Boring or penetrating the earth – With tool shaft detail – Helix or helically arranged structure
Reexamination Certificate
1997-12-03
2001-09-04
Bagnell, David (Department: 3673)
Boring or penetrating the earth
With tool shaft detail
Helix or helically arranged structure
C175S388000, C175S391000, C175S022000, C405S233000, C405S241000, C405S242000
Reexamination Certificate
active
06283231
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a soil-displacing screw auger which contains an auger tube; a double displacement body equipped with a hollow shaft fixed to the auger tube and containing an uppers part which constitutes a closed screw the radius of which increases spirally towards its lower extremity and a lower part which constitutes a closed screw the radius of which decreases towards its lower extremity, preferably with the same pitch as the upper part; a lower tube the diameter of which is smaller than twice the largest radius of the displacement body and which is situated between the lower part of the displacement body and the lower extremity of the auger; a screw blade welded onto the outer casing of the lower tube, which rotates in the same sense as the lower part of the displacement body; and an auger tip connected to the lower extremity of the lower tube.
This type of auger is used to make concrete piles in the ground, which are used as foundations for buildings if the top soil layers are compressible and normal foundations would lead to an inadmissible settlement.
2. Description of the Related Art
The soil is displaced by the double displacement body, so that pressure release in the soil is avoided during the creation of the pile and a smaller quantity of soil is removed from the borehole.
Once the auger has reached a sufficient depth, concrete is poured into the auger tube and the auger is screwed out of the soil. When screwing out, the auger is rotated in the same sense of rotation as during the screwing in. The tip is a lost tip and stays in the ground.
Such an auger has been described in EP-B-0.228.138 in the name of the applicant. In this auger, the lower tube has the same diameter as the auger tube and in practice, this lower tube is a part of the auger tube which extends both underneath and above the displacement body.
With this auger, only a limited depth in good soil, only one meter, can be reached.
The reason for this is that, when screwing into good soil, the soil will accumulate between the turns of the screw blade and very soon, no more soil will be transported to the surface. The entire underside of the auger then displaces the soil, causing the resistance to the screwing into good soil to become too large very soon.
Given their relatively small diameter, piles must have a very large permissible load and penetrate deeply into heavy ground, which is not possible with this type of auger.
BRIEF SUMMARY OF THE INVENTION
The purpose of the present invention is to create a soil-displacing screw auger which avoids this and other advantages and allows the creation of the piles relatively deep into heavy ground.
According to the invention, this purpose is obtained because of the fact that the lower tube of the auger is an intermediate tube with an outer diameter which is smaller than twice the largest radius of the displacement body but larger than the outer diameter of the auger tube, whereas the auger tip contains a displacement part with a closed screw rotating in the same sense as and preferably with a smaller pitch than the screw blade on the intermediate tube and a maximal radius equalling half the diameter of the intermediate tube.
When screwing in, the displacement of the soil is done in two phases, namely first by the displacement part of the auger tip and then by the displacement body, whereas the screw blade on the intermediate tube transports soil upwards.
The screw blade on the intermediate tube preferably has an outer diameter which approximately equals twice the above-mentioned largest radius of this displacement body.
The pitch of the screw blade on the intermediate tube preferably equals the pitch of the spirals of the two parts of the displacement body.
This auger tip could be equipped with a flap in order to allow the concrete to pass during the screwing out, but one extremity of this auger tip is preferably a detachable close-off tip which will be left in the ground as a lost tip; this close-off tip can be a displacement body itself and be equipped with a closed screw on the outside.
The auger tip can be exchangeable and be connected to the intermediate tube by means of a coupling.
In this case the auger tip can have at its upper extremity, above the displacement part, a cylindrical part the diameter of which corresponds to the diameter of the intermediate tube, and a screw blade can be welded onto this cylindrical part with the same diameter and sense of rotation as the screw blade on the intermediate tube and preferably also with the same pitch.
The intermediate tube obviously has a hollow shaft for the concrete, but this hollow shaft is preferably formed by a part of the auger tube passing through the intermediate tube to the lower displacement part or the close-off tip.
This invention also relates to a method for making a pile in the ground according to which the auger described above is screwed into the ground with a distance per revolution which is larger, in compressible soil, than the pitch of the screw blade and which in heavy ground is still larger than the smaller pitch of the displacement part of the auger tip, after which the auger is screwed out with the same sense of rotation, while concrete is poured in the borehole through the auger tube and an opening in the auger tip, for example by leaving behind its extremity.
REFERENCES:
patent: 4496011 (1985-01-01), Mazo et al.
patent: 4504173 (1985-03-01), Feklin
patent: 5722498 (1998-03-01), Van Impe et al.
patent: 5875860 (1999-03-01), Coelus
patent: 0131562 (1985-01-01), None
Bagnell David
Kreck John
Ostfeld David M.
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