AU2014201857A1 - A tensionable cable bolt assembly - Google Patents

Abstract

A TENSIONABLE CABLE BOLT ASSEMBLY A tensionable cable bolt assembly (100) has a cable (110) longitudinally extending between a cable leading end (111) and a cable trailing end (112). A tensioning member (120) is mounted on the cable (110) toward the cable trailing end (112). The tensioning member (120) comprises an externally threaded, leading tubular element (121) and a trailing drive head (122) fixed in relation to the tubular element (121). The tensioning member (120) has a cable aperture (123) extending through the tubular element (121) and the drive head (122). The cable (110) extends through the cable aperture (123). An external member (130) is mounted on the tubular element (121). The external member (130) has an external member trailing face (132) and an external member leading face (131) adapted to engage a rim of a mine plate through which the cable (110) extends in use. The external member (130) has an internally threaded external member aperture (133) threadingly engaging the tubular element (121). A barrel and wedge assembly (150) is mounted on the cable (110) between the drive head (122) and the cable trailing end (112). The cable (110) is freely rotatable relative to the external member (130) and freely rotatable relative to the tensioning member (120), at least upon application of a predetermined torque.

Description

1 A TENSIONABLE CABLE BOLT ASSEMBLY Field [0001] The present invention relates to strata control in civil engineering and mining 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 [0002] To secure the roof and/or walls of underground mines, tunnels and other ground 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 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 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 fitted to the lower end of the cable bolt. The cable bolt may be pre-tensioned with an hydraulic jack that grips the end of the cable adjacent the barrel and wedge assembly. Alternatively, it has also previously been proposed to incorporate a threaded tensioning device within the design of the cable bolt assembly itself. Summary of Invention [0003] In a first aspect, the present invention provides a tensionable cable bolt assembly comprising: a cable longitudinally extending between a cable leading end and a cable trailing end; a tensioning member mounted on said cable toward said cable trailing end, said tensioning member comprising an externally threaded, leading tubular element and a trailing drive head fixed in relation to said tubular element, said tensioning member having a cable aperture extending through said tubular element and said drive head, said cable extending through said cable aperture; 2 an external member mounted on said tubular element, said external member having an external member trailing face and an external member leading face adapted to engage a rim of a mine plate through which said cable extends in use, said external member having an internally threaded external member aperture threadingly engaging said tubular element; and a barrel and wedge assembly mounted on said cable between said drive head and said cable trailing end; wherein said cable is freely rotatable relative to said tensioning member and said external member. [0004] In a preferred form, said cable bolt assembly further comprises a thrust bearing mounted on said cable between said drive head and said barrel and wedge assembly. [0005] The thrust bearing may be located within a recess provided in a trailing face of said drive head, said thrust bearing protruding beyond said trailing face of said drive head for engagement with a leading end of said barrel and wedge assembly. [0006] In a preferred form, said cable bolt assembly further comprises an anti-friction washer mounted on said tubular element and located between said external member trailing face and said drive head, said external member trailing face and said anti-friction washer protruding radially beyond said drive head. [0007] In a preferred form, said external member leading face is substantially semi-spherical. [0008] Typically, a leading end of said tubular element is located between said external member leading face and said cable leading end. [0009] In a preferred embodiment, said cable bolt assembly further comprises a mixing device fixed to said cable trailing end. [0010] In one form, said cable bolt assembly further comprises an elongate sleeve mounted on said cable and extending from said leading tubular element and a grout passage communicating an exterior of said drive head with an interior of said elongate sleeve.

3 [0011] Typically, said grout passage includes a grout port formed on an exterior drive face of said drive head. [0012] In a second aspect, the present invention provides a tensionable cable bolt assembly comprising: a cable longitudinally extending between a cable leading end and a cable trailing end; a tensioning member mounted on said cable toward said cable trailing end, said tensioning member comprising an externally threaded, leading tubular element and a trailing drive head fixed in relation to said tubular element, said tensioning member having a cable aperture extending through said tubular element and said drive head, said cable extending through said cable aperture; an external member mounted on said tubular element, said external member having an external member trailing face and an external member leading face adapted to engage a rim of a mine plate through which said cable extends in use, said external member having an internally threaded external member aperture threadingly engaging said tubular element; and a barrel and wedge assembly mounted on said cable between said drive head and said cable trailing end; wherein said cable is freely rotatable relative to said external member and freely rotatable relative to said tensioning member upon application of a predetermined torque. [0013] In one form, said assembly further comprises a locking means adapted to fix said tensioning member in relation to said cable until application of said predetermined torque upon which said locking means fails, allowing said tensioning member to freely rotate relative to said cable. [0014] Typically, said locking means comprise a shear pin extending between and into said tensioning member and said barrel and wedge assembly, said shear pin being configured to fail upon application of said predetermined torque. [0015] In a preferred form, said cable bolt assembly further comprises a thrust bearing mounted on said cable between said drive head and said barrel and wedge assembly.

4 [0016] The thrust bearing may be located within a recess provided in a trailing face of said drive head. [0017] In a preferred form, said cable bolt assembly further comprises an anti-friction washer mounted on said tubular element and located between said external member trailing face and said drive head, said external member trailing face and said anti-friction washer protruding radially beyond said drive head. [0018] In a preferred form, said external member leading face is substantially semi-spherical. [0019] Typically, a leading end of said tubular element is located between said external member leading face and said cable leading end. Brief Description of Drawings [0020] Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings wherein: [0021] Figure 1 is a front elevation view of a cable bolt assembly according to a first embodiment; [0022] Figure 2 is a partially cross-sectioned front elevation view of the cable bolt assembly of Figure 1; [0023] Figure 3 is a perspective view of the cable bolt assembly of Figure 1; [0024] Figure 4 is a partially cross-sectioned perspective view of the cable bolt assembly of Figure 1; [0025] Figure 5 is a partially cross-sectioned view of a partially complete cable bolt installation utilising the cable bolt assembly of Figure 1, immediately prior to rupture of a resin cartridge; [0026] Figure 6 is a partially cross-sectioned view of the cable bolt installation of Figure 5 during tensioning of the cable; 5 [0027] Figure 7 is a partially cross-sectioned view of the cable bolt installation of Figure 5 following completion of the installation; [0028] Figure 8 is a perspective view from above of a two stage dolly, in a first operative position, for an alternate means of installing the cable bolt assembly of Figure 1; [0029] Figure 9 is a perspective view from below of the two stage dolly of Figure 8 in the first operative position; [0030] Figure 10 is a perspective view from above of the two stage dolly of Figure 8 in a second operative position; [0031] Figure 11 is a perspective view from below of the two stage dolly of Figure 8 in the second operative position; [0032] Figure 12 is a cross-sectional view of the insert of the two stage dolly of Figure 8; [0033] Figure 13 is a partially cross-sectioned front elevation view of a cable bolt assembly according to a second embodiment; [0034] Figure 14 is a perspective view of the cable bolt assembly of Figure 13; [0035] Figure 15 is a partially cross-sectioned perspective view of the cable bolt assembly of Figure 13; [0036] Figure 16 is a front elevation view of a cable bolt assembly according to a third embodiment; [0037] Figure 17 is a partially cross-sectioned front elevation view of the cable bolt assembly of Figure 16; [0038] Figure 18 is a perspective view of the cable bolt assembly of Figure 16; [0039] Figure 19 is a partially cross-sectioned perspective view of the cable bolt assembly of Figure 7; 6 [0040] Figure 20 is a partially cross-sectioned view of a partially complete cable bolt installation utilising the cable bolt assembly of Figure 16, immediately prior to rupture of a resin cartridge; [0041] Figure 21 is a partially cross-sectioned view of the cable bolt installation of Figure 20 during tensioning of the cable; [0042] Figure 22 is a partially cross-sectioned view of the cable bolt installation of Figure 20 following completion of the installation; [0043] Figure 23 is a fragmentary partially cross-sectioned view of a partially complete cable bolt installation utilizing a cable bolt assembly according to a fourth embodiment; and [0044] Figure 24 is a fragmentary further partially cross-sectioned view of the cable bolt installation of Figure 23. Description of Embodiments [0045] Referring to Figures 1 to 4 of the accompanying drawings, a cable bolt assembly 100 according to a first embodiment has a cable 110 longitudinally extending between a cable leading end 111 and a cable trailing end 112. In the usual manner, the cable 110 will typically be formed of a plurality of steel wires helically wound about a central steel king wire. A mixing device 113, here in the form of a rectangular prism defining four drive faces 114, is fixed to the cable trailing end 112, here by welding. The mixing device 113 has a transverse cross-section that fits entirely within the periphery of the cable 110, thereby allowing the remaining components of the cable bolt assembly 100 to be readily assembled onto the cable 110 from the cable trailing end 112. [0046] The cable bolt assembly 100 further comprises a tensioning member 120 mounted on the cable 110, toward the cable trailing end 112. The tensioning member 120 comprises an externally threaded leading, tubular element 121 and a trailing drive head 122 that is fixed in relation to the tubular element 121. The drive head 122 may be integrally formed with the tubular element 121, or otherwise fixed to the tubular element 121, for example by welding. A cable aperture 123 extends through the length of the tensioning member 120, through the tubular 7 element 121 and drive head 122. The cable 110 extends through the cable aperture 123, which is sized slightly larger than the diameter of the cable 110 to allow the cable 110 to freely rotate in the cable aperture 123 relative to the tensioning member. In the arrangement depicted, the external thread on the tubular element 121 is a left hand thread, extending along the full length of the tubular element 121. The drive head 122 is here in the form of a hexagonal drive head defining six drive faces 124. [0047] The cable bolt assembly 100 further comprises an external member 130 mounted on the tubular element 121. The external member 130 is mounted on the tubular element 121 such that the tubular element 121 extends through the external member 130 with the tubular element leading end 127 located between the external member 130 and the cable leading end 111. The external member 130 has an external member leading face 131 that is adapted to engage the rim 141 of a standard domed mine plate 140 through which the cable 110 extends in use. In the particular arrangement depicted, the external member 130 is a standard dome washer, having a generally semi-spherical external member leading face 131. The external member 130 also has an external member trailing face 132 that is here generally planar. The external member 130 has an internally threaded external member aperture 133 which threadingly engages the tubular element 121 by way of the external thread of the tubular element 121. The internal thread of the external member aperture 133 is thus like-handed to the external thread of the tubular element 121, being a left-handed thread in the arrangement depicted. [0048] A standard barrel and wedge assembly 150 is mounted on the cable 110 between the drive head 122 and the cable trailing end 112. The barrel and wedge assembly 150 is of standard configuration, comprising a barrel 151 defining a frusto-conical barrel aperture 152 in which are mounted a plurality of wedge elements 153 which grip the cable 110. The barrel and wedge assembly 150 will typically be preloaded on the cable 110 such that the barrel 151 firmly engages the wedge elements 153 to hold the barrel and wedge assembly 150 in place on the cable 110. [0049] In the arrangement depicted, the cable bolt assembly 100 further comprises a thrust bearing 160 mounted on the cable 110 between the drive head 122 and barrel and wedge assembly 150. The thrust bearing 160 allows the transfer of compressive load between the drive head 122 and barrel and wedge assembly 150 while still allowing free relative rotation therebetween without transferring any significant torque load. Here the thrust bearing 160 is 8 located within a recess 125 defined in the trailing face 126 of the drive head 122. The thrust bearing 160 protrudes beyond the trailing face 126 of the drive head 122 such that it is able to engage with the leading end of the barrel and wedge assembly 150. Locating the thrust bearing 160 within the recess 125 assists in preventing the thrust bearing 160 from becoming clogged with foreign matter within the mine environment and also retains the ball elements of the thrust bearing 160 captive in the event that the thrust bearing 160 fails. [0050] An anti-friction washer 170 is also mounted on the tubular element 121 and located between the external member trailing face 132 and drive head 122. The anti-friction washer 170 and external member trailing face 132 radially project beyond the drive head 122 (as best depicted in Figure 4), allowing a dolly to transfer a thrust load to the external member 130 via the anti-friction washer 170 during installation as will be discussed below. [0051] Installation of the cable bolt assembly 100, according to a first method of installation utilising two separate dollys, will now be described with reference to Figures 5 through 7 of the accompanying drawings. [0052] Firstly referring to Figure 5, a bore hole 200 is first drilled through a rock face 201 into a strata 202 to be secured by the cable bolt assembly 100. The bore hole 200 is drilled with an oversized bore hole section 203 adjacent the rock face 201 for accommodation of the tubular element 121. A standard frangible resin cartridge 210 housing a two-component resin is then inserted into the bore hole 200, followed by the cable 110 with the cable leading end 111 leading. The cable bolt assembly 100 is installed into the bore hole 200 by way of a first dolly 220 having a square sectioned socket 221 sized to receive the mixing device 113 and engage the drive faces 114. The first dolly 220 is rotated as it thrusts the cable 110 toward the top of the bore hole 200, such that the cable 110 rotates as it advances, puncturing and shredding the resin filled cartridge 210 and mixing the two-component resin 211. In the usual manner, the two component resin 211 fills the leading end of the bore hole 200 in the annulus defined between the wall of the bore hole 200 and the leading portion of the cable 110. [0053] The barrel and wedge assembly 150 rotates with the cable 110, however the thrust bearing 160 and the clearance between the cable 110 and the cable aperture 123 prevents any significant torque being applied to the tension member 120. Whilst some small transfer of torque may result in the tension member 120 rotating to some degree, some inevitable 9 interference with the wall of the oversized bore hole section 203 will typically result in the tension member 120 not rotating during the mixing process. Friction between the external member 130 and rim 141 of the mine plate 140, resulting from the axial load applied by the first dolly 220, will also typically be sufficient to prevent the external member 130 rotating during the mixing process. [0054] Rotation of the first dolly 220 is then stopped, allowing the resin 211 to set. [0055] As depicted in Figure 6, a second dolly 230, having a hexagonal socket 231 sized to receive and engage the hexagonal drive head 122 is then mounted over the trailing end of the cable bolt assembly 100, with the hexagonal socket 231 engaging the drive faces 124 of the drive head 122. Initial upward thrust is applied to the second dolly 230 such that the leading end of the second dolly 230 engages the radially protruding portion of the anti-friction washer 170 which in turn engages the external member trailing face 132. The thrust load is thus transferred to the external member 130 to provide initial engagement between the external thread of the tubular element 121 and the internal thread of the external member 130. The anti-friction washer 170 reduces the friction that would otherwise exist between the second dolly 230 and the external member trailing face 132 upon rotation of the second dolly 132. The second dolly 230 is then rotated to drive the drive head 122, drawing the tensioning member 120 rearwardly in relation to the external member 130, with which it is threadingly engaged. Friction between the external member 130 and rim 141 of the mine plate 140 again generally prevents the external member 140 from rotating with the tubular element 121, thereby allowing the tubular element 121 to retract through the external member 130 as the second dolly 230 is rotated. The clearance fit of the cable 110 in the cable aperture 123 also prevents the tensioning member 120 from applying any significant torque to the cable 110. The drive head 122 acts through the thrust bearing 160 to draw the barrel and wedge assembly 150 rearwardly. The standard reverse taper configuration of the barrel 151 and wedge elements 152 ensure that the barrel and wedge 150 remains firmly affixed to the cable 110 under this load and, therefore, acts to pre-tension the cable 110. [0056] The second dolly 230 continues to rotate until the desired degree of pre-tension in the cable 110 is achieved, following which the second dolly 230 is removed, leaving the completed cable bolt installation as depicted in Figure 7. Pre-tensions of the order of 10 tonne would be typical. As can be seen from a comparison of Figures 6 and 7, at the beginning of the pre- 10 tension process the tubular element 121 extends well through the external member 130 and mine plate 140 into the oversized bore hole section 203, with the drive head 122 bearing against the anti-friction washer 170 which, in turn, bears against the external member 130. Following pre tensioning by retraction of the tensioning member 120, however, the bulk of the tubular element 121 can be seen to extend rearwardly of the external member 130, leaving a gap between the external member 130 and the drive head 122. [0057] The entire tensioning process does not rely on the application of any torque to the cable 110, as is the case with one or more previously proposed methods. [0058] Rather than utilising two separate dollies 220, 230 as described above, the cable bolt assembly 100 may alternately be installed utilising a two stage dolly 250 as depicted in Figures 8 through 12. The two stage dolly comprises a shank 251 configured to be mounted in a standard rotary cable installation drive, a hollow body 252 and an insert 253 mounted in the hollow body 252. At its leading open end 252a the interior face of the body 252 is configured as a hexagonal drive socket 254 sized to engage the drive faces 124 of the drive head 122 of the cable bolt assembly 100. The insert 253 has a recess 254 in its leading face 253a sized to receive the cable trailing end 112. The recess communicates with a square drive socket 255, opening onto the insert trailing face 253b, which is sized to engage the drive faces 114 of the mixing device 113 of the cable bolt assembly 100. The insert 254 is displaceable through the body 252, with such displacement being guided by way of a cam member 256 that protrudes from the side wall of the insert 253 and engages a cam slot 257 formed in the side wall of the body 252. The slot 257 has a laterally extending slot first portion 258 at its leading end 257a which communicates with a longitudinally extending slot second portion 259. The slot second portion 259 extends to the slot lower end 257b adjacent the closed lower end 252b of the body 252. [0059] During installation of the cable bolt assembly 100, the insert 253 is located in a first operative position, depicted n Figures 8 and 9, with the cam member 256 engaging the slot upper end 257a within the slot first portion 258. The socket 252 is placed over the mixing device 113 and cable trailing end 112 with the mixing device 113 engaged in the square drive socket 255. In this first operative position, the socket 252 does not engage the tensioning member 120.

11 [0060] The cable bolt assembly 100, mounted on the two stage dolly 250, is then installed into the bore hole 200. The two stage dolly 250 is then rotated in a clockwise direction during this first stage of installation, such that the cam member 256 remains seated against the slot upper end 257a, thereby retaining the insert 253 in its first operative position and allowing for transmission of torque from the socket 252 to the insert 253. The two stage dolly 250 thrusts the cable 110 towards the top of the bore hole 200, as it is rotated, puncturing and shredding the resin filled cartridge 210 and mixing the two-component resin in the manner described above. As with the installation method described above, the barrel and wedge assembly 150 rotates with the cable 110 at this stage. The thrust applied to the cable bolt lower end 112 via the insert 153 during resin mixing ensures that the external member 130 and mine plate 140 are located hard up against the rock face 201. However the thrust bearing 160 and the clearance between the cable 110 and cable aperture 123 prevents any significant torque being applied to the tension member 120. [0061] Rotation of the two stage dolly 250 is then stopped, allowing the resin 211 to set. [0062] The two stage dolly 250 is then rotated in the reverse anti-clockwise direction, which initially results in the cam member 256 to being displaced along the slot first portion 258, along and into the slot second portion 259, allowing the cam member 256 to drop down to the slot second end 257b, corresponding to the second operative position of the insert 253 depicted in Figures 10 and 11. As the insert 253 moves towards the second operative position adjacent the body lower end 252b, the body 252 advances over the cable bolt assembly 100 such that the hexagonal drive socket 254 engages the drive faces 124 of the drive head 122. Further rotation of the two stage dolly 250 results in rotation of the drive head 122 drawing the tensioning member 120 rearwardly in relation to the external member 130 in the same manner as that described above in relation to the first method of installation, thereby pre-tensioning the cable. [0063] Referring to Figures 13 to 15, a cable bolt assembly 300 according to a second embodiment is depicted. The cable bolt assembly 300 is particularly suited for applications where post grouting is desired. Features of the cable bolt assembly 300 that are identical to those of the cable bolt assembly 100 are provided with an identical reference numeral, whereas equivalent features are provided with the same reference numeral to that of the first embodiment, increased by 200.

12 [0064] The cable bolt assembly 300 has a cable 310 of the same basic construction as that described above in relation to the first embodiment, and longitudinally extending between a cable leading end 311 and a cable trailing end 312. The cable 310 has a series of three bulbs 315 formed towards the cable leading end 311 in a known manner. First and second ferrules 316, 317 are crimped on to the cable 310, leading and trailing the series of three bulbs 315 respectively. The second ferrule 317 also acts as a resin dam to inhibit the flow of resin through the annular cavity defined between the cable 310 and the wall of the bore hole 200 in use. A mixing device 113 defining four drive faces 114 is fixed to the cable trailing end 112. [0065] The cable bolt assembly 300 further comprises a tensioning member 320 of the same basic form as the tensioning member 120 described above in relation to the first embodiment. The tensioning member 320 is mounted on the cable 310, towards the cable trailing end 312. The tensioning member 320 comprises an externally threaded leading, tubular element 321 and a trailing drive head 322 that is fixed in relation to the tubular element 321. In the arrangement depicted, the drive head 322 is integrally formed with the tubular element 321. A cable aperture 323 extends through the length of the tensioning member 320, through the tubular element 321 and drive head 322. The cable 310 extends through the cable aperture 323. The cable aperture 323 is sized larger than the diameter of the cable 310 so as to allow the cable 310 to freely rotate in the cable aperture 323 relative to the tensioning member 320 and to define, in part, a grout passage 328 communicating the tubular element leading end 327 and the exterior of the drive head 322. For example, for a 23.5 mm diameter cable 310, the cable aperture 323 may suitably have a diameter of approximately 32 mm. [0066] In the arrangement depicted, the grout passage 328 is further defined by a grout port 329 formed in an exterior surface of the drive head 322, and particularly in one of the six drive faces 324 of the hexagonal drive head 322. The grout port 329 is adapted to receive a grout delivery tube. An annular seal 380 is located in the cable aperture 323 immediately aft of the grout port 329 and sized to lightly engage the cable 310, so as to inhibit passage of grout past the annular seal 360, while still allowing free rotation of the tensioning member 320 relative to the cable 310. In the arrangement depicted, the external thread on the tubular element 321 is a left-hand thread extending along the full length of the tubular element 321.

13 [0067] As with the first embodiment, the cable bolt assembly 300 further comprises a thrust bearing 160 mounted on the cable 310 between the drive head 322 and a barrel and wedge assembly 350. The thrust bearing 160 is located within a recess 325 defined in the trailing face 326 of the drive head 322, with the leading end of the recess 325 being defined by the annular seal 380. The thrust bearing 160 has a longitudinal depth equal to that of the recess 325, such that it is substantially flush with the base of the recess 325. Again as with the first embodiment, a standard barrel and wedge assembly 150, comprising a barrel 151 and wedge elements 153, is mounted on the cable 310 between the drive head 322 and the cable trailing end 112. [0068] The cable bolt assembly 300 further comprises an external member 130 mounted on the tubular element 321 as described above in relation to the first embodiment, having an external member leading face 131 adapted to engage the rim 141 of the standard domed mine plate 140 through which the cable 310 extends in use. As described above in relation to the first embodiment, the external member 130 has an external member trailing face 132 that is generally planar and an internally threaded external member aperture 133 which threadingly engages the tubular element 321 by way of the external thread of the tubular element 321. An anti-friction washer 170, as also described above in relation to the first embodiment, is also mounted on the tubular element 321 and located between the external member trailing face 132 and drive head 322. The anti-friction washer 170 and external member trailing face 132 radially project beyond the drive head 324, allowing a dolly to transfer a thrust load to the external member 130 via the anti-friction washer 170 during installation as discussed above in relation to the first embodiment. [0069] An elongate plastic sheath 390 is mounted on the cable 310 and is fixed to and extends from the tubular element leading end 327. The grout passage 328 communicates the interior of the sheath 390 with the exterior of the drive head 322 via the grout port 329. [0070] The initial phases of installation of the cable bolt assembly 300 are as described above in relation to the cable bolt assembly 100 of the first embodiment, either utilising the first and second dollys 220, 230 described in relation to Figures 5 to 7, or the two stage dolly 250 described in relation to Figures 8 to 12. During the pre-tensioning phase of installation, either the second dolly 230 or hexagonal socket 254 of the two stage dolly 250 engage the drive faces 324 of the drive head 322.

14 [0071] Following pre-tensioning, the cable bolt installation may be post grouted by injecting cementitious grout through the grout port 329, up the grout passage 328 and along the interior of the elongate sheath 390, then back down the annular cavity defined between the elongate sheath 390 and the wall of the bore hole 200. Injection of grout is ceased once evidence of the grout having flowed down to the opening of the bore hole 200 is noted. The annular seal 380, being located between the grout port 329 and the barrel and wedge assembly 150, ensures that the grout does not flow into, and potentially foul, the barrel and wedge assembly 150. [0072] Referring to Figures 16 to 19, a cable bolt assembly 400 according to a third embodiment is depicted. The cable bolt assembly 400 is again particularly suited for applications where post grouting is desired. Features of the cable bolt assembly 400 that are identical to those of the cable bolt assembly 300 of the second embodiment are provided with an identical reference numeral, whereas equivalent features are provided with the same reference numeral to that of the first embodiment, increased by 100. [0073] The cable bolt assembly 400 differs from the cable bolt assembly 300 primarily by omitting the mixing device 113 and providing a modified form of tensioning member 420 and barrel and wedge assembly 450 with a shear pin arrangement used to fix the tensioning member 420 in relation to the cable 310 for the purposes of mixing the resin during the initial stages of installation. The cable bolt assembly 400 of the third embodiment is otherwise identical to the cable bolt assembly 300 of the second embodiment. [0074] The barrel and wedge assembly 450 is of a standard configuration as described above in relation to the first embodiment, except that the leading end portion 45 1a of the barrel 451 has a reduced diameter enabling the leading portion 45 1a to fit within the recess 425 and engage the trailing end of the thrust bearing 160, which here has a shorter longitudinal depth than that of the recess 425 such that it remains recessed within the recess 425. The recess 425 is formed deeper than the recess 325 of the tensioning member 320 of the cable bolt assembly 300 of the second embodiment. The wedge elements 453 of the barrel and wedge assembly 450 are of standard configuration. The barrel and wedge assembly 450 is fixed in relation to the cable 310 in the usual manner.

15 [0075] The leading portion 451a of the barrel 451 is provided with a radially extending aperture 454 that is alignable with a radially extending aperture 455 formed adjacent the trailing face 426 of the drive head 422. [0076] A shear pin 456 extends through the apertures 454 and 455 so as to lock the tensioning member 420 relative to the barrel and wedge assembly 450 and, thereby, fixes the tensioning member 420 in relation to the cable 310. The shear pin 456 is configured to fail upon application of a predetermined torque, which would typically be of the order of 200 - 340 Nm, thereby allowing the tensioning member 420 to freely rotate relative to the barrel and wedge assembly 450 and cable 310. The shear pin 456 thus acts as a locking means which may also take various other known forms. [0077] Installation of the cable bolt assembly 400 will now be described with reference to Figures 20 to 22 of the accompanying drawings. [0078] A bore hole 200 with an oversized bore hole section 203 adjacent the rock face 201 is drilled in the rock strata 202 in the same manner as described above in relation to the first embodiment. The resin cartridge 210 is then inserted into the bore hole 200, followed by the cable 310 with the cable leading end 311 leading. [0079] Rather than utilising first and second dollys to install the cable bolt assembly 300, as utilised in the first installation method of the first embodiment, a single dolly 240 having a hexagonal socket 241 sized to receive and engage the hexagonal drive head 422 is utilised. The dolly 240 is mounted over the trailing end of the cable bolt assembly 400, with the hexagonal socket 241 engaging the drive faces 424 of the drive head 422. The dolly 240 is rotated as it thrusts the cable 310 towards the top of the bore hole 200. The shear pin 456, fixing the tensioning member 420 in relation to the cable 310, ensures that the torque applied by the dolly 240 to the drive head 422 is transferred to the cable 310, causing rotation of the same. Accordingly, the cable 310 rotates as it advances, puncturing and shredding the resin filled cartridge 210 and mixing the two-component resin. The resin 211 fills the leading end of the bore hole 200, flowing over and into the bulbs 315 down towards the second ferrule 317.

16 [0080] As the resin 211 begins to set, the torque load required to spin the cable 310 increases, thereby increasing the torque transferred between the drive head 422 and barrel 451 by the shear pin 456. Once this torque reaches the predetermined torque as described above, the shear pin 456 fails such that, rather than rotating the barrel and wedge assembly 450 and cable 310 with the tensioning member 420 as the dolly 240 continues to rotate, the tensioning member 420 freely rotates relative to the cable 310 and barrel and wedge assembly 450. Failure of the shear pin 456, also enables the tubular element 421 to retract through the external member 130 as the dolly 240 is rotated by way of the threaded engagement of the external thread of the tubular element 421 and the internal thread of the external member 130 in the same general manner as described above in relation to the first embodiment. [0081] As noted above, friction between the external member 130 and rim 141 of the mine plate 140 generally prevents the external member 130 from rotating with the tubular element 421, allowing the retraction of the tubular element 421 through the external member 130. The dolly 240 continues to rotate until the desired degree of pre-tension in the cable 310 is achieved, following which the dolly 240 is removed, leaving the cable bolt installation as depicted in Figure 22. [0082] Following pre-tensioning, the cable bolt installation may be post grouted via the grout port 429 and grout passage 428 in the same manner descried above in relation to the cable bolt assembly 300 of the second embodiment. [0083] Referring to Figures 23 and 24, a cable bolt assembly 500 according to a fourth embodiment is depicted. Features of the cable bolt assembly 500 that are identical to those of the cable bolt assembly 100 are provided with an identical reference numeral, whereas equivalent features are provided with the same reference numeral to that of the first embodiment, increased by 400. [0084] The cable bolt assembly 500 is of identical construction to the cable bolt assembly 100 of the first embodiment, apart from the configuration of the external member 530. Rather than being of a short dome washer form, as with the external member 130 of the cable bolt assembly 100 of the first embodiment, the external member 530 is of elongate form, extending over the length of the tubular element 121.

17 [0085] The external member 530 has a leading end wall 535 that extends across and encloses the tubular element leading end 127 and defines the external member leading face 531 that is of generally semi-spherical form and is adapted to engage the rim 141 of the mine plate 140. The cable 110 extends through an opening 536 provided in the external member leading wall 535. The external member trailing face 532 is generally planar. The external member 530 has an internally threaded external member aperture 533 which threadingly engages the tubular element 121 by way of the external thread of the tubular element 121. The internal thread of the external member aperture 533 is thus like-handed to the external thread of the tubular element 121, being a left-handed thread in the arrangement depicted. [0086] Given that the tubular element 121 does not extend beyond the leading end of the external member 530, there is no need to drill an oversized borehole section adjacent the rock face 201 for accommodation of the tubular element 121, that is typically the case when installing the cable bolt assembly 100 of the first embodiment. The tubular element 121 is instead retained within the external member aperture 533, with the tubular element leading end 127 being located adjacent the external member leading wall 535 prior to tensioning. The cable bolt assembly 500 is otherwise installed in the same manner as the cable bolt assembly one of the first embodiment, with the tubular element 121 being drawn rearwardly through the external member aperture 533 during tensioning by way of driving of the drive head 122 in the same manner as described above. [0087] A person skilled in the art will appreciate various features of the embodiments described above may be interchanged as desired. For example, the shear pin 456 or equivalent locking means described in relation to the third embodiment may be utilised in place of the mixing device 113 in the cable bolt assembly 100 of the first embodiment to enable mixing of resin in the initial stage of installation. Other forms of single or two stage mixing dolly may also be utilised to installed the various cable bolt assemblies described. It is also envisaged that the arrangement of bulbs 315 and ferrules 316, 317 of the cable 310 of the second and third embodiments will typically be utilised in the cable 110 of the cable bolt assembly 100 of the first embodiment.

Claims (17)

1. A tensionable cable bolt assembly comprising: a cable longitudinally extending between a cable leading end and a cable trailing end; a tensioning member mounted on said cable toward said cable trailing end, said tensioning member comprising an externally threaded, leading tubular element and a trailing drive head fixed in relation to said tubular element, said tensioning member having a cable aperture extending through said tubular element and said drive head, said cable extending through said cable aperture; an external member mounted on said tubular element, said external member having an external member trailing face and an external member leading face adapted to engage a rim of a mine plate through which said cable extends in use, said external member having an internally threaded external member aperture threadingly engaging said tubular element; and a barrel and wedge assembly mounted on said cable between said drive head and said cable trailing end; wherein said cable is freely rotatable relative to said tensioning member and said external member.

2. The cable bolt assembly of claim 1, further comprising a thrust bearing mounted on said cable between said drive head and said barrel and wedge assembly.

3. The cable bolt assembly of claim 2, wherein said thrust bearing is located within a recess provided in a trailing face of said drive head, said thrust bearing protruding beyond said trailing face of said drive head for engagement with a leading end of said barrel and wedge assembly.

4. The cable bolt assembly of claim 1, further comprising an anti-friction washer mounted on said tubular element and located between said external member trailing face and said drive head, said external member trailing face and said anti-friction washer protruding radially beyond said drive head.

5. The cable bolt assembly of claim 1, wherein said external member leading face is substantially semi-spherical. 19

6. The cable bolt assembly of claim 1, wherein a leading end of said tubular element is located between said external member leading face and said cable leading end.

7. The cable bolt assembly of claim 1, further comprising a mixing device fixed to said cable trailing end.

8. The cable bolt assembly of claim 1, further comporising an elongate sleeve mounted on said cable and extending from said leading tubular element and a grout passage communicating an exterior of said drive head with an interior of said elongate sleeve.

9. The cable bolt assembly of claim 8, wherein said grout passage includes a grout port formed on an exterior drive face of said drive head.

10. A tensionable cable bolt assembly comprising: a cable longitudinally extending between a cable leading end and a cable trailing end; a tensioning member mounted on said cable toward said cable trailing end, said tensioning member comprising an externally threaded, leading tubular element and a trailing drive head fixed in relation to said tubular element, said tensioning member having a cable aperture extending through said tubular element and said drive head, said cable extending through said cable aperture; an external member mounted on said tubular element, said external member having an external member trailing face and an external member leading face adapted to engage a rim of a mine plate through which said cable extends in use, said external member having an internally threaded external member aperture threadingly engaging said tubular element; and a barrel and wedge assembly mounted on said cable between said drive head and said cable trailing end; wherein said cable is freely rotatable relative to said external member and freely rotatable relative to said tensioning member upon application of a predetermined torque.

11. The cable bolt assembly of claim 10, further comprising a locking means adapted to fix said tensioning member in relation to said cable until application of said predetermined torque upon which said locking means fails, allowing said tensioning member to freely rotate relative to said cable. 20

12. The cable bolt assembly of claim 11, wherein said locking means comprise a shear pin extending between and into said tensioning member and said barrel and wedge assembly, said shear pin being configured to fail upon application of said predetermined torque.

13. The cable bolt assembly of claim 10, further comprising a thrust bearing mounted on said cable between said drive head and said barrel and wedge assembly.

14. The cable bolt assembly of claim 13, wherein said thrust bearing is located within a recess provided in a trailing face of said drive head.

15. The cable bolt assembly of claim 10, wherein an anti-friction washer is mounted on said tubular element and located between said external member trailing face and said drive head, said external member trailing face and said anti-friction washer protruding radially beyond said drive head.

16. The cable bolt assembly of claim 10, wherein said external member leading face is substantially semi-spherical.

17. The cable bolt assembly of claim 10, wherein a leading end of said tubular element is located between said external member leading face and said cable leading end. DYWIDAG-Systems International Pty Limited Patent Attorneys for the Applicant/Nominated Person SPRUSON & FERGUSON