FR2746122A1 - Electro-injection electrode masking sleeve - Google Patents

Abstract

A masking sleeve for an electro-injection electrode comprises: (i) an inner rigid tube (3) round the electrode (1) buried in the soil; and (ii) an inflatable outer tube (4) forming an inflatable chamber which can seal against the inner walls of the surrounding well (2).

Description

MASKING SLEEVE FOR ELECTROINJECTION ELECTRODE
The present invention relates to the technique of consolidating and waterproofing soils, in particular clay soils, by electroinjection of products such as sodium silicates and the like.

 We recall, without needing to go into detail, that the principle of this technique is based on the fact that the silicate injected replaces the water in the soil eliminated by electro-osmosis and electromigration, polymerizes and becomes solid, its progression in the ground taking place in principle horizontally, along an ideally vertical front, between at least one anode and a cathode put under a voltage of the order of a hundred volts and driven vertically into the ground according to the desired treatment height.

 To do this, the silicate solution is injected into the well of one electrode (anode), and the soil water is collected in the other electrode (cathode). The PH is regulated at the two electrodes by adding acid or base to the circuit.

 Any injection of silicates must be homogeneous to be optimal. In practice, there can be a significant lack of homogeneity, due to the differences in the characteristics of the successive layers of the soil, namely their nature with regard to mineralogy, permeability or electrical conductivity, or their state as regards their water content or their compactness. These differences can promote or delay the horizontal progression of the silicate front in these layers, from one electrode to another. This heterogeneity manifests itself in a particularly harmful way when the sodium silicate reaches an electrode only over a small part of its height, which causes it to crystallize and practically stop the phenomenon.

 The object of the present invention is to remedy these drawbacks and to provide means making it possible to make the distribution in the soil of the product thus dispersed by electroinjection between the electrodes of at least one pair of electrodes comprising an anode and a more homogeneous. cathode.

 To this end, the invention relates to a masking sheath for an electro-injection electrode, this electrode normally being surrounded by a strainer tube or the like constituting a well for injection or extraction of water (or silicates), characterized in that it comprises on the one hand a rigid tube suitable for being engaged on the electrode, itself embedded in the ground, between this electrode and said well, and on the other hand an inflatable tubular envelope surrounding said rigid tube and connected by its ends at the ends of the tube so as to constitute around said tube a tight expandable air chamber suitable for being applied by its side wall against the corresponding portion of said well.

 Thanks to this arrangement, it is understood that one will be able to control the preferential paths of the progression of the silicate between the two associated electrodes: if one notices a too great progression at a certain level, one will lower a sheath on each of the electrodes, and we will stop it at the level in question. It will then suffice to inflate the envelope, which will block the sheath at this height in the well and will make it possible to neutralize the electrode on the height of the sheath, this for the time necessary for the silicate to catch up with the part in advance of the forehead, above and below the level considered. Then what we can deflate the envelope, extract the sheath, continue to monitor the progress of the silicate front and replace the sheath at the desired level on the electrodes, if we see at this level a new horizontal progression of the front , faster than at other levels.

 According to additional provisions of the invention, said tube carries at its two ends a rigid ring on the outer surface of which is fixed the corresponding end of said envelope, and in the case of an electro-injection electrode driven vertically into the ground , the upper rigid ring is traversed by a tube connected to an inflation valve.

 The upper rigid ring can also be connected to a guidance system on the electrode, this system being able to use slings or the like.

 Advantageously again, provision can be made for said rings to be made of PVC, as is said tube, and in that the respective ends of said envelope are glued to these rings.

In the attached drawings as examples
- Figure 1 shows schematically in axial section a sheath according to the present invention placed on an electrode but before inflation of the envelope;
- Figure 2 shows schematically the vertical section of a soil being treated before placement of the sleeves, for example during the 5th day of electroinjection; and
- Figures 3 to 5 are views similar to the previous showing the progression of the front of sodium silicate respectively during the 7th, 8th and 9th days of electroinjection, after placement of the sleeves according to the invention.

 In FIG. 1, the electrode, here an anode, has been referenced 1; it is surrounded by a strainer tube 2 forming an injection well for the electrolyte. The sheath according to the invention comprises a tube 3 made of PVC suitable for being engaged on the electrode and at the ends of which are fixed rings also made of rigid PVC 6. An inflatable envelope 4, for example made of rubber, is fixed by its ends on the rings 6, for example by gluing or using collars, so that a sealed annular chamber 5 is thus formed around the tube 3, in the annular space formed between this tube and the injection well 2 Finally, a tube 7 with an inflation valve crosses the upper ring 6, which allows the chamber 5 to be inflated with compressed air.

 As already indicated above, if one wishes to slow the horizontal progression of sodium silicate between two electrodes to a given level, it suffices to lower such a sheath in the deflated state around each electrode (using slings or analogs 8), until the sheath reaches the level considered, then inflate the air chamber 5 by the valve tube 7, this enough so that the inflatable envelope is applied sealingly over the corresponding height of the strainer tube 2, as indicated by the dashed line 4 '. The electrode is then completely neutralized over this height of the envelope, and it is thus possible to slow down the horizontal progression of the silicate front for the desired duration, at the level concerned.

FIG. 2 shows for example a horizontal progression of the silicate front Fs faster in layers of montmorillonite M than in layers of kaolin
K, between the electro-injection electrodes A and C, S representing an intermediate layer of sand. This being noted, the sleeves f of the invention are engaged, for example in accordance with the embodiment of FIG. 1, on the electrodes A and C, and the envelopes 4 are inflated to block the sleeves f at the level indicated on Figure 3.

After two days, it can be seen that the lower front Fi of silicate has progressed, while the upper front Fs has been practically stopped. Same observation the next day (Figure 4). Finally, on the following day (FIG. 5), it can be seen that the lower front Fi of silicate has completely caught up with the upper front Fs, the sleeves f still being in place at the same level.

 We see that we thus obtain a perfect control of the progression of the fronts F5 and Fi and that we will be able to ensure their arrival on the cathode practically at the same time, which guarantees an optimal homogeneity of the electroinjection, and consequently resistance and waterproofing of the treated soil between the electrodes.

Claims (5)

 1. Masking sleeve for electroinjection electrode, this electrode normally being surrounded by a strainer tube or the like constituting a liquid injection or extraction well, characterized in that it comprises on the one hand a rigid tube (3) suitable for being engaged on the electrode (1), itself driven into the ground, between this electrode and said well (2), and on the other hand an inflatable tubular envelope (4) surrounding said rigid tube ( 3) and connected by its ends to the ends of the tube (3) so as to constitute around said tube a tight expandable air chamber (5) adapted to be applied by its side wall (4 ') against the corresponding portion of said well ( 2).  2. Sheath according to claim 1, characterized in that said tube (3) carries at its two ends a rigid ring (6) on the outer surface of which is fixed the corresponding end of said envelope (4).  3. Sheath according to claim 2, characterized in that, in the case of an electro-injection electrode (1) driven vertically into the ground, the rigid rigid ring (6) is traversed by a tube (7) connected an inflation valve.  4. Sheath according to claim 2 or 3, characterized in that the rigid rigid ring (6) is connected to a guide system (8) on the electrode (1).  5. Sheath according to any one of claims 2 to 4, characterized in that said rings (6) are made of PVC, as is said tube (3), and in that the respective ends of said envelope (4) are glued to these rings (6).