Frozen soil forming device and frozen soil forming method

Abstract

To provide a frozen soil forming device and a frozen soil constructing method allowing the selection of a depth region of a ground to be cooled while suppressing installation space.SOLUTION: A frozen soil forming device 1 comprises a freezing tube 3 embedded in a ground G and provided with a refrigerant inlet pipe 7 and a refrigerant outlet pipe 9 at an upper end side. The freezing tube 3 includes: an outer tube portion 21 provided with the refrigerant outlet pipe 9 at an upper end side and having a bottom portion on a lower end side; and a short inner tube 23 and a long inner tube 25 including supply ports 23a, 25a disposed in a hollow portion 21h of the outer tube portion 21 and supplying a refrigerant from the refrigerant inlet pipe 7 into the hollow portion 21h of the outer tube portion 21. Positions of the supply ports 23a, 25a in a depth direction are variable.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a frozen soil forming device and a frozen soil creating method. [Background technology]

[0002] Conventionally, a frozen soil creation method is known as a technology in this field, for example, as described in Patent Document 1 below. As shown schematically in FIG. 6 , this frozen soil creation method involves burying multiple freezing pipes 103 in ground G and circulating a refrigerant through each freezing pipe 103 to create a frozen soil impermeable wall. Each freezing pipe 103 has a double-pipe structure including an outer pipe 21 and an inner pipe 25. The freezing pipe 103 includes a refrigerant inlet pipe 7 connected to a feed refrigerant pipe 11 and a refrigerant outlet pipe 9 connected to a return refrigerant pipe 13. When the refrigerant from the feed refrigerant pipe 11 is introduced into the freezing pipe 103 through the refrigerant inlet pipe 7, the refrigerant flows sequentially through the inner pipe 25, a supply port 25a at the lower end of the inner pipe 25, and a hollow portion 21h of the outer pipe 21, and is returned to the return refrigerant pipe 13 through the refrigerant outlet pipe 9. The ground G is cooled by each of these freezing pipes 103, forming a frozen soil impermeable wall.

[0003] In this type of frozen soil creation method, maintenance operations are carried out to limit the time that cold energy is supplied in order to prevent excessive growth of frozen soil. During maintenance operations, the circulation of the refrigerant is stopped when the frozen soil temperature is sufficiently low. Then, when the frozen soil temperature rises above a predetermined level, the circulation of the refrigerant is resumed. This type of control maintains the temperature of the frozen soil at an appropriate level, thereby maintaining the strength of the frozen soil. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6997614 Summary of the Invention [Problem to be solved by the invention]

[0005] Here, the temperature of frozen soil in shallow areas, which are relatively close to the surface, tends to be higher than that in deeper areas due to the influence of air temperature. Therefore, even if frozen soil has grown sufficiently deep, if the temperature of the frozen soil in shallow areas is high, it is necessary to circulate a coolant during maintenance operations. This makes it more likely that frozen soil F will grow excessively deep in the ground, as shown in Figure 7. If frozen soil F grows excessively, the expansion of the ground can cause deformation of the surrounding ground, which can have adverse effects on surrounding structures. Furthermore, thawing frozen soil F can also have adverse effects on the surrounding ground and structures. In addition, excessive growth of frozen soil F results in wasted cooling power.

[0006] Therefore, it is necessary to be able to select the depth region of the ground to be cooled by the embedding depth direction of the freezing pipe 103, and to be able to cool the ground rationally. In the frozen soil creation method of Patent Document 1, a horizontal freezing pipe 107 extending horizontally near the ground surface G1 is additionally embedded so that only the shallow part of the ground can be cooled.

[0007] However, in general, this type of frozen soil creation method requires that the freezing pipes 103 be installed at a relatively narrow pitch (e.g., 80 cm pitch), and the freezing pipes 103 themselves have a diameter (e.g., 10 cm diameter) that is not too small compared to the pitch. Furthermore, near the ground surface G1, piping such as the refrigerant inlet pipe 7 and refrigerant outlet pipe 9 exists for each freezing pipe 103, and insulation and other materials are also installed, so the shallow part of the ground is relatively narrow. Therefore, it may be difficult to add the horizontal freezing pipes 107 and the associated piping and other equipment required for them in terms of installation space.

[0008] In view of these problems, the present invention aims to provide a frozen soil formation device and a frozen soil creation method that enable selection of the depth region of the ground to be cooled while minimizing installation space. [Means for solving the problem]

[0009] The gist of the present invention is as follows.

[0010] [1] A frozen soil formation device comprising a freezing pipe that is buried in the ground and has a refrigerant inlet and outlet on the shallow side in the burial depth direction, and through which the refrigerant flows, wherein the freezing pipe has an outer pipe portion with the outlet on the shallow side and a bottom on the deep side in the burial depth direction, and a supply portion that is disposed within the hollow portion of the outer pipe portion and includes a supply port that supplies the refrigerant from the inlet into the hollow portion of the outer pipe portion, and wherein the position of the supply port of the supply portion in the burial depth direction is variable.

[0011] [2] The supply section of the frozen soil formation device described in [1] comprises a plurality of inner pipes arranged in parallel within the hollow portion of the outer pipe section, each of which has a supply port positioned at a different position in the embedding depth direction, and a switching means capable of selectively switching the destination of the refrigerant from the inlet to one of the plurality of inner pipes.

[0012] [3] The supply section comprises a first inner pipe provided in the hollow portion of the outer pipe section, a second inner pipe passing through the hollow portion of the first inner pipe and extending deeper than the first inner pipe, a first supply port formed at one end of the deep side of the first inner pipe as an opening in the gap between the first inner pipe and the second inner pipe and functioning as the supply port, a second supply port formed at one end of the deep side of the second inner pipe as an opening and functioning as the supply port, and a switching means capable of selectively switching the destination of the refrigerant from the inlet to at least the first inner pipe and the second inner pipe.

[0013] [4] The frozen soil formation apparatus described in [1], wherein the supply section comprises an inner pipe extending through the hollow portion of the outer pipe section and the supply port formed as an opening at one end of the inner pipe on the deeper side, and the position of the inner pipe is variable in the embedding depth direction relative to the outer pipe section.

[0014] [5] A frozen soil creation method for creating frozen soil in the ground using the frozen soil creation device described in any one of [1] to [4], comprising: a frozen soil creation process for supplying the refrigerant from the supply port into the hollow portion on the deeper side in the embedding depth direction to form frozen soil in the ground; and a frozen soil maintenance process for supplying the refrigerant from the supply port into the hollow portion on the shallower side in the embedding depth direction than the frozen soil creation process to maintain the frozen soil. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a frozen soil formation device and a frozen soil creation method that can select the depth region of the ground to be cooled while reducing installation space. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a cross-sectional view showing the ground on which the frozen soil formation device according to the present embodiment is installed. [Figure 2] FIG. 2(a) is a vertical cross-sectional view showing one of the freezing pipes of the first embodiment, and FIG. 2(b) is a cross-sectional view taken along line IIb-IIb thereof. [Figure 3] FIG. 3(a) is a vertical cross-sectional view showing one of the freezing pipes of the second embodiment, and FIG. 3(b) is a cross-sectional view taken along line IIIb-IIIb thereof. [Figure 4] 4(a) and 4(c) are vertical cross-sectional views showing one freezing pipe of the third embodiment, and FIG. 4(b) is a cross-sectional view taken along line IVb-IVb thereof. [Figure 5] 1 is a cross-sectional view showing the ground on which a frozen soil forming apparatus according to a reference embodiment is installed. [Figure 6] FIG. 1 is a cross-sectional view showing the ground on which a conventional frozen soil forming device is installed. [Figure 7] FIG. 1 is a cross-sectional view showing frozen soil formed by a freezing pipe of a conventional frozen soil forming device. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of a frozen soil forming apparatus and a frozen soil creating method according to the present invention will be described in detail with reference to the drawings. Hereinafter, identical or equivalent components will be designated by the same reference numerals in the drawings, and redundant description will be omitted.

[0018] [First embodiment] FIG. 1 is a cross-sectional view showing ground G on which a frozen soil formation apparatus 1 according to this embodiment is installed. The frozen soil formation apparatus 1 creates a frozen soil wall in the ground G to block water. The frozen soil formation apparatus 1 includes multiple freezing pipes 3 embedded in the ground G vertically downward from the ground surface G1. The frozen soil formation apparatus 1 cools the ground G and forms frozen soil by causing a refrigerant to flow through each of these freezing pipes 3. The freezing pipes 3 are arranged one-dimensionally at equal intervals in a plan view along the planned location for constructing the frozen soil wall. The arrangement interval of the freezing pipes 3 is, for example, approximately 80 cm.

[0019] Each freezing pipe 3 has a freezing pipe main body 5 embedded in the ground G, and a refrigerant inlet pipe 7 and a refrigerant outlet pipe 9 attached to the upper end of the freezing pipe main body 5. The freezing pipe main body 5 is cylindrical with a diameter of approximately 10 cm and a vertical axis. The embedding depth of the freezing pipe main body 5 is set according to the depth of the planned frozen soil development area, for example, approximately 10 to 50 m. The upper end of the freezing pipe main body 5 protrudes above the ground surface G1, and one end of the refrigerant inlet pipe 7 and one end of the refrigerant outlet pipe 9 are connected to this protruding upper end of the freezing pipe main body 5. A refrigerant flow path is formed inside the freezing pipe main body 5, allowing the refrigerant to flow from the refrigerant inlet pipe 7 to the refrigerant outlet pipe 9. The other end of the refrigerant inlet pipe 7 is connected to a feed refrigerant pipe 11, and the other end of the refrigerant outlet pipe 9 is connected to a return refrigerant pipe 13. The feed refrigerant pipe 11 and the return refrigerant pipe 13 are connected to a predetermined refrigeration system (not shown).

[0020] In the frozen soil formation apparatus 1 described above, a refrigerant is supplied from the refrigeration equipment through the refrigerant supply pipe 11 and introduced into each freezing pipe 3 through each refrigerant inlet pipe 7. The temperature of the supplied refrigerant is, for example, −30°C. The introduced refrigerant flows through the refrigerant flow path inside the freezing pipe main body 5 of each freezing pipe 3 and is then discharged from each refrigerant outlet pipe 9. The refrigerant is then returned to the refrigeration equipment through the refrigerant return pipe 13. This circulation of the refrigerant causes moisture in the ground G to freeze around the freezing pipe main body 5 of each freezing pipe, forming frozen soil. This frozen soil connects with each other in the arrangement direction of the freezing pipes 3, creating a frozen soil wall. For example, a sodium chloride aqueous solution, a calcium chloride aqueous solution, or the like is used as the refrigerant.

[0021] Next, the freezing pipe 3 will be described in more detail. Fig. 2(a) is a vertical cross-sectional view showing one freezing pipe 3, and Fig. 2(b) is a cross-sectional view taken along line IIb-IIb thereof. As shown in the figure, the freezing pipe main body 5 of the freezing pipe 3 includes an outer pipe 21, a short inner pipe 23, and a long inner pipe 25. The outer pipe 21, the short inner pipe 23, and the long inner pipe 25 are all circular pipes. The outer pipe 21 is a tubular body with a bottom having a bottom wall 21b at its lower end, and forms the outer shell of the freezing pipe main body 5. A refrigerant outlet pipe 9 is connected to the upper end of the outer peripheral wall of the outer pipe 21.

[0022] The short inner pipe 23 and the long inner pipe 25 are installed in parallel in the hollow portion 21h of the outer pipe portion 21, and extend in the pipe axis direction of the outer pipe portion 21. The refrigerant inlet pipe 7 branches into two branch pipes 7a and 7b, and the branch pipe 7a is connected to the upper end of the short inner pipe 23 via a valve Va, and the branch pipe 7b is connected to the upper end of the long inner pipe 25 via a valve Vb. Note that the branch pipes 7a and 7b and the valves Va and Vb are not shown in Figure 1.

[0023] The lower ends of the short inner pipe 23 and the long inner pipe 25 are each located within the hollow portion 21h of the outer pipe portion 21. The lower end of the long inner pipe 25 is located immediately adjacent to the bottom wall 21b of the outer pipe portion 21. The lower end of the short inner pipe 23 is located at a shallower position than the lower end of the long inner pipe 25. The pipe opening at the lower end of the short inner pipe 23 functions as a first supply port 23a that supplies the refrigerant from the refrigerant inlet pipe 7 into the hollow portion 21h of the outer pipe portion 21 at a relatively shallow position. The pipe opening at the lower end of the long inner pipe 25 functions as a second supply port 25a that supplies the refrigerant from the refrigerant inlet pipe 7 into the hollow portion 21h of the outer pipe portion 21 at a relatively deep position.

[0024] In the freezing pipe 3 described above, when valve Va is closed and valve Vb is open, the refrigerant from the refrigerant inlet pipe 7 is supplied through the long inner pipe 25 from second supply port 25a into hollow portion 21h at a position near bottom wall 21b. The refrigerant then rises within hollow portion 21h and is discharged into refrigerant outlet pipe 9. In other words, in this case, the refrigerant flows throughout the entire depth of freezing pipe main body 5. Therefore, the ground G around freezing pipe main body 5 is cooled throughout the entire depth of freezing pipe main body 5, i.e., the entire depth region of the frozen soil wall to be constructed is cooled.

[0025] On the other hand, when valve Va is open and valve Vb is closed, the refrigerant from the refrigerant inlet pipe 7 is supplied through the short inner pipe 23 from the first supply port 23a into the hollow portion 21h at a relatively shallow position. Because the portion of the hollow portion 21h deeper than the first supply port 23a is already filled with refrigerant, the refrigerant supplied from the first supply port 23a does not flow downward and tends to flow toward the refrigerant outlet pipe 9 within the hollow portion 21h. Therefore, most of the refrigerant rises within the hollow portion 21h and is discharged into the refrigerant outlet pipe 9. In other words, in this case, the refrigerant flows only in the portion of the freezing pipe main body 5 that is generally shallower than the first supply port 23a. Therefore, only the portion of the ground G around the freezing pipe main body 5 that is generally shallower than the first supply port 23a is cooled.

[0026] As described above, the short inner pipe 23 and the long inner pipe 25 constitute the supply section 20, including the refrigerant supply ports 23a and 25a into the hollow section 21h. The valves Va and Vb of the freezing pipe 3 in the frozen soil formation apparatus 1 function as switching devices that selectively switch the destination of the refrigerant from the refrigerant inlet pipe 7 to one of the multiple inner pipes (the short inner pipe 23 and the long inner pipe 25). The frozen soil formation apparatus 1 may also include a control device that controls the refrigerant circulation path, including the valves Va and Vb. This switching device allows the depthwise positions of the supply ports (first supply port 23a and second supply port 25a) that supply the refrigerant from the refrigerant inlet pipe 7 to the hollow section 21h of the outer pipe section 21 to be variable. The depthwise position of the first supply port 23a is set to a depth of, for example, 1 to 5 m from the ground surface G1. The depthwise position of the second supply port 25a is set to a position immediately adjacent to the bottom wall 21b of the outer pipe section 21.

[0027] The effects of the frozen soil formation apparatus 1 described above will now be explained. With the frozen soil formation apparatus 1, the depthwise position of the supply port, which supplies the refrigerant from the refrigerant inlet pipe 7 to the hollow portion 21h of the outer pipe portion 21, can be varied in each freezing pipe 3. Then, in each freezing pipe 3, the ground G is cooled generally only at a position shallower than the supply port (first supply port 23a or second supply port 25a). Therefore, with the frozen soil formation apparatus 1, it is possible to select the depth region of the ground to be cooled. For example, as mentioned above, it is possible to select whether the depth region of the ground to be cooled is the entire depth region of the planned frozen soil wall construction area, or only a depth region of the planned construction area that is shallower than a predetermined depth.

[0028] Furthermore, in the freezing pipe 3, the short inner pipe 23 and the long inner pipe 25 are housed within the outer pipe 21 that forms the outer shell of the freezing pipe main body 5, so the area occupied by each freezing pipe 3 can be kept to the same level as that of the freezing pipe 103 described in FIG. 6, for example. Furthermore, there is no need to add large equipment, such as the horizontal freezing pipe 107 in FIG. 6, to the outside of the outer pipe 21. Therefore, the installation space for the frozen soil formation apparatus 1 is kept to a minimum, and the frozen soil formation apparatus 1 can be applied even in narrow locations where there are restrictions on installing equipment.

[0029] Furthermore, the refrigerant circulation lines connected to the freezing pipe 3, such as the refrigerant inlet pipe 7, the refrigerant outlet pipe 9, the feeding refrigerant pipe 11, and the returning refrigerant pipe 13, are the same as those in the freezing pipe 103 described in FIG. 6, so no special piping work is required, and there is little risk of refrigerant leakage from joints, for example.

[0030] Furthermore, since the outer pipe portion 21 of the freezing pipe 3 has the same structure as the outer pipe portion 21 of the freezing pipe 103 as described in Fig. 6, the configuration of the freezing pipe 3 can also be applied to freezing pipes that have already been installed. That is, for example, in a freezing pipe 103 that has already been buried in the ground G, the structure inside the hollow portion of the outer pipe portion 21 can be replaced to modify it to the structure of the freezing pipe 3.

[0031] A frozen soil creation method implemented using the frozen soil creation apparatus 1 described above is, for example, as follows. In this frozen soil creation apparatus 1, first, before a frozen soil wall is created in the ground G, valve Va is closed and valve Vb is open in each freezing pipe 3, and a refrigerant is supplied from second supply port 25a into hollow portion 21h of outer pipe portion 21. As described above, this cools all depths of the area where the frozen soil wall is to be created, and the frozen soil wall is finally completed (frozen soil creation process). Then, both valves Va and Vb are closed, and the circulation of the refrigerant is stopped.

[0032] Subsequently, because the temperature of shallow portions of the frozen soil wall is easily affected by air temperature, when a frozen soil temperature above a predetermined level is detected, valve Va is opened and valve Vb is closed. This causes refrigerant to be supplied from first supply port 23a into hollow portion 21h of outer pipe 21. As described above, this coolant cools only the area of ​​the planned frozen soil wall construction that is generally shallower than first supply port 23a, lowering the temperature of the frozen soil wall in that area. Since the area of ​​the planned frozen soil wall construction that is generally deeper than first supply port 23a is not cooled, promoting the growth of the deeper portion of the frozen soil wall is avoided. After the frozen soil wall is formed in the above-described frozen soil formation process, this control is executed to maintain the temperature of the frozen soil wall and appropriately maintain the frozen soil (frozen soil maintenance process). To enable this control, a temperature measuring pipe (not shown) for measuring the frozen soil temperature is installed in the planned frozen soil wall construction area.

[0033] This frozen soil creation method avoids cooling the deep parts of the frozen soil wall, which do not need to be cooled during the frozen soil maintenance process, and prevents excessive growth of the deep parts of the frozen soil wall. This reduces the waste of cooling power, which is essentially unnecessary. It also suppresses the adverse effects of excessive growth of the deep parts of the frozen soil wall on the surrounding ground and surrounding structures.

[0034] Second Embodiment A second embodiment of the frozen soil formation apparatus of the present invention will be described with reference to FIG. 3. The frozen soil formation apparatus 1B of this embodiment includes a freezing pipe 3B shown in FIG. 3, instead of the freezing pipe 3 in the frozen soil formation apparatus 1 of the first embodiment. FIG. 3(a) is a vertical cross-sectional view of one of the freezing pipes 3B, and FIG. 3(b) is a cross-sectional view taken along line IIIb-IIIb of FIG. 3(a). As shown in the figure, the freezing pipe 3B includes a long inner pipe 25B instead of the long inner pipe 25 of the freezing pipe 3. The long inner pipe 25 is arranged parallel to the short inner pipe 23, while the long inner pipe 25B (second inner pipe) passes through the hollow portion 23h of the short inner pipe 23 (first inner pipe). The long inner pipe 25B extends deeper than the short inner pipe 23, and the lower end of the long inner pipe 25B is located immediately adjacent to the bottom wall 21b of the outer pipe portion 21. That is, the short inner pipe 23 and the long inner pipe 25B form a double pipe structure.

[0035] According to this structure, the annular opening at the lower end of the short inner pipe 23, which is located in the gap between the short inner pipe 23 and the long inner pipe 25B, functions as the first supply port 23a. The pipe opening at the lower end of the long inner pipe 25B functions as the second supply port 25a. As in the first embodiment, the depthwise positions of the supply ports (first supply port 23a and second supply port 25a) that supply the refrigerant from the refrigerant inlet pipe 7 to the hollow portion 21h of the outer pipe portion 21 can be varied using the switching means including the valves Va and Vb. Therefore, the frozen soil formation apparatus 1B of this embodiment, which includes the above-described freezing pipe 3B, can achieve the same effects as the frozen soil formation apparatus 1 of the first embodiment and can also perform the same frozen soil creation method as the first embodiment.

[0036] Third Embodiment A third embodiment of the frozen soil formation apparatus of the present invention will be described with reference to FIG. 4. The frozen soil formation apparatus 1C of this embodiment includes a freezing pipe 3C shown in FIG. 4, instead of the freezing pipe 3 in the frozen soil formation apparatus 1 of the first embodiment. FIG. 4(a) is a vertical cross-sectional view showing one of the freezing pipes 3C, and FIG. 4(b) is a cross-sectional view taken along line IVb-IVb of FIG. 4(b). FIG. 4(c) is a vertical cross-sectional view showing one of the freezing pipes 3C in a state different from that shown in FIG. 4(a). The freezing pipe 3C includes a movable long inner pipe 25C, instead of the long inner pipe 25 of the freezing pipe 3. Furthermore, the short inner pipe 23 of the freezing pipe 3 is omitted from the freezing pipe 3C.

[0037] The long inner pipe 25C penetrates the upper wall 21k of the outer pipe portion 21 and is inserted into the hollow portion 21h. The long inner pipe 25C extends parallel to the outer pipe portion 21 and is movable in the pipe axis direction relative to the outer pipe portion 21. A predetermined watertight movable mechanism is provided at the joint between the upper wall 21k and the long inner pipe 25C to watertightly close the gap between them while allowing the long inner pipe 25C to move relative to the upper wall 21k. A drive device (not shown) may also be provided to move the long inner pipe 25C up and down.

[0038] The upper end of the long inner pipe 25C is connected to the refrigerant inlet pipe 7 via a valve V, and a pipe opening at the lower end of the long inner pipe 25C functions as a supply port 25d that supplies the refrigerant from the refrigerant inlet pipe 7 into the hollow portion 21h of the outer pipe portion 21. As shown in FIG. 4(a), the long inner pipe 25C can be moved to a position where the supply port 25d is located immediately adjacent to the bottom wall 21b of the outer pipe portion 21. Furthermore, as shown in FIG. 4(c), the long inner pipe 25C can also be moved to a position where the supply port 25d is located at a shallower position away from the bottom wall 21b.

[0039] With this structure, the long inner pipe 25C can be moved in the pipe axial direction, thereby varying the depth position of the supply port 25d, which supplies the refrigerant from the refrigerant inlet pipe 7 to the hollow portion 21h of the outer pipe portion 21. Therefore, the frozen soil formation apparatus 1C of this embodiment, which is equipped with the above-mentioned freezing pipe 3C, can also obtain the same effects as the frozen soil formation apparatus 1 of the first embodiment, and can perform the same frozen soil creation method as the first embodiment.

[0040] A frozen soil creation method implemented using the frozen soil creation apparatus 1C of this embodiment is, for example, as follows. First, before a frozen soil wall is created in the ground G, as shown in FIG. 4(a), the long inner pipe 25C is installed so that the supply port 25d is located immediately adjacent to the bottom wall 21b of the outer pipe portion 21. Then, when a refrigerant is supplied from the supply port 25d into the hollow portion 21h of the outer pipe portion 21 of each freezing pipe 3C, all depths of the area where the frozen soil wall is to be created are cooled, and the frozen soil wall is finally completed (the frozen soil creation process). Then, the valve V is closed to stop the circulation of the refrigerant.

[0041] Then, as shown in FIG. 4(c), the long inner pipe 25C is raised in the pipe axis direction relative to the outer pipe portion 21 so that the supply port 25d is positioned at a shallower position away from the bottom wall 21b. The depth direction position of the supply port 25d is set to, for example, a depth of 1 to 5 m from the ground surface G1. At this time, since the long inner pipe 25C protrudes upward from the upper wall 21k of the outer pipe portion 21, a protruding portion of the long inner pipe 25C may be removed. Then, similar to the frozen soil maintenance process in the first embodiment, when a frozen soil temperature higher than a predetermined value is detected, control is executed to open the valve V (frozen soil maintenance process). In this frozen soil maintenance process, a refrigerant is supplied to the hollow portion 21h of the outer pipe portion 21 from the supply port 25d, which is located at a relatively shallow position. This cools only a relatively shallow depth region of the planned frozen soil wall construction area. Furthermore, since a depth region deeper than the supply port 25d is generally not cooled, promoting the growth of the deep portion of the frozen soil wall is avoided. This frozen soil maintenance process maintains the temperature of the frozen soil wall and keeps the frozen soil in an appropriate state.

[0042] Furthermore, if it becomes necessary to move the supply port 25d closer to the bottom wall 21b of the outer pipe portion 21 again after a portion of the long inner pipe 25C has been cut off as described above, the long inner pipe 25C can be extended by adding a pipe material to the upper end of the long inner pipe 25C by welding or the like, and then the long inner pipe 25C can be lowered in the pipe axis direction relative to the outer pipe portion 21.

[0043] The present invention can be embodied in various forms, including the above-described embodiment, with various modifications and improvements based on the knowledge of those skilled in the art. Furthermore, it is also possible to create modified versions by utilizing the technical details described in the above-described embodiment. The configurations of the respective embodiments may be appropriately combined and used. For example, in the first embodiment, an example was described in which two inner tubes 23, 25 with lower end positions different from each other are used. Following this example, the number of inner tubes with lower end positions different from each other may be further increased, allowing the depth direction positions of the supply ports 23a, 25a, etc. to be switched in even more stages.

[0044] In the second embodiment, an example has been described in which the inner pipes 23, 25B of a double-pipe structure are used, but following this example, the inner pipes may have a further multiple-pipe structure, and the depth positions of the supply ports 23a, 25a, ... may be switched in even more stages. In this way, by switching the depth positions of the supply ports 23a, 25a, ... in even more stages, the depth region of the ground to be cooled may be controlled even more precisely.

[0045] In addition, a configuration in which the inner tubes 23, 25, ... are arranged in parallel as in the first embodiment, a configuration in which the inner tubes 23, 25B, ... are made into a multiple structure as in the second embodiment, and a configuration in which the inner tube 25C is movable in the tube axis direction as in the third embodiment may be appropriately combined and adopted.

[0046] Furthermore, although the freezing pipe 3 in each embodiment is embedded in the ground G vertically downward from the ground surface G1, this is not limiting. That is, the present invention can also be applied to a frozen soil formation device including a freezing pipe embedded in the ground in various directions (for example, horizontally).

[0047] [Reference form] An example of a frozen soil formation device that allows selection of the depth region of the ground to be cooled is a frozen soil formation device 201 shown in Figure 5. Figure 5 is a cross-sectional view showing ground G on which a frozen soil formation device 201 according to a reference embodiment is installed. As shown in Figure 5, frozen soil formation device 201 includes freezing pipes 103 of a conventional double-pipe structure as described in Figure 6, and short freezing pipes 104 that are additionally buried between the freezing pipes 103 and are shorter than the freezing pipes 103. The short freezing pipes 104 have the same double-pipe structure as the freezing pipes 103, but differ from them in that they are shorter than the freezing pipes 103.

[0048] With this type of frozen soil formation apparatus 201, it is possible to cool all depth regions in the area where the frozen soil wall is to be created by circulating refrigerant only through each freezing pipe 103. Also, it is possible to cool only areas of the area where the frozen soil wall is to be created that are shallower than a predetermined depth by circulating refrigerant only through each short freezing pipe 104. Compared to this type of frozen soil formation apparatus 201, with the frozen soil formation apparatuses 1, 1B, and 1C of the first to third embodiments described above, there is no need to install additional short freezing pipes 104 between each of the freezing pipes 3, which reduces installation space and makes them easy to apply even in narrow locations where there are restrictions on equipment installation. [Explanation of symbols]

[0049] 1, 1B, 1C...frozen soil formation device, 3, 3B, 3C...freezing pipe, 7...refrigerant inlet pipe, 9...refrigerant outlet pipe, 20...supply section, 21...outer pipe section, 21b...bottom wall, 21h...hollow section, 23...short inner pipe (first inner pipe), 23a...first supply port (supply port), 23h...hollow section, 25...long inner pipe, 25B...long inner pipe (second inner pipe), 25C...long inner pipe (switching means), 25a...second supply port (supply port), 25d...supply port, G...ground, Va, Vb...valve (switching means).

Claims

1. A frozen soil forming device that is embedded in the ground and has a refrigerant inlet and outlet on the shallow side of the embedment depth direction, and includes a freezing pipe through which the refrigerant flows, The freezing tube is an outer tube portion having the outlet on the shallow side and a bottom on the deep side in the embedding depth direction; a supply section that is disposed in the hollow section of the outer pipe section and includes a supply port that supplies the refrigerant from the inlet into the hollow section of the outer pipe section, The supply unit includes: a first inner pipe and a second inner pipe arranged in parallel in the hollow portion of the outer pipe portion, the first inner pipe and the second inner pipe including the supply ports at different positions in the embedding depth direction; a first supply port formed as an opening at one end of the first inner tube on the deep side and functioning as the supply port; a second supply port formed as an opening at one end of the second inner tube on the deep side and functioning as the supply port; a switching means for selectively switching a destination of the refrigerant from the inlet to at least the first inner pipe and the second inner pipe, the second supply port is located deeper than the first supply port, the first supply port and the second supply port are both located deeper than the outlet, A frozen soil formation device in which the refrigerant supplied from the first supply port into the hollow portion and flowing within the hollow portion, and the refrigerant supplied from the second supply port into the hollow portion and flowing within the hollow portion, are both discharged from the same outlet.

2. A frozen soil forming device that is embedded in the ground and has a refrigerant inlet and outlet on the shallow side of the embedment depth direction, and includes a freezing pipe through which the refrigerant flows, The freezing tube is an outer tube portion having the outlet on the shallow side and a bottom on the deep side in the embedding depth direction; a supply section that is disposed in the hollow section of the outer pipe section and includes a supply port that supplies the refrigerant from the inlet into the hollow section of the outer pipe section, The supply unit includes: a first inner tube provided in the hollow portion of the outer tube portion; a second inner pipe passing through a hollow portion of the first inner pipe and extending to a deeper portion than the first inner pipe; a first supply port formed as an opening in a gap between the first inner tube and the second inner tube at one end of the first inner tube on the deep side, the first supply port functioning as the supply port; a second supply port formed as an opening at one end of the second inner tube on the deep side and functioning as the supply port; a switching means for selectively switching a destination of the refrigerant from the inlet to at least the first inner pipe and the second inner pipe, the first supply port and the second supply port are both located deeper than the outlet, A frozen soil formation device in which the refrigerant supplied from the first supply port into the hollow portion and flowing within the hollow portion, and the refrigerant supplied from the second supply port into the hollow portion and flowing within the hollow portion, are both discharged from the same outlet.

3. A frozen soil creation method for creating frozen soil in the ground using the frozen soil creation device according to claim 1 or 2, a frozen soil forming step of supplying the refrigerant from the second supply port into the hollow portion at a deep portion in the embedding depth direction and causing the refrigerant to flow to the outlet to form frozen soil in the ground; A frozen soil creation method comprising a frozen soil maintenance process for supplying the refrigerant from the first supply port into the hollow portion at a shallower side in the embedding depth direction than the frozen soil formation process and flowing it to the outlet to maintain the frozen soil.

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