Note: Descriptions are shown in the official language in which they were submitted.
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10 Patent Application of
Rock Mongrain
For
A SELF CENTERING CABLE BOLT'
CROSS-REFERENCE TO RELATED APPLCATIONS
Not applicable.
BACK GROUND OF THE INVENTION
Field of the Invention
This invention relates to a rock stabilizing apparatus for anchoring unstable
rock
formations in underground mines and more particularly relates to a self
centering
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tensionable cable bolt adapted to be anchored by cementaceous oh~ resinous
grout in a drill
hole.
Background of the Invention
In underground mines it is important to secure the roof and walls of a tunnel
against collapse of unstable rock formations that will hang from stable rock
formations.
Such situations may be caused by having to tunnel through naturally fractured
rock
formations or by blasting operations within the mine. Scaling the roof and
walls of a
newly formed tunnel is necessary to remove loose rock that could easily
collapse.
Scaling is a process whereby a miner uses a long pole to pry and remove loose
rock,
called scale, from the roof and walls of the tunnel.
After removing the scale it is necessary to anchor the walls and roof of the
tunnel
to more stable rock formations. This is accomplished through the use o.f
devices that are
called rock bolts or cable bolts. Holes are drilled into the walls and roof of
the tunnel a
sufficient distance to penetrate the unstable formations suurounding the roof
and walls of
the tunnel and enter stable formations. Bolts of adequate length are then
inserted into the
holes. The inserted end of the bolt is anchored to the stable rock formation
using
mechanical expansion clamps or hardenable adhesion material such as cement
grout or
polyester resins.
Rock bolts tend to be a solid length of rebar. It may be a steel rod, from
four to
12 feet long and up to one inch in diameter, inserted into open rock faces for
roof and
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wall support in underground mines. Mechanical anchors, epoxy resin, or grout
secures the
bolts. One example of a typical rock bolt is found in United States Patent
4,051,683
"Method and Apparatus for Supporting a Mine Roof' issued to Koval in 1977. A
cable
bolt is a type of rock bolt consisting of pre-stressed, multi-strand steel
cable used for
supplemental and primary roof support in underground mires. The objective of
rock or
cable bolting is to improve the shear and tensile strength of the rock mass.
One example
of a cable bolt is found in United States Patent 5,785,463 "Combination Cable
Bolt
System" by Eaton et al issued in 1998. Cable bolts comprise a wire strand or
central rope
to take axial tensile loads and a plurality of wrapped wires. Since axial
tension loads on a
cable tend to create a moment which forces rotation in the wire core, the
wrapped wires
are would so that a counter torque is created.
In order to mix the grouting compound in the drill hole, the cable or rock
bolt may
be attached to a rotating head and rotated within the drill hole. The cable or
rock bolt
may be bent to better mix the grouting compound. In some cable bolt
installations, as
illustrated in Koval, the cable bolt may have a plurality of destranded,
unravelled or
bulbous sections regularly spaced along their length. These are often referred
to as
"birdcages". Birdcages are used to provide agitation means in order to improve
the
mixing of the grouting compound and the bond strength of the resulting
anchorage. This
can result in displacing the core of the wire rope. Therefore, while birdcages
in the cable
may provide a useful means for mixing the resin in the drill hole the result
may be a
weakened cable less able to withstand axial tension. This could potentially
lead to failure
of the wire core and the cable and place workers in jeopardy.
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Therefore, there are disadvantages with using cable bolts having birdcages. To
manufacture a cable bolt with a birdcage requires complex and expensive
machines to
rotate the cable in the opposite direction of the cable lay. much machines are
not easily
transported to the site of a rock bolting operation and therefore creating
cables bolts with
birdcages must be done off site. This leads to extra expense in manufacturing
such cable
bolts. Additionally, the grouting compound, because of its viscosity, may not
be able to
penetrate the void surrounding the birdcage. This creates undesirable voids in
the
anchorage.
Another disadvantage of rock and cable bolts presently available is that once
they
are inserted into the drill hole and grouted, the action of pumping the grout
into the drill
hole under pressure can result in the axis of the bolt being off set from the
axis of the drill
hole. This off setting of the drill hole and bolt axis results in an
inefficient transfer of
forces from the rock structure to the bolt. Therefore it is important that the
bolt remain as
co-axial as possible with the drill hole to optimize the transfer of tensile
and compressive
loads between the rock and the bolt.
Another disadvantage of using a straight cable member for the rock bolt is
that,
once grouted, the member may have sections that are unsupported by grout. That
is, void
may form between the wall of the drill hole in which the member is placed and
the
member itself. This is a problem that is difficult to detect during the
installation process.
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Fence, there is a continued need for an apparatus and method for anchoring
unstable rock formations in underground mines using a substantially self
centering cable
bolt tension member. There is also a need for an apparatus that will promote
the support
of the member by grout along its entire length. There is also a continued need
for an
apparatus that is adapted for use with cementaceous and resinous grouting
materials, that
is simple and inexpensive to manufacture and use; does nol: rely upon
deformation of the
l0
cable bolt and the resulting loss of axial tensile strength that such
deformation causes;
and, maintains itself substantially co-axial with the drill hole to optimize
the strength of
the reinforcing member.
OBJECTS OF THE INVENTION
It is an object of the present invention to overcome the deficiencies in the
prior
art.
It is a further objective of the invention to provide a substantially self
centering
cable bolt that remains substantially co-axial with the drill hole after
grouting.
It is a further object of the invention to provide an improved cable bolt and
method of manufacturing the same that can be used in anchoring unstable rock
formations in underground mines.
Yet another object of the present invention is to provide a cable bolt and
method
for manufacturing the same that can be transported to a drill site.
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Still another object of the invention is to provide a cable bolt for rock
stabilizing
that does not rely upon birdcaging or other similar deformations in the cable.
Another object of the invention is to ensure that the cable bolt is supported
along its entire length by grouting compound.
SZTMMARY OF THE INVENTION
The objects of the present invention are satisfied through the provision of a
rock
bolting apparatus for use with adhesive grouting material for insertion into a
drilled hole
penetrating the face of the rock formation. The grouting material may be
resinous or
cementaceous. The drill hole transverses unstable rock strata and penetrates
into stable
rock strata in underground mines. The rock bolting apparatus of the present
invention
comprises a substantially self centering tensionable reinforcing member
inserted into the
drilled hole. Self centering is accomplished by the member being provided with
a
plurality of permanent congruent arcuate concavities. The concavities are
disposed
perpendicular from the axis of the member in an aligned regular spaced
relationship along
the length of the member. The rock bolt is preferably a cable bolt. Once
installed in the
drill hole and grouted the concavities act to retain the cable bolt
substantially co-axial
with the drill hole. This optimizes the ability of the bolt to 'transfer and
resist axial loads.
The drill hole in which the reinforcing member is installed is generally 2
inches to
2.5 inches in diameter. Once the reinforcing member is placed into the drill
hole,
grouting compound is pumped into the drill hole by way of a tube inserted into
the drill
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hole. As the grout is pumped into the drill hole with the member already
placed in the
drill hole, the grout will act on the member and cause it to move off centre
from the axis
of the drill hole. It may also contact the walls of the drill hole in the
early stages of
pumping grout in the drill hole. Ultimately as the drill hole fills with
grout, the grout will
S exert a pressure against the member concavities that becomes generally equal
on both
sides of the member. The result is that the grout will act to substantially
centre the
member within the drill hole. An equal amount of grout will he forced between
the sides
of the concavities of the member and the walls of the drill hole acting as
spacers to keep
each of the arcuate concavities spaced away from contacting the sides of the
drill hole.
In one embodiment, the alternate concavities are at right angles to each other
along
the member x-y axis. In a preferred embodiment of the invention there is a
parade of
arcuate concavities along the length of the member wherein each subsequent
concavity is
disposed ninety degrees from the previous concavity along the member x-y axis.
I S Generally, the linear distance along the member between the apexes of any
two adjacent
concavities is one of I2 inches, 18 inches or 26 inches. However, the distance
may be
any multiple of six inches or it may be varied as demanded by operational
conditions.
In one embodiment of the invention the radius of the arcuate concavities is
less than
the radius of the drill hole. I-Iowever the radius of the arcuate concavities
may be a
function of the diameter of the member.
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Also disclosed in the invention is an apparatus for making the cable bolt
described
herein. The apparatus comprises a source of wire cable suitable for making
cable bolt
members; a means for drawing the wire cable from the source of wire cable;
means for
measuring the amount of wire cable drawn for the source of wire cable; a
cutter for
cutting the wire cable into desired lengths; means for disposing a plurality
of concavities
along axis of the member in a predetermined and spaced manner so that each
subsequent
concavity is rotated positive 90 degrees or some other desired angle from the
previous
concavity. The means for disposing a plurality of concavities along the axis
of the
member comprises: a first ram and die block set disposed along the positive x
axis of the
member for imparting a first concavity to the member in the negative x
direction; a
second ram and die block set disposed along the positive y axis of the member
for
imparting a second concavity to the member in the negative y direction; a
third ram and
die block set disposed along the negative x axis of the member for imparting a
third
concavity in the positive x direction; and, a fourth ram and die block set
disposed along
the negative y axis for imparting a fourth concavity in the positive y
direction. 'fhe
distance between the ram and die block sets is variable permitting the
distance between
concavities to be varied. Each ram and die block set comprises: a die block
having a
concave working surface. The radius of the surface is equal to desired radius
ofthe
concavity to be imparted to the member. The ram portion of the set also has a
radius
equal to that of the surface of the die so that when the ram pushes the cable
into the die,
concavity is formed in the cable.
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Also disclosed in the invention is a method of making a cable bolt comprising
the
steps of: obtaining a section of wire cable of a desired length; defining the
number of
concavities to be disposed into the wire rope; determining the distance
between the apex
of the concavities; imparting the predetermined number of concavities into the
wire cable
each being a predetermined distance apart and each being rotated by positive
90 degrees
from the previous concavity; and, cutting the wire cable into a desired
length.
Further objects and advantages of this invention will become apparent from a
consideration of the following drawings, detailed description and claims.
BRIEF DESCRIPTION OF TI-IE DRAWINGS
Figure 1 is a sectional side view of one embodiment of the invention placed
and
grouted inside a drill hole in order to stabilize a rock formation.
IS
Figure 2 is an axial view of a preferred embodiment of the invention.
Figure 3 comprises two views of a cable bolt of a preferred embodiment of the
invention.
Figure 4 is a perspective view of a preferred embodiment of the invention.
Figure 5 is a sectional side view of a preferred embodiment of the invention
installed in a drill hole.
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Figure 6 is a view of an apparatus for making a preferred embodiment of the
invention.
Figure 7 is a view of a ram and die block set of one embodiment of the
invention.
DESCRIPTION OF THE INVENTION
Referring to Figure l, there is shown a preferred embodiment of the invention
comprising a cable bolt (10) inserted into a drill hole (12) drilled between
stable (14) and
unstable (16) rock formations. A fracture line (IS) delineates stable from
unstable rock.
The cable bolt (10) is grouted into the drill hole by grout (18). The grout
(18) may be a
cement grout or a resin grout. Cable bolt ( 10) comprises a length of wire
cable having a
plurality of permanent arcuate concavities (20, 22, 24, 26) disposed therein.
Each
successive concavity is disposed positive 90 degrees from its previous
concavity. In
other embodiments of the invention, the angle may be more: or less than 90
degrees.
Figure 2 illustrates a preferred embodiment of the invention placed on a three-
dimensional x-y-z axis grid where the axis (31) ofthe cable bolt (10) is
aligned with the
z-axis (30). The view is directly along the z axis (30). Each ofthe arcuate
concavities
(20, 22, 24, 26) is disposed along the "x" and "y" axes of the grid.
Therefore, in a
preferred embodiment of the invention as shown in Figure 2, if concavity (20)
is disposed
along the negative x axis (32) then concavity (22) will be disposed along the
negative y
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axis (34), concavity (24) will be disposed along the positive x axis (36) and
concavity
(26) will be disposed along the positive y axis (38).
Referring to Figure 3, there is shown a preferred embodiment of the invention
in two
perspectives. In Figure 3a, cable bolt (10) is shown oriented along an x-y-z
axis grid.
Axis of the cable bolt is co-axial with the z axis. Therefore the observer is
looking down
onto the cable bolt from the positive y axis direction. Concavity 20 is shown
disposed on
its side along the negative x axis. Concavity 22 is shown disposed downward
along the
negative y axis. Concavity 24 is shown disposed along the positive x axis and
concavity
26 is shown disposed upwards along the positive y axis . The perspective of
Figure 3b is
that of Figure 3a turned negative 90 degrees. T herefore concavity 20 is now
oriented
downwards along the negative y axis; concavity 22 is oriented on its side to
the left along
the negative x axis; concavity 24 is oriented upwards along the positive y
axis; and,
concavity 26 is oriented to the right along the positive x axis. Therefore,
each successive
concavity in the parade of concavities is oriented negative 90 degrees from
its adjacent
predecessor. The concavities are regularly spaced along the z-axis. In one
embodiment
of the invention the distance between successive concavities may be a multiple
of six
inches. However, the spacing between the apexes of the successive concavities
may vary
to suit operational conditions.
While the preferred embodiment illustrates successive concavities at ninety
degrees to
its predecessor congruity, it is to be understood that the concavities may
repeat axially
along the same plane dually or in greater repetitions and may be oriented at
angles other
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than ninety degrees from predecessor to successor concavity, such as 180
degrees. These
configurations will be established to suit the operating conditions of the
rock bolting
operation and all will retain the grouted rock bolt substantially co-axial
with the drill
hole.
Referring to Figure 4, there is shown a perspective view of a preferred
embodiment of
the cable bolt (10) shown arcuate concavities (20, 22, 24, 26).
Referring now to Figure 5, there is shown in a sectional side view a preferred
embodiment of the cable bolt (10) inserted into a drill hole (12). Concavities
(20, 22, 24,
26) are disposed along the length of the bolt. Grout (18) is pumped under
pressure into
the drill hole (12) so that it surrounds the cable bolt (10). The self
centering process
works as follows. The radii of the arcuate concavities are all equal and less
than the
radius of the drill hole. The radii of the arcuate concavities is variable to
suit the desires
of the operators and the diameter of the drill hole. Referring to Figure Sb,
once the grout
(18) fills the hole (12), an amount of grouting material (38) will be disposed
between the
outer surface (40) of the concavity (22) and inner surface (42) of the drill
hole ('l2}.
Similarly, as shown in Figure Sc, grouting material will fill the space 46
between the
outer surface of concavity (24) and the inner surface of the drill hole. The
grout will act
with generally equal pressure against the concavities thereby substantially
centering the
cable bolt within the drill hole. Once the grouting material hardens, the
cable bolt will
remain centered within the drill hole. As well, the shape of the concavities
along the
length of the rock bolt promotes a thorough mixing of the grouting compound
inside of
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the drill hole and complete contact of the rock bolt with the grouting
compound thus
avoiding voids.
Referring to Figure 6, there is shown an apparatus (50) for manufacturing a
cable bolt
of the invention. The apparatus may be mountable to a transportable platform
so that the
apparatus may be transported to a drill site within a mine. The apparatus
comprises a
source of wire cable (52) suitable for making cable bolt members; means (54)
for
drawing the wire cable (56) from the source of wire cable; means (58) for
measuring the
amount of wire cable drawn for the source of wire cable; a cutter (60) for
cutting the wire
cable into desired lengths; and, means for disposing a plurality of
concavities along axis
of the member in a regularly spaced manner so that each subsequent concavities
is rotated
a negative 90 degrees from the previous concavity. The cable bolts may then be
gathered
and stored on a magazine (61).
Still referring to Figure 6, the means for disposing a plurality of
concavities along the
axis of the member comprise: a first ram and die block set (62) disposed along
the
negative x axis of the member for imparting a first concavity along the
positive x axis; a
second ram and die block set (64) disposed along the positive y axis of the
member for
imparting a second concavity to the member in the negative y direction; a
third ram and
die block set (66) disposed along the positive x axis of the member for
imparting a third
concavity in the negative x direction; and, a fourth ram and die block set
(68) disposed
along the negative y axis for imparting a fourth concavity in the positive y
direction. The
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distance (d) between the ram and die block sets is variable permitting the
distance
between the apex of the concavities to be varied.
Referring to Figure 7, there is shown a representative ram and die block set
of one
embodiment of the invention. Cable supply drum (52) is located to the left of
the cable
(10). The cable is moving left to right. In one embodiment, puller (54) may
comprise a
pair of opposed pullies (70) and (72) in a frictional engagement with the
cable (10). The
pullies rotate in a respective counter clockwise and clockwise direction to
pull cable from
the supply drum. Measuring device (58) measures the length of cable being
pulled from
the supply drum and pushed into the space between the ram and die block sets
(62).
Once the desired length of cable has been pulled from the drum the cutter (60)
operates to
cut the cable into the desired length. The feed of cable from the supply drum
is not
continuous and the operation ceases once the desired amount of wire cable has
been
pushed between the ram and die block sets and 'the cable is cut. The next
phase of cable
manufacture involves the formation of the arcuate concavities in the cable.
The distance
(d) between each die and block set is established by moving each die and block
set
axially along the cable length to a desired position. The ram and block set
comprises a
die block (78) having a concave working surface (80). The working surface has
a radius
equal to desired radius of the concavity to be imparted to the cable. The
radius of the
arcuate concavity can be adjusted by varying the height of die shoes (82). The
higher the
die shoes the deep the concavity. Ram (84) is actuated by piston (86). The ram
and
piston may be air operated or it may be hydraulically operated. Die (88) is
fixed to ram
(84) and is variable depending on the depth of the concavity desired. In
operation, all
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four ram and die block sets will be actuated simultaneously or in a suitable
sequence all
controllable by an operator. Once .the concavities are formed in the cable,
the formed
cable length is ejected from the apparatus and a new cable length is inserted.
The
operation is repeated until the desired numbers of cables are made.
The present invention also discloses a method for making a cable bolt having a
plurality of arcuate concavities comprising the following steps:
a. obtaining a section of wire cable suitable for rock bolting applications;
b. measuring a desired length of cable;
c. cutting the cable into a desired length;
d. feeding the desired length between a plurality of die and block sets for
forming
arcuate concavities;
e. compressing cable length between the die and block sets thereby forming the
arcuate concavities;
f. ejecting the formed cable bolt.
Although the description above contains many specifications, these should not
be
construed as limiting the scope of the invention but as merely providing
illustrations of
some of the presently preferred embodiments of this invention. Thus the scope
of the
invention should be determined by the appended claims and their legal
equivalents rather
than by the examples given.
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