Mounting structure of air purification equipment in tunnel

Abstract

The invention relates to a mounting structure of air purification equipment in a tunnel, which is arranged between the inner top wall of the tunnel and an air purification equipment body, and is characterized in that the mounting structure comprises a transverse connecting piece, a plurality of upper screws, a plurality of lower screws and connecting nuts, the transverse connecting piece is fixed on the inner top wall of the tunnel, the upper screws are fixed on the transverse connecting piece at intervals, and the lower screws are fixed on the transverse connecting piece at intervals; the upper screw rods and the lower screw rods are fixed on the air purification equipment body at intervals, the upper screw rods and the lower screw rods are arranged in a one-to-one correspondence mode, the lower screw rods are located under the upper screw rods, each pair of the upper screw rods and the lower screw rods are connected together through one connecting nut, namely, the upper screw rods are in threaded connection with the upper sections in the connecting nuts, and the lower screw rods are in threaded connection with the lower sections in the connecting nuts. And the lower screw rod is in threaded connection with the lower section in the connecting nut. According to the mounting structure, the air purification equipment in the tunnel can be conveniently, quickly and firmly mounted on the inner top wall of the tunnel.

Description

Technical Field

[0001] The invention belongs to the technical field of air purification in tunnels, and in particular relates to an installation structure of air purification equipment in tunnels. Background Art

[0002] The air pollutants in tunnels mainly come from automobile exhaust smoke emissions, tire friction, braking, diesel engine smoke emissions and surface friction of ancillary equipment in tunnels. The main pollutants are ultrafine particles and nitrogen compounds. Ultrafine particles, namely PM10 particles and PM2.5 particles, are easily inhaled into the bronchi and cause diseases including asthma, bronchitis and cardiovascular disease. Nitrogen compounds NOX are mainly NO and NO2. NO is an unstable gas and is easily oxidized to NO2, which will not only cause harm to the human body, but also increase the risk of tunnel accidents.

[0003] The most commonly used tunnel bypass air purification system currently uses an axial flow fan and an air purifier in combination, using the axial flow fan to provide operating power to the air purification system; the combination achieves an air purification effect, such as the Chinese invention patent application "A Tunnel Air Purification System" with application number ZL202110762243.9 (publication number CN113577915A) discloses such a bypass air purification system. However, the tunnel bypass air purification system using axial flow fans requires a large installation space, high civil engineering and equipment investment, high operating and maintenance costs, high energy consumption, and poor economic benefits; the tunnel bypass air purification system using axial flow fans is only suitable for new projects and is not suitable for the transformation of air purification systems in already operating tunnels.

[0004] Although there are also hanging air purification systems for tunnels on the market, such as the Chinese utility model patent "Air purification system for tunnels" with patent number ZL202122591394.0 (publication number CN216518096U) discloses such a hanging system. This system is heavy, and how to achieve rapid hanging in the tunnel is a technical problem that must be solved to realize the practical application of this equipment. However, the aforementioned patent does not disclose the installation structure of this air purification equipment. Summary of the invention

[0005] In view of the deficiencies of the prior art, the present invention provides a mounting structure for an air purification device in a tunnel, which can conveniently, quickly and securely mount the air purification device in the tunnel on the top wall in the tunnel.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] A mounting structure for air purification equipment in a tunnel is arranged between the inner top wall of the tunnel and the main body of the air purification equipment, and comprises a transverse connector, an upper screw, a lower screw and a connecting nut. The transverse connector is fixed on the inner top wall of the tunnel, a plurality of the upper screws are fixed on the transverse connector at intervals, and a plurality of the lower screws are fixed on the main body of the air purification equipment at intervals. The upper screws and the lower screws are arranged in a one-to-one correspondence and the lower screws are located directly below the upper screws. Each pair of upper screws and lower screws are connected together by a connecting nut, that is, the upper screw is threadedly connected to the upper section inside the connecting nut, and the lower screw is threadedly connected to the lower section inside the connecting nut.

[0008] In order to make the transverse connector conveniently and firmly fixed on the inner top wall of the tunnel, as an improvement, the inner top wall of the tunnel is pre-embedded with multiple iron plates arranged at intervals, and the transverse connector is welded and fixed on the iron plates. The iron plates constitute a part of the inner top wall of the tunnel, and the iron plates can facilitate the transverse connector to be welded thereon, so that the transverse connector and the inner top wall of the tunnel are quickly and firmly fixed.

[0009] In order to make the upper screw conveniently and firmly fixed on the transverse connecting member, further improvement is made, the top end of the upper screw has a complete side rod portion facing inward so that the upper screw is L-shaped as a whole, the transverse connecting member is a channel steel, the upper screw is passed through the channel steel, and the side rod portion is placed and welded on the bottom of the groove of the transverse connecting member. The upper screw is L-shaped as a whole so that the upper screw can hook the channel steel and increase the contact area with the channel steel, that is, increase the welding area, and the side rod portion can also be hidden in the groove of the channel steel, without interfering with the inner top wall of the tunnel.

[0010] Preferably, the upper screws and lower screws are six in number, arranged in two rows and three columns, the transverse connecting members are two in number, arranged at intervals in front and back, and the iron plates are six in number, arranged in two rows and three columns. Of course, the number of the upper screws, lower screws, transverse connecting members and iron plates can be selected according to the size and weight of the air purification device body. Generally, at least four upper screws and four lower screws are required.

[0011] In order to firmly connect the lower screw rod to the air purification device body and to achieve adjustment and convenient disassembly and assembly, the above-mentioned lower screw rod has an upper threaded section, a lower threaded section and a bare rod section, the bare rod section is located between the upper threaded section and the lower threaded section, the lower screw rod is passed through the air purification device body, the upper threaded section passes through the top surface of the air purification device body and is threadedly connected with an upper nut, the upper nut is pressed against the top surface of the air purification device body, the lower threaded section passes through the bottom surface of the air purification device body and is threadedly connected with a lower nut, the lower nut is pressed against the bottom surface of the air purification device body.

[0012] To prevent the upper nut and the lower nut from loosening, an upper gasket is provided between the upper nut and the top surface of the air purification device body, and a lower gasket is provided between the lower nut and the bottom surface of the air purification device body.

[0013] In order to facilitate the transportation of the air purification device body out of the factory, the top surface of the air purification device body is provided with a plurality of lifting rings for convenient lifting.

[0014] By arranging a reinforcing rib plate between the transverse connector and the iron plate, the overall strength and stability of the installation structure are further improved. The transverse connector is designed to be arc-shaped, and its curvature matches the curvature of the inner top wall of the tunnel, so that the transverse connector can fit closely to the inner top wall of the tunnel.

[0015] Compared with the prior art, the advantages of the present invention are:

[0016] The installation process of the air purification equipment is simple, fast and firm by welding and fixing the transverse connector to the pre-embedded iron plate in the top wall of the tunnel. The upper screw and the lower screw are connected by connecting nuts, which not only enhances the stability of the overall structure, but also provides a convenient installation method. The air purification equipment can be hoisted through simple operations in a short time, greatly improving the construction efficiency. The upper screw is designed as an L-shaped structure, which enhances the contact area with the transverse connector and provides a larger welding area, making the connection structure more solid and significantly improving the seismic performance, which is suitable for complex environmental conditions in the tunnel. The lower screw is provided with an upper threaded section, a lower threaded section and a bare rod section, so that the cooperation between the nut and the screw can achieve height adjustment, which is convenient for adaptive installation in different tunnel environments. At the same time, the disassembly and assembly process of the equipment is also extremely simple. The equipment can be quickly dismantled by reverse operation, reducing the difficulty of maintenance and replacement. The transverse connecting piece is designed to be arc-shaped, and its curvature matches the curvature of the inner top wall of the tunnel, which allows the installation structure to fit closely to the surface of the inner top wall of the tunnel, avoiding the problem of unstable installation caused by the irregular shape of the inner top wall of the tunnel, and improving the overall firmness and safety of the equipment.

[0017] This installation structure can quickly and securely install the air purification device under the inner top wall of the tunnel. During installation, the connecting nut is pre-threaded on the upper screw rod, and then the air purification device body is lifted to a position close to the inner top wall of the tunnel by a lifting device, and the lower screw rod on the air purification device body is aligned with the upper screw rod, and the connecting nut is rotated so that the connecting nut is also threaded on the lower screw rod, and then the air purification device body is suspended under the upper screw rod through the connecting nut to complete the assembly. When disassembling, the process is opposite to the installation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the three-dimensional structure of an embodiment of the present invention;

[0019] Figure 2 for Figure 1 A magnified image of point A;

[0020] Figure 3 is a cross-sectional view of an embodiment of the present invention;

[0021] Figure 4 for Figure 3 A magnified view of point B;

[0022] Figure 5 for Figure 3 Enlarged view of point C;

[0023] Figure 6 A schematic diagram of fixing a transverse connecting member to an iron plate member in an embodiment of the present invention;

[0024] Figure 7 It is a three-dimensional schematic diagram of the air purification device body in an embodiment of the present invention;

[0025] Figure markings: 1-tunnel; 1a-inner top wall; 2-air purification equipment body; 3-transverse connecting piece; 4-iron plate; 5a-upper screw; 5a1-side rod; 5b-lower screw; 5b1-upper threaded section; 5b2-lower threaded section; 5b3-bare rod section; 6-connecting nut; 7a-upper nut; 7b-lower nut; 8a-upper gasket; 8b-lower gasket; 21-lifting ring. DETAILED DESCRIPTION

[0026] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention belong to the present invention.

[0027] In addition, described feature, structure or characteristic can be combined in one or more embodiments in any suitable manner. In the following description, many specific details are provided to provide a full understanding of the embodiments of the present application. However, those skilled in the art will appreciate that the technical scheme of the present application can be put into practice without one or more of the specific details, or other methods, components, devices, steps, etc. can be adopted. In other cases, known methods, devices, realizations or operations are not shown or described in detail to avoid blurring the various aspects of the present application.

[0028] like Figure 1-7As shown, this embodiment discloses an installation structure for an air purification device in a tunnel, and the structure is arranged between the inner top wall 1a of the tunnel 1 and the air purification device body 2. In order to facilitate the installation and hoisting of the equipment, the top surface of the air purification device body 2 is provided with a plurality of lifting rings 21 for convenient hoisting. The design of the lifting ring can realize rapid positioning and hoisting by using lifting equipment during the transportation and installation of the equipment, reduces the difficulty of manual operation, and ensures the efficiency and safety of the installation process. The specific structure of the air purification device body 2 can refer to the existing technology in the background patent to ensure that the equipment is highly compatible with the present installation structure on the basis of satisfying the air purification function.

[0029] The installation structure includes a transverse connector 3, an upper screw 5a, a lower screw 5b and a connecting nut 6. In order to ensure the stability of the equipment, the upper screw 5a and the lower screw 5b are both M24 screws with a large load-bearing capacity to support the weight of the air purification equipment. The transverse connector 3 is fixedly installed on the inner top wall 1a of the tunnel 1. The selection and arrangement of the transverse connector 3 directly affect the strength and firmness of the entire installation structure. Therefore, it is firmly connected to the top wall of the tunnel by welding or the like to cope with various external forces that the equipment is subjected to during long-term use, such as vibration, impact of air flow, etc.

[0030] Multiple upper screws 5a are fixed at intervals on the transverse connector 3 to ensure that each screw can evenly distribute the weight of the equipment and avoid imbalance of the installation structure caused by excessive local force. Similarly, multiple lower screws 5b are also fixed at intervals on the air purification device body 2. The one-to-one correspondence design of the upper screw 5a and the lower screw 5b ensures that the equipment can be accurately aligned during installation and the two are firmly connected together through the connecting nut 6. Specifically, the upper section of the upper screw 5a is threadedly connected to the upper section of the connecting nut 6, and the lower section of the lower screw 5b is threadedly connected to the lower section of the connecting nut 6, forming a stable connection structure.

[0031] In order to ensure the long-term stability and seismic resistance of the equipment, the connection nut 6 used is a black hexagonal nut of 8.8 grade M24L70. This nut has excellent corrosion resistance and high strength grade after surface treatment, and can maintain its mechanical properties in the humid and complex environment of the tunnel, preventing the connection from loosening or failure due to environmental corrosion or long-term use. At the same time, the design of the hexagonal nut makes it easy for installers to operate tools to tighten in a limited space, thereby improving the convenience and reliability of equipment installation.

[0032] The inner top wall 1a of the tunnel 1 is pre-embedded with multiple iron plates 4 arranged at intervals. These iron plates 4 play a key bearing role. By tightly combining with the tunnel top wall, they provide a stable connection platform to ensure that the installation structure of subsequent equipment can be firmly fixed on the inner top wall of the tunnel. The pre-embedded design of the iron plates 4 not only improves the convenience of the installation process, but also avoids large-scale destructive operations directly on the tunnel structure, thereby protecting the integrity of the tunnel. The transverse connector 3 is welded and fixed to the iron plate 4. The welded connection ensures the strength between the transverse connector 3 and the iron plate 4, and also improves the seismic resistance and durability of the equipment during long-term operation.

[0033] The top of the upper screw 5a has a complete inward side rod portion 5a1, and this design makes the upper screw 5a as a whole L-shaped. The L-shaped structure not only increases the contact area between the screw and the transverse connector 3, but also improves the overall stability of the screw. Especially when the equipment is running, the L-shaped screw can better resist the tension and torque caused by the weight of the equipment and reduce the risk of loosening. In addition, the transverse connector 3 is No. 12 channel steel, which has high strength and durability and is suitable for use in places with complex environments such as tunnels. The bottom of the channel steel is perforated, and the upper screw 5a is inserted through the perforation of the channel steel to ensure that the screw can be firmly installed on the transverse connector 3. The side rod portion 5a1 is placed and welded on the bottom of the groove of the transverse connector 3. This design not only enhances the connection strength between the screw and the channel steel, but also reduces the complexity of the operation during installation, while ensuring that the screw will not be affected by loosening or sliding during use.

[0034] The upper screw rods 5a and the lower screw rods 5b in this embodiment each have six, arranged in two rows and three columns. This arrangement ensures the uniform distribution of the weight of the equipment and avoids structural deformation or damage caused by excessive local force. In particular, when the equipment is running, the multi-point support design of the upper and lower screw rods can effectively disperse the pressure on the equipment and improve the overall stability and reliability of the installation structure. The transverse connector 3 has two, front and back intervals, to ensure the stability of the equipment in the front and back directions, and will not shake back and forth due to uneven force or external vibration. The iron plate parts 4 are six, arranged in two rows and three columns. Such a design not only provides sufficient support points, but also provides a more balanced force structure for the installation of the entire equipment. Among them, front and back refer to the length direction of the tunnel 1, and left and right refer to the width direction of the tunnel 1. This arrangement is highly matched with the shape and layout of the tunnel space, ensuring that the equipment can be reasonably arranged in the tunnel and maximize the use of the tunnel's space resources.

[0035] The lower screw rod 5b has an upper threaded section 5b1, a lower threaded section 5b2 and a bare rod section 5b3, and the bare rod section 5b3 is located between the upper threaded section 5b1 and the lower threaded section 5b2. This design not only gives the screw a multi-segment thread structure so that it can be fixed and adjusted by nuts at different positions, but also the presence of the bare rod section 5b3 provides a sliding space for the screw during installation, which is conducive to fine-tuning when installing the air purification device, ensuring that the device can be in an ideal installation position. The lower screw rod 5b is arranged on the air purification device body 2, ensuring the close connection between the device and the mounting structure, and at the same time, the upper and lower ends are firmly fixed by the threaded section.

[0036] The upper threaded section 5b1 passes through the top surface of the air purification device body 2 and is threadedly connected with the upper nut 7a. The upper nut 7a not only plays the role of firmly pressing the screw rod on the top surface of the device body, but also provides the function of adjusting the installation height of the device through threaded matching to ensure the stability of the device after installation. The upper nut 7a is pressed against the top surface of the air purification device body 2, further enhancing the connection strength between the device and the lower screw rod, and avoiding loosening caused by vibration or external force during the operation of the device.

[0037] Similarly, the lower threaded section 5b2 passes through the bottom surface of the air purification device body 2 and is threadedly connected with the lower nut 7b. The design of the lower nut 7b is similar to that of the upper nut 7a, and its function is to firmly fix the lower screw on the bottom surface of the device body to ensure the tightness and stability of the entire installation structure. The lower nut 7b is pressed against the bottom surface of the air purification device body 2, further enhancing the stability of the device and preventing loosening or displacement caused by vibration or external force during the operation of the device.

[0038] In order to further prevent the nut from loosening during long-term use, an upper gasket 8a is provided between the upper nut 7a and the top surface of the air purification device body 2, and a lower gasket 8b is provided between the lower nut 7b and the bottom surface of the air purification device body 2. These gaskets not only provide additional friction and enhance the close contact between the nut and the surface of the device, but also effectively reduce the direct friction between the nut and the surface of the device, thereby extending the service life of the device and the threaded connection. The design of the gasket also plays a shock-absorbing role to a certain extent, which can absorb part of the vibration caused by the operation of the equipment, reduce the impact on the threaded connection, and further improve the reliability and durability of the entire installation structure.

[0039] A reinforcing rib plate is also provided between the transverse connector 3 and the iron plate 4. The provision of the reinforcing rib plate can effectively enhance the structural strength of the transverse connector 3 and prevent the connector from being deformed or loosened due to vibration or external impact during the long-term operation of the equipment. The transverse connector 3 is arc-shaped. Since the inner top wall 1a of the tunnel 1 is usually an arc-shaped structure, if a traditional linear connector is used, it may cause uneven local force after the equipment is installed, affecting the stability and life of the equipment. By designing it into an arc shape, the transverse connector 3 can perfectly fit the structure of the inner top wall 1a of the tunnel 1, thereby achieving a tighter installation. This fitting design ensures that the equipment will not shake or become unstable after installation, and improves the stability of the entire system. The curvature of the transverse connector 3 matches the curvature of the inner top wall 1a of the tunnel 1, so that the transverse connector can be smoothly fitted into the top structure of the tunnel, which not only avoids the gap caused by the mismatch of the curvature, but also improves the force performance as a connector.

[0040] During installation, the connecting nut 6 is threadedly connected to the upper screw rod 5a in advance. This step ensures that the upper screw rod 5a and the connecting nut 6 are initially fixed, so that the subsequent installation work can proceed smoothly. By threading in advance, time delays or unnecessary alignment operations that may occur during the lifting of the equipment are avoided. Then, the lifting device is used to lift the air purification device body 2 to a position close to the inner top wall of the tunnel 1. In this process, the lifting device can stably and accurately move the device to the predetermined position, ensuring that the device will not shake or deviate from the predetermined trajectory during the lifting process, thereby ensuring the safety and efficiency of the entire installation process. When the air purification device body 2 reaches the predetermined position, it is necessary to ensure that the lower screw rod 5b on the air purification device body 2 is directly opposite to the upper screw rod 5a. At this time, accurate alignment is very critical, because the precise alignment of the lower screw rod and the upper screw rod will directly affect the smooth installation of the connecting nut 6 and the overall stability of the equipment. The two screw rods are aligned by using a measuring tool to ensure that they are on the same axis. On this basis, the connecting nut 6 is turned so that the connecting nut 6 is also threadedly connected to the lower screw rod 5b. Through this threaded connection method, the connecting nut can not only firmly connect the upper and lower screw rods, but also adjust the height and position of the equipment according to actual needs, ensuring that the air purification equipment is in the best working state after installation, and then the air purification equipment body 2 is suspended under the upper screw rod 5a through the connecting nut 6 to complete the assembly. This step ensures the stable installation of the equipment. Relying on the threaded connection structure of the upper screw rod 5a and the connecting nut 6, the equipment can be safely suspended below the top wall in the tunnel to achieve the expected installation effect. This hoisting method not only ensures the installation firmness of the equipment, but also simplifies the installation process and reduces the complexity of manual operation.

[0041] When disassembling, the process is the opposite of the installation process. When the equipment needs to be maintained, adjusted or replaced, it is only necessary to follow the reverse steps of the installation, that is, first loosen the connecting nut 6, and then lower the air purification equipment body 2 steadily by lifting the equipment to avoid shaking or instability of the equipment during disassembly, thereby ensuring the safety of the equipment and personnel.

[0042] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. Under the concept of the present invention, the technical features in the above embodiments or different embodiments may also be combined, the steps may be implemented in any order, and there are many other changes in different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity. Although the present invention has been described in detail with reference to the above embodiments, a person of ordinary skill in the art should understand that the technical solutions described in the above embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A mounting structure for an air purification device in a tunnel, arranged between an inner top wall (1a) of a tunnel (1) and a body (2) of the air purification device, characterized in that: The invention comprises a transverse connecting member (3), an upper screw rod (5a), a lower screw rod (5b) and a connecting nut (6); the transverse connecting member (3) is fixed on the inner top wall (1a) of the tunnel (1); a plurality of the upper screw rods (5a) are fixed on the transverse connecting member (3) at intervals; a plurality of the lower screw rods (5b) are fixed on the air purification device body (2) at intervals; the upper screw rods (5a) and the lower screw rods (5b) are arranged in a one-to-one correspondence and the lower screw rods (5b) are located directly below the upper screw rods (5a); each pair of the upper screw rods (5a) and the lower screw rods (5b) are connected together by a connecting nut (6), that is, the upper screw rod (5a) is threadedly connected to the upper section inside the connecting nut (6), and the lower screw rod (5b) is threadedly connected to the lower section inside the connecting nut (6).

2. The installation structure of the air purification equipment in the tunnel according to claim 1 is characterized in that: The inner top wall (1a) of the tunnel (1) is pre-buried with a plurality of iron plates (4) arranged at intervals, and the transverse connecting members (3) are welded and fixed on the iron plates (4).

3. The installation structure of the air purification equipment in the tunnel according to claim 2 is characterized in that: The top end of the upper screw rod (5a) has a complete inward side rod portion (5a1) so that the upper screw rod (5a) is L-shaped as a whole. The transverse connecting member (3) is a channel steel. The upper screw rod (5a) is inserted into the channel steel. The side rod portion (5a1) is placed on and welded to the bottom of the groove of the transverse connecting member (3).

4. The installation structure of the tunnel air purification equipment according to claim 3 is characterized in that: There are six upper screw rods (5a) and six lower screw rods (5b) each, arranged in two rows and three columns.

5. The installation structure of the air purification equipment in the tunnel according to claim 4 is characterized in that: There are two transverse connecting members (3) which are spaced apart from each other.

6. The installation structure of the air purification equipment in the tunnel according to claim 5, characterized in that: The iron plate members (4) are six in number and are arranged in two rows and three columns.

7. The installation structure of the tunnel air purification equipment according to any one of claims 1 to 6, characterized in that: The lower screw rod (5b) comprises an upper threaded section (5b1), a lower threaded section (5b2) and a bare rod section (5b3), wherein the bare rod section (5b3) is located between the upper threaded section (5b1) and the lower threaded section (5b2), and the lower screw rod (5b) is passed through the air purification device body (2), the upper threaded section (5b1) passes through the top surface of the air purification device body (2) and is threadedly connected to an upper nut (7a), and the upper nut (7a) is pressed against the top surface of the air purification device body (2), the lower threaded section (5b2) passes through the bottom surface of the air purification device body (2) and is threadedly connected to a lower nut (7b), and the lower nut (7b) is pressed against the bottom surface of the air purification device body (2).

8. The installation structure of the tunnel air purification equipment according to claim 7, characterized in that: An upper gasket (8a) is provided between the upper nut (7a) and the top surface of the air purification device body (2), and a lower gasket (8b) is provided between the lower nut (7b) and the bottom surface of the air purification device body (2).

9. The installation structure of the air purification equipment in the tunnel according to claim 1, characterized in that: The top surface of the air purification device body (2) is provided with a plurality of lifting rings (21) for convenient lifting.

10. The installation structure of the air purification equipment in the tunnel according to claim 2, characterized in that: A reinforcing rib plate is also provided between the transverse connecting member (3) and the iron plate member (4); the transverse connecting member (3) is arc-shaped, and the curvature of the transverse connecting member (3) matches the curvature of the inner top wall (1a) of the tunnel (1).

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