
adhesive to the bolt shank. An annuala~ dam around
the bolt shank retains the resin adhesive around the
shank, minimizes voids and air pockets in the resin,
and forces the resin into cracks and crevices in the
rock formation. A stiffner sleeve prevents cable
buckle as the bolt is being urged into the bore hole
and also protects the cable from abrasive wear from
the mine roof plate as the bolt is being spun into
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the bore hole. A resin protector cap protects resin
cartridges from premature rupture by the sharp end of
the bolt shank cable, and retains the resin
~artridges in-pl-ace within the bore hole when the
bolt is subsequently withdrawn. A plurality of cap
sleeves fit over the bolt heads and are
interconnected in a manner to contain bo]ts that
break within the bore hole.
---Lastly, a "yieldable" cable bolt-design
incorporates means that permit the bolt shank tO slip
or "yield" relative to the resin a & esive within the
bore hole while maintaining a consistent resistance
force along the shank, even as the shank is pulled
outwardly from the bore hole and out of contact with
the resin adhesive.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a partial sectional view of the
improved mine roof bolt of the present invention,
illustrating the two-piece tapered plug and, in
section, the internally tapered hexagonal head
collar.
Fig. 2 is an end view of the improved mine
roof bolt.
Fig. 3 is a perspective view of one section
of a two-piece tapered plug.
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Fig. 4 is a perspective view of an
alternative embodiment of one section of a two-piece
tapered plug.
Figi 5 is a side elevation view of the
improved mine roof bolt positioned in the mine roof
bore hole under the resin cartridge, the mine roof
plate, spherical washerj and internally tapered
hexagonal head being shown in section.
Fig. 6 is a view of the improved mine roof
bolt of Fig. 5, shown in installed position within
~he mine roof bore hole, with the resin adhesive
material thoroughly mixed and completely filling the
annulus around the shank of the mine roof bolt.
Fig. 7 is a graph of tensile strength vs.
elongation for a 9/16 inch diameter improved mine
roof bolt of the present invention.
Fig. 8 is a side elevation view of the mine
roof bolt of the present invention illustrating a
number of alternative embodiments.
Fig. 9 is an end view of the second
alternative embodiment mine roof bolt taken along
lines 9-9 in Fig. 8.
Fig. 10 is a side elevation view of a resin
protector cap used with the mine roof bolt of the
present invention.
Fig. 11 is a partial side elevation view of
the upper end of the mine roof bolt of Fig. 8 and
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incorporating the resin protector cap of Fig. 10,
shown positioned in a mine roof bore hole prior to
puncturing the resin cartridge.
Pig. 12 is-a side elevation view of a~=
plastic hex-head cap sleeve for use with the mine
roof bolt of the present invention.
Fig. 13 is a top view of the plastic
hex-head cap sleeve, taken along lines 13-13 in Fig.
12. - -
Fig. 14 is a side elevation view of a number
of mine roof bolts installed in bore hol~s i~ a mine
tunnel roof, illustrating the concept of the wire
interconnecting the plastic hex-head cap sleeves of
adjacent mine roof bolts.
Fig. 15 is a side elevation view of another
alternative embodiment of the mine roof bolt of the
present invention, illustrating the yieldable concept
of the mine roof bolt.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings, and initially
to Fig. 1, the improved mine roof bolt is shown,
generally illustrated by the numeral 10. The mine
roof bolt comprises a shank 12 made up of a length of
pre-tensioned steel stranded cable, which in the
embodiment shown, is made up of six peripheral
pre-tensioned steel strands 14 spirally wrapped
around a central steel strand 16 (more clearly shown
in Fig. 2).
At one end of the steel stranded cable is
affixed a-two-piece tap~red plug 20 which comprises
two identical diametrically opposed essentially
half-cylinders that define the outer surface of a
right conical frustum. The frusto-conical outer
surface 22 of the two-piece tapered plug 20 is
designed to engage a mating inside funnel surface of
an internally tapered hexagonal head ~ollar 26-.
Although the collar 26 is shown as a hexagonal head,
obviously a square head or any other shaped head-that
accepts a mine roof bolt driver mechanism and boom
should function adequately for the intended purpose.
Fig. 2 is an end view of the improved mine
roof bolt of the present invention, and illustrates
how the two-piece tapered plug fits concentrically
around the pre-tensioned steel cable shank of the
bolt, and also nests concentrically within the
internally tapered hexagonal head collar 26. Note
that the individual sections of the two-piece tapered
plug 20 are not fully semi-frusto-conical. When
functionally positioned within the hexagonal head
collar 26 and around the steel cable shank 12, the
two individual plug sections 20 define a diametric
space 28 between the two plug sections to enable the
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plug sections to be urged together tightly when
pressed against the steel stranded cable.
Fig. 3 is a perspective view of one section
of the two-piece t~pered plug 2~0-, and mo~re clearly ~
shows a series of serrations or knurls 30 that define
the inner essentially semi-t.ubular surface of the
tapered plug. These serrations 30 are designed to
"bite" into the steel cable defining the roof bolt
shank 12 as the two-piece tapered plug 20 is urged -
further into the hexagonal head co-1-lar---26 to-define
the rigid hex-head of the improved mine roof bolt.-
Creating this rigid-hex-he~ad on t-he-mine-~-
roof bolt can be accomplished in either of two ways:
(1) By pressing the two-piece tapered plug 20 and
steel cable shank 12 into the hexagonal head collar
26 as the mine roof bolt is factory-manufactured; or
(2) After having cut the steel cable to the desired
length at the mine site, assembling the steel cable,
two-piece tapered plug 20, and hexagonal head collar
26, and then tensioning the steel cable against the
hexagonal head collar, or otherwise pressing the
tapered plug and cable into the collar. In either
instance, the "head" of the improved mine roof bolt
10 should be rigid and secure sufficiently to remain
intact as the mine roof bolt is being inserted into
the bore hole, forced up into the bore hole against
the resin cartridge(s), and rotated or spun within
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the bore hole in order to rupture the resin
cartridge(s) and mix and distribute the resin
adhesive material.
Fig. 4 is a perspective view of one section
of an alternative embodiment of the two-piece tapered
plug, shown at 32. This alternative embodiment
tapered plug includes a different type of knurl 34
formed in a diamond pattern resulting from diagonally
oriented serrations. Those skilled in the art will
appreciate that this diamond pattern knurl will
better retain the tapered plug 32 on the steel cable
against both torsion as the improved mine roof bolt
10 is rotated during installation, and against
tension as the bolt remains in place within mine roof
rock formation to retain the rock formation in place.
Fig. 5 illustrates the improved mine roof
bolt and its arrangement as inserted up into a mine
tunnel roof bore hole. Assuming that the improved
mine roof bolt has previously been assembled as shown
in Fig. 1, and the two-piece tapered plug 20 has been
pressed into the hexagonal head collar 26 to define a
rigid bolt head, the user first places a spherical
washer 40 having a partial spherical surface 42 over
the bolt shank and down against the hexagonal head
collar 26, as shown. ~ext, the user slips on a dome
mine roof plate 44, the through-hole of the roof
plate having an angled surface 46 that mates with the
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partial spherical surface 42 of the spherical washer
40.
~ Those skilled in the art will appreciate
that this spherical washer 40 and the angled surface
46 of the dome mine roof plate 44 define a "ball and
socket"-like arrangement that permits the improved
mine roof bolt and dome mine roof plate to be used in
mine tunnel roofs wherein (1) the bore holes are
angled or otherwise not normal to the surface of the
mine ceiling -4-8, (2) the mine ceiling surfaces are
extremely rough or otherwise uneven, or (3) a
combination o~ ~1) and-(2)-that res~lts in;the
entrance to the mine roof bore hole not being exactly
normal to the mine ceiling surface at the location of
the bore hole. Additionally, such an arrangement
permits the improved mine roof bolt 10 to shift
slightly as the rock formation above shifts, and
still maintain an essentially uniform force
distribution against the dome mine roof plate 44.
To this end, the inventor has determined
that, alternatively, the hexagonal head 26 of the
improved mine roof bolt of the present invention and
the spherical washer 40 may be formed as a single
piece. This simplifies installation and more easily
maintains the mine roof bolt in alignment with the
roof plate during insertion and rotation of the mine
roof bolt in the roof bore hole.
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The spherical washer 40 and dome mine'roof
plate 44 having been installed on the improved mine
roof bolt 10, the user then inserts a resin cartridge
50 into the bore hole 3-&,-follQwed by the improved
mine roof bolt of the present invention. The user
then forces the bolt 10 upwardly into the bore hole
38 under the force of the bolter boom (not shown),
while simultaneously rotating the bolt to rupture the
resin cartridge 50 and thoroughly mix and distribute
the resin adhesive material contained therein.
Continued rotation of the mine roof bolt 10 after the
dome mine roof plate 44 has been urged up against the
mine tunnel ceiling 48, further mixes and distributes
the resin adhesive material within the annulus
between the steel cable and the mine roof bore hole
38, and causes the resin adhesive material to be
forced into the cracks and crevices within the rock
formation, and also into the crevices and spaces
between the individual peripheral steel strands 14 of
the steel cable. After the resin adhesive material
is thoroughly mixed, the assembled bolt is held in
place against the mine ceiling 48 as shown in Fig. 6,
by the boom, for a period of time sufficient to
permit the resin to cure.
Fig. 7 is a graph of tensile strength vs.
elongation for a 9/16 inch diameter cable mine roof
bolt of the present invention. When pulled in
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tension until fracture, the mine roof bolt begins to
yield at approximately 57,000 pounds of force, and
will withstand over 60,00 pounds of force before
fracturing.
As the graph of Fig. 7 illustrates, in
testing, the fracture of the seven-strand cable mine
roof bolt actually occurs in a stepped progression,
rather than all at-once. Typically, one, two~ or
three individual ~abl~ strand-s will fail at
approximately 60,000 pounds, the remaining four,
five, or six strands remaining intact to continue to
support the rock formation above the mine roof.
These remaining four-to six strands will continue to
withstand from 25,000 to 35,000 pounds of force
before the next set of one, two, or three strands
fails in tension. The steel cable strands remaining
intact after the second set of strands fails (from
one to four) will continue to withstand approximately
15,000 pounds of force before ultimate total failure
of the mine roof bolt.
By comparison, a convential 5/8 inch
diameter smooth shank mine roof bolt will fail at
under approximately 30,000 pounds of force,
approximately one-half of the maximum force of
approximately 60,000 pounds that a 9/16 inch diameter
cable mine roof bolt will withstand before the
initial partial failure.
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It is important to note that when the 9/16
inch cable mine roof bolt "fails" at 60,000 pounds,
its failure is only partial, in that four to six
steel strands remain intact through the first
"stepped failure". Therefore, the improved mine roof
bolt of the present invention remains intact after
initial "failure" to continue to support the rock
formation to permit the rock formation to stabilize
with the bolt intact and is still able to withstand
approximately 30,000 pounds of force before a
subsequent "failure" occurs.
The inventor has also determined in testing,
that the multi-strand cable defining the shank of the
improved mine roof bolt of the present invention
fractures adjacent the point of attachment to the
two-piece tapered plug, leaving essentially the total
length of the steel cable shank remaining in the mine
roof bolt bore hole to continue to support the rock
formation. This is to be contrasted with
conventional mine roof bolts formed of shank sections
collared together that generally fracture either at
or adjacent a collar. In the event the collar has
prevented complete resin return along the total
length of the bolt section(s), that portion of the
mine roof bolt below the fracture, if not
resin-bonded into the rock formation, is rendered
--19--
totally ineffective as structural support, and
possibly will even fall out of the bore hole.
It is this aspect of the improved mine roof
bolt o~ the~present inve~tion that permits it to
better withstand rock formation lateral movement, in
that the cable mine roof bolt (1) will not fracture
along the shank or coupler (there is no coupler), but
will fracture adjacent the hexagonal head, and (2)
will remain inta-ct along essentially its total length
of the shank within the bore hole, even following a
partial "stepped fracture".
Fig. 8 illustrates a number of alternative
embodiments in the mine roof bolt of the present
invention, generally illustrated at 60. As in the
first embodiment of Figs. 1-7, the mine roof bolt 60
comprises a shank 12 of a length of multi-strand
steel cable, which conventionally is made up of six
peripheral steel strands 14 spirally wrapped around a
central steel strand 16.
At one end of the stranded steel cable is
affixed the two-piece tapered plug 20, which
comprises the two identical diametrically opposed
tapered semi-cylinders that define the outer surface
of a right conical frustum. The hexagonal head
collar 26 is pressed down upon and around the
two-piece tapered plug 20 to define the hexagonal
bolt head.
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-20-
The mine roof bolt 60 includes a number of
alternative embodiments that function to enhance its
ability to be retained within the bore hole, and
therefore to suppo-rt the rock ~ormation. The first
of these retention enhancements defines a second
embodiment mine roof bolt, and comprises one or more
sleeves or "buttons" 62 attached to the bolt shank 12
at various points along the cable. These cable
buttons 62 take the form of steel cylinders that are
swaged down upon the bolt shank cable 12. In one
embodiment,-the steel-cylinder has initial dimensions
of one inch outside diameter, 5/8 inch inside
diameter and one and 1/2 inches in length. When this
cylinder is swaged down upon a 0.600 diameter
stranded steel cable with 500 tons of force, it
deforms down into the interstices between the
individual peripheral steel strands of the shank
cable, and is transformed into the cylindrical button
62 having a 7/8 inch outside diameter and a length of
approximately two inches.
The steel cylinder that becomes the cable
shank button 62 is swaged onto the cable by a
piston-ram swaging device (not shown). The swaging
device has a stationary semi-cylindrical die, and an
opposing semi-cylindrical die mounted on the ram
piston for swaging the steel cylinder onto the cable
in diametrical fashion. As a practical matter, the
2 1 7? ~ ~ 7 ~ ~ ~
two semi-cylindrical dies are not 100% completely
semi-cylindrical. The result is that, when the steel
cylinder is swaged onto the shank cable, swaging
causes some of the cylinder material to be forced
radially outwardly between the dies, forming two
diametrically aligned ears or fins 64 that are
subsequently trimmed down to a symmetric diammetric
distance that corresponds to the inside diameter of
the mine roof bore hole. This is best shown in Fig.
10~ 9. For example, the previously described steel
cylinder that is swaged down to a 7/8 outside
diameter and two inch long button 62 would have fins
64 approximately 1/32 inch thick and 1/16 inch long
(radial dimension) for use in a one inch diameter
bore hole. Likewise, the buttons, including the
fins, can be made to any outside diameter to
accommodate the particular bore hole size. These
fins 64 serve to center the bolt shank 12 within the
bore hole, and also aid in puncturing the resin
cartridge 50 and mixing the resin adhesive within the
bore hole as the bolt is being rotated and inserted
into the bore hole.
It still may be possible that swaging the
buttons 62 onto the cable with 500 tons of force
would not totally prevent a button from slipping
along the cable under extreme tension, as when the
supported rock formation shifts. To minimize the
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possibility of this happening, shallow threads (not
shown) may be cut into the cable at locations where
buttons are to b~e.swaged. Swaging the-buttons onto
these "threaded"-areas o.f-the~bolt shank cable forces
the button material into these threads to minimize,
if not totally prevent, any axial movement of the
buttons along the cable. As an added measure, the
cylinders that become buttons may also be formed with
internal threads ~not shown) that can easily align
with the shallow ca-ble threads as the buttons are
being swaged onto the cable. This insures optimum
grip betwee-n the buttons and-th@-cable. -
Once the resin adhes iV@ has been thoroughlymixed and has set within the bore hole, the buttons
62 are surrounded by hardened resin, and it is then
virtually impossible to retract the mine roof bolt
from the bore hole. This is because the resin has
worked itself into the cracks and crevices within the
rock formation in the bore hole, and has also
surrounded each of the buttons 62 along the length of
the bolt shank cable, forming a barrier of solid
resin around and below the button and into the rock
formation.
Fig. 8 also illustrates a third embodiment
of the mine roof bolt of the present invention that
can be used either by itself or in conjunction with
one or more of the buttons 62 along the shank of the
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bolt. Specifically, the third embodiment bolt
includes a dam 66 mounted on the bolt shank 12. A
preferred and simple construction of this dam 66
takes the ~orm of a plastic or rubber washer of the -
appropriate outside diameter (1 inch in a l-inch
diameter bore hole, for example), and an inside
diameter-appropriate-to-enable the washer 66 to fit
snugly around the..bolt shank-12.- A washer 66 of
approximately-l/4.in~h-thi~ck is -app-r-opriate to
achieve its intended function,-that.heing to retain
the mixed liquid resin adhesive within the bore hole
along the entire length of the bolt shank above the
dam in order to improve the forcing of the resin
adhesive into the cracks and crevices of the rock
formation within the bore hole, and into the
interstices between the individual steel strands of
the shank cable, in order to optimize the resin's
ability to adhere to both the bolt shank and the bore
hole rock formation. A second function of the dam 66
is to insure a uniform consistency of the resin
adhesive along the entire length of the mine roof
bolt shank 12 above the dam, with no air pockets,
voids, or other nonuniform areas within the annulus
between the bolt shank and the bore hole.
The inventor has determined that a preferred
manner of retaining the dam 66 in the appropriate
functional position along the bolt shank 12 is to
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utilize a conventional screw-type compression clamp
68 secured tightly to the shank cable at the
appropriate location to prevent the dam 66 from
slipping downwardly~ along the bolt shank either as
the bolt is being inserted into the mine roof bore
hole or as the resin adhesive is being mixed and
"returning" downwardly in the annulus hetween the
bolt shank~-and the b~re hole wall under the force of
the bolt's being-ins-erted-into~the-b~re hole.
-- Fig. 8 illus~rates yet a-fourth~alternat-ive
embodiment of the~mine roof bolt-of the pEesent~
inventio-n. This fQurth embodiment incorporates the
use of a stiffner sleeve 70, which takes the form of
a metal pipe or cylinder. The stiffner sleeve has an
inside diameter slightly larger than the outside
diameter of the cable (a 5/8 inch inside diameter for
a .600 diameter cable, for example), and an outside
diameter that is essentially the same as the diameter
of the borehole (one inch O.D. or one and 3/8 inches
O.D., for example). Such an outside diameter the
same as the diameter of the bore hole works quite
well, inasmuch as, as a practical matter, the actual
diameter of the bore hole is generally slightly
larger than the indicated drill bit diameter, due to
drill bit wobble, etc. The particular outside
diameter of the stiffner sleeve 70 also permits the
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sleeve to fit inside the spherical washer 40 and
directly against the hexagonal head collar 26.
As those skilled in the art can appreciate,
the purpose of the stiffner sleeve 70 is two-fold.
As a stiffner, it prevents the shank cable 12 from
buckling as the cable bolt is being inserted into the
bore hole, and as the blind end of the shank 12
"bottoms out" against the resin cartridges (not shown
in Fig. 8). It should be appreciated that, as the
blind end of the bolt shank 12 engages the resin
cartridge(s), additional linear force is necessary
for further inserting the bolt into the bore hole
against the resistance provided by the resin
cartridge(s). But for the stiffner sleeve 70, the
bolt shank cable 12 could tend to buckle due to this
additional linear force.
The second aspect of the stiffner sleeve 70
is that it is a "sleeve" around the shank cable that
protects the shank cable from abrasive wear from the
dome mine roof plate 44 as the cable bolt is rotated
and spun during insertion into the bore hole. It can
be appreciated that, but for the stiffner sleeve 70,
spinning the bolt into the bore hole with the mine
roof plate 44 loose causes the inside edge 46 of the
mine roof plate to cut and wear into the outer
surface of the peripheral steel strands 14 at the
location on the shank cable where the mine roof plate
f ~ ~ ~
-26-
"rides" as the bolt is being spun and inserted into
the bore hole.
The inventor has determined that the length
of the stiffner sleeve-70-can be -anywhere from-a
minimum of approximately six inches to any desired
functional length, typically 10 feet or more. This
maximum length, of course, is relative to the overall
mine roof bolt length, and may also be in part
dictated by the amount (total- length-of c-artridges)
of resin-adhesive inseEted into th~ bore hole ahead
of the mine roof bolt.
Fig. 10 illustrates a shouldered resin
protector plastic cap 72 that functions to (1)
protect the resin cartridge from premature rupture as
the blind end of the mine roof bolt is being utilized
to insert and otherwise "ram" the resin cartridge
into the bore hole, and (2) retain the resin
cartridge in the blind end of the bore hole, as when
subsequent resin cartridges are inserted into the
bore hole sequentially.
As shown in Fig 10, the shouldered resin
protector cap 72 takes the form of a closed plastic
cup that is sized to fit snugly on the end of the
bolt shank cable. The resin protector cap 72
includes a cylindrical thin wall 74 having a closed
end 76 that enables the resin protector cap to fit
snugly on the end of the bolt shank cable. The
-27- _~ v
protector cap 72 includes an annular shoulder 78 that
is dimensioned to be slightly larger than the inside
diameter of the bore hole.
~- When---the res-iniprotect-Q-r ca~ Z2 is inserted
into the bore hole, the annual shoulder 78 is forced
downwardly and functions as a one-way mechanism to
permit the cap to travel only in one direction (up as
shown in Figs. 10 and 11), while essentially
preventing movement in the opposite direction (down
in the drawings3. In this manner, when the resin
protector cap 72 is placed on the end of the mine
roof bolt shank 12 as shown in Fig. 11, and-this
combination (bolt shank and resin protector cap) is
used to insert and urge a resin cartridge 50 up into
the blind end of the bore hole, it should be apparent
that the resin protector cap will remain in place and
retain the resin cartridge in place within the bore
hole after the bolt is withdrawn from the bore hole.
Therefore, the mine roof bolt can be utilized as a
plunging device to insert a plurality of resin
cartridges into the bore hole in sequential fashion,
each being protected from the sharp edges of the
shank cable by the resin protector cap 72, then each
being subsequently retained in position within the
blind end of the bore hole by its own resin protector
cap, and therefore prevented by the action of the
-
f ~
-28-
downward direction of the annular shoulder 78 from
slipping downwardly within the hole.
Figs. 12 and 13 illustrate a hex-head cap
sleeve 80 for use with a plurality of mine roof holts
of the present invention. As shown, the hex-head cap
sleeve 80 comprises a hollow, blind hex-shaped closed
wall "cylinder" 82 that is di-mensioned to fit snug-ly
over the hexagona-l he-ad collar 26 of the mine roof
bQlt. In-a p-re~er-red-embodiment,- the closed wall
cylinder 82 is approximately 1~4 inch thick, as is
the end section that defines the blind end 84.
A 1/4 inch thick semi-circular wing 86 is
formed with the outer edge of the blind end 84 of the
cap sleeve, diametrically as shown in Figs. 12 and
13. This semi-circular wing 86 includes a through
hole 88, for use in indirectly attaching a plurality
of hex-head cap sleeves together, as will be
explained in greater detail hereinbelow with
reference to Fig. 14.
Even though the cable mine roof bolt of the
present invention is considerably stronger than a
prior art solid steel shank bolt of comparable
diameter, the cable mine roof bolt can eventually
fail under sufficient force. When these cable bolts
have actually failed in testing, failure of the cable
shank has almost always been relatively close to the
hexagonal head collar 26 where there is little or no
-29- ~ 2 ~ ~
resin adhesive. Almost consistantly, these cable
mine roof bolts have failed in a stepped fashion, as
illustrated in Fig. 7, and therefore, are generally
retained in the bore hole by the cable strands
remaining intact. Occasionally, however, the bolt
shank fractures totally at once. When this occurs in
a mine tunnel, the broken end of the bolt frequently
falls out of the bore hole to the tunnel floor, where
it becomes an obstacle to men and equipment. And
occasionally when the bolt fails in total, the
tapered plug "pops" loose from the hexagonal head
collar and cable, both the plug sections and collar
separating from the cable, further complicating the
situation.
With this background in mind, Fig. 14
illustrates a plurality of mine roof bolts
interconnected in functional position withln a mine
roof. Each of the bolt hexagonal head collars 26 has
affixed thereon a hex-head cap sleeve 80. A suitably
strength steel wire 90 is passed through the through
holes 88 of each hex-head cap sleeve in a manner to
interconnect the cap sleeves, and therefore the
hexagonal head collars 26 of adjacent mine roof bolts
in order to retain the broken bolt within the bore
hole, and thereby, prevent or at least minimize the
detrimental effect of the broken cable bolt's falling
to the tunnel floor when it breaks.
-30- ~ 6 ~
Those skilled in the art will readily
appreciate that a plurality of mine roof bolts can be
interconnected with a suitable steel wire 90 in
continuous patterns that insure that all hex-head cap
sleeves 80 are interconnected to at least two
adjacent mine roof bolts, so that in the event any
bolt within the pattern breaks, the fractured section
of broken bolt will be constrained to movement
limited by the taughtness of the interconnecting wire
90 and the broken bolt's proximity to the two
adjacent interconnecting bolts within the wire
pattern.
As one can appreciate, a downward force at
the location of any mine roof bolt results in
essentially only a lateral force at each of the
adjacent bolt hex-head cap sleeves 80, and only a
lateral force at each of the remaining hex-head cap
sleeves. Because of these lateral only forces, the
inventor has determined that it is extremely unlikely
that a broken mine roof bolt's falling out of the
bore hole would cause the hex-head cap sleeves 80 of
adjacent bolts to be pulled off of their respective
bolt heads. This is because the force necessary to
remove a hex-head cap sleeve 80 from a hexagonal bolt
head collar should be axial, and that the forces
created by the broken bolt are essentially
transverse, thereby effectively operating to "bind"
- CA 02107X26 1999-01-21
the hex-head cap sleeve 80 more tightly onto its
corresponding hexagonal head collar 26.
- Fig. 15 illustrates a fifth embodiment of
the mine roof bolt of the present invention. The
mine roof bolt of Fig. i~ is what is called in the
industry a yieldable bolt, in that it is designed to
slip or "yield" within the bore hole under
substantial force, rather than fail and er.d up
supporting nothirg. In some mine rcof boltins
systems, it is possible for each mine roof bolt to
slip within the bore hole a certain amount. This
s}ippage may be either between the bolt shank 12 and
the resin adhesive surrounding the shank, or may be
~etween the resin adhesive and the interior wall of
t~e bore hole. In either event, the retaining force
of the resin adhesive against the bolt shank is a
direct function of the length of direct attachment of
the resin adhesive with the bol~ shan~. Therefore,
as the bolt shank slips-o~t of the resin adhesive,
this length of direct attachment is decreased, and
the retaining force of the resin adhesive within the
bore hole to retain the bolt shank decreases directly
in proportion. For example, assume that a ten foot
mine roof bolt is completely surrounded by hardened
resin adhesive. In the event that shifting in the
rock formation causes the bolt to "slip" downwardly
one foot, the result is that only nine feet of the
-
-32-
ten foot bolt shank would now be retained in the
resin adhesive within the bore hole, resulting in
only 90% of the original resin adhesive bonding force
retaining the bolt shank in the bore hole.
It would be preferable to utilize a mine
roof bolt that maintained a consistent resistance
force along the entire ten foot length of the bolt
shank, even after the bolt had "slipped" within the
bore hole and otherwise out of the bore hole by a
small amount. This fifth embodiment of Fig 15
accomplishes this result by in effect "extending" the
length of the bolt shank into an area in which the
bolt shank is not bonded to the resin adhesive along
the "extended" portion of the bolt shank. This is
accomplished by covering the extended end of the bolt
shank with a material that prevents the resin
adhesive from bonding to the "extended" end of the
bolt shank, so that the distance along the bolt shank
that is in actual and continuous contact with the
resin adhesive remains the same, even as the bolt
"slips" relative to the resin adhesive within the
bore hole.
This concept is explained with reference to
Fig. 15. A bore hole is drilled to a depth of X. A
mine roof bolt of this same length, X, includes a
cover material 92 that covers the blind end of the
bolt shank 12 down for a distance of approximately
-33- ~ 7
two feet from the end of the shank. This particular
structure of Fig. 15 also includes a stiffner sleeve
70 that is four feet in length. Therefore, as shown
in Fig. 15, the length of exposed shank cable 12 is Y
= X - 6 feet. This distance, Y, is the length of
shank cable that will have the resin adhesive tightly
fitted into the annulus around the bolt shank and
into the rock formation for resin-bonding the mine
roof bolt in the bore hole. Although the two foot
length of bolt shank at the blind end will also have
resin adhesive material forced into the annulus
therearound, the cover material 92 prevents the resin
adhesive from bonding to the very end two foot
section of the bolt shank. As the mine roof bolt
"slips" out of the bore hole, the gripping length, Y,
of the bolt shank 12 in the resin material remains
the same, even though the bolt "slips" up to a
maximum of two feet within the bore hole. In this
manner, this "yieldable concept" of the mine roof
bolt of the present invention permits the bolt to
"yield" within the bore hole a certain specified
amount while maintaining constant the resistance
force that retains the bolt within the bore hole.
It should be obvious to those skilled in the
art that the improved mine roof bolt of the present
invention, not utilizing mine roof bolt shank
couplers, does not require an overly large bore hole
CA 02107826 1999-01-21
-34-
in the mine tunnel roof. Therefore, less potential
damage is done to the structural integrity of the
rock formation above the mine tunnel. Additionally,
less resin adhesive is required in the bore hole, and
therefore the resin tha~ is in the bore hole is more
ef-ective. Also, the improved mir.e rocf bolt, not
utilizing bolt shank couplers, does not have the
p.~blem oS bolt or coupler fracture when the mine
rccf rock formation shifts.
The improved mine roof bolt, not utilizing
bo;t shank couplers, facilitates complete mixture o~
the resln material and complete distribution of the
resin material along the ~otal length of the mine
rocf bolt shank and mine roof bore hole wall, if
desired.
Inasmuch as the improved mine roof bolt of
the present invention is constructed of a
multi-strand cable rather than a sGli~ shank, the
mine roof bolt will bend sufficiently to follow the
path of an irregular bore hole. The multi-strand,
- flexible cable mine roof bolt can also be bent to
facilitate installation into a bore hole that
requires a roof bolt that is considerably longer than
the height of the mine tunnel at the location of the
bore hole, and will also bend rather than break, when
the mine roof rock formation shifts.
-35-
From the foregoing it will be seen that this
invention is one well adapted to attain all of the
ends and objectives herein set forth, together with
other advantages which are obvious and which are
inherent to the apparatus. It will be understood
that certain features and subcombinations are of
utility and may be employed with reference to other
features and subcombinations. This is contemplated
by and is within the scope of the claims. As many
possible embodiments may be made of the invention
without departing from the scope of the claims. It
is to be understood that all matter herein set forth
or shown in the accompanying drawings is to be
interpreted as illustrative and not in a limiting
sense.
