Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
WO 2012/012392 CA 02809138 2013-01-17
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Anchoring Device
TECHNICAL FIELD
This invention relates to an anchoring device.
In particular, the present invention relates to anchoring devices in the form
of rock
bolts and a method for installing rock bolts and in particular to rock bolts
suitable for
use in the mining and tunnelling industry to provide roof and wall support.
The
invention has been developed primarily for rock bolts used in mining
applications and
will be described hereafter with reference to this application.
However, it will be appreciated that the invention is not limited solely to
mining
o applications. For example, other materials and applications may include
coal,
concrete, dams, retaining walls, civil engineering, building construction and
the like.
BACKGROUND ART
Rock bolts are now a common apparatus used to support the roof and walls of
tunnels and mines worldwide. There are a wide variety of rock bolts available
including steel, fibreglass and plastic rock bolts. Rock bolts usually consist
of a long
elongate shaft which is anchored into a borehole in rock or coal to provide
reinforcement support to the rock or coal mass.
Rock bolts can be anchored into a borehole by having a frictional contact with
an
internal surface of the borehole itself. For example, US Patent No. 5,219,248
discloses a mine roof expansion anchor having a conventional tapered camming
plug
and radially expansible shell formed as two identical, physically separate
halves which
engage the wall of a borehole.
In use, the anchor enters the hole with little or no frictional resistance
until outwardly
extending portions contact the surface of the rock formation at the entrance
to the
hole. Continued advancement of a bolt causes inward deformation of bail
portions or
barbs. Due to the springy, resilient nature of the bail material, the terminal
ends tend
to engage the borehole wall in a tightly gripping engagement, enhanced by the
sharp
edges and corners of the terminal ends.
Securing the anchor is performed by rotation of the bolt to move a plug
axially down
the bolt thread, forcing leaves of the shell halves into a tightly gripping
engagement
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with the walls of the borehole.
However, a disadvantage of this configuration is that the shell halves or
wedges need
to be held together by additional components, such as studs which extend
through
holes in the shell halves. The studs do not provide a robust means for
connection and
the additional components increase the cost of manufacture and assembly time.
Also, this rock bolt embodiment is not self drilling and requires a pre-
drilled hole
before the rock bolt can be inserted increasing the installation time.
Further, the rock
bolt may not be easily re-configured for self drilling as the studs holding
the wedges
are unlikely to withstand the rotational forces of a drilling operation
potentially leading
io to destruction of the rock bolt during that operation.
International Patent Application No. WO 00/47871 also discloses a rock anchor
which
is configured to be inserted into a pre-drilled hole. It has an elongate body
member
which defines a longitudinal wedging surface that tapers outwardly in the
direction of
the leading end of the anchor. The anchor also has a wedging member that can
slide
along the wedging surface from a retracted position to an extended position
where it
engages the inner surface of the borehole and wedges the body member within
the
borehole. There is also an actuator in the form of a resilient finger
formation for
moving the wedging member to its extended position.
Like US 5,219,248, a disadvantage of this configuration is that the wedging
member
is secured by an additional component, in this case a (preferably frangible)
band or
strap which permits sliding movement of the wedge. This band is unlikely to be
of a
sufficient strength to retain the wedge member in position during a self
drilling rock
bolt operation (leading to destruction of the wedging element). Additional
components such as the band also increase both the cost of manufacture and
assembly time, and complexity of use.
As discussed above, a disadvantage of these conventional types of rock bolts
is that
a borehole needs to be drilled before the rock bolt can be inserted and
secured within
the rock or coal face. To overcome this problem, self drilling rock bolts were
developed.
Initially such self drilling rock bolts were predominantly chemically set.
One example is the self drilling rock anchor manufactured by Hilti Corporation
of
Liechtenstein and sold under the trade mark OneStep rock anchor (HILT! HOS-W
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250/320). This rock anchor is a single action (or one step) rock anchor
whereby the
anchor can be driven into place (without pre-drilling). The anchor includes a
hollow
tube which functions as a drill rod, and a chemical connection anchor to an
integrated
adhesive cartridge. The tube allows a chemical resin from the cartridge to
secure the
anchor into the rock or coal face.
A disadvantage of this rock anchor is that for the resin to work, it has to be
fast-
setting. This is not particularly suitable for coal faces as the resin in
action can
generate sufficient heat to cause a fire. Further only a limited amount of
material that
can be applied by the integrated adhesive cartridge leading to a weak bond.
o To address these problems self drilling mechanically set or friction
anchored rock
bolts were developed.
As with the non-self drilling rock bolts previously discussed, the mechanical
or
frictional anchoring device may be of several different designs.
One common frictional anchoring device is an expansion shell mechanism which
is
located at the leading end of the rock bolt and which is expanded against the
wall of
the borehole by rotating the rock bolt. The expansion shell mechanism
typically has a
wedge (such as a mandrel) which is pulled between two or more moveable shells
such that the shells are forced outwards against the wall of the borehole.
This is
typically achieved by using a screw thread located on a leading end of the
rock bolt
with a complementary thread on the expansion mechanism. Reverse rotation of
the
rock bolt causes the shaft and wedge to retract (relative to the shells)
thereby pulling
the wedge between the expansion shells and forcing them against the sides of
the
borehole.
An example of this configuration can be seen in International Patent
Application No.
WO 2007/053893. This document discloses a self drilling rock bolt
incorporating a
shaft and an anchoring device. A first end of the bolt has a drill tip to
penetrate rock
and a second end is adapted to be connected to a drilling apparatus. A
circulation
passage is provided to allow fluid to be passed to the drill tip and a central
passage is
formed in the shaft to form part of this circulation passage. The anchoring
device has
a mandrel having one or more inclined external surfaces where the expansion
elements overlay the mandrel. The expansion elements are displaced radially
outwardly when movement occurs between the mandrel and the expansion elements.
A disadvantage of this configuration is that the expansion elements or wedges
are
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connected by a band of material to the shaft. This configuration does not
provide a
robust means for connection and hence a weak mechanical set. Also, additional
components (such as the band) increase the cost of manufacture and assembly
time
and complexity of use.
These limitations of self drilling mechanically set rock bolts led to the
development of
yet another type of rock bolt: a combined mechanical and chemically set rock
bolt.
This type of rock bolt uses a resin compound in combination with a mechanical
expansion assembly to form an anchor.
For example, International Patent Application No. WO 2008/00015 discloses a
self
o drilling rock bolt similar to the invention disclosed in WO 2007/053893
discussed
above. However this rock bolt also includes a sleeve along a major part of the
shaft.
The sleeve extends from adjacent the anchoring device or expansion assembly
through to and adjacent the nut end. The purpose of the sleeve is to provide
at least
part of a circulation path to allow fluid or resin to be passed between the
nut end to
the drilling end and provide an additional chemical set combined with the
mechanical
set.
Again, a disadvantage of this configuration is that the expansion elements or
wedges
are connected by a band of material to the shaft. This configuration does not
provide
a robust means for connection and hence a weak mechanical set (leading to the
need
for an additional, chemical set).
Also, additional components (such as the band) increase the cost of
manufacture and
assembly time, and the complexity of use.
Furthermore, as with other chemically set rock bolts, this type of rock bolt
may not be
suitable for use in the coal mining industry as a fast setting chemical resin
can
generate sufficient heat to cause a fire as aforesaid.
From the above, it can be seen that there is a requirement for an improved
rock bolt
or anchor which is of a robust construction for self drilling, provides a
strong
connection to the rock mass, reduces the risk of fire in coal mining
operations, has
minimal components, is cost effective to manufacture and assemble and is easy
to
use.
It is an object of the present invention to address the foregoing problems or
at least to
provide the public with a useful choice.
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All references, including any patents or patent applications cited in this
specification
are hereby incorporated by reference. No admission is made that any reference
constitutes prior art. The discussion of the references states what their
authors
assert, and the applicants reserve the right to challenge the accuracy and
pertinency
of the cited documents. It will be clearly understood that, although a number
of prior
art publications are referred to herein, this reference does not constitute an
admission
that any of these documents form part of the common general knowledge in the
art, in
New Zealand or in any other country.
Throughout this specification, the word "comprise", or variations thereof such
as
o "comprises" or "comprising", will be understood to imply the inclusion of a
stated
element, integer or step, or group of elements integers or steps, but not the
exclusion
of any other element, integer or step, or group of elements, integers or
steps.
Further aspects and advantages of the present invention will become apparent
from
the ensuing description which is given by way of example only.
DISCLOSURE OF THE INVENTION
According to one aspect of the present invention there is provided an
anchoring
device including:
a drilling assembly including an elongate shaft with a drill head at one end,
and
another end configured to connect to a drilling apparatus; and
at least one expansion element;
characterised in that
the drill head and expansion element(s) are configured to cooperatively
interlock with
each other to provide for directed movements of the drill head relative to a
longitudinal
axis of the shaft; wherein
co-operating contact surfaces between the drill head and the expansion
element(s)
are configured such that relative longitudinal movement of the drill head with
respect
to the expansion element(s) displace(s) the expansion element(s) outwardly so
the
expansion element(s) can provide frictional contact with a borehole once
inserted
therein.
In a preferred embodiment the drill head and expansion element engage with
each
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other via a first engagement portion on the drill head cooperatively fitting
with a
second engagement portion on the expansion element.
Preferably, the first engagement portion is a protrusion configured to co-
operatively
engage with a second engagement portion in the form of a corresponding
channel.
More preferably, the combination of first and second engagement portions forms
a
dovetail arrangement.
It should be appreciated by those skilled in the art that the engagement
portions may
include any number and other types of 'key and lock' configuration(s) that
allows or
guides movement on the drill head relative to a longitudinal axis of the
drilling
o assembly shaft. Also, a 'key and lock' configuration may be referred to as
an
interlock mechanism which includes interlock portions to facilitate outward
radial
displacement of the expansion elements. For example, this may occur with a
tapered
outer surface of a drill head co-operating with a reverse taper on the
expansion
element and/or other such combinations described later in the specification.
In a preferred embodiment the engagement configuration restricts radial and
thus,
circumferential movement of the expansion element relative to the longitudinal
axis of
the drilling assembly shaft.
Preferably, the first engagement portion is positioned on the inner surface of
the
expansion element and the second engagement portion is positioned on the outer
surface of the drilling assembly.
More preferably, the second engagement portion is positioned on or about the
leading
edge of the drill head of the drilling assembly.
It will be apparent to those skilled in the art that the drill head and
expansion
element(s) of the present invention may be retrofitted to existing rock bolts
known in
the art.
According to another aspect of the present invention there is provided an
anchoring
device including:
= a drilling assembly including an elongate shaft with first and second
ends, a
drill head at the first end, and the second end suitable for connection to a
drilling apparatus; and
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= at least one expansion element;
wherein
= the at least one expansion element includes a first engagement portion;
= the drill head includes a second engagement portion;
= the first and second engagement portions co-operate for retention of the
expansion element(s) on the drilling assembly during a drilling operation;
= the first and second engagement portions are configured to co-operate
to:
o permit longitudinal movement of the expansion element(s) relative to a
longitudinal axis of the drilling assembly;
o substantially prevent radial movement of the expansion element(s)
relative to the longitudinal axis of the drilling assembly; and
o substantially prevent circumferential movement of the expansion
element(s) relative to the drilling assembly;
= the drill head and the expansion element respectively include co-
operating
contact surfaces for outward radial displacement of the expansion element(s)
on relative longitudinal movement of the drill head.
According to another aspect of the present invention there is provided a
component
for an anchoring device including:
a drill head; and
at least one expansion element;
characterised in that
the drill head and expansion element are configured to cooperatively interlock
with
each other and provide for directed movements of the drill head relative to a
longitudinal axis of the shaft; wherein
co-operating contact surfaces between the drill head and the expansion
elements are
configured such that movement of the drill head with respect to the expansion
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elements displaces the expansion element outwardly so the expansion element
can
provide frictional contact with a borehole once inserted therein.
According to another aspect of the present invention there is provided a
component
for an anchoring device including:
a drill head; and
at least one expansion element;
wherein
the at least one expansion element comprises a first engagement portion;
the drill head includes a second engagement portion;
= the first and second engagement portions co-operate for retention of the
expansion element(s) on the drill head during a drilling operation;
= the first and second engagement portions are configured to co-operate to:
o permit longitudinal movement of the expansion element(s) relative to a
longitudinal axis of the drill head;
0 substantially prevent radial movement of the expansion element(s)
relative to the longitudinal axis of the drill head; and
o substantially prevent circumferential movement of the expansion
element(s) relative to the drill head;
the drill head and the expansion element respectively include co-operating
contact
surfaces for outward radial displacement of the expansion element(s) on
relative
longitudinal movement of the drill head.
According to another aspect of the present invention there is provided a use
of an
interlock mechanism to connect at least one expansion element to a drill head;
wherein
a first interlock portion is located on an internal surface of the expansion
element and
at least one second interlock portion is located on an outer surface of the
drill head,
wherein said first and second interlock portions are configured to:
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= permit movement of the expansion element relative to the drill head along
a
longitudinal axis of the drill head; and
= facilitate outward radial displacement of the expansion element.
According to another aspect of the present invention there is provided a
method of
using the anchoring device including the steps of:
a) attaching the anchoring device to a drilling apparatus via a drive
coupler;
b) positioning the drill head of the anchoring device against a surface;
c) rotating the anchoring device in a first direction of rotation via the
drilling
apparatus so that the rock bolt is drilled into the surface creating a
borehole to
a required depth;
d) rotating the shaft and drill head via the drilling apparatus in a second
reverse
direction of rotation to partially withdraw the shaft and drill head from the
borehole thereby causing at least one expansion element located about the
drill head to displace and provide frictional contact of the expansion
element(s)
within an internal surface of the borehole.
According to another aspect of the present invention there is provided a
method of
using the anchoring device including the steps of:
a) attaching the anchoring device to a drilling apparatus via a drive
coupler;
b) engaging the drive coupler with a nut positioned on an elongate shaft of
the
anchoring device;
c) if required, winding the nut in a first direction of rotation on the shaft
until it
abuts against a stop;
d) positioning a drill head of the anchoring device against a surface;
e) rotating the drill head in a first direction of rotation via the drilling
rig so that the
anchoring device is drilled into the surface such that the surface abuts a
plate
attached to the shaft;
f) rotating the nut on the shaft in a second reverse direction of rotation
via the
drilling apparatus until the nut abuts the plate;
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g) further rotating the nut in the second reverse direction to partially
withdraw the
shaft and drill head from the borehole thereby causing at least one expansion
element located about the drill head to displace and provide frictional
contact
of the expansion element(s) within an internal surface of the borehole.
According to another aspect of the present invention there is provided a
method of
installing an anchoring device including the step of utilising the anchoring
device
substantially as described herein.
According to another aspect of the present invention there is provided a
method of
connecting a drill head to at least one expansion element in an anchor
characterised
by the step of positioning the connecting portions which hold the expansion
elements
to the drill head so that they are shielded from the edges of the borehole
during a
drilling operation.
It should be appreciated that the term 'rock' as used in the specification is
to be given
a broad meaning to cover applications in the mining and tunnelling industry
and any
other industry that requires sub-terranean roof and wall support. The
invention is
suitable for use in hard rock applications as well as in softer strata, such
as that found
in coal mines. Other materials and other applications may include concrete,
dams,
retaining walls, civil engineering, building construction and the like.
BRIEF DESCRIPTION OF DRAWINGS
Further aspects of the present invention will become apparent from the
following
description which is given by way of example only and with reference to the
accompanying drawings in which:
Ficiure 1 is a perspective view of a preferred embodiment of the present
invention in the form of an anchoring device;
FiClure 2 is a perspective view of the wedge of Figure 1;
Ficiure 3 is a top sectional view of the wedge of Figure 1;
Figure 4 is a perspective view of the drill head of Figure 1;
Ficiure 5 is a perspective view of the anchoring device of Figure 1 in
assembled
form;
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Figure 6 is a side view of the assembled anchoring device of Figure 5;
Figure 7 is a cross section taken along the line E-E in Figure 6;
Fiuure 8 is a side view of the assembled anchoring device of Figures 6 and 7
attached to a drilling apparatus and drive coupler;
Fiuure 9 is a side cross sectional view of the anchoring device of Figure 8
with
components attached to the drive coupler; and
Figure 10 is a perspective view of the nut and bearing plate of Figure 9;
Figure 11 is a side view of the second end of the anchoring device of Figure
1
with a double coil spring component; and
io Figure 12 is a bottom perspective view of an alternative wedge
embodiment.
DETAILED DESCRIPTION INCLUDING BEST MODES
Figure 1 shows a preferred embodiment of an anchoring device in the form of a
rock
bolt (1) of the present invention in its unassembled form.
Rock bolt (1) incorporates a drilling assembly (2) which includes an elongate
shaft (3)
with a first (drilling) end (4) and a second (drive) end (5), a drill head (6)
at the first
end (4), and the second end (5) being configured for connection to a drilling
apparatus (not shown) in known fashion.
The shaft (3), which is typically manufactured from steel, is a hollow tube
and
incorporates a left hand thread (7) along a length of the shaft (3). For
clarity, part of
the shaft (3) in Figure 1 is shown without the thread.
The rock bolt (1) includes expansion elements or wedges (8A, 8B). For ease of
reference the expansion elements (8A, 8B) will now simply be referred to as
"wedges"
throughout this specification.
Wedges
With reference to Figures 1, 2 and 3, the wedges (8A, 8B) include ridges (13A,
13B)
on the upper surface which provide additional bonding to the inner surface of
a
borehole for the first mechanical set. Figure 3 is a top view of the wedges
(8A, 8B)
depicted in Figures 1 and 2. However, for illustrative purposes, detail which
would not
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ordinarily be seen in such a view (such as the engagement portion (11) and
taper
(12A, 12B)) is depicted in dotted lines.
The inner surface of the wedges (8A, 8B) includes a first engagement portion
(11) in
the form of a protrusion with a dove tail cross-section (11A) (shown in Figure
3). The
first engagement portion is configured to co-operatively slide and engage with
a
second engagement portion (10) (shown in Figures 1 and 5) of the drilling head
(6).
The second engagement portion (10) is in the form of dovetail shaped groove or
channel and the combination of engagement channels to form a dovetail
connection
in a manner described later in this specification.
o The profile of the leading portion (11A) when viewed from the above (as
shown in
Figure 3) is 'T-Shaped' and is dimensioned so that it does not extend the full
length of
the second engagement portion (10) of the drill head (6). This is to prevent
jamming
of the wedges (8A, 8B) during sliding engagement which could otherwise occur
from
the changing diameter of drill head (6) to wedge(s) (8A, 8B) interface.
The inner surface of the wedges (8A, 8B) is also tapered (12A,12B) to
cooperate with
the tapered surface (25) (as shown in Figure 1) of the drill head (6) in a
manner
described later in this specification.
The wedges (8A, 8B) also include integrated barbs or skirts (14A, 14B) which
have
curved raised edges located at the distal end of the wedges (8A, 8B).
The profile surface detail of the wedges (8A, 8B) is best seen in Figure 2. It
should
be appreciated by those skilled in the art that the configuration of the
profile surface
of the wedges (8A, 8B) and/or the barbs (14A, 14B) should not be seen as
limiting.
For example, alternative barb embodiments may include separate barbs which are
riveted directly into a recess of the wedge and manufactured out of resilient
spring
steel. Similarly, the upper surface of wedges (8A, 8B) may be profiled in
configurations other than the series of repeating ridges depicted in the
Figures.
Drill Head
Drill head (6) is depicted in more detail in Figure 4. With reference to that
Figure, drill
head (6) incorporates two drill tips or cutters (9A, 9B) at a distal end
thereof and
aperture (15) to allow drilling fluid and/or cementitous material to pass
through in a
manner described later in this specification. It should be appreciated that
other drill
tips could conceivably be used with this invention. For example, a single
cutter with a
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tungsten tip for use in hard rock mining applications.
A further aperture (16) is shown which is located on both sides of the drill
head (6)
(although only one aperture is shown for illustrative purposes). This aperture
(16) is a
sight and welding hole used to check that the drill head (6) has been
correctly
screwed on to the shaft (not shown) and provides a further welding fixture for
permanent attachment of the drill head (6) to the shaft.
It should be appreciated that in alternative embodiments, further apertures
may be
incorporated in to the drill head (6). For example, a further aperture on each
side of
the drill head (6) might be incorporated to allow further drilling fluid,
cementitous
io material etc to pass through the drill head (6).
Drill head (6) includes a tapered surface (25) to co-operate with reverse
tapers (12A,
12B) located on the inner surface of expansion elements (8A, 8B) as shown in
Figures 1 and 3. The corresponding tapered surface of drill head (6) and
expansion
elements (8A, 8B) allows for displacement of the expansion elements (8A, 8B)
during
the mechanical set operation described later in this specification.
Drill head (6) includes a second engagement portion (10) configured so that it
partially
extends along the length of the drill head (6). The second engagement portion
(10) is
a trapezoid (or "dovetail") shaped groove positioned and formed on the leading
front
edge of the drill head (6) of the drilling assembly (2). This groove is
configured to
receive complementary first engagement portion (11) (in the form of a
trapezoid (or
"dovetail") shaped projection on wedges (8A or 8B) as shown in Figures 1 to 3.
It should be appreciated that the longitudinal position of the first
engagement portion
(11) on the wedges (8A, 8B) defines where the wedges (8A, 8B) are located and
the
range of movement permitted relative to the second engagement portion (10) of
the
drill head (6). The length of the first engagement portion (11) is dimensioned
to allow
the required range of longitudinal movement before the first engagement
portion (11)
abuts the distal end of the second engagement portion (10) (discussed in more
detail
below).
Assembled Rock bolt
Figures 5 and 6 show the rock bolt (1) of Figure 1 in assembled form. During
assembly, the drill head (6) which includes an internal screw thread (not
shown) is
screwed onto the shaft (3) at the first (drilling) end (4) and permanently
fixed by
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welding onto the shaft (3). The wedges (8A, 8B) are attached to each side of
the drill
head (6) by the second engagement portion or groove (10) of the drill head (6)
capturing first engagement portion or projection (11). The taper (25) of the
drill head
(6) co-operates with corresponding reverse tapers (12A, 12B) located on the
inner
surface of wedges (8A, 8B) such that the wedges (8A, 8B) lay flat against the
drill
head (6) and shaft (3) such that they are disposed generally co-extensively
with, or
within, the lateral extent or circumference of the drill head.
Engagement (Dovetail Connection)
The manner in which the first engagement portion (11) is captured and retained
in the
o second engagement portion (10) is best seen in Figure 7. Figure 7 shows a
cross
section of the assembled drill head (6) and wedges (8A, 8B) taken along the
line E-E
in Figure 6.
The inner surface of the wedges (8A, 8B) includes first engagement portion
(11) in
the form of an elongate projection of which the leading section (11A) (Figure
3) is
formed in a trapezoid (or "dovetail") shape.
Drill head (6) includes a second engagement portion (10) which in the form of
a
trapezoid shaped groove extending from the leading edge to approximately half
way
along the drill head (6) (best seen in Figure 4). The first and second
engagement
portions (11, 10) are complementary such that the groove slidingly receives
the
projection to form a dovetail connection as depicted in Figure 7.
It will be appreciated by those skilled in the art that the close contact of
the walls of
projection (11) with the walls of groove (10) will restrict radial and/or
circumferential
movement of the wedges (8A, 8B) during a drilling operation. This is important
as
displacement of the wedges (8A, 8B) during the drilling operation may cause
them to
be damaged and compromise (or even prevent) the mechanical set which they
provide. As will be readily apparent, other complementary shapes might be used
to
achieve the same purpose (for example a T-shape projection and corresponding
shaped groove).
It will also be appreciated that a range of longitudinal movement of the
wedges (8A,
8B) relative to the longitudinal axis of the drilling assembly (2) is
permitted by this
configuration. The configuration restricts longitudinal movement of the wedges
(8A,
8B) towards the second (drive) end (5) of the rock bolt (1) by abutment of the
projection (11) against the closed end of the groove (10). An advantage of
this
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configuration is that the wedges (8A, 8B) are prevented from sliding the
entire length
of the drilling assembly (2) during a drilling operation and thus dislodging
from the
drilling assembly (2). However the configuration will permit a large range of
longitudinal movement of the wedges towards the first (drilling) end (4) of
the drilling
assembly (2). This is important as longitudinal movement of the wedges (8A,
8B) in
that direction with respect to the drill head will be required during the
mechanical set
operation (discussed in more detail below).
Rock bolt Attachment to Drilling Apparatus
Figure 8 illustrates the second (drive) end (5) of the assembled rock bolt (1)
attached
o to a drive coupler (16). The drive coupler (16) is arranged to engage with
a drilling
apparatus (17) on the shaft (3) so as to allow rotation and thrust to be
imparted to the
shaft (3).
Rock Bolt Modes of Operation
The rock bolt (1) has three modes of operation: setting-up, drilling and
mechanical set
which are described with reference to Figures 8, 9,10 and 11 as follows:
Setting-up Mode
Once the rock bolt (1) has been assembled as previously described and with
reference to Figures 9 and 10, a bearing plate (18) with corresponding concave
and
convex faces is inserted onto the shaft (3) with the concave face directed
towards the
first (drilling) end (4) of the rock bolt (1). Prior to the bearing plate (18)
being inserted
onto the shaft (3) a mesh or "W" plate (not shown) may also be inserted onto
the
shaft (3) to abut against the bearing plate (18) as known in the industry.
As is known in the industry, the bearing plate (18) by convention includes a
convex/concave face to assist with abutment to the rock face (for example, in
situations where the borehole has not been drilled substantially perpendicular
to the
rock face). The concave face provides an additional tolerance (usually an
angle
between 15 ¨ 20 ) when abutted to the rock face.
Aperture (19) (shown in Figure 10) of bearing plate (18) is dimensioned so
that it can
be disposed on the shaft (3) of the second (drive) end (5). The assembled
configuration is best seen in Figure 9.
A spherical nut (20) with corresponding left hand thread is then wound onto
the
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WO 2012/012392 CA 02809138 2013-01-17 PCT/US2011/044490
second (drive) end (5) of the shaft (3). Thus the bearing plate (18) is
captured by the
spherical nut (20) and arranged to bear against the outer face of the rock
during a
mechanical set operation in a manner described below. As is known in the
industry,
the use of a spherical shaped nut (20) complements the convex/concave bearing
plate (18) to provide maximum contact and permit a range of movement against
the
bearing plate.
As aforesaid, the thread on the shaft (3) and spherical nut (20) are left
handed.
Accordingly, during the drilling operation, the torque applied to the
spherical nut (20)
tends to cause it to wind off the second (drive) end (5) of the shaft (3). To
prevent
o this, a stop assembly in the form of a ring (21) is welded to the shaft (3)
to prohibit
axial movement of the spherical nut (20) beyond a pre-determined location
along the
shaft (3). Preferably, the welded ring (21) is secured to a terminal end
portion of the
shaft (3). This prevents the spherical nut (20) from unwinding during the
drilling mode
as described below. In alternative embodiments, the welded ring (21) may be
replaced by a bayonet fitting, pin fitting and/or equivalent embodiment and
should not
be seen as limiting.
In practice, the applicant has found that under some conditions the spherical
nut (20)
which abuts the bearing plate (18) can bind the ring (21) and prevent the
spherical nut
(20) from releasing when the rotation is reversed in the mechanical set
operation (as
described further below). If the hole has been over drilled and there is not
enough
friction in the system to overcome the binding, the shaft (3) may spin in the
bore hole
of the rock face and the rock bolt may not set as desired. To alleviate this
problem, a
spring washer in the form of a double coil spring (26) (shown in Figure 11)
may be
utilised at the second end (5) of the shaft (3) between the ring (21) and
spherical nut
(20). This spring (26) assists in the release of the spherical nut (20) during
the
mechanical set operation. It should be appreciated that other means of
preventing
binding of the nut could conceivably be used with this invention. The
applicant has
also found that it may be beneficial to grease the thread in front of the ring
(21). Test
results conducted show that the torque to release the spherical nut (20) can
be
reduced from 100 ft lbs to 40 ft lbs with the double coil spring (26) in
combination with
grease.
Drilling Operation Mode
A drive coupler (16) attached to the drilling rig (17) is engaged with the
spherical nut
(20) (best seen in Figure 9). The drilling rig (17) is then operated in a
clockwise
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WO 2012/012392 CA 02809138 2013-01-17 PCT/US2011/044490
direction which unwinds the spherical nut (20) until it locks against the
welded ring
(21) which forms part of the drilling assembly (4). Further rotation of the
spherical nut
(20) drives the shaft (3) in a clockwise direction which in turn rotates the
drill head (6)
(welded to the shaft (3)) in a clockwise direction so that the rock bolt (1)
is driven or
bores into the rock face.
During the above drilling operation, wedges (8A, 8B) are prevented from
sliding
longitudinally toward the second (drive) end (5) of the rock bolt by abutment
of the
projection (11) against the end of groove (10) (as previously described). In
this way
wedges (8A, 8B) cannot dislodge from the drilling assembly (2) during
drilling. Also,
io as previously described, the taper (25) of the drill head (6) co-operates
with
corresponding reverse tapers (12A, 12B) located on the inner surface of wedges
(8A,
8B) such that the wedges (8A, 8B) are disposed generally co-extensively with,
or
within, the lateral extent or circumference of the drill head and will not
catch against
the sides of the bore hole during drilling.
In preferred embodiments during the drilling operation, drilling fluid may be
pumped
through the hollow shaft (3) and drill head apertures (15, 16) of the rock
bolt (1) to
flush the cutting surface of the rock bolt (1).
Once the rock bolt (1) has been driven or bored into the rock face at the
required
depth (normally determined by a mesh or "W" plate (not shown) contacting the
bearing plate (19) which in turn bears against the rock face with minimum
shaft (3)
exposed), the mechanical set operation is engaged as described below.
Mechanical Set Operation
On completion of the drilling operation phase, the drilling apparatus (17) is
then used
to rotate the spherical nut (20) in the reverse i.e. anti-clockwise direction.
The
spherical nut (20) freely rotates on the shaft (3) until the bearing plate
(18) is captured
by the spherical nut (20) and the bearing plate (18) bears hard against the
outer face
of the rock. Further rotation of the spherical nut (20) causes counter
rotation, and
withdrawal, of the shaft (3) and drill head (6) from the borehole.
This relative longitudinal movement between the wedges (8A, 8B) and the drill
head
(6) enables the drill head (6) to slide back through the wedges (8A, 8B). The
taper of
drill head (6) acts against the co-operating reverse taper of wedges (8A, 8B),
such
that the longitudinal movement of the drill head (6) toward the second (drive)
end (5)
of the rock bolt (1) displaces the wedges (8A, 8B) to an extent sufficient to
allow
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WO 2012/012392 CA 02809138 2013-01-17 PCT/US2011/044490
barbs (14A, 14B) to grip against the rock face providing sufficient initial
frictional
resistance to prevent the rock bolt (1) from sliding out of the borehole.
Further rotation of the spherical nut (20) in the anti-clockwise direction
enables the
drill head (6) to slide back further through the wedges (8A, 8B), where the
tapered
drill head (6) again acts against the co-operating reverse taper of wedges
(8A, 8B),
such that the sliding longitudinal movement displaces the wedges (8A, 8B)
further to
provide additional frictional contact of the wedges (8A, 8B) with an internal
surface of
the borehole to mechanically set the rock bolt (1) into the rock face.
To ensure the rock bolt (1) is mechanically set, it can be placed in tension
by
io continuing to apply torque in the reverse direction to the spherical nut
(20) resulting in
the nut (20) locking up against the bearing plate (18). At that particular
point, the
wedges (8A, 8B) will pull hard against the rock bore surface so that the
wedges (8A,
8B) cannot be moved further. This then effectively binds the rock bolt (1) and
inhibits
it from rotating any further. Once the rock bolt (1) is under sufficient
tension, the
drilling apparatus (17) can be removed.
If required, once the drilling apparatus (17) is detached cementitious
material such as
High Early Strength (HES) Grout, resin or equivalent bonding material can be
injected
into the borehole directly and/or through the hollow shaft (3) and aperture
(15) of the
rock bolt (1) for additional bonding in known fashion. It should be
appreciated that
channels may be located between the wedges (8A, 8B) and either side of the
drill
head (6) to clear drilled material and allow cementitous material to be
injected into
and flow through the channels.
Alternative Wedge Embodiment
Figure 12 shows an alternative embodiment of a wedge (8C) which includes a
similar
profile and features to that of the embodiment depicted in Figures 2 and 3
(like
features have like reference numbers). However in this embodiment a barb (14C)
is
fashioned a coil spring wire welded at the distal end of the wedge (8C). The
spring
wire is a compression spring and is dimensioned such that the diameter of the
coil
spring is substantially flush with the profiled surface (13A, B) of the wedge
(8C).
An advantage of using a spring wire with this dimension and configuration is
that the
spring wire or barb (14C) does not cut its own groove or hole during the
drilling
process. The applicant has found that under certain conditions the wedges
depicted
in Figures 2 and 3 with barbs (14A, 14B) that protrude from the profile
surface of the
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wedge can increase the bore hole size thereby reducing the friction within the
system.
As previously described, if there is not enough friction in the system, the
rock bolt
may not set as desired in the mechanical set operation.
There are many advantages associated with this invention.
For example, the rock bolt includes engagement portions which are integrated
into the
componentry. Therefore, the rock bolt does not require additional components
such
as metal straps to keep the expansion elements in place thereby reducing
assembly
time and the cost of manufacture.
Also, the engagement portions provide a robust means for connection between
the
o drilling assembly and the expansion elements in order to retain the
expansion
elements during a self drilling operation.
Furthermore, a connection system comprising engagement portions in a 'key and
lock' configuration e.g. a pin/tongue configured to co-operatively slide and
engage
with a corresponding socket/groove simplifies the mechanism of operation as
there
are less moving parts.
Aspects of the present invention have been described by way of example only
and it
should be appreciated that modifications and additions may be made thereto
without
departing from the scope of the appended claims.
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