GB2331533A

GB2331533A - Foundation anti-friction device

Info

Publication number: GB2331533A
Application number: GB9825526A
Authority: GB
Inventors: Jean-Paul Fundenberger; Jean-Michel Jeanty
Original assignee: SOL COMP DU; Compagnie du Sol SARL
Current assignee: SOL COMP DU; Compagnie du Sol SARL
Priority date: 1997-11-21
Filing date: 1998-11-20
Publication date: 1999-05-26
Anticipated expiration: 2018-11-20
Also published as: GB9825526D0; HK1020204A1; GB2331533B; FR2771427A1; FR2771427B1

Abstract

A device for reducing the friction between a cast reinforced wall and the surrounding soil comprises, a 'sandwich' of first (8) and second (7) sheets of plastic material spaced apart from each other and surrounding a cellular plastic structure (9). The whole 'sandwich' is spaced apart from the wall reinforcement (12) by means of spacer devices (11). In use the cellular structure (9) remains filled with mud after the concrete has been poured in place over the reinforcement cage in an attempt to reduce force transferral between the wall structure and surrounding soil.

Description

1 2331533 AN ANTIFRICTION DEVICE FOR A STRUCTURE BURIED IN THE GROUND The

present invention relates to an antifriction device for a structure buried in the ground. 5 In the field of building and civil engineering, it is often necessary to make structures out of reinforced concrete or the like. This applies, for example, to the cast walls of wall elements cast in the ground, or of foundations. It is also true of concrete foundations reinforced by reinforcing bars that serve as anchor points in the ground for vertical items such as posts. When such structures are subjected to loads, the transmitted load gives rise to stresses in the mass of is concrete, and thus in the surrounding ground.

A known method of making cast walls or cast wall elements includes the use of reinforcing cages.

Those conventional cast walls or wall elements can be used in particular as a base on which to make a surface structure. Accompanying Figure 1 shows cast walls such as 1 and 2 made in the ground 3, these cast walls defining an inside space 4 beneath an overlying building 5. Unfortunately, the loads constituted by such an overlying building can give rise to large amounts of friction at the ground/wall interface as represented by arrow F. In some cases, it is desirable to limit the transfer of these loads, particularly when the wall is situated close to some other underground work 6, as shown in Figure 1.

The object of the present invention is thus to make such a cast wall (or wall element) which is provided with an antifriction system so as to enable the cast wall to be decoupled from the adjacent portion of ground in order to minimize the transmission of these forces.

For this purpose, according to the invention, a cast wall (or wall element) is made that is provided with a reinforcing cage, said cage being fitted with a 2 "sandwich" system of high density polyethylene (HDPE) type which constitutes the device for deccupling forces between the wall and the surrounding ground.

Said cage, or more generally said structure, which comprises reinforcing elements forming two substantially parallel and vertical faces together with transverse reinforcing elements interconnecting said vertical faces, thus also includes at least one antifriction sandwich system, together with means for fixing and spacing said antifriction structure on one of its faces.

The ground/wall (or ground/wall element) decoupling in terms of transmitting friction is provided by the sandwich system of HDPE type plastics material which is selected to be of sufficient strength to enable it to be is handled easily, as shown in Figure 2.

More precisely, said structure is constituted by:

9 a first sheet 7 of plastics material, of thickness of millimeter order, having a first face fixed to the selected face 12 of the reinforcement of the wall by means of an appropriate fixing device as described below; a second sheet of plastics material 8; a deformable cellular structure 9 of plastics material in between the two above main sheets, and of thickness of the order of a plurality of millimeters; 0 said set of three sheets being fixed to form said sandwich by means of fixing pin type devices 10 connecting said set to spacer devices 11 for spacing relative to the face of the reinforcing structure of the wall; and 0 a certain amount of freedom exists between the two main sheets because of the cellular structure 9.

When making a wall (or a wall element) the method of making the invention and its preferred mode of operation comprise the following steps:

0 a section of trench is dug having the shape of a portion of cast wall to be made, said trench then being filled with a mud such as bentonite; 3 the reinforcing cage is placed in the section concerned, said reinforcing cage having the abovedescribed antifriction sandwich device on at least one of its faces, thereby enabling the mud to fill the cellular 5 structure 9 and the empty space in the reinforcing cage; 9 the concrete of the wall is cast into said trench, thereby replacing the mud in the empty space with wall concrete, the HDPE type plastic sandwich device preventing said concrete from penetrating into the cellular structure 9, given its small thickness, so said sandwich remains filled with mud; and 9 given the degree of freedom provided between the two main sheets 7 and 8 by the mud-filled cellular structure 9 constituting the antifriction sandwich, it will be understood that forced transmission from one sheet to the other is greatly limited.

In this way, the friction forces F coming from the final upper buildings 5 are thoroughly decoupled at the final ground/wall interface, and the resulting displacements are absorbed by said above-described antifriction sandwich, so force is no longer transmitted to the surrounding ground.

Other characteristics and advantages of the invention appear more clearly on reading the following description of various embodiments given as non-limiting examples. The description refers to the accompanying figures, in which:

Figure 1, described above, shows the transmission of force via a cast wall (or wall element) using a standard type of reinforcing cage; Figure 2 is a fragmentary section view of the cage showing how the antifriction sandwich is fixed to a face of said reinforcing cage by means of a spacer device; and Figure 3 is a plan view showing how reinforcement including the antifriction device of the invention is put into place in the trench for the wall (or wall element) that is to be made.

4 Figure 3 shows a preferred implementation of the invention while the cast wall is being made: this figure is a plan view showing a first section of trench 13 in which a first cast wall panel has already been made, with the corresponding reinforcing cage being referenced 15. As is well known in the present state of the art, this first section can be defined at its ends by removable partitions 16 or 161. The same figure shows a second section of trench 17 adjacent to the first and in which a second panel of cast wall is to be made. For this purpose, a reinforcing cage 18 is placed in the section of trench 17 which is full of a drilling mud, e.g. based on bentonite. The cage is provided with an antifriction device as described above. Said reinforcing cage 18 thus has two main faces referenced 19 and 20 which are constituted, for example, by horizontal and vertical round bars 21 and 22, said main faces being interconnected, e.g. by cross bars 23.

In accordance with the invention, an antifriction sandwich structure 24 is previously fixed on one of the faces of the reinforcing cage 19 and is spaced apart from the cage by the spacer device 25. It is also possible to fix another such an antifriction structure on the other face of the reinforcing cage 20.

With reference to Figure 3, and the implementation and operation of the antifriction sandwich as described above, the implementation and the operation of the antifriction device as installed in this way in the second panel 17 can be understood, which panel will subsequently be in line with the preceding panel 13 which is fitted with an identical antifriction device 241.

As shown in Figure 2, the antifriction sandwich is constituted by two parallel sheets, e.g. of high density polyethylene, that are secured to an inner deformable cellular sheet (e.g. HDPE netting) by any appropriate means, said sandwich being placed parallel to the selected face of the reinforcing cage and being fixed thereto by any appropriate means, in particular by means of a metal spacer device associated with the main cage in a preferred embodiment.

The mud used during excavation (of the bentonite type) is thus imprisoned in the cellular structure of the sandwich made in this way, thereby creating a thin "pad" of mud. Because of the degree of freedom between the two main sheets of said sandwich, a zone is thus obtained that is saturated in hentonite and that can deform vertically under the effect of a load subsequently applied by a future building, thereby decoupling mechanical stresses at the wall/ground interface so that the stresses are no longer transmitted to the ground on the outside.

It would naturally be possible to implement such decoupling on each of the faces of the reinforcing cage, should that be necessary.

Such an antifriction device can be made on any wall element, for the purpose of protecting existing underground works from any top loading on said wall elements.

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Claims

CLAIMS:

1. A device comprising an antifriction reinforcing structure used when making cast walls or when making cast wall elements, the device comprising a first sheet of plastics material of sufficient strength and thickness together with a second sheet of plastics material spaced apart from the first by a cellular structure also made of plastics material, the assembly being f ixed on a selected face of a reinforcing cage for the future cast wall (or future cast wall element) by means of spacers, or spacer devices, and by means of appropriate fixing means, so that the resulting sandwich is of small thickness and leaves sufficient clearance between the two main plastics sheets to ensure that once the reinforcing cage fitted with the antifriction sandwich has been put into place in the mud-filled trench, the cellular structure fills with said mud, and remains full of mud after the concrete of the wall proper has subsequently been cast therein, thus forming a vertically deformable side pad of mud on the corresponding face of the cast wall, thus having the effect of decoupling lateral friction at the ground/wall interface and greatly limiting residual forces on the surrounding ground during subsequent in-service loading.

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2. A device according to claim 1, wherein each of said plurality of spacers have a first end secured to the main face of the reinforcing cage and an opposite end secured to the main face of the first sheet of plastics material forming the antifriction sandwich, said spacers being disposed outside the reinforcing cage for the cast wall or cast wall element.

3. A device according to claim 1, wherein the sheets constituting the antifriction sandwich are made of high density polyethylene, and the internal deformable cellular structure of said sandwich is constituted by high density polyethylene netting.

4. A method of making a cast wall fitted with an antifriction device according to claims 1 to 3, the method comprising the following steps: a section of trench is dug having the shape of a portion of cast wall to be made, said trench being filled with a conventional type of mud such as bentonite; the reinforcing cage fitted with said antifriction system is put into place in said section of trench, thereby enabling the mud to fill the cellular structure of the antifriction sandwich; and 8 concrete is cast into the said section of trench concerned, the antifriction sandwich remaining saturated in mud, thereby forming a side pad of mud that is deformable relative to future loading of said wall.

5. A method of making a wall according to claim 4, in which an antifriction device is installed on a plurality of faces of the reinforcing cage.

6. A friction reducing structure, said device which is fixable to a structure to be spaced fixed to and spaced arrangement being such to deposit between said sheet and concrete is depositing between said sheet.

device for comprising a cage of such a reinforced first sheet a reinforced therefrom and a second sheet from said first sheet, the that, in use, mud is allowed first sheet and said second substantially prevented from first sheet and said second

7. A friction reducing device or a method of using same in casting a wall substantially as herein described with reference to Figures 2 and 3.