Hydraulic and earth engineering – Foundation – Columnar structure
Reexamination Certificate
2002-08-08
2003-11-04
Shackelford, Heather (Department: 3673)
Hydraulic and earth engineering
Foundation
Columnar structure
C405S244000, C405S256000
Reexamination Certificate
active
06641333
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to a method of installing a pre-cast pile in the ground, the method involving the construction of an enlarged diameter pile head.
2. Prior Art
Piles are used in the construction industry to provide foundation support for buildings and the like. Two common piling techniques involve the use of cast-in-situ piles and pre-cast piles. Cast-in-situ methods involve the use of an auger to penetrate the ground to a certain depth so as to form an underground void. Concrete is then pumped into the underground void left by the auger so as to form an underground column. In driven piling operations, a pre-cast concrete pile is driven into the ground, usually by means of successive percussive forces applied to the head of the pile, until a predetermined depth is reached. The top of the pile column may need to be trimmed to a level at, or just below, the ground.
It is advantageous in some applications for the top, or head, of a foundation pile to have a larger diameter than the main shaft, since this allows the load of the building structure to be spread over a wider area.
Known methods for achieving what is called an “enlarged diameter pile head” involve casting a pile in the ground, either by pre-cast driven or cast-in-situ techniques, and subsequently excavating a volume of soil around the head of the pile. Additional concrete is then poured or pumped into the excavated void so as to form the enlarged diameter head. This method however suffers from the disadvantage that it is often necessary for the top of the installed pile to be broken as the head volume is excavated. This can cause discontinuities or cracks to occur in the pile shaft, which will inevitably weaken the load bearing capacity of the pile.
Alternatively, an enlarged pile head may be formed by affixing an enlarged head former, in the form of a collar device having a central aperture, to the lower end of the piling tool. The tool and enlarged head former are then driven into the ground by a predetermined distance so as to displace or excavate an area of soil whose diameter is larger than the section or diameter of the main shaft. The enlarged head former is then disconnected and the hole forming process continues as the piling tool passes freely through the central aperture of the former. During withdrawal of the piling tool, concrete or grout is supplied to the lower end of the tool so as to form a cast-in-situ underground pile. As the lower end of the piling tool is brought up to ground level, the enlarged head former is re-connected to the piling tool and is thereby lifted from the ground. The void left behind is filled with concrete or grout so as to form an enlarged pile head. Techniques employing the use of an enlarged head former, or collar device, are described in GB 2334543, the disclosure of which is incorporated herein by way of reference thereto.
OBJECT AND SUMMARY OF THE INVENTION
While this method is found to be quite effective, in many piling operations it is more appropriate to use techniques which employ pre-cast piles. There is therefore a need to provide a method of forming an enlarged diameter pile head at the top of a pre-cast pile, without detriment to the continuity of the pile shaft.
According to the present invention, there is provided a method of installing a pre-cast pile in the ground, the method comprising the steps of:
i) applying an enlarged head forming tool to the ground until a volume of soil has been displaced or removed, thereby forming a void at the surface of the ground;
ii) driving a pre-cast pile into the ground to a predetermined depth below the void formed in step i);
iii) filling the void with concrete or grout to form a cast-in-situ pile head, wherein the diameter of the pile head is greater than the diameter of the pile shaft.
Preferably, the enlarged head forming tool has a substantially central aperture. This allows a drive dolly to be positioned in the enlarged head forming tool to facilitate the penetration of the tool into the ground. Preferably the tool is driven into the ground by means of a percussive force being applied to the top of the drive dolly by means of a hammer. Alternatively, the enlarged head forming tool may be driven into the ground by means of rotation. This may be facilitated by means of an auger which is releasably fitted to the tool.
In preferred embodiments of the present invention, the pre-cast pile may be driven into the ground through the central aperture in the enlarged head forming tool; the latter being removed after the installation of the pre-cast pile. This is preferably achieved by means of a percussive force being applied to the top of the pile.
Once the pile has been driven into the ground, and the enlarged head former has been removed, the pre-cast pile is broken down to a predetermined level below the ground. Preferably, the pile is broken down to between 100 mm and 150 mm below the ground. A reinforcement cage may also be placed within the void above the trimmed pre-cast pile before the void is filled with concrete or grout. The reinforcement cage advantageously serves to supplement the strength and load bearing capacity of the enlarged diameter pile head.
A number of configurations are envisaged for the enlarged pile head forming tool including those of circular, square or hexagonal cross section. The tool may comprise a collar device having a longitudinal section with two substantially parallel sides and a tapered section. Alternatively, the tool may comprise a first cylindrical section of greater diameter, a second cylindrical section having a smaller diameter and a tapered section extending between said first and second cylindrical sections. Furthermore, the outer surface of the tool may be provided with one or a number of blades which can be advantageously arranged to facilitate the radial flow of material in an outward direction as the tool penetrates the ground.
The enlarged 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.
REFERENCES:
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patent: 2332168 (1943-10-01), Riches
patent: 2923133 (1960-02-01), Muller
patent: 5234290 (1993-08-01), Collins
patent: 5486071 (1996-01-01), Bullivant
patent: 5683207 (1997-11-01), Mauer
patent: 5833399 (1998-11-01), Bullivant
patent: 6168350 (2001-01-01), Bartlett
patent: 2 284 843 (1995-06-01), None
patent: 2 293 850 (1996-04-01), None
Bartlett Graham
England Melvin Gerrard
Browdy and Neimark , P.L.L.C.
Cementation Foundations Skanska Limited
Lagman Frederick L.
Shackelford Heather
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