GB2267926A

GB2267926A - A tube for forming a pile

Info

Publication number: GB2267926A
Application number: GB9312655A
Authority: GB
Inventors: Michael Frank Ellis
Original assignee: ELLE VAN
Current assignee: ELLE VAN
Priority date: 1992-06-18
Filing date: 1993-06-18
Publication date: 1993-12-22
Also published as: GB9212936D0; GB9312655D0

Abstract

A tube for forming a pile, the tube being closed at one end and being provided at or towards it closed leading end with at least one cutter blade 6 and having one or more apertures 8 in the wall thereof, the apertures being disposed between said one or more cutter blades and the closed leading end of the tube. <IMAGE>

Description

Pile The invention relates to piles for supporting structures.

During the course of erecting a structure such as a building one of the preliminary stages is that of laying down foundations for the purpose of supporting the building. It is known in the art to provide additional support to the foundations and hence the building to reduce the effects of subsidence by embedding piles into the ground for communicating firm ground at substrata level with the foundations of the building. In this case the piles will pass through ground that may otherwise subside (known as "suspect ground") into firm ground that will provide additional support to the foundations of the building. There are many methods known in the art for embedding the piles in the ground, some of which are as follows 1. Driving, by vibration or otherwise, prefabricated piles into the ground.

2. Driving, by vibration or otherwise, tubes into the ground and filling the tubes with concrete or other grout.

3. Another method is to provide a cutter blade on the end of a tube and screw the tube into the ground, whilst at the same time pumping grout around the tube to provide a surrounding column of grout/soil mix. The tube, including the cutter blade, is sacrificial in that it is left in the ground to form part of the final pile.

The provision of grout into the soil loosened by the cutter blade, and behind the cutter blade, is not a simple matter, especially when the cutter blade advances beyond a superficial depth. Thus, it is likely that a non-uniform soil/grout mix will result.

Experiments have been conducted on the basis of supplying the grout to the soil via the interior of the tube and one or more apertures disposed behind the cutter blade. However, it has been found that with such an arrangement the grout tends to back flow up the outside of the tube rather than mix with the soil. This undesirably provides a narrow pile less than the diameter of the column of loosened soil created by the cutter blade.

According to one aspect of the present invention there is provided a method of forming a pile comprising the steps of : - screwing a tube, closed at one end, into the ground, the tube being provided with one or more cutter blades, - simultaneously supplying grout under pressure into the top of the tube, - arranging for the grout to exit the tube at one or more points disposed between said one or more cutter blades and the closed, leading end of the tube, - terminating the screwing action and the supply of grout when the required depth has been reached, and - severing the tube generally at ground level, whereby the pile is formed by the grout-filled tube and a surrounding column of soil/grout mix.

According to another aspect of the present invention there is provided a pile comprising a tube, closed at one end, filled with grout, and a surrounding column of soil/grout mix, the tube comprising at least one cutter blade, disposed at or towards its closed leading end, and having one or more apertures in the wall thereof, the apertures being disposed between said one or more cutter blades and the closed, leading end of the tube.

According to a further aspect of the invention there is provided a tube, closed at one end, for forming a pile, the tube being provided at or towards its closed leading end with at least one cutter blade and having one or more apertures in the wall thereof, the apertures being disposed between said one or more cutter blades and the closed leading end of the tube.

In all aspects of the invention at least, the leading cutter blade adjacent the end of the tube is preferably helical to define an auger and conveniently has an aggressive ie. a tooth shaped leading edge for cutting into the soil. The cutter blade may be in the form of substantially a single helix whereby a satisfactory cutting action is provided without any undue tendency for cut soil to be conveyed upwardly. Furthermore, a single helix or a small number of helices ensures that the cutter blade effectively seals the leading end of the tube from the trailing end and thus substantially prevents the grout from back flowing up the tube.

Furthermore, the supply of grout to the loosened soil in front of the cutter blade means that the latter helps mix the soil and grout together to provide a substantially uniform mix.

Advantageously, one or more additional blades are provided spaced along the tube from the leading blade. The additional blades help to further mix the grout with the soil and in addition help to maintain the tube co-axial within the column during the screwing action.

Preferably the diameter of the leading cutter blade determines the overall diameter of the pile.

During creation of the column, the action of the cutter blade(s) tends to compact the soil surrounding the column and so improves the self supporting nature of the surrounding soil.

After setting of the grout the tube is surrounded by a column of concrete.

This not only provides corrosive protection for the tube but also provides support to the tube against lateral deflection. Accordingly, the tube is able to provide an improved support to compressive loads.

By "soil", as used throughout this specification, is meant any type of ground through which the pile passes.

The present invention will now be described in greater detail, by way of example, with reference to accompanying drawings, in which: Figure 1 is a diagrammatic side elevation of a tube forming part of one embodiment of the invention, Figure 2 is a plan view of Figure 1, Figure 3 is a diagrammatic side elevation of an extension tube, Figure 4 is a diagrammatic side view of commencement of the formation of a pile in accordance with the present invention, Figures 5 to 7 illustrate successive steps in the formation of a pile, and Figure 8 is a diagrammatic view similar to Figure 7 showing a modification.

Referring first to Figures 1 and 2, there is illustrated a basic tube 1 used in the formation of a pile in accordance with the present invention. The tube is circular in cross-section and is closed at its leading end 2 which is also brought to a point. The open and trailing end of the tube is externally threaded at 3 and is provided with a pair of diametrically opposed lugs 4 by which the tube can be rotated typically at a speed of 30 - 100 rpm in the direction of the arrow 5 by a drive mechanism to be referred to hereinafter.

Towards the leading end 2 of the tube 1 there is provided a cutter blade 6 in the form of substantially a single helix having an aggressive leading edge 7.

One or more apertures 8 are provided in the wall of the tube 1 between the cutter blade 6 and the leading end 2, and preferably closely adjacent the cutter blade of the order of 50 mm. The inner and outer diameters of the tube 1 may be of the order of 60 mm and 90 mm, the diameter of the cutter blade of the order of 150 and 300 mm and the diameter of each aperture 8 of the order of 10 mm. The aperture 8 may be rectangular in shape, for example of the order of 15 mm wide by 25 mm long.

Preferably the blade 6 is formed from a circular piece of metal plate which is bent to form the helix with a pitch in the order of 5 - 30C depending on ground conditions and is preferably welded to the tube.

Turning now to Figure 3, this illustrates an extension tube 9 for the basic tube 1 of Figure 1, this having an internally threaded leading end 11 and an externally threaded trailing end 3 and a pair of diametrically opposed lugs 4 so as to be similar in this respect to the trailing end of the basic tube 1 of Figure 1. The extension tube 9 is fitted to the basic tube 1 by screwing the internally threaded leading end onto the externally threaded trailing end of the tube 1. Successive extension tubes, similar to that of Figure 3, can be added according to the required length of the pile to be formed.

To form a pile in accordance with the present invention, the basic tube 1 of Figure 1 is attached to a chuck 12, by engaging the lugs 4 therewith, as diagrammatically illustrated in Figure 4 of the drawings, the chuck 12 being rotatably driven by a drive indicated at 13. Simultaneously with rotating the tube 1, grout in the form of a sand and cement mix is supplied to the interior of the tube 1 from a tank 14 via a conduit 15. The grout is supplied under pressure and as the tube 1 is screwed into the ground, the cutter blade 6 loosens a column of soil and mixes with that loosened soil the grout which exits the tube 1 through the or each aperture 8. Thus, a column of grout/soil mix surrounding the tube 1 is formed as the latter is screwed into the ground.The positive mixing of the grout and soil by the cutter blade 6 provides a substantially uniform grout/soil mix and at the same time, the cutter blade 6 effectively acting as a baffle to spread the grout across the full width of the column and prevent the grout from back flowing along the outside of the tube.

When the tube 1 is substantially totally embedded in the ground, a first extension tube 9 is fitted as illustrated in Figure 6 and then a third extension tube fitted, when the first is substantially embedded in the ground as indicated in Figure 7, and so on. Figure 7 illustrates the case in which the basic tube 1 and two extension tubes 9, the extended tube bridges the surface of the ground with firm ground indicated at 16, the initial layer of ground 17 being assumed to be suspect ground. When this condition has been reached, the rotation of the tube 1 and extension tubes 9 is terminated, as is the supply of grout to the interior of these tubes, at which time the overall pile is formed, without any further action being necessary.Although in Figure 7 the second extension tube is shown as terminating substantially flush with ground level, if it were to extend beyond, then it would be severed substantially flush with ground level.

It will be seen that with the simple, but highly significant, expedient of providing exit apertures for the grout in front of the cutter blade, instead of behind, there is formed a reliable pile having a central core in the form of a tube filled with grout and a surrounding column of grout/soil mix, this mixture being substantially uniform and without any grout being wasted by back flawing up the tubes 1 and 9.

As seen in Figure 1, in broken lines, a second blade 6' may be provided spaced along the tube 1 from the leading blade 6 adjacent to the end 2. The second blade 6' is preferably the same diameter as blade 6. The shape of blade 6' is preferably adapted so as to promote mixing of the grout and soil. If desired, apertures 8 may be located between blades 6 and 6'.

If desired, additional blades may be mounted on the extension tubes 9. This is schematically shown in Figure 8.

The blades on the extension tubes 9 may be similar to blade 6' or the blades may be in the form of three generally radially projecting fingers 6" which define mixing means for further mixing of the grout and soil mix. The fingers are spaced about the periphery of the tube 9' and are preferably located at different inclined positions.

Preferably the outer diameter defined by the fingers 6" is less than the outer diameter of the blade 6.

In the embodiment shown in Figure 8 a series of plain extension tubes 9' are alternated with extension tubes having a helical blade 6' and extension tubes having fingers 6". The combination of these tubes may be varied to cater for different soil conditions.

Claims

1. A tube for forming a pile, the tube being closed at one end and being provided at or towards it closed leading end with at least one cutter blade and having one or more apertures in the wall thereof, the apertures being disposed between said one or more cutter blades and the closed leading end of the tube.

2. A tube according to claim 1 wherein the cutter blade is helical.

3. A tube according to claim 2 wherein the cutter blade defines a single helix.

4. A tube according to claim 3 wherein the cutter blade is formed from a circular piece of metal plate which is bent to form said helix.

5. A tube according to any preceding claim wherein the trailing end of the tube is adapted for connection to an extension tube.

6. A tube for forming a pile substantially as herein described with reference to and as illustrated in the accompanying drawings.

7. A pile comprising a tube according to any preceding claim filled with grout and a surrounding column of soil/grout mix.

8. A pile substantially as herein described with reference to and as illustrated in the accompanying drawings.

9. A method of forming a pile comprising the steps of : - screwing a tube, closed at one end, into the ground, the tube being provided with one or more cutter blades, - simultaneously supplying grout under pressure into the top of the tube, - arranging for the grout to exit the tube at one or more points disposed between said one or more cutter blades and the closed, leading end of the tube, - terminating the screwing action and the supply of grout when the required depth has been reached, and - severing the tube generally at ground level, whereby the pile is formed by the grout-filled tube and a surrounding column of soil/grout mix.