Field

[0001] The present invention relates to strata control in civil engineering and mining operations and in particular relates to a friction bolt for securing the roof or wall of a mine, tunnel or other ground excavation.

Background

[0002] A current method of stabilising the roof or wall of an underground mine involves the use of friction bolts, otherwise known as friction rock stabilisers. Friction bolts have a generally cylindrical body and typically have a collar, in the geometric form of a torus, welded to the trailing end of the body. The leading end portion of the body is generally tapered to assist in inserting the friction bolt into a bore hole drilled into the rock strata. The body is split down one side such that, when it is driven into a slightly undersized hole in the rock strata the friction bolt body elastically deforms to reduce the size of the split in the body. This elastic deformation exerts radial forces against the wall of the bore hole, providing a corresponding frictional force, retaining the friction bolt within the bore hole. A plate washer is typically fitted to the body directly above the collar such that the collar bears the plate washer against the rock face of the mine to distribute axial loads carried by the friction bolt across the face of the roof.

[0003] Where the bore hole (and accordingly the friction bolt) is oriented perpendicular to the rock face (and accordingly perpendicular to the plate washer), there is an even load transfer between the collar and the plate washer around the periphery of the friction bolt. Said typical friction bolts have been known to fail when misaligned with the rock face. Previous workers have attempted to address failure due to misalignment by using a ball washer or similar device to increase contact between the friction bolt and the plate washer around the periphery of the rock face. Said ball washers may be integrated with the collar, alternatively be formed of a separate item locating proximal to the collar. It has been found that this approach has only achieved limited success in improving the failure rate due to misalignment of the friction bolt. Object of the Invention

[0004] It is an object of the present invention to substantially overcome or at least ameliorate the above disadvantage.

Summary of Invention

[0005] The present invention provides a friction bolt comprising:

a generally tubular friction bolt body having a central longitudinal axis and

longitudinally extending between a friction bolt body leading end and a friction bolt body trailing end, said friction bolt body defining a cavity longitudinally extending through said friction bolt body and having a split longitudinally extending along said friction bolt body to said friction bolt body leading end; and

a collar fixed to, and extending about, said friction bolt body adjacent said friction bolt trailing end, said collar having a collar leading end wall projecting radially beyond said friction bolt body and defining an annular shoulder for engaging a plate washer to be mounted on said friction bolt body, a collar radially outer side wall, a collar radially inner side wall and a collar trailing end wall;

wherein said collar radially inner side wall and said collar radially outer side wall each define a substantially right cylindrical surface.

[0006] In one or more embodiments, said collar leading end wall has a radially inner annular recessed region adjacent said collar radially inner side wall, said friction bolt further comprising a weld fixing said friction bolt body to said collar, said weld being at least partially located in said recessed region and extending about said friction bolt body.

[0007] In one or more embodiments, said collar further comprises a tab projecting longitudinally beyond said collar leading end wall and located in said split of said friction bolt body.

Preferably said tab at least substantially bridging said split, or is sized to engagingly fit within the split. In a preferred embodiment, the tab is integrally formed with the collar.

[0008] In one form, said friction bolt body extends through said collar, such that said friction bolt body trailing end longitudinally projects beyond said collar, said collar radially inner side wall abutting said friction bolt body. [0009] In an alternative form, said collar is mounted on, and longitudinally projects beyond, said friction bolt body trailing end, said collar leading end wall abutting said friction bolt body trailing end.

[0010] In one or more embodiments, said collar has a longitudinally extending slot located approximately radially opposite said tab.

[0011] In one or more embodiments, said collar leading end face has a radially outer annular tapered region adjacent said collar radially outer side wall, said tapered region tapering from said collar radially outer side wall toward said collar radially inner side wall.

[0012] In an aspect, the present invention provides a collar when used with the rock bolt of the preceding aspect and preferred features.

[0013] As a result of extensive study, the present inventors have identified a failure mode for typical prior art friction bolts that can occur where there is misalignment and the borehole is not oriented perpendicular to the rock face, or the plate washer is otherwise not arranged

perpendicular to the friction bolt, such that the collar and the plate washer are asymmetrically loaded with an increased load transfer (and an increased contact) on one side. As a result, the plate washer may deform at the point of increased contact and / or the collar may bend, particularly if the point of contact with the plate washer is located across the open split of the friction bolt body. When the collar bends, the weld fixing the collar to the friction bolt body may also start to fail, by bending or peeling, gradually tearing the welded metal in this region and resulting in failure of the friction bolt. As a result of the discovery of this failure mode, the present inventors have surprisingly found that incorporating a ball washer type assembly into the friction ring, as previous workers have proposed, may actually exasperate failure, since cross sectional area of the collar may be sacrificed to incorporate the ball washer shape.

Brief Description of Drawings

[0014] Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings wherein:

[0015] Figure 1 is a front elevation view of a friction bolt according to a first embodiment; [0016] Figure 2 is a rear elevation view of the friction bolt assembly of Figure 1;

[0017] Figure 3 is a fragmentary isometric view from below of the trailing region of the friction bolt of Figure 1;

[0018] Figure 4 is a fragmentary isometric view from above of the trailing region of the friction bolt of Figure 1;

[0019] Figure 5 is an enlarged plan view of the friction bolt of Figure 1;

[0020] Figure 6 is a fragmentary cross-sectional view of the trailing region of the friction bolt of Figure 1, taken at Section 6-6 of Figure 5;

[0021] Figure 7 is an isometric view of the collar of the friction bolt of Figure 1;

[0022] Figure 8 is an isometric of a modified form of the collar of Figure 7;

[0023] Figure 9 is a partially cross sectioned view of a friction bolt installation utilizing the friction bolt of Figure 1;

[0024] Figure 10 is a front elevation view of a friction bolt according to a second embodiment;

[0025] Figure 11 is a rear elevation view of the friction bolt assembly of Figure 10;

[0026] Figure 12 is a fragmentary isometric view from below of the trailing region of the friction bolt of Figure 10;

[0027] Figure 13 is a fragmentary isometric view from above of the trailing region of the friction bolt of Figure 10;

[0028] Figure 14 is an enlarged plan view of the friction bolt of Figure 10;

[0029] Figure 15 is a fragmentary cross-sectional view of the trailing region of the friction bolt of Figure 1, taken at Section 15-15 of Figure 14;

[0030] Figure 16 is an isometric view of the collar of the friction bolt of Figure 10; [0031] Figure 17 is an isometric of a modified form of the collar of Figure 16; and

[0032] Figure 18 is a partially cross sectioned view of a friction bolt installation utilizing the friction bolt of Figure 10.

Description of Embodiments

[0033] A friction bolt 100 according to a first embodiment is depicted in Figures 1 to 7 of the accompanying drawings. The friction bolt 100 has a generally tubular friction bolt body 110 that longitudinally extends between a friction bolt body leading end 111 and a friction bolt body trailing end 112. The friction bolt body 110 defines a cavity 113 longitudinally extending through the friction bolt body 110. The friction bolt body 110 has a split 114 extending along the friction bolt body 110 to the friction bolt body leading end 111 to allow for radial compression of the friction bolt body 110 in the usual manner. Here the split 114 extends along the full length of the friction bolt body 110 from the friction bolt body trailing end 112. The friction bolt body 110 has a tapered leading portion 115 that tapers toward the friction bolt body leading end 111 in the usual manner to enable the friction bolt body 110 to be driven into a bore hole having a smaller diameter than the constant diameter of the primary portion 116 of the friction bolt body 110.

[0034] In one embodiment, the external diameter of the primary portion 116 of the friction bolt body 110 is approximately 47 mm, whilst the cross-section of the leading portion 115 of the friction bolt body 110 at the friction bolt body leading end 111 is of a reduced cross-sectional area. The wall thickness of the friction bolt body 110 is here approximately 3 mm. The friction bolt body 110 is typically formed of structural grade steel. In one embodiment, the friction bolt body 110 is formed of steel having a yield strength of 350 to 400 MPa and a hardness of about 119 Vickers hardness (64 Rockwell B hardness). In other embodiment, the dimensions of the friction bolt may vary. For example, other embodiments may include an external diameter of the primary portion 116 of the friction bolt body 110 of approximately 33 mm or 39mm, for example, with other dimension also finding use in industry.

[0035] The collar 130 is fixed to, and extends about, the friction bolt body 110 adjacent the friction bolt body trailing end 112. The collar 130 is typically formed of structural grade steel. In the first embodiment, the friction bolt body 110 extends through the collar 130, such that the friction bolt trailing end 112 longitudinally extends beyond the collar 130. The collar 130 has a collar leading end wall 131 that projects radially beyond the friction bolt 110. The collar leading end wall 131 defines an annular shoulder 132 for engaging a plate washer to be mounted on the friction bolt body 110, as will be discussed below. The collar 130 further has a collar radially outer side wall 133, a collar radially inner side wall 134 and a collar trailing end wall 135. The collar radially inner side wall 134 abuts the outer wall of the friction bolt body 110.

[0036] The collar radially outer side wall 133 has the geometric form of a right cylindrical surface. That is, the geometric form of the radially outer side wall 133 is formed by a straight line oriented parallel to the central longitudinal axis of the friction bolt (and of the collar 130) moved around the central longitudinal axis. The collar radially inner side wall 134 also has the form of a right cylindrical surface. The radially outer and inner side walls 134, 133 do not need to have the exact form of right cylindrical surfaces, as long as they are substantially right cylindrical, slight irregularities in the surface profiles are thus envisaged. The cross section of the thickness of the collar 130 between the radially inner and outer side walls 134, 133 is thus generally rectangular, as best shown in Figure 6 (apart from the collar leading and trailing end walls 131, 135, which are not necessarily planar in form). This can be contrasted with a standard friction bolt collar which has a torus form, with any cross section being circular in form. Forming the collar 130 with this more rectangular-cross section, particularly having the collar radially outer wall 133 and collar radially inner wall 134 formed at least substantially as right cylindrical surfaces, maximises the cross-sectional area of the cylinder 130 for any given overall diameter of the collar 130 (and for any given form of the collar leading end wall 131 and collar trailing end wall 135). This increased cross-sectional area of the collar 130 increases the stiffness of the collar 130 for any given overall diameter of the collar 130. The maximum diameter of the collar is generally dictated by installation equipment, and particularly the centraliser provided on the installation boom to help hold and guide the friction bolt body. The overall diameter of a collar of a friction bolt is thus typically restrained to being no greater than 63 mm for a standard 47 mm friction bolt so that the collar can pass through the centraliser. The present inventors have found that stiffening of the collar reduces the risk of bending of the collar.

[0037] The collar leading end wall 131 has a radially inner annular recessed region 136. The recessed region 136, together with the outer wall of the friction bolt body 110, defines an annular channel for receipt of a weld 150 fixing the friction bolt body 110 to the collar 130. The weld 150 is at least partially located in the recessed region 136 and extends about the friction bolt body 110. Typically, the weld 150 extends about the entire periphery of the friction bolt body 110, however it is also envisaged that the weld 150 may extend only part way around the friction bolt body 110, typically through at least 325 degrees of the full 360 degrees periphery.

A blind locating hole 139 is formed in the collar trailing end wall 135 for the purpose of identifying the orientation of the collar when welding the collar 130 to the friction bolt body 110

[0038] The collar 130 further comprises a tab 137 that projects longitudinally beyond the collar leading end wall 131. The tab 137 is also located radially inwardly of the collar radially inner side wall 134 and is located in the split 114 of the friction bolt body 110. The tab 137 at least substantially bridges the gap defined by the split 114. The tab 137 thus forms a bridging structure that supports the friction bolt body 110 against collapsing about the split 114 when the collar is asymmetrically loaded in the event of misalignment of the friction bolt 100 relative to the rock face and plate washer. The tab 137 is typically integrally formed with the remainder of the collar 130, typically by casting.

[0039] The annular shoulder 132 defined by the collar leading end wall 131 between the weld 150 and the collar radially outer side wall 133 forms a tapered region, which tapers from the collar radially outer end wall 133 toward the collar radially inner end wall 134. In the specific embodiment depicted, the shoulder 132 has a rounded form, however it is also envisaged that the shoulder 132 may be of a chamfered or filleted form. This tapering of the shoulder 132 further assists in maintaining contact between the collar 130 and a plate washer about its periphery in the event of misalignment. For configurations where the weld 150 does not extend around the entire periphery of the friction bolt 110, weld 150 will typically extend up to, and slightly beyond, the edges of the tab 137.

[0040] Figure 8 depicts a modified form of collar 130’ for use in the friction bolt 100 of the first embodiment. The modified collar 130’ is identical to the collar 130 shown in Figure 7, apart from a slot 138 that extends through the thickness of the collar 130’ between the radially outer and inner side walls 133, 134, approximately radially opposite the tab 137. The slot 138 allows for some expansion of the collar 130’ so as to accommodate a compressive fit of the collar 130’ on to the trailing region of the friction bolt body 110. [0041] Referring to Figure 9, the friction bolt 100 is installed in a bore hole 50 in the same manner as a standard friction bolt. Specifically, the bore hole 50 is drilled into the rock face 51 of a rock strata to be stabilised in the usual manner. The bore hole 50 is typically drilled with a standard installation rig with the drill bit having a diameter typically of 43-44 mm, which will typically result in a bore hole diameter of 43-45 mm, depending upon the rock strata type and hardness. Before inserting the friction bolt 100 into the bore hole 50, a plate washer 60 is mounted on the friction bolt body 110 adjacent the collar 130 and the friction bolt 100 is mounted on an installation rig. The installation rig then drives the friction bolt 100 into the bore hole 50, applying percussive force to the friction bolt 100 until the plate washer 60 is firmly engaged with the rock face 51, sandwiched between the rock face 51 and the collar 130, with the shoulder 132 of the collar 130 engaging the rim of the plate washer 60.

[0042] A friction bolt 200 according to a second embodiment is depicted in Figures 10 to 16 of the accompanying drawings. The friction bolt assembly 200 has the same friction bolt body 110 as the friction bolt 100, and accordingly will not be further discussed. The friction bolt 200 has a collar 230 of similar form to the collar 130 of the friction bolt 100. In the accompanying drawings, the collar 230 is provided with reference numerals equivalent to those of the collar 130, increased by 100.

[0043] The collar 230 is fixed to, and extends about, the friction bolt body 110 adjacent the friction bolt body trailing end 112. However, in the second embodiment, the collar 230 is mounted on, and longitudinally projects beyond, the friction bolt trailing end 112. The collar 230 has a collar leading end wall 231 that projects radially beyond the friction bolt 110. The collar leading end wall 231 defines an annular shoulder 232 for engaging a plate washer to be mounted on the friction bolt body 110, in a similar manner to the first embodiment. The collar 230 further has a collar radially outer side wall 233, a collar radially inner side wall 234 and a collar trailing end wall 235. The collar leading end wall 231 abuts the friction bolt body trailing end 112. In particular, the collar leading end wall 231 has a radially inner annular recessed region 236 that abuts the friction bolt body trailing end 112. The collar 230 has a smaller inner diameter, defined by the collar radially inner side wall 234, than that of the collar 130 of the first embodiment, such that the collar radially inner side wall 134 is generally aligned with the inner wall of the friction bolt body 110. The recessed region 236 is sufficiently broad to accommodate the friction bolt body trailing end 112 and to form, with the outer wall of the friction bolt body 110, an annular channel for receipt of the weld 150 fixing the friction bolt body 110 to the collar 230. The weld 150 is again at least partially located in the recessed region 236 and extends about the friction bolt body 110.

[0044] The collar radially outer and inner side walls 233, 234 each have the geometric form of a right cylindrical surface, as with the collar 130 of the first embodiment, so as to allow a relatively stiff collar for a given maximum collar diameter.

[0045] The collar 230 further comprises a tab 237 that projects longitudinally beyond the collar leading end wall 231. As best shown in Figure 16, the radially inner face of the tab 237 is generally aligned with the collar radially inner side wall 133. The tab 237 is located in the split 114 of the friction bolt body 110 and at least substantially bridges the gap defined by the split 114. The tab 237 is again typically integrally formed with the remainder of the collar 230, typically by casting.

[0046] The annular shoulder 232 defined by the collar leading end wall 231 between the weld 150 and the collar radially outer side wall 233 forms a tapered region, as with the collar 130.

[0047] Figure 17 depicts a modified form of collar 230’ for use in the friction bolt 200 of the second embodiment. Consistent with the modified collar 130’, the modified collar 230’ is identical to the collar 230 shown in Figure 16, apart from a slot 238 that extends through the thickness of the collar 230’ between the radially outer and inner side walls 233, 234, approximately radially opposite the tab 237.

[0048] Referring to Figure 18, the friction bolt 200 is also installed in a bore hole 50 in the same manner as a standard friction bolt. Specifically, the bore hole 50 is drilled into the rock face 51 of a rock strata to be stabilised in the usual manner. Before inserting the friction bolt 200 into the bore hole 50, a plate washer 60 is mounted on the friction bolt body 110 adjacent the collar 230 and the friction bolt 100 is mounted on an installation rig. The installation rig then drives the friction bolt 200 into the bore hole 50, applying percussive force to the friction bolt 200 until the plate washer 60 is firmly engaged with the rock face 51, sandwiched between the rock face 51 and the collar 230, with the shoulder 232 of the collar 230 engaging the rim of the plate washer 60.

[0049] Although specific embodiments of the invention are illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations exist. It should be appreciated that the exemplary embodiment or exemplary embodiments are examples only and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents. Generally, this application is intended to cover any adaptations or variations of the specific embodiments discussed herein.

[0050] It will also be appreciated that in this document the terms "comprise", "comprising", "include", "including", "contain", "containing", "have", "having", and any variations thereof, are intended to be understood in an inclusive (i.e. non-exclusive) sense, such that the process, method, device, apparatus or system described herein is not limited to those features or parts or elements or steps recited but may include other elements, features, parts or steps not expressly listed or inherent to such process, method, article, or apparatus. Furthermore, the terms "a" and "an" used herein are intended to be understood as meaning one or more unless explicitly stated otherwise. Moreover, the terms "first", "second", "third", etc. are used merely as labels, and are not intended to impose numerical requirements on or to establish a certain ranking of importance of their objects.