GB2126630A

GB2126630A - Tunnel linings

Info

Publication number: GB2126630A
Application number: GB08323089A
Authority: GB
Inventors: Christopher Richard Grad Smith; Charles William Forrester
Original assignee: FAIRCLOUGH CIVIL ENG
Current assignee: FAIRCLOUGH CIVIL ENG
Priority date: 1982-09-08
Filing date: 1983-08-26
Publication date: 1984-03-28
Also published as: GB2126630B; GB8323089D0

Abstract

A concrete segment 1 for a tunnel lining of reduced weight has a hollow interior between its inner and outer walls which is filled with a filling material 3, such as foam plastics material, having a density less than concrete. The segment may be formed by casting concrete around a solid block of the filler material in a mould. <IMAGE>

Description

SPECIFICATION Tunnel linings This invention relates to concrete segments for tunnel linings.

Tunnels for drainage and other purposes are commonly lined with curved concrete segments which are joined end-to-end to form an annulus, a series of such annuli being joined together sideby-side to form a continuous tunnel lining. It is often desirable to produce such a lining with a smooth interior surface. Linings of this type built up from segments are described in British Patent Specification 2092644A. The segments are composed of solid concrete and are very heavy.

Assembly of a concrete lining inside a tunnel can be a difficult operation as the segments have to be manoeuvred into place in the confined space within the tunnel and when the tunnel is relatively narrow, as is the case with drainage tunnels for example, it is not generally possible to use heavy iifting machinery and the segments have to be moved and supported manually during assembly. These difficulties are increased when the tunnel has a steep gradient.

The segments are generally easier to handle in a tunnel if their weight is reduced. However it is normally necessary for the segments to have a certain minimum thickness to provide a lining having adequate strength. It is sometimes possible to reduce the weight of the segments by providing recesses in their outside surfaces and filling the recesses with grouting material after assembly of the lining to increase the effective thickness of the lining, but such grouting increases the complexity of the operation and there is a substantial risk that grouting of the recesses may be omitted or at least incomplete.

According to the present invention a concrete segment for a tunnel lining has a hollow interior between the inner and outer walls of the segment which is filled with a filling material of lower density than the concrete. The filling material may be a solid plastics foam such as expanded polyurethane foam or polystyrene. The foam may be a lightweight expanded cementitious foam.

The foam may contain additives such as fillers and reinforcing materials, such as glass fibre, to increase its stability and strength.

The segment according to the invention may be made by placing a solid block of the filler material in a mould having the shape of the desired segment and pouring concrete into the mould around the filler to foam the segment.

A segment according to an embodiment of the invention is shown by way of example in the accompanying drawings in which: Figure 1 is a cross-section of an annulus of a tunnel lining formed of segments according to the invention, Figure 2 is a cross-section along A-A of Figure 1.

The annulus shown in Figure 1 comprises a number of identical concrete segments 1 joined end-to-end, the annulus being completed by a key segment 2. The annulus has substantially smooth inner and outer surfaces and the segments may be joined by several different methods, some of which are described in Patent Application 2092644 A.

The segments are provided with totally enclosed voids 3 which are filled with a rigid foam such as expanded polystyrene foam containing reinforcing components in known manner. The dimensions of the voids and of the concrete walls surrounding them are such that the weight of the segments are reduced to the maximum possible extent while retaining adequate strength for the segment. The foam material may be chosen such that the foam itself contributes significantly to the strength of the segment. In known manner, the segments may incorporate reinforcing bars extending through the concrete walls and, if desired, through the foam filled voids.

The segments shown in Figure 1 may be made by casting concrete in moulds having the desired external shape of the segments; however before filling the mould with concrete a block of solid foam having dimensions corresponding to the desired dimensions of the void is inserted in the mould and supported in place while the mould is filled. A typical casting procedure is to pour concrete into the mould to form a bottom layer about 5 cm thick, insert the block of foam and then pour concrete to surround and cover the foam in the mould. On solidification the foam is completely surrounded by the concrete, forming a segment as shown in the drawings.

Claims

1. A concrete segment for a tunnel lining having a hollow interior between the inner and outer walls of the segment which is filled with a filling material of lower density than the concrete.

2. A segment according to claim 1, in which the filling material is a plastics foam.

3. A segment according to claim 2, in which the filling material is a lightweight expanded cementitious foam.

4. A segment according to claim 2, in which the filling material is a lightweight expanded cementitious foam.

4. A segment according to claim 2, in which the filling material is reinforced polystyrene foam.

5. A segment according to any preceding claim, in which the segments incorporate reinforcing bars extending through the concrete walls and/or the hollow interior of the segment.

6. A concrete segment, substantially as hereinbefore described with reference to the accompanying drawings.

7. A method of making a segment according to any preceding claim, in which a solid block of the

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Tunnel linings This invention relates to concrete segments for tunnel linings. Tunnels for drainage and other purposes are commonly lined with curved concrete segments which are joined end-to-end to form an annulus, a series of such annuli being joined together sideby-side to form a continuous tunnel lining. It is often desirable to produce such a lining with a smooth interior surface. Linings of this type built up from segments are described in British Patent Specification 2092644A. The segments are composed of solid concrete and are very heavy. Assembly of a concrete lining inside a tunnel can be a difficult operation as the segments have to be manoeuvred into place in the confined space within the tunnel and when the tunnel is relatively narrow, as is the case with drainage tunnels for example, it is not generally possible to use heavy iifting machinery and the segments have to be moved and supported manually during assembly. These difficulties are increased when the tunnel has a steep gradient. The segments are generally easier to handle in a tunnel if their weight is reduced. However it is normally necessary for the segments to have a certain minimum thickness to provide a lining having adequate strength. It is sometimes possible to reduce the weight of the segments by providing recesses in their outside surfaces and filling the recesses with grouting material after assembly of the lining to increase the effective thickness of the lining, but such grouting increases the complexity of the operation and there is a substantial risk that grouting of the recesses may be omitted or at least incomplete. According to the present invention a concrete segment for a tunnel lining has a hollow interior between the inner and outer walls of the segment which is filled with a filling material of lower density than the concrete. The filling material may be a solid plastics foam such as expanded polyurethane foam or polystyrene. The foam may be a lightweight expanded cementitious foam. The foam may contain additives such as fillers and reinforcing materials, such as glass fibre, to increase its stability and strength. The segment according to the invention may be made by placing a solid block of the filler material in a mould having the shape of the desired segment and pouring concrete into the mould around the filler to foam the segment. A segment according to an embodiment of the invention is shown by way of example in the accompanying drawings in which: Figure 1 is a cross-section of an annulus of a tunnel lining formed of segments according to the invention, Figure 2 is a cross-section along A-A of Figure 1. The annulus shown in Figure 1 comprises a number of identical concrete segments 1 joined end-to-end, the annulus being completed by a key segment 2. The annulus has substantially smooth inner and outer surfaces and the segments may be joined by several different methods, some of which are described in Patent Application 2092644 A. The segments are provided with totally enclosed voids 3 which are filled with a rigid foam such as expanded polystyrene foam containing reinforcing components in known manner. The dimensions of the voids and of the concrete walls surrounding them are such that the weight of the segments are reduced to the maximum possible extent while retaining adequate strength for the segment. The foam material may be chosen such that the foam itself contributes significantly to the strength of the segment. In known manner, the segments may incorporate reinforcing bars extending through the concrete walls and, if desired, through the foam filled voids. The segments shown in Figure 1 may be made by casting concrete in moulds having the desired external shape of the segments; however before filling the mould with concrete a block of solid foam having dimensions corresponding to the desired dimensions of the void is inserted in the mould and supported in place while the mould is filled. A typical casting procedure is to pour concrete into the mould to form a bottom layer about 5 cm thick, insert the block of foam and then pour concrete to surround and cover the foam in the mould. On solidification the foam is completely surrounded by the concrete, forming a segment as shown in the drawings. Claims

7. A method of making a segment according to any preceding claim, in which a solid block of the filler material is placed in a mould having the shape of the desired segment and concrete is poured into the mould around the block of filler material.