AU2015204352A1 - Tensionable, Flush Ended Rock Bolt - Google Patents

Abstract

Abstract A rock bolt comprising a tubular tensioning sleeve 20 that screws onto the back of a solid 24 or hollow bar 21 such that when the tensioning sleeve 20 is rotated in one direction it will not unscrew from the bar 21,24 because a thread stop 4 on the back end of the bar 21,24 prevents this, but when the sleeve 20 is rotated in the opposite direction it will screw further onto the bar 21,24. The tubular tensioning sleeve 20 fits up the borehole 27 and only the larger diameter collar 10 and domed ball sections 9 protrude from the borehole after the sleeve 20 is tensioned up against a bearing plate 25 which then supports a rock face. Tensioning of the sleeve 20 occurs on the threaded connection between the sleeve 20 and the bar 21,24 which is located up the borehole 27. The tubular tensioning sleeve 20 is hollow and when screwed onto a hollow bar 21, the bolt assembly can be used as a self drilling rock bolt, or a bolt that can be post grouted with resin or cement grout. The bolt assembly can also be used with solid bars and be anchored with a resin cartridge and or a mechanical anchor device. K - N A -~ N, A~ ~ 'A' A" A~'A A- ~'A A" ,.A -' - -A A .A ' <"-' N ~A"' K §2< '4 A 'Nfl, 4) N > ~,-A 4 I"' -~ 44 ~ -A' A~ C) N A' "" A' A' A> it -A' -A - I A' 9 A -AiA~A i A"'' - AA A "NJ I .A' I"" A-,'>A ~A A ' IN ~ '24 / I N A i"A A""' A"' A A' I' ,§~ A' 1~' "N ' i/fr>1 if / 4) I 0 t I N 4) I 'k*' U w A' it 1 -t -~ C)N r~ L,. ""N, C)> ~ -~ - 'N f--A'/ 7 SN / 6Th

Description

TENSIONABLE, FLUSH ENDED ROCK BOLT Field of the Invention [0001] The present invention relates to a rock bolt with a substantially flush end that protrudes only a minor amount into a roadway or tunnel, but that can also be tensioned up against the roadway or tunnel wall by having a tensioning system up the borehole. Background to the Invention [0002] Rock bolts are in widespread use in mining, tunnelling and civil engineering, and there are a wide range of bolts available. In many geotechnical conditions, it is advantageous to apply a confining force to the rock face being supported, typically by tensioning up a nut on a threaded section on the exposed bottom end of the rock bolt. As the nut is tensioned up along the thread on the bolt, it then forces a bearing plate forwards against the rock face to apply a confining load to support the roadway or tunnel roof or wall. Typically, a nut that is tensioned up on a rock bolt could apply a confining load of between 2 and 7 tonnes depending on the torque applied to the nut, the thread pitch of the nut and the bolt, and the friction on the threads and on the front of the nut face applying the load. [0003] Alternatively, a rock bolt could be tensioned up by having a threaded section on the top end of the rock bolt which is up the borehole, and this threaded section then screws through and into a mechanical anchor type device up in the borehole. Typical the mechanical anchor device used is an expansion shell type anchor, which has a wedge which is pulled down the borehole and forces two or more shells outwards against the borehole wall. In this case, the wedge has a threaded central hole that the rock bolt screws through such that rotation of the rock bolt causes this wedge to move downwards or backwards down the borehole and forces the wedges outwards against the borehole wall to lock it in position in the borehole. As the wedge up the borehole becomes locked in position, further rotation of the drive head on the bottom end of the bolt causes it to be pulled upwards against the rock face. [0004] Both of these types of rock bolts are known as tensionable rock bolts, and they could be used with either solid or hollow bars, but they have the general ability to apply a confining force to support a rock face by rotation of either the nut or the bolt. [0005] For the case of a nut being tensioned up along a thread on the lower end of the rock bolt, a section of this threaded bolt is left protruding into the roadway or tunnel depending on how far the nut can be tensioned up along the thread on the rear end of the bolt. This is commonly known as the tail on the end of the rock bolt. The length of this tail depends primarily on the evenness or flatness of the rock face, and how broken or intact the rock is. In the case of flat rock face in competent rock, the length of tail would be small, typically only 20-30mm. However, in the case of a broken, uneven rock face, the length of tail may be 200mm or more. [0006] In the case of self-drilling rock bolts having a drill bit incorporated in their end, the nut fits into a drive dolly which rotates the bolt in one direction to drill the borehole, then in the opposite direction to tension the bolt. However, in the tensioning operation, the bolt tail is drawn into the dolly, and may force the nut to rise up out of full engagement with the drive dolly. The solution is to provide a longer dolly, to receive a longer tail length, but this may be cause practical difficulties when working in limited spaces. [0007] For the case of a rock bolt being tensioned up along a thread on the upper end of the rock bolt using a mechanical anchor up the borehole, the exposed drive end of the rock bolt typically has a forged head, such as a forged square or hex nut, that can be used to rotate the bolt. In this case the forged head forms a very short tail on the bolt and protrudes only a minimum amount into the roadway or tunnel. However, this tensioning method requires the use of a mechanical anchor up the borehole, and this mechanical anchor is pre-assembled onto the front end of the rock bolt. This then requires the use of a large diameter borehole such that the mechanical anchor can fit into the borehole and can be pushed up into it. The requirement to use a large diameter borehole has the disadvantage that it takes longer to drill than a smaller diameter borehole, and requires more cement grout or resin to fill it if the bolt is subsequently grouted. Typically, point anchored bolts using expansion shell mechanical anchors are used with solid bolts and are therefore not post grouted. If this type of bolt is not post grouted, then it has the disadvantage that it has limited anchor capacity from its mechanical anchor only. [0008] There are also split set bolts that have a steel ring welded onto the end of a split steel tube, and these split set bolts protrude only a very small amount into a roadway or tunnel. These split set bolts are hammered into a borehole which is smaller in diameter than the steel tube, such that the steel tube closes slightly to fit into the borehole. Friction then holds the steel tube in the borehole. However these split set bolts have the disadvantage that they cannot be tensioned up. Summary of the Invention [0009] It is an object of the disclosure to provide a rock bolt that which overcomes some or all of the above disadvantages. [0010] The present invention provides a rock bolt of the type that can be tensioned up against a rock face such that a bearing plate can be forced against a rock face or against steel mesh to support the rock face. [0011] The rock bolt may be fully encapsulated with resin using a resin cartridge using the solid bar embodiment of the invention, or can be pumped full of cement grout or resin using the hollow bar embodiment of the invention. [0012] In addition, the present invention may provide a bolt assembly that is better able to resist shear and bending forces near the borehole collar, because of the larger diameter sleeve section used on the lower end of the bolt at the borehole collar. [0013] Further, the present invention may provide a bolt assembly that incorporates semi hemispherical faces on its rear end such that a bearing plate can swivel with respect to the end of the bolt to allow the bolt to be installed at a range of angles to a rock face. [0014] In accordance with one aspect of the disclosure, there is a rock bolt comprising: a bar having a leading end and a trailing end, the bar having an externally threaded portion proximal the trailing end; a tensioning sleeve having a front end and a rear end, having an internally threaded portion adjacent the front end adapted to mate with the externally threaded portion of the bar such that the bar may be threadably extended or retracted relative to the tensioning sleeve, the sleeve having an enlarged diameter portion adjacent the rear end adapted to co operate with a bearing plate and a hollow rear end adapted to receive a drive stub; thread stop means limiting threaded extension of the bar relative to the tensioning sleeve; a drive stub inserted within the hollow rear end of the tensioning sleeve, having a drive socket recess for receiving a drive member; whereby upon rotation of the drive stub and tensioning sleeve in the first direction, the thread stop means causes the bar also to rotate in the first direction, and whereby after fixing of the bar within the borehole, rotation of the drive stub and tensioning sleeve in an opposite, tensioning direction causes relative retraction of the bar and the sleeve and tightening of the bolt. [0015] The rock bolt may be a self-drilling rock bolt, the bar having a drill bit adjacent the leading end adapted to drill a borehole when the bar is rotated in the first direction, and wherein the thread stop causes the bar to rotate with the tensioning sleeve in the first direction to drill the borehole. [0016] The drive stub may include a passage through a base of the drive socket for injection of a fluid into the rock bolt. [0017] The drive stub further may further include a seal in said passage for sealing to a fluid injector, and the drive stub socket may be adapted to receive a combined drive member and injector device. [0018] In one optional form, the drive stub includes an internally threaded portion adapted to allow threaded attachment of an article - such as a measuring device to test strength of attachment of the rock bolt in the borehole, or a hook, hanger, or similar - to the rock bolt after the rock bolt is secured in the borehole. [0019] Further example embodiments are described below. [0020] Example forms of the disclosure include a tubular tensioning sleeve which has a section of internal thread at its front end, and a larger diameter external section at its rear end which may comprise a larger diameter shoulder and or a larger diameter semi hemispherical surface or surfaces. Between the larger diameter rear end of the sleeve and the internal threaded section at the front end of the sleeve, is a plain hollow section which has a larger diameter internal hole than the threaded section at the front of the sleeve such that there is a small shoulder created between the plain hollow section and the threaded section of the sleeve. This shoulder forms a barrier against which the thread stop on the end of the bar stops against when the sleeve is unscrewed with respect to the bar. [0021] The threaded section of the tubular tensioning sleeve can then be screwed onto a threaded section on the rear end of a bar or bolt. The threaded section on the rear end of the bar or bolt is long enough such that the sleeve can be fully screwed onto the bar or bolt. [0022] The internal threaded section in the sleeve is long enough such that when the thread engagement between the sleeve and the bar or bolt is at a minimum engagement length when the sleeve is in the fully unscrewed position against the internal thread stop on the bar or bolt, that the tensile strength of the thread engagement is greater than the tensile strength of either the sleeve or of the bar or bolt. [0023] The bar or bolt has a thread stop fixed to its rear end which prevents this thread stop from being screwed through the internal thread in the sleeve. Typically for manufacturing assembly, the sleeve is screwed onto the bar or bolt until the rear end of the bar or bolt is protruding through the rear end of the sleeve. The thread stop can then be welded or otherwise fixed onto the rear end of the bar or bolt, and then the sleeve can be unscrewed with respect to the bar or bolt until the thread stop contacts the shoulder at the start of the thread inside the sleeve. The length of the sleeve can be any suitable length depending on the amount of tensioning required. For example, for flat rock faces in competent rock, a short tensioning length may be all that is required. However, for broken or irregular rock faces in weak rock, a longer tensioning length may be required. [0024] There may also be provided a rock bolt comprising a bar which has an external thread, and a tubular tensioning sleeve with an internal threaded section. The sleeve can be screwed onto the thread on the bar and be threadably connected to it. The internal threaded section in the sleeve is long enough such that the tensile strength of the threaded connection between the bar and the sleeve, is optionally at least equal to the tensile strength of the bar and of the sleeve. [0025] The sleeve may also have a section of plain hole which has an internal diameter which is slightly larger than the internal diameter of the thread inside the sleeve. This section of the sleeve with the plain hole, is typically longer than the threaded section of the sleeve, and is immediately behind it, and comprises most of the length of the middle section of the sleeve. The back end of the sleeve comprises a larger diameter section with a domed, e.g. semi-hemispherical external surface or surfaces. This semi-hemispherical external surface acts like a hemispherical washer or hemispherical domed ball and allows this end of the bolt to engage with the hole in a bearing plate at a range of different angles to accommodate uneven rock surfaces. [0026] The extreme back end of the sleeve also has a large diameter shoulder or collar on its outer surface to prevent the sleeve being pulled through the hole in a bearing plate at extreme loads. [0027] The internal hole at the back end of the sleeve has a short threaded section to enable a female drive stub to be screwed into the sleeve. This female drive stub has a noncircular internal hole which may be a square or hex or any other suitable shaped internal hole to enable a drive dolly to be inserted into this non-circular shaped hole, such that this drive dolly is then able to rotate the stub and hence rotate the whole bolt assembly. This female drive stub is inserted into the sleeve after assembly with the bar, and is typically permanently fixed to the sleeve by welding. [0028] The tubular tensioning sleeve is designed such that it has approximately the same tensile strength as the bar. The bar at least has a section of thread on its rear end that the sleeve can screw onto. Alternatively, the bar could be threaded along its entire length. [0029] The back end of the threaded bar typically has a thread stop which fits closely into the plain hole section inside the sleeve. This thread stop also typically has an external 0 ring to create a seal between the thread stop and the plain hole in the sleeve, such that any drilling water or resin or grout pumped along the sleeve will not leak through the threaded connection between the sleeve and the bar, but will be forced along the central hole inside the hollow bar. This thread stop is fixed to the end of the bar typically by welding. [0030] To assemble the components of the whole bolt, the sleeve is first screwed onto the threaded bar such that the back end of the threaded bar protrudes through the back end of the sleeve. The thread stop can then be welded onto the back end of the threaded bar while the threaded bar is already screwed into the sleeve. The sleeve is then unscrewed along the threaded bar until the thread stop moves further into the plain hole inside the central section of the sleeve until it hits the shoulder at the start of the internal thread inside the sleeve. Once the thread stop hits the shoulder at the start of the thread inside the sleeve, it cannot advance past this shoulder. Consequently further unscrewing rotation of the sleeve will force the bar to rotate with it in this rotational direction. [0031] The female drive stub can then be fitted to the back end of the sleeve and be fixed to it typically by welding and or by screw threads. The female drive stub has a hexagonal or other non circular internal hole which will typically accommodate a drive dolly which is used to rotate the whole bolt assembly. [0032] In one embodiment of the invention, a hollow threaded bar is used and this enables the invention to be used as a self drilling bolt, or as a groutable bolt. For the self drilling bolt version of the invention, the sleeve can be rotated in an unscrewing direction such that the thread stop on the threaded bar prevents the sleeve from being unscrewed off the threaded bar and the thread stop forces the bar to rotate with the sleeve and hence drill the borehole. The diameter of the borehole is sufficient to allow clearance for the sleeve in the lower part of the borehole. Once the borehole has been drilled, resin or cement grout can then be pumped through the sleeve and through the hollow bar to encapsulate the bolt. Once the grout or resin has hardened sufficiently to anchor the threaded bar, the sleeve can then be rotated in the opposite direction to the drilling direction, and can be screwed up along the threaded bar to tension the collar at the rear end of the sleeve up against the bearing plate and up against the rock face. [0033] In an alternative embodiment of the invention, a mechanical anchor device may be used on the front end of the self drilling rock bolt version of the invention. This mechanical anchor device may be similar to the one described in patent number PCT/AU2011001146 ("Mechanical Anchor for Bolts, Rock Bolts and Self Drilling Rock Bolts"). The bar and sleeve are rotated in one direction to drill the borehole, and once the borehole is completed, the sleeve is rotated in the opposite rotation direction to the drilling direction. As the sleeve is rotated in the opposite direction to the drilling direction, the initial resistance of the threads of the sleeve and the bar to unscrew causes the threaded bar to also rotate in the same direction, and this in turn causes the mechanical anchor device to activate and lock the bar into the borehole. Further rotation of the sleeve, then breaks the thread resistance and enables the sleeve to be tensioned up along the thread on the bar, and in turn tension up against the bearing plate and up against the rock face. Once the bolt has been tensioned up, cement grout or resin can then be pumped through the bolt and into the borehole to completely encapsulate the bolt in the borehole. [0034] The advantage of using a mechanical anchor on the leading end of the rock bolt with this invention is that the sleeve can be fully tensioned up against the rock face prior to resin or grout being pumped into the borehole. Consequently the sleeve is in its final position with most of it being positioned inside the rear end of the borehole. Therefore the resin or cement grout can be pumped into the borehole to completely encapsulate the bolt, without the need to monitor or restrict the volume of grout being pumped to allow room for the sleeve to move further into the borehole during tensioning of the sleeve. [0035] In another embodiment of the invention, a solid threaded bar is used and this enables the bolt to be used with resin cartridges. In this case, a borehole is drilled with a drill rod, and then a resin cartridge is inserted into this borehole, and is then pushed to the back of the borehole by the solid threaded bar. As the threaded bar is pushed further into the borehole, -0 the resin cartridge ruptures and resin flows back down the borehole into the annulus space between the threaded bar and the borehole wall. The whole bolt assembly is then rotated by the drilling machine to thoroughly mix the resin. [0036] This rotation can be achieved by rotating the sleeve in a direction tending to extend the bar until the thread stop prevents the sleeve from being unscrewed off the bar, and the thread stop forces the bar to rotate with the sleeve and hence mix the resin. Once the resin has been mixed and hardened, rotation of the sleeve in the opposite direction will cause the sleeve to screw onto the threaded bar, and tension up against the rock face. [0037] The invention could be used with either solid or hollow threaded bars, or other bars with a threaded section long enough to accommodate the tensioning length in the sleeve. For example, solid deformed bars with a threaded section on its back end. [0038] Further aspects of the disclosure will be apparent from the description and drawings, and from the claims. Description of the Drawings [0039] In order that the invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings illustrating optional embodiments of the disclosure, in which: [0040] Figure 1 is a plan view of a tensionable, substantially flush-ended, self drilling rock bolt 1 with a tensioning sleeve 20, a hollow threaded bar 21 and a drill bit 12. The tensioning sleeve 20 has a larger diameter collar 10 and a domed/semi-hemispherical face or faces 9 at its back end, together forming a wider portion at the rear of the tensioning sleeve for applying force to a bearing plate, as will be described further below. [0041] Figure 2 is a sectional view A-A shown in Figure 1 of a tensionable, substantially flush-ended, self drilling rock bolt 1 with a tensioning sleeve 20, a hollow threaded bar 21 and a drill bit 12 with the sleeve 20 in the fully unscrewed position or in the rotational drilling (i.e. fully extended) position. [0042] The bar 21 has an internal hole 8 and a thread stop 4 fixed to the back end of the bar 21. The thread stop 4 has an 0 ring 18 that hydraulically seals between the hole 7 and the thread stop 4. The tensioning sleeve 20 has a section of internal female thread 5 at the front end of the sleeve 20, and the back end of this threaded section 5 has a small shoulder 11 between the threaded section 5 and the plain hole 7. The sleeve 20 has a plain internal hole 7 in the middle part of the sleeve 20. The back end of the sleeve 20 has the larger diameter collar 10 and the semi-hemispherical faces 9, as well as an internal, fitted threaded stub 23. This threaded stub 23 is fixed to the sleeve 20 via mating internal thread 34 in the tensioning sleeve and external thread 40 in the drive stub, plus weld 33, and has a non circular - for example square or hex - drive socket recess 22 which is used to rotate the sleeve 20. The base of the drive socket communicates with fluid passages 29 and 30 through the drive stub, communicating in turn with the hole 7 of the tensioning sleeve, and through that to the internal passage 8 of the bar. [0043] The combination of threaded engagement and weld between the tensioning sleeve and the drive stub provides improved resistance to tension forces, with the weld preventing the drive stub from unscrewing from the tensioning sleeve. [0044] Passage 32 of the drive stub includes an internal threaded portion 32, which may be used for attachment of measurement sensors or gauges after the rock bolt is installed, or may be used to screw in hangers or other useful articles. [0045] Figure 3 is an expanded view of Area C shown in Figure 2 showing the detail of the threaded connection between the sleeve 20 and the bar 21 where the thread stop 4 on the bar 21 is against the shoulder 11 at the start of the threaded section 5 in the sleeve 20. The thread stop 4 is typically fixed onto a machined section 6 of the bar 21. [0046] Figure 4 is a sectional end view B-B shown in Figure 2 of the end collar 10 showing the threaded stub 23 and the non-circular hexagonal drive socket 22. [0047] Figure 5 is another sectional view of a tensionable, substantially flush ended, self drilling rock bolt 1 similar to Figure 2 except showing the bolt 1 in a borehole 27 in rock 26. The sleeve 20 is in the fully unscrewed position or in the rotational drilling position with the thread stop 4 against the shoulder 11. The sleeve 20 has rotated the bar 21 and the bar 21 has rotated the drill bit 12 fixed to its front end to drill the borehole 27 in the rock 26. Figure 5 shows that a bearing plate 25 has been positioned on the sleeve 20 prior to drilling the borehole 27. [0048] Figure 6 is another plan view of a tensionable, substantially flush-ended, self drilling rock bolt 1 with a tensioning sleeve 20, a bar 21 and a drill bit 12 with the sleeve 20 in the tensioned position. Reamer/cutter projections 31 on the front end of the tensioning sleeve serve to widen the borehole drilled by drill bit 12 to accommodate the larger diameter of the tensioning sleeve.

_1 V_ [0049] Figure 7 is a sectional view E-E shown in Figure 6 with a sleeve 20, a bar 21 and a drill bit 12 with the sleeve 20 in the tensioned position. The sleeve 20 has been screwed along the thread on the bar 21 and the thread stop 4 and the rear end of the bar 21 have moved further backwards into the central hole 7 of the sleeve 20. [0050] Figure 8 is an expanded view of Area F shown in Figure 7 showing the detail of the threaded connection between the sleeve 20 and the bar 21 where the threaded section 5 in the sleeve 20 has screwed further onto the bar 21. The plain hole 7 in the sleeve 20 allows clearance for the thread on the bar 21 such that the bar 21 can move into the hole 7. [0051] Figure 9 is another sectional view of a tensionable, substantially flush ended, self drilling rock bolt 1 similar to Figure 7 except showing the bolt 1 in a borehole 27 in rock 26. The sleeve 20 is in the tensioned or tightened or screwed-on position with respect to the bar 21. The drill bit 12 has drilled a borehole 27 which provides clearance for the sleeve 20 such that the sleeve 20 can be screwed into the borehole 27. Rotation of the sleeve 20 with respect to the bar 21 in the tightening direction causes the sleeve 20 to advance into the borehole 27 and the semi hemispherical faces 9 on the sleeve 20 contact the bearing plate 25 and force the bearing plate 25 against the rock face 28 being supported by the bolt 1. The sleeve 20 is rotated and tightened by using a drive dolly (such as that in Figure 34) in the drive socket 22 and rotating the drive dolly with a drilling machine (not shown). Tightening rotation of the sleeve 20 is continued until the bearing plate 25 cannot be forced any further against the rock face 28. [0052] Figure 10 is a plan view of another embodiment of a tensionable, substantially flush-ended, rock bolt 2 with a tensioning sleeve 20 and a solid threaded bar 24. The tensioning sleeve 20 has a larger diameter collar 10 and a semi-hemispherical face or faces 9 at its back end. [0053] Figure 11 is a sectional view H-H shown in Figure 10 of a tensionable, substantially flush-ended, solid rock bolt 2 with a tensioning sleeve 20, a bar 24 with the sleeve 20 in the fully unscrewed position. The bar 24 has a thread stop 4 fixed to the back end of the bar 24. The tensioning sleeve 20 has a section of internal female thread 5 at the front end of the sleeve 20, and the back end of this threaded section 5 has a small shoulder 11 between the threaded section 5 and the plain hole 7. The sleeve 20 has a plain internal hole 7 in the middle part of the sleeve 20. The back end of the sleeve 20 has the larger diameter collar 10 and the semi-hemispherical faces 9, as well as an internal, fitted threaded stub 23.

This threaded stub 23 is fixed to the sleeve 20 and has a non circular internal drive socket 22 which is used to rotate the sleeve 20. [0054] Figure 12 is an expanded view of Area I shown in Figure 11 showing the detail of the threaded connection between the sleeve 20 and the bar 24 where the thread stop 4 on the bar 24 is against the shoulder 11 at the start of the thread 5 in the sleeve 20. [0055] Figure 13 is another sectional view of a tensionable, substantially flush ended, rock bolt 2 similar to Figure 11 except showing the bolt 2 in a borehole 27 in rock 26. The sleeve 20 is in the fully unscrewed position or in the rotational drilling position with the thread stop 4 against the shoulder 11. The sleeve 20 is in its fully unscrewed (i.e. extended) position with respect to the bar 24. Figure 5 shows that a bearing plate 25 has been positioned on the sleeve 20 prior to inserting the bolt 2 in the borehole 27. [0056] Figure 14 is another plan view of a tensionable, substantially flush-ended, rock bolt 2 with a sleeve 20, and a bar 24 where the sleeve 20 is in the tensioned position. [0057] Figure 15 is a sectional view K-K shown in Figure 14 with a sleeve 20, and a bar 24, with the sleeve 20 screwed on to the threaded bar in the almost fully tensioned position. [0058] Figure 16 is an expanded view of Area L shown in Figure 15 showing the detail of the threaded connection between the thread in the sleeve 5 and the bar 24 where the sleeve 20 has screwed onto the bar 24 and the bar 24 has moved further into the hole 7 in the sleeve 20. [0059] Figure 17 is another sectional view of a tensionable, substantially flush ended, rock bolt 2 similar to Figure 15 except showing the bolt 2 in a borehole 27 in rock 26. The sleeve 20 is in the tensioned or tightened or screwed-on position with respect to the bar 24. The borehole 27 provides clearance for the sleeve 20 such that the sleeve 20 can be screwed into the borehole 27. Rotation of the sleeve 20 with respect to the bar 24 in the tightening direction causes the sleeve 20 to advance into the borehole 27 and the semi hemispherical faces 9 on the sleeve 20 contact the bearing plate 25 and force the bearing plate 25 against the rock face 28 being supported by the bolt 2. The sleeve 20 is rotated and tightened by using a drive dolly (not shown) in the hole 22 and by rotating the drive dolly with a drilling machine (not shown). Tightening rotation of the sleeve 20 is continued until the bearing plate 25 cannot be forced any further against the rock face 28. Typically the bar 24 is anchored in the borehole 27 by mixing a resin cartridge (not shown).

[0060] Figure 18 is another plan view of a tensionable, substantially flush-ended, rock bolt 3 with a sleeve 17, and a solid deformed bar 16 with a section of fine thread 13 that the sleeve 17 can screw onto. [0061] Figure 19 is a sectional view N-N shown in Figure 18 with a sleeve 17, and a deformed bar 16 with a fine threaded section 13 where the thread stop 4 on the back end of the deformed bar 16 is hard up against the shoulder 11 at the start of the thread 15 in the sleeve 17 such that the sleeve 17 is in the fully unscrewed position with respect to the fine thread 13 on the bar 16. [0062] Figure 20 is an expanded view of Area 0 shown in Figure 19 showing the detail of the threaded connection 15 between the sleeve 17 and the threaded section 13 of the deformed bar 16. The thread stop 4 is touching the shoulder 11 at the start of the threaded section 15 in the sleeve 17 such that the sleeve 17 is in its fully unscrewed position with respect to the threaded section 13 on the bar 16. [0063] Figure 21 is another sectional view of a tensionable, substantially flush ended, rock bolt 3 similar to Figure 19 except showing the bolt 3 in a borehole 27 in rock 26. The sleeve 17 is in the unscrewed position with respect to the bar 16. The borehole 27 provides clearance for the sleeve 17 such that the sleeve 17 can fit into the borehole 27. A bearing plate 25 is typically installed onto the bolt 3 before the bolt 3 is inserted into the borehole 27. [0064] Figure 22 is another plan view of a tensionable, substantially flush-ended, rock bolt 3 with a sleeve 17, and a solid deformed bar 16 with a section of fine thread 13 that the sleeve 17 can screw onto. The sleeve 17 has screwed onto the thread 13 on the bar 16 and is in the tensioned or tightened up position. [0065] Figure 23 is a sectional view Q-Q shown in Figure 22 with a sleeve 17, and a deformed bar 16 with a fine threaded section 13 where the sleeve 17 has been screwed along the thread 13 on the bar 16 and is in the almost fully tensioned or tightened up position. Rotation of the sleeve 17 with respect to the bar 16 has caused the sleeve 17 to screw further onto the thread 13 on the bar 16. [0066] Figure 24 is an expanded view of Area R shown in Figure 23 showing the detail of the threaded connection 15 between the sleeve 17 and the threaded section 13 of the deformed bar 16.

[0067] Figure 25 is another sectional view of a tensionable, substantially flush ended, rock bolt 3 similar to Figure 23 except showing the bolt 3 in a borehole 27 in rock 26. The bar 16 has been anchored in the borehole 27 by a resin cartridge or mechanical anchor (not shown). Once the bar 16 has been anchored in the borehole 27, rotation of the sleeve in the tensioning direction will cause the sleeve 17 to advance along the thread 13 on the bar 16 and the sleeve 17 will advance further into the borehole 27. The sleeve 17 continues to advance into the borehole until the semi hemispherical faces contact the bearing plate 25 and force the bearing plate 25 against the rock face 28. Even further rotation of the sleeve 17 in this same direction, causes it to continue to tighten up until the bearing plate 25 cannot be pushed any further against the rock face 28 and the maximum rotational torque of the drilling machine (not shown) is reached. The bolt 3 is then fully tensioned up or tightened up against the bearing plate 25 to support the rock face 28. [0068] Figures 26 to 28 are, respectively, side, sectional and a cut away isometric views of an example drive stub, showing the drive socket 22 leading to axial passages 29 and 30. O-ring 19 is adapted to seal against a fluid injector such as that illustrated in Figures 29 to 34. [0069] The location of internal thread 32, and external thread 40, of the drive stub previously described, are indicated. [0070] Figures 29 and 30 are, respectively, side and sectional views illustrating connection between an example drive dolly and injector 35 and the drive stub. [0071] The dolly 35 has a drive formation 37 - for example square or hex - toward the rear end of its shaft and a collar 38 towards its front adapted to abut the end surface of the drive stub, while the front end of the dolly includes a hex drive formation 39 for engaging within the drive recess 22 of the stub. [0072] Extending forward beyond the drive formation is a cylindrical injector portion, including a groove 36 for locating with the internal O-ring 19 of the drive stub. [0073] The front end of the injector portion may be bevelled 43 to assist engagement and disengagement with the drive stub. [0074] Figures 31 and 32 are further side and sectional views of a drive dolly engaging with the drive stub.

[0075] Figure 33 is an isometric view of the tensioning sleeve with the drive stub fitted. [0076] Figure 34 is an isometric of an example drive dolly and injector unit. Detailed Description of the Preferred Embodiments [0077] In common to the illustrated embodiments is the basic principle of a tubular tensioning sleeve being able to advance along a thread on a bar or bolt. [0078] In the drawings, the same numerals have been used to designate similar integers in each Figure to avoid duplication of description. [0079] In the embodiment shown in Figures 1 to 9 there is shown a tensionable, flush ended, self drilling rock bolt 1 with a tubular tensioning sleeve 20, a hollow threaded bar 21 and a drill bit 12. In operation, the bolt 1 can drill a borehole by rotating the tubular tensioning sleeve 20 such that the sleeve 20 tends to unscrew off the bar 21 until the thread stop 4 prevents the sleeve 20 from unscrewing completely off the bar 21, and further rotation of the sleeve 20 forces the bar 21 to rotate with it. As the bar 21 rotates, the drill bit 12 which is fixed to the leading end of the bar 21 can drill a borehole 27. The sleeve 20 is rotated by the drilling machine (not shown) using the non circular drive recess hole 22 at the rear end of the sleeve 20. The non circular drive recess hole 22 is typically contained within a threaded stub 23 that is fixed to the rear end of the sleeve 20 after the bar 21 has been assembled into the sleeve 20. The internal non circular hole 22 in the stub 23 is smaller in diameter than the diameter of the thread stop 4, such that the thread stop 4 and bar 21 cannot pass through the non circular hole 22 in the stub 23. The stub 23 therefore acts as the limit to which the sleeve 20 can be screwed onto the bar 21. [0080] During the drilling operation, flushing water is pumped through the bolt 1, firstly through the internal hole 7 in the sleeve 20, and subsequently through the hole 8 in the bar 21. Hydraulic sealing of the flushing water between the drilling machine and the bolt 1 is achieved by having one or more 0 rings 19 located along the passages of the stub 23, and by having one or more 0 rings 18 on the thread stop 4 such that the 0 rings 18 hydraulically seal between the thread stop 4 and the internal wall of the hole 7 in the sleeve 20. [0081] Once the bolt 1 has drilled a borehole, resin or cement grout can be pumped into the bolt 1 through holes 7 and 8 and into the borehole 27 to anchor the bar 21 in the borehole. In practice, a measured amount of grout or resin is pumped into the bolt 1 such that the bottom end of the borehole is not grouted such that there is room for the sleeve 20 to advance into the borehole 27. [0082] Once the bar 21 is anchored in the borehole, the drilling machine can then rotate the sleeve 20 in the opposite direction to the drilling direction, such that the sleeve 20 will screw along the thread on the bar 21 and the thread stop 4 on the rear end of the bar 21 will move into the hole 7 inside the sleeve 20. As the sleeve 20 advances forwards along the thread on the bar 21, the larger diameter rear end 9, 10 of the sleeve 20 will force a bearing plate 25 forwards against a rock face 28 to support it. [0083] The semi hemispherical surface or surfaces 9 at the rear end of the sleeve 20 is designed to fit into a round hole in a bearing plate 25 and to substantially maintain contact with the bearing plate even if the bearing plate 25 is not at right angles to the sleeve 20. This is to enable the sleeve 20 to have good contact with the bearing plate 25 even when the bearing plate 25 is supporting a rock face 28 which is not at right angles to the bolt 1. [0084] In another optional embodiment, the self drilling bolt 1 may have a mechanical anchor at the top end of the bar 21 (similar to the mechanical anchor disclosed in patent number PCT/AU2011001146 "Mechanical Anchor for Bolts, Rock Bolts and Self Drilling Rock Bolts"). In this case the bolt 1 drills its own borehole, by having the drilling machine (not shown) rotate the sleeve 20 in the drilling direction. The thread stop 4 then forces the bar 21 to also rotate in the drilling direction and the drill bit 12 can drill a borehole 27. Once the borehole is drilled, rotation of the bolt 1 is stopped, and then the bolt 1 is then rotated in the opposite direction to the drilling direction by the drilling machine. [0085] With reference for example to Figures 2 and 3, when the bar is at full extension and the thread stop is engaged as seen in Figure 3, the threads will be tightened hard against each other by the relative torque between the sleeve, which is being driven by the drive dolly, and the bar which is meeting resistance in drilling through the rock. This causes the threads to 'lock up' and provides initial resistance to unthreading of the sleeve 20 and the bar 21 in the opposite direction , such initially that the bar 21 also rotates along with the sleeve 20 in the opposite direction to the drilling direction. This rotation of the bar 21 in the opposite direction to the drilling direction, activates the mechanical anchor (not shown) on the leading end of the bar 21 immediately behind the drill bit 12. When the mechanical anchor activates it locks the bar 21 in the borehole and the bar 21 cannot be rotated any further. Further rotation of the sleeve 20 then causes the threads to release, and the sleeve 20 can then screw along the thread on the bar 21 and tension up the sleeve 20 against a bearing plate 25 which in turn supports the rock face 28. [0086] In another embodiment shown in Figures 10 to 17 there is shown a tensionable, flush-ended, solid rock bolt 2 with a tubular tensioning sleeve 20, and a solid threaded bar 24. In operation, the bolt 2 can be inserted into a pre-drilled borehole 27 with a resin cartridge (not shown). The leading end of the bar 24 is used to push the resin cartridge into the borehole and up to the top of the borehole 27. As the bolt 2 and the bar 24 are pushed further into the borehole, the resin cartridge ruptures and the resin begins to flow back around the bar 24 in the annulus space between the borehole 27 and the bar 24. [0087] The sleeve 20 can then be rotated in the direction that would tend to unscrew the sleeve 20 off the bar 24, however the thread stop 4 prevents the sleeve 20 from unscrewing from the bar 24 and forces the bar 24 to rotate with the sleeve 20. The bar 24 can therefore be rotated to thoroughly mix the resin in the borehole. Once the resin is thoroughly mixed, it is then allowed to harden typically between 10 and 45 seconds. Once the resin has hardened, the resin anchors and secures the bar 24 in the borehole 27. The sleeve 20 can then be rotated in the opposite direction such that the thread 4 stop moves away from the shoulder 11 at the start of the threaded section 5 in the sleeve 20, and the thread stop 4 and bar 24 move further into the hole 7 in the sleeve 20, and the sleeve 20 can then screw forwards and tension up against a bearing plate to support a rock face. In practice, the volume of resin in the cartridge is designed such that there is sufficient annulus space at the bottom of the borehole 27 to allow for the sleeve 20 to be screwed up into the borehole 27. [0088] Once the resin in the borehole 27 has hardened and secured the bar 24 in the borehole 27, further rotation of the sleeve 20 in the tensioning direction will cause the sleeve 20 to advance along the thread on the bar 24 and tighten the sleeve 20 against the bearing plate 25 to support the rock face 28. [0089] In another embodiment shown in Figures 18 to 25 there is shown a tensionable, flush-ended, solid rock bolt 3 with a tubular tensioning sleeve 17, and a solid deformed bar 16 with a threaded section 13 which can screw into the threaded section 15 inside the sleeve 17. The threaded section 13 on the bar 16 and the threaded section 15 inside the sleeve 17 typically have a fine thread pitch of approximately 3mm. [0090] In operation, the bolt 3 can be inserted into a pre-drilled borehole 27 with a resin cartridge (not shown). The leading end of the bar 16 is used to push the resin cartridge into the borehole 27 and up to the top of the borehole 27. As the bolt 3 and the bar 16 are pushed further into the borehole 27, the resin cartridge ruptures and the resin begins to flow back around the bar 16 in the annulus space between the borehole 27 and the bar 16. [0091] Once the resin is thoroughly mixed, it is then allowed to harden typically between 10 and 45 seconds. Once the resin has hardened, the resin anchors and secures the bar 16 in the borehole 27. The sleeve 17 can then be rotated to screw the sleeve 17 further onto the threaded section 13 on the bar 16. The sleeve 17 can then screw forwards and tension up against a bearing plate 25 to support a rock face 28. In practice, the volume of resin in the cartridge is designed such that there is sufficient annulus space at the bottom of the borehole 27 to allow for the sleeve 17 to be screwed up into the borehole 27. [0092] Figures 26 to 27 show the drive stub in more detail, including the drive socket 22 leading to axial passages 29 and 30. O-ring 19 is adapted to seal against a fluid injector such as that illustrated in Figures 29 to 34. [0093] The external thread 40 of the drive stub is adapted to mate with the internal thread at the enlarged mouth portion of the tensioning sleeve, to add strength to the connection. A weld 33 (shown for example in Figure 32) helps secure this threaded connection against unscrewing during installation and use. [0094] The internal thread 32 at passage 29 of the drive stub allows threaded connection of articles to the rock bolt in situ after installation. Examples include measurement equipment (not shown) such as for testing the strength of the rock bolt connection, or hangers or other useful items. [0095] Figures 29 to 32 show the connection between an example drive dolly and injector 35 and the drive stub and tensioning sleeve. Figure 33 shows the drive stub and tensioning sleeve when assembled, and Figure 34 is an isometric view of the drive dolly and injector 35. [0096] As shown, the rear end of the drive dolly and injector 35 has a drive formation 37, typically square or hex, for attachment to the drilling machine rotary drive (not shown) and a hollow shaft with bore 42. [0097] The front end of dolly 35 has a collar/shoulder 38 which abuts the end of the tensioning sleeve and drive stub (Figure 30).

_1 0 [0098] The dolly 35 has a drive formation 37 - for example square or hex - toward the rear end of its shaft and a collar 38 towards its front adapted to abut the end surface of the drive stub, while the front end of the dolly 35 includes a hex drive formation 39 for engaging within the drive recess 22 of the stub. [0099] Extending forward beyond the drive formation 39 is a cylindrical injector portion, including a groove 36 for locating with the internal O-ring 19 of the drive stub. [0100] The front end of the injector portion may be bevelled at 41 and 43 to assist engagement and disengagement with the drive stub, with groove 36 sealing against the O-ring 19 in the drive stub internal passage 30 to form a sealed hydraulic connection from the bore 42, through passage 29 of the drive stub, into the central passage 7 of the tensioning sleeve. [0101] Figure 34 is an isometric of an example drive dolly and injector unit. [0102] It should be noted that when the different embodiments of the invention use the thread stop system to rotate the bolt assembly, and use conventional right hand threaded bars, the direction of rotation of the bar to mix the resin is left hand rotation, and the sleeve is then tensioned up with right hand rotation. When using bars with left hand threads, the direction of rotation of the bar to mix the resin is right hand rotation, and the sleeve is then tensioned up with left hand rotation. [0103] The components of the rock bolt, including the bar, tensioning sleeve and drive stub, can be formed from any suitable materials of sufficient strength and durability for the harsh environment and high forces to which they are subjected. Typically, they will be made of steel. [0104] The example embodiments of the disclosure enable a rock bolt to be substantially flush with the rock face even after tensioning and even where the rock face is irregular. The only parts of the bolt protruding into a roadway or tunnel are the large diameter collar and the integrated domed ball section of the sleeve, a distance of approximately 60mm. Where the integrated domed ball section is not required because of an even, flat rock face, the only section of the bolt that would protrude into the roadway would be the larger diameter collar, a distance of less than 15mm. The in-built domed ball with its semi hemispherical faces at the rear end of the sleeve enable the bearing plate to swivel with respect to the sleeve on uneven rock faces but still maintain substantial contact with the sleeve.

[0105] The disclosure provides for a female internal rotational drive in the sleeve using a non-circular drive socket recess in a stub in the rear end of the sleeve. This eliminates the need for an external hex or square drive nut, and instead the external end of the sleeve is designed with an integrated domed ball with semi hemispherical (i.e. quasi hemispherical) faces to accommodate articulation of the bearing plate as previously described. This integrated dome ball design also has the advantage that where the sleeve has a larger diameter at the rear end of the sleeve, it also strengthens the sleeve at this end where it has to support the bearing plate. [0106] In addition, the disclosure provides for a large diameter tensioning sleeve which when pumped full of cement grout or resin provides a very strong bottom end section to a rock bolt to resist shear and bending forces which are common in the immediate roof and walls of mines and tunnels. [0107] Different embodiments of the invention can be used with self drilling rock bolts, with hollow threaded bar rock bolts, and with solid bar or deformed bar rock bolts using resin cartridges, or mechanical anchors, or pumpable grout or resin. [0108] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications. The invention also includes all of the steps, features, compositions, and compounds referred to or indicated in this specification (unless specifically excluded) individually or collectively, and any and all combinations of any two or more of said steps or features. [0109] Throughout this specification, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising" will be understood to imply the inclusion of a stated integer or group of integers, but not to the exclusion of any other integer or group of integers. [0110] Where the specification refers to a "sleeve" or to a "tensioning sleeve" or to a "tubular tensioning sleeve" it is to be understood that the invention includes all such variations and modifications of the above, and any other member that could be used to screw onto a thread form on a bolt or a bar. [0111] Reference to "semi-hemispherical" or similar will be understood as referring to approximately hemispherical, i.e. domed, not to half of a hemisphere.

[0112] Where the specification refers to a "bar" or to a "threaded bar" or to a "hollow bar" or to a "solid bar" or to a "deformed bar" it is to be understood that the invention includes bars and rods and all such variations and modifications of the above, and any other member that could be used as part of a rock bolt. [0113] Where the specification refers to a "stub" or to a "threaded stub" or to a "threaded stub with a non-circular hole" it is to be understood that the invention includes any part that can be fixed to a sleeve with a female non-circular drive socket that can be used to rotate the sleeve, and all such variations and modifications of the above. [0114] Where the specification refers to a "non-circular hole" it is to be understood to include square, hexagonal, splined, slotted, grooved, keyways or any other shaped hole that can be used to rotate a part.

Claims (7)

1. 2. A rock bolt according to claim 1, wherein the rock bolt is a self-drilling rock bolt, the bar having a drill bit adjacent the leading end adapted to drill a borehole when the bar is rotated in the first direction, and wherein the thread stop causes the bar to rotate with the tensioning sleeve in the first direction to drill the borehole.
2. 3. A rock bolt according to claim 1 or claim 2, wherein the drive stub includes a passage through a base of the drive socket for injection of a fluid into the rock bolt.
3. 4. A rock bolt according to claim 3 wherein the drive stub further includes a seal in said passage for sealing to a fluid injector.
4. 5. A rock bolt according to claim 4 wherein the drive stub socket is adapted to receive a combined drive member and injector device.
5. 6. A rock bolt according to any preceding claim wherein the drive stub includes an internally threaded portion adapted to allow threaded attachment of an article to the rock bolt after the rock bolt is secured in the borehole.
6. 7. A rock bolt according to claim 6 wherein the internally threaded portion is adapted for attachment of a measuring device to test strength of attachment of the rock bolt in the borehole.
7. 8. A rock bolt according to claim 6 wherein the internally threaded portion is adapted for attachment of a hanger device.