AU2017204341A1 - Tensioning assembly for a cable bolt - Google Patents

Abstract

TENSIONING ASSEMBLY FOR A CABLE BOLT A tensioning assembly (100) for a cable bolt has a head fitting (110) arranged at a rearward end of the assembly for fixing to a cable. The head fitting (110) comprises a barrel (111), wedges (112) mounted in a rearward end of the barrel (111) and displaceable relative to the barrel (111) and a detent (117) to limit longitudinal displacement of the wedges (112) rearwardly relative to the barrel (111). A tensioning fitting (130) is arranged at a forward end of the assembly and comprises a threaded first tensioning element (131) and a threaded second tensioning element (132). The first tensioning element (131) is threadingly mounted to the second tensioning element (132) and is associated with the head fitting (110) such that relative rotation in a first direction between the first and second tensioning elements (131, 132) longitudinally displaces the first tensioning element (131) and the head fitting (110) in a rearward direction relative to the second tensioning element (132). The second tensioning element (132) has a forward facing surface configured to engage a plate washer, in use, mounted on the cable. A retainer (160) extends between the barrel (111) and the first tensioning element (131). The retainer (160) secures the head fitting (110) to the tensioning fitting (130). An aperture (101) extends longitudinally through the head fitting (110) and the tensioning fitting (130) for receipt of the cable. sic _____k £10

Description

TENSIONING ASSEMBLY FOR A CABLE BOLT

Field [0001] The present invention relates to strata control in civil engineering and mining operations and in particular relates to a tensioning assembly for a cable bolt and associated methods of installing and tensioning a cable bolt for securing the roof or wall of a mine, tunnel or other ground excavations.

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, a cable bolt is fixed into a borehole drilled into a rock face with a two-component resin. A resin cartridge containing the two-component resin is first inserted into the borehole, 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 point anchor the upper end of the cable bolt in the borehole once the resin has set. The cable bolt is typically supplied with a tensioning assembly pre-assembled onto the lower end portion of the cable. In a common form the tensioning fitting comprises a barrel and wedge assembly. The cable is pre-tensioned utilising the barrel and wedge assembly by gripping the end of the cable with a hydraulic jack adjacent the barrel and wedge assembly and pulling the cable through the barrel and wedge assembly, which bears against the rock face via a plate washer. Rather than relying on hydraulic pretensioning, mechanical tensioning assemblies have also previously been proposed which rely on a threaded tensioning device to mechanically pre-tension the cable. One such form of tensioning assembly is as disclosed in International PCT Publication No. WO 2013/033760, the entire contents of which are incorporated herein by cross-reference.

Summary of Invention [0003] In a first aspect, the present invention provides a tensioning assembly for a cable bolt, said tensioning assembly having a longitudinal axis and comprising: a head fitting arranged at a rearward end of said assembly for fixing to a cable, said head fitting comprising a barrel; a plurality of wedges mounted in a rearward end of said barrel and displaceable relative to said barrel; and a detent associated with said barrel to limit longitudinal displacement of said wedges rearwardly relative to said barrel; a tensioning fitting arranged at a forward end of said assembly, said tensioning fitting comprising a threaded first tensioning element and a threaded second tensioning element, said first tensioning element being threadingly mounted to said second tensioning element and associated with said head fitting such that relative rotation in a first direction between said first and second tensioning elements longitudinally displaces said first tensioning element and said head fitting in a rearward direction relative to said second tensioning element, said second tensioning element having a forward facing surface configured to engage a plate washer, in use, mounted on the cable; a retainer extending between said barrel and said first tensioning element, said retainer securing said head fitting to said tensioning fitting; and an aperture extending longitudinally through said head fitting and said tensioning fitting for receipt of the cable.

[0004] In a preferred form, said retainer is separate to said barrel and said first tensioning element.

[0005] In a preferred form, said first tensioning element includes a recess in a trailing end of said first tensioning element and said barrel has a forward portion sized to fit within said first tensioning element recess.

[0006] In a preferred form, said tensioning element has a first tensioning element channel defined in a wall of the recess, and wherein said retainer is adapted to be received within said first tensioning element channel.

[0007] In a preferred form, said barrel has a barrel channel defined in the forward portion, wherein said retainer extends between the barrel channel and the first tensioning element channel.

[0008] In a preferred form, said first tensioning element channel and said barrel channel are radially aligned.

[0009] In a preferred form, said first tensioning element is externally threaded and said second tensioning element is internally threaded.

[0010] Typically, said tensioning assembly further comprises a thrust bearing mounted within said first tensioning element recess forward of said barrel.

[0011] In a preferred form, said retainer comprises a split ring. Preferably, said split ring is hexagonal in shape.

[0012] In a preferred form, said detent of said head fitting comprises a cap mounted at a rearward end of said barrel adjacent to a rearward end of said wedges.

[0013] In a second aspect, the present invention provides a cable bolt assembly comprising of a tensioning assembly as described above and a cable, wherein said cable extends through said aperture.

[0014] In a third aspect, the present invention provides a method of tensioning a cable of a cable bolt in a borehole of a rock strata to be stabilised, the cable being point anchored at an upper end portion thereof in said borehole, the method comprising the steps of: a) fitting a tensioning assembly as defined in the first aspect above onto a lower end portion of said cable; b) operating said tensioning assembly by rotating said first tensioning element relative to said second tensioning element, thereby displacing said first tensioning element and said head fitting relative to said second tensioning element away from said rock face, thereby tensioning said cable.

[0015] In a fourth aspect, the present invention provides a method of installing a cable bolt comprising the steps of: a) drilling a borehole in a rock face of a rock strata to be stabilized; b) inserting a cable into said borehole; c) point anchoring an upper end portion of said cable in said borehole; d) fitting a tensioning assembly as defined in the first aspect above onto a lower end portion of said cable; e) operating said tensioning assembly by rotating said first tensioning element relative to said second tensioning element, thereby displacing said first tensioning element and said head fitting relative to said second tensioning element away from said rock face, thereby tensioning said cable.

[0016] In a preferred form, step c) is carried out prior to step d).

[0017] In an alternate form, step d) is carried out prior to step c). As a further alternate, step d) may be carried out prior to step b), or prior to step a).

Brief Description of Drawings [0018] Preferred embodiments of the present invention will be described hereinafter, by way of examples only, with reference to the accompanying drawings, wherein: [0019] Figure 1 is a front elevation view of a tensioning assembly according to a first embodiment; [0020] Figure 2 is a cross-sectional view of the tensioning assembly of Figure 1; [0021] Figure 3 is a cross-sectional view of a cable bolt installation utilising the tensioning system of Figure 1, during tensioning of a cable; [0022] Figure 4 is a cross-sectional view of the cable bolt installation of Figure 3 in a tensioned state; [0023] Figure 5 is a cross-sectional view of an alternate cable bolt installation utilising the tensioning assembly of Figure 1, immediately prior to rupture of a resin cartridge; [0024] Figure 6 is a cross-sectional view of the cable bolt installation of Figure 5, after rupture of the resin cartridge; [0025] Figure 7 is a front elevation view of a tensioning assembly according to a second embodiment; and [0026] Figure 8 is a cross-sectional view of the tensioning assembly of Figure 7.

Description of Embodiments [0027] Figures 1 and 2 of the accompanying drawings depict a first embodiment of a tensioning assembly 100 for a cable bolt and having a central longitudinal axis L. The tensioning assembly 100 comprises a head fitting 110 arranged at a rearward end of the tensioning assembly 100 and a tensioning fitting 130 arranged at a forward end of the tensioning assembly 100. The head fitting 110 is configured to be fixed to a cable (as will be discussed further below). The head fitting 110 comprises a barrel 111 and a plurality of wedges 112 mounted in the barrel 111 in the usual manner. In particular, the barrel 111 has a rearwardly facing frusto-conical barrel inner surface 113 that tapers toward the forward end of the barrel 111. The wedges 112 each have a part frusto-conical wedge outer surface 114 that tapers towards the forward end of the wedges 112 and which is adapted to engage the barrel inner surface 113. The wedges 112 each have a part cylindrical wedge inner surface 115 configured to engage and grip a cable in the usual manner. The wedges 112 project beyond the rearward end of the barrel 111. A fine spring wire 116 is received in a channel extending circumferentially about the set of wedges 112 in the projecting rear portion of the wedges 112 to assist in holding the wedges 112 together in the usual manner.

[0028] The head fitting 110 further comprises a detent associated with the barrel 111 to limit longitudinal displacement of the wedges 112 rearwardly relative to the barrel 111. In this particular configuration, the detent comprises a cap 117 mounted at a rearward end of the barrel 111 and which extends over the length of the projecting rear portion of the wedges 112. In the particular configuration depicted, the cap 117 is press fit onto the rearward end of the barrel 111. The cap 117 has a trailing end wall 118 that extends across and encloses the trailing end of the wedges 112 and defines a cap trailing end inner surface 119 that is configured to engage the trailing end of the wedges 112, thus limiting longitudinal displacement of the wedges 112 rearwardly relative to the barrel 111. A cap aperture 120 is provided in the trailing end wall 118 of the cap 117 for receipt of a cable (as will be discussed further below). The cap aperture 120 has a maximum width less than a maximum width of the set of wedges 112 so as to restrict passage of the wedges 112 through the cap aperture 120, thereby retaining the wedges 112 within the barrel 111. A cavity is also defined between the cap 117 and the barrel inner surface 113, within which the wedges 112 are contained and freely displaceable both radially and longitudinally. When the wedges 112 are in their rearward most position within the cavity, such that the trailing end of the wedges 112 is against the cap trailing end inner surface 119 as can be seen in Figure 2, an initial clearance is provided between the wedge outer surface 114 and the barrel inner surface 113 which allows for radial displacement of the wedges 112 to allow passage of a cable therethrough (as will be discussed further below). In this particular configuration, the initial clearance is between 3 to 4 mm.

[0029] The tensioning fitting 130 is of the general form described in International PCT Publication No. WO 2013/033760, being in the form of a threaded first tensioning element 131 and a threaded second tensioning element 132. The first tensioning element 131 is threadingly mounted to the second tensioning element 132 such that relative rotation between the first and second tensioning elements 131, 132 displaces the first tensioning element 131 relative to the second tensioning element 132. In the particular configuration depicted, the first tensioning element 131 is externally threaded and comprises a drive head 133 having an outer drive surface in the form of a hexagonal drive nut and an externally threaded tube 134 that extends within the second tensioning element 132.

[0030] Whilst in International PCT Publication No. WO 2013/033760 the second tensioning element is in the form of a dome washer, the second tensioning element 132 is here of a generally elongate form and extends over the length of the first tensioning element 131. The second tensioning element 132 has a leading wall 135 that extends across and encloses the leading end of the first tensioning element 131 and defines a second tensioning element forward facing surface 136 of generally part spherical form that is adapted to engage a plate washer, in use, as will be discussed further below. An opening 137 is provided in the leading wall 135 of the second tensioning element 132 for receipt of a cable. The second tensioning element 132 has an internally threaded second tensioning element aperture 138 which threadingly engages the first tensioning element 131 by way of the external thread of the first tensioning element 131. The internal thread of the second tensioning element aperture 138 is thus like-handed to the external thread of the first tensioning element 131, being a left-handed thread in the arrangement depicted.

[0031] An anti-friction washer 139 is mounted between a rear face 140 of the second tensioning element 132 and a forwardly facing shoulder 141 of the first tensioning element 131, defined between the drive head 133 and the tube 134.

[0032] The drive head 133 comprises a recess 142 formed in the rear end of the drive head 133 and sized to receive a forward portion 121 of the barrel 111. A thrust bearing 150 is mounted in the recess 142 forward of the barrel 111. The thrust bearing 150 is configured to engage with the front face 122 of the barrel 111, and allows for the transmission of compressive forces between the first tensioning element 131 and the head fitting 110, thereby providing an association between the first tensioning element 131 and the head fitting 110 such that rotation of the first tensioning element 131 in a first direction tending to displace the first tensioning element 131 rearwardly relative to the second tensioning element 132 also acts to displace the head fitting 110 rearwardly relative to the second tensioning element 132. The thrust bearing 150 inhibits the transmission of torque from the first tensioning element 131 to the head fitting 110.

[0033] A cable aperture 101 extends longitudinally through the length of the tensioning assembly 100, particularly through the heading fitting 110, thrust bearing 140 and tensioning fitting 130. The cable aperture 101 is sized for receipt of a cable (as will be discussed further below). Within the first tensioning element 131, the cable aperture 101 has a diameter of approximately 25 mm, allowing it to freely receive a standard cable with a 23.5 mm diameter, or a smaller cable such as a cable with a 21.8 mm diameter.

[0034] Whilst in International PCT Publication No. WO 2013/033760 the tensioning fitting and an associated barrel and wedge assembly are pre-assembled onto a cable, thereby securing the various components relative to each other, the tensioning assembly 100 is here supplied separate to the cable. Providing the tensioning assembly 100 separate to the cable avoids transport and handling difficulties with a pre-assembled cable bolt, and avoids damage to the tensioning assembly 100 during cable bolt handling, which regularly involves dragging the cable bolt across the muddy floor of a mine. Separate supply of the tensioning assembly 100 also enables operators to maintain separate stocks of cable and decide at the mine site as to whether to utilise a mechanical tensioning assembly or a simple barrel and wedge assembly for hydraulic tensioning.

[0035] A mechanical tensioning assembly comprises multiple components, which will be prone to falling apart if not preinstalled onto a cable. However, the present tensioning assembly 100 further comprises a retainer 160 extending between the barrel 111 and the first tensioning element 121 to retain the thrust bearing 150 within the drive head recess 142 and secure the head fitting 110 to the tensioning fitting 130. Specifically, in this particular configuration, the retainer 150 is in the form of a hexagonal split ring extending between a barrel channel 123 defined in the forward portion 123 of the barrel 111 and a radially aligned drive head channel 143 defined in the drive head recess 142. Alternatively, it is also envisioned that the retainer 160 may be integrally formed with the barrel 111, the first tensioning element 121, or both. In these alternate configurations, the barrel 111 may be secured to the first tensioning element 121 through a snap-fit engagement.

[0036] The installation and tensioning of a cable bolt utilising the tensioning assembly 100, according to a first method of installation, will now be described with reference to Figures 3 and 4. In the first method of installation, a cable 500 is pre-installed in a borehole 400 of a rock strata 401 in the usual manner. Specifically, a leading end 510 of the cable 500 is point anchored in the borehole 400, with the trailing end 511 of the cable 500 extending from the rock face 402 of the rock strata 401. The leading end 510 of the cable 500 may be point anchored through use of a resin filled cartridge that is ruptured as the cable 500 is driven upwardly into the bore hole 400, with the cable 500 being rotated by way of a socket of an installation spanner so as to mix the resin, which is subsequently allowed to set, thereby point anchoring the leading end 510 of the cable 500.

[0037] As depicted in Figure 3, a tensioning spanner 700, having a hexagonal socket 710 sized to receive and engage the hexagonal drive head 133 is mounted over the trailing end of the tensioning assembly 100, and the tensioning spanner 700 with the tensioning assembly 100 is attached to a drill rig (not shown). A plate washer 300 is fitted over the cable 500 and the drill rig positioned to align the aperture 101 extending through the tensioning assembly 100 with the cable 500. The drill rig is then lifted, pushing the tensioning assembly 100 over the cable 500 such that the cable 500 extends through the length of the aperture 101. As the cable 500 passes between the wedges 112 from the leading end of the wedges 112 to the rearward of the aperture 101, the wedges 112 are displaced radially toward the barrel inner surface 113, reducing the gap between the wedge outer surfaces 114 and the barrel inner surface 113 to approximately 1 mm, and longitudinally toward the cap trailing end inner surface 119 due to contact between the wedge inner surfaces 115 and the cable 500. The cap trailing end inner surface 119 then bears against the trailing end of the wedges 112, thus retaining the wedges 112 within the barrel 111 as the cable 500 advances through. The drill rig continues to advance the tensioning spanner 700 and the tensioning assembly 100 over the cable 500 until the forward facing surface 136 of the second tensioning element 132 of the tensioning fitting 130 engages the plate washer 300 firmly against the rock face 402.

[0038] The tensioning spanner 700 is then rotationally driven by the drill rig, therefore rotationally driving the first tensioning element 131 of the tensioning fitting 130 by way of the drive head 133. Specifically, the tensioning spanner 700 is driven in a direction tending to displace the first tensioning element 131 rearwardly (away from the rock face 402) relative to the second tensioning element 132, as depicted in Figure 3. For the left-handed threads of the first and second tensioning elements 131, 132, the tensioning spanner 700 is driven in a right handed direction. The relative longitudinal displacement of the first tensioning element 131 is achieved by way of the threaded connection between the first and second tensioning elements 131, 132. The rearward displacement of the first tensioning element 131 is conveyed to the barrel 111 of the head fitting 110 via the thrust bearing 150. The thrust bearing 150 at least substantially prevents the transmission of torque from the rotating first tensioning element 131 to the cable 500 via the head fitting 110, which accordingly does not tend to rotate. The antifriction washer 139 also limits the application of any torque to the second tensioning element 132 of the tensioning fitting 130, which is further inhibited against rotation by virtue of the compression of the second tensioning element 132 against the plate washer 300. The load acting against the barrel 111 by virtue of the longitudinal displacement of the first tensioning element 131 drives the barrel 111 along the wedges 112, the longitudinal displacement of which is sufficiently inhibit by friction between the cable 500 and the wedge inner surfaces 115. The taper of the wedges 112 and inner barrel surface 113 thus acts to firmly grip the cable 500. Further rotation of the drive head 133 further longitudinally displaces the first tensioning element 121 and head fitting 110 rearwardly, thus pre-tensioning the cable.

[0039] The drill rig is then lowered to remove the tensioning spanner 700 from the now fully installed and tensioned cable bolt assembly, as depicted in Figure 4.

[0040] Whilst the above installation method has been described in terms of first mounting the tensioning spanner 700 over the tensioning assembly 100 and then pushing the tensioning assembly 100 over the cable 500, it is envisioned that the tensioning assembly 100 may be manually pushed onto the cable 500 prior to mounting the tensioning spanner 700 over the tensioning assembly 100.

[0041] It is also envisioned that there may be situations in which the cable 500 is not preinstalled into the rock strata 401. Accordingly, a second method of installing and tensioning a cable bolt utilising the tensioning assembly 100 will now be described with reference to Figures 5 and 6. A borehole 400 is drilled though the rock face 402 of a rock strata 401 to be stabilised in the usual manner. A resin cartridge 200 having a frangible casing and housing a two-component resin 210 is inserted into the borehole 400 with the cable leading end 510 leading.

[0042] An installation spanner 600, with the tensioning assembly 100 received in a socket of the installation spanner 600, is attached to the drill rig. The plate washer 300 is fitted over the cable 500 and the cable rear end 511 is then manually pushed through the length of the aperture 101 in the manner described above. The cable 500 is pushed through the tensioning assembly 100 until the cable rear end 511 engages drive faces of the installation socket. The installation socket is then driven upwardly, thrusting the cable 500 into the resin cartridge 200 and rupturing the resin cartridge 200. The cable 500 is then rotated by way of the cable rear end 511 engaging the drive faces of the installation socket, which is rotationally driven by the drill rig. Rotation of the cable 500 mixes the two-component resin 210 in the usual maimer. The drill rig continues to advance the installation spanner 600 until the forward facing surface 136 of the second tensioning element 132 of the tensioning fitting 130 engages the plate washer 300 firmly against the rock face 402. Rotation of the cable 500 is then stopped, allowing the resin to cure, thereby point anchoring the upper end of the cable 500 in the usual manner, as depicted in Figure 6.

[0043] The installation spanner 600 is then removed from the drill rig and the tensioning spanner 700 is attached to the drill rig. The tensioning spanner 700 is then mounted over the trailing end of the cable bolt assembly 100 and the cable 500 is pre-tensioned in the same manner described in relation to the first method of installation, with the first tensioning element 131 and barrel 111 being drawn rearwardly away from the rock face 402 relative to the second tensioning element 132 during tensioning.

[0044] Whilst the above second installation method has been described in terms of first mounting the installation spanner over the tensioning assembly and then manually pushing the cable through the aperture 101 of the tensioning assembly 100, it is envisaged that the tensioning assembly 100 may be manually pushed onto the cable 500 (either on site or above ground) prior to mounting the installation spanner 600 over the tensioning assembly 100.

[0045] Figure 7 and 8 of the accompanying drawings depict a second embodiment of a tensioning assembly 100’. The tensioning assembly 100’ of the second embodiment is substantially identical to the tensioning assembly 100 of the first embodiment, except that the tensioning fitting 130’ is more closely aligned to the specific form described in International PCT Publication No. WO 2013/033760, with the second tensioning element 132’ being in the form of a dome washer in place of the elongate second tensioning element 132 of the tensioning assembly 100 of the first embodiment that extends over the leading end of the first tensioning element 131. The remaining features of the tensioning assembly 100’ of the second embodiment are substantially identical to those of the tensioning assembly 100 of the first embodiment, as reflected with the use of identical reference numerals in Figure 7 and 8. Operation of the tensioning assembly 100’ of the second embodiment is the same as that described above in relation to the tensioning assembly 100 of the first embodiment. The dome washer forming the second tensioning element 132’ has a forward facing surface 136’ of generally part spherical form that engages a plate washer in the same manner that the forward facing surface 136 of the second tensioning element 132 of the tensioning assembly 100 of the first embodiment engages a plate washer. In the second embodiment, the externally threaded tube 134 of the first tensioning element 131 extends through the opening 137’ extending through the dome washer forming the second tensioning element 132’. The externally threaded tube 134, in use, extends through the plate washer 300 and into an annular recess formed about the bore hole adjacent the rock face of the rock strata to be stabilised.

[0046] A person skilled in the art will appreciate other possible modifications to the tensioning assembly and installation methods described. For example, whilst the tensioning assembly has been described as being supplied separate to the cable, it is envisioned that the tensioning assembly and the cable may be supplied as a single pre-assembled unit to the installation site.

Claims (18)

1. A tensioning assembly for a cable bolt, said tensioning assembly having a longitudinal axis and comprising: a head fitting arranged at a rearward end of said assembly for fixing to a cable, said head fitting comprising a barrel; a plurality of wedges mounted in a rearward end of said barrel and displaceable relative to said barrel; and a detent associated with said barrel to limit longitudinal displacement of said wedges rearwardly relative to said barrel; a tensioning fitting arranged at a forward end of said assembly, said tensioning fitting comprising a threaded first tensioning element and a threaded second tensioning element, said first tensioning element being threadingly mounted to said second tensioning element and associated with said head fitting such that relative rotation in a first direction between said first and second tensioning elements longitudinally displaces said first tensioning element and said head fitting in a rearward direction relative to said second tensioning element, said second tensioning element having a forward facing surface configured to engage a plate washer, in use, mounted on the cable; a retainer extending between said barrel and said first tensioning element, said retainer securing said head fitting to said tensioning fitting; and an aperture extending longitudinally through said head fitting and said tensioning fitting for receipt of the cable.

2. The tensioning assembly of claim 1 wherein, said retainer is separate to said barrel and said first tensioning element.

3. The tensioning assembly of either one of claims 1 and 2 wherein said first tensioning element includes a recess in a trailing end of said first tensioning element and said barrel has a forward portion sized to fit within said first tensioning element recess.

4. The tensioning assembly of claim 3 wherein said first tensioning element has a first tensioning element channel defined in a wall of the recess, further wherein said retainer is adapted to be received within said first tensioning element channel

5. The tensioning assembly of claim 4 wherein said barrel has a barrel channel defined in the forward portion, further wherein said retainer extends between the barrel channel and the first tensioning element channel.

6. The tensioning assembly of claim 5 wherein said first tensioning element channel and said barrel channel are radially aligned.

7. The tensioning assembly of any one of claims 3 to 6 wherein said first tensioning element is externally threaded and said second tensioning element is internally threaded.

8. The tensioning assembly of any one of claims 3 to 7 wherein said tensioning assembly further comprises a thrust bearing mounted within said first tensioning element recess forward of said barrel.

9. The tensioning assembly of any one of claims 1 to 8 wherein said retainer comprises a split ring.

10. The tensioning assembly of claim 9 wherein said split ring is hexagonal in shape.

11. The tensioning assembly of any one of claims 1 to 10 wherein said detent of said head fitting comprises a cap mounted at a rearward end of said barrel adjacent to a rearward end of said wedges.

12. A cable bolt assembly comprising of a tensioning assembly as defined in any one of claims 1 to 11 and a cable, wherein said cable extends through said aperture.

13. A method of tensioning a cable of a cable bolt in a borehole of a rock strata to be stabilised, the cable being point anchored at an upper end portion thereof in said borehole, the method comprising the steps of: a) fitting a tensioning assembly as defined in any one of claims 1 to 11 onto a lower end portion of said cable; b) operating said tensioning assembly by rotating said first tensioning element relative to said second tensioning element, thereby displacing said first tensioning element and said head fitting relative to said second tensioning element away from said rock face, thereby tensioning said cable.

14. A method of installing a cable bolt comprising the steps of: a) drilling a borehole in a rock face of a rock strata to be stabilized; b) inserting a cable into said borehole; c) point anchoring an upper end portion of said cable in said borehole; d) fitting a tensioning assembly as defined in any one of claims 1 to 11 onto a lower end portion of said cable; e) operating said tensioning assembly by rotating said first tensioning element relative to said second tensioning element, thereby displacing said first tensioning element and said head fitting relative to said second tensioning element away from said rock face, thereby tensioning said cable.

15. The method of claim 14 wherein step c) is carried out prior to step d).

16. The method of claim 14 wherein step d) is carried out prior to step c).

17. The method of claim 14 wherein step d) is carried out prior to step b).

18. The method of claim 14 wherein step d) is carried out prior to step a).