For many purposes, it is desirable to set up concrete piers, which piers project a certain distance above ground level and are used to support concrete structures. Such piers are used to good effect, inter alia, for supporting viaducts and the like.

An important aspect of such piers is that it must be possible to position them in the ground within as short a time as possible and in an environmentally friendly way, in order to limit the costs and inconvenience to a minimum.

Especially when building viaducts and the like, this is an important requirement, in order to minimize the disruption to traffic.

Moreover, such piers must have a high load-bearing capacity and must be stably anchored in the ground.

Hitherto, piers have been built up by firstly positioning a number of foundation piles in the ground, on which piles a concrete baseplate or pedestal footing is arranged, and ultimately the pier is then built on top of this. It is built up either by casting concrete into the site or by assembling prefabricated elements.

Consequently, anchoring and building up the pier takes a long time and entails all the adverse consequences mentioned above.

Therefore, one object of the present invention is to provide a pier which can be anchored in the ground quickly, easily and efficiently.

According to the invention, this object is achieved by means of a pile which has the characterizing features given in Claim 1. A pile of this nature can be entirely prefabricated and at the desired location can simply be screwed into a solid layer of earth to the desired depth using a suitable driving tool.

By designing the pile as a single unit, with a foundation section which can be screwed into the ground and a pier section which lies above the ground, the overall work involved in positioning the pillar can be carried out considerably more quickly than was previously possible. This is partly because the pier section, which remains visible, of the pile does not require any further work. While the pile is being screwed in, the surrounding ground is only displaced slightly, and the pile can be exposed to its full load-bearing capacity immediately after it has been set up. In addition, materials are saved, since there is no need for any formwork material in the construction. Also, there is an environmental advantage that when the pile is being screwed in, in contrast to the traditional introduction of piles, there is no need to use any polluting pile-drivers. Finally, the pile according to the

invention provides sufficient resistance to vertical and horizontal forces, as well as to moment forces, with the result that it can be used on its own.

It should be noted that it is known per se to screw a concrete pile into the ground, for example from EP-A-0,127,221. However, this relates to a foundation pile which is screwed entirely into the ground and on which a construction is later built. It must be realized that the pile according to the present invention, referred to below as pier pile, is a pile with a considerable length of approximately 20-30 m and a diameter of approximately 1.5 m.

Since the pier section of the pier pile forms a single unit with the foundation section, it is of essential importance for the pier pile to be screwed into the ground in the correct (vertical) position. In order to achieve this, it is proposed, according to the invention, to supply the outside of the pile, while it is being screwed in, with a liquid medium via the ducts, in order to reduce the resistance between the external surface of the pile and the surrounding ground and to control the position of the pile while it is being screwed in by varying the quantity and/or the pressure of the liquid medium supplied locally along the external circumference. Thus, while the pile is being screwed in, its position is measured and, in the event of the measured position deviating from the desired position, the volume of fluidization liquid supplied is varied locally in order to eliminate this deviation. In this way, the position of the pile is accurately controlled while it is being screwed in and the possibility of the pile being pulled out of position is prevented in a simple and efficient manner.

It should be noted that the use of a liquid medium to reduce the resistance between a pile and the surrounding ground is known per se, for example from NL-A-1003072. In this document, however, this liquid is distributed uniformly over the circumference and is not used to correct or control the position of the pile.

The pier pile can be screwed into the ground by means of a suitable driving tool which drives the pier pile in rotation. It is also possible to utilize an auger which is arranged in the hollow space inside the pier pile and guides upwards the earth which enters via the open bottom end. In order to be able to discharge the earth which is guided upwards, this earth will be mixed with sufficient liquid, which liquid is preferably supplied via the hollow core of the said auger.

If appropriate, the pier pile may be driven via the auger, although the auger may also be driven separately in an opposite direction of rotation, in which case the reaction forces generated by the pier pile-while it is being screwed in- on the driving tool and the underlying structure are compensated for to some extent.

The invention is explained in more detail with reference to the appended drawing, which diagrammatically depicts a preferred embodiment of the pile according to the invention.

Figure 1 diagrammatically shows a view of a pile according to the invention which has been screwed into the ground; Figure 2 shows a side view of the bottom section of a pile according to the invention; Figure 3 shows a vertical section through the pile from Figure 2, with a driving member arranged inside it; and Figure 4 diagrammatically shows the top side of the pile according to the invention, with a device for supplying fluidization liquid.

Figure 1 shows the pier pile, which is denoted overall by reference numeral 1, in the position in which it has been screwed into the ground. As can clearly be seen from this figure, the pile comprises a continuous, hollow cylindrical shaft 2, which has a top pier section 2a, which lies above ground level M, and a bottom foundation section 2b, which lies below ground level M. An external screw thread 4,5, which is illustrated in more detail in Figure 2, is arranged on the shaft at the bottom end of the foundation section. Depending on the ground in which the pier pile is arranged, it may be provided with further anchorage by means of so-called grouted anchors A, which are known per se and are therefore not described in detail. Figure 1 diagrammatically depicts only one grouted anchor. In order to increase the mass of the pile, so as to increase its resistance to transverse forces, it is filled with grout B after it has been screwed into the ground.

In order to make it easy to remove the pier pile when it is no longer economically viable, a number of bushes H are cast into the wall of the shaft, distributed over its circumference, approximately half a metre below ground level, as can be seen from the enlarged detail I in Figure 1. These bushes in fact enclose an elongate blind hole in the said wall, for accommodating an explosive charge. In this way, the pier section of the pier pile can be separated from the foundation section, which remains behind in the ground.

Figure 2 shows the bottom section of the pier pile 1, with an open bottom end 3. In the vicinity of the open end 3, the outside of the foundation section is provided with one or more ribs 4,5 which extend helically along it. In the embodiment shown here, there are two ribs, which together form a two-start screw thread. With the aid of this screw thread, the pier pile is screwed into the ground, the ribs creating a strong and stable anchorage for the pier pile.

At the open bottom end 3, each rib ends in a steel cutting edge 6,7. In the embodiment illustrated here, the cutting edges are directed vertically and extend as far as the adjoining rib.

In the cross section shown in Figure 3, there is a centring mandrel, which is fitted into the inside of the shaft and is used to manoeuvre the pier pile which is to be screwed in to the correct position. This centring mandrel comprises a hollow axle or core 9, which at its bottom end is provided with a closed, sharp point 9a. In the vicinity of this sharp point, there is an outlet opening 9b, so that liquid can be fed into the inside of the shaft via the hollow axle 9, for purposes which are to be described below. A conveyor screw 10, which extends a certain distance along the axle from the said sharp point, is formed around the axle 9. The top end of the conveyor screw is surrounded by a cylindrical sleeve 11, which is fixedly connected to the external circumference of the conveyor screw. The design is such that the sleeve fits into the space inside the shaft with a slight clearance, thus forming a guide for the hollow axle 9. The diameter of the conveyor screw 10 decreases gradually from the bottom edge of the sleeve 11 to the sharp point 9a.

The centring mandrel may be arranged fixedly or removably inside the pier pile, with the point 9a, in the fitted position, always projecting a certain distance beyond the bottom, open end of the shaft and serving as a centring point.

The conveyor screw 10 of the centring mandrel functions as an auger for guiding the ground upwards inside the pier pile.

In the embodiment illustrated here, the centring mandrel is removably connected to the pier pile. After the pier pile has been positioned at a suitable depth, the centring mandrel can be removed entirely and reused for a following pier pile.

As has been stated, the said ribs 4 and 5 together form a two-start screw thread for screwing the pier pile into the ground. In addition, in the screwed- in position, these ribs also have the role of providing a stable and strong anchorage for the pier pile, thus conferring a high load-bearing capacity on the pier pile. As can be seen from Figure 2, these ribs each have a bottom, downwardly directed surface 15 which is essentially perpendicular to the external surface of the shaft, which surface, via a bevel 15a, merges into the external surface of the shaft. A radially outer surface 16 of the rib runs virtually parallel to the external surface of the shaft, and from this radially outer surface a surface 17 runs obliquely upwards towards the external surface of the shaft. The radially outer surface 16 is to some extent hollow in cross section and is covered with a steel strip 18 which is anchored in the concrete. This strip 18 is used as a cutting strip in order to make it easier to screw the pier pile into the ground. The aim of the concave shape is to reduce adhesion of the ground and to improve the cutting action.

A number of ducts 20, which extend in the longitudinal direction of the shaft from the top edge of the pile, are distributed over the circumference of the shaft. These ducts, which are indicated by dashed lines in Figure 3, open out on the outside of the shaft, in the area of the screw thread. In the case illustrated, there are two ducts 20, both of which open out, in the vicinity of the bottom opening 3, in the surface 15 of the respective ribs. However, it will be clear that there may be a plurality of ducts which may open out at various locations on the outside of the shaft or in the ribs. The purpose of these ducts is to supply a liquid medium or fluidization liquid, in order to be able to reduce the friction between the outside of the pile and the surrounding ground while the pier pile is being screwed in. By varying the volume and/or pressure of liquid medium supplied locally along the circumference of the pier pile, it is possible to correct the position of the pile while it is being screwed in.

Fig. 4 shows the top side of the pier pile, with an annular reservoir 30, which contains the liquid medium or fluidization liquid, positioned on this top side. A number of metering or control valves 31 can be seen on the outside of the reservoir, which valves are each connected, on the one hand, to a feedline 32 which comes out of the reservoir, and on the other hand to a line 33, which for its part is connected to one of the longitudinal ducts 20 in the wall of the pier pile.

Each valve also has a return line 34 which runs from the valve to the reservoir 30, in order to return excess medium. In the embodiment illustrated in this figure, the valves 31 are distributed at intervals of 120° over the circumference. This means that there are three valves and the same number of ducts 20. The annular configuration of the reservoir 30 allows the hollow axle 9 of the centring mandrel to pass through. The liquid medium used is preferably water.

The pier pile described above is positioned in the ground by means of a driving tool, which is not shown in more detail. This driving tool preferably acts at the location where the pier pile experiences most resistance when it is being screwed in, i. e. in the area of the screw thread. Thus the driving tool may act on or be connected to the centring mandrel 8. While the pile is being screwed in, the ground is cut up by the cutting edges 6,7. On the inside of the shaft, the ground is guided upwards by the conveyor screw 10. The injection of liquid in the vicinity of the bottom, open end 3 via the hollow axle 9 and via the outlet 9b improves the conveying of the drilled earth inside the pier pile.

When the pier pile has been screwed in to the desired depth in the manner described above, the mass of the pier pile is increased by filling the space inside the shaft with suitable mortar or grout and, if appropriate, by introducing a reinforcement. The top end of the pile is then dealt with according to its desired use. The top section of the pile, i. e. the section above the screw thread, has a

smooth finish on its outside, so that the pier section 2a which remains visible does not require any further treatment.

The pile according to the invention is made from prestressed concrete and can be entirely prefabricated by means of centrifugal casting, with the cutting edges 6,7, the ducts 20 and the cutting strips 18 which are arranged along the ribs being cast in and anchored in a suitable way.

It will be clear that the invention is not limited to the pier pile illustrated and described here, but rather a large number of variants within the scope of the appended claims will be obvious to the person skilled in the art. For example, the ducts 20 may be distributed in groups over the circumference, in which case the ducts of each group open out at different levels in the area of the external screw thread. Also, each duct could have a number of outlet openings lying at different levels.

The pile according to the invention is particularly suitable for use as a pier for viaducts and the like. The pile, which is entirely prefabricated, can quickly be put in position in the ground, so that the inconvenience to traffic is minimal.