FRICTION BOLT WITH FLEXIBLE CORE The present invention relates generally to the mining and construction industries where it is required to stabilise earth or rock formations or the like, for example in excavating a drive in mining operations or in excavating a tunnel in construction operations. In particular, the present invention relates to improvements in rock stabilisers used to stabilise earth or rock formations, such as for example the roof of a tunnel or the roof of a drive in a mine. More particularly, the present invention relates to an improved rock stabiliser having an outer hollow metallic sheath and an inner flexible core. Even more particularly, the present invention relates to an improved rock stabiliser which is in effect a combined friction roof bolt and cable bolt which provides improved holding power when located within a bore in the rock formation. The present invention finds particular application as a new and improved rock stabiliser which has improved initial holding power when first located in the bore of the rock formation prior to admitting grout or other liquid adhesive material into the bore, and has increased holding power after the grout or adhesive has cured.

Although the present invention will be described with particular reference to one form of the improved rock stabiliser, such as in the form of an outer hollow metallic sheath and an inner flexible core of cables, it is to be noted that the scope of the present invention is not limited to the described embodiment, but rather the scope of the present invention is more extensive so as to include other arrangements and forms of the rock stabiliser and their uses in other applications.

Although the term"rock stabiliser"will be used to describe the device of the present invention, it is to be noted that the present invention is not limited in scope to this term but rather this term is used for ease of

description and clarity of expression. Rock stabilisers are variously termed rock bolts, roof bolts, roof stabilisers, friction bolts, combination tube bolts and the like, all of which are included within the scope of the present invention. Each of these terms is used interchangeably in this specification, and all have the same meaning except where the context of their use clearly indicates otherwise. The present invention includes all such devices within its scope.

Roof bolts have found widespread use in strengthening or reinforcing the earth or rock formation in which tunnels or drives are being formed, in order to stabilise the formation and to provide increased safety for miners or construction workers. The roof bolts may take many forms. One form of the roof bolt is a hollow cylindrical tube which is usually known as a friction bolt.

Another form of the roof bolt is known as a cable bolt, which is made from a number of lengths of individual cables twisted or braided together. A still further form of the roof bolt is known as a combination tube bolt or a CT bolt, which is provided with a solid inner core. Until now all roof bolts have been used individually and only a single type has been used within the one bore. The tubular roof bolts and the cable bolts can each be separately grouted or otherwise retained in place in the bores in the rock formation in which they are located using a liquid adhesive material to increase their holding power. However, whilst friction bolts have good initial holding power when first inserted into the bores due to the interference or friction fit of the bolts in the bores, cable bolts, even when provided with point anchors, have little or no initial holding power until grouted in place due to there being little or no interference fit or friction fit between the cable bolt and the bore into which it is inserted.

However, cable bolts have good long term holding power when they are cemented into place and the cement cured.

One defect of currently available CT bolts is

that they are provided with an outer plastic sleeve surrounding a solid inner core. Grout is pumped into the space between the sleeve and the solid core and after flowing along the length of the bolt the grout exits from the end of the bolt into the bore. Often, as the CT bolt is forced into the bore, the plastic sleeve is destroyed by being ripped by the rough surface of the wall of the bore or at the opening of the bore to produce tears, holes or other discontinuities in the plastic sleeve. When grout or other liquid adhesive mixture is pumped internally between the plastic sleeve and the solid core instead of being pumped to the very end of the bolt, the grout escapes from the tears or holes before it has a chance to be pumped to the very end of the bolt and flows into the space or gap between the outer surface of the plastic sleeve and the wall of the bore to emerge prematurely from the entrance to the bore. This provides a false indication to the workmen inserting the CT bolt that the bore is full of grout, as they erroneously believe that the entire length of the bore has been filled with grout or other liquid adhesive when in reality only that length of the bore between the entrance to the bore and the position corresponding to where the tear or hole in the sleeve occurs is actually filled with grout. If the grout or liquid adhesive does not extend to the entire length of the bore, the holding power of the CT bolt is considerably reduced as it is being retained in place by the grout only along a part of the length of the bolt which is that length extending from near to the entrance of the bore to the position of the tear or hole, and not along the full length of the bolt. Clearly, this is undesirable as the safety of miners or tunnellers working below the rock formation having the improperly secured roof bolt is compromised due to the reduced holding power of the roof bolt.

Whilst cable bolts provide very good holding power when they are finally grouted into place they have little or no initial holding power when first located in

the bore of a rock formation. A problem associated with the use of existing cable bolts is that the cable bolts cannot be retained in the bore without the assistance of some external support until the grout has set or cured, and often such bolts fall from the bore as soon as they are inserted or shortly thereafter. Thus, the cable bolts must be held in position by some external support until sufficient retaining strength has been developed so that the cable bolts are retained in the bore by themselves.

After the cable bolt has been inserted into the bore and grout introduced into the bore, it takes some time for the grout to cure or harden in order to provide sufficient holding power for the cable bolt. Whilst the grout or cement is setting or curing, work in the immediate vicinity of this particular cable bolt must be stopped in the interests of safety so as to avoid prematurely dislodging the cable bolt from the bore. This adds to the time taken to complete the tunnel or drive.

Even when the cable bolts are provided with end fittings, such as point anchors or similar, to temporarily hold the bolts in the bore for a time sufficient to allow grout to be pumped into the bore and at least partially cure, the point anchors do not always retain the cable bolts in the bore long enough for the bolts to be grouted in place permanently. The failure of various forms of the rock stabilisers to be initially retained in the bores is further exacerbated by the movement of the rock formation immediately after the bore is formed as the rock formation settles. Often the bore expands during settling of the rock formation which contributes to the various forms of the bolts being initially dislodged from the bores before there is a chance to permanently grout them in place.

Thus, there is a need to provide an improved rock stabiliser which provides a more accurate indication of when the bore in which the rock stabiliser is located is full of grout or similar, and which allows faster installation of the rock stabilisers by providing improved

initial holding power.

Therefore, it is an aim of the present invention to provide an improved rock stabiliser which has increased initial holding power to retain the stabiliser in the bore, is faster to install and which provides increased resistance to damage, thus allowing a more accurate visual indication of its correct installation. These aims are at least in part achieved by the improved rock stabiliser of the present invention, in which the hollow outer tube acts as a sleeve for the flexible inner core and thus provides increased resistance against damage and also provides improved initial holding power whilst the flexible inner core of the bolt provides improved long term holding power after grouting.

According to the present invention there is provided an improved rock or roof stabiliser for stabilising an earth or rock formation by being located within a bore formed in the formation, including an outer sleeve in the form of a longitudinally extending hollow tube provided with a channel means or similar extending at least partly in the lengthwise extending direction of the bolt, and a flexible core located within the hollow tube arranged such that one end of the flexible core extends outwardly of the outer sleeve, so that when the stabiliser is inserted into the bore it has improved holding power.

Typically, the improved stabiliser of the present invention has improved initial holding power when located in the bore of a rock formation or similar when compared to that of a conventional cable bolt.

Typically, the improved stabiliser of the present invention has improved permanent holding power after the flexible inner core has been grouted in place in the bore.

Typically, the outer sleeve of the present invention is in the form of a hollow cylindrical tube.

More typically, one end of the tube is tapered or provided with a tapered portion for facilitating entry of the tube into the bore drilled into the rock formation or similar.

More typically, the tapered portion is a truncated conical section located at the forward end of the stabiliser in use. Most typically, the outer sleeve is a friction bolt.

Typically, the channel means provided in the outer hollow tube is a flute, groove, trough or similar channel means extending along at least a part or all of the side wall of the tube. More typically, the channel means is V-shaped and extends along the side wall of the truncated conical tapered portion of the hollow tube, in addition to extending along all or part of the remaining side wall.

Typically, the rear end of the tube, is provided with a fastening means. Typically, one part or aspect of the fastening means is for fastening roof plates, dome plates or similar to the end of the tube. Even more typically, another part or aspect of the fastening means is adapted for connection to a quick-connect grouting connector or similar for introducing cement, grout or liquid adhesive to the stabiliser.

Typically, the outer tube is provided with a hollow breather tube. More typically, the breather tube is aligned to extend substantially along the lengthwise extending axis of the stabiliser. Even more typically, the breather tube extends beyond the forward end of the tube, preferably towards or at the distal end of the flexible core which extends beyond the end of the tapered forward end of the stabiliser. More typically, the breather tube is received into or is in fluid communication with the V- shaped channel. Even more typically, the proximal end of the breather tube is frictionally fitted into the V-shaped groove so that the breather tube is in fluid communication with the flute to allow air, grout, cement or adhesive to flow therethrough into and/or out of the bore.

Typically, the breather tube is made from plastics or metal materials. More typically, the breather tube allows air to escape from the bore as it is being filled with grout, and then allows grout to flow into the

end of the bolt as it is being grouted into position.

Typically, the flexible core is one or more cables, wire ropes or similar. More typically, there are one, two, three, four or more cables or wire ropes twisted or braided together. More typically, the twisted cables are provided with a birdcage or similar in which the individual strands forming the cables are spread or spaced apart from each other over a short distance to form an enlargement, sometimes referred to as a birdcage, to increase the holding power of the stabiliser. More typically, there are two birdcages, one located at or towards either end of the cables. The birdcages provide additional holding power for the stabiliser as their shape allows grout to flow around the individual strands of the cable. Preferably, the flexible core is held by friction fit within the hollow outer tube.

Typically, the fastening member or element allowing coupling of the stabiliser to a supply of grout or the like is a fitting which is received over the non- tapered end of the stabiliser, which end remains protruding from the rock formation in which the stabiliser is located.

More typically, the fitting is a cap, preferably a hollow cap. Even more typically, the cap is provided with a flange for co-operating with the end of the stabiliser to assist in locating the fastening member on the end of the stabiliser.

Typically, the fastening member or fitting on the rear end of the stabiliser is arranged for co-operative engagement with a quick-release or quick-connect grouting clamp allowing introduction of grout or other liquid adhesive to the inside of the hollow tube. Typically, the grout admitted to the inside of the hollow tube emerges from the end of the tube to flow through the breather tube and V-shaped flute in the gap between the outer wall of the sleeve and the wall of the bore to emerge at the entrance of the bore to provide a visual indication that the bore has been filled with grout or liquid adhesive.

Typically, liquid is a grout, cement adhesive or the like. More typically, a cement slurry, preferably a 1: 4 cement to water slurry. Typically, additives, such as rust preventatives can be added to the liquid.

The present invention will now be described by way of example with particular reference to the accompanying drawings, in which: -Figure 1 is a side view of one embodiment of the stabiliser of the present invention ; -Figure 2 is an enlarged side view of the forward portion in use of the stabiliser of Figure 1 ; -Figure 3 is a cross-sectional view along the line 3-3 of Figure 2 ; -Figure 4 is a cross-sectional view along the line 4-4 of Figure 2 ; -Figure 5 is an enlarged perspective view of the rear end of the stabiliser of figure 1 showing the end fitting in detail.

-Figure 6 is a partial cross-sectional view and partial side view of the rear end of the stabiliser showing the end fitting of Figure 5.

-Figure 7 is a side view of the stabiliser of Figure 1 about to be coupled to a hose through a quick-release connector for admitting grout or similar to the interior of the stabiliser.

-Figure 8 is a partial cross-section view of the end of the stabiliser and the coupling in an intermediate position in the process of being clamped together.

-Figure 9 is a partial cross-section view of the coupling fully clamped to the end of the stabiliser.

In Figures 1 to 4, in particular, there is shown one form of the stabiliser of the present invention which can be briefly described as a friction bolt including an outer hollow tube within which is located one or more twisted cables of wire or similar for insertion into a bore

located in a rock formation or similar.

Stabiliser, generally denoted as 2, comprises an outer sleeve in the form of an elongate, hollow, circular cross-sectional tube 4, preferably made from metal, such as steel, having a channel in the form of a flute 6 provided in the side wall of tube 4 extending along the lengthwise extending axis of tube 4, preferably almost along the entire length of tube 4. It is to be noted that in some embodiments flute 6 may extend only partially along the length of tube 4. Similarly, flute 6 may extend into the tapered portion 14 or tapered end of tube 4. Flute 6 can take any suitable size, shape or cross-section with a generally V-shape being a preferred shape as shown in figure 4.

Flute 6 comprises a pair of opposed wall portions 8,10 which meet at their respective inboard ends along their respective entire lengths. The region along which the ends meet, denoted by 12, is located internally within tube 4 and extends radially inwards towards the central axis of tube 4. However, it is to be noted that the amount of radially inboard extension can vary from being only a small indentation in the wall of tube 4 to extending almost to the opposite wall of the tube, in other words, flute 6 can take any suitable size or shape. Further, it is to be noted that the amount of radial extension of flute 6 radially into tube 4 can vary over the length of the tube, as can the size and shape of the flute ie. flute 6 need not be of a constant size or shape over its length.

Flute 6 acts as a hinge allowing opposed wall portions 8,10 to deform or otherwise flex with respect to each other depending upon the compressive loads applied radially to the roof bolt in the bore in use. It is to be noted that side walls 8,10 are free to deform and flex in response to loads applied longitudinally and transversely to the tube as well as radially. This construction assists in the stabiliser being initially retained in the bore and being retained in the bore as the bore enlarges or moves as

the rock formation settles after the bore is formed by drilling.

Flute 6 is typically formed integrally with tube 4 at the rolling stage of tube 4 in whatever form is required depending on the end use of the roof bolt.

One end 14 of tube 4 is tapered. This end is the forward end in use and is the end inserted into the bore in the rock formation as will be described in more detail later in this specification.

A cable assembly 20 in the form of a braid 22 of individual twisted cables 24 or strands of cables is located internally with tube 4 to extend lengthwise along the longitudinal axis of the tube. The cable assembly 20 is provided with a birdcage 26 located at or towards either end of the braid of cables 22. A birdcage is formed from the individual cables 24 being spaced apart from each other over a short length of the cables to collectively define an open walled cavity formed internally within the spaced apart cables such that there are gaps between adjacent cables. It is to be noted that the presence of the birdcages 26 at either end of the cable assembly 20 prevents the cable assembly 20 from being disengaged from within tube 4 at either end. Further, it is to be noted that braid 22 of the cables is frictionally fitted within the inner diameter of the hollow tube and is retained in place therewith. The birdcage at the distal or forward end of the bolt is used to retain the bolt in place after grouting. Thus, the birdcages not only assist in retaining the cables within the outer sheath but also assist in retaining the stabiliser in the bore.

As shown more particularly in Figure 4, the braid of cables 22 is arranged to extend internally within tube 4 longitudinally along one side of flute 6.

A breather tube 30 is associated with the cable assembly 20 and takes the form of a hollow tube extending longitudinally from the forward end of cable assembly 20 at its distal end to the forward end of tube 4 at its proximal

end as shown in Figure 2. The free end of breather tube 30 at the distal end is located in close proximity to the free ends of cables 24 at their distal ends whereas the other end, the proximal end, of breather tube 30 is frictionally fitted into the end of V-shaped flute 6 at or towards the forward end of tube 4. Fluid admitted to the free or distal end of tube 30 flows through this tube into V-shaped flute 6 whereupon it can travel the entire length of tube 4 to emerge from the rear end of tube 4.

Although one form of breather tube 30 is shown in which the breather tube 30 is partially located within birdcage 26, it is to be noted that breather tube 30 may take any suitable form, may be of any suitable length, may be attached to tube 4 by any suitable means, and may be associated with individual cables 24 in any suitable way.

Breather tube 30 need not be straight but may be curved, arcuate or any suitable shape allowing fluid to flow through it.

With particular reference to Figures 1 and 5 to 9, stabiliser 2 is provided with an end cap or fitting 40 which is received over the rearward end of tube 4. End cap 40 can take a variety of forms. One form is essentially of a hollow cylindrical shape provided with an internal flange 41 located around the inboard edge of one end of fitting 40, so that when the cap 40 is located over the rear end of tube 4, the flange 41 contacts the end of the tube to locate cap 40 and prevent it from sliding axially along the length of the tube. Thus, the end of tube 4 is received in cap 40 and retained in place to this position. The outer profile of cap 40 includes an end collar ring or similar 44 located at the distal end as tube 4 and a more axially inboard second collar ring 46 spaced from the end collar ring 46 defining a space 48 therebetween. As fitting 40 is formed as a single piece, and collars 44,46 are parallel to each other, the spacing 48 between the two collar rings 44,46 is constant around the circumference of fitting 40.

The inboard edge 45 of end collar ring 44 is

angled back or undercut in the direction towards the end of tube 4 in order to provide for more positive engagement of this fitting with a coupling or similar to be described later in this specification.

The inboard facing surface 50 of inboard collar ring 46 is curvedly tapered 52 or is provided with a bull nose profile or similar in the axial direction from a maximum diameter at the more distal end of the stabiliser in a direction towards tube 4. The curved taper 52 allows a dome plate 54 or similar to adopt a number of different alignments or orientations with respect to tube 4 when received on the end of stabiliser 2 in use. The curved taper surface 52 allows up to about 17° of flexibility of alignment from the perpendicular in either direction when the stabiliser 2 is received through the dome plate 54 or similar to take into account the unevenness or changes in n the profile of the entrance to the bore located in the rock formation into which the stabiliser is inserted.

Dome plate 54 is fitted over the end of tube 4 and is retained on tube 4 by the curved surface 52 of cap 40. The dome plate 54 may take any suitable, convenient or desired form. The dome plate is used to stabilise the area of the rock formation around the bore into which the rock stabiliser is received or may be used to provide support for further stabilisation such as a wire-net or wire-mesh, or may be used as an attachment from which other fittings may be suspended, such as for example conveyors or the like.

With particular reference to Figures 7,8 and 9, one form of the quick release coupling or connector used in connection with the stabiliser of the present invention is illustrated. Briefly, the connector 60 is provided with a pair of diagonally opposite flanges 61 to which are pivotally connected a pair of operating levers 62,64 respectively. Operating levers 62,64 are moved between two extreme positions to securely clamp the connector 60 onto the fitting 40 attached to the end of tube 4. Arms 66

are pivotally connected to operating levers 62,64 on either side of connection 60. Claws 68 are provided on the respective distal ends of arms 66. Claws 68 are received in the space 48 located between collars 44,46 and bear against undercut surface 45. Operation of levers 62,64 tighten claws 68 in space 48 so that the tips of claws 68 grip against surface 45 to securely clamp connector 60 to cap 40. Grout or other liquid adhesive material can be pumped through hose 70 connected to the end 72 of connector 60 internally into tube 4 when connector 60 is secured to tube 4 and then through tube 4 to exit at its forward end.

Another form of the cap and quick release coupling for use with tube 4 is a coupling known under the name"Chemlok"which is a standard hose connection. The Chemlok quick release coupling (not shown) which is an alternative to the fitting described previously comprises an internally threaded female portion for threading engagement with a complementary fitting attached to the end of a hose or flexible conduit. The female portion having an internal threaded portion is located contiguously with a side skirt portion having a pair or spaced-apart apertures.

Typically, the apertures are located diagonally opposite each other. A pivot pin is located in or close to each aperture. An actuating lever is pivotally connected to the side skirt by a pivot pin. An actuating lever is provided with a cam surface located at one end, being the proximal end, and a lever portion at the other end, being the distal end. In use, the actuating lever can be moved between two extreme positions in which one position allows the coupling to be attached to the cap and a second position in which the actuating lever engages against the cap to secure the cap to the coupling by the cam surface bearing against the cap.

In use of the stabiliser of the present invention, a bore or similar is formed in the rock formation or the like by drilling a hole of a diameter corresponding to the diameter of the stabiliser,

particularly the outer diameter of tube 4. It is to be noted that the length of the bore being drilled is longer than the stabiliser with cable assembly 20 and breather tube 30 at their respective maximum extension to allow the stabiliser to be received fully in the bore.

The free or forward end of the roof bolt 2 is inserted into the opening of the bore so that the free ends of cables 24, breather tube 30 and tube 4 are located in or at the opening of the bore. A dolly or similar is placed against the rear end of tube 4 ie. against the end of cap 40, and hammered or otherwise driven to force roof bolt 2 into the bore until dome plate 54 contacts the rock formation surrounding the opening. In this position with the roof bolt received fully in the bore, the free ends of cables 24 extend into and towards the blind end of the bore.

After waiting for the required period of time for the rock formation to settle down and without the stabiliser 2 dislodging from the bore because it is now held in place by the interference or friction fit of the tube 4 against the wall of the bore, quick-release coupling 60 is connected to cap 40 and securely clamped thereto by operating levers 62,64. Grout or other liquid adhesive is pumped internally through hollow tube 4 to exit through the open end of tube 4 into the blind end of the bore whereupon it fills this cavity, including flowing in and around the birdcage at the end of the stabiliser. Additionally, the grout flows into the entrance of breather tube 30 as the blind end of the bore becomes full of grout and is pressurised. It is to be noted that air within the bore escapes through breather tube 30 as the end of the bore fills with grout.

Excess grout flows through breather tube 30 into the V-shaped flute 6 which forms a channel along the wall of the bore thus allowing excess grout to flow along the V- shaped flute 6 the entire length of tube 4 to emerge from the rear end of tube 4 at or near to the entrance of the

bore. This provides a visual indication that the blind end of the bore has been filled completely with grout and that grout extends along the entire length of the bore to securely retain the stabiliser thus ensuring that the stabiliser is safely installed in the bore when the grout sets or cures. Accordingly safer working conditions are provided for the miners or tunnellers and the stabilisers can be installed more quickly since the initial holding power of the stabiliser is sufficient to allow an adjacent stabiliser to be installed without risk of the stabiliser disengaging or coming loose from the bore in which it had been installed just moments before.

Advantages of the stabiliser of the present invention include the following: 1) Increased initial holding power because of the friction fit of the outer tube in the bore; 2) Improved overall holding power because of the combined effect of the holding power of the friction fit outer tube and the grouting in and/or around the birdcage of the cable assembly in the blind end of the bore; 3) The improved visual indication that the entire bore is full of grout and that the stabiliser has been grouted in over its entire length.

The described arrangement has been advanced by explanation and many modifications may be made without departing from the spirit and scope of the invention which includes every novel feature and novel combination of features hereindisclosed.

Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is understood that the invention includes all such variations and modifications which fall within the spirit and scope.