AU2006200094A1

AU2006200094A1 - Cable bolt

Info

Publication number: AU2006200094A1
Application number: AU2006200094A
Authority: AU
Inventors: Anthony Paul Steains
Original assignee: Jennmar Corp
Current assignee: FCI Holdings Delaware Inc
Priority date: 2003-11-20
Filing date: 2006-01-11
Publication date: 2007-07-26
Anticipated expiration: 2023-11-20
Also published as: AU2006200094B2

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Applicant: JENNMAR CORPORATION Invention Title: CABLE BOLT The following statement is a full description of this invention, including the best method of performing it known to us: 2 CABLE BOLT FIELD OF THE INVENTION The present invention relates to tensionable cable bolts suitable for cement grouted applications and in particular to tensionable cable bolts that are resin anchored prior to tensioning, tensioned, then post grouted with cement. However, it will be appreciated that the invention is not limited to this particular field of use and may also be applicable to other applications where an improved point anchor system is desirable.

BACKGROUND OF THE INVENTION 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 the common general knowledge in the field.

Known methods for reinforcing rock faces include the use of tensionable cable bolts that are configured to allow post tensioning grouting of the cable into a bore hole. These cable bolts are usually made from a plurality of steel filaments wound together to form a tendon. These tendons may also have a number of uniformly sized deformations in the form of, for example, "bulbs", "cages", "buttons" (sleeves), "swages" (rings or barrels that lock onto the cable using tapered cable gripping wedge elements) or other deformations along the length of the cable to provide improved anchorage and load transfer between the cable and the resin or cement grout and the strata. Bulbs and cages are formed by deforming at least some of the cable filaments so that they extend radially outwardly from the rest of the cable periphery. Buttons (sleeves) and swages are respectively crimped on and pressed on to the plain cable.

3 To facilitate post grouting of these types of cables, the bore holes must be oversized to thereby enable a breather tube and/or a grout tube to be inserted into the hole alongside the bolt and to allow the grout to flow freely into the bore.

However, prior to installing the cement grout, the cable bolt is first point anchored with resin at the distal end of the bore.

Point anchoring is achieved by locating a resin cartridge(s) in the closed end of the bore and then inserting and rotating the cable bolt to burst the resin cartridge(s) and mix its contents after which the mixed resin is allowed to cure. Once the resin is sufficiently set, the bolt is tensioned and cement grout can then be inserted, as required, in the remainder of the bore. Typically this is done by either inserting a grout tube to a location just below the point anchor so the grout enters from the top and displaces the air in the bore, or alternatively by filling from the end by inserting grout from adjacent the bore opening and displacing the air in the bore via a breather tube that has an opening just below the point anchor.

DISCLOSURE OF THE INVENTION According to a first aspect, the present invention provides a resin anchorable cable bolt adapted for use in pre-tensioned cement post grouting applications in a suitably sized bore, the cable bolt comprising: a cable formed from a plurality of wound coextending steel filaments, the cable having a first distal portion adapted primarily for resin point anchoring, and a second proximal portion adapted predominantly for cement grouting, the first portion including one or more radially outwardly extending resin mixing protrusions, and the second portion including one or more radially outwardly extending grout 4 engagable protrusions; and a resin retainer affixed to the cable between the first portion and the second portion, the retainer extending radially outwardly from the cable so as to substantially reduce the migration of resin from the first portion to the second portion within the bore; wherein in use the resin mixing protrusions are arranged to be disposed in close proximity to the wall of the bore and wherein a passage is provided that extends along at least a substantial part of the second portion to receive an air breather tube or grout tube so that the tube may be located within the bore in the passage.

The term resin mixing protrusion is not intended to limit the function of this feature to resin mixing, as such protrusions may also have the function of improving load transfer between the bolt and the resin.

In use the cable bolt is installed in a bore with an end part of the second portion of the cable bolt projecting from the bore opening. By incorporating the passage along the second portion, a cable bolt according to the first aspect of the present invention is configured to allow a breather tube and/or grout tube to be inserted into the bore without requiring that bore hole to be oversized along the first portion of the cable bolt. In this way, the resin mixing protrusions are arranged to be disposed in close proximity to the wall of the bore thereby ensuring that there is good mixing of the resin which is necessary to ensure the strength effectiveness of the point anchor. Furthermore, the second portion of the cable bolt includes the radially outwardly extending grout engageable protrusions which advantageously improve load transfer and pull-out strength effectiveness of the cable after grouting has occurred.

In one form, the passage extends along the entire length 5 of the second portion so as to enable a distal end of the tube to be disposed just below the resin retainer.

The cable bolt may be configured in different ways to provide the passage along the second portion.

In one embodiment, the grout engageable protrusions include apertures that form part of the passage. In this arrangement, the passage extends, at least in part, through the cable.

In another form, the resin mixing protrusions of the first portion are arranged to extend radially outwardly further than the grout engageable protrusions of the second portion. As the bore is typically formed of constant diameter, the passage for the air breather tube or grout tube may extend between the cable and bore wall with the gap between the wall of the bore and the grout engageable protrusions being part of the passage and being sufficiently wide to receive the air breather or grout tube.

According to a further aspect, the invention provides a resin anchorable cable bolt adapted for use in pre-tensioned cement post grouting applications in a suitably sized bore, the cable bolt comprising: a cable formed from a plurality of wound coextending steel filaments, the cable having a first distal portion adapted primarily for resin point anchoring, and a second proximal portion adapted predominantly for cement grouting, the first portion including one or more radially outwardly extending resin mixing protrusions, and the second portion including one or more radially outwardly extending grout engagable protrusions, the resin mixing protrusions of the first portion extending radially outwardly further than the grout engagable protrusions of the second portion; and a resin retainer affixed to the cable between the first portion and the second portion, the retainer extending radially 6outwardly from the cable so as to substantially reduce the migration of resin from the first portion to the second portion within the bore.

In accordance with this aspect, the different sizes of the protrusions allow the cable to be installed so that the resin mixing protrusions may be located in close proximity to the bore wall, whereas the grout engageable protrusions are spaced sufficiently from the bore wall to provide a passage along the second portion to enable an air breather or grout tube to extend along the second portion.

In any form of the invention described above, the breather or grout tube may be located in place after the resin anchorable cable is installed within the bore or alternatively the cable bolt may be provided with the breather or grout tube already fitted and affixed to the cable bolt.

In one arrangement where the tube is affixed to the cable bolt and where the resin mixing protrusions of the first portion extend radially outwardly further than the grout engageable protrusions, the tube is affixed to the cable and is disposed radially inwardly from an outermost point of the resin mixing protrusions.

In one form, a cover is arranged to extend about the distal end of the tube and arranged to inhibit the ingress of material into the end of the tube.

In a particular form, the cover forms part of the resin retainer. In a particular embodiment of this latter arrangement, the resin retainer comprises a sleeve portion, and a skirt that extends radially outwardly from the sleeve and along the cable so as to form the cover arranged to receive the end of the tube.

7- In one form, the resin retainer is affixed to the cable by crimping of the sleeve to the cable. However it is to be appreciated that the resin retainer may be affixed in any other form such as by welding or by capturing the retainer between stops provided on the cable which limit the movement of the resin retainer along the cable. These stops may be in the form of swages or other protrusions which extend radially outwardly from the cable.

In another form, the resin retainer may be of a simpler form and be provided in the form of a washer or other radially outwardly extending element which prevents the migration of resin from the first portion to the second portion.

In one form at least one of the resin mixing protrusions or the grout engagable protrusions are in the form of bulbs formed by spacing apart and forcing outwardly all of the steel filaments around the periphery of the cable. In a particular arrangement where the grout engageable protrusions are in the form of bulbs, these bulbs include means for retaining the bulb shape under tensile load. In one form these means are substantially incompressible objects (such as ball bearings) enclosed within the steel filaments of the bulbs.

In one form, at least one of the resin mixing protrusions or the grout engageable protrusion are spaced apart sleeves crimped along that length of the cable.

In one form where the grout engageable protrusions comprise a plurality of spaced sleeves clinched along the length of the cable, those sleeves include apertures to receive the air breather or grout tube so as to enable that tube to extend along the second portion of the cable bolt to locate just below the resin retainer.

In one form, the resin mixing protrusions or the grout r 8 engageable protrusions are in the form of nut cages, each having one or more nuts spaced along one or more central steel filaments with the remaining filaments wrapped around the periphery of the nut such that the nut is encased within a cage formed by the remaining steel filaments.

It will be appreciated that while preferred combinations of protrusions are discussed above, the invention is not limited to these particular embodiments and is equally applicable to different combinations of resin mixing and grout engagable protrusions not specifically disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Fig. 1 is a side view of a cable bolt; Fig. 2 is a detailed view to an enlarged scale of a bulb in a first portion of the cable bolt of Fig. 1; Fig. 3 is a detailed view of a resin retainer of the cable bolt of Fig. 1; Fig. 4 is a detailed view of bulb in a second portion of the cable bolt of Fig. 1; Fig. 5 is a schematic part view of the cable bolt of Fig.

1 installed in a bore; Fig. 6 is a variation of the cable bolt shown in Fig. with the breather tube removed; Fig. 7 is a variation of the cable bolt of Fig. 1; Fig. 8 is a further variation of the cable bolt of Fig. 1; Fig. 9 is yet a further variation of cable bolt of Fig. 1; and Fig. 10 is yet a further variation of a cable bolt of Fig. i.

-9- DETAILED DESCRIPTION As illustrated in Figs. 1 to 4, a resin anchorable cable bolt 10 comprises a cable 11 formed from a plurality of spiral wound coextending steel filaments 12 that extends between opposite ends (being, relative to the direction the bolt 10 is installed in a bore, a distal end 13 and a proximal end 14).

CThe cable 11 has a first portion 15 adapted primarily for ND resin point anchoring, and a second portion 16 adapted Spredominantly for cement grouting. The first portion includes a plurality (three in the illustrated case) of radially outwardly extending resin mixing protrusions 17. As best illustrated in Fig. 2, these protrusions 17 are in the form of bulbs formed by spacing apart and forcing outwardly all of the steel filaments 12 along a discrete section of the cable 11. Other types of protrusions may be used as is discussed below.

The second portion 16 includes a plurality of grout engagable protrusions 18. In a similar manner to the resin mixing protrusions 17, the grout engagable protrusions 18 extend radially outwardly and are formed by bulbing of the cable (as best illustrated in Fig. However the grout engagable protrusions extend radially outwardly to a lesser extent than the resin mixing protrusions 17. As will be explained in more detail below, this variation in the size of the protrusions (17, 18) provides a sufficient space to enable the cable bolt 10 to be installed in a bore 50 (see Fig. with a breather or grout tube 23 to extend along the second portion 16 without diminishing the effectiveness of the resin mixing protrusions 17 to adequately mix one or more resin cartridges to point anchor the cable bolt in the bore The grout engagable protrusions 18 incorporate substantially incompressible elements 19 disposed within the respective bulbs 18. In the illustrated form, these elements 0 6 10 are in the form of steel ball bearings, however it is to be appreciated that other elements may be used. The elements are designed to ensure that the grout engagable protrusions do not collapse on tensioning of the bolt 10 as will be discussed in more detail below.

The cable bolt 10 further comprises a resin retainer disposed between the first and second portions (15, 16) of the cable 11. The resin retainer is affixed to the cable 11 and extends radially outwardly from the cable so as to substantially reduce the migration of resin from the first portion to the second portion within the bore 50 during point anchoring of the bolt As best illustrated in Fig. 3, the resin retainer is typically formed from metal and comprises a sleeve portion 21, and a skirt 22 that extends radially outwardly from the sleeve and along the cable and is arranged to receive an end 24 of the tube 23 to inhibit the ingress of material into the end of the tube. To substantially prevent the migration of resin in the bore 50 from the first portion 15 to the second portion 16, the skirt 22 has a first flange portion 25 that projects substantially perpendicular to the axis of the cable bolt The flange 25 is ring shaped and extends out to be proximate to the bore wall 51 thereby providing a retaining face 26, which provides a very effective barrier to resin migration.

To affix the retainer 20 to the cable 11, in the illustrated form, the sleeve 21 is crimped to the cable.

However, it is to be appreciated that the fixing of the retainer 20 to the cable 11 could take many other forms such as welding, shrink fitting, by using mechanical fasteners or by capturing the retainer between stop elements disposed on the cable on opposite sides of the retainer The air breather or grout tube 23 extends along the J t

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11 second portion 16 of the cable 11, and is fixed in place by ties 27. These ties keep the tube against the surface of the cable. Further, the bolt, in the illustrated form, is configured so that the tube 23 stays approximately on line of the outermost point of the resin mixing protrusions 17. This is able to be achieved because of the different size of the resin mixing protrusions 17 as compared to the grout engagable protrusions 18.

As indicated above, one (distal) end 24 of the tube locates within the skirt 22 of the retainer 20. In the illustrated form, this end is chamfered at an angle of approximately 450 to ensure that access to the tube passage is not blocked by the tube end 24 bearing against the inner wall of the skirt 22.

The other end 28 of the tube 23 extends beyond the proximal end 14 of the cable bolt so that it can be open to atmosphere (when used as a breather tube), or connected to a grout pump line (not shown) in the case where the tube 23 is a grout tube.

Turning to Fig. 5, in use, the bore 50, typically of constant diameter along its length, is drilled into the rock strata. Resin cartridge(s) are inserted into the bore and are pushed to the closed end of the bore by the subsequent insertion of the cable bolt 10 into the bore 50. The amount of resin required will depend on the analysis of the rock strata on site. The bore is sized so that the resin mixing protrusions are in close proximity to the wall 51 of the bore As the grout engageable protrusions 18 do not extend as far out as the resin mixing protrusions, the second portion 16 of the bolt 10 is spaced sufficiently from the bore wall so that a passage 40 is provided between the cable 11 and the bore wall 51 to accommodate the tube 23 so that the tube is unlikely to snag against the bore wall 51.

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12 As an example, typical dimensions of the bolt 10 and bore that have been found by the Applicant to work satisfactory are as follows: Bore diameter 42mm Nominal cable diameter 21.8mm Resin mixing protrusion diameter 38mm Outer diameter of the resin retainer 38mm Grout engageable protrusions diameter 32mm Tube diameter 6mm With these dimensions, there is a 4mm clearance provided at the three widest points of the cable; being at the resin mixing protrusions, the resin retainer, and the grout engageable protrusions. Further, because of the attachment of the tube to the cable, the cable bolt is not symmetrical along the second portion. As such, the cable bolt does not locate perfectly along the centre line of the bore, but rather tends to have a wavy orientation where the bolt axis is slightly offset from the bore axis along parts of its length to accommodate the tube. This is not problematic as the cable is flexible and not rigid.

The first stage of fixing of the cable bolt 10 in the rock strata is to point anchor the bolt 10. To do this, the cable bolt 10 is further inserted into the bore to be forced into the resin cartridges, and rotated. This combined action causes the cartridge(s) to burst. Further rotation of the bolt allows the resin to mix and the protrusions 15 by being in close proximity to the bore wall ensure that there is effective mixing to cause curing of the resin.

After the cable bolt is point anchored by the resin, it can be tensioned. During tensioning of the cable 11, the grout engagable protrusions 18 are kept from straightening out by the ball bearings 19 disposed in the bulbs 18.

13 In a final stage of fixing the cable bolt to the rock strata, the second portion of the cable bolt is grouted in the bore. By having the end 24 of the tube just below the resin retainer allows the grout to be disposed along the entire length of the second portion thereby maximising the strength of the fixing. However, it is to be appreciated that the end 24 of the tube may be disposed proximal of the resin retainer but this would limit the ability to fully fill the bore up to the resin retainer.

In one process, grout is pumped from the bore opening, and air in the bore is able to escape through the breather tube. A plug (not shown) is typically inserted in the bore opening to keep the grout within the bore until it cures sufficiently.

In another process, grout is introduced in the tube and thereby fills the bore from the distal end 24 of the tube to the proximal end 14 of the bolt.

In one variation of the bolt 10, the breather tube 23 is not supplied affixed to the cable 11, but rather is inserted in the bore after the bolt is installed. This is possible because of the passage 40 between the cable 11 and the bore wall 51 provides a space to allow the tube 23 to be inserted.

This is best illustrated in Fig.6. As the cable may be of considerable length 8m or more), the threading of the tube into the bore with the cable bolt installed, may be difficult, even with the existence of the passage 40. As sch, to simplify the installation of the cable bolt 10, it is preferred to have the tube affixed to the cable prior to installation.

Other variations of the cable bolt 10 are illustrated in Figs.7 to 10. As these different embodiments share many of 14 the same features as the bolt 10, like features have been given like reference numerals. The main differences are in the formation of the protrusions 17, 18. These resin mixing and grout engaging protrusions may take many different forms other than bulbs including nut cages, swages and crimped sleeves known in the trade as "buttons".

Nut cages, as used in the first portion 16 of the bolt of Fig. 9, are formed by unwinding the steel filaments 12 of the cable 11, and sliding a nut 41 along one or more central steel filaments. The remaining filaments are then wrapped around the periphery of the nut, encasing it within a cage formed by the remaining steel filaments. Both the resin mixing protrusions 17 in the first portion 15 and the grout engagable protrusions 18 in the second portion 16 may be in the form of nut cages.

Alternatively, crimped buttons may form the grout engagable protrusions 18 on the second portion 16 as seen in Fig. 7. These are formed by crimping a plurality of spaced sleeves 42 securely along the length of the cable 11. The crimped buttons may also incorporate apertures 43 so as to provide part of the passage to pass the air breather tube or grout tube 23 to just below the resin retainer 20 as seen in Fig. Alternatively, crimped buttons may form the resin mixing protrusions 17 in the first portion 15 and smaller buttons may be used as the grout engagable protrusions 18 in the second portion 16 as seen in Fig. 8.

Alternatively, pressed on swages may form the protrusions in at least one of the first portion 15 and the grout engagable protrusions 18 in the second portion 16.

It will be appreciated that the illustrated cable bolts substantially reduces the risk of resin migrating from the 15 first portion to the second portion of the bore. Furthermore, the increased size of the deformations in the first portion in comparison to the second portion provides improved point anchoring by providing effective mixing of the resin due to the close proximity of the protrusions to the bore wall.

Additionally, by maintaining the integrity of the grout engagable protrusions after tensioning of the cable improves the load transfer between the grout and the cable, particularly where bulbs are used as the grout is able to penetrate into the bulb.

Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.

Claims

2. A cable bolt according to claim 1, wherein said resin mixing protrusions of said first portion extend radially outwardly further than said grout engagable protrusions of said second portion so that said passage extends between the cable and the wall of said bore.
3. A cable bolt according to claim i, wherein said grout engagable portions include apertures that form part of said passage.
4. A cable bolt according to any preceding claim, wherein the passage extends along the entire length of the 17 second portion so as to enable a distal end of the tube to be disposed just below the resin retainer. A cable bolt according to any preceding claim, further comprising a said breather or grout tube disposed in said passage.
6. A resin anchorable cable bolt adapted for use in pre-tensioned cement post grouting applications in a suitably sized bore, said cable bolt comprising: a cable formed from a plurality of wound coextending steel filaments, said cable having a first distal portion adapted primarily for resin point anchoring, and a second proximal portion adapted predominantly for cement grouting, said first portion including one or more radially outwardly extending resin mixing protrusions, and said second portion including one or more radially outwardly extending grout engagable protrusions, said resin mixing protrusions of said first portion extending radially outwardly further than said grout engagable protrusions of said second portion; and a resin retainer affixed to said cable between said first portion and said second portion, the retainer extending radially outwardly from said cable so as to substantially reduce the migration of resin from said first portion to said second portion within said bore.
7. A cable bolt according to either claim 2 or 6, further comprising a breather or grout tube extending about an outer surface of the second portion of the cable.
8. A cable bolt according to claim 7, wherein said tube is affixed to said cable and is disposed so that a radial outermost point of the tube aligns approximately with an outermost point of the resin mixing protrusions. A cable bolt according to any preceding claim, 18 wherein the resin retainer is affixed to the cable by any one or combination of crimping, welding, shrink fitting, by using mechanical fasteners, or by capturing the retainer between stops provided on the cable which limit the movement of the resin retainer along the cable. A cable bolt according to any preceding claim, further comprising a cover arranged to extend about the end of the tube and arranged to inhibit the ingress of material into the end of the tube.
11. A cable bolt according to claim 10, wherein the cover forms part of the resin retainer.
12. A cable bolt according to claim 11, wherein the resin retainer comprises a sleeve portion, and a skirt that extends radially outwardly from the sleeve and along the cable so as to form said cover arranged to receive the end of the tube to inhibit the ingress of material into the end of the tube.
13. A cable bolt according to claim 12, wherein the retainer is affixed to the cable by crimping of the sleeve to the cable, by welding, shrink fitting, by using mechanical fasteners, or by capturing the retainer between stops provided on the cable which limit the movement of the resin retainer along the cable.
14. A cable bolt according to any preceding claim, wherein at least one of said resin mixing protrusions or said grout engagable protrusions is in the form of bulbs formed by spacing apart and forcing outwardly all of said steel filaments around the periphery of the cable.
15. A cable bolt according to claim 14, wherein at least some of said bulbs form said grout engageable portions and include means for retaining the bulb shape 19 under tensile load.
16. A cable bolt according to claim 15, wherein said means is a substantially incompressible object enclosed within said steel filaments of said respective bulbs.
17. A cable bolt according to any preceding claim, wherein at least one of said resin mixing protrusions or said grout engagable protrusions is in the form of nut cages each having one or more nuts spaced along one or more central steel filaments with the remaining filaments wrapped around the periphery of said nut such that said nut is encased within a cage formed by said remaining steel filaments.
18. A cable bolt according to any preceding claim, wherein at least one of said resin mixing protrusions or said grout engagable protrusions are in the form of spaced sleeves crimped to the cable.
19. A cable bolt according to claim 18, wherein said grout engageable protrusions comprise a plurality of said spaced sleeves crimped along the length of said cable, said sleeves being adapted to receive a said air breather/grout tube so as to enable an end of that tube to locate just below said resin retainer. A cable bolt according to any preceding claim, wherein at least one of said resin mixing protrusions or said grout engagable protrusions is in the form of swages pressed on to the cable. 20
21. A cable bolt substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings and/or examples. Dated this llth day of January 2006 JENNMAR CORPORATION By its Patent Attorneys GRIFFITH HACK