AU2006246523A1 - Ground Support System - Google Patents

Description

P/00/009 28/5/91 Regulation 3.2

ORIGINAL

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION Invention title: "GROUND SUPPORT SYSTEM" Applicant: DAVID JOHN WILKIE The following statement is a full description of this invention, including the best method of performing it known to me: I-2-

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"GROUND SUPPORT SYSTEM" Field of the Invention The present invention relates to a ground support system made from high tensile plastics material and relates particularly, though not exclusively, to a rock bolt for a ground support system.

Background to the Invention CIn many underground mines rock bolts are the primary component in the roof Osupport system, and therefore it is essential for the safety of personnel that the rock bolts perform according to specifications. The collapse of mine roofs, especially in tunnels, is one of the primary causes of fatalities in the mining industry. Prior art rock bolts for ground support systems come in a variety of designs and configurations. Some rock bolts are in the form of tensioned steel reinforcing bar which is anchored in a drill hole by encapsulation with a suitable resin. Another common form of rock bolt is in the form of a spilt tube made by rolling flat steel plate into a tubular shape with a split extending the full length of the bolt. The outer diameter of the split tube is larger than the diameter of the drill hole, so that when the rock bolt is driven into the drill hole it is compressed and is retained in the drill hole by a tight friction fit. This type of split tube rock bolt may also be grouted.

One of the problems with prior art rock bolts is their susceptibility to corrosion in situ where they are commonly exposed to groundwater and corrosive salts from the surrounding rock formation. Hence it is essential to regularly check all of the rock bolts to ensure the integrity of the ground support system. This checking procedure is labour intensive and susceptible to human errors.

Another problem arises from the crystalline structure of the metallic materials from which prior art rock bolts are manufactured. Whilst tensioned steel can be manufactured with a degree of resiliency, the crystalline structure of the metal means that the rock bolt is still subject to fatigue. Hence, over time the I-3rock bolt loses its resiliency and is no longer capable of remaining firmly 0 anchored in the rock.

The present invention was developed with a view to providing a rock bolt made from a high tensile plastics material such as a high strength polymer plastics material that is capable of providing a reliable ground support system.

Several other inventive aspects of the ground support system are also described.

References to prior art in this specification are provided for illustrative purposes only and are not to be taken as an admission that such prior art is part of the common general knowledge in Australia or elsewhere.

Summary of the Invention According to one aspect of the present invention there is provided a rock bolt for a ground support system, the rock bolt comprising: an elongate tubular structure made from a suitably high tensile plastics material, the tubular structure having a head at one end and a tip at the other, and having an elongate gap extending along the length of the tubular structure, wherein when the bolt is driven into a drill hole of smaller diameter than an outer diameter of the tubular structure, said gap permits the tubular structure to flex inwards, and to exert an outwards force so as to grip a wall of the drill hole in its rest position.

Preferably the high tensile plastics material is a resilient high strength polymer plastics material. Preferably the resilient high strength polymer plastics material is fibre-reinforced polypropylene. More preferably, the fibre of the fibre-reinforced polypropylene is glass fibre.

Alternatively, the high tensile plastics material may be fibre-reinforced plastic or carbon fibre.

Preferably said elongate gap extends almost the full length of the structure from the tip to a termination adjacent the head. Typically said elongate gap is I-4-

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of a width selected to permit the tubular structure to flex inwards so as to reduce its outer diameter by up to 30%. More typically said elongate gap is of _a width selected to permit the tubular structure to flex inwards so as to reduce its outer diameter by between 15% and Preferably said tip of the tubular structure is tapered to facilitate insertion of the rock bolt into the drill hole. In one embodiment said tubular structure is of substantially uniform cross-section throughout substantially its length. In another embodiment an outer surface of said tubular structure is formed by a series of frusto-conical surfaces joined end to end to give the structure a serrated or barbed longitudinal cross-sectional shape.

Preferably the tubular structure is formed by moulding the high strength polymer plastics material. More preferably the moulding takes place by means of pressure or vacuum forming.

The rock bolt for a ground support system may further comprise an accessory, the accessory comprising: a fixture having an external profile adapted to engage with the head of a matching rock bolt wherein the accessory can be quickly fixed to the rock bolt in said ground support system.

Advantageously said head of the tubular structure is hollow and is formed with an internal profile adapted to engage with a mating fixture for fixing an accessory of the ground support system to the rock bolt.

In one embodiment said external profile of the fixture is in the form of a bayonet fitting which is adapted to engage with a mating fitting provided in the head of the matching rock bolt.

Alternatively said external profile of the fixture is preferably in the form of a screw threaded fitting which is adapted to engage with a corresponding screw threaded fitting provided in the head of the matching rock bolt. In this case the screw threaded fitting of the fixture is preferably adapted to be positioned in the head of the matching rock bolt so that the screw threaded fitting of the

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fixture extends beyond the corresponding screw threaded fitting in the head of the matching rock bolt to allow free movement of the fitting in the rock bolt.

Preferably said accessory further comprises attachment means formed integral with said fixture for attaching an article to the rock bolt. Typically said attachment means is in the form of an pin, or it could be in the form of an eye bolt or a plate. Alternatively said accessory may further comprise a pivotable attachment means pivotally mounted on said fixture, for example, by a hinge connection. In one embodiment said pivotable attachment means comprises a pipe or cable support having one or more open-ended recesses adapted to removably support a pipe or cable therein. Preferably each of said open-ended recesses has an access opening of reduced width through which a pipe or cable can be pushed into the recess, said access opening helping to retain the pipe or cable in the pipe or cable support once it is pushed into the recess. Preferably the pipe or cable support has one or more lips extending into the open-ended recesses to assist in retaining the pipe or cable in the support once it is pushed into the recess.

The rock bolt for the ground support system may still further comprise a pop plate, the pop plate comprising a substantially planar structure made from a suitably resilient high strength polymer plastics material and having a top surface that is normally convex in a relaxed condition of the pop plate and concave in a compressed condition, said structure having a central aperture provided therein for receiving the shaft of a rock bolt wherein when the rock bolt is driven into a drill hole a head of the rock bolt will press said top surface of the structure to a compressed condition, and wherein if the forces holding the rock bolt in the drill hole are reduced below a threshold value said top surface of the structure will automatically pop-out to its relaxed condition.

Typically said top surface of the pop plate is of circular shape when viewed in plan.

The present invention further provides a method of forming a rock bolt for a ground support system comprising: O -6- Si) placing a sheet of high tensile plastics material in a mould shaped to Sproduce an elongate tubular structure having a head at one end and a tip at the other, and having an elongate gap extending along the length of the tubular structure to form the rock bolt; Sii) heating the sheet to achieve melt-flow; Siii) applying pressure or a vacuum to the mould to form the rock bolt in Sthe mould; Siv) rapidly cooling the mould; and v) releasing the rock bolt from the mould for positioning in the ground.

Preferably the high tensile plastics material is fibre-reinforced polypropylene.

Preferably the heating of the sheet takes place at about 200 degrees Celsius.

More preferably, the cooling of the mould takes place by cooling with water.

Throughout the specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. Likewise the word "preferably" or variations such as "preferred", will be understood to imply that a stated integer or group of integers is desirable but not essential to the working of the invention.

Brief Description of the Drawings The nature of the invention will be better understood from the following detailed description of several specific embodiments of the rock bolt and other aspects of the ground support system, given by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a first embodiment of a rock bolt in accordance with the present invention; I-7- Figure 2 is a perspective view of a second embodiment of a rock bolt in 0 accordance with the present invention; Figure 3 is a section view of a third embodiment of a rock bolt in accordance with the present invention; Figure 4 illustrates the rock bolt of Figure 2 about to be driven into a drill hole in a rock formation; Figure 5 illustrates the rock bolt of Figure 2 driven into the drill hole in Sthe rock formation; Figure 6 illustrates a first embodiment of an accessory for the ground support system according to the present invention; Figure 7 illustrates a second embodiment of an accessory for the ground support system according to the present invention; Figure 8a illustrates the accessory of Figure 6 prior to insertion into the head of a matching rock bolt; Figure 8b illustrates the accessory of Figure 6 after insertion into the.

head of the matching rock bolt; Figure 9a illustrates an accessory prior to insertion into the head of a matching rock bolt; Figure 9b illustrates the accessory of Figure 9a after insertion into the head of the matching rock bolt; Figure 10 is a perspective view of a preferred embodiment of a pop plate according to the present invention fitted to a rock bolt; Figure 11 is a side view of the pop plate of Figure 10 shown in its relaxed condition; Figure 12 is a side view of the pop plate of Figure 10 shown in its compressed condition;

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Figures 13a, 13b and 13c illustrate three different types of taper a provided at the tip of a rock bolt in accordance with the present _invention; Figure 14a and 14b illustrate a third embodiment of an accessory for Sthe ground support system according to the present invention; \Figure 15 illustrates a pipe support of the accessory of Figure 14 shown with pipes inserted; SFigure 16 illustrates a section view of a further embodiment of a rock S 10 bolt in accordance with the present invention; Figure 17 illustrates a fourth embodiment of an accessory for the ground support system of the invention; and Figure 18 illustrates the upper portion of a fifth embodiment of an accessory for the ground support system of the invention.

Detailed Description of Preferred Embodiments A first embodiment of a rock bolt 10 for a ground support system, as illustrated in Figure 1, comprises an elongate tubular structure 12 made from a high tensile plastics material such as a suitably resilient high strength polymer plastics material, in this case fibre-reinforced polypropylene.

Importantly, polymer plastics materials are formed from long chain molecules that give the polymer material its resiliency or memory. Hence, unlike the crystalline structure of a metal, they are far less susceptible to fatigue. A suitable high strength polymer plastics material is fibre-reinforced polypropylene since this material is very strong and has high tensile strength.

Polymers such as nylon and polyethylene are of lower strength and therefore not generally suitable materials for this present invention.

Typically a sheet of the fibre-reinforced polypropylene is placed in a mould and then compressed and super-heated to fill the mould and produce the N-9desired shape of the tubular structure 12 as described in more detail later in the specification.

The tubular structure 12 has a head 14 at one end and a tip 16 at the other end, and has an elongate gap 18 extending along the length of the tubular structure 12. Due to the use of fibre-reinforced polypropylene, the tubular structure may be formed as a single piece without the need to weld together the separate components such as having to weld the head to the tubular structure. The formation of the rock bolt in a single piece adds greatly to the strength of the rock bolt which is of course critical in its application as a ground support structure. When the bolt 10 is driven into a drill hole of smaller diameter than an outer diameter of the tubular structure 12, the gap 18 permits the tubular structure 12 to be compressed and to flex inwards as it is driven into the drill hole, and to exert an outwards force so as to grip a wall of the drill hole in its rest position. In this embodiment the elongate gap 18 extends almost the full length of the tubular structure 12 from the tip 16 to a termination 20 adjacent the head 14. However, it will be appreciated that in an alternative embodiment it would be possible for the gap 18 to extend the full length of the tubular structure 12.

Typically the elongate gap 18 is of a width selected to permit the tubular structure to flex inwards so as to reduce its outer diameter by up to More typically the elongate gap 18 is of a width selected to permit the tubular structure to flex inwards so as to reduce its outer diameter by between and 25%. The elongate gap 18 is large enough that the outer circumference of the rock bolt 10 in its compressed state will be equal to the internal circumference of the drill hole. In this embodiment the tubular structure 12 is of substantially uniform cross-section throughout its length, so as to maximise the contact area (and hence the friction grip) between the outer surface of the tubular structure 12 and the inner surface of the drill hole.

Typically the outer diameter of the tubular structure 12 is about 48mm and the gap 18 is about 26mm wide. If the drill hole is about 40mm in diameter, this

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means the tubular structure 12 must flex inwards so as to reduce its outer diameter by about 17% (8mm). It is not unusual for the internal diameter of _the drill hole to decrease as the drill bit wears out, so that the tubular structure 12 has to be compressed to a greater extent. The wall of the tubular structure 12 is typically about 2.5mm thick, and the head 14 is about 60mm in diameter cand 8mm thick. The thickness of the tubular structure 12 may be altered to Igain or reduce the friction by making the structure 12 thicker or thinner Nrespectively.

The tip 16 of the tubular structure 12 is preferably tapered to facilitate insertion of the rock bolt 10 into the drill hole. Figures 13a, 13b and 13c illustrate three different kinds of taper that can be provided at the tip 16 of the tubular structure 12. The rock bolt 10 is typically driven into the drill hole by a "jumbo" hammer. The taper at the tip 16 ensures that as the end of the tubular structure 12 is driven into the mouth of the drill hole the wall of the tubular structure is forced to flex inwards.

Figure 2 illustrates a second embodiment of a rock bolt 22 made from fibrereinforced polypropylene in accordance with the present invention. The same reference numerals are used to identify the similar parts in this embodiment.

The main difference between this embodiment and the previous embodiment is that an outer surface of the tubular structure 12 of this embodiment is formed by a series of frusto-conical surfaces 24 joined end to end to give the structure a serrated cross-sectional shape. The use of the fibre-reinforced polypropylene together with a suitable moulding technique allows for the production of a rock bolt with a shaped external profile such as one having these frusto-conical surfaces. The edges of the frusto-conical surfaces 24 are designed to bite into the inner wall of the drill hole and thereby improve the grip. This design has particular application for soft or broken rock.

In other respects the rock bolt 22 of Figure 2 is similar in design and function to that of Figure 1 and will not be described again. Figure 4 illustrates the rock bolt 22 about to be driven into a drill hole 26 in a rock formation of a mine roof. The inner diameter of the drill hole 26 is smaller than the outer diameter

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of the tubular structure 12 of the rock bolt 22. Figure 5 illustrates the rock bolt 22 after it has been partially driven into the drill hole 26. As can be clearly _seen the width of the gap 18 in the tubular structure 12 is reduced after the rock bolt has been driven into the drill hole.

Figure 3 is a cross-sectional view of a third embodiment of a rock bolt 28, which is similar to the second embodiment 22 and therefore the same reference numerals are used to identify the similar parts. Like the rock bolt 22, this embodiment also has a series of frusto-conical surfaces 24 joined end to end to give the structure a serrated cross-sectional shape. However in this embodiment the edges of the surfaces 24 are cut back underneath to give them a barbed profile. It is thought that this will give the edges of the frustoconical surfaces 24 improved grip in certain types of rock formations such as soft or broken ground.

The head 14 of the tubular structure 12 is preferably hollow and is formed with an internal profile adapted to engage with a mating fixture 30 for fixing an accessory 34 of the ground support system to the rock bolt, as shown in Figures 8a and 8b. In this embodiment the head 14 has an internal locking ring 32 formed integral with the rock bolt 22. Preferably the internal locking ring 32 is tapered on one side to permit the mating fixture 30 to be readily inserted therein, and is flat on the other side to prevent the fixture 30 from being easily withdrawn as shown in Figure 8b. The use of fibre-reinforced polypropylene and a suitable moulding technique as described below allows for the shaping of the internal profile of the rock bolt 22 to form the internal locking ring 32.

Alternatively, other internal shapes such as threaded sections, pull-push sections, and so on, may also be formed in accordance with the invention due to the use of fibre-reinforced polypropylene and using a moulding technique.

In this way, the rock bolt of the invention can be tailored to the needs of the particular application, for example by using a threaded internal section for attachment of a screw threaded accessory as shown in these Figures 9a and 9b which shows a fourth embodiment of a rock bolt 70. The rock bolt 70 is of I-12-

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tubular structure and has a head 72 and tip 74. The internal surface of the 0 rock bolt 70 has a female threaded portion 76 near the head 72 of the rock _bolt as shown in the Figures. An accessory 80 (which is similar in many respects to the accessory 34) has an attachment means 82, a fixture provided with a slot 92, and a male threaded portion 94 for mating with the N female threaded portion 76. In use, the accessory 80 is screwed into the rock Ibolt 70 past the female threaded portion 76 as shown in Figure 9b. In this way, the male threaded portion 94 may be secured into the rock bolt beyond the female threaded section 76 which allows the accessory 80 to

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"spin" in the rock bolt without overtightening either of the threaded sections.

This embodiment of the rock bolt and accessory is easy to manufacture in accordance with the invention and may be readily positioned on site, in particular without the need for concern regarding over-tightening of the screw threaded sections.

In an alternative arrangement as shown in Figure 16, the internal profile of the tubular structure 12 is provided with a series of internal locking rings 28 to allow the mating fixture 30 to be driven into the tubular structure at various depths (not shown). This feature is beneficial in the case of positioning of a rock bolt 10 in uneven ground so that the depth of the fixture 30 may be adjusted as required, in particular when fixing mesh to the roof over uneven ground. As an alternative, the upper end of the fixture may be provided with a series of frusto-conical surfaces 62 joined end to end (as shown in Figure 18) to give the fixture a serrated cross-sectional shape. In this way, the fixture may be inserted into the hollow rock bolt at an appropriate depth to be held in place by one of the internal locking rings 28. Clearly the series of surfaces 62 allow the fixture to be positioned at different depths as required. The upper end of the fixture shown in Figure 18 has a slot 64 which allows the fixture to flex inwards.

Thus by making the rock bolt of the invention from fibre-reinforced polypropylene, the rock bolt may be formed in a single piece without the need for having to weld any separate components such as the head to the tubular I-13structure. However due to the nature of the polymer material, the rock bolt has some flex allowing it to be secured on site by a friction fit in a positioning hole. Certain prior art rock bolts have been made from chemical resins but they are costly, and require glue to secure them into the holes on site which is a complicated and expensive process.

Figure 6 illustrates the same embodiment of an accessory 34, having an attachment means 36 provided integral with the mating fixture 30. The Sattachment means of this embodiment is in the form of an pin 36, which may be employed, for example, as a hook to attach an article to a rock formation. The fixture 30 has an external profile adapted to engage with the internal locking ring 32 in the head 14 of a matching rock bolt 22 (as shown in Figure 8) wherein the accessory can be quickly fixed to the rock bolt in the ground support system. In this embodiment the external profile of the fixture 30 is in the form of a tapered bayonet fitting which is adapted to engage with a mating locking ring 32 provided in the matching rock bolt 22. The tapered bayonet fitting is formed with a slot 38 which allows the fixture to flex inwards as it is pushed into the locking ring 32. The accessory 34 is preferably also made from the same resilient high strength polymer plastics material as the rock bolt 22. Hence, once the fixture 30 has been pushed through the locking ring 32 it returns to its expanded condition and cannot be easily withdrawn as the external diameter of the tapered bayonet fitting is larger than the internal diameter of the locking ring 32.

Figure 7 illustrates another embodiment of an accessory 40 having an attachment means in the form of an eye bolt 42 formed integral with the fixture for attaching an article to the rock bolt. Many other types of accessories can be provided for a suitable fixture with an external profile adapted to engage with the head of a matching rock bolt. For example, the attachment means may take the form of a plate or flat plate. Alternatively the accessory may further comprise a pivotable attachment means 44 pivotally mounted on the fixture 30, for example, by a hinge connection.

ID-14- Figures 14a and 15 illustrate an accessory in which the pivotable attachment d means comprises a pipe support 44 having one or more open-ended recesses 46 adapted to removably support a pipe 48 therein. Each of the open-ended recesses 46 has an access opening 50 of reduced width through which a pipe 48 can be pushed into the recess. Because the access opening r 50 is of reduced width it helps to retain each of the pipes 48 in the pipe IDsupport 44 once it is pushed into its recess 46. In addition, the pipe support N 44 is provided with lips 52 extending into the recesses 46 which assist in

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gripping the pipes 48 in position as can be seen in Figure 15. In Figure 14b is N shown the locking pin 58 and clasp 60 which retain the pipe support 44 in position by means of the fixture 30. Clearly the pin 58 and the clasp 60 allow attachment of other suitable accessories in place of the pipe support 44 as required.

In an alternative arrangement and as shown in Figure 17, an accessory is illustrated in which the fixture 30 is used to secure mesh 54 to the surface of a rock formation by means of a cover plate 56. The fixture 30 is positioned in a hole (not shown) in the cover plate 56, the cover plate and fixture are then placed under the mesh 54, following which the fixture is placed in the hollow head of a rock bolt so that the accompanying mesh is secured to the rock formation. In a typical example, the openings in the mesh 54 are 100mm by 100mm and the cover plate 56 is dimensioned to cover an area of about 200mm by 200mm so as to securely hold the mesh in place. A single sheet of mesh would typically be spread over an area serviced by a number of rock bolts 10 so that the mesh is held in place by a number of cover plates 56 and corresponding fixtures Figures 10 to 12 illustrate a pop plate 60 according to the invention for a ground support system. The pop plate 60 comprises a substantially planar structure 62 made from a suitably resilient high strength polymer plastics material and having a top surface 64 that is normally convex in a relaxed (unstressed) condition of the pop plate 60, as shown in Figure 11. The planar structure 62 has a central aperture 66 provided therein for receiving the shaft

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of a rock bolt 22, as shown in broken outline in Figure 10. When the rock bolt 22 is driven all the way into a drill hole (not shown), a head 14 of the rock bolt _will press against the top surface 64 of the structure forcing it down to a compressed condition, in which it is concave, as shown in Figure 12. This is the condition in which it will remain so long as the rock bolt 22 is securely anchored in the rock formation.

IN However, if the forces holding the rock bolt 22 in the drill hole fall below a Nthreshold value, for example, if the ground slips such as in a shear or slip, the top surface 64 of the structure will automatically pop-out to its relaxed condition as shown in Figure 11. Below this threshold value the friction forces holding the rock bolt in the drill hole will be less than the resilient force of the top surface as it tries to return to its relaxed condition. The top surface 64 of the pop plate 60 is typically of circular shape as shown in Figure 10; however it could be of other shapes. The diameter of the top surface, together with the thickness of the material of the pop plate, will determine the magnitude of the force required to keep the top plate in its concave compressed condition.

A key advantage of the pop plate 60 is that it provides a simple yet effective indication of the condition of the rock bolt, namely, whether or not it is still securely anchored in the drill hole. Inspection of the rock bolts is a simple matter of detecting which, if any, of the pop plates have popped out due to a failure of the rock bolt. Clearly the pop plate of the invention can be used with conventional rock bolts as well.

Now that preferred embodiments of the rock bolt have been described in detail, it will be apparent that it provides a number of advantages over the prior art, including the following: Since it is made from a resilient high strength polymer plastics material it is not subject to fatigue like prior art metal rock bolts; (ii) Likewise it is not prone to corrosion due to groundwater and salts in the surrounding rock formation; ID-16- (iii) The formation of the rock bolt from a high strength polymer plastics Smaterial using moulding techniques allows for the shaping of the internal and external profiles of the rock bolt.

(iv) The rock bolt of the invention is relatively inexpensive to manufacture and Scan be readily mass-produced; and S(v) The rock bolt lends itself to having a wide variety of accessories fixed thereto in a simple modular fashion.

S(vi) The use of pressure or vacuum forming allows the rock bolt to be made (N 10 as a single piece which adds significantly to the strength of the rock bolt.

It will be readily apparent to persons skilled in the relevant arts that various modifications and improvements may be made to the foregoing embodiments, in addition to those already described, without departing from the basic inventive concepts of the present invention. For example, in each of the illustrated embodiments the head of the rock bolt is shown as being hollow.

However this is not an essential feature of the invention; it could be solid without in any way compromising the function of the rock bolt. Therefore, it will be appreciated that the scope of the invention is not limited to the specific embodiments described.

Claims (20)

1. A rock bolt for a ground support system, the rock bolt comprising: an elongate tubular structure made from a suitably high tensile plastics Smaterial, the tubular structure having a head at one end and a tip at the N other, and having an elongate gap extending along the length of the V) tubular structure, wherein when the bolt is driven into a drill hole of Ssmaller diameter than an outer diameter of the tubular structure, said gap permits the tubular structure to flex inwards, and to exert an outwards force so as to grip a wall of the drill hole in its rest position.

2. A rock bolt for a ground support system according to claim 1, wherein the high tensile plastics material is a resilient high strength polymer plastics material.

3. A rock bolt for a ground support system according to claim 2, wherein the resilient high strength polymer plastics material is fibre-reinforced polypropylene.

4. A rock bolt for a ground support system according to claim 3, wherein the fibre of the fibre-reinforced polypropylene is glass fibre.

5. A rock bolt for a ground support system according to claim 1, wherein the high tensile plastics material is fibre-reinforced plastic or carbon fibre.

6. A rock bolt for a ground support system according to any one of claims 1 to 5, wherein said elongate gap extends almost the full length of the structure from the tip to a termination adjacent the head.

7. A rock bolt for a ground support system according to any one of the preceding claims, wherein said elongate gap is of a width selected to

18- permit the tubular structure to flex inwards so as to reduce its outer diameter by up to 8. A rock bolt for a ground support system according to claim 7, wherein said elongate gap is of a width selected to permit the tubular structure (-i n to flex inwards so as to reduce its outer diameter by between 15% and 9. A rock bolt for a ground support system according to any one of the (preceding claims, wherein said tip of the tubular structure is tapered to facilitate insertion of the rock bolt into the drill hole. A rock bolt for a ground support system according to any one of the preceding claims, wherein said tubular structure is of substantially uniform cross-section throughout substantially its length. 11. A rock bolt for a ground support system according to any one of the claims 1 to 9, wherein an outer surface of said tubular structure is formed by a series of frusto-conical surfaces joined end to end to give the structure a serrated or barbed longitudinal cross-sectional shape. 12. A rock bolt for a ground support system according to any one of the preceding claims, wherein the tubular structure is formed by moulding the high tensile plastics material. 13. A rock bolt for a ground support system according to claim 12, wherein moulding takes place by means of pressure or vacuum forming. 14. A rock bolt for a ground support system according to any one of the preceding claims, the rock bolt further comprising an accessory, the accessory comprising: a fixture having an external profile adapted to engage with the head of a matching rock bolt wherein the accessory can be quickly fixed to the rock bolt in said ground support system. ID-19- A rock bolt for a ground support system according to claim 14, wherein d said head of the tubular structure is hollow and is formed with an internal profile adapted to engage with the external profile of the fixture for fixing the accessory of the ground support system to the rock bolt. 16. A rock bolt for a ground support system according to claim 14 or claim wherein said external profile of the fixture is in the form of a bayonet fitting which is adapted to engage with a mating fitting Sprovided in the head of the matching rock bolt. 17. A rock bolt for a ground support system according to claim 14 or claim wherein said external profile of the fixture is in the form of a screw threaded fitting which is adapted to engage with a corresponding screw threaded fitting provided in the head of the matching rock bolt. 18. A rock bolt for a ground support system according to claim 17, wherein the screw threaded fitting of the fixture is adapted to be positioned in the head of the matching rock bolt so that the screw threaded fitting of the fixture extends beyond the corresponding screw threaded fitting in the head of the matching rock bolt to allow free movement of the fitting in the rock bolt.

19. A rock bolt for a ground support system according to any one of claim 14 to claim 18, wherein said accessory further comprises attachment means formed integral with said fixture for attaching an article to the rock bolt. A rock bolt for a ground support system according to claim 19, wherein said attachment means is in the form of an pin, in the form of an eye bolt, or in the form of a plate.

21. A rock bolt for a ground support system according to any one of claim 14 to 20, wherein said accessory further comprises a pivotable attachment means pivotally mounted on said fixture. N- O O

22. A rock bolt for a ground support system according to claim 21, wherein said pivotable attachment means comprises a pipe or cable support having one or more open-ended recesses adapted to removably support a pipe or cable therein.

23. A rock bolt for a ground support system according to claim 22, wherein each of said open-ended recesses has an access opening of reduced width through which a pipe or cable can be pushed into the recess, said access opening helping to retain the pipe or cable in the pipe or cable support once it is pushed into the recess.

24. A rock bolt for a ground support system according to claim 23, wherein the pipe or cable support has one or more lips extending into the open- ended recesses to assist in retaining the pipe or cable in the support once it is pushed into the recess. A rock bolt for a ground support system according to any one the preceding claims further comprising a pop plate, the pop plate comprising a substantially planar structure made from a suitably resilient high strength polymer plastics material and having a top surface that is normally convex in a relaxed condition of the pop plate, and concave in a compressed condition, said structure having a central aperture provided therein for receiving the shaft of a rock bolt wherein when the rock bolt is driven into a drill hole a head of the rock bolt will press said top surface of the structure to a compressed condition, and wherein if the forces holding the rock bolt in the drill hole are reduced below a threshold value said top surface of the structure will automatically pop-out to its relaxed condition.

26. A rock bolt for a ground support system according to claim 25, wherein said top surface of the pop plate is of circular shape when viewed in plan. -21-

27. A method of forming a rock bolt for a ground support system comprising: i) placing a sheet of high tensile plastics material in a mould shaped to Sproduce an elongate tubular structure having a head at one end and a Stip at the other, and having an elongate gap extending along the length C of the tubular structure to form the rock bolt; Sii) heating the sheet to achieve melt-flow; iii) applying pressure or a vacuum to the mould to form the rock bolt in the mould; iv) rapidly cooling the mould; and v) releasing the rock bolt from the mould for positioning in the ground.

28. A method of forming a rock bolt for a ground support system according to claim 27, wherein the high tensile plastics material is fibre-reinforced polypropylene

29. A method of forming a rock bolt for a ground support system according to claim 27 or claim 28, wherein the heating of the sheet takes place at about 200 degrees Celsius.

30. A method of forming a rock bolt for a ground support system according to any one of claim 27 to claim 29, wherein the cooling of the mould takes place by cooling with water.

31. A rock bolt for a ground support system substantially as herein described with reference to and as illustrated in any one or more of the accompanying drawings. NO -22- O

32. A method of forming a rock bolt for a ground support system a substantially as herein described with reference to and as illustrated in any one or more of the accompanying drawings. t' Dated this 1st day of December 2006 SDavid John Wilkie Sby his Patent Attorneys Janet Stead Associates