Note: Descriptions are shown in the official language in which they were submitted.
CA 02490111 2004-12-20
WO 2004/001192 PCT/AU2003/000760
ROCK BOLTING SYSTEM
Field of the Invention
The present invention relates to rock bolts, whether the bolt tendon is formed
from a
flexible cable or a rigid rod, the grout delivery tube for such bolts, and the
fabrication
of such tubes.
Background Art
Rock bolts are widely used in civil engineering and mining applications to
stabilise
rock strata.
Essentially a blind hole or bore is drilled in the rock and a rock bolt having
an anchor
at its far end is inserted into the hole. The anchor is operated so as to grip
the far end
of the hole and secure the bolt in the hole. The bolt is surrounded by a tube
and grout
is pumped into the gap between the bolt and the tube. The grout passes down
the tube
until it reaches the anchor and then begins to flow back out of the hole
between the
interior of the hole and the exterior of the tube. The operator ceases to pump
grout
when the returning grout is observed escaping from the hole. The grout hardens
and
provides a force transmitting structure between the interior of the hole and
the length
of the rock bolt. In this way the steel bolt can react effectively against any
movement
in the surrounding ground.
Object of the Invention
The object of the present invention is to provide an improved tube, a cable
bolt
incorporating the tube, bolt fittings and fabrication techniques all of which
together
constitute an improved rock bolting system.
Summary of the Invention
In accordance with the first aspect of the present invention there is
disclosed a tube for
cable or rod bolt applications, said tube being extruded from plastics
material and
deformed beyond its yield point at a plurality of longitudinally spaced apart
locations,
along the length of the tube, each said deformation occurring in at least two
different
directions.
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In accordance with the second aspect of the present invention there is
disclosed a rock
bolt having a tendon located within the above defined tube.
In accordance with a still further aspect of the present invention there is
disclosed an
end fitting for a rock bolt, said fitting comprising a barrel having a
substantially flat
front end, a rear end, a curved side wall, and a longitudinal axis, a cable
passageway
passing between said front and rear ends, and a grouting orifice extending
from said
front end into said cable passageway.
In accordance with a fourth aspect of the present invention there is disclosed
a method
of fabricating a tube for a rock bolt, said method comprising the step of
radially
deforming the side wall of said tube beyond its yield point in at least two
different
directions, at each of a plurality of longitudinally spaced locations.
In accordance with another aspect of the present invention there is disclosed
a rock
bolt for use in poor ground conditions, said bolt having a near end and a far
end,
anchor means at said far end to anchor the far end adjacent the base of a
blind hole
formed in said ground, and tension means at said near end to tension said bolt
after
said far end has been anchored, wherein said anchor means comprises at least
two
anchor devices, each known per se, and connected in series adjacent said far
end.
In accordance with a still further aspect of the present invention there is
disclosed a
method of securing a rock bolt in poor ground conditions, said method
comprising the
steps of:
providing at least two anchor devices, each known per se, at the far end of
said
rock bolt,
inserting said rock bolt into a blind hole drilled in said ground,
activating all said anchor devices, and
tensioning said rock bolt.
Preferably, following tensioning of the rock bolt, the bolt is surrounded with
grout.
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CA 02490111 2010-04-29
Application No. 2,490,111 Attorney Docket No. 27678-1
In accordance with a yet still further aspect of the present invention there
is disclosed
a tube for grouted rock bolts having either a cable tendon or a rod tendon,
the tube
being extruded from plastics material and deformed beyond its yield point at
each of a
plurality of longitudinally spaced apart locations extending along the length
of the
tube, the deformation at each location occurring in at least two different
directions to
create bulges in the tube to provide a mechanism to enable load transfer from
the rock
bolt to surrounding ground when grout is applied to the inside and outside of
the tube.
In accordance with a still further aspect of the present invention there is
disclosed
method of fabricating a tube for a grouted rock bolt, the method comprising
the step
of radially deforming the side wall of the tube beyond its yield point at each
of a
plurality of longitudinally spaced apart locations extending along the length
of the
tube, the deformation at each location occurring in at least two different
directions to
create bulges in the tube to provide a mechanism to enable load transfer from
the rock
bolt to surrounding ground when grout is applied to the inside and outside of
the tube.
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Brief Description of the Drawings
The prior art and the embodiments of the present invention will now be
described
with reference to the drawings in which,
Fig. 1 is an exploded perspective view of a prior art rock bolt prior to
installation,
Fig. 2 is longitudinal partly cross sectional view through the rock bolt of
Fig. 1
as installed,
Fig. 3 is a perspective view of the tube of the preferred embodiment,
Fig. 4 is an end view of the tube of Fig. 3,
Fig. 5 is a plan view of the tube of Fig. 3,
Fig. 6 is a side elevation of the tube of Fig. 3,
Fig. 7 is perspective view of the near end of a cable bolt incorporating the
tube
of Fig. 3-6,
Fig. 8 is a plan view of the cable bolt end of Fig. 7,
Fig. 9 is an end elevation of the arrangement of Figs. 7 and 8,
Fig. 10 is a longitudinal cross sectional view taken along the line X-X of
Fig.
9,
Fig. 11 is an end view of the free end of the cable bolt of Fig. 7,
Fig. 12 is a perspective view of another embodiment of the end fitting of the
cable bolt of Fig. 7,
Fig. 13 is an end view of the fitting of Fig. 12,
Fig. 14 is the opposite end view of the fitting of Fig. 12,
Fig. 15 is an alternative perspective view of the fitting of Fig. 12, and
Fig. 16 is a longitudinal partly cross-sectional view of the far end of a rock
bolt.
Figs. 1 and 2 illustrate a prior art rock bolt known as the "CT bolt" which is
generally
as described in Australian Patent No. 669,393 (Application No. 49856/93 and
WO 94/05900). The CT bolt 1 has a solid steel tendon 2 with an anchor 3
(illustrated
only in a general cylindrical form in Fig. 1) located at its far end. A tube 4
having a
plurality of papillae 13 surrounds the tendon 2 and the near end of the CT
bolt 1 has a
washer plate 5, a hollow dome ball 6, and nut 7.
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As seen in Fig. 2, a blind hole 8 is drilled in the ground 9 and the CT bolt
inserted
therein. The anchor 3 is expanded so that it grips the interior of the hole 8
thereby
locating the CT bolt 1 in its final position. The bolt can be tensioned by
means of the
nut 7 engaging a thread on the near end of the bolt. Then a flowable
hardenable
cementitious grout 10 is pumped into a small grout orifice 11 from where the
grout
passes between the tendon 2 and the interior of the tube 4. As the grout moves
down
the hole 8 between the tendon 2 and tube 4, air is being expelled from the
hole 8 by
passing between the interior of the hole 8 and the exterior of the tube 4.
Eventually
the grout 10 reaches the end of the hole 8 and the anchor 3 and then passes
between
the hole interior and the external surface of the tube 4. Eventually grout is
expelled
from the hole 8 adjacent the washer plate 5 indicating to the operator to
cease
pumping grout.
The purpose of small papillae 13 formed in the tube 4 is to provide a keying
mechanism to enable longitudinal shearing forces to be transferred between the
ground 9 and the tendon 2 by means of the grout 10.
Current methods of deforming the tube 4 involve processing the tube when it is
hot
and soft immediately after being formed and upon the tube exiting from the
plastic
extruder which creates the tube 4 from raw granular material. The tube in this
soft
and hot state enters another machine termed a "corrugator" which has a series
of
external moulds into which the tube is forced by compressed air from the
inside, or
vacuum applied from the outside, or both, so that the hot tube takes the shape
of the
moulds.
Such corrugatons are known to produce corrugated plastic drainage pipe and
corrugated swimming pool hose. Corrugated tube is known to be used in relation
to
rock bolts but suffers from a number of disadvantages. Firstly, the
corrugating
process is slow and therefore relatively expensive. Secondly, although the
corrugated
tubing has the advantage of being flexible and resistant to crushing, the
geometry of
corrugated tubing creates a number of disadvantages. In particular, the close
corrugations, extending in an annular fashion relative to the axis of the
tube,
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commonly trap air when the grout material is pumped therepast. These pockets
of
trapped air very substantially reduce the capacity of the tube to transfer
mechanical
loads. A similar problem is that the small amount of grouting material in the
annular
corrugations does not have the strength, because of its small mass and volume,
to
resist the shearing forces experienced in use. Therefore corrugated tube
easily shears
the grout from one annular deformation to the next.
In addition, the annular deformations of the corrugated tube catch on many
types of
objects during the installation procedure such as load plates, wire mesh, the
parts of
the installing machinery, and the like, all of which can lead to damage of the
tube. If
the corrugated tube is damaged the bolt can be uninstallable and/or unable to
be
grouted. This is because a hole in the tube will effectively "short circuit"
the grouting
procedure and result in grout not being delivered to the full length of the
hole.
Whilst the known corrugated tube is flexible, and thus is able to be looped
into a coil,
the tube 4 of Figs. 1-2 is not. This tube, for example fabricated for
installation in
45mm bore holes, is substantially round and has a diameter of approximately
35mm.
Each papilla 13 is formed as one of three outwardly extending bumps spaced
equally
around the tube at locations spaced apart by approximately 50mm along the
tube. The
maximum "diameter" of the tube at the location of the papillae is
approximately
42mm. The tube 4 is produced on a corrugator machine but without producing
corrugations. The tube is stiff and thus cannot be bent or coiled up as this
results in
the tube kinking and/or breaking. The papillae 13 on the tube 4 are also
susceptible to
being sheared off if the tube is handled roughly prior to installation.
The cost of the tube 4 is approximately three times the cost of similar tube
(so called
polytube made from high density polyethylene (HDPE)) used extensively in
irrigation
applications. It would therefore be desirable if this inexpensive tubing could
be used
for rock bolting applications.
Figs. 3-6 illustrate a deformed irrigation polytube 14 which has been deformed
in
such a way as to still retain its flexibility and thereby permit the polytube
14 to be
coiled or looped into a coil. The polytube 14 is deformed by being placed
between
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forming tools, which yield the material of the tube 14 in small areas. The
yielding
stops the material of the polytube 14 from returning to its original
configuration.
With reference to Fig. 3, in one embodiment, the tube 14 is compressed by
having
inwardly oppositely directed forces F1 and F2 applied to its "sides" whilst
substantially simultaneously two inwardly oppositely directed forces F3 and F4
are
applied to its "top" and "bottom" (spaced from but adjacent to the location of
the F1
and F2 forces) so as to create generally rectangular bulges 17 having
triangularly
shaped slopes 18.
Because the yielding zones 50 which create the bulges 17 are arranged in
sequential
fashion along the length of tube 14, these deformed patterns remain deformed
and
provide a mechanism to enable load transfer from the bolt to the surrounding
ground
via the grouting applied to both sides of the tube 14. In particular, the
shape of the
bulges 17 provide a number of advantages in that they reduce the occurrence of
damage prior to, or during, installation. Similarly, the shape of the bulges
17 reduces
the risk of air voids developing during the grouting operation.
Because the tube 14 thus deformed is able to be rolled into a coil, long
lengths of rock
bolt utilising steel cable as the rock bolt tendon, rather than solid steel
rod, are able to
be formed and also coiled prior to installation. This provides substantial
advantages
as regards packaging and handling of the bolts prior to installation. It also
allows
installation of long post grouted bolts in limited access areas.
Figs. 7-11 illustrate the near end of such a cable bolt, the far end being
substantially
conventional. As seen in Figs. 7-11, a cable bolt 21 has a cable 22 which
passes
through the polytube 14 and is provided with a barrel like end fitting 26 at
the near
end. The barrel 26 has a flat end face 28 and a domed front face 29 with a
substantially cylindrical side wall 30. A grouting orifice 31 is formed in the
end face
28 and, as seen in Fig. 10, leads into a grouting passage 32 which is inclined
to the
longitudinal axis of the polypipe 14 and cable 22.
In addition, the barrel 26 has a main passage 34 which includes a frusto-
conical
wedge 35 which acts a gripping mechanism for the cable 22. Thus the grouting
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passage 32 delivers grout above the cable gripping wedges 35 which hold the
barrel
26 to the cable 22.
That is, after the hole in the ground has been drilled, the far end of the
cable bolt 21
(not illustrated) is inserted into the hole and an anchor at the far end is
activated so as
to fix the far end of the bolt in the hole. Then the cable 22 can be placed
under
tension and the barrel 26 moved towards the far end until the barrel 26 comes
into
contact with a washer plate, or the like (not illustrated).
With the cable 22 thus tensioned, grout is able to be pumped through the
grouting
orifice 31 and grouting passage 32 into the interior of the polytube 14. The
grout then
travels along the length of the cable bolt 21, passes out the end of the
polytube 14 and
returns back towards the barrel 26 this time passing between the interior of
the hole
and the exterior of the polypipe 14.
It will be appreciated that the main passage 34 is not concentric with the
cylindrical
side wall 30 and thus at the near end of the cable bolt 1 the cable 22 is not
concentric
with the longitudinal axis of the tube 14.
Figs. 12-15 illustrate a second embodiment of a barrel 46 in which the front
face 39 is
flat. The end face 28 and grouting orifice 31 are substantially as before.
The foregoing describes only some embodiments of the present invention and
modifications, obvious to those skilled in the art, can be made thereto
without
departing from the scope of the present invention. For example, the bulges 17
in Figs.
3-10 extend in two directions which are substantially perpendicular to each
other. It is
also possible to arrange to have the bulges extend in three directions which
are
approximately 120 apart but that the longitudinally adjacent set of bulges
should be
rotated by 60 relative to the tube axis so that those bulges extend
intermediate the
bulges of the adjacent deformation. This is thought to assist shear load
transfer.
In addition, the end fitting or barrel 26, 46 (in addition to being relatively
inexpensive
to manufacture) can also be used in a cable or rod bolt without the outer
plastic tube 4,
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14. In this arrangement a breather tube passes through the grouting orifice 31
and
grouting passage 32 and then extends alongside the bolt to its far end. Under
this
arrangement grout is introduced between the bolt and hole and moves towards
the far
end of the hole but the air displaced by the grout is pushed out through the
breather
tube. Eventually the grout reaches the far end of the hole and then beings to
fill the
breather tube. The grouting process is stopped when the grout is seen
returning
through the breather tube.
Turning now to Fig. 16, the far end of a rock bolt 51 intended for use in poor
ground,
such as sandstone, is illustrated. In this particular embodiment the cable
tendon 52 is
formed from multistrand steel cable 22, but a solid tendon could equally be
used.
Mounted on the cable 22 are a pair of spaced apart conventional shell anchors
53 such
as those disclosed in Australian Patent Application No. 22992/02 which each
include
a restraining device in the form of a rupterable band 57. The anchors 53 are
able to be
expanded in known fashion by being spring loaded. In this way the two pivoted
halves of the anchors 53 pivot outwardly to grip the interior of the
surrounding blind
hole S.
The installation procedure is as follows. The rock bolt 51 is inserted fully
into the
blind hole S. The spring expansion shells grip the sandstone surrounding the
blind
hole 8 with sufficient combined force to enable the cable 22 to be tensioned.
Then the
entire hole 8 is grouted in a single operation. The entire operation takes
only a few
minutes.
This is to be contrasted with the previous procedure where, following
insertion of a
rock bolt in poor ground, a sophisticated grout delivery system was used to
grout only
the far end of the rock bolt. Only after this grout had cured was the rock
bolt
tensioned. Then the remainder of the bolt was grouted. This prior art process
took
several weeks.
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The foregoing describes only some embodiments of the present invention and
modifications, obvious to those skilled in the art, can be made thereto
without
departing from the scope of the present invention.
The term "comprising" (and its grammatical variations) is used in the sense of
"having" or "including" and not in the sense of "consisting only of'.
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