Note: Descriptions are shown in the official language in which they were submitted.
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FIELD OF THE INVENTION
This invention relates to friction rock stabilizers which are used for
controlling stress-induced fracturing and strain bursts in rock in
underground mining or tunnelling operations and in general ground
support applications. More particularly, the invention relates to a friction
rock stabilizer of the split tube kind.
BACKGROUND TO THE INVENTION
Friction rock stabilizers have been in widespread use for many years in
rock support applications in underground mining and tunnelling
operations.
A friction rock stabilizer generally consists of an elongated metal tube
which carries a slot in its wall which extends over its length from one end
to the other. In use, the tube is hammered or pressed into a hole which has
been pre-drilled into rock from a face with the tube initially having a greater
transverse dimension than the hole with the result that the tube is inwardly
deforrned on entry into the hole. The inward deformation is accomplished
by a narrowing of the slot in the tube and the radial force generated by the
~5 natural resilience of the steel from which the tube is made anchors it
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frictionally in the hole.
Early rock stabilizers were unadorned parallel sided tubes with perhaps a
slight laper at one end to facilitate their insertion into a hole of a smaller
diametler than the stabilizer tube. More modern stabilizer tubes, however,
have siome form of stop, such as a solid metal ring which is welded
circumlferentially to the tube over its end which is outermost in use, for
r~tainil,u a face washer on the tube. When the stabilizer tube has been fully
presse,d into a hole the washer is pressed by the tube ring up against the
rock face to suprort the face rock around the hole and frequently to anchor
rock retaining mesh to the rock face.
A problem with rock stabilizer tubes which include the washer stops is that
the en~d of the stabilizer tube which carries the stop is held by the stop
against radial compression as that end of the tube is hammered into the
hole in which it is to be located. The result of this problem, particularly
with accurately and undersized holes, is twofold. Firstly an abnormal
transve!rse spalling inducing load is imposed on the rock surrounding the
mouth of the hole by the portion of the tendon tube which is outwardly
taperecl as a result of the mouth of the tube being held, with the slot at the
mouth open, by the washer stop and secondly, full penetration of the tube
into the hole may be prevented if the end of the tube which carries the stop
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should become jammed with the stop short of the hole to result in a loose
face washer which is not pressed against the rock face and can therefore
offer no face support of any kind. Yet a further problem with
conventional rock stabilizers of the above type is that the face washers are
generally a close fit on the tendon tubes and should the hole, for any
reason, be drilled into the rock face at an angle the washer on the tube
cannot readily move angularly on the tube to be flush with and evenly load
bearing on the face to provide face support around the stabilizer hole.
SUMMARY OF THE INVENTION
A friction rock stabilizer according to the invention comprises an
elonga1ed telldon tube which is re~ ce~l in cross-sectional dimension over
a portion of its length towards one end of the tube, a slot which extends
over at least the unreduced length of the tube and a radially extending stop
which is located on the reduced dimension portion of the tube for trapping
a face washer on the stabilizer. Preferably, the reduced cross-sectional
length of the tube is parallel sided and is conveniently circular in cross-
section.
In one form of the invention the dimensionally reduced portion of the tube
is threaded over at least a portion of its length from its free end and the
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washer stop is threadedly engaged with the threads on the tube.
In anolther form of the invention the washer support stop is fixed to the
tube by welding.
The washer trapping stop may be convexly domed in the direction of the
unreduced portion of the tendon tube to enable a face washer in use to
move angularly relatively to the stabilizer tube axis on the washer.
In a va,riation of the invention the dimensionally reduced portion of the
length of the tendon tube may be tapered inwardly towards said end of the
tube.
Conveniently, a portion of the length of the tendon tube from its end
orposilte to that on which the stop is loc~e~ I is tapered to a smaller cross-
sectional Ji,-,ension at the end of the tube to facilitate location of that en
of the tube in a hole in which the stabilizer is to be located in use.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is now described by way of example only with reference to
the drawings in which:
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FIGURE 1 is a side elevation of one embodiment of the friction rock
stabilizer of the invention,
FIGURE 2 is an end view of the Figure 1 stabilizer as seen from below in
Figure 1,
FIGURE 3 is a fragmentary side elevation of an end of the Figures 1 and 2
stabilizer of the invention,
FIGURE 4 is a fray"le"ta. y side view of the end of a variation of the Figure
1 stabilizer including a face washer, and
FIGURE 5 is a fragmentary side elevation of an end of yet a further
variation of the rock stabilizer of the invention.
DETAIILED DESCRIPTION
The friction rock stabilizer of the invention shown in Figure 1 of the
drawings to co"sist of an elongated tubular tendon 10 which is circular in
cross-section. The lower end 12 of the tendon tube is reduced in diameter
to a parallel sided extension of the major portion of the tube and is
threaded as shown in the drawing. The upper end portion 14 of the tube is
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inwardly tapered towards the end of the tube for facilitating the location of
that end of the stabilizer in a hole in which the stabilizer is to be located inuse. A slot 16 extends over the length of the tube 10 and, although not
essential, the slot 16 is pressed closed over the length of the extended end
12 of the tube. It is important to the invention that the edges of the slot 16
are spaced from one another at least over the unprofiled central portion of
the tube 10.
The end portion 12 of the tendon tube 10 carries a domed stop 18, a
shown in Figure 3, which is threadedly engaged with the threads on the
extended end 12 of the tube 10.
In the Figure 4 variation of the stabilizer of the invention the reduced
diameter end portion 12 of the tube 10 is unthreaded and the domed stop
18 is welded to the end portion of the tube as illustrated in the drawing.
The purpose of the stop 18, in whatever form it may take, is to trap a face
washer 20 on the rock stabilizer, as shown in Figure 4, under pressure up
against the face of the rock into which a borehole is drilled and into which
the tendon tube is fully pressed in use. The purpose of the domed stop 18,
as illusitrated in the drawings, is to enable the washer 20 to skew on it
relatively to the axis of the tube 10, as indicated by the chain line 22 in
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Figure 4, to enable the washer to bear with an even pressure on the rock
face surrounding the hole in which the tube 10 is located when the axis of
the hole is out of perpendicular with the rock face.
The large domed area of stop 18 enables face washers having holes of
various sizes to be used on a single stop 18.
In the Fiaure 5 variation of the rock stabilizer of the invention both ends of
the tendon tube 10 are tapered to a smaller diameter with the stop 18 being
loc~ted, by welding, adjacent the end of one of the tapered portions of the
tube 10. In both the Figure 4 and 5 embodiments of the rock stabilizer of
the invention the domed side of the washer may be welded to the tendon
10 instead of or in addition to the lower weld shown in the drawings.
In use, referring to the stabilizer of Figures 1 to 3, the end 14 of the tendon
tube 10 is located in the mouth of a predrilled hole of smaller diameter than
that of the major length of the tube 10. Using any of the conventional
method.s for locating split tube stabilizers, the tendon tube is pressed into
the hole until only the threaded end 12 of the stabilizer tube protrudes from
the hole in the rock face.
As the tube 10 is pressed into the hole the tapered wall of the tube end 14
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engag0s the mouth of the hole and continued penetration of the tube into
the hole under pressure causes the tube to be reduced in diameter by a
narrowing and even closure of the slot 16 against the resilience of the tube
material. The outward radial pressure generated by the resilience of the
tube metal frictionally anchors the tube over the untapered portion of its
length in the hole. A face washer 20, such as that illustrated in Figure 4, is
locatedl over the protruding end of the stabilizer tube and is held in place
on the l!ube by the domed stop 18 which is screwed up against the washer.
As is the case with many tube bolts or rock stabilizers of the above type,
either the holes in which they are located are slightly oversized or the
tubes are slightly ul ,Jar~i~eJ to reduce the radial gripping force of the tube
on the hole wall in which it is located to result in a far lower pull-out force
to extract the tube from the hole than the rock stabilizer was designed to
accomlmodate. Conventionally, this lower than design frictional gripping
force remains undetected with perhaps serious consequences for the
installaltion for which the stabilizer was specified. To check that the pull-
out force of the rock stabilizer of the invention is at or above specification
the stop 18, which may be flat sided or even hexagonal in plan, is pulled
up against the washer 20 by means of a suitable torque measuring device
to a palticulartorque at which the stabilizer should remain fully anchored
in the hole. Should the stabilizer, however, be pulled from the hole at below
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the pre!determined torque resistance level this will serve as an indication
that the stabilizer might not initially be able to resist and so hold the stressinduced fracturing and strain bursts in the rock in which it is located and
the effects of which it is intended at least to minimise.
In using the rock stabilizers of Figures 4 and 5 the tube hole of the face
washer 20 may be of such a dimension that the washer is trapped on the
stabilizer between the stop 18 and the major diameter portion of the tube
prior to the welding of the stop to the tube. The washer hole may
alternatively be large enough for the washer to slip over the tube 10 from
its end which does not carry the stop 18. These rock stabilizers are located
in the holes in which they are intended to be used in exactly the same
manner as described above with reference to the stabilizer of Figures 1 to
3. With these stabilizers the stops obviously cannot be moved on the
tendon tubes and the pressure of the washer 20 on the face surrounding
the hole when the tubes are finally located is dependent on the force with
which the tube was finally located in the hole.
The invention is not limited to the precise details as herein described. For
examplle the stop 18 need not necessarily be domed and could be in the
form ot a flat robust washer, nut or the like which is threadedly engaged
with or welded to the tube.
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From the above it will be appreciated that, unlike the prior art stabilizers,
the smaller diameter end portion 12 of the tendon tube will not be capable
of imposing any form of radial spalling pressure on the rock surrounding
the mouth of the hole as that portion of the tube is out of contact with the
hole at its mouth. Furthermore, the possibility of the outer end portion of
the stabilizer tube jamming in the mouth of the hole prior to full location of
the tube is entirely eliminated.
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