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Title:
REINFORCING OF FORMATIONS
Document Type and Number:
WIPO Patent Application WO/2008/128301
Kind Code:
A1
Abstract:
A bolt (10,20) for use in the reinforcing of formations (S) comprises a plurality of first wires (14) arranged around a core (12) in a first lay direction along a length of the core, and a plurality of second wires (16) arranged around the first wires in a second different lay direction along the core length. A third layer of wires (22) can be provided in a different or same lay direction as the first or second layer. The core can comprise a tube (eg. of a steel or polymer) that has sufficient flexibility such that it can be bent in an arcuate manner. This can provide flexibility to the bolt. A method of forming and a method of installing the bolt are disclosed, as is a system which employs two or more bolts which have in-use protruding portions that can be fastened together.

Inventors:
MORGAN, Andrew James (Ingall Street, Mayfield, New South Wales 2304, AU)
Application Number:
AU2008/000571
Publication Date:
October 30, 2008
Filing Date:
April 23, 2008
Export Citation:
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Assignee:
ONESTEEL WIRE PTY LIMITED (Level 40, 259 George StreetSydney, New South Wales 2000, AU)
MORGAN, Andrew James (Ingall Street, Mayfield, New South Wales 2304, AU)
International Classes:
E21D21/00; D07B1/08; D07B1/12; D07B1/14; D07B3/00; E21D20/00; E21D20/02
Domestic Patent References:
WO1993003256A1
WO1993012324A1
Foreign References:
EP0379388A2
GB1373814A
US5443332A
SU1469162A1
RU2177550C1
Attorney, Agent or Firm:
GRIFFITH HACK (Level 29, Northpoint100 Miller Stree, North Sydney New South Wales 2060, AU)
Download PDF:
Claims:
Claims

1. A bolt for use in reinforcing formations, the bolt comprising:

- a plurality of first wires arranged around a core in a first lay direction along a length of the core; - a plurality of second wires arranged around the first wires in a second different lay direction along a length of the core.

2. A bolt as claimed in claim 1 wherein each of the first and second wires is arranged to extend in a helical spiral around the core along its length.

3. A bolt as claimed in claim 2 wherein each wire is arranged to extend side-by- side to wires on adjacent opposing sides thereof.

4. A bolt as claimed in any one of the preceding claims wherein the core is defined by a tube.

5. A bolt as claimed in claim 4 wherein the tube is formed of a flexible material.

6. A bolt as claimed in claim 5 wherein the flexible material is a metal or polymeric material.

7. A bolt as claimed in claim 6 wherein the metal is a steel of sufficient softness such that it can be coiled prior to use, and the polymeric material is fire-resistant and anti-static.

8. A bolt for use in reinforcing formations, the bolt comprising:

- an elongate tube that has sufficient flexibility such that it can be bent in an arcuate manner;

- a plurality of wires arranged around the tube along a length thereof so as to define the bolt.

9. A bolt for use in reinforcing formations, the bolt comprising:

- an elongate polymeric tube;

- a plurality of wires arranged around the tube along a length thereof so as to define the bolt.

10. A bolt as claimed in claim 8 or 9 wherein the tube is as defined in claim 6 or 7, and the plurality of wires are as defined in any one of claims 1 to 3.

11. A bolt as claimed in any one of the preceding claims that is a cable bolt.

12. A method for forming a bolt that is as defined in any one of the preceding- claims, the method comprising the steps of:

- feeding an elongate core into a rope-making machine; and

- operating the machine to arrange one or more layers, that each comprise a plurality of wires, around and along a length of the core to thereby define the bolt.

13. A method as claimed in claim 12 wherein, after a first layer is arranged around the core, the resulting bolt is re-fed through the rope-making machine to arrange each of one or more further layers around the first layer.

14. A method as claimed in claim 13 or 14 wherein each successive layer has its wires layed in an opposite lay direction to the immediately preceding layer.

15. A method for forming a bolt that is as defined in any one of claims 1 to 11 , the method comprising arranging on the core or tube, the one or more plurality of wire layers, around and along a length of the core or tube using a rope-making methodology, to thereby define the bolt.

16. A method as claimed in claim 16 that is otherwise as defined in any one of claims 12 to 14.

17. A method for installing a bolt in a formation, the method comprising the steps of:

(i) fastening an end of the bolt in a hole that has been formed in the formation;

(ii) applying tension to the bolt; and

(iii) introducing a fastening medium into the hole to surround and fasten the tensioned bolt in the formation.

18. A method as claimed in claim 17 wherein in (ii) the tension applied to the bolt is a proportion of the bolt' s capacity to be tensioned.

19. A method as claimed in claim 17 or 18 wherein the bolt is as defined in any one of claims 1 to 11 and, when the bolt comprises a tubular core, step (iii) involves introducing the fastening medium into the hole via the tubular core.

20. A method as claimed in any one of claims 17 to 19 wherein the fastening medium is a grout that adhesively fastens the tensioned bolt in the formation.

21. A method as claimed in any one of claims 17 to 20 wherein in (i) the bolt end is fastened in the hole using a mechanical or adhesive fastener.

22. A bolt system for use in supporting a formation, the system comprising two or more flexible elongate bolts which, when positioned in the formation, can each be configured to protrude, whereby a protruding portion of a bolt can be manoeuvred into adjacency with another bolt protruding portion to enable fastening together of the bolt protruding portions.

23. A system as claimed in claim 22 wherein the adjacent bolt protruding portions are fastened together by a coupling.

Description:

Reinforcing of Formations

Technical Field

Disclosed is an improved bolt for use in the reinforcing of formations, such as rooves, ceilings, walls etc, especially in mining and construction applications. Whilst the improved bolt finds primary application in secondary support applications, particularly in underground mines to hold layers of rock strata together, it should be appreciated that it can readily be adapted for use in other formation-reinforcing applications.

Background Art

Roof bolting is a technique employed in the mining industry to provide roof support, primarily in mine tunnels etc. Boreholes are drilled upwards into the roof and bolts are inserted into the holes and anchored at the top, sometimes by a split cone, a mechanical anchor, or by resin grout. The bolts are usually installed using a definite pattern so as to clamp together several roof beds to form a composite beam. Such a beam can have a strength considerably greater than the sum of the individual beds acting separately.

The bolts employed in roof bolting may be formed from a solid rod or tube, or can be a "composite" bolt, for example, being formed from a series of wire strands. Such a composite bolt is referred to as a "cable bolt".

One such bolt is marketed in Australia under the trade mark MEGABOLT (owned by Quantax Pty Ltd) and constructional details of the MEGABOLT product are disclosed in Australian patent application number 2003200816. This application discloses wires arranged longitudinally (ie. lengthwise) along a wire core (king wire) or a steel tube. AU 2003200816 is directly concerned with providing ribs on at least some of the specific outermost wires, to avoid the need for a significantly larger core wire.

Summary of the Disclosure In a first aspect there is provided a bolt for use in reinforcing formations, the bolt comprising:

- a plurality of first wires arranged around a core in a first lay direction along a length of the core;

- a plurality of second wires arranged around the first wires in a second different lay direction along a length of the core.

The provision of a second layer of wires having a different lay direction along the length of the core can improve the bolt's torque characteristics and overall strength, in that the torque produced under load can be balanced by the oppositely wound directions of the first and second wire layers. The different lay direction can also allow individual wire diameters in each layer to be optimised to provide for an increased overall bolt strength.

In one form, each of the first and second wires is arranged to extend in a helical spiral around the core along its length. For example, each wire can be arranged to extend side-by-side to wires on adjacent opposing sides thereof (eg. so as to effectively surround the core). The helical spiral configuration contributes to the strength of the bolt, whilst the extension of the wires along the bolt length provides flexibility to the bolt.

In one form, the core is defined by a tube. The provision of a tube within the bolt allows the bolt to have an in-built grout feed tube (ie. to enable resin grout to be fed through the bolt via the tube, to exit the tube end, then set and anchor the bolt in a borehole).

Optimally, though not exclusively, the tube is formed of a flexible material such as a metal or polymeric material. This tube flexibility can be sufficient to allow the bolt to be coiled or wound onto a reel. Whilst the core is optimally defined by a flexible tube, in variations the core may be defined by an elongate rigid tube, or a flexible or rigid wire (eg. of metal), or may in the resultant bolt, simply be a space defined by the plurality of first wires.

The tube metal can be of steel (eg. a mild steel) having sufficient softness such that it can be coiled prior to use, but having sufficient strength to not collapse when the wires are arranged around it.

The tube polymeric material can be a fire-resistant and/or anti-static polymer, such as a polypropylene PTFE or CPVC polymer.

In a second aspect there is provided a bolt for use in reinforcing formations, the bolt comprising:

- an elongate tube that has sufficient flexibility such that it can be bent in an arcuate manner;

- a plurality of wires arranged around the tube along a length thereof so as to define the

bolt.

As mentioned above, an elongate tube provides the bolt with an in-built grout feed tube. In addition, by providing the bolt with sufficient flexibility such that it can be bent in an arcuate manner, this can allow the bolt to be supplied as part of a longer feedstock and coiled or wound onto a reel. This can allow for eg. in-situ un-reeling (eg. from a bolting apparatus) and/or for custom specification of bolt length. It can also help facilitate insertion of the bolt into rough-formed and/or non-linear boreholes.

In a third aspect there is provided a bolt for use in reinforcing formations, the bolt comprising:

- an elongate polymeric tube;

- a plurality of wires arranged around the tube along a length thereof so as to define the bolt.

The provision of, specifically, a polymeric tube within the bolt again allows the bolt to have an in-built grout feed tube, and the use of a polymer can also provide the bolt with sufficient flexibility for coiling/winding onto a reel etc.

The bolt of the second and third aspects can be as defined as the bolt of the first aspect. However, in the bolt of the second and third aspects the helical spiral of the second wires can have the same lay direction as the helical spiral of the first wires. When a similar lay direction is provided in the layer of wires, the length of wire lay can be different in the adjacent layers to enhance the flexibility of the bolt. Also, the same lay direction of adjacent layers also helps when installing the bolt, as it can eliminate the incidence of "birdcaging" (eg. as a result of one layer (eg. the outer layer) spinning/slipping on the other and burgeoning out when torque is applied to the bolt). The bolt of the first to third aspects typically defines and is employed as a cable bolt for use in the reinforcing of formations such as rooves, ceilings, walls etc in mining and construction applications.

In a fourth aspect there is provided a method for forming a bolt that is as defined in the first to third aspects, the method comprising the steps of:

- feeding an elongate core into a rope-making machine; and

- operating the machine to arrange one or more layers, that each comprise a plurality of wires, around and along a length of the core to thereby define the bolt.

Such a method can produce continuous bolts in a continuous manner, whereby production efficiencies can be attained, as can the capacity to customise bolt sizing (especially length). Such a method can also produce long bolts for reels that can then be customised on site. Also, in the method of the fourth aspect, after a first layer is arranged around the core, the resulting bolt can re-fed through the rope-making machine to arrange each of one or more further layers around the first layer. Further, the machine can be configured in the method such that each successive layer can have its wires layed in an opposite lay direction to the immediately preceding layer. To enable the production of long (eg. endless) bolts in a continuous manner the elongate core can be flexible (and it may be defined by a tube) with the flexibility allowing the bolt to be directly wound onto a reel as it leaves the rope-making machine.

In a fifth aspect there is provided a method for forming a bolt that is as defined in the first to third aspects, the method comprising arranging on an elongate core one or more layers, that each comprise a plurality of wires, around and along a length of the core using a rope-making methodology, to thereby define the bolt.

By using a rope-making methodology a helical spiral configuration of each wire in the (or each) layer can be effected which again enhances the torque characteristics and strength of the resulting bolt.

Whilst usually a rope-making machine as per the fourth aspect will be employed to effect the rope-making methodology, it should be appreciated that other apparatus may be adapted to this effect.

The bolt of the first to third aspects also enables a number of bolt installation and system configurations to be achieved.

In this regard, in a fifth aspect there is provided a method for installing a bolt in a formation, the method comprising the steps of:

(i) fastening an end of the bolt in a hole that has been formed in the formation; (ii) applying tension to the bolt; and (iii) introducing a fastening medium into the hole to surround and fasten the tensioned bolt in the formation.

The pre-tensioning of step (ii) has been observed to assist in resisting strata movement earlier in the process of reinforcing a formation.

In one form in step (ii) the tension applied to the bolt can be a proportion of the bolt's capacity to be tensioned, for example, at around 30% of the bolt's rated capacity.

Li the method of the fifth aspect the fastening medium can comprise a grout that adhesively fastens the tensioned bolt in the formation. Further, in step (i) the bolt end can be fastened in the hole using a mechanical or adhesive fastener (eg. a chemical resin).

The bolt employed in the method of the fifth aspect can be as defined in the first to third aspects. When the bolt comprises a tubular core, step (iii) can involve introducing the fastening medium into the hole via the tubular core.

Further, in a sixth aspect there is provided a bolt system for use in supporting a formation. The system may comprise two or more flexible elongate bolts which, when positioned in the formation, can be configured to protrude. The protruding portions can be manoeuvred (eg. bent), whereby adjacent bolt sections can be fastened to each other, for example, fastened together using a coupling (such as a slide/sleeve coupling).

Brief Description of the Drawings

Notwithstanding any other forms which may fall within the scope of the bolt, methods and system as defined in the Summary, a number of specific bolt embodiments will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure IA shows a schematic cross-section through a stratum of rock in which a tunnel has been formed, with a roof in the tunnel being supported by a specific bolt system embodiment; Figure IB shows an enlarged detail of the cross-section of Figure IA;

Figure 2 shows a schematic cross-section through a stratum of rock in and to which another specific bolt has been introduced and fastened;

Figures 3 and 3 A show perspective and detail schematic views of a first bolt embodiment; and Figures 4 and 4A show perspective and detail schematic views of a second bolt embodiment.

Detailed Description of Specific Embodiments

Prior to describing bolt applications and bolt systems (eg. as described with reference to Figures 1 and 2), two different bolt embodiments will first be described in Figures 3 and 4, where like reference numerals are used in the drawings to indicate similar or like parts.

Bolt Configurations

Referring firstly to Figures 3 & 3 A, a bolt for use in reinforcing formations is shown in the form of a roof bolt 10. Roof bolt 10 comprises an elongate, flexible tube 12 at its core. The actual tube material is selected so as to provide the bolt with sufficient in-use flexibility for arcuate bending, in particular coiling and winding onto a reel, and to be of a long (endless) lengths of a roof bolt material. However, the tube material is also selected so as to withstand and support the winding therearound of one or more wire layers (ie. so as not to collapse in on itself). A flexible bolt is able to be supplied as part of a longer feedstock such that, when wound onto a reel, it can allow for on-site un-reeling (eg. from a bolting apparatus). The use of long flexible lengths can also help facilitate insertion of the bolt into rough- formed and/or non-linear boreholes. Also, supply from a longer feedstock can allow for custom specification of bolt length (eg. on-site). When the tube material is a metal, desirably a metal is selected that can provide the bolt with the flexibility characteristics for coiling and winding onto a reel. An optimal tube material has been found to be a mild steel pipe of a grade used in the automotive and refrigeration industries, comprising a single-walled, electric resistance welded tube. In one example, the tube had a diameter of 14.2 mm and a wall thickness of just 0.8 mm. Such a steel tube can be supplied in a coiled form (eg. of lengths up to

1000 m) and can be uncoiled, and wound onto a reel for feeding into a bolt formation stranding process. Such a steel tube can also have a thinner wall for a given diameter of pipe, compared to a polymer tube. This can allow for a greater volumetric flow of grout therethrough in use. When the tube material is a polymer desirably a material is selected that also provides the bolt with fire resistance and anti static properties, to enable the bolt to comply with the statutory mining regulations that exist in a number of countries (including Australia). For example, the polymer may comprise a polypropylene, a PTFE

(polytetrafluoroethylene), or a CPVC (Chlorinated polyvinyl chloride) plastic tube.

As mentioned, use of the tube 12 provides the bolt with an in-built grout feed tube, to enable resin grout to be fed directly through and via the bolt to exit the tube and anchor the bolt in a borehole in use (see Figure 2). The bolt 10 further comprises a first layer of wires 14 arranged around the tube

12 along the bulk of its length, so as to define an initial bolt configuration. Each wire is arranged to extend in a helical spiral around the tube 12 along its length, with typically each wire in the layer touching (or closely facing) an adjacent wire on either side along its length (ie. so as to effectively surround the tube). The helical spiral configuration contributes to the strength of the bolt, whilst the extension of the wires along the bolt length provides flexibility to the bolt.

Usually, a second similar layer of wires 16 is arranged around the first layer 14 along its length and so as to define a final bolt configuration (as shown). Again, each second layer wire is arranged to extend in a helical spiral around the first layer along its length but, in one optimal configuration, in an opposite lay direction to the helical spiral of the first wires (as shown). The second layer of wires can improve the torque characteristics and overall strength of the bolt, as can the opposite wire lay configuration.

In another configuration the helical spiral of the second wires can have the same lay direction as the helical spiral of the first wires. In this case, the length of wire lay can be different in the adjacent layers to further enhance the flexibility of the bolt. Also, the same lay direction of adjacent layers also helps when installing the bolt, as it can eliminate the incidence of "birdcaging" (eg. as a result of the second layer spinning/slipping on the first layer and burgeoning out when torque is applied to the bolt).

The depicted bolt configuration can also allow individual wire diameters to be optimised to provide for an increased overall bolt strength at a given bolt diameter (ie. without increasing bolt diameter).

It should be noted in Figures 3 and 3 A that the second layer 16 is shown as terminating prior to the first layer 14, but this is only to reveal the opposite spiral configuration of the first wire layer. In practice the first and second wire layers would be terminated at the same location.

Referring now to Figure 4 & 4A 5 a bolt for use in reinforcing formations is

shown in the form of a second roof bolt 20. Roof bolt 20 again comprises a flexible tube 12 at its core, and also comprises first and second wire layers 14, 16. However, bolt 20 further comprises a third similar layer of wires 22 that is arranged around the second layer 16 along its length to define a final bolt configuration (as shown). Again, in one optimal format each third layer wire is arranged to extend in a helical spiral around the second layer along its length, and in an opposite lay direction to the helical spiral of the second wires. The third wire layer can thus further improve the torque characteristics and overall strength of the bolt, as can the additional opposite wire lay configuration. In an alternative form all three layers can have the same direction, or just the inner two or the outer two. These different configurations can each impart difference performance characteristics to the bolt.

Again, it should be noted in Figures 4 and 4A that the second and third layers 16, 22 are shown as terminating prior to the first and second layers 14, 16 respectively. Again, this is only to reveal the opposite spiral configurations of the adjacent wire layers. In practice the first, second and third wire layers would be terminated at the same location.

Bolt Applications

The roof bolts 10 and 20 are each referred to as a "cable bolt". Cable bolts are typically employed in the reinforcing of formations such as rooves, ceilings, walls etc in mining and construction applications, usually in secondary reinforcing applications, to complement the primary reinforcing performed by rod- or tube-type roof bolts.

With known cable bolts, to grout a borehole a separate tube must be attached to the outside of a strand of the bolt and fed into the borehole with the strand. This is very inefficient from a drilling perspective as a quite large hole has to be drilled and grouted to support the strand. The bolts 10 and 20 each overcome this problem in that the grout tube 12 is located within the confines and forms part of the bolt itself.

In this regard, and referring now to Figure 2, one such fully formed roof bolt 50 (which can be formed using either one of roof bolts 10 or 20 as its basis) is shown positioned in a borehole B drilled into rock stratum S. It will be seen how the tube 12 protrudes slightly from both the proximal and distal ends of the bolt to enable a resin- based grout to be easily introduced into the tube, and to be released from the tube distal end and into the borehole adjacent to the bolt. When this grout cures it anchors the bolt

in the bolthole.

In one mode of installation, the upper end of the bolt 50 was fastened in the borehole B using a mechanical fastener (eg. split cone or anchor) or an adhesive fastener (eg. a chemical resin capsule). Tension was then applied to the bolt at a proportion of the bolt's capacity to be tensioned (eg. typically at around 30% of the bolt's rated capacity). A bolt fastening grout was then fed into the hole, being pumped up through the tube 12, to surround and fasten the tensioned bolt in the borehole. This mode of installation (ie. pre-tensioning of the bolt prior to grouting) was observed to assist in resisting strata movement early (ie. during the early stages of reinforcing and prior to the subsidence of the rock stratum S).

The bolt 50 includes an externally threaded section 52 fastened (typically by swaging) to the proximal end of the cable portion 54 of the bolt. The threaded section 52 protrudes beyond the borehole as shown to enable a retaining plate 56 to be coupled thereto. In this regard, the borehole B is widened at W adjacent to its entry to accommodate therein a collar 58 that carries the plate 56. The collar is screw-mounted onto the threaded section 52, until the plate 56 engages against the roof surface S adjacent to the borehole, thereby causing an annular gasket 60 to seal against the roof surface S. The plate is locked in position by a locking nut 62 that is also screw-mounted onto the threaded section 52.

Bolt Support System

The flexibility of the roof bolts 10 and 20 also enables a number of bolt support system configurations to be achieved in mining and construction applications. In this regard, and referring now to Figures IA & IB, a bolt system 100 for use in supporting a formation in the form of the roof R of a tunnel T in a rock stratum S is depicted, hi its simplest form the system is shown and described as employing two flexible elongate bolts 102, 104 (which again can each be formed using any one of roof bolts 10 or 20 as its basis). However, multiple bolts and bolt connectors may be employed depending on the application.

As shown, each bolt 102, 104 extends into a respective borehole B where it can be secured by a resin-based grout (as mentioned above). Each bolt is sized (eg. cut to size on site) so that a respective protruding portion 106 or 106' extends out from the

borehole. Due to the flexibility of the bolt the protruding portion can be manoeuvred such that adjacent sections can be located next to and be fastened to each other (as best shown in the detail of Figure IA). The adjacent sections are fastened to each other using a sleeve coupling 108 (which may additionally be bonded/fastened to the adjacent sections by the resin-based grout, or by welding, crimping etc).

The resultant joined bolts 102. 104 combine to provide a type of beam that underlies and thus supports an overlying part of the roof R. When a matrix of multiple bolts are so employed a supporting "net"-type structure can rapidly and economically be defined.

Bolt Formation

To form each of the bolts 10 and 20, a rope-making methodology was employed that generally comprised successively arranging on the core 12 the one or more wire layers 14, 16, 22 to thereby define the bolt. This methodology was best facilitated by feeding the core 12 into a rope-making machine, and then operating the machine to arrange the one or more wire layers around and along the length of the core to thereby define the bolt.

More specifically, after the first wire layer 14 was arranged around the core 12 the strand was passed into another stranding (rope-making) machine that was operated in the opposite direction, so that the second layer 16 was arranged in an opposite lay direction over the first layer. In this regard, wire spools in the machines were configured to achieve the opposite wire-lay direction.

In the case of bolt 20 the two-layered bolt was again re-fed through the rope- making machine to arrange the third wire layer 22 around the second layer, hi this regard, the wire spools were configured to achieve an opposite wire-lay direction to the second layer.

These methods were able to continuously produce the bolts, whereby production efficiencies were attained, together with the capacity to customise bolt sizing (especially length). The final bolts were able to be directly wound onto reels that can then be used on site (ie. loaded onto a bolting apparatus).

Examples

Non-limiting Examples that relate to specific cable bolts produced in

accordance with the method disclosed herein will now be provided.

Example 1 - Manufacture of a Cable Bolt

A cable bolt as per Figures 2 to 4 was produced on a multi cage rope-making machine having two separate cages which each held a respective bobbin of wire. Each bobbin was loaded with a drawn high tensile 1770 MPa grade bright steel wire having a smooth external surface (ie. no ribs or deformation made on the surface of the wire during drawing).

A flexible tube of steel or plastic was fed through the centre of the machine from a payoff stand. The cages were then successively rotated in opposite directions for each wire layer, laying up the wire in one direction over the tube then in the other direction over the first layer, and so on. A plastic tube was selected that had fire resistant and anti static properties to comply with statutory requirements of mining cable bolt usage. The machine produced a 500m (3Tonne) cable bolt reel comprising wire of 1 x

29 strand (17 outer strands/12 inner strands/1 tube core). To make customised use of the reeled bolt, the wire was subjected to a preforming step in which the desired helix was preformed in the wire before it was laid over the tube or the wire layer below. This reduced the load on the layer below at the forming point and minimised any residual stress in the finished strand. The finished strand was then post-formed through a series of offset rollers to remove any remaining stress in the product. The product was then straightened and cut into lengths by an automatic cut-off saw (but so as not to result in stress relief). Standard bolt lengths of 4.1m, 6.1m, 8.1m were produced.

The resultant bolt ends could optionally be ground to a smooth finish, and a 12mm square was welded on to one end of each strand. One such two-layered bolt had

17 second layer wires laid over 12 first layer wires, inturn laid over the tube core. Wire tensile force was observed to be in an acceptable range (ie. comparable to cable bolt product currently available).

A number of tube core alternatives were also investigated to produce a bolt that was durable, was able to be reeled and loaded on take up, and that did not crush when wire was laid over it. In the case of a plastic core tube, it was surmised that drawn poly tube would not be viable so extruded poly tube was employed.

A theoretical cable breaking load of 1010 kN was predicted. The breaking load and top feeding were identified as the key product elements. In one trial a bolt having a steel core tube, with 14 inner wires and 17 oppositely laid outer wires was produced that had a 634kN capacity. Because the bolt was continuously made on a ropemaking machine it was able to be made in continuous (un-ending) lengths. Existing cable bolts such as the Megabolt are made in discrete lengths, whereas the present bolt was able to be produced into a bulk reel of eg. 1000 - 2000 m of bolt product, which could subsequently be cut to length as required.

Example 2 - Installation of the Cable Bolt

In an installation procedure the following steps occurred:

• Clearance holes were drilled up into rock strata.

• An upper end of the bolt was then mechanically or chemically fastened in the borehole.

Tension was applied to the bolt using a tensioner unit, to a level that was around 30% of the bolt's capacity (ie. in the case of a 634kN capacity, a tension force of around 19OkN was applied to the bolt to pre-tension it).

• A resin-based grout was then bottom fed up through the central tube hole, to exit the tube distal end and flow down and around the bolt, and was provided with sufficient time to set/cure.

As necessary, the tensioner unit was then re-activated to the bolt strand and further tension was applied.

The length of bolt was able to be varied on site, depending upon the composition of the rock strata to be supported.

The bolts were typically used in a secondary support role (ie. to be used in conjunction with primary support (standard rod) roof bolts made from solid rod. The bolts were used to provide extra reinforcing where underground crossovers, or access areas to longwall, required a permanent structure.

Bolt Benefits

The observed benefits of a multi-layer bolt construction were greater flexibility, higher breaking force for a given diameter and better torque balance. These and other benefits can be more fully expressed as: - much lower torque values when tensioned, as the bolt can be made from two or more oppositely laid layers;

- much more efficient drilling and grouting as the grout tube was internal and didn't require an external grout tube;

- more reliable grouting as the grout tube was protected during insertion into the hole; - better torque characteristics due to oppositely laid layers;

- better strength for a given diameter due to a greater steel density achieved in the bolt configurations;

- greater length availability due to the continuous nature of the cable bolt product;

- greater flexibility due to the multi-layer construction and the employment of smaller wire sizes;

- when same lay was employed with adjacent wire layers, the avoidance of "birdcaging" when torque was applied to the bolt.

Whilst a number of embodiments of the cable bolt, method of forming and installation, and a bolt system have been described, it will be appreciated that these can be embodied in many other forms. For example, in potential cable bolt variations the core may be defined by an elongate rigid tube (eg. of metal), or may simply comprise a space defined by the plurality of first wires in a resultant formed bolt. The core may in some forms (eg. with the opposite lay directions of adjacent layers) comprise a king wire. In the claims which follow and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments.




 
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