Note: Descriptions are shown in the official language in which they were submitted.
CA 02599522 2007-08-21
WO 2006/091724 PCT/US2006/006393
1
IMPROVED RESIN GROUTABLE EXPANSION ANCHOR AND METHOD OF
INSTALLING SAME
FIELD OF T'HE INVENTION
The present invention relates to rock bolts and methods for installin.g rock
bolts
and in particular to rock bolts which are used in combination with a cementing
material.
The invention has been developed primaril.y for rock bolts used in nvning
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 applications.
BACKGROUND
Any discussion of the prior art throughout the specification should in no way
be
considered as an admission that such prior art is widely known or forms part
of common
general knowledge in the field.
There are three main types of rock bolt known for securing supporting
structures
in mine cavities. The first is a resin anchored rock bolt, which is installed
in a borehole
by inserting the bolt into the borehole, which contains a quick-setting resin
compound.
Once the resin is cured the bolt can be tensioned thereby to support the
sttucture.
The second type is a mechanically anchored rock bolt, which uses an expansion
assembly located at the distal end of the rock bolt. The expansion assembly
expands
upon a forward rotation to anchor the rock bolt in a borehole.
The tbird type is a combined mechanical and resin anchored rock bolt. This
type
uses a resin compound in combination with a mechanical expansion assembly to
form an
anchor with the advantages of both types mentioned above.
Typically this type of rock bolt is installed by first inserking a frangible
capsule
containing a resin compound into a borehole. The rock bolt is then inserted
into the
borehole to rupture the resin capsule. Once the resin is released, the bolt is
further
inserted into the borehole until the desired position is reached. A forward
rotation is
CA 02599522 2007-08-21
WO 2006/091724 PCT/US2006/006393
2
then applied to activate the expau.sion assembly thereby locking the rock bolt
in the
borehole whilst the resin cures.
A disadvantage of this type of rock bolt is that during the insertion process,
a
user often has to axially reciprocate the bolt to sufficiently mix and
distribute the resin
compound such that the rock bolt foims a strong bond once the resin cures. As
such, the
time required to perform this reciprocation can add significantly to the
installation cost.
Additionally, the axial insertion force required has been found to be
excessive
due to the fine clearance between the bore and the expansion assembly
providing only a
very small path for the resin to flow.
It should be understood that during this insertion process, and before the
rock
bolt reaches its desired position, only minimal rotation may be applied. That
is, a
forward rotation causes the expansion assembly to immediately and irreversibly
lock the
rock bolt before it reaches its final position, - and a reverse rotation v*ill
cause the
expansion assembly to potentially disengage from the rock bolt shank.
It is an object of the present invention to overcome or ameliorate at least
one of
the disadvantages of the prior art, or to provide a useful alternative.
SUR9MARff OF THE INVENTION
According to a first aspect of the invention there is provided a rock bolt
having:
an elongate shank;
an expansion assembly at the distal end of the shank, the expansion assembly
being expandable to lock the rock bolt in a borehole upon relative forward
rotation of the rock bolt; and
stop means to lock the expansion assembly with respect to the rock bolt for
conjoined rotation upon a reverse rotation of the rock bolt.
CA 02599522 2007-08-21
WO 2006/091724 PCT/US2006/006393
3
Preferably, the expansion assembly includes an expansion shell having two or
more longitudinally extending elongate expansion leaves for locking of the
rock bolt in
the borehole.
Preferably, the expansion shell is slidably engaged with the shank and is
sapported on the shank by an abutment member. More preferably, the abutment
member is a nut threadedly engaged with the shank.
Preferably, the diameter of the expansion shell is substantially equal to the
diameter of the rock bolt shank such that the cementing material flows more
freely to the
region of the rock bolt shank below the expansion shell.
Preferably, the expansion assembly includes a chuck in threaded engagement
with the shank such that rotation of the rock bolt with respect to the chuck
causes axial
movement of the chuck, the chuck having surfaces in sliding keying engagement
with
complementaty surfaces on the expansion leaves to cause outward divergent
deformation of the leaves upon the relative forward rotation of the rock bolt.
The chuck
and expansion shell are preferably adapted for conjoined rotation.
Preferably, the stop means is a stop formation disposed at the distal end of
the
rock bolt shank. More preferably, the stop formation is a flange member
fixedly
connected to the rock bolt shank. Alternatively, the stop formation may be
formed from
a portion of the rock bolt shank and the distal end of the rock bolt may be
pressed flat to
define the stop formation.
Preferably, each leaf includes a plurality of gripping formations disposed on
its
outer surface for gripping engagement with the borehole.
Preferably, the chuck surfaces are tapered.
Preferably, the chuck includes one or more fluid flow passageways.
CA 02599522 2007-08-21
WO 2006/091724 PCT/US2006/006393
4
According to a second aspect of the invention there is provided a method for
installing a rock bolt of the first aspect in a borehole of a rock formation,
including the
steps of:
(i) inserting a frangible capsule containing a cementing material into the
borehole;
(ii) inserting the rock bolt into the borehole until the capsule is rapfizred
and
rotating in a reverse direction whilst applying an insertion force to fiirther
insert into the borehole; and
(iii) rotating the bolt in a forward direction to expand the expansion
assembly and
thereby lock the rock bolt in the borehole.
Preferably, a substantial portion of the rock bolt shank is encapsulated by
the
cementing material after step (ii).
Preferably, the reverse rotation mixes the cementing material.
Preferably, the frangible capsule in substantially shredded by the reverse
rotation.
Preferably, the rock bolt head is substantially 50 mm away from the surface of
the rock formation after step (ii).
Preferably, the cementing material is a two-part epoxy resin compound.
$RiEF DESCRIEPT'ION OF'THE DRAWIlrIGS
Preferred embodiments of the invention will now be described, by way of
example only, with reference to the accompanying drawings in vcFhich:
Figure 1 is a side view of a rock bolt according the present invention;
Figure 2 is an enlarged view of the expansion assembly of the rock bolt of
Figure
1 shown releasably locked to the shank of the rock bolt; and
CA 02599522 2007-08-21
WO 2006/091724 PCT/US2006/006393
Figure 3 is sectional view of another embodiment of the rock bolt of Figure 1,
shown installed in a borehole.
DESCRIPTION OF THE PREFERI2ED EMSODIlI'IENTS
Referring to the drawings, the rock bolt includes an elongate shank 1 and an
5 expansion assembly 2 located at the distal end of the shauk. The arrangement
is such
that the expansion assembly expands to lock the rock bolt in a borehole 3 in a
rock
formation upon relative forward rotation of the rock bolt. As is common to the
art, the
illustrated rock bolt is used in combination with a two-part epoxy resin
compound to
secure the rock bolt in the borehole.
A stop formation in the form of a pressed flat 4 is located at the distal end
of the
rock bolt shank 1 and is used to lock the expansion assembly with respect to
the rock
bolt for conjoined rotation upon a relative reverse rotation of the rock bolt,
as best shown
in Figure 2. In another embodiment (not shown), the stop formation takes the
form of a
flange member fixedly connected to the distal end of the rock bolt.
The expansion assembly 2 includes an expansion shell 5 having three
longitud"znally extending leaves 6 for locking the rock bolt in the borehole.
Each leaf
includes a plurality of gripping serrations 7 peripherally disposed about its
outer surface,
for gripping engagement with the borehole.
The expansion shell 5 includes a clearance bore 8 for sliding engagement with
a
threaded portion 9 of the rock bolt shank 1. A threaded nut 10 supports the
expansion
shell on the shank so that the expansion assembly 2 is retained at the distal
end of the
shank.
The expansion assembly furth.er includes a chuck 11 having a threaded bore 12
for threaded engagement with the shank I so that rotation of the rock bolt
with respect to
the chuck causes axial movement of the chuck. The chuck includes tapered
surfaces 13
CA 02599522 2007-08-21
WO 2006/091724 PCT/US2006/006393
6
in sliding keying engagement with complimentary surfaces on the leaves 6 such
that the
axial movement of the chuck results in outward divergent deform.a.tion of the
leaves
upon relative forward rotation of the rock bolt. Moreover, engagement between
the
leaves and the tapered surfaces allows for conjoined rotation between the
expansion
shell and the chuck. The chuck 11 further includes fluid flow passageways 14
to allow
the resin to flow through the chuck and onto the shank 1.
In the embodiment shown in Figure 2, the expansion shell 5 has a diameter
substantially equal to the diameter of #he rock bolt shank 1. Since the outer
surface of
the expansion shell is substantially in line with the outer surface of the
rock bolt shank,
the resin will flow more freely to the region below the expansion shell during
insta.llation..
Ideally, the borehole diameter is approximately equal to, or slightly less
than, the
diameter of the expansion shell so that rotational resistance is created
between the
periphery of the expansion shell and the borehole.
As best shown in Figure 3, to install the rock bolt into a borehole 3, a
fraugible
resin capsule (not shown) is first inserted into the borehole. The rock bolt,
having been
already inserted tbrough fihe muvng structure 15 to be supported, is then
inserted into the
borehole to rupture the resin capsule and allow the resin to flow out onto the
assembly.
The bolt is then rotated in a reverse direction, to initially cause the chuck
11 to move to
abut the pressed flat 4 and thereby lock the expansion assembly with respect
to the rock
bolt for conjoined rotation.
The rock bolt is then fiuther inserted iuto the borehole by continued reverse
rotation and upward axial force. The resin will flow from the area above
expansion
assembly 2 on to the shank 1 through the passageways 14 and around the
periphery of
the expansion shell. It will be appreciated that due to the expansion assembly
being
CA 02599522 2007-08-21
WO 2006/091724 PCT/US2006/006393
7
locked with respect to the rock bolt, there is no risk of the expansion
assem.bly
disengaging the rock bolt during the reverse rotation.
The reverse rotation insertion process continues to perform three main
functions;
firstly, to force the resin down the rock bolt thereby encapsulating a
substantial portion
of the shank 1. Secondly, the locked expansion assembly efficiently mixes the
two-part
epoxy resin compound. Finally, the rotation of the expansion assembly 2
subsfan.tially
shreds the frangible resin capsule.
Once the rock bolt head 16 is approximately 50 mm away from the surface of the
rock formation, it is rotated in a forward direction in the conventional
manner to move
1o the chuck axially away from th.e pressed flat and thereby expan.d the
expansion assembly
2 to lock the rock bolt in the borehole.
It will be appreciated that the illustrated rock bolt reduces installation
times
because the reverse rotation makes it easier to overcome the resistance of
inserting the
expansion assembly tbrough the resin. Further, the resin compound is
efficiently mixed
and the resin capsule is substantially shredded during the insertion process,
which also
saves significantly on installation time.
Although the invention has been described with reference to specific examples;
it
wil]. be appreciated by those skilled in the art that the invention may be
embodied in
many other forms. For example, it should be understood that many other
suitable
stopping formations may be used to perform the same function without departing
from
the scope of the invention.
