AU2012202298A1 - Rock bolt - Google Patents

Abstract

A rock bolt (100) has a longitudinally extending rigid bar (101) having a leading end portion (119) and a threaded trailing end portion (103). An end fitting (102) having a longitudinally extending barrel (104) and a drive head (105) is mounted on, or integrally formed with, a trailing end portion (106) of the barrel (104). The drive head (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 the drive head (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 (101). The end fitting (102) is mounted on the bar (101) with the threaded trailing end portion (103) of the bar (101) threadingly engages the threaded internal wall (110) of the barrel (104) with a trailing end 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. A wire (118) is secured to and helically extends along the leading end portion (119) of the bar (101). (133 tog (007 Fig. 1

Description

S&F Ref: P032448 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, Bennett's Green, New South Wales, 2290, Australia Actual Inventor(s): Gary Anthony Davey David William Evans Andrew Simon Boychuk 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 2011901501 20 Apr 2011 The following statement is a full description of this invention, including the best method of performing it known to me/us: 5845c(6215344_1) ROCK BOLT Field of the Invention 100011 The present invention relates to strata control in civil engineering and mining 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 [00021 One known method of stabilising the wall or roof of an underground mine is to 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 rigid steel bar with the trailing end of the bar being threaded over a length typically equal to about 150 mm. [00031 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 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 frangible cartridge casing, pushing it towards the top of the bore hole. Rotation of the rock bolt is 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. 100041 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 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. 100051 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. Further, when utilising resin anchored rock bolts in hard rock mining applications, there is typically an enlarged annulus between the 2 rock bolt and bore hole wall as larger holes are typically drilled in hard rock applications than in coal mining applications. This enlarged annulus may result in inadequate mixing of the resin by the plain leading end portion of the rock bolt. Object of the Invention 100061 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. Summary of the Invention 100071 In a first aspect, the present invention provides a rock bolt comprising: a longitudinally extending rigid bar having a leading end portion and 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 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 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; 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 portion of said bar; and a wire secured to and helically extending along said leading end portion of said bar. [0008] 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. [0009] In one form, said wire is welded to said bar. 100101 In one form, said drive head is integrally formed with said barrel. [00111 In an alternate form, said drive head may be in the form of a nut threaded onto an external thread provided on said barrel.

3 100121 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. [0013] The trailing end portion of said aperture typically has a length of between 90 and 255 mm. [00141 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. [00151 The threaded internal wall of said barrel typically has a length of between 14 and 48 mm. [00161 Typically said barrel is substantially cylindrical. [00171 Typically, said trailing end portion of said aperture is cylindrical. Brief Description of the Drawings [00181 A preferred embodiment of the present invention will now be described, by way of an example only, with reference to the accompanying drawings wherein: [00191 Figure 1 is a partially cross-sectioned front elevation view of a rock bolt; and [00201 Figure 2 is a partially cross-sectioned front elevation view of a rock bolt installation incorporating the rock bolt of Figure 1. Detailed Description of the Preferred Embodiments [00211 Referring to Figure 1, a rock bolt 100 comprises a longitudinally extending rigid bar 101 and an end fitting 102. The bar 101 is a standard 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 may have a length of 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. In the specific arrangement depicted, the thread major diameter is 24 mm. A coarse left handed thread 116, formed by a series of protrusions on the bar 101, extends from adjacent the trailing end portion 103 to the leading end 117 of the bar 101 in a standard manner.

4 100221 The end fitting 102 has a longitudinally extending barrel 104 and a drive head 105 that may either be integrally formed with, or mounted on, 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. In embodiments where the drive head 105 is mounted on the trailing end portion 106 of the barrel 104, it will typically be in the form of a standard hexagonal nut that is threaded onto a thread provided on the trailing end portion 106 of the barrel 104. The drive head 105 defines an external shoulder 108 on a leading face of the drive head 105 adjacent to the barrel 104, extending about the barrel 104 in a generally annular form. The barrel 104 is typically cylindrical. 10023] 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 internal wall 110 of the barrel 104 and a trailing end portion 111 that has a cross-section 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 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 IIl 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. 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 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. [00241 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 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 104.

5 100251 The end fitting 102 is fixed in relation to the bar 101 by way of a locking means here in the form of two shear pins 113. The shear pins 113 extend through holes in the side of the barrel 104 and into the bar 101. The shear pins 113 are configured to fail by shearing 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. A single shear pin (or more than two shear pins) may be used rather than two shear pins if desired. 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. 100261 An anti-friction washer 114 and ball washer 115 are mounted on the barrel 104 and are prevented from being removed from the trailing end 106 of the barrel 104 by engagement with the shoulder 108 of the drive head 105. 100271 A wire 118 is secured to and helically extends along a leading end portion 119 of the bar 101. The wire 118, typically formed of steel, and here having a diameter of about 3.15 mm, will typically helically extend in a direction opposing the intended direction of rotation of the bolt 100 during installation. Accordingly, for a standard left handed installation rig, the wire 118 will helically extend in a right handed direction as depicted in the accompanying drawings. The wire 118 will typically extend over a length of the leading end portion 119 of the bar which is intended to be resin encapsulated. Lengths of the order of 500 mm will be typical. [00281 In the arrangement depicted, the wire 118 is fixed to the leading end portion 119 of the bar 101 by welding, here being welded at the leading and trailing ends 11 8a, 11 8b of the wire 118 and approximately half way along the length of the wire 118. In an alternative embodiment, the leading end 11 8a of the wire 118 may be secured in a slot formed in the leading end 117 of the bar 101. In a further alternative embodiment, particularly suitable for use with high tensile steel bars that might otherwise be weakened through inadvertent heat treatment of the bar during a welding process, the trailing end 11 8b of the wire 118 may be fixed to the rigid bar 101 by way of a ferrule that is crimped onto the bar 101. The trailing end of the wire 118 would typically be sandwiched between the ferrule and bar without the need for any welding, thus avoiding heat treatment of the bar. It is also envisaged, however, that the trailing end of the wire might be welded to the exterior face of such a ferrule, thereby at least avoiding welding the wire directly to the bar. The middle and leading end 11 8a of the wire 118 may also be fixed to the bar 101 in the same manner if so desired.

6 100291 Figure 2 depicts a rock bolt installation utilizing the rock bolt 1, immediately prior to tensioning of the rock bolt 100. The anti-friction washer 114 and ball washer 115 are mounted on the barrel 104, followed by a standard plate washer 120. A bore hole 201 is drilled into the rock face 200 . To enable the barrel 104 to fit within the bore hole 201, a trailing portion 203 of the bore hole 201 may be counterbored with an increased diameter, in the example depicted being 45 mm as compared to the 35 mm diameter of the rest of the bore hole 201. Then a two component resin filled cartridge is inserted into the bore hole 201. The rock bolt 100, with the assembled anti-friction washer 114, ball washer 115 and plate washer 120 is then inserted into the bore hole 201 with the leading end 117 of the bar 101 leading, pushing the resin filled cartridge up the bore hole 201 as the rock bolt 100 is advanced. The rock bolt 100 is thrust towards the end of the bore hole 201, utilising a standard rock bolt installation rig, thereby rupturing the cartridge. [00301 At the same time, the installation rig rotates the drive head 105 of the rock bolt 100, resulting in the leading end portion 119 of the bar 101, and particularly the wire 118, mixing the resin 202. With the wire 118 helically extending in an opposing direction to the direction of rotation of the rock bolt 100, the resin is actively pumped towards the end of the bore hole 201. The resin 202 is then allowed to cure for a few seconds before rotatably driving the drive head 105 at an increased torque that is equal to or in excess of the predetermined torque, thereby shearing the shear pins 113. The torque applied to the drive head 105 then threads the threaded internal wall 110 of the barrel 104 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 anti-friction washer 114 which, in turn, bears against the ball washer 115 and plate washer 120. The plate washer 120 bears against the rock face 200, resulting in tensioning of the bar as frther torque is applied to the drive head 105. Use of the ball washer 115 allows for some misalignment of the bore hole 201 in cases where the bore hole 201 is not drilled at right angles to the rock face 200 or where the rock face is uneven. The ball washer 115 allows the plate washer 120 to still properly engage the rock face 200 in such misaligned installations. 100311 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 101, the trailing end 112 of the bar 101 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 trailing end 112 of the bar 101 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, however, does allow 7 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. [00321 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 (12)

1. A rock bolt comprising: a longitudinally extending rigid bar having a leading end portion and 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 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 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; 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 portion of said bar; and a wire secured to and helically extending along said leading 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 application of said predetermined torque.

3. The rock bolt of either one of claims I and 2, wherein said wire is welded to said bar.

4. The rock bolt of any one of claims I to 3, wherein said drive head is integrally formed with said barrel.

5. The rock bolt of any one of claims I to 3, wherein said drive head is in the form of a nut threaded onto an external thread provided on said barrel.

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

7. The rock bolt of any one of claims I to 5, wherein said trailing end portion of said aperture has a length of between 90 and 255 mm. 9

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

9. The rock bolt of any one of claims I to 7, wherein said threaded internal wall of said barrel has a length of between 14 and 48 mm.

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

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

12. A rock bolt substantially as hereinbefore described with reference to the accompanying drawings. Dated 19 April, 2012 DYWIDAG-Systems International Pty Limited Patent Attorneys for the Applicant/Nominated Person SPRUSON & FERGUSON