AU2021105904A4

AU2021105904A4 - Self-drilling rock bolt

Info

Publication number: AU2021105904A4
Application number: AU2021105904A
Authority: AU
Inventors: Matthew Holden; Jason Matthews
Original assignee: FCI Holdings Delaware Inc
Current assignee: FCI Holdings Delaware Inc
Priority date: 2020-11-17
Filing date: 2021-08-19
Publication date: 2021-10-21
Anticipated expiration: 2029-08-19

Abstract

A rock bolt (10) comprises an externally elongate rod (12) having a central bore (11). A drill bit (18) is mounted on the distal end for drilling a bore in strata. The sides of the drill bit taper outwardly towards the cutting end of the drill typically at an angle of about 5°. An expansion shell (22) is mounted about the exterior of the rod adjacent the drill bit. The shell (22) has at least one longitudinal slot to allow the shell to expand and contract. A stop (20) maintains the expansion shell (22) in close proximity to the drill bit and limits the movement of the expansion shell towards the proximal end of the rock bolt. The exterior of the shell is contoured to define a series of ridges (40) the interior of the shell is wider than the exterior of the elongate rod to allow the rod to rotate relative to the shell. The shell (22) is free to rotate relative to the drill bit, and is tapered inwardly towards the proximal end preferably at an angle of about 50. In use as the rock bolt is installed in strata, the drill bit forms a bore in the strata and the shell tends to drag along the bore wall when thrust forward during drilling and remains largely clear of the spinning rod and drill bit. When drilling in complete movement of the rock bolt out from the bore causes the drill bit to engage with and expand the shell. L-n N) (06

Description

L-n

N)(06

Self-drilling rock bolt

Technical Field

[0001] This invention relates to reinforcement systems and in particular to a self drilling rock bolt for use in mining and civil applications.

Background

[0002] 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.

[0003] With adherence anchors, 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.

[0004] In contrast, friction bolt arrangements make use of the resistance generated against the rock as their fastening method, taking advantage of the friction or rubbing between the rock/strata and the element as the latter is deformed during installation made through impact with a shank or adapter.

[0005] More recently methods of installing rock bolts using a self-drilling rock bolt which uses a sacrificial drill bit attached to a hollow rock bolt have become more commonplace. This allows rock bolts to be used in poor ground conditions where the self-drilling rock bolt acts as the drill steel and remains in the borehole after drilling. Using this method, there are often difficulties in uncoupling the installation dolly used to install the rock bolt from the self-drilling rock bolt, if the rock bolt is not properly engaged with or locked into the borehole. A secondary related issue arises where the boreholes are vertical or greater than horizontal, where the rock bolts have a tendency to drop out of the borehole when they are disconnected from the installation dolly, if they are not properly engaged with or locked into the borehole.

[0006] Such self-drilling rock bolts can be cement grouted or resin injected to lock them into the borehole and this typically involves a further step of connecting adaptors and setting up additional pumping equipment to inject the self-drilling rock bolt with resin or cement to lock it into the bore hole after disconnection from the installation dolly.

[0007] Often the grouting step takes place some time after the rock bolt has been disconnected, and the delay often leads to problems with the rock bolts falling from the bores in the interim.

[0008] The present invention seeks to at least address some of the deficiencies of existing methods and provide for efficient and reliable rock bolt installation.

[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] According to a first aspect of the present invention, there is provided a rock bolt comprising:

an elongate rod having a central bore and being externally threaded, the rod having a first or distal end and a second or proximal end; a drill bit mounted on the distal end for drilling a bore in strata such as rock or the like wherein the sides of the drill bit taper outwardly towards the cutting end of the drill at an angle of from about 1 to 100, preferably about 50; an expansion shell mounted about the exterior of the rod adjacent the drill bit, the shell defining at least one longitudinal slot to allow the shell to expand and contract; a stop for maintaining the expansion shell in close proximity to the drill bit and limiting the movement of the expansion shell towards the proximal end of the rock bolt; wherein the exterior of the shell is contoured to define a series of ridges or the like and wherein the widest part of the shell is preferably wider than the drill bit and wherein the interior of the shell is wider than the exterior of the elongate rod to allow the rod to rotate relative to the shell and wherein the shell is free to rotate relative to the drill bit, and is tapered inwardly towards the proximal end and wherein the interior taper of the shell is from 10 to 100, preferably about 50; the arrangement being such that as the rock bolt is installed in strata, the drill bit forms a bore in the strata and the shell tends to drag along the bore wall when thrust forward during drilling and remains largely clear of the spinning rod and drill bit and when drilling ceases, movement of the rock bolt out from the bore causes the drill bit to engage with and expand the shell.

[0011] The interior taper of the shell may be from 10to 200, more preferably, 1 to 100 most preferably about 50;

[0012] The rock bolt may be suitable for both hard rock and civil applications. Not only does the shell assist in retaining the rock bolt in the bore, it also allows for a pre tension, typically of 50kN or more to be applied to the rock bolt, which is often a requirement or at least desirable for civil applications, although not typically used in underground mining applications.

[0013] The rock bolt may include a nut (typically a hex nut) on the proximal end for use in tensioning the rock bolt against the rock/strata face adjacent the bore using a washer plate or the like.

[0014] Typically, the sides of the drill bit taper outwardly towards the drill end at an angle of from 1 to 100, preferably 50 and the interior taper of the shell is also from 1 to 100, preferably 5°.

[0015] It is preferred the longitudinal slot in the shell is a full length slot and extends the length of the shell. This assists in allowing the shell to expand and contract as well as allowing the passage of drilling fines.

[0016] The shell may define a plurality of additional partial longitudinal slots which are closed at one end. The plurality of additional partial longitudinal slots also help to ensure unrestricted flow/path of the resin or grout when encapsulating the installed rock bolt"

[0017] Typically, the ridges are generally wedge shaped, and are from 5 to 20 in number.

[0018] Ina related aspect, the invention provides a method of installing a rock bolt in rock strata or the like comprising the steps of

providing a rock bolt comprising:

an elongate rod having a central bore and being externally threaded, the rod having a first or distal end and a second or proximal end;

a drill bit mounted on the distal end for drilling a bore in strata such as rock or the like;

an expansion shell mounted on the exterior of the rod adjacent the drill bit, the shell defining at least one longitudinal split to allow the shell to expand and contract; a stop for maintaining the expansion shell in close proximity to the drill bit and limiting the movement of the expansion shell towards the proximal end of the rock bolt; wherein the exterior of the shell is contoured to define a series of ridges or the like and wherein the widest part of the shell is preferably wider than the drill bit and wherein the interior of the shell is wider than the exterior of the elongate rod to allow the rod to rotate relative to the shell and wherein the shell is free to rotate relative to the drill bit, and is tapered inwardly towards the proximal end; applying rotation to the rod and drill bit to drill a bore into the rock strata during which step the shell tends to drag along the bore wall when thrust forward during drilling, remains largely clear of the spinning rod and drill bit, and generally does not rotate; and when the bore is drilled to a desired depth, causing the drill bit to move backwards out from the hole causing the drill bit to engage with and expand the shell and subsequently encasing the rock bolt in resin, cement or the like by pumping liquid resin/cement through the central bore of the rock bolt.

[0019] For civil applications, apre-tension of 50kN or more is applied to the rod prior to the step of encasing the rock bolt. The pre-tension is applied by tensioning the rod using a nut and washer plate against the rock face adjacent the bore.

[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] A specific embodiment of the invention will now be described, by way of example only, and with reference to the accompanying drawings, in which:

Figure 1 is a side view of an embodiment of a rock bolt;

Figure 2 is an end view of the rock bolt shown in Figure 1 showing the end of the drill bit;

Figure 3 is a cross-section through the rock bolt shown in Figure 1 on A-A;

Figure 4 is a side view of an expansion shell of the rock bolt; and

Figure 5 is an end view of the expansion shell shown in Figure 4.

Description of Embodiments

[0022] Referring to the drawings, Figure 1 shows a self-drilling rock bolt 10. As shown in Figures 1 to 3, the rock bolt comprises an elongate hollow rod/bar 12 having a central bore 11 and external R32 thread which is industry standard, although the dimensions and thread on the bar could be varied. The rod/bar will typically be made from steel. An R32 hexagonal nut 14 is threaded onto the proximal end 16 of the rod. In he described embodiment, an R32 button head drill bit 18 with an internal R32 thread is mounted on the distal end of the rock bolt, although other types of drill bits and configurations may be employed. Also shown in Figure 1 is a coupler 20 which is a length of rod having an R32 internal thread which is typically used to connect two R32 rods together when a longer rock bolt is required than the typical length of about 3m. An expansion shell 22, described in more detail below, is located on the rod between the drill bit 18 and the coupler 20.

[0023] The R32 button head drill bit 18 has a drilling end 30 for drilling through strata, typically rock, and has an external side surface 32 which is tapered outwardly from the threaded end to the bit end at an angle of 50 relative to the longitudinal axis LA of the rock bolt.

[0024] The shell 22 which is best shown in Figures 3 to 5 has a generally annular cross section. The exterior of the shell is serrated defining a series of ridges in the form of wedges 40. The exterior diameter of the shell is oversized compared to the exterior diameter of the drill bit 30 and the bore hole formed by the drill bit 30 in use.

[0025] The interior surface 50 of the shell has a greater diameter than the external diameter of the R32 bar so that the shell floats on the bar and the bar can rotate/spin relative to the shell 22. The interior 52 of the shell has a 5° taper reactive to the longitudinal axis of the rock bolt and expands outwards towards the distal end of the rock bolt, as is best seen in Figure 3.

[0026] As is best seen in Figures 4 and 5, the shell defines a channel in the form of an elongate slot which extends the full length of the shell allowing the shell to expand and compress. Five additional channels in the form of partial slots 56 are provided also, which help to reduce the force required to compress the shell, and allow for the clearing of fines, as discussed below. The plurality of additional partial longitudinal slots also help ensure unrestricted flow/path of the resin or grout when encapsulating the installed rock bolt.

[0027] The shell 22 is typically made from cast steel, although other suitable materials could be used.

[0028] In use, the rock bolt 10 is attached to an installation dolly and drilling of a borehole in the strata is commenced by a combination of rotation of the rock bolt and percussion using the dolly. The rotation of the rock bolt rotates the drill bit 30 and that, in conjunction with the percussion applied to the drill bit, forms a bore in the rock strata. Water is flushed through the central bore 11 of the rock bolt and this washes the rock fines generated by the drilling out from the borehole along the outside of the rock bolt. The slots/channels in the drill bit and the slots 54, 56 in the shell 22 assist in the clearing of the fines from the distal (drilling) end of the rock bolt.

[0029] The rock bolt is drilled in to the required depth, with the shell 22 dragging against the bore hole. When the rock bolt is pushed forward under percussive forces during drilling of the hole, the shell 22 will be dragged along the wall, and the friction will keep the shell clear of the drill bit 30. In particular, the interior of the shell 22 should remain clear of the spinning drill bit as it is dragged back by friction. In addition, as its interior diameter is greater than the external diameter of the R32 rod, the shell 22 should remain clear of that spinning rod also.

[0030] The longitudinal splits in the shell also allow it to collapse inwards during drilling and assist with pushing the shell 22 forwards in the bore formed by the rotating drill bit 30.

[0031] As discussed above, the shell 22 will tend to be forced backwards along the rock bolt towards the proximal end of the rock bolt by contact with the bore which drags on the shell 22, however the coupler 20 acts as a backstop and prevents the shell from sliding backwards beyond the coupler.

[0032] Once the hole has been drilled to the required depth, drilling ceases. The installation dolly can be disconnected. The rod can then be pulled backwards, for example, by rotation of the nut 14 against a washer or the like (not shown) to cause the distal end of the rod and the drill bit 30 to move backwards. The shell 22, being larger than the bore hole should grip the walls of the bore and remain in position due to friction/drag in the bore hole. As the drill bit 30 is pulled backwards the tapered sides 32 of the drill bit slide along the internal 50 tapered surface 52 of the expansion shell and cause the shell 22 to expand and engage more firmly in the bore.

[0033] The expanded shell retains the rock bolt in the bore.

[0034] In civil applications, where it is required that the rock bolt is pre-tensioned prior to grouting a pre-tension may be applied to the rod using the hex nut and a washer or the like. Pre-tensioning the bolt prior to grouting provides a much improved result over grouting an un-tensioned bolt with the pre-tensioned bolt able to safely handle much greater loads.

[0035] In mining applications, the rock bolt will typically not be pre-tensioned to any great degree and the expanded shell 20 simply assists in retaining the rock bolt in the bore, which may be a vertical bore in a roof or at an angle, such as 450 to the vertical, prior to a later grouting step.

[0036] In vertical installations and angled installations where there is a significant vertical component, the weight of the bolt itself should engage the shell and self-hold the rock bolt into the drilled hole.

[0037] This system is not limited to the R32 self-drilling rod as shown and described but can be used with any self-drilling rock bolt application using hollow bolts.

[0038] The coupler which is used in the described embodiment is commonly used for linking two rods together, but could be replaced with a simple collar swaged or welded onto the bar to limit the backwards movement of the shell.

[0039] 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 present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims

CLAIMS:

1. A rock bolt comprising:

a drill bit mounted on the distal end for drilling a bore in strata such as rock or the like wherein the sides of the drill bit taper outwardly towards the cutting end of the drill at an angle of from about 1 to 100, preferably about 50;

an expansion shell mounted about the exterior of the rod adjacent the drill bit, the shell defining at least one longitudinal slot to allow the shell to expand and contract;

a stop for maintaining the expansion shell in close proximity to the drill bit and limiting the movement of the expansion shell towards the proximal end of the rock bolt;

wherein the exterior of the shell is contoured to define a series of ridges or the like and wherein the widest part of the shell is wider than the drill bit and wherein the interior of the shell is wider than the exterior of the elongate rod to allow the rod to rotate relative to the shell and wherein the shell is free to rotate relative to the drill bit, and is tapered inwardly towards the proximal end;

the arrangement being such that as the rock bolt is installed in strata, the drill bit forms a bore in the strata and the shell tends to drag along the bore wall when thrust forward during drilling and remains largely clear of the spinning rod and drill bit and when drilling ceases, movement of the rock bolt out from the bore causes the drill bit to engage with and expand the shell.

2. A rock bolt as claimed in claim 1 wherein the interior taper of the shell is from to 200, more preferably 10 to 100 and most preferably about 50;

3. A rock bolt as claimed in claim 1 or 2 further including a nut on the proximal end for use in tensioning the rock bolt.

4. A rock bolt as claimed in in any one of claims 1 to 3 wherein the elongate rod is continuously threaded along substantially its entire length including the area enclosed by the shell.

5. A rock bolt as claimed in any one of claims 1 to 4 wherein the longitudinal slot in the shell is a full length slot and extends the length of the shell.

6. A rock bolt as claimed in claim 5 wherein the shell defines a plurality of additional partial longitudinal slots which are closed at one end.

7. A rock bolt as claimed in any one of claims 1 to 6 wherein the ridges are generally wedge shaped, and are from 5 to 20 in number.

8. A method of installing a rock bolt in rock strata or the like comprising the steps of

providing a rock bolt comprising:

an expansion shell mounted on the exterior of the rod adjacent the drill bit, the shell defining at least one longitudinal split to allow the shell to expand and contract;

a stop for maintaining the expansion shell in close proximity to the drill bit and limiting the movement of the expansion shell towards the proximal end of the rock bolt; wherein the exterior of the shell is contoured to define a series of ridges or the like and wherein the widest part of the shell is preferably wider than the drill bit and wherein the interior of the shell is wider than the exterior of the elongate rod to allow the rod to rotate relative to the shell and wherein the shell is free to rotate relative to the drill bit, and is tapered inwardly towards the proximal end; applying rotation to the rod and drill bit to drill a bore into the rock strata during which step the shell tends to drag along the bore wall when thrust forward during drilling, remains largely clear of the spinning rod and drill bit, and generally does not rotate; and when the bore is drilled to a desired depth, causing the drill bit to move backwards out from the hole causing the drill bit to engage with and expand the shell and subsequently encasing the rock bolt in resin, cement or the like by pumping liquid resin/cement through the central bore of the rock bolt.

9. A method as claimed in claim 8 wherein a pre-tension is applied to the rod prior to the step of encasing the rock bolt.

10. A method as claimed in claim 9 wherein the pre-tension is applied by tensioning the rod using a nut and washer plate.