Construction method for assembling large-diameter shield tunneling in soft surrounding rock large-section branch tunnel

Abstract

The application provides a construction method for converting a large-section branch tunnel into a large-diameter shield assembly tunnel in soft surrounding rock, and belongs to the technical field of tunnels and underground engineering. It solves the problems of large roof removal range, long roof removal distance and high construction risk of the existing large-section branch tunnel into large-diameter shield assembly tunnel. It comprises the following steps: tunnel variable cross-section construction is performed when the large-section branch tunnel construction is performed to a certain distance from the planned shield assembly tunnel, the excavation range is reduced, the large-section branch tunnel is converted into a small-section branch tunnel into the shield assembly tunnel, and the primary support structure of the small-section branch tunnel is constructed. Compared with the existing construction process, the variable cross-section construction method is adopted to reduce the excavation area of the large-section branch tunnel into the main tunnel, the disturbance of the construction to the surrounding rock is reduced, the stress concentration of the surrounding rock is reduced, the construction risk is greatly reduced, and the method can be widely popularized in the fields of tunnel branch tunnel into main tunnel roof removal construction in soft surrounding rock geological conditions.

Description

Technical Field

[0001] This invention belongs to the field of tunnel and underground engineering technology, and relates to a construction method for converting a large-section branch tunnel in weak surrounding rock into a large-diameter shield tunnel assembly tunnel. Background Technology

[0002] Shield tunneling machines (TBMs) are widely used in urban tunnel construction due to their advantages such as high degree of mechanization, fast tunneling speed, and minimal environmental impact. With continuous breakthroughs in TBM technology, the application of large-diameter TBM tunnels is becoming increasingly widespread. However, as infrastructure development continues to improve, engineering construction conditions are becoming more complex, and the requirements for engineering construction are becoming increasingly stringent. As a result, sites suitable for launching or receiving large-diameter TBMs are becoming increasingly scarce, leading to the growing prevalence of in-tunnel launching or receiving methods for large-diameter TBM tunnels.

[0003] When launching or receiving large-diameter shield tunnels inside a tunnel, conventional horseshoe or circular cross-sections are often adopted to meet the space requirements for shield assembly or disassembly operations. These cross-sectional areas are large, resulting in a wide excavation impact range. Simultaneously, to create working faces, adjoint tunnels are often used to enter the shield assembly (disassembly) tunnel. When these adjoint tunnels are used as ventilation ducts or safety escape routes for later operation, large cross-sectional profiles are also adopted. However, under conditions of weak surrounding rock, when entering the large-section shield assembly (disassembly) tunnel through a large-section adjoint tunnel with a cantilevered opening, the large excavation profile is detrimental to the stability of the surrounding rock. The stress concentration at the cantilevered intersection is high, posing a risk of large deformation or even collapse in the soft rock.

[0004] The current method of cantilevering the tunnel from the cross passage 1a to the main tunnel 3a often adopts the following approach: Figure 1 The top-lifting method shown has a top-lifting profile 1b that is larger than the main tunnel 3a. The top-lifting distance is longer and the range is larger. If this technology is used to convert a large-section branch tunnel into a large-diameter shield assembly (disassembly) tunnel under weak surrounding rock conditions, the construction will be difficult and risky. Summary of the Invention

[0005] The purpose of this invention is to address the aforementioned problems in existing technologies by proposing a construction method for converting large-section branch tunnels into large-diameter shield tunnels in weak surrounding rock with low construction risk.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A construction method for converting a large-section adit tunnel into a large-diameter shield tunnel assembly tunnel in weak surrounding rock includes the following steps:

[0008] Step 1: Construct the large-section adit tunnel and build the initial support structure and secondary lining structure of the large-section adit tunnel; when the large-section adit tunnel is constructed to a certain distance from the planned shield assembly tunnel, the tunnel cross-section is changed to reduce the excavation range, and the tunnel is transferred from the large-section adit tunnel to the small-section adit tunnel to enter the shield assembly tunnel, and the initial support structure of the small-section adit tunnel is built.

[0009] The excavation span and height of the small-section adit are smaller than those of the large-section adit, in order to reduce the excavation area and lower the construction risk. The distance between the variable cross-section construction site and the shield assembly tunnel is 10 to 12 meters.

[0010] Step 2: When the construction of the small cross-section branch tunnel reaches the intersection with the planned shield assembly tunnel arch, erect a portal steel frame and climb uphill along the arc contour of the shield assembly tunnel roof in the width direction to provide temporary support for the cantilevered part.

[0011] The portal steel frame consists of horizontal and vertical supports, which are made of I 20b I-beams and connected by steel pads to facilitate the removal of the vertical supports during the construction of the shield tunnel assembly tunnel.

[0012] The temporary support for the cantilevered section consists of portal steel frames, spaced 0.5 to 0.8 meters apart. The portal steel frames are connected by a double-layer steel mesh with a diameter of 6.5 mm. C25 concrete is sprayed onto the portal steel frames, with a thickness of 260 mm.

[0013] Step 3: Install multiple closely spaced steel arch frames on both sides of the small section support tunnel after entering the shield assembly tunnel, and weld them to the portal steel frame. Then spray concrete to complete the initial support of the cantilevered part of the shield assembly tunnel arch.

[0014] After the small-section branch tunnel enters the shield assembly tunnel, it is expanded to the left and right sides by 0.6m each, so that three closely spaced steel arch frames can be placed within the expanded area. The closely spaced steel arch frames are part of the initial support of the arch of the shield assembly tunnel. The material used is I 25b type I-beams. The initial support of the arch of the shield assembly tunnel adopts the form of shotcrete and anchor support, which is located below the temporary support of the cantilever section.

[0015] The closely spaced steel arch frame is welded to the portal steel frame to support and stabilize the portal steel frame. This allows for the initial support of the shield assembly tunnel arch section only by spraying concrete on the cantilevered section, thus saving on the material used for this part of the steel arch frame.

[0016] Step 4: Remove the vertical support of the portal steel frame in the temporary support of the shield assembly tunnel roof section, and use the single-side wall pilot tunnel method to successively expand the left upper step, left lower step, right upper step and right lower step of the shield assembly tunnel in the direction of the large / small mileage of the shield assembly tunnel, and promptly implement the corresponding temporary support and initial support of the main tunnel.

[0017] Only the vertical support of the portal steel frame in the temporary support is removed, and the horizontal support of the portal steel frame is used as permanent support to protect the surrounding rock, ensuring construction safety, while saving main tunnel support materials, construction time and cost.

[0018] The tunnel advances 1m in each cycle towards the large / small mileage direction of the shield assembly tunnel. After each excavation cycle, the corresponding temporary and initial support of the main tunnel is completed. The temporary support is composed of double-span I 22a I-beams, and the initial support adopts anchor spraying support.

[0019] Step 5: Remove the temporary support of the main tunnel of the shield assembly tunnel and construct the arch secondary lining structure and arch foot support beam of the shield assembly tunnel;

[0020] The arch lining structure of the shield assembly tunnel and the arch foot support beam together constitute the arch lining structure of the shield assembly tunnel, with the arch foot support beam located below the arch lining of the shield assembly tunnel.

[0021] Step 6: Return to the position where the large-section adit becomes a small-section adit and expand the small-section adit according to the excavation outline of the large-section adit. After the expanded section is completed, break the initial support structure of the small-section adit and complete the initial support structure and secondary lining structure of the expanded section of the large-section adit.

[0022] The expansion section of the small-section branch tunnel is excavated mechanically to avoid damage to the initial support of the already constructed shield tunnel arch, the secondary lining structure of the arch, and the arch foot support beam caused by drilling and blasting.

[0023] Step 7: Excavate the lower part of the shield assembly tunnel in stages, and successively complete the rib-type anchor retaining walls on both sides of the lower sidewall of the shield assembly tunnel, the secondary lining of the sidewall, and the secondary lining of the bottom slab.

[0024] The lower part of the shield assembly tunnel is excavated using a step-by-step method, with a step height not exceeding 5m. The rib-type anchor retaining walls on both sides of the lower sidewall of the shield assembly tunnel are composed of reinforced concrete capping beams, panels, ribs, and anchor bolt bundles.

[0025] The reinforced concrete capping beam acts on the top of the panel and rib columns. The reinforced concrete capping beam is the same width as the rib columns and has a height of 0.5 to 1.5 m. The reinforced concrete rib columns are 0.3 to 1 m thick and 0.5 to 1.5 m wide, with a longitudinal spacing of 2 to 5 m. The reinforced concrete panel is 0.15 to 0.5 m thick and has a width equal to the net width between the rib columns. The anchor bolts act on the rib columns and are spaced 1.5 to 3 m along the height direction, with a denser anchor bolts within the top 2 m range.

[0026] Compared with existing technologies, this invention has the following advantages: Compared with existing construction processes, the variable cross-section construction method reduces the excavation area of ​​the large-section branch tunnel into the main tunnel, reduces the disturbance to the surrounding rock during construction, reduces stress concentration in the surrounding rock, and greatly reduces construction risks. It can be widely promoted in fields such as the construction of tunnel branch tunnels into the main tunnel under weak surrounding rock geological conditions. The temporary support of the cantilevered section is located above the initial support of the shield assembly tunnel. When constructing the shield assembly tunnel, only the vertical support of this temporary support needs to be removed, and the horizontal support serves as permanent support to protect the surrounding rock. This improves construction safety and saves support materials for this part of the main tunnel, saving construction costs and time. The vertical support and the horizontal support are connected by steel plates, which facilitates the removal of the vertical I-beams when constructing the shield assembly tunnel in both the large and small mileage directions. Attached Figure Description

[0027] Figure 1 This is a construction process diagram for a large-section branch tunnel leading to a large-section main tunnel in existing technology.

[0028] Figure 2 This is a top view of the large-section branch tunnel leading to the large-diameter shield assembly tunnel in this invention.

[0029] Figure 3 This is a front view of the small-section branch tunnel leading to the large-diameter shield assembly tunnel in this invention.

[0030] Figure 4 This is a side view of the small-section branch tunnel leading to the large-diameter shield assembly tunnel in this invention.

[0031] Figure 5 This is a schematic diagram of the temporary and initial support of the cantilevered section in this invention.

[0032] Figure 6 This is a schematic diagram of the upper and lower step excavation and support method on the left side of the tunnel arch section of the shield assembly in this invention.

[0033] Figure 7 This is a schematic diagram of the upper and lower step excavation and support method on the right side of the tunnel arch section of the shield tunnel assembly in this invention.

[0034] Figure 8 This is a schematic diagram of the small-section support tunnel expansion and support in this invention.

[0035] Figure 9 This is a schematic diagram showing the completion of the shield tunnel arch lining structure construction in this invention.

[0036] Figure 10 This is a schematic diagram showing the completion of the excavation and lining of the lower part of the shield tunnel assembly hole in this invention.

[0037] In the diagram: 1. Large-section adit; 101. Secondary lining structure of the large-section adit; 102. Initial support structure of the large-section adit; 2. Small-section adit; 201. Initial support structure of the small-section adit; 202. Enlarged excavation section; 3. Shield assembly tunnel; 301. Initial support; 302. Secondary lining structure of the arch; 303. Temporary support for the main tunnel; 304. Densely packed steel arch frame; 305. Arch foot support beam; 306. Rib-type anchor bolt. Retaining wall; 306a, reinforced concrete capping beam; 306b, panel; 306c, ribbed column; 306d, anchor bolt bundle; 307, secondary lining of side wall; 308, secondary lining of bottom slab; 31, upper left step; 32, upper right step; 33, lower left step; 34, lower right step; 4, cantilevered section; 401, temporary support; 402, portal frame; 402a, horizontal support; 402b, vertical support. Detailed Implementation

[0038] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.

[0039] A construction method for converting a large-section adit tunnel into a large-diameter shield tunnel assembly tunnel in weak surrounding rock includes the following steps:

[0040] Step 1, such as Figure 2 As shown, a large-section adit 1 is constructed, including its initial support structure 102 and secondary lining structure 101. To reduce the excavation area and lower construction risks, as... Figure 2 As shown, when the large-section adit 1 is constructed to a distance of 110-12m from the planned shield assembly tunnel 3, the tunnel cross-section is changed to reduce the excavation range. The large-section adit is then converted to a small-section adit 2 to enter the shield assembly tunnel. The excavation span and height of the small-section adit 2 are smaller than those of the large-section adit 1, and the initial support structure 201 of the small-section adit 2 is constructed.

[0041] Step Two, as follows Figures 2-5 As shown, when the small cross-section branch tunnel 2 is constructed to the position where it intersects with the arch of the planned shield assembly tunnel 3, a portal steel frame 402 is erected and the tunnel is raised and lifted along the arc contour of the tunnel top of the shield assembly tunnel 3 in the direction of its width. 260mm thick C25 concrete is sprayed onto the portal steel frame 402 to provide temporary support 401 for the cantilevered part 4 of the arch of the shield assembly tunnel 3.

[0042] Specifically, such as Figure 4 As shown, the portal steel frame 402 consists of a horizontal support 402a and a vertical support 402b. The horizontal support 402a and the vertical support 402b are made of I 20b I-beams and are connected by steel pads to facilitate the removal of the vertical support 402b during the construction of the shield assembly tunnel 3.

[0043] The temporary support 401 of the cantilever section has a portal steel frame 402. The portal steel frame 402 is laid out at intervals of 0.5 to 0.8 m and is connected by a double-layer steel mesh with a diameter of 6.5 mm.

[0044] Step 3, as follows Figure 4 As shown, three closely spaced steel arch frames 304 are installed on both sides of the small section branch tunnel 2 after entering the shield assembly tunnel 3, and welded to the portal steel frame 402. Then, concrete is sprayed to complete the initial support 301 of the cantilevered part 4 of the arch of the shield assembly tunnel 3.

[0045] After the small cross-section branch tunnel 2 enters the shield assembly tunnel 3, it is expanded to the left and right by 0.6m each, so that three closely spaced steel arch frames 304 can be placed within the expanded excavation range. The closely spaced steel arch frames 304 are part of the initial support 301 of the arch of the shield assembly tunnel 3. The material is I25b type I-beams. The initial support 301 of the arch of the shield assembly tunnel 3 adopts the form of shotcrete and anchor support, and is located below the temporary support 401 of the cantilever section 4.

[0046] The closely spaced steel arch frame 304 is welded to the portal steel frame 402 as a whole to support and stabilize the portal steel frame 402. As a result, only the arch of the shield assembly tunnel 3 of the cantilevered part 4 needs to be sprayed with concrete as the initial support 301 for this part of the shield assembly tunnel 3 arch, thus saving the material used for this part of the steel arch frame.

[0047] Step 4, as follows Figure 3 and Figure 6 As shown, the vertical support 402b of the portal steel frame 402 in the temporary support 401 of the cantilever section 4 of the shield assembly tunnel 3 was removed, and the single-side wall pilot tunnel method was used to successively excavate the upper left step 31, the lower left step 33, the upper right step 32, and the lower right step 34 of the shield assembly tunnel 3 in the direction of the large mileage of the shield assembly tunnel 3, and the corresponding temporary support 303 and initial support 301 of the main tunnel were promptly implemented.

[0048] Specifically, such as Figure 3 and Figure 7 As shown, only the vertical support 402b of the portal steel frame 402 in the temporary support 401 is removed, and the horizontal support 402a of the portal steel frame 402 is used as permanent support to protect the surrounding rock, ensuring construction safety, while saving main tunnel support materials, construction time and cost. The cyclical advance towards the shield assembly tunnel 3 major mileage direction is 1m. After each excavation cycle, the corresponding main tunnel temporary support 303 and initial support 301 are completed. The temporary support 303 is composed of double-span I 22a I-beams, and the initial support 301 adopts anchor spraying support.

[0049] Step 5, as follows Figure 2 and Figure 8As shown, the temporary support 303 of the main tunnel of the shield assembly tunnel 3 is removed, and the arch secondary lining structure 302 and the arch foot support beam 305 of the shield assembly tunnel 3 are constructed.

[0050] The arch lining structure 302 and the arch foot support beam 305 of the shield assembly tunnel 3 together form the arch lining structure of the shield assembly tunnel 3, with the arch foot support beam 305 located below the arch lining structure 302 of the shield assembly tunnel 3.

[0051] Step Six, as Figure 2 and Figure 9 As shown, return to the position of the large-section branch tunnel 1 and the small-section branch tunnel 2. Expand the small-section branch tunnel 2 according to the excavation outline of the large-section branch tunnel 1. After the expanded section 202 is excavated, break the initial support structure 201 of the small-section branch tunnel 2 and complete the initial support structure 102 and the secondary lining structure 101 of the expanded section of the large-section branch tunnel 1.

[0052] The small cross-section branch tunnel 2 expansion section 202 adopts mechanical excavation to avoid damage to the initial support 301 of the arch of the shield assembly tunnel 3, the secondary lining structure 302 of the arch, and the arch foot support beam 305 caused by drilling and blasting excavation.

[0053] Step 7, as follows Figure 10 As shown, the lower part of the shield assembly tunnel 3 was excavated in stages, and the rib-type anchor retaining walls 306 on both sides of the lower sidewall of the shield assembly tunnel 3, the secondary lining of the sidewall 307, and the secondary lining of the bottom plate 308 were completed successively.

[0054] The lower part of the shield assembly tunnel 3 is excavated using a step-by-step method, with a step height not exceeding 5m. The rib-type anchor retaining walls 306 on both sides of the lower sidewall of the shield assembly tunnel 3 are composed of reinforced concrete capping beams 306a, panels 306b, rib columns 306c, and anchor bundles 306d.

[0055] The reinforced concrete capping beam 306a acts on the top of the panel 306b and the rib column 306c. The reinforced concrete capping beam 306a and the rib column 306c are of the same width and have a height of 0.5 to 1.5m. The reinforced concrete rib column 306c has a thickness of 0.3 to 1m and a width of 0.5 to 1.5m, with a longitudinal spacing of 2 to 5m. The reinforced concrete panel 306b has a thickness of 0.15 to 0.5m and a width equal to the net width between the rib columns. The anchor bolt bundle 306d acts on the rib column 306c and has a spacing of 1.5 to 3m along the height direction, with a denser anchor bolt bundle within the top 2m range.

[0056] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A construction method for converting a large-section branch tunnel into a large-diameter shield tunnel assembly tunnel in weak surrounding rock, characterized in that, Includes the following steps: Step 1: Construct the large-section branch tunnel (1) and construct the initial support structure (102) and secondary lining structure (101) of the large-section branch tunnel (1); when the large-section branch tunnel (1) is constructed to a certain distance from the planned shield assembly tunnel (3), tunnel cross-section construction is carried out to reduce the excavation range, and the tunnel is transferred from the large-section branch tunnel to the small-section branch tunnel (2) to enter the shield assembly tunnel, and the initial support structure (201) of the small-section branch tunnel (2) is constructed. Step 2: When the small cross-section branch tunnel (2) is constructed to the position where it intersects with the arch of the planned shield assembly tunnel (3), a portal steel frame (402) is erected, and the tunnel is raised along the arc contour of the tunnel top (3) in the width direction, and temporary support (401) is provided for the raised part (4). Step 3: Set up multiple closely spaced steel arch frames (304) on both sides of the small section support tunnel (2) after entering the shield assembly tunnel (3), and weld them to the portal steel frame (402). Then spray concrete to complete the initial support (301) of the cantilevered part (4) of the shield assembly tunnel (3). Step 4: Remove the vertical support (402b) of the portal steel frame (402) in the temporary support (401) of the cantilever section (4) of the shield assembly tunnel (3), and use the single-side wall pilot tunnel method to successively excavate the upper left step (31), lower left step (33), upper right step (32), and lower right step (34) of the shield assembly tunnel (3) in the direction of the large / small mileage, and promptly implement the corresponding main tunnel temporary support (303) and initial support (301); Step 5: Remove the temporary support (303) of the main tunnel of the shield assembly tunnel (3), and construct the arch secondary lining structure (302) and arch foot support beam (305) of the shield assembly tunnel (3); Step 6: Return to the cross-section position of the large cross-section branch tunnel (1) and the small cross-section branch tunnel (2). Expand the small cross-section branch tunnel (2) according to the excavation outline of the large cross-section branch tunnel (1). After the expanded section (202) is completed, break the initial support structure (201) of the small cross-section branch tunnel (2) and complete the initial support structure (102) and secondary lining structure (101) of the expanded section of the large cross-section branch tunnel (1). Step 7: Excavate the lower part of the shield assembly tunnel (3) in stages, and successively complete the rib-type anchor retaining walls (306) on both sides of the lower sidewall of the shield assembly tunnel (3), the secondary lining of the sidewall (307), and the secondary lining of the bottom plate (308).

2. The construction method for converting a large-section branch tunnel into a large-diameter shield tunnel assembly tunnel in weak surrounding rock according to claim 1, characterized in that, In step two, the excavation span and height of the small cross-section branch tunnel (2) are smaller than those of the large cross-section branch tunnel (1), and the distance between the variable cross-section construction site and the shield assembly tunnel (3) is 10-12m.

3. The construction method for converting a large-section auxiliary tunnel into a large-diameter shield tunnel assembly tunnel in weak surrounding rock according to claim 1, characterized in that, In step two, the portal steel frame (402) consists of a horizontal support (402a) and a vertical support (402b). The horizontal support (402a) and the vertical support (402b) are made of I 20b I-beams and are connected by steel pads.

4. The construction method for converting a large-section branch tunnel into a large-diameter shield tunnel assembly tunnel in weak surrounding rock according to claim 1, characterized in that, In step two, the temporary support (401) of the cantilever section (4) has a portal steel frame (402). The portal steel frame (402) is laid out at a spacing of 0.5 to 0.8 m. The portal steel frames (402) are connected by a double-layer steel mesh with a diameter of 6.5 mm. C25 concrete is sprayed onto the portal steel frame with a thickness of 260 mm.

5. The construction method for converting a large-section branch tunnel into a large-diameter shield tunnel assembly tunnel in weak surrounding rock according to claim 1, characterized in that, In step three, after the small cross-section branch tunnel (2) enters the shield assembly tunnel (3), it is expanded to the left and right sides by 0.6m each, so that multiple closely spaced steel arch frames (304) can be placed within the expanded area. The closely spaced steel arch frames (304) are part of the initial support (301) of the arch of the shield assembly tunnel (3). The material is I 25b type I-beams. The initial support (301) of the arch of the shield assembly tunnel (3) adopts the form of shotcrete and anchor support, located below the temporary support (401) of the cantilever section (4).

6. The construction method for converting a large-section branch tunnel into a large-diameter shield tunnel assembly tunnel in weak surrounding rock according to claim 1 or 5, characterized in that, Three closely spaced steel arch frames (304) are installed on both sides of the small section branch tunnel (2) after entering the shield assembly tunnel (3).

7. The construction method for converting a large-section branch tunnel into a large-diameter shield tunnel assembly tunnel in weak surrounding rock according to claim 1, characterized in that, In step four, the tunnel advances 1m in the direction of the large / small mileage of the shield assembly tunnel (3). After each excavation cycle, the corresponding temporary support (303) and initial support (301) of the main tunnel are completed. The temporary support (303) of the main tunnel is composed of double I 22a I-beams, and the initial support (301) adopts anchor spraying support.

8. The construction method for converting a large-section branch tunnel into a large-diameter shield tunnel assembly tunnel in weak surrounding rock according to claim 1, characterized in that, In step five, the arch secondary lining structure (302) and the arch foot support beam (305) of the shield assembly tunnel (3) together form the arch lining structure of the shield assembly tunnel (3), and the arch foot support beam (305) is located below the arch secondary lining structure (302) of the shield assembly tunnel (3).

9. The construction method for converting a large-section branch tunnel into a large-diameter shield tunnel assembly tunnel in weak surrounding rock according to claim 1, characterized in that, In step six, the small cross-section branch tunnel (2) expansion section (202) is excavated mechanically.

10. The construction method for converting a large-section branch tunnel into a large-diameter shield tunnel assembly tunnel in weak surrounding rock according to claim 1, characterized in that, In step seven, the ribbed anchor retaining walls (306) on both sides of the lower sidewall of the shield assembly tunnel (3) are composed of reinforced concrete capping beams (306a), panels (306b), rib columns (306c) and anchor bundles (306d). A reinforced concrete capping beam (306a) is applied to the top of the panel (306b) and the rib column (306c). The reinforced concrete capping beam (306a) and the rib column (306c) are of the same width and have a height of 0.5 to 1.5m. The rib column (306c) is 0.3 to 1m thick and 0.5 to 1.5m wide, with a longitudinal spacing of 2 to 5m. The panel (306b) is 0.15 to 0.5m thick and has a width equal to the net width between the rib columns. Anchor bolt bundles (306d) are applied to the rib column (306c) and are spaced 1.5 to 3m apart along the height direction, with denser anchor bolts installed within a 2m range at the top.

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