JP6720765B2 - Construction method of large section tunnel - Google Patents

Description

TECHNICAL FIELD The present invention relates to a large-section tunnel construction method for constructing a branch/junction portion of a main-line shield tunnel with a branch-line shield tunnel as a large-section tunnel.

Conventionally, when constructing a large-section tunnel as a large-section tunnel at the junction with a branch-line shield tunnel in a main-line shield tunnel in a deep underground, constructing a reinforcement body that separates the large-section tunnel construction planned area from the outer ground, A method of constructing a large-section tunnel inside the reinforcement is known.

Then, as a method of constructing the reinforcing body, for example, in Patent Document 1, a ground excavation chamber is constructed by using shield excavators above and below the main line shield tunnel and the branch line shield tunnel, respectively, and a plurality of locations of the underground start chamber are provided. To start the roof shield machine in sequence, and by arranging multiple roof shield tunnels around the junction at the predetermined intervals, construct a shield roof pre-reception surrounding the junction, then freeze between the roof tunnels. There is disclosed a method of joining by a construction method or chemical solution injection so as to function as a support work for the surrounding ground.

Further, in Patent Document 2, in constructing a starting base for a roof shield machine, a ring-shaped outer shell shield starting section is used in front of the branching and joining section in the main line shield tunnel by using a circumferential shield machine. The roof shield machine is sequentially started from the outer shell shield starting part in the extension direction of the branching and merging part to construct a shield roof front receiving work surrounding the branching and merging part.

Japanese Patent No. 4958035 JP, 2014-43738, A

However, in the method of Patent Document 1, an underground starting room is constructed separately from the main line shield tunnel and the branch line shield tunnel in order to construct the shield roof preparatory work. Therefore, shield excavation for constructing the underground starting chamber is performed. Machine construction and chemical injection or freezing construction work will be required to construct the ground improvement section, which not only requires large-scale construction and prolongs the work period, but also a space for constructing an underground launch room. Therefore, a series of operations for constructing the underground starting room becomes complicated.

Further, when the method of Patent Document 2 is adopted, it is necessary to move the roof shield machine started from the outer shell shield starting portion provided in the main line shield tunnel in the longitudinal direction before reaching the area surrounding the branching and joining portion. However, this method cannot be adopted if the running space for moving in the longitudinal direction cannot be secured. In addition, since the outer shell shield starting part is provided in the main line shield tunnel, it is necessary to provide a working space inside the main line shield tunnel when constructing the outer shell shield starting part and the roof front work. It is easy to get confused with the work space for carrying out.

The present invention has been made in view of the above problems, and its main purpose is to safely and efficiently work, and to construct a branching junction with a branch shield tunnel in a main shield tunnel as a large-section tunnel. The purpose is to provide a construction method for large-section tunnels.

In order to achieve such an object, the method for constructing a large-section tunnel of the present invention is to construct at least a part of the periphery of a large-section tunnel construction planned area in order to construct a branch merged portion with a branch line shield tunnel in a main line shield tunnel as a large-section tunnel. In a construction method of a large cross-section tunnel surrounded by a tubular skeleton, the branch line shield tunnel is extended from a first end which is an end on the branch side of the large cross-section tunnel construction planned region and is opposite to the first end. A first step of building so as to reach at least the second end on the side, and an extension portion of the branch line shield tunnel, which is sandwiched between the second end or the second end and the first end. A second step of setting a starting and arriving area at an arbitrary position, and constructing a ring-shaped skeleton along the outer periphery of the large cross-section tunnel construction scheduled region, and a side surface of the ring-shaped skeleton facing the first end. A starting area is set at an arbitrary position, and a plurality of outer shell shield tunnels are formed along the outer periphery of the large-section tunnel construction planned area and toward the first end, and the plurality of outer shell shield tunnels and the branch line shields are constructed. A third step of surrounding the periphery of the large cross-section tunnel construction scheduled area by a tunnel, and a step of constructing the tubular skeleton by utilizing a plurality of extending portions of the outer shell shield tunnel and the branch line shield tunnel. And the process of 4 are provided.

According to the above-mentioned construction method of a large-section tunnel, the branch line shield tunnel that is generally constructed up to the first end, which is the end on the branch side of the large-section tunnel construction planned area, is extended as it is to Build up to the second end opposite the first end. Accordingly, the ring-shaped frame, which is a starting area for constructing a plurality of outer shell shield tunnels, can be constructed by using the extended portion of the branch line shield tunnel as a starting and reaching area. For this reason, compared to the case where a starting area for constructing the outer shell shield tunnel is newly constructed, it is possible to omit the work of separately securing a work space and also to omit the large-scale ground improvement work as a preparatory work. It becomes possible.

Further, since the extension of the branch line shield tunnel is constructed in parallel with the plurality of outer shell shield tunnels, the large cross section tunnel construction area is surrounded by the extension of the branch line shield tunnel and the plurality of outer shell shield tunnels. , These can be used to construct a tubular body. Therefore, the number of outer shell shield tunnels to be newly constructed can be reduced, the construction period can be shortened, and the construction cost can be significantly reduced.

Furthermore, as the work area and work flow line related to the construction of the ring-shaped skeleton, the extended portion of the branch line shield tunnel can be used, and as the work area and work flow line related to the construction of the outer shell shield tunnel, a ring-shaped structure and The extension of the branch line shield tunnel can be used. As a result, all the work related to the construction of the tubular frame can be carried out without complication with the work related to the construction of the main line shield tunnel, so that the construction efficiency can be significantly improved and safe and reliable construction can be performed. As it contributes to shortening the construction period, it is possible to significantly reduce the construction cost.

Further, the method for constructing a large cross-section tunnel of the present invention is characterized in that, in the second step, the ring-shaped skeleton is constructed at a position corresponding to the second end of the large-section tunnel construction planned region.

According to the above-mentioned construction method of a large cross section tunnel, the extension part of the branch line shield tunnel and a plurality of outer shell shield tunnels are used for the entire length of the large section tunnel construction planned area from the first end to the second end. Since the constructed tubular skeleton is placed, it is possible to construct a large cross-section tunnel without performing the slitting method conventionally used when widening a shield tunnel to the main line shield tunnel. It is possible to carry out reliable construction.

According to the present invention, a branch line shield tunnel which is generally constructed up to the first end portion of the large cross-section tunnel construction planned region is extended as it is and constructed up to the second end portion of the large section tunnel construction planned region, and this branch line shield is constructed. By using the extended part of the tunnel, it is possible to construct a tubular frame that surrounds the planned area for constructing a large-section tunnel. It is possible to build.

It is a figure which shows the outline of the large cross-section tunnel of this invention. It is a figure showing plane alignment of a main line shield tunnel and a branch line shield tunnel of the present invention. It is a figure which shows the ring-shaped body of this invention. It is a figure which shows the outer shell shield tunnel of this invention. It is a figure showing the plane of the large section tunnel construction scheduled area of the present invention. It is a figure showing the section of the large section tunnel construction scheduled field of the present invention. It is a figure which shows the cross section of the cylindrical skeleton of this invention. It is a figure which shows the detail of the cylindrical skeleton of this invention. It is a figure which shows the plane of the cylindrical skeleton of this invention. It is a figure which shows the plane of the large cross-section tunnel of this invention. It is a figure which shows the other Example of the cylindrical skeleton of this invention. It is a figure which shows the construction method of the RC skeleton which comprises a part of cylindrical skeleton in the other Example of this invention.

TECHNICAL FIELD The present invention relates to a construction method for constructing a branch/junction portion of a main line shield tunnel with a branch line shield tunnel as a large-section tunnel. Note that the main line shield tunnel can be applied to either a new tunnel or an existing tunnel, but in the present embodiment, a case of newly installing with a known shield excavator (not shown) is taken as an example, It demonstrates using 1-FIG.

The large section tunnel 3 to be constructed by the construction method of the present invention is an enlarged part of the main line shield tunnel 1 as shown in the schematic view of FIG. Among them, as compared with a first end that is a branch-side end that is constructed so that the main line shield tunnel 1 and the branch line shield tunnel 2 are adjacent to each other, Is constructed in a substantially frustoconical shape with the second end on the opposite side having a small cross section. The large-section tunnel 3 is not necessarily limited to the above-described aspect, and may be constructed, for example, in a cylindrical shape in which the first end portion and the second end portion have the same cross-sectional diameter.

In constructing the large cross-section tunnel 3 having such a shape, as shown in the cross-sectional view of FIG. 7A, after the surrounding area of the large cross-section tunnel construction planned area 4 is preliminarily surrounded by the tubular skeleton 5, By excavating the inside, the main shield tunnel 1 located in the large-section tunnel construction planned region 4 is widened to construct the large-section tunnel 3 as shown in FIG. 7B. Hereinafter, a method of constructing a large-section tunnel using the tubular skeleton 5 in the large-section tunnel construction planned region 4 will be described.

<STEP1>
In the first step, as shown in FIG. 2, the main line shield tunnel 1 is constructed by underground excavation of a shield excavator, passes through a large cross-section tunnel construction planned area 4, and is adjacent to the main line shield tunnel 1 by a branch line. The shield tunnel 2 is also constructed by underground excavation of a shield excavator. The branch line shield tunnel 2 is originally built up to the first end 41 which is the end on the branch side in the axial direction of the large cross-section tunnel construction planned region 4, but it is extended to at least the first end 41. The extending portion 21 is constructed so as to reach the second end portion 42 opposite to the end portion 41 of the.

The extended portion 21 of the branch line shield tunnel 2 extends from the first end portion 41 to the second end portion 42 of the large cross-section tunnel construction planned area 4 in plan view to the branch line shield tunnel 2 side in the large cross section tunnel construction planned area 4. The plane alignment is ensured so that the boundary with the ground is located in the branch line shield tunnel 2. For this reason, in the present embodiment, after the plane alignment of the extended portion 21 of the branch line shield tunnel 2 is shaken once in the direction away from the main line shield tunnel 1 before the first end 41 of the large cross-section tunnel construction planned region 4, The shape is such that it approaches the main line shield tunnel 1 as it approaches the second end 42.

<STEP2>
In the second step, as shown in FIG. 3, the starting and arriving areas are set at the extended portion 21 of the branch line shield tunnel 2 and at a position corresponding to the second end 42 of the large cross-section tunnel construction scheduled region 4. A rectangular shield excavator (not shown) is started to construct a ring-shaped skeleton 6 along the outer periphery of the large cross-section tunnel construction planned area 4. As a result, at the position corresponding to the second end 42 of the large cross-section tunnel construction planned region 4, the main line shield tunnel 1 is arranged inside the ring-shaped frame 6, and the extended portion 21 of the branch line shield tunnel 2 is arranged at the ring-shaped frame 6. It becomes a mode which constitutes a part of.

When constructing the ring-shaped frame 6, the ground is adjacent to the extended portion 21 of the branch line shield tunnel 2 and around the position where the rectangular shield excavator is started, that is, the second area of the large cross-section tunnel construction planned region 4. A ground improvement zone 43 is previously formed around the position corresponding to the end 42 by a chemical injection method or a freezing method to take measures against water stoppage and soil retention. After this, a part of the segment of the branch line shield tunnel 2 facing the ground improvement zone 43 is removed, the rectangular shield excavator is started, and the branch line shield is circled so as to surround the planned area 4 of the large cross section tunnel, and then the branch line shield. The extended portion 21 of the tunnel 2 is reached.

At this time, the rectangular shield excavator digs into the ground while controlling its posture so that the cross section of the ring-shaped body 6 is always parallel to the tunnel axis of the large-section tunnel 1, and assembles the segment at the tail part. A reaction force is taken from the assembled segment with and it advances. In the present embodiment, the two ring-shaped skeletons 6 are constructed and connected, but the number is not limited to this, and the number may be one or three or more. In addition, in the present embodiment, the ring-shaped skeleton 6 is constructed by the rectangular shield excavator, but it is not necessarily limited to this and may be constructed by a circumferential propulsion method.

In this way, when constructing the ring-shaped skeleton 6, since the extended portion 21 of the branch line shield tunnel 2 can be used as a work area and a work flow line, the above work is performed independently of the underground work of the main line shield tunnel 1. Therefore, it is possible to prevent confusion with the work space and work flow line necessary for the construction work of the main line shield tunnel 1.

<STEP3>
In the third step, as shown in FIG. 4, the ring-shaped skeleton 6 is set as the starting area, and the small cross-section shield excavator (from the one side surface 61 facing the first end 41 of the large-section tunnel construction scheduled area 4) (Not shown) are sequentially started to construct a plurality of linear outer shell shield tunnels 7 along the outer periphery of the large cross-section tunnel construction planned region 4. Accordingly, as shown in FIGS. 5 and 6, between the first end portion 41 and the second end portion 42 in the large cross-section tunnel construction planned region 4, a plurality of outer shell shield tunnels 7 and branch line shield tunnels are provided around the periphery. It is surrounded by two extended portions 21.

In this way, the extended section 21 of the branch line shield tunnel 2 and the plurality of outer shell shield tunnels 7 can surround the large cross-section tunnel construction planned region 4, so that the outer shell shield tunnel 7 can be surrounded, The quantity can be reduced. In this embodiment, as shown in FIG. 6, 18 outer shell shield tunnels 7 were constructed, but the present invention is not limited to this, and the cross-sectional shape of the large-section tunnel construction-scheduled region 4 and the tubular skeleton 5 are not limited thereto. The optimum quantity and arrangement interval may be selected in consideration of the rigidity required, the ground condition of the ground, work efficiency, economic efficiency, and the like.

When constructing the above-mentioned outer shell shield tunnel 7, as shown in FIG. 5, the ground contacting one side surface 61 of the ring-shaped body 6 and the vicinity of the position where the small cross-section shield excavator starts are beforehand prepared. A soil improvement zone 43 is formed by a chemical injection method or a freezing method to take measures against water stoppage and soil retention. After that, a part of the segment in contact with the ground improvement zone 43 is removed, the small-section shield excavator is started, and the large-section tunnel construction planned area is reached until the first end 41 of the large-section tunnel construction planned area 4 is reached. Excavate straight along the circumference of 4.

At this time, in the present embodiment, since the arrival area of the small cross section shield excavator is not provided, the small cross section shield excavator after the excavation is appropriately disassembled and only the reusable equipment is collected. As a method for this, for example, reusable equipment such as a shield jack and a control panel and the remaining equipment such as a skin plate, a cutter head, and a partition wall are uncoupled, and the outer shell shield is applied from the ring-shaped body 6 side. A carrier device such as a carriage is carried in through the tunnel 7.

Then, the skin plate, the cutter head, the partition wall, etc. are left, and only the reusable equipment is loaded into the carrying device and collected on the side of the ring-shaped body 6. As a result, a new small-section shield excavator can be assembled in the ring-shaped skeleton 6 by using the recovered reusable equipment, and this can be used when constructing another outer-shell shield tunnel 7. Is possible.

The method of using the small-section shield excavator is not necessarily limited to the above-described method. For example, the small-section shield excavator is connected to the ground or branch line shield tunnel 2 near the first end 41 of the large-section tunnel construction scheduled area 4. An arrival area may be constructed and collected from the arrival area via the branch line shield tunnel 2.

Thus, in constructing the outer shell shield tunnel 7, the ring-shaped skeleton 6 can be reused not only as a starting area for starting the small-section shield excavator but also in the small-section shield excavator after the excavation. It will be a work area for carrying out all operations related to the construction of the outer shell shield tunnel 7, such as collection of equipment and assembly of a new small-section shield excavator using reusable equipment.

Further, since the ring-shaped skeleton 6 is connected to the extended portion 21 of the branch line shield tunnel 2, the work flow line related to the construction of the outer shell shield tunnel 7 can be secured. This makes it possible to carry out the work relating to the construction of the outer shell shield tunnel 7 independently of the underground work of the main line shield tunnel 1, and the work space and work flow line necessary for the construction work of the main line shield tunnel 1. It is possible to prevent the complication of.

<STEP4>
In the fourth step, as shown in the cross-sectional view of FIG. 7A, the extended portion 21 of the branch line shield tunnel 2 and the plurality of outer shell shield tunnels 7 are used to surround the large cross-section tunnel construction planned region 4. The tubular skeleton 5 is constructed.

In order to construct the tubular skeleton 5, first, the ground improvement portion 8 is constructed on the extended portion 21 of the branch line shield tunnel 2 and the ground surrounding the outer shell shield tunnels 7 by the freezing method or the chemical solution injection method. Then, as shown in FIG. 8, the extending portion 21 of the branch line shield tunnel 2 and the opposing segments in each of the plurality of outer shell shield tunnels 7 are removed, and the ground is excavated.

Using the space between the extended portion 21 of the branch line shield tunnel 2 and the outer shell shield tunnel 7 which are in communication with each other, and between the outer shell shield tunnels 7 adjacent to each other, the reinforcement bar and the concrete are placed. Thus, the tubular skeleton 5 including the large-section tunnel construction planned region 4 is constructed. Further, after the construction of the tubular skeleton 5 is completed, the hollow portion of the ring-shaped skeleton 6 used as the work area is filled with concrete.

As a result, around the large-section tunnel construction-scheduled region 4, the tubular frame 5 is formed of the extended portion 21 of the branch line shield tunnel 2 and the plurality of outer shell shield tunnels 7, which later functions as a lining body of the large-section tunnel 3. Is constructed over the entire length from the first end portion 41 to the second end portion 42 of the large-section tunnel construction planned region 4.

The work of constructing the tubular skeleton 5 may be performed after constructing all of the 18 outer shell shield tunnels 7, or may be performed while sequentially constructing the outer shell shield tunnels 7. It is not limited.

Further, the tubular skeleton 5 is constructed so as to have sufficient rigidity to ensure the stability of the large cross-section tunnel construction scheduled region 4, and at least has the soil retention function and the water stoppage function, the above-mentioned configuration is not always required. It is not limited to. For example, the outer shell shield tunnels 7 adjacent to each other and the extension portions 21 of the branch line shield tunnels 2 are constructed so that a part thereof overlaps with each other to construct a tubular body having a cross section surrounding the large cross-section tunnel construction planned region 4. The tubular body 5 may be used.

In this way, by constructing the extension portion 21 of the branch line shield tunnel 2, a series of operations relating to the construction of the tubular frame 5 surrounding the large cross-section tunnel construction planned region 4 is independent of the construction work of the main line shield tunnel 1. It becomes possible to carry out.

<STEP5>
In the fifth step, the main line shield tunnel 1 and the branch line shield tunnel 2 are excavated from the upper side to the lower side of the large cross-section tunnel construction planned region 4 surrounded by the tubular skeleton 5 as shown in FIG. 7A. The segment is removed and cut open, and the large-section tunnel 3 as shown in FIG. 7B is constructed in the large-section tunnel construction planned region 4.

Here, in the large cross-section tunnel construction planned region 4, the freezing method or the chemical solution injecting method is preliminarily applied to the vicinity of the ring-shaped body 6 forming the second end 42 and the vicinity of the first end 41 as shown in FIG. A soil improvement zone 43 is provided to take measures against water stoppage and soil retention. Then, in the vicinity of the first end portion 41, concrete is sequentially pour from the upper side in parallel with the excavation, thereby constructing the chest wall 9. On the other hand, in the vicinity of the second end 42, concrete is placed in the ring-shaped skeleton 6 after the excavation is completed by the normal winding method to construct the case wall 10.

As a result, the main wall shield tunnel 1 and the branch line shield tunnel 2 as shown in FIG. 10 are joined to the container wall 9 formed at the first end portion 41 so as to penetrate therethrough, and the container wall 10 of the second end portion 42 is joined. Is joined so that the main line shield tunnel 1 passes through.

The excavation work described above does not need to be performed on the entire cross section of the large-section tunnel construction-scheduled region 4, and at least at the planned height position 11 in the large-section tunnel 3 as shown in FIG. 7B. It is sufficient to excavate internal structures such as road floor boards to a depth that allows construction. Therefore, in the present embodiment, the earth and sand and the segments of the main line shield tunnel 1 and the branch line shield tunnel 2 located at the planned height 11 or more of the internal structure are left in the tubular skeleton 5.

In this way, a large cross-section tunnel 3 as shown in FIG. 10 is constructed at the junction of the main line shield tunnel 1 and the branch line shield tunnel 2, and the ring-shaped frame 6 is located at the second end of the large cross-section tunnel 3. Becomes The inner space of the extended portion 21 of the branch line shield tunnel 2 located outside the tubular frame 5 is generated, for example, when the large-section tunnel construction planned region 4 is excavated, as shown in FIG. 7B. It is backfilled by the backfill soil 15 using the earth and sand etc.

The construction method of the large cross-section tunnel of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.

In the present embodiment, the ring-shaped skeleton 6 is constructed at the position corresponding to the second end 42 of the large cross-section tunnel construction-scheduled region 4, but the construction position is not necessarily limited to this. For example, there is a large difference in cross-sectional diameter between the first end portion 41 where both the main line shield tunnel 1 and the branch line shield tunnel 2 are arranged and the second end portion 42 where only the main line shield tunnel 1 is arranged. If the outer shell shield tunnel 7 cannot be properly arranged, the ring-shaped skeleton 6 is constructed at an arbitrary position between the first end portion 41 and the second end portion 42 of the large cross-section tunnel construction planned region 4. Good.

By doing so, a plurality of outer shell shield tunnels 7 can be arranged with an optimum interval in the section from the first end portion 41 to the ring-shaped body 6 in the large cross-section tunnel construction planned region 4. Therefore, in the section from the first end portion 41 of the large cross-section tunnel construction scheduled region 4 to the ring-shaped skeleton 6, the cylindrical skeleton 5 as shown in FIG. 11 can be efficiently and safely prepared by the method shown in STEP 3 to STEP 4 described above. It can be constructed, and the large cross-section tunnel 3 can be constructed inward by STEP 5.

On the other hand, in the section from the ring-shaped body 6 to the second end portion 42, a pipe roof front receiving work is performed between the main line shield tunnel 1 and the extension portion 21 of the branch line shield tunnel 2, and the pipe roof front receiving work is performed on the inside. The large cross-section tunnel 3 may be constructed by the slitting method adopted when the shield tunnel is further widened.

Specifically, as shown in FIG. 12( a ), the extended portion of the main line shield tunnel 1 and the branch line shield tunnel 2 over the section from the ring-shaped frame 6 to the second end 42 of the large cross-section tunnel construction planned region 4. The pipe roof 12 is constructed by arranging a plurality of pipes 13 in parallel in the horizontal direction at predetermined intervals above and below the region sandwiched between the two.

When driving the pipe 13 as described above, as shown in FIG. 11, the ground contacting the other side surface 62 of the ring-shaped frame 6 facing the second end 42 of the large cross-section tunnel construction planned region 4, A ground improvement zone is formed in advance around the position where the pipe 13 starts by a chemical injection method or a freezing method. After that, a part of the segment of the ring-shaped frame 6 contacting with the ground improvement zone is removed, the pipe 12 is started by the propulsion method, and is linearly propelled until it reaches the second end 42 of the large-section tunnel construction planned region 4. ..

Next, as shown in FIG. 12A, the pipe 13 is used as a freezing pipe, and the ground around the pipe roof 12, between the pipe roof 12 and the main line shield tunnel 1, and between the pipe roof 12 and the branch line shield tunnel 2 is used. The ground between the stretched portion 21 and the stretched portion 21 is frozen by the freezing method, and measures for stopping water and retaining soil are taken. As a result, pipe roof pre-building is constructed above and below the region sandwiched between the extended portions 21 of the main line shield tunnel 1 and the branch line shield tunnel 2.

Thereafter, as shown in FIG. 12B, the extended portion 21 of the branch line shield tunnel 2 is backfilled with the backfill soil 15, and the roof shield front receiving work and the main line shield tunnel 1 and the branch line shield tunnel provided above and below are provided. A space is provided by excavating a region surrounded by two extended portions 21. Then, the segments of the main line shield tunnel 1 and the branch line shield 2 are partially disassembled and cut open, and an RC skeleton 14 that functions as a lining body of the large cross-section tunnel 3 is constructed in this space. Thereafter, by disassembling the segment of the main line shield tunnel 1 facing the RC skeleton 14, a large-section tunnel 3 as shown in FIG. 12C is constructed in the section from the ring-shaped skeleton 6 to the second end 42. can do.

1 main line shield tunnel 2 branch line shield tunnel 21 extended part 3 large cross section tunnel 4 large cross section tunnel construction planned area 41 first end 42 second end 43 ground improvement zone 5 tubular skeleton 6 ring skeleton 61 one side 62 the other Side surface 7 Outer shell shield tunnel 8 Ground improvement section 9 Bursal wall 10 Bursting wall 11 Planned height of internal structure 12 Pipe roof 13 Pipe 14 RC skeleton 15 Backfill soil

Claims (2)

In order to construct the branching and merging portion with the branch line shield tunnel in the main line shield tunnel as a large section tunnel, in the construction method of the large section tunnel surrounding at least a part of the large section tunnel construction planned area with a tubular skeleton,
The branch line shield tunnel is extended from a first end that is an end on the branch side of the large cross-section tunnel construction planned region so as to reach at least a second end opposite to the first end. The first step,
The extension section of the branch line shield tunnel, the starting and arriving area is set at an arbitrary position sandwiched between the second end or the second end and the first end, and the large-section tunnel construction plan A second step of constructing a ring-shaped body along the outer periphery of the region,
A starting area is set at an arbitrary position on a side surface of the ring-shaped body facing the first end, and a plurality of outer shell shield tunnels are formed along the outer circumference of the large-section tunnel construction planned region and toward the first end. Then, a third step of surrounding the periphery of the large cross-section tunnel construction planned region by a plurality of the outer shell shield tunnels and the branch line shield tunnels,
A fourth step of constructing the tubular skeleton using a plurality of extended portions of the outer shell shield tunnel and the branch line shield tunnel;
A construction method for a large-section tunnel, which is characterized by including. A method for constructing a large cross-section tunnel according to claim 1,
In the second step, the ring-shaped skeleton is constructed at a position corresponding to the second end of the large-section tunnel construction-scheduled region, wherein a large-section tunnel construction method is provided.