Note: Descriptions are shown in the official language in which they were submitted.
CA 02767209 2011-09-21
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A Yielding Spiral Rolt Appendage f o r a Rock Raft
DESCRIPTION
Technical Field
[1] This invention relates in general to the field of mining and construction
and particularly
to ground support equipment and specifically to a yielding spiral bolt
appendage for a
rock bolt.
Background Art
[2] Rock bolting is well known in civil engineering and mining operations.
Bolting is done to
secure loose rock to stable formations behind. This prevents rock falls and
rock bursts
which are known to be a major cause of death and injury in the construction
and mining
industries.
[3] The rock surrounding an excavation subjected to stress, fractures into
slabs sub-parallel
to the tunnel outline. The fractures extend into the surrounding rock to
varying depths,
depending on such factors as the magnitude and orientation of the stress and
the strength
of the rock. Dilation occurs during the fracturing process and more
significantly, as a
result of subsequent stress increases brought about by subsequent mining in
the vicinity.
The rock bolt is a yielding tendon capable of providing effective support in
areas prone to
seismic events or high stress changes.
[4] A resin is used to adhere the yielding tendon to the rock. Often the resin
is a binary type
of adhesive contained in cartridges comprising a bonding agent and a hardening
catalyst.
Once the capsules are pierced the bonding agent and catalyst mix and the resin
begins to
set. In operation the resin cartridge(s) is inserted into a predrilled hole
that passes through
an unstable rock formation into a stable rock formation. A rock bolt is
inserted into the
drilled hole. The exposed end of the rock bolt that extends outside of the
drilled hole is
typically equipped with a nut for connection to a rotating device. The
insertion end is
often tipped with an apparatus to pierce the resin cartridges and mix the
resin as the rock
bolt is being rotated. It is important to the strength of the bond between the
rock bolt, the
resin and the rock body that the mixing be thorough. Less than adequate mixing
will
result in a weakened rock bolt installation.
[5]
A number of resin mixing apparatus have been proposed. One such device is
shown in
US Patent #4,704,052 VERSATILE ROOF BOLT ASSEMBLY issued to Hipkins et al
on November 3, 1987. Hipkins discloses an anchor bolt assembly including a
helical coil
external of and connected to a bolt shaft that is coupled to the end of the
rock bolt. The
tip of the bolt shaft has a frustoconical plug that is used to pierce the
resin cartridges as
the bolt is rotated to mix the resin. The disadvantage associated with the
Hipkins
apparatus is that it is a relatively complicated apparatus and hence expensive
to
manufacture and use in the quantities necessary for rock bolting a major
excavation. The
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B I B ~ = u p F e r t o ~t I l h e _ p ~ a r a t u fi t T i r o c Tx f Ih JkaI
coil welded to the outside of the apparatus and the frustoconical plus at the
head of the
apparatus. The coupler itself may present a possible yield point when the
assembly is
under tension during rock displacement.
[6] Therefore, there is a continued requirement for a mixing apparatus that is
easy to
manufacture and cost-effective for use in large quantities while providing the
necessary
mixing results to establish a strong bond between the rock bolt and the rock
formation.
Technical Problem
[7]
Technical Solution
[8] In a preferred embodiment of the invention, there is a spiral bolt
appendage for a rock
bolt comprising a body having a shank portion for attachment to the rock bolt
integral
with a helical flute portion for acting on a resin system placed within a
drill hole. In one
embodiment of the invention the appendage is threaded onto the end of a rock
bolt. In
another embodiment the appendage is welded to the end of a rock bolt. In one
embodiment of the invention the body is cast from a suitable metal alloy such
as
hardened steel. In another embodiment of the invention the body is forged. In
another
embodiment of the invention the helical flute portion may be welded to the
shank portion.
In one embodiment of the invention the helical flute portion comprises an one-
half pitch
helix. However, in other embodiments of the invention the helical flute
portion may be
longer than one-half pitch to suit the installation requirements. The shank
portion
comprises a bore having a closed end and an open end for receiving an end of
the rock
bolt. The bore includes a threaded portion for threaded attachment with the
end of the
rock bolt. The shank portion comprises a cylinder having a first tapered
portion and a
second tapered portion and an apex between the two tapers. In another
embodiment of the
invention there is provided a rock bolt comprising a tension member comprising
a first
end for insertion into a predrilled hole in a rock formation and a second end
disposed
outside of the predrilled hole having a nut for attachment to a rotating
machine. The first
end of the rock bolt is threaded to a spiral bolt appendage. In yet another
embodiment of
the invention there is provided a rock bolting system comprising at least one
resin
cartridge for placement into a predrilled hole in a rock formation, a rock
bolt comprising
a tension member having an insertion end having a spiral bolt attached thereto
for
insertion into the predrilled hole and for piercing the resin cartridge
thereby releasing and
mixing the resin so that it sets adjacent to the spiral bolt. The tension
member exposed
end is disposed outside of the predrilled hole for attachment to a rotating
machine for
rotating the tension member and thereby mixing the resin
[9] Before explaining one preferred embodiment of the invention in detail, it
is to be
understood that the invention is not limited in its application to the details
of construction
and to the arrangements of the components set forth in the following
description or
illustrated in the drawings. The invention is capable of other embodiments and
of being
2
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rr~ficed-and Barr ecT 1 - Tszr if be=irlders~e~d th he
phraseology and terminology employed herein are for the purpose of description
and
should not be regarded as limiting.
Advantageous Effects
[10]
Description of Drawings
[11] Tfi better uircle~ s ~~d aird dhj_ects::of ti-e]nve tiorrwill b
apparent when consideration is given to the following detailed description
thereof. Such
description makes reference to the annexed drawings wherein:
[12] Figure 1 is a diagram of one preferred embodiment of the invention
attached to a rock
bolt and installed in a drilled hole.
[13] Figure 2 comprises a side view of the invention 'A', a top view of the
invention 'B' and a
bottom view of the invention U.
[14] Figure 3 is a cross-sectional view of the invention along its axis.
[15] Figure 4 is a perspective view of the invention.
Best Mode
[16] Referring to Figure 1, there is shown one embodiment of the invention, a
spiral bolt
appendage for a rock bolt 10, installed in a drilled hole 2 in order to fix an
unstable rock
formation 3 to a stable sub-parallel rock formation 4. The invention 10 is
attached to the
end of a rock bolt 5 and embedded in a resin 6 to fix the rock bolt to the
rock formation.
The appendage may be threaded to the end of the rock bolt as described herein
or it may
be welded to the end of the thread bolt in alternate embodiments. The portion
of the rock
bolt that extends outside of the drilled hole 2 includes a nut 7 and a bearing
plate 8. The
nut is tightened against the bearing plate by a rotating device (not shown) to
tension the
rod. During a yielding event wherein the unstable formation is displaced from
the stable
formation, tension is placed on the rock bolt until the spiral bolt appendage
begins to pull
out of the hardened resin. In this manner, yielding forces are absorbed by the
resin and
transmitted to the stable rock formation thereby slowing the yielding event.
[17]
Referring now to Figure 2, there is shown one embodiment of the invention in
three
views. View 'A' is a side view of the invention. View 'B' is a top view of the
invention
and view 'C' is a bottom view of the invention. The invention has a length 12,
a width 20
and an axis 18 about which is it rotated. The invention comprises a body 10
that is cast
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T rni a-SUTlahfie=metal e= the fzsr e p iec l hody I
embodiment the metal is a hardened steel alloy. Other alloys are possible. In
other
embodiments the body can be forged. In a preferred embodiment the body 10 is
cast per
ASTM 536 grade 120-90-02. The body 10 is comprised of a fluted section 14 and
a
cylindrical shank section 16. The fluted section 14 has a top surface 22
having a width 24
that is adequate to pierce resin cartridges placed in a drilled hole. In other
embodiments
of the invention the fluted section 14 can be welded to the shank portion 16.
In the cast or
forged embodiment of the body 10 the bottom 30 of the fluted section 14 is
integral to the
top surface 28 of the shank portion 16. The bottom 32 of the shank portion 16
comprises
a bored hole 30 in which the bottom end of the rock bolt is inserted in a
threaded
arrangement. In another embodiment of the invention, the body is welded to the
bottom
of the rock bolt.
[18] Still referring to Figure 2, there is a first taper that is represented
by angle 17 that extends
from the apex line 38 to the top 28 of the shank 16. There is also a second
taper that is
represented by angle 19 that extends from apex line 38 to the bottom 32 of the
shank 16.
In static testing, the tapers have been found to further improve the yielding
characteristics
of the rock bolt and resin. Referring back to Figure 1, the tapers are
embedded in the
resin 6. Taper 17 and taper 19 will resist tensioning forces attempting to
push the rock
bolt further into the drilled hole or pull the rock bolt out of the drilled
hole. The tapers
transfer more of the yielding forces to the resin and thereby slow the
yielding of the rock
bolt.
[19] In a preferred embodiment of the invention the first taper 17 angle is
0.7 degrees and the
second taper 19 angle is 1.5 degrees. Other angles can also be used. The
length of the
body 12 is preferably 3.25 inches with the shank 16 being preferably 2.25
inches long
and the fluted portion 14 being one inch long. The width of the shank 16 at
end 32 is
preferably 0.78 inches and at apex 38 the width of the shank is preferably
0.82 inches.
The width 24 of tip 22 is preferably 0.25 inches and the width of the fluted
portion at its
maximum is 0.78 inches. The flute section 14 comprises a one-half pitch helix
and in a
preferred embodiment the pitch of the helix is 2 inches. Other dimensions are
possible to
suit a particular rock bolt installation.
[20] Referring now to Figure 2 and Figure 3, there is shown (in Figure 3) a
cross-section along
axis 18 one preferred embodiment of the invention 10 comprising the shank
portion 16
and the fluted portion 16. The first taper 17 extends along length 39 from
apex 38 to the
top of the shank portion 28. The second taper 19 extends along length 36 from
apex 38 to
the end 32 of the shank portion 16. Bore 30 is illustrated as extending from
end 32 of the
shank substantially to the top of the shank. The inside surface of the bore 40
is threaded
to accept the threaded end of the rock bolt.
[21] Referring now to Figure 4, there is shown a perspective view of the body
10 comprising
the fluted section 14 and the shank portion 16. The first taper extends from
apex 38 along
length 39 to the top of the shank portion and the second taper extends from
apex 38 along
length 36 to the bottom 32 of the shank portion. Within bore 30 the inside
surface 40 is
threaded to mesh with the end of the rock bolt to which the body is attached.
In one
embodiment of the invention the thread is 3/4-10 UNC 2B LH.
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[22] it hasihn f~ in shat]fi io~tTie invenfi mAhIa[Il eb~dy Iof ~ rweI1Iiim
pests
effective mixing of the resin within the drill hole so that there is a
consistent yield
strength of the rock bolt across a sample tested.
[23] It will be appreciate by those skilled in the art that other variations
of the embodiments
described herein may also be practiced without departing from the scope of the
invention.
Other modifications are therefore possible.
Mode for Invention
[24]
Industrial Applicability
[25]
Sequence List Text
[26]
