WO2004055282A1

WO2004055282A1 - Concrete enclosures for buried installation

Info

Publication number: WO2004055282A1
Application number: PCT/GB2003/003598
Authority: WO
Inventors: Martin James Tomlinson; Andrew David Tomlinson
Original assignee: Martin James Tomlinson; Andrew David Tomlinson
Priority date: 2002-12-13
Filing date: 2003-08-19
Publication date: 2004-07-01
Also published as: AU2003267549A1

Abstract

A reinforced concrete enclosure for burying in the ground and providing entry to personnel to attend to machinery or equipment housed within the enclosure (for example serving for the temporary storage of stormwater during period of exceptional rainfall, and for separating stormwater and foul water). The enclosure (25) comprises a tube of reinforced concrete having a wall thickness in the range of 100 to 200mm, the tube being closed at its opposite ends and formed in its top with an opening for entry of maintenance or repair personnel. The enclosure is installed in the ground by forming an excavated void protected by a surrounding cofferdam (21), lowering the enclosure (25) into the void, and discharging pre-mixed concrete into the space around the enclosure, without the need for personnel to enter the space around the enclosure once in the excavated void.

Description

CONCRETE ENCLOSURES FOR BURIED INSTALLATION

The present invention relates to enclosures of reinforced concrete for burying in the ground and providing entry to maintenance or repair personnel to attend to machinery or systems housed within the enclosure. The present invention relates in particular, but not solely, to tanks which serve for the temporary storage of stormwater during periods of exceptional rainfall, in order to prevent the overloading of the drainage and sewage treatment system.

Much of the world still has extensive combined sewer systems, in which rainwater is used to flush foul water along the pipe system and into the sea or into a river. Modern standards require sewage to be treated prior to discharge into the sea or river. Under normal conditions, the rainwater portion of the mixture is small and the whole flow is treated prior to discharge. During storm conditions, however, the flow increases dramatically and sewage treatment works are unable to cope .

Combined sewer overflows (CSO) are nowadays installed, which separate out the coarse fraction of sewage. A CSO comprises an enclosure buried in the ground, and housing electro-mechanical separation equipment, including screens to separate out the solid portions of the mix. The primary cost of the CSO is the buried enclosure within which the plant is housed, not the equipment itself. The CSO enclosure may be formed of concrete and built in-situ: the building process takes several weeks, which makes it undesirable and increasingly unacceptable if, as is common, the CSO is to be located under a main road, in which case the road has to be closed for a long time. The CSO may instead be pre-formed of plastics material, but then has to be of circular cross-section to give it strength and rigidity in the hoop direction, although it cannot be made strong enough to be buried under a main road. Ideally the enclosure would be rectangular in section, giving a far superior internal space for the layout of equipment. Also, in the case of CSO's of plastics material, there are problems in anchoring these in place, to prevent against uplift due to groundwater pressure. In accordance with the present invention there is provided an enclosure for burying in the ground and providing entry to personnel to attend to machinery or systems housed within said enclosure, the enclosure comprising a tube of reinforced concrete having a wall thickness in the range of 100 to 200mm, the tube being closed at its opposite ends and formed with an opening for entry of maintenance or repair personnel. Preferably the enclosure is of rectangular cross- section with the corners, between each of its side walls and the top and bottom walls, round internally and externally, to impart substantial strength to the enclosure. The enclosure may be pre-made, then transported to the site, where it is lowered into an excavated void. Typically the enclosure might be of 4 to 7 metres in length, 2.5 to 3.5 metres in width, and 2.5 to 3.5 metres in height. The enclosure is however light enough and strong enough to be lifted by a crane and transported by road.

The wall thickness of the enclosure may be uniform or it may vary, for example with its side walls reducing in thickness towards the top so that the outer surfaces of these walls slope inwards. Also in accordance with the present invention, there is provided a method of installing an enclosure as defined above, the method comprising forming an excavated void protected by a surrounding cofferdam, lowering the preformed enclosure into said void, and discharging pre-mixed concrete into the space around the enclosure.

The pre-made enclosure can accordingly be installed or buried in the ground without any personnel entering the space, in the excavated void, around the outside of the enclosure.

Preferably the opposite, outer surfaces of the enclosure are pre-formed with a key such that the subsequently- introduced concrete unites with the opposite side walls of the enclosure, as this concrete sets, thus substantially increasing the strength of these walls. The enclosure walls must, however, be sufficiently strong initially to resist the substantial pressures exerted on them by the concrete discharged into the space around the enclosure.

Preferably the outer surfaces of the opposite side walls of the enclosure slope or taper inwardly towards the top of the enclosure, so that the concrete introduced around the enclosure will act in a wedging manner, to oppose any uplift forces acting on the enclosure.

We have also devised an effective method of casting the concrete tube of the above-defined enclosure. Thus, further in accordance with the present invention, there is provided a method of casting a concrete tube, comprising the steps of providing an inner liner which tapers along its length, providing an outer liner, positioning the inner and outer liners so that the inner liner is disposed within the outer liner and an annular void is provided between the inner and outer liners, filling said void with pre-mixed concrete and permitting said concrete to set, thus forming a concrete tube, and withdrawing said inner liner longitudinally from within said concrete tube.

Because the inner liner tapers along its length, it can simply be withdrawn longitudinally from the cast concrete tube. For example, the inner liner may be supported at its wider end in cantilever manner. Preferably the tube tapers in width and height, both internally and externally, at a slope in the range 1 in 150 to 1 in 250, preferably 1 in 200. The outer liner, which is generally tubular in form, may also be removed from the cast tube by relative longitudinal movement, if the inner surface of the outer liner also tapers along its length. Instead, the outer liner may comprise two shells movable towards and away from each other transversely of the inner liner. In this case, preferably cover plates are positioned across the ends of the annular void between the inner and outer liners, and are fixed to the inner and outer liners, before the annular void is filled with pre-mixed concrete in order to cast the tube. It will be appreciated that the cover plates tie the inner and outer liners together in a manner to resist the forces due to the "hydrostatic" pressure derived from the concrete . Once the concrete has hardened, the cover plates are removed and the inner liner may be withdrawn longitudinally of the tube and the outer liner shells are moved apart, to leave the cast tube resting on two or more supports (which also form portions of the outer liner, along the bottom wall of the tube) .

Embodiments of the present invention will now be described by way of examples only and with reference to the accompanying drawings, in which:

FIGURE 1 is a side view of an apparatus for use in casting a horizontal, reinforced concrete tube, the ends of which are subsequently closed to form an enclosure or tank in accordance with the present invention; FIGURE 2 is an end view of the apparatus, shown with the two halves of its outer liner separated;

FIGURE 3 is a similar end view of the apparatus, shown with the two halves of the outer liner closed together;

FIGURE 4 is an enlarged view of an arrangement provided for bolting the two halves of the outer liner together;

FIGURE 5 is an enlarged sectional view showing an arrangement for bolting the inner and outer liners together via end cover plates;

FIGURE 6 shows the inner liner, fitted with reinforcing bars for the tube to be cast, being advanced into the space defined by the outer liner;

FIGURE 7 is a similar view, showing the inner liner after it has been withdrawn from the cast tube;

FIGURE 8 is an end view of the cast tube, showing the two halves of the outer liner being retracted from it; FIGURE 9 is a side view of the cast tube, showing a concrete bulkhead being fitted to one end of the cast tube;

FIGURE 10 is an isometric view of the concrete bulkhead once cast horizontally and before application to the cast tube; FIGURE 11 is a cross-section through an excavation protected by a cofferdam;

FIGURE 12 is a similar sectional view, showing a tank in accordance with the present invention being lowered into the excavated void protected by the cofferdam; FIGURE 13 is a similar sectional view, showing the tank lowered onto the bottom of the excavated void and the space between the tank and the cofferdam filled with pre-mixed concrete to a level just below the lower waling of the cofferdam; FIGURE 14 is a similar sectional view, showing the lower waling lifted and the space between the tank and the cofferdam filled with further pre-mixed concrete to an appropriate level;

FIGURE 15 is a similar sectional view, showing the cofferdam removed altogether, the tank covered over and a roadway over the tank re-instated;

FIGURE 16 is a view showing the tank being lifted from a delivery vehicle by a mobile crane and lowered into the excavated void protected by the cofferdam; FIGURE 17 is a similar view showing the space between' the tank and the cofferdam being filled with pre-mixed concrete from a mixer truck;

FIGURE 18 is a sectional view of an excavation which is protected by a cofferdam but partially filled with ground water;

FIGURE 19 is a similar sectional view of the excavation showing a levelling gravel bed formed on the bottom of the excavation;

FIGURE 20 is a similar sectional view, showing a tank in accordance with the present invention being lowered into the excavation, the tank being shown partly filled with water ballast;

FIGURE 21 is a similar sectional view, showing the tank lowered onto the bottom of the excavation; FIGURE 22 is a similar sectional view, showing the space between the tank and the cofferdam partly filled with pre-mixed concrete;

FIGURE 23 is a plan view and FIGURE 24 is a corresponding sectional view, showing the tank once lowered into the void protected by the cofferdam;

FIGURE 25 is a similar plan view and FIGURES 26 and 27 are similar sectional views showing the same tank and indicating the much larger size of the cofferdam and excavation which would be necessary if working space for a workman were required around the tank;

FIGURE 28 is a view of the tank with a slab laid on its top, providing access into the tank.

FIGURE 29 is a view of a second embodiment of tank in accordance with the present invention; and FIGURE 30 is a sectional view of the tank of Figure 29 shown lowered into an excavation protected by a cofferdam.

The principles of the present invention are applicable to any enclosure which is to be buried in the ground, the enclosure being arranged or intended to house equipment or systems which require the entry of personnel into the enclosure to maintain or repair the equipment. The invention will be described, with reference to the drawings and by way of example only, in relation to an enclosure in the form of a tank which serves for the temporary storage of stormwater during periods of exceptional rainfall: the tank comprises a reinforced concrete tube of wall thickness in the range 100 to 200mm, the tube being of generally rectangular cross-section with the corners (between its side walls and its top and bottom walls) rounded both internally and externally to provide strength; the ends of the reinforced concrete tube are closed by reinforced concrete bulkheads which may be flat but which preferably bow outwardly, to better resist axial compressive forces on the enclosure. One end of the tank is formed, adjacent its bottom, with an inlet port for mixed stormwater and foul water: the opposite end of the tank is formed, also adjacent its bottom, with two ports, one for stormwater and the other for foul water. Equipment is installed in the tank, either before it is buried in the ground or afterwards, for separating the incoming, mixed stormwater and foul water into the separate stormwater and foul water flows: this equipment typically comprises one or more separation weirs and one or more filtering screens. The equipment requires periodic maintenance, involving personnel entering the tank to remove and replace the filtering screens: the top of the tank is formed with a longitudinal opening through which equipment may be lowered into or lifted out of the enclosure, and a separate aperture or man-hole to provide man-access; the latter aperture may however be dispensed with, in which case the longitudinal opening is used for man-access . Referring firstly to Figures 1 to 10 of the drawings, a description will be given of a method of forming a reinforced concrete tank of the form just described, the tank comprising a thin-walled tube with its ends closed by separately-cast bulkheads. Figure 1 shows a trolley 2 having flanged wheels 3 which run in a recessed rail 3a on the floor: a tapered, tubular inner liner 1 projects from a forward end of the trolley 2, which is balanced at its rear by a counterweight 4. The construction of the concrete tube, for forming the tank, is commenced by fitting reinforcing bars 5 around the inner liner 1. The apparatus further comprises an outer liner 6 in the form of two half-shells supported by respective trolleys 7, which are wheeled together to close around the inner liner, then bolted together through mating flanges 8 along their top and bottom. Cover plates 9 are applied to both ends of this structure, and bolted to respective flanges of the inner and outer liners by means of bolts 14. The space between the inner and outer liners is then filled with concrete 10, the cover plates 9 acting as stop-ends and also to counter the forces acting on the inner and outer liners, due to the "hydrostatic" pressures developed by the concrete. This concrete hardens to form a concrete tube, reinforced by the bars 5. The cover plates 9 are then removed and, because the inner liner 1 tapers in both height and width towards its end remote from the trolley 2, the trolley 2 can be retracted to withdraw the inner liner from within the cast tube (Figure 7) . Then the two halves of the outer lining 6 are unbolted from each other and separated (Figure 8) , leaving the concrete tube 11 resting on supports 12 (around which the two halves of the outer lining fit when closed together) . In the next stage of manufacture, the opposite ends of the concrete tube are closed by concrete bulkheads 14, which are cast as flat, reinforced slabs with protruding starter bars 15 (Figure 10) .- each bulkhead 14 is lifted and suspended vertically (Figure 9) , then offered up to the respective end of the tube 11; the protruding starter bars engage into a series of sockets formed in the end of the concrete tube 11 and concrete is used to seal the bulkhead to the tube.

The outer surface of the tube 11 is water-jetted, to a level above half-way, to provide a key 13 for the ballast concrete which is poured into the space around the tank, after the latter is lowered into its excavated void.

The procedure for installing the tank in an excavated void will now be described with reference to Figures 11 to 17 of the accompanying drawings. The tank is being installed under a major road 20 and it is important that the road is closed for as short a time period as possible. Sheet piles 21 are sunk into the roadway to define a rectangular area, which is then excavated progressively: upper and lower walings 22,23 are installed in position to buttress the sheet piles 21, as excavation proceeds; these walings include hydraulic actuators for applying them against the piles 21. The final, excavated void is shown in Figure 11, its sides protected by the cofferdam formed by the sheet piles 21 and waling 22,23. A layer 24 of gravel is then laid on the base of the excavation, and the tank 25 is lifted from its delivery vehicle 29 by a mobile crane 30 and lowered into the void to rest on the layer of gravel (Figures 16 and 12) .

Pre-mixed concrete is then discharged from a mixer truck 31 (Figure 17) into the space between the tank 25 and the cofferdam, to form a layer 27 up to the underside of the lower waling 23 (Figure 13) . Once this ballast concrete has hardened, it takes over the earth-support function of the lower waling 23, which is then released and raised to below the upper waling 22 (Figure 14) under remote control of its hydraulic actuators from ground level: further pre-mixed concrete is then discharged into the space around the tank 25, to form a layer 28 up to a level above its half-height but below its top. Both walings 22,23 are now removed, the sheet piles 21 extracted and the road construction 109 reinstated. It will be noted that the opposite side walls 26 of the tank 25 slope inwards or taper towards its top (typically the wall thickness decreasing from e.g. 160mm at the bottom to e.g. 135mm at the top) so that the ballast concrete 27,28 acts as a wedge on the tank to lock it against uplift forces caused by groundwater. Also, as the concrete around the tank sets, it unites with the surfaces of the tank (owing to the key 13 formed on these surfaces) , and so acts compositely with the walls of the tank to strengthen these by a factor of at least 2.

The whole operation of installing the tank takes a few days, instead of perhaps 4 to 5 weeks required when building a tank in-situ using conventional casting techniques.

Figures 18 to 22 illustrate a similar procedure where ground water 32 enters the void 37 and cannot be controlled easily or effectively. Typically this situation could be controlled by deepening the excavation by say one meter and placing a concrete plug at the base of the cofferdam. In accordance with the present invention, however, a levelling layer of gravel 33 is laid on the bottom of the excavation, under the water 32. The tank 25 has its entry and exit ports (at its opposite ends) sealed and is then lowered into the cofferdam void 37, where the tank may or may not float, depending on the ground water depth. .Water ballast 34, if required, is pumped into the tank 25 until the tank comes to rest on the gravel bed 33. Concrete is then introduced into the space around the lower part of the tank 25, the concrete being passed through a tremmie pipe 36, thus sealing the base of the excavation against water entry. When this initial layer 35 of concrete has hardened, the cofferdam void 37 is pumped dry and the procedure continued as described above with reference to Figures 14 and 15.

It will be appreciated that the procedures which have been described, for installing or burying the pre-made tank underground, avoid the need for workmen to enter the excavation whilst the tank is being lowered into it, or subsequently when the space around the tank is filled with ballast concrete.

The space between the tank and the sheet piles need only be about 300mm, allowing for the width of the walings 22,23. Figures 23 to 27 graphically illustrate the differences in length and width of the excavation required, as compared with the excavation which would be required if, in installing a tank of the same size, sufficient space was needed around the tank for workmen to enter and work safely. For example, a workman 39 is shown, in Figure 26, compacting gravel 40 in thin layers for backfill: Figure 27 shows a ballast slab 41 cast on top of the tank, in accordance with conventional practice.

Figure 28 shows an elongate slab 50 laid on the top of the tank, the slab 50 having an elongate opening and a separate man-hole to register with the elongate opening 25a and man-hole

25b in the top of the tank. The slab 50 (or several such slabs stacked one-on-another) form an access from ground level into the tank.

Figure 29 shows a tank 25 of - modified form, but constructed in the same manner as described with reference to Figures 1 to 10 of the accompanying drawings. The tank comprises a circular tube 42 of reinforced concrete, again of wall thickness in the range 100 to 200mm (preferably 120 to 150mm), the opposite ends of the tube being closed by flat, reinforced-concrete bulkheads 14 each of which comprises a semi-circular upper portion and a rectangular lower portion, the lower portions 43 of the two bulkheads providing support feet for the tank, to prevent it turning on its axis when temporarily located. Figure 30 shows the tank positioned in a cofferdam-protected excavation, with an initial layer of ballast concrete formed at the bottom of the excavation to stabilise the tank.

Claims

1) An enclosure for burying in the ground and providing entry to personnel to attend to machinery or systems housed within said enclosure, the enclosure comprising a tube of reinforced concrete having a wall thickness in the range of 100 to 200mm, the tube being closed at its opposite ends and formed with an opening for entry of maintenance or repair personnel .

2) An enclosure as claimed in claim 1, in the form of a tank for the temporary storage of stormwater, having an inlet port for mixed stormwater and foul water, and outlet ports respectively for stormwater and foul water.

3) An enclosure as claimed in claim 2, having equipment installed therein for the separation of stormwater and foul water.

4) An enclosure as claimed in claim 2, having a longitudinal slot formed in its top to enable equipment to be lowered into or lifted out of said enclosure.

5) An enclosure as claimed in claim 4, having a separate aperture formed in its top, for entry of maintenance or repair personnel.

6) An enclosure as claimed in any preceding claim, in which said tube is generally rectangular in cross-section.

7) An enclosure as claimed in claim 6, in which the corners of said tube, between its side walls and its top and bottom walls, are rounded both internally and externally.

8) An enclosure as claimed in claim 6 or 7, in which the outer surfaces of the opposite side walls of said tube slope inwardly towards its top.

9) An enclosure as claimed in any one of claims 1 to 5, in which said tube is generally circular in section and is closed at its opposite ends by members formed to provide supporting feet .

10) An enclosure as claimed in any preceding claim, in which opposite outer side surfaces thereof are formed with a key for concrete, subsequently poured against said surfaces, to unite therewith.

11) A method of installing an enclosure as claimed in any preceding claim, the method comprising forming an excavated void protected by a surrounding cofferdam, lowering the preformed enclosure into said void, and discharging pre-mixed concrete into the space around the enclosure.

12) A method as claimed in claim 11, which is performed without personnel entering the space around said enclosure when in said void.

13) A method of casting a concrete tube, comprising the steps of providing an inner liner which tapers along its length, providing an outer liner, positioning the inner and outer liners so that the inner liner is disposed within the outer liner and an annular void is provided between the inner and outer liners, filling said void with pre-mixed concrete and permitting said concrete to set, thus forming a concrete tube, and withdrawing said inner liner longitudinally from within said concrete tube.

14) A method as claimed in claim 13, in which said inner liner is supported at its wider end thereof in cantilever manner .

15) A method as claimed in claim 13 or 14, in which said outer liner comprises two shells movable towards and away from each other transversely of the inner liner.

16) A method as claimed in claim 15, further comprising the steps of fixing the two outer-liner shells together when closed together, positioning cover plates across the ends of said annular void and fixing said cover plates to the inner and outer liners, before said void is filled with pre-mixed concrete .