Box-shaped piece for underpass

Abstract

To provide a caisson piece for an underpass configured to efficiently connect and integrate a plurality of segmentalized precast concrete pieces in a narrow vertical shaft.SOLUTION: A caisson piece for an underpass is configured to include: a plurality of upper side part precast pieces 13 in which sheath pipes 12 constituting an upper side part 10a are arranged; a plurality of lower side part precast pieces 14 in which sheath pipes 12 constituting a lower part 10b are arranged; a plurality of side precast pieces 15 in which sheath pipes 12 constituting a side part 10c are arranged; and four hollow steel cells 16 arranged in four corner parts 10d. PC steel wires 17 are inserted into sheath pipes 12 in communication with each other of the plurality of precast pieces 13, 14, 15 of each of side parts linked to each other, and each of these end parts is fixed on a fixation solidified body 18 inside of the hollow steel cell 16 in a state prestress is loaded thereon.SELECTED DRAWING: Figure 1

Description

【Technical Field】 【0001】 The present invention relates to a casing piece for an underpass, and particularly to a casing piece for an underpass that constitutes a casing structure having a rectangular cross-sectional shape, which forms an underground space by being propelled from a working shaft toward the ground under an existing structure in an underpass construction method. 【Background Art】 【0002】 The underpass construction method is employed, for example, as a method for forming an underground space that crosses existing structures such as existing railways and roads. The R&C method (registered trademark) (see, for example, Patent Document 1) and the SFT method (registered trademark) (see, for example, Patent Document 2) are known. In the underpass construction method, for example, a box-shaped pipe member is continuously installed on the ground under an existing structure where an underground space is to be formed, and then a top surface box-shaped roof and a side surface box-shaped roof that support the existing structure from below are formed. After that, the formed top surface box-shaped roof and side surface box-shaped roof are replaced by propelling a casing structure having a rectangular cross-sectional shape to the location where the underground space is to be formed, thereby forming an underground space with the replaced casing structure. 【0003】 In addition, in the underpass construction method, if a casing structure to be replaced with a top surface box-shaped roof or a side surface box-shaped roof formed in advance on the ground under an existing structure is to be formed by cast-in-place concrete inside a working shaft, a considerable period is required from the assembly of the formwork to the curing of the cast concrete. Therefore, in advance, in a factory or the like, the casing structure is formed as a precast concrete product divided into a plurality of pieces, and after these are carried into the working shaft, they are joined and integrated in the circumferential and axial directions via PC steel wires or the like to form the casing structure. A technology has also been developed (see, for example, Patent Document 3). 【Prior Art Documents】 【Patent Documents】 【0004】 [Patent Document 1] Japanese Patent Publication No. 2007-177553 [Patent Document 2] Japanese Patent Publication No. 2012-144942 [Patent Document 3] Japanese Patent Publication No. 2005-264552 [Overview of the project] [Problems that the invention aims to solve] 【0005】 On the other hand, in recent years, there has been a demand for the creation of underground spaces with larger hollow cross-sectional shapes, for example, by underpass construction methods. Furthermore, in urban areas, for example, it may not be possible to secure a site large enough to form a working shaft. Therefore, there is a demand for the development of technology that enables the efficient formation of large-section box structures with a hollow rectangular cross-section using multiple precast concrete pieces, which can create underground spaces with larger hollow cross-sectional shapes in narrow working shafts. 【0006】 In other words, when forming a large-section box-shaped structure using multiple precast concrete pieces, there are weight constraints when transporting each piece from the factory to the construction site, and weight constraints when lifting each piece into the work shaft using heavy machinery at the construction site. Therefore, each precast concrete piece that is joined and integrated in the work shaft needs to be subdivided. There is a need for the development of technology that enables the efficient joining and integration of these subdivided precast concrete pieces in a narrow work shaft, allowing them to be smoothly used as components of the box-shaped structure. 【0007】 The present invention aims to provide an underpass box-shaped piece that enables efficient joining and integration of multiple subdivided precast concrete pieces in a narrow working shaft, and that can be smoothly used as a component of a box-shaped structure. [Means for solving the problem] 【0008】 The present invention relates to an underpass box piece that forms a box structure having a rectangular cross-section, which is propelled from the work shaft toward the ground directly beneath the existing structure to form an underground space in an underpass construction method, by replacing at least the top box-shaped roof and top surface that have been installed in advance in the ground beneath the existing structure, and is configured to form the box structure by being connected and integrated in multiple units in the propulsion direction, and the underpass box piece consists of multiple upper precast pieces that constitute the upper part of the rectangular front shape, each with a sheath pipe disposed at a predetermined position, multiple lower precast pieces that constitute the lower part of the rectangular front shape, each with a sheath pipe disposed at a predetermined position, and both side parts of the rectangular front shape each with a sheath pipe disposed at a predetermined position The objective is achieved by providing an underpass box-shaped piece in which the multiple precast side pieces are joined and integrated circumferentially via the four hollow steel cells, with the multiple precast pieces being joined and integrated with PC steel wires inside each of the hollow steel cells. The PC steel wires are inserted into the sheath pipes that communicate with each other of the multiple precast pieces that are connected at each side of the rectangular front shape, and the ends of the prestressed PC steel wires are fixed to the fixed solidified bodies formed by pouring concrete inside each of the hollow steel cells. 【0009】 Furthermore, in the underpass box piece of the present invention, it is preferable that concrete is filled and solidified in the working space inside the hollow steel cell, excluding the portion of the fixed solidified body, after the PC steel wires have been fixed to the solidified body. 【0010】 Furthermore, it is preferable that each of the multiple precast pieces in the underpass box body piece of the present invention has a rectangular front shape. 【0011】 Furthermore, it is preferable that each of the four hollow steel cells in the underpass box piece of the present invention has a front shape that includes the side portion of the rectangular front shape and the end portion of the upper or lower portion of the rectangular front shape. 【0012】 Furthermore, the underpass box piece of the present invention is preferably used in the R&C method (registered trademark) in which excavation work is carried out at the face, with only the launching shaft being used as the working shaft. [Effects of the Invention] 【0013】 The box-shaped underpass piece of the present invention makes it possible to efficiently join and integrate multiple subdivided precast concrete pieces in a narrow working shaft, allowing them to be smoothly used as a component of a box-shaped structure. [Brief explanation of the drawing] 【0014】 [Figure 1] A partially perspective schematic front view illustrating a preferred embodiment of an underpass box piece of the present invention. [Figure 2] This is a schematic longitudinal cross-sectional view illustrating the process of forming an underpass box section inside a working shaft. [Figure 3] This is a schematic perspective view illustrating the process of forming an underpass box section inside a working shaft. [Figure 4] This is a schematic longitudinal cross-sectional view illustrating the situation in which a box-shaped structure is advanced while excavating the ground inside the box-shaped roof using the R&C method. [Figure 5] This is a schematic longitudinal cross-sectional view illustrating the situation in which a box-shaped structure is advanced while excavating the ground inside the box-shaped roof using the R&C method. [Figure 6]It is a schematic vertical sectional view for explaining an underground space formed by a box structure crossing below an existing structure. [Figure 7] It is a schematic perspective view for explaining an underground space formed by a box structure crossing below an existing structure. 【Mode for Carrying Out the Invention】 【0015】 The box piece 10 for underpass according to a preferred embodiment of the present invention shown in FIG. 1 is, as an underpass method, for example, as shown in FIGS. 2 to 7, in the ground below an existing structure 30, another newly constructed underground space 26 (see FIGS. 6 and 7) is formed by a box structure 11 installed across the directly below part of the existing structure 30. In the R&C method (registered trademark), it is used as a member constituting the box structure 11 by being connected and integrated in a plurality in the transverse direction. In this embodiment, a site wide enough to form the working shaft 31 cannot be secured. Therefore, in the narrow-space working shaft 31, each working process of the R&C method is carried out. Also, since an existing equipment structure 40 (see FIGS. 2, 4, and 6) is formed as an underground structure on the arrival side of the box structure 11 sandwiching the existing structure 30, only the starting-side shaft is used as the working shaft 31, and each working process of the R&C method (registered trademark) is carried out without providing a shaft on the arrival side. 【0016】 The box piece for underpass of this embodiment can also be easily assembled in the circumferential direction with a plurality of precast concrete pieces 13, 14, and 15 that are subdivided even in such a narrow-space working shaft 31, and can be smoothly used as a constituent member of the box structure 11 by efficiently joining and integrating them. 【0017】 Furthermore, the underpass box piece 10 of this embodiment is a box piece for an underpass construction method that preferably uses the R&C method, and is propelled from a working shaft 31 toward the ground directly below the existing structure 30 to form an underground space 26, by replacing at least the top box-shaped roof 21 and top surface 11a that have been installed in advance in the ground below the existing structure 30, as shown in Figures 2 to 7. The box piece 10 is arranged in a series in the propulsion direction and integrated to form the box structure 11. As shown in Figure 1, the underpass box-shaped piece 10 is composed of multiple upper precast pieces 13, each with a sheath pipe 12 positioned at a predetermined location, which constitute the upper part 10a of the rectangular front shape; multiple lower precast pieces 14, each with a sheath pipe 12 positioned at a predetermined location, which constitute the lower part 10b of the rectangular front shape; multiple side precast pieces 15, each with a sheath pipe 12 positioned at a predetermined location, which constitute the side parts 10c on both sides of the rectangular front shape; and four hollow steel cells 16, each positioned at one of the four corners 10d of the rectangular front shape. Within the hollow steel cell 16 at each corner portion 10d, these precast pieces 13, 14, and 15 are joined and integrated using PC steel wires 17. As a result, the PC steel wires 17 are inserted through the interconnected sheath pipes 12 of the multiple precast pieces 13, 14, and 15 that are connected at each side portion 10a, 10b, and 10c of the rectangular front shape, and the ends of the prestressed PC steel wires 17 are fixed to the fixed solidified body 18 formed by pouring concrete inside each hollow steel cell 16 via known fixing devices 19. Thus, the multiple precast pieces 13, 14, and 15 are joined and integrated circumferentially via the four hollow steel cells 16 to have a hollow rectangular front shape. 【0018】 In this embodiment, preferably by the R&C method, prior to the operation of forming the underground space 26 by the box structure 11 in the ground below the existing structure 30, a working shaft 31 (see Fig. 2) serving as a work base is formed on one side sandwiching the existing structure 30. In this embodiment, as described above, since another existing facility structure 40 is formed on the other side sandwiching the existing structure 30, the working shaft 31 is formed only on one side, and each working process is carried out. The working shaft 31 can be easily formed, for example, in the same manner as a shaft formed in the shield method using a shield tunneling machine, by forming a ground improvement preferably by the SMW method rich in water stoppage and a soil retaining wall 32 using sheet piles, and excavating to a predetermined depth while retaining the inside of it. The surface on the working shaft 31 side is protected by sheet piles and supported by support works such as crossbeams. In the formed working shaft 31, propulsion equipment for propelling the box pipe member 25 and the box structure 11, removal equipment when removing the box pipe member 25, etc. will be appropriately installed (see Figs. 2 and 4). 【0019】 Also, in this embodiment, propulsion equipment for the box pipe member 25 is installed in the formed working shaft 31, and in the same manner as the conventional R&C method, each of the plurality of box pipe members 25 is arranged and continuously installed along the top surface part, both side surface parts, and both end parts of the bottom surface part of the planned installation area of the box structure 11 in the circumferential direction of a cross-section perpendicular to the transverse direction of the box structure 11 in the planned installation area, and is propelled and pushed from the working shaft 31 into the ground below the existing structure 30. Thereby, in addition to the top surface box roof 21 and the side surface box roof 22 crossing the directly below part of the existing structure 30, a box roof 20 including preferably the bottom surface box roof 23 at both end corner parts on both sides can be formed (see Fig. 3). 【0020】 Here, each of the box pipe members 25 has, for example, a hollow substantially square cross-sectional shape with a size of about 800 to 1,400 mm in length and width, and is preferably installed in the ground with an extension sufficient to cross the ground directly below the existing underground structure 30 while sequentially adding unit pipes 25a with a length of about 1 m (see Figs. 2 and 3). 【0021】 Once a box-shaped roof 20, including a top box-shaped roof 21, side box-shaped roofs 22, and bottom box-shaped roof 23, is formed in the planned installation area of ​​the box-shaped structure 11 that crosses the portion directly beneath the existing structure 30, in this embodiment, preferably the side box-shaped roofs 22 and bottom box-shaped roofs 23 are left in the ground, and only the top box-shaped roof 21 is replaced with the top portion 11a. The box-shaped structure 11 is then propelled from the working shaft 31 toward the ground directly beneath the existing structure 30 by a propulsion device 27 installed in the working shaft 31, thereby forming an underground space 26 with the box-shaped structure 11 (see Figures 4 to 7). 【0022】 In this embodiment, as described above, since the work is performed in a narrow working shaft 31, the box structure 11 is formed by a plurality of precast concrete unit boxes that are continuously connected and integrated in the axial direction. The underpass box piece 10 in this embodiment is used as such a unit box, and is formed to have a thickness of, for example, about 1 m by assembling a plurality of precast pieces 13, 14, and 15, which are divided pieces in the circumferential direction, as a single unit in the working shaft 31 via hollow steel cells 16 at the corners. In other words, each underpass box-shaped piece 10 is formed by assembling precast pieces 13, 14, 15 and hollow steel cells 16 that are suspended from the ground into the working shaft 31, as shown in Figures 2 and 3. The formed underpass box-shaped pieces 10 are then sequentially connected in the axial direction and propelled as a box-shaped structure 11 toward the ground directly beneath the existing structure 30 by propulsion equipment 27 installed in the working shaft 31 (see Figures 4 and 5). 【0023】 In this embodiment, the upper precast piece 13, lower precast piece 14, and side precast piece 15 that constitute the underpass box body piece 10 are manufactured in advance as precast concrete products with high precision in a factory or the like. As shown in Figure 1, they are formed as a hexahedral block body with a rectangular front shape, preferably a roughly square front shape, and for example, a size of about 3m in length and width and 1m in thickness. Because these concrete precast pieces 13, 14, and 15 are heavy, their thickness is determined first by the jack stroke of the propulsion equipment 27, and then they are divided to a weight that can be transported and lifted, and their weight and shape can be appropriately designed and formed. Furthermore, in order to reduce the production cost of formwork in a factory or the like, it is preferable to keep the number of types of sizes and shapes to a minimum, and it is preferable to use butt joints for the joint portions. 【0024】 Furthermore, in this embodiment, each of the precast pieces 13, 14, and 15 has multiple sheath pipes 12 embedded and attached at predetermined positions where they will communicate with each other when these precast pieces 13, 14, and 15 are assembled in a continuous manner along the upper, lower, and side portions 10c of the underpass box body piece 10 during manufacturing at a factory or the like. Because multiple sheath pipes 12 are embedded and attached to each of the precast pieces 13, 14, and 15 during manufacturing at a factory or the like, it becomes possible to accurately attach the sheath pipes 12 at predetermined design positions where prestressing force can be effectively generated by the PC steel wires 17 through which they are inserted. 【0025】 The hollow steel cells 16, each positioned at one of the four corners of the underpass box-shaped piece 10 in this embodiment, are hollow outer shells formed using, for example, steel plates with a thickness of about 32 mm. In this embodiment, the hollow steel cell 16 is formed as a hollow three-dimensional outer shell by connecting a pair of front and rear front plates, each having an L-shaped front shape, with one corner of a square approximately 5 m in length and width cut out by a square cutout portion 16a approximately 2 m in length and width. The pair of inner sides of the cutout portion 16a are connected via inner surface connecting plates approximately 1 m wide and 2 m long, while the pair of outer sides opposite the cutout portion are connected via outer surface connecting plates approximately 1 m wide and 5 m long. 【0026】 As a result, each hollow steel cell 16 has open end faces 16b on both sides of the L-shaped cutout portion 16a of the front plate. When the four hollow steel cells 16 are assembled together with the precast pieces 13, 14, and 15 to form a hollow rectangular front shape and placed at the four corners of the underpass box body piece 10, these open end faces 16b are connected to the end faces of the upper precast piece 13, the lower precast piece 14, and the side precast piece 15, all of which are connected to each other and have their sheath pipes 12s open. Furthermore, as a result, each of the four hollow steel cells 16 located at the corners has its protruding portions 16c on both sides of the notched portion 16a in its L-shaped front form positioned at the ends of the rectangular front form of the underpass box piece 10, as part of the side portion 10c and the upper portion 10a or lower portion 10b of the rectangular front form. 【0027】 Furthermore, in this embodiment, a fixed solidification body 18 is formed in the hollow steel cell 16 for fixing the end of the PC steel wire 17 that has been subjected to prestressing. The fixed solidification body 18 can be formed in advance at a factory or the like when the hollow steel cell 16 is manufactured, by pouring concrete with the sheath pipe 12a embedded in a predetermined position that communicates with the sheath pipe provided in the precast pieces 13, 14, and 15. The fixed solidified body 18 can also be formed by assembling the hollow steel cells 16 together with the upper precast piece 13, the lower precast piece 14, and the side precast piece 15 to form a rectangular front shape, then assembling the formwork by working inside each of the four corners of the hollow steel cells 16, and connecting the sheath pipes 12a of the cell sections to the end faces of the upper precast piece 13, the lower precast piece 14, and the side precast piece 15, thereby attaching the sheath pipes 12a of the cell sections to the inside of the formwork, and then pouring concrete. 【0028】 Furthermore, according to this embodiment, the hollow steel cell 16 is assembled together with the upper precast piece 13, the lower precast piece 14, and the side precast piece 15 to form a rectangular front shape. In each of the upper portion 10a, lower portion 10b, and side portion 10c of the rectangular front shape, a sheath pipe 12 is connected from one end to the other end of the fixed solidified body 18. Then, PC steel wires 17 are inserted through each of the connected sheath pipes 12. After applying prestress to the inserted PC steel wires 17, both ends of the PC steel wires 17 are fixed to the fixed solidified body 18 using a known fixing device 19. This makes it possible to smoothly form each of the underpass box body pieces 10 of this embodiment, in which the hollow steel cell 16 and the multiple precast pieces 13, 14, and 15 are firmly joined and integrated in the circumferential direction via the PC steel wires 17. Here, the arrangement and number of PC steel wires 17, and the prestress to be applied, can be appropriately designed taking into account the earth pressure and other factors that are applied to the underpass box section 10 from the surrounding ground. The hollow steel cell 16 and the multiple precast pieces 13, 14, and 15 are firmly joined and integrated in the circumferential direction via the PC steel wires 17, making it possible to reliably avoid water leakage even when installed below the groundwater level. 【0029】 In this way, the box-shaped underpass pieces 10 of this embodiment, formed for example with each jack stroke of the propulsion equipment 27, are assembled as components of the box-shaped structure 11, as shown in Figures 4 and 5, in the propulsion direction of the box-shaped structure 11, sequentially connected from the rear side. The box-shaped structure 11 formed in this way is propelled from the working shaft 31 toward the ground directly beneath the existing structure 30, replacing the top surface 11a with the top surface box-shaped roof 21. This makes it possible to form an underground space 26 by the box-shaped structure 11 across the existing structure 30 in the ground directly beneath it (see Figures 6 and 7). 【0030】 Furthermore, in this embodiment, as described above, preferably as an underpass construction method using the R&C method, as shown in Figure 4, the box structure 11 is advanced while excavating the ground remaining inside the box-shaped roof 20 that surrounds the face 28, and since only the starting shaft is used as the working shaft 31, the box-shaped pipe members 25 that constitute the box-shaped roof 20 are recovered into the working shaft 31 unit by unit pipe 25a, while the box structure 11 is advanced into the ground below the existing underground structure 30. 【0031】 In this way, in this embodiment, the box structure 11 is driven into the ground, and when the tip of the box structure 11 reaches, for example, the improved ground at the tip end on the forward side in the direction of propulsion, sandwiching the existing structure 30, an underground space 26 is formed by the box structure 11 to which the underpass box piece 10 installed across the portion directly beneath the existing underground structure 30 is connected (see Figures 6 and 7). The formed underground space 26 can be used in communication with the existing equipment structure 40 by, for example, removing the side wall 40a in the portion corresponding to the underground space 26 of another existing equipment structure 40 (see Figure 6). 【0032】 Furthermore, the underpass box body piece 10 of this embodiment, having the above-described configuration, makes it possible to efficiently join and integrate multiple subdivided precast concrete pieces in a narrow working shaft 31, and to use them smoothly as components of the box body structure 11. 【0033】 In other words, according to this embodiment, each underpass box body piece 10 that constitutes the box body structure 11 by being connected and integrated in multiple units in the direction of propulsion is composed of multiple upper precast pieces 13, multiple lower precast pieces 14, multiple side precast pieces 15, and four hollow steel cells 16. These precast pieces 13, 14, 15 and hollow steel cells 16 have a thickness of about 1 m and are compact enough to be easily lifted using heavy machinery, so they can be easily transported into the narrow working shaft 31. Furthermore, within the narrow working shaft 31, for example, after assembling these precast pieces 13, 14, 15 and hollow steel cells 16 via support frames to form a rectangular front shape, a series of operations can be performed to efficiently join and integrate them. This involves inserting PC steel wires 17 through connecting sheath pipes 12, 12a inside each hollow steel cell 16 to apply prestress, and then fixing both ends to the anchoring solidification body 18. This allows each of the underpass box body pieces 10 formed by joining and integrating these precast pieces 13, 14, 15 and hollow steel cells 16 can be easily and smoothly used as a component of the box body structure 11. 【0034】 It should be noted that the present invention is not limited to the above embodiments and can be modified in various ways. For example, the existing structure from which the underground space formed by the box-shaped structure is created in the ground below does not necessarily have to be an existing facility structure for a subway, but may be an existing structure for a road, or any other type of existing structure such as a building basement or a sewer pipeline. If there are no construction problems, the side box-shaped roof may be replaced with the side portion of the box-shaped roof when the box-shaped structure is advanced toward the ground directly beneath the existing structure. Furthermore, the box-shaped structure using the underpass box-shaped piece of the present invention may be advanced toward the working shaft on the receiving side, with a working shaft also provided on the receiving side, sandwiching the existing structure. If a working shaft is provided on the receiving side, the box-shaped structure using the underpass box-shaped piece of the present invention can also be adopted as an underpass construction method in the SFT method (registered trademark), in which the ground and soil remaining inside the box-shaped roof are removed in the working shaft on the receiving side. 【0035】 10 box-shaped pieces for underpasses 10a Upper part 10b Lower edge 10c side part 10d corner part 11 Box structure 11a Top section 11b Side part 12,12a Sheath pipe 13. Upper precast piece 14 Lower precast piece 15 Side precast pieces 16 Hollow steel cells 16a Notch part 16b Open end face 16c End portions of each side of the rectangular front shape of the underpass box piece 17 PC steel wire 18 Fixed solidified body 19 Fixing device 20 Box-shaped roof 21 Top box roof 22 Side box-shaped roof 23 Box-shaped roof at the bottom 25 Box-shaped pipe members 25a Unit Pipe 26 Underground space 27 Propulsion equipment 28. The face of the pipe 30 Existing structures 31. Working shaft 32 Retaining wall 40 Existing equipment structures 40a Side wall of the section corresponding to the underground space

Claims

[Claim 1] An underpass box piece having a rectangular front shape similar to the rectangular cross-sectional shape of the box structure, which is used in an underpass construction method that forms an underground space by propelling a box structure from a working shaft toward the ground directly below the existing structure so as to replace at least the top box-shaped roof and top surface that have been installed in advance on the ground below the existing structure, the box piece for the underpass having a rectangular cross-sectional shape, which constitutes the box structure having a rectangular cross-sectional shape, The box-shaped pieces for the underpass are formed for each jack stroke of the propulsion equipment installed in the work shaft, and multiple pieces are connected and integrated in the propulsion direction to form the box-shaped structure. The underpass box piece comprises a plurality of upper precast pieces with sheath pipes positioned at predetermined locations, forming the upper part of a rectangular front shape; a plurality of lower precast pieces with sheath pipes positioned at predetermined locations, forming the lower part of a rectangular front shape; a plurality of side precast pieces with sheath pipes positioned at predetermined locations, forming the side parts on both sides of the rectangular front shape; and four hollow steel cells positioned at each of the four corners of the rectangular front shape. Each of the hollow steel cells has an L-shaped front surface that includes the ends of the side portions of the rectangular front surface and the ends of the upper or lower portions of the rectangular front surface. Furthermore, when the hollow steel cell is manufactured, a fixed solidified body is pre-formed inside the hollow steel cell by pouring concrete to fix the ends of the prestressed PC steel wires, with the sheath pipes embedded in predetermined positions that communicate with the sheath pipes disposed in the upper precast piece, the lower precast piece, or the side precast piece. An underpass box piece in which multiple precast pieces are joined and integrated circumferentially via four hollow steel cells, such that the multiple precast pieces have a hollow rectangular front shape, as a result of the process of joining and integrating these precast pieces with PC steel wires inside each of the hollow steel cells, so that the PC steel wires are inserted through the sheath tubes that communicate with each of the multiple precast pieces that are connected at each side of the rectangular front shape, and the ends of the prestressed PC steel wires are fixed to the fixed solidified body, so that the multiple precast pieces have a hollow rectangular front shape, as a result of the process of joining and integrating these precast pieces with PC steel wires inside each of the hollow steel cells, so that the PC steel wires are inserted through the sheath tubes that communicate with each of the multiple precast pieces that are connected at each side of the rectangular front shape, and the ends of the PC steel wires that are prestressed are fixed to the fixed solidified body, so that the multiple precast pieces have a hollow rectangular front shape, as a unit. [Claim 2] The underpass box piece according to claim 1, wherein, after the PC steel wires are each fixed to the fixed solidified body, concrete is filled and solidified in the working space inside the hollow steel cell, excluding the portion of the fixed solidified body. [Claim 3] The underpass box piece according to claim 1 or 2, wherein each of the plurality of precast pieces has a rectangular front shape. [Claim 4] An underpass box piece according to claim 1 or 2, used in the R&C method (registered trademark) in which excavation work is performed at the tunnel face, with only the launching shaft being used as the aforementioned working shaft.

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