GB2329651A

GB2329651A - An inflatable foundation formwork support

Info

Publication number: GB2329651A
Application number: GB9819569A
Authority: GB
Inventors: Paul Kiss; Gary Eaton
Original assignee: SUBSIDENCE SURVEYS Ltd
Current assignee: SUBSIDENCE SURVEYS Ltd
Priority date: 1997-09-11
Filing date: 1998-09-08
Publication date: 1999-03-31
Anticipated expiration: 2018-09-08
Also published as: GB9819569D0; GB2329651B; GB9719343D0

Abstract

A method of constructing a concrete foundation raft or low level beam when building on ground which is liable to subsidence or heave comprises erecting formwork (15), which is held spaced above the ground (14) by at least one interposed waterproof bag (17) that is inflated with water or other liquid, pouring concrete in or on the formwork (15) to form the raft or beam and, when the concrete has set, removing the water from the bag(s) (17) to allow the bag(s) to collapse leaving a void (13) between the underside of the raft or beam and the ground.

Description

IMPROVEMENTS RELATING TO FOUNDATION RAFTS When building on ground, which is liable to subsidence or heave, it is well known to erect the building or other superstructure on a raft or beam, itself supported by piles, with the underside of the raft spaced above the ground by a void or compressible material. The void or compressible material, which prevents any heave from being significantly transmitted to the underside of the raft or beam, has taken a variety of forms. Typically, a collapsible or crushable spacer, made for example of hardboard, cardboard, and/or polystyrene has been used.

Generally these techniques are expensive. Collapsible spacers can collapse prematurely, particularly in wet weather, and crushable spacers require extra space to avoid the transmission of heave to the raft through the crushed material.

In accordance with the present invention, a method of constructing a concrete foundation raft or low level beam for a building or other superstructure comprises erecting formwork, which is held spaced above the ground by at least one interposed waterproof bag that is inflated with water or other liquid, pouring concrete in the formwork to form the raft or beam and, when the concrete has set, removing the water from the bag(s) to allow the bag(s) to collapse leaving a void between the underside of the raft or beam and the ground.

This new method has a number of advantages. Thus the sealed bag of water provides a firm support for the formwork throughout the pouring and setting of the concrete, and is substantially unaffected by weather, particularly wet weather, conditions. The resulting void which is formed avoids any danger of heave beneath the raft or beam from being transmitted as an upward force to the underside of the raft or beam. Furthermore, it is readily possible to make the empty bag(s) recoverable, after collapse, for re-use.

One construction of bag which is promising consists of a cylindrical, sausage-like tube, which is closed at one end and has fitted to its other end the end of a hose through which the bag can be filled with, and emptied of, water. The part of the hose remote from the bag may be provided with a non-return valve and a tap to, respectively, maintain the water in the bag when filled, and allow the water to be drained from the bag.

The bag may have a coupling device fitted at its other end, the coupling device having a narrow end to attach to the hose and a wider, laterally elongate, e.g. of rectangular or oval cross section, end to attach to the bag. The coupling device may then be of such a size that it can pass through a conventional building block or brick sized hole, e.g. a house brick sized hole, i.e. 225mm x 75mm. The elongate coupling device thus facilitates the removal of the bag from the underside of the formwork.

In view of the typical size of such building rafts, it is anticipated that a plurality of bags would be used spaced from one another beneath the formwork.

One example of the present invention will now be described with reference to the accompanying drawings, in which: Figure 1 shows a vertical section through a typical foundation raft; Figure 2 is a vertical section showing how the void is formed according to the present invention; Figure 3 is a partially sectioned elevation of a bag for supporting the formwork; Figure 4 shows a plan view of a possible arrangement of the bags beneath the formwork; and, Figure 5 is a perspective view of a bag and a laterally elongate coupling device.

Figure 1 shows a typical foundation raft 10 consisting of a reinforced concrete slab 10 supporting building walls 11 and itself supported by piles 12. The piles are first put down and the slab is integrated with pile caps. A void 13 spaces the bottom of the slab 10 from the ground 14.

Figure 2 indicates in vertical section how the void 13 might be created. Thus decking 15 forming the bottom wall of formwork is spaced above a layer of blinding 16 on the ground 14 by an array of tubular waterproof bags 17, which may be laid out as seen in plan in Figure 4.

As Figures 3 and 4 show, each bag 17 has a closed end 18 and, at its opposite end, is connected to a hose 19 leading to a terminal 20, or a common terminal 20a in Figure 4, containing a non return valve and a tap. The hose may be a waterproof canvas hose similar to a fireman's hose. In use, a pump could be connected to the block 20 to inflate the respective bag. The hose 19 could be used to pull the bag from the void after use.

Fig. 5 shows a bag 17 with a coupling device 21 having its wider, oval shaped end inserted in the end of the bag opposite the closed end 18. The size of the largest part of the coupling device can pass through a 225mm x 75mm hole. The coupling device has a narrow inlet/outlet tube 22 extending away from the bag. The tube can be connected to the hose.

The substantially tubular bag, connected to the hose, and preferably provided with the non-return valve and tap, forms an independent feature of the invention.

Claims

1. A method of constructing a concrete foundation raft or low level beam for a building or other superstructure comprising erecting formwork, which is held spaced above the ground by at least one interposed waterproof bag that is inflated with water or other liquid, pouring concrete in the formwork to form the raft or beam and, when the concrete has set, removing the water from the bag(s) to allow the bag(s) to collapse leaving a void between the underside of the raft or beam and the ground.

2. A method according to claim 1, further comprising recovering the bag, after collapse, for re-use.

3. A bag for supporting a formwork comprising a cylindrical, sausage-like tube, which is closed at one end and has fitted to its other end the end of a hose through which the bag can be filled with, and emptied of, water.

4. A bag according to claim 3 wherein the part of the hose remote from the bag is provided with a non-return valve and a tap to, respectively, maintain the water in the bag when filled, and allow the water to be drained from the bag.

5. A bag according to either claim 3 or claim 4 wherein the bag has a coupling device fitted at its other end, the coupling device having a narrow end to fit with the hose and a wider, laterally elongate end to attach to the bag.

6. A bag according to either claim 5 wherein the coupling device is oval or rectangular in shape.

7. A bag according to claim 5 or claim 6, wherein the coupling device is of such a size that it can pass through a hole of substantially 225mm x 75mm.

8. A method of constructing a concrete foundation raft or low level beam for a building or other superstructure, substantially as described with reference to the accompanying drawings.

9. A bag, substantially as described with reference to the accompanying drawings.