Structure and method for maintaining frozen ground

Abstract

To suppress melting of frozen soil.SOLUTION: A frozen soil maintaining structure for maintaining frozen soil 2 includes a bag body 60 arranged in an underground space and inflated by supplying gas to the inside, and movement of air near the frozen soil 2 in the underground space is suppressed by the inflated bag body 60.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a frozen soil maintenance structure and a frozen soil maintenance method for maintaining frozen soil. [Background technology]

[0002] Patent Document 1 discloses a method of creating frozen soil by freezing the ground around a shield machine in order to replace a cutter bit attached to the cutter head of the shield machine underground. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-107674 Summary of the Invention [Problem to be solved by the invention]

[0004] Because tunnels constructed underground using shield machines such as those described in Patent Document 1 are connected to the surface, the frozen soil formed around the shield machine is exposed to air that flows in from the surface through the tunnel and the shield machine, causing it to gradually thaw. One way to prevent the frozen soil from thawing is to attach insulating material such as glass wool to the exposed surface of the frozen soil, but it is difficult to secure the space necessary to attach the insulating material, and the larger the outer diameter of the tunnel, the larger the exposed area of ​​frozen soil becomes, which increases the time required to attach the insulating material, which could lengthen the construction period and increase construction costs.

[0005] The present invention aims to easily suppress the melting of frozen soil. [Means for solving the problem]

[0006] The present invention is a frozen soil maintenance structure for maintaining frozen soil in an underground structure in which an underground space is formed facing frozen soil formed by cooling the ground, and is equipped with a bag body that is placed within the underground space and expands when gas is supplied to the interior, and the movement of air near the frozen soil within the underground space is suppressed by the expanded bag body.

[0007] The present invention also provides a method for maintaining frozen soil in an underground structure in which an underground space is formed facing frozen soil formed by cooling the ground, and by supplying gas to the inside of a bag placed in the underground space and expanding the bag, the movement of air near the frozen soil within the underground space is suppressed. [Effects of the Invention]

[0008] According to the present invention, the melting of frozen soil can be easily suppressed. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view showing a schematic configuration of a tunnel boring machine. [Figure 2] 2 is a schematic diagram of the tunnel boring machine as seen from the direction indicated by arrow A in FIG. 1. [Figure 3] FIG. 3 is a cross-sectional view showing a cross section taken along line BB in FIG. 2. [Figure 4] FIG. 4 is a cross-sectional view showing a cross section taken along line CC in FIG. [Figure 5] FIG. 2 is a cross-sectional view taken along line DD in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, a frozen soil maintenance structure and a frozen soil maintenance method according to an embodiment of the present invention will be described with reference to the drawings.

[0011] The frozen soil maintenance structure and frozen soil maintenance method according to an embodiment of the present invention maintain frozen soil by suppressing the melting of frozen soil in an underground structure in which an underground space is formed facing frozen soil formed by cooling the ground. For example, as shown in Figure 1, the frozen soil maintenance structure and frozen soil maintenance method suppress the melting of frozen soil 2 after an excavation shaft 110 (underground space) is formed by a shield machine 100 (tunnel boring machine) facing frozen soil 2 formed by cooling the ground 1.

[0012] In the following, we will explain the case where the underground space is an excavation hole 110 formed by a shield machine 100 (tunnel boring machine), but the underground space formed facing the frozen soil 2 can be a space formed by any method as long as it is a space formed within the ground 1, and is not limited to an excavation hole 110.

[0013] First, with reference to FIG. 1, a shield machine 100 (tunnel boring machine) that faces frozen soil 2 and forms an excavation hole 110 (underground space) will be described.

[0014] The shield machine 100 excavates underground (ground 1) to form an excavation hole 110, and constructs a shield tunnel T (tunnel) by assembling segment rings 112 described below to cover the inner wall of the excavation hole 110.

[0015] Fig. 1 is a cross-sectional view showing the general configuration of a shield machine 100, and Fig. 2 is a schematic diagram of the shield machine 100 as seen from the direction indicated by arrow A in Fig. 1. Note that Fig. 2 omits illustration of configuration other than the cutter head 20. In the following description, the tunnel face side, which is the direction in which the shield machine 100 advances, is referred to as the "front," and the tunnel entrance side, which is the opposite direction, is referred to as the "rear."

[0016] As shown in Figure 1, the shield machine 100 is a mud pressure shield machine used in mud pressure shield tunneling, and comprises a cylindrical forward section 10, a cylindrical aft section 30, and a center bending section 40 that flexibly connects the forward section 10 and the aft section 30.

[0017] The forward body section 10 has a cylindrical outer shell 11 (body) extending along the axial direction of the shield tunnel T, a cutter head 20 (excavation section) that is rotationally driven in front of the outer shell 11, and a partition wall 12 that is provided inside the outer shell 11 and arranged opposite the cutter head 20 in the axial direction of the shield tunnel T. The cross-sectional shape of the outer shell 11 is not limited to a circle, and may be an ellipse or a rectangle.

[0018] A rotating drum 13 is supported on the partition wall 12 so as to be rotatable about a rotation axis C1. A cutter head 20 is connected to the rotating drum 13 via a connecting rod 13a. Therefore, the cutter head 20 can rotate together with the rotating drum 13 about the rotation axis C1. The rotation axis C1 substantially coincides with the central axis of the outer shell 11.

[0019] The rotating drum 13 is connected to a motor 14 via a speed reduction mechanism (not shown) and is driven to rotate by the motor 14. When the rotating drum 13 is driven to rotate by the motor 14 while the cutter head 20 is pressed against the ground 1 (natural bedrock), the cutter head 20 rotates and the ground 1 is excavated.

[0020] The cutter head 20 is a disk-shaped structure having an outer diameter approximately equal to the outer diameter of the outer shell 11, and has a face plate portion 21 facing the working face 3 (excavation surface), an annular ring portion 22 provided at the outer peripheral end of the face plate portion 21, a plurality of slit-shaped openings 23 formed in the face plate portion 21, and a plurality of cutter bits 24 attached to the face plate portion 21 at predetermined intervals in the circumferential and radial directions.

[0021] The earth and sand excavated by the multiple cutter bits 24 protruding toward the working face 3 turns into a muddy liquid and is guided through the opening 23 into the chamber 15 defined by the cutter head 20, the partition wall 12, and the outer shell 11. In order to agitate the muddy liquid containing the excavated earth and sand retained in the chamber 15, the face plate 21 on the chamber 15 side is provided with multiple agitating blades 28 protruding into the chamber 15, as shown in FIG.

[0022] The partition wall 12 may be provided with a plurality of fixed blades (not shown) protruding into the chamber 15 in order to agitate the inside of the chamber 15 together with the agitating blades 28. The cutter head 20 may also be provided with a copy cutter (not shown) configured to be able to freely protrude from and retract into the ring portion 22 in radial directions centered on the rotation axis C1.

[0023] The shield tunneling machine 100 is further equipped with a supply and discharge device 50 that supplies mud water into the chamber 15 and discharges the mud water from the chamber 15, thereby transporting the excavated soil and sand that has accumulated in the chamber 15 to the rear of the shield tunneling machine 100.

[0024] The supply and discharge device 50 has a supply pipe 51a whose one end opens in the chamber 15 and supplies muddy water into the chamber 15, a supply pump 51b attached to the supply pipe 51a and pumps muddy water toward the chamber 15, a discharge pipe 52a whose one end opens in the chamber 15 and pumps the excavated soil and muddy water in the chamber 15 to the outside, and a discharge pump 52b attached to the discharge pipe 52a and pumps the excavated soil and muddy water in the chamber 15 out of the chamber 15.

[0025] The excavated soil in the chamber 15 is discharged to the rear of the partition wall 12 through the discharge pipe 52a by controlling the operation of the supply pump 51b and the discharge pump 52b of the supply and discharge device 50. It is also possible to provide a bypass pipe 53 that can connect the supply pipe 51a and the discharge pipe 52a without passing through the chamber 15, and to stop the discharge of soil from the chamber 15 by operating a switching valve (not shown) to switch the flow of mud water to the bypass pipe 53.

[0026] The aft section 30 has a shell 31 having the same cross-sectional shape as the shell 11 of the forward section 10, an erector 33 that assembles the segment rings 112, a plurality of shield jacks 34 that move the shield tunneling machine 100 forward, a backfill injection device 35 that injects grout material between the inner surface of the borehole 110 excavated by the cutter head 20 and the outer surface of the segment rings 112, a roundness maintaining device (not shown) that maintains the shape of the segment rings 112, and a support 32 that supports these devices provided inside the aft section 30. The backfill injection device 35 and the roundness maintaining device are optional and may not be provided.

[0027] The erector 33 is configured to be able to grip the arc-shaped segment pieces 113 and to be able to move in the central axis direction and circumferential direction of the outer shell 31 along the inner circumferential surface of the outer shell 31. The erector 33 assembles the multiple segment pieces 113 along the inner circumferential surface of the outer shell 31, thereby constructing a cylindrical segment ring 112.

[0028] A plurality of annular tail seals 31a that seal the gap between the outer shell 31 and the segment ring 112 are provided at predetermined intervals in the axial direction on the inner peripheral surface of the outer shell 31. The tail seals 31a are provided to prevent soil and water from entering the shield machine 100 through the gap between the outer shell 31 and the segment ring 112.

[0029] The shield jacks 34 are hydraulic jacks consisting of a cylinder 34a and a rod 34b, and multiple shield jacks are arranged at predetermined intervals circumferentially inside the front end of the outer shell 31. When the shield jacks 34 are extended with the tips of the rods 34b protruding from the cylinders 34a of the shield jacks 34 in contact with the side surfaces of the segment rings 112, the cutter head 20 is pressed against the natural ground by the reaction force obtained from the segment rings 112. In this way, the shield tunneling machine 100 uses the reaction force obtained when the shield jacks 34 press against the existing segment rings 112 as the propulsion force for excavating forward.

[0030] The bending section 40 has a forward body connection section 41 provided at the aft end of the forward section 10 and having a concave spherical surface formed on its inner periphery, aft body connection section 42 provided at the forward end of the aft section 30 and having a convex spherical surface formed on its outer periphery that slides against the concave spherical surface of the forward body connection section 41, and multiple bending jacks 43 provided between the forward section 10 and the aft section 30.

[0031] The articulating jack 43 is a hydraulic jack composed of a cylinder 43a and a rod 43b. The rod 43b is fixed to the front of the rear fuselage section 30 via a universal joint, and the cylinder 43a is fixed to the rear of the forward fuselage section 10 via a universal joint.

[0032] In this way, by appropriately extending and retracting the bending jacks 43 connected to the forward section 10 and the rear section 30, it is possible to bend the direction of the forward section 10 relative to the rear section 30, i.e., the direction of the rotation axis C1 relative to the central axis direction of the rear section 30, in any direction. Note that the shield machine 100 may not be configured with a bending section 40.

[0033] Behind the shield tunneling machine 100, multiple trailing carriages (not shown) are arranged to move in tandem with the excavation of the shield tunneling machine 100. The trailing carriages are provided to transport a control device that controls the operation of the shield tunneling machine 100, a power supply device that supplies power to the shield tunneling machine 100, and components for constructing the shield tunnel T.

[0034] The shield machine 100 configured as described above rotates the cutter head 20, transports excavated earth using the supply and discharge device 50, and extends the shield jacks 34 to excavate the natural ground. A borehole 110 is excavated in the natural ground, and the shield tunnel T is constructed by assembling segment rings 112 one after another along the inner surface of the borehole 110. Grout material is injected by the backfill injection device 35 into the gaps that form between the inner surface of the borehole 110 and the outer surfaces of the segment rings 112, and the segment rings 112 become firmly bonded to the natural ground via the grout material.

[0035] The cutter bit 24 attached to the cutter head 20 of the shield tunneling machine 100 that excavates the ground and constructs the shield tunnel T in this manner is replaced periodically or irregularly to maintain excavation performance, and in some cases is replaced underground.

[0036] When replacing cutter bit 24 underground, frozen soil 2 is formed in the ground 1 in front of shield machine 100 using a known ground freezing method, such as running a cooled refrigerant through piping buried in the ground 1 to freeze the area around the piping, and then shield machine 100 is excavated into the area that has become frozen soil 2 (area surrounded by a dotted line), as shown in Figure 1. Then, by excavating part of or the entire face 3 formed in the frozen soil 2, a working space for replacing cutter bit 24 is secured in the frozen soil 2 in front of cutter head 20.

[0037] Here, since the shield tunnel T constructed underground by the shield tunneling machine 100 is connected to the ground, the frozen soil 2 created around the shield tunneling machine 100 is exposed to air that flows in from the ground through the shield tunnel T and the shield tunneling machine 100, and gradually melts.

[0038] In order to prevent the frozen soil 2 from melting, it is possible to consider, for example, attaching insulating material such as glass wool to the exposed surface of the frozen soil 2, but it is difficult to secure the space necessary to attach the insulating material, and the larger the outer diameter of the tunnel, the larger the exposed area of ​​the frozen soil 2 and the longer it takes to attach the insulating material, which could result in a longer construction period and increased construction costs.

[0039] Therefore, in the frozen soil maintenance structure and frozen soil maintenance method of this embodiment, a bag that expands when gas is supplied to its interior is placed inside the excavation hole 110 (underground space), thereby preventing air near the frozen soil 2 from moving within the excavation hole 110 and preventing the frozen soil 2 from being exposed to air at a temperature close to that on the ground.

[0040] First, a case where the bag body that expands when gas is supplied thereto is bag body 60 that is placed in opening 23 of cutter head 20 will be described with reference to Fig. 2 to Fig. 4. Fig. 3 is an enlarged cross-sectional view taken along line BB in Fig. 2, showing a state in which bag body 60 is placed in opening 23, and Fig. 4 is an enlarged cross-sectional view taken along line CC in Fig. 3.

[0041] Bag body 60 is configured in a bag-like shape that expands when gas such as compressed air is supplied to the interior, and is pre-formed to expand to a shape that matches the shape of opening 23. More specifically, it is pre-formed to expand slightly larger so as to be supported by the opening edge (face plate portion 21) that borders opening 23. The membrane material of bag body 60 is made of, for example, PVC (polyvinyl chloride) with reinforcing fibers, and bag body 60 expands in a relatively short time when compressed air is supplied from a compressor (not shown).

[0042] As shown in Figures 3 and 4, the bag body 60 is formed to fit the width of the opening 23 and has an insertion portion 60a that is inserted into the opening 23 and an expanded portion 60b that has a width greater than the width of the opening 23, and is installed at the opening 23 with the expanded portion 60b positioned on the chamber 15 side.

[0043] By providing an expanded portion 60b in the bag body 60 placed in the opening 23 in this manner, the pressure on the chamber 15 side increases depending on the temperature difference between the cutting edge 3 side and the chamber 15 side, and even if the pressure in the chamber 15 acts on the bag body 60, the bag body 60 is prevented from leaking out to the cutting edge 3 side.

[0044] The length of the bag body 60, i.e., the length in the vertical direction in Fig. 4, is set to match the length of the opening 23 in the radial direction of the cutter head 20. In other words, bag bodies 60 are formed to fit the various shapes of openings 23 shown in Fig. 2. Note that when the length of the opening 23 is long, multiple bag bodies 60 may be arranged side by side in the radial direction of the cutter head 20 for one opening 23.

[0045] When the bag body 60 formed to fit the shape of the opening 23 is inflated, it is placed in each opening 23, thereby blocking the flow of air from the chamber 15 toward the frozen soil 2 through the opening 23 and the flow of air from the frozen soil 2 toward the chamber 15 through the opening 23.

[0046] This suppresses the movement of air within the excavation hole 110, making it difficult for the frozen soil 2 to be exposed to air with a temperature close to that of the ground, and as a result, it is possible to suppress the frozen soil 2 from melting.

[0047] Furthermore, since the bag 60 is filled with air, which has low thermal conductivity, heat transfer between the frozen soil 2 side and the chamber 15 side via the bag 60 is also suppressed.

[0048] This also suppresses the transfer of heat within the excavation hole 110, making it possible to more reliably suppress the melting of the frozen soil 2.

[0049] It is possible to use a gas with a thermal conductivity as low as that of air, such as nitrogen, as the gas to be filled into the bag body 60. However, since it is necessary to bring a cylinder filled with a gas such as nitrogen into the excavation hole 110, it is preferable that the gas to be filled into the bag body 60 be air, from the standpoint of ease of inflating the bag body 60 and safety within the excavation hole 110.

[0050] In addition, the bag body is used not only for the working face 3 but also to prevent the inner surface of the excavation hole 110 formed by excavating in the frozen soil 2, particularly the area close to the working face 3, from being exposed to air at a temperature close to that of the ground.

[0051] 1 and 5, in order to block the flow of air from the chamber 15 toward the frozen soil 2 through the gap between the outer shell 11 of the front body 10 and the cutter head 20, and the flow of air from the frozen soil 2 toward the chamber 15 through the gap, a bag 64 that expands when gas is supplied thereto is placed in the chamber 15. Note that FIG. 5 is a cross-sectional view taken along line DD in FIG. 1, showing the state in which the bag 64 is placed; in order to make the position of the bag 64 in the chamber 15 easier to understand, components other than the outer shell 11 and the stirring blades 28 are not shown.

[0052] Like the bag body 60 described above, the bag body 64 is configured in a bag shape that expands when gas such as compressed air is supplied to the interior, and as shown in Figure 5, it is pre-formed so that it expands to a shape that matches the shape between two adjacent stirring blades 28 (e.g., an arc shape).

[0053] Furthermore, the bag body 64 is formed to a size that allows it to come into contact with the two adjacent agitating blades 28, the face plate portion 21, and other components that make up the cutter head 20, but not the outer shell 11 or the partition wall 12. In other words, the length of the bag body 64 in the direction of the rotation axis C1 is limited, and the size extending radially outward from the cutter head 20 is also limited. Furthermore, it is preferable that the shape of the portion of the bag body 64 that comes into contact with the agitating blades 28 is shaped to match the surface shape of the agitating blades 28 so that the bag body 64 is held by the two adjacent agitating blades 28.

[0054] By positioning the bag body 64 in such a manner that it can rotate together with the cutter head 20, even if it becomes necessary to rotate the cutter head 20 by a predetermined angle (for example, 90 degrees) in order to replace the cutter bit 24, the bag body 64 can be maintained in a state in which it can block the flow of air without first shrinking, i.e., it is possible to continue to prevent the frozen soil 2 from melting while the cutter bit 24 replacement work is being performed.

[0055] In addition, in order to block the flow of air from the chamber 15 toward the frozen soil 2 through the gap between the outer shell 11 of the front body 10 and the cutter head 20, and the flow of air from the frozen soil 2 toward the chamber 15 through the gap, a bag body 66 may be provided in place of or in addition to the above-mentioned bag body 64, and positioned radially inward of the multiple stirring blades 28 of the cutter head 20, as shown by the dashed line in Figure 5.

[0056] Like the above-mentioned bags 60 and 64, the bag body 66 is configured in a bag-like shape that expands when gas such as compressed air is supplied to the interior, and is pre-formed so that it expands into a shape in which the radially outer surface is supported by multiple stirring blades 28, as shown in Figure 5.

[0057] Specifically, like the bag body 64 described above, the length of the bag body 66 in the direction of the rotation axis C1 is set so that it does not come into contact with the partition wall 12, and the cross section shown in Figure 5 is not circular, but is formed so that it is approximately C-shaped with a slight interruption in one part.

[0058] By placing a bag body 66 of this shape in the chamber 15, even when it becomes necessary to rotate the cutter head 20 by a predetermined angle in order to replace the cutter bit 24, it is possible to maintain a state in which the bag body 66 can block the flow of air without first shrinking.

[0059] Furthermore, the bags 60, 64, and 66 may be placed not only within the chamber 15, but also within the excavation hole 110 (underground space), particularly within the shield machine 100 (tunnel boring machine), as in the bag 68 shown by the dashed line in Figure 1.

[0060] In this way, by disposing bag body 68, which is configured in a bag shape that expands when a gas such as compressed air is supplied to the interior, inside borehole 110 (underground space), the flow of air from the ground toward the frozen soil 2 through borehole 110 and the flow of air from the frozen soil 2 toward the ground through borehole 110 are almost blocked. In particular, as shown in Figure 1, by disposing bag body 68 inside shield machine 100 (tunnel boring machine), the flow of air from the ground toward the frozen soil 2 through the inside of shield machine 100 and the flow of air from the frozen soil 2 toward the ground through the inside of shield machine 100 are almost blocked.

[0061] This suppresses the movement of air within the excavation hole 110, making it difficult for the frozen soil 2 to be exposed to air with a temperature close to that of the ground, and as a result, it is possible to suppress the melting of the frozen soil 2. Furthermore, by using the above-mentioned bags 60, 64, 66, 68 in combination, it is possible to more reliably suppress the melting of the frozen soil 2 due to exposure to air with a temperature close to that of the ground.

[0062] The bag body 68 may be placed within the front body 10 of the shield tunneling machine 100, or may be placed within the shield tunnel T at the rear of the shield tunneling machine 100 so as to block the shield tunnel T.

[0063] Furthermore, since the above-mentioned bags 60, 64, 66, 68 can be easily deflated by releasing the air (gas) inside, when it is necessary to move materials toward the frozen soil 2 or when it is necessary for workers to move toward the frozen soil 2, the movement can be easily permitted by deflating the bags 60, 64, 66, 68 that are placed in places that are obstructing the movement. The same applies when it is necessary to move materials from the frozen soil 2 side or when it is necessary for workers to move from the frozen soil 2 side.

[0064] Furthermore, since the bags 60, 64, 66, and 68 contract in a short time and then expand in a short time, it is possible to shorten the time that the frozen soil 2 is exposed to air at a temperature close to that of the ground, and as a result, it is possible to reliably prevent the frozen soil 2 from melting.

[0065] According to the above-described embodiment, the following advantageous effects are achieved.

[0066] According to the frozen soil maintenance structure and frozen soil maintenance method of this embodiment, by arranging the expanded bags 60, 64, 66, 68 in the excavation hole 110 (underground space), the flow of air from the ground toward the frozen soil 2 through the excavation hole 110 and the flow of air from the frozen soil 2 toward the ground through the excavation hole 110 are blocked, and as a result, the movement of air near the frozen soil 2 within the excavation hole 110 is suppressed. By arranging the bags 60, 64, 66, 68 in the excavation hole 110 (underground space) in this way, it is possible to easily suppress the frozen soil 2 from being exposed to air at a temperature close to that of the ground and melting.

[0067] Furthermore, according to the frozen soil maintenance structure and frozen soil maintenance method of this embodiment, the melting of the frozen soil 2 can be suppressed simply by expanding the bag bodies 60, 64, 66, 68 placed in the excavation shaft 110 (underground space). Therefore, even if, for example, the outer diameter of the tunnel exceeds 10 m and the exposed area of ​​the frozen soil 2 is relatively large, it is possible to complete the work to suppress the melting of the frozen soil 2 in a relatively short time, and as a result, the construction period can be shortened and construction costs can be reduced.

[0068] Furthermore, according to the frozen soil maintenance structure and frozen soil maintenance method of this embodiment, the bags 60, 64, 66, 68 can be easily deflated by expelling the air (gas) inside them. Therefore, by temporarily shrinking the bags 60, 64, 66, 68 placed in locations that hinder the movement of people and materials, it is possible to easily allow the movement of people and materials while preventing the frozen soil 2 from being exposed to air with a temperature close to that of the ground.

[0069] Next, modified examples of this embodiment will be described. Note that the following modified examples are also within the scope of the present invention, and it is possible to combine the configuration shown in the modified example with the configuration described in the above embodiment, or to combine the configurations described in the following different modified examples.

[0070] In the above embodiment, the underground space formed facing the frozen soil 2 is the excavation hole 110 or a shield tunnel T constructed within the excavation hole 110. The underground space formed facing the frozen soil 2 is not limited to a space formed in a substantially horizontal direction such as the above-mentioned excavation hole 110 or shield tunnel T, but may be, for example, a vertical shaft formed along a substantially vertical direction, and in this case too, it is possible to suppress the flow of air through the vertical shaft toward the frozen soil by placing an inflated bag within the vertical shaft.

[0071] Furthermore, in the above embodiment, the bags 60, 64, 66, and 68 are disposed within the shield machine 100. The locations where the bags 60, 64, 66, and 68 are disposed are not limited to within the shield machine 100, but may be within the excavation hole 110 (underground space) at any location that can prevent air movement near the frozen soil 2 within the excavation hole 110. For example, the bags may be disposed so as to fill the gap between the face plate 21 of the cutter head 20 and the working face 3. In this case, disposing the bags in the gap can prevent heat generated during the operation of replacing the cutter bit 24, which is performed in a work space formed in front of the cutter head 20, from being transferred to the frozen soil 2 around the work space. Note that the bags disposed in the gap are temporarily contracted when it becomes necessary to rotate the cutter head 20 by a predetermined angle in order to replace the cutter bit 24.

[0072] Furthermore, in the above embodiment, the shield machine 100 is a so-called mud pressure shield machine. Alternatively, the shield machine 100 may be a so-called mud pressure shield machine, in which excavated soil retained in the chamber 15 is discharged to the rear of the shield machine 100 by a discharge mechanism such as a screw conveyor. Generally, the opening formed in the cutter head of a mud pressure shield machine is larger than that of a mud pressure shield machine, but by forming the shape of the above-mentioned bag body 60 to match the shape of the opening, the same effect can be achieved in a mud pressure shield machine.

[0073] Although the embodiments of the present invention have been described above, the above embodiments merely illustrate some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above embodiments. [Explanation of symbols]

[0074] 100···Shield tunneling machine (tunnel boring machine) 1...ground 2...Frozen soil 3. Cutting edge 11. Shell (body) 12...Bulkhead 15. Chamber 20. Cutter head (excavation part) 23 Opening 24···Cutter Bit 28. Mixing blade 60,64,66,68...Bag body 110···Excavation pit (underground space)

Claims

1. In an underground structure in which an underground space is formed facing frozen soil formed by cooling the ground, a frozen soil maintenance structure for maintaining the frozen soil, a bag body that is disposed in the underground space and expands when gas is supplied thereto; The movement of air near the frozen soil in the underground space is suppressed by the expanded bag body. Frozen soil maintenance structure.

2. The underground space is an excavation hole formed in the ground including the frozen soil by a tunnel boring machine, The bag is disposed inside the tunnel boring machine. The frozen soil retention structure according to claim 1 .

3. The tunnel boring machine a cylindrical body extending along the axial direction of the tunnel; an excavation unit that is rotationally driven at the front of the body; A partition wall provided within the body and arranged opposite the excavated portion in the axial direction of the tunnel; a chamber partitioned by the body, the excavation section, and the partition wall, in which soil excavated by the excavation section accumulates; The bag is placed in the chamber or in an opening formed in the excavation portion to take excavated soil and sand into the chamber. The frozen soil retention structure according to claim 2 .

4. A frozen soil maintenance method for maintaining frozen soil in an underground structure in which an underground space is formed facing frozen soil formed by cooling the ground, comprising: a bag disposed in the underground space is supplied with gas to expand the bag, thereby suppressing the movement of air near the frozen soil within the underground space; How to maintain frozen soil.

5. The gas inside the bag is discharged and the bag is deflated, thereby allowing movement of people and materials within the underground space. The frozen soil maintenance method according to claim 4.

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