Device for improving shear resistance of deformable primary support joint and construction method

Abstract

The invention discloses a device for improving the shear resistance of a deformable primary support joint and a construction method. The device comprises a first steel plate, a second steel plate, a third steel plate and a plurality of shear reinforcements, the first steel plate, the second steel plate and the third steel plate are assembled into a groove-shaped structure, the first steel plate and the second steel plate are oppositely arranged, the two side faces of the third steel plate are connected with the first steel plate and the second steel plate correspondingly, and the multiple shear-resistant steel bars penetrate through the surfaces of the first steel plate and the second steel plate. A lining stress controller is arranged on the shear reinforcement in a sleeving mode and arranged between the first steel plate and the second steel plate. The supporting structure is reasonable in structural design, easy to install and moderate in manufacturing cost, the shear resistance of a primary supporting connector is effectively improved, the adverse effect caused by the force concentration effect is reduced, and the adaptability of the supporting structure and the long-term stability and construction safety of a tunnel are enhanced.

Description

Technical Field

[0001] The invention belongs to the technical field of tunnel and underground engineering, and in particular to a device and a construction method for improving the shear resistance of a deformable initial support joint. Background Art

[0002] In the process of tunnel and underground engineering construction, primary support plays a vital role. It is an important technical means to control the deformation of surrounding rock and maintain the safety and stability of tunnel. Primary support should not only provide necessary support during the construction process, but also maintain its effectiveness during long-term operation to resist the challenges of various natural factors such as geological changes and groundwater pressure.

[0003] Under complex geological conditions, the surrounding rock of the tunnel may experience large displacement and shear deformation. In this case, the traditional initial support joint structure is prone to insufficient shear resistance during the stress process. When the support structure is subjected to complex stress, these traditional joint structures may not be able to effectively disperse and resist the shear force, thereby causing local damage or overall instability. This will not only threaten the safety of construction workers, but also prolong the construction period, increase costs, and may even cause irreversible damage to the long-term stability and service life of the tunnel. Especially in the use of steel arches, as one of the main bearing structures of the initial support, the connection between the arch and the lining becomes the most complex stress and the most uneven deformation area. These connection parts often become stress concentration areas due to complex stress and uneven deformation, resulting in reduced shear resistance of the joint parts, further affecting the overall stability of the support structure. In addition, in the existing design, the initial support lacks targeted optimization measures when dealing with large deformation conditions. The traditional steel plate connection method is prone to fracture or concentrated deformation when subjected to large pressure, and it is often difficult to maintain its structural integrity. This deficiency makes the support system unable to meet the high reliability requirements of the support system when facing a complex geological environment. Summary of the invention

[0004] The purpose of the present invention is to provide a device and a construction method for improving the shear resistance of deformable initial support joints, so as to solve the problem of insufficient shear resistance of initial support joints in the prior art.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: A device for improving the shear resistance of a deformable initial support joint, comprising a first steel plate, a second steel plate, a third steel plate and a plurality of shear steel bars; The first steel plate, the second steel plate and the third steel plate are assembled into a trough structure, the first steel plate and the second steel plate are arranged opposite to each other, the two side surfaces of the third steel plate are respectively connected to the first steel plate and the second steel plate, a plurality of shear steel bars pass through the surfaces of the first steel plate and the second steel plate, a lining stress controller is sleeved on the shear steel bars, and the lining stress controller is arranged between the first steel plate and the second steel plate.

[0006] Furthermore, the first steel plate, the second steel plate and the third steel plate are all Q235B low carbon steel plates.

[0007] Furthermore, the two side edges of the third steel plate are respectively connected to the first steel plate and the second steel plate by spot welding, and a plurality of welding spots are arranged on the two side edges of the third steel plate.

[0008] Furthermore, the lengths of the first steel plate, the second steel plate and the third steel plate are all equal to the spacing between steel arch frames in the tunnel.

[0009] Furthermore, the width of the third steel plate is greater than or equal to the height of the lining stress controller.

[0010] Furthermore, the length of the shear steel bar is greater than the width of the third steel plate, the exposed portion of the shear steel bar passing through the first steel plate and the second steel plate is wrapped with a shotcrete lining, and the width of the first steel plate and the second steel plate is equal to the thickness of the shotcrete lining.

[0011] Furthermore, a plurality of circular holes are provided on the surfaces of the first steel plate and the second steel plate on the central axis along the length direction, the diameter of the circular holes is larger than the diameter of the shear steel bars, and the shear steel bars pass through the circular holes.

[0012] Furthermore, a plurality of reserved defects are arranged on one side surface of the third steel plate, and the other side surface of the third steel plate is welded to the steel mesh between the steel arch frames.

[0013] Furthermore, the third steel plate is welded to the spandrel, waist or bottom of the steel arch frame.

[0014] A construction method of the device for improving the shear resistance of a deformable initial support joint comprises: Cutting the first steel plate, the second steel plate and the third steel plate, reserving a plurality of circular holes on the first steel plate and the second steel plate respectively, and setting a plurality of reserved defects on the third steel plate; The lining stress controller is installed between the first steel plate and the second steel plate, and the shear reinforcement passes through the reserved circular hole and the lining stress controller at the same time; The first steel plate, the second steel plate and the third steel plate are connected into a groove shape by spot welding, and one side surface of the third steel plate is welded to the steel mesh between the steel arch frames; The shotcrete lining is constructed, and the shear reinforcement passes through the first steel plate and the exposed part of the second steel plate and is wrapped in the shotcrete lining.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a device for improving the shear resistance of a deformable initial support joint. By assembling a first steel plate, a second steel plate and a third steel plate into a trough structure, the shear force from all directions can be effectively dispersed and resisted, thereby improving the stability of the entire support structure. A plurality of shear steel bars are passed through the surfaces of the first steel plate and the second steel plate that are relatively arranged. These shear steel bars are like a "skeleton" that tightly connects the two steel plates together, greatly enhancing the shear resistance of the joint. Even under the action of external forces, the joint is not prone to shear damage. A lining stress controller is sleeved on the shear steel bar. The lining stress controller is located between the first steel plate and the second steel plate. Lining stress controllers of different heights are set, which can adjust stress according to the actual deformation of the surrounding rock, can provide different yield resistances at different stages, can better adapt to the deformation of the surrounding rock, and ensure that the support structure maintains a more uniform and stable state during the stress process, thereby extending the service life of the support structure. The invention has a reasonable structural design, is easy to install, and has a moderate cost. Through the three reasonably designed low-carbon steel plates and the lining stress controller with shear steel bars, a system structure is formed that can significantly improve the shear resistance of the deformable initial support joint, effectively improve the shear resistance of the initial support joint, reduce the adverse effects caused by the force concentration effect, and enhance the adaptability of the support structure and the long-term stability and construction safety of the tunnel. It is suitable for the construction of deformable initial support structures in soft rock tunnels and underground projects, and has good engineering application value and promotion potential.

[0016] Furthermore, the reserved defects provided on the third steel plate of the present invention can guide the deformation path when under pressure, avoid stress concentration, and extend the service life of the support system.

[0017] Furthermore, the design of connecting the first steel plate and the second steel plate to the third steel plate by spot welding can make the three steel plates fall off by themselves when subjected to less pressure, preventing the bending of the third steel plate from adversely affecting the deformation of the lining stress controller and reducing damage to the surrounding rock and other supporting structures.

[0018] Furthermore, the shear reinforcement wrapped in the shotcrete lining is able to resist a certain shear force, effectively preventing the joints from becoming weak points in the entire deformable initial support, making it more suitable for tunnel projects under complex geological conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0020] Figure 1 The present invention is a front view of a device for improving the shear resistance of a deformable initial support joint.

[0021] Figure 2 A side view of a device for improving the shear resistance of a deformable initial support joint according to the present invention.

[0022] Figure 3 A top view of a device for improving the shear resistance of a deformable initial support joint according to the present invention.

[0023] Among them: 1-steel arch, 2-first steel plate, 3-second steel plate, 4-third steel plate, 5-first lining stress controller, 6-second lining stress controller, 7-third lining stress controller, 8-fourth lining stress controller, 9-shear reinforcement, 10-reserved defects, 11-welding points, 12-sprayed concrete lining. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0025] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0027] In the description of the embodiments of the present invention, it should be noted that if the terms "upper", "lower", "horizontal", "inner", etc. indicate an orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the invention is usually placed when in use, it is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0028] In addition, if the term "horizontal" appears, it does not mean that the component must be absolutely horizontal, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", which does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0029] In the description of the embodiments of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0030] The present invention is further described in detail below in conjunction with the accompanying drawings: See also Figure 1 The present invention provides a device for improving the shear resistance of a deformable initial support joint, comprising a first steel plate 2, a second steel plate 3, a third steel plate 4, a lining stress controller, a plurality of shear steel bars 9, a reserved defect 10 and a shotcrete lining 12.

[0031] The first steel plate 2 and the second steel plate 3 are arranged opposite to each other, and a plurality of welding points 11 are selected at the edges of the two sides of the third steel plate 4, and the first steel plate 2 and the second steel plate 3 are connected by spot welding at the edges of the two sides of the third steel plate 4, so that the first steel plate 2, the second steel plate 3 and the third steel plate 4 are assembled into a groove structure, which can make the steel plate fall off by itself when subjected to a small pressure, and prevent the bending of the third steel plate 4 from having an adverse effect on the deformation of the lining stress controller. Through this design, the stability of the steel plate under normal stress can be guaranteed, and the deformable initial support joint under extreme stress can be ensured to be properly deformed to avoid the generation of undesirable stress concentration.

[0032] The materials of the first steel plate 2, the second steel plate 3 and the third steel plate 4 are all Q235B low carbon steel plates, the lengths of the first steel plate 2, the second steel plate 3 and the third steel plate 4 are all equal to the spacing of the tunnel steel arch frame 1, the widths of the first steel plate 2 and the second steel plate 3 are equal to the thickness of the shotcrete lining 12, and a number of circular holes are reserved on the surface along the central axis in the length direction, respectively, and the diameter of the circular hole is slightly larger than the diameter of the shear steel bar 9, so as to pass the shear steel bar 9. The width of the third steel plate 4 is greater than or equal to the height of the lining stress controller, and reserved defects 10 are set in the width direction of the surface on both sides, so that the third steel plate 4 is deformed according to the path of the reserved defects 10 after being compressed.

[0033] The length of the shear reinforcement 9 is greater than the width of the third steel plate 4. A through hole is provided on the lining stress controller. The lining stress controller is set between the first steel plate 2 and the second steel plate 3. The through hole is aligned with the circular hole provided on the first steel plate 2 and the second steel plate 3, and passes through the shear reinforcement 9 at the same time, so that the lining stress controller is sleeved on the shear reinforcement 9. The back of the third steel plate 4 is welded to the steel mesh between the steel arch frames 1, and the installation position is the arch shoulder, arch waist or arch bottom, and the sprayed concrete lining 12 is applied, and the exposed shear reinforcement 9 on both sides of the first steel plate 2 and the second steel plate 3 is wrapped in the sprayed concrete lining 12, and finally the shear resistance of the deformable initial support joint is improved. After the tunnel is excavated, the deformable initial support is combined with the low-carbon steel plate and the lining stress controller with shear reinforcement 9, which can effectively solve the problem of insufficient shear resistance of the initial support joint in the prior art.

[0034] The present invention also provides a construction method for a device for improving the shear resistance of a deformable initial support joint, which specifically comprises the following steps: Step 1: Cut the first steel plate 2, the second steel plate 3 and the third steel plate 4 according to their size requirements, reserve a number of circular holes on the first steel plate 2 and the second steel plate 3 respectively, the diameter of the circular holes is slightly larger than the diameter of the shear reinforcement 9, and set a number of reserved defects 10 on the third steel plate 4; Step 2: Install the lining stress controller between the first steel plate 2 and the second steel plate 3, align the shear steel bar 9 with the reserved circular holes on the first steel plate 2 and the second steel plate 3, pass through the reserved circular holes, and pass through the lining stress controller at the same time; Step 3: Connect the first steel plate 2, the second steel plate 3 and the third steel plate 4 into a groove shape by spot welding, the spot welding position is located at the upper and lower edges of the third steel plate 4, and weld one side surface of the third steel plate 4 in the assembled device to the steel mesh between the steel arch frames 1, and the installation position is the spandrel, the haunch or the bottom of the arch; Step 4: construct the shotcrete lining 12 , pass the shear steel bars 9 through the first steel plate 2 and the second steel plate 3 and wrap the exposed parts in the shotcrete lining 12 .

[0035] The present invention is further described in detail below in conjunction with specific embodiments: Embodiment 1: This embodiment provides a device for improving the shear resistance of a deformable initial support joint, such as Figure 1 As shown, it includes three low-carbon steel plates and a lining stress controller with shear-resistant steel bars 9. The three low-carbon steel plates are connected into a groove shape by spot welding, and the back of the third steel plate 4 in the assembled device is welded to the steel mesh between the steel arch frames 1.

[0036] The material of the steel plate is Q235B low carbon steel plate with a thickness of 3~5mm. The length (l) of the three steel plates is equal to the spacing of the tunnel steel arch frame 1. The width (b1) of the first steel plate 2 and the second steel plate 3 is equal to the thickness of the shotcrete lining 12 (20~30cm). Four circular holes are reserved at 1 / 8, 3l / 8, 5l / 8 and 7l / 8 on the longitudinal center axis to pass the shear steel bars 9 (steel bar diameter Φ18~24mm). The diameter of the circular hole is slightly larger than the diameter of the shear steel bar 9; Figure 2 As shown, the width (b2) of the third steel plate 4 is equal to the height of the first lining stress controller 5 and the fourth lining stress controller 8, and prefabricated defects 10 are set on the surfaces of both sides at b2 / 4, b2 / 2, and 3b2 / 4 respectively according to the width, so that the third steel plate 4 is deformed along the path of the prefabricated defects 10 after being compressed.

[0037] The shear steel bar 9 passes through the lining stress controller, wherein the length of the shear steel bar 9 is equal to the width (b2) of the third steel plate 4 plus 60 cm, the height of the first lining stress controller 5 and the fourth lining stress controller 8 is equal to the width (b2) of the third steel plate 4, the height of the second lining stress controller 6 and the third lining stress controller 7 is 5-8 cm smaller than the height of the first lining stress controller 5 and the fourth lining stress controller 8, the shear steel bars 9 of the first lining stress controller 5 and the fourth lining stress controller 8 are aligned with the circular holes reserved at l / 8 and 7l / 8 on the first steel plate 2 and the second steel plate 3, the shear steel bars 9 of the second lining stress controller 6 and the third lining stress controller 7 are respectively aligned with the circular holes reserved at 3l / 8 and 5l / 8 on the first steel plate 2 and the second steel plate 3, and pass through the shear steel bars 9 at the same time, wherein the first lining stress controller 5 and the fourth lining stress controller 8 are in contact with the first steel plate 2 and the second steel plate 3.

[0038] The first steel plate 2, the second steel plate 3 and the third steel plate 4 are connected into a groove shape by spot welding. Figure 3As shown, the positions of the welding points 11 are located at 1 / 4, 1 / 2 and 31 / 4 of the upper and lower edges of the third steel plate 4, which can make the steel plate fall off by itself when subjected to a small pressure, preventing the bending of the third steel plate 4 from having an adverse effect on the deformation of the lining stress controller. Through this design, the stability of the steel plate under normal stress conditions can be guaranteed, and the joint can be properly deformed under extreme stress to avoid undesirable stress concentration.

[0039] The back of the third steel plate 4 in the assembled device is welded to the steel mesh between the steel arch frames 1, and the installation positions are the arch shoulder, arch waist and arch bottom, and the shotcrete lining 12 is applied. The exposed shear steel bars 9 on both sides of the first steel plate 2 and the second steel plate 3 in the device (30 cm on each side) are wrapped in the shotcrete lining 12, ultimately improving the shear performance of the deformable initial support joint.

[0040] The construction method of the device for improving the shear resistance of a deformable initial support joint provided in this embodiment comprises the following steps: Step 1: Cut three Q235B low-carbon steel plates with a thickness of 3~5mm as the first steel plate 2, the second steel plate 3 and the third steel plate 4. The length (l) of the three steel plates is equal to the spacing of the steel arch frame 1 in the tunnel, and the width (b1) of the first steel plate 2 and the second steel plate 3 is equal to the thickness of the shotcrete lining 12 (20~30cm). Four circular holes are reserved at 1 / 8, 3l / 8, 5l / 8 and 7l / 8 on the longitudinal center axis of the first steel plate 2 and the second steel plate 3, respectively, for passing the shear steel bar 9 (steel bar diameter Φ18~24mm). The diameter of the circular hole is slightly larger than the diameter of the shear steel bar 9; Step 2: Cut the length of the shear steel bar 9 to be equal to the width (b2) of the third steel plate 4 plus 60cm, adjust the height of the first lining stress controller 5 and the fourth lining stress controller 8 to be equal to the width (b2) of the third steel plate 4, and install them in contact with the first steel plate 2 and the second steel plate 3; the height of the second lining stress controller 6 and the third lining stress controller 7 is 5-8cm smaller than the height of the first lining stress controller 5 and the fourth lining stress controller 8, and they are installed between the first steel plate 2 and the second steel plate 3; Step 3: the shear steel bars 9 of the first lining stress controller 5 and the fourth lining stress controller 8 are aligned with the circular holes reserved at 1 / 8 and 71 / 8 of the steel plate, and the shear steel bars 9 of the second lining stress controller 6 and the third lining stress controller 7 are aligned with the circular holes reserved at 31 / 8 and 51 / 8 of the steel plate, respectively, and pass through the shear steel bars 9 at the same time, wherein the first lining stress controller 5 and the fourth lining stress controller 8 are in contact with the first steel plate 2 and the second steel plate 3; Step 4: Prefabricated defects 10 are respectively provided on both sides of the third steel plate 4 at positions b2 / 4, b2 / 2, and 3b2 / 4 according to its width, so that the third steel plate 4 is deformed along the path of the prefabricated defects 10 after being compressed; Step 5: Connect the first steel plate 2, the second steel plate 3 and the third steel plate 4 into a groove shape by spot welding, and the positions of the welding points 11 are located at 1 / 4, 1 / 2 and 31 / 4 of the upper and lower edges of the third steel plate 4; Step 6: Weld the back of the third steel plate 4 in the device assembled in the first five steps to the steel mesh between the steel arch frames 1, and the installation positions are the spandrel, the haunch and the bottom of the arch; Step 7: construct the shotcrete lining 12, and the exposed shear reinforcement 9 parts (30 cm on each side) on both sides of the first steel plate 2 and the second steel plate 3 in the device are wrapped in the shotcrete lining 12, and finally form a device for improving the shear performance of the deformable initial support joint.

[0041] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A device for improving the shear resistance of a deformable initial support joint, characterized in that: It comprises a first steel plate (2), a second steel plate (3), a third steel plate (4) and a plurality of shear steel bars (9); The first steel plate (2), the second steel plate (3) and the third steel plate (4) are assembled into a trough structure; the first steel plate (2) and the second steel plate (3) are arranged opposite to each other; two side surfaces of the third steel plate (4) are respectively connected to the first steel plate (2) and the second steel plate (3); a plurality of shear steel bars (9) pass through the surfaces of the first steel plate (2) and the second steel plate (3); a lining stress controller is sleeved on the shear steel bars (9); and the lining stress controller is arranged between the first steel plate (2) and the second steel plate (3).

2. A device for improving the shear resistance of a deformable initial support joint according to claim 1, characterized in that: The first steel plate (2), the second steel plate (3) and the third steel plate (4) are all Q235B low-carbon steel plates.

3. The device for improving the shear resistance of a deformable initial support joint according to claim 1, characterized in that: The two side edges of the third steel plate (4) are respectively connected to the first steel plate (2) and the second steel plate (3) by spot welding, and a plurality of welding spots (11) are provided on the two side edges of the third steel plate (4).

4. The device for improving the shear resistance of a deformable initial support joint according to claim 1, characterized in that: The lengths of the first steel plate (2), the second steel plate (3) and the third steel plate (4) are all equal to the spacing between the steel arch frames (1) in the tunnel.

5. The device for improving the shear resistance of a deformable initial support joint according to claim 1, characterized in that: The width of the third steel plate (4) is greater than or equal to the height of the lining stress controller.

6. The device for improving the shear resistance of a deformable initial support joint according to claim 1, characterized in that: The length of the shear steel bar (9) is greater than the width of the third steel plate (4); the exposed portion of the shear steel bar (9) passes through the first steel plate (2) and the second steel plate (3) and is wrapped with a shotcrete lining (12); the width of the first steel plate (2) and the second steel plate (3) is equal to the thickness of the shotcrete lining (12).

7. The device for improving the shear resistance of a deformable initial support joint according to claim 1, characterized in that: A plurality of circular holes are provided on the surfaces of the first steel plate (2) and the second steel plate (3) along the central axis in the length direction, the diameter of the circular holes being larger than the diameter of the shear steel bars (9), and the shear steel bars (9) pass through the circular holes.

8. The device for improving the shear resistance of a deformable initial support joint according to claim 1, characterized in that: A plurality of reserved defects (10) are provided on one side surface of the third steel plate (4), and the other side surface of the third steel plate (4) is welded to the steel mesh between the steel arch frames (1).

9. A device for improving the shear resistance of a deformable initial support joint according to claim 8, characterized in that: The third steel plate (4) is welded to the spandrel, haunch or base of the steel arch frame (1).

10. A construction method for the device for improving the shear resistance of a deformable initial support joint according to any one of claims 1 to 9, characterized in that: include: Cutting the first steel plate (2), the second steel plate (3) and the third steel plate (4), reserving a plurality of circular holes on the first steel plate (2) and the second steel plate (3), and providing a plurality of reserved defects (10) on the third steel plate (4); The lining stress controller is installed between the first steel plate (2) and the second steel plate (3), and the shear steel bar (9) passes through the reserved circular hole and the lining stress controller at the same time; The first steel plate (2), the second steel plate (3) and the third steel plate (4) are connected into a groove shape by spot welding, and one side surface of the third steel plate (4) is welded to the steel mesh between the steel arch frames (1); A shotcrete lining (12) is constructed, and the shear steel bars (9) are passed through the first steel plate (2) and the second steel plate (3), and the exposed parts are wrapped in the shotcrete lining (12).

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