U.S. patent application number 10/518340 was filed with the patent office on 2006-05-04 for rock bolting system.
This patent application is currently assigned to INDUSTRIAL ROLL FORMERS PTY LIMITED. Invention is credited to JeffreyR Fergusson.
Application Number | 20060093438 10/518340 |
Document ID | / |
Family ID | 3836668 |
Filed Date | 2006-05-04 |
United States Patent
Application |
20060093438 |
Kind Code |
A1 |
Fergusson; JeffreyR |
May 4, 2006 |
Rock bolting system
Abstract
The present invention discloses a tube (14) for rock bolts
having either a cable tendon or a rod tendon. The tube is deformed
to permit the tube to be coiled and yet also provide good keying
between the tube and grout. In addition, a fitting (26, 46) for the
rear end of the bolt is disclosed in which a grouting orifice (31)
communicates with a cable passageway (34). Furthermore, the use of
two or more cable anchors (57) at the far end of the bolt is
disclosed where the bolt is intended to be used in poor ground
conditions, such as sandstone.
Inventors: |
Fergusson; JeffreyR;
(Glenorie, AU) |
Correspondence
Address: |
CONNOLLY BOVE LODGE & HUTZ LLP
SUITE 800
1990 M STREET NW
WASHINGTON
DC
20036-3425
US
|
Assignee: |
INDUSTRIAL ROLL FORMERS PTY
LIMITED
8 TARLINGTON PLACE
SMITHFIELD
AU
2164
|
Family ID: |
3836668 |
Appl. No.: |
10/518340 |
Filed: |
June 20, 2003 |
PCT Filed: |
June 20, 2003 |
PCT NO: |
PCT/AU03/00760 |
371 Date: |
September 27, 2005 |
Current U.S.
Class: |
405/259.3 ;
405/259.1; 405/259.6 |
Current CPC
Class: |
E21D 20/02 20130101;
E21D 21/0046 20130101; E21D 21/0033 20130101; E21D 21/006
20160101 |
Class at
Publication: |
405/259.3 ;
405/259.1; 405/259.6 |
International
Class: |
E21D 21/00 20060101
E21D021/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 21, 2002 |
AU |
PS 3107 |
Claims
1. A tube for rock bolts having either a cable tendon or a rod
tendon, said 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, said deformation at each said location occurring in at
least two different directions.
2. The tube as claimed in claim 1 and deformed by inwardly directed
compression.
3. The tube as claimed in claim 2 wherein at each said location
said inwardly directed compression extends in two different
directions making an angle with each other.
4. The tube as claimed in claim 3 wherein said angle iS
substantially 90.degree..
5. The tube as claimed in claim 2 wherein at each said location
said inwardly directed compression extends in three different
directions.
6. The tube as claimed in claim 5 wherein the angle between said
three directions is approximately 120.degree..
7. The tube as claimed in claim 1 and able to be looped into a
coil.
8. The tube as claimed in claim 1 and fabricated from irrigation
water supply tube.
9. The tube as claimed in claim 1 and fabricated from high density
polyethylene (HDPE).
10. A rock bolt having a tendon located within a tube as claimed in
claim 1.
11. The cable bolt as claimed in claim 10 wherein said tendon is
formed from multi-strand steel cable and said bolt is looped into a
coil.
12. An end fitting for a rock bolt, said fitting comprising a
generally barrel-like shape having a front end, a rear end, a
curved side wall and a longitudinal axis, and said fitting further
having a tendon passageway extending between said front and rear
ends, and a grouting orifice in said front end and leading into
said cable passageway.
13. The fitting as claimed in claim 12 wherein said tendon
passageway includes a cable anchor.
14. The fitting as claimed in claim 13 wherein said cable anchor
includes a frusto-conical wedge.
15. The fitting as claimed in claim 12 wherein said front end is
substantially domed.
16. The fitting as claimed in claim 12 wherein said front end is
substantially flat.
17. The fitting as claimed in claim 1 wherein said rear end is
substantially flat.
18. The fitting as claimed in claim 17 wherein said substantially
flat rear end is substantially perpendicular to said longitudinal
axis.
19. 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 at each of a plurality of
longitudinally spaced apart locations extending along the length of
the tube, said deformation at each said location occurring in at
least two different directions.
20. The method as claimed in claim 19 including the step of
creating said deformation by inwardly directed compression.
21. The method as claimed in claim 20 including the step of: at
each said location inwardly directing said compression in two
different directions making an angle with each other.
22. The method as claimed in claim 21 wherein said angle is
substantially 90.degree..
23. The method as claimed in claim 20 including the step of: at
each said location inwardly directing said compression in three
different directions.
24. The method as claimed in claim 23 wherein the angle between
said three directions is approximately 120.degree..
25. 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 on said bolt adjacent said far end.
26. The rock bolt as claimed in claim 25 wherein said anchor
devices comprise shell anchors.
27. 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.
28. The method as claimed in claim 27 wherein following tensioning
of said rock bolt, said rock bolt is surrounded with grout.
Description
FIELD OF THE INVENTION
[0001] 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
[0002] Rock bolts are widely used in civil engineering and mining
applications to stabilise rock strata.
[0003] 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
[0004] 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
[0005] 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.
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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.
[0010] 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:
[0011] providing at least two anchor devices, each known per se, at
the far end of said rock bolt,
[0012] inserting said rock bolt into a blind hole drilled in said
ground,
[0013] activating all said anchor devices, and
[0014] tensioning said rock bolt.
[0015] Preferably, following tensioning of the rock bolt, the bolt
is surrounded with grout.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The prior art and the embodiments of the present invention
will now be described with reference to the drawings in which,
[0017] FIG. 1 is an exploded perspective view of a prior art rock
bolt prior to installation,
[0018] FIG. 2 is longitudinal partly cross sectional view through
the rock bolt of FIG. 1 as installed,
[0019] FIG. 3 is a perspective view of the tube of the preferred
embodiment,
[0020] FIG. 4 is an end view of the tube of FIG. 3,
[0021] FIG. 5 is a plan view of the tube of FIG. 3,
[0022] FIG. 6 is a side elevation of the tube of FIG. 3,
[0023] FIG. 7 is perspective view of the near end of a cable bolt
incorporating the tube of FIG. 3-6,
[0024] FIG. 8 is a plan view of the cable bolt end of FIG. 7,
[0025] FIG. 9 is an end elevation of the arrangement of FIGS. 7 and
8,
[0026] FIG. 10 is a longitudinal cross sectional view taken along
the line X-X of FIG. 9,
[0027] FIG. 11 is an end view of the free end of the cable bolt of
FIG. 7,
[0028] FIG. 12 is a perspective view of another embodiment of the
end fitting of the cable bolt of FIG. 7,
[0029] FIG. 13 is an end view of the fitting of FIG. 12,
[0030] FIG. 14 is the opposite end view of the fitting of FIG.
12,
[0031] FIG. 15 is an alternative perspective view of the fitting of
FIG. 12, and
[0032] FIG. 16 is a longitudinal partly cross-sectional view of the
far end of a rock bolt.
[0033] 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.
[0034] 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.
[0035] 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.
[0036] 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.
[0037] Such corrugators 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, 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.
[0038] 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.
[0039] 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 45 mm bore holes,
is substantially round and has a diameter of approximately 35 mm.
Each papilla 13 is formed as one of three outwardly extending bumps
spaced equally around the tube at locations spaced apart by
approximately 50 mm along the tube. The maximum "diameter" of the
tube at the location of the papillae is approximately 42 mm. 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.
[0040] 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.
[0041] 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 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.
[0042] 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.
[0043] 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.
[0044] 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.
[0045] 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 passage 32 delivers grout above
the cable gripping wedges 35 which hold the barrel 26 to the cable
22.
[0046] 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).
[0047] 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.
[0048] 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.
[0049] 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.
[0050] 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.degree. apart but that the
longitudinally adjacent set of bulges should be rotated by
60.degree. 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.
[0051] 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, 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.
[0052] 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.
[0053] 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 8.
[0054] The installation procedure is as follows. The rock bolt 51
is inserted fully into the blind hole 8. 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.
[0055] 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.
[0056] 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.
[0057] 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".
* * * * *