AU779374B2 - A rock bolt apparatus - Google Patents

Description

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT (Original) APPLICATION NO:

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COMPLETE SPECIFICATION LODGED:

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RELATED ART: NAME OF APPLICANT: ACTUAL INVENTOR: ADDRESS FOR SERVICE: GARFORD PTY LTD NEVILLE ALLAN HEDRICK LORD COMPANY Patent Trade Mark Attorneys 4 Douro Place West Perth, Western Australia, 6005

AUSTRALIA.

"A ROCK BOLT APPARATUS" INVENTION TITLE: DETAILS OF ASSOCIATED PROVISIONAL APPLICATION NO'S: Australian Provisional Application No PQ6874 filed on April 14, 2000 Australian Provisional Application No. PR1528 filed on November 16, 2000 The following Statement is a full description of this invention including the best method of performing it known to me/us: The present invention relates to a Rock Bolt Apparatus.

Seismic disturbances in underground mines are very common, and the forces involved in these disturbances can cause underground tunnels to collapse. This presents a major concern for miners' safety. In order to alleviate this problem, rock bolts are secured into holes drilled through tunnel walls of the mine to help maintain the structural integrity of the tunnel walls.

It is desirable for such rock bolts to yield, or to fail progressively rather than catastrophically. Such yielding behaviour can be monitored by miners, and thus warning of possible collapse can be given well in advance.

Rock bolts are commonly held in place by means of grout. Such grout can fail when S* subjected to a shearing force by the action of known rock bolts.

The present invention attempts, among other things, to overcome at least in part some ooooe of the aforementioned disadvantages of previous rock bolts.

15 In accordance with one aspect of the present invention there is provided a rock bolt apparatus including a rock bolt cable and an anchoring mechanism, the anchoring mechanism comprising a tubular portion and a wedge means, the tubular portion having a first end and a second end, the anchoring means being arranged such that the application of force to the rock bolt cable causes the wedge means to pass at least partially through the tubular portion in a direction towards the second end, wherein the anchoring mechanism includes a frusto-conical portion adjacent the second end of the tubular portion, the frusto-conical portion having a tapered surface arranged to distribute longitudinal forces over a relatively wide area.

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a rock bolt apparatus in accordance with the present invention, and Figure 2 is a diagrammatic cross sectional view of the rock bolt apparatus of Figure 1.

Referring to the Figures, there is shown a rock bolt apparatus 10, comprising a rock bolt cable 12 and a first anchoring mechanism 13.

An outer sheath 15 constructed of a suitable material, for instance plastics material, i 10 surrounds a substantial portion of the rock bolt cable 12.

The first anchoring mechanism 13 includes a tubular portion in the form of an elongate substantially cylindrical tube 14 fitted over the rock bolt cable 12. The tube oooo• 14 includes a first end 16 adjacent a first end 17 of the cable 12 and a second end 18 remote from the first end 17 of the cable 12.

o 15 The tube 14 has an inwardly facing first surface 20 which locates, in use, adjacent the rock bolt cable 12, and an outwardly facing second surface 22.

The tube 14 has a generally constant external diameter, with the second surface 22 being substantially parallel to the rock bolt cable 12.

The inwardly facing first surface 20 has a first portion 32 which extends from the first end 16 of the tube 14 to a first location 28 along the tube 14. The first portion 32 tapers from a first diameter at the end 16 of the tube 14 towards a second, smaller diameter at the first location 28 so as to define a gap of generally frusto-conical shape between the first location 28 and the first end 16.

The inwardly facing first surface 20 has a second portion 31 which extends from the first location 28 to a second location 21 adjacent the second end 18 of the tube 14.

The second portion 31 may taper slightly from the second diameter at the first location 28 to a third, smaller diameter at the second location 21, so defining a gap of generally frusto-conical shape between the first location 28 and the second location 21. The third diameter at the second location 21 is approximately equal to the external diameter of the outer sheath The inwardly facing first surface 20 has a third portion 35 which extends from the second end 18 of the tube 14 to the second location 21. The third portion 35 is substantially cylindrical in shape, and defines a cylindrical recess 37 with a diameter similar to that of the first portion 32 at the first end 16.

The first anchoring mechanism 13 further includes a frusto-conical portion extending from the second end 18 of the tube 14 in a direction away from the first end 17 of the cable 12. The external diameter of the frusto-conical portion 40 tapers from a diameter similar to that of the tube 14 adjacent the tube 14 to a diameter slightly S-larger than that of the outer sheath 15 at an end remote from the tube 14. Thus, the frusto-conical portion has a tapered outer surface 41 which is laterally curved. The frusto-conical portion 40 also includes a projection 42 extending axially from an end of the frusto-conical portion 40 adjacent the tube 14. The projection 42 has an external diameter equal to the internal diameter of the third portion 35 of the tube 14, and the projection 42 is arranged to locate, in use, within the recess 37.

The internal diameter of the frusto-conical portion 40 is substantially identical to the external diameter of the outer sheath Wedge means in the form of a wedge member 26 are secured by any suitable fixing means to the rock bolt cable 12 adjacent the first end 17 of the cable 12. The wedge member 26 is of appropriate size and shape to fit snugly in the gap defined by the first portion 32 of the inwardly facing first surface 20. In this embodiment the wedge member 26 is formed of a plurality of wedge shaped members held about the cable 12 by a resilient band 33 and together forming wedge means of appropriate size and shape to fit snugly in the gap. In an alternative embodiment the wedge means may be formed from a single, frusto-conically shaped member.

S 10 A further outer resilient sheath 36 constructed of suitable material, for instance soft plastics material, forms part of the tube 14 and extends over the outwardly facing second surface 22 from the first end 16 of the tube to the second end 18.

.os..i A securing means 42 is attached at the first end 17 of the rock bolt cable 12. The securing means 42 includes two strands 43 extending outwardly of the first anchoring 15 means 13.

A second anchoring means 44 is provided at a second end 19 of the rock bolt cable 12. The second anchoring means comprises a base portion 46 and wedge means 48.

The base portion 46 is substantially externally cylindrical, and includes a frustoconical shaped internal surface 50 arranged about the rock bolt cable 12. The internal surface 50 tapers from a diameter approximately equal to that of the rock bolt cable 2 at an end remote from the second end 19 of the rock bolt cable to a greater diameter at an end adjacent the second end 19 of the rock bolt cable 12.

The wedge means 48 is arranged in a similar fashion to the wedge means 33, and is arranged to fit snugly into the gap defined by the internal surface 50 and the rock bolt cable 12.

The outer sheath 15 extends along the rock bolt cable 12 from a first end within the frusto-conical portion 40 to a second end adjacent the second anchoring means 44.

In use, the rock bolt apparatus 10 is inserted into a hole drilled in a rock face with the first end 17 oriented towards the far end of the hole. The strands 43 of the securing .o S 10 means 42 engage the side walls of the hole, and allow the rock bolt apparatus 10 to be held in position. The hole is then filled with grout, which is allowed to cure and solidify. The second anchoring means 44 is located adjacent the near end of the hole, preferably on the outside ofa plate arranged over the hole.

In the event of a seismic disturbance, where a force is experienced by the rock bolt cable 12 in a direction away from the first end 17, the wedge member 26 will be caused to move toward the second end 18 of the tube 14. The force acting through the rock bolt cable 12 will be absorbed by radial expansion of the tube 14 as the wedge member 26 acts against the inwardly facing surface 20. The force absorbed by the tube 14 will be in turn transmitted to the outer sheath 36, which will compress against the grout surrounding it.

In this manner the wedge member 26 will progress along the tube 14, deforming the tube 14 as it passes within until it reaches the second end 18 of the tube. The wedge member 26 will then be forced against the frusto-conical portion During the movement of the wedge member 26 through the tube 14, longitudinal forces acting on the first anchoring mechanism 13 will be distributed over the tapered outer surface 41 of the frusto-conical portion 40, due to the lack of potential stress concentrations along the interface between the frusto-conical portion and the grout.

It will be appreciated that the invention could be performed with the first anchoring means 13 positioned at the near end of the hole, and the second anchoring means 44 at the far end.

Modifications and variations as would be apparent to a skilled addressee are deemed S: to be within the scope of the present invention.

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Claims (12)

1. A rock bolt apparatus including a rock bolt cable and an anchoring mechanism, the anchoring mechanism comprising a tubular portion and a wedge means, the tubular portion having a first end and a second end, the anchoring mechanism being arranged such that the application of force to the rock bolt cable causes the wedge means to pass at least partially through the tubular portion in a direction towards the second end, wherein the anchoring mechanism includes a frusto-conical portion adjacent the second end of the tubular portion, the frusto- conical portion having a tapered surface across which longitudinal forces are distributed.

2. A rock bolt apparatus as claimed in Claim 1, wherein the frusto-conical portion has an outer diameter at an end adjacent the tubular portion which is substantially the same as an outer diameter of the tubular portion.

3. A rock bolt apparatus as claimed in Claim 2, wherein the tubular portion includes a recess at the second end, and the frusto-conical portion includes a projection, the projection being arranged to locate, in use, within the recess.

4. A rock bolt apparatus as claimed in any one of the preceding claims, wherein *the frusto-conical portion has a tapered outer surface.

A rock bolt apparatus as claimed in any one of the preceding claims, wherein the tubular portion has an inner surface having a first portion and a second portion, the first portion being substantially frusto-conical in shape and extending inwardly from the first end of the tubular portion.

6. A rock bolt apparatus as claimed in Claim 5, wherein the second portion of the inner surface is also substantially frusto-conical in shape, wherein the larger part of the frusto-conical shape is directed towards the first end of the tubular portion.

7. A rock bolt apparatus as claimed in Claim 5 or 6, wherein the wedge means comprises a plurality of wedge shaped members, the wedge shaped members being arranged to locate, in use, within the first portion of the inner surface of the tubular portion.

8. A rock bolt apparatus as claimed in Claim 5 or 6, wherein the wedge means 0. O°, S: comprises a single substantially frusto-conical shaped member, the frusto-conical 10 shaped member being arranged to locate, in use, within the first portion of the inner surface of the tubular portion.

9. A rock bolt apparatus as claimed in any one of the preceding claims, wherein the anchoring means includes a resilient sheath surrounding the tubular portion. A rock bolt apparatus as claimed in any one of the preceding claims, wherein the rock bolt cable is at least partially covered by an outer sheath.

So°

11 A rock bolt apparatus as claimed in any one of the preceding claims, wherein the rock bolt apparatus includes a further anchoring mechanism, the further anchoring mechanism disposed on the rock bolt cable remote from the first anchoring mechanism

12. A rock bolt apparatus as hereinbefore described with reference to the accompanying drawings. DATED THIS 12 TH DAY OF APRIL 2001 GARFORD PTY LTD By their Patent Attorneys LORD COMPANY io PERTH, WESTERN AUSTRALIA