Ground excavation method and frozen outer pipe used therein

Abstract

To shorten the work period while efficiently using cold energy in a ground freezing method using a shield machine. [Solution] The ground excavation method comprises the steps of erecting a resin freezing outer pipe in the ground, inserting an inner pipe into the freezing outer pipe erected in the ground, supplying a refrigerant from the inner pipe, and freezing a frozen area with cold heat from the freezing outer pipe, changing the cold heat range so that cold heat is applied mainly to a surface-side non-excavation area of ​​the frozen area that is located closer to the ground surface than the excavation area through which the shield machine passes, thereby maintaining the frozen state of the surface-side non-excavation area, and excavating the excavation area with the shield machine while leaving the freezing outer pipe in place within the excavation area.

Description

[Technical Field]

[0001] The present disclosure relates to a ground excavation method and a frozen outer pipe used therein. [Background technology]

[0002] A ground freezing method has been known for some time, in which freezing pipes are erected into the ground, the ground is frozen using the freezing pipes to create frozen soil, and a shield machine is then driven into the frozen soil to form a tunnel, etc. According to this ground freezing method, the ground can be frozen using the outer freezing pipes, which prevents the collapse of the excavated hole wall.

[0003] When a shield machine is used to enter a site where a frozen pipe is present, the frozen pipe must be removed before excavating the frozen ground with the shield machine. However, in the ground freezing method, the frozen pipe and the ground are frozen, so in order to remove the frozen pipe, high-temperature water must be supplied into the frozen pipe to thaw it before it can be removed. This not only makes the work complicated, but also tends to lengthen the work period.

[0004] Therefore, in the ground excavation method described in Patent Document 1, the ground is frozen using freezing pipes made of mild steel. By freezing the ground using freezing pipes made of mild steel, the mild steel can be cut along with the ground when the ground is excavated with a shield machine. This eliminates the need to pull out the freezing pipes from the ground, shortening the work period. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-105030 Summary of the Invention [Problem to be solved by the invention]

[0006] However, around the hole created by the shield machine, the part facing the ground is more likely to collapse than the part facing the ground, so applying cold and heat evenly around the excavation area is inefficient.

[0007] The present invention has been made in consideration of the above circumstances, and its purpose is to provide a ground excavation method that can shorten the work period while efficiently using cold energy in a ground freezing method using a shield machine, and a freezing outer pipe to be used therein. [Means for solving the problem]

[0008] A ground excavation method according to one aspect of the present disclosure includes the steps of erecting a resin freezing outer pipe in the ground, inserting an inner pipe into the freezing outer pipe erected in the ground, supplying a refrigerant from the inner pipe, and freezing a frozen area using the cold heat from the freezing outer pipe, changing the cold heat range so that the cold heat is applied mainly to a ground-side non-excavation area of ​​the frozen area that is located closer to the ground surface than an excavation area through which a shield machine passes, thereby maintaining the frozen state of the ground-side non-excavation area, and excavating the excavation area with the shield machine while leaving the freezing outer pipe in place within the excavation area.

[0009] A freezing outer pipe according to one embodiment of the present disclosure is a freezing outer pipe used in a ground excavation method, and comprises a first pipe made of polyethylene in a cylindrical shape with a bottom, a second pipe made of polyethylene having openings on both end faces, and a resin joint connecting the first pipe and the second pipe. [Effects of the Invention]

[0010] According to the above-described aspects of the present disclosure, in a ground freezing method using a shield machine, the work period can be shortened while efficiently using cold energy. [Brief explanation of the drawings]

[0011] [Figure 1]FIG. 1 is a flowchart of a ground excavation method according to an embodiment. [Figure 2A] FIG. 2A is a schematic cross-sectional view showing a casing embedding step according to the embodiment. [Figure 2B] FIG. 2B is a schematic cross-sectional view showing a part of the frozen outer pipe installation process according to the embodiment. [Figure 2C] FIG. 2C is a schematic cross-sectional view showing a part of the frozen outer pipe installation process according to the embodiment. [Figure 2D] FIG. 2D is a schematic cross-sectional view showing a frozen soil creating step according to the embodiment. [Figure 2E] FIG. 2E is a schematic cross-sectional view illustrating a cooling / heating range changing step according to the embodiment. [Figure 3] 3(a) to 3(d) are schematic cross-sectional views showing a ground excavation method according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0012] [Description of the embodiments of the present disclosure] First, embodiments of the present disclosure will be listed and described. (1) A ground excavation method according to the present disclosure includes the steps of: erecting a resin outer freezing pipe into the ground; inserting an inner pipe into the outer freezing pipe erected in the ground, supplying a refrigerant through the inner pipe, and freezing a frozen region using cold heat from the outer freezing pipe; modifying the cold heat range so that cold heat is applied mainly to a surface-side non-excavation region of the frozen region located closer to the ground surface than an excavation region through which a shield machine passes, thereby maintaining the frozen state of the surface-side non-excavation region; and excavating the excavation region with the shield machine while leaving the outer freezing pipe in the excavation region. This configuration allows for efficient use of cold heat, thereby reducing the risk of hole wall collapse. Furthermore, the excavation region can be excavated using the shield machine without removing the outer freezing pipe from the ground, eliminating the need to remove the outer freezing pipe and shortening the work period.

[0013] (2) In the step of maintaining the frozen state of the non-excavated area on the surface side in the above-mentioned (1), a small cylindrical freezing pipe made of metal and having a bottom and capable of generating cold may be inserted into the outer freezing pipe, and the bottom end of the small freezing pipe may be positioned in the non-excavated area on the surface side. With this configuration, the only object cut together with the ground by the shield machine is the outer freezing pipe made of resin, and cold can be efficiently applied to the ground by the small freezing pipe made of metal.

[0014] (3) In the above (2), the method may further include a step of supplying cement milk to form cement between the bottom of the outer freezing pipe and the bottom end of the small freezing pipe before the step of excavating the excavation area with the shield machine. With this configuration, the portion of the outer freezing pipe that overlaps with the excavation area becomes hard and brittle, making it easier to crush the outer freezing pipe with the shield machine.

[0015] (4) In any one of (1) to (3) above, the freezing outer pipe may include a first pipe made of polyethylene and having a cylindrical shape with a bottom, a second pipe made of polyethylene and having openings on both ends, and a joint made of resin that connects the first pipe and the second pipe. With this configuration, the freezing outer pipe can be inserted into the ground while connecting them on site, reducing the effort required for transportation.

[0016] (5) In any one of the above (1) to (4), the outer freezing pipe may have a heat insulating material that forms a non-freezing region between the frozen region and the ground surface. This configuration can reduce freezing of the ground surface.

[0017] (6) In any one of the above (1) to (5), the outer freezing pipe may be a vertical pipe erected on a ground having a horizontal surface. This configuration makes it easy to shorten the work period while efficiently using cold energy on a ground having a horizontal surface.

[0018] (7) In any one of the above (1) to (6), the outer freezing pipe may be a horizontal pipe that is erected into the ground via a water-stopping device fixed to the ground surface. This configuration makes it easy to shorten the work period while efficiently using cold energy for ground having a ground surface that intersects a horizontal plane.

[0019] (8) In the above (7), a metal connecting pipe may be connected to the ground surface end of the freezing outer pipe formed from the horizontal pipe. With the horizontal pipe inserted into the ground, the connecting pipe may be welded to a metal waterstop plate fixed to the ground surface, thereby erecting the freezing outer pipe into the ground. This configuration makes it easier to achieve the ground drilling method while preventing groundwater leakage in ground having a ground surface that intersects a horizontal plane.

[0020] (9) In any one of the above (1) to (8), the refrigerant may be brine. This configuration makes it easier to achieve efficient ground freezing.

[0021] (10) A freezing outer pipe according to the present disclosure may be a freezing outer pipe used in the ground excavation methods (1) to (9) above, and may include a first pipe made of polyethylene and having a cylindrical bottom, a second pipe made of polyethylene and having openings on both end faces, and a resin joint connecting the first pipe and the second pipe. This configuration can reduce the work of pulling out the freezing outer pipe, and a freezing outer pipe suitable for a ground excavation method that can shorten the work period can be used.

[0022] [Details of the embodiment] Next, embodiments of the ground excavation method according to the present disclosure will be described below with reference to the drawings. In the following drawings, the same or corresponding parts are designated by the same reference numerals, and description thereof will not be repeated.

[0023] (Outline of ground excavation method) The ground excavation method according to this embodiment is suitable for use in construction using a shield machine when a ground freezing technique is being implemented. The ground excavation method includes a freezing outer pipe installation step S2 in which a resin freezing outer pipe 2 is installed in the ground 4, a frozen soil creation step S3 in which an inner pipe 6 is inserted into the freezing outer pipe 2 installed in the ground 4 and the frozen region R2 is frozen with the cold heat from the freezing outer pipe 2 to form frozen soil, a cold heat range change step S4 in which cold heat is applied mainly to a surface-side non-excavation region of the frozen region R2 that is located closer to the ground surface than an excavation region R3 through which the shield machine passes, thereby maintaining the frozen state of the surface-side non-excavation region, and a shield machine excavation step S6 in which the freezing outer pipe 2 is left in the excavation region R3 and the shield machine excavates the excavation region R3.

[0024] In the ground excavation method according to this embodiment, the cold heat range change step S4 changes the cold heat range so that cold heat is applied mainly to the non-excavation area on the ground surface, and then the shield machine excavates the excavation area R3, thereby efficiently using cold heat and reducing the collapse of the hole wall. Furthermore, because the excavation area can be excavated with the shield machine without pulling out the frozen outer pipe 2 from the ground 4, the work of pulling out the frozen outer pipe 2 can be reduced, making it easier to shorten the work period.

[0025] For ease of explanation, the side deeper underground in the central axis direction of the freezing outer pipe 2 will be referred to as the "underground side," and the opposite side will be defined as the "surface side." In addition, in this disclosure, "parallel" not only includes cases where two straight lines, planes, etc. (hereinafter referred to as "straight lines") do not intersect when extended, but also includes cases where the angle between the two straight lines, etc. is within a range of 10°. Furthermore, "perpendicular" means cases where two straight lines, etc. intersect within a range of 90°±10°. However, even if two straight lines, etc. do not intersect directly, if they intersect when extended, they are included in the term "perpendicular."

[0026] 1, the ground excavation method according to this embodiment includes a casing embedding step S1, a freezing outer pipe installation step S2, a frozen soil creation step S3, a cold-heat range changing step S4, and a shield machine excavation step S6. The ground excavation method also includes a cement formation step S5 between the cold-heat range changing step S4 and the shield machine excavation step S6. The ground excavation method according to this embodiment executes the casing embedding step S1, the freezing outer pipe installation step S2, the frozen soil creation step S3, the cold-heat range changing step S4, the cement formation step S5, and the shield machine excavation step S6 in this order. Each step will be described in detail below.

[0027] (Casing burying process S1) 2A is a schematic cross-sectional view for explaining the casing burying step S1. In the casing burying step S1, the casing 1 (casing tube) is buried in the ground 4. By burying the casing 1 in the ground 4 in the casing burying step S1, a hole can be drilled in the ground 4. This reduces the risk of the hole wall collapsing, and in the next step, the frozen outer pipe erection step S2, the frozen outer pipe 2 can be erected in the ground 4.

[0028] The casing 1 is a cylindrical steel pipe used for drilling holes. Both end faces of the casing 1 in the central axis direction are open faces. A plurality of bits 11 are formed around the periphery of the opening at the tip of the casing 1. In the casing burying step S1, for example, a full-circle rotation device is used to rotate the casing 1 around its central axis as the axis of rotation, while inserting it into the ground 4 to the desired depth. In the casing burying step S1 according to this embodiment, the casing 1 is inserted so that it is perpendicular to the ground surface 41 (i.e., in the vertical direction). However, the casing 1 does not have to be inserted perpendicular to the ground surface 41. In the casing burying step S1, a plurality of casings 1 are erected into the ground 4. The casing burying step S1 is completed when all of the casings 1 have been inserted into the ground 4 to the desired depth.

[0029] (Frozen outer pipe installation process S2) 2B and 2C are schematic cross-sectional views for explaining the freezing outer pipe installation step S2. In the freezing outer pipe installation step S2, the freezing outer pipe 2 is installed in the ground 4. The freezing outer pipe 2 in this embodiment is formed from a vertical pipe. In the present disclosure, a vertical pipe is a pipe that is installed in the ground surface 41 without using a water-stopping device (see modified example). The vertical pipe in this embodiment is installed along the vertical direction. The vertical pipe may be inserted into a horizontal ground surface 41, or may be inserted into a ground surface 41 that is uneven with respect to the horizontal plane. Here, "along the vertical direction" includes an inclination within a range of ±30° from the vertical.

[0030] In the frozen outer pipe installation step S2, as shown in Fig. 2B, the frozen outer pipe 2 is inserted into the casing 1 erected in the casing burying step S1, and the frozen outer pipe 2 is placed in the ground 4 to the desired depth. Then, as shown in Fig. 2C, the casing 1 is pulled out from the ground 4, thereby erecting the frozen outer pipe 2 into the ground 4. The frozen outer pipe installation step S2 is completed when the frozen outer pipes 2 have been inserted into all of the casings 1 and all of the frozen outer pipes 2 have been erected into the ground 4.

[0031] Each freezing outer pipe 2 is made of resin. Examples of resins that can be used to form the freezing outer pipe 2 include polyethylene and polyvinyl chloride. Because the freezing outer pipe 2 is made of resin, it can be cut at the same time as drilling a hole using a shield machine, which will be described later. As shown in FIG. 2C , the freezing outer pipe 2 has a cylindrical first pipe 21 with a bottom, multiple cylindrical second pipes 22, and a joint (hereinafter referred to as a first joint 24) that connects the first pipe 21 and the second pipe 22.

[0032] The first pipe 21 is a portion of the outer freezing pipe 2 that includes the end portion on the ground side in the central axis direction. The first pipe 21 has a peripheral wall 211 that is open at both ends in the central axis direction, a reduced diameter portion 213 connected to the opening on the ground side of the peripheral wall 211, and a bottom wall 212 that closes the opening on the ground side of the peripheral wall 211. The bottom wall 212 and the reduced diameter portion 213 are fixed to the peripheral wall 211 by, for example, welding or fusing. As described above, the first pipe 21 is made of resin. The first pipe 21 in this embodiment is made of polyethylene. The first pipe 21 may be made of polyvinyl chloride.

[0033] The second pipe 22 is connected to the end of the first pipe 21 on the ground surface side in the central axis direction. The second pipe 22 is a straight pipe and includes openings on both end surfaces in the central axis direction. As described above, the second pipe 22 is made of resin. The second pipe 22 according to this embodiment is made of polyethylene. The second pipe 22 may be made of polyvinyl chloride.

[0034] The second piping 22 has a plurality of straight pipe sections 221 and a joint (second joint 222). The straight pipe section 221 is formed to have the same diameter as the outer diameter of the end of the reduced diameter section 213 on the ground surface side. The straight pipe section 221 is formed to have a diameter smaller than the outer diameter of the peripheral wall 211 of the first piping 21. The second joint 222 connects the plurality of straight pipe sections 221 together. The outer diameter of the second joint 222 is larger than the outer diameter of the straight pipe section 221 and smaller than the inner diameter of the casing 1. Because the second piping 22 is formed from the plurality of straight pipe sections 221 and the second joint 222, the length of the second piping 22 can be set on-site according to the depth of the planned freezing position relative to the ground surface 41, and transportation of each component is facilitated.

[0035] Heat insulating material 23 is attached so as to surround the outer peripheral surface of second piping 22. Heat insulating material 23 can form a non-freezing region R1, which is a region that will not freeze in the ground 4. By forming non-freezing region R1, it is easy to minimize the area in the ground 4 that will actually freeze.

[0036] The heat insulating material 23 is formed in a cylindrical shape. The heat insulating material 23 has better heat insulating properties than the second pipe 22. The outer diameter of the heat insulating material 23 is formed to be approximately the same as the outer diameter of the peripheral wall 211 of the first pipe 21. The outer diameter of the heat insulating material 23 is formed to be smaller than the inner diameter of the casing 1. Examples of materials for the heat insulating material 23 include urethane foam, rock wool, and glass wool. The heat insulating material 23 may be one that provides insulation by using an air layer.

[0037] The first joint 24 connects the first pipe 21 and the second pipe 22. The first joint 24 is made of resin. The resin first joint 24 may be made mostly of resin, and may use an electric heating wire in part. The first joint 24 may be, for example, an electrofusion joint (EF joint).

[0038] (Frozen soil creation process S3) 2D is a schematic cross-sectional view illustrating the frozen soil creation step S3. In the frozen soil creation step S3 according to this embodiment, an inner pipe 6 is inserted into the freezing outer pipe 2 erected in the freezing outer pipe erection step S2, a refrigerant is supplied from the inner pipe 6 into the freezing outer pipe 2, and the ground 4 is frozen by the cold heat from the freezing outer pipe 2. In this disclosure, the area of ​​the ground 4 that is to be frozen by the cold heat from the freezing outer pipe 2 is referred to as the "freezing region R2." Furthermore, the range over which cold heat is applied to the ground 4 from the freezing outer pipe 2 is referred to as the "cold heat range."

[0039] The inner pipe 6 extends from above the ground surface 41 to the ground-side end of the first piping 21. The inner pipe 6 is connected to the chiller 5 installed on the ground via an outgoing path 51. The upper end of the freezing outer pipe 2 is connected to the chiller 5 via a return path 52. The chiller 5 supplies the refrigerant to the inner pipe 6 via the outgoing path 51. The refrigerant supplied to the inside of the inner pipe 6 is supplied into the freezing outer pipe 2 from near the bottom wall 212 of the freezing outer pipe 2, rises from the bottom wall 212 along the peripheral wall 211 of the freezing outer pipe 2, and returns to the chiller 5 from the opening surface of the freezing outer pipe 2 on the ground surface side via the return path 52. The refrigerant circulates between the chiller 5 and the freezing outer pipe 2, thereby cooling the ground 4 and forming frozen soil.

[0040] The refrigerant is, for example, brine, which is a cooling liquid. For example, an aqueous solution of calcium chloride is used as the brine. The brine is cooled to about -30°C by the refrigerator 5. The refrigerant is not limited to brine, and liquefied gases such as liquid nitrogen and liquefied carbon dioxide may also be used. If the refrigerator is a so-called low-temperature liquefied gas type refrigerator that uses liquid gas as the refrigerant, the vaporized gas may be released into the atmosphere from the end of the outer freezing pipe 2 on the ground surface side.

[0041] (Cold / hot range change process S4) FIG. 2E is a schematic cross-sectional view illustrating the cooling range changing process S4. The cooling range changing process S4 changes the cooling range so that cooling is applied mainly to the surface-side non-excavation region of the frozen region R2, which is located closer to the ground than the excavation region R3. The frozen state of the surface-side non-excavation region that was frozen by the frozen soil creation process S3 can be maintained by the cooling range changing process S4. The "excavation region R3" here refers to the area through which the shield machine passes. The cooling range changing process S4 can change the cooling range between the ground surface 41 and the excavation region R3, or more specifically, between the non-freezing region R1 and the excavation region R3. The cooling range in the frozen soil creation process S3 is a first range H1 extending from the lower end of the non-freezing region R1 to the bottom wall 212 of the frozen outer pipe 2, while the cooling range in the freezing range changing process is a second range H2 extending from the lower end of the non-freezing region R1 to the upper end of the excavation region R3. As a result, the freezing range is reduced by the freezing range changing process.

[0042] In the cold / heat range changing step S4, a small freezing pipe 7 is inserted into the outer freezing pipe 2, and the bottom end of the small freezing pipe 7 is positioned in the non-excavated area on the ground surface side. The small freezing pipe 7 has a cylindrical second outer pipe 71 with a bottom and a second inner pipe 72 placed inside the second outer pipe 71. The second outer pipe 71 and the second inner pipe 72 are made of metal. Examples of metals that form the second outer pipe 71 and the second inner pipe 72 include iron, copper, and aluminum.

[0043] The second inner pipe 72 is connected to the refrigerator 5 via an outgoing path 51. The upper end of the second outer pipe 71 is connected to the refrigerator 5 via a return path 52. The refrigerator 5 supplies a cooling liquid, which is a refrigerant, to the second inner pipe 72 via the outgoing path 51. The cooling liquid supplied to the inside of the second inner pipe 72 is supplied into the second outer pipe 71 from near the bottom wall of the second outer pipe 71, rises along the circumferential wall from the bottom wall 212 of the second outer pipe 71, and returns to the refrigerator 5 from the opening surface of the second outer pipe 71 on the ground surface side via the return path 52. The refrigerant circulates between the refrigerator 5 and the small freezing pipe 7, allowing cold to be applied from the small freezing pipe 7. The cold radiated from the small freezing pipe 7 can be applied to the ground 4 from the freezing outer pipe 2 via the refrigerant or cement milk filled in the freezing outer pipe 2.

[0044] This allows the cold heat range change step S4 to change the cold heat range so that cold heat is applied mainly to the non-excavated area on the surface side. By applying cold heat mainly to the non-excavated area on the surface side and maintaining the frozen state of the non-excavated area on the surface side, the cold heat range change step S4 is completed.

[0045] (Cement formation process S5) The cement formation step S5 is a step of forming cement in the freezing outer pipe 2 by supplying cement milk between the bottom wall 212 of the freezing outer pipe 2 and the bottom end of the small freezing pipe 7 before the shield machine excavation step S6. In the cement formation step S5 according to this embodiment, cement milk is supplied through the gap between the outer peripheral surface of the small freezing pipe 7 and the inner peripheral surface of the freezing outer pipe 2. By supplying cement milk between the bottom wall 212 of the freezing outer pipe 2 and the bottom end of the small freezing pipe 7 in the freezing outer pipe 2, the refrigerant filled during the frozen soil creation step S3 is replaced with cement milk. In the freezing outer pipe 2, the cement milk filled between the bottom wall 212 of the freezing outer pipe 2 and the bottom end of the small freezing pipe 7 hardens to form cement, making the portion of the freezing outer pipe 2 that overlaps with the excavation area hard and brittle. As a result, the freezing outer pipe 2 is more likely to be crushed by the shield machine. Furthermore, by replacing the refrigerant with cement milk, even if the outer freezing pipe 2 is cut by the shield machine, the flow of the refrigerant into the ground can be reduced.

[0046] In the ground excavation method according to this embodiment, the cement formation step S5 is performed between the cooling / heating range changing step S4 and the shield machine excavation step S6, but the cement formation step S5 may be performed before the cooling / heating range changing step S4. For example, before inserting the small freezing tube 7 into the freezing outer tube 2, cement milk may be injected into the freezing outer tube 2 to replace the refrigerant with the cement milk. In this case, it is preferable that the specific gravity of the cement milk is heavier than that of the brine.

[0047] (Shield machine excavation process S6) The shield machine excavation process S6 is a process of excavating the excavation area R3 with the shield machine while leaving the frozen outer pipe 2 in the excavation area R3. After the cold / heat range change process S4 is completed, the shield machine enters the excavation area R3 and performs excavation.

[0048] At this time, the frozen outer pipe 2 is left in the excavation area R3 and interferes with the shield machine, but because the frozen outer pipe 2 is made of resin, it can be easily crushed together with the ground 4. Moreover, the part of the frozen outer pipe 2 that overlaps the excavation area is filled with cement, making it hard and brittle, making it even easier to crush.

[0049] Thus, according to the ground excavation method of this embodiment, the cold energy range is changed prior to excavation using the shield machine, and the frozen state of the non-excavation area on the surface side is maintained. Then, the ground 4 in the excavation area R3 is excavated together with the frozen outer pipe 2 placed within the excavation area R3. Because the frozen outer pipe 2 is made of resin, it can be excavated together with the ground 4 in the excavation area. This allows the shield machine to excavate the excavation area R3 without pulling out the frozen outer pipe 2 from the ground 4. As a result, compared to conventional construction methods, the work of pulling out the frozen outer pipe 2 can be reduced, making it easier to shorten the work period. Moreover, because the cold energy range is changed to maintain the frozen state of the non-excavation area on the surface side, the cold energy from the freezing outer pipe 2 can be concentrated in the non-excavation area on the surface side, allowing for efficient use of the cold energy and reducing the collapse of the hole wall.

[0050] In addition, while a small metal freezing pipe 7 is used to provide cold heat to the non-excavated area on the surface side, only a plastic freezing outer pipe 2 is placed in the excavation area R3, so cold heat can be used more efficiently while reducing the work of pulling out the freezing outer pipe 2.

[0051] (Application example) In the ground excavation method according to this embodiment, in the frozen soil creation step S3, construction work on the ground 4 can be carried out in the frozen soil created state, as in a general ground freezing method. For example, after the frozen soil creation step S3, tunnel widening work may be carried out, and then, when connecting the tunnel to the widened section, the cold / heat range change step S4 and the shield machine excavation step S6 may be carried out.

[0052] In another aspect, the ground excavation method according to the present disclosure can also be used to replace the shield machine bit 11. That is, after creating frozen soil through the frozen outer pipe installation step S2, frozen soil creation step S3, cold range change step S4, and shield machine excavation step S6 and excavating the frozen region R2 with the shield machine, the shield machine can be positioned in the borehole, and the bit 11 can be replaced in the borehole after preventing the hole wall from collapsing.

[0053] [Variations] The ground excavation method according to the above embodiment uses a freezing outer pipe 2 formed from a vertical pipe erected into ground 4 having a horizontal ground surface 41, but as shown in Fig. 3, a freezing outer pipe 2 formed from a horizontal pipe may also be used. The "horizontal pipe" referred to in this disclosure means a freezing outer pipe 2 erected via a water stopping device 8 fixed to the ground surface 41. In this embodiment, the horizontal pipe extends along a horizontal plane so as to be approximately perpendicular to the ground surface 41 that intersects with the horizontal plane.

[0054] 3, the ground excavation method according to the modification includes a casing embedding step S1, a frozen outer pipe installation step S2, a frozen soil creation step S3, a cold / heat range changing step S4, and a shield machine excavation step S6, in this order. The ground excavation method according to the modification does not include the cement formation step S5, but may include the cement formation step S5.

[0055] Referring to FIG. 3(a), the casing burying step S1 is a step of inserting the casing 1 horizontally into ground 4 having a ground surface 41 that intersects with a horizontal plane, and erecting the casing 1. The ground surface 41 of the ground 4 is formed, for example, by a retaining wall. The surface of the retaining wall may be a vertical plane or may be an inclined plane that is inclined relative to the vertical plane. The ground surface 41 of the ground 4 may be formed by a retaining wall, may be formed by a retaining block, or may be formed by natural ground.

[0056] When inserting the casing 1 into the ground 4, a water stop device 8 fixed to the ground surface 41 is used. The water stop device 8 can hold the casing 1 while sealing the gap between the periphery of the opening on the ground surface 41 and the outer circumferential surface of the casing 1. The water stop device 8 can reduce groundwater leaking from the opening on the ground surface 41.

[0057] The casing 1 has a casing body 12 and a tip portion 13 provided at the end of the casing body 12 on the ground side in the central axis direction. The tip portion 13 has a bit 11 and a check valve 14. The tip portion 13 is detachably attached to the casing body 12.

[0058] 3(b) and (c), in the freezing outer pipe installation step S2, a resin freezing outer pipe 2 is inserted into the casing 1 erected in the ground 4. At this time, a water stop device 8 is used to insert the freezing outer pipe 2. In this modified example, a device (referred to as a "freezing outer pipe device 3") is used in which a metal pipe (referred to as a "connecting pipe 31") is connected to the resin freezing outer pipe 2.

[0059] The freezing outer pipe device 3 is coaxially connected to the ground surface end of the resin freezing outer pipe 2 so that the metal connecting pipe 31 passes through. The freezing outer pipe 2 and the connecting pipe 31 are connected by a transition joint 32.

[0060] When the freezing outer pipe 2 is inserted into the casing 1, the connecting pipe 31 protrudes from the ground surface 41. After this, as shown in Figure 3(c), the casing 1 is pulled out from the ground 4. The casing 1 is removed from the ground 4 by pulling out only the casing body 12 from the ground 4 while leaving the tip portion 13 in the ground 4.

[0061] The casing 1 is pulled out while the water is stopped by the water stop device 8. Then, the frozen soil creation step S3 is carried out while the water is stopped by the water stop device 8. After the frozen soil has been created, the water stop device 8 is removed from the ground surface 41, and the metal water stop plate 9 fixed to the ground surface 41 is fixed to the connecting pipe 31 by welding. The welding between the connecting pipe 31 and the water stop plate 9 is performed by full-circumference welding along the entire length of the outer surface of the connecting pipe 31. The water stop plate 9 and the ground surface 41 are joined, for example, by welding, screwing, or the like.

[0062] Referring to Figure 3(d), after the frozen soil creation step S3, the cold heat range change step S4 is carried out. A small freezing pipe 7 is inserted inside the outer freezing pipe 2, and the cold heat range is changed so that cold heat is applied mainly to the non-excavation area on the ground surface. This keeps the non-excavation area on the ground surface frozen. After this, the shield machine excavation step S6 is carried out.

[0063] The freezing outer pipe 2, which consists of a horizontal pipe, may be formed from a first pipe 21 made of polyethylene and having a cylindrical bottom, a second pipe 22 made of polyethylene and including openings on both end faces, and a first fitting 24 made of resin that connects the first pipe 21 and the second pipe 22.

[0064] [Other variations] While the first pipe 21 according to the above embodiment has only one peripheral wall 211, for example, the peripheral wall 211 may have a first portion to which the bottom wall 212 is connected, a second portion to which the reduced diameter portion 213 is connected, an intermediate portion interposed between the first portion and the second portion, and multiple joints. One of the multiple joints can connect the first portion and the intermediate portion, and another can connect the intermediate portion and the second portion. The joints can also connect the first portion and the second portion. This allows the length of the first pipe 21 to be adjusted on-site depending on the freezing region R2, and also makes transportation easier.

[0065] In the cement formation step S5 according to the above embodiment, the refrigerant is replaced with cement milk, and as a result, in the cold / heat range change step S4, cement milk is filled between the small freezing pipe 7 and the outer freezing pipe 2. However, the cement formation step S5 may be omitted. In this case, a refrigerant may be interposed between the small freezing pipe 7 and the outer freezing pipe 2 in the cold / heat range change step S4. Also, in the cold / heat range change step S4, the refrigerant may be replaced with water. This reduces the risk of the refrigerant flowing into the ground even when the outer freezing pipe 2 is cut in the shield machine excavation step S6. Also, in the cold / heat range change step S4, the refrigerant may be removed from the outer freezing pipe 2 by a pump before the outer freezing pipe 7 is inserted into the outer freezing pipe 2.

[0066] It should be understood that the embodiments disclosed herein are illustrative in all respects and are not limiting in any respect. The scope of the present invention is defined not by the above description but by the claims, and it is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0067] S1 casing burying process, S2 frozen outer pipe installation process, S3 frozen soil creation process, S4 cold range change process, S5 cement formation process, S6 shield machine excavation process, 1 casing, 11 bit, 2 frozen outer pipe, 21 first pipe, 211 surrounding wall, 212 bottom wall, 213 diameter reduction section, 22 second pipe, 23 insulation material, 24 joint, 3 frozen outer pipe equipment, 31 connecting pipe, 32 transition joint, 4 ground, 41 ground surface, 5 freezing machine, 51 outward path, 52 return path, 6 inner pipe, 7 small frozen pipe, 71 second outer pipe, 72 second inner pipe, 8 water stop device, 9 water stop plate, H1 first range, H2 second range, R1 non-frozen area, R2 frozen area, R3 excavation area.

Claims

1. A process of erecting a resin outer freezing pipe into the ground; a step of inserting an inner pipe into the outer freezing pipe erected in the ground, supplying a refrigerant from the inner pipe, and freezing a freezing region by cold heat from the outer freezing pipe; A process of changing the cold heat range so that cold heat is applied mainly to a surface-side non-excavation area located on the ground surface side of the excavation area, which is an area through which the shield machine passes, and maintaining the frozen state of the surface-side non-excavation area; and excavating the excavation area by the shield machine while leaving the frozen outer pipe in the excavation area, In the step of maintaining the frozen state of the non-excavated area on the ground surface, a ground excavation method is performed in which, while maintaining the freezing outer pipe that was erected in the step of freezing the frozen area, a small, bottomed, cylindrical metal freezing pipe that generates cold is inserted into the freezing outer pipe with the inner pipe pulled out from the freezing outer pipe, and the bottom end of the small freezing pipe is positioned in the non-excavated area on the ground surface, thereby changing the cold range.

2. The ground excavation method according to claim 1, further comprising a step of supplying cement milk between the bottom of the outer freezing pipe and the bottom end of the small freezing pipe within the outer freezing pipe to form cement before the step of excavating the excavation area with the shield machine.

3. The outer freezing tube is a first pipe made of polyethylene and having a bottomed cylindrical shape; a second pipe made of polyethylene including openings on both end surfaces; a resin joint that connects the first pipe and the second pipe, 3. The ground excavation method according to claim 1 or 2.

4. 3. The ground excavation method according to claim 1, wherein the outer freezing pipe has a heat insulating material that forms a non-freezing region between the frozen region and the ground surface.

5. 3. The ground excavation method according to claim 1, wherein the outer freezing pipe is a vertical pipe.

6. 3. The ground excavation method according to claim 1, wherein the outer freezing pipe is a horizontal pipe erected in the ground via a water-stopping device fixed to the ground surface and intersecting a horizontal plane.

7. 3. The ground excavation method according to claim 1, wherein the refrigerant is brine.

8. A freezing outer pipe used in the ground excavation method according to claim 1, a first pipe made of polyethylene and having a bottomed cylindrical shape; a second pipe made of polyethylene including openings on both end surfaces; a resin joint that connects the first pipe and the second pipe.

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