Note: Descriptions are shown in the official language in which they were submitted.
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FRICTION BOLT ASSEMBLY
Field
[0001] The present invention relates to strata control in civil engineering
and mining operations
and in particular relates to a friction bolt assembly for securing the roof or
wall of a mine, tunnel
or other ground excavations.
Background
[0002] A current method of stabilizing the roof or wall of an underground mine
involves the use
of friction bolts, otherwise known as friction rock stabilizers. Friction
bolts have a generally
cylindrical body and a collar welded to the trailing end of the body. The
leading end portion of
the body is generally tapered to assist in inserting the friction bolt into a
bore hole drilled into the
rock strata. The body is split down one side such that, when it is driven into
a slightly
undersized hole in the rock strata, the friction bolt body elastically deforms
to reduce the size of
the split in the body. This elastic deformation exerts radial forces against
the wall of the hole,
providing a corresponding frictional force, retaining the friction bolt within
the hole. A plate
washer is fitted to the body directly above the collar such that the collar
bears the plate washer
against the rock face of the mine to distribute axial loads carried by the
friction bolt across the
face of the roof.
[0003] The frictional forces generated between the friction bolt and bore hole
wall are at times
insufficient to properly anchor the friction bolt within the bore hole.
Accordingly, developments
have been proposed to improve the transfer of load between the friction bolt
and bore hole wall,
including by filling the friction bolt with grout to increase its rigidity and
to outwardly radially
deform the friction bolt body following initial installation.
Object of the Invention
[0004] It is an object of the present invention to provide an improved
friction bolt, or at least to
provide a useful alternative to presently available friction bolts.
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Summary of Invention
[0005] In a first aspect the present invention provides a friction bolt
assembly comprising:
a generally tubular friction bolt body longitudinally extending between a
friction bolt
body leading end and a friction bolt body trailing end, said friction bolt
body defining a cavity
longitudinally extending through said friction bolt body and having a split
longitudinally
extending along said friction bolt body;
a rod longitudinally extending through said cavity between a rod leading end
and a rod
trailing end;
an expansion element mounted on, or integrally formed with, said rod at or
adjacent said
rod leading end, said expansion element having an engagement surface tapering
toward said rod
trailing end;
a sleeve mounted on said expansion element adjacent said friction bolt body
leading end,
said sleeve having a sleeve trailing end and an interior sleeve surface; and
a drive head mounted on, or integrally formed with, said rod at or adjacent
said rod
trailing end, said rod being actuatable by rotation of said drive head to draw
said expansion
element toward said friction bolt body trailing end such that said sleeve
trailing end abuts said
friction bolt body leading end and said engagement surface engages said sleeve
interior surface,
radially outwardly deforming said sleeve.
[0006] Typically, said sleeve has a substantially cylindrical outer sleeve
surface.
[0007] Typically, said inner sleeve surface tapers towards said sleeve
trailing end. In one foil'',
the taper of said inner sleeve surface matches the taper of said engagement
surface.
[0008] In one or more embodiments, said interior sleeve surface and said
engagement surface are
of substantially matching generally frustoconical form.
[0009] In one or more alternative embodiments said interior sleeve surface has
a plurality of
substantially planar regions extending between a sleeve leading end of said
sleeve and said
sleeve trailing end, said engagement surface having a plurality of
substantially matching
substantially planar regions for engagement with said substantially planar
regions of said interior
sleeve surface. In one form, said sleeve may be provided with a weakened zone
between each of
said substantially planar regions of said interior sleeve surface.
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[0010] Typically, said friction bolt assembly further comprises means for at
least substantially
preventing rotation of said expansion element relative to said friction bolt
body.
[0011] Typically, said means comprises a key projecting from said engagement
surface into said
split of said friction bolt body.
[0012] Typically, said sleeve has a longitudinally extending split. Typically,
said key extends
into said split of said sleeve.
[0013] In one or more embodiments, said drive head is threadingly mounted on a
threaded
trailing portion of said rod such that, upon actuation of said rod by rotation
of said drive head,
said threaded trailing portion of said rod is drawn through said drive head.
In a preferred
embodiment, said expansion element is threadingly mounted on a threaded
leading portion of
said rod, said threaded leading portion and said threaded trailing portion of
said rod being like-
handed, such that, upon actuation of said rod by rotation of said drive head,
said rod rotates with
said drive head, drawing said expansion element along said threaded leading
portion of said rod.
[0014] In one embodiment, said friction bolt assembly further comprises a load
transfer fitting
mounted on said rod between said drive head and said friction bolt body
trailing end, said load
transfer fitting having a profiled leading face configured to engage and
support said friction bolt
body trailing end.
[0015] In one or more embodiments, said friction bolt assembly further
comprises:
a stopping means mounted on, or integrally formed with, said rod and being
longitudinally positioned between said friction bolt body leading end and said
friction bolt body
trailing end; and
a collar fixed to said friction bolt body at or adjacent said friction bolt
body trailing end;
wherein said stopping means and said collar are dimensioned to cooperate to at
least
substantially prevent said rod from ejecting completely from the friction bolt
body through the
friction bolt body trailing end.
[0016] In one or more embodiments, said stopping means comprises one or more
swaged
portions of the rod.
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[0017] In a second aspect the present invention provides a method of
installing the friction bolt
assembly defined above, comprising the steps of:
drilling a bore hole into a rock face of a rock strata to be stabilized, said
bore hole having
a diameter greater than the maximum diameter of said expansion element and
less than the
maximum diameter of said friction bolt body;
inserting said friction bolt assembly into said bore hole with said expansion
element
leading;
applying percussive force to said friction bolt body to drive said friction
bolt body into
said bore hole with an interference fit;
rotating said drive head to actuate said rod, drawing said expansion element
towards said
friction bolt body trailing end, abutting said sleeve trailing end with said
friction bolt body
leading end and engaging said engagement surface with said sleeve interior
surface, thereby
outwardly radially deforming said sleeve into bearing engagement with the wall
of said bore
hole.
Brief Description of Drawings
[0018] Preferred embodiments of the present invention will now be described,
by way of
example only, with reference to the accompanying drawings wherein:
[0019] Figure. 1 is a front elevation view of a friction bolt assembly
according to a first
embodiment;
[0020] Figure 2 is a front elevation view of the leading portion of the
friction bolt assembly of
Figure 1;
[0021] Figure 3 is a cross-sectional view of the leading portion of the
friction bolt assembly of
Figure 1;
[0022] Figure 4 is an isometric view of the leading portion of the friction
bolt assembly of
Figure 1;
[0023] Figure 5 is a front elevation view of the trailing portion of the
friction bolt assembly of
Figure 1;
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[0024] Figure 6 is a cross-sectional view of the trailing portion of the
friction bolt assembly of
Figure 1;
[0025] Figure 7 is an isometric view of the trailing portion of the friction
bolt assembly of Figure
I;
[0026] Figure 8 is a front elevation view of the expansion element and sleeve
of the friction bolt
assembly of Figure 1;
[0027] Figure 9 is a transverse cross-sectional view of the expansion element
and sleeve of
Figure 8, taken at cross section 9-9;
[0028] Figure 10 is an isometric view of the expansion element and sleeve of
Figure 8;
[0029] Figure 11 is a longitudinal cross-sectional view of the expansion
element and sleeve of
Figure 8;
[0030] Figure 12 is a partially cross-sectioned view of a partially completed
installation of the
friction bolt assembly of Figure 1;
[0031] Figure 13 is a partially cross-sectioned view of the completed
installation of Figure 12;
[0032] Figure 14 is a partially cross-sectioned view of the installation of
Figure 11, following
elongation under load;
[0033] Figure 15 is a front elevation view of a friction bolt assembly
according to a second
embodiment;
[0034] Figure 16 is a front elevation view of the trailing portion of the
friction bolt assembly of
Figure 15;
[0035] Figure 17 is a cross-sectional view of the trailing portion of the
friction bolt assembly of
Figure 15;
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[0036] Figure 18 is a partially cross-sectioned view of a partially completed
installation of the
friction bolt assembly of Figure 15;
[0037] Figure 19 is a partially cross-sectioned view of the completed
installation of Figure 18;
[0038] Figure 20 is a partially cross-sectioned view of the installation of
Figure 18 following
failure;
[0039] Figure 21 is a front elevation view of an alternate form of expansion
elements and sleeve;
[0040] Figure 22 is a transverse cross-sectional view of the expansion element
and sleeve of
Figure 21 taken at section 22-22;
[0041] Figure 23 is an isometric view of the expansion element and sleeve of
Figure 21; and
[0042] Figure 24 is a longitudinal cross-sectional view of the expansion
element and sleeve of
Figure 21.
Description of Embodiments
[0043] A friction bolt assembly 100 according to a first embodiment is
depicted in Figures Ito
II of the accompanying drawings. The friction bolt assembly 100 has a
generally tubular
friction bolt body 110 that longitudinally extends between a friction bolt
body leading end ill
and a friction bolt body trailing end 112. The friction bolt body 110 defines
a cavity 113
longitudinally extending through the friction bolt body 110. The friction bolt
body 110 has a
split 114 extending along the friction bolt body 110 to the friction bolt body
leading end 111 to
allow for radial compression of the friction bolt body 110 in the usual
manner. Here the split
114 extends along the full length of the friction bolt body 110 from the
friction bolt body trailing
end 112. The friction bolt body 110 has a tapered leading portion 115 that
tapers toward the
friction bolt body leading end 111 in the usual manner to enable the friction
bolt body 110 to be
driven into a bore hole having a smaller diameter than the constant diameter
of the primary
portion 116 of the friction bolt body 110. A collar 117, in the general form
of a torus, is welded
to the friction bolt body 110 adjacent the friction bolt body trailing end
112.
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[0044] In one embodiment, the external diameter of the primary portion 116 of
the friction bolt
body 110, being the maximum diameter of the friction bolt body 110, is
approximately 47 mm,
whilst the cross-section of the leading portion 115 of the friction bolt body
110 at the friction
bolt body leading end 111 is of a reduced cross-sectional area, being the
minimum cross-
sectional area of the friction bolt body 110. In one embodiment, the cross-
section of the leading
portion 115 at the friction bolt body leading end 111 is of an oval
configuration having a major
axis (maximum) diameter of 40 mm and minor axis diameter of 26 mm, although it
is also
envisaged that the leading portion 115 at the friction bolt leading 111 may be
generally circular.
The wall thickness of the friction bolt body 110 is here approximately 3 mm.
The friction bolt
body 110 is typically formed of structural grade steel. In one embodiment, the
friction bolt body
110 is formed of steel having a yield strength of 350 to 400 MPa and a
hardness of about 119
Vickers hardness (64 Rockwell B hardness).
[0045] The friction bolt assembly 100 further includes an elongate rod 120
longitudinally
extending through the cavity 113 in the friction bolt body 110 between a rod
leading end 121 and
a rod trailing end 122. The rod 120 is typically formed of rigid steel bar.
[0046] An expansion element 130 is mounted on the rod 120. The expansion
element 130 is
typically located toward the rod leading end 121 and in the embodiment
depicted the expansion.
element 130 is located at or adjacent the rod leading end 121. As best Shown
in Figures 3 and 4,
in the embodiment depicted, the expansion element 130 is threadingl.y mounted
onto a threaded
leading portion 123 of the rod 120. The threaded leading portion 123 of the
rod 120 is received
within an aperture 133 extending through the expansion element 130. The
aperture 133 has a
threaded central portion 139 to .threadingly engage the threaded leading
portion 123 of the rod
120. In the first embodiment, the expansion element 130, best depicted in
Figures 8 to 11, is in
the general form of a body of revolution having a frusto-conical tapered
leading surface 134
extending and tapering to an open expansion element leading end 131, a
generally cylindrical
intermediate surface 135 trailing the leading surface 134 and defining the
maximum diameter of
the expansion element 130, a generally frusto-conical engagement surface 136
that tapers, here
in a substantially linear manner, from the intermediate surface 135 towards
the expansion.
element trailing end 132 and a cylindrical trailing surface 138, that extends
from the engagement
surface 136 to the expansion element trailing end 132. In the embodiment
depicted, the
maximum diameter of the expansion element 130, defined by the intermediate
surface 135, is
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approximately 43 mm. This is greater than the internal diameter of the
friction bolt body 110 at
the friction bolt body leading end 111 and less than the maximum diameter of
the friction bolt
body 110.
[0047] As best depicted in Figures 2 and 4, the expansion element 130 may
further comprise
means for at least substantially preventing rotation of the expansion element
130 relative to the
friction bolt body 110. In the first embodiment, the means is in the form of a
surface feature of
the expansion element 130, particularly in the form of a key 137. The key 137
projects from,
and is integrally formed with, the engagement surface 136 and in the
embodiment depicted
extends from the expansion element trailing end 132 to the mid-surface 135. It
is also envisaged
that the key 137 may be of a shorter length, extending only along the trailing
surface 138. As
shown in Figures 1 and 6, the key 137 projects into the split 114 formed in
the friction bolt body
110. As a result, rotation of the rod 120, which would tend to rotate the
expansion element 130,
results in the key 137 engaging an edge of the friction bolt body 110 bounding
the split 114,
preventing relative rotation, at least beyond minor movement associated with
the free play of the
key 137 within the slightly broader width of the split 114 at the friction
bolt leading end 111.
[0048] The expansion element 130 is mounted on the rod 120 at a location such
that the
cylindrical trailing surface 138 extends through the friction bolt body
leading end 111 into the
cavity 113 defined by the friction bolt body 110.
[0049] The friction bolt assembly 100 further comprises a sleeve 180 mounted
on the expansion
element 130 adjacent the friction bolt body leading end 111. The sleeve 180,
best depicted in
Figures 8 to 11, is of a generally tubular form longitudinally extending
between a sleeve leading
end 181 and a sleeve trailing end 182. This sleeve 180 has a split 183 that
extends along its
length to readily allow for radial expansion. The sleeve 180 is mounted on the
expansion
element 130 with the key 137 extending therethrough. The sleeve 180 has a
substantially
cylindrical outer surface 184 and tapered frusto-conical inner surface 185
that generally matches
the taper of the engagement surface 136 of the expansion element 130 on which
it is mounted.
The inner surface 185 tapers towards the sleeve trailing end 182, such that
the thickness of the
wall 186 of the sleeve 180 tapers towards the sleeve leading end 181. In a
preferred
embodiment, the thickness of the wall 186 tapers from about 5.2 mm to about 2
mm. The sleeve
181 is typically formed of a material that is harder and more abrasion
resistant than the material
from which the friction bolt body 110 is formed. In a preferred embodiment,
the sleeve 180 is
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formed of 4140 grade steel with a hardness of about 547 Vickers hardness
(about 28 to 32
Rockwell C hardness). The steel could be heat treated to an increased hardness
of about 50
Rockwell C hardness. An annular shoulder may be defined at the junction
between the
intermediate surface 135 and engagement surface 136 of the expansion element
136 (or
elsewhere toward the leading end of the expansion element 130) to limit
displacement of the
sleeve 180 along the expansion element 130.
[0050] The friction bolt assembly 100 further comprises a drive head 140
mounted on the rod
120 at or adjacent the rod trailing 122. In the particular embodiment
depicted, the drive head
140 is in the fon-n of an open hexagonal nut that is threadingly mounted on a
threaded trailing
portion 124 of the rod 120. The threaded leading portion 123 and threaded
trailing portion 124
of the rod 120 are like handed, each having a left handed thread for
installation with a standard
installation rig configured to rotate in an anti-clockwise direction, although
it is also envisaged
that both the threaded leading portion 123 and threaded trailing portion 124
may be right handed,
for installation by clockwise rotation of an installation rig. In the
configuration depicted, the
drive head 140 is provided with a coarse thread 141 on its hexagonal drive
faces to allow for
securing of a roof mesh to the friction bolt assembly 100 after installation.
A sacrificial plastic
sheathing may cover the exposed region of the threaded trailing portion 124 so
as to avoid the
thread of the threaded trailing portion 124 being fouled by debris during
transport and handling
in the mine.
[0051] Between the drive head 140 and the friction bolt body trailing end 112,
a washer 150 and
load transfer fitting 160 are mounted on the threaded trailing portion 124 of
the rod 120. The
load transfer fitting 160 has a profiled leading face 161 configured to engage
and support the
friction bolt body trailing end 112 and collar 117 to transfer percussive
loads applied during
installation, as will be discussed further below, to the friction bolt body
110 without locally
damaging the friction bolt body 110.
[0052] To initially secure the expansion element 130 and drive head 140 on the
rod 120 during
transportation and handling, the expansion element 130 may be tack welded to
the rod 120
adjacent the rod leading end 121 and the drive head 140 tack welded to the rod
120 adjacent the
rod trailing end 122. The tack welds would then fail during rotation of the
expansion element
130 and drive head 140 relative to the rod 120 during installation.
Alternatively, after mounting
the expansion element 130 and drive head 140 on the rod 120, the thread of the
threaded leading
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portion 123 and threaded trailing portion 124 of the rod 120 may be crimped or
otherwise
deformed adjacent to the rod leading and trailing ends 121, 122 respectively.
The expansion
element 130 and drive head 140 may then be reverse threaded to abut against
the crimp to
temporarily lock the expansion element 130/drive head 140 to the rod 120 and
specifically
prevent the expansion element 130 and drive head 140 from unscrewing off the
rod 120 during
transport and handling. As another alternative, heat shrink material may be
applied over the
expansion element 130 and adjacent portion of the threaded leading portion 123
of the rod 120,
both to protect the expansion element 130 during transport and any rough
handling and also to
secure the expansion element 130 on the rod 120. During installation, the heat
shrink would be
torn away by rotation of the rod 120, allowing relative movement between the
expansion head
130 and rod 120. As another alternative, the drive head 140 may be driven
along the threaded
trailing portion 124 of the rod 120 sufficiently to provide a light pretension
of the rod 120.
[0053] Installation of the friction bolt assembly 100 will now be described
with reference to
Figures 12 and 13. Firstly, a bore hole 10 is drilled into the rock face 12 of
a rock strata 11 to be
stabilized. In the embodiment depicted, the bore hole 10 is drilled with a
standard installation rig
with a drill bit having a diameter typically of 43 to 44mm, which will
typically result in a bore
hole diameter of 43 to 45mm, depending on strata type and hardness.
Accordingly, the
maximum diameter of the friction bolt body 110 (being approximately 47mm in a
preferred
embodiment) is slightly greater than the diameter of the bore hole 10, so as
to provide for an
interference fit in the usual manner, whilst the maximum diameter of the
expansion element 130,
here being approximately 43mm, is less than the maximum diameter of the
friction bolt body
110 and slightly less than the diameter of the bore hole 10 such that the
expansion element 130
may be readily inserted into the bore hole 10. It is also envisaged that
slightly larger bore holes
(such as about 46 mm), only slightly smaller than the maximum diameter of the
friction bolt
body 110 (here approximately 47 mm) may be utilised, resulting in a reduced
interference fit of
the friction bolt body 110.
[0054] Before inserting the friction bolt assembly 100 into the bore hole 10,
a plate washer 170
(and optionally a ball washer) is mounted on the friction bolt body 110
adjacent the collar 117
and the friction bolt assembly 100 is mounted on the installation rig,
particularly with the drive
head 140 being received within a mating socket of the installation rig. The
installation rig then
drives the friction bolt assembly 100 into the bore hole 10, applying
percussive force via the load
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transfer fitting 160 until the plate washer 170 is thinly engaged with the
rock face 12. The
frictional forces due to the interference fit between the friction bolt body
110 and bore hole wall
13 retain the friction bolt assembly 100 in the bore hole 10, and allow for
the transfer of loads
between the rock strata 11 and the friction bolt body 110.
[0055] Referring to Figure 13, additional anchoring of the friction bolt
assembly 100 in the bore
hole 10 is achieved by way of the expansion element 130, which provides a
point anchoring
effect. This is achieved by actuating the rod 120 by rotating the drive head
140. Specifically,
the drive head 140 is driven in a direction tending to advance the drive head
140 along the
threaded trailing portion 124 of the rod 120 (here in an anti-clockwise
direction). During
rotation of the drive head 140, as tension in the rod 120 increases, friction
due to inter-
engagement of the threaded trailing portion 124 of the rod 120 with the
internal thread of the
drive head 140 will tend to rotate the rod 120. Even if the drive head 140
does initially rotate
relative to the rod 120, it will only move along the rod 120 until it reaches
the end of the
threaded trailing portion 124 of the rod 120. Rotation of the rod 120 will in
turn tend to advance
the threaded leading portion 123 of the rod 120 through the expansion element
130, rotation of
which is substantially prevented by virtue of the key 137 as described above.
Accordingly,
during rotation of the drive head 140, the expansion element 130 will be drawn
toward the
friction bolt body trailing end 112 further into the cavity 113. The sleeve
180 will also tend to be
drawn toward the friction bolt body trailing end 112 by virtue of movement of
the expansion
element 130, however the sleeve trailing end 182 will abut the friction bolt
body leading end
III, thereby limiting longitudinal displacement of the sleeve 130 relative to
the friction bolt
body 110. As the expansion element 130 is drawn further into the cavity 113,
the tapers of the
engagement surface 136 of the expansion element 130 and inner surface 185 of
the sleeve 180
will result in the sleeve 180 radially outwardly deforming as the engagement
surface 136 is
displaced through the interior of the sleeve 180, opening the split 183 formed
in the sleeve 180.
The radial outward deformation of the sleeve 180 bears the outer surface 184
of the sleeve 180
against the bore hole wall 13, thereby point anchoring the friction bolt body
110 within the bore
hole. The point anchor thus provided is effectively mechanically independent
of the anchoring
provided by the friction bolt body 110, with the friction bolt body 110 merely
serving to assist in
establishment of the point anchoring by limiting relative longitudinal
displacement of the sleeve
180 during the installation process.
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[0056] Whilst the expansion element 130 is being drawn into the cavity 113 of
the friction bolt
body 110 during the installation process, the engagement surface 136 of the
expansion element
130 will also typically engage the friction bolt body 110 at the friction bolt
body leading end
111, radially outwardly deforming the tapered leading portion 115 of the
friction bolt body 110.
As a result of this deformation, the leading portion 115 of the friction bolt
body 110 may be
radially outwardly deformed sufficiently to bear against the bore hole wall
13, however this will
be relatively insignificant as compared to the point anchoring effect provided
by the sleeve 180.
This will particularly be the cases in the first embodiment depicted where the
thickness of the
wall 185 of the sleeve 180 at the sleeve trailing end 182 is greater than the
thickness of the
friction bolt body 110 at the friction bolt body leading end 111. The
compressive load acting on
the sleeve 180 between the expansion element 130 and bore hole wall 13
adjacent the sleeve
trailing end 82, providing the point anchoring effect, is thus greater than
any compressive load
acting on the friction bolt body 110 between the expansion element 130 and
bore hole wall 13
adjacent the friction bolt body leading end 111.
[0057] Figure 14 depicts the installation of the friction bolt assembly 100
following sudden
movement of the strata resulting from a seismic event, resulting in plastic
elongation of the rod
120. With the friction bolt body 110 being separate to the sleeve 180 forming
the point anchor,
it is able to displace through the bore hole 10 relative to the rod leading
end 121, whilst the point
anchoring provided by the sleeve 180 remains firmly in place. Further tensile
load acting on the
rod 120 as a result of the strata movement will tend to further draw the
expansion element 130
through the sleeve 180, further radially deforming the sleeve 180 by virtue of
the taper of the
engagement surface 136, further enhancing the point anchoring of the friction
bolt assembly 100.
[0058] The rod leading and trailing ends 121, 122 will tend to protrude
through the open ends of
the expansion element 130 and drive head 140 respectively. Protrusion of the
rod trailing end
122 through the drive head 140 will provide a visual confirmation that the
point anchoring of the
friction bolt body 110 within the bore hole 10 has been achieved.
[0059] A friction bolt assembly 200 according to a second embodiment is
depicted in Figures 15
to 20 of the accompanying drawings. Features of the friction bolt assembly 200
that are identical
to those of the friction bolt assembly 100 of the first embodiment are
provided with identical
reference numerals, whilst equivalent or alternate features of the friction
bolt assembly 200 are
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provided with reference numerals equivalent to those of the friction bolt
assembly 100 of the first
embodiment, incremented by 100.
[0060] The friction bolt assembly 200 is essentially identical to the friction
bolt assembly 100,
apart from the configuration of the rod 220 and the trailing portion of the
friction bolt assembly
200. In place of the toroidal collar 117 and separate load transfer fitting
160 of the friction bolt
assembly 100 of the first embodiment, an alternate form of collar 217 is
welded to a friction bolt
body 110 adjacent the friction bolt body trailing end 112. The collar 217
effectively integrates
the functions of the toroidal collar 117 and load transfer fitting 160 of the
friction bolt assembly
100 of the first embodiment and fixes the load transfer fitting to the
friction bolt body. The
collar 217 has a forward facing surface 218 extending about the friction bolt
body 110 at the
friction bolt body trailing end 112 for engaging a plate washer 170 in the
same manner as the
collar 117 of the friction bolt assembly 100 of the first embodiment. The
collar 217 also has a
central aperture 219 extending therethrough and having a diameter slightly
larger than the
diameter of the rod 220, in the embodiment depicted having a diameter between
approximately
23.8 to 24.0 mm.
[0061] The rod 220 is provided with stopping means configured to cooperate
with the collar 217
to at least substantially prevent the rod 220 ejecting completely from the
friction bolt body 110
upon failure of the rod 220. In the embodiment depicted, the stopping means
comprises three
swaged portions 225a, 225b, 225c formed in the rod between the friction bolt
body leading end
111 and friction bolt body trailing end 112, particularly toward the friction
bolt body trailing end
112. The swaged potions 225a, 225b, 225c are dimensioned such as not to pass
through the
aperture 219 in the collar 217, particularly having a transverse cross-
sectional area greater than a
maximum cross-sectional area of the aperture 219. In a preferred embodiment,
each of the
swaged portions 225a, 225b, 225c is wider than the diameter of the aperture
219 of the collar 217
in one or more lateral directions. In the embodiment depicted, the effective
lateral width of each
of the swaged portions 225a, 225b, 225c is between approximately 25 to 27 mm,
being greater
than the diameter of the aperture 219 of the collar 217, so as to prevent the
rod 220 from ejecting
completely from the friction bolt body 110. In place of the swaged portions
225a, 225b, 225c,
the stopping means could take the form of one or more ferrules mounted on the
rod 120, welds
applied to the rod 120 or more pronounced ribs formed on the rod 120.
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[0062] Referring to Figures 18 and 19 of the accompanying drawings, the
friction bolt assembly
200 is installed in the same manner as the friction bolt assembly 100 of the
first embodiment, as
described above in relation to Figure 12 and 13.
[0063] Figure 20 depicts the installation of the friction bolt assembly 200
following a seismic
event resulting in strata movement loading the rod 220 exceeding the tensile
strength of the rod
220, with the rod 220 failing by fracture, breaking the rod 220 into separate
leading and tail rod
portions 220a, 220b. Upon fracture, the tail rod portion 220b of the rod 220
would tend to be
ejected towards and through the friction bolt body trailing end 112 due to the
diameter of the rod
220 being less than the diameter of the aperture 219 of the collar 217.
However, the stopping
means, particularly the swaged portions 225a, 225b, 225c prevent the tail rod
portion 220b from
ejecting completely from the friction bolt body 110 by engaging with the
collar 217, as shown in
Figure 20. A potential safety hazard associated with rapid ejection of the
tail rod portion 220b is
thus prevented. Further, protrusion of the tail rod portion 220b through the
collar 217 provides a
visual indication of failure of the friction bolt assembly 200 due to
mechanical overload.
[0064] Provision of the multiple swaged portions 225a, 225b, 225c provides
additional tiers of
engagement with the collar 217 in the event that the first swaged portion 225a
or both the first
and second swaged portions 225a, 225b are sufficiently deformed by virtue of
the initial impact
with the collar 217 upon attempted ejection of the tail rod portion 220b, or
in the event that the
rod 220 fractures at or adjacent one of the swaged portions 225a, 225b, 225c.
[0065] An alternative fonn of expansion element 330 and sleeve 380 to those
utilised in the first
and second embodiments discussed above is depicted in Figures 21 to 24.
Features of the
expansion element 330 and sleeve 380 that are identical to those of the
expansion element 130
and sleeve 180 of the first and second embodiments are provided with identical
reference
numerals, whilst equivalent or alternate features of the expansion element 330
and sleeve 380 are
provided with reference numerals equivalent to those of the expansion element
330 and sleeve
380 of the first and second embodiments, incremented by 200.
[0066] The expansion element 330 is substantially identical to the expansion
element 130, except
that the outer surface of the expansion element 330, particularly those
portions defined by the
engagement surface 336 (and, in the embodiment depicted, the intermediate
surface 335 and
trailing surface 338) is provided with a plurality, here four, longitudinally
extending planar
15
regions 339. The planar regions 339 may effectively be foimed by machining
flat surfaces into
the outer surface of the expansion element 130 described above in relation to
the first and second
embodiments. Alternatively, the expansion element 130 could be cast or forged
with the planar
regions 339 in place. The inner surface 385 of the sleeve 380 is configured to
substantially
match, as best depicted in Figure 23, with any transverse cross-section of the
sleeve 380 through
the engagement surface 336 being characterised by a series of planar surface
regions 387
separated by curved intermediate surface regions 388. Longitudinally extending
weakening
grooves 389 may be provided in the inner surface 385 of the sleeve 380 between
each planar
surface region 387, each forming a weakened zone, and particularly between
each planar surface
region 378 and each adjacent intermediate surface region 388. When the sleeve
180 discussed
above in relation to the first embodiment, having a frusto-conical inner
surface 185 deforms
during the point anchoring process, the wall 186 of the sleeve 180 must
distort by virtue of the
frusto-conical inner surface 185 sliding against the frusto-conical engagement
surface 136. With
the configuration of the expansion element 330 and sleeve 380, however, having
planar surfaces
slide on each other generally prevents distortion of those parts of the wall
386 of the sleeve 380
corresponding to the planar surface regions 387. The intermediate surface
regions 388 are
allowed to distort and/or tear (by virtue of the weakening grooves 389) to
peimit the required
radial expansion of the sleeve 380. This may enhance point anchoring
efficiency. It is
inconsequential if the wall 386 of the sleeve 380 tears at the intermediate
surface portions 388,
with the point anchoring effect being provided at the planar surface regions
387.
[0067] In addition to the above described and other envisaged modifications of
the expansion
element and sleeve, the person skilled in the art will appreciate various
other modifications of the
friction bolt assemblies described above. For example, rather than having the
expansion element
and drive head threadingly mounted on threaded leading and trailing portions
of the rod, such
that both the expansion element and drive head move longitudinally relative to
the rod during
actuation of the rod, it is envisaged that the expansion element or drive head
might be integrally
formed with, or otherwise fixed in relation to the rod, in the manner
described in International
(PCT) Publication No. WO 2015/013743. In embodiments where the expansion
element is fixed
in relation to the rod, actuation of the rod by rotationally driving the drive
head will result in the
drive head advancing along the rod, drawing the expansion element and rod
rearwardly through
the drive head. In
Date recue/Date received 2023-05-08
CA 03008179 2018-06-12
WO 2017/100818
PCT/AU2016/000392
16
embodiments where the drive head is fixed in relation to the rod, actuation of
the rod by
rotationally driving the drive head will draw the expansion element along the
rod.
