AU2007221783B2 - Rock bolt - Google Patents

Abstract

A rock bolt (100) comprises a longitudinally extending rigid bar (101) having a threaded trailing end portion (103) and an end fitting (102). The end fitting (102) has a longitudinally extending barrel (104) and a drive head (105, 105') mounted on, or integrally formed with, a trailing end portion (106, 106') of the barrel (104). The drive head (105, 105') defines an external shoulder (108) on a leading face of the drive head (105) adjacent the barrel (104). The end fitting (102) has an aperture (109) extending longitudinally through the barrel (104) and drive head (105, 105'). The aperture (109) has a leading end portion defining a threaded internal wall (110) of the barrel (104) and a trailing end portion (111) having a cross-section larger than the major diameter of the thread of the threaded trailing end portion (103) of the bar (10 1). The end fitting (102) is mounted on the bar (101) with the threaded trailing end portion (103) of the bar (101) threadingly engaging the threaded internal wall (110) of the barrel (104) with a trailing end (112) of the bar (101) located within the aperture (109). A locking means (113) is adapted to fix the end fitting (102) in relation to the bar (101) until application of a predetermined torque upon which the locking means (113) fails, allowing the threaded internal wall (110) of the barrel (104) to be threadingly advanced along the threaded trailing end portion (103) of the bar (101).

Description

S&F Ref: 827319 AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name and Address DYWIDAG-Systems International Pty Limited, of Applicant: an Australian company, ACN 093 424 349, of 25 Pacific Highway, Bennetts Green, New South Wales, 2290, Australia Actual Inventor(s): Mieczyslaw Stanislaw Rataj, Derek Colin Hird Address for Service: Spruson & Ferguson St Martins Tower Level 35 31 Market Street Sydney NSW 2000 (CCN 3710000177) Invention Title: Rock bolt Associated Provisional Application Details: [33] Country: [31] Appl'n No(s): [32] Application Date: AU 2006904574 24 Aug 2006 The following statement is a full description of this invention, including the best method of performing it known to me/us: 5845c(971273_I) ROCK BOLT Field of the Invention The present invention relates to strata control in civil engineering and mining 5 operations, and in particular relates to a rock bolt for securing the roof or wall of a mine, tunnel or other ground excavation. Background of the Invention One known method of stabilising the wall or roof of an underground mine is to 1o secure a rock bolt into a bore hole drilled into the face of the rock to be stabilised. Rock bolts are typically formed of a solid steel bar with the trailing end of the bar being threaded over a length typically equal to about 150 mm. A known method of installing a rock bolt involves first drilling a bore hole, having a length about 100 mm shorter than the total length of the rock bolt, into the rock face. A is sausage like two-component resin filled cartridge is then inserted into the bore hole, followed by the rock bolt which pushes the resin filled cartridge towards the top of the bore hole. The rock bolt is then rotated by the installation rig which also thrusts the rock bolt upwardly whilst it is rotating to mix the resin components and shred the fragile cartridge casing, pushing it towards the back of the bore hole. Rotation of the rock bolt is 20 then stopped for a few seconds to allow the resin to cure. The bolt is then tensioned by threading a nut along the threaded trailing end portion of the rock bolt, bearing the nut against a washer that engages the rock face adjacent to the bore hole opening. Once the bolt is tensioned, part of the threaded trailing end portion of the bolt protrudes beyond the nut. This protruding portion is referred to in the art as the "bolt 25 tail". The length of the bolt tail depends upon the rock conditions and the application of other supporting structures, such as a rock face supporting wire mesh, placed between the washer and the rock face. The length of the bolt tail will also vary depending upon the precise length of the bore hole drilled. Accordingly, there is usually significant variation in the length of the bolt tails, typically between 20mm and 120 mm. 30 In low seam conditions, and/or in excavations where side walls are also reinforced with rock bolts, any significant bolt tail is undesired as it presents a hazard to personnel and equipment moving in the confined space of the mine. One previously proposed solution to this problem is the use of a rock bolt 1, as depicted in Figure 1, comprising two threaded bar portions 2, 3 and a threaded coupler 4. 35 The trailing bar portion 3 has a fixed drive head 5. This rock bolt 1 is tensioned after 2 curing of the resin encasing the leading end of the leading bar portion 2 by driving the drive head 5, advancing the threaded ends of the threaded bar portions 2, 3 into the coupler 4. As a result no bolt tail protrudes from the rock face. However, the length of the coupler 4 is typically limited by manufacturing costs, resulting in scenarios where 5 rock bolts cannot be tensioned properly due to the gap between the rock face and bolt head 5 and washer 6 being greater than the thread length available in the coupler 4. To lengthen the coupler would also result in lengthening of the internal thread within the coupler 4. However, as a result of the process of rolling the thread onto the threaded portions 2, 3 of the rock bolt not being precise, there is considerable variation in pitch of 1o the threads formed on the rock bolt portions 2, 3. This pitch variation is not a problem when a standard nut, with a relatively short thread, is utilised. However, when screwing a coupler 4 with a long thread onto the threaded bolt portions 2, 3, the coupler 4 may jam, preventing it from being threaded onto the threaded portions 2, 3 the required distance. 15 Object of the Invention It is the object of the present invention to substantially overcome or at least ameliorate one or more of the above disadvantages, or at least to provide a useful alternative. 20 Summary of the Invention In a first aspect, the present invention provides a rock bolt comprising: a longitudinally extending rigid bar having a threaded trailing end portion; an end fitting having a longitudinally extending barrel and a drive head mounted on, or integrally formed with, a trailing end portion of said barrel, said drive head defining an 25 external shoulder on a leading face of said drive head adjacent said barrel, said end fitting having an aperture extending longitudinally through said barrel and said drive head, said aperture having a leading end portion defining a threaded internal wall of said barrel and a trailing end portion having a cross-section larger than the major diameter of the thread of said threaded trailing end portion of said bar, said end fitting being mounted on said bar 30 with said threaded trailing end portion of said bar threadingly engaging said threaded internal wall of said barrel with a trailing end of said bar located within said aperture; and locking means adapted to fix said end fitting in relation to said bar until application of a predetermined torque upon which said locking means fails, allowing said threaded internal wall of said barrel to be threadingly advanced along said threaded trailing end 35 portion of said bar.

3 Typically said locking means comprises a shear pin extending through said barrel into said bar, said shear pin being configured to shear upon application of said predetermined torque. Typically, said drive head is integrally formed with said barrel. 5 Alternatively, said drive head may be in the form of a nut threaded onto an external thread provided on said threaded trailing end portion of said barrel. In a preferred form, said trailing end portion of said aperture has a length of between 0.6 and 0.85 times the length of said thread. The trailing end portion of said aperture typically has a length of between 90 and 10 255 mm. In a preferred form, said threaded internal wall of said barrel has a length of between 1.2 and 1.6 times the major diameter of said thread. The threaded internal wall of said barrel typically has a length of between 14 and 48 mm. is Typically said barrel is substantially cylindrical. Typically, said trailing end portion of said aperture is cylindrical. In a second aspect the present invention provides a rock bolt installation comprising: a bore hole extending through a rock face; 20 a rock bolt as defined above inserted in said bore hole with a leading end portion of said bar being fixed to a wall of said bore hole with resin and said barrel extending into said bore hole; and a washer mounted on said barrel with said shoulder bearing against said washer and said washer bearing against said rock face. 25 In a third aspect the present invention provides a method of installing a rock bolt as defined above, said method comprising the steps of: drilling a bore hole in a rock face; mounting a washer on said barrel; inserting a two-component resin filled cartridge into said bore hole; 30 inserting said rock bolt into said bore hole with said bar leading; thrusting said rock bolt towards the end of said bore hole, rupturing said cartridge; rotatably driving said drive head, mixing said resin with a leading end portion of said bar; allowing said resin to cure; and 4 rotatably driving said drive head with a torque equal to or in excess of said predetermined torque, threading said threaded internal wall of said barrel along said threaded trailing portion of said bar, bearing said shoulder against said washer and said washer against said rock face, and tensioning said bar. 5 Brief Description of the Drawings Preferred embodiments of the present invention will now be described, by way of an example only, with reference to the accompanying drawings wherein: Figure 1 is a perspective view of a prior art rock bolt; to Figure 2 is a partially cross-sectioned front elevation view of a rock bolt according to a first embodiment; Figure 3 is a partially cross-sectioned front elevation view of a rock bolt according to a second embodiment; and Figure 4 is a partially cross-sectioned front elevation view of a rock bolt installation is incorporating the rock bolt of Figure 3. Detailed Description of the Preferred Embodiments Referring to Figure 2, a rock bolt 100 according to a first embodiment comprises a longitudinally extending rigid bar 101 and an end fitting 102. The bar 101 is a standard 20 bar as otherwise used in rock bolting applications, being formed of steel and having a threaded trailing end portion 103. The threaded trailing end portion 103 of the bar 101 typically has a length of the order of 150 mm, but in some applications is about 300 mm. The threaded trailing end portion 103 of the bar 101 typically has a thread major diameter of between 12 and 30 mm, with common diameters being 16, 20 and 24 mm. 25 The end fitting 102 has a longitudinally extending barrel 104 and a drive head 105 integrally formed with a trailing end portion 106 of the barrel 105. The drive head 105 typically has a hexagonal cross-section defining a peripheral drive surface 107 for driving by way of a standard rock bolt installation rig. The drive head 105 defines an external shoulder 108 on a leading face of the drive head 105 adjacent to the barrel 104, extending 30 about the barrel 104 in a generally annular form. The barrel 104 is typically cylindrical and has an outer diameter smaller than that of the bore hole in which the rock bolt 100 is intended to be installed. The end fitting 102 has an aperture 109 extending longitudinally through the barrel 104 and drive head 105. The aperture 109 has a leading end portion defining a threaded 35 internal wall 110 of the barrel 104 and a trailing end portion 111 that has a cross-section 5 larger than the major diameter of the thread of the threaded trailing end portion 103 of the bar 101, thereby enabling the threaded trailing end portion 103 of the bar 101 to freely pass through the trailing end portion 111 of the aperture 109. The threaded internal wall 110 of the barrel 104 typically has a length of between 1.2 and 1.6 times the major 5 diameter of the thread of the threaded trailing end portion 103 of the bar 101. Specifically, for bars 101 having a major thread diameter of 12 to 30 mm, the threaded internal wall 110 of the barrel 104 will typically have a length of between 14 and 48 mm. The trailing end portion 111 of the aperture 109 typically has a length of between 0.6 and 0.85 times the length of the thread of the threaded trailing end portion 103 of the bar 101. 10 Specifically, for bars 101 having a major thread length of 150 to 300 mm, the trailing end portion 111 of the aperture 109 will typically have a length of between 90 and 255 mm. Accordingly, the total length of the end fitting is typically between 107 and 297 mm. In a particular embodiment, where the threaded trailing end portion 103 of the bar 101 has a major thread diameter of 16 mm and a length of 150 mm, the trailing end portion 111 of is the aperture 109 has a length of 98 mm and the threaded internal wall 110 of the barrel 104 has a length of 22 mm. The end fitting 102 is mounted on the bar 101 with the threaded trailing end portion 103 of the bar 101 threadingly engaging the threaded internal wall 110 of the barrel 104, with the trailing end 112 of the bar 101 located within the aperture 109. Typically, the 20 rock bolt 100 will be supplied with the trailing end 112 of the bar 101 located approximately at the trailing end of the threaded internal wall 110 of the barrel 102. The end fitting 102 is fixed in relation to the bar 101 by way of a locking means here in the form of a shear pin 113. The shear pin 113 extends through a hole in the side of the barrel 104 and into the bar 101. The shear pin 113 is configured to fail by shearing 25 upon application of a predetermined torque, allowing the threaded internal wall 110 of the barrel 104 to be threadingly advanced along the threaded trailing end portion 103 of the bar 101. The locking means may alternatively be in the form of a slightly deformed or "pinched" thread of the threaded trailing end portion 103 of the bar 101. A standard washer 114 is mounted on the barrel 102 and is prevented from being 30 removed from the trailing end 106 of the barrel 102 by engagement with the shoulder 108 of the drive head 105. A rock bolt 100' according to a second embodiment is depicted in Figure 3. Features of the rock bolt 100' of the second embodiment that are common with the rock bolt 100 of the first embodiment are provided with identical reference numerals. The 35 rock bolt 100' of the second embodiment is essentially identical to the rock bolt 100 of 6 the first embodiment except that the drive head 105' is formed separately to, and mounted on, the trailing end portion 106' of the barrel 104. Specifically, the drive head 105' is in the form of a nut and is threaded onto a thread provided on the trailing end portion 106' of the barrel 104. 5 Figure 4 depicts a rock bolt installation utilizing the rock bolt 100' of the second embodiment. The rock bolt installation is formed by first drilling a bore hole 201 in a rock face 200, mounting the washer 114 on the barrel 102, inserting a two-component resin filled cartridge into the bore hole 201, inserting the rock bolt 100' into the bore hole 201 with the bar 101 leading utilizing a standard rock bolt installation rig. The rock bolt 1o 100' is thrust toward the end of the bore hole 201, rupturing the cartridge. The drive head 105' is rotatably driven by the installation rig, mixing the resin 202 with a leading end portion 115 of the bar 101. The resin 202 is then allowed to cure before rotatably driving the drive head 114 at an increased torque that is equal to or in excess of the predetermined torque, thereby shearing the shear pin 113. The torque applied to the drive head 105' then is threads the threaded internal wall 110 of the barrel 102 along the threaded trailing portion 103 of the bar 101. Continued driving of the drive head 105' bears the shoulder 108 of the drive head 105' against the washer 114 which, in turn, bears against the rock face 200, resulting in tensioning of the bar. During the driving process, as the threaded internal wall 110 of the barrel 104 is advanced along the threaded trailing portion 103 of the bar 20 101, the trailing end 112 of the bar moves through the trailing portion 111 of the aperture 109 of the barrel 104. For most typical applications, subject to the bore hole 201 being correctly drilled, the bar trailing end 112 will not project beyond the drive head 105' out of the aperture 109 once the installation is complete. Leaving the trailing end of the aperture 109 open, 25 however, does allow for the trailing end 112 of the bar 101 to project beyond the drive head 105 in instances where the bore hole 201 is of an insufficient length, thereby still enabling adequate tensioning of the bar 101, albeit perhaps with the trailing end 112 of the bar 101 projecting slightly beyond the drive head 105'. Of course the end fitting 102 may be formed with a greater length if desired to completely eliminate this risk. 30 A person skilled in the art will appreciate that various other modifications or alterations of the rock bolt may be made to suit specific applications.

Claims (14)

1. A rock bolt comprising: a longitudinally extending rigid bar having a threaded trailing end portion; an end fitting having a longitudinally extending barrel and a drive head mounted on, 5 or integrally formed with, a trailing end portion of said barrel, said drive head defining an external shoulder on a leading face of said drive head adjacent said barrel, said end fitting having an aperture extending longitudinally through said barrel and said drive head, said aperture having a leading end portion defining a threaded internal wall of said barrel and a trailing end portion having a cross-section larger than the major diameter of the thread of 1o said threaded trailing end portion of said bar, said end fitting being mounted on said bar with said threaded trailing end portion of said bar threadingly engaging said threaded internal wall of said barrel with a trailing end of said bar located within said aperture; and locking means adapted to fix said end fitting in relation to said bar until application of a predetermined torque upon which said locking means fails, allowing said threaded is internal wall of said barrel to be threadingly advanced along said threaded trailing end portion of said bar.

2. The rock bolt of claim 1, wherein said locking means comprises a shear pin extending through said barrel into said bar, said shear pin being configured to shear upon 20 application of said predetermined torque.

3. The rock bolt of either one of claims I and 2, wherein said drive head is integrally formed with said barrel. 25

4. The rock bolt of either one of claims I and 2, wherein said drive head is in the form of a nut threaded onto an external thread provided on said threaded trailing end portion of said barrel.

5. The rock bolt of any one of claims I to 4, wherein said trailing end portion of 30 said aperture has a length of between 0.6 and 0.85 times the length of said thread.

6. The rock bolt of any one of claims 1 to 5, wherein said trailing end portion of said aperture has a length of between 90 and 255 mm.

7. The rock bolt of any one of claims 1 to 6, wherein said threaded internal wall 35 of said barrel has a length of between 1.2 and 1.6 times the major diameter of said thread. 8

8. The rock bolt of any one of claims 1 to 7, wherein the threaded internal wall of said barrel typically has a length of between 14 and 48 mm. 5

9. The rock bolt of any one of claims 1 to 8, wherein said barrel is substantially cylindrical.

10. The rock bolt of any one of claims 1 to 9, wherein said trailing end portion of said aperture is cylindrical. 10

11. A rock bolt installation comprising: a bore hole extending through a rock face; a rock bolt as defined in any one of claims I to 10 inserted in said bore hole with a leading end portion of said bar being fixed to a wall of said bore hole with resin and said is barrel extending into said bore hole; and a washer mounted on said barrel with said shoulder bearing against said washer and said washer bearing against said rock face.

12. A method of installing a rock bolt as defined in any one of claims 1 to 10, said 20 method comprising the steps of: drilling a bore hole in a rock face; mounting a washer on said barrel; inserting a two-component resin filled cartridge into said bore hole; inserting said rock bolt into said bore hole with said rigid bar leading; 25 thrusting said rock bolt towards the end of said bore hole, rupturing said cartridge; rotatably driving said drive head, mixing said resin with a leading end portion of said bar; allowing said resin to cure; and rotatably driving said drive head with a torque equal to or in excess of said 30 predetermined torque, threading said threaded internal wall of said barrel along said threaded trailing portion of said bar, bearing said shoulder against said washer and said washer against said rock face, tensioning said bar.

13. A rock bolt substantially as hereinbefore described with reference to either of 35 Figures 2 and 3 of the accompanying drawings. 9

14. A rock bolt installation substantially as hereinbefore described with reference to Figure 4 of the accompanying drawings. Dated 2 October 2007 DYWIDAG-Systems International Pty Limited Patent Attorneys for the Applicant/Nominated Person SPRUSON & FERGUSON