WO2003058033A1

WO2003058033A1 - A rock bolt

Info

Publication number: WO2003058033A1
Application number: PCT/AU2003/000026
Authority: WO
Inventors: Jeffery Robert Fergusson
Original assignee: Jeffery Robert Fergusson
Priority date: 2002-01-11
Filing date: 2003-01-10
Publication date: 2003-07-17
Also published as: AUPR994002A0

Abstract

The present invention discloses a rock bolt (1) and a method of using a rock bolt to support services within a mine. The rock bolt has a hollow tubular shaft (2) which is closed at its leading end (3) but open at its trailing end where a hollow drive nut (6) is secured. A treaded shank (10) of a support member (11) is able to engage the nut. Services (25) such as air supply ducts, electric cables etc can be supported from the roof or wall of a mine by the support members (11).

Description

A ROCK BOLT

FIELD OF INVENTION

The present invention relates to mining and, in particular, to a rock bolt which finds particular application in the provision of services within mines.

BACKGROUND ART

Various types of rock bolts are known and different bolts find different application in different types of mining, for example hard rock metalliferous mining or coal mining. Australian Patent No. 712,346 (to which US Patent No. 5,123,456 corresponds) describes a type of rock bolt which has found commercial acceptance in hard rock mining under the registered trade mark JUMBOLT. Essentially that specification describes a rock bolt with a hollow tubular shaft which is closed at its leading end and has a castellated drive ring welded or otherwise secured to its trailing end. The shaft of the bolt needs to be hollow in order that the bolt be light weight and of low material cost. The leading end of the bolt needs to be closed in order to prevent resin or grout used to cement the shaft of the bolt into the hole into which the bolt is placed, from entering the interior of the bolt. The tip of the bolt is normally provided with deformations or some other device which enables the tip of the bolt to act as an impeller which mixes the resin or grout constituents.

The above mentioned specification discloses the concept of rolling the wall of the shaft so as to simultaneously create keying deformations on the exterior of the shaft and an interior thread within the shaft which is able to accept threaded fasteners passed through the castellated driving ring.

OBJECT OF THE INVENTION

This procedure of rolling the shaft in order to produce the interior thread is both time consuming and expensive. The object of the present invention is to provide a rock bolt which can accept the threaded shaft of a member after it has been installed but which avoids the need to roll a thread in the interior of the hollow shaft of the rock bolt. SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention there is disclosed a rock bolt comprising a hollow tubular shaft closed at its leading end and open at its trailing end, and having a hollow drive nut mounted at said trailing end, the interior of said nut being threaded to threadably engage the threaded shank of a support member.

In accordance with a second aspect of the present invention there is disclosed a method of supporting services within a mine, said method comprising the steps of:-

(i) inserting a plurality of the above defined rock bolts each into a corresponding hole drilled in the roof or wall of a mine,

(ii) threadably engaging the threaded shank of a corresponding support member with each of said plurality of rock bolts, and

(iii) engaging each of said services to be supported with said support members.

BRIEF DESCRIPTION OF THE DRAWINGS

Two preferred embodiments of the present invention will now be described with reference to the drawings in which:

Fig. 1 is a truncated perspective view of a rock bolt in accordance with the first embodiment,

Fig. 2 is an exploded perspective view of the rock bolt including a load distributing plate and a support member,

Fig. 3 is a vertical sectional view of a rock bolt and showing a support member in side elevation,

Fig. 4 is a similar view to Fig. 3 but illustrating the shaft of the rock bolt in side elevation and support services depending from the support member,

Fig. 5 is a side elevational, partly sectional, view inside a mine showing elongate services supported by a plurality of the rock bolts of Figs. 1-4, Fig. 6 is an exploded longitudinal section through a rock bolt of a second embodiment; and

Fig. 7 is a view similar to Fig. 6 but showing the assembled installed rock bolt.

DETAILED DESCRIPTION

As seen in Figs. 1-4, the rock bolt 1 of the first embodiment has a shaft 2 which is a hollow cylinder of indefinite length. The shaft 2 is preferably fabricated from conventional tube or pipe and preferably has a nominal bore of from 10-30 mm approximately. The shaft 2 has a tip 3 or leading end which is swaged closed so as to create impellers 4 which are used to mix the resin or grout used to hold the shaft of the rock bolt in position.

At the opposite, trailing end of the shaft 2 a chamfered hexagonal nut 6 is secured by a means either of a frictional press fit or by welding, or by some other conventional such means. The interior of the nut 6 is provided with an internal thread 7 which is able to be threadably engaged with an external thread 9 on the shank 10 of a support member 11. A typical support member 11 is fabricated from a conventional bolt to which is welded a U-shaped link 12.

As best seen in Fig. 2, prior to insertion of the rock bolt 1 into a hole 14 (Figs. 3 and 4) previously drilled in a mine roof 15, the shaft 2 is passed through a support plate 17 which has a recessed collar 18 which mates with the chamfered nut 6.

As seen in Figs. 3 and 4, following installation of the rock bolt 1, a two-part epoxy resin or grout 20 surrounds the shaft 2 and fills the space between the shaft 2 and the hole 14. This quick setting resin or grout 20 secures the bolt in position and a hollow tubular spanner (conventional but not illustrated) is used to drive the rock bolt 1 so as to rotate it about its longitudinal axis during the installation procedure. This drives the nut 6 into the recessed collar 18 and ensures that the support plate 17 compresses the mine roof 15 in the vicinity of the hole 14. The result is that not only is the mine roof 15 stabilised but that the rock bolt 1 is very securely mounted in the mine roof 15. Following installation of the rock bolt 1, the support member 11 is able to be threadably engaged with the nut 6. Mine services are then supported by means, for example, of a chain 22 and shackle or D-bolt 23 which engages the U-link 12.

Turning now to Fig. 5, a multiplicity of the rock bolts 1 are illustrated secured at spaced apart intervals to the mine roof 15 each being provided with a corresponding length of chain 22 which supports an elongated service 25 which can be a water supply pipe, a compressed air supply conduit, a ventilation supply duct, electric cabling, and the like or some or all of the above. It will be appreciated by those skilled in the art that by suspending such services 25 from the roof 15, the floor of the mine is kept clear for vehicles and other equipment.

In particular, the air ventilation ducts are normally fabricated from plastic covered fabric and like sheet material which is both flexible and liable to rip or tear. Hitherto rock bolts with a threaded trailing end and a sheet or plate which is screwed along the thread to compress the rock strata of the mine roof, have been used to support mine services. Since each of these rock bolts is inserted to a slightly different depth the threaded tails of these bolts protrude from the mine roof and represent a snagging hazard for the large diameter air ducts. Previously, before installation of the air duct, it has been necessary to cut the excess threaded tail from each bolt using an oxy- acetylene torch. The present invention avoids this extra work.

The conventional JUMBOLT is fabricated from hollow steel stock of special size and grade (and strength). The ability in the present invention to use standard tube or pipe which is less expensive provides a substantial cost advantage. In order to ensure adequate keying or adhesion between the grout 20 and the shaft 2, the shaft 2 is preferably provided with a plurality of keying deformations 8 illustrated schematically in order to ensure good adhesion between the grout 20 and the shaft 2. This does not significantly degrade the protection against corrosion created if the tube has previously been galvanised. Preferably the keying deformations are provided in the form of an intermittent rolled helical thread.

The following table specifies a typical product range.

The largest size given in the above table represents the current practical limit to enable the nut 6 to be engaged by spanners able to be accommodated by present day bolt insertion machinery.

A particular advantage of the above described arrangements is that a wide range of tubular stock is readily available to suit urgent requests for manufactured rock bolts. The availability extends not only to size but also to the grade of material. For example, pipe with a nominal bore of 25 mm is available in a range of metal qualities which result in a typical range of ultimate tensile strengths (UTS) of from 8 to 15 tonnes.

Turning now to Figs. 6 and 7, a second embodiment of the rock bolt 100 is illustrated. The shaft 102 is essentially as before, however, at the trailing end of the shaft a nut or a length of internally threaded tube 106 is welded in place of the nut 6 of the first embodiment. The tube 106 preferably has an outer diameter substantially equal to that of the shaft 102. In addition, the tube 106 has a hole in one side into which a breakable pin 121 is secured by means of a friction fit.

An externally threaded drive member 111 having a shank 110 with thread 109 and a chamfered nut 116 is passed through the support plate 17. The shank 110 can then have its tip only partially threadably inserted into the tube 106 until the tip of the shank 110 abuts the pin 121. In this pre-assembled condition, the entire bolt 100 can be mounted in the hole 140 in the rock or coal face 150 as seen in Fig. 7 but with the conventional driving machinery engaging the nut 116 rather than the tube 106. The tube 106 is also driven some distance into the hole 140. Also the support plate 17 is driven against the face 150 by the shank 110 breaking the pin 121 and passing through the tube 106. If subsequently the rock or coal face 150 should crumble away, the support plate 17 can be brought to bear against the new face 150 in the following fashion. The nut 116 is rotated thereby causing the shank 110 to rotate relative to the tube 106 which is now fixed by hardened grout. The shank 110 therefore progresses through the tube 106 until the front of the support plate 17 again bears against the face 150. This re- engagement of the support plate 17 against the face 150 can be repeated several times, if necessary. Also the nut 116 and shank 110 can be replaced with an equivalent nut and longer shank, if necessary.

The foregoing describes only some 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 support member 11 can comprise a conventional eye-bolt. Similarly, a variety of thread sizes, types, and profiles can be utilized for the various needs of the mine.

The term "comprising" 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 comprising a hollow tubular shaft closed at its leading end and open at its trailing end, and having a hollow drive nut mounted at said trailing end, the interior of said nut being threaded to threadably engage the threaded shank of a support member.

2. The bolt as claimed in claim 1 wherein said tubular shaft is closed at its leading end by swaging to form a resin impeller.

3. The bolt as claimed in claim 1 or 2 wherein said hollow tubular shaft is fabricated from pipe or tube of standard size and/or grade.

4. The bolt as claimed in any one of claims 1-3 wherein the exterior of said shaft is provided with a plurality of keying deformations.

5. The bolt as claimed in any one of claims 1-4 wherein the leading end of said nut is chamfered.

6. A method of supporting services within a mine, said method comprising the steps of:-

(i) inserting a plurality of the above rock bolts claimed in any one of claims 1-5 each into a corresponding hole drilled in the roof or wall of a mine,

(ϋ) threadably engaging the threaded shank of a corresponding support member with each of said plurality of rock bolts, and

(iii) engaging each of said services to be supported with said support members.

7. The method as claimed in claim 6 wherein said services are elongated and are supported by all said support members. The method as claimed in claim 7 wherein said elongated services are selected from the group consisting of a water supply pipe, a compressed air supply conduit, a ventilation supply duct, and electric cabling.