Shield tunnel construction method

Abstract

To suppress the occurrence of displacement of the surrounding ground due to the excavation of a shield machine.SOLUTION: A construction method for a shield tunnel excavated into the ground by a shield machine 1 includes: a first ground improvement step (step S2) of performing ground improvement from the ground side to form a first improvement body 20α having a circular cross-sectional shape that encompasses an area (planned excavation area 10) planned to be excavated by the shield machine 1; and a first excavation step (step S3) of excavating the inside of the first improvement body 20α with the shield machine 1.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a construction method for a shield tunnel excavated and formed underground by a shield machine.

Background Art

[0002] A shield tunnel used as a pipeline such as a road or a railway is constructed by the shield method. In the shield method, a shield machine (shield tunneling machine) is used. The shield machine includes, for example, a cylindrical skin plate forming the outer shell of the shield machine body, a cutter head provided at the front end (face side end) of the skin plate for excavating the ground, and a propulsion jack provided inside the skin plate.

[0003] In the shield method, for example, while excavating the ground with a shield machine, segments are successively assembled in the circumferential direction of the tunnel inside the rear part of the skin plate to construct a segment ring, and adjacent segment rings are connected in the tunnel axis direction to construct a cylindrical lining structure. In this method, the shield machine presses the existing segment ring behind it backward with the propulsion jack, and advances while excavating the ground by the thrust generated as the reaction force.

[0004] Patent Document 1 discloses that, for the purpose of preventing the settlement of a shield machine when excavating soft ground such as near the ground surface with a shield machine, only the lower part of the planned excavation area of the shield machine and the ground below the lower part are ground-improved, and then the shield machine is advanced.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, if we consider applying the technology disclosed in Patent Document 1 to, for example, soft cohesive soil with an N-value of approximately 0, the soil in question has low self-supporting properties. As the shield machine excavates, deformation (displacement, etc.) of the surrounding ground may occur, which in turn may cause displacement or deformation of the foundations of existing structures in the vicinity. In other words, applying only the technology disclosed in Patent Document 1 may be insufficient as a countermeasure against soft soil with low self-supporting properties.

[0007] In view of these circumstances, the present invention aims to suppress the occurrence of displacement of the surrounding ground and other phenomena associated with the excavation of a shield machine. [Means for solving the problem]

[0008] Therefore, the present invention In the first mode, The construction method for shield tunnels involves the area to be excavated by the shield machine. The planned excavation area It has a circumferential cross-sectional shape that encloses ru kai Ground improvement work is carried out from the surface to create a good foundation. land Panel improvement process, After the aforementioned ground improvement process, before Note revision The inside of the body is excavated with a shield machine. ru hori This includes the cutting process. The shield machine comprises a cylindrical skin plate, an excavation cutter head provided at the front end of the skin plate, and an erector device positioned inside the skin plate behind the cutter head. During the excavation process, the shield machine excavates the improved body while the cutter head rotates, and the erector device assembles segments to construct segment rings and constructs a lining that connects adjacent segment rings in the tunnel axis direction. The area to be excavated is excavated by the shield machine such that the outer diameter of the outer surface substantially matches the outer diameter of the skin plate or the outer diameter of the cutter head. The improved body and the area to be excavated are configured such that the inner surface of the improved body is tangent to the outer surface of the area to be excavated, or the outer surface of the area to be excavated is located inward from the inner surface of the improved body, or the inner surface of the improved body and the outer surface of the area to be excavated intersect and a part of the outer surface of the area to be excavated is located outward from the inner surface of the improved body. In a second aspect of the present invention, a method for constructing a shield tunnel excavated in the ground by a shield machine includes a ground improvement step of performing ground improvement from the surface side to form a downwardly open improved body that surrounds the area to be excavated by the shield machine from above and on both sides, and an excavation step of excavating the improved body with a shield machine after the ground improvement step. The shield machine comprises a cylindrical skin plate, an excavation cutter head provided at the front end of the skin plate, and an erector device disposed within the skin plate behind the cutter head. In the excavation step, the shield machine excavates the improved body while the cutter head rotates, and the erector device assembles segments to construct segment rings and constructs a lining that connects adjacent segment rings in the tunnel axis direction. The planned excavation area is excavated by the shield machine such that the outer diameter of the outer surface substantially matches the outer diameter of the skin plate or the outer diameter of the cutter head, and the improved body and the planned excavation area are set such that the inner surface of the improved body is tangent to the outer surface of the planned excavation area, or the outer surface of the planned excavation area is located inward from the inner surface of the improved body, or the inner surface of the improved body and the outer surface of the planned excavation area intersect so that a part of the outer surface of the planned excavation area is located outward from the inner surface of the improved body. In a third aspect of the present invention, a shield tunnel construction method includes a first ground improvement step of performing ground improvement from the surface side to form a first improved body having a circumferential cross-sectional shape encompassing an area to be excavated by a shield machine, and a first excavation step of excavating the first improved body with a shield machine, wherein the first improved body has an overhang that extends into the area to be excavated by the shield machine, and the overhang is excavated by the shield machine in the first excavation step. In a fourth aspect of the present invention, a shield tunnel construction method includes: a first ground improvement step of performing ground improvement from the ground side to form a first improved body having a circumferential cross-sectional shape encompassing the area to be excavated by the shield machine; a first excavation step of excavating the first improved body with a shield machine; a second ground improvement step of performing ground improvement from the ground side to form a second improved body having a downward-open cross-sectional shape surrounding the area to be excavated by the shield machine from above and both sides; and a second excavation step of excavating the second improved body with a shield machine, wherein the first ground improvement step and the first excavation step are performed on one side in the tunnel axis direction, and the second ground improvement step and the second excavation step are performed on the other side in the tunnel axis direction, and the second improved body has an overhang that extends into the area to be excavated by the shield machine, and the overhang is excavated by the shield machine in the second excavation step. [Effects of the Invention]

[0009] According to the present invention, even when constructing a shield tunnel in soft ground with low self-supporting properties, it is possible to suppress the occurrence of displacement of the surrounding ground and other phenomena associated with the excavation of the shield machine. [Brief explanation of the drawing]

[0010] [Figure 1] A diagram showing the schematic configuration of the shield machine in the first embodiment of the present invention. [Figure 2] A diagram showing the schematic configuration of the planned excavation area in the first embodiment. [Figure 3] Cross-sectional view of the first improvement in the first embodiment [Figure 4] Cross-sectional view of the second improvement in the first embodiment [Figure 5] Flowchart of the construction method of the shield tunnel in the first embodiment [Figure 6] Cross-sectional view of the first improvement in the second embodiment of the present invention [Figure 7] Cross-sectional view of the second improvement in the second embodiment [Figure 8] Cross-sectional view of the first improvement in the third embodiment of the present invention [Figure 9] Cross-sectional view of the second improvement in the third embodiment

Mode for Carrying Out the Invention

[0011] Embodiments of the present invention will be described below based on the drawings.

[0012] FIG. 1 is a diagram showing a schematic configuration of a shield machine 1 in the first embodiment of the present invention. FIG. 2 is a diagram showing a schematic configuration of an excavation planned area 10 which is an area planned to be excavated by the shield machine 1. FIG. 3 is a cross-sectional view of a first improvement body 20α constituting the ground improvement body 20. FIG. 4 is a cross-sectional view of a second improvement body 20β constituting the ground improvement body 20. Here, FIG. 3 corresponds to the A-A cross-section of FIG. FIG. 4(a) corresponds to the B-B cross-section of FIG. FIG. 4(b) corresponds to the C-C cross-section of FIG. That is, FIGS. 3, 4(a) and 4(b) respectively show cross-sections orthogonal to the tunnel axis direction in the ground improvement body 20.

[0013] The shield machine (shield tunneling machine) 1 is used for the construction of shield tunnels, or in other words, it excavates and forms a shield tunnel in the ground G (underground). In this embodiment, for convenience, the tunnel construction direction (tunnel excavation direction) is defined as the forward direction, and the front, back, left, and right directions are defined accordingly. In this embodiment, the configuration of the shield machine 1 is explained using a so-called earth pressure balance type shield machine as an example, but the type of shield machine 1 is not limited to this, and for example, a slurry type shield machine may also be used.

[0014] The shield machine 1 is composed of a cylindrical skin plate 2 that forms its main body, a cutter head 3 for excavation provided at the front end of the skin plate 2, and a shield bulkhead 4 positioned on the skin plate 2 at a distance behind the cutter head 3.

[0015] The cutter head 3 is rotatably supported on the shield bulkhead 4. The cutter head 3 rotates and excavates the ground G, driven by a drive motor (not shown) installed on the rear surface of the shield bulkhead 4.

[0016] Between the cutter head 3 and the shield bulkhead 4, a cutter chamber (not shown) is formed by the cutter head 3 and the skin plate 2. Excavated soil generated by excavation by the cutter head 3 accumulates in this cutter chamber. The shield machine 1 is equipped with a screw conveyor (not shown) that transports the excavated soil from this cutter chamber to the rear of the shield bulkhead 4.

[0017] The shield machine 1 is equipped with an erector device (not shown) within the skin plate 2 behind the cutter head 3 and shield bulkhead 4. This erector device constructs a segment ring by assembling segments 7 having an arc-shaped cross-section, and constructs a cylindrical lining body 8 by connecting adjacent segment rings in the tunnel axis direction.

[0018] Inside the skin plate 2 of the shield machine 1, multiple propulsion jacks 5 are arranged along the inner surface of the skin plate 2, spaced apart from each other in the circumferential direction of the skin plate 2. The propulsion jacks 5 are hydraulic jacks composed of a cylinder and a rod, and are extendable and retractable. The front end of the cylinder of the propulsion jack 5 is fixed to the skin plate 2, and the rod of the propulsion jack 5 can extend and retract at the rear end. By extending the propulsion jack 5 with the rear end of the rod of the propulsion jack 5 in contact with the existing segment 7, the shield machine 1 can obtain thrust. In this way, the propulsion jacks 5 take a reaction force from the existing segment 7 and propel the shield machine 1.

[0019] As shown in Figures 1 and 2, the planned excavation area 10 in this embodiment is the area in the ground G that is to be excavated by the shield machine 1. By excavating the planned excavation area 10 with the shield machine 1, a shield tunnel is formed underground.

[0020] The planned excavation area 10 extends underground along the direction of tunnel construction (the direction of the tunnel axis). In this embodiment, the planned excavation area 10 has a downward slope as it moves forward in the direction of tunnel construction, but conversely, the planned excavation area 10 may have an upward slope as it moves forward in the direction of tunnel construction. Alternatively, the planned excavation area 10 may extend substantially horizontally.

[0021] The outer diameter of the planned excavation area 10 (the diameter of the outer circumferential surface 10s of the planned excavation area 10 (see Figures 3 and 4)) is approximately equal to the outer diameter of the skin plate 2 and / or the outer diameter of the cutter head 3 of the shield machine 1. The planned excavation area 10 has an upper end 11 and a lower end 12 that extend in the direction of tunnel construction (tunnel axis direction). A reference line SL is set at the lower end 12 of the planned excavation area 10, extending in the direction of tunnel construction (tunnel axis direction).

[0022] In this embodiment, the ground G is divided into a first layer G1 having a ground surface GS and a second layer G2 located below the first layer G1 and having a higher ground strength than the first layer G1. In this embodiment, for example, the N value of the first layer G1 is 0 or more and less than 30, and the N value of the second layer G2 is 30 or more. Furthermore, it is preferable that the N value of the first layer G1 is 0 or more and less than 20, and even more preferable that it is 0 or more and 5 or less. For example, the N value of the second layer G2 may be 3 times or more the N value of the first layer G1. Here, "N value" is a numerical value obtained by the standard penetration test (JIS A 1219) and is an example of a numerical value indicating the strength of the ground. In this embodiment, the "N value" is evaluated by a representative value for each layer of a predetermined thickness, for example, the average value of the N values ​​obtained for each layer. The first geological layer G1 is, for example, an alluvial deposit, and the second geological layer G2 is, for example, a diluvial deposit.

[0023] The boundary surface GB between the first stratum G1 and the second stratum G2 is a hypothetical surface that serves as both the lower surface of the stratum classified as the first stratum G1 and the upper surface of the stratum classified as the second stratum G2. In this embodiment, the point where the aforementioned reference line SL intersects with the boundary surface GB (the lower surface of the first stratum G1 and the upper surface of the second stratum G2) is set as the reference point SP.

[0024] Existing buildings and other structures exist on the ground surface GS (above ground), and their foundations (for example, piles 9 shown in Figures 3 and 4) are already installed on both the left and right sides of the planned excavation area 10 underground. In this embodiment, the distance (separation distance) CL (see Figure 3) between the foundations and the planned excavation area 10 is, for example, about 5 to 10 m. That is, in this embodiment, the planned excavation area 10 is set in the vicinity of the foundations, and therefore, the shield machine 1 can excavate in the vicinity of the foundations.

[0025] In this embodiment, a ground improvement body 20 is formed so as to cover from the outside the portion of the outer surface 10s of the planned excavation area 10 that extends underground in the direction of tunnel construction (tunnel axis direction) that is located within the first geological layer G1.

[0026] The ground improvement body 20 is composed of a first improvement body 20α (see Figure 3) formed at a predetermined position behind the reference point SP in the direction of tunnel construction, and a second improvement body 20β (see Figure 4) formed at a predetermined position in front of the reference point SP in the direction of tunnel construction. In this embodiment, the second improvement body 20β is configured to include the reference point SP (see Figure 4(a)), but instead, the first improvement body 20α may be configured to include the reference point SP. Alternatively, neither the first improvement body 20α nor the second improvement body 20β may include the reference point SP, and the first improvement body 20α and the second improvement body 20β may be separated from each other with the reference point SP in between.

[0027] Here, both the first improved body 20α and the second improved body 20β are formed within the first geological layer G1. However, the lower end of the second improved body 20β must reach (come into or penetrate) the second geological layer G2, whereas the lower end of the first improved body 20α does not need to reach the second geological layer G2.

[0028] As shown in Figure 3, the first improved body 20α has a circumferential cross-sectional shape that encloses the planned excavation area 10 and extends underground in the direction of tunnel construction (tunnel axis direction). In this embodiment, the first improved body 20α has a rectangular frame shape (square-shaped) in cross-sectional view, with a rectangular outer surface 20a and a rectangular inner surface 20b. However, the cross-sectional shape of the first improved body 20α is not limited to a rectangular frame shape (see, for example, Figures 6 and 8 described later). Furthermore, the aforementioned outer surface 20a and inner surface 20b are set in the planning and design when performing ground improvement.

[0029] In this embodiment, a circular design line P is set radially outward from the planned excavation area 10 in a cross-sectional view. This design line P is set to ensure the necessary ground improvement thickness t1 when ground improvement is carried out along the outer surface 10s of the planned excavation area 10. In this embodiment, in a cross-sectional view, the thickness t2 of the rectangular frame of the first improved body 20α (the distance between the outer surface 20a and the inner surface 20b of the first improved body 20α) is set to be greater than or equal to this thickness t1. Here, the aforementioned thickness t1 can be appropriately set according to the strength (N value) of the first geological layer G1, etc., so that deformation (displacement, etc.) of the surrounding ground does not occur due to the construction of the shield tunnel. For example, with respect to the diameter of the circular cross-section of the planned excavation area 10 (the diameter of the outer surface 10s), the aforementioned thickness t1 is set to be 10% or more and 30% or less, preferably 10% or more and 20% or less. Specifically, when the diameter of the circular cross-section of the planned excavation area 10 (diameter of the outer surface 10s) is 8.0m or more and 15.0m or less, the aforementioned thickness t1 is set to 0.8m or more and 4.5m or less with respect to that diameter, preferably to 0.8m or more and 3.0m or less.

[0030] In this embodiment, the outer circumferential surface 20a of the first improved body 20α is set to be externally tangent to the planned line P in a cross-sectional view. However, the positional relationship between the outer circumferential surface 20a of the first improved body 20α and the planned line P is not limited to this. For example, the outer circumferential surface 20a of the first improved body 20α may not be tangent to the planned line P, and the planned line P may be located inward from the outer circumferential surface 20a of the first improved body 20α. In this regard, it is preferable that at least a portion of the planned line P is included within the range of the first improved body 20α (within the region between the outer circumferential surface 20a and the inner circumferential surface 20b).

[0031] In this embodiment, the inner circumferential surface 20b of the first improved body 20α is set to be externally tangent to the outer circumferential surface 10s of the planned excavation area 10 in cross-sectional view. However, the positional relationship between the inner circumferential surface 20b of the first improved body 20α and the outer circumferential surface 10s of the planned excavation area 10 is not limited to this. For example, the inner circumferential surface 20b of the first improved body 20α may not be in contact with the outer circumferential surface 10s of the planned excavation area 10, and the outer circumferential surface 10s of the planned excavation area 10 may be located inward from the inner circumferential surface 20b of the first improved body 20α. Alternatively, the inner circumferential surface 20b of the first improved body 20α and the outer circumferential surface 10s of the planned excavation area 10 may intersect with each other, and a part of the outer circumferential surface 10s of the planned excavation area 10 may be located outward from the inner circumferential surface 20b of the first improved body 20α. In this case, the outer surface 20a of the first improved body 20α may be positioned outward from the planned line P such that the aforementioned thickness t2 is greater than or equal to the thickness t1.

[0032] In this embodiment, as shown in Figure 3, the first improved body 20α comprises columnar bodies 21 that constitute the left and right sides of a rectangular frame-shaped cross-section, and a plurality of columnar bodies 22 that constitute the top and bottom sides. Each of the columnar bodies 21 and 22 extends in the vertical direction and is, for example, cylindrical. In Figure 3, adjacent columnar bodies 21 and 22 are shown touching each other, and adjacent columnar bodies 22 and 22 are shown touching each other, but in reality, they can be formed so that they partially overlap each other in the front, back, left, and right directions (i.e., partially wrap around each other).

[0033] As shown in Figures 4(a) and (b), the second improved body 20β has a downward-opening cross-sectional shape that surrounds the planned excavation area 10 from above and on both sides, and extends underground in the direction of tunnel construction (tunnel axis direction). In this embodiment, the second improved body 20β has a U-shape (gate-type) cross-sectional view, with a downward-opening U-shaped outer peripheral surface 20a and a downward-opening U-shaped inner peripheral surface 20b. Note that the cross-sectional shape of the second improved body 20β is not limited to a downward-opening U-shape (gate-type), but may be, for example, a downward-opening C-shape or U-shape (in other words, arch-shaped) (see, for example, Figures 7 and 9 described later).

[0034] In this embodiment, in a cross-sectional view, the thickness t2 of the U-shaped cross-section of the second improved body 20β (the distance between the outer circumferential surface 20a and the inner circumferential surface 20b of the second improved body 20β) is set to be greater than or equal to the aforementioned thickness t1. In the second improved body 20β, as with respect to the diameter of the circular cross-section of the planned excavation area 10 (the diameter of the outer circumferential surface 10s), for example, the aforementioned thickness t1 is set to be 10% or more and 30% or less, preferably 10% or more and 20% or less. Specifically, when the diameter of the circular cross-section of the planned excavation area 10 (the diameter of the outer circumferential surface 10s) is 8.0m or more and 15.0m or less, the aforementioned thickness t1 is set to be 0.8m or more and 4.5m or less, preferably 0.8m or more and 3.0m or less.

[0035] In this embodiment, the outer circumferential surface 20a of the second improved body 20β is set to be externally tangent to the planned line P in a cross-sectional view. However, the positional relationship between the outer circumferential surface 20a of the second improved body 20β and the planned line P is not limited to this. For example, the outer circumferential surface 20a of the second improved body 20β may not be tangent to the planned line P, and the planned line P may be located inward from the outer circumferential surface 20a of the second improved body 20β. In this regard, it is preferable that a part of the planned line P is included within the range of the second improved body 20β (within the region between the outer circumferential surface 20a and the inner circumferential surface 20b).

[0036] In this embodiment, the inner circumferential surface 20b of the second improved body 20β is set to be externally tangent to the outer circumferential surface 10s of the planned excavation area 10 in a cross-sectional view. However, the positional relationship between the inner circumferential surface 20b of the second improved body 20β and the outer circumferential surface 10s of the planned excavation area 10 is not limited to this. For example, the inner circumferential surface 20b of the second improved body 20β may not be in contact with the outer circumferential surface 10s of the planned excavation area 10, and the outer circumferential surface 10s of the planned excavation area 10 may be located inward from the inner circumferential surface 20b of the second improved body 20β. Alternatively, the inner circumferential surface 20b of the second improved body 20β and the outer circumferential surface 10s of the planned excavation area 10 may intersect with each other, and a part of the outer circumferential surface 10s of the planned excavation area 10 may be located outward from the inner circumferential surface 20b of the second improved body 20β. In this case, the outer surface 20a of the second improved body 20β may be positioned outward from the planned line P such that the aforementioned thickness t2 is greater than or equal to the thickness t1.

[0037] In this embodiment, as shown in Figures 4(a) and (b), the second improved body 20β comprises columnar bodies 21 that constitute the left and right sides of the U-shaped cross-section, and a plurality of columnar bodies 21' that constitute the top side. Each of the columnar bodies 21 and 21' extends in the vertical direction and is, for example, cylindrical. In Figures 4(a) and (b), adjacent columnar bodies 21 and 21' are shown touching each other, and adjacent columnar bodies 21' and 21' are shown touching each other. However, in reality, they can be formed so that they partially overlap each other in the front, back, left, and right directions (i.e., partially wrap around each other).

[0038] The ground improvement bodies 20 (the first improvement body 20α and the second improvement body 20β) can be formed by construction from the ground side (on the ground surface GS). The strength of the ground improvement bodies 20 is determined by the unconfined compressive strength according to the "Unconfined Compressive Strength Test of Soil (JIS A 1216)". The strength of the ground improvement bodies 20 is 0.7 MPa (700 kN / m) in unconfined compressive strength. 2 ) or more, more preferably 1.0 MPa (1000 kN / m²). 2 That's all.

[0039] For example, a mechanical mixing method can be used to form the ground improvement body 20. In this mechanical mixing method, cement, lime, etc. are added to the area to be improved in the first geological layer G1 (the area where the columnar bodies 21, 21', and 22 are to be formed), and the soil in that area is mechanically mixed with the cement, lime, etc. using a mixing device such as a stirring blade, thereby forming, for example, cylindrical columnar bodies 21, 21', and 22, and thus forming the ground improvement body 20.

[0040] Furthermore, a high-pressure injection mixing method may be used to form the ground improvement body 20. In the high-pressure injection mixing method, first, a high-pressure injection mixing device is installed on the ground side (on the ground surface GS), and an improvement rod is inserted into a borehole (extending vertically) that has been pre-drilled into the first geological layer G1 from the ground surface GS side. Next, high-pressure cement grout and compressed air are injected into the first geological layer G1 via the improvement rod, and the improvement rod is rotated or oscillated to mix the soil and cement grout in the area to be improved in the first geological layer G1 (the area where the columnar bodies 21, 21', 22 are to be formed). By performing this mixing while raising the improvement rod, cylindrical columnar bodies 21, 21', 22 with a diameter of 2m or more can be formed in the first geological layer G1.

[0041] In the formation of the first improved body 20α when the high-pressure injection mixing method is employed, one columnar body 21 can be continuously formed from bottom to top by the aforementioned lifting of the improvement rod in one pass. Furthermore, in the formation of the columnar bodies 22 that constitute the upper and lower sides of the rectangular frame-shaped cross-section of the first improved body 20α, the lower columnar body 22 is formed first by the aforementioned lifting of the improvement rod, and then the upper columnar body 22 is formed. In other words, two columnar bodies 22, upper and lower, can be formed in a series of operations by the aforementioned lifting of the improvement rod in one pass.

[0042] Furthermore, in the formation of the second improved body 20β when the high-pressure injection mixing method is employed, one columnar body 21 can be continuously formed from bottom to top by the aforementioned lifting of the improvement rod in one pass. Similarly, one columnar body 21' can be continuously formed from bottom to top by the aforementioned lifting of the improvement rod in one pass.

[0043] In this embodiment, while mechanical mixing and high-pressure injection mixing methods were described as possible techniques for constructing the ground improvement bodies 20 (the first improved body 20α and the second improved body 20β) from the ground side (on the ground surface GS), the techniques are not limited to these methods, and for example, chemical grouting may be used. Furthermore, it is preferable that the formation of the ground improvement bodies 20 (the first improved body 20α and the second improved body 20β) be carried out from the ground surface GS side, directly below it.

[0044] As shown in Figure 3, within the first improved body 20α, there is an unimproved area 30α, which is an area where ground improvement is not performed. This unimproved area 30α is surrounded by the inner circumferential surface 20b of the first improved body 20α. In this embodiment, in a cross-sectional view, the unimproved area 30α includes the area 10 to be excavated.

[0045] As shown in Figures 4(a) and (b), an unimproved area 30β exists inside the second improved body 20β, which is an area where ground improvement is not carried out. This unimproved area 30β is surrounded by the inner surface 20b of the second improved body 20β and the upper surface (boundary surface GB) of the second geological layer G2. Furthermore, the lower end of the second improved body 20β reaches the second geological layer G2, and therefore, the lower opening of the second improved body 20β is blocked by the second geological layer G2.

[0046] Next, the construction of the shield tunnel in this embodiment will be explained using Figure 5 in addition to Figures 1 to 4 mentioned above. Figure 5 is a flowchart showing the construction method for shield tunnels.

[0047] In the construction of a shield tunnel, first, in step S1, the planned excavation area 10 in the ground G is set (excavation area setting step). In this embodiment, since the shield tunnel is formed underground in an area where existing buildings and other structures are densely concentrated on the surface, existing piles 9 and the like may exist adjacent to the planned excavation area 10.

[0048] Next, in step S2, a ground improvement body 20 is formed by performing ground improvement from the ground side (ground improvement body formation process). This process includes a first ground improvement process (first improvement body formation process) in which ground improvement is performed from the ground side to form a first improvement body 20α having a circumferential cross-sectional shape that encloses the planned excavation area 10, and a second ground improvement process (second improvement body formation process) in which ground improvement is performed from the ground side to form a second improvement body 20β having a downward-open cross-sectional shape that surrounds the planned excavation area 10 from above and both left and right sides. The first ground improvement process (first improvement body formation process) is performed behind the reference point SP in the direction of tunnel construction (one side in the tunnel axis direction), and the second ground improvement process (second improvement body formation process) is performed in front of the reference point SP in the direction of tunnel construction (the other side in the tunnel axis direction). In this case, it is preferable to carry out the first ground improvement process (first improved body formation process) and the second ground improvement process (second improved body formation process) as a series of ground improvement processes (ground improved body formation process). Furthermore, it is preferable that the columnar bodies 21 that constitute the left and right ends of the ground improved body 20 extend vertically in a manner approximately parallel to and spaced apart from adjacent existing piles 9, etc.

[0049] Next, in step S3, the planned excavation area 10 is excavated using the shield machine 1 (shield machine excavation process). This process includes a first excavation process in which the shield machine 1 excavates within the first improved body 20α, and a second excavation process in which the shield machine 1 excavates within the second improved body 20β. This second excavation process may include excavating the second geological layer G2 with the shield machine 1. The first excavation process is carried out behind the reference point SP in the direction of tunnel construction (one side in the direction of the tunnel axis), and the second excavation process is carried out in front of the reference point SP in the direction of tunnel construction (the other side in the direction of the tunnel axis). Here, it is preferable to carry out the first excavation process and the second excavation process as a series of excavation processes (shield machine excavation process). Needless to say, the first excavation process and the second excavation process each include excavating the unimproved areas 30α and 30β with the shield machine 1. This is how the shield tunnel is constructed.

[0050] According to this embodiment, the construction method for a shield tunnel excavated underground (in the ground G) by a shield machine 1 includes a first ground improvement step (step S2) in which ground improvement is performed from the surface side (on the ground surface GS) to form a first improved body 20α having a circular cross-sectional shape that encloses the area to be excavated by the shield machine 1 (excavation area 10), and a first excavation step (step S3) in which the shield machine 1 excavates within the first improved body 20α. This makes it possible to suppress the occurrence of displacement of the surrounding ground and other phenomena associated with the excavation of the shield machine 1, even when constructing a shield tunnel in a first geological layer G1 with low ground strength.

[0051] Furthermore, according to this embodiment, the method for constructing a shield tunnel further includes a second ground improvement step (step S2) in which ground improvement is performed from the surface side to form a second improved body 20β having a downward-open cross-sectional shape that surrounds the area to be excavated by the shield machine 1 (excavation area 10) from above and both sides, and a second excavation step (step S3) in which the shield machine 1 excavates within the second improved body 20β. The first ground improvement step (step S2) and the first excavation step (step S3) are carried out on one side in the tunnel axis direction (rear side in the direction of tunnel construction), and the second ground improvement step (step S2) and the second excavation step (step S3) are carried out on the other side in the tunnel axis direction (front side in the direction of tunnel construction). This makes it possible to optimize the shape of the improved ground body 20 according to the distribution of ground strength in the tunnel axis direction.

[0052] In this embodiment, if the planned excavation area 10 has a downward slope that increases as it moves forward in the tunnel construction direction, it is preferable to perform the second ground improvement process after the first ground improvement process in step S2, and the second excavation process may be performed after the first excavation process in step S3. Conversely, if the planned excavation area 10 has an upward slope that increases as it moves forward in the tunnel construction direction, the first ground improvement process (step S2) and the first excavation process (step S3) will be performed on the front side in the tunnel construction direction, and the second ground improvement process (step S2) and the second excavation process (step S3) will be performed on the rear side in the tunnel construction direction. In this case, it is preferable to perform the first ground improvement process after the second ground improvement process in step S2, and the first excavation process may be performed after the second excavation process in step S3.

[0053] Furthermore, according to this embodiment, the second improved body 20β is formed in the first geological layer G1, and the downward opening of the second improved body 20β is blocked by the second geological layer G2, which is located below the first geological layer G1 and has higher ground strength than the first geological layer G1. Therefore, the planned excavation area 10 can be well surrounded by the second improved body 20β and the second geological layer G2 with higher ground strength. In this embodiment, the N value of the first geological layer G1 is 0 or more and less than 30 (preferably 0 or more and less than 20, more preferably 0 or more and 5 or less), and the N value of the second geological layer G2 is 30 or more.

[0054] Furthermore, according to this embodiment, a reference point SP is set as the point where a reference line SL extending in the tunnel axial direction intersects with the upper surface (boundary surface GB) of the second geological layer G2 at the lower end 12 of the area to be excavated by the shield machine 1 (excavation area 10). The first ground improvement process (step S2) and the first excavation process (step S3) are carried out on one side of the reference point SP in the tunnel axial direction (rear side in the direction of tunnel construction), and the second ground improvement process (step S2) and the second excavation process (step S3) are carried out on the other side of the reference point SP in the tunnel axial direction (front side in the direction of tunnel construction). Therefore, with respect to the excavation area 10 that gradually enters the second geological layer G2 from the first geological layer G1, the shape of the ground improvement body 20 can be easily optimized with reference point SP as the basis.

[0055] In this embodiment, the planned excavation area 10 has a downward slope that increases as it moves forward in the direction of tunnel construction. However, if, conversely, the planned excavation area 10 has an upward slope that increases as it moves forward in the direction of tunnel construction, then the first ground improvement process (step S2) and the first excavation process (step S3) will be carried out in front of the reference point SP in the direction of tunnel construction, and the second ground improvement process (step S2) and the second excavation process (step S3) will be carried out behind the reference point SP in the direction of tunnel construction.

[0056] Furthermore, according to this embodiment, the first ground improvement process (step S2) and the second ground improvement process (step S2) are carried out as a series of ground improvement processes (step S2), and the first excavation process (step S3) and the second excavation process (step S3) are carried out as a series of excavation processes (step S3). This makes it possible to carry out the construction of the shield tunnel efficiently.

[0057] Furthermore, according to this embodiment, the area to be excavated by the shield machine 1 (excavation area 10) has unimproved areas 30α and 30β within it where no ground improvement is carried out. The excavated soil generated by excavating the unimproved areas 30α and 30β with the shield machine 1 has not undergone ground improvement with cement or the like, so it can be effectively utilized as ordinary soil.

[0058] Next, a second embodiment of the present invention will be described with reference to Figures 6 and 7. Figure 6 is a cross-sectional view of the first improved body 20α' that constitutes the ground improved body 20' in this embodiment. Figure 7 is a cross-sectional view of the second improved body 20β' that constitutes the ground improved body 20' in this embodiment. Here, Figure 6 corresponds to the AA section of Figure 2, but the second soil layer G2 and the pile 9 are not shown. Similarly, Figure 7 corresponds to the CC section of Figure 2, but the pile 9 is not shown. The differences from the first embodiment described above will now be explained.

[0059] In this embodiment, the ground improvement body 20' is composed of a first improvement body 20α' formed at a predetermined position behind the reference point SP in the direction of tunnel construction, and a second improvement body 20β' formed at a predetermined position in front of the reference point SP in the direction of tunnel construction.

[0060] As shown in Figure 6, in this embodiment, in cross-sectional view, the first improved body 20α' is formed to include (overlap) an annular region of thickness t1 enclosed by the planned line P and the outer circumferential surface 10s of the planned excavation area 10. Therefore, the first improved body 20α' has an overhanging portion 25 that extends into the planned excavation area 10 (radially inward from the outer circumferential surface 10s).

[0061] As shown in Figure 6, within the first improved body 20α', there is an unimproved area 30α' where ground improvement is not performed. This unimproved area 30α' is surrounded by the inner circumferential surface 20b formed by the overhang portion 25 of the first improved body 20α'. In this embodiment, in a cross-sectional view, the area to be excavated 10 includes the unimproved area 30α'.

[0062] With respect to the first improved body 20α', the protruding portion 25 and the unimproved region 30α' can be excavated together by the shield machine 1.

[0063] As shown in Figure 7, in this embodiment, the second improved body 20β' is the second improved body 20β in the first embodiment described above, with the aforementioned protruding portion 25 added.

[0064] As shown in Figure 7, within the second improved body 20β', there is an unimproved area 30β' where no ground improvement is performed. This unimproved area 30β' is surrounded by the inner circumferential surface 20b formed by the overhang 25 of the second improved body 20β' and the upper surface (boundary surface GB) of the second geological layer G2. Furthermore, the lower end of the second improved body 20β' reaches the second geological layer G2, and therefore, the lower opening of the second improved body 20β' is blocked by the second geological layer G2.

[0065] With respect to the second improved section 20β', the protruding section 25 and the unimproved section 30β' can be excavated together by the shield machine 1.

[0066] In particular, according to this embodiment, the first improved body 20α' has an overhang portion 25 that extends into the area (excavation area 10) to be excavated by the shield machine 1, and the overhang portion 25 is excavated by the shield machine 1 in the first excavation step (step S3). This ensures that the required thickness t1 of ground improvement in the design is secured.

[0067] Furthermore, according to this embodiment, the second improved body 20β' has an overhang portion 25 that extends into the area (excavation area 10) to be excavated by the shield machine 1, and the overhang portion 25 is excavated by the shield machine 1 in the second excavation step (step S3). This ensures that the required thickness t1 of ground improvement in the design is secured.

[0068] Next, a third embodiment of the present invention will be described with reference to Figures 8 and 9. Figure 8 is a cross-sectional view of the first improved body 20α" that constitutes the ground improved body 20" in this embodiment. Figure 9 is a cross-sectional view of the second improved body 20β" that constitutes the ground improved body 20" in this embodiment. Here, Figure 8 corresponds to the AA section of Figure 2, but the second soil layer G2 and the pile 9 are not shown. Similarly, Figure 9 corresponds to the CC section of Figure 2, but the pile 9 is not shown. The differences from the second embodiment described above will now be explained.

[0069] In this embodiment, the ground improvement body 20" is composed of a first improvement body 20α" formed at a predetermined position behind the reference point SP in the direction of tunnel construction, and a second improvement body 20β" (not shown) formed at a predetermined position in front of the reference point SP in the direction of tunnel construction.

[0070] As shown in Figure 8, in this embodiment, the first improved body 20α'' has a reduced portion located radially outward from the planned line P in a cross-sectional view compared to the first improved body 20α' in the second embodiment described above. Therefore, in a cross-sectional view, the contour of the outer surface 20a of the first improved body 20α'' is stepped (zigzag). In this way, the area to be improved can be reduced.

[0071] As shown in Figure 8, within the first improved body 20α", there is an unimproved area 30α", which is an area where ground improvement is not performed. This unimproved area 30α" is surrounded by the inner circumferential surface 20b formed by the overhang portion 25 of the first improved body 20α". In this embodiment, in a cross-sectional view, the area to be excavated 10 includes the unimproved area 30α".

[0072] With respect to the first improved body 20α'', the protruding portion 25 and the unimproved region 30α'' can be excavated together by the shield machine 1.

[0073] As shown in Figure 9, in this embodiment, the portion of the second improved body 20β” located radially outward from the planned line P is reduced, similar to the first improved body 20α” described above. Therefore, in a cross-sectional view, the outline of the outer surface 20a of the second improved body 20β” is stepped (zigzag). In this way, the area to be improved can be reduced.

[0074] As shown in Figure 9, within the second improved body 20β”, there is an unimproved area 30β”, where no ground improvement is performed. This unimproved area 30β”, is surrounded by the inner circumferential surface 20b formed by the protruding portion 25 of the second improved body 20β”, and the upper surface (boundary surface GB) of the second geological layer G2. Furthermore, the lower end of the second improved body 20β”, reaches the second geological layer G2, and therefore, the lower opening of the second improved body 20β”, is blocked by the second geological layer G2.

[0075] With respect to the second improved section 20β”, the protruding section 25 and the unimproved section 30β” can be excavated together by the shield machine 1.

[0076] Next, we will describe modified examples of the first to third embodiments described above. In the first to third embodiments described above, the areas designated as unimproved regions 30α, 30α', 30α”, 30β, 30β', 30β”, may be partially or entirely improved to have a lower strength than the ground improvement bodies 20, 20', 20” (first improvement bodies 20α, 20α', 20α”, second improvement bodies 20β, 20β', 20β”). In other words, for example, at least a portion of the areas indicated by the symbols 30α, 30α', 30α”, 30β, 30β', 30β”, in Figures 3, 4, and 6 to 9 may be improved to have a lower strength than the ground improvement bodies 20, 20', 20” (first improvement bodies 20α, 20α', 20α”, second improvement bodies 20β, 20β', 20β”), resulting in low-strength improved regions.

[0077] In other words, in this modified example, within the ground improvement bodies 20, 20', 20” (the first improvement bodies 20α, 20α', 20α”, and the second improvement bodies 20β, 20β', 20β”), there may be low-strength improved areas (for example, the areas indicated by the symbols 30α, 30α', 30α”, 30β, 30β', 30β”) in Figures 3, 4, and 6 to 9).

[0078] The construction of the low-strength improved area (and the improved body that constitutes it) can be carried out from the ground side (on the ground surface GS). Preferably, this construction is carried out from the ground surface GS side, directly below it. For this construction, any of the aforementioned mechanical mixing method, high-pressure injection mixing method, or chemical grouting method may be employed.

[0079] The strength of the low-strength improved area (and the improved bodies that comprise it) is determined by the unconfined compressive strength measured by the "Unconfined Compressive Strength Test of Soil (JIS A 1216)," similar to the ground improvement bodies 20, 20', 20” (first improvement bodies 20α, 20α', 20α”, second improvement bodies 20β, 20β', 20β”). The strength of the low-strength improved area is 0.7 MPa (700 kN / m²) in unconfined compressive strength. 2 ) less than, more preferably 0.3 MPa (300 kN / m²). 2 It is less than ).

[0080] In the construction method for shield tunnels, the process of forming the low-strength improved area can be incorporated into step S2 (ground improvement body formation process) shown in Figure 5. In other words, the process of forming the ground improvement bodies 20, 20', 20" (first improvement bodies 20α, 20α', 20α") and the second improvement bodies 20β, 20β', 20β") may include the process of forming the low-strength improved area. For example, when a high-pressure injection mixing method is used to form the ground improvement bodies 20, 20', 20" (first improvement bodies 20α, 20α', 20α") and the second improvement bodies 20β, 20β', 20β") and the low-strength improved area (the improvement bodies that constitute it) can be formed in a series of operations by simply lifting the improvement rod.

[0081] In particular, according to this modified example, the area to be excavated by the shield machine 1 (excavation area 10) has the aforementioned low-strength improved area inside it (for example, the area indicated by the symbols 30α, 30α', 30α”, 30β, 30β', 30β” in Figures 3, 4, and 6 to 9). This low-strength improved area (and the improved bodies that constitute it) has a lower strength than the first improved bodies 20α, 20α', 20α”, and / or the second improved bodies 20β, 20β', 20β”. The excavated soil generated by excavating this low-strength improved area with the shield machine 1 may have a low proportion of cement, etc., and can therefore be effectively utilized in the same way as ordinary soil.

[0082] Regarding the cross-sectional shapes of the ground improvement bodies 20, 20', and 20” shown in the first to third embodiments and modified examples described above, it is possible to partially select and combine each embodiment. For example, instead of the portion corresponding to the upper half of the planned excavation area 10 in the cross-sectional shape of the ground improvement body 20 shown in Figure 3, the portion corresponding to the cross-sectional shape of the ground improvement body 20' shown in Figure 6, or the portion corresponding to the cross-sectional shape of the ground improvement body 20” shown in Figure 8, may be used. Also, instead of the portion corresponding to the lower half of the planned excavation area 10 in the cross-sectional shape of the ground improvement body 20 shown in Figure 3, the portion corresponding to the cross-sectional shape of the ground improvement body 20' shown in Figure 6, or the portion corresponding to the cross-sectional shape of the ground improvement body 20” shown in Figure 8, may be used. Also, instead of the portion corresponding to the upper half of the planned excavation area 10 in the cross-sectional shape of the ground improvement body 20' shown in Figure 6, the portion corresponding to the cross-sectional shape of the ground improvement body 20” shown in Figure 8 may be used. Alternatively, instead of the portion corresponding to the lower half of the planned excavation area 10 in the cross-sectional shape of the ground improvement body 20' shown in Figure 6, the portion in the cross-sectional shape of the ground improvement body 20'' shown in Figure 8 may be used.

[0083] The columnar bodies 21, 21', and 22 shown in the first to third embodiments and modified examples described above may have diameters equal to or greater than the aforementioned thickness t1, or less than the aforementioned thickness t1. In this regard, for example, a thickness of t1 or greater may be ensured by combining multiple such columnar bodies.

[0084] In the first to third embodiments and modifications described above, the cross-sectional shape of the planned excavation area 10 is circular, but this cross-sectional shape is not limited to a circle, and may be an ellipse or a polygon such as a rectangle.

[0085] The illustrated embodiments are merely illustrative of the present invention, and it goes without saying that the present invention includes not only those directly shown by the described embodiments, but also various improvements and modifications made by those skilled in the art within the scope of the claims. [Explanation of symbols]

[0086] 1...Shield machine, 2...Skin plate, 3...Cutter head, 4...Shield bulkhead, 5...Push jack, 7...Segment, 8...Lining body, 9...Pile, 10...Excavation area, 10s...Outer surface, 11...Upper end, 12...Lower end, 20, 20', 20”...Ground improvement body, 20a...Outer surface, 20b...Inner surface, 20α, 20α', 20α”...First improvement body, 20β, 2 0β',20β”…Second improved section, 21,21',22…Columnar section, 25…Protruding section, 30α,30α',30α”,30β,30β',30β”…Unimproved area (or low-strength improved area), t1,t2…Thickness, CL…Distance, G…Ground, G1…First layer, G2…Second layer, GB…Boundary surface, GS…Ground surface, P…Planned line, SL…Reference line, SP…Reference point

Claims

1. A method for constructing a shield tunnel by excavating and forming it underground using a shield machine, A ground improvement process is carried out from the surface side to improve the ground so as to form an improved body having a circumferential cross-sectional shape that encloses the planned excavation area, which is the area to be excavated by the shield machine, and Following the ground improvement process, there is an excavation process in which the improved body is excavated with a shield machine, Includes, The shield machine comprises a cylindrical skin plate, a cutter head for excavation provided at the front end of the skin plate, and an erector device positioned within the skin plate behind the cutter head. In the excavation process, the shield machine excavates the improved body while the cutter head rotates, the erector device assembles segments to construct segment rings, and constructs linings that connect adjacent segment rings in the tunnel axis direction. The area to be excavated is excavated by the shield machine such that the outer diameter of the outer surface substantially matches the outer diameter of the skin plate or the outer diameter of the cutter head. The improved body and the planned excavation area are configured such that the inner surface of the improved body is tangent to the outer surface of the planned excavation area, or the outer surface of the planned excavation area is located inward from the inner surface of the improved body, or the inner surface of the improved body and the outer surface of the planned excavation area intersect, with a portion of the outer surface of the planned excavation area located outward from the inner surface of the improved body. Construction methods for shield tunnels.

2. The method for constructing a shield tunnel according to Claim 1, wherein the distance between the outer and inner surfaces of the improved body is set to be 10% or more and 30% or less of the diameter of the outer surface of the area to be excavated.

3. A method for constructing a shield tunnel excavated and formed underground by a shield machine, A ground improvement process is carried out from the ground side to form an improved body that is open downwards and surrounds the area to be excavated by the shield machine from above and on both sides, and Following the ground improvement process, there is an excavation process in which the improved body is excavated with a shield machine, Includes, The shield machine comprises a cylindrical skin plate, a cutter head for excavation provided at the front end of the skin plate, and an erector device positioned within the skin plate behind the cutter head. In the excavation process, the shield machine excavates the improved body while the cutter head rotates, the erector device assembles segments to construct segment rings, and constructs linings that connect adjacent segment rings in the tunnel axis direction. The area to be excavated is excavated by the shield machine such that the outer diameter of the outer surface substantially matches the outer diameter of the skin plate or the outer diameter of the cutter head. The improved body and the planned excavation area are configured such that the inner surface of the improved body is tangent to the outer surface of the planned excavation area, or the outer surface of the planned excavation area is located inward from the inner surface of the improved body, or the inner surface of the improved body and the outer surface of the planned excavation area intersect, with a portion of the outer surface of the planned excavation area located outward from the inner surface of the improved body. Construction methods for shield tunnels.

4. The shield tunnel construction method according to Claim 3, wherein the distance between the outer and inner surfaces of the improved body is set to 10% or more and 30% or less of the diameter of the outer surface of the area to be excavated.

5. The improved body is formed in the first stratum. The method for constructing a shield tunnel according to claim 3, wherein the downward opening of the improved body is blocked by a second geological layer located below the first geological layer and having a higher ground strength than the first geological layer.

6. A method for constructing a shield tunnel excavated and formed underground by a shield machine, A first ground improvement step involves performing ground improvement from the surface side to form a first improved body having a circular cross-sectional shape that encloses the area to be excavated by the shield machine, A first excavation step involves excavating the first improved body with a shield machine, Includes, The first improved body has an overhang that extends into the area to be excavated by the shield machine, and the overhang is excavated by the shield machine in the first excavation step. Construction methods for shield tunnels.

7. A method for constructing a shield tunnel excavated and formed underground by a shield machine, A first ground improvement step involves performing ground improvement from the surface side to form a first improved body having a circular cross-sectional shape that encloses the area to be excavated by the shield machine, A first excavation step involves excavating the first improved body with a shield machine, A second ground improvement step involves performing ground improvement from the ground side to form a second improved body having a downward-open cross-sectional shape that surrounds the area to be excavated by the shield machine from above and on both sides, A second excavation step involves excavating the second improved body with a shield machine, Includes, The first ground improvement process and the first excavation process are carried out on one side in the axial direction of the tunnel. The second ground improvement process and the second excavation process are carried out on the other side in the tunnel axial direction. The second improved body has an overhang that extends into the area to be excavated by the shield machine, and the overhang is excavated by the shield machine in the second excavation step. Construction methods for shield tunnels.

8. The first ground improvement process and the second ground improvement process are carried out as a series of ground improvement processes. The method for constructing a shield tunnel according to claim 7, wherein the first excavation step and the second excavation step are carried out as a series of excavation steps.

9. A method for constructing a shield tunnel according to any one of claims 1 to 5, wherein the area to be excavated by the shield machine has an unimproved area within it where no ground improvement is performed, or a low-strength improved area where the ground has been improved to have a lower strength than the improved body.

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