AU2013251196A1

AU2013251196A1 - Drill Bit for a Drill Assembly Including a Friction Bolt

Info

Publication number: AU2013251196A1
Application number: AU2013251196A
Authority: AU
Inventors: Matthew David Mclaren
Original assignee: MCLAREN MATTHEW
Current assignee: Fero Strata Systems Pty Ltd
Priority date: 2012-10-30
Filing date: 2013-10-29
Publication date: 2014-05-15
Also published as: AU2018201286A1; AU2020201155A1

Abstract

Abstract A drill bit for a drill assembly including a friction bolt defining a longitudinal axial passage, the drill bit comprising a first bit body at its leading end said first bit body including a first cutting part and being adapted to releasibly engage with a second bit body; wherein the drill bit is adapted to pass through the longitudinal axial passage in the friction bolt. nL ) C(N (O cL (No (No (NL I(N (ND

Description

Regulation 3.2 Australia Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT APPLICANT(S): Matthew David McLaren INVENTION TITLE: Drill Bit for a Drill Assembly Including a Friction Bolt The following statement if a full description of this invention, including the best method of performing it known to me: - 2 Drill Bit for a Drill Assembly Including a Friction Bolt Field of the Invention 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.

3 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 The present invention provides a drill bit for a drill assembly including a friction bolt defining a longitudinal axial passage, the drill bit comprising: (i) a first bit body at its leading end said first bit body including a first cutting part and being adapted to releasibly engage with a second bit body; wherein the drill bit is adapted to pass through the longitudinal axial passage in the friction bolt. The present invention also provides a two piece drill bit for a drill assembly including a friction bolt defining a longitudinal axial passage, the two piece drill bit comprising: (i) a first bit body at its leading end said first bit body including a first cutting part; and (ii) a second bit body including a second leading end that defines a second cutting part; wherein the first bit body and second bit body are adapted to releasibly engage with each other. The present invention also provides a drill assembly comprising: (i) a drill string; (ii) a drill bit according to claim 1 or 2 mounted on the leading end of the drill string; and 4 (iii) a friction bolt defining a longitudinal axial passage. Further the present invention provides a drilling system comprising: (i) a drill string; (ii) a drill bit according to claim 1 or 2; (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 and the friction bolt. Still further the present invention provides a method inserting a friction bolt, defining a longitudinal axial passage, into a formation, the method comprising the steps of: (i) providing a drill assembly including a friction bolt, and a two piece drill bit according to claim 2 mounted on a drill string and including a first bit body and a second bit body in releasable engagement with each other; (ii) drilling a hole in the formation using the drill assembly; (iii) disengaging the second bit body from the first bit body; and (iv) retrieving the drill string and the first bit body from the hole through the longitudinal axial passage. The present invention also provides a drill bit for a drill assembly including a friction bolt defining a longitudinal axial passage, the drill bit comprising: (i) a bit body at its leading end including a cutting part; (ii) a means for releasibly engaging with the friction bolt; and (iii) a means for releasibly engaging with another bit body. Still further the present invention provides a friction bolt comprising a drill bit according to claim 6.

5 Brief Description of the Drawings Figure 1a is a cross sectional side view of a drill bit for a drill assembly according to a first embodiment of the first aspect of the present invention; Figure 1 b is a cross sectional side view of a second bit body that forms part of embodiments of the second, third, fourth, fifth, sixth and seventh aspects of the present invention; Figure 1c is a plan view of the leading end of a two piece drill bit according to an embodiment of the second aspect of the present invention; Figure id is a side view of an embodiment of the drill assembly and drilling system according to the third and fourth aspects of the invention including the two piece drill bit of Figure 1c; Figures le, 1f and 1g depict the drilling process using the drill assembly and drilling system of Figure 1d with Figure 1e showing the friction bolt partially inserted, Figure 1f showing it fully inserted and still attached to the drill string and Figure 1g showing the friction bolt fully inserted and with the drill string retrieved; Figure 2 is a plan view of the leading end of a two piece drill bit according to another embodiment of the second aspect of the present invention; Figure 3 is a plan view of the leading end of a two piece drill bit according to another embodiment of the second aspect of the present invention; Figure 4a is a cross sectional side view of a drill bit for a drill assembly according to another embodiment of the first aspect of the present invention; Figure 4b is a plan view of the leading end of a two piece drill bit according to another embodiment of the second aspect of the present invention including the drill bit of Figure 4a; Figure 5a is a cross sectional side view of a drill bit for a drill assembly according to another embodiment of the first aspect of the present invention; 6 Figure 5b is a plan view of the leading end of a two piece drill bit according to another embodiment of the second aspect of the present invention including the drill bit of Figure 5a; Figure 5c is a cross sectional side view of the drill bit of Figure 5a taken from a 90 angle to the view in Figure 5a; Figure 5d is a cross sectional side view of a drill bit for a drill assembly according to another embodiment of the first aspect of the present invention; Figure 5e is a plan view of the leading end of a two piece drill bit according to another embodiment of the second aspect of the present invention including the drill bit of Figure 5d; Figure 5f is a cross sectional side view of a drill bit for a drill assembly according to another embodiment of the first aspect of the present invention; Figure 5g is a plan view of the leading end of a two piece drill bit according to another embodiment of the second aspect of the present invention including the drill bit of Figure 5f; and Figure 6 is a side view of a friction bolt according to an embodiment of the seventh aspect of the present invention including the drill bit body according to an embodiment of the sixth aspect of the invention. 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 comprising: (i) a first bit body at its leading end said first bit body including a first cutting part and being adapted to releasibly engage with a second bit body; wherein the drill bit is adapted to pass through the longitudinal axial passage in the friction bolt.

7 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"). Thus, preferably, the drill bit according to the first aspect of the present invention is adapted to pass through the longitudinal axial passage in the friction bolt when the friction bolt is in its stressed 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 first bit body is multi-use or reusable. The first bit body can be adapted to releasibly engage with the second bit body in a variety of ways. Preferably, the first bit body is adapted to frictionally engage with the second bit body. For the purposes of the present invention the term "frictionally engage" means an engagement that is sufficiently positive to enable a drive applied to the first bit body to be transferred to the second bit body. When the first body is adapted to frictionally engage with the second bit body, it may define a male member adapted to form a friction fit with a compatible female member in the second bit body. Thus, the male member may comprise at least one surface that is adapted to engage and form a friction fit with a compatible surface on the second bit body.

8 Preferably, the at least one male member of the first bit body comprises a taper, such as a taper that narrows towards its leading end. Examples of tapers include those in general accordance with a MorseTM, Brown & SharpeTM, R8TM, Jacobs T M , JarnoTM or NMTBTM taper. As an alternative or in addition to the taper, the at least one male member of the first bit body may comprise a cross sectional shape designed to frictionally engage with at least one compatible female member of the second bit body. Preferably, the at least one male member is adapted to be received in a compatible female member in the second bit body and form a releasibly interlocking arrangement. The shape of the male member may be varied provided it is capable of forming a releasable engagement with a suitably shaped female member. Suitable cross-sectional shapes of the first bit body include, but are not limited to elliptical, such as circular or oval cross-section. Alternatively, the first bit body may have a polygonal cross section such as a triangle, square or rectangle. Another example of a cross sectional shape for the first bit body is a cross or "X" shape. To assist the engagement between the first and second bit bodies the first bit body may include a spline element that engages with a compatible spline element on the second bit body. The spline arrangement can provide a more positive engagement between the first and second bit bodies that may be required in certain situations. Different spline arrangements include parallel key splines, where the sides of equally-spaced grooves are parallel in both directions. Thus, the first bit body may further comprise a spline or groove arrangement. The first cutting part of the first bit body may comprise one or more cutting elements. The cutting elements may define a smooth or an angular cutting surface on the first bit body. For example, the cutting elements can be of the button or blade type or a combination thereof. Preferably, the cutting elements comprise a material with a hardness that is greater than the hardness of the cutting elements on the second bit body. For example, the hardness of the cutting elements on the first bit body may be at least 6, 7, 8, 9 or 10 on the Mohs scale of hardness. Examples of material suitable for the cutting element on the first bit body include, cobalt steel, carbides such as tungsten carbide and polycrystal diamond (PCD). Tungsten carbide tips may comprise 15% cobalt and have a volume of 0.226cm 3

.

9 As indicated above, it is preferred that the drill bit comprising the first bit body is adapted to pass through the longitudinal axial passage in the friction bolt in situ i.e. when the friction bolt has been inserted into a formation. Thus, it is preferred that the largest diameter or width of the drill bit is sized to enable the drill bit to pass through the longitudinal axial passage in the friction bolt when the friction bolt is inserted into a body of rock or other material. With this in mind it is preferred that the largest diameter or width of the first bit body of the drill bit according to the first aspect of the present invention is less than or equal to the largest diameter or width of the remainder of the drill bit. The drill bit may further comprise at least one conduit for delivering fluid to the interface between the first bit body and the material being drilled. Preferably, the at least one conduit defines one more apertures in the leading end of the first bit body. The drill bit may further comprise a shank at its following end adapted to engage with a drill string. Preferably, the shank includes a thread compatible with a thread on a drill string. According to a second aspect the present invention provides a two piece drill bit for a drill assembly including a friction bolt defining a longitudinal axial passage, the two piece drill bit comprising: (i) a first bit body at its leading end said first bit body including a first cutting part; and (ii) a second bit body including a second leading end that defines a second cutting part; wherein the first bit body and second bit body are adapted to releasibly engage with each other. The first bit body of the two piece drill bit according to the second aspect of the present invention is described elsewhere herein, particularly in relation to the first aspect of the present invention. Preferably, the second bit body is single use or disposable.

10 The second bit body can be adapted to releasibly engage with the first bit body in a variety of ways and is dependent on the configuration of the first bit body. Preferably, the second bit body is adapted to frictionally engage with the first bit body. When the second bit body is adapted to frictionally engage with the first bit body, it may comprise a surface that is adapted to engage with a compatible surface on the first bit body. In this form of the invention, the second bit body can define at least one female member adapted to frictionally engage with a compatible male member on the first bit body. Preferably, the at least one female member of the second bit body comprises a taper, for example a tapered socket. As an alternative or in addition to the taper, the at least one female member of the second bit body may define a bore or opening with a cross sectional shape that makes it suitable for frictionally engaging with the first bit body. In this regard, the at least one female member may define a bore or opening adapted to receive a compatible male member on the first bit body. Suitable cross-sectional shapes of the bore or opening in the female member of the second bit body include, but are not limited to elliptical, such as circular or oval cross section. Alternatively, the cross sectional shape of the bore or opening in the female member of the second bit body may be polygonal such as a triangle, square or rectangle. Examples of other cross-sectional shapes of the bore or opening in the female member include a cross or "X" shape. Preferably, the bore or opening extends entirely through the second bit body to allow at least part of the first bit body to extend through the second bit body. Thus, in this regard, the second bit body may be cylindrical or ring shaped with the inside of the cylinder or ring defining the bore or opening of the female member. It is preferred that, when releasibly engaged, the first and second bit bodies co-operate to form an integral cutting surface. The outer shape of the second bit body can be varied as required and can be elliptical, such as circular or oval or polygon shaped such as a triangle, square, rectangle or pentagon.

11 Preferably, the largest diameter or width of the two piece drill bit is defined by the diameter or width of the second bit body. 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 two piece drill bit is designed for use with. Preferably, the largest diameter or width of the two piece drill bit is slightly larger than internal diameter or width of the friction bolt in situ. This allows for the two piece drill bit to be used to drill a hole of a predetermined width to suit the friction bolt, and for the second bit body to then be disengaged from the first bit body so the first bit body can be retrieved through the longitudinal axial passage in the friction bolt with the remainder of the drill string for re-use. The operation of drill assemblies employing the two piece drill bits of the present invention is described in more detail elsewhere herein. The second cutting part of the second bit body may comprise one or more cutting elements. Preferably, the cutting elements comprise a material with a hardness that is less than the hardness of the cutting elements on the first bit body. For example, the hardness of the cutting elements on the second bit body may be less than 6, 7, 8, 9 or 10 on the Mohs scale of hardness. Examples of material suitable for the cutting element on second bit body include those used on the first bit body. The cutting elements may be of the button or blade type and can be any shape as required. Preferably, the second bit body is also adapted to releasibly engage with the leading end of a friction bolt. The releasable engagement may be varied provided the second bit body can be conveniently detached and attached to the friction bolt but does not detach unintentionally. Preferably, the releasable engagement is a friction fit such as where a part of the second bit body is adapted to be received in the leading end of the friction bolt but welding and glue could also be used. To further reduce the chances of the second bit body detaching unintentionally, a wrap or shroud could be applied to retain the second bit body on the friction bolt. According to a third aspect the present invention provides a drill assembly comprising: (i) a drill string, 12 (ii) a drill bit according to a first or 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 according to a first or 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 method inserting a friction bolt, defining a longitudinal axial passage, into a formation, the method comprising the steps of: (i) providing a drill assembly including a friction bolt, and a two piece drill bit according to a second aspect of the present invention mounted on a drill string and including a first bit body and a second bit body in releasable engagement with each other; (ii) drilling a hole in the formation using the drill assembly; (iii) disengaging the second bit body from the first bit body; and (iv) retrieving the drill string and the first bit body from the hole through the longitudinal axial passage. According to a sixth aspect the present invention provides a drill bit for a drill assembly including a friction bolt defining a longitudinal axial passage, the drill bit comprising: (i) a bit body at its leading end including a cutting part; (ii) a means for releasibly engaging with the friction bolt; and (iii) a means for releasibly engaging with another bit body. Preferably, the bit body that forms part of the drill bit according to the sixth aspect of the present invention includes one or more of the features described herein in 13 relation to the second bit body that forms part of the two piece drill bit according to the second aspect of the present invention. Preferably, the means for releasibly engaging with the friction bolt is a friction fit member such as a part of the bit body adapted to be received in the leading end of the friction bolt. According to a seventh aspect the present invention provides a friction bolt comprising a drill bit according to a sixth aspect of the present invention. Preferably, the drill bit is releasibly engaged on the leading end of the friction bolt by a friction fit. Preferably, the outside diameter or width of the drill bit is greater than the inside diameter of the longitudinal axial passage. 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, 14 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. A drill bit for a drill assembly, including a friction bolt defining a longitudinal axial passage, according to a first embodiment of the first aspect of the present invention is depicted in Figure 1a and generally indicated by the numeral 10. The drill bit is reusable and comprises a first bit body 12 at its leading end 14 and a shank 16 at its following end 18 adapted to engage with a drill string 54 (see Figure 1d) via an internal threaded portion 20 in the shank 16. The first bit body 12 forms a frustoconical shaped male member that tapers towards its leading end defining a tapered outer surface 24 that is adapted to form a frictional engagement with a compatible female member in a second bit body in the form of a frustoconical shaped socket 26 (described more fully with respect to Figure 1 b) and also includes a first cutting part comprising cutting elements in the form of buttons 22a formed of tungsten carbide or some other suitable hard material. The outer diameter defined by the drill bit including the first bit body 12 is such that the drill bit 15 10 is adapted to pass through the longitudinal axial passage in a friction bolt. This is described in more detail later herein in relation to Figures 1 d-1 g. Figure 1 b depicts a second bit body that forms part of embodiments of the second, third, fourth, fifth, sixth and seventh aspects of the present invention, generally indicated by the numeral 28, and being adapted to releasibly engage with the first bit body 12 of the drill bit 10 in Figure 1a. The second bit body 28 is in the form of a cylindrical female member with a bore defining a frustoconcial shaped socket 26, the narrower end of the socket 26 being the leading end, and the socket 26 further defining a tapered inner surface 27 shaped to friction fit with the tapered outer surface 24 of the first bit body 12. The second bit body 28 is readily disposable and also defines a second cutting part comprising cutting elements in the form of buttons 22b formed of tungsten carbide. The main body 29 of the second bit body 28 is formed of a suitable metal such as a 4140 grade metal. Figure 1c shows a two piece drill bit according to an embodiment of a second aspect of the present invention. The two piece drill bit generally indicated by the numeral 40 comprises the first and second bit bodies 12, 28 releasibly engaged via a friction fit between respective and compatible tapered surfaces 24, 27. This two piece drill bit 40 is useful for one pass drilling that simultaneously inserts a friction bolt into a formation as it is being drilled. The first bit body 12 may include an aperture (not shown) that is part of a conduit (not shown) for delivering fluid to the interface between the two piece drill bit 40 and the formation being drilled during the drilling process. Figure 1d illustrates an embodiment of the drill assembly and drilling system according to the third and fourth aspects of the invention in a form ready for drilling. The drill assembly generally indicated by the numeral 50 includes a friction bolt 52 that surrounds a drill string 54. The two piece drill bit 40 is threaded on the leading end of the drill string 54 via the thread 20 in the shank 16 at the trailing end 18 of the drill bit 10 and includes the second bit body 28 friction fitted on drill bit 10 via first bit body 12.

16 The friction bolt 52 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 52 are provided by the slot 56 in the friction bolt 52 that allows the friction bolt 52 to contract as it enters the drill hole during the drilling process. Figures le, 1f and 1g are a series of images depicting the drilling process using the drill assembly and drilling system of Figure 1 d. The insertion process for the friction bolt 52 is best illustrated in Figures le and 1f that show, respectively, the friction bolt 52 partially and fully inserted into a body of rock 60. Figure 1 e shows that the part of the friction bolt 52 that has entered the drill hole contracts causing a reduction in the width of the slot 56. When fully inserted (Figure 1f), the width of slot 56 is reduced along its entire length. The resilient nature of the friction bolt 52 means that it is biased towards a position at which the slot 56 is open (see Figure 1d) thus the inserted friction bolt 52 provides outward pressure on the inside surface of the drill hole. Figure 1g show the friction bolt 52 full inserted and the drill string 54 fully retracted from the drill hole. When drilling is completed and the friction bolt 52 is full inserted (Figure 1f) the operator retracts the drill string 54 to move the two piece bit 40 away from the end of the hole and release the force which was holding the two pieces 10, 28 together. The operator then gives a short burst of percussion through the drill string 54 (free hammer) to dislodge or detach the second bit body 28 from the first bit body 12 on the bit 40. (Figure 1g). With the second bit body 28 disengaged, the drill string 54, including drill bit 10 and first bit body 12 can be retrieved from the hole (Figure 1g) and reused as required. In this regard, once the second bit body 28 is disengaged the drill string including the first bit body 12 is able to pass through the longitudinal axial passage in the friction bolt 52. The second bit body 28 remains behind in the drill hole 60. Figure 2 depicts a two piece drill bit for a drill assembly similar to that depicted in Figures 1c and is generally indicated by the numeral 140. The main difference being that the two piece drill bit 140 in Figure 2 has a second bit body 128 with a pentagonal outer cross sectional shape. The first bit body 112 of the two piece drill bit 140 is similar to the first bit body 12 in Figure 1a and 1c but includes a different 17 arrangement of cutting elements in the form of buttons 122a formed of tungsten carbide or some other suitable hard material. The first bit body 112 also includes an aperture 23 that is part of a conduit (not shown) for delivering fluid to the interface between the two piece drill bit 140 and the formation being drilled during the drilling process. The second bit body 128 is readily disposable and also defines a second cutting part comprising cutting elements in the form of buttons 122b arranged around the periphery of the second bit body 128. Again, the outer diameter defined by the drill bit including the first bit body 112 is such that the drill bit incorporating the first bit body 112 but with the second bit body 128 detached is adapted to pass through the longitudinal axial passage in a friction bolt. Figure 3 shows a two piece drill bit for a drill assembly similar to that depicted in Figures 1 c and 2 and is generally indicated by the numeral 240. The main difference being that the two piece drill bit 240 in Figure 3 has a first bit body 212 with a rectangular outer cross sectional shape and includes a different arrangement of cutting elements in the form of buttons 222a formed of tungsten carbide or some other suitable hard material. The first bit body 212 also includes apertures 223 that are parts of conduits (not shown) for delivering fluid to the interface between the two piece drill bit 240 and the formation being drilled during the drilling process. The second bit body 228 of the two piece drill bit 240 is readily disposable and similar to the second bit body 28 in Figure 1 b and 1 c but includes a different arrangement of cutting elements in the form of buttons 222b. Again, the outer diameter defined by the drill bit including the first bit body 212 is such that the drill bit incorporating the first bit body 212 but with the second bit body 228 detached is adapted to pass through the longitudinal axial passage in a friction bolt. Figure 4a depicts a drill bit for a drill assembly according to another embodiment of the first aspect of the present invention generally indicated by the numeral 410. The drill bit is reusable and comprises a first bit body 412 at its leading end 414 and a shank 416 at its following end 418 adapted to engage with a drill string 54 (see Figure 1d) via an internal threaded portion 420 in the shank 416.

18 The first bit body 412 forms a cross shaped male member that is adapted to form a frictional engagement with a compatible female member in a second bit body in the form of a cross shaped socket and also includes a first cutting part comprising cutting elements in the form of blades 455 formed of tungsten carbide or some other suitable hard material. The outer diameter defined by the drill bit including the first bit body 412 is such that the drill bit 410 is adapted to pass through the longitudinal axial passage in a friction bolt. This is described in more detail with respect to another embodiment in relation to Figures 1d-1g. Figure 4b depicts a two piece drill bit according to an embodiment of a second aspect of the present invention. The two piece drill bit generally indicated by the numeral 440 comprises the first and second bit bodies 412, 428 releasibly engaged via a friction fit. This two piece drill bit 440 is useful for one pass drilling that simultaneously inserts a friction bolt into a formation as it is being drilled. The first bit body 412 includes an aperture 423 that is part of a conduit (not shown) for delivering fluid to the interface between the two piece drill bit 440 and the formation being drilled during the drilling process. Figures 5a and 5c depict a drill bit for a drill assembly according to another embodiment of the first aspect of the present invention generally indicated by the numeral 510. The drill bit is reusable and comprises a first bit body 512 at its leading end 514 and a shank 516 at its following end 518 adapted to engage with a drill string 54 (see Figure 1d) via an internal threaded portion 520 in the shank 516. The first bit body 512 forms a wedge shaped male member that is adapted to form a frictional engagement with a compatible female member in a second bit body in the form of a socket and also includes a first cutting part comprising a cutting element in the form of a blade 555 formed of tungsten carbide or some other suitable hard material. The outer diameter defined by the drill bit including the first bit body 512 is such that the drill bit 510 is adapted to pass through the longitudinal axial passage in a friction bolt. This is described in more detail with respect to another embodiment in relation to Figures 1d-1g. Figure 5b depicts a two piece drill bit according to an embodiment of a second aspect of the present invention. The two piece drill bit generally indicated by the 19 numeral 540 comprises the first and second bit bodies 512, 528 releasibly engaged via a friction fit. This two piece drill bit 540 is useful for one pass drilling that simultaneously inserts a friction bolt into a formation as it is being drilled. Figures 5d and 5e depicts a two piece drill bit for a drill assembly according to another embodiment of the second aspect of the present invention generally indicated by the numeral 540 and including a drill bit according to another embodiment of the first aspect of the invention that is generally indicated by the numeral 510 and a second bit body generally indicated by the numeral 528 frictionally engaged therewith. The two piece drill bit has a leading end 514 and a shank 516 at its following end 518 adapted to engage with a drill string 54 (see Figure 1d) via an internal threaded portion 520 in the shank 516. The first bit body 512 of the two piece drill bit forms a male member that is tapered towards its leading end defining a tapered outer surface 524 and is adapted to form a frictional engagement with the compatible female member in the second bit body 528 in the form of a tapered socket or bore. The first bit body 512 has a generally circular cross section but includes three concave cut-outs or grooves 525 that are shaped and positioned to engage with compatible splines on the inside surface of the tapered socket or bore in the second bit body 528. The inclusion of the grooves 525 and splines allows for a more positive frictional engagement between the first and second bit bodies 512, 528. It will be appreciated that the grooves could be included in the second bit body 528 and the splines provided in the first bit body 512, if required. The first bit body 512 also includes a first cutting part comprising cutting elements in the form of buttons 522a formed of tungsten carbide or some other suitable hard material. The first bit body 512 also includes three apertures 523 that delivering fluid to the interface between the two piece drill bit 540 and the formation being drilled during the drilling process via conduit 527. The second bit body 528 has a generally circular cross section but also includes three concave cut-outs or grooves 529 that are positioned equidistant apart on its outer face. The inclusion of the grooves 529 allows for a more positive frictional engagement between the second bit body 528 and the formation being drilled and to 20 allow for the cuttings created during the drilling process to pass around the sides of the bit and hence be removed from the drilling interface. The second bit body 528 also includes a second cutting part comprising cutting elements in the form of buttons 522b formed of tungsten carbide or some other suitable hard material. The outer diameter defined by the first bit body 512 is such that the drill bit 510, with the second bit body 528 detached, is adapted to pass through the longitudinal axial passage in a friction bolt after it has been inserted into a hole in the formation being drilled. This is described in more detail with respect to another embodiment in relation to Figures 1d-1g. The two piece drill bit 540 comprises the first and second bit bodies 512, 528 releasibly engaged via a friction fit. This two piece drill bit 540 is useful for one pass drilling that simultaneously inserts a friction bolt into a formation as it is being drilled. Figures 5f and 5g depicts a two piece drill bit for a drill assembly according to another embodiment of the second aspect of the present invention generally indicated by the numeral 640 and including a drill bit according to another embodiment of the first aspect of the invention that is generally indicated by the numeral 610 and a second bit body generally indicated by the numeral 628 frictionally engaged therewith. The two piece drill bit has a leading end 614 and a shank 616 at its following end 618 adapted to engage with a drill string 54 (see Figure 1d) via an internal threaded portion 620 in the shank 616. The first bit body 612 of the two piece drill bit forms a male member that is tapered towards its leading end defining a tapered outer surface 624 and is adapted to form a frictional engagement with the compatible female member in the second bit body 628 in the form of a tapered socket or bore. The first bit body 612 has a cross section that is generally shaped in the form of a blunt reuleaux triangle the enables the first bit body 612 to engage with a suitable shaped inside surface of the tapered socket or bore in the second bit body 628. The cross sectional shape of the first and second bit bodies 612, 628 allows for a more positive frictional engagement therebetween. The first bit body 612 also includes a first cutting part comprising cutting elements in the form of buttons 622a formed of tungsten carbide or some other suitable hard 21 material. The first bit body 612 also includes three apertures 623 that deliver fluid to the interface between the two piece drill bit 640 and the formation being drilled during the drilling process via conduit 627. The second bit body 628 also has a generally circular cross section but also includes a first set of three concave cut-outs or grooves 629 that are positioned equidistant apart on its outer face and second set of three smaller concave cut-outs 631 located equidistant between each groove 629. The inclusion of the grooves 628 and 629 allows for a more positive frictional engagement between the second bit body 628 and the formation being drilled. The second bit body 628 also includes a second cutting part comprising cutting elements in the form of buttons 622b formed of tungsten carbide or some other suitable hard material. The outer diameter defined by the first bit body 612 is such that the drill bit 610, with the second bit body 628 detached, is adapted to pass through the longitudinal axial passage in a friction bolt after it has been inserted into a hole in the formation being drilled. This is described in more detail with respect to another embodiment in relation to Figures 1d-1g. The two piece drill bit 640 comprises the first and second bit bodies 612, 628 releasibly engaged via a friction fit. This two piece drill bit 640 is useful for one pass drilling that simultaneously inserts a friction bolt into a formation as it is being drilled. Figure 6 illustrates a friction bolt 52 according to an embodiment of the seventh aspect of the present invention including a slot 56, a collar 55 and drill bit 28 releasibly engaged at its leading end by a friction fit. The friction bolt 52 is adapted to be received on a drill rod including a drill bit that is shaped to frictionally engage in a socket (not shown) in drill bit 28. Once received thereon the drill assembly can be used to drill a hole and fit a friction bolt as generally outlined in Figures 1e, 1f and 1g. 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 22 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.

Claims

1. A drill bit for a drill assembly including a friction bolt defining a longitudinal axial passage, the drill bit comprising a first bit body at its leading end said first bit body including a first cutting part and being adapted to releasibly engage with a second bit body; wherein the drill bit is adapted to pass through the longitudinal axial passage in the friction bolt.

2. A drill bit according to claim 1, adapted to pass through the longitudinal axial passage in the friction bolt is when the friction bolt is in situ.

3. A drill bit according to claim 1 or 2 wherein the first bit body is adapted to frictionally engage with the second bit body wherein said frictional engagement is sufficiently positive to enable rotational drive applied to the first bit body to be transferred to the second bit body.

4. A drill bit according to claim 3 wherein the first bit body comprises a male member adapted to form a friction fit with a compatible female member in the second bit body.

5. A drill bit according to claim 4 wherein the male member defines at least one surface that is adapted to engage and form a friction fit with a compatible surface on the second bit body.

6. A drill bit according to claim 4 or 5 wherein the first bit body tapers towards its leading end.

7. A drill bit according to claim 6 wherein the taper comprises a taper selected from the group consisting of Morse TM, Brown & Sharpe TM, R8TM, JacobS TM , JarnoTM or NMTB TM .

8. A drill bit according to claim 4 or 5 wherein the first bit body is adapted to form an interlocking friction fit with the second bit body.

9. A drill bit according to claim 8 wherein the first bit body has a cross sectional shape selected from elliptical, circular, oval, polygonal, triangle, square, rectangle or cross or "X" shaped. 24

10.A drill bit according to claim 8 wherein the first bit body has a cross sectional shape that defines a reuleaux polygon.

11. A drill bit according to claim 8 wherein the first bit body has a cross sectional shape that defines a blunt reuleaux polygon.

12. A drill bit according to claim 9 or 10 wherein the reuleaux polygon is a reuleaux triangle.

13. A drill bit according to any one of the preceding claims further comprising at least one spline or groove.

14.A drill bit according to any one of the preceding claims wherein the first cutting part comprises a button or blade type cutting element or a combination thereof.

15.A drill bit according to any one of the preceding claims wherein the hardness of the first cutting part is greater than the hardness of the cutting part on the second bit body.

16. A drill bit according to any one of the preceding claims further comprising at least one conduit for delivering fluid to the interface between the first bit body and the material being drilled.

17. A drill bit according any one of the preceding claims further comprising a shank at its following end adapted to engage with a drill string.

18. A drill bit according to claim 17 wherein the shank is adapted to be threaded on to a drill string.

19.A two piece drill bit for a drill assembly including a friction bolt defining a longitudinal axial passage, the two piece drill bit comprising: (i) a first bit body at its leading end said first bit body including a first cutting part; and (ii) a second bit body including a second leading end that defines a second cutting part; wherein the first bit body and second bit body are adapted to releasibly engage with each other. 25

20.A two piece drill bit according to claim 19 wherein the first bit body comprises a first bit body according to any one of claims 1-18.

21.A two piece dill bit according to claim 19 or 20 wherein the second bit body is disposable.

22.A two piece drill bit according to any one of claims 19 to 21 wherein the second bit body is adapted to frictionally engage with the first bit body.

23.A two piece drill bit according to claim 22 wherein the second bit body comprises a surface that is adapted to engage with a compatible surface on the first bit body.

24. A two piece drill bit according to claim 23 wherein the second bit body defines at least one female member adapted to frictionally engage with a compatible male member on the first bit body.

25.A two piece drill bit according to claim 24 wherein the at least one female member of the second bit body comprises a tapered socket.

26. A two piece drill bit according to any one of claims 19 to 25 wherein the at least one female member has a cross-sectional shape that is elliptical, polygonal or "X" shaped.

27.A two piece drill bit according to claim 25 or 26 wherein the tapered socket extends entirely through the second bit body to allow at least part of the first bit body to extend through the second bit body.

28.A two piece drill bit according to claim 27 wherein the second bit body is cylindrical or ring shaped with the inside of the cylinder or ring defining the bore or opening of the female member.

29.A two piece drill bit according to any one of claims 19 to 28 wherein the first and second bit bodies co-operate to form an integral cutting surface.

30.A two piece drill bit according to any one of claims 19 to 29 wherein the largest diameter or width of the two piece drill bit is defined by the diameter or width of the second bit body. 26

31.A two piece drill bit according to claim 30 wherein the largest diameter or width of the two piece drill bit is slightly larger than internal diameter or width of the friction bolt in situ.

32.A drill bit according to claim 1 or a two piece drill bit according to claim 19 wherein said cutting parts comprise at least one cutting element in the form of a button formed of tungsten or some other suitable material.

33.A two piece drill bit according to claim 9 wherein the second bit body is adapted to releasibly engage with the leading end of a friction bolt.

34.A two piece drill bit according to claim 33 wherein the releasable engagement is a friction fit.

35. A drill assembly comprising: (i) a drill string; (ii) a drill bit according to claim 1 mounted on the leading end of the drill string; and (iii) a friction bolt defining a longitudinal axial passage.

36. A drilling system comprising: (i) a drill string; (ii) a drill bit according to claim 1; (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 and the friction bolt.

37.A method inserting a friction bolt, defining a longitudinal axial passage, into a formation, the method comprising the steps of: 27 (i) providing a drill assembly including a friction bolt, and a two piece drill bit according to claim 19 mounted on a drill string and including a first bit body and a second bit body in releasable engagement with each other; (ii) drilling a hole in the formation using the drill assembly; (iii) disengaging the second bit body from the first bit body; and (iv) retrieving the drill string and the first bit body from the hole through the longitudinal axial passage.

38.A drill bit for a drill assembly including a friction bolt defining a longitudinal axial passage, the drill bit comprising: (i) a bit body at its leading end including a cutting part; (ii) a means for releasibly engaging with the friction bolt; and (iii) a means for releasibly engaging with another bit body.

39. A drill bit according to claim 38 wherein the means for releasibly engaging with the friction bolt is a friction fit member.

40.A drill bit according to claim 39 wherein the friction fit member is a part of the bit body adapted to be received in the leading end of the friction bolt.

41. A friction bolt comprising a drill bit according to claim 38.

42.A friction bolt according to claim 41 wherein the drill bit is releasibly engaged on the leading end of the friction bolt by a friction fit.

43.A friction bolt according to claim 41 or 42 wherein the largest outside diameter or width of the drill bit is greater than the largest inside diameter of the longitudinal axial passage.