阅读说明：本技术 岩石锚杆 (Rock anchor rod ) 是由 M·霍克斯 A·W·卡普托 E·J·罗宾逊 于 2020-01-23 设计创作，主要内容包括：本发明公开了一种在形成于岩体中的钻孔中用作锚定锚杆或摩擦锚杆的岩石锚杆。该岩石锚杆包括具有内部轴向通道以及前端和相对的后端的细长构件。柱塞被构造为在前端处由所述细长构件支撑,且该柱塞支撑冲头,该冲头向外突出超过所述细长构件的所述前端。在使用过程中,所述冲头设置为抵靠所述岩体,以将冲压力施加到所述柱塞上并迫使所述柱塞进入所述细长构件的所述内部轴向通道中,以使所述细长构件的一部分向外偏转,从而将其楔入所述钻孔中。(A rock bolt for use as an anchoring bolt or a friction bolt in a borehole formed in a rock body is disclosed. The rock bolt includes an elongate member having an internal axial passage and a front end and an opposite rear end. A plunger is configured to be supported by the elongated member at a forward end and supports a punch that projects outwardly beyond the forward end of the elongated member. In use, the punch is arranged against the rock mass to apply a punching force to the plunger and force the plunger into the internal axial passage of the elongate member to deflect a portion of the elongate member outwardly to wedge it into the borehole.)

1. A rock bolt for use as an anchoring bolt or a friction bolt in a borehole formed in a rock body, the rock bolt comprising

An elongated member having an internal axial passage and having a forward end and an opposite rearward end;

a plunger configured to be supported by the elongated member at a forward end of the elongated member; and

a punch supported by the plunger and configured to protrude outwardly beyond the front end of the elongated member,

wherein, in use, the punch is arranged to bear against the rock mass to apply a punching force on the plunger and force the plunger into the internal axial passage of the elongate member, thereby deflecting a portion of the elongate member outwardly.

2. The rock bolt claimed in claim 1 wherein said elongate member comprises a tube having an axially extending slot such that a cross sectional view of said tube is substantially C-shaped.

3. A rock bolt according to claim 1 or 2, wherein a portion of the elongate member adjacent the leading end is tapered.

4. A rock bolt according to any one of claims 1 to 3, wherein the plunger comprises a plunger front end and a plunger rear end, the plunger front end defining a bearing wall configured to project outwardly beyond the front end of the elongate member prior to insertion into a borehole, the plunger further comprising a tapered nose extending from the bearing wall towards the plunger rear end, the nose configured to be at least partially received within the internal axial passage at the front end of the elongate member.

5. The rock bolt claimed in claim 4 wherein said plunger rear end includes a cylindrical post configured such that said plunger is axially aligned within said internal axial passage of said elongate member.

6. A rock bolt according to claim 4 or 5, wherein the leading end of the elongate member is press fitted onto the nose of the plunger.

7. A rock bolt according to claim 4 or 5, wherein the leading end of the elongate member is a close friction fit with the nose of the plunger.

8. The rock bolt claimed in any one of claims 1 to 7 wherein the plunger includes an axial bore.

9. The rock bolt claimed in claim 8 wherein the diameter of the bore is larger at the forward end of the plunger and decreases along its length towards the rearward end of the plunger.

10. The rock bolt claimed in claim 8 or 9 wherein the bore is tapered along a portion of the axial length of the plunger.

11. The rock bolt claimed in claim 10 wherein said bore has a morse taper.

12. A rock bolt according to any one of claims 1 to 11, wherein the punch is an elongate rod having a punch leading end and a punch trailing end, wherein, in use, the punch leading end is configured to abut the rock mass and the punch trailing end is supported by the plunger.

13. A rock bolt according to claim 12, wherein the profile of the trailing end of the punch is configured to assist in the support of the punch by the plunger.

14. A rock bolt according to any one of claims 1 to 13, wherein the punch is configured to: in use, the punch applies a temporary impact force to the plunger such that the impact force is released after a threshold is exceeded.

15. A rock bolt according to any one of claims 1 to 14, wherein the punch is made of a ductile material capable of undergoing plastic deformation in use.

16. A rock bolt according to claim 15 when claim 15 is dependent on any one of claims 8 to 14, wherein the punch is configured to be pressed through the bore of the plunger.

17. A rock bolt according to any one of claims 1 to 14, wherein the punch is made of a brittle material which can fracture or collapse in use.

18. A method of installing a rock bolt in a borehole formed in a rock mass, the method comprising the steps of:

supporting a plunger at a front end of the rock bolt and engaging a punch to the plunger such that the punch projects outwardly beyond the front end of the rock bolt;

inserting the rock bolt into the borehole such that the punch is coaxially aligned and positioned downhole of the rock bolt; and

forcing the rock bolt into the bore hole such that the punch abuts the rock mass to apply a ram pressure on the plunger and force the plunger into the internal axial passage of the rock bolt to deflect a portion of the rock bolt outwardly.

19. The method of claim 18, further comprising the step of releasing the punching force applied by the punch after the punch is sufficiently inserted into the internal axial passage of the rock bolt.

20. The method of claim 19, further comprising the step of plastically deforming the punch.

21. The method of claim 20, further comprising the step of pressing the punch through an axial bore extending through the plunger.

22. The method of claim 19, further comprising the step of the punch collapsing or breaking and breaking.

23. A method according to any one of claims 18 to 22, further comprising the step of engaging the rock bolt to the plunger by press fitting the leading end onto the plunger.

24. A plunger for use with a rock bolt or a friction bolt in a borehole formed in a rock body, the plunger comprising

A body having a front end and an opposing rear end; and

a punch supported by the body and configured to project outwardly beyond the front end,

wherein, in use, the punch is arranged to bear against the rock mass to apply a ram force to the body and force the body into the internal axial passage of the rock bolt and thereby deflect a portion of the rock bolt outwardly.

25. The plunger according to claim 24, wherein the body comprises an axial bore.

26. The plunger according to claim 25, wherein the diameter of the bore is larger at the forward end and smaller at the rearward end.

27. The plunger according to claim 25 or 26, wherein the bore tapers along a portion of the axial length of the body.

28. The plunger according to claim 27, wherein the bore is tapered with a morse taper.

29. The plunger of any one of claims 24 to 28, wherein the punch is an elongate rod having a punch leading end and a punch trailing end, wherein, in use, the punch leading end is configured to abut the rock mass and the punch trailing end is supported by the body.

30. The plunger according to claim 29, wherein the punch tail end is contoured to facilitate the punch being supported by the body.

31. The plunger according to any one of claims 24 to 30, wherein the punch is made of a ductile material capable of plastic deformation in use.

32. The plunger according to any one of claims 24 to 30, wherein the plunger is made of a brittle material that can break in use.

Technical Field

The present invention relates to a rock bolt.

More particularly, the invention relates to a rock bolt having an anchor member for securing the rock bolt in a borehole in a rock body.

Background

Rock bolts, also known as anchor bolts or friction bolts, are used in the mining industry to brace and stabilize rock masses against creep or collapse. Rock bolts are then used to position the bearing or thrust plate to exert a compressive force on the rock strata to stabilise the rock mass. It is also known to use rock bolts to support a wire mesh adjacent the rock face and to spray settable concrete over the wire mesh to reinforce the rock face.

Rock bolts come in many different forms and are selected based on a variety of factors including the material and mass of the rock mass to be reinforced and the amount of geological stress and movement common to a particular rock mass.

Rock bolts are typically in the form of an elongate element, such as a pipe, cable, rod or combination thereof, which can be fitted into a borehole drilled into the rock mass and subsequently secured within the borehole. Typically, rock bolts are secured in the borehole by mechanical or chemical means. One type of rock bolt is an anchoring bolt that includes an expansion sleeve that surrounds the rock bolt and pulls or pushes a plunger attached to the rock bolt into the sleeve. The plunger expands the sleeve by deflecting outwardly to press against the side of the rock mass in the borehole, thereby compressing the rock bolt in place and providing point anchoring.

Other types of rock bolts, such as friction bolts, can yield gradually under load to avoid sudden and catastrophic failure of the rock bolt. These types of bolts comprise a tube split longitudinally along its length, the tube having a radius slightly larger than the radius of the borehole into which it is to be inserted. During insertion, the tube is radially compressed to partially or fully close the fracture therein. The friction bolt is then held in place in the borehole due to frictional contact between the pipe and the surrounding rock mass.

In general, it is easier and faster to insert friction bolts than to insert anchoring bolts. This is due to the fact that the friction bolt is installed by simply impact hammering the friction bolt into the borehole, i.e. it is a one-step process. Most anchor bolts are more time consuming to install as it is a two-step process in which the anchor bolt first has to be inserted into the borehole and thereafter the plunger has to be actuated, for example by screwing a screw to pull the plunger into the expansion sleeve.

It will be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms part of the common general knowledge in the art, in australia or in any other country.

Disclosure of Invention

According to a first aspect of the present invention there is provided a rock bolt for use as an anchor bolt or a friction bolt in a borehole formed in a rock body, the rock bolt comprising

An elongated member having an internal axial passage and having a forward end and an opposite rearward end;

a plunger configured to be supported by the elongated member at a forward end of the elongated member; and

a punch supported by the plunger and configured to protrude outwardly beyond the front end of the elongated member,

wherein, in use, the punch is arranged to bear against the rock mass to apply a punching force on the plunger and force the plunger into the internal axial passage of the elongate member, thereby deflecting (deflect) a portion of the elongate member outwardly.

The elongate member may be a tube having a slot extending along its axial length such that the tube is substantially C-shaped in cross-sectional view. In one embodiment, a portion of the elongated member near the front end thereof tapers inwardly.

The plunger may include a plunger front end and a plunger rear end, the plunger front end defining a bearing wall configured to project outwardly beyond the front end of the elongate member prior to insertion into the bore, the plunger further including a tapered, conical nose extending from the bearing wall toward the plunger rear end, the nose configured to be at least partially received within the internal axial passage at the front end of the elongate member.

The plunger rear end may include a cylindrical post configured to axially align the plunger within the inner axial passage of the elongated member. In one embodiment, the forward end of the elongate member may be press fit onto the nose of the (crimped onto) plunger. In another embodiment, the forward end of the elongate member may be a tight friction fit with the nose of the plunger.

The plunger may comprise an axial bore, wherein the diameter of the bore is larger at the front end of the plunger and decreases along its length towards the rear end of the plunger. The bore may taper along a portion of the axial length of the plunger. In this case, the holes may have a morse taper. Alternatively, the holes may have an internal reduced step or notch.

The punch may be an elongate rod having a punch leading end and a punch trailing end, wherein, in use, the punch leading end is configured to abut the rock mass and the punch trailing end is supported by the plunger. The profile of the punch tail end may be configured to facilitate the punch being supported by the plunger.

The punch may be configured to apply a temporary impact force to the plunger in use such that the impact force is released after a reaction force threshold is exceeded. In one embodiment, the punch is made of a ductile material that is capable of undergoing plastic deformation in order to release the punching force, in use. In this case, the punch may be configured to be pressed through the hole of the plunger. In another embodiment, the punch may be made of a brittle material that can collapse (collapse) or break in use.

According to a second aspect of the invention there is provided a method of installing a rock bolt in a borehole formed in a rock body, the method comprising the steps of:

supporting a plunger at a front end of the rock bolt and engaging a punch to the plunger such that the punch projects outwardly beyond the front end of the rock bolt;

inserting the rock bolt into the borehole such that the punch is coaxially aligned and positioned downhole of the rock bolt; and

forcing the rock bolt into the bore hole such that the punch abuts the rock mass to apply a ram pressure on the plunger and force the plunger into the internal axial passage of the rock bolt to deflect a portion of the rock bolt outwardly.

The method may include the step of releasing the punching force applied by the punch after the punch has been fully inserted into the internal axial passage of the rock bolt. In one embodiment, the punch force may be released by plastic deformation of the punch. In this case, the punch may be pressed through an axial bore extending through the plunger. In another embodiment, the punch force may be released by the punch breaking and breaking.

The method may include the step of engaging the rock bolt to the plunger by pressing the leading end onto the plunger.

According to a third aspect of the present invention there is provided a plunger for use with a rock bolt or friction bolt in a borehole formed in a rock body, the plunger comprising

A body having a front end and an opposing rear end; and

a punch supported by the body and configured to project outwardly beyond the front end,

wherein, in use, the punch is arranged to bear against the rock mass to apply a punching force to the body and force the body into the internal axial passage of the rock bolt and thereby deflect a portion of the rock bolt outwardly.

The body may include an axial bore, wherein the diameter of the bore is larger at the forward end and smaller at the rearward end. The bore may taper along a portion of the axial length of the body. In this case, the holes may be of morse taper. Alternatively, the holes may have an internal reduced step or notch.

The punch may be an elongate rod having a punch leading end and a punch trailing end, wherein, in use, the punch leading end is configured to abut the rock mass and the punch trailing end is supported by the body. The profile of the punch tail end may be configured to facilitate the punch being supported by the body.

The punch may be made of a ductile material capable of plastic deformation in use. Alternatively, the punch may be made of a brittle material which is capable of collapsing or breaking in use.

Drawings

The above and other features will become more apparent by referring to the following description of the accompanying schematic drawings given as examples. The drawings are for illustration purposes only and are not intended to be limiting in any way, wherein:

fig. 1 is a perspective view of a rock bolt including a split sleeve friction bolt and a plunger device arranged to provide an anchor point;

FIG. 2 is an enlarged side view of the plunger assembly shown in FIG. 1;

FIG. 3 is a side cross-sectional view of the plunger assembly shown in FIG. 2;

fig. 4 is a side sectional view showing use of the rock bolt of fig. 1 with the rock bolt in a partially installed, non-anchoring position;

fig. 5 is a side sectional view illustrating use of the rock bolt of fig. 1 in a partially installed anchoring position; and

fig. 6 is a side sectional view showing use of the rock bolt of fig. 1 with the rock bolt in a fully installed anchoring position.

Detailed Description

Referring to fig. 1, there is shown a rock bolt 10 for use as an anchoring bolt or friction bolt in a borehole formed in a rock body. The installation and use of the rock bolt 10 is illustrated in fig. 4 to 6, which show successive partial and full installation positions of the rock bolt 10 within a borehole 12 provided in a rock body 14.

The bore hole 12 has an opening 16 at a rock face 18 and a bore hole base 20 remote from the rock face 18. For the purposes of the following description, it will be understood that the terms "forward" and "rearward" refer to an operative drilling position or rock bolt insertion position relative to the borehole 12. Thus, "forward" as used herein refers to a location deeper within the borehole 12, or to a feature or portion of the rock bolt 10 furthest or away from the opening 16. Conversely, "rear" refers to a location closest to the opening 16, or to a feature or portion of the rock bolt 10 closest to or proximate to the opening 16.

The rock bolt 10 comprises a load bearing elongate member in the form of a hollow rod or tube 30 having an internal axial passage. The tube 30 has a tube forward end 32 and an opposite tube rearward end 34. The tube 30 is configured to be inserted and secured in the borehole 12 with the tube forward end 32 positioned at an uphole (uphole) within the borehole 12 and the tube rearward end 34 protruding from the borehole 12 beyond the rock face 18. In this example, the tube 30 has a slot 36 extending along its axial length, resulting in the tube 30 being substantially C-shaped in cross-section or end view, i.e., the tube 30 is of the split type generally known in the art. However, in other examples, it is contemplated that the tube 30 may be completely enclosed in the form of a tube.

The tube 30 is typically made of metal, such as steel, so that it has a suitably high tensile strength. It will be appreciated that the outer diameter of the tube 30, as well as the thickness of its side walls and its inherent compressive resilience, may be preselected so that the rock bolt 10 is able to exert the required outward pressure on the rock mass 14 surrounding the borehole 12 into which it is inserted. In most cases this is achieved by making the outer diameter of the tube 30 (pre-installed) slightly larger than the diameter of the borehole 12. Thus, when the tube 30 is inserted into the bore hole 12, the tube 30 is compressed in the circumferential direction, which results in a complete or partial closure of the groove 36. In some examples, the tube 30 may be formed with a knurled outer surface to increase its coefficient of friction with the rock mass 14.

The portion of the tube 30 along its axial length adjacent the tube forward end 32 tapers inwardly, which taper facilitates insertion of the tube 30 into the borehole 12 during use.

A ring or collar 38 is welded around the tube 30 at the tube tail end 34, the collar 38 being configured to press the bearing plate 40 against the rock face 18 in use. In some embodiments, a small protrusion 39 of metal may be located on the interior of the collar 38 to bridge the slot 36, the protrusion 39 enabling the collar 38 to be welded to the tube 30 around its entire circumference, thereby strengthening the engagement of the collar 38 with the tube 30.

The rock bolt 10 further comprises a plunger 42 and a punch 44, in some examples the plunger 42 is provided separately from the tube 30 and is arranged to engage with the tube 30 as it is inserted into the bore hole 12. In the exemplary embodiment, plunger 42 is engaged to tube 30 from the beginning.

The plunger 42 and punch 44 are more clearly shown in fig. 2 and 3.

The plunger 42 includes a body 46 with an axial bore 48 extending through the body 46. The plunger 42 has a plunger front end 50 and a plunger rear end 52, the body 46 being substantially cylindrical over a portion of its length adjacent the plunger front end 50, which portion is configured to act as a bearing wall 54 in use; the front mid-portion of the body 46 has a tapered taper 56; the rear intermediate portion 58 of the main body 46 is also substantially cylindrical over a portion of its length; and towards the rear end of the body 46 is provided a cylindrical post 60, the intermediate portions 56, 58 and the post 60 being configured to act as a projection 62, and the opening of the bore 48 through the post 60 being configured to act as a nozzle in use. Thus, the plunger 42 has a larger diameter bearing wall 54 at the plunger front end 50, a smaller diameter waist at the intermediate portions 56, 58 of the plunger 52, and a larger diameter post 60 at the plunger rear end 52.

In the illustrative example, the entrance to the bore 48 is shaped similarly to the exterior of the plunger 42, i.e., with a larger cylindrical opening at the plunger front end 50, with an intermediate conical or tapered portion that then becomes cylindrical again and extends through to a smaller opening at the plunger rear end 52. However, in other examples, the bore 48 may include an internal tapered step or notch instead of the previously described tapered portion.

The plunger 42 is typically made of a material that is harder than the material from which the tube 30 is made. In the present example, the plunger 42 is also made of steel.

The punch 44 is in the form of an elongate rod. In some examples, the punch 44 is substantially cylindrical along its entire length. In other examples, the punch may be non-cylindrical in shape, for example, may be a square rod. In the illustrated example, the punch 44 is cylindrical and has a contoured tail end that conforms to the shape of the bore 48. The punch 44 is configured with an outer diameter such that the punch 44 can engage the plunger 42 by inserting the punch tail end into the hole 48 so that it is held securely in place. The larger outer diameter of the punch 44 is therefore equal to the diameter of the bore 48 so that the punch 44 will mate with the bore 48 when inserted therein.

In one example, the taper of the hole 48 is consistent with the taper of the punch 44 and is configured as a morse taper.

The punch 44 is configured to apply a temporary impact force to the plunger 42 in use, but to release the impact force after a reaction force threshold is exceeded. This is achieved by a punch 44 which abuts the plunger 42 (or an internal reduced step) at the tapered portion of the bore.

In an exemplary embodiment, the punch 44 is made of a malleable material such that, in use, the punch 44 is initially rigid and capable of applying a punching force to the plunger 42, but after the punching force exceeds a threshold value, the punch 44 undergoes plastic deformation such that the punch 44 is pressed through the aperture 48 and thereby releases the punching force. In some examples, the punch 44 is made of a plastic material, such as, but not limited to, high density polyethylene, polypropylene, polyvinyl chloride, nylon, or combinations thereof. Such plastic material may be reinforced with fibers. In other examples, the punch 44 is made of a metal, such as copper, aluminum, magnesium, or iron or their ductile alloys.

In other embodiments, the punch 44 may be made of a brittle material, such that in use, the punch 44 is initially rigid and is capable of applying a punching force to the plunger 42, but after the punching force exceeds a threshold value, the punch 44 collapses or fractures and fractures to release the punching force. In some examples, the punch 44 is made of a brittle plastic material, such as polycarbonate or wood.

Referring now to figures 4 to 6, in use, a borehole 12 is drilled into the rock mass 14 to a desired depth. If not already assembled as shown in FIG. 1, the punch 44 is inserted into the plunger 42, and the plunger 42 is then bonded to the tube 30 by inserting its nose 62 into the tube nose 32 so that the plunger 42 and punch 44 are axially aligned with the tube 30. The cylindrical post 60 helps to maintain the plunger 42 in axial alignment with the tube 30 after the plunger 42 is inserted into the bore 48. The forward end of the tube 30 is then press fit over the legs 60 onto the waists of the intermediate portions 56, 58 of the plunger 52. There is a slight clearance between the outer circumference of the post 60 and the inner circumference of the tube 30 so that the post 60 is still easily moved longitudinally within the tube 30. Desirably, there is a clearance of about 0.5-1mm around the struts 60, such that the total radial clearance is about 1-2 mm.

However, in other embodiments, the forward end of tube 30 may be a tight friction fit with post 60, such that it is not necessary to press fit tube 30 to plunger 60.

The rock bolt 10 is then inserted into the borehole 12 with the plunger 42 and punch 44 located downhole of the tube 30. This insertion is typically performed by impact hammering the rock bolt 10 into the borehole 12 until the bearing plate 40 abuts the rock face 18. During this insertion, the tube 30 is compressed circumferentially and engages the rock mass 14 in a friction fit.

In the initial stage of insertion, the plunger 42 and punch 44 are held centrally within the bore hole 12 and do not contact the rock mass 14, as shown in figure 4. Thus, at this stage of insertion, only the tube 30 undergoes circumferential compression. This circumferential compression is not sufficient to eliminate the clearance around the post 60, and therefore, at this stage, the plunger 42 is still relatively easily moved axially within the internal axial passage of the tube 30.

Subsequently, as shown in fig. 5, as the rock bolt 10 approaches its fully inserted position, the punch 44 contacts the base 20 at the downhole end of the bore hole 12, the punch 44 bearing against the base 20 and acting as a support between the base 20 and the plunger 42 to prevent further downhole movement of the plunger 42, i.e. the punch 44 begins to exert a punching force on the plunger 42 and force the plunger 42 into the internal axial passage of the tube 30. Thus, as the tube 30 is inserted further into the bore 12, the tube nose 32 slides over and past the plunger 42 such that the plunger 42 enters the internal axial passage of the tube 30. In this way, the tapered tube nose 32 is forced to "ride" on the slope formed by the tapered portion 56 of the plunger and deflect outwardly so that the tube nose 32 expands and wedges between the support wall 54 of the plunger and the rock mass 14.

It will be appreciated that as the tube 30 slides further over the plunger 42 and engages the greater length of the bearing wall 54, frictional forces (F) exist between the tube 30 and the plunger 42 and rock mass 14_f) Will be increased. At some stage during insertion (as shown in FIG. 6), friction force F_fThe plunger 42 will be wedged into the tube 30 such that the tube 30 will no longer be able to slide over and past the plunger 42, i.e., the plunger 42 will not move further into the internal axial passage of the tube 30. When the rock bolt 10 is fully inserted into the borehole 12, the plunger 42 will move with the tube 30. This final movement of the plunger 42 will compress the punch 44. After the pressure exceeds the threshold, the punch 44 assumes plastic deformation and begins to extrude through the bore hole 48, thereby releasing the impact force.

Depending on the type of material used for the punch 44 and the size of the bore hole 12, it is envisaged that in some embodiments the punch 44 may begin to extrude through the hole 48 at an earlier stage of insertion of the rock bolt 10 into the bore hole 12, i.e. before the plunger 42 is fully wedged into the tube 30. However, even so, the punch 44 will still be able to apply a punching force to the plunger 42 sufficient to force the plunger 42 into the internal axial passage of the tube 30, such that the tube nose 32 eventually becomes wedged between the bearing wall 54 of the plunger and the rock mass 14.

Once fully inserted, the rock bolt 10 acts as a combination anchor bolt and friction bolt, i.e. the frictional securement of the tube 30 around the plunger 42 acts as a point anchor for the anchor bolt, while the frictional engagement of the rock mass 14 along the length of the tube 30 acts as a friction bolt.

Thus, from the above description, it will be appreciated that the rock bolt 10 can be inserted into an anchor bolt (i.e. a rock bolt having an anchor point) in a single step process, for example by using impact hammering only. Furthermore, the use of the punch 44 and its ability to plastically deform avoids the need to precisely drill the bore hole 12 to a specified depth and within a specified radial tolerance. This is due to the fact that only the frictional force F is present_fThe punch 44 undergoes plastic deformation only when a threshold value associated with the anchor being properly frictionally engaged with the rock mass 14 is reached.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the rock bolt as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

For example, it will be appreciated that the same function may be achieved using a solid plunger having no central bore extending therethrough. Such a plunger will only have a recess at the forward end of the plunger for receiving and retaining a punch. During use, once the yield stress exceeds a threshold, the punch will still be able to plastically deform, collapse, or fracture; plastic deformation will only occur at different locations, for example adjacent to the base 20.

In the appended claims and the foregoing description, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the rock bolt.