Rock bolt

Abstract

A rock bolt (10) includes an elongate rod defining a proximal end (12) and a distal end (14). The proximal end (14) is threaded for receiving nut (16) or the like. A smooth and unthreaded central portion extends between the proximal end (12) and the distal end (14). At least the distal end (12) defines a mixing and anchoring section defining a series of deformed portions (22) which project beyond the diameter of the smooth central portion and wherein the mixing and anchoring section is ribbed, most typically threaded, so that edges of the deformed portions define a series of teeth.

Description

Rock boltCross-reference to related applicationsThis application claims priority from Australian provisional application No 2024903593 entitled “Rock bolt” filed on 4 November 2024, the entire contents of which are hereby incorporated by reference.Technical Field

[0001] This invention relates to a rock bolt, particularly for use in dynamic applications.Background

[0002] Rock bolts are extensively used for strata reinforcement applications such as soil nailing and most often in underground mining applications to consolidate the rock mass and fix mesh to tunnel walls and roofs. There are various reinforcement techniques and elements currently in use for strata control. Reinforcement systems can be classified in a variety of ways. Reinforcement systems can be classified according to work force, including passive anchors, active anchors, and mixed anchors.Reinforcement systems can also be classified according to the support mechanism, including adherence anchors and friction anchors. This application concerns adherence anchors rather than friction anchors.

[0003] Historically installing rock bolts to form adherence anchors has involved an operator of an automated drilling rig first drilling a hole using a hollow steel rod having a screw-in replaceable steel bit. The drill bit is then removed.

[0004] The second stage in the process is the insertion of a capsule containing a two- part resin mix in the drilled hole. In third stage a spanner for rotating a rock bolt is inserted into the drilling rig.

[0005] In a fourth stage the bolt is attached to the spanner, inserted into the hole and spun to mix the resin. In this step the spinning breaks the capsule and mixes the hardener into the resin. The annular space between the bolt and the perforation or borehole is filled with mortar made out of resin or cement which, upon setting, ensures sufficient adherence to solidify the rod into the ground / strata.

[0006] With adherence anchors, more recent developments have involved the use of self-drilling rock bolts which include a sacrificial drill bit and the injection of grout through the rock bolt rather than the use of resin capsules. The present disclosure is concerned with anchors which utilise resin capsules.

[0007] One known issue with rockbolts is that, in underground applications, ground conditions can be unstable. Such unstable conditions can apply large forces to the rockbolts and can cause the rock bolts to be pulled from the bore or become damaged and fracture. This is a particular problem in ground conditions that are unstable and / or prone to high stress.

[0008] Various solutions have been proposed to address that problem, and the present disclosure aims to provide an improved rock bolt that can be installed as an adherence anchor and can cope with dynamic and squeezing ground conditions.

[0009] Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each of the appended claims.Summary

[0010] In a first aspect, according to the present invention, there is provided a rock bolt including an elongate rod defining proximal and distal ends, the proximal end being threaded for receiving nut or the like and a central portion extending between theproximal and distal ends, wherein the central portion is smooth and generally cylindrical and wherein at least the distal end defines a mixing and anchoring section defining a series of deformed portions which project beyond the diameter of the smooth central portion and wherein the mixing and anchoring section is ribbed, most typically threaded, so that edges of the deformed portions define a series of teeth and wherein the rock bolt is integrally formed from a single length of metal rod, typically steel.

[0011] The threading / ribbing of the distal end has two significant benefits. First, the teeth formed on the edges of the deformed portions engage better with the resin capsules and assist in breaking up the capsules and mixing the resin. Secondly, after the resin has set the teeth, by providing a more roughened surface, improve the engagement of the distal end of the rock bolt with the resin by providing both a greater surface area of contact and more resistance to separation from the resin.

[0012] In one embodiment, the distal end is threaded and there are at least two threads per inch (TP I), or most preferably two to four TPI, or two to six TPI or two to ten or more threads per inch.

[0013] In some embodiments an additional deformed threaded section of the rock bolt may be provided near or at the proximal end, similar to, or duplicating, the distal end of the rock bolt. This still allows stretching of the central portion of the rock bolt but helps ensure that the proximal end of the rock bolt is secured in the bore hole.

[0014] Typically, the one-piece rock bolt is manufactured from a cylindrical steel rod by threading the distal end and then deforming the distal end, typically in a press. This is a more efficient manufacturing process than manufacturing the rock bolt in parts and also resultant rock bolt is also stronger in tension as the bolt is continuous without connections / discontinuities.

[0015] The paddles may define a generally planar surface for mixing or agitating a resin mix and the edge defining teeth is typically curved. The edges of the paddles maydefine at least five teeth, more preferably at least ten teeth and most preferably at least about fifteen teeth.

[0016] The length of the threaded portion at the distal end is preferably between 350mm and 500mm, and is most preferably about 450mm.

[0017] In a related aspect, there is provided a method of manufacturing a one-piece rock bolt, according to the first aspect, including the steps of providing a length of steel rod having a proximal end a distal end and a central portion, the steel rod being smooth and generally cylindrical; forming a thread on the proximal end of the steel rod for receiving nut; forming ribbing on the distal end of the rod, typically by forming a thread on the distal end, preferably for a distance of 350mm to 500mm from the tip of the distal end; and deforming the distal end to define a series of paddles for moving, fluids, typically viscous fluids, such as resin when the rock bolt is spun, such that edges of the paddles define teeth or ribbing.

[0018] The length of the threaded end is preferably about 450mm.

[0019] The invention also provides a method of reinforcing strata including the steps of forming a bore hole in the strata; inserting a resin capsule into the bore hole inserting a rock bolt according to the first aspect into the bore hole;spinning the rock bolt to break the capsule and mix the resin; and allowing the resin to solidify and tensioning the rock bolt.

[0020] Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.Brief Description of Drawings

[0021] Specific embodiments of the present invention will now be described, by way of example only, and with reference to the accompanying drawings in which: -Figure 1 is an isometric view of a rock bolt embodying the present invention;Figure 2 is a side elevation of the rock bolt of Figure 1;Figure 3 is a top view of the rock bolt of Figure 1;Figure 4 repeats Figure 3 showing a highlighted section of the rock bolt;Figure 5 is a detailed view of the highlighted section shown in Figure 4; andFigure 6 is a photographic view of the distal end of a rock bolt embodying the present invention.Description of Embodiments

[0022] Referring to the drawings, Figures 1 to 5 show a first embodiment of a rock bolt 10. The rock bolt if formed from a cylindrical steel rod and although the exact length is not critical would typically be about 2.4m long, although other common lengths are used and lengths range between 1.2 m and 3.0 m.

[0023] The rock bolt 10 has a proximal end 12 and a distal end 14. The proximal end 12 is threaded and carries a hexagonal nut 16 for use in tensioning the rock bolt using a washer plate (not shown), although other nut shapes may be used, including square.

[0024] Between the distal end 14 and the proximal end 12, there is a smooth cylindrical central portion 20. The central portion is quite long, being the longest part of the bolt, but is shown truncated in the Figures.

[0025] The distal end of the bolt 14 is also threaded. Figures 2 to 5 illustrate that a series of paddles 22 are formed in the distal end 14 of the rock bolt which provides a mixing and anchoring section. Although the shape of the paddles may be varied, in the described embodiment, as is shown most clearly in Figure 6, the paddles have one generally planar face 24 which in use mixes the resin, and one curved (generally concave) face 26. As is best seen with reference to Figures 2 and 3, the paddles are aligned in lines of four longitudinally spaced paddles with one partial paddle at the tip 28. In the described embodiment of Figure 5 there are 4 lines of paddles spaced at 90° around the rod, although this number can be varied and the paddles in one line may be offset from paddles in an adjacent line.

[0026] As is best seen in Figures 5 and 6, the respective edges 24A and 26B of the paddles define a series of teeth 30 / corrugations / ribs caused by the external threading of the distal end 14. In the specific embodiment shown, the edges each define about fifteen teeth 30. The specific thread used is not critical and a number of different threads may be used including Metric M22, M24 or M27, with a threads per inch (TPI) or 2.5, 2.5 or 3, UNC (TPI 4-6), or RD22 or RD24 with a TPI of 3.175. Most typically the thread will provide from 2 to 6 TPI.

[0027] The rock bolt can be manufactured as follows. First, a length of steel rod is cut to a suitable size, commonly 2.4m. The steel used for the rod is preferably a steel alloy, which has at least 15% elongation capacity, preferably at least 20% before failure. The proximal end of the rod is the threaded to form a thread to receive a nut 16. The distal end is then also threaded up to about 450mm from the tip of the bolt,although the length of the threaded portion on the distal end may be from 350mm to 500mm. The distal end is then inserted into a press and shaped / deformed to form the scoop / paddles in the bolt.

[0028] In use, the rock bolt is installed in the same way that a typical adherence anchor. First, an automated drilling rig, or handheld rock drill, is used to drill a bore hole using a drill bit. The drill bit is then removed and a capsule containing a two-part resin mix is inserted in the bore hole. A rock bolt is inserted into the drilling rig and inserted into the bore hole and spun to mix the resin. In this step, the spinning of the bolt, the deformations which act as paddles or scoops and the teeth move and mix the resin and the teeth in particular assist in breaking up the capsule and mixing the hardener into the resin.

[0029] One the resin has been thoroughly mixed the spinning is stopped and, after a short time to allow the resin to harden and engage and adhere the rock bolt in the bore, the rock bolt can be tensioned. In the event of a dynamic event due to unstable ground conditions the smooth central portion can elongate and absorb stress while the distal end 14 retains the rock bolt within the bore. The threading on the distal end by providing a more roughened surface, improves the engagement of the distal end of the rock bolt with the resin by providing both a greater surface area of contact and provides more resistance to separation of the bolt from the resin.

[0030] In a variant (not shown in the drawings) a further mixing and anchoring section may be defined adjacent the proximal end. The section may have the same or similar form to the distal end of the rock bolt being threaded and defining deformations in the form of paddles or the like. This variant still allows stretching of the central portion of the rock bolt but helps ensure that the proximal end of the rock bolt is also secured in the bore hole.

[0031] It will be appreciated by persons skilled in the art that numerous variations and / or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The presentembodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims

CLAIMS:

1. A rock bolt including an elongate rod defining proximal and distal ends, the proximal end being threaded for receiving nut or the like and a central portion extending between the proximal and distal ends, wherein the central portion is smooth and generally cylindrical having a diameter, and wherein at least the distal end defines a mixing and anchoring section defining a series of deformed portions which project beyond the diameter of the smooth central portion and wherein the mixing and anchoring section is ribbed, most typically threaded, so that edges of the deformed portions define a series of teeth and wherein the rock bolt is integrally formed from a single length of metal rod, typically steel.

2. A rock bolt as claimed in claim 1 wherein the mixing and anchoring section is threaded and there are at least five threads per inch, preferably at least ten or more threads per inch.

3. A rock bolt as claimed in any preceding claim wherein the rock bolt is manufactured in one piece from a cylindrical steel rod, by threading the mixing and anchoring section and then deforming the mixing and anchoring section typically in a press.

4. A rock bolt as claimed in any preceding claim wherein the paddles define a generally planar surface for mixing or agitating a resin mix and wherein the edge defining a series of teeth is curved.

5. A rock bolt as claimed in any preceding claim wherein the edges of the paddles define at least five teeth.

6. A rock bolt as claimed in claim 5 wherein the edges of the paddles define at least ten teeth and more preferably at least about fifteen teeth.

7. A rock bolt as claimed in any preceding claim wherein the mixing and anchoring section is formed at the distal end only.

8. A rock bolt as claimed in any one of claims 1 to 6 wherein a mixing and anchoring section is formed at the distal end and adjacent to the proximal end.

9. A method of manufacturing a one-piece rock bolt, preferably as claimed in any one of claims 1 to 7, including the steps of: providing a length of steel rod having a proximal end a distal end and a central portion, the steel rod being smooth and generally cylindrical; forming a thread on the proximal end of the steel rod for receiving nut; forming a thread on the distal end, preferably for a distance of from 350mm, to 500mm from the tip of the distal end; and deforming the distal end to define a series of paddles for moving, fluids, typically viscous fluids, such as resin when the rock bolt is spun, such that edges of the paddles define teeth.

10. A method as claimed in claim 9 wherein the edges of the paddles define at least five teeth.

11. A method of reinforcing strata including the steps of forming a bore hole in the strata; inserting a resin capsule into the bore hole inserting a rock bolt as claims in any one of claims 1 to 8 into the bore hole; spinning the rock bolt to break the capsule and mix the resin; andallowing the resin to solidify and tensioning the rock bolt.

12. A rock bolt as claim in any one of claims 1 to 8 when inserted in a bore hole and encased in resin, grout or the like.

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