Ground freezing method

Abstract

A method and a device for freezing the ground are provided with a freeze pipe closed on one front side, and an inner pipe extending into the freeze pipe for supplying a cooling agent, and wherein a hollow body is provided, whose inner diameter is larger than the outer diameter of the freeze pipe.

Claims

1. A ground freezing method comprising using a freeze pipe and an inner pipe extending into the freeze pipe, wherein a cooling agent selected from the group consisting of liquid nitrogen and aqueous saline solution is guided into the freeze pipe via the inner pipe, wherein a hollow body comprising a polymer material having a wall thickness less than 6 millimeters with an inner diameter larger than the outer diameter of the freeze pipe is introduced into the ground, and the freeze pipe is introduced into the hollow body, wherein a contact medium having a freeze point of at most 0 C. is introduced into a op between the hollow body and the freeze pipe and the freeze pipe and/or the contact medium are heated by an electric heater before removing the freeze pipe and the freeze pipe is removed from the hollow body after the ground has been frozen.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention along with additional details of the invention will be explained in more detail below based on exemplary embodiments schematically depicted on the drawings. Shown on:

(2) FIG. 1 is a first embodiment of a ground freezing device according to the invention,

(3) FIG. 2 is a second embodiment,

(4) FIG. 3 is a third embodiment,

(5) FIG. 4 is a fourth embodiment,

(6) FIG. 5 is a fifth embodiment, and

(7) FIG. 6 is a sixth embodiment of the invention.

(8) In all figures, the same elements are provided with the same reference numbers.

DETAILED DESCRIPTION OF THE INVENTION

(9) FIG. 1 schematically depicts a first embodiment of the invention. A freeze pipe 1 made out of a readily heat conducting material, in particular out of copper, has a diameter of 50 to 100 mm, for example. For example, the length of the freeze pipe measures 1 to 50 m, often 10 m to 30 m.

(10) The freeze pipe 1 is closed on its lower front side 2. The upper front surface 3 is also closed, but exhibits two passages 4, 5 for an inner pipe 6 and an exhaust pipe 7. The inner pipe 6 is open at the lower end 8. A nitrogen tank is connected to the inner pipe 6 by a supply line not shown on the drawing.

(11) A borehole is drilled into the ground 9 to be iced, into which a hollow body 10 is introduced. The hollow body 10 consists of a polytetrafluoroethylene, and has a wall thickness of 0.5 to 6 mm. The hollow body 10 is designed as a cladding tube, and closed at its lower, front end 12.

(12) A heat carrier line 11 is then placed in the hollow body 10. The heat transfer line 11 can be designed either as a hose or as a flexible or inflexible pipe. The heat carrier line 11 is situated in such a way as to be located as close as possible to the hollow body 10, thereby leaving enough space for the freeze pipe. The heat carrier line 11 runs both along the jacket of the hollow body 10 as well as along its floor or front surface 12. The heat carrier line is connected to a feeder for a warm or hot fluid, in particular air or an aqueous saline solution.

(13) The freeze pipe is then pushed into the hollow body 10, so that the heat carrier line 11 comes to lie in the gap 13 between the freeze pipe 1 and hollow body 10.

(14) The gap 13 is finally filled with a liquid contact medium 14, for example with an aqueous saline solution or water.

(15) In order to ice the ground 9, liquid nitrogen is supplied via the inner pipe 6, and guided into the interior of the freeze pipe 1. The liquid nitrogen cools the ground 9 via the surrounding contact medium 14. The nitrogen evaporates in the process. The evaporated, cold gaseous nitrogen, which is also referred to as exhaust, extracts additional heat from the ground. A solenoid valve (not shown) is controlled via the temperature of the exhaust. This ensures a constant flow of nitrogen at an optimal efficiency.

(16) After some time, a frozen region forms around the freeze pipe 1. Once icing is complete, it is in some instances advantageous to remove the freeze pipes 1 from the ground, since the latter may impede subsequent construction progress. For example, whole section boring machines may not be able to pass through the steel or copper pipes used as the freeze pipes 1.

(17) According to the invention, the freeze pipes 1 are pulled out of the ground 9 or out of the hollow body 10 in such a case. To this end, a gaseous heat carrier is first guided through the heat carrier line 11. If the freeze pipe cooled beforehand with liquid nitrogen, a heat carrier with a temperature exemplarily ranging between 50 C. and 0 C. can initially also be used. For example, evaporated gaseous nitrogen can be taken directly out of a nitrogen tank in this phase. As a rule, however, use is made of a heat carrier with a higher temperature, for example of 50 C. to 200 C., e.g., heated air or heated nitrogen gas, so as to more quickly melt and heat the contact medium.

(18) The heat carrier flows through the heat carrier line 11, and in the process heats the surrounding contact medium 14. If the contact medium 14 was in a solid aggregate state, it is again liquefied. Otherwise, at least the viscosity of the contact medium 14 is decreased by heating, so that the contact medium 14 becomes more flowable, and the freeze pipe 1 can be moved more easily in the contact medium 14.

(19) If the contact medium 14 is liquid or has reached a specific flowability, the freeze pipe 1 is pulled out of the hollow body 10 with a pulling device not shown on the drawing.

(20) FIG. 2 shows an alternative embodiment of the invention. This embodiment differs from the one on FIG. 1 in that the heat carrier line 11 is wound around the freeze pipe 1. The heat carrier line 11 is helically wrapped around the freeze pipe 1. On the one hand, the advantage to this is that the freeze pipe 1 together with the heat carrier line 11 can be easily pushed into the hollow body 10. On the other hand, winding the heat carrier line 11 around the freeze pipe 1 results in a uniform heating of the contact medium 14.

(21) FIG. 3 shows an embodiment of the invention in which the heat carrier line 11 runs partially through the ground 9. A borehole 15 having a larger diameter than the hollow body 10 is here first drilled. The heat carrier line 11 is guided through the wall of the hollow body 10, runs along the lower front surface 12 of the hollow body, and is taken out again on the opposite side of the hollow body 10.

(22) The hollow body 10 is introduced into the borehole 15 along with heat carrier line 11. As described above, the freeze pipe 1 and contact medium 14 are then placed in the hollow body 1. The heat carrier line 11 is guided toward the top outside of the hollow body 10, and the remaining borehole 15 is again filled with soil or aqueous or pasty building materials, for example cement suspension, bentonite or insulating material. The heat carrier line 11 can further be provided with a predetermined breaking point 16 in the section where it runs inside of the hollow body 10. The predetermined breaking point 16 is designed in such a way as to rupture when a specific pressure has been exceeded, for example 3 bar, and releases an opening. The heat carrier then flows through this opening into the interior of the hollow body 10, and thereby accelerates the melting and heating of the contact medium 14.

(23) The embodiment according to FIG. 4 is essentially a combination of FIGS. 2 and 3. However, several holes or perforations 17 are provided in place of the predetermined breaking point 16 in the section of the heat carrier line 11 that runs inside of the hollow body 10. For example, the holes or perforations 17 have a diameter of between 0.05 mm and 0.4 mm, for example 0.15 mm or 0.2 mm, so that a portion of the heat carrier can flow through these holes 17 into the interior of the hollow body 10.

(24) In the variant according to FIG. 5, an electric heater 18 is provided to heat the contact medium 14 instead of a heat carrier line. A heating wire 18 is helically wrapped around the freeze pipe 1, and pushed into the hollow body 10 with the freeze pipe 1. The gap 13 between the freeze pipe 1 and hollow body 10 is filled with the contact medium 14. As described above, the freeze pipe 1 is then cooled with liquid nitrogen, and the surrounding soil is frozen. In order to thaw and heat the contact medium 14, the heating wire 18 is hooked up to a current source 19, and a heating current is passed through the heating wire 18.

(25) The electric heater shown on FIG. 5 can be used not just as an alternative to a heat carrier line, but also in addition thereto. In the latter case, the heating of the contact medium 14 is significantly accelerated via heat transfer from the heat carrier and the electric heater.

(26) Finally, FIG. 6 reveals another variant of the invention. In this case, the contact medium 14 is heated by supplying a heat carrier into the freeze pipe 1. To this end, a heat carrier, in particular a warm gas, for example gaseous nitrogen with a temperature of 50 to 450 C., is guided into the freeze pipe 1. The contact medium 14 is in direct contact with the exterior of the freeze pipe 1, and is heated by the heat carrier. For example, the heat carrier can be supplied via the inner pipe 6 and withdrawn again via the exhaust pipe 7, thereby generating a circulation of heat carrier. The heat carrier circulation can be further improved by opening the upper front surface 3 of the freeze pipe 1.

(27) Of course, heating the contact medium 14 via the freeze pipe 1 as described based on FIG. 6 can also take place in addition to the methods described on FIGS. 1 to 5. The contact medium 14 can be heated with one or more of the following methods: Heating with a heat carrier introduced into the freeze pipe Heating with a heat carrier that flows through a heat carrier line in heat exchanging contact with the contact medium Heating with a heat carrier, which is directly guided into the contact medium, and/or Heating with an electric heater.