AU2014215939A1 - Tensioning system and assembly for a cable bolt - Google Patents

Abstract

TENSIONING SYSTEM AND ASSEMBLY FOR A CABLE BOLT A tensioning assembly (100) for a cable bolt comprises a head fitting (110) arranged at a rearward end of the assembly (100) for fixing to a cable. The head fitting (110) comprises a barrel (111) and a plurality of wedges (112) mounted in the barrel (111). The assembly (100) further comprises a tensioning fitting (120) arranged at a forward end of the assembly (100). The tensioning fitting (120) comprises a threaded first tensioning element (121) and a threaded second tensioning element (122). The first tensioning element (121) is threadingly mounted to the second tensioning element (122) and is associated with the head fitting (110) such that relative rotation in a first direction between the first and second tensioning elements (121, 122) longitudinally displaces the first tensioning element (121) and the head fitting (110) in a rearward direction relative to the second tensioning element (122). The second tensioning element (122) has a forward facing surface (125) configured to engage a plate washer, in use, mounted on the cable. An aperture (101) extends longitudinally through the head fitting (110) and the tensioning fitting (120) for receipt of the cable. A tie (140) forms a loop extending through the aperture (101) and along an exterior of the head fitting (110) and the tensioning fitting (120). The tie (140) secures the wedges (112) within the barrel (111) and secures the head fitting (110) to the tensioning fitting (120). 14"2 (24 A loo3

Description

1 TENSIONING SYSTEM AND ASSEMBLY FOR A CABLE BOLT Field [0001] The present invention relates to strata controlling in civil engineering and mining operations and in particular relates to a tensioning assembly and system for a cable bolt, and an associated method of installing 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 utilized. 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 utilizing 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 pre tensioning, 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 and a plurality of wedges mounted in said barrel; 2 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; an aperture extending longitudinally through said head fitting and said tensioning fitting for receipt of the cable; and a tie forming a loop extending through said aperture and along an exterior of said head fitting and said tensioning fitting, said tie securing said wedges within said barrel and securing said head fitting to said tensioning fitting. [0004] In a preferred form, said tensioning assembly further comprises a locator mounted within said aperture, said locator having a rear portion positioned in said head fitting for centralizing said wedges within said barrel and a forward portion positioned in said tensioning fitting for centralizing said tensioning fitting relative to said head fitting. [0005] In a preferred form, said head fitting further comprises a detent mounted in said barrel adjacent to a forward end of said wedges to limit displacement of said wedges in a forward direction relative to said barrel. [0006] In a preferred form, said detent comprises a split ring located between said wedges and an annular shoulder defined in said barrel. [0007] In a preferred form, said locator is connected to said tie such that, upon extracting said tie from said aperture through said tensioning fitting, said tie extracts said locator from said aperture. [0008] In a preferred form, said tie comprises one or more cable ties with a head of one of said cable ties and located within a passage extending through said locator and engageable with a shoulder defined at an opening of said passage at a forward end of said locator.

3 [0009] In a preferred form, said first tensioning element is externally threaded and said second tensioning element is internally threaded. [0010] In a preferred form, said tensioning assembly further comprises a thrust bearing mounted between said head fitting and said first element. [0011] In a second aspect, the present invention provides a tensioning spanner for use with the tensioning assembly defined above, said tensioning spanner comprising: a spanner body defining a forwardly facing socket configured to receive said tensioning assembly, an internal wall of said spanner body having one or more drive faces configured to engage drive faces of said tensioning assembly for rotationally driving one of said first and second tensioning elements; a compression spring mounted in said socket; and a seat mounted on said spring for supporting said head fitting of said tensioning assembly. [0012] Typically, said tensioning spanner further comprises a detent mounted in said socket for limiting displacement of said seat toward an opening of said socket. [0013] In a preferred form, said seat comprises a peripheral annular rim for supporting said barrel of said tensioning assembly, a central opening and a recessed annular support surface for supporting said wedges of said tensioning assembly. [0014] In a third aspect, the present invention provides a tensioning system for a cable bolt, said tensioning system comprising: a tensioning spanner as defined above; a tensioning assembly as defined above received in said socket of said tensioning spanner. [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 onto a lower end portion of said cable projecting from said borehole, said tensioning assembly comprising a head fitting in the form of a 4 barrel and wedge assembly and a tensioning fitting in the form of a threaded first tensioning element mounted to a threaded second tensioning element; 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, said tensioning assembly is the tensioning assembly defined above. [0017] In a preferred method, said tensioning assembly is received in the tensioning spanner defined above and said first tensioning element is rotationally driven by said tensioning spanner. [0018] In a preferred form, step c) is carried out prior to step d). [0019] In an alternate form, step d) is carried out prior to step c). Brief Description of Drawings [0020] A preferred embodiment of the present invention will now be described, by way of an example only, with reference to the accompanying drawings wherein: [0021] Figure 1 is a front elevation view of a tensioning assembly; [0022] Figure 2 is a cross-sectional view of the tensioning assembly of Figure 1; [0023] Figure 3 is a cross-sectional view of a tensioning spanner for use with the tensioning assembly of Figure 1; [0024] Figure 4 is an isometric cross-sectional view of the tensioning spanner of Figure 3; [0025] Figure 5 is a cross-sectional view of a tensioning system comprising the tensioning assembly of Figure 1 and tensioning spanner of Figure 3 with a tie securing the tensioning assembly intact; [0026] Figure 6 is a cross-sectional view of the tensioning system of Figure 5 with the tie cut; 5 [0027] Figure 7 is a cross-sectional view of the tensioning system of Figure 5 with the tie and locator removed; [0028] Figure 8 is a cross-sectional view of a cable bolt installation utilizing the tensioning system of Figure 5, prior to tensioning; [0029] Figure 9 is a cross-sectional view of the cable bolt installation of Figure 8 in a tensioned state; [0030] Figure 10 is a fragmentary view of a partially complete cable bolt installation utilising an alternate tensioning fitting; and [0031] Figure 11 is a fragmentary partially cross-sectioned view of the cable bolt installation of Figure 10. Description of Embodiments [0032] Figures 1 and 2 of the accompanying drawings depict 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 120 arranged at forward end of the tensioning assembly 100. The head fitting 110 is configured to be fixed to a cable and is in the general form of a barrel and wedge assembly comprising 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 and which engages 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. A detent 117 is located within the barrel 111 between the forward end of the wedges 112 and the forward end of the barrel 111 to limit displacement of the wedges 112 toward the forward end of the barrel 111. Specifically, the detent 117 is in the form of a split plastic ring located between the forward end 6 of the wedges 112 and an annular shoulder 118 defined in the barrel adjacent the forward end of the barrel inner surface 113. [0033] The tensioning fitting 120 is of the general form described in International PCT Publication No. WO 2013/033760, being in the form of a threaded first tensioning element 121 and a threaded second tensioning element 122. The first tensioning element 121 is threadingly mounted to the second tensioning element 122 such that relative rotation between the first and second tensioning elements 121, 122 displaces the first tensioning element 121 relative to the second tensioning element 122. In the particular configuration depicted, the first tensioning element 121 is externally threaded and comprises a drive head 123 having an outer drive surface in the form of a hexagonal drive nut and an externally threaded tube 124 that extends through the second tensioning element 122. The second tensioning element 122 is in the general form of an internally threaded dome washer and has a forward facing surface 125 that is of a generally part spherical form and that is configured to engage a plate washer, in use, as will be discussed further below. An anti-friction washer 126 is mounted between a rear face 127 of the second tensioning element 122 and a forwardly facing shoulder 128 of the first tensioning element 121, defined between the drive head 123 and tube 124. [0034] A thrust bearing 130 is mounted in a recess formed in the rear end of the drive head 123, with a load indicating washer 131 optionally being mounted between the thrust bearing 130 and the front face 119 of the barrel 111. The thrust bearing 130, and load indicating washer 131, allow for the transmission of compressive forces between the first tensioning element 121 and the head fitting 110, thereby providing an association between the first tensioning element 121 and the head fitting 110 such that rotation of the first tensioning element 121 in a first direction tending to displace the first tensioning element 121 rearwardly relative to the second tensioning element 122 also acts to displace the head fitting 110 rearwardly relative to the second tensioning element 122. [0035] A cable aperture 101 extends longitudinally through the length of the tensioning assembly 100, particularly through the heading fitting 110, load indicator washer 131, thrust bearing 130 and tensioning fitting 120. The cable aperture 101 is sized for receipt of a cable (as will be discussed further below). Within the first tensioning element 121, 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.

7 [0036] 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 utilize a mechanical tensioning assembly or a simple barrel and wedge assembly for hydraulic tensioning. [0037] 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 tie 140 forming a loop extending through the cable aperture 101 and along the exterior of the head fitting 110 and tensioning fitting 120. The tie 140 secures the wedges 112 within the barrel 111 and secures the head fitting 110 to the tensioning fitting 120. The tie 140 additionally secures the remaining components of the tensioning assembly 100, including the thrust bearing 130 and load indicator washer 131. [0038] In the arrangement depicted, the tie 140 comprises two standard cable ties 141, each comprising a cable tie head 142 and cable tie tail 143 extending from the cable tie head 142 and receivable within a slot formed in the cable tie head 142 in the usual manner. It is also envisaged that a single longer cable tie 141 may be utilized in place of the two cable ties 141 depicted. The cable ties 141 are passed through the cable aperture 101 and longitudinally along the exterior of the head fitting 110 and tensioning fitting 120 to form a complete loop securing the various components of the tensioning assembly 110 together. [0039] A locator 150 is mounted in the cable aperture 101, with a rear portion 151 of the locator 150 positioned within the head fitting 110 and a forward portion 152 of the locator 150 positioned within the tensioning fitting 120, particularly within the first tensioning element 121. The rear and forward portions 151, 152 of the locator 150 are each generally cylindrical. The forward portion 152 of the locator 150 is sized to fit neatly within the first tensioning element 121, having a diameter of 24.5 mm, slightly less than the 25 mm diameter of the aperture 101 at the first tensioning element 121. The rear portion 151 of the locator 150 is of a reduced diameter 8 as compared to that of the forward portion 152, here having a diameter of 21.5 mm, being less than the diameter of the 23.5 mm cable intended to be fixed within the head fitting 110. The rear portion 151 of the locator 150 and the detent 117 are particularly configured such that, when the forward end of the wedges 112 engage the detent 117, they do not become bound between the rear portion 151 of the locator 150 and the barrel inner surface 113. The tie 140 passes through a passage 153 extending longitudinally through the length of the locator 150. The passage 153 has a reduced diameter opening 154 at the forward end of the locator 150, that is sized to inhibit passage of the head 142 of one of the cable ties 141 therethrough, defining a shoulder that engages the head 142. [0040] Figures 3 and 4 depict a tensioning spanner 200 for use with the tensioning assembly 100 described above. The tensioning spanner 200 comprises a spanner body 201 and a shank 202 extending rearwardly from the spanner body 201. The shank 202 is configured to be received in, and rotationally driven by, a drill rig by way of drive faces 203 formed on the shank 202. The spanner body 201 has a forward facing socket 204 configured to receive the tensioning assembly 100 as will be discussed further below. A compression spring 205 is mounted in the socket 204 between the base 206 of the socket and a seat 207 mounted on the forward end of the spring 205. The seat 207 has a peripheral annular rim 211, a central opening 213 and a recessed annular support surface 212 located between the opening 212 and rim 211. [0041] A detent 208 is located in the socket 204 to limit displacement of the seat 207 toward the opening 209 of the socket 204. In the embodiment depicted, the detent 208 is in the form of a circlip mounted in a groove formed in the inner wall of the body 201. Toward the opening 209 of the socket 204, the inner wall of the spanner body 201 is formed with drive faces 210 configured to engage the drive faces of the drive head 123 of the first tensioning element 121. [0042] The tensioning assembly 100 and tensioning spanner 200 together form a tensioning system, as depicted in Figure 5, for installation of a cable bolt. The tensioning system is assembled by receiving the head fitting 110 and drive head 123 of the first tensioning element 121 of the tensioning fitting 120 in the socket 204 of the tensioning spanner 200. In this position, as depicted in Figure 5, the drive faces of the drive head 123 engage the drive faces 210 of the tensioning spanner 200 and the rear face of the barrel 111 engages the rim 211 of the seat 207. As can be seen from Figure 5, the detent 208 formed in the socket 204 is positioned such 9 that the anti-friction washer 126 and second tensioning element 122 of the tensioning fitting 120 are located adjacent the opening of the socket 204 of the tensioning spanner 200. [0043] With the tensioning assembly 100 securely received within the tensioning spanner 200, one of the cable ties 141 is then cut and the tie 140 is extracted from the aperture 101 by lifting the tie 140 through the first tensioning element 121, as depicted in Figure 6. The head 142 of the cable tie 141 engages the shoulder at the opening 154 in the forward end of the locator 150, such that the head 142 lifts the locator 150 through the aperture 101. With the locator 150 and cable tie 140 extracted, the wedges 112 and detent 117 are able to drop rearwardly (downwardly, with the tensioning spanner 100 arranged in a generally vertical orientation), with the rear end of the wedges 112 engaging the recessed annular support surface 212 of the seat 207 located within the socket 204. [0044] Now referring to Figures 8 and 9, the installation and tensioning of a cable bolt utilizing the tensioning system described above will now be further described. A borehole 400 is drilled though the rock face 401 of a rock strata 402 to be stabilized in the usual manner. The borehole 400 is drilled with an enlarged diameter portion 403 adjacent the rock face 401 for receipt of the tube 124 of the first tensioning element 121 of the tensioning fitting 120. A resin cartridge having a frangible casing and housing a two-component resin (not depicted) is inserted into the borehole 400, followed by a cable 500 which will typically be mounted in an installation spanner (not depicted) fitted to the drill rig. A mixing device 501, here in the form of a rectangular prism defining four drive faces, is fixed to the cable rear end 502, here by welding. The mixing device 501 engages drive faces of the installation socket which is driven upwardly, thrusting the cable 500 into the resin cartridge, rupturing the frangible casing. The cable 500 is then rotated by way of the mixing device 501 engaging the installation socket, which is rotationally driven by the drill rig. [0045] Rotation of the cable mixes the two-component resin in the usual manner. Rotation of the cable is then stopped, allowing the resin to cure, thereby point anchoring the upper end of the cable in the usual manner. [0046] The installation spanner is then removed from the drill rig, and the tensioning spanner 200, with the tensioning assembly 100 received in the socket 204 and the tie 140 and locator 150 removed as described above, is attached to the drill rig. A plate washer 510 is fitted over the 10 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 depicted in Figure 8. As the cable 500 is being pushed through the aperture 101 the cable rear end 502 impinges the detent 117 located within the barrel 111. The detent 117 is, however, free to expand to allow passage of the cable 500 therethrough. Expansion of the detent 117 is allowed for by being in the form of a split ring, and having dropped with the wedges 112 to a position within the barrel 111 providing a gap between the detent 117 and the barrel inner surface 113. Whilst the tensioning assembly 100 is pushed over the cable 500, the spring 205 mounted in the socket 204 is able to compress to accommodate any shock movement as the tensioning spanner 200 advances. As the cable 500 extends through the detent 117, the forward end of the wedges 112 push the detent 117 along the cable 500, maintaining the detent 117 perpendicular to the longitudinal axis L and ensuring the detent 117 does not foul the wedges 112 when they grip the cable 500 during the tensioning process. As the cable 500 advances between the wedges 112, 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. As the lower end of the cable 500 passes through the rearward end of the aperture 101, it further passes through the central opening 213 in the seat 207 and through spring 205. The recessed annular support surface 212 of the seat 207 continues to bear against the rear face of the wedges 111, maintaining light contact with the cable 500 as it passes therethrough. [0047] The drill rig continues to advance the tensioning spanner 200 and tensioning assembly 100 over the cable 500 until the forward facing surface 125 of the second tensioning element 122 of the tensioning fitting 120, driven by the forward end of the spanner body 201 via the anti friction washer 126, engages the plate washer 510 firmly against the rock face 401. [0048] The tensioning spanner 200 is then rotationally driven by the drill rig, therefore rotationally driving the first tensioning element 121 of the tensioning fitting 120 by way of the drive head 123. Specifically, the tensioning spanner 200 is driven in a direction tending to displace the first tensioning element 121 rearwardly (away from the rock face 401) relative to the second tensioning element 122, which is fixed in position against the plate washer 510 by engagement of the forward end of the spanner body 201 with the anti-friction washer 126. The relative longitudinal displacement of the first tensioning element 121 is achieved by way of the 11 threaded connection between the first and second tensioning elements 121, 122. The rearward displacement of the first tensioning element 121 is conveyed to the barrel 111 of the head fitting 110 via the thrust bearing 130 and load indicator washer 131. The thrust bearing 130 at least substantially prevents the transmission of torque from the rotating first tensioning element 121 to the cable 500 via the head fitting 110, which accordingly does not rotate. The anti-friction washer 126 also limits the application of any torque to the second tensioning element 122 of the tensioning fitting 120, which is further inhibited against rotation by virtue of the compression of the second tensioning element 122 against the plate washer 510. The load acting against the barrel 111 by virtue of the longitudinal displacement of the first tensioning element 121 drives the barrel 111 along the wedges 112, the longitudinal displacement of which is inhibited by virtue of the spring 205 and seat 207 mounted in the socket 204. The taper of the wedges 112 and inner barrel surface 113 thus acts to firmly grip the cable 500, with further rotation of the drive head 123 further longitudinally displacing the first tensioning element 121 and head fitting 110 rearwardly, pre-tensioning the cable. [0049] The load indicating washer 131 is configured to fail under compression at a pre determined load which equates to the desired pre-tensioning load in the cable 500. On failure of the load indicator washer 131, the failed material of the load indicating washer 131 is effectively radially extruded outwardly between the thrust bearing 130 and the barrel 111, providing a visual indication to the operator that an appropriate pre-tensioning load has been achieved in the cable 500. This visual indication can be enhanced by forming the load indicating washer 131 in a bright colour. [0050] The drill rig is then lowered to remove the tensioning spanner 200 from the now fully installed and tensioned cable bolt assembly. [0051] Whilst the above installation process has been described in terms of point anchoring the cable 500 within the borehole 400 prior to fitting the tensioning assembly 100 onto the cable 500, it is envisaged that the cable may be point anchored subsequent to having fitted the tensioning assembly 110 onto the cable 500. In such an installation method, the resin cartridge and cable 500 would typically be inserted into the borehole 400 by hand and manually held in position whilst the plate washer 510 and tensioning fitting 100 is fitted onto the protruding lower end of the cable 500. A modified form of the tensioning spanner will also need to be utilized which enables initial rotation of the cable 500 by way of the mixing device 501 to rupture and 12 mix the resin, point anchoring the cable 500, prior to subsequent tensioning of the cable by way ) of the tensioning fitting 120. [0052] Figures 10 and 11 depict a cable bolt installation that is substantially identical to the cable bolt installation described above, except that the tensioning assembly 100' has a tensioning fitting 120' of a modified configuration. Specifically, in the tensioning fitting 120', the second tensioning element 122', rather than being in the form of a short dome washer, as with the second tensioning element 122 of the embodiment described above, is of elongate form, extending over the length of the tubular first tensioning element 121. [0053] The second tensioning element 122' has a leading end wall 170 that extends across and encloses the leading end of the first tensioning element 121 and defines a second tensioning element forward facing surface 125' of generally part spherical form that is adapted to engage the plate washer 510. The cable 500 extends through an opening 171 provided in the second tensioning element leading end wall 170. The second tensioning element trailing face 172 is generally planar. The second tensioning element 122' has an internally threaded second tensioning element aperture 173 which threadingly engages the first tensioning element 121 by way of the external thread of the first tensioning element 121. The internal thread of the second tensioning element aperture 173 is thus like-handed to the external thread of the first tensioning element 121, being a left-handed thread in the arrangement depicted. [0054] Given that the first tensioning element 121 does not extend beyond the leading end of the second tensioning element 122', there is no need to drill an oversized bore-hole section adjacent the rock face 401 for accommodation of the first tensioning element 121, that is typically the case when utilising the tensioning assembly 100 of the first embodiment. The first tensioning element 121 is instead retained within the second tensioning element aperture 173 with the leading end of the first tensioning element 121 located adjacent the second tensioning element leading end wall 170 prior to tensioning. The cable bolt assembly utilising the tensioning assembly 100' is otherwise installed in the same manner as described in relation to the first embodiment, with the first tensioning element 121 being drawn rearwardly through the second tensioning element aperture 173 during tensioning by way of driving of the drive head 123 utilising the tensioning spanner 200 described above.

13 [0055] A person skilled in the art will appreciate other possible modifications to the tensioning ) assembly, tensioning spanner and installation method described. For example, whilst in the embodiment described the tensioning fitting has the first tensioning element externally threaded and the second tensioning element internally threaded, it is envisaged that the first tensioning element might be internally threaded and the second tensioning element externally threaded. It is also envisaged that, rather than having drive faces formed on the first tensioning element, the drive faces might be formed on the second tensioning element, such that the second tensioning element is rotationally driven as opposed to the first tensioning element. It is still further envisaged that the first tensioning element might be fixed to, or integrally formed with, the barrel of the head fitting in such an application where it is the second tensioning element that is rotationally driven. It is still further envisaged that the second tensioning element may indirectly engage the plate washer by way of a further intervening washer located between the second tensioning element and the plate washer.

Claims (17)

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 and a plurality of wedges mounted in 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; an aperture extending longitudinally through said head fitting and said tensioning fitting for receipt of the cable; and a tie forming a loop extending through said aperture and along an exterior of said head fitting and said tensioning fitting, said tie securing said wedges within said barrel and securing said head fitting to said tensioning fitting.

2. The tensioning assembly of claim 1 wherein said tensioning assembly further comprises a locator mounted within said aperture, said locator having a rear portion positioned in said head fitting for centralizing said wedges within said barrel and a forward portion positioned in said tensioning fitting for centralizing said tensioning fitting relative to said head fitting.

3. The tensioning assembly of either one of claims 1 and 2 wherein said head fitting further comprises a detent mounted in said barrel adjacent to a forward end of said wedges to limit displacement of said wedges in a forward direction relative to said barrel.

4. The tensioning assembly of claim 3 wherein said detent comprises a split ring located between said wedges and an annular shoulder defined in said barrel. 15

5. The tensioning assembly of claim 2 wherein said locator is connected to said tie such ) that, upon extracting said tie from said aperture through said tensioning fitting, said tie extracts said locator from said aperture.

6. The tensioning assembly of claim 5 wherein said tie comprises one or more cable ties with a head of one of said cable ties and located within a passage extending through said locator and engageable with a shoulder defined at an opening of said passage at a forward end of said locator.

7. The tensioning assembly of any one of claims 1 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 1 to 7 wherein said tensioning assembly further comprises a thrust bearing mounted between said head fitting and said first element.

9. A tensioning spanner for use with the tensioning assembly of any one of claims 1 to 8, said tensioning spanner comprising: a spanner body defining a forwardly facing socket configured to receive said tensioning assembly, an internal wall of said spanner body having one or more drive faces configured to engage drive faces of said tensioning assembly for rotationally driving one of said first and second tensioning elements; a compression spring mounted in said socket; and a seat mounted on said spring for supporting said head fitting of said tensioning assembly.

10. The tensioning spanner of claim 9 wherein said tensioning spanner further comprises a detent mounted in said socket for limiting displacement of said seat toward an opening of said socket.

11. The tensioning spanner of either one of claims 9 and 10 wherein said seat comprises a peripheral annular rim for supporting said barrel of said tensioning assembly, a central opening and a recessed annular support surface for supporting said wedges of said tensioning assembly. 16

12. A tensioning system for a cable bolt, said tensioning system comprising: a tensioning spanner as defined in any one of claims 9 to 11; a tensioning assembly as defined in any one of claims 1 to 8 received in said socket of said tensioning spanner.

13. 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 onto a lower end portion of said cable projecting from said borehole, said tensioning assembly comprising a head fitting in the form of a barrel and wedge assembly and a tensioning fitting in the form of a threaded first tensioning element mounted to a threaded second tensioning element; 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.

14. The method of claim 13 wherein said tensioning assembly is the tensioning assembly defined in any one of claims 1 to 8.

15. The method of either one of claims 13 and 14 wherein said tensioning assembly is received in the tensioning spanner defined in any one of claims 9 to 11 and said first tensioning element is rotationally driven by said tensioning spanner.

16. The method of any one of claims 13 to 15 wherein, step c) is carried out prior to step d).

17. The method of any one of claims 13 to 15 wherein, step d) is carried out prior to step c). DYWIDAG-Systems International Pty Limited Patent Attorneys for the Applicant/Nominated Person SPRUSON & FERGUSON