KR102286225B1 - Method for constructing underground structure busing PC integrating method without support - Google Patents

Abstract

The present invention uses a factory-made PC member for the retaining wall construction process of the non-pole top-down method, the brace construction process, and the synthesis process of the steel frame internal column, and integrates it with the cast-in-place concrete to improve the workability and structural safety. A PC complex construction method for an underground structure is presented.
A non-pole top-down underground structure PC complex construction method according to an appropriate embodiment of the present invention comprises the steps of: (P1) constructing a retaining wall using a hollow PC wall capable of post tension; (P2) installing a steel frame inner column at a location where the main column of the building will be installed; (P3) excavating to build a floor plate on the first floor above the ground; (P4) constructing a floor plate on the first floor above the ground; (P5) excavating to construct the first basement floor plate; (P6) supporting the retaining wall by installing a PC brace between each steel frame inner column and between the steel frame inner column and the hollow PC wall at the floor plate level of the first basement floor; (P7) constructing a floor plate slab on the first basement floor; (P8) repeating the steps of (P5) to (P8) for each basement floor by excavating one basement floor and installing a PC brace on the floor to construct a floor plate; (P9) assembling a reinforcing bar-integrated PC formwork on the outside of the steel frame inner column of the entire basement floor, and pouring concrete from the first floor floor plate to construct the inner column of the entire basement floor as an SRC column at the same time; and (P10) excavating the bottom surface of the lowest floor and constructing the bottom plate.

Description

{Method for constructing underground structure busing PC integrating method without support}

The present invention relates to a construction method for constructing an underground structure, and more particularly, using a factory-made PC member for the retaining wall construction process of the non-pole top-down construction method, the brace construction process, and the synthesis process of the steel frame internal column, etc. It relates to a PC composite construction method for a non-pole top-down underground structure that improves workability and structural safety by integrating it with concrete.

Recently, in narrow downtown areas, high-rise and large-scale buildings are being constructed in close proximity to the site boundary in order to secure a high land price, secure a parking space, and maximize the use of the site.

Against this background, as a construction method suitable for urban construction, a top-down construction method that can be safely implemented among the methods developed so as to be able to construct an underground structure without adversely affecting the surrounding ground during construction of an underground structure is being applied.

The Top-Down method (top-down method, reverse perforation method) means that the retaining wall is first built, the columns and foundation are constructed, and then the ground work can be carried out simultaneously with the construction from the first floor floor slab to the basement. In the substructure construction, a Diaphragm Wall, Slurry Wall is constructed to prevent subsidence of nearby ground and buildings and damage to underground facilities, and then excavated to construct an underground structure. is a construction method developed so that stability and shortening of the total construction period can be expected during underground construction by excavating from the first floor down and simultaneously constructing the superstructure construction. This method is widely applied to large-scale building construction in downtown redevelopment projects, such as close-up construction, large-scale excavation, and narrow working area.

Since this method constructs the first floor above the ground in advance, it can be used as a workshop, so it is advantageous to bring in vehicles and store materials during construction in densely populated areas of the city. As it minimizes the effects of subsidence and building subsidence, it is possible to structurally safely perform underground construction during construction. In addition, since the above-ground frame can be constructed separately from the excavation work, the total construction period can be shortened as much as the underground excavation period. It is possible to manage and prevent the occurrence of civil complaints such as noise and vibration, enabling smooth construction.

In recent years, the solid top-down method has been studied and constructed as a type of top-down method. It is a construction method that dramatically improved the disadvantages of the top-down method of concrete, and it is a method that solves the waiting period during the concrete curing period and simplifies the repetitive installation, dismantling, transport, and lifting processes of copper bars and forms. In addition, it contributes to environmental improvement by minimizing the disposal and discharge of discarded concrete and mold remnants, and it is also effective in improving safety through the use of earthworks and structure work areas.

Therefore, it is necessary to continue the invention of various non-pole top-down methods in the future.

As the background technology of the present invention, there is Patent Registration No. 10-0775767 'reverse casting construction method using vertical reinforcing bars for columns of SRC frame' (Patent Document 1). This patent proposes a reverse casting construction method advantageous for improving workability and saving materials by using vertical reinforcing bars for columns of SRC frames in building a multi-story underground structure by lowering the beam-slab suspension form in stages. However, this patent uses beam-slab suspension forms to construct beams and slabs as cast-in-place concrete structures. There is a disadvantage in that the amount of cast-in-place concrete increases and the work of the lower layer cannot be carried out until the beam-slab concrete of the upper layer is cured, so the construction is delayed.

As another technology that is the background of the present invention, there is Patent Registration No. 10-0788623 'top-down method using a PC column' (Patent Document 2). This patent proposes a top-down construction method using a PC column instead of a steel column as a column that is pre-buried underground in the conventional top-down method. However, this patent has the disadvantage that it is difficult to secure the integrity between the upper and lower basement PC columns and the workability of the junction between the PC column and the cheolgol beam supporting the retaining wall is poor.

Patent Registration No. 10-0775767 'Reverse casting construction method using vertical reinforcement for columns of SRC frame' Patent Registration No. 10-0788623 ‘Top-down method using PC pillar’

The present invention fully utilizes the advantages of the conventional non-pole top-down construction method, and half-precasts the main structural members used for retaining construction (partial PCization) and pours cast-in-place concrete to integrate these members, resulting in constructability and structural stability. Its purpose is to provide a PC composite construction method for a non-pole top-down underground structure that can secure

A non-pole top-down underground structure PC complex construction method according to a suitable embodiment of the present invention comprises the steps of: (P1) constructing a retaining wall using a hollow PC wall capable of post tension; (P2) installing a steel frame inner column at a location where the main column of the building will be installed; (P3) excavating to build a floor plate on the first floor above the ground; (P4) constructing a floor plate on the first floor above the ground; (P5) excavating to construct the first basement floor plate; (P6) supporting the retaining wall by installing a PC brace between each steel frame inner column and between the steel frame inner column and the hollow PC wall at the floor plate level of the first basement floor; (P7) constructing a floor plate slab on the first basement floor; (P8) repeating the steps of (P5) to (P8) for each basement floor by excavating a basement floor and installing a PC brace on the floor to construct a floor plate; (P9) assembling a reinforcing bar-integrated PC formwork on the outside of the steel frame inner column of the entire basement floor and pouring concrete from the first floor floor plate to construct the inner column of the entire basement floor as an SRC column at the same time; and (P10) excavating the lowermost floor and constructing the lowermost floor plate.

The hollow PC wall capable of post-tension in the step (P1) is a PC wall fixing member for coupling the first PC plate and the second PC plate, the first PC plate and the second PC plate positioned in parallel to each other by a predetermined distance, It includes a U-shaped sheath pipe inserted between the first PC plate and the second PC plate, and the first PC plate has an embedded plate installed at the position where it is coupled with the PC brace, and the second PC plate has a half truss muscle installed on one side. It is a PC board, and concrete is poured between the first PC board and the second PC board to form a retaining wall, and post tension is possible through a U-shaped sheath pipe.

In addition, in step (P6), the P-bracket is respectively joined to the embedded plate of the steel frame inner column and the hollow PC wall to fix the PC brace between the steel frame inner column and between the steel frame inner column and the hollow PC wall, and the lower part of the PC support end end It is characterized in that it comprises a pair of web plates that connect the lower plate providing a size that can support the PC and the upper plate of a size that can fix the position of the PC brace, and the upper and lower plates, and the shear key is installed to protrude outward.

In addition, the PC brace in step (P6) is a factory-made PC beam, and its end is manufactured in a U shape, and it is characterized in that it has an opening that facilitates assembly and on-site concrete pouring.

In addition, in step (P9), the reinforcing bar-integrated PC formwork is a reinforcement-integrated PC formwork including a PC plate and an integral reinforcing bar, which is assembled on the outside of the inner column of the steel frame and forms a part of the SRC column after the concrete is poured and cured. .

The non-pole top-down PC composite construction method according to the present invention fully utilizes the advantages of the conventional non-pole top-down construction method, while half-precast concrete (partial PCization) of the main structural members used for retaining construction and pouring cast-in-place concrete. By integrating these members, it is possible to secure workability and structural stability.

The following drawings attached to the present specification illustrate preferred embodiments of the present invention, and serve to further understand the technical spirit of the present invention together with the detailed description of the present invention, so the present invention is limited to the matters described in the accompanying drawings It should not be construed as being limited.
1 is a cross-sectional view schematically showing the construction sequence of the non-pole top-down underground structure PC complex construction method according to the present invention.
2 is a view showing a hollow PC wall capable of post tension applied to the present invention, 2a is a view showing the installation of the hollow PC wall, 2b is a perspective view showing the components of the hollow PC wall.
Figure 3 is a perspective view showing a PC brace applied to the present invention.
4 is a perspective view showing a P-bracket applied to the present invention.
5 is a perspective view showing the appearance of one basement floor constructed according to the present invention.
Figures 6a, 6b is a perspective view showing the state of installing the PC formwork to configure the steel frame inner column as the main column of the steel frame reinforced concrete structure.

Hereinafter, the present invention will be described in detail with reference to the embodiments shown in the accompanying drawings, but the presented embodiments are illustrative for a clear understanding of the present invention, and the present invention is not limited thereto.

The PC composite construction method of the non-pole top-down underground structure according to the present invention introduces the PC composite construction method to the retaining wall construction process of the conventional non-pole top-down construction method, the brace construction process, and the synthesis process of the steel frame internal column, thereby reducing the amount of concrete cast-in-place. It was developed to significantly shorten the construction period by reducing Therefore, below, the characteristic process of the present invention, which is distinguished from the conventional non-pole top-down method, will be mainly described.

The basic component of the top-down method is a retaining wall to support transverse earth pressure, water pressure and vertical load during excavation work, and it is installed between the facing retaining walls to transmit the lateral pressure acting on one retaining wall to the other retaining wall. After the excavation work is completed, the unsupported length of the transverse support and the transverse support used as beams of the underground structure is reduced to prevent buckling and transfer the load of the upper structure to the foundation. It is an inner column used as a column.

In the present invention, an underground continuous wall method is adopted as a retaining wall, but post tension is possible and a precast concrete wall (hereinafter, a hollow PC wall) 10 capable of on-site concrete pouring is introduced in the excavation work as a retaining wall during excavation work. After completion, it should be used as a permanent wall (outer wall) of the underground structure. In addition, when constructing the floor, a non-cast construction method is introduced, but a precast concrete beam (hereinafter referred to as a PC brace) 30 is used instead of an H-beam used as a normal lateral support. In addition, by using a formwork (hereinafter referred to as PC formwork) 60 composed of a reinforcing bar-integrated precast concrete plate, the inner column of the steel frame is composed of a steel frame reinforced concrete (hereinafter referred to as SRC) composite column.

1 is a cross-sectional view schematically showing the construction sequence of the non-pole top-down underground structure PC complex construction method according to the present invention.

As shown in Figure 1, the PC composite construction method for a non-pole top-down underground structure according to the present invention comprises the steps of (P1) constructing a retaining wall using a hollow PC wall 10 capable of post tension (a); (P2) a step (b) of installing the inner pillars of the steel frame 20 at the location where the main pillars of the building will be installed; (P3) excavating to build the first floor above the ground (c); (P4) building the first floor above the ground (d); (P5) excavating for the installation of the first basement floor (d); (P6) Installing a PC brace 30 between each steel frame inner column 20 and between the steel frame inner column 20 and the hollow PC wall 10 at the floor plate level of the first basement floor to support the retaining wall (e) ); (P7) step (f) of constructing the first basement floor slab; (P8) repeating the steps of (P5) to (P8) of excavating one basement floor and installing a PC brace on the floor to build a slab (g) for each basement level; (P9) Assemble the reinforcing bar integrated PC formwork (60) on the outside of the steel frame inner column (20) of the entire basement floor, and pour concrete from the first floor floor plate above the ground, and the inner column (20) of the entire basement floor is composed of SRC columns at the same time step (g); and (P10) excavating the bottom surface of the lowest floor and constructing the bottom plate (h).

Hereinafter, each step of the PC composite construction method of the non-pole top-down underground structure according to the present invention will be described in detail.

1. (P1) stage - retaining wall construction work

In the top-down method, the retaining wall has to support vertical loads in addition to the main role of supporting transverse earth pressure and water pressure, so the Diaphragm Wall, Slurry Wall is mainly used.

First, the ground is excavated using a conventional excavator to a required depth in consideration of the outer boundary where the underground structure will be formed according to a specific actual design, and then a stabilizing solution made of bentonite is injected into the excavation space.

Next, as shown in FIG. 2A, a precast concrete wall (hereinafter, a hollow PC wall) 10 manufactured by a factory in the excavation space in which the stabilizing liquid is injected is continuously inserted in the vertical direction to form a retaining wall.

The hollow PC wall 10 applied to the present invention shown in FIG. 2b is a state manufactured in a factory, and the first PC plate 11 and the second PC plate 12 of the hollow PC wall are positioned in parallel, and the first A PC wall fixing member 13 for coupling the PC plate 11 and the second PC plate 12 with a certain distance apart is installed at regular intervals in the longitudinal direction of the PC plate. The first PC plate 11 used as the outer wall of the underground structure is provided with a buried plate 15 at a position for coupling with the PC brace 30 to be described later (see FIG. 1A ). The second PC board is a half PC board with truss muscles installed on one side, and a U-shaped sheath tube 14 for post tension is inserted between the first PC board 11 and the second PC board 12 . The position of the buried plate 15 is manufactured by calculating the joint position with the PC brace 30, but the size is made larger than the end size of the PC brace 30 in consideration of the error.

After the hollow PC wall 10 is continuously inserted, concrete is poured between the first PC plate 11 and the second PC plate 12 of the hollow PC wall 10 to form a continuous retaining wall. A portion of the stabilizing solution injected in the above process is recovered, and the concrete pouring method and the stabilizing solution recovery method may be arbitrarily selected from methods known in the art.

After the concrete is cured, the PS steel wire 16 in the U-shaped sheath 14 installed inside the hollow PC wall 10 is tensioned by a known method to introduce prestress to the retaining wall.

The retaining wall using the hollow PC wall 10 installed in this step can realize the high-strength wall required as an underground structural wall rather than a simple retaining wall compared to the conventional continuous underground wall, and the first PC plate 11 is a finishing wall. and the hollow PC wall 10 is factory-manufactured, so assembly is easy and on-site installation is simple. In addition, the thickness of the wall can be significantly reduced by post-tension construction, and cracking can be prevented due to its strong resistance to cracking moment caused by earth pressure.

2. Step (P2) - Installation of internal steel columns

This step is a step of drilling a location where the main pillar of the building will be installed and installing the steel frame internal pillar 20 in a conventional manner.

In the plan design of the building, the steel frame inner column is vertically inserted from the ground into the perforated hole at the position where the column as the main structure should be installed, and then the base is formed at the lower end of the steel frame inner column 20 . In the present invention, the steel frame internal column 20 is connected to a lateral support that transmits lateral pressure such as earth pressure and water pressure acting on the retaining wall to the other retaining wall during the construction of the basement floor, and serves as a center pile to resist earth pressure. After the underground construction is completed, it will serve as a column, the main structure of the building, that transmits the axial force from the upper part as a basis. A foundation is formed at the lower end of the steel frame internal pillar 20 installed as described above so as to transmit the load from the upper structure to the ground. Widely applied RCD (Reverse Circulation Drill), PRD (Percussion Rotary Drill), Barrette Pile method, etc. can be applied.

3. Step (P3) - Excavation for the construction of the first floor above the ground

After the retaining wall and the internal steel frame are installed in the ground as described above, the first excavation of the soil inside the retaining wall is performed. At this time, it is preferable that the first excavation depth is not excavated more deeply than necessary and excavated only as much as the minimum depth capable of pouring the beam-slab structure on the floor of the first floor above the ground.

4. Step (P4) - Construction of the first floor above the ground

When the first excavation is completed as described above, the first floor is built on the ground level except for the work area. At this time, the ground floor on the first floor can be used as a workplace where vehicles can be brought in and out and materials are stored during construction, and since it is hardly affected by the climate during underground construction, accurate process management is possible, and it plays a role in preventing civil complaints such as noise and vibration.

5. Step (P5) - Excavation for the installation of the first basement floor

This step is a step of excavating the basement to construct the first basement floor after the ground floor is built. The soil inside the retaining wall is excavated to a depth enough to place PC braces and slab structures on the floor of the first basement floor, and the excavated soil is carried out through the work area of the floor slab on the first floor above the ground.

6. Step (P6) - Step of installing PC braces between each inner column and between the inner column and the hollow PC wall at the ground level of the first basement floor

During top-down construction, the transverse support receives moment and shear force by its own weight, wall load, finishing load, and working load, and receives axial pressure from transverse earth pressure and water pressure from the retaining wall. The conventional transverse support is composed of steel frame or RC structure, and depending on the method of forming the floor structure, the top-down method is largely conventional, BRD (Bracket Supported RC Downward), NSTD (Non Supporting Top Down), SPS (Strut as Permanent System) (New Technology No. 294, Samsung), etc.

In the present invention, the brace corresponding to the main structure of the basement is used as a lateral support, as a retaining support during excavation work, and as a main structural member in the main building immediately without dismantling during the frame work after excavation work, which is a disadvantage of the conventional construction method It improves workability and material loss due to the risk that occurs during construction, such as installation or dismantling, and the mutual interference with the main structure. In addition, since the material cost is high and the material supply and demand is not stable, the PC brace 30 is introduced instead of the steel frame, which is a factor that increases the construction cost, to construct the lateral support.

The PC brace 30 shown in FIG. 3 is exemplary and the size or shape of the cross-section is not limited to that shown in FIG. 3 . The PC brace 30 is manufactured in a U-shape at its end to provide an opening 31 of a certain space, which facilitates assembly when combined with a retaining wall or an internal column, as will be described later, and facilitates on-site concrete pouring. The purpose of this is to make the rigidity of the coupling part sufficient.

The P-shaped connecting material (hereinafter referred to as "P-bracket") 40 shown in Fig. 4a is the connection of the steel frame inner column and the PC brace 30 installed in the step (P2) and the retaining wall and the PC brace installed in the step (P1). As a means for connection with (30), its shape is a PC brace in the connection between the lower plate 41 and PC brace 30 and the retaining wall or internal pillar providing a size that can support the lower part of the PC brace 30 end. It connects the upper plate 42 and the upper and lower plates 41 and 42 of a size capable of fixing the position of and includes a pair of webs 43 with a plurality of shear keys 44 installed to protrude outward.

As shown in Fig. 4b, the P-bracket 40 installed on the weak axis of the inner column has a back plate 45 that can be joined to the flanges 21 and 22 rather than the web 23 of the inner column 20. may include

After the P-shaped bracket 40 is joined to the embedded plate 15 of the strong and weak axis of the inner column and the hollow PC wall 10, respectively, the PC brace 30 is placed between each inner column 20 and between the inner column 20 and the inner column 20. It is positioned between the hollow PC walls (10).

7. Step (P7) - Pouring the first basement floor slab

The first basement floor slab 50 is poured. A flat slab or a wide beam slab system is preferable for the non-pole top-down method, but there is no restriction on the slab system constructed according to the structural design. However, as shown in FIG. 5 , when pouring the slab 50 , each opening 51 is left in the portion corresponding to the corner of the inner column. The opening 51 is used for installing connecting bars and pouring concrete when configuring the internal columns to be described later as the columns of the SRC structure.

8. Step (P8) - Repeated reverse hitting construction

This step is a step of excavating the lower part of the slab and repeating steps (P5), (P6) and (P7) until a predetermined underground layer is formed.

9. Step (P9) - A step of assembling a reinforcing bar-integrated PC formwork on the outside of the pre-construction steel frame inner column and pouring concrete from the first floor deck to simultaneously configure the inner columns (20) of all basement floors as SRC columns

This step is the process of installing the reinforcing bar integrated PC formwork 60 on the outside of the steel frame inner column 20 installed in the step (P2) and building it as an SRC column. 60) is used as the main structure without removing the formwork after curing the concrete, which omits the formwork removal step and has the advantage of easy assembly.

The PC formwork 60 shown in FIG. 6a is a reinforcement-integrated PC formwork 60 including an integral reinforcing bar 62 that is reinforced when the PC plate is manufactured in addition to the PC plate 61, and it does not require on-site reinforcement and its assembly is simple. .

As shown in FIG. 6b, the connecting main bar 63 and the PC formwork 60 are assembled, and the on-site formwork 64 is installed thereon, and concrete is poured through the opening 51 manufactured in the slab in step (P6).

When using the PC formwork (60) to construct the steel frame internal column as an SRC column, it can be constructed in units of each floor, but by pouring concrete from the first floor above the ground, the inner column (20) of the entire basement floor is built as an SRC column at the same time. It is preferable to do

10. Step (P10) - Excavating the bottom surface of the lowest floor and constructing the bottom plate

This step is a step of excavating the bottom surface of the basement structure in a conventional way and constructing the bottom plate.

As described in detail above, the PC composite construction method of the non-pole top-down underground structure according to the present invention fully utilizes the advantages of the conventional non-pole top-down construction method and half-precasts the main structural members used in the retaining construction (partial PC). It has the effect of securing workability and structural stability by integrating these members by pouring cast-in-place concrete.

So far, the present invention has been described in detail with reference to the presented embodiments, but those skilled in the art can make various modifications and modified inventions without departing from the technical spirit of the present invention with reference to the presented embodiments. will be. The present invention is not limited by such variations and modifications, but only by the claims appended hereto.

10: hollow PC wall 11: 1st PC version
12: 2nd PC plate 13: PC wall fixing member
14: U-shaped sheath tube 15: Embedded Plate
16: PS strand 20: internal column of steel frame
21: the first flange of the inner column of the steel frame 22: the second flange of the inner column of the steel frame
23: web of steel frame inner column 30: PC brace PC brace
40: P-shaped bracket 41: P-shaped bracket lower plate
42: upper plate of p-bracket 43: web of p-bracket
44: shear key of the letter-shaped bracket 45: the back plate of the letter-shaped bracket
50: slab 51: opening of the slab
60: PC die 61: PC version of PC die
62: integral main bar of PC formwork 63: connecting main bar
64: field formwork

Claims (5)

(P1) constructing a retaining wall using a hollow PC wall 10 capable of post-tension;
(P2) installing a steel frame inner pillar 20 at a location where the main pillar of the building is to be installed;
(P3) excavating to build a floor plate on the first floor above the ground;
(P4) constructing a floor plate on the first floor above the ground;
(P5) excavating to construct the first basement floor plate;
(P6) supporting the retaining wall by installing a PC brace 30 between each steel frame inner pillar 20 and between the steel frame inner pillar 20 and the hollow PC wall 10 at the basement level of the first floor;
(P7) constructing a floor plate slab on the first basement floor;
(P8) repeating the steps of (P5) to (P8) for each basement floor by excavating one basement floor and installing a PC brace on the floor to construct a floor plate;
(P9) Assemble the reinforcing bar integrated PC formwork (60) on the outside of the steel frame inner column (20) of the entire basement floor, and pour concrete from the first floor deck above the ground to build the inner column (20) of the entire basement floor as an SRC column at the same time to do; and
(P10) excavating the lowermost floor and constructing the lowermost floor plate; including,
The hollow PC wall 10 capable of post-tension in the step (P1),
A PC wall fixing member 13 for coupling the first PC plate 11 and the second PC plate 12, the first PC plate 11 and the second PC plate 12 positioned in parallel by a predetermined distance apart, It includes a U-shaped sheath tube 14 inserted between the first PC plate 11 and the second PC plate 12,
The first PC plate 11 has an embedded plate 15 installed at the coupling position with the PC brace 30, and the second PC plate is a half PC plate with truss muscles installed on one side, and the first PC plate and the second PC plate Concrete is poured between them to form a retaining wall, and post tension is possible through the U-shaped sheath pipe (14).
In the step (P6),
The P-shaped bracket 40 is respectively joined to the embedded plate 15 of the steel frame inner column 20 and the hollow PC wall 10, and between the steel frame inner column 20 and the steel frame inner column 20 and the hollow PC wall 10 Fixing the PC brace (30) between,
The P-bracket 40 is a lower plate 41 providing a size that can support the lower portion of the end of the PC brace 30 and an upper plate 42 of a size that can fix the position of the PC brace, the upper and lower plates 41, 42) and the shear key 44 is installed to protrude to the outside, the non-pole top-down underground structure PC complex construction method, characterized in that it includes a pair of web plates (43). delete delete The method according to claim 1,
In step (P6), the PC brace 30 is,
A PC composite construction method for a non-pole top-down underground structure, characterized in that it has an opening that facilitates assembly and on-site concrete pouring by producing a C-shaped end with a factory-made PC beam. The method according to claim 1,
In the step (P9), the reinforcing bar integrated PC formwork (60) is,
A non-pole, characterized in that it forms a part of the SRC column after the concrete is poured and cured by being assembled on the outside of the steel frame internal column 20 with the reinforcement-integrated PC formwork 60 including the PC plate 61 and the integral reinforcing bar 62 Top-down underground structure PC complex construction method.

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