CA3008179C

CA3008179C - Friction bolt assembly

Info

Publication number: CA3008179C
Application number: CA3008179A
Authority: CA
Inventors: David William Evans
Original assignee: DSI Underground Australia Pty Ltd
Current assignee: DSI Underground Australia Pty Ltd
Priority date: 2015-12-16
Filing date: 2016-12-09
Publication date: 2024-01-02
Anticipated expiration: 2036-12-09
Also published as: CA3008179A1; AU2016369657B2; WO2017100818A1; AU2016369657A1

Abstract

A friction bolt assembly (100) has a longitudinally extending generally tubular friction bolt body (110) defining a cavity (113) and having a split longitudinally extending along the friction bolt body (110). A rod (120) longitudinally extends through the cavity (113). An expansion element (130) is mounted on, or integrally formed with, the rod (120) at or adjacent the rod leading end (121). The expansion element (130) has an engagement surface (136) tapering toward the rod trailing end (122). A sleeve ( 180) is mounted on the expansion element (130) adjacent the friction bolt body leading end (111). A drive head (140) is mounted on, or integrally formed with, the rod (120) at or adjacent the rod trailing end (122). The rod (120) is actuatable by rotation of the drive head (140) to draw the expansion element (130) toward the friction bolt body trailing end (112) such that the sleeve trailing end (182) abuts the friction bolt body leading end (111) and the engagement surface (136) engages the sleeve interior surface (185), radially outwardly deforming the sleeve (180).

Description

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

[0002] A current method of stabilizing the roof or wall of an underground mine involves the use of friction bolts, otherwise known as friction rock stabilizers. Friction bolts have a generally cylindrical body and a collar 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 hole, providing a corresponding frictional force, retaining the friction bolt within the hole. A plate washer is 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] The frictional forces generated between the friction bolt and bore hole wall are at times insufficient to properly anchor the friction bolt within the bore hole.
Accordingly, developments have been proposed to improve the transfer of load between the friction bolt and bore hole wall, including by filling the friction bolt with grout to increase its rigidity and to outwardly radially deform the friction bolt body following initial installation.
Object of the Invention

[0004] It is an object of the present invention to provide an improved friction bolt, or at least to provide a useful alternative to presently available friction bolts.

Summary of Invention

[0005] In a first aspect the present invention provides a friction bolt assembly comprising:
a generally tubular friction bolt body 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;
a rod longitudinally extending through said cavity between a rod leading end and a rod trailing end;
an expansion element mounted on, or integrally formed with, said rod at or adjacent said rod leading end, said expansion element having an engagement surface tapering toward said rod trailing end;
a sleeve mounted on said expansion element adjacent said friction bolt body leading end, said sleeve having a sleeve trailing end and an interior sleeve surface; and a drive head mounted on, or integrally formed with, said rod at or adjacent said rod trailing end, said rod being actuatable by rotation of said drive head to draw said expansion element toward said friction bolt body trailing end such that said sleeve trailing end abuts said friction bolt body leading end and said engagement surface engages said sleeve interior surface, radially outwardly deforming said sleeve.

[0006] Typically, said sleeve has a substantially cylindrical outer sleeve surface.

[0007] Typically, said inner sleeve surface tapers towards said sleeve trailing end. In one foil'', the taper of said inner sleeve surface matches the taper of said engagement surface.

[0008] In one or more embodiments, said interior sleeve surface and said engagement surface are of substantially matching generally frustoconical form.

[0009] In one or more alternative embodiments said interior sleeve surface has a plurality of substantially planar regions extending between a sleeve leading end of said sleeve and said sleeve trailing end, said engagement surface having a plurality of substantially matching substantially planar regions for engagement with said substantially planar regions of said interior sleeve surface. In one form, said sleeve may be provided with a weakened zone between each of said substantially planar regions of said interior sleeve surface.

[0010] Typically, said friction bolt assembly further comprises means for at least substantially preventing rotation of said expansion element relative to said friction bolt body.

[0011] Typically, said means comprises a key projecting from said engagement surface into said split of said friction bolt body.

[0012] Typically, said sleeve has a longitudinally extending split. Typically, said key extends into said split of said sleeve.

[0013] In one or more embodiments, said drive head is threadingly mounted on a threaded trailing portion of said rod such that, upon actuation of said rod by rotation of said drive head, said threaded trailing portion of said rod is drawn through said drive head.
In a preferred embodiment, said expansion element is threadingly mounted on a threaded leading portion of said rod, said threaded leading portion and said threaded trailing portion of said rod being like-handed, such that, upon actuation of said rod by rotation of said drive head, said rod rotates with said drive head, drawing said expansion element along said threaded leading portion of said rod.

[0014] In one embodiment, said friction bolt assembly further comprises a load transfer fitting mounted on said rod between said drive head and said friction bolt body trailing end, said load transfer fitting having a profiled leading face configured to engage and support said friction bolt body trailing end.

[0015] In one or more embodiments, said friction bolt assembly further comprises:
a stopping means mounted on, or integrally formed with, said rod and being longitudinally positioned between said friction bolt body leading end and said friction bolt body trailing end; and a collar fixed to said friction bolt body at or adjacent said friction bolt body trailing end;
wherein said stopping means and said collar are dimensioned to cooperate to at least substantially prevent said rod from ejecting completely from the friction bolt body through the friction bolt body trailing end.

[0016] In one or more embodiments, said stopping means comprises one or more swaged portions of the rod.

[0017] In a second aspect the present invention provides a method of installing the friction bolt assembly defined above, comprising the steps of:
drilling a bore hole into a rock face of a rock strata to be stabilized, said bore hole having a diameter greater than the maximum diameter of said expansion element and less than the maximum diameter of said friction bolt body;
inserting said friction bolt assembly into said bore hole with said expansion element leading;
applying percussive force to said friction bolt body to drive said friction bolt body into said bore hole with an interference fit;
rotating said drive head to actuate said rod, drawing said expansion element towards said friction bolt body trailing end, abutting said sleeve trailing end with said friction bolt body leading end and engaging said engagement surface with said sleeve interior surface, thereby outwardly radially deforming said sleeve into bearing engagement with the wall of said bore hole.
Brief Description of Drawings

[0018] Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings wherein:

[0019] Figure. 1 is a front elevation view of a friction bolt assembly according to a first embodiment;

[0020] Figure 2 is a front elevation view of the leading portion of the friction bolt assembly of Figure 1;

[0021] Figure 3 is a cross-sectional view of the leading portion of the friction bolt assembly of Figure 1;

[0022] Figure 4 is an isometric view of the leading portion of the friction bolt assembly of Figure 1;

[0023] Figure 5 is a front elevation view of the trailing portion of the friction bolt assembly of Figure 1;

[0024] Figure 6 is a cross-sectional view of the trailing portion of the friction bolt assembly of Figure 1;

[0025] Figure 7 is an isometric view of the trailing portion of the friction bolt assembly of Figure I;

[0026] Figure 8 is a front elevation view of the expansion element and sleeve of the friction bolt assembly of Figure 1;

[0027] Figure 9 is a transverse cross-sectional view of the expansion element and sleeve of Figure 8, taken at cross section 9-9;

[0028] Figure 10 is an isometric view of the expansion element and sleeve of Figure 8;

[0029] Figure 11 is a longitudinal cross-sectional view of the expansion element and sleeve of Figure 8;

[0030] Figure 12 is a partially cross-sectioned view of a partially completed installation of the friction bolt assembly of Figure 1;

[0031] Figure 13 is a partially cross-sectioned view of the completed installation of Figure 12;

[0032] Figure 14 is a partially cross-sectioned view of the installation of Figure 11, following elongation under load;

[0033] Figure 15 is a front elevation view of a friction bolt assembly according to a second embodiment;

[0034] Figure 16 is a front elevation view of the trailing portion of the friction bolt assembly of Figure 15;

[0035] Figure 17 is a cross-sectional view of the trailing portion of the friction bolt assembly of Figure 15;

[0036] Figure 18 is a partially cross-sectioned view of a partially completed installation of the friction bolt assembly of Figure 15;

[0037] Figure 19 is a partially cross-sectioned view of the completed installation of Figure 18;

[0038] Figure 20 is a partially cross-sectioned view of the installation of Figure 18 following failure;

[0039] Figure 21 is a front elevation view of an alternate form of expansion elements and sleeve;

[0040] Figure 22 is a transverse cross-sectional view of the expansion element and sleeve of Figure 21 taken at section 22-22;

[0041] Figure 23 is an isometric view of the expansion element and sleeve of Figure 21; and

[0042] Figure 24 is a longitudinal cross-sectional view of the expansion element and sleeve of Figure 21.
Description of Embodiments

[0043] A friction bolt assembly 100 according to a first embodiment is depicted in Figures Ito II of the accompanying drawings. The friction bolt assembly 100 has a generally tubular friction bolt body 110 that longitudinally extends between a friction bolt body leading end ill 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. A collar 117, in the general form of a torus, is welded to the friction bolt body 110 adjacent the friction bolt body trailing end 112.

[0044] In one embodiment, the external diameter of the primary portion 116 of the friction bolt body 110, being the maximum diameter 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, being the minimum cross-sectional area of the friction bolt body 110. In one embodiment, the cross-section of the leading portion 115 at the friction bolt body leading end 111 is of an oval configuration having a major axis (maximum) diameter of 40 mm and minor axis diameter of 26 mm, although it is also envisaged that the leading portion 115 at the friction bolt leading 111 may be generally circular.
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).

[0045] The friction bolt assembly 100 further includes an elongate rod 120 longitudinally extending through the cavity 113 in the friction bolt body 110 between a rod leading end 121 and a rod trailing end 122. The rod 120 is typically formed of rigid steel bar.

[0046] An expansion element 130 is mounted on the rod 120. The expansion element 130 is typically located toward the rod leading end 121 and in the embodiment depicted the expansion.
element 130 is located at or adjacent the rod leading end 121. As best Shown in Figures 3 and 4, in the embodiment depicted, the expansion element 130 is threadingl.y mounted onto a threaded leading portion 123 of the rod 120. The threaded leading portion 123 of the rod 120 is received within an aperture 133 extending through the expansion element 130. The aperture 133 has a threaded central portion 139 to .threadingly engage the threaded leading portion 123 of the rod 120. In the first embodiment, the expansion element 130, best depicted in Figures 8 to 11, is in the general form of a body of revolution having a frusto-conical tapered leading surface 134 extending and tapering to an open expansion element leading end 131, a generally cylindrical intermediate surface 135 trailing the leading surface 134 and defining the maximum diameter of the expansion element 130, a generally frusto-conical engagement surface 136 that tapers, here in a substantially linear manner, from the intermediate surface 135 towards the expansion.
element trailing end 132 and a cylindrical trailing surface 138, that extends from the engagement surface 136 to the expansion element trailing end 132. In the embodiment depicted, the maximum diameter of the expansion element 130, defined by the intermediate surface 135, is approximately 43 mm. This is greater than the internal diameter of the friction bolt body 110 at the friction bolt body leading end 111 and less than the maximum diameter of the friction bolt body 110.

[0047] As best depicted in Figures 2 and 4, the expansion element 130 may further comprise means for at least substantially preventing rotation of the expansion element 130 relative to the friction bolt body 110. In the first embodiment, the means is in the form of a surface feature of the expansion element 130, particularly in the form of a key 137. The key 137 projects from, and is integrally formed with, the engagement surface 136 and in the embodiment depicted extends from the expansion element trailing end 132 to the mid-surface 135. It is also envisaged that the key 137 may be of a shorter length, extending only along the trailing surface 138. As shown in Figures 1 and 6, the key 137 projects into the split 114 formed in the friction bolt body 110. As a result, rotation of the rod 120, which would tend to rotate the expansion element 130, results in the key 137 engaging an edge of the friction bolt body 110 bounding the split 114, preventing relative rotation, at least beyond minor movement associated with the free play of the key 137 within the slightly broader width of the split 114 at the friction bolt leading end 111.

[0048] The expansion element 130 is mounted on the rod 120 at a location such that the cylindrical trailing surface 138 extends through the friction bolt body leading end 111 into the cavity 113 defined by the friction bolt body 110.

[0049] The friction bolt assembly 100 further comprises a sleeve 180 mounted on the expansion element 130 adjacent the friction bolt body leading end 111. The sleeve 180, best depicted in Figures 8 to 11, is of a generally tubular form longitudinally extending between a sleeve leading end 181 and a sleeve trailing end 182. This sleeve 180 has a split 183 that extends along its length to readily allow for radial expansion. The sleeve 180 is mounted on the expansion element 130 with the key 137 extending therethrough. The sleeve 180 has a substantially cylindrical outer surface 184 and tapered frusto-conical inner surface 185 that generally matches the taper of the engagement surface 136 of the expansion element 130 on which it is mounted.
The inner surface 185 tapers towards the sleeve trailing end 182, such that the thickness of the wall 186 of the sleeve 180 tapers towards the sleeve leading end 181. In a preferred embodiment, the thickness of the wall 186 tapers from about 5.2 mm to about 2 mm. The sleeve 181 is typically formed of a material that is harder and more abrasion resistant than the material from which the friction bolt body 110 is formed. In a preferred embodiment, the sleeve 180 is formed of 4140 grade steel with a hardness of about 547 Vickers hardness (about 28 to 32 Rockwell C hardness). The steel could be heat treated to an increased hardness of about 50 Rockwell C hardness. An annular shoulder may be defined at the junction between the intermediate surface 135 and engagement surface 136 of the expansion element 136 (or elsewhere toward the leading end of the expansion element 130) to limit displacement of the sleeve 180 along the expansion element 130.

[0050] The friction bolt assembly 100 further comprises a drive head 140 mounted on the rod 120 at or adjacent the rod trailing 122. In the particular embodiment depicted, the drive head 140 is in the fon-n of an open hexagonal nut that is threadingly mounted on a threaded trailing portion 124 of the rod 120. The threaded leading portion 123 and threaded trailing portion 124 of the rod 120 are like handed, each having a left handed thread for installation with a standard installation rig configured to rotate in an anti-clockwise direction, although it is also envisaged that both the threaded leading portion 123 and threaded trailing portion 124 may be right handed, for installation by clockwise rotation of an installation rig. In the configuration depicted, the drive head 140 is provided with a coarse thread 141 on its hexagonal drive faces to allow for securing of a roof mesh to the friction bolt assembly 100 after installation.
A sacrificial plastic sheathing may cover the exposed region of the threaded trailing portion 124 so as to avoid the thread of the threaded trailing portion 124 being fouled by debris during transport and handling in the mine.

[0051] Between the drive head 140 and the friction bolt body trailing end 112, a washer 150 and load transfer fitting 160 are mounted on the threaded trailing portion 124 of the rod 120. The load transfer fitting 160 has a profiled leading face 161 configured to engage and support the friction bolt body trailing end 112 and collar 117 to transfer percussive loads applied during installation, as will be discussed further below, to the friction bolt body 110 without locally damaging the friction bolt body 110.

[0052] To initially secure the expansion element 130 and drive head 140 on the rod 120 during transportation and handling, the expansion element 130 may be tack welded to the rod 120 adjacent the rod leading end 121 and the drive head 140 tack welded to the rod 120 adjacent the rod trailing end 122. The tack welds would then fail during rotation of the expansion element 130 and drive head 140 relative to the rod 120 during installation.
Alternatively, after mounting the expansion element 130 and drive head 140 on the rod 120, the thread of the threaded leading portion 123 and threaded trailing portion 124 of the rod 120 may be crimped or otherwise deformed adjacent to the rod leading and trailing ends 121, 122 respectively.
The expansion element 130 and drive head 140 may then be reverse threaded to abut against the crimp to temporarily lock the expansion element 130/drive head 140 to the rod 120 and specifically prevent the expansion element 130 and drive head 140 from unscrewing off the rod 120 during transport and handling. As another alternative, heat shrink material may be applied over the expansion element 130 and adjacent portion of the threaded leading portion 123 of the rod 120, both to protect the expansion element 130 during transport and any rough handling and also to secure the expansion element 130 on the rod 120. During installation, the heat shrink would be torn away by rotation of the rod 120, allowing relative movement between the expansion head 130 and rod 120. As another alternative, the drive head 140 may be driven along the threaded trailing portion 124 of the rod 120 sufficiently to provide a light pretension of the rod 120.

[0053] Installation of the friction bolt assembly 100 will now be described with reference to Figures 12 and 13. Firstly, a bore hole 10 is drilled into the rock face 12 of a rock strata 11 to be stabilized. In the embodiment depicted, the bore hole 10 is drilled with a standard installation rig with a drill bit having a diameter typically of 43 to 44mm, which will typically result in a bore hole diameter of 43 to 45mm, depending on strata type and hardness.
Accordingly, the maximum diameter of the friction bolt body 110 (being approximately 47mm in a preferred embodiment) is slightly greater than the diameter of the bore hole 10, so as to provide for an interference fit in the usual manner, whilst the maximum diameter of the expansion element 130, here being approximately 43mm, is less than the maximum diameter of the friction bolt body 110 and slightly less than the diameter of the bore hole 10 such that the expansion element 130 may be readily inserted into the bore hole 10. It is also envisaged that slightly larger bore holes (such as about 46 mm), only slightly smaller than the maximum diameter of the friction bolt body 110 (here approximately 47 mm) may be utilised, resulting in a reduced interference fit of the friction bolt body 110.

[0054] Before inserting the friction bolt assembly 100 into the bore hole 10, a plate washer 170 (and optionally a ball washer) is mounted on the friction bolt body 110 adjacent the collar 117 and the friction bolt assembly 100 is mounted on the installation rig, particularly with the drive head 140 being received within a mating socket of the installation rig. The installation rig then drives the friction bolt assembly 100 into the bore hole 10, applying percussive force via the load transfer fitting 160 until the plate washer 170 is thinly engaged with the rock face 12. The frictional forces due to the interference fit between the friction bolt body 110 and bore hole wall 13 retain the friction bolt assembly 100 in the bore hole 10, and allow for the transfer of loads between the rock strata 11 and the friction bolt body 110.

[0055] Referring to Figure 13, additional anchoring of the friction bolt assembly 100 in the bore hole 10 is achieved by way of the expansion element 130, which provides a point anchoring effect. This is achieved by actuating the rod 120 by rotating the drive head 140. Specifically, the drive head 140 is driven in a direction tending to advance the drive head 140 along the threaded trailing portion 124 of the rod 120 (here in an anti-clockwise direction). During rotation of the drive head 140, as tension in the rod 120 increases, friction due to inter-engagement of the threaded trailing portion 124 of the rod 120 with the internal thread of the drive head 140 will tend to rotate the rod 120. Even if the drive head 140 does initially rotate relative to the rod 120, it will only move along the rod 120 until it reaches the end of the threaded trailing portion 124 of the rod 120. Rotation of the rod 120 will in turn tend to advance the threaded leading portion 123 of the rod 120 through the expansion element 130, rotation of which is substantially prevented by virtue of the key 137 as described above.
Accordingly, during rotation of the drive head 140, the expansion element 130 will be drawn toward the friction bolt body trailing end 112 further into the cavity 113. The sleeve 180 will also tend to be drawn toward the friction bolt body trailing end 112 by virtue of movement of the expansion element 130, however the sleeve trailing end 182 will abut the friction bolt body leading end III, thereby limiting longitudinal displacement of the sleeve 130 relative to the friction bolt body 110. As the expansion element 130 is drawn further into the cavity 113, the tapers of the engagement surface 136 of the expansion element 130 and inner surface 185 of the sleeve 180 will result in the sleeve 180 radially outwardly deforming as the engagement surface 136 is displaced through the interior of the sleeve 180, opening the split 183 formed in the sleeve 180.
The radial outward deformation of the sleeve 180 bears the outer surface 184 of the sleeve 180 against the bore hole wall 13, thereby point anchoring the friction bolt body 110 within the bore hole. The point anchor thus provided is effectively mechanically independent of the anchoring provided by the friction bolt body 110, with the friction bolt body 110 merely serving to assist in establishment of the point anchoring by limiting relative longitudinal displacement of the sleeve 180 during the installation process.

[0056] Whilst the expansion element 130 is being drawn into the cavity 113 of the friction bolt body 110 during the installation process, the engagement surface 136 of the expansion element 130 will also typically engage the friction bolt body 110 at the friction bolt body leading end 111, radially outwardly deforming the tapered leading portion 115 of the friction bolt body 110.
As a result of this deformation, the leading portion 115 of the friction bolt body 110 may be radially outwardly deformed sufficiently to bear against the bore hole wall 13, however this will be relatively insignificant as compared to the point anchoring effect provided by the sleeve 180.
This will particularly be the cases in the first embodiment depicted where the thickness of the wall 185 of the sleeve 180 at the sleeve trailing end 182 is greater than the thickness of the friction bolt body 110 at the friction bolt body leading end 111. The compressive load acting on the sleeve 180 between the expansion element 130 and bore hole wall 13 adjacent the sleeve trailing end 82, providing the point anchoring effect, is thus greater than any compressive load acting on the friction bolt body 110 between the expansion element 130 and bore hole wall 13 adjacent the friction bolt body leading end 111.

[0057] Figure 14 depicts the installation of the friction bolt assembly 100 following sudden movement of the strata resulting from a seismic event, resulting in plastic elongation of the rod 120. With the friction bolt body 110 being separate to the sleeve 180 forming the point anchor, it is able to displace through the bore hole 10 relative to the rod leading end 121, whilst the point anchoring provided by the sleeve 180 remains firmly in place. Further tensile load acting on the rod 120 as a result of the strata movement will tend to further draw the expansion element 130 through the sleeve 180, further radially deforming the sleeve 180 by virtue of the taper of the engagement surface 136, further enhancing the point anchoring of the friction bolt assembly 100.

[0058] The rod leading and trailing ends 121, 122 will tend to protrude through the open ends of the expansion element 130 and drive head 140 respectively. Protrusion of the rod trailing end 122 through the drive head 140 will provide a visual confirmation that the point anchoring of the friction bolt body 110 within the bore hole 10 has been achieved.

[0059] A friction bolt assembly 200 according to a second embodiment is depicted in Figures 15 to 20 of the accompanying drawings. Features of the friction bolt assembly 200 that are identical to those of the friction bolt assembly 100 of the first embodiment are provided with identical reference numerals, whilst equivalent or alternate features of the friction bolt assembly 200 are provided with reference numerals equivalent to those of the friction bolt assembly 100 of the first embodiment, incremented by 100.

[0060] The friction bolt assembly 200 is essentially identical to the friction bolt assembly 100, apart from the configuration of the rod 220 and the trailing portion of the friction bolt assembly 200. In place of the toroidal collar 117 and separate load transfer fitting 160 of the friction bolt assembly 100 of the first embodiment, an alternate form of collar 217 is welded to a friction bolt body 110 adjacent the friction bolt body trailing end 112. The collar 217 effectively integrates the functions of the toroidal collar 117 and load transfer fitting 160 of the friction bolt assembly 100 of the first embodiment and fixes the load transfer fitting to the friction bolt body. The collar 217 has a forward facing surface 218 extending about the friction bolt body 110 at the friction bolt body trailing end 112 for engaging a plate washer 170 in the same manner as the collar 117 of the friction bolt assembly 100 of the first embodiment. The collar 217 also has a central aperture 219 extending therethrough and having a diameter slightly larger than the diameter of the rod 220, in the embodiment depicted having a diameter between approximately 23.8 to 24.0 mm.

[0061] The rod 220 is provided with stopping means configured to cooperate with the collar 217 to at least substantially prevent the rod 220 ejecting completely from the friction bolt body 110 upon failure of the rod 220. In the embodiment depicted, the stopping means comprises three swaged portions 225a, 225b, 225c formed in the rod between the friction bolt body leading end 111 and friction bolt body trailing end 112, particularly toward the friction bolt body trailing end 112. The swaged potions 225a, 225b, 225c are dimensioned such as not to pass through the aperture 219 in the collar 217, particularly having a transverse cross-sectional area greater than a maximum cross-sectional area of the aperture 219. In a preferred embodiment, each of the swaged portions 225a, 225b, 225c is wider than the diameter of the aperture 219 of the collar 217 in one or more lateral directions. In the embodiment depicted, the effective lateral width of each of the swaged portions 225a, 225b, 225c is between approximately 25 to 27 mm, being greater than the diameter of the aperture 219 of the collar 217, so as to prevent the rod 220 from ejecting completely from the friction bolt body 110. In place of the swaged portions 225a, 225b, 225c, the stopping means could take the form of one or more ferrules mounted on the rod 120, welds applied to the rod 120 or more pronounced ribs formed on the rod 120.

[0062] Referring to Figures 18 and 19 of the accompanying drawings, the friction bolt assembly 200 is installed in the same manner as the friction bolt assembly 100 of the first embodiment, as described above in relation to Figure 12 and 13.

[0063] Figure 20 depicts the installation of the friction bolt assembly 200 following a seismic event resulting in strata movement loading the rod 220 exceeding the tensile strength of the rod 220, with the rod 220 failing by fracture, breaking the rod 220 into separate leading and tail rod portions 220a, 220b. Upon fracture, the tail rod portion 220b of the rod 220 would tend to be ejected towards and through the friction bolt body trailing end 112 due to the diameter of the rod 220 being less than the diameter of the aperture 219 of the collar 217.
However, the stopping means, particularly the swaged portions 225a, 225b, 225c prevent the tail rod portion 220b from ejecting completely from the friction bolt body 110 by engaging with the collar 217, as shown in Figure 20. A potential safety hazard associated with rapid ejection of the tail rod portion 220b is thus prevented. Further, protrusion of the tail rod portion 220b through the collar 217 provides a visual indication of failure of the friction bolt assembly 200 due to mechanical overload.

[0064] Provision of the multiple swaged portions 225a, 225b, 225c provides additional tiers of engagement with the collar 217 in the event that the first swaged portion 225a or both the first and second swaged portions 225a, 225b are sufficiently deformed by virtue of the initial impact with the collar 217 upon attempted ejection of the tail rod portion 220b, or in the event that the rod 220 fractures at or adjacent one of the swaged portions 225a, 225b, 225c.

[0065] An alternative fonn of expansion element 330 and sleeve 380 to those utilised in the first and second embodiments discussed above is depicted in Figures 21 to 24.
Features of the expansion element 330 and sleeve 380 that are identical to those of the expansion element 130 and sleeve 180 of the first and second embodiments are provided with identical reference numerals, whilst equivalent or alternate features of the expansion element 330 and sleeve 380 are provided with reference numerals equivalent to those of the expansion element 330 and sleeve 380 of the first and second embodiments, incremented by 200.

[0066] The expansion element 330 is substantially identical to the expansion element 130, except that the outer surface of the expansion element 330, particularly those portions defined by the engagement surface 336 (and, in the embodiment depicted, the intermediate surface 335 and trailing surface 338) is provided with a plurality, here four, longitudinally extending planar regions 339. The planar regions 339 may effectively be foimed by machining flat surfaces into the outer surface of the expansion element 130 described above in relation to the first and second embodiments. Alternatively, the expansion element 130 could be cast or forged with the planar regions 339 in place. The inner surface 385 of the sleeve 380 is configured to substantially match, as best depicted in Figure 23, with any transverse cross-section of the sleeve 380 through the engagement surface 336 being characterised by a series of planar surface regions 387 separated by curved intermediate surface regions 388. Longitudinally extending weakening grooves 389 may be provided in the inner surface 385 of the sleeve 380 between each planar surface region 387, each forming a weakened zone, and particularly between each planar surface region 378 and each adjacent intermediate surface region 388. When the sleeve 180 discussed above in relation to the first embodiment, having a frusto-conical inner surface 185 deforms during the point anchoring process, the wall 186 of the sleeve 180 must distort by virtue of the frusto-conical inner surface 185 sliding against the frusto-conical engagement surface 136. With the configuration of the expansion element 330 and sleeve 380, however, having planar surfaces slide on each other generally prevents distortion of those parts of the wall 386 of the sleeve 380 corresponding to the planar surface regions 387. The intermediate surface regions 388 are allowed to distort and/or tear (by virtue of the weakening grooves 389) to peimit the required radial expansion of the sleeve 380. This may enhance point anchoring efficiency. It is inconsequential if the wall 386 of the sleeve 380 tears at the intermediate surface portions 388, with the point anchoring effect being provided at the planar surface regions 387.

[0067] In addition to the above described and other envisaged modifications of the expansion element and sleeve, the person skilled in the art will appreciate various other modifications of the friction bolt assemblies described above. For example, rather than having the expansion element and drive head threadingly mounted on threaded leading and trailing portions of the rod, such that both the expansion element and drive head move longitudinally relative to the rod during actuation of the rod, it is envisaged that the expansion element or drive head might be integrally formed with, or otherwise fixed in relation to the rod, in the manner described in International (PCT) Publication No. WO 2015/013743. In embodiments where the expansion element is fixed in relation to the rod, actuation of the rod by rotationally driving the drive head will result in the drive head advancing along the rod, drawing the expansion element and rod rearwardly through the drive head. In Date recue/Date received 2023-05-08 embodiments where the drive head is fixed in relation to the rod, actuation of the rod by rotationally driving the drive head will draw the expansion element along the rod.

Claims

17

1. A friction bolt assembly comprising:
a generally tubular friction bolt body 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;
a rod longitudinally extending through said cavity between a rod leading end and a rod trailing end;
an expansion element mounted on, or integrally folined with, said rod at or adjacent said rod leading end, said expansion element having an engagement surface tapering toward said rod trailing end;
a sleeve mounted on said expansion element adjacent said friction bolt body leading end, said sleeve having a sleeve trailing end and an interior sleeve surface; and a drive head mounted on, or integrally formed with, said rod at or adjacent said rod trailing end, said rod being actuatable by rotation of said drive head to draw said expansion element toward said friction bolt body trailing end such that said sleeve trailing end abuts said friction bolt body leading end and said engagement surface engages said interior sleeve surface, radially outwardly deforming said sleeve.

2. The friction bolt assembly of claim 1 wherein said sleeve has a substantially cylindrical outer sleeve surface.

3. The friction bolt assembly of either one of claims 1 and 2 wherein said interior sleeve surface tapers towards said sleeve trailing end.

4. The friction bolt assembly of claim 3 wherein the taper of said interior sleeve surface matches the taper of said engagement surface.

5. The friction bolt assembly of claim 4 wherein said interior sleeve surface and said engagement surface are of substantially matching generally frustoconical form.

6. The friction bolt assembly of any one of claims 1 to 5 wherein said interior sleeve surface has a plurality of substantially planar regions extending between a sleeve leading end of said sleeve and said sleeve trailing end, said engagement surface having a plurality of substantially matching substantially planar regions for engagement with said substantially planar regions of said interior sleeve surface.

7. The friction bolt assembly of claim 6 wherein said sleeve is provided with a weakened zone between each of said substantially planar regions of said interior sleeve surface.

8. The friction bolt assembly of any one of claims 1 to 7 wherein said friction bolt assembly further comprises means for at least substantially preventing rotation of said expansion element relative to said friction bolt body.

9. The friction bolt assembly of claim 8 wherein said means comprises a key projecting from said engagement surface into said split of said friction bolt body.

10. The friction bolt assembly of any one of claims 1 to 9 wherein said sleeve has a longitudinally extending split.

11. The friction bolt assembly of claim 10, when appended to claim 9, wherein said key extends into said split of said sleeve.

12. The friction bolt assembly of any one of claims 1 to 11 wherein said drive head is threadingly mounted on a threaded trailing portion of said rod such that, upon actuation of said rod by rotation of said drive head, said threaded trailing portion of said rod is drawn through said drive head.

13. The friction bolt assembly of claim 12 wherein said expansion element is threadingly mounted on a threaded leading portion of said rod, said threaded leading portion and said threaded trailing portion of said rod being like-handed, such that, upon actuation of said rod by rotation of said drive head, said rod rotates with said drive head, drawing said expansion element along said threaded leading portion of said rod.

14. The friction bolt assembly of any one of claims 1 to 13 wherein said friction bolt assembly further comprises a load transfer fitting mounted on said rod between said drive head and said friction bolt body trailing end, said load transfer fitting having a profiled leading face configured to engage and support said friction bolt body trailing end.

15. The friction bolt assembly of any one of claims 1 to 14 wherein said friction bolt assembly further comprises:
a stopping means mounted on, or integrally formed with, said rod and being longitudinally positioned between said friction bolt body leading end and said friction bolt body trailing end;
and a collar fixed to said friction bolt body at or adjacent said friction bolt body trailing end;
wherein said stopping means and said collar are dimensioned to cooperate to at least substantially prevent said rod from ejecting completely from the friction bolt body through the friction bolt body tailing end.

16. The friction bolt assembly of claim 15 wherein said stopping means comprises one or more swaged portions of the rod.

17. A method of installing the friction bolt assembly of claim 1 comprising the steps of:
drilling a bore hole into a rock face of a rock strata to be stabilized, said bore hole having a diameter greater than the maximum diameter of said expansion element and less than the maximum diameter of said friction bolt body;
inserting said friction bolt assembly into said bore hole with said expansion element leading;
applying percussive force to said friction bolt body to drive said friction bolt body into said bore hole with an interference fit;
rotating said drive head to actuate said rod, drawing said expansion element towards said friction bolt body trailing end, abutting said sleeve trailing end with said friction bolt body leading end and engaging said engagement surface with said interior sleeve surface, thereby outwardly radially deforming said sleeve into bearing engagement with the wall of said bore hole.