Technical Field

The present disclosure relates to rock bolts suitable for use in the mining and tunneling industry to provide rock and wall support. The rock bolt is suitable for softer strata, such as that often found in coal mines, as well as hard rock applications. It is to be appreciated that the term "rock" as used in the specification is to be given a broad meaning to cover both of these applications.

Background

Roof and wall support is vital in mining and tunneling operations. Mine and tunnel walls and roofs consist of rock strata, which must be reinforced to prevent the possibility of collapse. Rock bolts are widely used for consolidating the rock strata.

In conventional strata support systems, a bore is drilled into the rock by a drill rod, which is then removed and a rock bolt is then installed in the drilled hole and secured in place typically using a resin or cement based grout. The rock bolt is tensioned which allows consolidation of the strata by placing that strata in compression. The rock bolt is typically formed from a steel rod.

To allow the rock bolt to be tensioned, the end of the bolt may be adhesively bonded to the rock formation with a bonding material inserted into the bore hole.

Alternatively, a combination of mechanical anchoring and bonding can be employed by using both an expansion assembly and resin bonding material.

When bonding material is used, the material adheres to the rock bolt and penetrates the surrounding rock formation to adhesively unite the rock^lrala_and to hold firmly the rock bolt within the bore hole. In one form of anchoring, resin is inserted into the bore hole in the form of a two component plastic cartridge having one component containing a curable resin composition and another component containing a curing agent (catalyst). The two component resin cartridge is inserted into the blind end of the bore hole and the rock bolt is inserted into the bore hole such that the end of the rock bolt ruptures the two component resin cartridge. Upon rotation of the mine rock bolt about its longitudinal axis, the compartments within the resin cartridge are shredded and the components are mixed. The resin mixture fills the annular area between the bore hole wall and the shaft of the mine rock bolt. The mixed resin cures and binds the rock bolt to the surrounding rock.

The resin cartridge is ordinarily made from thin plastic type film which encases and separates the mastic and catalyst. A significant concern with resin anchored rock bolts is that the plastic film is not sufficiently shredded and/or pushed back to the rear of the bore during mixing. As a result the plastic film can sit between the rock bolt and the bore hole wall and prevent the bonding of the rock bolt to the rock of the bore hole. Another concern is creating the required turbulence and torque for mixing the resin to evening combine the catalyst through the mastic. Under-mixing of the resin results in an unset resin which is low in strength.

Summary of the Disclosure

Disclosed is a rock bolt comprising an elongate shaft extending between opposite leading and trailing ends and a deformed section disposed proximal to the leading end, the deformed section being configured such that a protrusion extends outwardly beyond an outer surface of the shaft.

In one form the protrusion extends radially outwardly from the outer surface of the shaft.

In one form the protrusion comprises a flat face extending outwardly from the outer surface of the shaft and terminating at an edge.

In one form the protrusion comprises two opposing flat faces extending outwardly from the outer surface of the shaft and connected by a periphery of the protrusion.

In one form the rock bolt has an axis of rotation extending longitudinally through the shaft and the protrusion is oriented such that during rotation at least one flat face is forwardly facing with respect to the rotary movement.

In one form the deformed section is configured such that a depression extends radially inwardly from the outer surface of the shaft. The deformed section of the rock bolt allows for shredding of the resin capsule through rotation of the deformed section with the rock bolt causing the edge portions to contact and shred the resin capsule membrane. The deformed section further increases turbulence in the resin about the rock bolt and allows a reduction in the annular region about the deformed section of the rock bolt once within the bore. This allows resin contained within the bore to be more effective.

In a second aspect, disclosed is a rock bolt comprising an elongate shaft extending between opposite leading and trailing ends and a deformed section disposed proximal to the leading end, the deformed section being configured to have at least one edge, at least a portion of the edge being disposed radially outwardly from the periphery of the shaft.

In one form the deformed section includes two edges.

In one form a face extends from the edge to the shaft, the face being oriented such that during rotation of the shaft about its longitudinal axis, the face is forwardly facing with respect to the rotary movement.

In a third aspect, disclosed is a method of installing a rock bolt in a bore comprising the steps of drilling a bore hole, positioning a resin capsule in the distal end of the bore hole, inserting the leading end of a rock bolt into the bore hole and applying rotation to the rock bolt such that the resin capsule is shredded, wherein the rock bolt includes a deformed section adapted to shred the capsule.

In one form the deformed section is configured such that a protrusion extends outwardly beyond an outer surface of the shaft.

In one form the protrusion extends radially outwardly from the outer surface of the shaft.

In one form the protrusion comprises a flat face extending outwardly from the outer surface of the shaft and terminating at an edge.

In one form the protrusion comprises two opposing flat faces extending outwardly from the outer surface of the shaft and connected by a periphery of the protrusion.

In one form the protrusion is oriented such that during rotation at least one flat face is forwardly facing with respect to the rotary movement. In one form the deformed section is configured such that a depression extends radially inwardly from the outer surface of the shaft.

In one form the shaft is sized such that the space between the inner wall of the bore hole and the outer surface of the shaft is less than 3mm.

In one form the deformed section facilitates chemical fixing of the rock bolt by the resin within the bore by promoting turbulence within the resin.

In one form the deformed section facilitates chemical fixing of the rock bolt by the resin within the bore by promoting mixing of the resin components on rotation of the deformed section.

Brief Description of the Drawings

Preferred embodiments of the rock bolt will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 illustrates a side view of one embodiment of a rock bolt according to the disclosure;

Figure 2 illustrates a side view of the rock bolt of Figure 1 rotated through 90°; Figure 3 illustrates a cross-sectional view of the rock bolt of Figure 2 through X-X; Figure 4 illustrates a side view of the rock bolt of Figure 1.

Detailed Description of Preferred Embodiments

Referring to the Figs, disclosed is a rock bolt 1 comprising a shaft 2 extending from a leading end 3 to a trailing end 4. The rock bolt 1 is adapted to be inserted into a borehole within a reek formation to reinforce and apply tension to the rock formation.

The rock bolt 1 includes a deformed section 6 which is positioned proximal the leading end 3 of the shaft 2. In the illustrated form, the deformed section comprises two protrusions 8 which extend radially outwardly from the outer surface 10 of the shaft 2. The deformed section further comprises four depressions 11 which are radially indented from the outer surface 10 of the shaft 2. The protrusions 8 include two faces 13 which each extend from a respective depression 11 outwardly of the shaft. The faces 13 terminate at an edge 14 which forms an approximate right angle with a periphery 16 of the protrusion. The periphery 16 of the protrusion 8 extends between two edges 14 and therefore extends between two faces 13.

The deformed section 6 is formed by pinching or pressing the material of the rock bolt during manufacture.

The deformed section 6 of the device has a cross sectional length A-A through the protrusions 8 that is larger than the diameter of the drill bit that forms the bore hole. The cross sectional length A-A is greater than the diameter of the drill bit by between 1 and 3 mms. In one embodiment the cross sectional length A-A is greater than the diameter of the drill bit by 2 mm.

The deformed section of the device has a cross sectional length B-B through the depressions 11 that is less than the diameter of the drill bit that forms the bore hole. The cross sectional length B-B is less than the drill bit diameter of the bore hole by between 0.5 and 2 mms. In one embodiment the cross sectional length B-B is less than the diameter of the drill bit by 1 mm.

The deformed section 6 of the rock bolt can be inserted into the bore as the point at which the deformed section is wider than the diameter of the bore hole is simply a point contact with a rifled hole. Further as the bore hole is typically 0.5 - 2mm greater in diameter than the drill bit, the tolerance for inserting a larger deformed section is greater. Use of hydraulic bolting rigs allows an installer to insert the deformed section 6 and the rock bolt 1 into the bore hole despite the close fit. This is especially the case in softer rock formations but is possible in a variety of rock formations. Use of a high break out shear pin or reverse twist drive mechanisms can also allow insertion of the rock boh 1 with the deformed section into the bore hole.

In use, the rock bolt 1 with the deformed section 6 is inserted into a bore along with a resin capsule. The resin capsule which includes resin mastic and catalyst is positioned at the distal end of the bore. The rock bolt 1 is rotated resulting in rotation of the deformed section 6. The edges 14 have a cutting or shredding action that shreds the film membrane of the resin capsule allowing mixing of the mastic and the catalyst. Further, the close fit of the deformed section 6 within the bore hole acts to further shred the capsule. The faces 13 of the deformed section 6 create interference and turbulence within the resin to promote mixing of the mastic and the catalyst allowing for a more effective resin.

It can be seen that the present embodiment improves the mixing of the resin mastic and catalyst within the bore and reduces the problem of a rock bolt being "gloved" or surrounded by the casing of the resin capsule. This results in an effective bond between the bore surface and the rock bolt.

As will be understood, variations of the above described rock bolt can be made without departing from the scope of the appended claims. For example, in an alternative embodiment of the deformed section, the deformed section may comprise...

While the rock bolt has been described in reference to its preferred embodiments, it is to be understood that the words which have been used are words of description rather than limitation and that changes may be made without departing from its scope as defined by the appended claims.

It is to be understood that a reference herein to a prior art document does not · constitute an admission that the document forms part of the common general knowledge in the art in Australia or in any other country.

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 of the rock bolt.