ROCK BOLT AND ITS FABRICATION AND INSTALLATION

Field of the Invention

The present invention relates to rock bolts and, in particular, to rock bolts which are installed using a resin cartridge.

Background Art

Resin cartridges are well known and have the appearance of a sausage with a skin formed from sheet plastics material which constitutes a tube which is sealed at each end with a metal crimp, or similar. The interior of the tube is divided into two substantially equal compartments by means of a wall extending along the interior of the tube. The two components of the resin are maintained each in their separate compartment and do not mix prior to installation. At installation the skin of the cartridge is ripped so as to permit the two resin components to mix together. As a consequence a rapid chemical reaction takes place and the resin is rapidly solidified thereby maintaining the rock bolt in position.

One form of rock bolt which has been used in the past is a cone bolt where the leading end of the bolt is forged such that the diameter of the generally cylindrical shaft of the bolt at its leading end expands to form a cone having a base which forms the tip of the bolt. In recent years this type of bolt has been modified so as to form the bolt illustrated in Figs. 1 and 2 where the forging creates a projection which extends forwardly from the base of the cone.

As seen in Figs. 1 and 2, the prior art bolt 1 has a leading end 2, a trailing end 3 and a shaft 4. The shaft 4 is a plain steel bar and the trailing end 3 is provided with a conventional securing means (not illustrated) such as a thread, washer and nut which enables the shaft 4 to be placed in tension after the bolt 1 has been installed.

The leading end 2 has a cone 6 with a base 7 and a generally rectangular and planar projection 8 which is intended to cut the skin of the resin cartridge during installation.

The present applicant has tested four bolts of the prior art such as those illustrated in Figs. 1 and 2 by installing same into a corresponding steel tube. Then a two tonne weight moving at six metres/second was applied as a load to the shaft 4 of each prior art bolt 1 in order to test the bond between the bolt 1 and the interior of the tube.

These tests produced very variable results, namely two pull outs which indicates a catastrophic failure, and two arrests with 300-400mm of travel of the bolt relative to the tube (which is a poor result). This variability indicates that the installation procedure was producing the variation since there was almost no different between the individual bolts and the individual resin cartridges used in the test.

By examining the failed test rigs, it became apparent to the inventor that the installation procedure resulted in the plastic membrane or skin of the resin cartridge being cut to allow the resin constituents to be mixed together; however, large pieces of the cut skin were found to be bunched into a substantial volume in the set resin. As a consequence of this volume of sheet plastic material being present in the set resin, the load able to be sustained by the bolt 1 was found to be substantially less than expected.

Genesis of the Invention

The genesis of the present invention is a desire to seek to ameliorate the abovementioned disadvantages.

Summary of the Invention In accordance with the first aspect of the present invention there is disclosed a rock bolt for use in mining and civil engineering operations and having a shaft extending between a trailing end and a leading end, said leading end expanding from said shaft into a cone having a base, a projection extending forwardly from said base, and the leading end of said projection being bifurcated to form a shredding means at said leading end to shred the skin of a dual compartment cartridge containing dual resin components.

In accordance with a second aspect of the present invention there is disclosed a method of installing a rock bolt having a shaft extending between a trailing end and a leading end, said leading end expanding from said shaft into a cone having a base, said method comprising the steps of: (i) forming a projection extending forwardly from said base, the leading end of said projection being bifurcated,

(ii) inserting a dual compartment cartridge containing dual resin components within a skin of said cartridge, into a blind hole drilled in a rock or mineral face, (iii) rotating said rock bolt whilst contacting said cartridge with said bifurcated projection whereby said bifurcated projection shreds said skin and mixes said dual resin components, and

(iv) maintaining said rock bolt stationary in said hole until said mixed resin constituents set.

In accordance with a third aspect of the present invention there is disclosed a method of manufacturing a rock bolt having a steel shaft, one end of which is to be transformed into the leading end of said rock bolt, said method comprising the steps of: (i) forging said one end to expand said shaft to form a cone having a base and a projection extending from said base away from said shaft end, and

(ii) shearing said projection to create a bifurcated leading end thereof.

Brief Description of the Drawings

A preferred embodiment of the present invention will now be described with reference to the accompanying drawings in which:

Fig. 1 is a perspective view of the modified cone rock bolt of the prior art looking from the trailing end towards the leading end,

Fig. 2 is a perspective view of the modified cone bolt of Fig. 1 looking from the leading end towards the trailing end, and Figs. 3 and 4 are views corresponding to Figs. 1 and 2 but in respect of the rock bolt of the preferred embodiment.

Detailed Description

Turning now to Figs. 3 and 4, the rock bolt 1 1 of the preferred embodiment is illustrated with like parts to the rock bolt 1 being indicated by designations increased by 10. Thus the rock bolt 11 of the preferred embodiment has a leading end 12, a trailing end 13 and a shaft 14. The cone 16 is substantially as before having a base 17 and a projection 18.

However, the leading end of the projection 18 is bifurcated to form two tangs 21 and 22 which are bent out of the plane of the projection 18 in opposite directions. Preferably the cone 16 and projection 18 are formed by means of forging. The projection 18 after forging is then sheared in order to produce the two tangs 21, 22.

Preferably the tangs 21, 22 extend beyond the cone base 17 which typically has a diameter of approximately 26mm with the tips of the tangs 21, 22 when rotated travelling in a circle of approximately 32mm which is less than the hole diameter of approximately 38mm. The projection before deformation is approximately 25mm in vertical extent, approximately 5mm thick and approximately 45mm long.

Australian Patent Application No. 2006 252 071 to the present applicant discloses a rock bolt with a tip or leading end which is sheared to produce a bifurcated tip which, during insertion of the rock bolt, creates a stirring action which sweeps the mixing constituents outwardly so as to force the constituents into small crevices, cracks and the like in the surface of the hole in the rock or mineral face. This is to be contrasted with the arrangement of the present invention where the tangs 21, 22 do not face forwardly as do the blades 21, 22 or 121, 122 of the abovementioned Australian patent specification. Instead, the tangs 21 and 22 of the present application face sideways and therefore engage the central membrane of the resin cartridge and shred it. However, since the resin cartridge central membrane is also attached to the outer skin, the outer skin is drawn inwardly into the rotating tangs 21 , 22 and is also thereby shredded. Thus both the outer skin and the inner membrane are converted into small pieces of shredded sheet plastic material which are dispersed well within the mixing resin constituents. As a consequence, none of the plastic skin is present in a sufficient quantity to form a localised weakness.

The result of this mixing activity is that equivalent tests on four of the bolts 11 produced the result of no pull outs and all four bolts producing an arrest with travel in the narrow range of only 130-140 mm. Not only is this a much smaller travel distance than was able to be achieved by the prior art bolt 1 , but there is almost no variability in the results so the cartridge shredding and resin mixing are clearly both superior and consistent.

The foregoing describes only one embodiment of the present invention and modifications, obvious to those skilled in the rock bolt arts, can be made hereto without departing from the scope of the present invention.

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 '.