GB2299112A

GB2299112A - Tunnel linings

Info

Publication number: GB2299112A
Application number: GB9606215A
Authority: GB
Inventors: Allen W Kittlety
Original assignee: ROM Ltd
Current assignee: ROM Ltd
Priority date: 1995-03-23
Filing date: 1996-03-25
Publication date: 1996-09-25
Anticipated expiration: 2016-03-25
Also published as: GB9606215D0; GB2299112B

Abstract

A reinforced tunnel lining for lining at least part of a tunnel wall comprises a plurality of sections providing reinforcement contained in a concrete mass 27 applied in the tunnel, each section abutting adjacent sections and being arranged to distribute the reinforcement substantially uniformly over the lining. The sections are preformed and self-supporting during assembly. The sections are conveniently of wire mesh, and two or more layers of them may be used to form the reinforcement. A method of lining a tunnel is also described,

Description

IMPROVEMENTS IN AND RELATING TO TUNNEL LININGS This invention concerns improvements in and relating to tunnel linings, particularly of the reinforced concrete type.

The vast majority of modern tunnels are lined following their tunnelling out. Indeed in poor or inconsolidated ground strict limits are placed on how far a tunnel can be cut before a structurally strong lining must be installed.

Currently reinforced concrete tunnel linings are primarily provided in one of two ways. In the first, preformed reinforced concrete sections are brought into the tunnel and positioned. Each section forms a part of the perimeter of the tunnel cross-section. Usually starting from the base, adjacent sections are stacked on one another and linked to form the tunnel shape. Various means are employed for locking the sections together and a layer of concrete or sealing compound may subsequently be applied to the inner surface. The problem with this technique is its lack of versatility as the tunnel has a predefined shape.

In the second way, known as the NATM technique, high strength girders are provided at intervals along the tunnel. The girders are assembled in the tunnel from preformed sections to form a hoop or part hoop. The girders are usually anchored to the surrounding tunnel wall for support during installation. When the girders are in place, the gap between adjacent girders is bridged by wire mesh tied to the girders.

Several sections of mesh are normally required to form a canopy between adjacent girders. Concrete is then sprayed onto the girder/wire mesh assembly to create the lining.

This NATM technique also has a number of problems. Firstly, the girder sections are preformed and allow no adjustment to their configuration when being installed. The girders also require relatively good anchoring to the surrounding walls during assembly as they are not self-supporting at this stage. The girder sections are also heavy and frequently awkward to handle in the confined space of the tunnel. Most significantly, though, the tunnel lining is very strong close to the girders, but far less support is provided between them, as the mesh (manufactured from wires normally only 5-10 mm in diameter) is not designed to provide structural support.

It is an aim of the present invention to provide a more versatile and easily handled reinforced concrete tunnel lining which gives a consistent degree of support over the length of the tunnel.

According to a first aspect of the invention, a reinforced concrete tunnel lining for lining at least part of a tunnel wall comprises a plurality of sections providing reinforcement contained in a concrete mass applied in the tunnel, each section abutting adjacent sections and being so arranged that the reinforcement is distributed substantially uniformly over the lining.

Such a tunnel lining offers substantially consistent strength over its entire length.

The lining preferably lines the part of the tunnel wall defining the side walls and roof in use. It may also be used to line the tunnel base.

Preferably the distribution of the reinforcement is arranged so that reinforcement by weight of any two given square metres in a six metre tunnel length varies by no more than 30%.

The variations referred to preferably exclude those merely caused by variations in the tunnel profile and/or changes in the strength requirements, for instance due to changes in the ground through which the tunnel passes.

According to a second aspect of the invention a reinforced concrete tunnel lining for lining at least part of a tunnel wall comprises a plurality of sections providing reinforcement contained in a concrete mass applied in the tunnel, the reinforcement being exclusively in the form of a metallic mesh.

In either aspect additional features may be provided as follows.

Preferably the reinforcement sections are of wire mesh, which gives uniform reinforcement and readily allows the application of the concrete mass.

The reinforcement sections may be preformed. They can then be made off-site, by mass production techniques. However, as they are made of wire they can be adapted or altered on site, as required.

The mesh may comprise one set of wires extending round the tunnel, and another set extending longitudinally along the tunnel in use.

This construction is easy to manufacture. A set of diagonal wires may also be used, as an alternative or in addition. The diameter of the wires preferably range from 5mm to 16mm, depending on the strength required.

All the wires may have the same diameter, or some may be of greater diameter than others. For example, a set of wires extending round the tunnel may be of greater diameter than a longitudinally-extending set, to accommodate different loading on the tunnel.

The wires may have a circular, or non-circular cross-section.

The reinforcement may be provided in two or more layers to increase the reinforcement. Most preferably adjacent layers are spaced from one another to facilitate the introduction and retention of the concrete. The spacing may be uniform, to given even strength, or may vary as required to give greater strength and/or wall thickness at certain locations.

Spacer members may be used to maintain the required spacing between adjacent layers in a convenient manner.

Stiffening members may be provided on or in proximity to at least one layer, so as to increase the rigidity of the reinforcement. Preferably the members extend longitudinally of the tunnel in use. The stiffening members may also act as the spacer members, so providing a useful double function.

According to a third aspect of the invention a method of lining at least part of a tunnel wall by reinforced concrete comprises arranging sections providing reinforcement to the configuration of the tunnel wall, each reinforcement section abutting adjacent reinforcement sections, and applying concrete to the reinforcement to embed the reinforcement in an integral concrete mass wherein the distribution of reinforcement Is substantially uniform.

This method is considerably more versatile than the prior art techniques because it produces an integral lining, with no joints, or practically no joints, in which the reinforcement is such that the tunnel has a uniform strength rather than strong and weaker sections.

The concrete is preferably sprayed on to the reinforcement.

Preferably, after arrangement of a first layer of reinforcement section, one or more further layers are arranged. Adjacent layers are preferably spaced from one another. Spacer members may be provided on one or more of the layers to achieve this.

It is particularly preferred that the spacer members be applied to the reinforcement sections before they are arranged in the tunnel, i.e.

during manufacture or even on site.

Further features may be provided in the method, similar to those of the first and second aspects of the invention.

Various aspects of the invention will now be described with reference to specific embodiments and the prior art, by way of example only, and with reference to the drawings, in which: Figure 1 shows a prior art embodiment for a reinforced concrete tunnel lining for a section of tunnel; Figure 2 shows part of one of the girders of Figure 1; Figure 3 shows the reinforcement for a reinforced concrete tunnel lining for a section of tunnel in an embodiment of the present invention; Figure 4 shows the sequence of construction for the reinforcement of Figure 3; and Figure 5 illustrates an advantage of the present invention over the prior art with regard to "shadowing".

Figure 1 shows a type of reinforcement 1 used in the prior art for a reinforced concrete tunnel lining. The reinforcement 1 consists of a series of preformed girder sections 2 which are fastened together at their junctions by nut and bolt 3 and to which a wire mesh canopy is attached.

The assembled reinforcement 1 takes on the precise shape shown as the sections 2 are rigid.

As illustrated in Figure 2 the girder sections 2 comprise three ribbed bars 4, 5, 6 in a triangular array. The lower bars 5, 6 are spaced by lateral members (not shown) and corrugated members 8 bridge the spacing between the lower bars 5, 6 and upper bar 4.

During assembly the girder sections 2 are fixed relative to the tunnel wall (not shown) to provide support for the girder until it is fully assembled. Wire mesh sections 9 are then tied to the girder and tied to each other at their ends 11 to generate the continuous canopy of the mesh 9. Concrete is then sprayed onto the reinforcement to form the tunnel lining by enclosing the girders and the wire mesh.

Whilst the resulting lining has a uniform appearance its strength varies along its length. It is strong near the girders, which provide the majority of the support, but weaker further away, where only the wire mesh sections provide support. The wire mesh may have a diameter of only Smm or so, and so does not give much structural support.

In the present invention, as illustrated in Figure 3, the girder sections 2 are omitted from the reinforcement, and a stronger mesh 20 is used.

The reinforcement of Figure 3, as illustrated in Figure 4, comprises a first canopy of structural wire mesh 20 which is formed from a number of preformed sections 22. Each section 22 has a set of wires extending round the tunnel in use, and another set extending longitudinally. The wires, which may be of circular or non-circular cross-section, have a diameter between Smm and 16mm. The sets of wires may have different diameters, depending on the reinforcement required. At the boundaries 21 between the sections 22 of mesh it is undesirable to have the sections stacked on one another. The corner of a section 22 may be adjacent to up to three other sections, so a maximum of four layers could be involved.

The thickness of four layers would reduce the depth of concrete that can be applied. To avoid this problem each side of each section is not defined by a wire, but by protruding ends 30 of the perpendicular wires. The protruding ends 30 of one section, as illustrated in Figure 4a, can then pass between the equivalent ends 31 on the other section to maintain the spacing of the cross wires. The percentage overlap at an end of a reinforcement section may amount to 10-50% of the reinforcement area.

These sections 22 require minimal support from the tunnel wall during assembly. After they are assembled into the appropriate shape, a series of longitudinally extending U-section stiffening members 24 are then introduced, Figure 4b, and spot-welded to the sections 22. The members 24 provide added stability to the sections 22 and prevent twisting or other undesirable movement.

Once the first layer of mesh 20 has been assembled a second layer 25 is assembled under it by tying onto the members 24, which also therefore serve to maintain an even spacing between the layers 20, 25, Figure 4c.

Once the double layer of reinforcement has been assembled, Figure 4d, concrete 27 is sprayed onto the reinforcement to complete the lining, Figure 4e.

The main advantage of the invention is that a tunnel lining of substantially uniform strength over its entire length is obtained. In fact, the variation in distribution weight of reinforcement between any two square metres of the lining in a six metre tunnel length is no more than 30%. However, other advantages, such as the one illustrated in Figure 5, are also obtained.

When concrete is sprayed onto a structure, such as that represented by the prior art in Figure 5a, the relatively large dimensions of the bars 40 are such that the sprayed material 42 passes the bars 40 without fully enclosing them despite its natural spreading tendency. Thus cavities 44 on the opposing side of the bars 40 to the direction from which it is sprayed (arrow A shows direction) may arise. This is undesirable as it causes a significant reduction of the strength of the bar/concrete bond, as not all the bar is bonded.

The present invention, by employing a larger number of smaller diameter bars 50 ensures that this problem is partially eliminated or at least significantly reduced as any cavities 44 are much smaller.

Furthermore, as each wire in the present invention has a true structural action a few bars affected by cavities has a very limited effect, compared with the girder construction where a few bars may be all that section of tunnel has by way of true structural members.

Claims

1. A reinforced concrete tunnel lining for lining at least part of a tunnel wall, comprising a plurality of sections providing reinforcement contained in a concrete mass applied in the tunnel, each section abutting adjacent sections and being so arranged that the reinforcement is distributed substantially uniformly over the lining.

2. A reinforced concrete tunnel lining as claimed in claim 1, in which the lining lines the part of the tunnel wall defining the side walls and roof in use.

3. A reinforced concrete tunnel lining as claimed in claim 2, in which the lining lines the part of the tunnel defining the base in use.

4. A reinforced concrete tunnel lining as claimed in any preceding claim, in which the distribution of the reinforcement is arranged so that reinforcement by weight of any two given square metres in a six metre tunnel length varies by no more than 30%.

5. A reinforced concrete tunnel lining for lining at least part of a tunnel wall, comprising a plurality of sections contained in a concrete mass applied in the tunnel, the reinforcement being exclusively in the form of a metallic mesh.

6. A reinforced concrete tunnel lining as claimed in any preceding claim, in which the reinforcement sections are of wire mesh.

7. A reinforced concrete tunnel lining as claimed in any preceding claim, in which the reinforcement sections are preformed.

8. A reinforced concrete tunnel lining as claimed in claim 6 or claim 7, in which one set of wires of the mesh extend round the tunnel, and another set extend longitudinally along the tunnel.

9. A reinforced concrete tunnel lining as claimed in claim 6 or claim 7, in which a set of wires extends diagonally to the tunnel in use.

10. A reinforced concrete tunnel lining as claimed in any of claims 6 to 9, in which the diameter of wires in the mesh range from 5mm to 16mm.

11. A reinforced concrete tunnel lining as claimed in any of claims 6 to 10, in which all the wires have the same diameter.

12. A reinforced concrete lining as claimed in any of claims 8 to 11, in which at least some wires have a circular cross-section.

13. A reinforced concrete tunnel lining as claimed in any of claims 8 to 12, in which at least some wires have a non-circular cross-section.

14. A reinforced concrete tunnel lining as claimed in any preceding claim, in which the reinforcement is provided in two or more layers.

15. A reinforced concrete tunnel lining as claimed in claim 14, in which adjacent layers are spaced from one another.

16. A reinforced concrete tunnel lining as claimed in claim 15, in which the spacing is uniform.

17. A reinforced concrete tunnel lining as claimed in claim 15, in which the spacing is variable.

18. A reinforced concrete tunnel lining as claimed in any of claims 15 to 17, in which spacer members maintain the spacing between adjacent layers.

19. A reinforced concrete tunnel lining as claimed in any of claims 14 to 18, in which stiffening members are provided on or in proximity to at least one layer.

20. A reinforced concrete tunnel lining as claimed in claim 19, in which the stiffening members extend longitudinally of the tunnel in use.

21. A reinforced concrete tunnel lining as claimed in claim 18 and claim 19 or claim 20, in which the stiffening members act as the spacer members.

22. A method of lining at least part of a tunnel wall by reinforced concrete, comprising arranging sections providing reinforcement to the configuration of the tunnel wall, each reinforcement section abutting adjacent reinforcement sections, and applying concrete to the reinforcement to embed the reinforcement in an integral concrete mass wherein the distribution of reinforcement is substantially uniform.

23. A method as claimed in claim 22, in which the concrete is sprayed on to the reinforcement.

24. A method as claimed in claim 22 or claim 23, in which, after arrangement of a first layer of reinforcement sections, one or more further layers are arranged.

25. A method as claimed in claim 24, in which adjacent layers are spaced from one another.

26. A method as claimed in claim 25, including providing spacer members on at least one layer.

27. A method as claimed in claim 26, in which the spacer members are applied to the reinforcement sections before they are arranged in the tunnel.

28. A reinforced concrete tunnel lining substantially as described herein with reference to and as illustrated in Figures 3 , 4 and 5b of the accompanying drawings.

29. A method of lining by least part of a tunnel wall by reinforced concrete substantially as described herein with reference to and as illustrated in Figures 3, 4 and 5b of the accompanying drawings.