"Ground displacement auger head for making piles in the ground" This invention relates to a ground displacement auger head for making piles in the ground, comprising a tip, a displacement body having at least over a lower portion a core diameter increasing in a direction away from said tip, and at least one screw flange extending at least over said lower portion of the displacement body. Such a ground displacement auger head is known from German patent No. 4 220 976. This known auger head has between the lower portion of the displacement body, being conical, and the tip a relatively long cylindrical portion. 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 Figure 1 of this German patent to extend the screw flange until over the conical portion of the displacement body.

Another ground displacement auger head is known from European patent No. 0228 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.

The invention described hereafter has as object to present an auger head by which the ground can be displaced more efficiently and reguiring furthermore less energy during screwing in, and which allows also to

screw through more resistive, 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 moments are required to screw the auger head in the ground.

Concerning a varying 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 US-A-4 458 765. This known auger head has however no clear screw flange, and certainly no screw flange increasing the pitch of which increases.

According to the present invention, the discontinuous diameter increase has been found now, in combination with the increase of the pitch of the screw flange, to contribute particularly to the reduction of the energy required for making the hole in the ground, manifesting especially during screwing through resistive, incoherent 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 ground is kneaded and transported before each transition slope of the displacement body. This can be illustrated

for example on the basis of the relation shown in claim 4.

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 out through resistive 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 as indicated in claims 8 and 9.

Further particularities and advantages of this ground displacement auger head will become apparent from the following description of some particular embodiments of the auger head according to this invention. This description is only given as an example and is clearly not intended to limit the scope of the invention. The used reference numbers refer to the annexed figures, wherein :

Figure 1 shows schematically a side view of an apparatus for making piles in the ground by means of an auger head according to the invention;

Figure 2 shows schematically the different steps for making a pile in the ground by means of the apparatus according to Figure 1; Figure 3 shows a side view of a ground displacement auger head according to the invention;

Figures 4 and 5 show respectively on a larger scale a cross section according to lines IV-IV and V-V in Figure 3;

Figure 6 shows a side view of a ground displacement auger head according to a variant embodiment of Figure 3;

Figure 7 and 8 show respectively on a larger scale a cross section according to lines VII-VII and V II-v II in Figure 6 ;

Figure 9 shows a side view of a ground displacement auger head, more particularly of the lower portion thereof, according to another variant embodiment of Figure 3 or 6;

Figure 10 shows the increase of the pitch of the screw flange of the auger head according to Figure 3 in function of a number of variables.

In these different Figures the same reference numbers relate to the same or analog elements.

In Figure 1 a screwing apparatus is schematically shown for making concrete piles in situ in the ground by means of a ground displacement auger head 1 according to the invention. This screwing apparatus comprises a crane 2 with a vertical mast 3 provided with an auger motor 4. The auger motor 4 is preferably mounted at the bottom of the mast 3 so that said mast can be constructed as light as possible. Of course use can also be made of an auger motor 4 which is movable up and down the mast 3.

The different steps for making a concrete pile in the ground are schematically shown in Figure 2. In a first phase the auger head 1 is screwed through the intermediary of an up and downwards movable platform 5 and an auger tube 6 in the ground, so that the ground is displaced laterally. Possibly a downward force can further be exerted onto platform 5 by means of traction ropes 7. Then a reinforcement 8 is put in through the auger tube 6 and concrete is injected by means of a pump 9 through the auger tube 6 and the auger head 1 in the formed hole 10, while the latter elements are removed

out of this hole 10 by means of the hook 11. It this phase, the same rotation direction is maintained as during screwing in. The tip 12 of the auger head 1 remains at the bottom in the ground. If desired the reinforcement 8 may be pushed afterwards in the just formed pile 13.

Upon forming the piles 13 in less resistive or weak grounds, one sometimes nevertheless has to drill through harder, usually more sandy intermediate layers. Also one has to screw sufficiently far in the resistive underground to give to pile 13 enough bearing capacity. Most of the ground displacement auger heads existing at present do not allow to screw through such harder layers or require thereto very large penetrating forces. As will become apparent hereinafter this invention describes, however, a ground displacement auger head which can be screwed under a larger displacement efficiency with a reduced penetrating force even through more resistive layers. In general the auger head 1 according to the invention comprises a tip 12, a displacement body 14 having at least over a lower portion 15 a core diameter increasing in a direction away from said tip and a screw flange 16 extending at least over the lower portion 15 of the displacement body 15. To obtain an axial penetration force which is as large as possible during screwing in, the screw flange 16 has preferably at least over the lower portion 15 of the displacement body 14 a substantially constant outer diameter. This auger flange 16 delimits a mainly spiral strip with an increasing core diameter on the displacement body 14.

To achieve the objectives mentioned hereinabove, the invention provides first of all that the screw flange 16 has over the lower portion 15 of the displacement body 15 a pitch 1 increasing in the

direction away from the tip 12. The increase of this pitch will be described hereafter further into detail. In the represented auger head 1 the displacement efficiency is still further increased because, as provided according to a further aspect of the invention, the core diameter of the lower portion 15 of the displacement body 14 increases over said spiral strip discontinuously via a predetermined number of transition slopes 17. It has been found that in this way a more efficient ground displacement can be obtained, especially in resistive, more sandy layers. The result is that smaller forces and/or moments are to be exerted onto the auger head to screw this through such layers, and this notwithstanding the fact that the slopes 17 give at first sight additional resistance.

In an efficient embodiment the discontinuous transition slopes 17 form an angle α comprised between 20 and 40 degrees and preferably between 25 and 35 degrees. The angle is formed by the tangent plane to the surface of the displacement body 14 after the respective slope 17. In the embodiment according to Figures 3 and 4 the angle α comprises about 30 degrees which appeared particularly efficient for screwing through compacted sand layers. In this embodiment four discontinuous transition slopes 17 are provided regularly divided over the lower portion 15 of the displacement body 14, more particularly each time turned over an angle of 450 degrees. In general, this angle is preferably larger than 360 degrees. At the slopes 17 the core diameter increases with at least 2 cm, preferably with 3 cm to 15 cm and in particular with 4 cm to 10 cm. The number of slopes 17 will depend from the difference between the minimum d ₀ and the maximum diameter d,,, of the displacement body 14. Between two successive slopes 17 the surface of the auger head 1 may be somewhat conical, but this surface

between two successive slopes 17 is preferably cylindrical. Preferably the displacement body 14 extends further substantially upto said tip 12, although an additional portion with a screw flange or not can further be provided between this displacement body 14 and the tip 12.

As already indicated hereinabove, the screw flange 16 has over the lower portion 15 of the displacement body 14 a pitch 1 increasing in the direction away from the tip 12. The pitch 1 of the screw flange 16 increases each time between two successive diameter transitions, particularly in such a manner that, during screwing in, substantially the same volume of ground is kneaded and transported before each transition slope 17. The radial displacement of the ground is achieved then mainly at the place of the last discontinuous transition slope 17, in other words before the maximum diameter d _m is reached. Indeed, since the pitch increases each time between two slopes 17, the distance between the top of the slopes 17 and the outer diameter of the screw flange 16 does become smaller, but the successive transition slopes 17 have a larger width, so that the displaced ground is divided at these slopes mainly over a wider area. This is in particular not the case for the first slope 17 unless an increase of the pitch is also provided before this slope ; for example placed on a small additional cylindrical part between the displacement body 14 and the tip 12 of the auger head 1. Of course, a certain radial displacement occurs at each slope.

The increase of the pitch of the screw flange 16 may, on the contrary, be a continuous increase. However, preference is given to a discontinuous increase of the pitch as in the shown embodiments. In the embodiment according to Figure 3, the increase of the pitch is achieved each time at about one rotation after

each slope 17, as indicated by means of arrows 18, except of course for the last slope 17. In this way the strip between the different windings of the screw flange 16 starts to diverge thus each time after each slope 17. In a preferred embodiment, the increase of the pitch lj over the lower portion 15 of the displacement body 14 is determined on the basis of the following relations : li = 1„ • β; with β, = n(d,*-dlθ,--n - d,*-d,*n n(d _m *-d. ² ) wherein 1 ₀ is the pitch at the first slope; 1; is the pitch at the i + 1 ^st slope; n is the rotational speed at which the auger head is to be turned; v is the vertical penetration speed of the auger head in the intended ground; d___ is the maximum core diameter of the displacement body; d ₀ is the minimum core diameter of the displacement body; and d- is the core diameter before the i + 1 ^st slope.

When designing an auger head on the basis of this formula the minimum d ₀ and the maximum diameter d _m of the displacement body is first of all determined in function of the pile diameter to be achieved. Further, the number of slopes necessary for this diameter increase is also determined. Then the pitch 1 ₀ at the first slope is determined and also the rotational speed n, all in function of the desired vertical penetration speed. Of course the power of the auger motor 4 will have to be taken into account because a larger pitch 1 ₀ and a higher rotational speed require a higher power. On the basis of the pitch 1 ₀ and the rotational speed n, the theoretical vertical penetration speed can be determined. The real penetration speed v will be at the

most equal to this theoretical value and can be determined more exactly on the basis of experimental data. Since the auger head according to this invention is especially provided to drill through resistive sand layers, the optimal penetration speed v is determined experimentally for such layers. Further, account has to be taken in this respect with the fact that possibly an additional downward force can be applied onto the auger head. On the basis of this formula the relation between the pitch increases βl , β2 , β3 for the three last slopes of the embodiment according to Figure 3 and the real penetration speed v is given in Figure 10 and this for a rotational speed of 6 and 30 rpm and for a minimum diameter d ₀ of 21 cm and a maximum diameter d _m of 46 cm.

As it appears from Figures 3 and 6, the slopes 17 on the lower portion 15 of the displacement body 14 are preferably directed downwards each under a predetermined angle 7 with respect to the longitudinal direction of the auger head 1. This predetermined angle 7 further decreases as the respective slope is further removed from tip 12. Due to such an orientation of the discontinuous transition slopes 17 the required penetration force can be reduced further. In a particular embodiment, the transition slope 17 which is the closest to the tip 12 forms an angle 7 of 0 to 20 degrees and preferably of 5 to 10 degrees with the longitudinal direction of the auger head 1 while the slope which is the farthest removed from the tip 12 forms an angle of 0 to 5 degrees with this longitudinal direction. The possible transition slopes 17 situated between the first and the last slope form then an angle of an intermediate value.

On the front of tip 12 of the auger head 1, teeth 19 may further be provided for grinding the ground. The embodiment according to Figure 3 comprises two teeth 19,

one of which being fixed onto the screw flange 16 and the other on an additional screw flange part 20, which terminates already before the first slope 17. The tip 12 itself is, in the usual way, removably mounted onto the auger head 1 in such a manner that it remains in the ground upon screwing the auger head 1 out as a result of the contrete injected under an over pressure in the auger head 1. The auger tip can also be fastened to the auger in such a way that it can be recuperated, for example hingedly between an open and a closed position.

In order to displace again laterally any possible ground situated on top of the auger head, during screwing the auger head 1 out, the displacement body 14 has in the embodiment according to Figure 3 an upper portion 21 with a core diameter decreasing in the direction away from said tip. This upper portion comprises further four screw flange parts 22', 22", 22" ' and 22"", each extending over about 225 degrees and overlapping each other over about 45 degrees, as it appears from Figure 5. Since the screw flange parts 22 have a screw direction opposite to the screw direction of the screw flange 16, these screw flange parts 22 will provide that, during screwing the auger head out, the ground situated on top of this auger head, will be displaced once again by the upper portion 21 of the displacement body 14. During screwing in itself, the division in screw flange parts 22 permits that any possible ground which nevertheless would penetrate till above the displacement body 14, can escape between these screw flange parts 22 so that no stop is formed which could hamper the operation of the auger head.

Preferably, the upper portion 21 of the displacement body 14 has also a core diameter decreasing discontinuously via a predetermined number of transition slopes 23. Contrary to the transition slopes 17 on the lower portion 15 these transition slopes 23 are in

particular directed upwardly under a predetermined angle 7 with respect to the longitudinal direction of the auger head 1, more particularly under an angle 7 of 0 to 30 degrees and preferably under an angle of 10 to 15 degrees.

In the variant embodiment according to Figure 6, the upper portion 21 of the displacement body 14 comprises first of all a series of fins 24, in this case eight, overlapping each other partially. These fins 24 are disposed according to a screw direction opposite to the screw direction of the screw flange 16 and extend in particular over about one turn around the auger head 1. The use of mutually overlapping fins 24 offers also in this embodiment the advantage that upon screwing in ground can escape between these used fins 24 reducing once more the penetration energy.

For displacing the ground radially when screwing the auger head 1 out, an inclined displacement surface 25 is arranged underneath each of the fins 24. Starting from the displacement surface 25 which is situated underneath the fins 24 and which is the farthest removed from the tip 12, each of these displacement surfaces 25 project further radially. In this way the displacement surface 25, which is situated underneath the fin 24, which is the closest to the tip 12, extends to about the maximum diameter d _m of the displacement body 14. In this way the ground is also displaced to a further extend radially by each of the successive displacement surfaces 25. As it appears from Figures 5 and 6 these displacement surfaces 25 are preferably curved.

In the embodiment according to Figure 9, an additional part 26 with at least one lateral opening 27 of a concrete duct 28 extending through the auger head 1 is provided between the displacement body 14 and the tip 12 of the auger head 1. Before this lateral opening 27 the auger head 1 has preferably an increasing core

diameter which decreases discontinuously at the opening 27. In this way ground is displaced laterally before the opening during screwing in so that at the opening 27 a space arises in the ground which can be filled up via this opening 27 with pressurized concrete. During screwing in itself concrete is pumped through the auger tube and escapes under pressure through this opening. The so introduced concrete is mixed somewhat with the kneaded ground and is together therewith laterally displaced in the surrounding ground, as the displacement body goes further downwards so that a reinforced contact wall pile-ground is obtained.

From the previous description it will be clear that the invention is not limited to the embodiments described herein before, but that all kinds of detail modifications could be applied thereto for example concerning the shape and the arrangement of the different components of the auger head without leaving the scope of this invention. The outer diameter of the screw flange 16 could possibly be larger than the maximum core diameter d _nι of the lower portion of the displacement body 14. In this case the upper portion 21 of the displacement body 14 has, in particular in the embodiment according to Figure 6, then preferably also a maximum core diameter which is substantially equal to the outer diameter of the screw flange 16. In this way, a larger part of the ground can penetrate between the fins 24 during screwing in, till above the auger head 1, whereby less energy is required during screwing in. When screwing out, which clearly requires obviously less energy, this ground can be displaced further radially.