Note: Descriptions are shown in the official language in which they were submitted.
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ROCK BOLT
Technical Field
The present disclosure relates to rock bolts suitable for use in the mining
and
tunneling industry to provide rock and wall support. The rock bolt is suitable
for softer
strata, such as that often found in coal mines, as well as hard rock
applications. It is to
be appreciated that the term "rock" as used in the specification is to be
given a broad
meaning to cover both of these applications.
Background
Roof and wall support is vital in mining and tunneling operations. Mine and
tunnel walls and roofs consist of rock strata, which must be reinforced to
prevent the
possibility of collapse. Rock bolts are widely used for consolidating the rock
strata.
In conventional strata support systems, a bore is drilled into the rock by a
drill
rod, which is then removed and a rock bolt is then installed in the drilled
hole and
secured in place typically using a resin or cement based grout. The rock bolt
is
tensioned which allows consolidation of the strata by placing that strata in
compression.
The rock bolt is typically formed from a steel rod.
To allow the rock bolt to be tensioned, the end of the bolt may be adhesively
bonded to the rock formation with a bonding material inserted into the bore
hole.
Alternatively, a combination of mechanical anchoring and bonding can be
employed by
using both an expansion assembly and resin bonding material.
When bonding material is used, the material adheres to the rock bolt and
penetrates the surrounding rock formation to adhesively unite the rock strata
and to hold
firmly the rock bolt within the bore hole. In one form of anchoring, resin is
inserted
into the bore hole in the form of a two component plastic cartridge having one
component containing a curable resin composition and another component
containing a
curing agent (catalyst). The two component resin cartridge is inserted into
the blind end
of the bore hole and the rock bolt is inserted into the bore hole such that
the end of the
rock bolt ruptures the two component resin cartridge. Upon rotation of the
mine rock
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bolt about its longitudinal axis, the compartments within the resin cartridge
are
shredded and the components are mixed. The resin mixture fills the annular
area
between the bore hole wall and the shaft of the mine rock bolt. The mixed
resin cures
and binds the rock bolt to the surrounding rock.
The resin cartridge is ordinarily made from thin plastic type film which
encases
and separates the mastic and catalyst. A significant concern with resin
anchored rock
bolts is that the plastic film is not sufficiently shredded and/or pushed back
to the rear
of the bore during mixing. As a result the plastic film can sit between the
rock bolt and
the bore hole wall and prevent the bonding of the rock bolt to the rock of the
bore hole.
3.0 Another concern is creating the required turbulence and torque for
mixing the resin to
evening combine the catalyst through the mastic. Under-mixing of the resin
results in
an unset resin which is low in strength.
Summary of the Disclosure
Disclosed is a rock bolt comprising an elongate shaft extending between
opposite
leading and trailing ends and a deformed section disposed proximal to the
leading end,
the deformed section being configured such that a protrusion extends outwardly
beyond
an outer surface of the shaft.
In one form the protrusion extends radially outwardly from the outer surface
of
the shaft.
In one form the protrusion comprises a flat face extending outwardly from the
outer surface of the shaft and terminating at an edge.
In one form the protrusion comprises two opposing flat faces extending
outwardly
from the outer surface of the shaft and connected by a periphery of the
protrusion.
In one form the rock bolt has an axis of rotation extending longitudinally
through
the shaft and the protrusion is oriented such that during rotation at least
one flat face is
forwardly facing with respect to the rotary movement.
In one form the deformed section is configured such that a depression extends
=
radially inwardly from the outer surface of the shaft.
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The deformed section of the rock bolt allows for shredding of the resin
capsule
through rotation of the deformed section with the rock bolt causing the edge
portions to
contact and shred the resin capsule membrane. The deformed section further
increases
turbulence in the resin about the rock bolt and allows a reduction in the
annular region
about the deformed section of the rock bolt once within the bore. This allows
resin
contained within the bore to be more effective.
In a second aspect, disclosed is a rock bolt comprising an elongate shaft
extending
between opposite leading and trailing ends and a deformed section disposed
proximal to
the leading end, the deformed section being configured to have at least one
edge, at
io least a portion of the edge being disposed radially outwardly from the
periphery of the
shaft.
In one form the deformed section includes two edges.
In one form a face extends from the edge to the shaft, the face being oriented
such
that during rotation of the shaft about its longitudinal axis, the face is
forwardly facing
is with respect to the rotary movement.
In a third aspect, disclosed is a method of installing a rock bolt in a bore
comprising the steps of drilling a bore hole, positioning a resin capsule in
the distal end
of the bore hole, inserting the leading end of a rock bolt into the bore hole
and applying
rotation to the rock bolt such that the resin capsule is shredded, wherein the
rock bolt
20 includes a deformed section adapted to shred the capsule.
In one form the deformed section is configured such that a protrusion extends
outwardly beyond an outer surface of the shaft.
In one form the protrusion extends radially outwardly from the outer surface
of
the shaft.
25 In one form
the protrusion comprises a flit Tke extending outwardly from the
outer surface of the shaft and terminating at an edge.
In one form the protrusion comprises two opposing flat faces extending
outwardly
from the outer surface of the shaft and connected by a periphery of the
protrusion.
In one form the protrusion is oriented such that during rotation at least one
flat
30 face is forwardly facing with respect to the rotary movement.
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In one form the deformed section is configured such that a depression extends
radially inwardly from the outer surface of the shaft.
In one form the shaft is sized such that the space between the inner wall of
the
bore hole and the outer surface of the shaft is less than 3mm.
In one form the deformed section facilitates chemical fixing of the rock bolt
by
the resin within the bore by promoting turbulence within the resin.
In one form the deformed section facilitates chemical fixing of the rock bolt
by
the resin within the bore by promoting mixing of the resin components on
rotation of
the deformed section.
Brief Description of the Drawings
Preferred embodiments of the rock bolt will now be described, by way of
example
only, with reference to the accompanying drawings in which:
Figure 1 illustrates a side view of one embodiment of a rock bolt according to
the
disclosure;
Figure 2 illustrates a side view of the rock bolt of Figure I rotated through
90';
Figure 3 illustrates a cross-sectional view of the rock bolt of Figure 2
through X-X;
Figure 4 illustrates a side view of the rock bolt of Figure 1.
Detailed Description of Preferred Embodiments
Referring to the Figs, disclosed is a rock bolt 1 comprising a shaft 2
extending
from a leading end 3 to a trailing end 4. The rock bolt 1 is adapted to be
inserted into a
bore hole within a rock formation to reinforce and-apply tension to the
rock formation.
The rock bolt 1 includes a deformed section 6 which is positioned proximal the
leading end 3 of the shaft 2. In the illustrated form, the deformed section
comprises two
protrusions 8 which extend radially outwardly from the outer surface 10 of the
shaft 2.
The deformed section further comprises four depressions 11 which are radially
indented
from the outer surface 10 of the shaft 2.
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The protrusions 8 include two faces 13 which each extend from a respective
depression 11 outwardly of the shaft. The faces 13 terminate at an edge 14
which forms
an approximate right angle with a periphery 16 of the protrusion. The
periphery 16 of
the protrusion 8 extends between two edges 14 and therefore extends between
two faces
5 13.
The deformed section 6 is formed by pinching or pressing the material of the
rock
bolt during manufacture.
The deformed section 6 of the device has a cross sectional length A-A through
the
protrusions 8 that is larger than the diameter of the drill bit that forms the
bore hole. The
3.0 cross sectional length A-A is greater than the diameter of the drill
bit by between 1 and
3 mms. In one embodiment the cross sectional length A-A is greater than the
diameter
of the drill bit by 2 mm.
The deformed section of the device has a cross sectional length B-B through
the
depressions 11 that is less than the diameter of the drill bit that forms the
bore hole. The
cross sectional length B-B is less than the drill bit diameter of the bore
hole by between
0.5 and 2 mms. In one embodiment the cross sectional length B-B is less than
the
diameter of the drill bit by 1 mm.
The deformed section 6 of the rock bolt can be inserted into the bore as the
point
at which the deformed section is wider than the diameter of the bore hole is
simply a
point contact with a rifled hole. Further as the bore hole is typically 0.5 ¨
2mm greater
in diameter than the drill bit, the tolerance for inserting a larger deformed
section is
greater. Use of hydraulic bolting rigs allows an installer to insert the
deformed section 6
and the rock bolt 1 into the bore hole despite the close fit. This is
especially the case in
softer rock formations but is possible in a variety of rock formations. Use of
a high
break out shear pin or reverse twist drive mechanisms can also allow insertion
of the
rock bolt I with the deformed section 6- into the bore hole.
In use, the rock bolt 1 with the deformed section 6 is inserted into a bore
along
with a resin capsule. The resin capsule which includes resin mastic and
catalyst is
positioned at the distal end of the bore. The rock bolt 1 is rotated resulting
in rotation of
the deformed section 6. The edges 14 have a cutting or shredding action that
shreds the
film membrane of the resin capsule allowing mixing of the mastic and the
catalyst.
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Further, the close fit of the deformed section 6 within the bore hole acts to
further shred
the capsule. The faces 13 of the deformed section 6 create interference and
turbulence
within the resin to promote mixing of the mastic and the catalyst allowing for
a more
effective resin.
It can be seen that the present embodiment improves the mixing of the resin
mastic and catalyst within the bore and reduces the problem of a rock bolt
being
"gloved" or surrounded by the casing of the resin capsule. This results in an
effective
bond between the bore surface and the rock bolt.
As will be understood, variations of the above described rock bolt can be made
3.o without departing from the scope of the appended claims. For example,
in an
alternative embodiment of the deformed section, the deformed section may
comprise...
While the rock bolt has been described in reference to its preferred
embodiments,
it is to be understood that the words which have been used are words of
description
rather than limitation and that changes may be made without departing from its
scope as
defined by the appended claims.
It is to be understood that a reference herein to a prior art document does
not =
constitute an admission that the document forms part of the common general
knowledge
in the art in Australia or in any other country.
In the claims which follow and in the preceding description, except where the
context requires otherwise due to express language or necessary implication,
the word
"comprise" or variations such as "comprises" or "comprising" is used in an
inclusive
sense, i.e. to specify the presence of the stated features but not to preclude
the presence
or addition of further features in various embodiments of the rock bolt.
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