CA2728807A1 - Mine roof anchor assembly - Google Patents

Abstract

In a preferred construction, the present invention provides a combined resin-mechanical anchor assembly that includes a mechanical expansion unit. The expansion unit includes a wedge assembly which includes a camming wedge having a compressible biasing member or spring fixedly secured thereto, and an expansion shell. The expansion shell includes a bail and a plurality of deformable steel leaves, and more preferably includes between three and five leaves disposed radially about a sheet axis.
The bail is provided with a corresponding leg attached respectively to each leaf and an axially positioned end ring or yoke, and which generally define a cage in which the wedge assembly is housed. The yoke acts as a seating surface against which the spring rests to maintain the plug in a desired axial alignment. The yoke further has an opening sized to permit the relative movement of an anchor tendon or rod therethrough on a deformation/activation of the leaves.

Description

MINE ROOF ANCHOR ASSEMBLY
SCOPE OF THE INVENTION
The present invention relates to an anchor assembly for securing a conventional rod-like reinforcing tendon or mine roof bolt under tension in a bore hole.
More preferably, the present invention pertains to an anchor assembly which incorporates a mechanical anchoring or expansion unit for securing the tensioned bolt within the bore hole to compress and consolidate ground forces.

BACKGROUND OF THE INVENTION
Various anchor assemblies have been used to reinforce tunnel and retaining walls, underground passageways and mine shaft wall and roofs (hereinafter collectively referred to as mine roofs), to reduce the likelihood of rock bursts and control ground movement and the hazards associated therewith. Conventional anchor assemblies typically include a reinforcing tendon or bolt which is secured in place with a bore hole by the use of partial or full column resin systems or mechanical expansion systems typically incorporate a two compartment cartridge system consisting of a resin and a catalyst which are slid ahead of the bolt into the bore hole. When mixed, the resins chemically affixes the rock bolt in place, allowing the bolt to thereafter be tensioned by the use of a nut or threaded fastener.

Mechanical anchor expansion units are provided with an expansion shell or unit having a plurality of fingers or leaves which are secured to a bail and a camming plug which is positioned and moveable relative to the leaves. The roof bolt or tendon is threaded along its distal end so as to threadedly engage an internally threaded bore formed in the plug. In use, a bore hole formed in an anchor assembly with the expansion unit partially threaded onto the end of a bolt is inserted into the bore hole.
The mechanical expansion unit is activated by rotating the bolt relative to the expansion shell.
The threaded engagement of between the tendon and the plug acts to axially draw the camming plug outwardly. As the camming plug moves, it engages and forcing the leaves of the expandable shell radially outwardly and into bearing contact with the sidewalls of the bore hole. In this manner, the bolt is mechanically secured to the sides of the bore hole. Once the expansion shell is fully expanded, further rotation of the bolt advantageously effects the tensioning of the bolt along its length to compress the competent strata and consolidate ground forces.

Various expansion units have been proposed to ensure that the end of the rock bolt remains axially aligned with the bail and camming plug, to ensure correct operation of the expansion shell during tensioning. Canadian Patent No. 618,342 describes an expansion anchor shell having a U-shaped bail, having an enlarged bight portion. A
circular aperture is provided in the end of the bail which is sized to receive the end of a rock bolt therethrough. Canadian Patent No. 618,343 describes a similar modified bail assembly in which a flat knockout plug is positioned in the circular aperture of the enlarged bight. However, in conventional expansion units, the camming plug remains liable to be knocked out of axial alignment with the anchor tendon as the anchor assembly slides into place resulting in tendon jamming and/or the incomplete deformation of the expansion shell leaves.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an improved mechanical bolt anchor assembly for use in the securement of an elongated rock bolt or anchor tendon within a bore hole formed in a mine roof.

Another object of the present invention is to provide a mechanical expansion unit for use with a rock bolt or anchor tendon, and which incorporates a camming or wedge plug assembly which is configured to maintain an optimum plug alignment relative to the expansion shell as the rock bolt is initially positioned, and the expansion unit is activated.
A further object of the present invention is to provide a mechanical expansion unit for anchor assembly which has a plurality of deformable elongated vertical leaves.
The leaves may be of a generally transverse planar or arcuate configuration, and are provided with a gripping surface. Each of the leaves is joined at its top to a bail having an open or a solid top portion with a frangible central dome through which a rock bolt can move, and in which is disposed a camming plug which has a biasing member or spring pre-coupled thereto, to assist in maintaining the plug in a desired initial axial alignment within the bail.

Yet a further object of the present invention is to provide a mechanical bolt anchor assembly having pre-positioned therein a camming plug assembly pre-positioned, and which includes a camming plug having a biasing spring secured to a distal end thereof to maintain the camming plug in a desired axially alignment relative to both the expansion shell, the bail and/or anchor rod both during each of initial positioning within a bore hole, and the activation of the anchor.

In a preferred construction, the present invention provides a mechanical anchor assembly that includes a mechanical expansion unit. The expansion unit includes an expansion shell and a wedge assembly which is adapted to radially expand into bearing contact with the sides of a bore hole. The wedge assembly preferably includes a camming wedge having a compressible biasing member or spring fixedly secured at one end thereof. The expansion shell includes a bail and a plurality of deformable steel leaves, and preferably between three and five leaves which are disposed radially about an axis. The bail is provided with a corresponding number of steel finger members which are attached respectively at one end to each leaf and at their other end an axially positioned end ring or yoke. The fingers and yoke generally define a cage in which the wedge assembly is housed. More preferably, the yoke acts as a seating surface against which the spring rests to bias the plug in a desired axial alignment. An opening formed through the yoke sized to permit the relative movement of an anchor tendon or rod therethrough on activation of the expansion unit and deformation/activation of the leaves.

Accordingly, in one aspect, the present invention resides in a mine roof anchor assembly for use in a predrilled bore hole formed in a rock face comprising, an elongated tendon which extends longitudinally from a first proximal portion to a threaded distal portion, a mechanical assembly defining a through-passage extending axially therethrough from a proximalmost end to a distalmost end and including: a plurality of leaf members, said leaf members being displaceable radially relative to said through-passage into bearing contact with side portions of said bore hole; a bail member defining a distally disposed end member having an opening therethrough, said bail member including a plurality of fingers, each said fingers extending from said end member to a respective first end secured to an associated one of said leaf members; and a wedge plug generally housed within said bail member so as to be retained thereby, said wedge plug including a tapered sidewall tapering inwardly towards the proximalmost end and having formed therethrough an axially oriented threaded though bore sized to threadedly receive the distal portion of said tendon therein, the wedge plug having secured integrally thereto a resiliently compressible spring, said spring having a length selected to maintain engagement with said end member to assist in maintaining bearing contact between said wedge plug and said leaf members.

BRIEF DESCRIPTION OF THE DRAWINGS
Reference is now made to the following detailed description taken together with the accompanying drawings in which:
Figure 1 is an exploded perspective, top view showing a mechanical expansion unit for use in a mine roof anchor assembly in accordance with the present invention;
Figure 2 shows a perspective top and first view of the expansion unit shown in Figure 1 in an assembled state prior to pre-positioning on an anchor rod;
Figure 3 shows a perspective front and bottom view of the expansion unit shown in Figure 2;
Figures 4 to 6 show an exploded perspective bottom and side views of the expansion unit of Figure 2; and Figures 7 to 9 show the positioning of the mine roof anchor assembly within a bore hole in accordance with a preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As will be described with reference to Figures 7 to 9, the present invention relates to a mine roof anchor assembly 10 used as part of a mine roof support system in the compression and consolidation of a rock complex 6. The anchor assembly includes an elongated steel rock bolt or anchor rod 12, and a mechanical expansion unit 14 which is operable to mechanically secure the rod 12 in place, positioned within a bore hole 8 formed within the rock complex 6.

The anchor rod 12 is of a conventional design and has a longitudinal length chosen for insertion into the bore hole 8, extending axially along Al-Al from an externally threaded outermost proximal end 16 to an innermost distal end portion 18. As will be described, the mechanical expansion unit 14 is configured for threaded coupling directly to the distal end portion 18, wherein the relative rotation of the rod 12 about its longitudinal axis A,-A, activates the expansion unit 14 to mechanically secure rod 12 within the bore hole 8.

Figure 1 shows best the expansion unit 14 as including an expansion shell 20, a camming plug assembly 22, and a plastic retention sleeve or positioning collar 24. The camming plug assembly 22 is shown best in Figures 1 to 5 as including wedge shaped steel plug 40 which has an internal bore 42 formed therethrough. The bore 42 is threaded along its entire length, extending axially along a central plug axis Ap-Ap (Figure 6). The steel plug 40 tapers radially outwardly relative to the plug axis Ap-Ap from a narrow diameter proximalmost end 44 to an enlarged diameter distalmost end 46. A
distalmost seating surface 48 is formed as a recessed groove in the end 46, and which extends annularly about the bore 42. The camming plug assembly 22 is further provided with a resiliently compressible steel spring 52. The steel spring 52 is preferably formed as a helical spring having an inner diameter which is greater than a lateral diameter of the distal end 18 of the anchor rod 12 so as to allow for its substantially unobstructed movement therethrough. The spring 52 is fixedly secured to the plug seating surface 48 by one or more weldments 54 to provide the camming plug assembly 22 as a single preformed and preassembled unit. It is to be appreciated that providing the spring 52 and camming plug 40 as to a single integral, in addition to simplifying the shell preassembly, advantageously ensures that the spring 52 and plug 40 are maintained in the desired coaxial alignment during initial installation of the expansion unit 14 and its subsequent activation.

Optionally recesses 50a-c may be formed in the external tapered surface of the steel plug 40. The recesses 50a-c are equally spaced apart from each other, and taper such that segment narrows as it extends totally towards the distalmost end 46.

While the use of the weldments 54 to secure the spring 52 to the plug 40 provides a preferred simplified construction, it is to be appreciated that the invention is not so limited. Other modes of securement could also be used including without restriction by the use of adhesives, or by the use of mechanical attachments such as crimpings or the like.

The mechanical expansion shell 20 is shown best in Figure 1 to 6 as having steel a bail assembly 26 and three axially elongated leaves 36a,36b,36c. Each of the leaves 36a,36b,36c are preferably of a generally transverse arcuate configuration and are attached to the bail 26 towards their respective uppermost ends. In this regard, each leaf 36a-c preferably is formed as a segment of a hollow cylinder, the outer diameter of which is substantially equal to the outer diameter of the bail 26 and marginally less then the diameter of the bore hole 8. The leaves 36a,36b,36c are preferably also wedge shaped along their axial length, with the top of each leaf being thinner than the bottom. The interior diameter of the hollow cylinder formed by the leaves 36 is selected such that prior to shell 14 activation, the leaves 36a,36b,36c loosely surround the proximal end 18 of the anchor rod 12 and are engaged by the narrower proximalmost end 44 of the plug 40 so as to limit its sliding movement therethrough. The exterior of each leaf 36 may also be provided with a plurality of circumferential ribs, bosses or other serrations 38 which are adapted for better mechanical engagement with the sides of the bore hole 8.

The bail assembly 26 is formed from stamped steel or other metal and includes an annular collar or yoke 30 from which extend three evenly radially spaced deformable fingers 28a,28b,28c. Each of the fingers 28 extend axially and are integrally formed at one end to the annular yoke 30, and are joined at their other ends to a respective leaf 36a,36b,36c by weldments. More preferably, the yoke 30 defines a through-aperture 32 which has a diameter selected smaller than that of the spring 52, so as to engage a distal end of the spring 52 thereagainst, whilst allowing substantially unimpeded movement of the distal end 18 of the anchor rod 12 therethrough. Optionally, a knockout plug 34 may be secured over the aperture 32 to facilitate the positioning of the camming plug assembly 22 with wedge plug 40 and spring 52 therebetween.

It is to be appreciated that in the construction shown the yoke 30 and fingers advantageously act as a cage in which the camming plug assembly 22 is housed.
With the camming plug assembly 22 positioned in the initial preassembled position shown in Figure 2, the spring 52 is under partial compression and in bearing contact against the yoke 30. The steel plug 40 in turn only partially engages the adjacent ends of each of the leaves 36a,36b,36c. It is to be appreciated that the biasing force of the spring 52 and its pre-securement to the plug 40 advantageously not only simplifies the initial positioning of the camming plug assembly 22 within the bail assembly 26 cage; but also ensures that the wedge plug 40 is maintained with the desired alignment with the plug axis Ap-Ap coaxially aligned with the rod axis Al-A1, as the expansion unit 14 is initially pre-positioned on the rod 12, slide into position within the bore hole 8 and subsequently activated as the rod 12 is tensioned.

The threaded axial bore 42 is adapted to receive and threadedly engage the external threads along the distal end 18 of the anchor rod 12. Although not essential, preferably the length of the threading along the anchor rod end 18 is selected to permit only a limited amount of travel of the bolt end portion 18 through the wedge plug 40, and which is selected to result in maximum expansion or splaying of the leaves 36.
The resulting maximum expansion of the anchor shell leaves 36 and limited plug assembly 22 movement advantageously ensures the wedge plug 40 is not drawn axially completely through the shell 20.

In the preassembly and initial positioning of the expansion shell 20 on the distal end 18 of the anchor rod 12, the positioning collar 24 functions to maintain the expansion shell 20 in an optimum initial orientation during transport upto the time of installation of the anchor assembly 10 into the bore hole 8. The positioning collar 24 is preferably provided in the form of a plastic sleeve which includes an enlarged diameter radial flange 62 extending outwardly about one end.

It will be readily appreciated that the anchor rod 12 has a conventional head formed at the exposed proximal end 16 thereof which protrudes from the bore hole 8. On assembly, a conventional bearing plate 80 and threaded nut 82 are secured on the proximal end 16 for tensioning against the rock face 100 in the compression and consolidation of ground forces.

Figures 7 to 9 show best the positioning of the mine roof assembly 10 in the bore hole 8. In initial pre-assembly, the camming plug assembly 22 is slid axially into the expansion shell 20 so that the spring 52 is compressed against the yoke 30, and the wedge plug 40 is disposed in partial engagement with the leaves 36 as shown in Figure 2. The collar 24 is then slid over the opposing ends of the leaves 36 to maintain the expansion unit 14 as a preassembled unit. With the expansion unit 14 is so preassembled, the spring 52 biases the plug 40 axially to maintain its bearing contact with the ends of the leaves 36, minimizing the possibility it may shift from the designed axial alignment.

At the time of use, the expansion unit 14 is pre-secured onto the anchor rod 12.
With wedge plug 40 prepositioned within the expansion shell 20, the plug 40 is threaded partially over the distal end 18 of the anchor rod 12 until the end 18 engages the knockout plug 34. Once the expansion shell 20 is fully seated, the mine roof anchor assembly 10 is inserted into the hole 8. As the expansion unit 14 is initially moved into the bore hole 8, the enlarged diameter radial flange 62 on the positioning collar 24 is brought into contact with the rock face 100. This in turn prevents further insertion of the collar 24 in the bore hole 8 and results in the collar 24 being slid relative to the anchor assembly 10, free of the expansion shell 20 allowing outward movement of the leaves 36. At the same time, the use of a plug 34 to cover the distal end 18 and wedge plug 40, prevents any fouling of their respective threads. Once the anchor assembly 10 is fully positioned, the head of the rod 12 is rotated with a power tool (not shown), drawing the plug 40 axially along the rod end 18 towards the distal end 16.

As the bolt 12 is rotated, the initial movement causes bolt 12 to move inwardly into the bore hole 8 until it contacts the top of the bail and dislocates the plug 34, breaking it free of the surrounding edge of the raised yoke 30. The end 18 of the bolt 12 draws the plug 40 outwardly from the bore hole 8 along the axis Al-A1 into the space between the leaves 36. As the layer diameter end 46 moves between the leaves 36, the plug 40 splays the leaves 36 radially apart and splaying them against the rock sides of the bore hole 8. The camming plug assembly 22 is thus drawn downwardly between the leaves 36a,36b,36c, thereby causing them to splay outwardly and the fingers 28a,28b,28c to deform.

It is to be appreciated that the serrations 38 on the leaves 36 advantageously also serve to prevent the expansion shell 20 from rotating relative to the sidewalls of bore hole 8 upon rotation of rod 12.

In an alternate possible manner of use, the anchor assembly 10 is secured within the bore hole 8 in conjunction with a two compartment resin used in conjunction with the mechanical expansion unit 14. The spaces or slots formed between the adjacent fingers 36 of the expansion shell 20 advantageously allow for the flow of the anchoring resin axially outwardly about the camming plug assembly 22 and shell leaves 36a, 36b, 36c to further facilitate the securement of the anchor rod 12 within the bore hole 8.
The construction of assembly the expansion unit 14 allows for the substantially uninterrupted flow of resin and catalyst downwardly about the components of the mechanical expansion unit 14, to better provide secondary attachment between the components of the anchor assembly 10 and the sidewalls of the bore hole 8.

Although the detailed description describes and illustrates various preferred aspects and designs, it is understood that the invention is capable of further modifications. Many modifications and variations will now become apparent to those skilled in the art to which the invention pertains. For a definition of the invention reference may be had to the appended claims.

Claims (13)

1. A mine roof anchor assembly for use in a predrilled bore hole formed in a rock face comprising, an elongated tendon which extends longitudinally from a first proximal portion to a threaded distal portion, a mechanical expansion assembly defining a through-passage extending axially therethrough from a proximalmost end to a distalmost end and including:

a plurality of leaf members, said leaf members being displaceable radially relative to said through-passage into bearing contact with side portions of said bore hole;
a bail member defining a distally disposed end member having an opening therethrough, said bail member including a plurality of fingers, each said fingers extending from said end member to a respective first end secured to an associated one of said leaf members; and a wedge plug generally housed within said bail member so as to be retained thereby, said wedge plug including a tapered sidewall tapering inwardly towards the proximalmost end and having formed therethrough an axially oriented threaded though-bore sized to threadedly receive the distal portion of said tendon therein, the wedge plug having secured integrally thereto a resiliently compressible spring, said spring having a length selected to maintain engagement with said end member to assist in maintaining alignment and bearing contact between said wedge plug and said leaf members.

2. The anchor assembly as claimed in claim 1 wherein said leaf members each comprise a generally rigid metal member.

3. The anchor assembly as claimed in claim 1 or claim 2 wherein said through-passage is sized to permit movement of said threaded distal portion axially therethrough.

4. The anchor assembly as claimed in any one of claims 1 to 3 wherein said expansion assembly consists of three of said leaf members.

5. The anchor assembly as claimed in any one of claims 1 to 4 wherein each said leaf members include a beveled surface for bearing contact with part of said tapered sidewall.

6. The anchor assembly as claimed in any one of claims 1 to 5 wherein said bail comprises a cap portion detachably secured over at least part of said end opening.

7. The anchor assembly as claimed in any one of claims 1 to 6 wherein said spring is secured to a distalmost end of said wedge plug by way of weldments.

8. The anchor assembly as claimed in any one of claims 1 to 6 wherein said spring is secured to a distalmost end of said wedge plug by way of an adhesive.

9. The anchor assembly as claimed in any one of claims 1 to 8, wherein said expansion assembly comprises preassembled mechanical expansion shell, said expansion shell includes a retention sleeve releasably disposed about said plurality of leaf members, wherein the positioning of the retention sleeve about the leaf members substantially preventing their radial displacement.

10. The anchor assembly as claimed in claim 9 wherein said retention sleeve further includes a radially extending release flange, said release flange sized to engage said rock face on initial insertion of said expansion shell in said bore hole to effect release of said retention sleeve from a remainder of said expansion shell.

11. A mine roof anchor assembly as claimed in any one claims 1 to 10 wherein said wedge plug includes an annular recess concentrically disposed about said through-bore, at least part of said spring being seated in said annular recess.

12 12. A mine roof anchor assembly as claimed in any one of claims 1 to 11 wherein said spring comprises a helical steel spring having an internal spring diameter selected greater than a diameter of the threaded distal portion of said tendon.

13. A mine roof anchor assembly as claimed in any one of claims 1 to 10, wherein said wedge plug includes an annular recess.