FIELD OF THE INVENTION

The present invention relates to a rock-bolt safety system as well as to a method of protecting against a hazard of rock-bolt failure. Thus, it will be appreciated that the invention has particular application or use in the mining industry and/or in the construction industry, where rock-bolts are often employed and where a rock-bolt failure may represent a serious occupational health and safety hazard for workers active in a rock-bolted environment.

BACKGROUND OF THE INVENTION Where extensive excavation of earth is conducted, and particularly in underground environments associated, for example, with tunnelling in the mining industry and/or in the construction industry, the rock-faces and rock strata exposed by the work will typically need to be stabilized and rock-bolts are a commonly employed means to achieve such a stabilization. A common rock-bolting technique involves drilling a hole into the rock-face to accommodate the rock-bolt, which is then inserted into and fixed in the hole. The techniques of fixing a rock-bolt in the hole may include mechanical fixation, for example, with a wedge mechanism or an expansion shell, and/or grouting, for example, with a synthetic resin or cement. Once the rock-bolt is fixed in the hole, the rock-bolt can be mechanically tensioned and locked under tension via a washer plate and a nut at its free end projecting from the excavated and exposed rock-face. The tensile loading on the rock-bolt applies or imparts compressive forces to the rock strata, which in turn stabilize the excavated area. The particular geology of an area being excavated, together with the dimensions, geometry, and the purpose of the excavation, will dictate the number of rock-bolts required to achieve the desired degree of stability. Where the exposed surface of the rock-face has a tendency to crumble or to break away in lumps, surface support, such as metal mesh and/or concrete, may also be installed over the rock- face in addition to the rock-bolts. The surface support is secured to and covers the rock-face to prevent any lumps of rock inadvertently breaking away and falling on any worker or equipment in the vicinity. Although the above techniques have been used with success for many years and continue to be used today, it has been found that, depending on the particular geology of the area concerned, the rock-bolts can be subject to rupture and failure. As will be appreciated, excavations occurring underground, e.g. in mining and/or construction operations, create cavities within the local rock strata that previously did not exist and these cavities alter the pre-existing geological load distribution in the area. This altered load distribution can, in some circumstances, give rise to a sudden shift in the ground structure, e.g. through subsidence. Also, other seismic movement in the local ground structure can cause shifts in the rock strata. When such shifts occur in rock-bolted areas, the rock-bolts can be overloaded to failure.

Because the rock-bolts are placed under a high tensile loading, a sudden failure or rupture of a rock-bolt by such an overload can cause a portion of the ruptured rock-bolt to become a projectile. That is, as the tension in the rock-bolt is suddenly released, an end portion of the rock-bolt may be propelled from the rock-face in the underground cavity or tunnel, posing a potentially serious hazard to personnel or equipment in the area.

SUMMARY OF THE INVENTION In view of the above, it is an object of the present invention to provide a rock-bolt safety system and an associated method for protecting against a hazard of rock- bolt failure, especially the hazard posed by an end portion of the rock-bolt being propelled as a projectile into an excavated area. According to one aspect, therefore, the present invention provides a rock-bolt safety system for protecting against a hazard of rock-bolt failure. The rock-bolt safety system comprises a retainer member for securing an end portion of a rock- bolt projecting from a rock-face. The retainer member includes a first attachment element at a first region thereof for connection to the projecting end portion of the rock-bolt, and at least one second attachment element at one or more second region thereof spaced from or remote from the first region for receiving and cooperating with a fastener or anchor to secure the retainer member to the rock- face or to a local fixed structure.

In a preferred embodiment, the retainer member is generally elongate and may, for example, have a generally flat, rectangular form. The first region thereof is preferably a first end region of the retainer member and the second region thereof is preferably a second, opposite end region of the retainer member. In another, alternative embodiment, however, if the retainer member is elongate and includes more than one second region with a respective second attachment element, the first region having the first attachment element may be a central region of the retainer member and the retainer member may, for example, include two second regions at opposite end regions of the elongate retainer member.

Thus, the rock-bolt safety system of the invention effectively forms a tethering system for the projecting end portion of the rock-bolt. Accordingly, in the event of a rock-bolt rupture due to an overload, e.g. caused by seismic activity or movement in the earth strata being reinforced, the projecting end portion is no longer able to form a projectile impelled out of the rock-face as the tension in the failing rock-bolt is released. Rather, the retainer member is connected to and holds the projecting end portion fastened or anchored to the rock-face so that it cannot become a projectile and potentially cause serious injury to workers or damage to equipment in the vicinity.

The rock-bolt typically comprises a steel rod or steel cable that may be of various diameters, e.g. a rod of about 25 mm (i.e. 1 inch) diameter. Accordingly, the failure loads acting will be high and the tension forces in the rock-bolt which are released on rupture are also high. For this reason, the retainer member itself should be of a robust material and sufficiently strong to withstand the forces exerted by the rock- bolt upon failure. In a preferred form, therefore, the retainer member is comprised of a material selected from the group consisting of: a metal, such as steel, a fibre- reinforced composite, such as carbon fibre-reinforced polymer or glass fibre- reinforced polymer, and/or a high-strength polymer.

As noted above, the retainer member is preferably elongate and may be designed or configured generally flat and rectangular; for example, in the form of a strip, a strap, or a band, e.g. as a steel strap. In this regard, the retainer member desirably has a length in the range of about 200 mm to about 800 mm, although a length in the range of about 300 mm to 500 mm is particularly preferred. It will be noted that a length below 300 mm is considered less desirable as such shorter retainer members have been found to transfer a higher load to the fastener or anchor. Furthermore, the retainer member preferably has a width in the range of about of about 40 mm to 100 mm, and more preferably in the range of about 60 mm to 80 mm. The thickness of the retainer member, e.g. when configured as a strip, strap, or band of steel, is preferably in the range of about of about 1 mm to about 5 mm, e.g. about 3 mm.

In a preferred embodiment, the retainer member is configured to exhibit resilient flexibility and/or plastic deformability. In the event of a rock-bolt rupture, therefore, the retainer member is able or configured to absorb the forces released upon failure of the rock-bolt via an elastic and/or a plastic deformation of the retainer member. That is, the retainer member may operate to absorb and dampen the forces imparted to the ruptured or broken end portion of the rock-bolt. By way of example, selecting an elongate configuration for the retainer member having the second region at an end region of the retainer member, such that the retainer member is secured or anchored to the rock-face or other structure at that end region, the retainer member may thereby be configured to flex or deform in use in the manner of a cantilever or leaf-spring about the anchored or secured second end region to absorb and dampen the forces released on rock-bolt rupture. In a preferred embodiment, the first attachment element comprises an aperture or hole which is sized to receive a free end of the rock-bolt projecting from the rock- face. The aperture may be smaller in diameter than a tensioning nut fastened at the end portion of the rock-bolt, so that the first region of the retainer member is configured to seat against the tensioning nut. Alternatively, the first attachment element may comprise an aperture sized to at least partially receive the tensioning nut fastened at the end portion of the rock-bolt, particularly where the tensioning nut is a domed nut having a widened base or flange. In that case, the aperture is preferably smaller than the base or flange of the domed nut, such that the first region of the retainer member is configured to seat against that widened base or flange of the nut.

In an alternative preferred embodiment, the first attachment element comprises a cover member or receptacle for at least partially (preferably entirely) receiving and accommodating a tensioning nut fastened at the end portion of the rock-bolt. The cover member or receptacle is preferably configured as a sleeve or a tube and preferably has a closed end at the retainer member and an opposite open end for receiving the nut. This embodiment has been conceived for rock-bolts in which the tensioning nut has no real flange or shoulder against which the retainer member around an aperture-type first attachment element may seat and engage. In this way, the cover member or receptacle can be placed over and accommodate the tensioning nut at the end portion of the rock-bolt. In the event of rupture or failure of the rock-bolt, the end of the rock-bolt is already captured and held within the cover member or receptacle and force released by rupture or failure is absorbed by the flexibility and deformation of the retainer member, as described above.

In a preferred embodiment, the second attachment element comprises an opening or hole that is sized to receive and to engage with the fastener for securing the retainer member to the rock-face or to the local structure. It is contemplated by this invention that the second (end) region of the retainer member may include two or more second attachment elements, with each being configured to receive and cooperate with a respective fastener or anchor to secure the retainer member to the rock-face or to a local fixed structure. Thus, each second attachment element may comprise an opening or hole sized to receive and engage with the fastener. By having two or more second attachment elements, a more stable securement of the retainer member can be achieved, especially when the retainer member is to be secured to surface support, such as mesh, rather than to the rock-face directly. As noted above, the surface support may also comprise concrete or "shot-crete" which is applied in a layer to cover and bind the excavated rock-face. For the purposes of this disclosure, therefore, securing the retainer member to a layer of concrete or "shot-crete" on the rock-face will be deemed equivalent to securing the retainer member to the rock-face itself.

In a preferred embodiment, the rock-bolt safety system further includes a fastener or an anchor for cooperation with each second attachment element to secure the retainer member to the rock-face or to a local fixed structure. In this regard, each fastener may comprise a bolt or expansion anchor configured to be secured to the rock-face or "shot-crete" on the rock-face. Alternatively, or in addition, the fastener may comprise a clip, shackle or tie fastener configured to be secured to a locally fixed structure, such as mesh surface support provided on or attached to the rock- face.

In a preferred embodiment, despite comprising a robust material, such as steel, the elongate retainer member will typically have a degree of flexibility which may assist a deployment or installation of the retainer member. In this regard, as the first attachment element in a first end region of the elongate retainer member is for connection to the end portion of the rock-bolt that projects out of the rock-face some distance, and the second attachment element in a second end region of the retainer member is for securing to the rock-face itself or to the fixed local structure (e.g. mesh on the rock-face), upon attachment of the end regions to the rock-bolt and the rock-face or mesh, respectively, those first and second end regions may typically be flexed and/or deformed relative to a central region of the retainer member to facilitate installation. In a preferred embodiment, the rock-bolt safety system further comprises a holding element for attachment to the end portion of the rock-bolt after installation of the retainer member. The holding element is positioned on the end portion of the rock- bolt outward of the retainer member, and the holding element has a size which, when attached on the rock-bolt, is larger than the first attachment aperture. In use, in the event of a rock-bolt failure, the retainer member absorbs the forces released and tethers or retains the end portion of rock-bolt to prevent it from becoming a projectile. After this, the holding element prevents the ruptured or broken end portion of the rock-bolt from separating from the retainer member, e.g. dropping out of the retainer member under gravity. That is, the holding element may form a collar which grips the rock-bolt or nut on the outer side of the retainer member (which itself is typically seated against the tensioning nut) and prevents separation of the end portion of the rock-bolt from the retainer member after rupture. Preferably, this holding element is configured for attachment to the end portion of the rock-bolt in a friction fit. The holding element may be adjustable to a variety of sizes, particularly for attachment to either a free end of the rock-bolt or to the tensioning nut fastened at the end portion of the rock-bolt. In this regard, in a particularly preferred embodiment, the holding element comprises a cable tie fastener.

According to another aspect, the invention provides a method of protecting against a hazard of rock-bolt failure, especially the hazard posed by an end portion of the rock-bolt becoming a projectile, comprising:

providing a retainer member for securing an end portion of a rock-bolt projecting from a rock-face, the retainer member having a first attachment element at a first region for connection to the projecting end portion of the rock-bolt and at least one second attachment element at one or more second region for receiving and engaging with a fastener;

connecting the first region of the retainer member to the projecting end portion of the rock-bolt by means of the first attachment element; and securing the second region of the retainer member to the rock-face or to a fixed local structure by means of a fastener that cooperates with and engages the second attachment element. Typically, the retainer member is generally elongate. The retainer member may, for example, be generally rectangular. In a preferred embodiment, therefore, the first region may be a first end region of the retainer member and the second region may be a second end region of the retainer member. In an alternative preferred embodiment, however, if the retainer member is elongate and includes more than one second region, the first region having the first attachment element may be a central region of the retainer member and the retainer member may include two second regions at opposite end regions of the elongate retainer member.

In a preferred embodiment, the first attachment element comprises an aperture sized to receive the projecting end portion of the rock-bolt, especially a free end of the rock-bolt or a tensioning nut fastened at the end portion of the rock-bolt, and the step of connecting the first region of the retainer member to the projecting end portion of the rock-bolt comprises placing the first region over the end portion of the rock-bolt such that the end portion of the rock-bolt is received or inserted within the aperture.

In a preferred embodiment of the method, the step of connecting the first region of the retainer member to the projecting end portion of the rock-bolt includes attaching a holding element on the end portion of the rock-bolt outward of the retainer member. The holding element when attached to the end portion of the rock-bolt preferably has a size larger than the first attachment aperture, such that the holding element at least partially obscures that aperture.

In an alternative preferred embodiment, the first attachment element comprises a cover member or receptacle sized to receive the projecting end portion of the rock- bolt, especially a free end of the rock-bolt or a tensioning nut fastened at the end portion of the rock-bolt. The step of connecting the first region of the retainer member to the projecting end portion of the rock-bolt then comprises placing the cover member or receptacle over the end portion of the rock-bolt such that end portion of the rock-bolt is received or accommodated within the cover member or receptacle. As noted above, the cover member or receptacle may comprise a tube or sleeve which is closed at one end, e.g. by the retainer member, and open at the other end for receiving the projecting end portion of the rock-bolt.

In a preferred example of the method, the second attachment element comprises an opening or hole sized to receive and engage with an anchor fastener and the step of securing the second region of the retainer member to the rock-face comprises inserting the anchor fastener through the opening and anchoring the anchor fastener in the rock-face. Alternatively, the second attachment element comprises an opening sized to receive and engage with a fastener and the step of securing the second region of the retainer member comprises inserting the fastener through the opening and attaching the fastener either to surface support, such as mesh, secured on the rock-face or to a fixed local structure.

BRIEF DESCRIPTION OF THE DRAWINGS For a more complete understanding of the invention and the advantages thereof, exemplary embodiments of the invention are explained in more detail in the following description with reference to the accompanying drawing figures, in which like reference characters designate like parts and in which: Fig. 1 is a schematic cross-sectional view of an excavated tunnel, drive, or adit in a mine environment illustrating a rock-bolting arrangement;

Fig. 2 is a schematic perspective view of a rock-bolt safety system and a method of using same to protect against a hazard of rock-bolt failure according to an embodiment of the invention; is a schematic perspective view of a rock-bolt safety system and a method of using same to protect against a hazard of rock-bolt failure according to another embodiment of the invention; Fig. 4 is a schematic perspective view of a rock-bolt safety system and a method of using same to protect against a hazard of rock-bolt failure according to a further embodiment of the invention; is a schematic perspective view of a rock-bolt safety system and a method of using same to protect against a hazard of rock-bolt failure according to yet another embodiment of the invention; is a schematic perspective view of a rock-bolt safety system and a method of using same to protect against a hazard of rock-bolt failure according to still a further embodiment of the invention; and is a flow diagram which schematically represents a method according to an embodiment of the invention. The accompanying drawings are included to provide a further understanding of the present invention and are incorporated in and constitute a part of this specification. The drawings illustrate particular embodiments of the invention and together with the description serve to explain the principles of the invention. Other embodiments of the invention and many of the attendant advantages of the invention will be readily appreciated as they become better understood with reference to the following detailed description.

It will be appreciated that common and/or well understood elements that may be useful or necessary in a commercially feasible embodiment are not necessarily depicted in order to facilitate a more abstracted view of the embodiments. The elements of the drawings are not necessarily illustrated to scale relative to each other. It will also be understood that certain actions and/or steps in an embodiment of a method may be described or depicted in a particular order of occurrences while those skilled in the art will understand that such specificity with respect to sequence is not actually required. DETAILED DESCRIPTION OF EMBODIMENTS

With reference firstly to Fig. 1 of the drawings, a schematic cross-sectional view of a tunnel or a drive or adit D in a mine environment is shown illustrating a typical arrangement of rock-bolts B in a rock-face F of the drive D. Each of the rock-bolts B typically has a length in the range of about 1 to 3 metres and extends approximately normal to the rock-face F at the location of its insertion. As shown in the example of Fig. 1 , the arrangement of eleven rock-bolts B spaced around the walls and roof of the drive cross-section is quite typical, although the number of rock-bolts B may, of course, vary depending on the dimensions of the drive D and the nature of the local geology. This cross-sectional pattern or array of rock-bolts B will usually then be repeated at varying intervals along the length of the drive D, for example, at 1 .5 metre intervals.

With reference now to drawing Fig. 2, a common rock-bolting technique involves drilling a hole H into the rock-face F deep enough to accommodate the rock-bolt B. The rock-bolt B is then inserted into the hole H together with the components of a grouting material M, such as a synthetic resin, e.g. a two-part epoxy-resin. The resin components are mixed in the hole H around the rock-bolt B until they polymerize and harden or set, fixing the rock-bolt B in the rock. Thereafter, the rock-bolt B can be tensioned and held under tension via a washer plate W and a tensioning nut N at an end portion E of the rock-bolt B projecting from the excavated and exposed rock-face F. The tensile loading on the rock-bolt applies or imparts compressive forces to the rock strata, which in turn stabilize the excavated area of the drive D.

A preferred embodiment of a rock-bolt safety system 1 for protecting against a hazard of rock-bolt failure, and especially the hazard posed by the end portion E of a rock-bolt B becoming a projectile, according to this invention is shown in Fig. 2. The rock-bolt safety system 1 comprises an elongate retainer member 2 provided in the form of a generally rectangular steel strap for securing the end portion E of the rock-bolt B which projects from the rock-face F. By way of example, the steel strap 2 of this embodiment may have a length of about 400 mm, a width of about 75 mm, and a thickness of about 3 mm. The retainer strap 2 has a first attachment element 3 provided at one end region 4 for connection to the projecting end portion E of the rock-bolt B. In particular, this first attachment element 3 is provided in the form of an aperture which is sized to receive a free end of the rock- bolt B. For example, the aperture 3 may be a circular hole having a diameter in the range of about 28 to 30 mm for receiving the free end of the rock-bolt steel rod of about 25 mm diameter. As the aperture 3 is smaller than the tensioning nut N, however, the retainer strap 2 seats against an outer side or face of the nut N. In this regard, during installation the end region 4 of the retainer strap 2 is placed over the end portion E of the rock-bolt B in the direction of the arrow in Fig. 2 in such a manner that the free end of the rock-bolt B is received or inserted within the aperture 3 and the inner side of the retainer strap 2 (i.e. towards the rock-face F) abuts the nut N. The retainer strap 2 further comprises a second attachment element 5 at its other opposite end region 6 for receiving and cooperating with an anchor fastener 8. In particular, after the one end region 4 of the retainer strap 2 is placed over the end portion E of the rock-bolt B, the opposite end region 6 is placed against the rock- face F and the anchor fastener 8, which may be an expanding mechanical anchor bolt, is inserted through the opening 5 and anchored in the rock-face F to secure the retainer strap 2 to the rock-face F, e.g. by drilling into the rock-face F and by deploying that fastener 8 in the usual way.

To assist the deployment and installation of the retainer strap 2, the strap 2 will typically have a degree of flexibility. In this regard, it will be noted that the end portion E of the rock-bolt B to which the one end region 4 of the retainer strap 2 is connected projects out of the rock-face F some distance, whereas the other end region 6 of the strap is to be secured to the rock-face F itself. Upon installation, therefore, it can be seen that the two end regions 4, 6 of the retainer strap 2 take up or assume a position in which they are flexed and/or deformed relative to a central portion 7 of the strap inclined at an angle between them.

As a preferred addition, the rock-bolt safety system 1 includes a holding element 9 which is attached to the end portion E of the rock-bolt B after installation of the retainer strap 2. More particularly, the holding element 9 is positioned on the end portion E of the rock-bolt B outward of the retainer member 2 and, in this example, is configured as a collar for attachment to the rock-bolt B in a friction fit. That is, the holding element 9 in this embodiment comprises a cable tie fastener which is placed over the free end of the rock-bolt B adjacent the outer side of the strap 2 and pulled tight to form a collar which grips the rock-bolt B in a friction fit. When attached to the rock-bolt in this manner, the holding tie 9 has a size which is larger in diameter than the aperture 3 through the strap 2. In this way, the holding tie 9 prevents the end portion E of the rock-bolt B from separating or detaching from the retainer strap 2, e.g. from dropping out of the strap 2 under gravity, in the event of rupture of the rock-bolt B. Referring now to drawing Fig. 3, a slightly modified embodiment of the rock-bolt safety system 1 and the method of the invention is illustrated. The same reference signs are used to identify the parts of this embodiment which correspond to those features described above with reference to Fig. 2. For the sake of economy, those features will not be described again. Rather, the description of Fig. 3 will focus on those features which differ from the embodiment in Fig. 2. In this regard, it will be noted that the tensioning nut N on the end portion E of the rock-bolt B is a domed nut and incorporates a widened base or flange G adjacent the washer plate W. In a corresponding manner, the aperture of the first attachment element 3 at the one end region 4 of the retainer strap 2 is larger in this embodiment (e.g. in the range of about 50 to 60 mm) in order to receive a portion of the nut N therein. However, the aperture 3 is smaller than the base or flange G of the tensioning nut N, such that the retainer strap 2 seats against this base or flange G. After placing the end region 4 of the strap 2 over end portion E of the rock-bolt B such that the nut N is received in the aperture 3, the opposite end region 6 of the strap is secured to the rock-face F as described with reference to Fig. 2. The holding element or cable tie fastener 9 is then placed around the nut N and tightened to form a collar on the outer side of the retainer strap 2 to again prevent separation of the end portion E of the rock-bolt B from the retainer strap 2 in the event of rock-bolt rupture. That is, the anchored strap member 2 absorbs the suddenly released forces and forms a tether for retaining the end portion E of the rock-bolt B preventing it from becoming a projectile in the event of rock-bolt rupture. Thereafter, the holding element 9 is able to hold the broken or ruptured end portion E of the rock-bolt B attached to the anchored retainer strap 2.

As an alternative to employing an anchor fastener 8 or an expanding mechanical anchor bolt which is typically deployed by drilling and anchoring in the rock-face F as described above, another type of fastener 8 may be contemplated for a drive or adit D in a mine environment where surface support, such as metal mesh, has in any case been secured to the rock-face F to protect against rock-fall, or where some other fixed structure is locally available for attachment of the retainer strap 2. In that case, it is conceivable that the fastener 8 is configured to simply secure the other end region 6 of the retainer strap 2 via the second attachment element or opening 5 directly to the metal mesh. As no drilling is required, this may provide a more efficient installation procedure for the rock-bolt safety system 1 and the method of the invention. Such an alternative embodiment of the rock-bolt safety system 1 and the method of the invention is illustrated in Fig. 4 of the drawings. In this instance, in addition to the rock-bolts B for stabilizing the rock-face F, metal mesh surface support S is installed on the rock-face F of the drive D to protect against rock-fall. The metal mesh S thus forms a fixed local structure to which the retainer strap 2 of the safety system 1 can be anchored or secured. In this embodiment, the retainer strap 2 of the rock-bolt safety system 1 is similar in construction to the embodiment of Fig. 3, but in this case comprises a plurality of second attachment elements 5 at the end region 6 for receiving and cooperating with a fastener (not shown) for securing the end region 6 of the strap 2 to the mesh S. More particularly, the second end region 6 of the retainer strap 2 is somewhat longer than in the embodiment of Fig. 3 and includes a pair of openings 5 for receiving a respective fastener spaced apart in a longitudinal direction of the strap 2 (e.g. by a distance which may be approximately equivalent to a width of the mesh spacing; preferably in the range of about 40 mm to about 120 mm; for example, about 80 to 100 mm). In this way, a first or one end region 4 of the retainer strap 2 is placed via the first attachment element or the opening 3 over the end portion E of the rock-bolt B, as was the case with the embodiment of Fig. 3, and a second or other end region 6 of the strap 2 is secured via the second attachment elements or openings 5 directly to the metal mesh S. By virtue of the fact that the retainer strap 2 can be attached directly to the metal mesh S, a bolt or expansion anchor is not necessary in this case. Rather, a flexible tie fastener (e.g. a cable tie, similar to the holding element 9 described above) may be used as the fastener 8. Such a tie fastener is able to be threaded through each of the second attachment elements or openings 5 and around an adjacent portion of the mesh S and back again to be drawn tight, thereby to attach or secure that end region 6 of the retainer strap 2 at two discrete points to the mesh S. As no additional drilling of the rock-face F is required in this embodiment, a quick and efficient installation of the rock-bolt safety system 1 of the invention is possible.

In each of the embodiments described with reference to Figs. 2 to 4, the retainer strap 2 is relatively stiff, but nevertheless exhibits resilient flexibility. Accordingly, in the event of a rock-bolt rupture, the retainer member 2 is desirably configured to flex and/or deform (i.e. bend) about the anchored second end region 6 under the action of the forces released upon failure of the rock-bolt B via an elastic and/or a plastic deformation of the retainer member. In this way, the retainer strap 2 can operate to absorb and dampen the forces imparted to the ruptured or broken end portion E of the rock-bolt B.

With reference now to Fig. 5 of the drawings, a further embodiment of a rock-bolt safety system 1 according to the invention is illustrated and this embodiment is again designed for use with rock-bolts B in a rock-face F which has surface support S, such as steel mesh. The retainer member 2 is again in the form of a rectangular steel strap, but in this embodiment the retainer strap 2 is longer, with a length in the range of about 800 mm to 900 mm. Furthermore, in this embodiment the first region 4 having the first attachment element or aperture 3 for receiving the projecting end portion E of the rock-bolt B is in a central region of the retainer strap 2. The opposite end regions 6 of the strap 2 therefore form two second regions, each of which has a respective second attachment element 5 in the form of a hole or opening designed to cooperate with a respective clip, shackle or C-fastener 8 which then secures each end region 6 of the strap member 2 to a neighbouring part of the mesh S. The second end regions 6 of the strap 2 may be fastened to either a vertically and/or horizontally extending mesh element.

As before, a cable tie fastener 9 may be employed as a holding element, which is fixed over the free end of the rock-bolt against an outer face of the retainer strap 2. Because the mesh S is separately anchored to the rock-face F, in the event of a rock-bolt failure, the forces released in the rupturing rock-bolt B can be transferred to and absorbed by the mesh S. In this way, the end portion E of the rock-bolt B remains tethered via the safety system 1 of this embodiment and is again inhibited from forming a potentially hazardous projectile.

Referring to Fig. 6 of the drawings, yet another embodiment of a rock-bolt safety system 1 according to the invention is illustrated. In this embodiment, the second attachment element 5 at the end region 6 of the retainer strap 2 for receiving and cooperating with an anchor fastener 8 essentially corresponds to the configuration of the embodiment described with reference to Fig. 3. It will be appreciated that this end region 6 of the retainer strap 2 could also be configured as shown in the embodiment of Fig. 4 or Fig. 5, depending on the circumstances of its application . The main point of difference in the embodiment of Fig. 6 concerns the design or configuration of the first attachment element 3 at the end region 4 of the retainer strap 2. In this case, the first attachment element 3 is configured as a receptacle to at least partially (and preferably entirely) receive and accommodate the tensioning nut N fastened at the end portion E of the rock-bolt B. The receptacle is formed as a sleeve or cap 3 having a generally cylindrical shape which is closed at one end 3' by the retainer strap 2 and open at the opposite end 3" for receiving the nut N. The sleeve or cap 3 is typically comprised of short length of steel tube connected to the steel retainer strap 2, e.g. by weld L. This embodiment has been conceived for rock-bolts B in which the tensioning nut N has no flange or shoulder against which the retainer strap 2 may properly seat and engage if the first attachment element 3 were configured as a hole or aperture, as shown in Fig. 3. In this way, the cover member or receptacle 3 accommodates the tensioning nut N and the end portion E of the rock-bolt B. In the event of rock-bolt rupture or failure, the end of the rock-bolt B is already captured and held within the receptacle 3, and the force released by the rupture or failure is absorbed by flexibility and deformation of the anchored retainer strap 2 as described above. Finally, referring to Fig. 7 of the drawings, a flow diagram is shown that illustrates schematically the steps in a method of protecting against a hazard resulting from rock-bolt failure, particularly the hazard posed by an end portion E of a rock-bolt B becoming a projectile, according to the embodiments of the invention described above with respect to Figs. 2 to 6. In this regard, the first box i of Fig. 7 represents the step of providing a retainer member 2 for securing an end portion E of a rock- bolt B projecting from a rock-face F. The retainer member 2 has a first attachment element 3 at a first region 4 for connection to the projecting end portion E of the rock-bolt B, and at least one second attachment element 5 at a second region 6 spaced from or remote from first region 4 for receiving and engaging with a fastener 8. The second box ii then represents the step of connecting the first region 4 of the retainer member 2 to the projecting end portion E of the rock-bolt B by means of the first attachment element 3. In this regard, the first attachment element 3 may comprise an aperture sized to receive the projecting end portion E of the rock-bolt B, especially a free end of the rock-bolt B or a tensioning nut N fastened at the end portion E of the rock-bolt B. Thus, the step of connecting the first region 4 of the retainer member 2 to the projecting end portion E of the rock- bolt B may comprise placing the first region 4 over the end portion E of the rock- bolt B such that end portion E of the rock-bolt B is received or inserted within the aperture. The third box iii represents the step of securing the second region 6 of the retainer member 2 to the rock-face F or to a local rigid structure by means of a fastener 8 that cooperates with and engages the second attachment element 5. Again, each second attachment element 5 may comprise a hole or opening in the retainer member. The final box iv in Fig. 7 of the drawings represents the step of fitting a holding element to the end portion of the rock-bolt after installation of the retainer member. The holding element is positioned on the end portion of the rock- bolt outward of the retainer member, and the holding element has a size which, when attached on the rock-bolt, is larger than the first attachment aperture. In the event of a rock-bolt failure, therefore, the retainer member absorbs the forces released and tethers or retains the end portion of the rock-bolt to prevent it from becoming a projectile, and the holding element prevents the ruptured or broken end portion of the rock-bolt from separating from the retainer member.

Although specific embodiments of the invention are illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations exist. It should be appreciated that the exemplary embodiment or exemplary embodiments are examples only and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents. Generally, this application is intended to cover any adaptations or variations of the specific embodiments discussed herein.

It will also be appreciated that in this document the terms "comprise", "comprising", "include", "including", "contain", "containing", "have", "having", and any variations thereof, are intended to be understood in an inclusive (i.e. non-exclusive) sense, such that the process, method, device, apparatus or system described herein is not limited to those features or parts or elements or steps recited but may include other elements, features, parts or steps not expressly listed or inherent to such process, method, article, or apparatus. Furthermore, the terms "a" and "an" used herein are intended to be understood as meaning one or more unless explicitly stated otherwise. Moreover, the terms "first", "second", "third", etc. are used merely as labels, and are not intended to impose numerical requirements on or to establish a certain ranking of importance of their objects.

List of reference signs

1 rock-bolt safety system

2 retainer member or strap

3 first attachment element

3' closed end of receptacle sleeve or cap

3" open end of receptacle sleeve or cap

4 one end region of retainer member

5 second attachment element

6 other end region of retainer member

7 central portion of retainer member

8 anchor or fastener

9 holding element

D tunnel, drive or adit

B rock-bolt

F rock-face

H hole

M grout material

E end portion of rock-bolt

W washer plate

N tensioning nut

G the base or flange of the tensioning nut

S mesh surface support

L weld line