GB2167796A - Temporary formwork for tunnel or sewer lining - Google Patents

Abstract

The formwork 84,86 is placed inside primary lining 80 so that a complete annular space is provided into which concrete 82 is cast. The formwork may comprise panels each comprising a sheet 10 and framing members 12,14. The panels are secured to, and spaced from, the primary lining by studs 38, and are secured to adjacent panels by fasteners passing through slots 18,20. Concrete is pumped through apertures 58. <IMAGE>

Description

SPECIFICATION Tunnel lining This invention relates to tunnel linings.

A known method of sewer construction comprises digging a trench, laying a primary lining in the trench in the form of precast concrete rings, typically of about 2 meters diameter and 1/2 meter axial length, with the rings bolted together. A secondary lining is laid inside the primary lining in the form of a continuous shell of concrete which requires to have a smooth internal surface to withstand erosion. This shell of concrete can be made using a form-work lining carried by a machine which supports individual segments of lining so as to complete a ring of the same, and braces the individual segments to withstand pressure when wet concrete is pumped into the annular space between the form-work and the primary lining.Subsequently, the segments are successively moved generally radially inwardly to free them from the formed shell, and the machine advances to a new position along the primary lining and the process is repeated. This system is eminently satisfactory with large contracts but too expensive to use for smaller contracts, and one reason for this is the wide range of sizes and crosssectional shapes required, all of which require different machines or at least different expensive form-work on the machine.

An alternative known system which is in general use for smaller contracts is known as "ribs and lagging" in which the form-work consists of planks assembled to form an annular shape, so that the external surface of the annulus defines the interior surface of the secondary lining, these planks being held in position by metal rings at say 1-1/2 meter intervals. The usual way of working with ribs and laggings is to start at the far end of the tunnel to be lined, laying a railway track along the tunnel from an access point to deliver concrete in skips. A few of the laggings (plank-like strips of wood) are laid generally at the lower part of the annular shell to be formed, and concrete is shovelled into the space between those planks and the primary lining. It will be appreciated that it is necessary to use spacers to provide the necessary gap.As the portion of the form-work provided by the planks is filled with concrete, more planks are pushed into place and more concrete shovelled in. The top of the annulus is particularly difficult to finish satisfactorily by this method. As the secondary lining is formed, length-by-length, the rail track is shortened correspondingly, and from time-to-time the planks and rings are removed from the finished portions.

It is found that the rib and lagging method is not only slow and difficult to provide satisfactory complete linings, but moreover leaves an unsatisfactory interior finish when the planks are reused for subsequent sections. It tends to be necessary to perform yet a third operation of plastering or lining the secondary lining in order to give the required degree of smoothness.

The problems with both of these discussed methods are well known to local Authorities, not only for sewers but for other tunnel purposes, but no satisfactory third method has yet emerged. The object of the present invention is to provide a new method which overcomes these problems.

In accordance with the invention a tunnel lining system comprises the use of form-work assembled manually to provide a complete annular space with the use of concrete pumped into that annular space to form the required concrete shell.

The form-work may comprise a series of segments, of a standard length, typically 2 meters, but of a suitable curvature or otherwise according to the requirements of the cross-sectional shape of the required tunnel.

The form-work may comprise a series of panels which extend essentially over less than 1800 of arc, and having at least side edges (preferably also end edges) which extend generally normally of the surface of the formwork and internally of the tunnel to be formed, said edges being apertured so that adjacent panels can be connected together by interference fit pegs knocked through aligned apertures.

Further features and advantages of the invention will be apparent from the following description of a presently preferred embodiment. In the drawings: Figures 1 is a fragmentary perspective view of a single form-work panel; Figure 2 is a diagrammatic end elevation on a reduced scale showing a number of segments generally similar to those of Figure 1 assembled together to complete a form-work lining; Figure 3 is a view similar to Figure 1, but on a reduced scale and showing a greater length of an individual panel; Figure 4 is an elevation on an enlarged scale showing one of the connecting pegs; Figure 5 is a diagrammatic sectional elevation of a typical sewer tunnel to illustrate the location of the individual segments which are to define the interior shape in forming the secondary lining; Figure 6 is a view similar to Figure 5 showing an alternative typical tunnel shape; and Figure 7 is a sectional elevation taken along the length of the sewer tunnel showing the secondary lining formation.

Turning now to the drawings, Figure 1 shows the end portion of a single form-work panel which consists of (preferably) a single sheet of steel curved to a radius corresponding to that of the internal radius of a substan tially finished tunnel lining required. The sheet 10 is fixed, for example by welding, to a peripheral framing of a heavier gauge metal strip including longitudinally extending members 12 and end members 14. The sheet material 10 and the reinforcing framing members 12 14 are selected, for material and dimensions to suit the loads imposed by the tunnel forming technique. If the sheet 10 is too thin it will bulge under concrete pressure, but if the strength is more than adequate, the framing members 12 and 14 might be unnecessary and could be replaced in whole or part by edges of the panel 10 appropriately bent by a press operation.If they are employed, and are of stronger materials then the sheet 10 they will contribute towards the strength of the panel.

As shown in Figure 3, additional frame supports may be provided, for example in the form of curved elements 16 similar to the end elements 14 and extending parallel to and between the end framing elements 14.

All of the framing elements around the periphery of the panel 10 are provided with a series of regularly spaced slots 18 20 and also holes 22 24. By regularly spaced is meant that, for example, that each slot 18 may be say 30 cm from a corner of the formwork panel, and each slot 20 may be say 10 cm from a corner. The holes 22 24 may similar be regularly positioned so that any two similar panels can be placed edge-to-edge and corner-to-corner and the holes will more or less coincide. In theory, the holes should identically coincide but owing to imperfections in the alignment of the primary lining, and/or places where the tunnel is not straight, this may not always be true. By having elongated slots 18 20, the chance of portions of those in one panel overlapping portions of those in the next adjacent assembled panel in such event is increased.

The fastener shown in Figure 4, on an enlarged scale, comprises a head 26 and a shank 28 having a tepered free end 30. The shank 28 is dimensioned to be a drive fit in the slots 18 20. the complete ring of panels is assembled together as in Figure 2 by locating the panels edge-to-edge and corner to corner and driving fastener pins through aligned pairs of slots, one to each of the two adjacent panels. Successive panels are secured together end-to-end to extend the length of the annular shell by driving fasteners through the aligned pairs of slots 20.

The holes 22 24 are intended to facilitate manipulation of one panel into appropriate alignment with the next adjacent one, in either direction, by using a tommy bar inserted through the holes possibly at a skew angle due to non-aligned holes in adjacent panels.

In order to centralise the form-work, for example of Figure 2, in the primary lining, a number of generally radially extending pins are provided. As shown in Figure 1, the panel is locally reinforced, on the side remote from the concrete when in use, with a patch plate 34 and a nut 36 is welded to the reinforcement.

A screwthreaded stud 38 is engaged with the nut to extend through a hole in the panel 10, and the stud may have a hexagon head to be turned by a spanner, an L-shaped head for manual operation or the T-shaped head shown, reference 40, to enable the studs to be manually screwed outwardly as shown in Figure 2 so that their free ends contact the primary lining.

As shown in figure 2, three different kinds of panels may be provided to make up the complete ring in this case including lower panels 44, distinguished by having a location and centering stud 38 adjacent each of the four corners of the panel, an uppermost panel 46 which differs in having generally centrally located studs 38, and lateral panels 48-54 which have studs at their upper corners, generally as shown in Figure 1, only. However, for many purposes it will be satisfactory to use panels such as 44 and use, or not, ones of the studs according to requirements.

It will be understood by the man skilled in the art that because the concrete is to be formed into a shell surrounding the Figure 2 structure, the studs will create holes in the formed concrete and when the form-work of Figure 2 is removed by unscrewing the studs before separating the panels one by one, the holes left by the pins will have to be filled by a plastering operation. This is however much less arduous and significant than the plastering operation necessary with the prior art where substantially the whole of the internal surface had to be dealt with.

Concrete is to be pumped into the annular shell between the form-work and the primary lining, and it is preferred to do this by delivering the concrete to a port in the centre of the uppermost panel 46. The port may be of several centimeters in diameter to suit the delivery pipe from the concrete pump, and if all of the panels are to be identical, then each will have a generally centrally located aperture such as the one shown by the reference numeral 58 Figure 3 and in all cases, except for the port actually in use, closed by a plug.

The plug may have a thin flange seating on the external surface of the panel 10 so that pressure in the annular space, when concrete is being pumped, will not free any of the plugs which are in place. It will be appreciated that where different panels are used such as 44-54, it will only be selected panels 46 which are provided with the concrete entry ports and plugs.

The concrete casting operation is preferably accompanied by a pulsating effect in the liquid concrete. This calls for a pump which is not particularly smooth running, and facilitates complete filling of the annular shell.

Whereas the machine erected form-work system mentioned as known, necessarily erects form-work over a comparatively limited length of tunnel at any one time, because of the great expense of the forms, and the ribs and laggings method which relies upon concrete being shovelled into place is similarly effective only over relatively short lengths of tunnel, the present invention can be employed over much longer lengths with satisfactory economics. It has been found experimentally that, depending upon the nature of the lining operation, much longer lengths of form-work can be used with only a single concrete entry point and yet satisfactory and complete filling of the form-work defined annulus can be achieved.It will further be appreciated that no railway etc is necessary in fact the present invention allows the lining to be constructed away from the access point rather than from the furthest points towards the access point.

It is simply the pipe leading from the concrete pump which has to be lengthened as the work progresses.

Figure 4 shows a different cross-sectional shape of sewer tunnel in which extra height is provided by using a relatively large radius over the upper portion and a small radius over the lower portion. In this case, typical meeting planes for different panels are indicated by the chain-dot lines, showing that in this arrangement the base or gulley of the tunnel 60 may be formed by one segment, the upper portion by three generally similar segments 62 64 66, and a pair of generally flat panels 68 70 may be used to complete the cross sectional shape.

Figure 5 shows another tunnel shape: in this case, the base or gulley of the sewer is to be brick reinforced and the concrete shell to be provided by the secondary lining is suitably modified in profile. Here, the smaller radius portion is to be defined by five generally similar panels 72, and the gulley to be brick lined, including the sides of the gulley, by a different panel 74. Irrespective of the cross sectional shape required, and whether all of the panels are similar or different, the methods of connecting together, the methods of spacing from the primary line, and of actual lining formation by pumping concrete, remain the same.

Figure 7 is a somewhat diagrammatic illustration showing a sewer lining operation in progress. In this case, a series of generally alike precast concrete rings 80 have been bolted together to form the primary lining. The secondary lining in the form of a continuous annulus of concrete 82 has been cast over a portion of the length, inside the primary lining.

The secondary lining has been cast using the form-work of the invention and the reference numerals 84 86 indicate two complete axial lengths of the form-work as Figure 2 connected together end to end left in place supporting the newest portion of the shell 82 whilst it cures. Similar rings 88-94 are all connected axially together and to the ring 84 to create the annular space 96 to receive the next increment of secondary lining in the form of concrete being pumped through the pipe 98 and the generally central port in the top of ring section 90. It will be appreciated that as the work proceeds, sections 84 and 86 are moved and reassembled at the lefthand end, and that in fact the secondary lining 82 advances from right to left in the figure.

The pumped concrete inherently provides better pressurisation of the space defined by the lining and hence a better surface finish.

Claims (8)

1. A tunnel lining system comprising the use or formwork assembled manually to provide a complete annular space with the use of concrete pumped into that annular space to form the required concrete shell.

2. A system as claimed in Claim 1 wherein the formwork conprises a series of segments conforming to the cross sectional shape of the required tunnel.

3. A system as claimed in Claim 2 wherein each of the segments comprises a panel extending essentially over less than 1800 of arc and having side edges extending normally of the surface of the formwork and internally of the tunnel.

4. A system as claimed in Claim 3 wherein said edges are apertured to be connected by interference fit pegs.

5. A system as claimed in Claim 4 wherein the end edges of the panels extend normally of the surface and internally of the tunnel.

6. A panel for use in carrying out the invention of Claims 1 to 5 provided with at least one radially extending pin for use in centralising the formwork in the tunnel.

7. A panel for use in the system of claims 1 to 5 comprising an aperture for a concrete delivery pipe and a closure for the aperture.

8. A system of making a tunnel lining substantially as described with reference to the accompanying drawings.