AU2009201044B2

AU2009201044B2 - Cable bolt

Info

Publication number: AU2009201044B2
Application number: AU2009201044A
Authority: AU
Inventors: David William Evans
Original assignee: Dywidag Systems International Pty Ltd
Current assignee: DSI Underground Australia Pty Ltd
Priority date: 2008-03-20
Filing date: 2009-03-16
Publication date: 2015-10-01
Anticipated expiration: 2029-03-16
Also published as: AU2009201044A1

Abstract

A cable bolt (1) includes a cable (2) with a grout passage (16) longitudinally extending centrally through the cable (2) such that the strands (3) of the cable (2) are helically wound about the grout passage (16). An annular resin dam (7) is mounted on the cable (2) toward the cable leading end (2a). At least one grout hole (8) is located adjacent the resin dam (7) between the resin dam (7) and the cable trailing end (2b). Each grout hole (8) communicates the grout passage (16) with the exterior of the cable (2).

Description

S&F Ref: 898877 AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name and Address DYWIDAG-Systems International Pty Limited, of Applicant: an Australian company, ACN 093 424 349, of 25 Pacific Highway, Bennett's Green, New South Wales, 2290, Australia Actual Inventor(s): David William Evans Address for Service: Spruson & Ferguson St Martins Tower Level 35 31 Market Street Sydney NSW 2000 (CCN 3710000177) Invention Title: Cable bolt Associated Provisional Application Details: [33] Country: [31] Appl'n No(s): [32] Application Date: AU 2008901389 20 Mar 2008 The following statement is a full description of this invention, including the best method of performing it known to me/us: 5845c(2017362_1) CABLE BOLT Field of the Invention The present invention relates to strata control in civil engineering and mining 5 operations and in particular relates to a rock bolt (in the form of a cable bolt) for securing the roof or wall of a mine, tunnel or other ground excavation. Background of the Invention To secure the roof and/or walls of underground mines, tunnels and other ground to excavations, long flexible cable bolts (otherwise referred to as strand bolts) are often utilised. In one form of installation, each cable bolt is fixed into a bore hole drilled into a rock face with both a two-component resin and cement grout. A resin cartridge containing the two-component resin is first inserted into the bore hole, followed by the cable bolt which is driven into the hole to puncture the resin cartridge. The cable bolt is is rotated to mix the resin so as to secure the upper end of the cable bolt in the bore hole once the resin has set. The cable bolt is then pre-tensioned with a hydraulic jack and the trailing end of the cable bolt secured to the rock face at the opening of the bore hole utilising a barrel and wedge assembly. A cement grout is then injected into the annular cavity between the cable bolt and the wall of the bore hole. 20 In one cement grouting method, a grout tube is inserted into the bore hole only a short distance, such that the grout injected into the grout tube is pushed up through the annular cavity from adjacent the bore hole opening. To evacuate air from the bore hole while the cement grout is being pumped from the bottom, a breather tube (typically in the form of a small diameter plastic tube) is located in the annular cavity extending toward 25 the top of the bore hole. The bore hole must also be sealed at the rock face to ensure that the injected grout is pumped toward the top of the bore hole rather than merely escaping out through the bore hole opening. The breather tube is also subject to damage during installation, and requires a relatively large annular cavity between the cable bolt and bore hole wall for location of the breather tube. 30 In an alternate cement grouting method, the grout tube extends from the bore hole opening to adjacent the top of the bore hole, such that grout injected through the grout tube flows down through the full length of the bore hole. Utilising this method, no breather tube is required and there is no need to seal the bore hole opening in the rock face. A large diameter bore hole is, however, required to be drilled into the rock to house 35 the grout tube in the annular cavity between the cable bolt and bore hole wall. Such a 2 relatively large diameter hole is generally, however, not desired for anchoring the top portion of the cable bolt with resin as the annular cavity between the cable bolt and the bore hole should be as small as possible to achieve the best fixation of the cable bolt. A smaller annular cavity is also desired for effective load transfer between the cable bolt and bore hole wall via the cement grout. Grout tubes are typically strapped to the exterior of the cable bolt, and may be subject to damage during installation of the cable bolt. In an alternative form, the strands of the cable bolt are unwound and the grout tube is helically wound along the length of the cable bolt with the strands of the cable bolt prior to installation. This is, however, a complicated and costly exercise and may be subject to the grout tube collapsing during pre-tensioning of the cable bolt. Object of the Invention It is the object of the present invention to substantially overcome or at least ameliorate one or more of the above disadvantages. Summary of the Invention The present invention provides a cable bolt comprising: a cable longitudinally extending between a cable leading end and a cable trailing end and comprising a plurality of helically wound strands; a grout passage longitudinally extending centrally through said cable such that said strands are helically wound about said grout passage; an annular resin dam mounted on said cable towards said cable leading end; and at least one grout hole laterally extending through said cable adjacent said resin dam between said resin dam and said cable trailing end, each said grout hole being drilled through at least one of said strands and communicating said grout passage with an exterior of said cable. Typically, said cable bolt further comprises a grout tube defining said grout passage 2013628_2:PRW 2a Typically said cable bolt further comprises a plug sealing said grout passage at said cable leading end. In a preferred form, said cable bolt further comprises a drive head at said cable trailing end, said drive head having an aperture extending therethrough communicating with said grout passage. Typically, said drive head is threaded for coupling to a grout delivery device. In one form, said drive head is internally threaded. 2013628 2:PRW 3 In an alternate form, said drive head comprises a leading portion having a plurality of drive faces for engaging a drive device and an externally threaded trailing portion for coupling to the grout delivery device. Typically, said cable is welded about its periphery adjacent said at least one grout 5 hole. In a preferred form, said cable is welded about the entire said periphery adjacent said at least one grout hole at a first location between said at least one grout hole and said resin dam and a second location between said at least one grout hole and said cable trailing end. 10 In one form, said cable comprises a first set of said strands helically wound about said grout tube in a first direction and a second set of said strands helically wound about said first set of strands in an opposing second direction. Brief Description of the Drawings is Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings wherein: Figure 1 is a fragmentary front elevation view of a cable bolt assembly; Figure 2 is a fragmentary side elevation view of the cable bolt assembly of Figure 1; Figure 3 is a fragmentary perspective view from above of the cable bolt assembly of 20 Figure 1; Figure 4 is a fragmentary perspective view from below of the cable bolt assembly of Figure 1; Figure 5 is a fragmentary cross-sectional front elevation view of the cable bolt assembly of Figure 1; 25 Figure 6 is a cross-sectional end view of the cable and grout tube of the cable bolt assembly of Figure 1; Figure 7 is a fragmentary perspective view from below of an alternate cable bolt assembly; Figure 8 is a fragmentary cross-sectional front elevation view of the cable bolt 30 assembly of Figure 1 during a first stage of installation; and Figure 9 is a fragmentary cross-sectional front elevation view of the cable bolt assembly of Figure 1 during a second stage of installation.

4 Detailed Description of the Preferred Embodiments Referring to Figures 1 to 6, a cable bolt I includes a cable 2 that longitudinally extends between a cable leading end 2a and a cable trailing end 2b. The cable 2 comprises a plurality of helically wound high tensile steel strands. As best depicted in Figures 5 and 5 6, the cable 2 is formed with an inner first set of strands 3 wound in a first direction, and an outer second set of strands 4 helically wound about the first set of strands 3 in an opposing second direction. A grout passage 16 longitudinally extends centrally through the cable 2 from the cable trailing end 2b to the cable leading end 2a. Here the grout passage 16 is defined by 1o the interior wall of a grout tube 5 so as to avoid potential leakage of grout within the cable 2 and for ease of winding the strands. The first set of strands 3 is helically wound about the grout tube 5 (and thus about the grout passage 16). The grout tube 5 is typically formed of steel, but may alternatively be formed of plastic or various other materials for a cable 2 with a nominal outer diameter of 30mm, the diameter of the grout passage 16 may is be about 12.6mm with the grout tube 5 having a wall thickness of 0.8mm. Various other grout tube sizes are envisaged, however, adapted to suit specific applications. The grout passage 16 here opens on to the end face of the cable 2. To seal the grout passage 16 at the cable leading end 2a, an internal plug or cap 6 is fixed to the cable leading end 2a. An annular resin dam 7 is mounted on the cable 2 toward the cable leading end 2a. 20 The location of the resin dam 7 is selected to correspond to the desired length of cable 2 that is to be fixed to the rock strata with resin. Typically, the resin dam 7 would be mounted on the cable 2 a distance of about I m from the cable leading end 2a, however, this distance may be adjusted as desired to suit specific applications. The distance would typically be increased where greater pre-tensioning is desired prior to grouting. The resin 25 dam 7 has an outer diameter similar to the diameter of the bore hole to be drilled into the rock face being supported. The resin dam 7 is typically formed of steel. Alternately, the resin dam 7 may be formed of plastic, or a combination of both steel and plastic. In embodiments where the resin dam 7 is formed of steel, the outer diameter of the resin dam 7 will be approximately the same as, or slightly less, than the diameter of the bore 30 hole. Where the resin dam 7 is formed of a plastics material, the resin dam 7 would typically be slightly oversized so as to provide an interference fit with the wall of the bore hole. It is envisaged that the resin dam 7 may be in the form of a thin steel collar welded to the cable 2 backing and supporting a plastic seal facing the cable leading end 2a. At least one grout hole 8 is located adjacent the resin dam 7 between the resin dam 35 7 and the cable trailing end 2b extending laterally through the cable 2. In the cable bolt I 5 depicted, two opposing grout holes 8 are provided. The grout holes 8 are drilled through one or more of the strands of the cable 2, communicating the interior of the grout tube 5 with the exterior of the cable 2. The grout holes 8 will typically have a diameter of the order of 5 to 15mm when used with cables having an outer diameter of the order of 5 30mm, most typically in such an embodiment the grout holes will have a diameter of 10mm. To stabilise the cable in the vicinity of the grout holes whilst the grout hole 8 are being drilled, preventing the strands from splaying apart, and to further stabilise the cable 2 in this vicinity after drilling of the grout holes 8, the cable 2 is welded about its periphery adjacent the grout holes 8. Particularly, a first weld 9 is made about the entire to periphery of the cable 2 between the grout holes 8 and the resin dam 7 and a second weld 10 is made between the grout holes 8 and the cable trailing end 2b. The welds 9, 10 will typically be ground down so as to maintain a low profile against the peripheral surface of the cable 2, minimising any protrusion beyond the profile of the cable so as not to inhibit the flow of cement grout and provide a relatively clean annular cavity when installed for 15 load transfer between the cable 2 and rock strata. A drive head 11 is welded to the cable trailing end 2b. In the arrangement depicted, the drive head 11 is in the form of an internally threaded hexagonal nut with an aperture 12 extending therethrough that communicates with the grout passage 16. A standard barrel and wedge assembly 13 and plate washer 14 are mounted on the 20 cable 2 toward the cable trailing end 2b in the usual manner. An alternative form of drive head 11' is depicted in Figure 7. The drive head 1' is again welded to the cable trailing end 2b. The drive head 11' comprises a leading portion 17 in the form of a hexagonal nut having a plurality of drive faces 18 for engaging a drive device (installation dolly) and an externally threaded trailing portion 19 that is integrally 25 formed with the leading portion 17 for engaging a grout adapter. An aperture 12 again extends through the drive head 11' so as to communicate with the grout passage 16. The trailing portion 19 of the drive head 11' has a smaller cross-section than that of the leading portion 17, with the outer diameter of the trailing portion 19 being slightly smaller than the distance across the opposing flat drive faces 18 of the leading portion 17. This 30 allows the hexagonal socket of the installation dolly to pass over the trailing portion 19 unimpeded so it is able to engage the drive faces 18 of the leading portion 17 to rotate the cable bolt as discussed below. Rather than externally threading the trailing portion 19 of the drive head 11', suitable alternate forms of connection may be provided to connect the drive head to a grout adapter.

6 Installation of the cable bolt I will now be described with reference to Figures 8 and 9. Firstly referring to Figure 8, a bore hole 100 is drilled into a rock face to be supported in the usual manner. With the absence of an external grout tube, the bore hole 100 may be drilled with a diameter only about 4mm to 8mm larger than the diameter of the cable 2, 5 so as to leave an annular cavity 104 having a thickness of about 2 to 4mm between the cable 2 and the wall of the bore hole 100. A two component resin filled cartridge 102 is then inserted into the bore hole 100 and pushed toward the top thereof. The cable bolt 1 is mounted on a standard installation rig and inserted into the bore hole 100. The cable bolt I is rotated by engagement of the drive head 11 with the dolly of the installation rig 1o as the cable bolt 1 is driven upwardly through the bore hole 100, piercing the resin cartridge 102 as the cable bolt is advanced. Continuing rotation of the cable bolt 2 aids in mixing of the two component resin from the resin cartridge 102. Referring to Figure 7, the mixed resin 103 flows down the annular cavity 104 between the cable 2 and wall of the bore hole 100, however, the resin 103 is restricted to the upper portion of the annular is cavity 104 by virtue of the resin dam 7. The grout holes 8, located below the resin dam 7, thus remain clear of resin. The plug 6 also prevents resin from entering the interior of the grout tube 5. After mixing of the resin, rotation of the cable bolt I is stopped and the resin allowed to cure. The cable 2 is then tensioned in the usual manner by applying tension to the lower portion of the cable 2 via the hydraulic jack of the installation rig and 20 driving the barrel and wedge assembly 13 against the washer plate 14 and rock face 101 in the usual manner. After removal of the installation rig, a grout adapter is threaded into the internally threaded drive head 11, and cement grout 105 is pumped up through the interior of the grout tube 5 and out through the grout holes 8 into the lower part of the annular cavity 25 104 between the cable 2 and wall of the bore hole 100. Once the cement grout fills the annular cavity 104 and starts escaping through a hole 15 provided in the plate washer, pumping of the cement grout is stopped and the grout adapter removed from the drive head 11. A person skilled in the art will appreciate that various modifications of the cable 30 bolt specifically described above may be readily made.

Claims

1. A cable bolt comprising: a cable longitudinally extending between a cable leading end and a cable trailing end and comprising a plurality of helically wound strands; a grout passage longitudinally extending centrally through said cable such that said strands are helically wound about said grout passage; an annular resin dam mounted on said cable towards said cable leading end; and at least one grout hole laterally extending through said cable adjacent said resin dam between said resin dam and said cable trailing end, each said grout hole being drilled through at least one of said strands and communicating said grout passage with an exterior of said cable.

2. The cable bolt of claim 1 further comprising a grout tube defining said grout passage.

3. The cable bolt of either one of claims 1 and 2, further comprising a plug sealing said grout passage at said cable leading end.

4. The cable bolt of any one of the preceding claims, further comprising a drive head at said cable trailing end, said drive head having an aperture extending therethrough communicating with said grout passage.

5. The cable bolt of claim 4 wherein said drive head is threaded for coupling to a grout delivery device.

6. The cable bolt of claim 5 wherein said drive head is internally threaded.

7. The cable bolt of claim 5 wherein said drive head comprises a leading portion having a plurality of drive faces for engaging a drive device and an externally threaded trailing portion for coupling to the grout delivery device.

8. The cable bolt of any one of the preceding claims wherein said cable is welded about its periphery adjacent said at least one grout hole.

9. The cable bolt of claim 8 wherein said cable is welded about the entire said periphery adjacent said at least one grout hole at a first location between said at least one 70nr167R 7PRW 8 grout hole and said resin dam and a second location between said at least one grout hole and said cable trailing end.

10. The cable bolt of any one of claims I to 9 wherein said cable comprises a first 5 set of said strands helically wound about said grout tube in a first direction and a second set of said strands helically wound about said first set of strands in an opposing second direction.

11. A cable bolt substantially as hereinbefore described with reference to Figures 1o 1 to 6 or Figures 1 to 6 as modified by Figure 7. Dated 16 March, 2009 DYWIDAG-Systems International Pty Limited Patent Attorneys for the Applicant/Nominated Person SPRUSON & FERGUSON