This application claims priority from Australian provisional patent application No 2015900154 filed on 20 January 2015 entitled "Point Anchored Friction Bolt", the entire contents of which are hereby incorporated by reference.

Technical Field

[0001] This invention relates to rock bolts, and in particular to friction bolts. Background

[0002] Rock bolts are used in rock strata for the purpose of stabilising the strata. One type of rock bolt commonly used in hard rock mines is known as a friction bolt. This type of bolt comprises a tube, typically made of steel, that is split longitudinally and which is forced into a bore, drilled into rock strata which is marginally smaller than the diameter of the tube. The tube becomes compressed so that the external surface of the tube engages the internal surface of the bore, anchoring the rock bolt inside the bore by friction forces.

[0003] Friction bolts are relatively cheap to manufacture and are easy to use compared with some other types of rock bolts which often require resin or cement to lock them into the bore. However, friction bolts do have a number of drawbacks. One significant drawback is the tendency for friction bolts to disengage from the bore when a sufficiently large force is applied to the bolt

[0004] It is known from US 4312604, to weld lands inside the tube, to narrow the internal diameter of the tube at a specific location along the tube, and use oversized, wedge shaped inserts which engage with the lands to expand the tube at that location to provided better engagement of the bolt in the bore at that location. However, the added complexity of the tube of US 4312604 increases manufacturing costs, particularly due to the additional components, and the additional step of welding the lands in the correct location inside the split tube.

[0005] Australian patent application No 2014215940, by the applicant for the present application, at least partly addresses the cost and complexity issues of US 4312604, by using a floating arrangement for the expander wedges which avoids the need for welding, and thus reduces the manufacturing costs. However while the performance of the friction bolt of AU 2014215940 is relatively good, it is still quite a heavy product and therefore is quite expensive to manufacture in terms of transport costs and materials used.

[0006] Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each claim of this application.

[0007] Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

Summary

[0008] According to the present invention there is provided rock bolt for frictionally engaging with the internal surface of a bore drilled into rock strata, the bolt comprising a generally circular tube defining a longitudinal split and a longitudinal axis, the tube being radially expandable, the bolt having a first leading end for insertion into a bore and a second end defining a head; and expander means for expanding the diameter of the tube at least one location along the tube, the expander means comprising first and second expander elements arranged so that relative movement of the two elements causes the diameter of the tube to expand at that location; wherein the first expander element is mounted on an elongate element which is aligned generally along the longitudinal axis of the tube, one end of the elongate element defining a first engagement means located inside the tube proximate to the expander elements and configured to receive a drive means defining a complementary, second engagement means, the second expander element locates between the rod and the tube; the arrangement being such that rotation of the elongate element by the drive means causes the relative movement of the two elements to cause the diameter of the tube to expand at the location.

[0009] By providing the engagement means for engagement with a drive inside the tube proximate to the expander elements reduces the weight of the friction bolt by avoiding the requirement for a relatively heavy solid threaded rod extending the length of the rock bolt. This reduces the weight and costs of the bolt, and also allows the bolt to be installed in mines/tunnels/slopes where solid bars cannot be used. The friction bolt may be used even in poor ground and has the advantage that it is lighter and cheaper than existing designs.

[0010] Preferably, the second expander element is not secured to the tube.

[0011] In a preferred embodiment a contraction is defined in the internal diameter of the tube which limits the movement of the second element towards the proximal end of the friction bolt.

[0012] Typically, the leading end of the bolt is tapered.

[0013] The elongate element may be a bar or rod which is externally threaded and defines one threaded end and at an opposite end which is preferably in the form of an head portion which is enlarged relative to the threaded part of the elongate element, which head portion defines the first engagement means, which will typically be in the form of a shaped socket for receiving a drive.

[0014] Typically the socket will be hexagonal for receiving a hexagonal drive steel, although other shapes are possible and may be used in certain applications, including square.

[0015] In a preferred embodiment, a floating ring locates on and/or around the elongate element between the head and the contraction and includes a face which is configured to seat against the contraction.

[0016] The first expander element may be in the form of a wedge which defines an internally threaded bore and wherein rotation of the elongate element/rod draws the wedge in the direction of the head of the bolt.

[0017] Preferably, the second expander element comprises a shell defining a plurality of leaves which are spaced from one another and the first expander element defines a projection, which projects outwardly from a longitudinal axis of the bolt and which locates in a longitudinal gap between two leaves of the shell to inhibit rotation of the first expander element relative to the second expander element, about the longitudinal axis. The projection may be in the form of a fin whose longitudinal axis is parallel to the longitudinal axis if the bolt.

[0018] In a preferred embodiment, the second expander element comprises a shell defining a plurality of leaves which are spaced from one another and wherein a projection is defined on the second expander element which projects outwardly from a longitudinal axis of the bolt and which locates in the longitudinal split to inhibit rotation of the second expander element relative to the tube about the longitudinal axis.

[0019] Preferably, the projection on the second expander element is in the form of a pair of fins whose longitudinal axes are parallel to the longitudinal axis if the bolt and which are located on adjacent leaves of the shell spaced by a distance approximately equal to the width of the split.

[0020] The invention also contemplates a method of installing a rock bolt according to any preceding aspect comprising: drilling a bore into a rock wall, strata or the like, inserting a leading end of the bolt/tube into the opening of the bore; engaging a first engagement means located inside the tube proximate to expander elements of the rock bolt with a drive means; driving the rock bolt into the bore using percussion; rotating the drive means to cause the expander elements to expand the tube; and disengaging the drive means and removing the drive means from inside the tube.

Brief Description of Drawings

[0021] A specific embodiment of the present invention will now be described, by way of example only, and with reference to the accompanying drawings in which:-

Figure 1 is a schematic view of a friction bolt embodying the present invention;

Figure 2 is an isometric view of a wedge and expansion shell assembly of the friction bolt of Figure 1 ;

Figure 3 is an isometric view of an opposite end of the wedge shown in Figure 2; Figure 4 is an end view of the expansion shell assembly shown in Figure 2;

Figure 5 is an end view of a stud drive;

Figure 6 is an isometric view of the stud drive of Figure 5;

Figure 7 shows a drive steel;

Figure 8 is a side view of the stud drive shown in Figure 5; Figures 9a to 9c show views of a split ring; and

Figure 10 is a side view of the expansion shell assembly and stud drive, omitting the external friction bolt tube.

Description of Embodiments

[0022] Referring to the drawings, Figure 1 shows components an embodiment of a friction bolt 10. As shown in Figure 1, the bolt 10 includes an elongate tube 12 made of steel, which is typically in the order of 2m long, but whose length can vary from 1 to 5m depending on the particular application. A longitudinal axis 10a is shown extending along the centre of the tube. In Figure 1, the main part of the tube between the head or proximal end 12a and the distal or leading end 12b is omitted. The tube 12 is split longitudinally along its length. The split 14 extends along the length of the tube. The tube tapers at the leading end 12b of the bolt. The tapered end 16 makes it easier to insert the tube into a pre-drilled bore.

[0023] Approximately 300mm from the leading end 12b of the tube there is an indent 18 which is rolled/crimped into the tube which narrows the internal diameter of the tube at that point. The indent extends around the perimeter of the tube 12. A ring 20 is welded onto the exterior of the tube at the head end. [0024] Figures 2 to 4 show components of an expansion assembly/anchor 30, also shown in Figure 10. The anchor comprises a first expander element in the form of a conical wedge element 32 and a second expander element in the form of an external shell 34. The external shell comprises four leaves 36 which are generally arcuate in a cross-section transverse to the longitudinal axis of the bolt and subtend an angle of about 90°. (In alterative embodiments, the shell could comprise only two leaves or four leaves). The inner surface of the leaves 36 is smooth and part cylindrical. The external surface defines a series of ridges 38 which, in use, engage with the internal walls of the tube 12. The thickness of the leaves gradually increases from the end 40 of the leaves closest to the wedge element to the distal end 43.

[0025] Longitudinal gaps 42 are defined between the leaves, three of which are closed at one end and one of which 42a is not. The wedge element 32 defines an external fin 44 which locates in the gap 42a between two adjacent leaves to prevent the wedge rotating relative to the shell. Gap 42a is a through gap and is not closed at the distal end 43 of the shell furthest from the wedge. The second expander element/shell 34 defines two fins 52 and 54 which are located at the distal end 42 of the shell, spaced apart on either side of the through gap 42a.

[0026] In use, the two fins 52 and 54 locate in the split 14 in the tube 12. The distance between the two fins is about the same/slightly larger than the width of the split 14 so that the fins help to centre and steady the position of the shell 32 in the tube 12, as well as preventing rotation of the shell 32 relative to the tube.

[0027] The wedge element 32 is generally conical and tapers towards the external shell, having a wider end 60 and a narrower end 62. The wedge defines a central through hole 33 which is internally threaded (typically an M24 thread) to engage with the externally threaded part of a elongate rotatable element in the form of a stud drive 70.

[0028] The stud drive 70 is best seen in Figures 5 to 8. It comprises an elongate element in the form of relatively short externally threaded rod/bar, one end 72 of which is threaded with an M24 thread and the opposite end of which 74 is enlarged and defines a head 74 in which is defined a hexagonal opening/socket 76 configured for receiving a drive steel 78.

[0029] Figures 9a to 9c show a split ring 80 which fits onto the stud drive, in a floating fit. One face of the ring 82 includes a concavely curved/shaped side portion to nest with the curved of the crimp 18. The opposite face 84 is planar.

[0030] The components of the friction bolt are assembled as shown in Figure 1, although the interaction between the components can best be seen in Figure 10, which omits the external tube.

[0031] In particular, during assembly the rod is inserted into the tube 12 with the floating split ring 80 mounted on the rod adjacent the head 74, with the planar face 84 facing the head 74. The floating ring is free to move on the rod and the curved face 82 seats into the radial crimp. The expansion assembly sits on the opposite side of the crimp 18. The stud drive 70 is located inside the expansion shell and is screwed onto the wedge until hand tight. Once assembled, the exposed thread that protrudes from the wedge is contoured/punched to prevent the assembly from loosening during

installation.

[0032] In use, the friction bolt is inserted in a pre-drilled hole which is marginally smaller than the external diameter of the tube. The drive steel 78 is mounted on a drilling rig drive and is inserted into the stud drive of the bolt when the bolt is mounted onto the drilling rig boom. The stud drive may remain inactive during insertion of the bolt into the hole, which relies on percussion to hammer the bolt into the rock, provided that the drive steel 78 is not rotated. Once the bolt 10 is completely installed with the split ring 80 hard against the crimp 18 and the head 74, left hand rotation is applied to the drive steel which rotates the stud drive turning the left hand M24 thread of the rod 70. The rotating wedge 32 is drawn along the rod into the expansion shell 34, and this expansion of the shell point anchors the friction bolt 10. This friction bolt may be used even in poor ground and has the advantage that it is lighter and cheaper than existing designs and it does not require a solid rod which extends to the head of the friction bolt, reducing material costs and weight.

[0033] The length of the hexagonal socket for receiving a drive steel is typically around 75mm as this improves the alignment of the stud drive and improves installation accuracy.

[0034] It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.