IE83774B1 - Method and apparatus for forming enlarged pile heads - Google Patents

Description

METHOD AND APPARATUS FOR FORMING ENLARGED PILE HEADS CEMENTATION FOUNDATIONS SKANSKA LIMITED METHOD AND APPARATUS FOR FORMING ENLARGED PILE HEADS The present invention relates to a method and apparatus for forming enlarged pile heads in continuous flight auger (CFA) piling techniques as well as driven cast—in—situ piling processes.

Piles are used in the construction industry to provide foundation support for buildings and the like.

Two common piling techniques are driven cast~in—situ and CFA piling. In driven cast—in—situ piling, a piling tool is driven into the ground to the required depth. The piling tool is then withdrawn, and concrete or grout is concomitantly pumped to the tip of the piling tool so as to fill the underground Void left by the tool during withdrawal. In CFA piling, a continuous flight auger is rotated and allowed to penetrate the ground to the required depth. The auger is then withdrawn, with or without rotation, and concrete or grout is pumped to the tip of the auger so as to form a pile in the same manner as described above. CFA piling techniques are discussed in more detail in GB 2 303 868, the disclosure of which is incorporated into the present application by way of reference thereto. H It is advantageous in some applications for the top, or head, of the resultant pile to have a larger diameter than the main shaft. The ground beam of a building which is to be supported by piles of this sort can be made more efficient than that of a building supported by conventional piles, since the load can be spread over a wider area. This can be achieved by casting a pile with a straight shaft and subsequently excavating a volume of soil around the head of the pile so as to enable additional concrete to be poured about the head of the pile.

Alternatively, an enlarged pile head may be formed by affixing a collar device, having a central aperture, to the lower end of the piling tool. The tool and collar device are then driven into the ground by a predetermined distance so as to excavate an area of soil whose diameter is larger than the diameter of the main shaft formed by the piling tool. The collar device is then disconnected and the hole forming process continues as the piling tool passes freely through the central aperture of the collar. During withdrawal of the piling tool, concrete or grout is supplied to the lower end of the tool so as to form an underground pile. As the lower end of the piling tool is brought up to ground level, the collar device is re—connected to the piling tool, and the collar is thereby lifted from the ground and the void left behind filled with concrete or grout so as to form an enlarged pile head.

Techniques employing the use of such a collar device are described in GB 2334543, the disclosure of which is incorporated herein by way of reference thereto.

During CFA piling applications which employ such a device, spoil is drawn into the tool and collar device therefore introducing material into the excavated region formed by the collar device. Consequently the enlarged void at the head of the pile can become contaminated with material thereby reducing the area of the resultant head.

According to a first aspect of the present invention, there is provided a method of pile installation, comprising the steps of: i) penetrating the ground with an auger to a predetermined distance; ii) withdrawing said auger from the ground while supplying concrete or grout to the lower end thereof so as to form an underground column of concrete or grout; iii) applying to the top of the newly formed concrete or grout column a pile head enlarging tool, comprising a first cylindrical section, a second cylindrical section and a tapered section extending between said first and second cylindrical sections, wherein the diameter of said second cylindrical section is greater than the diameter of said first cylindrical section; iv) rotating said pile head enlarging tool such that said tool penetrates the region at the head of the concrete or grout column and excavates material which is displaced radially outwards, wherein the first cylindrical section leads the motion of the tool in a downward direction; v) withdrawing said pile head enlarging tool from the ground while filling the void created thereby with concrete or grout so as to form an enlarged diameter pile head.

The enlarged pile head forming tool preferably exhibits two cylindrical shaped sections, one having a diameter substantially equal to the diameter of the pile to aid the tools penetration into wet concrete, and the other having a larger diameter. A tapered section extends between the two cylindrical sections thereby giving the tool a generally conical shape.

According to a second aspect of the present invention there is provided an enlarged pile head forming tool for use with a method embodying the first aspect, said tool having a longitudinal axis and comprising a first cylindrical section, a second cylindrical section and a tapered section extending between said first and second cylindrical sections, wherein the diameter of said first cylindrical section is greater than the diameter of the second cylindrical section, and wherein the second cylindrical section extends in a direction substantially parallel to the longitudinal axis.

Blades may be advantageously provided on the outer surface of the tool, and arranged to facilitate the radial flow of material in an outward direction during rotation. Preferred embodiments of the present invention employ an enlarged pile head forming tool which is adapted to be releasably fitted to the lower end of an auger. A substantially circular aperture may be provided through the centre of the tool, wherein said aperture exhibits attachment means adapted to fit about the auger. In the case of a CFA auger, the attachment means may comprise sliders on the tool which are designed to engage with slots provided on the flight(s) of the auger. Alternatively, bolts or clamps or any other suitable and releasable attachment means may be employed.

Advantageously, the tool may be affixed to the lower end of the auger, following the formation of the concrete or grout column. The auger is then caused to rotate, thereby rotating the enlarged pile head forming tool, such that the tool may penetrate the ground to a required distance. In particular, the cylindrical section of larger diameter is caused to penetrate beneath the surface of the ground, so as to excavate a region of larger diameter at the head of the pile shaft. Once this has been achieved, the auger and tool are withdrawn from the ground, with or without rotation, while concrete or grout is supplied to the void.

Advantageously, the volume of concrete or grout initially supplied to the piling tube is calculated so as to be just sufficient to form the shaft and the enlarged head of the pile. The enlarged pile head forming tool is advantageously provided on its upper surface with a pair of hooks or loops so as to allow it to be lifted by a fork—lift truck or the like, or alternatively to which a lifting winch may be attached.

Furthermore, a suitable pile reinforcement may then be inserted into the concrete or grout before it has set.

For a better understanding of the present invention, and to show how it may be carried into effect, reference shall now be made by way of example to the accompanying drawings, in which: Figure 1 shows a vertical cross section through an enlarged pile head forming tool; Figure 2 shows a plan view from above of the enlarged pile head forming tool shown in figure 1; Figures 3A and 3B show an exploded perspective view of a CFA auger and tool arrangement of the present invention.

Figure 1 shows a tool 1 for forming enlarged pile heads comprising a first cylindrical shaped section 2, a tapered section 3 and a second cylindrical shaped section 4. The tool 1 may be made of metal or any other substantially rigid material and is provided with a pair of loops 5, which allow the tool to be lifted by means of a fork-lift tuck or lifting winch. The diameter of the second cylindrical shaped section is larger than the diameter of the main shaft of the pre— formed pile.

Figure 2 shows a plan view, taken from above, of the enlarged pile head forming tool shown in figure 1.

The tool has a central aperture 6, which allows the tool to be releasably fitted to the lower end of an auger. Although not shown, the aperture is provided with suitable means of attachment for affixing the auger to the tool.

Once the main shaft of the pile has been filled with concrete or grout during removal of the auger from the ground, a tool for forming an enlarged pile head according to the present invention is then employed.

Figures 3A and 3B show an exploded perspective view of a CFA auger and tool arrangement, and shows the enlarged pile head forming tool 1, positioned on the ground 10 above a pre—formed pile 11. The tool 1 exhibits a plurality of blades 9, which serve to excavate the soil beneath the tool 1 as the auger l2 and the tool 1 are rotated. The blades are arranged on the outside of the tool so as to facilitate the flow of material in a radially outward direction during rotation of the tool into the ground. The CFA auger 12 exhibits a single continuous flight 13, and is lowered into the central aperture of the enlarged pile head forming tool. As shown in figure 3B, the lower tip of the auger is inserted into the pile head enlarging tool and is affixed thereto by means of a suitable attachment means (not shown). For example, sliding connectors may be provided so as to engage in slots provided in the flights of the auger 12. In this way, the tool can be releasably attached to the auger 12 so-” as to rotate and rise and fall therewith.

Once the tool 1 has been driven into the ground to the required depth, it is then removed, with or without rotation, while concrete or grout is concomitantly supplied to the base thereof. Consequently, the void excavated by the tool is filled with the concrete or grout, thereby forming an enlarged pile head.

Claims (9)

CLAIMS:

1. A method of pile installation, comprising the steps of: i) penetrating the ground with an auger to a predetermined distance; ii) withdrawing said auger from the ground while supplying concrete or grout to the lower end thereof so as to form an underground column of concrete or grout; iii) applying to the top of the newly formed concrete or grout column a pile head enlarging tool, comprising a first cylindrical section, a second cylindrical section and a tapered section extending between said first and second cylindrical sections, wherein the diameter of said second cylindrical section is greater than the diameter of said first cylindrical section; iv) rotating said pile head enlarging tool such that said tool penetrates the region at the head of the concrete or grout column and excavates material which is displaced radially outwards, wherein the first cylindrical section leads the motion of the tool in a downward direction; V) withdrawing said pile head enlarging tool from the ground while filling the void created thereby with concrete or grout so as to form an enlarged diameter pile head.

2. A method according to claim 1, wherein said auger is inserted into an aperture provided in the enlarged pile head forming tool and affixed thereto, prior to step iv), such that rotation of the tool into the ground can be facilitated by means of rotation of the auger.

3. A method according to claim 1 or 2, wherein said auger is a continuous flight auger.

4. An enlarged pile head forming tool for use with the method as claimed in any one of claims 1 to 3, said tool having a longitudinal axis and comprising a first cylindrical section, a second cylindrical section and a tapered section extending between said first and second cylindrical sections, wherein the diameter of said first cylindrical section is greater than the diameter of the second cylindrical section, and wherein the second cylindrical section extends in a direction substantially parallel to the longitudinal axis.

5. An enlarged pile head forming tool as claimed in claim 4, wherein an aperture is provided through the centre of said tool.

6. An enlarged pile head forming tool as claimed in claim 5, wherein said aperture is provided with attachment means adapted to releasably affix the tool about an auger.

7. An enlarged pile head forming tool as claimed in claim 6, wherein said attachment means comprise sliders which are designed to engage with slots provided on the flight(s) of a continuous flight auger.

8. An enlarged pile head forming tool as claimed in any one of claims 5 to 7, further comprising an arrangement of blades provided on the outer surface of the tool.

9. An enlarged pile head forming tool substantially as herein described with reference to the accompanying drawings. F. R. KELLY & CO., AGENTS FOR THE APPLICANTS