EP0041425A1 - Method of making drain trenches - Google Patents

Abstract

1. Process for providing drainage trenches according to which : (a) a trench (1) is dug in the ground, and (b) the trench is filled with a filtering material (3), characterized in that step (a) is carried out whilst the trench is filled with a degradable pseudoplastic slurry (2), then step (b) is carried out by introducing the filtering material into the trench filled with the slurry.

Description

The invention relates to a method of producing draining trenches as well as the draining trenches thus produced.

It is often necessary to get rid of the presence of water in the soil, either temporarily to facilitate the realization of buried works, or definitively to protect existing works against groundwater or to remove them. harmful effects, in particular from the point of view of stability, on the soil itself.

Draining trenches (trenches filled with permeable filtering material and equipped or not in their lower part with a longitudinal tubular drain) would in many cases provide a particularly well-suited response to the problems posed if their realization did not often come up against difficulties that are technically or economically difficult to overcome as soon as they have to penetrate more or less deeply into the aquifer.

It is known, in fact, to routinely make draining trenches of shallow depth, of the order of a meter, which are fitted with a flexible filter tube as the trench opens. The speed of the operations, given the small size of the structure, enables the trench to be fitted and closed before the phenomena of landslides in the walls of the excavation compromise the very execution of the structure. This is how agricultural drains are put in place allowing drainage of cultivable land to drain.

If it was desired to make deeper trenches, it would be essential to put in place shielding and retaining devices for the walls supplemented by means of dewatering infiltration water in the trench itself, or lowering the water table. phreatic by pumping boreholes installed on both sides of the excavation route, the works that we propose to execute being by definition located in aquiferous ground.

There is a well-known process for producing very deep trenches which makes it possible to overcome very technically and economically heavy constraints that constitute the shields, retaining and pumping mentioned above. This process consists in carrying out the excavation of the trench under the protection of a bentonite mud, as in the well-known technique of execution of the walls molded in the ground.

However, the use of bentonite mud as a temporary agent for supporting the walls of the excavation is fundamentally incompatible with the equipment and the very functioning of the draining trench. ,

On the one hand, in fact, the supporting effect of the bentonite suspension is schematically based on the penetration of this mud into the ground in the vicinity of the excavation, more or less deeply depending on the permeability of the formation, and the creation of 'a waterproof membrane, or "cake", on the same wall of the excavation. These two phenomena combined could only later oppose the circulation of the water contained in the soil towards the draining trench.

On the other hand, the very equipment of the trench in a draining trench could not be done due to the presence of the bentonite suspension. This equipment is, in fact, mainly constituted by filling the trench with a permeable filtering material (for example calibrated gravel), filling which would be completely clogged by the suspension at the very moment of its installation.

The object of the invention is therefore to provide a method which makes it possible to produce very deep draining trenches without requiring the use of equipment which is complicated to implement.

• a) on creuse une tranchée dans le sol, et
• b) on remplit la tranchée avec un matériau filtrant, caractérisé en ce qu'on effectue l'étape (a) tandis que la tranchée est remplie d'une boue pseudo-plastique dégradable, puis on effectue l'étape (b) en introduisant le matériau filtrant dans la tranchée remplie de boue.

The invention relates to a method of producing draining trenches according to which:

• a) a trench is dug in the ground, and
• b) the trench is filled with a filtering material, characterized in that step (a) is carried out while the trench is filled with a degradable pseudo-plastic mud, then step (b) is carried out by introducing the filter material in the trench filled with mud.

If desired, step (b) can be preceded by the installation, at the bottom of the trench, of a collection and drainage tube.

The invention also relates to the draining trenches produced by the method of the invention.

The degradable pseudoplastic mud used in the process of the invention is a known product which is used as a circulation fluid in carrying out drilling. This sludge consists of a colloidal solution of a natural or biopolymer polymer which is, at rest, in the form of a gel. This mud is easily prepared by dissolving the polymer in the dry state in water (dosage of the order of 5 to 10 parts of polymer per 1000 parts of water) and has the remarkable properties of having a pseudo behavior. - plastic (that is to say to be fludifiable by shearing) and to be degradable or reversible, that is to say to return to a fluid state (similar to that of water) at the end of 'some time. This return to the fluid state takes place by hydrolysis of the polymer, either by a phenomenon of enzymatic bio-degradation which can be controlled by the addition of inhibitors, or by a voluntary chemical action. The natural polymers or biopolymers suitable for the preparation of degradable pseudoplastic mud are, for the most part, heteropolysaccharides prepared from seeds of legumes and are commercially available from various sources. By way of nonlimiting examples, mention may be made of RHODOPOL 23 sold by the company RHONE-POULENC, FORAGUM HM sold by the company CECA S.A., and REVERT sold by the company JOHNSON. Advantageously, refer to the instructions for use of these products for more details on the preparation and degradation of pseudoplastic mud.

This gel-like mud makes it possible to excavate the trench without the risk of landslides or collapse of the walls of the trench. In a way, this mud plays the same role as bentonite mud used in the excavation of trenches intended to receive concrete for the realization of walls molded in the ground. However, the pseudoplastic mud used has the advantage of not clogging either the filtering material placed in the draining trench or the walls of the trench, being degradable into a fluid residue similar to water. Its pseudoplastic behavior (fluidizable by shearing) makes, moreover, that it does not hinder the installation of the filtering material, nor that of a tube of collection and possible drainage.

The nature of the filter material used is not critical. To date, it is preferred to use a calibrated, rolled or crushed natural gravel, but one could also use an artificial granular material such as balls of expanded clay, glass, etc.

Instead of filling the trench with loose filtering material, we could equip the trench with prefabricated drainage panels made, for example, of agglomerated granular materials (agglomerated calibrated gravel, agglomerated expanded clay balls, etc.) or materials permeable in their mass (porous concrete or any material with a high open porosity).

We can also consider a composite filling combining, for example, prefabricated draining panels occupying the central part of the trench and a loose filtering material (such as gravel) filling the lateral spaces existing between the panels and the walls of the trench. .

Finally, in the case of the use of a bulk filtering material, provision may be made to interpose a porous sheet, for example a nonwoven textile web, between the loose filter material, on the one hand, and the walls and bottom of the trench, on the other hand, in order to prevent the surrounding ground from mixing with the filter material and clogging it more or less at the end of a certain time. The use of such a porous separating sheet also allows the use of uncalibrated gravel.

The process of the invention can be carried out continuously or discontinuously.

The description which follows with reference to the appended drawing given by way of nonlimiting example will make it clear how the invention can be implemented, the features which emerge both from the drawing and from the text which, of course, form part of the said invention.

Figure 1 is a schematic sectional view illustrating a continuous implementation of the method of the invention; and Figure 2 is a schematic sectional view illustrating a discontinuous mode of implementation of the method of the invention.

Figure 1 illustrates the continuous construction of a draining trench. In this figure, we see a trench 1 excavated continuously under the protection of a degradable pseudoplastic mud 2 having, in the absence of shear, the consistency of a gel. As soon as a trench length greater than the length corresponding to the natural slope of the filtering gravel to fill the trench is executed, the placement of the filter gravel 3 begins, generally by directly pouring the gravel into the mud filling the trench . If, as illustrated in the figure, we have chosen to also equip the trench with a drainage tube and collection 4 serving of drainage water collector, this tube is placed on the bottom of the trench before pouring of the filter material 3. The tube 4 can consist, for example, of a flexible or semi-flexible tube, made of plastic, perforated on all or part of its circumference. The excavation of the trench progresses at 5 while the gravel 3 is poured into the portion of trench already excavated.

The lifespan of the sludge is adjusted according to the various parameters influencing it (pH of the water, chemical composition, temperature, etc.) so that the degradation of the sludge in a given area of the trench does not intervenes only after completion of the equipment of the trench with the drainage tube and of its filling with the filtering material. Any indication necessary for this adjustment of the lifespan of the sludge can be found in the notices relating to the natural polymers or biopolymers of commerce used.

Once the mud has degraded (after a time that can vary from a few hours to a few days) into a residue similar to water, the draining trench is ready to operate.

FIG. 2 illustrates an alternative implementation of the method of the invention according to which the draining trench is produced by successive sections. In this variant, one excavates, under the protection of the degradable pseudoplastic mud 2, a section In of trench. Once the section 1a has been excavated, the drainage and collection tube 4 is put in place, if one is used, at the bottom of the section 1a, then a temporary formwork element 6 is placed at the end of the section 1a, this element 6 used to retain the filter gravel on the one hand, and to protect the tube 4 on the other hand, the latter being housed in a recess in the formwork. It is then possible, after the installation of the formwork 6, pour the filtering gravel 3 into the section la of the trench.

Then, the section 1a of the draining trench being completed, the section 1b of the trench is excavated under degradable pseudoplastic mud, the tube 4 is unwound on its bottom, the formwork 6 is removed from the end of the section 1a to put it in the end of the section 1b, the gravel 3 is poured into the section 1b, and so on until completion of the draining trench.

Of course, instead of making the draining trench in successive sections, one could operate in alternating sections as will be obvious to those skilled in the art. However, in this case, it is not possible to install collection and drainage tubes, at least in a simple manner.

The geometrical characteristics of the draining trench (length, depth, location, etc.) must be adapted to the topography and nature of the terrain considered, ensuring in all cases the evacuation of the drainage water thus collected.

The invention is useful in particular for the stabilization by drainage of embankments and slopes in limit equilibrium. case frequently encountered during the execution of large earthworks necessary for the construction of motorways, railways, canals, etc. Until now, this stabilization by drainage was carried out from a network of slightly drilled ascending, generally executed from the side of the land concerned. It is easy to see that the "one-dimensional" works that constitute drainage boreholes are, in general, much less effective than one or more draining trenches suitably arranged continuously cutting the soil from which it is proposed to extract the water to stabilize it, and all the more so if the latter is in the form of circulation randomly distributed in the mass of the ground.

The improvement constituted by the present invention makes it possible to produce such draining trenches under excellent conditions of economy and result whatever the nature of the soft ground encountered.

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

Claims (7)

1. Method for making draining trenches according to which a) a trench (1) is dug in the ground, and b) the trench is filled with a filter material (3), characterized in that step (a) is carried out while the trench is filled with a degradable pseudoplastic mud (2), then the step ( b) by introducing the filtering material into the trench filled with mud. 2. Method according to claim 1, characterized in that step (b) is preceded by the establishment, at the bottom of the trench, of a collection and drainage tube. 3. Method according to claim 1, characterized in that the filtering material is a bulk material. 4. Method according to claim 1, characterized in that the filtering material consists of prefabricated panels. 5. Method according to claim 1, characterized in that the filtering material is constituted by a combination of prefabricated panels and bulk material. 6. Method according to claim 3 or 5, characterized in that a porous sheet is interposed between the bulk material, on the one hand, and the walls and the bottom of the trench, on the other hand. 7. The draining trenches produced by a method according to any one of claims 1 to 6.

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