Method and device for freezing a mass of soil

Abstract

A method for freezing and treating a mass of soil, making it possible to compensate for deformations of the mass of soil during thawing, including the following steps: a) producing at least one bore (2) in the mass of soil, b) at least partly freezing the mass of soil using a freezing fluid injected into the bore, and then c) injecting a compensation grouting into the mass of soil, using the bore (2) that was used for freezing, during the thawing phase in order to at least partly compensate for variations in the volume of the mass of soil when the latter thaws.

Claims

1. A method for freezing and treating a mass of soil, making it possible to compensate for deformations of the mass of soil during thawing, including the following steps: a) producing at least one bore in the mass of soil, b) at least partly freezing the mass of soil using a freezing fluid injected into the bore, and then c) injecting a compensation grouting into the mass of soil, using the bore that was used for freezing, during the thawing phase in order to at least partly compensate for variations in the volume of the mass of soil when the latter thaws, the bore being produced by means of a drilling tube with or without sleeves equipped at the end with a drilling tool, the drilling tube being left in place during the freezing step and during the step of injecting the compensation grouting, and the drilling tube being embedded in the mass of soil by injecting an embedding grouting and then being cleanable to drain it off the embedding grouting before the freezing operation.

2. The method as claimed in 1, the compensation grouting being injected at a pressure sufficient to fracture the embedding grouting.

3. The method as claimed in claim 1, the freezing operation being performed by introducing a freezing probe into the bore.

4. The method as claimed in claim 3, in which a thermally conductive fluid is used to fill a space provided around the freezing probe in the drilling tube.

5. The method as claimed in claim 3, the freezing probe including an outer tube and an inner tube disposed inside the outer tube.

6. The method as claimed in claim 1, the compensation grouting being injected with the aid of an injection tube introduced via a plug disposed in the drilling tube.

7. The method as claimed in claim 6, the compensation grouting being injected at least two levels into the mass of soil, by moving the plug in the drilling tube and using orifices of the latter located at least two different heights on the tube.

8. The method as claimed in claim 1, the freezing operation being performed by introducing a freezing probe into the drilling tube in place.

9. An assembly designed for execution of the method as claimed in claim 1, including a drilling tube equipped with a drilling tool, a tube for injecting compensation grouting, the drilling tube being configured to receive the injection tube during the thawing phase, and a freezing probe configured to be fixed removably in the drilling tube.

10. A method for freezing and treating a mass of soil, making it possible to compensate for deformations of the mass of soil during thawing, including the following steps: a) producing at least one bore in the mass of soil, b) at least partly freezing the mass of soil using a freezing fluid injected into the bore, and then c) injecting a compensation grouting into the mass of soil, using the bore that was used for freezing, during the thawing phase in order to at least partly compensate for variations in the volume of the mass of soil when the latter thaws, the freezing operation being performed by introducing a freezing probe into the bore, the method including a step of withdrawing the freezing probe before injecting the compensation grouting.

11. An assembly for freezing and treating a mass of soil, making it possible to compensate for deformations of the mass of soil during thawing, including the following steps: a) producing at least one bore in the mass of soil, b) at least partly freezing the mass of soil using a freezing fluid injected into the bore, and then c) injecting a compensation grouting into the mass of soil, using the bore that was used for freezing, during the thawing phase in order to at least partly compensate for variations in the volume of the mass of soil when the latter thaws, the freezing operation being performed by introducing a freezing probe into the bore, the freezing probe including an outer tube and an inner tube disposed inside the outer tube.

Description

DESCRIPTION OF THE FIGURES

(1) Other features and advantages of the present invention will emerge on reading the following detailed description of nonlimiting embodiments thereof and examining the appended drawings, in which:

(2) FIG. 1 is a diagrammatic partial view in longitudinal section of a drilling device according to the invention,

(3) FIG. 1a is a cross section taken along the line A-A in FIG. 1,

(4) FIGS. 1b and 1c are views analogous to FIG. 1a of variant embodiments,

(5) FIGS. 2 to 8 are views analogous to FIG. 1 illustrating the freezing and treatment method according to the invention, and

(6) FIGS. 2a to 6a are cross sections taken along the line A-A in FIGS. 2 to 6, respectively.

DESCRIPTION OF EXAMPLE EMBODIMENTS

(7) There has been shown in FIGS. 1 and 1a a drilling device 1 in place in a bore 2 produced in a mass of soil T. A segment V may be present, as shown, the drilling device 1, which remains accessible externally E, passing through it.

(8) The drilling device 1 is for example fixed to the segment V by a plate 4 that in the example described is curved to follow the curvature of the latter. Of course, the mass of soil T may have no segment V.

(9) The drilling device 1 includes a drilling tube 10 which in the example described is equipped at the end with a drilling tool 15.

(10) The tube 10 receives a freezing probe 20 mechanically coupled to the drilling tube 10 by a connecting strapping 16. The freezing probe 20 is configured to allow the circulation of a cold fluid, namely brine in the example considered.

(11) The freezing probe 20 includes an outer tube 21 and an inner tube 22 disposed inside the outer tube 21. The fluid circulates between an inlet 24 and an outlet 26, in the direction of the arrows, namely descends inside the tube 22 and rises via the tube 21 around the tube 22. The freezing probe 20 may as shown include purge valves 25.

(12) The tube 10 is provided in this example with outlets consisting of orifices made through the wall at various heights, these orifices being normally blocked by sleeves 11.

(13) The drilling tube 10 enables reception of a tube 30 for injecting compensation grouting and preferably includes means for selecting the height of injection of the compensation grouting into the bore by enabling selection of the grouting outlet orifices thanks to at least one plug, as described later.

(14) In the variant shown in FIG. 1b, the freezing probe introduced into the drilling tube 10 includes only one tube instead of an inner tube and an outer tube. In this case, the freezing fluid arrives via this single tube and exits via the exterior inside the drilling tube 10.

(15) In the variant from FIG. 1c the mass of soil is sufficiently coherent for it not to be necessary to leave the drilling tube 10 in place. In this case, the compensation grouting injection tube 30 and the freezing probe 20 may be embedded one beside the other in the bore 2 by means of an embedding grouting.

(16) The freezing method using the device from FIG. 1 will now be described in more detail with reference to FIGS. 2 to 8 and 2a to 6a.

(17) In a first embodiment shown in FIGS. 2 and 2a at least one bore 2 is produced in the mass of soil. The drilling tube 10 equipped at the end with a drilling tool 15 is used for this purpose. During drilling, the sleeves 11 are preferably protected, as shown, by protective sheaths 12 that cover them.

(18) The drilling tube 10 may be lubricated during the drilling operation in a manner known in itself thanks to a check valve 16 placed at the bottom of the drilling tube 10 that enables water to be injected onto the tool 15.

(19) In a second step shown in FIGS. 3 and 3a the drilling tube 10 may be embedded in the bore 2 by injecting an embedding grouting 50. The latter is injected into the drilling tube 10 and expands outside it via the valve 16.

(20) Residual embedding grouting inside the drilling tube 10 is then eliminated to leave only the useful embedding grouting 50, namely that situated between the wall of the bore 2 and the outside of the drilling tube 10, as shown in FIGS. 4 and 4a.

(21) The freezing operation is effected by first introducing the freezing probe 20 described above into the drilling tube 10 as shown in FIGS. 5 and 5a. The annular void between the probe 20 and the tube 10 is filled with a thermally conductive fluid, for example brine, so as to provide satisfactory thermal conductivity between the two and thereby to favor the cooling of the latter.

(22) Before effecting this filling, the seal of the embedding of the drilling tube to the ground may be tested with water so as not to introduce into the ground a fluid that cannot be frozen.

(23) The method then includes the step of chilling and freezing the mass of soil, during which a cryogenic fluid, in particular brine, is caused to circulate in the freezing probe, as shown in FIGS. 5 and 5a. The latter circulates in the probe between the inlet 24 and the outlet 26.

(24) When chilling is not necessary the thermally conductive fluid present around the freezing probe in the drilling tube 10 may be drained and the freezing probe withdrawn.

(25) The compensation grouting injection tube 30 is then introduced into the drilling tube 10, as shown in FIGS. 6 and 6a.

(26) A plug 61 may be placed in the drilling tube 10 so that the grouting exits only via the orifices of the tube 10 situated short of the plug 61. The latter is for example an inflatable bladder through which the injection tube 30 passes.

(27) Compensation grouting 55 is then injected into the mass of soil with the aid of the tube 30, using the bore 2 that was used for freezing.

(28) During injection of the compensation grouting the sheaths 12 protecting the sleeves 11 are expelled by the injection pressure. At the level of the orifices covered by the sleeves 11 the embedding grouting 50 bursts enabling the compensation grouting to pass because of the high pressure used to inject the latter.

(29) In FIG. 6 the plug 61 is disposed so that the compensation grouting is injected via the lowest outlets of the tube 10.

(30) The compensation grouting may nevertheless be injected at at least two different levels into the mass of soil, as shown in FIG. 7, rising once injection via the lowest outlets is finished, the plug 61 in the drilling tube 10 above other outlets. Other plugs may moreover be disposed so as to select the zones of the drilling tube where it is wished to inject the cement grouting.

(31) Injection may therefore be carried out selectively, and the timing and the depth of injection of compensation grouting may be controlled as a function of the progress of the thawing of the mass of soil and the evolution of the stability of the latter.

(32) Bulbs 40 of compensation grouting are obtained around the bore 2, in particular at the level of the sleeves 11 of the drilling tube 10.

(33) Finally, in a final step shown in FIG. 8, the drilling tube 10 may be cleaned after injection of the compensation grouting 55.

(34) Of course the invention is not limited to that examples that have just been described and the drilling tube as well as the freezing probe may be produced differently without departing from the scope of the present invention. The freezing probe is for example adapted to circulate liquid nitrogen. The drilling tube may have no sleeves or be configured differently.