Note: Descriptions are shown in the official language in which they were submitted.
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TITLE
"ROCK BOLT"
TECHNICAL FIELD
[0001] The present invention relates to a rock bolt.
BACKGROUND
[0002] It is known to use rock bolts for improving the structural integrity of
a rock
body to increase the environmental safety of a mining operation. Typically
rock bolts
are fitted into a bore hole in a rock face of a rock body such as in an
underground
mine roof or wall for example. The rock bolt is fitted in order to support the
rock face
in the event of a sudden rock body fault or creep movement and thereby prevent
or
limit a collapse of the rock face.
[0003] In applications where the rock body permits a generally constant bore
hole
diameter it is known to use rock bolts that are designed to yield and fail
progressively
under a load in order to avoid a sudden and catastrophic failure of the rock
bolt in the
event of a rock face movement.
[0004] In other rock body conditions where variations in a bore hole diameter
are
more common it is known to use generally tubular rock bolts having an outer
diameter arranged to accommodate changes in the bore hole diameter and still
be able
to safely support the rock face. Known means for allowing a variable outer
diameter
of a rock bolt include rock bolts having a longitudinal split that can be
closed to
accommodate a bore hole diameter that decreases in size after the rock bolt is
installed. Similarly, it is known to use a rock bolt having a single
longitudinal
channel running along the surface of the rock bolt, the channel is partially
compressed
for allowing both a degree of compression to accommodate a bore hole that
decreases
in diameter, and alternatively, a degree of expansion to accommodate a bore
hole that
increases in diameter.
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[0005] In such rock bolts the degree of compression and/or expansion is
limited. It is
known to use high pressure hydraulic systems to expand an installed rock bolt
however such methods are time consuming and costly to operate and in use it is
difficult to alter the expansion to suit the environmental conditions of the
bore hole
and/or rock body into which the rock bolt is fitted.
[0006] Problems arise with prior art rock bolts which have a single
longitudinal
channel as they lack symmetry when the rock bolt is installed into the bore
hole.
During installation the rock bolt is compressed and this has the effect of
changing a
cross sectional profile of the rock bolt from a generally circular
configuration to a
generally elliptical configuration. The result is that a circular bore hole is
fitted with
an elliptical rock bolt having a cross sectional profile with a major axis and
a minor
axis. A contact between the bore hole and the rock bolt being substantially
limited to
the two peripheral ends of the major axis. Accordingly the effectiveness of
such rock
bolts to engage the bore hole is compromised.
[0007] Further, it is known for rock bolt having a single longitudinal channel
or a
longitudinal split to twist about a longitudinal axis of the rock bolt during
installation
into a bore hole. Twisting of prior art rock bolts alters the rock bolt cross
sectional
profile and it is found that such twisting can lead to an irregular and
unpredictable
cross sectional profile along the length of the rock bolt. Accordingly the
effectiveness
of such rock bolts to engage the bore hole is compromised.
[0008] The present invention attempts to overcome at least in part the
aforementioned limitations of previous rock bolts.
[0009] It is an object of the present invention to provide a rock bolt which
does not
twist and in use retains a substantially symmetrical and generally circular
profile.
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[0010] It is an object of the present invention to provide a rock bolt
comprising
expansion means for selectively varying a radial expansion of the rock bolt in
situ in a
bore hole of a rock face.
[0011] It is an object of the present invention to provide a rock bolt which
provides at
least three spaced apart points of contact between the rock bolt and the bore
hole at
any point along a working length of the rock bolt.
SUMMARY OF THE IN'VENTION
[0012] In accordance with one aspect of the present invention there is
provided a
rock bolt comprising a body having a first end and a second end with a length
along a
longitudinal axis, the body comprising a wall having an internal surface
defining an
internal space, the wall comprising a plurality of elongate lobes, for
engaging a bore
hole surface each lobe having a radial and longitudinal dimension, adjacent
lobes
being spaced apart and connected together by channel means running, at least
in part,
along the length of the rock bolt, wherein the channel means comprises wall
sections
connected together and configured to provide a substantially resilient
inwardly
disposed junction between adjacent lobes.
[0013] In accordance with a further aspect of the present invention there is
provided
expansion means comprising a body having a first end and a second end defining
a
length along a longitudinal axis, the expansion means arranged to be
forcefully
inserted into the internal space of the rock bolt in situ in a bore hole,
wherein the
expansion means engages the internal surface of the rock bolt thereby urging
the rock
bolt to expand outwardly for improving the engagement with a bore hole
surface.
[0014] Preferably the plurality of elongate lobes are radially spaced about
the
longitudinal axis, and preferably there are three lobes.
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[0015] Preferably the rock bolt comprises connection means for assisting in
operation
and handling of the rock bolt. Preferably the connection means comprises a
collar
disposed proximal the second end.
[0016] In a preferred embodiment the rock bolt comprises a portion
substantially free
of channel means. Preferably the portion is disposed between the connection
means
and the second end.
[0017] Preferably each lobe comprises a contact surface for abutting a bore
hole
surface, preferably a curvature of the contact surface is configured to be
variable and
before fitting to a bore hole, each contact surface comprises a portion having
a greater
curvature than the bore hole surface.
[0018] Preferably the expansion means engages with one or more inwardly
disposed
junctions for urging the lobes into a radial expansion to improve a contact
between
the rock bolt and the bore hole surface.
BRIEF DESCRIPTION OF THE DRAWINGS
=
[0019] The present invention will now be described, by way of example, with
reference to the accompanying drawings, in which:
Figure 1 is a partial perspective view of a rock bolt in accordance with a
preferred
embodiment of the present invention;
Figure 2 is a partial side view of the rock bolt of Figure 1;
Figure 3 is an end view of a first end of the rock bolt of Figure 1;
Figure 4 is a simplified cross sectional of view along a-a of the rock bolt of
Figure 1;
Figure 5 is a perspective view of a connection means of the rock bolt of
Figure 1;
Figure 6 is a view in cross section of the connection means of Figure 5;
Figure 7 is a schematic cross sectional view showing the rock bolt of Figure 1
partially fitted with an expansion member and undergoing an outward expansion
Figure 8 is a perspective view of the rock bolt of Figure 1 receiving an
expansion
member; and
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Figure 9 is a partial perspective view of a second end of the rock bolt of
Figure 1.
DESCRIPTION OF THE EMBODIMENTS
[0020] Referring to Figures 1 and 2 there is shown a rock bolt 10 in
accordance with
a preferred embodiment of the present invention. The rock bolt 10 comprises an
elongate body 12 having a first end 14 and a second end 16 defining a length
along a
longitudinal axis. The body 12 is arranged to be substantially hollow having a
lumen
or internal space 18 extending substantially along the length of the body 12.
The
body 12 comprises a wall 15 having an outer surface 20 and an inner surface
21. The
wall 15 being configured to provide a plurality of elongate lobes 22, each
lobe 22
having a radial profile (see Figures 3 and 4) extending longitudinally along
the body
12. Adjacent lobes 22 being spaced apart and connected together by channel
means
running along, at least in part, the length of the rock bolt 10.
[0021] As seen in Figure 3 and Figure 4 (shown in cross section only), each
lobe 22
comprises a contact surface 41 which in use abuts with a surface of the bore
hole.
The contact surface 41 is configured to be arcuate and complementary at least
in part
with the bore hole surface.
[0022] It has been advantageously found that having the lobes 22 configured
with a
greater curvature than the bore hole allows the lobe 22 to be variable by
being
compressed and flattened out upon installation or expansion of the rock bolt
10 for
assisting in achieving an improved communication and engagement between the
contact surface 41 and the bore hole surface.
[0023] Further, when the rock bolt 10 is compressed to fit into a bore hole
the unique
configuration of the rock bolt 10 combined with a resilient property of the
metallic
construction material provides an internal tension in the rock bolt 10 that
biases the
lobes 22 to remain in contact with the bore hole surface. Preferably the rock
bolt 10
is made from a mild steel. In light of the resilient features of the rock bolt
10, it is
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envisaged a higher grade steel having a relatively high tensile strength will
give best
results. Given the known corrosive environment of a mine a material having
good
corrosion resistance is also be preferred.
[0024] As can be seen in the Figures, the body 12 comprises a generally
tubular
configuration and preferably a generally cylindrical tubular configuration. As
shown
in Figures 1 and 2, the body 12 first end 14 is arranged to be tapered such
that at least
a portion of first end 14 has a lesser cross sectional area than a cross
sectional area of
the second end 16, as seen in Figures 3. Preferably the first end 14 and the
second
end 16 are arranged to be open.
[0025] As seen in Figure 4, in a preferred embodiment of the present invention
the
channel means comprises a plurality of longitudinal and inwardly disposed
channels 24.
The channel means comprises three channels 24 with each channel 24 spaced
evenly
about the outer surface 20. As shown in Figure 4, each channel 24 comprises
adjacent
wall sections 26 having a first outer end 25 and a second inner end 27, the
outer end 25
connecting with an adjacent lobe 22. Adjacent wall section 26 inner ends 27
join
together to provide a junction 28. In a preferred embodiment of the present
invention as
seen in Figures 3 and 4 the channels 24 and thus the lobes 22 are generally
radially
spaced around the longitudinal axis by about 120 . It is advantageously found
that this
configuration also improves a torsional stiffness of the rock bolt 10 which in
use limits a
twisting of the rock bolt 10 during or after installation.
[0026] Accordingly, in a preferred embodiment as shown in the Figure 4 the
rock
bolt 10 comprises three independent contact surfaces 41. It is to be
understood that
the channel means general dimensions, such as the number of channels 24 or the
shape or configuration of each junction 28, may be altered to vary a strength
characteristic of the rock bolt 20. Preferably the channels 24 are integral
with the
body 12 and are formed during an initial roll forming operation to manufacture
the
body 12, or in a secondary cold drawing fabrication process upon an initially
substantially tubular body 12.
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[0027] In a preferred embodiment of the present invention the rock bolt 10
second
end 16 comprises a connection means. As seen in Figures 5 and 6 the connection
means comprises a collar 30. The collar 30 being arranged proximal the rock
bolt 10
second end 16 and held in position by, for example, swaging and/or welding. A
working length of the rock bolt 10 being disposed between the first end 14 and
the
collar 30.
[0028] As shown in Figures 5 an 6, the collar 30 comprises a body 32 having an
inner
end 34 and an outer end 36 defining a collar length along a longitudinal axis.
The
collar 30 comprises an outer surface 38 which is preferably contoured to
include a
curved, bevelled and/or tapered portion 40 proximal the inner end 34 and also
include
a recessed portion 42 between the inner end 34 and the outer end 36. The
collar 30 is
preferably hollow comprising a lumen 44 extending between the inner end 34 and
the
outer end 36. It is to be understood the lumen 44 is dimensioned to receive
the rock
bolt 10 second end 16.
[0029] In a preferred embodiment of the present invention shown in Figure 2
and
Figure 9 the rock bolt 10 comprises a portion 11 having no channel means
proximal to
the collar outer end 36. The portion Ills arranged to be substantially free
from any
channel means so as to provide a full circumferential join between the collar
30 and
the rock bolt 10. It has been advantageously found that having a full
circumferential
join, preferably a weld, between the collar 30 and portion 11 increases a pull
load
rating of the collar 30 and is more effective than prior art rock bolts which
have a
collar that does not have a full circumferential join and is therefore
weakened by a
break in the join.
[0030] In alternate embodiments (not shown) of the present invention the
connection
means may be integral with the rock bolt 10 second end 16. In such embodiments
it
is to be understood that the recessed portion 42 and tapered portion 40 would
be
integral with the rock bolt 10 outer surface 20.
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[0031] In further alternate embodiments the connection means may have
provision of
a first annular portion or pull ring (not shown) about the collar 30. In use,
such a pull
ring is utilised for conducting a pull test upon an installed rock bolt 10 to
determine a
load that the rock bolt 10 may carry. Preferably the connection means
comprises a
second annular portion or retaining ring (not shown) utilised for retaining
for example
a mesh bearing plate (not shown) to support wire meshing against the rock face
as is
known in the art.
[0032] Preferably the pull ring has a larger outer diameter than the retaining
ring and
is disposed between the retaining ring and the connection means outer end 36
so that
in the event that a mesh bearing plate detaches from the retaining ring it
will then be
substantially engaged by the pull ring and thus remain supported by the rock
bolt 10.
[0033] Preferably a method of fabrication is employed during manufacture of
the
rock bolt 10 for simultaneously forming the taper at the first end 14 and the
portion 11
at the second end 16. The method of fabrication comprising a taper block
having a
tapered opening for receiving and shaping the first end 14, one or more
holding
blocks spaced along the length of the rock bolt 10 for stabilising the rock
bolt 10, and
a hydraulic cylinder having a tapered mandrel adapted to be received within
the
second end 16.
[0034] Preferably the tapered mandrel also comprises a cylindrical wall
defining a
sleeve dimensioned to support the outer surface 20. In use the mandrel engages
the
second end 16 and urges the channel means outwardly until the second end 16
undergoes a plastic deformation as the channel means, at least along portion
11, are
compressed and the second end 16 takes on a substantially circular and tubular
configuration without channel means.
[0035] As seen in Figures 7 and 8, in a preferred embodiment of the present
invention the rock bolt 10 further comprises an expansion means. Preferably
the
expansion means comprises an insertion member 70. The insertion member 70
having a first end 72 and a second end 74 defining a length therebetween. The
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insertion member 70 comprises a substantially resilient body 75 having an
outer
surface 76. Preferably the body 75 has a circular configuration, such as for
example a
tubular cylinder, or rod.
[0036] It is to be understood that the insertion member 70 is arranged to be
inserted
into the internal space 18 of rock bolt 10 and therefore has a lesser outer
diameter `D'
than an inner diameter 'd' of the rock bolt 10. It should also be appreciated
that the
insertion member 70 is adapted to engage with the inner surface 21 of the rock
bolt 10
wall 15.
[0037] Preferably the insertion member 70 engages with the plurality of
inwardly
disposed junctions 28 thereby urging the lobes 22 to undergo an outward
displacement. The lobe 22 contact surface 41 and/or channel means may undergo
a
deformation which has a plastic and an elastic component as a scope of outward
displacement is maximised
[0038] The insertion member 70 may have a collar fixed to the second end 74
configured to support a mesh bearing plate (not shown) for holding mesh as is
known
in the art.
[0039] Preferably the insertion member 70 first end 72 may be tapered to
assist an
operator locating the insertion member 70 within the rock bolt 10 during
installation
of the insertion member 70. It is to be understood the portion 11 having no
channel
means also assists the operator to locate the insertion member 70 with the
second end
16 during installation.
[0040] It is to be understood that installation of an insertion member 70 to a
fitted
rock bolt 10 results in an improved and a tighter communication between lobe
22
contact surface 41 and the bore hole surface thereby increasing the efficiency
of the
rock bolt 10 to grip the bore hole surface for preventing or limiting a
collapse or
movement of the rock face.
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[0041] As seen in Figure 7 the insertion member 70 may comprise a collar 30
such as
that seen in Figures 5 and 6. In a preferred embodiment of the present
invention the
collar 30 may be fixed to the insertion member 70 by known means such as
welding,
crimping or a simple complementary threaded arrangement in which case the
collar
30 may be removable. The collar 30 may also provide a contoured surface, such
as
for example a threaded portion (not shown) or a recessed portion 42, arranged
for
engaging other equipment or apparatus such as, for example, a jumbo rig (not
shown)
for a forceful installation of the expansion member 70 into a rock bolt 10 or
for
supporting a mesh bearing plate (not shown) for holding a mesh against the
rock face
as is known in the art.
[0042] In use the insertion member 70 may be forcefully inserted into the
internal
space 18 of a rock bolt 10 in situ in a rock face bore hole. It is to be
understood that
the insertion member 70 is dimensioned such that the outer surface 76 engages
with at
least an internal surface 21 (see Figure 3) of a junction 28. As the insertion
member
70 penetrates into the internal space 18 it provides an outwardly deforming
force upon
the plurality of junctions 28 thereby urging the rock bolt 10 into a radial
expansion
and forcing the lobes 22 outwardly as shown schematically in Figure 8.
[0043] It is to be understood that fitting of an insertion member 70 to a rock
bolt 10
has the effect of urging the lobes 22 to expand outwardly as shown in Figure 8
and
consequently bring the rock bolt 10 into a tighter communication with the bore
hole.
It is also to be understood that the resilient nature of the rock bolt 10
provides a
feature which can act to grip and hold the insertion member 70 in place within
the
internal space 18. As such the present invention provides a rock bolt 10
within which
an insertion member 70 may be held in place by the plurality of junctions 28.
It
should be understood that the insertion member 70 can act to retain meshing
while
being held in place by the rock bolt 10. Accordingly a pull test may be
carried out on
an insertion member 70 alone, whereby if it fails another expansion member 70
having a slightly greater outer diameter `d' may be fitted, for example, to
increase the
grip and hold of the insertion member 70 to improve the pull test results.
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[0044] It should be understood the expansion means of the present invention
may
comprise any member capable of being inserted into the internal space 18
and/or
engaging with the inner surface 21. One typical expansion means may comprise a
wedge piece which may be inserted into the internal space 18 upon installation
and
then removed after the rock bolt 10 has been expanded.
[0045] As mentioned above, once inserted the expansion means is subject to a
substantially equal and opposite force to thereby hold the expansion means in
place
within the internal space 18. It should be understood this feature of the
present
invention may be utilized by fitting a collar 30 or plate to an insertion
member 70 and
in effect using the rock bolt 10 as a socket in which the insertion member 70
may be
reversibly held.
[00461 Alternatively after expanding a rock bolt 10 the expansion means, such
as a
wedge piece, may be removed from the internal space 18. In such cases it is to
be
understood the plastic deformation of the channel means and the lobe 22 ensure
the
rock bolt 10 has a lighter fit with the bore hole than prior to insertion of
the expansion
means.
[0047] A mesh plate having an elongate portion (not shown) may subsequently be
fitted to an expanded rock bolt 10 for holding mesh as is known. It should be
understood the elongate portion is forcefully inserted into the internal space
18
engaging with and elastically deforming the resilient junctions 28 which then
provide
a gripping force to hold the mesh plate in position. The elongate portion may
have a
solid or hollow configuration. Preferably the elongate portion is also around
880mm
in length, and may be subject to some deformation during and after
installation into
the internal space 18.
[0048] In use, a rock bolt 10 in accordance with the present invention is
installed into
a bore hole (not shown) in a rock face (not shown) by known means such that
the rock
bolt 10 first end 14 and a working length of the body 12 are substantially
contained
within the bore hole and the collar means is substantially external to the
bore hole and
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typically level with the rock face. Ills to be understood that a bore hole's
dimensions
will be complementary to the rock bolt 10 and vice versa. Typically a bore
hole will
have a slightly smaller cross sectional area approximately 42-22 mm than the
rock
bolt 10 approximately 46-48 mm so that the rock bolt 10 is compressed during
and
after installation. However, other embodiments may include a rock bolt 10
fitted to a
larger bore hole and expanded therein by using an insertion member 10.
[0049] In one embodiment of the present invention the rock bolt 10 comprises a
threaded portion (not shown) projecting from a first end 14 thereof. In use
such a
threaded portion may be used to point anchor the rock bolt 10 with the use of
a
complementary mechanical wedge member (not shown) as is known in the art
[0050] If required, an operator may apply a grout to the internal space 18 of
an
installed rock bolt 10. Typically grout is applied via the open second end 16
and
urged into the internal space 18. Air within the internal space 18 which is
displaced
by the grout can escape out of the open first end 14 and along the channels
24.
Similarly the grout applied to a rock bolt 10 will initially fill the internal
space 18
before flowing out the open end 14 and passing back externally to the rock
bolt 10 to
the second end 16 along the channel means. Accordingly, the appearance of
grout
exiting the channel means at the second end 16 provides the operator with an
effective
indicator of a maximum amount of grout to be used in any particular rock bolt
10
installation.
[0051] Following installation of the rock bolt 10 into a bore hole, an
insertion
member 70 may be inserted into the rock bolt 10 second end 16. In such cases
the
expansion means arealigned with the rock bolt 10 second end 16 and forced by
known
means, such as with a jumbo, into the internal space 18. As the expansion
means
penetrates into the internal space 18 it engages with the inwardly disposed
channel 24
displacing them outwardly as shown schematically in Figure 8. The displacement
of
the channel 24 urges the rock bolt 10 lobes 22 into an outward expansion for
effecting
a tighter communication between the rock bolt 10 and the bore hole.
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[0052] Once the outward expansion and contact between the lobes 22 and a bore
hole
surface is maximised any additional displacement caused by the expansion means
may be accommodated by a distortion of the channel means. Preferably the
distortion
has a plastic and elastic component, such that upon removal of the expansion
means a
channel 24 can substantially restore to its original shape and position
whereas the
lobes 22 contact surface 41 remains in a flattened out configuration
substantially
complementary to and in engagement which the bore hole surface.
[0053] It is to be understood that an installed rock bolt 10 with expansion
means
fitted may also be grouted by known means. A grout may be applied to the rock
bolt
second end 16 and pass through the portion internal space 18 which is
unobstructed by the expansion member 70. As with the above description the
displaced air can escape via the open first end 14 and between a bore hole
surface and
the external channel means to the rock face. Similarly, the grout may also
flow out
the first end 14 and back to the rock face externally, to the rock bolt 10
along the
channel means.
[00541 It is to be understood that the above description need not be carried
out in the
order described or with in any particular time frame. For example a rock bolt
10 may
be installed into a rock face without any further expansion. In the event of a
known
or suspected rock face movement or possible bore hole expansion an operator
may fit
one or more insertion members 70 to an installed rock bolt 10 in order to
tighten or re-
fix the rock bolt 10 within the bore hole. Similary mesh plates comprising an
elongate portion may be removed and replaced as required.
[0055] Alternatively a rock bolt 10 installed and grouted in accordance with
the
above description may subsequently have an insertion member 70 fitted therein.
[0056] Modifications and variations as would be apparent to a skilled
addressee are
deemed to be within the scope of the present invention.
