GB2280917A - Clip for tunnel lining - Google Patents

Abstract

A bolt strap 14 is fitted to a length of mesh for use in securing the mesh as reinforcement in underground tunnels. The strap is fitted using a clip 2 in the form of a strip of resilient material comprising a base section 4 with a flange 6, 8 at either end for enclosing substantially parallel strands of mesh 16. One flange 8 has an extension 10 for overlaying an edge of bolt strap, and means 18 are provided for securing the strip, and thereby a said bolt strap, to the mesh. <IMAGE>

Description

Reinforcement Mesh in Underground Tunnels This invention relates to the installation of reinforcement mesh in underground tunnels, and more particularly against a wall or roof surface therein.

The invention is especially concerned with the use of bolt straps which are secured to the wall or roof surface to effectively clamp the reinforcement mesh thereagainst.

The securement of reinforcement mesh to roof or wall surfaces in underground tunnels has been greatly facilitated by the use of bolt straps. However, difficulties have arisen in the manner of their location relative to the mesh and their attachment thereto. In use, the bolt strap is attached to rockbolts in the wall or roof surface which project through holes in the strap. This of course requires the holes to be aligned with openings in the mesh. The mesh openings are not particularly large, and particularly in the underground environment in which the mesh is used, misalignment often occurs. This leads to delay in the installation of the mesh and considerable additional work to correct the error.

Bolt straps are normally secured to reinforcement mesh before the combination is offered up to the wall or roof surface. However, because of the often unique situations that exist in the tunnel at different sections thereof, it is often preferred to make the attachment quite close to the point of application; ie, within the tunnel. The normal method of attachment is welding, but for safety reasons, welding underground is avoided where ever possible. As a consequence, it has been proposed to prepare the mesh with bolt straps welded thereto at the surface, but this leads to transport problems in transferring the welded assembly to the site. Additionally, the alignment problem also arises requiring mesh strands to be bent to enable the proper securement of the bolt straps to a wall or roof surface.

In addressing the above problems, the present invention provides a clip for fitting a bolt strap to a length of mesh, which is in the form of a strip of resilient material which wraps around two or more contiguous strands of mesh on one side thereof, and has an extended flange which overlays an edge of a bolt strap on the other. In theory, as few as three such strips can be sufficient to fit a bolt strap to a length of mesh, although in practice at least four, and normally six, would be used for a metre length of strap.

The use of such a clip has a number of advantages.

Firstly, they can be used to fit a bolt strap to a length of mesh at the point of installation against the tunnel surface without a significant fire risk and particularly, the risks associated with welding underground. Secondly, the manner of the fitment allows the bolt strap to be moved relative to the length of mesh again at the point of installation, thereby avoiding the risk of misalignment and the consequential delays. Overall, the invention offers all the advantages of the use of bolt straps in combination with mesh to reinforce underground tunnel walls, while minimising the problems associated therewith in the known exploitation of the practice.

A typical clip embodying the invention is in the form of a strip of resilient material comprising a base section with a flange at either end for enclosing parallel strands of mesh. One flange has an extension for overlaying a marginal edge portion of bolt strap, and the strip is formed with latching elements adjacent each junction between the base section and the flanges to hold the clip to the mesh. Normally, the latching element adjacent the junction with the extended flange comprises a raised portion of the strip material, normally from the base section, which resiliently secures the strand of mesh against the respective junction. This allows the clip to pivot around the respective strand as the bolt strap is located relative thereto.The latching element adjacent the junction with the other flange can comprise a more simple resilient latch formed by deformation of the strip material in the flange. This arrangement enables a number of clips to be pivotally attached to the mesh while the bolt strap is located with the holes therethrough aligned with openings in the mesh, and then secured in place by closing each clip against the mesh on one side and the strap on the other.

Even with the bolt strap secured to the mesh by the clips, some lateral movement can be made possible if for some reason the holes in the strap and the openings in the mesh become misaligned as the mesh is offered up to the tunnel surface. This is of particular benefit as bolt straps can be fitted to the mesh within the tunnel but spaced from the point of installation in the knowledge that some relative shifting of the strap and mesh prior to installation can be corrected. It also means of course, that substantial lengths of mesh can be fitted with bolt straps at the surface, and then transported to the installation site in the knowledge that any deficiencies in the fitting of a particular bolt strap to the mesh can be corrected at the installation site.Essentially, the invention provides an additional degree. of freedom in the use of meshed reinforced tunnel walls and roofs which was not previously available.

The invention will now be described by way of example and with reference to the accompanying schematic drawings wherein: Figure 1 is a perspective view of a clip according to the invention as shown in use holding a bolt strap against a section of reinforcement mesh; Figure 2 is a perspective view showing three clips in use; and Figure 3 is a cross-section illustrating how the assembled bolt strap and mesh is mounted against a tunnel surface.

As shown in the drawings, each clip 2 comprises a base section 4 with a flange 6, 8 extending substantially perpendicularly from either end thereof.

Flange 8 has an extension 10 which extends substantially parallel to the base section 4 to overlay a marginal edge portion 12 of a bolt strap indicated at 14.

The base section 4 of the clip 2 extends over adjacent strands 16 of mesh; two in Figures 1 and 2, but over three in Figure 3. At the junction between the base section 4 and the flange 8, a portion 18 is raised from the base section to overlay the respective strand 16 and latch the clip 2 thereto. At the junction between the base section and the flange 6, a resilient latch is created by the deformation of the strip material in the flange 6 to enable the clip 2 to be latched over the respective strand 16 at that point.

With the clip secured to the strands 16 of the mesh in this way, the extension 10 provides a resilient lip under which a marginal edge portion 12 of the bolt strap 14 can be held.

In fitting a bolt strap 14 to the reinforcement mesh illustrated, a plurality of clips 2 may first be attached to strands 16 by their respective latching raised portions 18. This enables the clips to pivot around the respective strands 16, as illustrated by the central clip shown in Figure 2. In this way, the bolt strap 14 can be accurately located relative to the mesh and more particularly openings therein, before the clips are pivoted into place with the flanges 6 latched onto their respective strands.

As is best shown in Figure 3, the cross-section of the bolt strap includes a central planar section 20, and this is formed with an opening for one or more rockbolts 22 which are used to secure the strap to the tunnel substrate 24. It will be appreciated that the holes in the bolt strap must be aligned with the openings in the mesh to enable the rockbolt to perform its function.

While the location of the openings relative to the strands 16 will be predetermined, its location with the perpendicular strands 26 is determined when the bolt strap is fitted to the mesh. The use of clips as described herein enables that location to be adjusted with a substantial amount of freedom prior to the final securement of the bolt strap to the substrate.

Claims (12)

1. A clip for fitting a bolt strap to a length of mesh, in the form of a strip of resilient material comprising a base section with a flange at either end for enclosing substantially parallel strands of mesh, of which one flange has an extension for overlaying an edge of bolt strap, the clip including means for securing the strip, and thereby a said bolt strap, to the mesh.

2. A clip according to Claim 1 wherein the securing means comprises latching elements adjacent each junction between the base section and the flanges.

3. A clip according to Claim 2 wherein the latching element adjacent the junction with the extended flange comprises a raised portion of the strip material.

4. A clip according to Claim 3 wherein said portion is raised from the base section.

5. A clip according to any of Claims 2 to 4 wherein the latching element adjacent the junction with the other flange is formed by deformation of the strip material.

6. A clip according to Claim 5 wherein said latching element is formed in the flange.

7. A clip for fitting a bolt strap to a length of mesh, substantially as described herein with reference to the accompanying drawings.

8. A method of installing a reinforcement mesh against a wall or roof surface in an underground tunnel comprising fitting a plurality of bolt straps to a length of mesh with clips according to any preceding Claim; offering the length of mesh up to the surface; and securing the mesh to the surface by attachment of the straps to bolts mounted therein.

9. A method according to Claim 8 including the step of adjusting at least one of the straps relative to the mesh prior to securement thereof.

10. A method according to Claim 9 wherein the adjustment is effected at the point of securement.

11. A method according to any of Claims 8 to 10 wherein the bolt straps are fitted to the mesh in the tunnel.

12. A method according to any preceding Claim including the step of removing the clips after the attachment of the straps to the bolts in the surface.