Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02728807 2011-01-18
MINE ROOF ANCHOR ASSEMBLY
SCOPE OF THE INVENTION
The present invention relates to an anchor assembly for securing a
conventional
rod-like reinforcing tendon or mine roof bolt under tension in a bore hole.
More
preferably, the present invention pertains to an anchor assembly which
incorporates a
mechanical anchoring or expansion unit for securing the tensioned bolt within
the bore
hole to compress and consolidate ground forces.
BACKGROUND OF THE INVENTION
Various anchor assemblies have been used to reinforce tunnel and retaining
walls,
underground passageways and mine shaft wall and roofs (hereinafter
collectively referred
to as mine roofs), to reduce the likelihood of rock bursts and control ground
movement
and the hazards associated therewith. Conventional anchor assemblies typically
include a
reinforcing tendon or bolt which is secured in place with a bore hole by the
use of partial
or full column resin systems or mechanical expansion systems typically
incorporate a two
compartment cartridge system consisting of a resin and a catalyst which are
slid ahead of
the bolt into the bore hole. When mixed, the resins chemically affixes the
rock bolt in
place, allowing the bolt to thereafter be tensioned by the use of a nut or
threaded fastener.
Mechanical anchor expansion units are provided with an expansion shell or unit
having a plurality of fingers or leaves which are secured to a bail and a
camming plug
which is positioned and moveable relative to the leaves. The roof bolt or
tendon is
threaded along its distal end so as to threadedly engage an internally
threaded bore
formed in the plug. In use, a bore hole formed in an anchor assembly with the
expansion
unit partially threaded onto the end of a bolt is inserted into the bore hole.
The
mechanical expansion unit is activated by rotating the bolt relative to the
expansion shell.
The threaded engagement of between the tendon and the plug acts to axially
draw the
camming plug outwardly. As the camming plug moves, it engages and forcing the
leaves
of the expandable shell radially outwardly and into bearing contact with the
sidewalls of
1
CA 02728807 2011-01-18
the bore hole. In this manner, the bolt is mechanically secured to the sides
of the bore
hole. Once the expansion shell is fully expanded, further rotation of the bolt
advantageously effects the tensioning of the bolt along its length to compress
the
competent strata and consolidate ground forces.
Various expansion units have been proposed to ensure that the end of the rock
bolt remains axially aligned with the bail and camming plug, to ensure correct
operation
of the expansion shell during tensioning. Canadian Patent No. 618,342
describes an
expansion anchor shell having a U-shaped bail, having an enlarged bight
portion. A
circular aperture is provided in the end of the bail which is sized to receive
the end of a
rock bolt therethrough. Canadian Patent No. 618,343 describes a similar
modified bail
assembly in which a flat knockout plug is positioned in the circular aperture
of the
enlarged bight. However, in conventional expansion units, the camming plug
remains
liable to be knocked out of axial alignment with the anchor tendon as the
anchor
assembly slides into place resulting in tendon jamming and/or the incomplete
deformation of the expansion shell leaves.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an improved mechanical bolt
anchor assembly for use in the securement of an elongated rock bolt or anchor
tendon
within a bore hole formed in a mine roof.
Another object of the present invention is to provide a mechanical expansion
unit
for use with a rock bolt or anchor tendon, and which incorporates a camming or
wedge
plug assembly which is configured to maintain an optimum plug alignment
relative to the
expansion shell as the rock bolt is initially positioned, and the expansion
unit is activated.
A further object of the present invention is to provide a mechanical expansion
unit for
anchor assembly which has a plurality of deformable elongated vertical leaves.
The
leaves may be of a generally transverse planar or arcuate configuration, and
are provided
with a gripping surface. Each of the leaves is joined at its top to a bail
having an open or
a solid top portion with a frangible central dome through which a rock bolt
can move, and
2
CA 02728807 2011-01-18
in which is disposed a camming plug which has a biasing member or spring pre-
coupled
thereto, to assist in maintaining the plug in a desired initial axial
alignment within the
bail.
Yet a further object of the present invention is to provide a mechanical bolt
anchor assembly having pre-positioned therein a camming plug assembly pre-
positioned,
and which includes a camming plug having a biasing spring secured to a distal
end
thereof to maintain the camming plug in a desired axially alignment relative
to both the
expansion shell, the bail and/or anchor rod both during each of initial
positioning within a
bore hole, and the activation of the anchor.
In a preferred construction, the present invention provides a mechanical
anchor
assembly that includes a mechanical expansion unit. The expansion unit
includes an
expansion shell and a wedge assembly which is adapted to radially expand into
bearing
contact with the sides of a bore hole. The wedge assembly preferably includes
a
camming wedge having a compressible biasing member or spring fixedly secured
at one
end thereof. The expansion shell includes a bail and a plurality of deformable
steel
leaves, and preferably between three and five leaves which are disposed
radially about an
axis. The bail is provided with a corresponding number of steel finger members
which
are attached respectively at one end to each leaf and at their other end an
axially
positioned end ring or yoke. The fingers and yoke generally define a cage in
which the
wedge assembly is housed. More preferably, the yoke acts as a seating surface
against
which the spring rests to bias the plug in a desired axial alignment. An
opening formed
through the yoke sized to permit the relative movement of an anchor tendon or
rod
therethrough on activation of the expansion unit and deformation/activation of
the
leaves.
Accordingly, in one aspect, the present invention resides in a mine roof
anchor
assembly for use in a predrilled bore hole formed in a rock face comprising,
an elongated
tendon which extends longitudinally from a first proximal portion to a
threaded distal
portion, a mechanical assembly defining a through-passage extending axially
3
CA 02728807 2011-01-18
therethrough from a proximalmost end to a distalmost end and including: a
plurality of
leaf members, said leaf members being displaceable radially relative to said
through-
passage into bearing contact with side portions of said bore hole; a bail
member defining
a distally disposed end member having an opening therethrough, said bail
member
including a plurality of fingers, each said fingers extending from said end
member to a
respective first end secured to an associated one of said leaf members; and a
wedge plug
generally housed within said bail member so as to be retained thereby, said
wedge plug
including a tapered sidewall tapering inwardly towards the proximalmost end
and having
formed therethrough an axially oriented threaded though bore sized to
threadedly receive
the distal portion of said tendon therein, the wedge plug having secured
integrally thereto
a resiliently compressible spring, said spring having a length selected to
maintain
engagement with said end member to assist in maintaining bearing contact
between said
wedge plug and said leaf members.
BRIEF DESCRIPTION OF THE DRAWINGS
Reference is now made to the following detailed description taken together
with
the accompanying drawings in which:
Figure 1 is an exploded perspective, top view showing a mechanical expansion
unit for use in a mine roof anchor assembly in accordance with the present
invention;
Figure 2 shows a perspective top and first view of the expansion unit shown in
Figure 1 in an assembled state prior to pre-positioning on an anchor rod;
Figure 3 shows a perspective front and bottom view of the expansion unit shown
in Figure 2;
Figures 4 to 6 show an exploded perspective bottom and side views of the
expansion unit of Figure 2; and
Figures 7 to 9 show the positioning of the mine roof anchor assembly within a
bore hole in accordance with a preferred embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As will be described with reference to Figures 7 to 9, the present invention
relates
to a mine roof anchor assembly 10 used as part of a mine roof support system
in the
4
CA 02728807 2011-01-18
compression and consolidation of a rock complex 6. The anchor assembly
includes an
elongated steel rock bolt or anchor rod 12, and a mechanical expansion unit 14
which is
operable to mechanically secure the rod 12 in place, positioned within a bore
hole 8
formed within the rock complex 6.
The anchor rod 12 is of a conventional design and has a longitudinal length
chosen for insertion into the bore hole 8, extending axially along Al-Al from
an
externally threaded outermost proximal end 16 to an innermost distal end
portion 18. As
will be described, the mechanical expansion unit 14 is configured for threaded
coupling
directly to the distal end portion 18, wherein the relative rotation of the
rod 12 about its
longitudinal axis A,-A, activates the expansion unit 14 to mechanically secure
rod 12
within the bore hole 8.
Figure 1 shows best the expansion unit 14 as including an expansion shell 20,
a
camming plug assembly 22, and a plastic retention sleeve or positioning collar
24. The
camming plug assembly 22 is shown best in Figures 1 to 5 as including wedge
shaped
steel plug 40 which has an internal bore 42 formed therethrough. The bore 42
is threaded
along its entire length, extending axially along a central plug axis Ap-Ap
(Figure 6). The
steel plug 40 tapers radially outwardly relative to the plug axis Ap-Ap from a
narrow
diameter proximalmost end 44 to an enlarged diameter distalmost end 46. A
distalmost
seating surface 48 is formed as a recessed groove in the end 46, and which
extends
annularly about the bore 42. The camming plug assembly 22 is further provided
with a
resiliently compressible steel spring 52. The steel spring 52 is preferably
formed as a
helical spring having an inner diameter which is greater than a lateral
diameter of the
distal end 18 of the anchor rod 12 so as to allow for its substantially
unobstructed
movement therethrough. The spring 52 is fixedly secured to the plug seating
surface 48
by one or more weldments 54 to provide the camming plug assembly 22 as a
single
preformed and preassembled unit. It is to be appreciated that providing the
spring 52 and
camming plug 40 as to a single integral, in addition to simplifying the shell
14
preassembly, advantageously ensures that the spring 52 and plug 40 are
maintained in
CA 02728807 2011-01-18
the desired coaxial alignment during initial installation of the expansion
unit 14 and its
subsequent activation.
Optionally recesses 50a-c may be formed in the external tapered surface of the
steel plug 40. The recesses 50a-c are equally spaced apart from each other,
and taper
such that segment narrows as it extends totally towards the distalmost end 46.
While the use of the weldments 54 to secure the spring 52 to the plug 40
provides
a preferred simplified construction, it is to be appreciated that the
invention is not so
limited. Other modes of securement could also be used including without
restriction by
the use of adhesives, or by the use of mechanical attachments such as
crimpings or the
like.
The mechanical expansion shell 20 is shown best in Figure 1 to 6 as having
steel a
bail assembly 26 and three axially elongated leaves 36a,36b,36c. Each of the
leaves
36a,36b,36c are preferably of a generally transverse arcuate configuration and
are
attached to the bail 26 towards their respective uppermost ends. In this
regard, each leaf
36a-c preferably is formed as a segment of a hollow cylinder, the outer
diameter of which
is substantially equal to the outer diameter of the bail 26 and marginally
less then the
diameter of the bore hole 8. The leaves 36a,36b,36c are preferably also wedge
shaped
along their axial length, with the top of each leaf being thinner than the
bottom. The
interior diameter of the hollow cylinder formed by the leaves 36 is selected
such that
prior to shell 14 activation, the leaves 36a,36b,36c loosely surround the
proximal end 18
of the anchor rod 12 and are engaged by the narrower proximalmost end 44 of
the plug
40 so as to limit its sliding movement therethrough. The exterior of each leaf
36 may
also be provided with a plurality of circumferential ribs, bosses or other
serrations 38
which are adapted for better mechanical engagement with the sides of the bore
hole 8.
The bail assembly 26 is formed from stamped steel or other metal and includes
an
annular collar or yoke 30 from which extend three evenly radially spaced
deformable
fingers 28a,28b,28c. Each of the fingers 28 extend axially and are integrally
formed at
6
CA 02728807 2011-01-18
one end to the annular yoke 30, and are joined at their other ends to a
respective leaf
36a,36b,36c by weldments. More preferably, the yoke 30 defines a through-
aperture 32
which has a diameter selected smaller than that of the spring 52, so as to
engage a distal
end of the spring 52 thereagainst, whilst allowing substantially unimpeded
movement of
the distal end 18 of the anchor rod 12 therethrough. Optionally, a knockout
plug 34 may
be secured over the aperture 32 to facilitate the positioning of the camming
plug
assembly 22 with wedge plug 40 and spring 52 therebetween.
It is to be appreciated that in the construction shown the yoke 30 and fingers
28
advantageously act as a cage in which the camming plug assembly 22 is housed.
With
the camming plug assembly 22 positioned in the initial preassembled position
shown in
Figure 2, the spring 52 is under partial compression and in bearing contact
against the
yoke 30. The steel plug 40 in turn only partially engages the adjacent ends of
each of the
leaves 36a,36b,36c. It is to be appreciated that the biasing force of the
spring 52 and its
pre-securement to the plug 40 advantageously not only simplifies the initial
positioning
of the camming plug assembly 22 within the bail assembly 26 cage; but also
ensures that
the wedge plug 40 is maintained with the desired alignment with the plug axis
Ap-Ap
coaxially aligned with the rod axis Al-A1, as the expansion unit 14 is
initially pre-
positioned on the rod 12, slide into position within the bore hole 8 and
subsequently
activated as the rod 12 is tensioned.
The threaded axial bore 42 is adapted to receive and threadedly engage the
external threads along the distal end 18 of the anchor rod 12. Although not
essential,
preferably the length of the threading along the anchor rod end 18 is selected
to permit
only a limited amount of travel of the bolt end portion 18 through the wedge
plug 40, and
which is selected to result in maximum expansion or splaying of the leaves 36.
The
resulting maximum expansion of the anchor shell leaves 36 and limited plug
assembly 22
movement advantageously ensures the wedge plug 40 is not drawn axially
completely
through the shell 20.
7
CA 02728807 2011-01-18
In the preassembly and initial positioning of the expansion shell 20 on the
distal
end 18 of the anchor rod 12, the positioning collar 24 functions to maintain
the expansion
shell 20 in an optimum initial orientation during transport upto the time of
installation of
the anchor assembly 10 into the bore hole 8. The positioning collar 24 is
preferably
provided in the form of a plastic sleeve which includes an enlarged diameter
radial flange
62 extending outwardly about one end.
It will be readily appreciated that the anchor rod 12 has a conventional head
formed at the exposed proximal end 16 thereof which protrudes from the bore
hole 8. On
assembly, a conventional bearing plate 80 and threaded nut 82 are secured on
the
proximal end 16 for tensioning against the rock face 100 in the compression
and
consolidation of ground forces.
Figures 7 to 9 show best the positioning of the mine roof assembly 10 in the
bore
hole 8. In initial pre-assembly, the camming plug assembly 22 is slid axially
into the
expansion shell 20 so that the spring 52 is compressed against the yoke 30,
and the wedge
plug 40 is disposed in partial engagement with the leaves 36 as shown in
Figure 2. The
collar 24 is then slid over the opposing ends of the leaves 36 to maintain the
expansion
unit 14 as a preassembled unit. With the expansion unit 14 is so preassembled,
the
spring 52 biases the plug 40 axially to maintain its bearing contact with the
ends of the
leaves 36, minimizing the possibility it may shift from the designed axial
alignment.
At the time of use, the expansion unit 14 is pre-secured onto the anchor rod
12.
With wedge plug 40 prepositioned within the expansion shell 20, the plug 40 is
threaded
partially over the distal end 18 of the anchor rod 12 until the end 18 engages
the knockout
plug 34. Once the expansion shell 20 is fully seated, the mine roof anchor
assembly 10 is
inserted into the hole 8. As the expansion unit 14 is initially moved into the
bore hole 8,
the enlarged diameter radial flange 62 on the positioning collar 24 is brought
into contact
with the rock face 100. This in turn prevents further insertion of the collar
24 in the bore
hole 8 and results in the collar 24 being slid relative to the anchor assembly
10, free of
the expansion shell 20 allowing outward movement of the leaves 36. At the same
time,
8
CA 02728807 2011-01-18
the use of a plug 34 to cover the distal end 18 and wedge plug 40, prevents
any fouling
of their respective threads. Once the anchor assembly 10 is fully positioned,
the head of
the rod 12 is rotated with a power tool (not shown), drawing the plug 40
axially along the
rod end 18 towards the distal end 16.
As the bolt 12 is rotated, the initial movement causes bolt 12 to move
inwardly
into the bore hole 8 until it contacts the top of the bail and dislocates the
plug 34,
breaking it free of the surrounding edge of the raised yoke 30. The end 18 of
the bolt 12
draws the plug 40 outwardly from the bore hole 8 along the axis Al-A1 into the
space
between the leaves 36. As the layer diameter end 46 moves between the leaves
36, the
plug 40 splays the leaves 36 radially apart and splaying them against the rock
sides of the
bore hole 8. The camming plug assembly 22 is thus drawn downwardly between the
leaves 36a,36b,36c, thereby causing them to splay outwardly and the fingers
28a,28b,28c
to deform.
It is to be appreciated that the serrations 38 on the leaves 36 advantageously
also
serve to prevent the expansion shell 20 from rotating relative to the
sidewalls of bore hole
8 upon rotation of rod 12.
In an alternate possible manner of use, the anchor assembly 10 is secured
within
the bore hole 8 in conjunction with a two compartment resin used in
conjunction with the
mechanical expansion unit 14. The spaces or slots formed between the adjacent
fingers
36 of the expansion shell 20 advantageously allow for the flow of the
anchoring resin
axially outwardly about the camming plug assembly 22 and shell leaves 36a,
36b, 36c to
further facilitate the securement of the anchor rod 12 within the bore hole 8.
The
construction of assembly the expansion unit 14 allows for the substantially
uninterrupted
flow of resin and catalyst downwardly about the components of the mechanical
expansion unit 14, to better provide secondary attachment between the
components of the
anchor assembly 10 and the sidewalls of the bore hole 8.
9
CA 02728807 2011-01-18
Although the detailed description describes and illustrates various preferred
aspects and designs, it is understood that the invention is capable of further
modifications. Many modifications and variations will now become apparent to
those
skilled in the art to which the invention pertains. For a definition of the
invention
reference may be had to the appended claims.
