A tunnel excavation support system

Abstract

This invention relates to the field of tunnel construction, specifically disclosing a tunnel excavation and support system, including a gantry assembly, several top formwork frames, several templates, a hydraulic unit, and a traveling unit for controlling the movement of the gantry assembly. The top formwork frame includes several horizontally supporting first support rods; several vertically supporting second support rods; the end of each first support rod away from the second support rods and the first fixed frame is detachably connected to the template; a first translation cylinder connected to the hydraulic unit is provided between the side wall of the second support rod near the first fixed frame and the first fixed frame; a lifting cylinder connected to the hydraulic unit is provided between the lower end of the second support rod and the traveling unit. This solution allows for the construction of the next grouting section by controlling the deployment of the second support rods, first support rods, and second fixed frames via the hydraulic unit. The entire process eliminates the need for multiple disassemblies and reassemblies of the top formwork frame and templates, and makes template position control more convenient and simple.

Description

Technical Field

[0001] This invention relates to the field of tunnel construction technology, and in particular to a tunnel excavation and support system. Background Technology

[0002] In tunnel excavation support, commonly used support devices include shotcrete support, anchor bolt support, metal mesh support, and steel arch support. Shotcrete support involves mixing cement, sand, stones, water, and other necessary materials in a specific ratio, stirring thoroughly, and then spraying the mixture onto the desired location using a nozzle. This method is simple and convenient to implement, allowing for rapid setting and effectively reinforcing and waterproofing the tunnel. Anchor bolt support involves driving steel bars or pipes of a certain length into the surrounding rock during excavation to reinforce it. Metal mesh support involves hanging metal mesh on or below the surface of the surrounding rock during excavation to prevent collapse. Steel arch support uses arched steel supports to support the surrounding rock during excavation.

[0003] In current tunnel support construction, various support devices combined with secondary lining trolleys are generally used to support the inner walls of tunnels. Therefore, secondary lining trolleys are indispensable specialized equipment in tunnel secondary lining construction. They generally consist of a formwork assembly, a top formwork frame, a translation mechanism assembly, a gantry assembly, a master-slave traveling mechanism, screw jacks, a hydraulic system, and an electrical system. The formwork assembly consists of two top formworks and two side formworks forming a cross-section, with the top formworks connected as a whole by bolts. The top formwork frame is equipped with rails to support the formwork. The translation mechanism assembly includes a translation trolley and a drive device to achieve lateral movement of the formwork. The gantry assembly includes a gantry and a support structure to support the formwork and ensure construction safety. The master-slave traveling mechanism includes a master traveling mechanism and a slave traveling mechanism to achieve longitudinal movement of the trolley. Screw jacks are used to adjust the height of the formwork. The hydraulic system and electrical system are used to control various parts of the trolley.

[0004] In conventional secondary lining trolleys, the height of the top formwork frame is basically fixed during use. Only the hydraulic rods at the ends of the top formwork frame can be extended or shortened within a small range under the control of the hydraulic system, resulting in a limited adjustable range. At the same time, when the template assembly and top formwork frame are moved by the translation mechanism assembly and the master-slave travel mechanism, the template assembly and top formwork frame are in an extended state. It is necessary to disassemble part of the template assembly and top formwork frame before they can be moved, which makes the movement of the entire structure difficult, the operation is relatively complicated, and it will affect the construction efficiency of the tunnel. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a tunnel excavation support system that solves the problem that existing formwork assemblies and top formwork frames can mostly only be disassembled and moved during use, resulting in difficulties in moving the entire structure, complicated disassembly and assembly operations during construction, and affecting the efficiency of tunnel grouting construction.

[0006] To achieve the above objectives, the basic solution of the present invention is as follows: A tunnel excavation support system, comprising a gantry assembly, several top formwork frames, several templates, a hydraulic unit, and a traveling unit for controlling the movement of the gantry assembly, wherein the gantry assembly includes:

[0007] A vertically arranged first fixing frame is slidably mounted on the gantry assembly.

[0008] A second fixing frame is set horizontally, with one end of the second fixing frame opposite to the upper end of the first fixing frame;

[0009] The top mold frame includes:

[0010] The first support rod of several horizontal supports;

[0011] Several vertically supporting second support rods, the top of the second support rods is connected to the second fixed frame, the first support rod is fixedly connected to the middle of the second support rods, and the end of the first support rod away from the second support rods and the first fixed frame is detachably connected to the template;

[0012] A first translation cylinder connected to the hydraulic unit is provided between the side wall of the second support rod near the first fixed frame and the first fixed frame; a lifting cylinder connected to the hydraulic unit is provided between the lower end of the second support rod and the traveling unit.

[0013] The technical principle of this invention is as follows: Before the concrete grouting construction on the lower side of the tunnel, the first translation cylinder is extended by the hydraulic unit according to the position of the inner wall of the tunnel. Then, the first support rod and the second support rod of the first translation cylinder extend to the vertical side wall of the tunnel. The first support rod pushes the template to the concrete pouring position to seal the inner wall of the tunnel. The first fixed frame, the second fixed frame and the second support rod can stably support the first support rod. Then, the grouting construction is carried out between the template and the inner wall of the tunnel.

[0014] After the concrete grouting on the lower side of the tunnel is completed, the hydraulic unit controls the extension of the lifting cylinder. The second support rod of the lifting cylinder pushes the first support rod, the first fixed frame, and the second fixed frame to move upward as a whole. At this time, the templates on the ends of the first support rod and the second fixed frame are aligned with the upper inner wall of the tunnel, and further grouting can be carried out.

[0015] After the grouting is completed and the concrete on the inner wall of the tunnel has solidified, the hydraulic unit controls the shortening of the lifting cylinder and simultaneously controls the shortening of the first translation cylinder, causing the second support rod, the first support rod, and the second fixed frame to retract. Then, the entire tunnel excavation support system is controlled to move along the tunnel axis as a whole, so that it is aligned with the next grouting section of the tunnel. Then, the hydraulic unit controls the extension of the second support rod, the first support rod, and the second fixed frame to carry out the construction of the next grouting section. The whole process does not require multiple disassemblies and reassemblies of the top formwork and templates, and the position control of the templates is also more convenient and simple.

[0016] Furthermore, an adjustable first support screw is provided on the end of the first support rod away from the first fixed frame. The axis of the first support screw is parallel to the axis of the first support rod, and the template is detachably connected to the end of the first support screw away from the first support rod.

[0017] With the above settings, after the horizontal positions of the second support rod, the first support rod and the second fixed frame are controlled by the first translation cylinder, the length of the first support screw can be adjusted again so that the template on the end of the first support screw can be more accurately aligned with the grouting point of the tunnel, thereby improving the grouting accuracy.

[0018] Furthermore, it also includes a second support screw, which is inclinedly disposed on the side wall of the lowest first support rod away from the upper first support rod. The second support screw is hinged to the side wall of the first support rod, and the template is detachably connected to the end of the second support screw away from the first support rod.

[0019] With the above configuration, the inclined second support screw can support the template at the lower arc of the tunnel. During the template position adjustment process, the relative position of the template and the tunnel wall can be controlled by first controlling the position of the second support screw. By rotating the hinge of the second support screw and the first support rod, the relative angle between the template and the tunnel wall can be controlled, thereby achieving precise adjustment of the template position and further improving the concrete forming accuracy on the tunnel wall.

[0020] Furthermore, an extension frame is hinged to the end of the second fixed frame away from the first fixed frame. A first bidirectional adjusting screw is vertically arranged between the extension frame and the uppermost first support rod. The upper end of the first bidirectional adjusting screw is hinged to the extension frame, and the lower end of the first bidirectional adjusting screw is hinged to the first support rod. The template is detachably connected to the end of the extension frame away from the second fixed frame.

[0021] When the second fixed frame moves up to the arch of the tunnel, the length of the first bidirectional adjusting screw is adjusted to control the extension frame to flip relative to the second fixed frame. After the extension frame is rotated, the end of the extension frame is opposite to the arch of the tunnel, and the extension frame can rotate the template to an arc shape, which facilitates grouting treatment at the arch of the tunnel.

[0022] Furthermore, a reinforcing rod is horizontally arranged between the second support rod and the second fixed frame. The reinforcing rod is fixedly connected to the second support rod. A second translation cylinder connected to the hydraulic unit is hinged between the reinforcing rod and the second fixed frame. One end of the second translation cylinder is hinged to the reinforcing rod, and the other end of the second translation cylinder is hinged to the second fixed frame. The second translation cylinder can rotate to a horizontal state.

[0023] With the above configuration, the second translation cylinder allows the second support rod and the second fixed frame to have horizontal misalignment. When the second translation cylinder and the first translation cylinder extend under the control of the hydraulic unit, the second support rod can push the first support screw on the end of the first support rod to move out of the extension frame at the end of the second fixed frame, so that the first support rod and the extension frame can be installed with an arc-shaped template, and high-precision concrete grouting can be carried out on the arc surface of the tunnel.

[0024] Furthermore, it also includes a rotating cylinder connected to the hydraulic unit, one end of which is hinged to the end of the reinforcing rod away from the first fixed frame, and the other end of which is hinged to the middle of the extension frame.

[0025] With the above settings, when controlling the angle of the extension frame relative to the second fixed frame, the hydraulic unit controls the extension of the rotating cylinder to extend. The rotating cylinder pushes the extension frame to flip upward. The first bidirectional adjusting screw provides stable support for the rotated extension frame. The rotating cylinder makes the angle control of the extension frame more convenient and simple, and the rotation accuracy can also be precisely controlled.

[0026] Furthermore, the hinge joint between the rotating cylinder and the extension frame is located at the same point as the hinge joint between the extension frame and the first bidirectional adjusting screw.

[0027] The above settings improve the linkage between the first bidirectional adjusting screw and the rotating cylinder during rotation, resulting in better support for the extension frame.

[0028] Furthermore, it also includes a section-adding unit, which includes a second bidirectional adjusting screw and a vertically arranged section-adding rod. The upper end of the section-adding rod is detachably connected to the lower end of the first fixed frame. One end of the second bidirectional adjusting screw is hinged to the lower end of the section-adding rod, and the other end of the second bidirectional adjusting screw is hinged to the moving end of the lifting cylinder.

[0029] With the above settings, when the grouting operation in the tunnel is performed from bottom to top, the first fixed frame can be extended by adding sections using the section-adding unit. The section-adding rod is installed at the lower end of the first fixed frame, and the section-adding rod and the moving end of the lifting cylinder are connected by the second bidirectional adjusting screw, so that the first fixed frame and the second support screw can be supported more stably.

[0030] Furthermore, it also includes a third bidirectional adjusting screw installed between the moving ends of two adjacent lifting cylinders, the third bidirectional adjusting screw being hinged to the moving ends of the two lifting cylinders.

[0031] With the above settings, when the lifting cylinder extends or retracts, the third bidirectional adjusting screw can improve the synchronization of the extension or retraction of two adjacent lifting cylinders, making the lifting of the second support rod, the first support rod, the first fixed frame, and the second fixed frame more stable; at the same time, when the first translation cylinder and the second translation cylinder extend or retract, the third bidirectional adjusting screw can stably connect the two adjacent lifting cylinders, making the horizontal movement of the second support rod, the first support rod, the first fixed frame, and the second fixed frame more stable.

[0032] Furthermore, the number of gantry assemblies, top formwork frames, traveling units, and additional sections are all two, with the two gantry assemblies, two top formwork frames, two traveling units, and two additional sections symmetrically arranged along the vertical centerline of the tunnel's longitudinal section.

[0033] With the above setup, grouting can be carried out symmetrically on both sides of the tunnel simultaneously, improving the efficiency of grouting. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the structure of a tunnel excavation support system in the main view direction according to an embodiment of the present invention.

[0035] Figure 2 for Figure 1 The left view.

[0036] In the above-mentioned attached figures: first fixed frame 101, second fixed frame 102, extension frame 112, rotating cylinder 122, first bidirectional adjusting screw 132, sliding support frame 103, first support rod 201, second support rod 202, lifting cylinder 203, first support screw 204, second support screw 205, first translation cylinder 206, reinforcing rod 207, second translation cylinder 208, extension rod 30, second bidirectional adjusting screw 301, third bidirectional adjusting screw 302, connecting frame 401, slide rail 402, roller 403, support frame 404, and travel motor 405. Detailed Implementation

[0037] The technical solutions of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0038] Example 1

[0039] This embodiment is basically as follows: Figure 1 and Figure 2As shown, this embodiment of the invention proposes a tunnel excavation support system, including a gantry assembly, several top formwork frames, several templates, a hydraulic unit, a section-adding unit, and a traveling unit for controlling the movement of the gantry assembly. The number of gantry assemblies, top formwork frames, traveling units, and section-adding units are all two. The two gantry assemblies, two top formwork frames, two traveling units, and two section-adding units are all symmetrically arranged along the vertical centerline of the tunnel longitudinal section.

[0040] like Figure 1 As shown, the gantry assembly includes a longitudinally arranged frame, a vertically arranged first fixed frame 101, a rotating oil cylinder 122 connected to a hydraulic unit, a horizontally arranged second fixed frame 102, and a sliding support frame 404103 located between the two first fixed frames 101 and allowing the two first fixed frames 101 to slide vertically. One end of the second fixed frame 102 is opposite to the upper end of the first fixed frame 101.

[0041] like Figure 1 As shown, the top mold frame includes two horizontally supporting first support rods 201, a second support screw 205, and two vertically supporting second support rods 202. The top of the second support rods 202 is connected to the second fixed frame 102. The first support rods 201 and the middle of the second support rods 202 are fixedly connected. The end of the first support rod 201 away from the second support rods 202 and the first fixed frame 101 is detachably connected to the template. A first translation cylinder 206 communicating with a hydraulic unit is provided between the side wall of the second support rod 202 near the first fixed frame 101 and the first fixed frame 101. A hydraulic cylinder 206 communicating with a hydraulic unit is provided between the lower end of the second support rod 202 and the traveling unit. The lifting cylinder 203 is connected to the pressure unit; at the same time, the first support rod 201 is provided with an adjustable length first support screw 204 at the end away from the first fixed frame 101. The axis of the first support screw 204 is parallel to the axis of the first support rod 201. The template is detachably connected to the end of the first support screw 204 away from the first support rod 201. The second support screw 205 is inclinedly arranged on the side wall of the lowest first support rod 201 away from the upper first support rod 201. The second support screw 205 is hinged to the side wall of the first support rod 201, and the template is detachably connected to the end of the second support screw 205 away from the first support rod 201.

[0042] like Figure 1As shown, an extension frame 112 is hinged to the end of the second fixed frame 102 away from the first fixed frame 101. A first bidirectional adjusting screw 132 is vertically arranged between the extension frame 112 and the uppermost first support rod 201. The upper end of the first bidirectional adjusting screw 132 is hinged to the extension frame 112, and the lower end of the first bidirectional adjusting screw 132 is hinged to the first support rod 201. The template is detachably connected to the end of the extension frame 112 away from the second fixed frame 102. At the same time, a reinforcing rod 207 is horizontally arranged between the second support rod 202 and the second fixed frame 102, and the reinforcing rod 207 is fixedly connected to the second support rod 202. A second translation cylinder 208, which is connected to the hydraulic unit, is hinged between the reinforcing rod 207 and the second fixed frame 102. One end of the second translation cylinder 208 is hinged to the reinforcing rod 207, and the other end is hinged to the second fixed frame 102. The second translation cylinder 208 can rotate to a horizontal state. One end of the rotating cylinder 122 is hinged to the end of the reinforcing rod 207 away from the first fixed frame 101, and the other end of the rotating cylinder 122 is hinged to the middle of the extension frame 112. The hinge point of the rotating cylinder 122 and the extension frame 112 is located at the same place as the hinge point of the extension frame 112 and the first bidirectional adjusting screw 132.

[0043] like Figure 1 As shown, the extension unit includes a second bidirectional adjusting screw 301, a vertically arranged extension rod 30, and a third bidirectional adjusting screw 302 installed between the moving ends of two adjacent lifting cylinders 203. The upper end of the extension rod 30 is detachably connected to the lower end of the first fixed frame 101. One end of the second bidirectional adjusting screw 301 is hinged to the lower end of the extension rod 30, and the other end of the second bidirectional adjusting screw 301 is hinged to the moving end of the lifting cylinder 203. The third bidirectional adjusting screw 302 is hinged to the moving ends of the two lifting cylinders 203.

[0044] like Figure 1 and 2 As shown, the traveling unit includes a horizontally arranged connecting frame 401, a slide rail 402, rollers 403 that roll horizontally on the slide rail 402, a support frame 404, and a traveling motor 405 that drives the rollers 403 to roll along the slide rail 402. The lower ends of several lifting cylinders 203 are all connected to the connecting frame 401 by bolts. The connecting frame 401 is arranged along the axial direction of the tunnel. The support frame 404 is fixedly connected to the end of the connecting frame 401 by bolts. Support frames 404 are installed on both ends of the connecting frame 401. The rollers 403 and the traveling motor 405 are all installed on the support frames 404.

[0045] In this embodiment, a tunnel excavation support system is used by first extending the first translation cylinder 206 and the second translation cylinder 208 according to the position of the tunnel inner wall via a hydraulic unit. This causes the first and second translation cylinders 206 and 208 to push the first support rods 201 and 202 on both sides towards the vertical sidewall of the tunnel. The first support rods 201 push the first support screw 204, the second support screw 205, and the formwork to the concrete pouring location to initially seal the tunnel inner wall. During this process, the length of the third bidirectional adjusting screw 302 between the moving ends of two adjacent lifting cylinders 203 is adjusted so that the third bidirectional adjusting screw 302 can provide stable support for the two adjacent lifting cylinders 203. Then, according to the tunnel excavation direction, a slide rail 402 is installed on the tunnel surface. The gantry assembly, top formwork frame, formwork, and hydraulic unit are then sequentially installed onto the connecting frame 401, positioned between the support frame 404 and the travel motor 405, forming a structure as shown in the image. Figure 2 The tunnel excavation support system shown.

[0046] Then, the lengths of the first support screw 204 and the second support screw 205 can be finely adjusted. Alternatively, the second support screw 205 can be rotated around the hinge point between the second support screw 205 and the first support rod 201 to finely adjust the installation angle of the template on the second support screw 205. This allows the templates at the ends of the first support screw 204 and the second support screw 205 to be more accurately placed inside the tunnel. Then, concrete is used to grout the tunnel.

[0047] When the tunnel grouting operation proceeds from bottom to top, the first fixed frame 101 can be extended using the extension unit. The extension rod 30 is installed at the lower end of the first fixed frame 101, and the extension rod 30 and the moving end of the lifting cylinder 203 are connected by the second bidirectional adjusting screw 301. Then, the lifting cylinder 203 is extended by controlling the hydraulic unit. The lifting cylinder 203 pushes the first support rod 201, the first fixed frame 101, and the second fixed frame 102 upwards as a whole via the second support rod 202. At this time, the first and second support screws 204 and 205 can be finely adjusted again using the first translation cylinder 206 and the second translation cylinder 208. The distance between the end template and the tunnel wall allows for grouting of the upper side of the tunnel wall. When the second fixed frame 102 moves up to the tunnel arch, the hydraulic unit controls the extension of the rotating cylinder 122, which pushes the extension frame 112 to rotate upward. At this time, the first bidirectional adjusting screw 132 rotates synchronously. During this process, the length of the first bidirectional adjusting screw 132 can be adjusted so that the first bidirectional adjusting screw 132 provides stable support for the rotated extension frame 112. The end of the rotated extension frame 112 is opposite to the tunnel arch, so the extension frame 112 can rotate the template to an arc shape, allowing for grouting of the tunnel arch.

[0048] After the grouting of the inner wall of a section of the tunnel is completed, the hydraulic unit controls the shortening of the lifting cylinder 203, causing the second support rod 202 to drive the first support rod 201, the first fixed frame 101, and the second fixed frame 102 to move downwards as a whole. This controls the shortening of the first bidirectional adjusting screw 132, and simultaneously controls the shortening of several first support screws 204 and second support screws 205. The hydraulic unit controls the retraction of the rotating cylinder 122, causing all the templates to separate from the solidified grouting concrete. Then, the travel motor 405 is started, controlling the rollers 403 to move horizontally along the slide rail 402, with the driving force transmitted through... The roller 403 transmits power to the support frame 404 and the connecting frame 401, which in turn drives the lifting cylinder 203 and the second support rod 202 to push the first support rod 201, the first fixed frame 101 and the second fixed frame 102 to move as a whole along the slide rail 402. This makes the movement of the entire tunnel excavation support system convenient and fast. When grouting is carried out on the next section of the tunnel, it is only necessary to control the support position of the first support screw 204, the second support screw 205 and the extension frame 112 on the template again. The adjustment is convenient, simple and reliable, and can adapt to the changes in the installation angle and position of the template on the inner wall of the tunnel, effectively improving the construction efficiency.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A tunnel excavation support system comprising a portal assembly, a number of top formwork bodies, a number of formworks, a hydraulic unit and a travelling unit controlling the movement of the portal assembly, characterized in that, The gantry assembly includes: A vertically arranged first fixing frame is slidably mounted on the gantry assembly. A second fixing frame is set horizontally, with one end of the second fixing frame opposite to the upper end of the first fixing frame; The top mold frame includes: The first support rod of several horizontal supports; Several vertically supporting second support rods, the top of the second support rods being connected to the second fixed frame, the first support rods being fixedly connected to the middle of the second support rods, and the end of the first support rod away from the second support rods and the first fixed frame being detachably connected to the template; A first translation cylinder connected to a hydraulic unit is provided between the side wall of the second support rod near the first fixed frame and the first fixed frame; a lifting cylinder connected to a hydraulic unit is provided between the lower end of the second support rod and the traveling unit. An extension frame is hinged to the end of the second fixed frame away from the first fixed frame. A first bidirectional adjusting screw is vertically arranged between the extension frame and the uppermost first support rod. The upper end of the first bidirectional adjusting screw is hinged to the extension frame, and the lower end of the first bidirectional adjusting screw is hinged to the first support rod. The template is detachably connected to the end of the extension frame away from the second fixed frame. A reinforcing rod is horizontally arranged between the second support rod and the second fixed frame. The reinforcing rod is fixedly connected to the second support rod. A second translation cylinder connected to the hydraulic unit is hinged between the reinforcing rod and the second fixed frame. One end of the second translation cylinder is hinged to the reinforcing rod, and the other end of the second translation cylinder is hinged to the second fixed frame. The second translation cylinder can be rotated to a horizontal state. It also includes a section-adding unit, which includes a second bidirectional adjusting screw and a vertically arranged section-adding rod. The upper end of the section-adding rod is detachably connected to the lower end of the first fixed frame. One end of the second bidirectional adjusting screw is hinged to the lower end of the section-adding rod, and the other end of the second bidirectional adjusting screw is hinged to the moving end of the lifting cylinder.

2. The tunnel excavation support system as described in claim 1, characterized in that, The first support rod has an adjustable length first support screw at the end away from the first fixed frame. The axis of the first support screw is parallel to the axis of the first support rod. The template is detachably connected to the end of the first support screw away from the first support rod.

3. The tunnel excavation support system as described in claim 2, characterized in that, It also includes a second support screw, which is inclinedly disposed on the side wall of the lowest first support rod away from the upper first support rod. The second support screw is hinged to the side wall of the first support rod, and the template is detachably connected to the end of the second support screw away from the first support rod.

4. The tunnel excavation support system as described in claim 3, characterized in that, It also includes a rotating cylinder connected to the hydraulic unit, one end of which is hinged to the end of the reinforcing rod away from the first fixed frame, and the other end of which is hinged to the middle of the extension frame.

5. A tunnel excavation support system as described in claim 4, characterized in that, The hinge joint between the rotating cylinder and the extension frame is located at the same point as the hinge joint between the extension frame and the first bidirectional adjusting screw.

6. The tunnel excavation support system as described in claim 5, characterized in that, It also includes a third bidirectional adjusting screw installed between the moving ends of two adjacent lifting cylinders, the third bidirectional adjusting screw being hinged to the moving ends of the two lifting cylinders.

7. A tunnel excavation support system as described in claim 6, characterized in that, The number of gantry assemblies, top formwork frames, traveling units, and extension units are all two, with the two gantry assemblies, two top formwork frames, two traveling units, and two extension units symmetrically arranged along the vertical centerline of the tunnel's longitudinal section.

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