GB2445675A

GB2445675A - Load Absorber

Info

Publication number: GB2445675A
Application number: GB0800381A
Authority: GB
Inventors: Graham Laurence Warwick-Adkins
Original assignee: MMTT
Current assignee: MMTT
Priority date: 2007-01-13
Filing date: 2008-01-10
Publication date: 2008-07-16
Also published as: GB0800381D0; GB0700673D0

Abstract

A load absorber (10) for use in a method of installing a rock bolt is arranged over a protruding end of the rock bolt; and is secured to the rock bolt by a fastener. The load absorber (10) defines a central aperture (12) to receive the rock bolt. The load absorber (10) has a central raised region (18) surrounding the aperture(12), and an outer raised region (20) extending from the central raised region to an edge region (14) of the load absorber (10).

Description

Load Absorber This invention relates to load absorbers. This invention

also relates to the use of load absorbers. More particularly, but not exclusively, this invention relates to load absorbers for use in mining and/or tunnelling applications and to the use of load absorbers in mining and/or tunnelling applications, such as in reinforcing the walls and roofs of tunnels. Embodiments of the invention relate to washer plates and to methods of using washer plates.

It is known to insert rock bolts into tunnel walls and roofs in order to reinforce them.

The process of inserting a rock bolt into a tunnel wall or roof involves initially drilling an elongate bore into the wall or roof, and then inserting capsules of curable fixing material into the bore.

The rock bolt is then mounted on a spinning tool and, while spinning about its longitudinal axis, pushed into the bore. This causes the capsules in the bore to burst and cure thereby fixing the rock bolt in the bore. A domed washer plate is then arranged over the protruding end of the rock bolt and a nut is then screwed onto the end of the rock bolt against the washer plate thereby securing it to the roof or wall of the tunnel.

According to one aspect of this invention, there is provided a method of installing a rock bolt into a wall or roof of a tunnel comprising: drilling an elongate bore in the wall or roof, inserting a curable material into the bore; inserting the rock bolt into the bore to activate the curable material and allowing the curable material to set, thereby fixing the rock bolt in the bore; arranging a load absorber over a protruding end of the rock bolt; and securing the load absorber to the rock bolt by a fastener; wherein the load absorber defines a central aperture to receive the rock bolt therethrough; and the load absorber has a central raised region surrounding the aperture, and an outer raised region extending from the central raised region to an edge region of the load absorber.

The rock bolt may comprise a distal end and a proximal end, wherein the distal end is inserted into the bore, and the proximal end may protrude from the bore.

The step of inserting the curable material into the bore may comprise inserting a first curable material into the bore, and thereafter inserting a second curable material into the bore. The first curable material may comprise a fast curing material, which may be curable within 15 to 30 seconds after activation. The second curable material may comprise a slow curing material, which may be curable within I to 3 minutes after activation, desirably between 1 and 2 minutes.

The first curable material may comprise a first cementing material and a first catalyst. The first curable material may be held a first capsule of said first curable material. The second curable material may comprise a second cementing material and a second catalyst. The second curable material may be held in a second capsule of said second curable material.

The insertion of the rock bolt into the bore may comprise spinning the rock bolt about its longitudinal axis during said insertion. Thus, on insertion of the rock bolt into the bore, the first and second capsules are burst by the rock bolt and the first and second curable materials therein are activated and commence curing.

The first curable material may cure to secure the distal end of the rock bolt in the bore. The load absorber may be arranged on the proximal end of the rock bolt.when the first curable material has cured. The fastener may be arranged on the proximal end of the rock bolt to secure load absorber thereto.

After the load absorber has been secured to the rock bolt, the second curable material may cure to secure the rock bolt in the bore.

A domed washer may be arranged between the fastener and the load absorber.

The domed washer may have a domed portion engaging in the central aperture of the load absorber. This has the advantage in one embodiment that the domed washer can be received In the aperture at an angle thereto, which may be up to substantIally 300 from the central axis. Thus, the rock bolt of this embodiment need not extend through the aperture in line with the central axis.

According to another aspect of this invention, there is provided a load absorber for use in a method of installing a* rock bolt, said load absorber defining a central aperture to receive the rock bolt therethrough, and having a central raised region surrounding the aperture, and an outer raised region extending from the central raised region to an edge region of the load absorber.

The central and outer raised regions may be convex, such that the convexity extends in the same directions The edge region of the load absorber may comprise a plurality of corners, and a respective edge extending between adjacent corners. Each edge of the load absorber may be a non linear edge, which may be curved.

The curvature of each edge may be convex in the same direction as the central and outer raised regions. The outer raised region may extend from the edges to the central raised region.

The load absorber may comprise a washer plate, whith may define the central aperture, and which may have the edge regions. The fastener may comprise a nut.

The corners may lie in generally the same plane. The edges and may extend out of the aforesaid plane. The central raised region may lie out of the aforesaid plane.

The outer raised region may lie out of the aforesaid plane.

The outer raised region may extend at a first angle to the aforesaid plane. The central raised region may extend at a second angle to the aforesaid plane. The second angle may be steeper than the first angle.

The outer raised region may comprise an outer generally frustoconical region, which may extend from the aforesaid edges. The central raised region may comprise a central generally frustoconicat region, and which may extend from the outer raised region to the central aperture.

The load absorber may have a thickness to provide sufficient absorption of the load applied by the fastener thereon. The thickness of the load absorber may provide a wall to the central aperture. The central aperture may have a central axis, and the wall may be angled relative to the central axis of the aperture at an angle of between and 30 .

An embodiment of the invention will now be described by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a top plan view of a load absorber; Figure 2 is a side view of the load absorber shown in Figure 1; Figure 3 is a sectional view of the load absorber along the lines Ill-Ill in Figure 2; Figure 4 is a perspective view of the load absorber, in use; Figure 51$ a sectional side view of a load absorber, in use; and Figures 6A to 6D are diagrammatic views of the steps of installing a rock bolt using a load absorber shown in Figures 1 to 5.

Referring to the drawings, Figure 1 is a top plan view of a load absorber in the form of a washer plate 10 for use with a rock bolt for reinforcing a tunnel wall or roof of a mine working. The washer plate 10 is of a generally square shape in top plan view, and defines a central circular aperture 12. The washer plate 10 has a strata facing side S, and a tunnel facing side T. The strata facing side S engages the tunnel wall or roof in use, and the tunnel facing side T faces away from the tunnel wall or roof.

The washer plate 12 has four edges 14, and four corners 16. It will be appreciated that, if desired, the washer plate 10 could be of any other suitable polygonal shape in top plan view having the appropriate number of edges 14 and corners 16.

The washer plate 10 has a central raised region 18 extending around the central aperture 12. The central raised region 18 is of a circular frustoconical configuration.

The washer plate 10 also has an outer raised region 20 which extends from the edges 14 to the central raised region 18. The outer raised region 20 also has a generally frustoconical configuration. The base of the frustoconical outer raised region 20 is truncated to fomi the square shape of the washer plate 10, which results in the edges 14 having an upwardly curved configuration, when the washer plate 10 is in the orientation shown in Figures 1 to 3.

Referring to Figure 2, there is shown a side view of the washer plate 10 from which it can be seen that the edges 14 curve in an upward direction between the corners 16.

Figure 3 shows that the outer raised region extends at a first angle a to the horizontal in Figure 3, and the central raised region extends at an angle to the horizontal in Figure 3. The angle is greater than the angle a, which means that the central raised region 18 is steeper than the outer raised region 20.

The washer plate 10 is used as part of a rock bolt assembly to reinforce a wall or roof of a tunnel in a mine working. A plurality of rock bolt assemblies are used in such mine workings, so that the rock bolt assemblies extend one after the other along the tunnel.

A rock bolt assembly is shown in Figures 4 and 5, and is designated 50. The rock bolt assembly 50 comprises a washer plate 10, a rock bolt 52 extending through the central aperture 12 of the washer plate 10, a domed washer 54 partially received in the aperture 12 from the tunnel facing side T, and a nut 56 threadably received on the rock bolt 52.

The rock bolt 52 extends through the domed washer 54. The domed washer 54 has a convex dome shaped curved outer face C, which engages the washer plate 10, as shown. The nut 56 is screwed onto the rock bolt 52, and engages the domed washer 54, to push the domed washer 54 against the washer plate 10, as explained more fully below.

Figures 6A to 6D are diagrammatic representations of the steps involved in installing a rock bolt into the wall or roof 60 of a tunnel of a mine working. An elongate bore 62is drilled into the wall or roof 60 to penetrate through the rock.

Referring to Figure 6A capsule of a first curable material 64 is inserted into the bore 62 to the distal end 62A thereof. The first curable material 64 is a fast curing material and comprises a cement to secure a rock bolt 52 in the bore 62, and a catalyst to bring about the curing of the first curable material 64. The first curable material cures in about 15 seconds.

A capsule of a second curable material 66 is inserted into the bore 62 after the capsule of the first curable material 64. The second curable material is a slower curing material and also comprises a cement to secure the rock bolt 52 in the bore 62, and catalyst to bring about the curing of a second curable material 68. The second curable material cures in about two to three minutes. In this way, the rock bolt 52is secured in the bore 62 by full column grouting.

Referring to Figure 6B, a rock bolt 52 is mounted on a driving tool (not shown), which spins the rock bolt 52 about it longitudinal axis. The rock bolt 52 has a distal end 52A and a proximal end 52B. The rock bolt 52 is mounted on the driving tool that it proximal end 52B, and the distal end 52A is inserted into the bore 62.

The rock bolt 52 is pushed into the bore 62 while it is still spinning. This causes the capsule of the second curable material 66 to burst initially, and when the distal end 52A of the rock bolt 52 reaches the capsule of the first curable material 64, that is also burst.

The spinning of the rock bolt 52 mixes the first and second curable materials 64, 66 with their respective catalysts, and the first and second curable materials 64, 66 begin to cure. The first curable material 64 cures within about 15 seconds and secures the distal end 52A of the rock bolt 52 In the bore 62.

Referring to Figure 6C, when the distal end 52A of the rock bolt 52 is secured in the bore 62, a washer plate 10 is mounted over the proximal end 52B, such that the strata facing side S faôes the wall 60. A domed washer 54 is then also mounted over the proximal end 52B. A nut 56 is then threadably mounted on the proximal end 52B and screwed against the domed washer 54 to push the domed washer 54 against the washer plate 10, as shown in Figure 4.

Referring to Figure 6D. the nut 56 is tightened on the rock bolt 52 until an appropriate level of tightening has been achieved. For example, when the nut 56 has been tightened to approximately 30 kN, a sufficient level of tightening will have been achieved to securely fasten the washer plate 10 against the tunnel wall 60.

The second curable material 66 cures after 2 to 3 minutes thereby further cementing the rock bolt 52 in the bore 62.

The tightening of the nut 56 against the washer plate 10 provides an advantageous feature in this embodiment, in that the nut 56 on the rock bolt 52 can be tightened against the washer plate 10 to an extent that the rock bolt 52 is pretensioned along its longitudinal axis. This pretension is held between nut 56 and the cured first curable material 64 while the second curable material 66 cures to further cement the rock bolt 52 within the bore 62. Once the second curable material 66 has cured, the rock bolt is held in its pretensioned state by the cured second curable material 66.

The provision of the outer raised region in the above described embodiment provides several further advantages. Firstly, it provides a visual indication of strata control loading of the rock bolt 52. After the rock bolt assembly 50 has been inserted into the bore 62 and secured in place, it is likely there will be some movement of the strata, particularly where the rock bolt is reinforcing the roof of a tunnel. During such movement, the outer raised region 20 deforms to flatten against the wall or roof. Thus, during inspection, it will be noted that the outer edges 14 and, therefore, the outer raised region 20 have flattened and that, therefore, the rock bolt 52 is performing its function of reinforcing the tunnel wall or roof.

Secondly, the provision of the two raised regions means that the washer plate 10 can gradually absorb the load on it, for example, the outer raised region 20 flattens and absoibs the load at approximately 60 kN. The central raised region 18 flattens and absorbs load at approximately 140 kN.

Thirdly, the rock bolts 52 have a coarse thread, which means that, with prior art methods, if there is slight movement of the rock, there can be a possibility of the nut 56 loosening. With the above deicribed embodiment, however, the outer raised region 20 provides the advantage that the washer plate 10 is more flexible and resilient than prior art washer plates. After the nut 56 has been tightened to provide a load on the washer plate 10, there will be some resilient deformation of the outer raised region 20. Thus, if there is movement of the rock after tightening, the resilient nature of the outer raised region 20 Will counteract this movement of the rock by relaxing, thereby 10 the tightness of the nut 56.

There is thus described an embodiment of a method of inserting a rock bolt into a wall or roof of a tunnel, which has the advantage of providing all the load absorbing characteristics of prior art washer plates, but also having further advantages as described above.

Various modifications can be made Without departing from the scope of the invention. For example, the thickness of the washer plate 10 can vary, as can the relative angles of the central and outer raised regions 18, 20. Also, the washer plate can be of any suitable dimensions. Further, the central aperture can be of any desired suitable shape.

Claims

* Claims 1. A method of installing a rock bolt into a wall or roof of a

tunnel comprising: drilling an elongate bore in the wall or roof, inserting a curable material into the bore; inserting the rock bolt into the bore to activate the curable material and allowing the curable material to set, thereby fixing the rock bolt in the bore; arranging a load * absorber over a protruding end of the rock bolt; and securing the load absorber to the rock bolt by a fastener; wherein the load absorber defines a central aperture to receive the rock bolt therethrough; and the load absorber has a central raised region surrounding the aperture, and an outer raised region extending from the central raised region to an edge region of the load absorber.
2. A method according to Claim 1, wherein the central and outer raised regions are convex, such that the convexities of the central and outer raised regions extend in the same directions
3. A method according to Claim 1 or 2, wherein the edge region of the load absorber comprises a plurality of corners, and a respective edge extending between adjacent corners.
4. A method according to Claim 3, wherein the corners lie in substantially the same plane, and each edge extends out of the plane.
5. A method according to Claim 4, wherein each edge of the load absorber is curved.
6. A method according to Claim 5, wherein the curvature of each edge is convex in the same direction as the central and outer raised regions, the outer raised region extending from the edges to the central raised region. I0
7. A method according to any of Claims 4 to 6, wherein the central raised region lies out of the aforesaid plane, and the outer raised region lies out of the aforesaid plane.
8. A method according to any of Claims 4 to 7, whereIn the central raised region is steeper relative to the aforesaid plane than the outer raised region
9. A method according to any of Claims 4 to 8, wherein the outer raised region extends at a first angle to the aforesaid plane.
10. A method according to Claim 9, wherein the central raised region extends at a second angle to the aforesaid plane, the second angle being greater than the first angle.
II. A method according to any preceding Claim, wherein the outer raised region comprises an outer generally frustoconical region, which extends from the aforesaid edges.
12. A method according to any preceding Claim, wherein the central raised region comprises a central generally frustoconical region, which extends from the outer raised region to the central aperture.
13. A method according to any preceding Claim, wherein the load absorber has a thickness to provide sufficient absorption of the load applied by the fastener thereon.
14. A method according to Claim 13, wherein the thickness of the load absorber may provides a wall to the central aperture.

I
15. A method according to Claim 14, wherein the central aperture has a central axis, and the wall is angled relative to the central axis of the aperture at an angle of between 10 and 300.
16 A method according to any preceding Claim, wherein the step of inserting the curable material into the bore comprises inserting a first curable material into the bore, and thereafter inserting a second curable material into the bore.
17. A method according to Claim 16, wherein the first curable material comprises a fast curing material, curable within 151030 seconds after activation.
18. A method according to Claim 16 or 17, wherein the second curable material comprises a slow curing material, curable within 1103 minutes after activation.
19. A method according to Claim 18, wherein the second curable material is curable within I and 2 minutes after activation.
20. A method according to Claim 16, 17, 18 or 19, wherein the first curable material comprises a first cementing material and a first catalyst,
21. A method according to any of Claims 16 to 20, wherein the second curable material comprises a second cementing material and a second catalyst.
22. A method according to any of Claims 16 to 21, wherein, the first curable material is held a first capsule of said first curable material, and the second curable material is held in a second capsule of said second curable material.
23. A method according to any of Claims 16 tofl, wherein the step of inserting the rock bolt into the bore comprises spinning the rock bolt about its longitudinal axis during said insertion, whereby, on insertion of the rock bolt into the bore, the first and second capsules are burst by the rock bolt and the first and second curable materials therein are activated and commence curing.
24. A method according to any of Claims 16 to 23, wherein the rock bolt has a distal end and proximal end, and the first curable material cures to secure the distal end of the rock bolt in the bore.
25. A method according to Claim 24, wherein the load absorber is arranged on the proximal end of the rock bolt when the first curable material has cured, and the fastener Is arranged on the proximal end of the rock bolt to secure the load absorber thereto.
26. A method according to Claim 25, wherein the load absorber is secured to the rock bolt, before the second curable material cures to secure the rock bolt in the bore.
27. A method according to any preceding Claim, wherein a domed washer is arranged between the fastener and the load absorber, the domed washer having a domed portion engaging in the central aperture of the load absorber.
28. A load absorber for use in a method of installing a rock bolt, said load absorber defining a central aperture to receive the rock bolt therethrough, and having a central raised region surrounding the aperture, and an outer raised region extending from the central raised region to an edge region of the load absorber.
29. A load absorber according to Claim 28, wherein the central and outer raised regions are convex, such that the convexities of the central and outer raised regions extend in the same directions
30. A load absorber according to Claim 28 or 29, wherein the edge region of the load absorber comprises a plurality of corners, and a respective edge extending between adjacent corners.
31. A load absorber according to Claim 30, wherein the corners lie in substantially the same plane, and each edge extends out of the plane.
32. A load absorber according to Claim 31, wherein each edge of the load absorber is curved.
33. A load absorber according to Claim 32, wherein the curvature of each edge is convex in the same direction as the central and outer raised regions, the outer raised region extending from the edges to the central raised region.
34. A load absorber according to any of Claims 30 to 33, comprising a washer plate defining the central aperture, and having the edge regions.
35. A load absorber according to any of Claims 31 to 34, wherein the central raised region lies out of the aforesaid plane, and the outer raised region lies out of the aforesaid plane.
36. A load absorber according to any of Claims 30 to 35, wherein the central raised region is steeper relative to the aforesaid plane than the outer raised region
37. A load absorber according to any of Claims 30 to 36, wherein the outer raised region extends at a first angle to the aforesaid plane.
38. A load absorber according to Claim 37, wherein the central raised region extends at a second angle to the aforesaid plane, the second angle being greater than the first angle.
39. A load absorber according to any of Claims 28 to 38, wherein the outer raised region comprises an outer generally frustoconical region, which extends from the aforesaid edges.
40. A load absorber according to any of Claims 28 to 39, wherein the central raised region comprises a central generally frustoconical region, which extends from the outer raised region to the central aperture.
41. A load absorber according to any of Claims 28 to 40, having a thickness to provide sufficient absorption of the load applied by the fastener thereon.
42. A load absorber according to Claim 41, wherein the thickness of the load absorber may provides a wall to the central aperture.
43. A load absorber according to Claim 42, wherein the central aperture has a central axis, and the wall is angled re!ative to the central axis of the aperture at an angle of between 10. and 30 .
44. A method substantially as herein described with reference to the accompanying drawings.
45. A load absorber substantially as herein described with reference to Figures 1 to 5 of the accompanying drawings.