The present invention relates to drilling tools and assemblies for installing friction bolts and more particularly drill bits for drill tools and assemblies for installing friction bolts. The present invention also relates to friction bolts and methods of drilling involving friction bolts.

Background of the Invention

Friction bolts are used to stabilise rooves and walls during underground mining and most often have a generally cylindrical body, a collar at the trailing end of the body and a tapered leading end portion of the body that assists in inserting the friction bolt into a bore hole.

Friction bolts often include a split down one side so that when they are driven into a slightly undersized hole in the rock strata, the rock bolt resiliently deforms to reduce the size of the split in the body. This resilient deformation exerts radial and frictional forces against the wall of the hole to retain the friction bolt within the hole and to reinforce the rock strata. The collar enables a rock bearing plate to be fitted to the body directly above the collar such that the collar bears the rock bearing plate against the rock face of the mine to distribute axial loads carried by the friction bolt.

Friction bolts can be installed in a two step process where the first step involves drilling a hole with one drill tool and the second step involves inserting the friction bolt with another tool. This two step process, whilst allowing for the recovery of the entire drill string used to drill the hole, is time consuming and otherwise inefficient.

The deficiencies with the two step process has lead to the development of one step processes where the friction bolt is inserted as the hole is drilled. A range of drilling tools and assemblies for the one step process have been developed and these tend to rely on the use of drill bits that are detached from the drill string, once the friction bolt has been installed, so the remainder of the drill string can be retrieved through the inside of the friction bolt and re-used. The loss of the drill bit with each friction bolt comes at a cost and also requires a new drill bit to be fitted before the next friction bolt can be installed.

Another one step solution for installing friction bolts involves the use of a self drilling friction bolt with an integrally provided drill bit. Once the friction bolt is installed with these systems the drill bit is retrieved leaving the friction bolt and the integrally provided drill bit in the hole.

The present invention seeks to provide an alternative that at least partially addresses one or more of the problems with existing friction bolt systems.

Summary of the Invention

According to a first aspect the present invention provides a drill bit for a drill assembly including a friction bolt defining a longitudinal axial passage, the drill bit being adapted to be releasibly attached to the friction bolt and comprising:

(i) a leading end including a cutting part;

(ii) a following end; and

(iii) an outer surface defining a friction bolt engaging means adapted to releasibly engage with the leading end of the friction bolt.

According to a second aspect of the present invention there is provided a drill bit assembly for use with a drill assembly including a friction bolt defining a longitudinal axial passage, the drill bit comprising:

(i) a drill bit according to a first aspect of the invention; and

(ii) a drive member adapted to pass through the longitudinal axial passage in the friction bolt when the friction bolt is in situ; wherein the drill bit and the drive member are adapted to be releasibly engaged with each other.

According to a third aspect the present invention provides a drill string assembly comprising: (i) a drill string;

(ii) a drill bit assembly according to a second aspect of the present invention mounted on the leading end of the drill string; and

(iii) a friction bolt defining a longitudinal axial passage.

According to a fourth aspect the present invention provides a drilling system comprising:

(i) a drill string;

(ii) a drill bit assembly according to a second aspect of the present invention;

(iii) a friction bolt defining a longitudinal axial passage; and

(iv) a drive means for imparting rotational and/or percussive force on the drill string.

According to a fifth aspect the present invention provides a friction bolt, defining a longitudinal axial passage, comprising a drill bit according to a first aspect of the present invention, releasibly engaged therewith.

According to a sixth aspect the present invention provides a method for inserting a friction bolt according to a fifth aspect of the present invention into a formation.

Brief Description of the Drawings

Figure 1A is an end view (from the leading end) of drill bit according to one embodiment of the first aspect of the present invention;

Figure 1 B is an end view (from the following end) of the drill bit in Figure 1 A;

Figure 1 C is an isometric view of the drill bit in Figure 1 A;

Figure 1 D is a side view of the drill bit in Figure 1 A;

Figure 1 E is the view of cross section G-G in Figure 1 A; Figure 1 F is the view of cross section H-H in Figure 1 A;

Figure 2A is a perspective view of a friction bolt according to an embodiment of the fifth aspect of the present invention including the drill bit in Figure 1A releasibly engaged therewith;

Figure 2B is a detailed view of the leading end of the friction bolt in Figure 2A illustrating the releasable engagement between the drill bit and the friction bolt;

Figure 3A is a perspective view of a drill string assembly (without the friction bolt) according to an embodiment of the third aspect of the present invention showing a drive member in the form of a drill bit, that forms part of a drill bit assembly according a second aspect of the present invention, fitted on the drill rod of a drill string;

Figure 3B is a perspective view of the drive member in the form of a drill bit referred to in Figure 3A;

Figure 3C is and end view (from the leading end) of the drive member in Figure 3B; Figure 3D is the view of cross section F-F in Figure 3C;

Figure 3E is a perspective view of a drive member in the form of a drill bit according to another embodiment of the drive member in Figures 3A-3D;

Figure 4 is a perspective view of a drilling system according to an embodiment of the fourth aspect of the present invention including the friction bolt of Figure 2A and the drill string assembly of Figure 3A;

Figure 5A is an isometric view of a drill bit according to another embodiment of the first aspect of the present invention;

Figure 5B is an end view (from the leading end) of the drill bit in Figure 5A; Figure 5C is a side view of the drill bit in Figure 5A;

Figure 6A is a perspective view of another drive member in the form of a drill bit, that could also form part of a drill bit assembly according to a second aspect of the present invention; Figure 6B is and end view (from the leading end) of the drive member in Figure 6A; Figure 6C is the view of cross section A-A in Figure 6B; Figure 6D is the view of cross section B-B in Figure 6B;

Figure 7A is an isometric view of the drill bit in Figure 5A and the drive member in Figure 6A aligned for releasable engagement;

Figure 7B is an isometric view of the drill bit in Figure 5A and the drive member in Figure 6A releasibly engaged;

Figure 7C is and end view (from the leading end) of the drill bit and drive member in Figure 7B; and

Figure 7D is the view of cross section K-K in Figure 7C. Detailed Description of the Invention

According to a first aspect the present invention provides a drill bit for a drill assembly including a friction bolt defining a longitudinal axial passage, the drill bit being adapted to be releasibly attached to the friction bolt and comprising:

(i) a leading end including a cutting part;

(ii) a following end; and

(iii) an outer surface defining a friction bolt engaging means adapted to releasibly engage with the leading end of the friction bolt.

The applicant has found that the manner in which the drill bit is attached to the friction bolt is important as it must be sufficiently positive to at least reduce and preferably avoid unintentional disengagement of the drill bit from the friction bolt. In this regard, the intent of the present invention is that the drill bit disengages from the friction bolt when drive, such as rotational and/or percussive drive, is applied to the drill bit. Such an arrangement allows for friction bolts including the drill bit to be sold and used as an integral unit and confers other efficiencies on the drilling process. For the purposes of the present invention the term "friction bolt" refers to a generally cylindrical structure adapted to be inserted into a rock or other formation to provide reinforcement. Friction bolts employ a range of measures to enable them to be deployed and provide the required reinforcement, the vast majority of which are based on the friction bolt being able to exert outward pressure on the hole into which they have been inserted. One particular type of friction bolt that the drill bit of the present invention can be used with has a configuration when inserted into a formation or in situ ("stressed configuration") where the width or diameter of the longitudinal axial passage therein is reduced relative to the width or diameter of the longitudinal axial passage prior to insertion of the friction bolt ("relaxed configuration").

For the purposes of the present invention the terms "leading" and "following" for example in the phrases "leading end" and "following end" refer to positions relative to the drilling process. "Leading" as used herein refers to a feature or part thereof that is closest or proximal to the drilling interface whereas "following" refers to a feature or part thereof that is furthest or distal to the drilling interface.

Preferably, the friction bolt engaging means comprises at least one recess. More preferably the friction bolt engaging means comprises a plurality of recesses adapted to releasibly engage with the leading end of the friction bolt. Preferably, the recess is adapted to releasibly engage with a portion of an inside lip of the leading end of the friction bolt.

Preferably, when there is a plurality of recesses, the recesses are spaced equidistantly apart from each other.

Preferably, the outer surface comprises three recesses.

Preferably, the recess is located approximately halfway between the leading and trailing ends of the drill bit.

Preferably, the recess comprises a channel member.

The drill bit may be of various shapes but preferably is formed of a body that is ring or cylinder shaped. Preferably, the drill bit comprises a longitudinal axial passage. The outer cross sectional shape of the drill bit can be varied as required and can be elliptical, circular or oval or polygon shaped such as a triangle, square, rectangle or pentagon.

Preferably, the outer surface of the drill bit tapers in towards its following end. The tapered outer surface may comprise a taper of 4° - 8°, 4° - 7.5°, 4° - 7°, 4° - 6.5°, 4° - 6°, 4° - 5.5°, 4° - 5°, 4° - 4.5°, 4.5° - 8°, 5° - 8°, 5.5° - 8°, 6° - 8°, 6.5° - 8°, 7° - 8°, 7.5° - 8°, 6°, 5.5 ⁰ or6.5°

Preferably, the outer surface of the drill bit includes one or more cut outs to reduce the amount of material used in the drill bit.

The drill bit may further comprise a socket, such as a tapered socket, extending at least partially between the leading end and the trailing end. Preferably, the socket extends the entire distance between the leading and trailing ends such that the leading end of the drill bit includes a first aperture and the trailing end of the drill bit includes a second aperture.

Preferably, the socket is adapted to releasibly receive a drive member for imparting rotational and/or percussive force on the drill bit. Even more preferably, the socket is adapted to releasibly receive a drive member in the form of a second drill bit.

Preferably, the socket comprises at least one spline or groove extending at least partially between the leading and trailing ends. Even more preferably, the socket comprises three splines extending at least partially between the leading and trailing ends.

Suitable cross-sectional shapes of the socket include, but are not limited to elliptical, such as circular or oval cross-section. Alternatively, the cross sectional shape of the socket may be polygonal such as a triangle, square or rectangle. Preferably, the cross sectional shape of the socket comprises a blunt triangular shape, such as a reuleaux triangular shaped cross section or a blunt reuleaux triangular shaped cross section.

When the socket is tapered it may taper in towards its leading end. Even more preferably the tapered socket comprises a taper of about 2.5° - 5.0°, 2.5° - 4.75°, 2.5° - 4.5°, 2.5° - 4.25°, 2.5° - 4°, 2.5° - 3.75°, 2.5° - 3.5°, 2.5° - 3.25°, 2.5° - 3°, 2.75° - 5.0°, 3° - 5.0°, 3.25° - 5.0°, 3.5° - 5.0°, 3.75° - 5.0°, 4° - 5°, 4.25° - 5°, 4.5° - 5°, 4.75° - 5°, 3.5°' 3.45°, 3.4°' 3.35°, 3.55°, 3.6° or 3.65°

Preferably, the drill bit is single use or disposable.

Preferably, the drill bit comprises a cutting part comprising a button or blade type cutting element or a combination thereof.

Preferably, the drill bit is not adapted to pass through the longitudinal axial passage in the friction bolt.

According to a second aspect of the present invention there is provided a drill bit assembly for use with a drill assembly including a friction bolt defining a longitudinal axial passage, the drill bit comprising:

(i) a drill bit according to a first aspect of the invention; and

(ii) a drive member adapted to pass through the longitudinal axial passage in the friction bolt when the friction bolt is in situ; wherein the drill bit and the drive member are adapted to be releasibly engaged with each other.

Preferably, the drill bit and the drive member are releasibly engaged via a taper fit. Preferably, the drive member comprises a second drill bit.

Preferably, the second drill bit comprises a shank, such as a tapered shank, that tapers in towards its leading end. Preferably, the taper of the tapered shank is compatible with the taper of the drill bit. Preferably, the tapered shank comprises a taper of about 2.5° - 5.0°, 2.5° - 4.75°, 2.5° - 4.5°, 2.5° - 4.25°, 2.5° - 4°, 2.5° - 3.75°, 2.5° - 3.5°, 2.5° - 3.25°, 2.5° - 3°, 2.75° - 5.0°, 3° - 5.0°, 3.25° - 5.0°, 3.5° - 5.0°, 3.75° - 5.0°, 4° - 5°, 4.25° - 5°, 4.5° - 5°, 4.75° - 5°, 3.5°' 3.45°, 3.4°' 3.35°, 3.55°, 3.6° or 3.65° The second drill bit may also comprise a tapered portion at its following end that tapers in towards the following end.

The second drill bit may also comprise at least one aperture to allow for the exit or assist in dislodging rocks or other debris that enters the space between the second drill bit and the inside wall of the friction bolt during the drilling process. The at least one aperture may be located is the lateral surface of the following end of the second drill bit. The at least one aperture may be a cut-out. The at least one aperture may be generally "V" shaped, be jagged edged and/or have a saw tooth or zig-zag configuration.

Preferably, the second drill bit comprises a cutting part comprising a button or blade type cutting element or a combination thereof.

The second drill bit may have an outer cross sectional shape that is compatible with the cross sectional shape of the tapered socket in the drill bit described above in respect of the first aspect of the invention. Preferably, the second drill bit comprises a generally polygonal cross section, such as a generally triangular cross section. Even more preferably the second drill bit comprises a blunt triangular shape, such as a reuleaux triangular shaped cross section or a blunt reuleaux triangular shaped cross section. In this regard, instead of the points that are usually seen on a reuleaux triangle there are gentle curves.

Preferably, the hardness of the second drill bit is greater than the hardness of the drill bit.

Preferably, the second drill bit further comprises at least one conduit for delivering fluid to the drilling interface.

Preferably, the second drill bit further comprises a second shank at its following end adapted to engage with a drill string. Preferably, the second shank is adapted to be threaded on to the drill string.

Preferably, the second drill bit is multi-use or reusable. Preferably, the first and second drill bits releasibly engage to form an integral cutting surface.

Preferably, the largest diameter or width of the drill bit assembly is defined by the diameter or width of the first drill bit. This largest diameter will be predetermined based on operational requirements and, in particular, the diameter or width of the friction bolt in the drill assembly that the drill bit assembly is designed for use with. Preferably, the largest diameter or width of the drill bit assembly is slightly larger than internal diameter or width of the friction bolt in situ. This allows for the drill bit assembly to be used to drill a hole of a predetermined width to suit the friction bolt, and for the first drill bit to then be disengaged from the second drill bit so the second drill bit can be retrieved through the longitudinal axial passage in the friction bolt for re-use.

Preferably, the second drill bit comprises an abutment means that is positioned to ensure the engagement between the first and second drill bits functions optimally when the drill bit assembly is in use. In this regard, it has been found that without a suitable abutment means the first drill bit can become stuck or wedged in engagement with the second drill bit, on the taper, and hence hamper the convenient disengagement of the first and second drill bits during operation. It has also been found that a suitable abutment means can assist with the disengagement process as it provides a surface against which the first drill bit can be worked against to disengage the first and second drill bits from each other. In this regard, the abutment means, such as a shoulder, prevents the first drill bit from being forced too far down the taper on the second drill bit. Furthermore, during the drilling process, the first drill bit continues to be forced against the abutment means which causes the engagement between the bits to be loosened which makes it easier to disengage them from each other when the drilling process is complete and the second drill bit is withdrawn from the hole.

Preferably, the abutment means is a shoulder or lip on the outer surface of the second drill bit. Preferably, the shoulder or lip extends around the entire outer surface of the second drill bit. The shoulder or lip may be tapered towards the leading end of the second drill bit or may be flat. According to a third aspect the present invention provides a drill string assembly comprising:

(i) a drill string;

(ii) a drill bit assembly according to a second aspect of the present invention mounted on the leading end of the drill string; and

(iii) a friction bolt defining a longitudinal axial passage.

According to a fourth aspect the present invention provides a drilling system comprising:

(i) a drill string;

(ii) a drill bit assembly according to a second aspect of the present invention;

(iii) a friction bolt defining a longitudinal axial passage; and

(iv) a drive means for imparting rotational and/or percussive force on the drill string.

According to a fifth aspect the present invention provides a friction bolt, defining a longitudinal axial passage, comprising a drill bit according to a first aspect of the present invention, releasibly engaged therewith.

The friction bolt can be varied as required, provided it is capable of releasibly engaging with a drill bit according to the first aspect of the present invention. Preferably, the leading end of the friction bolt is shaped and configured such that it is capable of releasibly engaging the drill bit. In this regard, it is preferred that the engagement between the friction bolt and the drill bit is such that the friction bolt and drill bit can be sold as an integral unit for use with a suitably designed drill string wherein they are only separated as part of the drilling process that installs the friction bolt.

According to a sixth aspect the present invention provides a method for inserting a friction bolt according to a fifth aspect of the present invention into a formation.

Preferably, the method comprises the steps of: (i) providing a friction bolt including a drill bit according to a first aspect of the present invention, releasibly engaged therewith;

(ii) fitting said friction bolt to a drill string assembly;

(iii) drilling a hole in the formation using the drill string assembly wherein said drilling results in the insertion of the friction bolt;

(iv) disengaging the drill bit and the friction bolt from the drill string; and

(v) retrieving the drill string from the hole, through a longitudinal axial passage in the friction bolt.

Preferably, the drilling of the hole and insertion of the friction bolt occurs in a single pass.

Preferably, the drill string assembly comprises a drill string assembly according to a third aspect of the invention.

Preferably, said drilling results in said drill bit disengaging from said friction bolt.

Preferably, the step of disengaging the drill bit from the drill string comprises the step of applying percussion to the drill string. Even more preferably, the step of disengaging the drill bit from the drill string comprises the step of stopping the percussion applied to the drill string and/or reversing the feed direction of the drill string.

General

Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. The invention includes all such variation and modifications. The invention also includes all of the steps and features referred to or indicated in the specification, individually or collectively and any and all combinations or any two or more of the steps or features.

Each document, reference, patent application or patent cited in this text is expressly incorporated herein in their entirety by reference, which means that it should be read and considered by the reader as part of this text. That the document, reference, patent application or patent cited in this text is not repeated in this text is merely for reasons of conciseness. None of the cited material or the information contained in that material should, however be understood to be common general knowledge.

The present invention is not to be limited in scope by any of the specific embodiments described herein. These embodiments are intended for the purpose of exemplification only. Functionally equivalent products and methods are clearly within the scope of the invention as described herein.

The invention described herein may include one or more range of values (e.g. size etc). A range of values will be understood to include all values within the range, including the values defining the range, and values adjacent to the range which lead to the same or substantially the same outcome as the values immediately adjacent to that value which defines the boundary to the range.

Throughout this specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Other definitions for selected terms used herein may be found within the detailed description of the invention and apply throughout. Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which the invention belongs.

The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.

Figures 1 A-1 F depict a drill bit according to one embodiment of the first aspect of the present invention, generally indicated by the numeral 10. The drill bit 10 is generally ring shaped and defines a leading end (best depicted in Figure 1A) that defines a cutting part comprising six raised buttons formed of tungsten carbide that are formed into three evenly spaced pairs 12a, 12b and 12c, a following end (best depicted in Figure 1 B) and a tapered socket 14 that extends between the leading and following ends so that each end defines an aperture therein.

The main body of the drill bit 10 is formed of a suitable metal such as a 4140 grade metal. The drill bit 10 is designed to be readily disposable after a single pass drilling to install a friction bolt. As the intention is for the drill bit 10 to be disposed of in the drill hole it is sized and shaped so as to not pass through the longitudinal axial passage in the friction bolt once installed.

The tapered socket 14 has a blunt reuleaux triangular shaped cross section, includes a taper 15 of about 3.5° in towards its leading end and is adapted to receive a drive member in the form of a drive means in the form of a second drill bit 40 (discussed in further detail below).

The outer cross sectional shape of the drill bit 10 is generally circular and the outside surface tapers in towards its following end at about 6o. The outer surface of the drill bit 10 includes three major cut outs 16a, 16b 16c and three channels 18a, 18b (not shown) and 18c that are evenly spaced and extend around the outer surface between each cut out 16a, 16b and 16c. The channels 18a-18c are adapted to releasibly engage with the inside lip of the leading end of a friction bolt 22 (best depicted in Figure 2B) in a manner that allows the friction bolt 22 and drill bit 10 to form an integral unit (best depicted in Figure 2A) according to an embodiment of a fifth aspect of the present invention. The outer surface of the drill bit 10 also includes three minor cut outs 19a, 19b, 19c. The cut outs 16a-16c and 19a-19c are made primarily to allow cuttings to be flushed away from the drilling face and escape past the face of the drill bit.

Figures 2A and 2B depict an embodiment of a friction bolt according to a fifth aspect of the present invention generally indicated by the numeral 20 and including a friction bolt 22 defining a longitudinal axial passage 24 and having a drill bit 10 releasibly engaged in its leading end.

The friction bolt 22 is resiliently deformable such that it can be driven into a drill hole during the drilling process and impart outward pressure on the inside of the drill hole once it is inserted. The resiliently deformable characteristics of the friction bolt 22 are provided by the slot 24 in the friction bolt 22 that allows the friction bolt 22 to contract as it enters the drill hole during the drilling process.

The drill bit 10 is releasibly engaged in the leading end of the friction bolt 22 via a frictional engagement between channels 18a-18c and the inside lip of the leading end of the friction bolt 22. This engagement is sufficiently positive to prevent the drill bit 10 and friction bolt 22 disengaging unintentionally but does allow for the components to be separated during the drilling process that installs the friction bolt 22 in a formation. This is discussed in more detail below but involves the drill bit 10 being detached from the drill string and left in the hole once the friction bolt has been installed in a formation and the remainder of the drill string (including the second drill bit - see below) being recovered and re-used to install the next friction bolt.

Figures 3A-3D depict one example of a drive member in the form of a second drill bit 40 that forms part of drill bit assembly according to an embodiment of the second aspect of the present invention. Figure 3A depicts the second drill bit 40 threaded on a drill rod 42 whereas Figures 3B-3D show the second drill bit 40 by itself.

The second drill bit 40 is designed to be reusable and comprises a cutting section 42 at its leading end and a shank 44 at its following end that includes a threaded portion 46 (see Figure 3D) to engage with a drill rod 42 (see Figure 3A).

The cutting section 42 also includes a tapered shank 48 with a blunt reuleaux triangle shaped cross section and tapers in at about 3.5° towards its leading end defining a tapered outer surface that is adapted to form a frictional engagement with the tapered socket 14 in the drill bit 10 and also includes a cutting part comprising cutting elements in the form of buttons 50 formed of tungsten carbide or some other suitable hard material. The second drill bit 40 also includes conduits 52 delivering drilling fluid to the drill face during the drilling process, as required. The greatest outer width or diameter defined by the second drill bit 40 is such that the drill bit 40 is adapted to pass through the longitudinal axial passage in a friction bolt 20.

Figures 3E depict another example of a drive member in the form of a second drill bit 140 that forms part of drill bit assembly according to an embodiment of the second aspect of the present invention. Figure 3E show the second drill bit 140, by itself, and is similar in configuration to the second drill bit 40 in figures 3A-3D but includes a different shank 144 that includes a skirt with an aperture in the form of a jagged edged or generally "V" shaped cut-out 151 located in the lateral surface of the following end of the shank 144 to allow for the exit of rocks or other debris that enters the space between the second drill bit and the inside wall of the friction bolt during the drilling process. Multiple cut-outs 151 can be included around the perimeter of the following end of the shank 144, if necessary.

Figure 4 illustrates an embodiment of a drilling system according to the fourth aspect of the invention in a form ready for drilling. The drill assembly generally indicated by the numeral 50 includes the friction bolt 22 from Figures 2A and 2B including drill bit 10 releasibly mounted thereon and surrounds a drill string 52 connected to the drive means 54 of a drill rig that can apply percussive and/or rotational force to the drill string 52. The friction bolt 22 has been mounted on the drill string 52 in a manner resulting in the second drill bit 40 (Figures 3A-3D) releasibly engaging with the following end of the drill bit 10 such that drive imparted on the second drill bit 40 by the drill string 52 is transferred to the drill bit 10.

The following end of the friction bolt 22 includes a plate 56, threaded on the friction bolt that enables for a more efficient engagement between the friction bolt and mesh (not shown), when the system is used to attach mesh to the formation.

The drilling system 50 can be used in a drilling process as follows. The friction bolt 22 is inserted in a formation, such as rock, in a single pass. The friction bolt 22 is inserted as the hole is being drilled simultaneously. Once drilling commences the drill bit 10 disengages from the friction bolt 22 and forms an integral cutting surface defined by the leading end of drill bit 10 and the leading end 42 of second drill bit 40. Once the friction bolt 22 has been fully inserted, the operator stops the percussion and reverses the feed direction to disengage the drill bit 10 from the second drill bit 40. Once disengaged, the drill string including the drill bit 40 is withdrawn from the hole through the longitudinal passage defined by the friction bolt 22. In this regard, the largest outer diameter defined by the drill bit 40 is such that the drill bit 40 is adapted to pass through the longitudinal axial passage in a friction bolt 22, once installed. The drill bit 10 remains behind in the drill hole. The next friction bolt 22 including drill bit 10 can then be mounted on the drill string 52 and the process repeated to install another friction bolt 22. Figures 5A-5C depict a drill bit according to a second embodiment of the first aspect of the present invention, generally indicated by the numeral 1 10. The drill bit 1 10 is generally ring shaped and defines a leading end (best depicted in Figure 5B) that defines a cutting part comprising three raised, evenly spaced buttons formed of tungsten carbide 1 12a, 1 12b and 1 12c, a following end and a socket 1 14 that extends between the leading and following ends so that each end defines an aperture therein.

As with the drill bit according to the first embodiment in Figures 1A-1 F, the main body of the drill bit 1 10 is formed of a suitable metal such as a 4140 grade metal. The drill bit 1 10 is designed to be readily disposable after a single pass drilling to install a friction bolt. As the intention is for the drill bit 10 to be disposed of in the drill hole it is sized and shaped so as to not pass through the longitudinal axial passage in the friction bolt once installed.

The socket 1 14 has a blunt reuleaux triangular shaped cross section and is adapted to receive a drive member in the form of a drive means in the form of a second drill bit 140 (discussed in further detail below).

The outer cross sectional shape of the drill bit 1 10 is generally circular and the outer surface of the drill bit 1 10 includes three major cut outs 1 16a, 1 16b 1 16c and three channels 1 18a, 1 18b (not shown) and 1 18c that are evenly spaced and extend around the outer surface between each cut out 1 16a, 1 16b and 1 16c. The channels 1 18a-1 18c are adapted to releasibly engage with the inside lip of the leading end of a friction bolt 22 in a manner that allows the friction bolt 22 and drill bit 1 10 to form an integral unit according to an embodiment of a fifth aspect of the present invention. The cut outs 1 16a-1 16c are primarily to allow cuttings to be flushed away from the drilling face and escape past the face of the drill bit.

Figures 6A-6D depict another example of a drive member in the form of a second drill bit 140 that forms part of drill bit assembly according to an embodiment of the second aspect of the present invention. The second drill bit 140 is adapted to be threaded on a drill rod in a similar fashion to that illustrated in Figure 3A with respect to the first example of the second drill bit 42. The second drill bit 140 is designed to be reusable and comprises a cutting section 142 at its leading end and a shank 144 at its following end that includes a threaded portion 146 (see Figures 6C and 6D) to engage with a drill rod such as that shown in Figure 3A. The second drill bit 140 also includes a tapered shoulder 147 between the cutting section 142 and the shank 144.

The cutting section 142 also includes a shank 148 with a cross section shaped and adapted to form a frictional engagement with the socket 1 14 in the drill bit 1 10 and also includes a cutting part comprising cutting elements in the form of buttons 150 formed of tungsten carbide or some other suitable hard material. The second drill bit 140 also includes conduits 152 delivering drilling fluid to the drill face during the drilling process, as required. The greatest outer width or diameter defined by the second drill bit 140 is such that the drill bit 140 is adapted to pass through the longitudinal axial passage in a friction bolt such as that depicted in Figure 2A.

Figures 7A-7D illustrate the drill bits 1 10 and 140 together to demonstrate the nature of their inter-engagement during the drilling process.

A drilling system according to the fourth aspect of the invention in a form ready for drilling including the drill bits 1 10 and 140 operates in a similar fashion to the drill assembly generally indicated by the numeral 50 in Figure 4.

The foregoing is illustrative of the present invention and is not to be construed as limiting thereof. Although a few exemplary embodiments of this invention have been described, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. Therefore, it is to be understood that the foregoing is illustrative of the present invention and is not to be construed as limited to the specific embodiments disclosed, and that modifications to the disclosed embodiments, as well as other embodiments, are intended to be included within the scope of the appended claims.