Ground excavation method and frozen outer pipe used therein

Abstract

This method allows for the use of ground freezing techniques, which involve freezing the ground using the cold heat from the freezing outer pipe that has passed through the impermeable wall, while simultaneously shortening the work period when excavating using a shield machine. [Solution] The ground excavation method comprises: a preparation step of installing a connecting pipe and a water-stopping device against a watertight wall; a casing burial step of burying a casing tube in the ground; a freezing outer pipe insertion step of inserting a freezing outer pipe into the inside of the casing tube, wherein the freezing outer pipe inserted into the casing tube has a resin cuttable portion located in the excavation area which is the area through which the shield machine passes, and a metal non-cuttable portion connected to the cuttable portion; a casing retraction step of moving the casing tube toward the working space side and retracting the casing tube at least to the working space side beyond the excavation area; a frozen soil creation step of freezing the ground with cold heat from the freezing outer pipe; a finishing step of removing the water-stopping device and cutting the connecting pipe, and sealing the opening between the cut end of the connecting pipe and the non-cuttable portion by welding; and a shield machine excavation step of excavating the excavation area with a shield machine while leaving the cuttable portion of the freezing outer pipe in the excavation area.

Description

Technical Field

[0001] The present disclosure relates to a ground excavation method and a freezing outer pipe used therefor.

Background Art

[0002] Conventionally, a ground freezing method is known in which a freezing pipe is installed in the ground, the ground is frozen using the freezing pipe to form frozen soil, and a shield machine is made to enter the frozen soil to form a tunnel or the like. According to the ground freezing method, since the ground can be frozen by the heat and cold from the freezing pipe, it is possible to prevent the collapse of the drilled hole wall.

[0003] By the way, when a shield machine is made to enter at a location where a freezing pipe exists, it is necessary to previously pull out the freezing pipe before excavating the frozen ground with the shield machine. However, in the ground freezing method, since the freezing pipe and the ground are frozen, in order to pull out the freezing pipe, high-temperature hot water needs to be supplied into the freezing pipe to thaw the frozen soil around the freezing pipe, and then the freezing pipe must be pulled out. For this reason, not only is the work complicated, but the work period is also likely to be prolonged.

[0004] Therefore, in the ground excavation method described in Patent Document 1, the ground is frozen using a freezing pipe formed of mild steel. By freezing the ground using a freezing pipe formed of mild steel, when the ground is excavated by a shield machine, the mild steel can be cut together with the ground. Thereby, the work of pulling out the freezing pipe from the ground can be omitted, and the work period can be shortened.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Incidentally, Patent Document 1 describes the case of installing freezing pipes through a watertight wall included in underground structures such as tunnels, but it does not consider specific methods for stopping groundwater flow or stopping water flow after freezing.

[0007] The present invention has been made in view of the above circumstances, and its purpose is to provide a ground excavation method and a freezing outer pipe used therein that can shorten the working period when excavating using a shield machine while performing a ground freezing method that freezes the ground by the cold heat from a freezing outer pipe that has passed through a watertight wall. [Means for solving the problem]

[0008] A ground excavation method according to one aspect of the present disclosure comprises a preparation step of installing a connecting pipe having a mud discharge valve and a water-stopping device connected to the connecting pipe in a watertight wall constructed between the ground and the work space; a casing burial step of passing a casing tube through the water-stopping device and the connecting pipe after the preparation step and burying the casing tube in the ground; and a freezing outer tube insertion step of inserting a freezing outer tube into the casing tube buried in the ground after the casing burial step, wherein the freezing outer tube inserted into the casing tube has a resin cuttable portion located in the excavation area which is the area through which the shield machine passes, and a metal non-cuttable portion connected to the cuttable portion and extending toward the work space. The method comprises: inserting a frozen outer tube; moving the casing tube, which has been erected in the ground after the frozen outer tube insertion step, toward the work space, thereby moving the casing tube at least toward the work space side beyond the excavation area; creating frozen soil after the casing retraction step, supplying a refrigerant into the frozen outer tube and freezing the ground with the cold from the frozen outer tube; finishing after the frozen soil creation step, removing the water-stopping device and cutting the connecting pipe, and sealing the opening between the cut end of the connecting pipe and the uncut portion by welding; and a shield machine excavation step in which the excavation area is excavated by the shield machine while the cuttable portion of the frozen outer tube remains in the excavation area.

[0009] A freezing outer tube according to one aspect of the present disclosure is a freezing outer tube for freezing the ground with a refrigerant supplied inside, comprising: a bottomed cylindrical resin cuttable portion; a metal non-cuttable portion connected to the cuttable portion and extending along the central axis of the cuttable portion; and a joint connecting the resin cuttable portion and the metal non-cuttable portion. [Effects of the Invention]

[0010] According to the above-described embodiment of this disclosure, the working period when performing excavation using a shield machine can be shortened while performing a ground freezing method that freezes the ground using the cold heat from the freezing outer pipe that has passed through the impermeable wall. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a flowchart of the ground excavation method according to the embodiment. [Figure 2] Figure 2 is a schematic cross-sectional view illustrating the preparation process in the ground excavation method according to the embodiment. [Figure 3] Figure 3 is a schematic cross-sectional view illustrating the casing installation process in the ground excavation method according to the embodiment. [Figure 4] Figure 4 is a schematic cross-sectional view illustrating the frozen outer pipe insertion process in the ground excavation method according to an embodiment. [Figure 5] Figure 5 is a schematic cross-sectional view illustrating the casing retraction process in the ground excavation method according to the embodiment. [Figure 6] Figures 6(a) and 6(b) are schematic cross-sectional views of the tip portion of the casing tube according to the embodiment. [Figure 7] Figure 7 is a schematic cross-sectional view illustrating the frozen soil preparation process and the finishing process in the ground excavation method according to the embodiment. [Figure 8] Figure 8 is a schematic enlarged cross-sectional view illustrating the finishing process in the ground excavation method according to the embodiment. [Figure 9] Figure 9 is a schematic cross-sectional view illustrating the sealing process in the ground excavation method according to the embodiment. [Figure 10] Figure 10 is a flowchart of the ground excavation method according to the first modified example. [Modes for carrying out the invention]

[0012] First, the embodiments of this disclosure will be listed and described. (1) A ground excavation method in accordance with the present disclosure comprises a preparation step of installing a connecting pipe having a mud discharge valve and a water-stopping device connected to the connecting pipe in a watertight wall constructed between the ground and the work space; a casing burial step of passing a casing tube through the water-stopping device and the connecting pipe after the preparation step and burying the casing tube in the ground; and a freezing outer pipe insertion step of inserting a freezing outer pipe into the casing tube buried in the ground after the casing burial step, wherein the freezing outer pipe inserted into the casing tube has a resin cuttable portion located in the excavation area which is the area through which the shield machine passes, and a metal non-cuttable portion connected to the cuttable portion and extending toward the work space. The method comprises: inserting the frozen outer tube; moving the casing tube, which has been erected in the ground after the frozen outer tube insertion step, toward the working space, thereby moving the casing tube at least toward the working space side beyond the excavation area; creating frozen soil after the casing retraction step, supplying a refrigerant into the frozen outer tube and freezing the ground with the cold from the frozen outer tube; finishing after the frozen soil creation step, removing the water-stopping device and cutting the connecting pipe, and sealing the opening between the cut end of the connecting pipe and the uncut portion by welding; and a shield machine excavation step in which the shield machine excavates the excavation area with the cuttable portion of the frozen outer tube remaining in the excavation area.

[0013] With this configuration, a ground freezing method can be performed in which a freezing outer pipe, having a resin cuttable section and a metal non-cuttable section, is installed so as to pass through a watertight wall, and the ground is frozen by the cold heat emanating from the freezing outer pipe. In this case, because the freezing outer pipe has a metal non-cuttable section, the opening between the non-cuttable section of the freezing outer pipe and the connecting pipe can be sealed by welding during the finishing process, ensuring reliable watertightness with good workability. Furthermore, since it is not necessary to pull the freezing outer pipe out of the ground before the shield machine enters the excavation area, the work period can be easily shortened, and cold heat can be continuously applied until the shield machine enters the excavation area.

[0014] (2) A ground excavation method in accordance with the present disclosure includes: a preparation step of installing a connecting pipe having a mud discharge valve and a water-stopping device connected to the connecting pipe on a water-stopping wall constructed between the ground and a work space; a casing burial step of passing a casing tube through the water-stopping device and the connecting pipe after the preparation step and burying the casing tube in the ground; a first freezing outer pipe insertion step of inserting a first freezing outer pipe into the casing tube buried in the ground after the casing burial step; a casing retraction step of moving the casing tube buried in the ground toward the work space after the first freezing outer pipe insertion step and retracting the casing tube toward the work space; a first frozen soil creation step of supplying a refrigerant into the first freezing outer pipe and freezing the ground by the cold from the first freezing outer pipe; and the first The method comprises: a second freezing outer pipe insertion step in which, after the frozen soil creation step, the first freezing outer pipe is withdrawn from the ground and a second freezing outer pipe is inserted into the ground, wherein the second freezing outer pipe has a resin cuttable portion located in the excavation area which is the area through which the shield machine passes, and a metal non-cuttable portion connected to the cuttable portion and extending toward the work space; a second frozen soil creation step in which, after the second freezing outer pipe insertion step, a refrigerant is supplied into the second freezing outer pipe and the ground is frozen by the cold heat from the second freezing outer pipe; a finishing step in which, after the frozen soil creation step, the water-stopping device is removed and the connecting pipe is cut, and the opening between the cut end of the connecting pipe and the non-cuttable portion is sealed by welding; and a shield machine excavation step in which, with the cuttable portion of the second freezing outer pipe remaining in the excavation area, the excavation area is excavated by the shield machine.

[0015] With such a configuration, it is possible to carry out a ground freezing method in which a second freezing outer pipe having a resin-made cuttable portion and a metal-made non-cuttable portion is built in so as to pass through the water-blocking wall, and the ground is frozen by the cold heat from the freezing outer pipe. At that time, since the freezing outer pipe has a metal-made non-cuttable portion, in the closing process, the opening between the non-cuttable portion in the freezing outer pipe and the connecting pipe can be closed by welding, and water can be surely stopped with good workability. Further, since it is not necessary to pull out the freezing outer pipe from the ground before the shield machine enters the excavation area, it is easy to shorten the working period, and it is also possible to continue applying cold heat until the shield machine enters the excavation area.

[0016] (3) In the above (1) or (2), further comprising a sealing process executed after the above closing process and before the shield machine excavation process, and in the sealing process, the opening in the non-cuttable portion may be closed by welding. With this configuration, the opening in the non-cuttable portion can be closed with good workability and high water-blocking performance.

[0017] (4) In any one of the above (1) to (3), in the preparation process, the connecting pipe may be fixed by welding to a metal plate fixed to the water-blocking wall and having a through hole leading to the connecting pipe. With this configuration, the connecting pipe can be installed with respect to a water-blocking wall that is not made of metal (for example, made of concrete).

[0018] (5) In any one of the above (1) to (4), in the casing retreat process, the casing tube may be held in a state where a part of the casing tube is located between the excavation area and the water-blocking wall. With this configuration, it is not necessary to completely pull out the casing tube, and other processes can be executed while maintaining the water-blocking by the water-blocking device.

[0019] (6) In (5) above, the finishing step may involve cutting off the portion of the casing tube that protrudes from the watertight wall and sealing the opening between the casing tube and the uncut portion by welding. This configuration allows for easy workability and high watertightness in sealing the opening between the casing tube and the uncut portion.

[0020] (7) In any one of (1) to (6) above, the casing retraction step may involve pulling the casing tube out of the ground. This configuration eliminates the need to cut the casing tube.

[0021] (8) A ground excavation method in accordance with the present disclosure includes: a preparation step of installing a connecting pipe having a mud discharge valve and a water-stopping device connected to the connecting pipe on a watertight wall constructed between the ground and the work space; a first freezing outer pipe insertion step of passing a first freezing outer pipe through the water-stopping device and the connecting pipe after the preparation step and burying the first freezing outer pipe in the ground; a first frozen soil creation step of supplying a refrigerant into the first freezing outer pipe after the first freezing outer pipe insertion step and freezing the ground with the cold from the first freezing outer pipe; and a second freezing outer pipe insertion step of pulling out the first freezing outer pipe from the ground and inserting a second freezing outer pipe into the ground after the first frozen soil creation step, wherein the second freezing outer pipe is a shield machine The shield machine includes: a second freezing outer pipe insertion step, which has a resin cuttable portion located in the excavation area through which the shield passes, and a metal non-cuttable portion connected to the cuttable portion and extending toward the work space; a second frozen soil creation step, which, after the second freezing outer pipe insertion step, supplies a refrigerant into the second freezing outer pipe and freezes the ground with the cold from the second freezing outer pipe; a finishing step, which, after the second frozen soil creation step, removes the water-stopping device and cuts the connecting pipe, and closes the opening between the cut end of the connecting pipe and the non-cuttable portion by welding; and a shield machine excavation step, which excavates the excavation area with the shield machine while leaving the cuttable portion of the second freezing outer pipe in the excavation area.

[0022] With this configuration, a second freezing outer pipe, which has a resin cuttable section and a metal non-cuttable section, is installed so as to pass through the watertight wall, and a ground freezing method is performed in which the ground is frozen by the cold heat emanating from the freezing outer pipe. In this case, since the freezing outer pipe has a metal non-cuttable section, the opening between the non-cuttable section of the freezing outer pipe and the connecting pipe can be sealed by welding during the finishing process, ensuring reliable watertightness with good workability. Furthermore, since it is not necessary to pull the freezing outer pipe out of the ground before the shield machine enters the excavation area, the work period can be easily shortened, and cold heat can be continuously applied until the shield machine enters the excavation area.

[0023] (9) In (8) above, a casing burying step may be further provided, which is performed between the preparation step and the first freezing outer pipe insertion step, and involves passing the casing tube through the water-stopping device and the connecting pipe, and burying the casing tube in the ground. The first freezing outer pipe insertion step may involve burying the first freezing outer pipe in the ground by inserting the first freezing outer pipe into the casing tube. In the first frozen soil creation step, the ground may be frozen by conducting the cold from the first freezing outer pipe to the ground through the casing tube. In the second freezing outer pipe insertion step, after the first frozen soil creation step, the first freezing outer pipe and the casing tube may be pulled out of the ground together. This configuration simplifies the work of pulling out the casing tube and the first freezing outer pipe.

[0024] (10) One embodiment of a freezing outer tube according to the present disclosure is a freezing outer tube into which an inner tube is inserted and which freezes the ground by cold heat from a refrigerant supplied from the inner tube, and may comprise a bottomed cylindrical resin cuttable portion, a metal non-cuttable portion connected to the cuttable portion and extending along the central axis of the cuttable portion, and a joint connecting the resin cuttable portion and the metal non-cuttable portion. This configuration makes it possible to provide a freezing outer tube suitable for a ground excavation method performed on the ground along a watertight wall.

[0025] Next, embodiments of the ground excavation method relating to this disclosure will be described below with reference to the drawings. In the following drawings, identical or corresponding parts will be given the same reference numeral, and their descriptions will not be repeated.

[0026] (Overview of ground excavation methods) The ground excavation method according to this embodiment is a method suitable for construction using a shield machine when a ground freezing method is being implemented to freeze the ground 2 inside the impermeable wall 1. As shown in Figure 1, the ground excavation method comprises a preparation step S1, a casing embedding step S2, a freezing outer pipe insertion step S3, a casing retraction step S4, a frozen soil creation step S5, a finishing step S6, a main construction step S7, a sealing step S8, and a shield machine excavation step S9, and these steps are executed in this order. As shown in Figure 4, the freezing outer pipe 6 used in this embodiment comprises a bottomed cylindrical resin cuttable portion 61, a metal non-cuttable portion 62 extending along the central axis of the cuttable portion 61, and a joint 63 connecting the resin cuttable portion 61 and the metal non-cuttable portion 62. According to the ground excavation method of this embodiment, as shown in Figure 7, in the finishing process S6, the resin cuttable portion 61 can be left in the excavation area excavated by the shield machine, while the opening between the metal non-cuttable portion 62 and the connecting pipe 3 can be closed by welding.

[0027] Therefore, the excavation area can be excavated by the shield machine without having to pull out the frozen outer pipe 6 from the ground 2, and the closing process S6 and sealing process S8 on the work space side can be carried out using welding. As a result, the opening between the non-cutting section 62 and the connecting pipe 3 can be reliably sealed with good workability, and the work of pulling out the frozen outer pipe 6 can be reduced. Thus, the work period when excavating the ground using a shield machine can be shortened while performing the ground freezing method, which freezes the ground with the cold heat from the frozen outer pipe 6 that has passed through the watertight wall 1.

[0028] In the following, for the sake of clarity, the side of the freezing outer pipe 6 that is further away from the working space in the ground, along its central axis, will be defined as the "underground side," and the opposite side as the "working space side." Furthermore, in this disclosure, "parallel" includes not only cases where two lines, planes, etc. (hereinafter referred to as "lines, etc.") do not intersect when extended, but also cases where the angle between the two lines, etc. intersects within a range of 10° or less. Furthermore, "orthogonal" means cases where two lines, etc. intersect within a range of 90° ± 10°. However, even if the two lines, etc. do not directly intersect, they are included in "orthogonal" if they intersect when extended.

[0029] (Preparation process S1) Preparation step S1 is the process of preparing to bury the casing tube 5 in the ground. Here, Figure 2 shows a schematic cross-sectional view illustrating preparation step S1. As shown in Figure 2, preparation step S1 involves attaching the connecting pipe 3 to the impermeable wall 1, and then installing the water-stopping device 4 on the connecting pipe 3 (see Figure 3).

[0030] The impermeable wall 1 is constructed between the ground 2 and the working space. In this embodiment, the ground 2 has sides that are aligned with a vertical plane. The ground 2 contains groundwater. The impermeable wall 1 is constructed so as to be in contact with the side of the ground 2. The impermeable wall 1 can reduce the outflow of groundwater from the ground 2. However, the side of the ground 2 does not have to be aligned with a vertical plane; for example, it may be an inclined surface, a horizontal surface, or a curved surface. Examples of the impermeable wall 1 include segments in shield tunneling and walls in shafts. Examples of the working space include the space inside a tunnel and the space inside a shaft.

[0031] The impermeable wall 1 has a first main surface 11 that is in contact with the ground 2 and a second main surface 12 on the opposite side. In this embodiment, the second main surface 12 is a vertical surface, but it does not have to be a vertical surface. The impermeable wall 1 may be made of concrete or metal.

[0032] A metal plate 13 is attached to the watertight wall 1. Through holes 131 are formed in the metal plate 13. Examples of materials for the metal plate 13 include iron and stainless steel. A water-stopping plate 14 may be placed between the watertight wall 1 and the metal plate 13. An example of the water-stopping plate 14 is a rubber sheet. For attaching the metal plate 13 to the watertight wall 1, for example, concrete anchors are used. The concrete anchors may be metal anchors or adhesive anchors. Note that if the watertight wall 1 is made of metal, the metal plate 13 may not be necessary.

[0033] A connecting pipe 3 is installed on the metal plate 13. The connecting pipe 3 connects the metal plate 13 to the water-stopping device 4. The connecting pipe 3 is formed in a cylindrical shape with open surfaces on both ends. The connecting pipe 3 is fixed to the metal plate 13 so as to pass through a through hole 131 in the metal plate 13. The connecting pipe 3 is fixed to the metal plate 13 by means of welding, bolting, screw joining which threads are formed between the outer surface of the connecting pipe 3 and the inner surface of the through hole 131, for example. In this embodiment, the connecting pipe 3 is welded all around the metal plate 13. If there is no metal plate 13, the connecting pipe 3 is welded directly to the water-stopping wall 1.

[0034] The connecting pipe 3 may have an injection valve 31 and a sludge discharge valve 32. By opening the sludge discharge valve 32, sludge that has moved from underground to the working space and accumulated in the connecting pipe 3 during drilling can be discharged. After the freezing outer pipe is buried, the cement bentonite solution can be injected around the freezing outer pipe using the injection valve 31. This allows for the replenishment of soil and sand discharged during excavation, and also improves heat transfer by filling gaps in the soil and sand (i.e., filling the gaps).

[0035] The inner surface of the connecting pipe 3 may be close to the outer surface of the casing tube 5. This allows the connecting pipe 3 to function as a guide when inserting the casing tube 5 into the ground. However, the connecting pipe 3 does not necessarily have to have a guiding function.

[0036] The water-stopping device 4 is installed at the end of the pair of ends of the connecting pipe 3 that is opposite to the metal plate 13. The water-stopping device 4 allows the casing tube 5 to move toward the ground 2, while preventing the passage of groundwater and sludge moving toward the working space along the outer surface of the casing tube 5.

[0037] Referring to Figure 3, the water-stopping device 4 comprises a housing 41, a connecting pipe connection port 42 connected to the connecting pipe 3, a casing tube insertion port 43 into which the casing tube 5 is inserted, and a water-stopping valve (not shown) located inside the housing 41. The connecting pipe connection port 42 and the casing tube insertion port 43 are located on the extension of the central axis of the connecting pipe 3. The casing tube 5 inserted into the casing tube insertion port 43 passes through the connecting pipe connection port 42, is inserted into the connecting pipe 3, and is then inserted into the ground 2. The water-stopping valve is a valve body that can open and close the gap between the housing 41 and the casing tube 5. The water-stopping device 4 makes it possible to reduce leakage of groundwater and sludge to the outside while inserting the casing tube 5 into the ground 2.

[0038] In this way, the preparation step S1 is completed by installing the connecting pipe 3 and the water-stopping device 4 on the watertight wall 1. After the completion of the preparation step S1, the casing burying step S2 is performed.

[0039] (Casing burial process S2) The casing burying process S2 is the process of embedding (laying) the casing tube 5 into the ground 2. Here, Figure 3 is a schematic cross-sectional view illustrating the casing burying process S2. Referring to Figure 3, in the casing burying process S2, a hole is drilled in the impermeable wall 1 along the extension of the central axis of the connecting pipe 3 using a drilling machine, and then the casing tube 5 is embedded toward the ground 2 while rotating through the water-stopping device 4 and the connecting pipe 3. With the casing tube 5, in the next process, the freezing outer pipe insertion process S3, the collapse of the hole wall can be reduced while the freezing outer pipe 6 can be embedded in the ground.

[0040] The casing tube 5 is a cylindrical steel tube for drilling. The end of the casing tube 5 on the underground side in the direction of the central axis (hereinafter referred to as the tip 51) has a plurality of bits 521. The plurality of bits 521 are arranged at intervals along the outer circumference of the tip of the casing tube 5. The tip 51 of the casing tube 5 also has a discharge port 531 and a check valve 54 connected to the discharge port 531.

[0041] In the casing embedding process S2, for example, a full-circumference rotating device is used to embed the casing tube 5 into the ground 2 (soil) while rotating it around its central axis. At this time, embedding the casing tube 5 can be made easier by discharging water from the discharge port 531 while embedding the casing tube 5. In this embodiment, the casing tube 5 is embedded horizontally, but it does not necessarily have to be horizontal. Also, the central axis of the casing tube 5 is perpendicular to the second main surface 12 of the impermeable wall 1, but it does not necessarily have to be perpendicular to the second main surface 12 of the impermeable wall 1.

[0042] In the casing burying process S2, multiple casing tubes 5 may be buried in the ground 2. The casing burying process S2 is completed when all the casings are buried in the ground 2 to the desired depth. After the completion of the casing burying process S2, the freezing outer tube insertion process S3 is performed.

[0043] (Freezing outer tube insertion process S3) The freezing outer pipe insertion process S3 is the process of inserting the freezing outer pipe 6 into the casing tube 5 that has been erected in the ground 2. Here, Figure 4 shows a schematic cross-sectional view illustrating the freezing outer pipe insertion process S3. Referring to Figure 4, the freezing outer pipe 6 used in the freezing outer pipe insertion process S3 has a cuttable portion 61, a non-cuttable portion 62, and a joint 63. The freezing outer pipe 6 also has a water-stopping portion 64 that stops groundwater from the ground between the non-cuttable portion 62 and the casing tube 5.

[0044] The cuttable portion 61 is formed in a bottomed cylindrical shape and has a peripheral wall 611 and a bottom wall 612. The cuttable portion 61 is made of resin. Examples of resins used to form the cuttable portion 61 include polyethylene, polyvinyl chloride, and fiber-reinforced plastic (FRP). At least a portion of the cuttable portion 61 is located in the excavation area when it is erected in the ground 2 (soil). The excavation area is the area in the ground 2 through which the shield machine passes when forming a tunnel or the like using the shield machine. Because the cuttable portion 61 is made of resin, it can be cut together with the shield machine while drilling. As a result, it is not necessary to remove the frozen outer pipe 6 from the ground before drilling with the shield machine.

[0045] In the central axis direction of the freezing outer pipe 6, the end of the cuttable portion 61 on the working space side may be formed with a smaller diameter than the end on the underground side. This allows the outer diameter of the joint 63 to be less than or equal to the outer diameter of the cuttable portion 61. This makes it possible to provide a non-cuttable portion 62 while maximizing the outer diameter of the cuttable portion 61.

[0046] The non-cutting portion 62 is formed in a cylindrical shape and is connected to the cuttable portion 61 by a joint 63. The central axis of the non-cutting portion 62 extends along the extension of the central axis of the cuttable portion 61 and extends from the cuttable portion 61 toward the work space. The non-cutting portion 62 is made of metal. Examples of metals that form the non-cutting portion 62 include iron and stainless steel. Because the non-cutting portion 62 is made of metal, it can be sealed by welding in the sealing process S8.

[0047] The joint 63 is a transition joint that connects a resin-made machinable portion 61 and a metal-made non-machinable portion 62. The joint 63 may be made of metal or resin. In this embodiment, the joint 63 is made of resin. The outer diameter of the joint 63 may be the same as the outer diameter of the machinable portion 61, or it may be less than or equal to the outer diameter of the machinable portion 61.

[0048] The water-stopping section 64 is fixed to the outer circumferential surface of the non-cutting section 62 and stops water from entering between the non-cutting section 62 and the casing tube 5. The water-stopping section 64 has a cylindrical body 641 fixed to the outer circumferential surface of the non-cutting section 62 and a gasket 642 fixed to the outer circumferential surface of the cylindrical body 641. The cylindrical body 641 may be fixed to the non-cutting section 62, for example, by welding. The water-stopping section 64 can stop groundwater from entering the working space by passing between the casing tube 5 and the frozen outer tube 6 (especially the non-cutting section 62) during the casing retraction process S4 and subsequent steps described later.

[0049] In the freezing outer tube insertion process S3, as shown in Figure 4, the freezing outer tube 6 is inserted into the casing tube 5. At this time, the freezing outer tube 6 passes through the water-stopping device 4, the connecting pipe 3, and the watertight wall 1, and is inserted to the desired position in the ground. The freezing outer tube insertion process S3 is completed when the freezing outer tube 6 is inserted in a one-to-one relationship for all of the casing tubes 5. After the completion of the freezing outer tube insertion process S3, the casing retraction process S4 is performed.

[0050] (Casing retraction process S4) The casing retraction process S4 is a process of moving the casing tube 5, which is embedded in the ground 2, toward the work space, thereby retracting the casing tube 5 at least toward the work space side beyond the excavation area. Here, Figure 5 shows a schematic cross-sectional view illustrating the casing retraction process S4.

[0051] As shown in Figure 5, in the casing retraction process S4, the casing tube 5 is moved toward the work space while the freezing outer tube 6 inserted inside the casing tube 5 remains in the ground.

[0052] The tip 51 of the casing tube 5 is configured to be removable from the casing tube body 58. Here, Figure 6 shows a schematic cross-sectional view of the connection structure between the casing tube body 58 and the tip 51. Referring to Figure 6, the tip 51 has an outer cylinder portion 52 on which a plurality of bits 521 are formed, an inner cylinder portion 53 on which a discharge port 531 is formed, a check valve 54, a pair of pins 55 connecting the tip 51 and the casing tube body 58, and an elastic body 56 that presses the pins 55. The inner cylinder portion 53 is fixed inside the outer cylinder portion 52. The check valve 54 has a valve seat 541, a ball-shaped valve body 542, and an elastic member 543 that presses the valve body 542 against the valve seat 541. The check valve 54 allows fluid to pass from the casing tube body 58 toward the discharge port 531, and prevents fluid from passing from the discharge port 531 toward the casing tube body 58.

[0053] The tip 51 and the casing tube body 58 have a pair of holes 57 through which a pin 55 is passed, in the portion that overlaps radially. The tip 51 and the casing tube body 58 are connected by passing the pin 55 through the holes 57. The elastic body 56 applies an elastic force to the pin 55 in a direction outward from the central axis. As shown in Figure 6(b), the elastic body 56 can be manipulated by a tool 59 inserted into the casing tube body 58, causing the pin 55 to move toward the central axis. This disconnects the tip 51 and the casing tube body 58, allowing the casing tube body 58 to be moved toward the working space while leaving the tip 51 in place.

[0054] In the casing retraction step S4 according to this embodiment, as shown in Figure 5, the casing tube body 58 is moved until a part of the casing tube 5 (in this case, the tip of the casing tube body 58) is positioned between the excavation area and the impermeable wall 1, and is held in this position. Groundwater may seep between the casing tube 5 and the frozen outer pipe 6, but this can be stopped by the water-stopping section 64. This allows most of the cuttable portion 61 of the frozen outer pipe 6 to come into contact with the ground 2.

[0055] The casing retraction process S4 is completed by moving all casing tubes 5 towards the work space, thereby retracting the casing tubes 5 from the excavation area towards the work space. After the completion of the casing retraction process S4, the frozen soil formation process S5 is executed.

[0056] (Frozen soil creation process S5) The frozen soil formation process S5 is a process in which the ground 2 is frozen by the cold heat from the freezing outer pipe 6. Here, Figure 7 shows a schematic cross-sectional view illustrating the frozen soil formation process S5 and the finishing process S6 described later. Referring to Figure 7, in the frozen soil formation process S5, an inner pipe 7 is inserted into the freezing outer pipe 6 which has been installed in the ground, a refrigerant is supplied from the inner pipe 7 into the freezing outer pipe 6, and the ground 2 is frozen by the cold heat from the freezing outer pipe 6.

[0057] The inner tube 7 is inserted from the tip of the non-cutting portion 62 of the freezing outer tube 6 and extends to the vicinity of the inner bottom surface of the cuttable portion 61. The inner tube 7 may be made of resin or metal. The inner tube 7 is connected to a refrigerator installed on the ground via a forward path. The end of the freezing outer tube 6 is connected to the refrigerator via a return path. The refrigerator supplies refrigerant to the inner tube 7 via the forward path. The refrigerant supplied to the inside of the inner tube 7 is supplied into the freezing outer tube 6 from the vicinity of the bottom wall 612 of the freezing outer tube 6, collides with the bottom wall 612 of the freezing outer tube 6, flows along the peripheral wall 611 of the freezing outer tube 6 toward the working space, and returns to the refrigerator via the return path from the opening of the non-cutting portion 62. The refrigerant circulates between the refrigerator and the freezing outer tube 6, cooling the ground and forming frozen soil.

[0058] The refrigerant is, for example, brine, which is a coolant. As the brine, for example, an aqueous solution of calcium chloride is used. The brine is cooled to about -30°C by a refrigerator. The refrigerant is not limited to brine; for example, liquefied gases such as liquid nitrogen or liquefied carbon dioxide may be used. If the cooler is a so-called low-temperature liquefied gas type cooler in which a liquid gas is used as the refrigerant, the vaporized gas may be released into the atmosphere from the working space side end of the freezing outer tube 6.

[0059] The frozen soil formation process S5 is completed when the ground freezes. The finishing process S6 is executed after or during the completion of the frozen soil formation process S5.

[0060] (Closing process S6) The finishing process S6 is a process in which the connecting pipe 3 is cut and the opening between the cut end of the connecting pipe 3 and the uncut portion 62 of the frozen outer pipe 6 is closed by welding. In the finishing process S6 according to this embodiment, a portion of the casing tube 5 protruding from the cut end of the connecting pipe 3 is also cut, and the opening between the cut end of the connecting pipe 3 and the uncut portion 62 of the frozen outer pipe 6 is closed by welding.

[0061] This prevents groundwater from leaking out from the opening between the connecting pipe 3 and the uncut portion 62. In this embodiment, a portion of the casing tube 5 remains in the ground 2, but groundwater leaking out from the opening between the casing tube 5 and the inner surface of the through hole 131 in the metal plate 13 can also be reduced. Since the uncut portion 62 is made of metal, it is possible to join the surrounding portion of the uncut portion 62 by full-circumferential welding. Therefore, high watertightness can be easily obtained.

[0062] As used in this disclosure, "welding" means metallurgical joining. Welding includes, for example, fusion welding (arc welding, laser welding, etc.), pressure welding, and brazing (brazing, soldering, etc.).

[0063] The finishing process S6 may be performed once the ground 2 has frozen to a certain extent through the frozen soil preparation process S5. Because the ground 2 is partially frozen, groundwater leakage is reduced, allowing construction by welding to be carried out.

[0064] Here, Figure 8 shows a schematic enlarged cross-sectional view illustrating the finishing process S6. Referring to Figure 8, in the finishing process S6, the water-stopping device 4 is removed while the ground 2 is frozen due to the frozen soil creation process S5. Then, the base of the connecting pipe 3 is cut, and the casing tube 5 protruding from the cut end of the connecting pipe 3 is cut. In this disclosure, "the cut end of the connecting pipe 3" refers to the tip portion of the part of the connecting pipe 3 that remains on the metal plate 13 side after the connecting pipe 3 has been cut. However, if the entire connecting pipe 3 is cut when it is cut from the metal plate 13, the peripheral edge of the opening of the through hole 131 in the metal plate 13 shall be considered the "cut end of the connecting pipe 3".

[0065] A metal annular plate 8 may be placed between the cut end of the connecting pipe 3 and the uncut portion 62 of the frozen outer pipe 6. The annular plate 8 and the connecting pipe 3 are joined by welding, and the annular plate 8 and the uncut portion 62 are joined by welding. At this time, the cut end of the casing tube 5 is located on the underground side relative to the annular plate 8. If the gap between the cut end of the connecting pipe 3 and the uncut portion 62 of the frozen outer pipe 6 is narrow, the opening between the cut end of the connecting pipe 3 and the uncut portion 62 may be closed by build-up welding using filler material, without using the annular plate 8.

[0066] This allows the opening between the cut end and the uncut portion 62 of the connecting pipe 3 to be sealed by welding. The finishing process S6 is completed by sealing the opening between the cut end and the uncut portion 62 for all connecting pipes 3. After the completion of the finishing process S6, the main construction process S7 is executed.

[0067] (Main construction process S7) Construction process S7 is a process in which construction is carried out while the ground is being frozen. Examples of work carried out in construction process S7 include widening the shield and removing underground obstacles buried underground. The work is carried out within the area surrounded by the frozen soil formed in frozen soil creation process S5. In other words, the work carried out in construction process S7 is carried out in an area that does not interfere with the frozen outer pipe. After the completion of construction process S7 or during construction process S7, sealing process S8 is carried out.

[0068] (Sealing process S8) The sealing step S8 is a step in which the opening surface of the uncut portion 62 of the frozen outer tube 6 is sealed by welding. Here, Figure 9 shows a schematic cross-sectional view illustrating the sealing step S8. Referring to Figure 9, in the sealing step S8, if the inner tube 7 is made of metal, with the inner tube 7 withdrawn from the frozen outer tube 6, the opening on the working space side of the uncut portion 62 is sealed by welding. In this embodiment, in the uncut portion 62, the portion protruding from the cut end of the connecting tube 3 is cut off, and a metal disc 9 is placed along the opening surface of the uncut portion 62. In this state, the outer edge of the disc 9 and the opening end of the uncut portion 62 are joined by welding. If the inner tube 7 is made of resin, the opening on the working space side of the uncut portion 62 may be sealed by welding without withdrawing the inner tube 7 from the frozen outer tube 6.

[0069] In the sealing process S8, before withdrawing the inner pipe 7 from the frozen outer pipe 6, the brine inside the frozen outer pipe 6 may be replaced with cement grout. That is, cement 65 may be formed by supplying cement grout into the frozen outer pipe 6. This reduces the amount of brine that flows into the ground 2 even when the cuttable portion 61 is cut by the shield machine excavation process S9 described later. Furthermore, as the cement grout filled inside the frozen outer pipe 6 hardens and cement is formed, the portion inside the frozen outer pipe 6 that overlaps with the excavation area becomes hard and brittle. As a result, the frozen outer pipe 6 becomes easier to crush by the shield machine.

[0070] The sealing process S8 is completed by closing the openings on the non-cutting side 62 of all frozen outer tubes 6. After the sealing process S8 is completed, the shield machine excavation process S9 is performed.

[0071] (Shield machine drilling process S9) The shield machine excavation process S9 is a process in which the excavation area is excavated by the shield machine while the cuttable portion 61 of the frozen outer pipe 6 is left in the excavation area. In this embodiment, after the sealing process S8 is completed, the shield machine is moved into the excavation area and excavation is performed.

[0072] When the shield machine enters the excavation area, the cuttable section 61 remains within the excavation area and interferes with the shield machine. However, since the cuttable section 61 is made of resin, it can be easily crushed together with the surrounding ground 2. Moreover, because the cuttable section 61 is filled with cement, it is hard and brittle, making it even easier to crush.

[0073] (Examples of application) In the ground excavation method according to this embodiment, the frozen soil creation process S5 also includes a process for maintaining the frozen soil after it has been created. In other words, the frozen soil creation process S5 performed during or after the finishing process S6 is a process for maintaining the frozen soil without creating new frozen soil (frozen soil maintenance process), and this is also included in the frozen soil creation process S5. In the ground excavation method, the main construction process S7 may be carried out while the frozen soil creation process S5 (frozen soil maintenance process) is being performed. For example, after the frozen soil creation process S5, tunnel widening work may be carried out as the main construction process S7, and then work to connect the tunnel to the widened section may be carried out as the shield machine excavation process S9.

[0074] In another embodiment, the ground excavation method according to this disclosure can also be used for replacing bits of a shield machine. Specifically, frozen soil may be created by the preparation step S1, casing embedding step S2, frozen outer pipe insertion step S3, casing retraction step S4, frozen soil creation step S5, finishing step S6, sealing step S8, and shield machine excavation step S9, and after excavating the excavation area with the shield machine, the shield machine may be positioned within the excavation area to prevent collapse of the hole wall, and then the bits may be replaced within the excavation area. In this case, the construction step S7 may be omitted.

[0075] [First variation] The ground excavation method according to the above embodiment includes a preparation step S1, a casing burying step S2, a frozen outer pipe insertion step S3, a casing retraction step S4, a frozen soil creation step S5, a finishing step S6, a main construction step S7, a sealing step S8, and a shield machine excavation step S9. However, as shown in Figure 10, it may also include a preparation step S11, a casing burying step S12, a first frozen outer pipe insertion step S13, a casing retraction step S14, a first frozen soil creation step S15, a main construction step S16, a second frozen outer pipe insertion step S17, a second frozen soil creation step S18, a finishing step S19, a sealing step S20, and a shield machine excavation step S21.

[0076] Preparation process S11, casing burying process S12, casing retraction process S14, main construction process S16, finishing process S19, sealing process S20, and shield machine excavation process S21 are the same as the ground excavation method according to the above embodiment, so their explanation will be omitted.

[0077] The first freezing outer tube insertion step S13 is performed after the casing burial step S12. In the first freezing outer tube insertion step S13, the first freezing outer tube is inserted into the casing tube 5 that has been erected in the ground 2 after the casing burial step S12.

[0078] The first freezing outer tube differs from the freezing outer tube 6 according to the above embodiment in that it is entirely made of metal. By using the first freezing outer tube made of metal, the freezing of the ground in the first frozen soil formation process S15 can be carried out efficiently.

[0079] After the first freezing outer tube insertion process S13, the casing retraction process S14 is performed. After the casing retraction process S14 is performed, the first frozen soil formation process S15 is performed.

[0080] In the first frozen soil formation process S15, the inner pipe 7 is inserted into the first freezing outer pipe, and a refrigerant is supplied from the inner pipe 7, freezing the ground 2 with the cold heat from the first freezing outer pipe. In the first frozen soil formation process S15, since the cold heat is supplied to the ground 2 from the metal first freezing outer pipe, efficient freezing can be easily achieved.

[0081] Following the first frozen soil preparation process S15, the main construction process S16 is executed. While the main construction process S16 is being executed, the second frozen outer pipe insertion process S17 is carried out. In the second frozen outer pipe insertion process S17, the first frozen outer pipe is withdrawn from the ground 2. Then, the second frozen outer pipe is inserted into the hole left by the withdrawal of the first frozen outer pipe. The first frozen outer pipe can be withdrawn by supplying high-temperature water into the first frozen outer pipe and partially melting the frozen soil.

[0082] The second freezing outer tube has the same structure as the freezing outer tube 6 according to the above embodiment. In this disclosure, the second freezing outer tube may be referred to as the freezing outer tube 6.

[0083] Following the second freezing outer pipe insertion process S17, the second frozen soil formation process S18 is executed. The second frozen soil formation process S18 causes the ground in the natural ground 2 to freeze again. After this, the finishing process S19, sealing process S20, and shield machine excavation process S21 are executed, completing the ground excavation method in this deformation.

[0084] In the modified ground excavation method, frozen soil is created by the first frozen soil creation process S15, after which the main construction process S16 can be carried out. That is, the second frozen outer pipe insertion process S17, the second frozen soil creation process S18, and the finishing process S19 can be carried out while the main construction process S16 is being carried out. Here, in conventional ground freezing methods, it was necessary to pull out the frozen outer pipe from the ground after the main construction process was completed and immediately before the shield machine excavation process. However, with the modified ground excavation method, the second frozen outer pipe insertion process S17, the second frozen soil creation process S18, and the finishing process S19 can be carried out while the main construction process S16 is being carried out, thus shortening the construction period. Moreover, since the second frozen outer pipe has a resin cuttable section, the frozen soil can be maintained until the second frozen outer pipe is cut by the shield machine. Note that the main construction process S16 may be started after the finishing process S19.

[0085] In the first modified example, the casing tube 5 is buried in the casing burying step S12, and the first freezing outer pipe is inserted into the casing tube 5 to erect the first freezing outer pipe in the ground 2. However, for example, a freezing outer pipe with drilling capability may be used as the first freezing outer pipe. For example, a metal freezing outer pipe with multiple bits formed at its tip can be used as the first freezing outer pipe. This allows the casing burying step S12 and the casing retraction step S14 to be omitted. That is, after the preparation step S11, the first freezing outer pipe insertion step may be performed, in which the first freezing outer pipe is passed through the water-stopping device 4 and the connecting pipe 3, and the first freezing outer pipe is buried in the ground 2.

[0086] Furthermore, in the first modified example, the casing tube 5 was retracted from the ground 2 while the first freezing outer tube remained in the ground 2 during the casing retraction step S14. However, the ground 2 may be frozen by conducting the cold from the first freezing outer tube to the ground 2 via the casing tube 5 without retracting the casing tube 5 from the ground 2. Then, in the second freezing outer tube insertion step, the first freezing outer tube and the casing tube 5 may be pulled out from the ground 2 together. This simplifies the work of pulling out each of the casing tube 5 and the first freezing outer tube, and eliminates the structure and work of separating the tip 51 of the casing tube 5 from the casing tube body 58.

[0087] The outer diameter of the second freezing outer pipe may be a size corresponding to the diameter of the holes in the frozen soil formed in the ground 2. For example, the outer diameter of the second freezing outer pipe may be larger than the outer diameter of the first freezing outer pipe.

[0088] [Other variations] The ground excavation method according to the above embodiment includes a sealing step S8 in which the opening of the non-cutting portion 62 is closed by welding. However, in the sealing step S8, it is not necessarily required to close the opening of the non-cutting portion 62 by welding. For example, the opening of the non-cutting portion 62 may be closed by a cap, a closing flange, a closing plug that is screwed into a thread formed on the inner circumferential surface near the opening of the non-cutting portion 62, or the like.

[0089] In the casing retraction step S4 according to the above embodiment, a portion of the casing tube 5 was retracted to a position where it was located within the ground. However, for example, the casing tube 5 may be completely withdrawn from the ground 2.

[0090] In the above embodiment, the freezing outer tube 6, the first freezing outer tube, and the second freezing outer tube radiated cold heat by being supplied with a refrigerant from an inner tube 7 inserted inside; however, the inner tube 7 is not necessarily a required component.

[0091] The embodiments disclosed herein should be understood to be illustrative in all respects and not restrictive in any way. The scope of the invention is defined by the claims and not by the foregoing description, and all modifications within the meaning and scope of the claims are intended to be included. [Explanation of Symbols]

[0092] S1 Preparation process, S2 Casing burial process, S3 Freezing outer pipe insertion process, S4 Casing retraction process, S5 Frozen soil creation process, S6 Finishing process, S7 Main construction process, S8 Sealing process, S9 Shield machine excavation process, S11 Preparation process, S12 Casing burial process, S13 First freezing outer pipe insertion process, S14 Casing retraction process, S15 First frozen soil creation process, S16 Main construction process, S17 Second freezing outer pipe insertion process, S18 Second frozen soil creation process, S19 Finishing process, S20 Sealing process, S21 Shield machine excavation process, 1 Impermeable wall, 11 First main surface, 12 Second main surface, 13 Metal plate, 131 Through hole, 14 Water stop plate, 2 Natural ground, 3 Connecting pipe, 31 Injection valve, 32 Sludge discharge valve, 4 Water stop device, 41 42 Casing, 42 Connecting pipe connection port, 43 Casing tube insertion port, 5 Casing tube, 51 Tip, 52 Outer cylinder, 521 Bit, 53 Inner cylinder, 531 Discharge port, 54 Check valve, 541 Valve seat, 542 Valve body, 543 Elastic member, 55 Pin, 56 Elastic body, 57 Hole, 58 Casing tube body, 59 Device, 6 Freezing outer tube, 61 Cuttable part, 611 Peripheral wall, 612 Bottom wall, 62 Non-cuttable part, 63 Joint, 64 Water-stopping part, 641 Cylindrical body, 642 Gasket, 7 Inner tube, 8 Annular plate, 9 Circular plate.

Claims

1. A preparatory step involves installing a connecting pipe having a sediment discharge valve and a water-stopping device connected to the connecting pipe to a watertight wall constructed between the ground and the work space, After the preparation step, a casing burial step is performed in which the casing tube is passed through the water-stopping device and the connecting pipe, and the casing tube is buried in the ground. A freezing outer tube insertion step, which follows the casing burial step, involves inserting a freezing outer tube into the casing tube buried in the ground, wherein the freezing outer tube inserted into the casing tube has a resin cuttable portion located in the excavation area which is the area through which the shield machine passes, and a metal non-cuttable portion connected to the cuttable portion and extending toward the work space, After the freezing outer tube insertion step, the casing tube erected in the ground is moved toward the work space, and the casing tube is moved away at least from the excavation area toward the work space, in a casing retraction step, After the casing retraction step, a frozen soil formation step is performed in which a refrigerant is supplied into the freezing outer pipe and the ground is frozen by the cold heat from the freezing outer pipe, After the frozen soil preparation process, the water-stopping device is removed and the connecting pipe is cut, and the opening between the cut end of the connecting pipe and the uncut portion is sealed by welding in a finishing process. The process includes a shield machine excavation step in which the shield machine excavates the excavation area while leaving the cuttable portion of the frozen outer tube in the excavation area. Ground excavation methods.

2. A preparatory step involves installing a connecting pipe having a sediment discharge valve and a water-stopping device connected to the connecting pipe to a watertight wall constructed between the ground and the work space, After the preparation step, a casing burial step is performed in which the casing tube is passed through the water-stopping device and the connecting pipe, and the casing tube is buried in the ground. Following the casing burial step, a first freezing outer tube insertion step is performed, in which the first freezing outer tube is inserted into the casing tube buried in the ground. After the first freezing outer tube insertion step, the casing tube embedded in the ground is moved toward the working space, and the casing tube is moved to the working space side in a casing retraction step, After the casing retraction step, a first frozen soil formation step is performed in which a refrigerant is supplied into the first freezing outer pipe and the ground is frozen by the cold heat from the first freezing outer pipe, The second frozen outer pipe insertion step involves, after the first frozen soil preparation step, withdrawing the first frozen outer pipe from the ground and then inserting the second frozen outer pipe into the ground, wherein the second frozen outer pipe has a resin cuttable portion located in the excavation area which is the area through which the shield machine passes, and a metal non-cuttable portion connected to the cuttable portion and extending toward the work space, A second frozen soil formation step is performed, in which, after the second freezing outer tube insertion step, a refrigerant is supplied into the second freezing outer tube, and the ground is frozen by the cold heat from the second freezing outer tube, After the second frozen soil preparation process, the water-stopping device is removed and the connecting pipe is cut, and the opening between the cut end of the connecting pipe and the uncut portion is sealed by welding in a finishing process. The process includes a shield machine excavation step in which the shield machine excavates the excavation area while leaving the cuttable portion of the second frozen outer tube in the excavation area. Ground excavation methods.

3. The sealing step is further performed after the finishing step and before the shield machine excavation step, wherein the sealing step closes the opening in the non-cut portion by welding. A ground excavation method according to claim 1 or claim 2.

4. In the preparation step, the connecting pipe is fixed by welding to a metal plate that is fixed to the watertight wall and has a through hole formed therein that leads to the connecting pipe. A ground excavation method according to claim 1 or claim 2.

5. The casing retraction step involves positioning the casing tube such that a portion of it is located between the excavation area and the impermeable wall. A ground excavation method according to claim 1 or claim 2.

6. The finishing process involves cutting off the portion of the casing tube that protrudes from the watertight wall, and sealing the opening between the casing tube and the uncut portion by welding. The ground excavation method according to claim 5.

7. The casing retraction step involves pulling the casing tube out of the ground. A ground excavation method according to claim 1 or claim 2.

8. A preparatory step involves installing a connecting pipe having a sediment discharge valve and a water-stopping device connected to the connecting pipe to a watertight wall constructed between the ground and the work space, After the preparation step, the first freezing outer pipe insertion step is performed, in which the first freezing outer pipe is passed through the water-stopping device and the connecting pipe, and the first freezing outer pipe is buried in the ground. After the first freezing outer tube insertion step, a first frozen soil creation step is performed in which a refrigerant is supplied into the first freezing outer tube and the ground is frozen by the cold heat from the first freezing outer tube, The second frozen outer pipe insertion step involves, after the first frozen soil preparation step, withdrawing the first frozen outer pipe from the ground and then inserting the second frozen outer pipe into the ground, wherein the second frozen outer pipe has a resin cuttable portion located in the excavation area which is the area through which the shield machine passes, and a metal non-cuttable portion connected to the cuttable portion and extending toward the work space, A second frozen soil formation step is performed, in which, after the second freezing outer tube insertion step, a refrigerant is supplied into the second freezing outer tube, and the ground is frozen by the cold heat from the second freezing outer tube, After the second frozen soil preparation process, the water-stopping device is removed and the connecting pipe is cut, and the opening between the cut end of the connecting pipe and the uncut portion is sealed by welding in a finishing process. The process includes a shield machine excavation step in which the shield machine excavates the excavation area while leaving the cuttable portion of the second frozen outer tube in the excavation area. Ground excavation methods.

9. The process further comprises a casing burying step, which is performed between the preparation step and the first freezing outer pipe insertion step, and involves passing the casing tube through the water-stopping device and the connecting pipe, and burying the casing tube in the ground. The first freezing outer tube insertion step involves inserting the first freezing outer tube into the casing tube to bury the first freezing outer tube in the ground, In the first frozen soil formation process, the cold from the first freezing outer pipe is transmitted to the ground via the casing tube, thereby freezing the ground. In the second freezing outer tube insertion step, after the first frozen soil creation step, the first freezing outer tube and the casing tube are together pulled out from the ground. The ground excavation method according to claim 8.

10. A freezing outer tube for freezing the ground with a refrigerant supplied to the inside, A bottomed cylindrical resin cuttable section, A non-cutting portion made of metal is connected to the cuttable portion and extends along the central axis of the cuttable portion, The device comprises a joint connecting the machinable part made of resin and the non-machinable part made of metal, Frozen outer tube.

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