WO2020240204A1

WO2020240204A1 - Prefabricated former for pumping station

Info

Publication number: WO2020240204A1
Application number: PCT/GB2020/051311
Authority: WO
Inventors: Timothy EAGLE; Robert Freeman; Austin Hill
Original assignee: Dutypoint Limited
Priority date: 2019-05-30
Filing date: 2020-05-29
Publication date: 2020-12-03
Also published as: GB2584313A; GB2584313B; GB201907660D0

Abstract

A prefabricated former 10 for an underground pumping station comprising: a main chamber 12 for housing water pumping apparatus 13; an antechamber 14 for, in use, keeping components 15 of the pumping station dry; and an opening in an upper end of the prefabricated former for receiving concrete; the main chamber 12 having a side wall having an inner layer 16 and an outer layer 18 defining a first cavity for receiving concrete therebetween; the antechamber being formed in a cut out of an upper end of the side wall of the main chamber, the antechamber having a side wall surrounding a base wall, both the side wall and base wall have an inner layer 22, 26 and outer layer 24, 28 defining a second cavity for receiving concrete therebetween; wherein the first cavity is in communication with the second cavity enabling concrete, poured through the opening, to flow from one cavity to the other; when set, the concrete forming a unitary structure. A method of constructing a subterranean pumping station using the disclose prefabricated former for an underground pumping station. The method involving excavating a hole; placing the prefabricated former; introducing concrete into either the first cavity of the first chamber or second cavity of the second chamber so that the concrete flows between the cavities.

Description

PREFABRICATED FORMER FOR PUMPING STATION

The present invention relates to a prefabricated former for an underground pumping station.

BACKGROUND TO THE INVENTION

In some areas, ground or sewage water may need to be pumped upwards to main drains for removal. It is necessary to install pumps for this purpose underground and pumps are typically installed in subterranean chambers, where they can be accessed for servicing.

Subterranean chambers for water pumps must be strong to resist the weight of structures above the chamber, and also hydrostatic pressure on the walls and base of the chamber in locations where the chamber extends below the water table. Such chambers are therefore often constructed with reinforced concrete walls and a separately poured concrete base. This construction process requires excavation of a hole, and assembly of shuttering within the hole for receiving the concrete. This requires operatives to work in the excavation for extended periods to assemble the shuttering, posing health and safety risks. Shuttering assembly also increases the time required for construction.

One solution is to provide a polyethylene or GRP tank which is placed on a concrete base and surrounded by concrete. Effectively, the tank provides a waterproof liner for the chamber. However, with this solution, a significant amount of groundwork is still required in forming the base and it is necessary to shutter around the tank before pouring the concrete around it.

Subterranean pump chambers, either built in situ or using the prefabricated solution above, tend to have a single chamber. The pump and other components, such as valves, are situated within the single chamber. Incoming liquid enters the chamber and is pumped out. However, if, for example, there is a blockage such as a faulty valve, then even if the pump is running, the liquid is prevented from being pumped out and the chamber floods. In this situation, the pump and components including valving are submerged and hence are inaccessible. This can be particularly problematic for servicing or replacing components as the chamber has to be drained and/or cleaned. Moreover, even when drained and/or cleaned non-target components may need to be removed because of the layout of the pump and components.

A further issue with installation of subterranean pump chambers below the water table is that the hydrostatic forces from water surrounding the chamber exert a significant upwards force, or buoyancy. This may cause even a strong walled chamber to gradually rise upwards from the ground, posing a hazard and potentially damaging other structures. It is therefore very important that the structural engineers on site ensure that there is sufficient weight of concrete in the structure to counter this buoyancy and prevent the chamber from rising up. In many cases, this is not properly considered and the chambers effectively float upwards, damaging pipework, electrical supplies and above ground works. Also, if the depth of the pump is no longer fit for purpose because it is too high in the ground, the chamber has to be dug up and a new chamber installed.

It is an object of the present invention to provide a prefabricated former suitable for building a subterranean chamber for a water pump which mitigates or substantially reduces the abovementioned problems.

STATEMENT OF INVENTION

According to a first aspect of the present invention, there is provided a prefabricated former for an underground pumping station including a first chamber for housing water pumping apparatus and a second chamber for valving, the prefabricated former comprising a floorpan and a side wall surrounding a floorpan forming the first chamber, the side walls having an inner layer and an outer layer defining a first cavity for receiving concrete therebetween; the second chamber being formed inset in an upper end of the side wall of the first chamber, the second chamber having a base wall and a side wall surrounding the base wall, both the side wall and base wall have an inner layer and outer layer defining a second cavity for receiving concrete therebetween; wherein an opening is provided in an upper end of the prefabricated former for receiving concrete; and the first cavity is in communication with the second cavity enabling concrete, poured through the opening, to flow from one cavity to the other; when set, the concrete forming a unitary structure.

The side walls of both the first chamber and second chamber allow for a strong unitary concrete structure with separate compartments to be created once the prefabricated former has been installed and filled with concrete. By having separate compartments, it is possible to locate some components in a dry compartment which allows fluid to remain in the main compartment during maintenance of the components in the dry compartment. To ensure that the strong unitary structure with separate compartments is formed communication between the cavities is provided. With communication between the cavities it is possible for the separate compartments to be created with a single pour and/or only having to pour through a single opening.

The first chamber may be considered a main chamber. The second chamber may be considered an antechamber.

The antechamber may extend at least partially into the main chamber.

The antechamber may extend at least partially out from the main chamber.

The antechamber may extend further out from the main chamber than it extends further in.

The prefabricated former may further comprise at least one opening for receiving a utility conduit between the main chamber and antechamber. The utility conduit may be a pipe.

The or each opening may be disposed on the base wall of the antechamber.

The or each opening may be disposed on the side wall of the antechamber. The or each opening may comprise a sealing means for, in use, sealing around the utility conduit. The sealing means may be a ring seal. Additionally or alternatively, the sealing means may be a curable or setable sealant applied at the interface between the opening and the utility conduit.

A port or further opening may be provided in the side wall of the antechamber for receiving a utility conduit between the antechamber and the environmental outside the prefabricated former.

The inner layer of the base wall may be known as the upper layer. The outer layer of the base wall may be known as the lower layer.

The inner layer of the base wall may be substantially sealed to the side wall of the antechamber.

The inner layer of the base wall may include a side wall receiving section for receiving a portion of the side wall of the antechamber. The receiving section may cap a lower end of a portion of the side wall of the antechamber, i.e. the receiving section closes the opening formed between the inner and outer layers of the side wall about one of its ends.

The outer layer of the base wall may be external to the main chamber. That is to say there is no outer layer of the base wall disposed within the main chamber.

The outer layer of the base wall may be inclined, i.e. non-parallel with the inner layer of the base wall. The outer layer may extend from the outer layer of the side wall of the main chamber to the side wall of the antechamber, preferably the outer layer extends to the outer layer of the side wall of the antechamber.

An inclined portion of the outer layer may be spaced from an opening in the lower end of the side wall of the antechamber. The outer layer of the base wall may extend substantially under the side wall of the antechamber.

The inclined outer layer improves the flow of concrete between the cavities of the chambers.

The base wall may include a single layered section for defining an area in which no cavity is provided. The single layered section comprising a portion of either the inner layer or outer layer, preferably the inner layer. The single layered section may be disposed between the first chamber and the second chamber.

An opening for providing a route between the first chamber and second chamber may be provided in the base wall, preferably in the single layered section. The opening may be optionally formed when the prefabricated former is on site.

Advantageously, by providing a single layered section in the base wall there is no defined cavity in that area meaning that once concrete is poured there will be less material to remove to provide a route between compartments.

A support element may be provided to support the side wall of the antechamber. The support element may be disposed within the main chamber. The support element may support a portion of the side wall disposed within the main chamber.

Advantageously, the support element provides structural support to the side wall of the antechamber within the main chamber during pouring of concrete and after the concrete has set.

The prefabricated former may further comprise a roof attached to the upper end of the prefabricated former.

The roof may include a first access opening for the main chamber and a second access opening for the antechamber. The side wall of the main chamber may be made from a plastics material. The side wall of the antechamber may be made from a plastics material.

The side wall of the main chamber may include polyvinyl chloride. The side wall of the antechamber may include polyvinyl chloride.

The side wall of the main chamber may be in the form of a prism.

The side wall of the main chamber may be in the form of an octagonal prism along at least a portion of the height of the prefabricated former.

The antechamber may extend from at least one side of the octagonal prism.

The main chamber may further comprise a water pumping apparatus. The water pumping apparatus may be disposed in the main chamber.

The antechamber may further comprise at least one valve.

The prefabricated former may further comprise utility conduit connecting the pumping apparatus to the at least one valve.

The side walls of the main chamber may include strengthening elements connecting the outer layer to the inner layer. The side walls of the antechamber may include strengthening elements connecting the outer layer to the inner layer.

The floorpan may comprise a floor former disposed in the main chamber. The side walls of the main chamber may extend both above and below the floor former defining a space above the floor former and a space below the floor former. An opening between the first cavity and the space below the floor former may be provided. The opening allows concrete to flow through the first cavity into the space below the base former. The floor former may be substantially concave. The floor former may be a frusto-conical or similar shape.

The floor former may be formed of glass reinforced plastic.

The space below the floor former, when filled with concrete, provides a strong and heavy base. This provides a ballast weight to resist buoyancy of the chamber caused by hydrostatic pressure, advantageously preventing the chamber from rising out of the ground.

The prefabricated former may include at least one rail adapted to guide and secure components in the main chamber. The or each rail may extend from an upper portion of the main chamber to a lower portion of the main chamber. The or each rail may be secured with a bracket to the upper portion of the main chamber.

A support structure having support elements may be included in the prefabricated former. The support structure may be located within the main chamber and antechamber, or there may be a support structure for each the main chamber and antechamber. The support structure may be removable. The support structure may provide support to the prefabricated former during transit and installation. In particular, the support structure resists compression forces of the wet concrete.

In the second aspect of the present invention there is provided a method of constructing a subterranean pumping station having a wet compartment and a dry compartment, the method comprises the steps of: excavating a hole in the ground or utilising an existing hole; placing a prefabricated former according to the first aspect of the present invention; introducing concrete into either the first cavity in the side wall of the main chamber or second cavity in the side wall of the antechamber so that concrete flows between the cavities.

The method may further comprise the step of mechanically agitating the concrete before the concrete has set. The method may further comprise the step of introducing material around the prefabricated former to bury the prefabricated former.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made by way of example only to the accompanying drawings, in which:

Figure 1 shows a partially cross-sectional perspective view of a prefabrication former for an underground pump station according to a first embodiment;

Figure 2 shows a perspective view of the prefabricated former of Figure 1 ;

Figure 3 shows a perspective view of a prefabricated former for an underground pump station according to a second embodiment;

Figure 4 shows a first side view of the prefabricated former of Figure 3;

Figure 5 shows a second side view of the prefabricated former of Figure 3;

Figure 6 shows a cross-sectional view of the prefabricated former of Figure 3; and

Figure 7 shows a cross-section view of the prefabricated former of Figure 3 filled with concrete.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring firstly to Figures 1 and 2, a first embodiment of a prefabricated former for an underground pump station is indicated generally at 10. The former includes a first chamber 12 and a second chamber 14. The first chamber 12 is the main chamber for housing a pumping assembly 13. The second chamber 14 is the antechamber for housing components, such as valves 15, in a dry space.

The first chamber 12 includes a side wall formed from an inner layer 16 and an outer layer 18. A cavity is provided between the inner layer 16 and outer layer 18 of the first chamber 12. The side wall of the main chamber forms an octagonal cross section when viewed from above for at least a portion of the prefabricated former’s height. The inner layer 16 and outer layer 18 of the first chamber 12 are concentric. The inner layer 16 has a smaller cross-section than the outer layer 18. The side wall is made from plastics and is waterproof.

In the current embodiment, the inner layer 16 has a shorter length, or areas of shorter length than the outer layer 18. The continuous inner layer 16 has a lower end, which is situated above an upper end of the outer layer 18. The inner layer 16 has an upper end which is situated substantially below the upper end of the outer layer 18. Alternative inner layer designs are possible, as long as a continuous inner layer is provided around one area for forming a chamber, and there are spaces or gaps in the inner layer close to the bottom for allowing concrete to flow out of the cavity into a floor section 20. In other embodiments, there may be no openings in the inner layer.

Between the inner layer 16 and outer layer 18 of the first chamber’s side wall, a plurality of strengthening webs 19 are provided. Each web is a planar elongate element, having a first long edge and a second long edge. The first long edge of each web 19 is joined to the outer layer 18 and the second long edge of each web is joined to the inner layer 16. Each web therefore bridges the cavity between the inner 16 and outer layers 18. Each web includes a plurality of apertures for allowing concrete to flow past the webs during pouring.

The second chamber 14 is disposed in a cut out in the side wall of the first chamber 12, in other words, it is inset in the side wall. The second chamber 14 includes a hollow base and a side wall perpendicular to the hollow base. In the current embodiment, the hollow base extends perpendicularly from the cut out into the first chamber 12 and away from the first chamber 12. In other embodiments, the hollow base may extend in one direction, either into or out of the first chamber 12. The hollow base includes an upper layer 22 and lower layer 24 forming a space for receiving concrete. The lower layer 24 includes two parts which are attached to, or integrally formed with, the side wall of the first chamber 12. The first part is attached to and extends perpendicularly from the outer layer 18 of the first chamber. The second part is attached to and extends perpendicularly away from the inner layer 16 of the first chamber 12. The hollow base is also attached, or integrally formed with, the side wall of the second chamber 14. The lower layer 24 includes two parts so that the concrete can move from or into the hollow base from a cavity in one of the side walls.

The side wall of the second chamber 14 includes a first layer 26 and a second layer 28 forming a space for receiving concrete. The first layer 26 is internal to the second chamber 14. The second layer 28 is external to the second chamber 14 but may be internal to the first chamber 12. The first layer 26 is attached to, or integrally formed with, the upper layer 22 of the hollow base. The second layer 28 is attached to, or integrally formed with, the lower layer 24 of the hollow base. The side wall of the second chamber 14 forms a quadrilateral cross- sectional area for the second chamber 14. The first layer 26 has a smaller cross-section than the second layer 28. The side wall is made from plastic and is waterproof.

The first layer 26 has a shorter length, or areas of shorter length than the second layer 28. The continuous first layer 26 has a lower end, which is situated above an upper end of the second layer 28. The first layer 26 has an upper end which is situated substantially below the upper end of the second layer 28. Alternative first layer designs are possible, as long as a continuous first layer is provided around one area for forming the second chamber 14, and there are spaces or gaps in the first layer close to the bottom for allowing concrete to flow out of or into the cavity. In the current embodiment the hollow base includes two conduits 29 extending from an opening in the lower layer 24 to an opening in the upper layer 22. In other embodiments, there is at least one conduit 29. The conduit provides a route for utility conduit to move from the first compartment 12 to the second compartment 14. For example, in the current embodiment, the pumping assembly 13 is connected to the valves 15 by means of pipes running through the conduits 29. The conduit 29 includes a sealing means (not shown) to seal the second chamber 14 from the first chamber 12. The sealing means may be a ring seal or a sealant.

Between the first layer 26 and second layer 28 of the second chamber’s side wall, a plurality of strengthening webs 19 are provided. Each web is a planar elongate element, having a first long edge and a second long edge. The first long edge of each web 19 is joined to the second layer layer 28 and the second long edge of each web is joined to the first layer 26. Each web therefore bridges the cavity between the first 26 and second layers 28. Each web includes a plurality of apertures for allowing concrete to flow past the webs during pouring.

At the upper end of the prefabricated structure 10, the cavity in both the first chamber 12 and the second chamber 14 is open for providing an entry point for concrete to be poured between the layers of both side walls.

By ensuring that there is a path between the cavities in both side walls and the hollow base it allows concrete to flow around the prefabricated former and create a unitary concrete structure. This is particularly advantageous as multiple compartments can be created in a single pour or by pouring into a single location on the prefabricated former.

In the current embodiment, the prefabricated former 10 also includes a floor former 30. The floor former 30 is a concave element. The floor former 30 is defined by an edge which follows the profile of the inner layer 16 of the first chamber’s side wall. The floor former 30 is disposed within the side wall. The floor former 30 divides the volume within the first chamber 12 into a volume above the floor former 30 and a volume below the floor former 30. The volume below the floor former forms the floor section 20.

The floor former 30 includes a central planar portion and an outer angled portion 31 which is angled up and away, for example, at around 120 degrees towards the side wall of the first chamber 12 from the periphery of the central planar portion. A circumferential flange extends around the upper edge of the angled portion 31 . The circumferential flange is disposed vertically, as viewed and in use. The circumferential flange lies against and is sealed to the inner layer 16 of the side wall. The central planar portion lies horizontally in use.

In other embodiments, the outer angled portion 31 includes a plurality of recesses. The recesses are formed by the meeting of corners of the central planar portion with substantially vertical joining surfaces, the joining surfaces connecting the corners of the central planar portion to the outer angled portion. The recesses allow the central planar portion to have a larger footprint for accommodating rectangular based objects, such as pumping apparatus 13.

The floor former 30 is fluid-tight. The floor former 30 is sealed to the inner layer 16 of first chamber’s 12 side wall. There is therefore no internal fluid flow path from the area above the floor former 30 to the area below the floor former 30.

The floor former 30 is preferably made of glass reinforced plastic, but may be made from steel, preferably galvanised steel.

The prefabricated former 10 includes two rails 32 which extend substantially the length of the first chamber 12. The two rails are used to guide the pumping apparatus 13 into or out of the first chamber 12. It may also be used to secure the pumping apparatus 13 in the first chamber 12. The rails are attached to the upper end of the first chamber 12 by means of a bracket.

The prefabricated former 10 includes a roof 34. A first access opening and a second access opening are provided in the roof 34. The first access opening provides access to the first chamber 12 and the second access opening provides access to the second chamber 14.

In the current embodiment, the roof 34 is preferably a hollow shell. The roof 32 is removed prior to pouring the concrete into the cavities. However, in other embodiments the roof is not removed prior to pouring concrete as the upper surface and lower surface of the roof 34 are both provided with at least one opening. The at least one opening in the lower surface is in communication with the cavity in the first and/or second chamber side walls allowing concrete poured through the opening in the upper surface of the roof 34 to flow into the cavities.

A method of constructing a subterranean pumping station with separate compartments using the prefabricated former 10 will now be described.

The prefabricated former 10 is assembled off-site and transported to the installation site, typically by lorry. At the installation site, a hole is excavated in the ground, typically to a depth equal to the height of the former 10. The hole may be finished with gravel or sand bulk. The former 10 is placed in the hole and the roof 32 removed. Concrete is introduced into an opening in the side walls of the former 10. In other embodiments, the opening is provided in the roof 34. The concrete flows into one of the cavities in the first chamber’s side wall or second chamber’s side wall. As the concrete flows, it will move through the cavity in the second chamber’s hollow base. In embodiments with a floor former 30, the concrete also flows into the space 20 bellow the floor former 30. While the concrete flows, the former 10 may be mechanically agitated to further liquefy the concrete and ease flow. In some embodiments, concrete pouring may be conducted in stages, allowing the concrete to at least partially set between each stage.

The excavation is re-filled around the former 10, either with excavated material or gravel or sand bulk. Re-filling may take place during, before or after pouring of the concrete. Re-filling may take place in stages, corresponding to the staged concrete pouring. Figures 3 to 7 show a further embodiment of a prefabricated former for an underground pumping station indicated generally at 100. The prefabricated former 100 has the same or similar features as the prefabricated former 10 discussed above, reference numerals will be maintained where appropriate.

The second chamber 14 of the prefabricated former 100 has a first side wall, a second side wall opposite the first side wall, a third side wall extending between the ends of the first and second side walls, and a fourth side wall opposite the third side wall. The fourth side wall of the second chamber 14 extends into the first chamber 12. The first, second, third and fourth side walls comprise an inner layer 26 and an outer layer 28 defining a cavity for receiving concrete therebetween. The cavities are in either direct or indirect communication with each other.

The cavity in the fourth side wall of the second chamber 14 is in communication with a cavity for receiving concrete defined by the inner layer 16 and outer layer 18 of the side wall of the first chamber 12.

The base wall of the second chamber 14 has an upper layer 36 forming a floor of the second chamber 14. The upper layer comprises a floor portion which extends between the inner layers 26 of the side wall of the second chamber 14. The floor portion comprises a recess portion 37 disposed between the side wall of the first chamber 12 and the fourth side wall of the second chamber 14.

The recess portion defines a single layered section of the base wall.

A section of the floor portion abuts an upper portion of the side wall of the first chamber 12, the section essentially bridging the inner layer 16 and outer layer 18.

A sealing flange extends from the periphery of the floor portion for sealing the upper layer 36 to the inner layers 26 of the side wall of the second chamber 14. The recess portion includes a base, a wall extending from the base to the floor portion and a section of the sealing flange depending from the base. The wall abuts, and can be sealed to, the inner layer 16 of the side wall of the first chamber 12. The portion of the sealing flange abuts and is sealed to the inner layer 26 of the fourth side wall of the second chamber 14.

At least one opening for a utility conduit such as a pipe is provided in the recess portion. A sealing element may be provided in the opening.

A side wall receiving section 38 extends from the section of the sealing flange of the recess portion. The receiving flange has an L-shaped cross section with a base and a wall extending from the base. The base extends between the inner and outer layer of forth side wall and the wall abuts with and is sealed to the fourth side wall.

The base wall of the second chamber 14 has a lower layer 40 extending between the side wall of the first chamber 12 and first, second and third side walls of the second chamber 14, specifically extends from the outer layer 18 to the outer layer 28. The upper layer 36 and lower layer 40 define a cavity for receiving concrete.

The side wall of the first chamber 12 includes openings which are in communication with the cavity defined by the upper and lower layers 36, 40. The openings are formed in the outer layer 18 of the side wall.

The first, second and third side walls of the second chamber 14 include openings disposed at a lower end which are in communication with the cavity defined by the upper and lower layers 36, 40.

The lower layer 40 includes a first portion which is angled from a horizontal plane providing an inclined surface to assist the flow of concrete during pouring and a second portion extending from the edge of the first portion. The second portion spaces the first portion from the lower ends of the first, second and third side walls to provide a less restrictive path for concrete to flow. The lower layer 40 includes a sealing flange 42 which extends from its periphery to abut the outer layer 18, 28 of both the first and second chamber 12, 14 side walls.

Structural support elements (not shown) may be provided to support the fourth side wall of the second chamber 14. The support elements are designed to support the weight of concrete within the fourth wall. The support elements may extend from a surface of the prefabricated former 100.

A method of constructing a subterranean pumping station with separate compartments using the prefabricated former 100 follows the same steps as those described above. The use of the former provides reduced site preparation time, the use of less concrete and a highly predictable amount of concrete for a given size of chamber, a quicker installation time, a stronger integral structure and reduced risk of buoyancy problems arising, compared with current methods of construction of subterranean pumping chambers.

The embodiments described above are provided by way of example only, and various changes and modifications will be apparent to persons skilled in the art without departing from the scope of the present invention as defined by the appended claims.

Claims

1. A prefabricated former for an underground pumping station including a main chamber for housing water pumping apparatus and an antechamber for valving,

the prefabricated former comprising a floorpan and a side wall surrounding a floorpan forming the main chamber, the side walls having an inner layer and an outer layer defining a first cavity for receiving concrete therebetween;

the antechamber being formed inset in an upper end of the side wall of the main chamber, the antechamber having a base wall and a side wall surrounding the base wall, both the side wall and base wall have an inner layer and outer layer defining a second cavity for receiving concrete therebetween;

wherein an opening is provided in an upper end of the prefabricated former for receiving concrete; and the first cavity is in communication with the second cavity enabling concrete, poured through the opening, to flow from one cavity to the other; when set, the concrete forming a unitary structure.

2. A prefabricated former as claimed in claim 1 , in which the antechamber extends at least partially into the main chamber.

3. A prefabricated former as claimed in claim 1 or claim 2, in which the antechamber extends at least partially out from the main chamber.

4. A prefabricated former as claimed in any preceding claim, in which the prefabricated former further comprises at least one opening for receiving a utility conduit between the main chamber and antechamber.

5. A prefabricated former as claimed in claim 4, in which the or each opening extends through the base wall of the antechamber.

6. A prefabricated former as claimed in claim 4 or claim 5, in which the or each opening extends through the side wall of the antechamber.

7. A prefabricated former as claimed in any of claims 4 to 6, in which the or each opening comprises a sealing means for, in use, sealing around the utility conduit.

8. A prefabricated former as claimed in any preceding claim, in which the prefabricated former further comprises a roof attached to the upper end of the prefabricated former.

9. A prefabricated former as claimed in claim 8, in which the roof includes a first access opening for the main chamber and a second access opening for the antechamber.

10. A prefabricated former as claimed in any preceding claim, in which the side wall of the main chamber and the side wall of the antechamber are made from a plastics material.

1 1 . A prefabricated former as claimed in claim 10, in which the side wall of the main chamber and the side wall of the antechamber include polyvinyl chloride.

12. A prefabricated former as claimed in any of the preceding claims, in which the side wall of the main chamber has the form of a prism.

13. A prefabricated former as claimed in claim 12, in which the side wall of the main chamber has the form of an octagonal prism.

14. A prefabricated former as claimed in claim 13, in which the antechamber extends from at least one side of the octagonal prism.

15. A prefabricated former as claimed in any preceding claim, in which the main chamber further comprises a water pumping apparatus.

16. A prefabricated former as claimed in any preceding claim, in which the antechamber further comprises at least one valve.

17. A prefabricated former as claimed in any preceding claim, in which the side walls of both the main chamber and antechamber including strengthening elements between the inner and outer layer.

18. A prefabricated former as claimed in any preceding claim, in which the floor is a floor former, the side walls of the main chamber extending both above and below the floor former defining a space above the floor former and a space below the floor former, and an opening being provided between the first cavity and the space below the floor former enabling concrete to flow through the first cavity into the space below the base former.

19. A prefabricated former as claimed in claim 18, in which the floor former is substantially concave.

20. A prefabricated former as claimed in claim 18 or claim 19, in which the floor former is formed of glass reinforced plastics or steel.

21. A prefabricated former as claimed in any preceding claim, in which the prefabricated former includes at least one rail adapted to guide and secure components in the main chamber, the or each rail substantially extending the length of the main chamber.

22. A method of constructing a subterranean pumping station having a wet compartment and a dry compartment, the method comprising:

excavating a hole in the ground or utilising an existing hole, placing a prefabricated former, the prefabricated former having two chambers, the first chamber having walls with an inner layer and outer layer defining a first cavity therebetween, the second chamber having walls with an inner layer and outer layer defining a second cavity therebetween, the first cavity being in communication with the second cavity so that concrete can flow from one cavity to the other;

introducing concrete into either the first cavity of the first chamber or second cavity of the second chamber so that the concrete flows between the cavities.

23. A method as claimed in claim 22, further comprising the step of mechanically agitating the concrete before the concrete has set.

24. A method as claimed in claim 22 or claim 23, further comprising the step of introducing material around the prefabricated former to bury the prefabricated former.