WO2014028966A1

WO2014028966A1 - A cable bolt assembly

Info

Publication number: WO2014028966A1
Application number: PCT/AU2013/000923
Authority: WO
Inventors: David William Evans; Noel EATHER; Simon Ross WORRALL
Original assignee: Dywidag Systems International Pty Ltd
Current assignee: DSI Underground Australia Pty Ltd
Priority date: 2012-08-22
Filing date: 2013-08-20
Publication date: 2014-02-27
Anticipated expiration: 2015-02-22
Also published as: AU2013305473A1; AU2013204193A1; AU2013204193B2

Description

A CABLE BOLT ASSEMBLY

FIELD OF THE INVENTION

[0001] The present invention relates to strata control in civil engineering and mining operations and in particular relates to a rock bolt assembly (in the form of a cable bolt assembly) for securing the roof or wall of a mine, tunnel or other ground excavation.

BACKGROUND OF THE INVENTION

[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 with a hydraulic jack and the trailing end of the cable bolt secured to the rock face at the opening of the bore hole utilising a barrel and wedge assembly. A cement grout is then injected into the annular cavity between the cable bolt and the wall of the bore hole.

[0003] In one cement grouting method, referred to as a "bottom up" grouting method, a grout tube is inserted into the bore hole only a short distance, such that the grout injected into the grout tube is pushed up through the annular cavity from adjacent the bore hole opening. To evacuate air from the bore hole while the cement grout is being pumped from the bottom, a breather tube (typically in the form of a small diameter plastic tube) is located in the annular cavity extending toward the top of the bore hole. The bore hole must also be sealed at the rock face to ensure that the injected grout is pumped toward the top of the bore hole rather than merely escaping out through the bore hole opening. The breather tube is also subject to damage during installation, and requires a relatively large annular cavity between the cable bolt and bore hole wall for location of the breather tube.

[0004] In an alternate cement grouting method, referred to as a "top down" grouting method, the grout tube extends from the bore hole opening to adjacent the top of the bore hole, such that grout injected through the grout tube flows down through the full length of the bore hole. Utilising this method, no breather tube is required and there is no need to seal the bore hole opening in the rock face. A large diameter bore hole is, however, required to be drilled into the rock to house the grout tube in the annular cavity between the cable bolt and bore hole wall. Such a relatively large diameter hole is generally, however, not desired for anchoring the top portion of the cable bolt with resin as the annular cavity between the cable bolt and the bore hole should be as small as possible to achieve the best fixation of the cable bolt. A smaller annular cavity is also desired for effective load transfer between the cable bolt and bore hole wall via the cement grout. Grout tubes are typically strapped to the exterior of the cable bolt, and may be subject to damage during installation of the cable bolt. Further, adopting a "top down" grouting method, it is difficult to ensure that the entire annular cavity between the cable and wall of the bore hole is fully grouted, as the grout passes down through the annular cavity (often unevenly) under gravity and injection of the grout is typically ceased as soon as the grout starts to seep through the opening at the bottom of the annular cavity.

[0005] In an alternative form, the wires of the cable bolt are unwound and the grout tube is helically wound along the length of the cable bolt with the wires of the cable bolt prior to installation. This is, however, a complicated and costly exercise and may be subject to the grout tube collapsing during pre-tensioning of the cable bolt.

OBJECT OF THE INVENTION

[0006] It is the object of the present invention to substantially overcome or at least ameliorate one or more of the above disadvantages.

SUMMARY OF THE INVENTION

[0007] The present invention provides a cable bolt assembly comprising:

a cable longitudinally extending between a cable leading end and a cable trailing end, said cable comprising a longitudinally extending breather tube defining a breather passage and at least one set of wires helically wound about said breather tube;

a tensioning assembly mounted on said cable adjacent said cable trailing end;

a breather bulb formed in said cable between said tensioning assembly and said cable leading end, a plurality of openings being defined by spaces between wires of said cable within said breather bulb, said openings communicating with said breather passage; and

an annular sealing sleeve extending about said cable and extending from said tensioning assembly towards said cable leading end, said sleeve being configured to sealingly engage the wall of a bore hole into which the cable bolt assembly is to be installed, about a periphery of said sleeve;

wherein said tensioning assembly is adapted to tension said cable and defines a grout delivery passage communicating an exterior of said tensioning assembly and the interior of said sleeve to facilitate the pumping of grout into an annular cavity defined, in use, between said cable and the wall of the bore hole.

[0008] Typically, said at least one set of wires comprises an inner set of wires helically wound about said grout tube and an outer set of wires helically wound about said inner set of wires.

[0009] In a preferred form, said cable bolt further comprises a drive head at said cable trailing end, said drive head having an aperture extending therethrough communicating with said breather passage.

[0010] In one form, said cable bolt further comprises an annular resin dam mounted on said cable between said breather bulb and said cable leading end.

[0011 ] In one form, a rigid support element is located within said breather bulb, so as to inhibit collapse of said breather bulb upon the application of a tensile load to said cable.

[0012] In one form, said rigid support element located within said breather bulb has an aperture extending therethrough communicating with said breather passage.

[0013] Typically, said breather tube is discontinuous at said breather bulb so as to provide for communication of said openings with said breather passage. Alternatively, said breather tube may be provided with an aperture so as to provide for communication of said openings with said breather passage. In another alternate form, a leading end of said breather tube may be located within or adjacent said breather tube so as to provide for communication of said openings with said breather passage.

[0014] In one form, at least one grout anchoring bulb is formed in said cable between said breather bulb and said cable trailing end. [0015] Preferably, a hollow rigid support element is located within each said grout anchoring bulb, so as to inhibit collapse of the respective said grout anchoring bulb on the application of a tensile load to said cable bolt, said hollow rigid support element in each said grout anchoring bulb having an aperture extending therethrough with said breather tube extending through said aperture.

[0016] Typically, at least one resin anchoring bulb is formed in said cable between said grouting bulb and said cable leading end. In one embodiment, three said resin anchoring bulbs are formed in said cable.

[0017] In one form, a rigid support element is located within each said resin anchoring bulb, so as to inhibit collapse of the respective said resin anchoring bulb upon the application of a tensile load to said cable bolt.

[0018] Typically, said rigid support element in each said resin anchoring bulb comprises a ball.

[0019] In one form, said tensioning assembly comprises a barrel and wedge assembly mounted on said cable towards said cable trailing end and a grout delivery fitting mounted on said cable adjacent said barrel and wedge assembly between said barrel and wedge assembly and said cable leading end, said grout delivery fitting defining said grout delivery passage.

[0020] In a second aspect, the present invention provides a method of installing the cable bolt assembly defined above, said method comprising:

drilling a bore hole in a rock face of a strata to be secured;

inserting said cable into said bore hole;

securing a leading region of said cable, between said breather bulb and said cable leading end, in said bore hole;

sealing between said cable bolt assembly and the wall of said bore hole with said sealing sleeve;

tensioning said cable utilising said tensioning head assembly;

pumping grout through said grout delivery passage, through said sealing sleeve and along an annular cavity defined between said cable and the wall of said bore hole to said breather bulb; allowing air to escape from said annular cavity through said breather bulb and said breather tube; and

stopping pumping of said grout when grout exits said breather tube at said cable trailing end.

[0021 ] Typically, securing said leading region of said cable comprises:

inserting a resin filled cartridge having a frangible casing into said bore hole before inserting said cable into said bore hole;

engaging said cable leading end with said resin filled cartridge;

thrusting said cable further into said bore hole and rotating said cable so as to rupture said frangible casing and mix said\resin; and

allowing said resin to cure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Preferred embodiments of the present invention will now be described, by way of an example only, with reference to the accompanying drawings wherein:

[0023] Figure 1 is a front elevation view of a cable bolt assembly according to a first embodiment;

[0024] Figure 2 is a perspective view of the cable bolt assembly of Figure 1 ;

[0025] Figure 3 is a cross-sectional front elevation view of the trailing portion of the cable bolt assembly of Figure 1 ;

[0026] Figure 4 is a cross-sectional perspective view of the trailing portion of the cable bolt assembly of Figure 1 ;

[0027] Figure 5 is a cross-sectional front elevation view of a mid portion of the cable bolt assembly of Figure 1 ;

[0028] Figure 6 is a partially cross-sectional view of a partially complete cable bolt installation utilising the cable bolt assembly of Figure 1 ; [0029] Figure 7 is a partially cross-sectional view of the cable bolt installation of Figure 6 upon completion;

[0030] Figure 8 is a partially cross-sectional perspective view of a trailing portion of the cable bolt installation of Figure 6 upon completion;

[0031 ] Figure 9 is a cross-sectional perspective view of an alternate mid portion

configuration of the cable bolt assembly of Figure 1 ;

[0032] Figure 10 is a cross-sectional perspective view of a further alternate mid portion configuration of the cable bolt assembly of Figure 1 ;

[0033] Figure 11 is a cross-sectional perspective view of a still further alternate mid portion configuration of the cable bolt assembly of Figure 1;

[0034] Figure 12 is a front elevation view of a cable bolt assembly according to a second embodiment;

[0035] Figure 13 is a perspective view of the cable bolt assembly of Figure 13;

[0036] Figure 14 is a perspective view of a trailing portion of the cable bolt assembly of Figure 12;

[0037] Figure 15 is a cross-sectional front elevation view of the trailing portion of the cable bolt assembly of Figure 12;

[0038] Figure 16 is a cross-sectional perspective view of the trailing portion of the cable bolt assembly of Figure 12;

[0039] Figure 17 is a cross-sectional view of a completed cable bolt installation utilising the cable bolt assembly of Figure 12.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] A cable bolt assembly 100 according to a first embodiment is depicted in Figures 1 to 5. The cable bolt assembly 100 has a cable 110 extending between a leading end 110a and a cable trailing end 1 10b. As is best depicted in Figures 3 to 5, the cable 110 comprises a longitudinally extending breather tube 1 1 1, an inner set of wires 1 12 helically wound about the breather tube 111 and an outer set of wires 113 helically wound about the inner set of wires 1 12. The inner set of wires 1 12 will typically be helically wound in a first direction with the outer set of wires 113 wound in the same direction, although it is envisaged that they may be wound in an opposing second direction. It is also envisaged that the cable 110 might comprise only a single set of wires helically wound about the breather tube 111. The sets of wires 112, 113 are typically formed of high tensile steel. The wires may either have a smooth uniform surface or an indented surface to improve load transfer along the wires. The breather tube 111 effectively takes the place of a central king wire in a standard cable bolt and defines a breather passage 1 14 extending from the cable trailing end 110b towards the cable leading end 1 10a.

[0041] The breather tube 111 will typically be formed of steel, but alternatively may be formed of plastic or various other materials. For a cable 110 having a nominal outer diameter of 25 mm, the diameter of the breather passage 114 may be about 7.7 mm with the breather tube 111 having a wall thickness of about 0.8 mm. Various other breather passage sizes are envisaged, and may be adapted to suit specific applications.

[0042] A drive head 120, here in the form of a rectangular prism defining four drive faces 121, is fixed to the cable trailing end 110b, here by welding. The drive head 120 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 110b and allowing cable tensioning equipment to grip the cable 110 adjacent the cable trailing end 110b without interference. An aperture 122 extends longitudinally through the drive head 120 and communicates with the breather passage 114, so as to communicate the breather passage 114 with the exterior of the trailing end of the cable bolt assembly 100.

[0043] The cable bolt assembly 100 further comprises a tensioning assembly 130 mounted on the cable 110 towards the cable trailing end 110b. In the cable bolt assembly 100 of the first embodiment, the tensioning assembly 130 comprises a barrel and wedge assembly 131 and a load bearing grout delivery fitting 132 mounted adjacent the barrel leading face 143. [0044] As best depicted in Figures 3 and 4, the grout delivery fitting 132 has a cable aperture 133 extending longitudinally through the grout delivery fitting 132 from a grout delivery fitting leading face 134 to a grout delivery fitting trailing face 135! The cable 110 extends through the cable aperture 133. The grout delivery fitting leading face 134 is configured to engage a bearer plate washer, as will be further discussed below. Particularly, the grout delivery fitting leading face 134 is in the form of a convexly curved body of revolution, which will typically be semi-spherical. This configuration allows for installations where the bearer plate washer does not extend perpendicular to the cable 1 10 on installation. The grout delivery fitting trailing face 135 is here generally planar and is configured to engage an anti -friction washer 136 that is mounted on the cable 1 10, separating the grout delivery fitting 132 and barrel and wedge assembly 131. The anti -friction washer 135 provides for relative rotation between the grout delivery fitting 132 and barrel and wedge assembly 131, whilst the cable 110 and barrel and wedge assembly 131 are being rotated during installation, as will be discussed further below. A grout delivery port 137 is defined in the side wall of the grout delivery fitting 132. The grout delivery port 137 extends generally perpendicular to the longitudinal axis of the cable 110 into the cable aperture 133 and in use receives a grout delivery lance for pumping grout into the grout delivery port 137. The cable aperture 133 has an enlarged diameter between the grout delivery port 137 and the opening 138, leaving an annular gap about the cable 110 for the passage of grout. The grout delivery port 137 and cable aperture 133 together form a grout delivery passage communicating the exterior of the tensioning assembly 130 with the opening 138 of the cable aperture 133 defined in the grout delivery fitting leading face 134. The grout delivery fitting 132 will typically be formed of steel.

[0045] The barrel and wedge assembly 131 comprises a barrel 139 and a set of standard wedges 140 mounted in the rearwardly facing tapered recess 141 defined in the barrel 139. An annular seal 142 is mounted on the cable 110 in the leading end of the recess 141, adjacent the wedges 140, so as to inhibit the passage of grout rearwardly through the barrel and wedge assembly 131 about the cable 1 10. Inhibiting the passage of grout will reduce the possibility of the wedges 140 becoming fouled in operation. The barrel leading face 143 is planar and is configured to engage the anti-friction washer 136.

[0046] Rather than the specific form of tensioning fitting 130 depicted in Figures 1 to 5, the tensioning assembly may alternatively have the grout delivery fitting and barrel integrally formed as a single fitting, in the manner described in International PCT Publication No. WO 2012/000016, the entire contents of which are incorporated herein by cross-reference. The tensioning fitting may also take the general form of the other equivalent fittings described in WO 2012/000016.

[0047] An annular sealing sleeve 150 extends about the cable 110 and particularly extends from the tensioning assembly 130 towards the cable leading end 110a. In the configuration depicted, the sleeve 150 is mounted on the grout delivery fitting 132, with the sleeve trailing end 150b located within the opening 138 of the cable aperture 133. The sleeve 150 is sized so as to leave an annular passage 151 between the cable 110 and the wall of the sleeve 150 for the passage of grout. The grout delivery passage defined by the grout port 137 and cable aperture 133 communicate the exterior of the tensioning fitting 130 with the annular passage 151 of the sleeve 150, allowing grout to be pumped through the grout port 137, up the cable aperture 133 and up the annular passage 151 to the sleeve leading end 150a. The sleeve 150 is configured to sealingly engage the wall of a bore hole into which the cable bolt assembly 100 is to be installed, here being provided with a series of flexible annular ribs 152, radially projecting from the wall of the sleeve 150, to engage the bore hole wall about the periphery of the sleeve 150. The ribs 152 are located towards the sleeve leading end 150a. In the arrangement depicted, the sleeve 150 is formed of two separate components, being a cylindrical trailing sleeve component 153 extending from the sleeve trailing end 150b and a leading sleeve component 154 mounted on the trailing sleeve component 153. The leading sleeve component 154 embodies the ribs 152 and extends to the sleeve leading end 150a. The sleeve leading component 154 will typically be formed of a urethane or other flexible plastics material, so as to enhance the sealing function of the ribs 152.

[0048] The length of the sleeve 150 may vary depending upon the application, however, the sleeve 150 will typically be relatively short in relation to the overall length of the cable bolt assembly 100, intended to project only a relatively short distance into the bore hole in which it is intended to be installed, sealing between the sleeve 150 and the wall of the bore hole relatively close to the bore hole opening. The length of the sleeve 150 will typically be between 0.1 m and 1.0 m. The sleeve 150 length may be dictated by the quality of the strata in the region of the rock face. It is common for fractured strata to be present close to the rock face, resulting in significant voids communicating with the bore hole. These voids can result in a significant amount of wasted grout if the grout is pumped directly into the bore hole from immediately adjacent the bore hole opening, at least partly filling the voids. The sleeve 150 may thus be provided with a length extending beyond such fractured strata adjacent to such rock face, such that the grout only engages the bore hole wall at locations beyond significant fractured strata.

[0049] As best depicted in Figures 1, 2 and 5, several bulbs 160, 170, 180 are formed in the cable 1 10, with each bulb 160, 170, 180 being formed by radially outwardly deforming a portion of each of the inner and outer sets of wires 112, 113 in any of various known manners. The bulbs 160, 170, 180 serve to inhibit relative longitudinal displacement between the inner and outer sets of wires 112, 1 13 effectively 'locking' the sets of wires 112, 113 together. For a 25 mm diameter cable 1 10, each of the bulbs 160, 170, 180 may have a diameter of the order of 40 mm.

[0050] One of the bulbs forms a breather bulb 160. Referring to Figure 5, the outward radial deformation of the inner and outer sets of wires 1 12, 113 within the breather bulb 160 provides a plurality of openings 161 between the individual wires of the cable 1 10 within the bulb 160. The openings 161 in the breather bulb 160 communicate with the breather passage 1 14 defined within the breather tube 111. This communication is provided in the arrangement depicted by forming a discontinuity in the breather tube 111, typically by cutting the breather tube 1 11 within the breather bulb 160 during bulb formation. It is alternatively envisaged that the breather tube 111 may be left intact, apart from forming one or more holes in the breather tube 1 11 at the location of the breather bulb 160. It is further envisaged that the breather tube 1 1 1 might only extend partway along the length of the cable 1 10, with the breather tube leading end being located within the breather bulb 160 or adjacent the breather bulb 160 (and towards the cable trailing end 110b). When a cementitious grout is pumped up the annular cavity between the cable and the bore hole wall (as will be discussed below) air in the annular cavity is able to pass through the openings 161 and down the breather passage 114 to the exterior of the cable 110 outside the rock face.

[0051 ] To assist in avoiding collapse of the breather bulb 160 upon application of a tensioning load on the cable 1 10 during installation, or further tensile loads in use, a rigid support element 165 is located within the breather bulb 160. The rigid support element 165 here has an aperture 166 extending therethrough and communicating with the grout passage 114. Specifically, here the rigid support element 165 is of a tubular form and is mounted on the grout tube 111, with the grout tube 111 extending into the aperture 166. The rigid support element 165 will typically be inserted into the breather bulb 160 during formation thereof whilst the breather bulb 165 is in a further radially expanded state, providing an increased gap defined by the openings 161 for placement of the rigid support element 165 into the breather bulb 160 and onto the breather tube 11 1. The rigid support element 165 may alternatively be slid onto the breather tube 111 during manufacture of the cable 110 and the inner and outer sets of wires 112, 133 subsequently helically wound about the breather tube 111 and rigid support element 165.

[0052] The bulbs located between the breather bulb 160 and the cable leading end 1 10a form resin anchoring bulbs 170. For the cable bolt assembly 100 depicted in Figures 1 to 5, three resin anchoring bulbs 170 are provided, equally spaced along the leading portion of the cable 110. As discussed below, this leading portion of the cable bolt 110 is anchored utilising a two-part component resin during installation. As well as locking the inner and outer sets of wires 1 12, 113, the resin anchoring bulbs 170 assist load transfer between the resin and the cable bolts by inhibiting slippage of the cable 1 10 through the resin when loaded. In the configuration depicted, the resin anchored leading portion of the cable 1 10 has a length of approximately one metre. Each of the resin anchoring bulbs 170 is of the same general configuration as the breather bulb 160. Each resin anchoring bulb 170 may include a rigid support element in the same manner as discussed above in relation to the breather bulb 160 to prevent collapse of the resin anchoring bulbs 170 during tensile loading of the cable bolt 110. Such rigid support elements within the resin anchoring bulbs 170 may be in the form of ball bearings. The resin itself, which would be infused through the resin anchoring bulbs 170 may, however, provide sufficient support to prevent collapse without the assistance of rigid support elements. Hence the resin anchoring bulb 170 depicted in Figure 5 is hollow.

[0053] To prevent resin travelling along the exterior of the cable bolt 110 towards the breather bulb 160 and blocking the openings 161, thereby preventing subsequent passage of air therethrough, an annular resin dam 178 will typically be mounted on the cable 110 adjacent the breather bulb 160, between the breather bulb 160 and the cable leading end 1 10a. The resin dam 178 is typically formed of steel but may be formed, for example, of plastic or a combination of both steel and plastic. In embodiments where the resin dam 178 is formed of steel, the outer diameter of the resiii dam 12 will be approximately the same as, or slightly less than, the diameter of the bore hole. Where the resin dam 178 is formed of a plastics material, the resin dam 178 will typically be slightly oversized so as to provide an interference fit with the wall of the bore hole during installation. The resin dam 178 may be in the form of a thin steel collar swaged to the cable 110, backing and supporting a steel washer facing the cable leading end 110a. It is envisaged that, in some applications, the series of three resin anchoring bulbs 170 might be sufficient to prevent any significant flow of resin along the cable 1 10 to the breather bulb 160, thereby enabling omission of the annular resin dam 178.

[0054] A ferrule may also be provided adjacent the cable leading end 110a both to restrain the wires 1 12, 1 13 and to assist in resin mixing.

[0055] One or more of the bulbs may form grout anchoring bulbs 180 located between the breather bulb 160 and the cable trailing end 110b. These grout anchoring bulbs 180 are again of the same basic configuration as the breather bulb 160 and may be provided at regular spaced intervals between the breather bulb 160 and the tensioning assembly 130. The grout anchoring bulbs 180 again act to lock the inner and outer sets of wires 112, 1 13 and assist in load transfer between the cable 110 and cementitious grout. A hollow rigid support element 185 is located in each grout anchoring bulb 180 as best depicted in Figure 5. Each hollow rigid support element 185 is of a tubular form the same as the rigid support element 165 and has an aperture 186 extending therethrough, for receipt of the breather tube 111. Each rigid support element 185 will typically be slid onto the breather tube 111 during manufacture of the cable 110 and the inner and outer sets of wires 112, 133 subsequently helically wound about the breather tube and rigid support element 185.

[0056] Installation of the cable bolt assembly 100 will now be described with particular reference to Figures 6 to 8. A bore hole 10 is drilled into a rock face 1 1 to be supported in the usual manner. With the absence of an external grout tube, the bore hole 10 may be drilled with a diameter only slightly larger than that of the bulbs 160, 170, 180, leaving a thin annular cavity between the cable 1 10 and the wall of the bore hole 10. A two-component resin cartridge 50 is loaded into the bore hole 10 and pushed toward the top thereof. The cable bolt assembly 100 is mounted on a standard installation rig and inserted into the bore hole 10. The cable 1 10 is rotated by engagement of the drive head 120 with the dolly of the installation rig as the cable 1 10 is driven upwardly through the bore hole 10, piercing the resin cartridge 50 as the cable 110 is advanced. Continuing rotation of the cable 1 10 aids in mixing of the two- component resin from the resin cartridge 50. Referring to Figure 7, the mixed resin 51 flows down the annular cavity between the cable 110 and wall of the bore hole 10. The flow of resin

51 is restricted to the upper portion of the annular cavity by virtue of the annular resin dam 178. The openings 161 in the breather bulb 160 thus remain clear of resin. During rotation of the cable 110, the barrel and wedge assembly 131 which is engaged with the cable 110, rotates with the cable 110. With the cable 110 being pushed towards the top of the bore hole 10, rotation of the grout delivery fitting 132 is inhibited by engagement with the washer plate

52 mounted on the cable 10 which in turn engages the rock face 1 1. The anti-friction washer 136 located between the grout delivery fitting 132 and barrel and wedge assembly 131 allows for the resultant relative rotation between the barrel and wedge assembly 131 and grout delivery fitting 132. After mixing of the resin, rotation of the cable 110 is stopped and the resin allowed to cure. The cable 110 is then pre-tensioned in the usual manner by applying tension, typically of the order of 20 tonnes for a 25 mm cable diameter, to the lower portion of the cable 110 via the hydraulic jack of the installation rig. The tensioning assembly 130 is thus driven against the washer plate 52 and against the rock face 11, with the grout delivery fitting leading face 134 engaging the rim of the washer plate 52.

[0057] After removal of the installation rig, a grouting lance is received in the grout delivery port 137. Cementitious grout is then pumped through the grout delivery port 137, up the cable aperture 133 in the grout delivery fitting 132 then up the annular passage 151 of the sleeve 150. The cemetitious grout then passes up the annular cavity between the cable 110 and the wall of the bore hole 10. The ribs 152 of the sealing sleeve 150 inhibit the passage of cementitious grout back out the bottom of the bore hole 10, sealing between the cable bolt assembly 100 and the wall of the bore hole 10. As the cementitious grout is pumped into the bore hole 10, air within the bore hole 10 passes through the openings 161 in the breather tube 160 and down the breather passage 1 14 defined by the breather tube 1 11. The air exits the trailing end of the cable bolt assembly 100 via the aperture 122 in the drive head 120. Once the grout is pumped up the bore hole 10 to the level of the breather bulb 1 0, grout starts to pass through the openings 161 in the breather bulb 160 and into the breather passage 114, where it falls down under pressure and gravity, exiting the cable bolt assembly 100 outside the rock face 1 1 via the aperture 122 in the drive head 120. When the operator pumping grout first notes grout exiting the aperture 122, pumping of grout is stopped and the grouting lance is removed from the grout delivery port 137, thus completing the installation process. Once the cementitious grout starts to escape from the aperture 122 in the drive head 120, the operator can be assured that the bore hole 10 has been effectively filled with cementitious grout from the sealing sleeve 150 up to the breathing bulb 160.

[0058] Figures 9 to 1 1 depict alternate configurations of mid portions of the cable bolt assembly 100, particularly depicting alternate configurations of rigid support elements mounted in the various bulbs 160, 170, 180.

[0059] In the arrangement depicted in Figure 9, the rigid support element 165 in the breather bulb 160 is again in a tubular form with the aperture 166 again communicating with the breather passage 114 defined in the breather tube 111, which has again been cut so as to form a discontinuity at the breather bulb 160. In this arrangement, however, the rigid support element 165 is not mounted over the breather tube 111, instead being wholly located within the discontinuity defined by the gap between sections of the breather tube 11 1. In this arrangement a rigid support element 175 in the form of a ball bearing is located within each of the resin anchoring bulbs 170. A discontinuity is again formed in the breather tube 111 to provide for positioning of the rigid support element 175. It is also envisaged, however, that the breather tube 111 may be omitted in this upper portion of the cable 110, or alternatively that the breather tube 11 1 may be crushed by installation of the rigid support element 175. The rigid support element 185 located within each grout anchoring bulb 180 is again in a tubular form and mounted on the breather tube 1 1 1.

[0060] In the arrangement depicted in Figure 10, the rigid support element 165' mounted in the breather bulb 165 is of a solid form without an aperture, here being in the form of a ball bearing. To allow for communication of the annular cavity about the cable bolt 110 through the openings 161 in the breather bulb 160 with the breather passage 114, the rigid support element 165 is spaced from the cut end portion of the section of the breather tube 111. The rigid support element 185' mounted in each grout anchoring bulb 180 has an open horseshoe or C-shaped cross-section which enables the rigid support element 185' to be mounted on the breather tube 1 1 1 during bulb formation, fitting the rigid support element 185 over the breather tube 111 when the grout anchoring bulb 180 is compressed into a more open configuration.

\ [0061 ] In the arrangement of Figure 1 1 , both the rigid support element 165 " in the breather bulb 160 and the rigid support element 185' in each grout anchoring bulb 180 have a generally horseshoe or C-shaped cross-section.

[0062] A cable bolt assembly 200 according to a second embodiment is depicted in Figures 12 through 16. Features of the cable bolt assembly 200 that are identical to those of the cable bolt assembly 100 are provided with identical reference numerals. The cable bolt assembly 200 of the second embodiment is effectively identical to the cable bolt assembly 100 of the first embodiment, apart from the configuration of the tensioning assembly 230 and annular sealing sleeve 250. The tensioning assembly 230 is of the same general configuration as that described in Australian Provisional Patent Application No. 2012902372, the entire contents of which are incorporated herewith by cross-reference. The tensioning assembly 230 comprises a tensioning member 231 , a barrel and wedge assembly 240 and a domed washer 245.

[0063] The tensioning member 231 comprises an externally threaded leading, tubular element 232 and a trailing drive head 233 that is fixed in relation to the tubular element 232. In the arrangement depicted, the drive head 233 is integrally formed with the tubular element 232. A cable aperture 234 extends through the length of the tensioning member 231 , through the tubular element 232 and drive head 233. The cable 110 extends through the cable aperture 234. The cable aperture 234 is sized larger than the diameter of the cable 110 so as to allow the cable 110 to freely rotate in the cable aperture 234 relative to the tensioning member 231 and to define, in part, a grout passage 235 communicating the tubular element leading end 232a and the exterior of the drive head 233. For example, for a 23.5 mm diameter cable 110, the cable aperture 234 may suitably have a diameter of approximately 32 mm.

[0064] In the arrangement depicted, the grout passage 235 is further defined by a grout delivery port 236 formed in an exterior surface of the drive head 233, and particularly in one of the six drive faces 237 of the hexagonal drive head 233. The grout delivery port 236 is adapted to receive a grout delivery lance as per the grout delivery port 137 of the cable bolt assembly 100 of the first embodiment. An annular seal 238 is located in the cable aperture 234 immediately aft of the grout delivery port 236 and sized to lightly engage the cable 1 10, so as to inhibit passage of grout past the annular seal 238, while still allowing free rotation of the tensioning member 231 relative to the cable 110. In the arrangement depicted, the external thread on the tubular element 232 is a left-hand thread extending along the full length of the tubular element 232.

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[0065] A thrust bearing 248 is mounted on the cable 1 10 between the drive head 233 and the barrel and wedge assembly 240. The thrust bearing 248 is located within a recess defined in the trailing face of the drive head 233. The thrust bearing 248 has a longitudinal depth equal to that of the recess, such that it is substantially flush with the base of the recess. The barrel and wedge assembly 240, comprising a barrel 241 and wedge elements 242, is mounted on the cable 1 10 between the drive head 233 and the cable trailing end 110b.

[0066] The washer 245 is mounted on the tubular element 232 and has a washer leading face 246 adapted to engage the rim of the standard plate washer 52 through which the cable 110 extends in use. The washer 245 has a washer trailing face 247 that is generally planar and an internally threaded washer aperture 248 which threadingly engages the tubular element 232 by way of the external thread of the tubular element 232. An anti-friction washer 249 is also mounted on the tubular element 232 and located between the washer trailing face 247 and drive head 233. The anti-friction washer 249 and washer trailing face 247 radially project beyond the drive head 233, allowing a dolly to transfer a thrust load to the washer 245 via the anti-friction washer 249 during installation.

[0067] In this embodiment, the sealing sleeve 250 is mounted on the tubular element leading end 232a. The sleeve 250 is again sized so as to leave an annular passage 251 between the cable 1 10 and the wall of the sleeve 250 for the passage of grout. The sleeve 250 is again configured with a series of flexible annular ribs 252 radially projecting from the wall of the sleeve 250. In the configuration depicted, the sleeve 250 is of a unitary construction, with ribs 252 being provided along its length. The length of the sleeve 250 will again be dictated by the same considerations as described above in relation to the sleeve 150 of the first embodiment.

[0068] Installation of the cable bolt assembly 200 is again first commenced by loading a two-component resin cartridge into the bore hole and pushing it towards the top thereof. The cable bolt assembly 200 is installed into the bore hole 10 by way of a dolly engaging the drive head 120. The dolly is rotated as it thrusts the cable 110 toward the top of the bore hole 10, ί

17

such that the cable 110 rotates as it advances, puncturing and shredding the resin filled cartridge and mixing the two-component resin.

[0069] The barrel and wedge assembly 240 rotates with the cable 110, however the thrust bearing 248 and the clearance between the cable 1 10 and the cable aperture 234 prevents any significant torque being applied to the tension member 231. Whilst some small transfer of torque may result in the tension member 231 rotating to some degree, some inevitable interference with the wall of the bore hole 10 will typically result in the tension member 231 not rotating during the mixing process. Friction between the washer 245 and rim of the plate washer 52, resulting from the axial load applied by the dolly, will also typically be sufficient to prevent the washer 245 rotating during the mixing process. Rotation of the dolly is then stopped, allowing the resin to set.

[0070] The hexagonal drive head 233 is then engaged, typically with a second dolly. Initial upward thrust is applied to the second dolly such that the leading end of the second dolly engages the radially protruding portion of the anti-friction washer 249 which in turn engages the washer trailing face 247. The thrust load is thus transferred to the washer 245 to provide initial engagement between the external thread of the tubular element 232 and the internal thread of the washer 245. The anti-friction washer 249 reduces the friction that would otherwise exist between the second dolly and the washer trailing face 247 upon rotation of the second dolly. The second dolly is then rotated to drive the drive head 233, drawing the tensioning member 231 rearwardly in relation to the washer 245, with which it is threadingly engaged. Friction between the washer 245 and rim of the washer plate 52 again generally prevents the washer 245 from rotating with the tubular element 232, thereby allowing the tubular element 232 to retract through the washer 245 as the second dolly is rotated. The clearance fit of the cable 110 in the cable aperture 234 also prevents the tensioning member 231 from applying any significant torque to the cable 110. The drive head 233 acts through the thrust bearing 248 to draw the barrel and wedge assembly 240 rearwardly. The standard reverse taper configuration of the barrel 241 and wedge elements 242 ensure that the barrel and wedge assembly 240 remains firmly affixed to the cable 110 under this load and, therefore, acts to pre-tension the cable 110.

[0071] The second dolly continues to rotate until the desired degree of pre-tension in the cable 110 is achieved, following which the second dolly is removed, leaving the completed cable bolt installation as depicted in Figure 17. Rather than using two separate dollys, the cable bolt assembly 200 may alternately be installed using a two stage dolly.

[0072] The tensioned cable bolt assembly 200 is then post-grouted in the same general manner as described above in relation to the first embodiments, pumping grout through the grout delivery port 236, up the grout passage 235 and up the annular cavity 251 into the bore hole. As shown in Figure 17, the sealing sleeve 150 may extend to beyond the voids 13 in the lower fractured region of the strata, such that significant volumes of grout are not wasted filling the voids.

[0073] A person skilled in the art would appreciate various modifications of the cable bolt assemblies specifically described above, without departing from the scope of the invention. One such modification would be to configure to cable bolt leading end portion with a mechanical anchor, such as a mechanical shell anchor, rather than relying on resin anchoring of the leading portion of the cable.

Claims

1. A cable bolt assembly comprising:

a tensioning assembly mounted on said cable adjacent said cable trailing end;

2. The cable bolt assembly of claim 1 , wherein said at least one set of wires comprises an inner set of wires helically wound about said grout tube and an outer set of wires helically wound about said inner set of wires. \

3. The cable bolt assembly of claim 1, wherein said cable bolt further comprises a drive head at said cable trailing end, said drive head having an aperture extending therethrough communicating with said breather passage.

4. The cable bolt assembly of claim 1, wherein said cable bolt further comprises an annular resin dam mounted on said cable between said breather bulb and said cable leading end.

5. The cable bolt assembly of claim 1, wherein a rigid support element is located within said breather bulb, so as to inhibit collapse of said breather bulb upon the application of a tensile load to said cable.

6. The cable bolt assembly of claim 5, wherein said rigid support element located within said breather bulb has an aperture extending therethrough communicating with said breather passage.

7. The cable bolt assembly of claim 1, wherein said breather tube is discontinuous at said breather bulb so as to provide for communication of said openings with said breather passage.

8. The cable bolt assembly of claim 1, wherein, said breather tube is provided with an aperture so as to provide for communication of said openings with said breather passage.

9. The cable bolt assembly of claim 1 , wherein a leading end of said breather tube is located within or adjacent said breather tube so as to provide for communication of said openings with said breather passage.

10. The cable bolt assembly of claim 1, wherein at least one grout anchoring bulb is formed in said cable between said breather bulb and said cable trailing end.

1 1. The cable bolt assembly of claim 10, wherein a hollow rigid support element is located within each said grout anchoring bulb, so as to inhibit collapse of the respective said grout anchoring bulb on the application of a tensile load to said cable bolt, said hollow rigid support element in each said grout anchoring bulb having an aperture extending therethrough with said breather tube extending through said aperture.

12. The cable bolt assembly of claim 10, wherein at least one resin anchoring bulb is formed in said cable between said grouting bulb and said cable leading end.

13. The cable bolt assembly of claim 11, wherein three said resin anchoring bulbs are formed in said cable.

14. The cable bolt assembly of claim 12, wherein a rigid support element is located within each said resin anchoring bulb, so as to inhibit collapse of the respective said resin anchoring bulb upon the application of a tensile load to said cable bolt.

15. The cable bolt assembly of claim 14, wherein said rigid support element in each said resin anchoring bulb comprises a ball.

16. The cable bolt assembly of claim 1 , wherein said tensioning assembly comprises a barrel and wedge assembly mounted on said cable towards said cable trailing end and a grout delivery fitting mounted on said cable adjacent said barrel and wedge assembly between said barrel and wedge assembly and said cable leading end, said grout delivery fitting defining said grout delivery passage.

17. A method of installing the cable bolt assembly of claim 1 , said method comprising: drilling a bore hole in a rock face of a strata to be secured;

inserting said cable into said bore hole;

tensioning said cable utilising said tensioning head assembly;

pumping grout through said grout delivery passage, through said sealing sleeve and along an annular cavity defined between said cable and the wall of said bore hole to said breather bulb;

allowing air to escape from said annular cavity through said breather bulb and said breather tube; and

18. The method of claim 17, wherein securing said leading region of said cable comprises: inserting a resin filled cartridge having a frangible casing into said bore hole before inserting said cable into said bore hole;

engaging said cable leading end with said resin filled cartridge;

thrusting said cable further into said bore hole and rotating said cable so as to rupture said frangible casing and mix said resin; and

allowing said resin to cure.