BACKGROUND OF INVENTION Rock bolts are used as reinforcing pins that are located inside a hole in rock, concrete and the like. The rock bolts inhibit movement within the rock. For instance, if a rock bolt is pinned across two regions of a rock, the bolt will inhibit the two regions from moving with respect to one another. Typically, such rock bolts are used in mines where the bolts are used to prevent parts of the rock face from moving and falling away.

A known rock bolt consists of a mechanical device that includes one or more expanding mechanisms, which expand to wedge the rock bolt within the hole. An example is the mechanical expansion-shell type of rock bolt. Typically, the expanding mechanism consists of a tapered wedge and a shell that can be mechanically expanded in order to wedge the bolt within the hole drilled in the rock. These forms of expanding rock bolts are able to anchor the bolt only at the point of contact where the expansion mechanism contacts the rock hole surface.

Thus, except for the limited point of contact, there is no connection between the bolt and the rock for the substantial length of the hole. The cost of these expansion type anchorages increases when the mechanisms are required to be of the size to expand inside large-diameter holes. Once the expansion rock bolt is installed, the bolt is held only by the part that has expanded to wedge the bolt in the hole. Such point anchor rock bolts are ineffective particularly for high loads or for long periods of service.

In the prior art, rock bolts which use mechanical anchorage mechanisms, have hollow regions. When these bolts are installed, the hollow regions can be filled with grout to seal the gap between the rock and the bolt. The disadvantage is that the step of adding the grout to the hole involves a further"pass", namely that the workers must re-visit the bolt at a later stage to perform steps that cannot

be done at the same time as the insertion steps. Hence, the installation of the rock bolt cannot be done in"one pass".

It often requires a workman to re-visit the rock bolt to insert the grout on a "second pass". Thus, the installation procedure requires two steps (a"two pass" process). The first pass includes the steps of tightening the wedge mechanism to anchor the bolt by creating a point anchorage. The second pass includes the step of filling the gaps in the hole with a grout. Typically, in the mining industry for example, the second pass requires the workmen to re-visit each of the installed rock bolts to apply the grouting material, and this is time consuming and expensive.

Moreover, it is appreciated that the components of the expansion anchor bolts do not fill the interior of the rock hole, and, particularly in the case of large- diameter holes, the components of the bolt may actually take up only a small portion of the hole diameter. This means that there is a large volume cavity of empty space that remains in the rock hole. If these holes are filled with grout, a large amount of grout is required to fill the empty space. As mentioned already, grouting cannot practically be performed on the same"pass"as the steps of inserting and tightening the rock bolts. This is because grout is usually prepared in batches, and it is inefficient or not generally feasible to prepare the grout at the same time as inserting and tightening the mechanical rock bolts. This means that the workers cannot fully install the rock bolt in a single session, i. e."one pass".

The workers must re-visit the rock bolt later on to perform the grouting process.

This need to re-visit the bolt to perform subsequent steps is regarded as a "second pass"in the process, and increases the cost and inefficiency of the overall installation process. The difficulty is compounded by the fact that the grouting operation requires different machinery and material to that used in the process of inserting and tightening the mechanical bolt.

There is also considered to be a problem with what is called"fully bonded bolts"when placed in relatively large diameter holes ; such as high cost of grout, poor grout mixing, poor load transfer between bar and grout when grout annulus is large.

Some prior art systems for installing bolts use pneumatic resin injection, and there are considered to be difficulties in using these systems in relatively small diameter holes.

A thick, strong, cementitious grout is also difficult to inject into a small annulus due the small diameter of grout pipes/tubes etc. that must travel along the length of the bolt when secondary grouting occurs and to the grout's high viscosity. Thick, inexpensive, cementitious grout is considered to be difficult to pump through small diameter tubes. An alternative is to fill the hole with grout before installation of the bolt. This is difficult to achieve in a situation where the holes are overhead and that are greater than approx. 50mm in diameter as the grout has been found to fall out of the hole under the action of gravity.

Another approach taken in constructing rock bolts is to form a solid generally cylindrical rock bolt from composite materials, which includes a first material such as fiberglass and a second material in the form of a resin for setting the glass fibers in the matrix. The reason for using composite materials such as fiberglass is to provide structural strength to the load transfer medium of the rock bolt that surrounds the tendon. However, the composite materials are expensive, and the manufacturing processes of such fiberglass rock bolts are also time- consuming and expensive.

Still other forms of rock bolts, upon installation, require a relatively large hole to be bored in the rock. The hole may be some 100 to 150 mm in diameter.

This requires special equipment because the standard hole drilling equipment used in mines has a nominal 45mm bit. This larger hole size is thus considered time consuming and expensive to drill to drill. The relatively large hole is required so that the prior art bolt can be installed into the rock. Because the hole is relatively larger than the rock bolt, centering devices are required around the rock bolt to hold the bolt relatively central in the hole. Often, in these circumstances, the bolt is anchored, but with a special collar which has a grout tube for enabling grout to be injected into the relatively large space remaining between the bolt and the hole bored into the rock. This grout is injected again by special equipment, and during a'second-pass', that is after the initial bolt is fixedly placed into the

bored hole. The grout has also found to be difficult to inject into the hole in a manner that it relatively completely fills the void between the bolt and the bored hole because of air locks and environmental conditions. Therefore, voids remain, even after injection of the grout. These voids serve to further weaken the load transfer capacity of the bolt, and may result in a dangerous failure of the bolt over a period of time whether due to corrosion or earth material moving or a relatively large load being placed on the bolt.

OBJECT An object of the invention is to provide a rock bolt that is cheaper and easier to manufacture and install than those in the prior art.

A preferred object is to provide a bolt which exhibits improved load bearing or load transferring characteristics.

A preferred object of the present invention is to provide a rock bolt, and a method of installing a rock bolt, that involves a"single pass".

SUMMARY OF INVENTION According to a first aspect of the present invention, there is provided a rock bolt shaped and adapted to be inserted and fixedly installed into a rock hole, the bolt including: a load-bearing tendon; and a load-transfer medium of at least a first material, the load-transfer medium being formed to completely surround the tendon over at least a portion of the length of the tendon, wherein, when the bolt is installed in the rock hole, the load-transfer medium functions to transfer to the tendon a force applied from a source external to the bolt so that the load is borne substantially by the tendon.

Preferably, the transfer medium has been formed by casting or moulding.

The first material is characterised in that it expands volumetrically on fracture. It has been found that this feature enables the bolt of the present invention to more effectively transfer load to the tendon (s).

The tendon and transfer medium may be mechanically interlocked.

The mechanical interlock of the tendon in the transfer medium may have been formed by a casting operation.

Preferably, the mechanical interlock is over at least a portion of the length of the bolt.

The transfer medium may be comprised substantially of a first material, although the present invention does not preclude a composite material (s) being used for the transfer medium. Preferably, the first material consists of a single homogeneous material. Preferably, the first material is substantially non- compressible. Preferably, the first material is characterised in that it has a degree of friability.

In essence, this aspect of the invention is based on realising that in loading bolts of the type of the present invention, obtaining an effective transfer of load to the tendon is important. This has been accomplished in this aspect of the present invention by utilising a transfer medium of the type which expands volumetrically upon fracture or distortion of the transfer medium. In other words, the transfer medium adopted in this inventive aspect is of a type or composition that when it fails, for example under load, it will increase in volume, whether by forming a series of particles, or some other means.

In a second aspect of the present invention, the bolt is designed to'de- bond'over a portion of its length, for use in certain circumstances. The de- bonding can be provided by designing that amount of full encapsulation of the load transfer medium, first material around the tendon, and/or grout or resin provided around the bolt of the present invention.

According to a third aspect of the present invention, there is provided a method of installing a bolt into a bole-hole, the bolt being formed of a load bearing tendon portion, and a load transfer medium portion, the method including the steps of: a. Drilling a hole to length that is substantially similar to length of the load transfer medium,

b. Providing a resin or other bonding medium preferably in cartridge form in association with the bolt near a first end of the bolt to be placed into the bore-hole, c. Inserting a portion of the bolt into the bore-hole, d. Mixing resin by rotation of the bolt whilst applying thrust to the bolt until the first end of the bolt nears the end of hole or by initially applying thrust until the first end of the bolt nears the end of the hole and thereafter by rotation of the bolt.

Preferably, the method includes the steps of pre-assembling on a second end, remote from the first end, of the bolt a fastening means, preferably a plate and drive nut, a drive head formed on or fixed to the second end of the bolt, or other suitable fixing at the second end.

Preferably, the method further includes the step of, after the mixing step, waiting until the prescribed resin anchor set time has elapsed, and thereafter applying torque to the nut to tighten the nut against the plate.

Preferably, the bolt is a bolt according to any one of claims 1 to 33, or 45 to 48.

Preferably, the method further includes the step of providing the bolt, its cover, and/or the grout/resin in a manner that enables the resin to flow between the bolt and the bore-hole perimeter along a substantial portion of the length of the bolt.

In another form, the present invention provides a method of installing a bolt into a bole-hole, the bolt being formed on a load bearing tendon portion, an a load transfer medium portion, the method solely consisting of steps a to d and/or e, above. Preferably, the method also consists of the step of fastening a plate and nut.

Preferably, the hole has a diameter of between 40 and 50mm, preferably 42 to 47mm, most preferably approximately 45mm.

In essence, this second aspect of the present invention is has come about by realising that a'single-pass'installation method can be provided, thus avoiding the need for a secondary-pass for filling the hole with grout or other secondary

activities, by using a relatively standard 45mm hole boring mechanism to drill a hole, and installing a bolt which has tendon and load transferring portions directly into the hole, which more closely conforms to the relative diameter of the bolt. In this way, a much smaller gap remains between the hole and the bolt (after the bolt is inserted into the hole) and thus a relatively standard resin or grout cartridge can be used to substantially fill a portion of that gap sufficient to provide relative good load transfer to the bolt. Furthermore, as the bonding agent, preferably in cartridge form is inserted into the hole ahead of the bolt and pushed into the hole by the bolt being inserted into the hole, the load transfer and bonding of the bolt to the surrounding earth/rock material by the cartridge material occurs along the total length of the bond which preferably is the full length of the bolt inserted into the borehole.

DRAWINGS In order that the present invention might be more fully understood, embodiments of the invention are described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 A is a perspective view of a first embodiment of a rock bolt ; Figure 1 B is a cross-sectional side view of the rock bolt of Figure 1 A ; Figure 1C is a cross-sectional side view of the rock bolt of Figures 1A and 1 B shown with the bolt in place within a rock hole ; Figure 2A is a perspective view of a second embodiment of a rock bolt ; Figure 2B is a cross-sectional side view of the rock bolt of Figure 2A; Figure 2C is a cross-sectional side view of the rock bolt of Figures 2A and 2B shown with the bolt in place within a rock hole ; Figure 3A to 3E show side and cross-sectional views of examples of tendons used in embodiments of rock bolts ; and Figures 4A to 4C show side views of examples of cover members used in some embodiments of rock bolts.

Figures 5 to 9 illustrate steps in the installation method according to the present invention.

The drawings are not necessarily drawn to scale, because some of the dimensions, particularly those relating to the size of the cover and the gap between the bolt and the rock surface, have been exaggerated for the sake of clarity in the drawings.

In the embodiments, similar components have, in many instances, been numbered with like numerals merely for the sake of ease of understanding the embodiments.

DESCRIPTION OF EMBODIMENTS First Embodiment Referring to the drawings, Figures 1A to C illustrate a first embodiment of a rock bolt. The rock bolt 1 includes a central tendon in the form of a threaded bar 10. The bar 10 is surrounded by a load-transfer medium 20.

Figure 1B is a cross-sectional view of the rock bolt 1 showing the bar 10 located along the central longitudinal axis of the rock bolt 1.

Figure 1C shows the rock bolt 1 installed in a rock hole 50. The load transfer medium of the rock bolt 1 extends substantially along the entire length of the hole, almost to the end of the hole. The bolt 1 is able to be attached or adhered to the rock surface along the continuous length of the bolt, and therefore does not suffer the drawbacks associated with the prior art point-anchor rock bolts.

The rock bolt 1 is secured in the hole 50 by resin or other joining/bonding medium that substantially fills the space 52 between the hole surface 53 and the bolt surface 21. The installation process is described previously in this specification.

Once the rock bolt 1 is inserted and adhered to the rock hole surface 53, the bolt 1 provides support to the rock in the sense that it pins the region 41 of the rock that surrounds the rock-bolt to the upper regions 40 of the rock. Hence, the rock bolt acts as a reinforcing pin in the rock. Initially, the rock bolt does not need to have tension in the bolt itself. Subsequently, any slight movement of the surrounding rock will develop tension and/or shear in the bolt. When the rock bolt becomes loaded, force is developed within to the tendon as the result of

deformation of the rock surrounding the bolt. For example, it could be that the lower portion 41 may be ready to fall away from the main portion 40 of the rock.

In effect, since the bolt is fastened to both the portion of the rock 41 that is attempting to move, and also fastened to the portion of rock 40 that is not moving, the rock bolt 1 effectively pins both portions 40,41 together. Thus, the load of the moving rock 41 is transferred to the load-bearing tendon 10 of the rock bolt.

Numeral 43 denotes the surface of the surrounding rock.

Second Embodiment Figures 2A to C illustrate a second embodiment of a rock bolt 2 that is similar to the first embodiment, except that the second rock bolt 2 is provided with a cover in the form of cylindrical cover member 300 that is shaped as a conduit.

The cover member 300 surrounds the load transfer medium 20.

In the embodiment, the cover member 300 is a largely cylindrical plastic sheath which is open at at least one end, and only the lateral sides of the load transfer medium 20 are surrounded by the cover member 300. Figure 4 also shows examples of other covers.

Nevertheless, the invention, in its broadest aspect, does not require a cover. Where the load transfer medium and tendon are manufactured in a factory by casting, for instance, the cover member is actually the mould that is filled with casting material. The mould can be removed before the bolt is installed in the rock hole. Alternatively, the mould can be retained surrounding the tendon and load transfer medium material. In effect, the cover, which during manufacture, functioned as the mould, later functions as a cover when the bolt is installed.

The rock bolt 1 without the cover can still perform the function of a rock bolt, although the cover-less rock bolt 1 would not have the same degree of surface abrasion resistance as the rock bolt 2 that has the cover member 300.

Hence, extra care is needed when transporting the cover-less rock bolt 1 from the manufacturing site to the intended installation location. However, once installed in the rock hole, the rock bolt 1 that lacks a cover can perform the same function of pinning the rock, albeit without the added degree of corrosion protection afforded by the cover member 300.

In the first embodiment in Figure 1A, the rock bolt 1 must be handled carefully while it is being transported to the installation location because the unprotected load transfer medium material 20 may crumble. The second embodiment of Figure 2A does not necessarily have this limitation because the load transfer medium material 20 is protected by the cover member 300.

CORROSION RESISTANCE In the first embodiment, the load transfer medium material 20 provides a measure of protection against corrosion of the load bearing tendon in the form of a threaded bar 10, because the load transfer medium acts as a barrier which prevents or inhibits moisture from reaching the bar.

In the second embodiment, when the cover member 300 is made from a water-impervious material, the cover member 300 acts as a further barrier to the entry of moisture into the rock bolt 2. The resin or bonding medium 70, that is used to adhere to the bolt to the rock, also acts as a barrier to moisture once it has spread into the gaps 52 around the bolt.

The cover member 300 also has an advantage in the manufacturing of the rock bolt in that the cover can act as a mould which is an integral part of a casting process, as will be described below.

The tendon, in the form of bar 10,100, is substantially or fully encased by the load transfer medium material 20,200, and is thus protected from mechanical and corrosive damage.

ROLE OF THE LOAD-TRANSFER MEDIUM Referring to Figure 2C, the bolt 1 is installed in the hole 50 in the rock. The dimensions of the bolt 1 and hole 50 are such that there is very little clearance 52 between the bolt surface 21 and the inner surface 53 of the rock hole 50. This is achieved either by drilling the hole 50 so as to provide a diameter that is slightly larger than the rock bolt diameter, or by manufacturing the rock bolt 2 with a diameter being only slightly smaller than the hole diameter.

Once installed, the load transfer medium 200 and cover member 300 are held fast to the rock surface 53 by the resin. Any tension or force, caused by the rock attempting to move relative to the bolt 2, is transferred, by the load transfer

medium 200, to the load-bearing tendon 100. The load transfer medium 200 thus acts as a transfer medium that transfers the external force to the bar 100. It is the tendon or cable 100 that ultimately bears the external load.

In the second embodiment in Figure 2C, the force is transferred from the rock to the cover member 300 via the resin layer, then from the cover to the load transfer medium material 200, finally to the threaded bar 100.

In the first embodiment in Figure 1C, the force is transferred from the rock to the load transfer medium material 20 via the resin layer, and from the load transfer medium to the bar 10.

MANUFACTURE OF THE LOAD TRANSFER MEDIUM In the embodiments, the load transfer medium of the rock bolt is manufactured by a casting, moulding extruding or forming process. An advantage of such processes is that the rock bolts can be manufactured, for example, in a factory away from the location where the bolts will eventually be used. There are economies of scale and efficiency in being able to manufacture the bolts in a factory in a controlled environment, as compared to those type of rock bolts that are created on site at the point of use, or which are created in situ inside the rock hole.

To manufacture the first rock bolt 1 of Figure 1A, a separate mould (not shown) is arranged to surround the threaded bar 10. Then, the mould is filled with a suitable casting material. The load transfer medium material can be injected or poured into the mould. The tendon 10 is inserted into the mould (not shown) before or after the casting material is added. The tendon 10 can be positioned in place even after the casting material has been added to the mould.

The embodiment in Figure 1 can be made using a cylindrical mould (not shown), which has a shape similar to the cover used in Figure 2C, except that the cylindrical mould is removed after the load transfer medium material 20 has set.

To manufacture the second rock bolt 2 of Figure 2A, a cylindrical cover member 300 is arranged with the threaded bar 100 located inside, and then the cover member 300 is filled with a suitable casting material 200. In other words, during the stage of manufacture, the cover member 300 acts as a mould.

Alternatively, the threaded bar 100 is inserted into the cover 300 after the casting material 200 is added.

In other embodiments, the mould may be removed after the load transfer medium material has set, or may be retained to act as an integral cover 300 for the rock bolt 2.

After the mould or cover member is filled with casting material, the casting is left to set and harden, after which the rock bolt 2 can be transported to the location where it is to be installed.

Thus, the casting process enables a rock bolt to be manufactured relatively quickly and cheaply using castable materials. The use of a casting, moulding or forming process addresses the higher expense involved with the machining of parts for rock bolts that include mechanical mechanisms, such as expansion shell anchored rock bolts and also addresses the problem of slow setting cement grout or the high cost of resin to fill large spaces.

Moreover, the casting process can readily be adapted to produce rock bolts of various sizes and diameters. This is achieved simply by altering the size of the mould. This is an easier modification to perform compared with the changes that would be required to scale-up the production process to produce larger mechanical expanding bolt anchor mechanisms. That would require a re- design of the mechanism and the manufacturing apparatus.

The casting process thus provides great flexibility in the range of rock bolts sizes and external shapes that can be produced. For instance, if different tendon materials are required, the overall casting process need not be altered, since it is a straightforward matter of replacing the tendon with the new tendon, and then casting the load transfer medium material around the new tendon.

Thus, the casting, moulding or forming processes enable the size of rock bolt of the present embodiments to be readily varied to suit the size of the rock hole, rather than rock holes having to be drilled to different dimensions to suit particular rock bolts. This means that, when rock holes are drilled, the most convenient size of rock hole can be created to minimise drilling costs. For instance, if a mining company finds it economical to drill rock holes of 45 mm

diameter, then the diameter of the rock bolt can be cast at a diameter of, say, 35 mm to 39 mm. When installed, this would achieve a gap 52 of three to five millimeters.

If an end user, such as a mining company, only has an ability to drill holes of 100 mm in diameter, the above method of manufacture can readily produce rock bolts of such larger size without significant increase in the overall cost of manufacture. It simply requires a change of mould size. Whereas, in the prior art, to produce bolts of this size would require larger and more expensive bolt mechanisms. These larger prior art mechanisms would have greater void spaces, which would require more grout to fill up the spaces. The need for grouting in the prior art means that such larger bolts would have to be installed with"two passes"rather than one. The present embodiments avoid these problems and can be made to such larger sizes while still maintaining the"one pass"installation.

The ease of varying the size of the moulds in the casting process means that the rock bolts can readily be made to fit into the rock hole with a slight clearance, and can be"glued/fixed"into place with a small amount of resin. The casting process therefore provides a great degree of flexibility in creating rock bolts of varying sizes and lengths. For instance, embodiments of the invention can be made with large diameters, whereas in the prior art bolts that use mechanical expansion mechanisms, it is difficult to install such bolts in very large bolt holes, because the expansion mechanisms need to be scaled up for the larger holes. Whereas, in the embodiments of rock bolts that are cast, there is no need to scale up the tendon within the actual bolt. The scaling-up is achieved easily by simply increasing the size of the mould.

The casting, moulding or forming processes also allow the length of the rock bolts to be readily altered. Once again, changes in bolt length can be achieved merely by altering the length dimensions of the mould. This is in contrast to other types of prior art rock bolts that require re-designing of the bolt mechanisms, or re-tooling of the machines that are used to manufacture the prior art rock bolts. In embodiments of the present invention, a typical length of a rock

bolt is around 2.4 meters. In practice, the length of the rock bolt is limited in that longer rock bolts are more difficult to bond to the rock over a substantial portion of their length within the rock holes.

In further embodiments, long rock bolts can be made by forming the load transfer medium in sections along the tendon, with each section joined with a flexible joint, such as a silicone rubber, placed across the joints. This type of configuration allows bolts of greater length to be inserted in holes in areas that have restricted access. Given the nature of an underground tunnel and the relative inflexibility of the rock bolt, a bolt cannot be longer than the height of the tunnel. This joining process overcomes this aspect.

In the manufacturing process of the present embodiments, the tendon is first positioned within the mould and then the load transfer medium material is cast around the tendon. In other embodiments of the manufacturing process, the load transfer medium material can be cast or formed separately in the mould with an opening ready to accept the tendon, and then the tendon can be inserted later on, either before or after the load transfer medium material has set.

LOAD TRANSFER MEDIUM MATERIAL PROPERTIES As mentioned above, the load transfer medium transfers the load or force to the tendon. Since it is the tendon, rather than the material that surrounds the tendon, that ultimately carries the load, the load transfer medium material need not be strong, particularly in tension. This is in contrast to the prior art where there has been an emphasis on creating rock bolts that, inherently, have sufficient structural strength in the material that surrounds the tendon. For instance, the reason for using fiberglass in the prior art to form the load transfer medium was the intention of imparting a degree of stiffness and resistance in the load transfer medium material of prior art rock bolts.

In the embodiments of Figures 1A and 2A, the load transfer medium 20, 200 is made from a material that has the characteristic of being essentially non- compressible. Such materials are strong in compression, and these characteristics are often found in materials that can be manufactured by casting, moulding or forming, such as cement. Conversely, materials such as resilient

polymers would be considered unsuitable for use as load transfer medium material in the present invention.

Because the load transfer medium material 20,200 is relatively incompressible, when a load or force is applied to the load transfer medium material, this load or force is transferred directly to the load-bearing tendon 10, 100, rather than allowing the force to be absorbed by the load transfer medium.

The load transfer medium 20,200 is made from a single material, such as cement, cement with sand, cement with flyash, cement-based grouts, and other low-cost substantially incompressible materials that are capable of transferring load. In the embodiments of Figures 1A and 2 A, the load transfer medium material is a single homogeneous material. The load transfer medium material can be a single material because the strength, that is associated with composite materials, is not needed here. Hence, the embodiments that use a single material load transfer medium are cheaper and simpler to manufacture than prior art bolts that use composites, although in other embodiments the load transfer medium material can be reinforced with non-continuous reinforcement material such as chopped glass or steel fibers. According to this definition, fiberglass is not a"single material". (Fiberglass is a composite of a plurality of materials, namely a first material of fibers and a second material of resin). However, having said this, the present invention does not preclude the use of a transfer medium which is a composite of various materials.

In the embodiments, the material of the load transfer medium is preferably a friable material, meaning that it can crumble readily. Preferably, the material should fail in a brittle manner. Such a material, when it fails, increases in volume.

When solid load transfer medium material is broken up, particles are formed which attempt to expand volumetrically. Nevertheless, when the rock bolt is installed, there is actually little or no room for the load transfer medium material to expand in terms of its volume, either due to the constriction of the surrounding resin in Figure 1 C, or the constriction of the cover member 300 in Figure 2C. This inability to expand means that the load transfer medium material cannot effectively loosen its hold on the tendon. There is, effectively, nowhere for the

load transfer medium material to expand. Thus, any incipient cracking of the load transfer medium material does not minimise the ability of the tendon to be held in place. Indeed, because the load transfer medium material seeks to expand when it cracks, there is a degree to which the tendon is gripped even more effectively, because the load transfer medium material is compressed to a greater degree as it seeks to expand volumetrically. The effect of this is that, even when the load transfer medium material crumbles, the load transfer medium material still serves to hold fast the tendon. In failure tests that have been performed on samples of embodiments of rock bolts, the tendency was for the tendon material to break before the load transfer medium material reached a point of disintegrating so as to release the tendon. This shows that friable or relatively incompressible materials, which are not necessarily strong in tension but are strong in compression, can act as a transfer medium that serves to hold the tendon in place.

In some instances, eg rock bursts, there may be a requirement for the end of the bolt closest to the rock surface to behave differently to the rest of the bolt.

To achieve this requirement, some de-bonding of a portion of the length of the load bearing material and the load transfer material can be incorporated during manufacture.

The material of the load transfer medium does not contribute significantly to the final strength of the rock bolt. Instead, the strength of the rock bolt is provided by the strength of the tendon material. The load transfer medium material merely acts as a transfer medium for transferring external force to the tendon. The transfer of force is achieved through the interfaces, namely the interface of the tendon and load transfer medium material, and the interface of the load transfer medium material and the cover, or the interface of the load transfer medium material and the resin, as the case may be. The present invention has an approach to creating rock bolts that places lesser emphasis on the structural strength of the load transfer medium material that surrounds the tendon. For example, in the first embodiment in Figure 1A, the load transfer medium material 20 of the rock bolt 1 is friable to the extent that it must be handled carefully while

being transported to the installation location. In other words, this degree of friability of the load transfer medium material does not detract from its ability to perform the function of a rock bolt.

In the embodiments, the performance of the rock bolt depends on the strength of the bond that exists between the tendon and the load transfer medium material, between the load transfer medium material and the cover, between the cover and grout, and between grout and the surface of the rock hole. The tendon and load transfer medium material may be a mechanically interlocked, with the tendon being anchored in the casting material by virtue of the mechanical interaction between these two materials. The casting process ensures that there is a perfect fit between the tendon and the load transfer medium material, and it is this"perfect fit"that ensures that there is a mechanical interlock between the tendon and the load transfer medium material.

ADVANTAGE OF CASTING, MOULDING OR FORMING It is the above realisation that the load transfer medium material need not be inherently strong in tension that has enabled embodiments of the present invention to be manufactured from materials that can be cast, moulded or formed, such as cement for example. These materials are low in cost, and the manufacturing processes associated with these materials are also low in cost.

Hence, the decreases in costs arise from those two areas.

This is in contrast to the prior art where the emphasis of creating bolts with strong load transfer medium materials has led to the need to use relatively expensive load transfer medium materials, such as fiberglass, which also necessitated relatively expensive manufacturing processes. Costs are therefore higher on two counts.

As mentioned, the preferable realisation that friable materials can be used has led to decreased costs, because such materials tend to be cheaper and also because friable materials are adapted to being manufactured using processes, such as casting, that are simpler and cheaper. The casting process is inherently a cheaper manner of manufacture, as compared to the prior art processes that,

for example, require fibers to be laid in precise orientation, or which require mechanical parts of the prior art rock bolts to be machined to precise dimensions.

The use of substantially incompressible, and cheap material which can be cast, for manufacture of the load transfer medium, means that as rock bolts of larger size are required, the cost of the manufacture of the bolt does not increase markedly. The cost of casting a large or small bolt does not vary significantly because the bulk of the size variation is made up from the relatively cheap casting material. This is in contrast to prior art rock bolts that use mechanical devices to lock the bolt in the rock hole, because these mechanisms increase significantly in cost as the size of the rock bolt increases. It becomes more expensive to create larger rock bolts.

Furthermore, there are some prior art rock bolts made of shaped metal, for instance, metal cylindrical rock bolts, that become very expensive to manufacture when large sized rock bolts are required.

Moreover, these type of rock bolts are susceptible to crushing, whereas the substantially incompressible material of the load transfer medium means that the bolts are not susceptible to crushing to such a degree as the prior art. Prior art rock bolts that have spaces or hollow regions will be susceptible to crushing due to compression. Whereas the present rock bolts, which use incompressible materials, will not be so susceptible to crushing to the same degree. For prior art rock bolts with hollow space in between the parts of the mechanisms, an increase in strength would require the use of thicker wall material, which would lead to higher costs.

Also, the casting process is often faster and/or simpler, and therefore cheaper, than more intricate techniques, such as those required to create composite or fiberglass structures. The manufacturing equipment can tend to be cheaper for casting processes.

Referring to Figures 1 C and 2C, when the rock bolt 1,2 is inserted into the hole 50 in the rock face 40, it is important that the gap 52 be as small as possible.

The reason is that minimising the lateral gap 52 has the effect of minimising the amount of resin needed to fill the space between the rock bolt 1,2 and the inner

bore surface 53. Another reason is that it has been found that in some situations, resin works best when the annular thickness of the resin in the gap 52 is no more than about three to five millimeters. If the resin is substantially thicker than this, there is an increased possibility of the resin shearing when an external load is applied. Since the casting process enables the rock bolts to be manufactured relatively precisely and cheaply to a size slightly smaller than the rock hole, this enables the amount of resin to be kept below the maximum annular thickness of three to five millimeters provided the hole is correctly sized.

Another advantage of the casting process is that it results in bolts that have a relatively uniform quality along the length of the bolt.

The advantages of the casting process have been mentioned, and the advantages of using friable material have been mentioned. It is observed that the advantages of casting, and of using friable materials, tend to go hand in hand, since many friable materials tend to be castable, but this is not always the case.

The invention in its broadest aspect is not limited to (a) castable materials that are friable, and also not limited to (b) friable materials that are castable. For instance, the invention can use an incompressible thermosetting polymer that would require a moulding process that may not regarded as a casting process. Thus, the invention in its broadest aspect can include a rock bolt with an incompressible material that cannot be made by casting or moulding.

METHOD OF INSTALLING THE ROCK BOLT Another advantage of the casting or forming process is how the process has a subsequent effect on the installation process of the rock bolt. The effect arises because the casting process enables a rock bolt to be produced, readily and cheaply, and of a dimension which can be more closely manufactured to suit a typical hole drilling apparatus as provided in a mine environment. By dimensioning the prefabricated bolt more closely to that of the hole size, the bolt, upon installation, can substantially fill the rock hole and with relatively minimal gap 52 between the bolt an the surrounding earth or rock.. In accordance with an aspect of the present invention, the method of installation can occur as a single series of steps that can be performed on one visit by the workmen ("one pass").

Prior art arrangements typically require the workers to make a two visits to perform the installation steps ("two pass"), where the first pass inserts the bolt, and the second pass serves to more securely fasten the bolt. In contrast, this second pass is considered unnecessary in the present invention.

Installation steps for a bolt according to the present invention incorporating a load bearing tendon, a precast load transfer medium and (optionally) a cover, include: 1. With reference to Figure 5, drill a hole 50 to length that is as close to length of the load transfer medium as possible. Preferably hole is standard 45mm diameter, but may be of any suitable diameter to suit the size of bolt/transfer medium and (optional) cover. The size will vary according to the particular requirements of the environment and/or weight/loadings to be applied to the bolt in situ.

2. With reference to Figure 6, a bonding material 70, typically resin cartridge (s), can be inserted or provided into the hole or attached to end of bolt.

3. With reference to Figure 7, pre-assemble bolt with plate and drive nut in position. This step, however may be omitted, depending on the fastening means used, and this may vary dependent on the application or environment the bolt is used in.

4. With reference to Figure 8, insert bolt by pushing (arrow A) bolt, or bolt with cartridge (s) attached into the hole and through resin cartridge (s) as far as possible. Typically, >80% of load transfer medium should be within the bore- hole at this stage. If the hole is of a depth that is greater than the length of the bolt, or, if the bolt is required to be of a length which is greater than the standard prefabrication length of the bolt, then a joining assembly can be used whereby the first bolt (already inserted partially into the hole) is fixedly coupled to a second bolt, before further inserting the joined first and second bolts more fully into the hole. In the case where a first and second bolt is used, the pre-assembly of step 3 is configured onto the last bolt to be inserted (second bolt). Obviously, more than 2 bolts can be fixedly coupled in a similar manner to that described above, without departing from the scope of the present invention.

5. Mix resin by rotation (arrow B or C) of bolt and/or by applying thrust and continue to apply thrust until bolt nears the end of hole or for an embodiment with a plate, when the plate is forced against the rock around the drill hole.

6. With reference to Figure 9, for a configuration that incorporates a drive nut and plate, wait until the prescribed resin anchor set time has elapsed then apply torque to the nut to tighten the nut against the plate.

Preferably, the outer surface of the cover is formed in an undulating shape in the form of a screw with its thread direction or other suitable shape such that when the bolt is rotated grout/resin flows in the thin annulus between the bolt and the hole edge in a direction towards the collar. A simple deflector or plug (not shown) may be used to stop excess grout/resin falling out of vertical holes.

An alternative shape of the outer surface of the cover may have undulations such as criss-cross grooves to mix grout when the bolt is pushed (not rotated) in the hole.

The"one pass"installation process of the rock bolt will be described in more detail with respect to the second embodiment of Figures 2A to C, but the process applies also to the first embodiment of Figures 1A to C.

Reference is made to Figure 2C. In one situation, as an example, before the bolt 1 is inserted into the hole 50, a resin cartridge or capsule 70 is placed in the hole. Then, the bolt 1 is inserted and jammed against the end 55 of the hole, such that the resin cartridge 70 bursts. The bolt is spun and resin flows back out towards the opening of the hole (towards the left of the diagram), thereby filling the gap 52 between the bolt and the rock.

In the exemplary embodiment, the resin is a fast-setting resin that is provided in two initially separate components within a cartridge. When the two components are mixed, the resulting resin sets rapidly. Rotation of the rock bolts assists, firstly, in distributing the resin along the length of the narrow gap 52, and also assists in mixing the two components of the resin. This process can be performed on one visit by the workmen, and this avoids the need of having a

"second pass"where the workmen have to add the grout after the prior art rock bolts have been secured in the hole.

The present invention, although described in relation to nuts, it should be realised that other fastening means as would be known within the art can be used, such as a barrel and wedge anchor or tendon gripping devices attached to the spinning head of the installation equipment The movement of resin in the hole (moving from right to left of the diagram) is enhanced by spinning the rock bolt in the hole. An example of a resin is a two- component polyester resin mixture. A catalyst is used to set the resin. The spinning aids the mixing of the components of the resin with a"single pass"the bolt becomes active immediately after its installation.

A bearing plate 65 may be attached to the end of the tendon, and a nut 60 is fixed to the end 11 of the tendon. The nut 60 is used to rotate the tendon, and thereby impart rotation to the rock bolt. Since the resin sets relatively quickly, the spinning lasts usually for only fifteen or so seconds. Then, the rock bolt is held stationary while the resin hardens.

The resin is forced to flow along the outside of the rock bolt in the gap 52 between the bolt and the rock surface. The resin should ideally fill the entire space that surrounds the rock bolt so that the bolt is fastened to the rock surface along its entire length. Thus, the rock bolt is held fast in the rock hole 50.

The tendon is capable of being tensioned. The end fixtures are attached to the tendon, and not to the load transfer medium, since it is the tendon that is capable of providing resistance to shear and tensile forces. In the embodiments, the load is applied directly to and only to the tendon, whereas in the prior art the load was also applied directly to the surrounding load transfer medium material which necessitated the load transfer medium being made of costly, strong materials that were also expensive to manufacture.

"ONE PASS"INSTALLATION PROCEDURE The installation procedure, described above, is regarded as a"one pass" process because the workmen can perform the entire procedure in one visit to the location, without having to return to the location later on to perform subsequent

steps, such as grouting or having to mix grout before bolt installation. The resin from the cartridge 70 is sufficient to hold fast the bolt in the hole, because the rock bolt has been cheaply and readily manufactured to have little clearance in the gap 52. This small gap can be filled with resin, rather than resorting to a separate grouting step that would require a"second pass".

LOAD-BEARING TENDON The load-bearing tendon defines the tensile and shear properties of the bolt. The load transfer medium material merely acts as a bulk medium which transfers force from the rock surface to the tendon. This is in contrast to prior art composite bolts where the tensile and shear properties are dependent on the fiberglass that surrounds the tendon. In the prior art, the tensile and shear strength is often provided by the strength of the container or the load transfer medium, whereas in the present embodiments these are provided by the tendon.

Hence, it is possible to achieve the same strength by relying on the strength of the tendon, rather than using expensive materials to form the load transfer medium. Also, the strength of the tendon can be achieved using relatively cheap materials for the tendon.

In the present embodiments, the materials that surround the tendon do not define the tensile and lateral shear properties. That is why cheap, castable and/or incompressible materials can be used to form the load transfer medium.

That is also why the present embodiments are cheaper than the prior art fiberglass bolts because expensive composite materials are avoided, and the complex and/or expensive manufacturing processes involving composites are also avoided.

In the embodiments, the tensile strength of the load transfer medium material is virtually zero. In other words, a similar performance can be achieved using cheaper castable materials, as compared to more expensive materials such as fiberglass.

The tendon material is selected from materials that are able to provide both tensile and shear strength. The tensile and shear properties of the rock bolt are defined by the characteristics of the tendon material only. A range of bolts of

varying strength can be manufactured, simpiy by varying the strength characteristics of the tendon. The strength of the rock bolt is selected to suit the load bearing requirements of the particular application in which the rock bolt is to be used. Greater loads require stronger tendon material.

In a other embodiments, the tendon can be made from straight metal bar material. The tendon can be made of various single materials, for example, steel cable, steel fiber, multiple steel cables, steel strand, high tension wires, polycarbonate, fiberglass rods, kevlar rods, and carbon fiber rods. For clarification, an alloy such as steel, though it may have various additives, is regarded in this specification as a single homogenous material, in the sense that it is not a composite which consists of a plurality of materials.

In the embodiments in Figures 1A and 2A, the tendon is rod-shaped and relatively smooth, but in further embodiments the surface of the tendon is roughened to aid the contact with the load transfer medium material.

Alternatively, the surface of the tendon can have a series of undulations. The degree of undulation depends on the surrounding material of the load transfer medium. Experimentation is required to select the degree of undulation depending on the load transfer medium material. Moreover, the tendon can have more complex shapes as shown in Figures 3A to E. In further embodiments, the tendon can have a simple or complex shape, and can be weave-shaped, and can be reinforcing strand or cable constructed in close packed, or open weave shapes.

Alternatively, the tendon may be hollow.

After installation only part of the tendon is exposed. To improve the bolt's corrosion resistant properties this exposed part may be made of more corrosion proof materials or coated with corrosion proof materials, eg hot dip zinc galvanised.

THE COVER The cover member 300 protects the rock bolt 2 from moisture, mechanical, chemical and/or corrosion damage. When the bolt is manufactured by a casting or moulding process, the cover 300 acts as a mould during the manufacturing

process. During installation of the bolt, the cover also provides a measure of protection for the load transfer medium material.

The cover member can be made from a range or combination of materials, such as metals, plastics, glass or ceramics; for example steel, stainless steel, aluminium, PVC, high density polyethylene, nylon, glass, polycarbonate, kevlar.

The cover member in Figure 2C is around 3 mm thick, but in other embodiments the thickness can vary.

The surfaces of the cover can be smooth. Alternatively, in order to enhance the contact or bond with adjoining surfaces, the inner and/or outer surfaces of the cover can be undulated or roughened. This can be achieved in a number of ways, such as by dimpling, or providing the surface with grooves or other protrusions. The cover can be made from a crinkled material or a roughened surface polyethylene, examples of which are shown in Figures 4A to 4C. The undulation of the surface of the cover can extend along the substantial length of the tendon and of the bolt.

FURTHER ALTERNATIVES The embodiments have been described by way of example only, and further modifications, other than those already mentioned, are possible within the scope of the invention as defined by the appended claims.

For instance, although the tendons, in the embodiments of Figures 1A and 2A, are shown as stopping short of the end of the rock bolt, other embodiments may include tendons that extend to the end of the rock bolt.

Although the tendon, in the form of a threaded bar 10, has been illustrated as being located axially and centrally, other embodiments may have tendons that are slightly displaced from the central axis of the rock bolt, although it is important that the exposed portion of the tendon aligns with the central axis of the rock bolt to allow the bolt to spun without difficulty during installation.

The embodiments in Figures 1 A and 2A are shown with one central tendon, but further embodiments can have two or more tendons.

In summary, the rock bolts of the embodiments have advantages, including one or more of the following: i) wide range of strength, ii) the flexibility to create

bolts of a large variety of sizes, iii) corrosion resistance, iv) low cost of the component materials, v) the ability to be installed in"one pass", vi) immediate acting, vii) relatively inexpensive as a fully installed rock bolt, viii) variable bonding properties along the bolt's length and viiii) ease of insertion of bonding agent into the hole. Preferably, the present invention is able to have all of these advantages.