Soil displacement auger head for installing piles in the soil

Details Soil displacement auger head for installing piles in the soil Soil displacement auger head for installing piles in the soil

1996-06-17

1998-03-03

Bagnell, David J.

Boring or penetrating the earth

Bit or bit element

With helical-conveying portion

405232, 405241, F21B 726, E02D 562, E02D 722

Patent

active

057224986

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
This invention relates to a soil displacement auger head for installing piles in the soil. A tip is provided with a displacement body having at least over a lower portion a core diameter increasing in a direction away from said tip. At least one screw flange extends at least over said lower portion of the displacement body.
2. Description of the Background Art
A soil displacement auger head is disclosed in German patent No. 4 220 976. This known auger head has a relatively long cylindrical portion between the lower portion of the conical displacement body, and the tip. On this cylindrical portion there is provided a screw flange with a constant pitch and a constant outer diameter. To increase the axial penetrating force during screwing, there was proposed in the embodiment according to FIG. 1 of this German patent to extend the screw flange until over the conical portion of the displacement body.
Another soil displacement auger head is known from European patent No. 0 228 138. In this known auger head the screw flange is however situated exclusively on the cylindrical portion between the displacement body and the tip and obviously doesn't extend over the displacement body itself.


SUMMARY AND OBJECT OF THE INVENTION

The invention described hereafter has as object to present an auger head by which the soil can be displaced more efficiently and requires less energy during screwing in, and which allows also to screw through more resistant, in particular more sandy, layers.
To this end, said screw flange has a pitch which increases at least over said lower portion of the displacement body in the direction away from said tip. indeed it has been found surprisingly that, by providing such an increasing pitch, lower torques are required to screw the auger head into the soil.
Concerning a variable pitch of the screw flange, reference can be made to DE-PS-576 831. In the auger head known therefrom the pitch of the screw flange, however, decreases over the displacement body.
In a particular embodiment of the auger head according to the invention the core diameter of the lower portion of the displacement body increases discontinuously according to said screw flange via a predetermined number of transition slopes.
Such a discontinuous diameter increase of the displacement body is already known per se from U.S. Pat. No. 4 458 765. This known auger head has however no clear screw flange, and certainly no screw flange wherein the pitch of which increases.
According to the present invention, the discontinuous diameter increase has been discovered which, in combination with the increase of the pitch of the screw flange, contributes particularly to the reduction of the energy required for making the hole in the soil. The auger head of the present invention may be used during screwing in through resistant, non-cohesive layers.
Preferably, the pitch of said screw flange increases in between two successive discontinuous diameter transitions, each time in such a way that, during screwing in, substantially a same volume of soil is squeezed and transported before each transition slope of the displacement body. This can be illustrated for example on the basis of the relationship: ##EQU1## wherein: 1.sub.o is the pitch at the first transition slope (17);
Said transition slopes form for example an angle comprised between 20 and 40 degrees, and in particular between 25 and 35 degrees with a tangent plane to the surface of the displacement body after the respective transition slope.
For screwing through incoherent layers, an angle of about 30 degrees was found the most suitable.
A further reduction of the required moments for screwing in through bearing layers can be obtained by arranging the slopes on the lower portion of the displacement body under a predetermined angle with respect to the longitudinal direction of the auger head wherein the predetermined angle is smaller as the core diameter before the concerned transition slope is larger.


BRIEF DESCRIPTION OF THE DRAWINGS



REFERENCES:
patent: 3226855 (1966-01-01), Smith
patent: 3485052 (1969-12-01), Turzillo
patent: 4458765 (1984-07-01), Feklin et al.

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