WO2008154683A1

WO2008154683A1 - Rock bolt tendon tensioning

Info

Publication number: WO2008154683A1
Application number: PCT/AU2008/000882
Authority: WO
Inventors: David James Fergusson
Original assignee: Industrial Roll Formers Pty Limited
Priority date: 2007-06-21
Filing date: 2008-06-19
Publication date: 2008-12-24

Abstract

A rock bolt tendon tensioning device comprising a hollow trumpet tube having one end flared and an externally threaded cylindrical portion. A nut is carried by the threaded portion and is engageable with a washer like pressure plate through an aperture of which the threaded portion can pass. The device also comprises a tendon clamp shaped to grasp the tendon and mate with the flared end.

Description

ROCK BOLT TENDON TENSLQNDs[G

Field of the Invention

The present invention relates to rock bolts and, in particular, to the tensioning of the tendons of rook bolts. Such tendons can be either cables or solid rods.

Background Art

At present rock bolts having cable tendons, in particular, are tensioned by means of a hydraulic cable jack which is a specialised and expensive piece of equipment. Such a jack is also heavy and difficult to use, particularly in those instances where the cable bolts ate placed in an overhead position.

Genesis of the Invention

The genesis of the present invention is a desire to provide a means whereby rock bolt tendons can be tensioned without the use of expensive and heavy hydraulic cable jacks.

Summary of the Invention

According to a first aspect of the present invention there is disclosed a rock bolt tendon tensioning device comprising a hollow trumpet tube having one end flared and an externally threaded cylindrical portion, a nut carried by said threaded portion and engageable with a Washer like pressure plate through an aperture of which said threaded, portion can pass, and a tendon clamp shaped to grasp said threaded tendon and mate with said flared end.

According to a second aspect of the present invention there is disclosed a method of tensioning a rock bolt having a tendon with an anchor at one end and the tensioning device as defined above at the other end, said method comprising the steps of: (t) inserting said tendon one end into a blind hole drilled in a rock or mineral face, (Ii) if necessary activating said anchor to secure same to the interior of said hole adjacent said anchor, (iii) clamping said tendon clamp onto said tendon and adjacent said flared end, and (iv) rotating said nut relative to said tube to simultaneously drive said flared end against said tendon clanip and drive said pressure plate into abutment with said rock or mineral face to thereby tension said tendon.

In accordance with a third aspect of the present invention there is disclosed a method of tensioning a rock bolt having a tendon with a leading end and the tensioning device as defined above at the other end, said method comprising the steps of: (i) inserting said tendon leading end into a blind hole drilled in a rock or mineral face, (ϋ) chemically anchoring said tendon in said hole to secure same to the interior of said hole,

(iii) clamping said tendon clamp onto said tendon and adjacent said flared end, and (vL) after the chemical anchor has set, rotating said nut relative to said tube to simultaneously drive said flared end against said tendon clamp and drive said pressure plate into abutment with said rock or mineral face to thereby tension said tendon.

In accordance with a fourth aspect of the present invention there is disclosed an arresting device for use in dynamic seismic shock events, said device comprising a rock bolt having a tendon having its leading end anchored ^"within a blind hole drilled in a rock or mineral face and having a tensioning device as defined above at its trailing end, wherein a seismic shock is indicated by deformation of said trumpet tube.

In accordance with the fifth aspect of the present invention there is disclosed a tensioning device for rock bolt tendons having a threaded trailing end, said device comprising a hollow tube having an externally threaded cylindrical portion, a first nut carried by said threaded portion and engageable with a washer like pressure plate through an aperture of which said threaded portion can pass, and a second nut threadably engaged with said tendon trailing end and abutting said tube,

In accordance with the sixth aspect of the present invention there is disclosed a method of tensioning a rock bolt having a tendon with an anchor at one end and the tensioning device as defined in the preceding paragraph at the other end, said method comprising the steps of: (i) inserting said tendon one end into a blind hole drilled in a rock or mineral face, (ϋ) if necessary activating said anchor to secure same to the interior of said hole adjacent said anchor, (iii) tightening said second nut to abut same against said tube, and

(iv) rotating said first nut relative to said tube to simultaneously drive said tube against said second nut and drive said pressure plate into abutment with said rock or mineral face to thereby tension said tendon.

In accordance with the seventh aspect of the present invention there is disclosed a method of tensioning a rock bolt having a tendon with a leading end and the tensioning device as defined in the fifth aspect at the other end, said method comprising of steps of:

(i) inserting said tendon leading end into a blind hole drilled in a rock or mineral face,

(ϋ) , chemically anchoring said tendon in said hole to secure same to the interior of said hole,

(iii) tightening said second nut to abut same against said tube, and (iv) after the chemical anchor has set, rotating said first nut relative to said tube to simultaneously drive said tube against said second nut and drive said pressure plate into abutment with said rock or mineral face to thereby tension said tendon.

In accordance with the eighth aspect of the present invention there is disclosed an arresting device for use in dynamic seismic shock events, said device comprising a rock bolt having a tendon having its leading end anchored within a blind hole drilled in a rock or mineral face and having a tensioning device as defined in the fifth aspect at its trailing end, wherein a dynamic seismic shock is indicated by deformation of said tube.

Brief Pes oritition of the Drawings

Two preferred embodiments of the present invention will now be described, by any of example only, with reference to the drawings in which: Fig. 1 is a side elevation of the trailing end of a first embodiment of a rock bolt having a cable tendon and carrying a tensioning device of the first preferred embodiment,

Fig. 2 is a longitudinal cross-section through the trailing end of the cable bolt of Fig. 1 but showing the bolt in the installed condition,

Fig. 3 is a view similar to that of Fig. 2 but of that of a bolt of a second preferred embodiment, and

Fig. 4 shows the bolt of Fig. 3 after plastic deformation,

Detailed Description

As seen in Figs. 1 and 2, a rock bolt 1 has a tendon 2 which in this instance takes the form of a braided steel cable but could equally be a solid rod. A hollow trumpet tube 4 has a flared trailing end 5 and a tubular portion 6 which has an external thread 7. The externally threaded portion 7 carries a conventional nut 8 and an apertured washer like pressure plate 9.

At the trailing end 12 of the tendon 2 there is located a cable clamp 13 which preferably takes the form of a longitudinally split sleeve having an external frusto- conical surface 14 and a rubber keeper ring 15 to maintain together its three portions.

As seen in Fig. 2_» the rock bolt 1 is installed in a blind hole 17 drilled in a iock or mineral face 18. The leading end (not illustrated) of the tendon 2 is anchored at the far end of the blind hole 17. It will be seen that with the cable clamp 13 installed on the tendon 12, rotating the nut 8 so as to drive it towards the pressure plate 9, simultaneously drives the flared end 5 into abutment against the cable clamp 13 and drives the pressure plate 9 into abutment against the rock face 18, thereby tensioning the tendon 2.

The above described device has a number of uses. The first use is as a substitute for a hydraulic cable jack for the tensioning of rock bolts having cable tendons. It will be , appreciated by those skilled in the art that the device can be tensioned merely by means of a spanner and that, if desired, a tube and a hammer can be used to drive the cable clamp 13 along the tendon 2 so as to engage the cable clamp 13 and the flared end of the "trumpet tube 4. This anchors the trumpet tube 4 relative to the tendon 2 and enables the nut 8 to be tightened in. order to place the tendon 2 into tension.

Where the leading end (not illustrated) of the tendon 2 carries a conventional mechanical anchor, then this anchor can be secured adjacent the uphole end of the blind hole 17 and the nut 8 rotated so as to tension the tendon 2. This tension can be either a pre-tension or a post-tension in terms of grouting. Typically the annular space between the tendon 2 and the blind hole 17 is filled with grout. There are various methods of applying the grout one of which uses a breather tube which extends to the uphole end of the blind hole so as to enable air within the blind hole to escape from the hole via the breather tube as the grout is progressively introduced into the blind hole 17 from adjacent the rock face 18.

In an alternative installation procedure, a length of cable which is to form the tendon 2 is fed into the blind hole 17 and retained in place by the use of a wire retaining device commonly known as a "fish hook". The tendon 2 is then grouted utilising grout, a breather tube, and a soft wadding or soft rubber material to plug the open end of the blind hole 17. Once the grout has cured, the pressure plate 9, trumpet tube 4 with its nut S, and the cable clamp 13 are slid over the trailing end 12 of the tendon 2 until the nut 8 is in contact with the pressure plate 9. The cable clamp 13 is then tapped into position to engage the flared end 5. The nut 8 is then rotated so as to drive the pressure plate 9 against the rock face 18 and thereby obtained the desired degree of tension within the tendon 2.

The two major operational advantages achieved by the above described arrangement are that, firstly, the rock bolt 1 can be pre-tensioned or post-tensioned in relation to the grouting process without the use of the conventional hydraulic cable jack. Thus the use of this specialised, expensive and heavy piece of equipment is completely avoided. Secondly a spanner for the nut 8 is essentially the only tool required for the installation. A piece of tube which is passed over the trailing end 12 in order to drive the cable clamp 13 into the flared end 5, and a hammer to drive the tube, are preferable, but optional pieces of additional equipment. In addition the abovernentioned arrangement can also be used as an arresting device for a dynamic event such as seismic shock loading.

^"When the rock or mineral of Fig. 2 is subjected to a seismic load, the mass of rock or mineral to be ejected is thrown or urged towards the excavated portion of the tunnel, which is to the left as seen in Fig. 2. This mass because of its velocity has considerable energy. This energy can be absorbed by the plastic deformation of the trumpet tube 4 and, in particular, the threaded portion 6 thereof to the left of the nut 8 as seen in Fig.2. Thus the tubular portion 6 is said to undergo a column collapse which results in the threads 7 to the left of the nut 8 as seen in Fig. 2 being crushed together in concertina fashion. This compression of the column formed by the trumpet tube 4 provides a visual indication of the event loading on the fixture and yet maintains a full loading capacity after the event. This is because the plastically deformed tube 4 has not let go of the tendon 2, even though it will have moved to the left as seen in Fig. 2. That is, the distance between the cable clamp 13 and the nut 8 will have been significantly shortened by the seismic event. It will be appreciated that the plastic deformation of the tube in response can be controlled by selection, of material thicknesses or chemistry, for example.

Turning now to Figs. 3 and 4, a second eiribodiment is illustrated in the form of a rock bolt 21 having a solid tendon 22. An externally threaded tube 24 is slid over the trailing end 32 of the tendon 22. The nut 8, pressure plate 9, hole 17 and rock face 18 are as before, However, the trailing end 32 of the tendon 22 is externally threaded and carries a second nut 39.

During the initial installation, after securing the leading end of the tendon, the second nut 39 is tightened to prevent the tube 4 moving to the left as seen in Fig. 3. Also the nut 8 is tightened to drive the pressure plate 9 into abutment with the rock face 18 and tension the tendon 22.

If now the rock or mineral body is subjected to a seismic shock, the portion 27 of the tube 24 immediately to the left of the nut 8 plastically yields as indicated in Fig. 4. This reduces the distance between the nut 8 and the second nut 39 but allows the tendon 22 to stretch without breaking, thereby absorbing the seismic energy. As with the first preferred embodiment, this provides a visual indication of the event loading on the tensioning device fixture and maintains a full loading capacity after an event

The foregoing describes only two preferred embodiments of the present invention and modifications, obvious to those skilled in the art, can be made thereto without departing from the scope of the present invention. For example, the tendon 2 can be a cable, a solid rod or even a hollow tubular rod.

The term "comprising" (and its grammatical variations) as used herein is used in the inclusive sense of "including" or "having" and not in the exclusive sense of "consisting only of.

Claims

1. A rock bolt tendon tensioning device comprising a hollow trumpet tube having one end flared and an externally threaded cylindrical portion, a nut carried by said threaded portion and engageable with a washer like pressure plate through an aperture of which said threaded portion can pass, and a tendon clamp shaped to grasp said threaded tendon and mate with said flared end.

2. The device according to claim 1 wherein said tendon clamp is substantially frusto-conical.

3. The device according to claim 1 or 2 wherein said clamp is a longitudinally split conical wedge.

4. The device according to any one of claims 1 to 3 wherein said tendon is a cable.

5. The device according to any one of claims 1 to 3 wherein said tendon is a solid rod.

6. A method of tensioning a rock bolt having a tendon with an anchor at one end and the tensioning device according to any one of claims 1 to 5 at the other end, said method comprising the steps of:

(i) inserting said tendon one end into a blind hole drilled in a rock or mineral face, (ii) if necessary activating said anchor to secure same to the interior αf said hole adjacent said anchor, (iii) clamping said tendon clamp onto said tendon and adjacent said flared end, and (iv) rotating said nut relative to said tube to simultaneously drive said flared end against said tendon clamp and drive said pressure plate into abutment with said rock or mineral face to thereby tension said tendon.

7. The method according to claim 6 including die further step of:

(v) re-tensioning said tendon by carrying out step (iv) on at least one later occasion,

8. A method of tensioning a rock bolt having a tendon with a leading end and the tensioning device according to any one of claims 1 to 5 at the other end, said method comprising the steps of : (i) inserting said tendon leading end into a blind hole drilled in a rock or mineral face, (ii) chemically anchoring said tendon in said hole to secure same to the interior of said hole, (iii) clamping said tendon clamp onto said tendon and adjacent said flared end, and (iv) after the chemical anchor has set, rotating said nut relative to said tube to simultaneously drive said flared end against said tendon clamp and drive said pressure plate into abutment with said rock or mineral face to thereby tension said tendon.

9. An arresting device for use in dynamic seismic shock events, said device comprising a rock bolt having a tendon having its leading end anchored within a blind hole drilled in a rock or mineral face and having a tensioning device according to any one of claims 1 to 5 at its trailing end, wherein a seismic shock is indicated by deformation of said trumpet tube.

10. The device according to claim 9 wherein said trumpet tube has undergone a column compression.

11. A tensioning device for rock bolt tendons having a threaded trailing end, said device comprising a hollow tube having an externally threaded cylindrical portion, a first nut carried by said threaded portion and engageable with a washer like pressure plate through an aperture of which said threaded portion can pass, and a second nutthreadably engaged, with said tendon trailing end and abutting said tube.

12. The device according to claim 11 wherein said tendon is a solid rod.

13. A method of tensioning a rock bolt having a tendon with an anchor at one end and the tensioning device according to claim 1 1 or 12 at the other end, said method comprising the steps of:

(i) inserting said tendon one end into a blind hole drilled in a rock or mineral face, (ii) if necessary activating said anchor to secure same to the interior of said hole adjacent said anchor, (iii) tightening said second nut to abut same against said tube, and (iv) rotating said first nut relative to said tube to simultaneously drive said tube against said second nut and drive said pressure plate into abutment with said rock or mineral face to thereby tension, said tendon.

14. The method according to claim 13 including the further step of:

(v) re-tensioning said tendon by carrying out step (iv) on at least one later occasion.

15. A method of tensioning a rock bolt having a tendon with a leading end and the tensioning device according to claim 1 or 2 at the other end, said method comprising of steps of:

(i) inserting said tendon leading end into a blind hole drilled in a rock or mineral face, (ii) chemically anchoring said tendon in said hole to secure same to the interior of said hole,

16. An arresting device for use in dynamic seismic shock events, said device comprising a rock bolt having a tendon having its leading end anchored within a blind hole drilled in a rock or mineral face and having a tensioning device according to claim 11 or 12 at its trailing end, wherein a dynamic seismic shock is indicated by deformation of said tube.

17. The device according to claim 9 wherein said tube has undergone a column compression.