EP0109397B1 - Hollow foundation element and manufacturing method thereof - Google Patents

Abstract

The hollow foundation element is made in the form of a pile. It has a constant cross-section, made of concrete, and is so installed that its lower end extends below the underground water level. The part of the element which extends below the water level is made of porous concrete which is made from gravel of a uniform size. The lower part (2), made of porous concrete, has steel reinforcing rods and its lower end is sealed by a plate (3). After the element has been installed the internal water level is reduced by pumping away the water and the inner surface is then sealed with cement. (First major country equivalent to AT8202031)

Description

The invention relates to a hollow foundation body of substantially constant cross-section, consisting of concrete, which is continued downwards through a water-permeable layer, a filter tube being arranged in the water-permeable layer, from which penetrating water can be removed through a tube guided in the foundation body.

Various proposals have already been made not to arrange drainage piles, which are customary for lowering the groundwater in the area of foundation piles or foundations, to the side of the foundation structure. Rather, a pipe is led through the foundation body into the depth, into which the groundwater penetrates from a water-permeable layer located below the foundation body, whereupon it is pumped up or sucked up. Viewed statically, in known devices of this type (cf. AT-PS 186 197, AT-PS 225629) the filter layer located below the foundation body is not part of the foundation body.

In contrast, the object of the invention is to design a foundation body of the type outlined at the outset, in particular a foundation pile, in such a way that it initially acts in a known manner as a drainage pile, but at the same time is statically effective over its entire length. This is achieved in that the water-permeable layer consists of filter concrete, especially in a manner known per se, single-grain concrete.

To the extent that filter concrete, in particular the single-grain material, has been produced, filter blocks were prefabricated from it, which were then laid. If the einkorn material, as described in AT-PS 358 997, was introduced into the groundwater area, care was taken to seal the wall of the borehole on the one hand and to make the einkorn concrete impermeable to the groundwater on the one hand by adding sufficient binding agents.

The filter concrete used already has greater compressive strength than natural water-permeable layers or as a gravel casing placed around the filter tube. It is also possible to provide the entire foundation body with continuous reinforcement. As soon as the groundwater level has dropped sufficiently, the filter concrete can also be grouted with a hardening injection material. This had previously been proposed (see AT-PS 168 946) in order to make a filter layer impermeable to water. In connection with the invention, this also leads to the fact that the lower end of the foundation body can absorb pressure forces transmitted from the upper part thereof to an increased extent.

• Fig. 1 einen Querschnitt durch einen Drainagepfahl darstellt und
• Fig. 2a bis 2g die Herstellung desselben illustrieren;
• Fig. 3a bis 3d zeigen die Verwendung der beschriebenen Pfähle bei der Herstellung eines Gebäudes;
• Fig. 4a bis 4c zeigen die Anwendung der Erfindung bei einer Drainagewand.

Details of the invention are described below with reference to the drawing, wherein

• Fig. 1 shows a cross section through a drainage pile and
• Figures 2a to 2g illustrate the manufacture of the same;
• 3a to 3d show the use of the piles described in the manufacture of a building;
• 4a to 4c show the application of the invention to a drainage wall.

The drainage pile shown in FIG. 1 consists of a lower part made of filter concrete 1 and an upper part made of water-impermeable normal concrete 7. It is continuously provided with longitudinal reinforcing bars 2, which are held together by a spiral in the circumferential direction of reinforcing bars. Pipes 6 and 4 run along the axis of the pile surrounded by the soil 8. The pipe surrounded by the filter concrete 1 is designed as a water-permeable filter pipe 4 and is accordingly provided with slots or the like. A base plate 3 with a sump tube 5 welded to it prevents the soil from being washed out below the drainage pile. With 9 a removable rubber packer is indicated, which prevents the penetration of concrete into the interior of the filter tube 4 during the production of the layer of filter concrete 1.

The drainage pile shown is produced by first lowering a casing pipe 10 into the ground 8 to below the groundwater level 11 (FIGS. 2a, 2b). The interior of the casing tube 10 is emptied using conventional construction machinery 13. The tube 6 is then introduced (FIG. 2c), which carries the filter tube 4, the sump tube 5 and the base plate 3 at its lower end. Filter concrete 1 is introduced around the reinforcing bars 2, while at the same time the casing tube 10 is pulled up (FIG. 2d).

The known filter or single-grain concrete is preferably composed of gravel with a uniform grain size between 2 mm and 32 mm and contains approximately 120 to 200 kg of cement per m ^{3 of} filter concrete. Only a relatively small amount of water is necessary, since the cement particles only need to be attached to the gravel grains. The water necessary for the concrete to set completely is supplemented by the groundwater present when it is introduced underwater. In order to ensure the binding of the cement to the gravel in the event of strong water ingress, commercially available additives can be used which prevent the cement from loosening from the gravel grains. Their proportion is usually between 0.3 and 0.8% by weight.

The entire concrete (including single-grain concrete) is, as is currently the case, poured into the corresponding height (depth) of the drainage pile using a concreting pipe.

As mentioned, the filter tube 4 can be sealed by a rubber packer 9 while the filter concrete 1 is being introduced, while the filter can during the setting process flushed concrete so that it remains permeable to water. Following the production of the layer of filter concrete 1, the upper part of the drainage pile is carried out in normal concrete 7 (FIG. 2e). The groundwater level 11 is lowered (FIG. 2f) by pumping up the water that has penetrated through the filter tube 4 from the drainage pile via a pump introduced through the tube 6, or by suctioning it off from above. As soon as no further drainage is required, the filter concrete 1 can be pressed through the filter tube 4 by a cement injection 12 and can thus be made water-impermeable and increasingly pressure-resistant.

The construction according to the invention of a foundation pile that can be used for drainage takes into account the differences to which such a component is exposed in its various height ranges: bending stresses are practically limited to the upper part, where the pile is constructed in a conventional manner, while the lower part occurs almost exclusively Pressure loads that can be easily absorbed, in particular by reinforced filter concrete. The lower part of the foundation pile, which is primarily used for drainage, is thus effective in its entire length in that it reduces the peak pressure on the pile base to the permissible level by jacket friction.

The mode of operation of the drainage pile according to the invention during the construction process is illustrated with the aid of FIGS. 3a-d. First, as described, a series of piles according to FIG. 3a is produced. The excavation pit is then excavated (Fig. 3b). In the course of the same, anchoring with anchors 14 as an additional safeguard against the occurring earth pressure is possible. Underwater excavation can be carried out below the groundwater. If this is not desired, it is already possible to lower the groundwater level in sections. The main stress on the pile is the absorption of bending moments caused by earth pressure. The bending moments that occur are absorbed by the existing reinforcement 2. The weakening of the cross-section through the well pipe 6 has only a very slight influence on this load-bearing behavior, since the well pipe 6 is arranged centrally and thus lies in the neutral zone of the bending stress.

After excavation (possibly also during this), the groundwater is sucked in through the lower filter concrete section 1 of the pile and pumped out through the well pipe 6. In terms of dimensioning, the same requirements apply here as for a normal well (Fig. 3c). Then the underground part of building 15 is built, so that a watertight tub is created.

After the construction of the underground component, the above-ground building is produced (Fig. 3d). As soon as the buoyancy safety of the structure is guaranteed by the increasing load, the groundwater lowering can be stopped. In order to increase the load-bearing capacity of the piles, there is the possibility that the single-grain concrete 1 is subsequently further improved by the filter tube 4 by means of injection 12. In addition to the load-bearing capacity of the pile, the jacket friction is also increased in this area, since the injection material partially penetrates into the surrounding subsoil. As far as the construction progresses, the pile is given a higher load-bearing capacity, which can usefully be coordinated with the increasing building load.

The invention is not limited to foundation bodies of cylindrical cross-section, that is to say to foundation piles in the narrower sense, rather it is possible to implement the same basic idea with foundation bodies, for example rectangular cross-section, for example with diaphragm walls.

The manufacture of such a drainage wall is shown in FIGS. 4a to c.

According to FIG. 4a, a shaft is first excavated and the wall thereof is protected by a supporting liquid 18 (for example, concrete suspension) introduced between guide walls 16. A partition 17 is then lowered (FIG. 4b), which is generally perforated, but has a closed component 17 'in the lower region. The further procedure is the same as that described for FIG. 2, with the difference that filter concrete 1 is introduced only on one side of the wall part 17 'and therefore the groundwater is only lowered on this side of the wall. The filter concrete 1 is only effective when the sealing of the adjacent area by the supporting liquid, for example by partial dissolution of the sealing layer, has been removed.

Claims (4)

1. Hollow foundation body of substantially constant cross-section, consisting of concrete (7), which is downwardly continued by a water-pervious layer (1), a filter pipe (4) being arranged in the water-pervious layer from which entering water can be removed through a pipe (6) extending through the foundation body, characterized in that the water-pervious layer is filtering concrete (1), in particular uniform-grained concrete known per se.

2. Hollow foundation body according to claim 1, characterized in that reinforcing irons (2) are arranged in the water-pervious layer.

3. Hollow foundation body according to claim 1 or 2, characterized in that the water-pervious layer is sealed by a bottom plate (3).

4. Method of making a foundation by using foundation bodies according to claim 1, characterized in that after lowering of the ground water the filtering concrete (1) is in a manner known per se injected under pressure with a hardenable injection material, e. g. thin cement mortar, through the filter pipe (4).

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