EP0565411B1 - Method for making an underground watertight screen and the screen so produced - Google Patents

Abstract

The invention relates to an underground watertight screen extending in a horizontal general direction, comprising at least one stratum consisting of a plurality of solid unitary elements (3) which intersect one another, formed from a mortar or puddled earth (8) or from a hardened slurry, the said unitary elements (3) having the shape of a cone with substantially vertical axis and whose vertex angle theta lies between 60 and 170 DEG inclusive. Application in the field of civil engineering works, for example for producing footings. <IMAGE>

Description

The production of waterproofing screens extending close to the horizontal in the mass of a permeable ground can be obtained by two main types of techniques, injection techniques and rotary jet techniques.

The objective in both cases is the same. It is a question of filling as completely as possible the voids existing between the grains constituting the ground considered so as to reduce the porosity and, consequently, to ensure sealing. This is obtained by the introduction into the ground of an exogenous material giving rise to a setting phenomenon.

In the case of the injection technique, the sealing material is introduced under pressure into the ground in question, in liquid form called grout (suspension or true liquid) from boreholes, so as to penetrate the existing porosity of the ground up to '' to impregnate it as completely as possible. In this technique, the existing structure of the land is practically preserved.

In the case of the jet technique, the exogenous material or grout is introduced into the ground considered also from drilling but in the form of a jet oriented horizontally at high speed which, on its trajectory, destructs the ground in place, and, depending on the nature of said terrain, either mixes with the constituent elements of the latter and leads, after setting, to the formation of a mortar or soil concrete (case, for example, gravelly or sandy soils), or replaces purely and simply the ground and leads, after setting, to the formation of a hardened grout (case, for example, clayey grounds). The jet, depending on the flow, the driving pressure and terrain characteristics, has a certain radius of action. If the tool ensuring the formation of the jet is set in slow rotation-translation inside the borehole, a more or less cylindrical volume of treated ground is obtained having as a radius the radius of action of the jet under the conditions considered, and a height corresponding to the amplitude of the translational movement.

It is easily understood that it is thus possible to produce, by this jet technique, sealing screens of extension close to the horizontal by the juxtaposition of a plurality of cylindrical elements (or columns) of ground thus treated. over a certain height, produced from a mesh of substantially vertical parallel boreholes of density such that the elements or columns intersect so as to constitute a continuous solid mass.

This continuity, imperative since we aim to achieve a watertight structure, requires a perfect mastery of all the construction parameters and, in particular, of the radius of action of the jet, of the precision of implantation of the wells and their precision. execution space (treatment rating, drilling impacts at the treatment level).

This control is difficult to ensure, on the one hand, due to the variability of the radius of action of the jet depending on the terrain encountered, but above all, on the other hand, due to the imprecision inherent in carrying out the drilling. processing, inaccuracy the greater the greater the screen depth.

All this leads to the provision of a density of treatment points and a treatment height (at least of the order of a meter) much greater than would be theoretically necessary.

The invention aims to provide in particular a method of producing, by a rotary jet technique, underground sealing screens of general extension close to the horizontal which overcomes the difficulties mentioned above and their repercussions on the design, safety and cost of the operation.

More specifically, the invention relates to a method for producing an underground sealing screen extending in a generally horizontal direction, by forming, by the rotary jet technique, a plurality of solid unitary elements which intersect continuously. between them, consisting of a mortar or concrete floor or a hardened grout of mineral nature, said process employing for the formation of said elements, at least one jet forming with the horizontal an angle α between 5 and 60 ° inclusive.

The invention also relates to an underground waterproofing screen, extending in a general horizontal direction, comprising at least one stratum consisting of a plurality of solid unitary elements intersecting without discontinuity with each other, formed of a mortar or concrete of soil or a hardened grout of a mineral nature, said unit elements having the shape of a cone with a substantially vertical axis and whose apex angle θ is between 60 and 170 ° inclusive, preferably between 100 and 160 °.

For the implementation of the method of the invention, one can use a jet device comprising a train of tubes fed with grout under high pressure, intended to be introduced into a borehole and comprising at its lower part at least one nozzle. ejection, said nozzle forming with the train of tubes an angle β between 30 and 85 ° inclusive, preferably between 50 and 80 ° inclusive.

The use of at least one jet inclined with respect to the horizontal leads to the formation of a unitary element of conical shape, resembling a Chinese hat. Depending on the operating conditions and the terrain encountered, each elementary cone may have, at its base, a diameter of 0.5 m to several meters.

Due to the taper of the unit elements, a unit element will overlap, without discontinuity, with the adjacent unit elements even if there is a certain level shift during the execution of these elements. In other words, the method of the invention allows greater tolerance in the precision of the drilling to be carried out.

In addition, because it provides a greater guarantee of continuity, the method of the invention makes it possible to considerably reduce the thickness of the sealing screen. While the prior art required to produce unit elements with a thickness of 1 meter or more to guarantee the continuity and therefore the sealing of the screen, the present process makes it possible to be satisfied with a thickness of the order of 5 to 100 cm, preferably 5 to 40 cm, for the elementary cones, which saves time, material and cost which can be significant.

The jets used for implementing the process of the invention can be of any known type, that is to say consist of a simple jet of grout of a mineral nature, or a jet of grout surrounded by '' an annular air jet to increase the radius of action, or a combination of a water jet surrounded by an annular air jet ensuring the destructuring of the ground and a separate grout jet , usually provided at a level lower than that of the water jet.

As an indication, a jet device can be used comprising a central for producing a cement grout supplying in grout one or more pumps connected, by means of a rotary joint, to a train of tubes introduced into the borehole vertical where the jet treatment should be done. The tube train can be driven in translation and rotation by means of a hydraulic rotary head enclosing the upper end of the tube train, which is itself mounted on a drilling slide. The pump (s) deliver the fluid destructuring agent (grout or water) at pressures of the order of 200 to 700 bars or more.

The tube train is formed of connectable unitary tubular sections provided with suitable seals and each section can be formed of a single tube (single jet) or of several coaxial tubes (double or triple jet). Liquids (grout, water) are ejected through one or more nozzles with a diameter of 2 to 4 mm approximately. The tube train sections can have a diameter of approximately 50 to 200 mm.

One can use a device producing a single jet, or two or more jets. In the case of a single jet, a conical unitary element can be produced simply by rotating the train of tubes introduced into the previously drilled hole while maintaining it at a given dimension. One can also make a first conical unitary element as described above, then make one or more others, superimposed on the previous one, simply by raising the train of tubes in the borehole and recommencing the operation of forming the unitary cone at the new rating reached. The dimensions chosen can be such that the successive cones produced are distinct from each other or else merged to form a thicker cone. In the case of the use of a two-jet ejection device, these can operate at the same level (2 jets at 180 ° for example) or at separate levels. These jets can both be oriented upwards or downwards, or one (the lower jet in general) can be directed downwards and the other (the upper jet in general) can be oriented upwards . One can also use a device simultaneously generating several jets, for example 3 or 4, as will be obvious to those skilled in the art. Rather than keeping the jets at a fixed dimension during the operation, the tool can also be animated with a vertical movement over a certain range of dimensions, so as to "thicken" the conical unitary element.

Depending on the device used and, consequently, the jet configuration produced, it is therefore possible to obtain a simple sealing screen, consisting of a single layer formed of a plurality of intersecting cones or a multiple sealing screen formed two or more superimposed strata each formed of a plurality of intersecting cones. The strata can be formed of cones oriented in the same direction, that is to say up or down, or of cones oriented in opposite directions (a lower stratum being formed for example of cones oriented up and another upper stratum being formed of cones oriented downwards). The strata can be spaced from each other, tangent to the point of the cone vertices, or even intersect each other, as desired.

The angle β that each jet forms with the vertical, whether this jet is oriented downwards or upwards, must be at most 85 ° because, above this value, elementary cones are obtained which are too flattened, it would not be possible to guarantee the intersection with the adjacent cones. Neither is it desirable for the angle β to be less than approximately 30 ° because below this value elementary cones are obtained which are too pointed, with a small diameter at the base, which would make it necessary to considerably increase the density of the drilling to be carried out for the implementation of the jet technique and would therefore be uneconomic. An angle β of between 50 and 80 ° is preferred, which corresponds to a conical unitary element whose apex angle θ ranges from 100 to 160 ° inclusive.

Finally, it should be noted that, if desired, the sealing screen of the invention can be formed of conical unitary elements whose apex angles θ may not be the same everywhere. The angles at the top can vary from one zone to another of a given stratum and / or vary from one stratum to another.

• La figure 1 est une vue schématique en coupe verticale d'un écran d'étanchéité souterrain selon l'invention ;
• La figure 2 est une vue schématique selon la ligne de coupe II-II de l'écran de la figure 1 ;
• La figure 3 est une coupe schématique partielle à plus grande échelle de l'écran de la figure 1 ; et
• Les figures 4 à 6 illustrent trois variantes de réalisation de l'écran selon l'invention.

The description which follows, made with reference to the drawings, will make the invention clear.

• Figure 1 is a schematic vertical sectional view of an underground sealing screen according to the invention;
• Figure 2 is a schematic view along the section line II-II of the screen of Figure 1;
• Figure 3 is a partial schematic section on a larger scale of the screen of Figure 1; and
• Figures 4 to 6 illustrate three alternative embodiments of the screen according to the invention.

Figures 1 and 2 show an underground sealing screen according to the invention which is a slab 1 made in the ground at the location of an excavation to be carried out later, but delimited by a wall 2 previously molded in the ground. The raft 1 is made up of a multiplicity of unitary elements 3, of conical shape, which intersect, as shown in FIG. 2.

As illustrated in FIG. 3, each unitary element is produced by supplying curable mineral grout, under high pressure, a train of tubes 4 provided at its lower part with a side nozzle 5 oriented downwards and introduced into an oversized borehole such as 6, then slowly rotating the train of tubes 4 on itself while maintaining it at a stationary level. The jet of grout 7 ejected destroys the ground encountered and either mixes with the constituent elements of the latter to form, after hardening, a mortar or concrete floor 8, or replaces the ground to form, after hardening, a hardened grout, depending on the nature of the soil.

Figures 4 to 6 illustrate various variants according to the invention.

In Figure 4, there is shown a screen formed of two superimposed strata 11 and 12 each formed of a plurality of conical unitary elements 3 similar to those of Figures 1-3. Such a screen can be produced simply by forming, from each borehole, a first unitary element, then slightly raising the conduit 4 in the borehole, a second unitary element overhanging the first. Alternatively, one could use a train of tubes provided with two spaced nozzles, maintained at a stationary level.

In Figure 5, there is shown a sealing screen formed of two layers 21 and 22 each formed of a plurality of conical unitary elements 3, the cones formed from the same borehole being in opposite directions with their vertices contiguous. Such geometry is easily obtained by using a train of tubes provided with two nozzles situated substantially at the same level but directed one downwards and the other upwards.

FIG. 6 shows a sealing screen similar to that of FIG. 5, except that the tops of the cones formed from the same borehole are spaced instead of being contiguous. Such a geometry is obtained by using a train of tubes provided with two superposed spaced nozzles, one directed downwards and the other upwards.

It goes without saying that the embodiments described are only examples and that they could be modified, in particular by substitution of technical equivalents, without departing from the scope of the invention as defined by the claims.

Claims (8)

1. An underground watertight screen (1), extending in a generally horizontal direction, caracterized in that it comprises at least one stratum consisting of a plurality of solid unit elements (3) intersecting each other without discontinuity between them and formed of a soil concrete or mortar (8) or of a hardened grout of inorganic nature, the said unit elements having the shape of a cone with a substantially vertical axis and of which the angle at the apex θ is between 60 and 170° inclusive.
2. Screen according to Claim 1, in which the angle at the apex of the cone is between 100 and 160° inclusive.
3. Screen according to Claim 1, in which the unit cones have their apex directed towards the ground surface.
4. Screen according to Claim 1, which comprises a single stratum of unit elements.
5. Screen according to Claim 1, which comprises two strata of unit elements.
6. Screen according to Claim 1, in which the conical unit elements have a thickness of the order of 5 to 40 cm.
7. A method for producing an underground watertight screen (1) extending in a generally horizontal direction, caracterized in that it comprises forming, by means of the rotary jet technique, a plurality of solid unit elements (3) intersecting each other without discontinuity between them, made of a soil concrete or mortar (8) or of a hardened grout of inorganic nature, the said method employing, for the formation of the said elements, at least one jet (4) forming with the horizontal an angle α of between 5 and 60° inclusive.
8. Method according to Claim 7, in which the angle α is between 10 and 40° inclusive.

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