Protection system for collapsed cavity at top of tunnel and on-site construction method of protection system

Abstract

The invention discloses a protection system for a collapsed cavity at the top of a tunnel and an on-site construction method. The protection system comprises at least two flexible protection nets and an air bag, the lower hole diameter of each flexible protection net is smaller than that of the upper part, and the flexible protection nets are connected to the side wall in the collapse cavity and used for intercepting falling rocks of different sizes. The air bag is located below, corresponds to the bottom opening of the collapse cavity and can be plugged in a conformal mode to form temporary support after being inflated, and the injected concrete in the inflated state can be converted into permanent support. The air bag is provided with a special exhaust channel and other structures. During construction, a collapsed cavity is cleaned, shotcrete and anchor supporting are conducted, three-dimensional data are obtained through scanning to construct a model, the protective net and the air bag are manufactured and installed on site according to the mode, and the protective net is formed by splicing prefabricated net pieces of different specifications. And after tunnel construction passes through the area, concrete is injected into the air bags to complete supporting conversion. The system and the method effectively improve the safety of tunnel construction, reduce protection dead angles and improve the construction efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel construction safety protection, and in particular to a protection system for a tunnel top collapse cavity and an on-site construction method. Background Art

[0002] Tunnel construction often encounters various complex geological conditions. For example, tunnel projects that pass through mountainous areas often encounter weak surrounding rocks, such as shale and mudstone, which have low strength and poor self-stabilization ability. During the tunnel excavation process, due to the change in the stress state of the surrounding rock and soil, the weak surrounding rock is difficult to withstand such changes and is prone to collapse, thus forming a collapse cavity. The existence of the collapse cavity makes the construction environment extremely dangerous and unstable. When a collapse cavity appears on the top of the tunnel, the collapsed rock and soil may hit the lining and construction workers without warning, causing direct economic losses and casualties. Even smaller rockfalls may cause secondary collapse during the impact, causing more rock and soil to fall, destroying the entire tunnel project and posing a serious threat to the lives of construction workers. Therefore, in order to ensure the safety of the tunnel structure and the safety of construction workers, it is very necessary to treat the collapsed cavity inside the tunnel.

[0003] The existing traditional methods for treating tunnel collapse, such as steel arch support and concrete backfill, have certain limitations. Although the steel arch support has high strength, its shape is relatively fixed and it is difficult to adapt to the complex and changeable shape of the collapse cavity. Concrete is heavy, and the method of backfilling the collapse cavity with concrete will increase the local bearing capacity of the lining under the collapse cavity, which is easy to cause deformation of the tunnel lining and affect the initial support effect. In modern tunnel construction, shortening the construction period and improving construction efficiency are the key. Therefore, an efficient method for treating collapse cavity is needed, which can quickly implement protection and treatment measures, reduce downtime during construction, and can work closely with other construction processes and seamlessly connect to ensure the smooth progress of tunnel construction and improve the overall benefits of the project. Summary of the invention

[0004] In view of the deficiencies in the above-mentioned prior art, the object of the present invention is to provide a protection system and on-site construction method for the collapsed cavity at the top of the tunnel, so as to solve the construction safety risks caused by the collapse of soft surrounding rock to form a collapsed cavity during tunnel construction, the limitations of traditional treatment methods, and other problems, so as to achieve effective protection of the collapsed cavity of the tunnel, ensure construction safety and efficiency, and improve the long-term stability of the tunnel.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] The first aspect of the present invention discloses a protection system for a tunnel top collapse cavity, comprising: a flexible protection net, at least two of which are arranged from top to bottom inside the tunnel top collapse cavity, and the aperture of the lower flexible protection net is smaller than the aperture of the upper flexible protection net; the flexible protection net is connected to the inner side wall of the tunnel top collapse cavity; an airbag, which is located below the flexible protection net and is arranged corresponding to the bottom opening of the tunnel top collapse cavity; the airbag is constructed to be able to conformally seal the bottom opening of the tunnel top collapse cavity after inflation to form a temporary support; the airbag is also constructed to be able to inject concrete into the interior of the airbag when the temporary support is inflated, so that the airbag is converted from a temporary support to a permanent support.

[0007] "Conformal sealing" means that after the airbag is inflated, it can adaptively deform according to the shape and size of the opening at the bottom of the collapsed cavity at the top of the tunnel, closely fit the boundary of the opening, achieve effective sealing and play a temporary support role.

[0008] The present invention adopts an innovative protection system for the protection of the collapsed cavity at the top of the tunnel. Among them, the flexible protection net plays a key role. It is arranged in at least two layers from top to bottom, and the aperture is in a decreasing state. This design allows the upper layer of the larger aperture protection net to intercept large-sized falling rocks first, while the lower layer of the smaller aperture protection net can further intercept small-sized falling rocks, greatly expanding the protection range. At the same time, the airbag at the bottom can conform to the bottom opening after inflation to form a temporary support, effectively preventing the collapsed rock and soil from directly hitting the construction area below. At a later stage, by injecting concrete into the airbag to convert it into a permanent support, the stability of the bottom of the collapsed cavity is enhanced. The flexible protection net and the airbag cooperate with each other to form a more comprehensive interception system, reduce blind spots in protection, and provide a strong guarantee for construction safety.

[0009] In the present invention, the flexible protective net is connected to the inner side wall of the collapsed cavity at the top of the tunnel, and its installation position is highly flexible and can be adjusted according to the actual shape and size of the collapsed cavity. The side shape and size of the airbag can be customized according to the actual situation of the inner wall at the bottom of the collapsed cavity in different projects. This means that whether it is a regular or irregular collapsed cavity, the airbag can fit the bottom opening tightly, thereby improving the adaptability of the protection system to different collapsed cavities, ensuring that the protection effect is stable and guaranteed, and meeting the needs of various complex tunnel construction environments.

[0010] In addition, during the construction process, the airbags, as temporary supports, can bear part of the rock and soil pressure, effectively reduce the burden on the lining, and reduce the risk of lining deformation. When the construction progresses to a certain stage, when the airbags are in the inflated state of temporary support, concrete is injected into them to convert them into permanent support. At this time, the airbags and the surrounding rock mass form a whole, further enhancing the stability of the bottom of the collapsed cavity, which not only reduces the adverse effects on the lining, but also lays a solid foundation for the long-term stability of the tunnel structure, ensuring the safety and reliability of the tunnel in subsequent use.

[0011] According to the protection system for the tunnel top collapse cavity disclosed in the first aspect of the present invention, the airbag includes a top surface portion, a bottom surface portion and a side surface portion connecting the top surface portion and the bottom surface portion and forming a circle on the side, the bottom surface portion of the airbag is provided with an inflation port and an exhaust port, and the airbag is provided with a tubular exhaust passage connected to the exhaust port and extending into the inner cavity of the airbag.

[0012] In the present invention, by providing a tubular exhaust passage connected to the exhaust port and extending into the inner cavity of the airbag, the concrete injection can be effectively ensured, that is, when the concrete is injected from the inflation port, it will not be immediately discharged from the exhaust port. At the same time, the tubular exhaust passage extending into the airbag can meet the monitoring of the amount of concrete injected into the airbag, that is, when the concrete injected into the airbag meets the required volume, it will enter the tubular exhaust passage from the inner cavity of the airbag and overflow from the exhaust port; that is, when the concrete overflows from the exhaust port, it means that a sufficient amount of concrete has been injected into the airbag.

[0013] According to the protection system for the tunnel top collapse cavity disclosed in the first aspect of the present invention, the tubular exhaust channel is constructed in an L-shape, including a transverse channel portion attached to the inner wall of the top surface portion of the airbag and connected to the inner cavity of the airbag at its end, and a vertical channel portion attached to the inner wall of the side portion of the airbag and connected to the exhaust port at its end, and the end of the transverse channel portion of the tubular exhaust channel is close to or located at the center of the airbag.

[0014] In the present invention, since the tubular exhaust channel is constructed to extend in the airbag along the inner wall of the side surface portion and the inner wall of the top surface portion, interference with the injection of concrete can be effectively prevented. Moreover, since the concrete rises from bottom to top in the inner cavity of the airbag during the injection process, and the transverse channel portion of the tubular exhaust channel is located on the inner wall of the top surface portion, the gas in the inner cavity of the airbag can be effectively discharged to the outside during the concrete injection process, thereby balancing the air pressure inside and outside the airbag, thereby ensuring smooth injection of concrete; at the same time, since the transverse channel portion of the tubular exhaust channel is located on the inner wall of the top surface portion, the injection amount of concrete can be effectively monitored without generating false alarms; in addition, since the end of the transverse channel portion of the tubular exhaust channel is close to or located at the center of the airbag, the air pressure inside and outside the airbag can be further effectively balanced to ensure smooth injection of concrete, while ensuring the accuracy of monitoring the injection amount of concrete.

[0015] According to the protection system for tunnel top collapse cavity disclosed in the first aspect of the present invention, the tubular exhaust channel includes a water-permeable spring steel pipe located inside and a rubber shell wrapped around the water-permeable spring steel pipe, and the rubber shell is connected to the inner wall of the airbag.

[0016] In the present invention, the hard water-permeable spring steel tube arranged in the tubular exhaust channel can effectively solve the problem that the exhaust channel is squeezed and cannot be exhausted when the air pressure inside the airbag is too high, and the rubber shell wrapped outside it not only protects the water-permeable spring steel tube, but is also connected to the inner wall of the airbag, so that the exhaust channel and the airbag form a whole, thereby improving the stability and reliability of the airbag structure.

[0017] According to the protection system for the tunnel top collapse cavity disclosed in the first aspect of the present invention, the flexible protection net includes a first flexible protection net and a second flexible protection net arranged from top to bottom, wherein the first flexible protection net is constructed as a wire rope protection net, and the second flexible protection net is constructed as a double-twisted hexagonal flexible net laid on the wire rope protection net.

[0018] In the present invention, the first flexible protection net adopts a steel wire rope protection net with high strength and good toughness, which can effectively intercept large-sized falling rocks. The second flexible protection net adopts a double-twisted hexagonal flexible net laid on the steel wire rope protection net. Its smaller grid can intercept smaller falling rocks and further disperse the impact energy. The two layers of protection nets work together to give full play to their respective advantages, and intercept falling rocks of different sizes in a graded manner, forming a more complete protection system, improving the overall protection capability, and reducing the damage to the tunnel caused by falling rocks.

[0019] According to the protection system for tunnel top collapse cavity disclosed in the first aspect of the present invention, the wire rope protection net is made of galvanized coated steel wire rope and is woven in a diamond mesh manner; the twisted hexagonal flexible net is woven with Class A galvanized coated steel wire.

[0020] In the present invention, the steel wire rope protection net is made of galvanic coated steel wire rope and the twisted hexagonal flexible net is made of Class A galvanic coated steel wire, which respectively improves the corrosion resistance of the steel wire rope and the steel wire, prolongs the service life of the protection net, and ensures that the protection system can operate stably for a long time in the harsh environment of the tunnel; at the same time, the diamond mesh weaving method adopted by the steel wire rope protection net makes its structure more stable, and the hexagonal mesh and the diamond mesh cooperate with each other, optimize the ability to intercept falling rocks, and ensure the protection performance of the protection system.

[0021] According to the protection system for tunnel top collapse cavity disclosed in the first aspect of the present invention, each wire rope protection net is spliced ​​by a plurality of prefabricated wire rope mesh pieces of different specifications.

[0022] In the present invention, the wire rope protection net is spliced ​​by a plurality of prefabricated wire rope meshes of different specifications, which not only enables it to be flexibly spliced ​​according to the actual shape and size of the collapsed cavity, better fits the internal structure of the collapsed cavity, improves the protection effect, and enhances the adaptability to different collapsed cavities, but also facilitates transportation and on-site splicing, reduces construction difficulty, improves construction efficiency, reduces construction time, and is easy to replace damaged meshes, reducing maintenance costs.

[0023] According to the protection system for the tunnel top collapsed cavity disclosed in the first aspect of the present invention, the flexible protection net and the airbag are both manufactured on-site at the construction site based on the three-dimensional structural data of the tunnel top collapsed cavity.

[0024] In the present invention, flexible protection nets and airbags are manufactured at the construction site based on the three-dimensional structural data of the collapsed cavity on the top of the tunnel, which can not only make the protection system highly matched with the actual situation of the collapsed cavity, ensuring that the size, shape, etc. of the protection nets and airbags meet the engineering requirements, improve the applicability and protection performance of the protection system, and reduce construction errors, but also reduce the trouble of transporting and adjusting prefabricated parts, make the construction process more compact, improve construction efficiency, reduce construction costs, and facilitate timely adjustment of the protection system according to the actual situation during the construction process.

[0025] The second aspect of the present invention discloses a method for implementing the on-site construction of the protection system for the tunnel top collapsed cavity disclosed in the first aspect of the present invention, comprising the following steps: S1, cleaning the cavity area of ​​the tunnel top collapsed cavity found during tunnel excavation and then spraying anchor support; S2, scanning the tunnel top collapsed cavity, obtaining the three-dimensional structural data of the tunnel top collapsed cavity, and then constructing a collapsed cavity model according to the three-dimensional structural data; S3, on-site manufacturing of a flexible protective net and an airbag capable of forming a conformal fit with the bottom opening of the tunnel top collapsed cavity after inflation based on the data of the collapsed cavity model; S4, arranging at least one flexible protective net from top to bottom inside the tunnel top collapsed cavity, and connecting the flexible protective net to the inner wall of the collapsed cavity; S5, assembling an airbag under the flexible protective net and corresponding to the bottom opening of the tunnel top collapsed cavity, and inflating it until it forms a fit with the surrounding side walls of the bottom opening of the tunnel top collapsed cavity; S6, when the tunnel excavation construction passes through the location of the tunnel top collapsed cavity, injecting concrete into the airbag to convert the airbag from temporary support to permanent support.

[0026] In the present invention, during the construction of the collapsed cavity at the top of the tunnel, sprayed anchor support is used to reinforce the surrounding rock of the collapsed cavity to improve its stability, creating safety conditions for subsequent operations. During construction, airbags are used as temporary supports to prevent collapsed rock and soil from injuring personnel and equipment, thereby achieving safe construction. By scanning and acquiring three-dimensional structural data to build a model, the on-site production and installation of protective nets and airbags are accurately guided, so that the protective system fits tightly to the collapsed cavity to play an effective protective role. The coherent construction process improves construction efficiency, shortens the construction period, and achieves efficient construction. After the construction is completed, the airbags are converted into permanent supports to enhance the stability of the tunnel structure, ensure the long-term safe use of the tunnel, and achieve stable support.

[0027] According to the on-site construction method disclosed in the second aspect of the present invention, in step S4, two flexible protection nets are arranged, including a first flexible protection net and a second flexible protection net from top to bottom, the first flexible protection net is constructed as a wire rope protection net, and the second flexible protection net is constructed as a double-twisted hexagonal flexible net laid on the wire rope protection net; before step S1, it also includes step S0, prefabricating multiple wire rope meshes of different specifications; in step S3, the wire rope protection net is spliced ​​on-site by multiple prefabricated wire rope meshes of different specifications based on the data of the collapsed cavity model.

[0028] In the present invention, the specific settings of the two-layer flexible protection net are clarified, which further enhances the protection capability and improves the interception effect of falling rocks of different sizes, thereby ensuring the safety of tunnel construction and operation; at the same time, prefabricated wire rope meshes of different specifications are convenient for on-site splicing, which improves construction efficiency, and the on-site splicing of the wire rope protection net based on the collapse cavity model data can be flexibly adjusted according to actual conditions to ensure the accurate installation of the protection net, which not only improves the protection effect, but also optimizes the construction process and ensures the safety and quality of tunnel construction.

[0029] The beneficial effects of the present invention are as follows:

[0030] 1) Traditional steel arch support and concrete backfilling methods are difficult to fully guarantee construction safety. The shape of the steel arch is fixed, and it is difficult to fit the complex and changeable collapse cavity, which has protection loopholes; concrete backfilling will not only increase the local bearing capacity of the lining, causing lining deformation, but also cannot effectively deal with the threat of falling rocks of different sizes. The flexible protection net of the present invention is arranged from top to bottom in at least two layers with decreasing apertures. The upper layer of the larger aperture protection net can first intercept large-sized falling rocks, and the lower layer of the smaller aperture protection net can further intercept small-sized falling rocks, greatly broadening the protection range. After the bottom airbag is inflated, it can conform to the bottom opening to form a temporary support to prevent the collapsed rock and soil from directly hitting the construction area below. The later injection of concrete will convert it into permanent support to enhance the stability of the bottom of the collapse cavity. The flexible protection net and the airbag cooperate with each other to build a comprehensive interception system, greatly reduce the blind spots of protection, provide reliable safety protection for construction personnel and equipment, and effectively reduce safety risks during construction.

[0031] 2) The steel arch support has a fixed shape. When faced with a collapsed cavity of complex shape, the support structure cannot be adjusted according to the actual situation, and its adaptability is poor. In the protection system of the present invention, the flexible protection net is connected to the inner side wall of the collapsed cavity at the top of the tunnel, and its installation position can be flexibly adjusted according to the actual shape and size of the collapsed cavity; the side shape and size of the airbag can be customized according to the actual situation of the inner wall at the bottom of the collapsed cavity in different projects. Whether it is a regular or irregular collapsed cavity, the protection system can fit tightly to ensure the reliability of the protection effect, meet the needs of various complex tunnel construction environments, and effectively solve the limitations of traditional support methods under complex working conditions.

[0032] 3) Using concrete to backfill the collapsed cavity can easily cause deformation of the tunnel lining, affect the initial support effect, and have an adverse effect on the long-term stability of the tunnel. In the present invention, the airbag is used as a temporary support during construction, taking on part of the rock and soil pressure and reducing the burden on the lining; concrete is injected into the inflated state of the temporary support to convert it into a permanent support, forming a whole with the surrounding rock mass, thereby enhancing the stability of the bottom of the collapsed cavity and reducing the adverse effects on the lining. Moreover, this conversion method from temporary support to permanent support makes the support structure more stable and more durable, ensuring the long-term safe use of the tunnel, improving the overall quality and service life of the tunnel, and reducing later maintenance costs and safety hazards.

[0033] 4) Modern tunnel construction has extremely high requirements for construction efficiency. The construction process of traditional treatment methods is complicated, which can easily lead to extended downtime and affect the progress of the project. The first layer of the protective net of the present invention is spliced ​​from steel wire rope meshes of various specifications. It can be prefabricated and spliced ​​off-site in a variety of ways according to the different collapse cavity conditions in actual construction and then transported into the collapse cavity, reducing the construction time and operation difficulty in the tunnel and reducing construction risks. At the same time, the various construction steps are closely coordinated, and the construction process is more efficient, which is conducive to improving construction efficiency, shortening the construction period, and thus reducing project costs. In addition, the protective net material has high strength and corrosion resistance, can adapt to the complex environmental conditions in the tunnel, reduces the replacement frequency of the protective net, and further reduces maintenance costs.

[0034] The protection system for tunnel top collapse cavity and the on-site construction method of the present invention are disclosed in detail below in conjunction with the embodiments shown in the accompanying drawings and the accompanying drawing numbers. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A schematic diagram of a tunnel structure after the construction method of the present invention is applied;

[0036] Figure 2 It is a schematic diagram of the structure of steel wire rope mesh of different specifications of the present invention;

[0037] Figure 3 It is a structural schematic diagram of the D-shaped buckle of the present invention;

[0038] Figure 4 It is a structural schematic diagram of the spring connector of the present invention;

[0039] Figure 5 This is a schematic diagram of the structure of the No. 03 protection net of the present invention from a top view;

[0040] Figure 6 for Figure 5 Enlarged view of part A.

[0041] Reference numerals

[0042] 1-collapse cavity, 2-open TBM, 3-anchor rod, 4-wire rope protection net, 41-01 wire rope protection net, 42-02 wire rope protection net, 43-03 wire rope protection net, 5-air bag, 51-inflation valve, 52-exhaust valve, 53-tubular exhaust channel, 531-water seepage spring steel pipe, 54-air pressure monitoring device, 6-D-type buckle, 61-U-shaped ring, 62-bolt, 63-nut, 7-spring connector, 71-hook end, 72-rope clamp end, 721-rope clamp end bolt, 73-spring middle section, 8-twisted hexagonal flexible net, 9-cable-stayed anchor cable, 91-decompression ring. DETAILED DESCRIPTION

[0043] The technical solutions in the embodiments of the present invention will be described clearly and completely below 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, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention. It should be noted that the embodiments in this application and the features in the embodiments can be combined with each other without conflict.

[0044] like Figure 1 As shown, the present invention discloses a protection system for a tunnel top collapse cavity, comprising: a flexible protection net, which is arranged in at least two rows from top to bottom inside the tunnel top collapse cavity 1, and the aperture of the lower flexible protection net is smaller than the aperture of the upper flexible protection net; the flexible protection net is connected to the inner side wall of the tunnel top collapse cavity 1; an airbag 5, which is located under the flexible protection net and is arranged corresponding to the bottom opening of the tunnel top collapse cavity 1; the airbag 5 is constructed to be able to conformally block the bottom opening of the tunnel top collapse cavity 1 after inflation to form a temporary support; the airbag 5 is also constructed to be able to inject concrete into the interior of the airbag 5 when the temporary support is inflated, so that the airbag 5 is converted from a temporary support to a permanent support.

[0045] The tunnel top collapse cavity protection system of the present invention uses a flexible protection net with layered settings and decreasing apertures to intercept falling rocks of different sizes to expand the protection range. The airbag 5 is inflated to seal the bottom opening of the collapse cavity 1 to form a temporary support, and concrete is injected later to convert it into a permanent support to enhance the bottom stability. Together, a comprehensive interception system is constructed to reduce protection blind spots, which not only enhances the protection capability, but also serves as a temporary support to bear the pressure of the rock and soil during construction, thereby improving construction safety. At the same time, the flexible protection net and the airbag 5 can be adjusted, installed and customized according to the shape, size and bottom inner wall conditions of the collapse cavity 1, respectively, to adapt to different working conditions to ensure the protection effect. After the airbag 5 is converted into a permanent support, it forms a whole with the surrounding rock mass, reducing the adverse effects on the lining, improving the support stability and durability, and ensuring the long-term safe use of the tunnel.

[0046] like Figure 1 and Figure 4 As shown, in one embodiment of the present invention, the flexible protective net is connected to the anchor rods 3 preset on the inner side wall of the tunnel top collapse cavity 1 through the spring connector 7. Specifically, the anchor rods 3 are arranged in a plum blossom shape, with a spacing of about 1 meter and a row spacing of 1-1.5 meters. The anchor rods 3 are surface pretreated for corrosion prevention, and the anchor head end is designed to be annular to facilitate cooperation with the spring connector 7.

[0047] The spring connector 7 is composed of a hook end 71, a rope clamp end 72 and a spring middle section 73. The C-shaped hook surface of the hook end 71 is installed with a rubber anti-skid sleeve, which can be tightly hooked on the annular end of the anchor rod 3 to increase the friction between the anchor rod 3; the inner diameter of the clamp hole of the rope clamp end 72 is 7mm, and a rubber anti-skid sleeve is also installed on the inner surface of the clamp hole to firmly clamp the edge wire rope of the flexible protective net and enhance the connection stability with the flexible protective net. The spring middle section 73 is a cylindrical helical tension spring with a bearing capacity of at least 200N and an allowable maximum elongation of 0.5 meters. This allows the spring connector 7 to be flexibly adjusted according to the actual distance between the edge of the flexible protective net and the inner wall of the collapsed cavity 1, ensuring that the flexible protective net can be stably fixed at a predetermined position inside the collapsed cavity 1.

[0048] In the above embodiment, the anchor rods 3 are arranged in a plum blossom shape, and the reasonable spacing and row spacing expand the distribution range of the support points of the flexible protective net, making it more evenly stressed. After anti-corrosion treatment, the service life is extended, and the protective net can be stably supported for a long time in a humid and complex tunnel environment to avoid failure of the protective net due to corrosion. The annular design of the anchor head end is precisely matched with the C-shaped hook of the hook end 71 of the spring connector 7, and the rubber anti-slip sleeve increases the friction to prevent the hook end 71 from falling off, ensuring a stable connection and reliable load transmission. The inner diameter of the clamping hole of the rope clamp end 72 is adapted to the steel wire rope of the protective net and the internal rubber anti-slip sleeve increases the friction, fixes the edge of the protective net to prevent shaking and displacement, and ensures the protective effect. At the same time, the spring middle section 73 of the spring connector 7 has a certain bearing capacity and elongation, which is convenient for construction personnel to easily adjust the position of the protective net according to the shape of the collapsed cavity 1 and the actual distance between the edge of the protective net and the inner wall, reduce the difficulty of installation, improve construction efficiency, and adapt to different site conditions of the collapsed cavity 1. The spring connector 7 and the anchor rod 3 work together to ensure the stable installation of the flexible protective net, so that it can effectively disperse the impact force when facing the impact of falling rocks of different sizes and speeds. The elasticity of the spring connector 7 can also buffer part of the impact force, reduce the damage to the protective net and the tunnel lining, and improve the safety and reliability of the entire protection system, providing reliable safety protection for tunnel construction personnel and subsequent operations.

[0049] like Figure 1 As shown, the airbag 5 includes a top surface portion, a bottom surface portion and a side surface portion connecting the top surface portion and the bottom surface portion and forming a circle on the side. An inflation port and an exhaust port are provided on the bottom surface portion of the airbag 5. A tubular exhaust channel 53 connected to the exhaust port and extending into the inner cavity of the airbag is provided in the airbag 5.

[0050] In the present invention, by providing a tubular exhaust passage 53 connected to the exhaust port and extending into the inner cavity of the airbag 5, the concrete injection can be effectively guaranteed, that is, when the concrete is injected from the inflation port, it will not be immediately discharged from the exhaust port. At the same time, the tubular exhaust passage 53 extending into the airbag 5 can meet the monitoring of the amount of concrete injected into the airbag 5, that is, when the concrete injected into the airbag 5 meets the required volume, it will enter the tubular exhaust passage 53 from the inner cavity of the airbag 5, and then overflow from the exhaust port; that is to say, when the concrete overflows from the exhaust port, it means that a sufficient amount of concrete has been injected into the airbag 5.

[0051] The material of the airbag 5 is rubber, with a thickness of 5mm. After inflation, the height of the airbag is 1m, and its side shape and size can be customized according to the actual situation of the bottom inner wall of the collapse cavity 1 in different projects. This customized design allows the airbag 5 to fit tightly at the bottom of the collapse cavity 1, effectively preventing tiny gravels from leaking through the flexible protective net and threatening the construction or operation area below the collapse cavity 1.

[0052] like Figure 1As shown, the tubular exhaust channel 53 is constructed in an L shape, including a transverse channel portion attached to the inner wall of the top surface portion of the airbag 5 and connected to the inner cavity of the airbag 5 at its end, and a vertical channel portion attached to the inner wall of the side portion of the airbag 5 and connected to the exhaust port at its end, and the end of the transverse channel portion is close to or located at the center of the airbag 5.

[0053] In the present invention, since the tubular exhaust passage 53 is constructed to extend in the airbag 5 along the inner wall of the side surface and the inner wall of the top surface, interference with the injection of concrete can be effectively prevented. Moreover, since the concrete rises from bottom to top in the inner cavity of the airbag 5 during the injection process, and the transverse channel portion of the tubular exhaust passage 53 is located on the inner wall of the top surface, the gas in the inner cavity of the airbag 5 can be effectively discharged to the outside during the concrete injection process, thereby balancing the air pressure inside and outside the airbag 5, thereby ensuring smooth injection of concrete; at the same time, since the transverse channel portion of the tubular exhaust passage 53 is located on the inner wall of the top surface, the injection amount of concrete can be effectively monitored without generating false alarms; in addition, since the end of the transverse channel portion of the tubular exhaust passage 53 is close to or located at the center of the airbag 5, the air pressure inside and outside the airbag 5 can be further effectively balanced to ensure smooth injection of concrete, while ensuring the accuracy of monitoring the injection amount of concrete.

[0054] like Figure 1 As shown, the tubular exhaust passage 53 is composed of a water-permeable spring steel tube 531 with an inner diameter of 100 mm, and is wrapped with a rubber shell on the outside and connected to the airbag 5. This structural design can prevent the problem that the exhaust passage 53 is squeezed and cannot be exhausted due to excessive air pressure inside the airbag 5, and on the other hand, its water-permeable function can prevent water accumulation inside the airbag 5 from affecting the performance and stability; at the same time, the rubber shell wrapped outside the water-permeable spring steel tube 531 not only protects the water-permeable spring steel tube 531, but is also connected to the inner wall of the airbag 5, so that the tubular exhaust passage 53 and the airbag 5 form a whole, thereby improving the stability and reliability of the airbag 5 structure.

[0055] like Figure 1 As shown, a fixed air pressure monitoring device 54 is installed at the top of the airbag 5 to monitor the air pressure in the airbag 5 in real time. An inflation valve 51 and an exhaust valve 52 are installed at the two openings of the airbag 5, respectively. The assembled airbag 5 is placed at the bottom of the collapsed cavity 1, and the exhaust valve 52 of the airbag 5 is ensured to be closed. The inflation valve 51 is connected to inflate, and the air pressure in the airbag 5 is monitored in real time according to the air pressure monitoring device 54 to ensure that the airbag 5 is inflated to a suitable pressure level, so that the airbag 5 can fit the bottom inner wall of the collapsed cavity 1 tightly.

[0056] When the tunnel construction passes through the collapsed cavity area smoothly, the foamed concrete is injected into the airbag 5. During the injection, the exhaust valve 52 is opened to release the air. When the foamed concrete flows out of the exhaust valve 52 evenly through the "L-shaped" tubular exhaust channel 53, the injection of the foamed concrete is stopped and the two valves of the airbag 5 are closed. At this point, the airbag 5 is converted from a temporary support to a permanent support.

[0057] like Figure 1 and Figure 2 As shown, the flexible protection net includes a first flexible protection net and a second flexible protection net, wherein the first flexible protection net is a wire rope protection net 4, which can be set from the top of the collapsed cavity 1 and multiple layers from top to bottom.

[0058] The wire rope mesh is made of high-strength galvanized steel core wire rope with a nominal diameter of 8mm. It is woven with diamond meshes with a side length of 80×80mm. The wire rope protection net 4 is made of multiple prefabricated wire rope meshes of different specifications. There are 6 specifications for a single mesh, namely 300×300mm, 600×600mm, 1200×1200mm small-size meshes and 1800×1800mm, 2400×2400mm, 3600×3600mm large-size meshes.

[0059] like Figure 2 and Figure 3 As shown, when splicing the wire rope mesh, follow the principle of large-sized mesh at the bottom and small-sized mesh at the top, splicing from the center to the periphery, and the minimum overlap width is not less than one mesh distance. The meshes are connected by a D-shaped buckle 6, which consists of a U-shaped ring 61 and a set of bolt fasteners (including bolts 62 and nuts 63). When connecting, first align the two wire ropes and insert them into the U-shaped ring 61, then pass the bolts 62 through the circular holes at both ends of the U-shaped ring 61, and tighten them with nuts 63. At least one D-shaped buckle 6 is installed for each overlapping mesh, and the distance between each two buckles is at least 50mm.

[0060] like Figure 1 and Figure 2 As shown, the second flexible protection net is a double-twisted hexagonal flexible net 8, which is made of A-grade galvanized steel wire, with a steel wire diameter of 3mm and a hexagonal mesh side length of 40mm. The double-twisted hexagonal flexible net 8 is laid and hung above the last wire rope protection net 4, overlapping the edge of the wire rope protection net 4 to 15 cm below, and works in conjunction with the first flexible protection net (wire rope protection net 4) to effectively intercept falling rocks of different sizes, providing reliable safety protection for tunnel construction and subsequent operations.

[0061] In the above embodiment, the first flexible protection net (wire rope protection net 4) is arranged in multiple layers from top to bottom, and cooperates with the second flexible protection net (twisted hexagonal flexible net 8) to construct a multi-level protection system. The large diamond-shaped mesh of the wire rope protection net 4 first intercepts large-sized fallen rocks, and the small mesh of the twisted hexagonal flexible net 8 captures missed small-diameter fallen rocks, which jointly widens the range of protected fallen rocks and reduces blind spots, providing reliable and safe protection for tunnel construction and subsequent operations. At the same time, the wire rope protection net 4 adopts high-strength galvanic coated steel core steel wire rope and the twisted hexagonal flexible net 8 adopts Class A galvanic coated steel wire. The good corrosion resistance enables it to adapt to the humid and complex environment in the tunnel, extending the service life of the protection net. , reduce maintenance costs, ensure long-term and stable operation of the protection system, and the wire rope protection net 4 is spliced ​​by 6 prefabricated meshes of different specifications. The mesh combination can be flexibly selected according to the actual collapse cavity 1 to improve adaptability. Specific principles are followed during splicing and connected with D-shaped buckles 6. Standard installation ensures a stable connection and enhances the overall strength of the protection net to effectively withstand the impact of falling rocks and ensure the protection effect. In addition, the twisted hexagonal flexible net 8 is laid on top of the last wire rope protection net 4 and overlaps the edge. This layout makes the two layers of protection nets closely combined, further enhancing the interception ability of falling rocks of different sizes, optimizing the overall performance of the protection system, and effectively preventing the damage to the tunnel caused by falling rocks, ensuring the safety of construction personnel and the stability of the tunnel structure.

[0062] like Figure 1 and Figure 5 As shown, when the span of the first flexible protective net (wire rope protective net 4) exceeds 8m, additional reinforcement measures need to be taken to ensure the stability and protective effect of the protective net. Four nodes are selected at the four directions of the protective net, and inclined anchor cables 9 are installed at these four nodes for reinforcement. One end of each inclined anchor cable 9 is tied to a suitable node of the wire rope protective net 4, and the other end is anchored at an angle of 30° upward to the annular end of the anchor rod 3 above the protective net. The reason for choosing an anchoring angle of 30° is that it has been verified by mechanical calculations and actual engineering experience. This angle can ensure that the inclined anchor cable 9 effectively disperses the tension on the protective net while maximizing the use of the anchoring force of the anchor rod 3 to enhance the stability of the overall structure.

[0063] During the installation of the inclined anchor cable 9, the construction personnel must operate in strict accordance with the design requirements. First, accurately measure and determine the anchoring position and tying node of the inclined anchor cable 9 to ensure that the installation angle and length of the inclined anchor cable 9 meet the design standards. When tying the wire rope protection net 4, use professional tying tools and materials to ensure that the connection is firm and reliable to prevent loosening or falling off during use. For operations anchored at the annular end of the anchor rod 3, the anchor rod 3 must be checked to ensure that the anchoring force of the anchor rod 3 meets the requirements. At the same time, a reliable anchoring method, such as welding or high-strength bolt connection, is used to ensure that the connection between the inclined anchor cable 9 and the anchor rod 3 is tight and can effectively transmit tension.

[0064] In the above embodiment, by taking reinforcement measures for the first flexible protective net when the span exceeds 8m, the protective capability of the protective net in the case of large span can be significantly improved, ensuring that during the tunnel construction process, even in the face of a complex collapse cavity 1 environment, it can effectively intercept falling rocks and ensure the safety of construction workers and the smooth progress of construction.

[0065] like Figure 1 As shown, in order to further optimize the protection effect, each inclined anchor cable 9 is also equipped with a pressure relief ring 91. The function of the pressure relief ring 91 is to buffer the instantaneous tension exerted on the inclined anchor cable 9 when the falling rock impacts the protection net. When a large impact force acts on the protection net, the pressure relief ring 91 can consume part of the energy through its own deformation, avoiding the inclined anchor cable 9 from breaking or loosening due to excessive instantaneous tension, thereby effectively extending the service life of the inclined anchor cable 9 and ensuring the reliability of the protection net during long-term use.

[0066] In the embodiment of the present invention, the flexible protective net and the airbag 5 are both manufactured on-site at the construction site based on the three-dimensional structural data of the collapsed cavity 1 on the top of the tunnel to ensure precise fit with the collapsed cavity 1 and improve the protective effect.

[0067] like Figure 1-Figure 6 As shown, the present invention also discloses an on-site construction method for realizing the protection system for the tunnel top collapse cavity disclosed by the present invention, comprising the following steps: step S0, prefabricating a plurality of steel wire rope meshes of different specifications; step S1, cleaning the cavity area of ​​the tunnel top collapse cavity 1 found during tunnel excavation and then spraying anchor support; step S2, scanning the tunnel top collapse cavity 1, obtaining the three-dimensional structure data of the tunnel top collapse cavity 1, and then constructing a collapse cavity model according to the three-dimensional structure data; step S3, on-site manufacturing of a flexible protection net and a protective net that can be inflated and connected to the tunnel top based on the data of the collapse cavity model; step S4, preparing a protective net on-site based on the data of the collapse cavity model; step S5, preparing a protective net that can be inflated and connected to the tunnel top after the collapse cavity is inflated; step S6, preparing a protective net on-site based on the data of the collapse cavity model; step S7, preparing a protective net that can be inflated and connected to the tunnel top after the collapse cavity is inflated; step S8, preparing a protective net on-site based on the data of the collapse cavity model; step S9, preparing a protective net that can be inflated and connected to the tunnel top after the collapse cavity is inflated; step S10, preparing a protective net on-site based on the data of the collapse cavity model; step S11, preparing a protective net that can be inflated and connected to the tunnel top after the collapse cavity is inflated; step S12, preparing a protective net on-site based on the data of the collapse cavity model; step S13, preparing a protective net that can be inflated and connected to the tunnel top after the collapse cavity is inflated; step S14, preparing a protective net on-site based on the data of the collapse cavity model; step S15, preparing a protective net that can be inflated and connected to the tunnel top after the collapse cavity is inflated; step S16, preparing a protective net on-site based on the data of the collapse cavity model; step S17, preparing a protective net that can The bottom opening of the collapsed cavity 1 is formed into an airbag 5 that fits conformably; S4, at least one flexible protective net is arranged from top to bottom inside the collapsed cavity 1 at the top of the tunnel, and the flexible protective net is connected to the inner wall of the collapsed cavity 1; S5, the airbag 5 is installed under the flexible protective net and corresponding to the bottom opening of the collapsed cavity 1 at the top of the tunnel, and it is inflated until it forms a fit with the surrounding side walls of the bottom opening of the collapsed cavity 1 at the top of the tunnel; S6, when the tunnel excavation construction passes the position of the collapsed cavity 1 at the top of the tunnel, concrete is injected into the airbag 5 to convert the airbag 5 from a temporary support to a permanent support.

[0068] In a specific embodiment, in step S0, a high-strength galvanic coated steel core steel wire rope is selected to make a steel wire rope mesh, the nominal diameter of the steel wire rope is 8mm, and a diamond mesh is woven, and the side length of the diamond mesh is 80×80mm. The mesh size is divided into 6 specifications, namely 300×300mm, 600×600mm, 1200×1200mm small-size meshes and 1800×1800mm, 2400×2400mm, 3600×3600mm large-size meshes. This material and specification design enables the steel wire rope mesh to have high strength and good toughness, and can effectively intercept large-size falling rocks. At the same time, multi-specification meshes are convenient for subsequent flexible splicing according to the actual situation of the collapsed cavity 1. Multi-specification steel wire rope meshes can be prefabricated off-site, reducing on-site processing time and difficulty, and improving construction efficiency. At the same time, high-strength and corrosion-resistant materials adapt to the complex environment of the tunnel, extend the service life of the protective net, reduce replacement costs, and ensure long-term protection effects. This not only reduces construction interruptions caused by frequent replacement of protective nets, but also reduces safety risks during the construction process, ensuring that construction can proceed continuously and stably.

[0069] In step S1, after the top collapsed cavity 1 is found during tunnel excavation, the open TBM2 excavation is stopped immediately, and the floating dust, loose stones and dangerous rocks on the inner wall of the collapsed cavity 1 are carefully cleaned to prevent these debris from affecting the stability and reliability of subsequent support and protection work. Reasonably determine the parameters such as the drilling position and depth of the anchor rod 3, and arrange the anchor rod in a plum blossom shape to ensure that the spacing of the anchor rod 3 is controlled at about 1 meter, and the upper and lower row spacing is between 1-1.5 meters. After the drilling is completed, the anchor rod 3 is driven into the drilled hole for anchoring. The anchor rod 3 arranged in a plum blossom shape can provide a stable installation positioning point for the subsequent high-strength protection net to ensure that the protection net is firmly installed. According to the geological conditions of the surrounding rock of the collapsed cavity 1, spray concrete is configured, and sprayed from the inner wall of the collapsed cavity 1 from bottom to top. During the spraying process, the spraying angle and distance are adjusted at all times to ensure that the concrete is evenly covered and closely combined with the surrounding rock. Spray concrete can seal and reinforce the surrounding rock, improve the stability of the surrounding rock, provide a stable foundation for the entire protection system, and reduce the risk of surrounding rock collapse again during construction.

[0070] In step S2, after the surrounding rock is initially stabilized, the construction personnel enter the collapsed cavity 1, set up a three-dimensional laser scanner to perform a comprehensive scan of the collapsed cavity 1, and obtain its accurate three-dimensional structural data. These data contain key information such as the shape, size, and spatial position of the collapsed cavity 1. According to the three-dimensional structural data obtained by scanning, a model of the collapsed cavity 1 is constructed. This model is an important basis for the subsequent production of the protective net and the airbag 5, which can ensure that the protective system is highly adapted to the actual situation of the collapsed cavity 1.

[0071] In step S3, based on the data of the collapsed cavity 1 model, the wire rope protection net 4 is spliced ​​on site. The wire rope protection net 4 is spliced ​​from a plurality of prefabricated wire rope meshes of different specifications. When splicing, it is spliced ​​from the center to the periphery according to the principle that the large-sized mesh is at the bottom and the small-sized mesh is at the top, and the minimum overlap width is not less than one mesh distance. The meshes are connected by a D-shaped buckle 6, which is composed of a U-shaped ring 61 and a group of bolt fasteners. When connecting, first align the two steel wires and insert them into the U-shaped ring 61, and then pass the bolts 62 through the circular holes at both ends of the U-shaped ring 61, and tighten them with nuts 63. At least one D-shaped buckle 6 is installed on each overlapping mesh, and each two buckles are at least 50 mm apart. After the wire rope protection net 4 is installed, a twisted hexagonal flexible net 8 is laid on top of it to form a second flexible protection net. The double-twisted hexagonal flexible net 8 is made of A-grade galvanized steel wire, the diameter of the steel wire is 3mm, and the side length of the hexagonal mesh is 40mm. In this combined flexible protective net, the wire rope protective net 4 can intercept large-sized falling rocks, and the double-twisted hexagonal flexible net 8 can intercept small-diameter falling rocks and further disperse the impact energy. According to the inner wall shape and size data within the one-meter height range at the bottom of the collapsed cavity 1, the rubber airbag 5 is made. The thickness of the airbag 5 is 5mm, and the height can reach 1 meter after inflation. Its side shape and size can be customized according to the actual situation at the bottom of the collapsed cavity 1. There are two openings at the bottom of the airbag 5, namely the inflation port and the exhaust port, and an "L-shaped" tubular exhaust channel 53 is arranged inside to connect to the exhaust port. The exhaust channel 53 is composed of a water-permeable spring steel pipe 531 with an inner diameter of 100mm, and a layer of rubber shell is wrapped outside to connect to the airbag 5, which can prevent the tubular exhaust channel 53 from being squeezed and unable to exhaust when the air pressure inside the airbag 5 is too high.

[0072] In step S4, flexible protective nets are installed from top to bottom in the tunnel top collapse cavity 1. Taking the installation of No. 01 steel wire rope protective net 41, No. 02 steel wire rope protective net 42, and No. 03 steel wire rope protective net 43 as an example, each protective net is connected to the ring head anchor rod 3 on the inner wall of the collapse cavity 1 through a spring connector 7. The spring connector 7 is composed of a hook end 71, a rope clamp end 72, and a spring middle section 73. The C-shaped hook of the hook end 71 is hung on the ring end of the anchor rod 3, and the rope clamp end 72 clamps the edge wire rope of the protective net. By continuously adjusting the position of the rope clamp end 72 on the wire rope and utilizing the stretching of the spring middle section 73, the entire protective net reaches the appropriate position specified inside the collapse cavity 1, and then the bolt 721 of the rope clamp end 72 is tightened to fix it. The spring bearing capacity of the spring connector 7 is at least 200N, the maximum allowable elongation is 0.5 meters, and the C-shaped hook surface of the hook end 71 and the inner surface of the spring clamp hole of the rope clamp end 72 are installed with rubber anti-slip sleeves, which can increase the friction and enhance the stability of the protective net. If the span of the protective net is greater than 8 meters, four nodes are selected at the four directions of the protective net, and four inclined anchor cables 9 are installed for reinforcement. One end of each inclined anchor cable 9 is tied to a suitable node of the wire rope net, and the other end is anchored at an angle of 30° upward to the annular end of the anchor rod 3 above the protective net. Each inclined anchor cable 9 is equipped with a pressure relief ring 91 to further enhance the stability of the protective net and prevent it from being deformed or displaced too much when subjected to force.

[0073] In step S5, the air pressure monitoring device 54 is installed and fixed at the top area inside the airbag 5 to monitor the air pressure inside the airbag 5 in real time. An inflation valve 51 is installed at the inflation port at the bottom of the airbag 5, and an exhaust valve 52 is installed at the exhaust port. The assembled airbag 5 is placed at the bottom of the collapsed cavity 1, ensuring that the airbag exhaust valve 52 is closed, and the inflation valve 51 is connected for inflation. During the inflation process, the inflation volume is controlled according to the air pressure data inside the airbag 5 monitored in real time by the air pressure monitoring device 54 to ensure that the airbag 5 is inflated to a suitable pressure level, so that the airbag 5 fits tightly around the open bottom sidewall of the collapsed cavity 1 at the top of the tunnel to prevent small gravel from invading the outer contour of the tunnel lining.

[0074] In step S6, when the tunnel excavation construction passes smoothly through the position of the collapsed cavity 1 at the top of the tunnel, the exhaust valve 52 of the airbag 5 is opened to release air, and at the same time, foam concrete is injected into the airbag 5 through the inflation valve 51. When the foam concrete flows out of the exhaust valve 52 evenly through the "L-shaped" tubular exhaust channel 53, the injection of foam concrete is stopped, and finally the two valves of the airbag 5 are closed. At this time, the airbag 5 is converted from a temporary support to a permanent support, which enhances the stability of the bottom of the collapsed cavity 1.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A protection system for tunnel top collapse cavity, characterized in that: include: At least two flexible protective nets are arranged from top to bottom inside the tunnel top collapse cavity (1), and the aperture of the lower flexible protective net is smaller than the aperture of the upper flexible protective net; The flexible protective net is connected to the inner side wall of the collapsed cavity (1) at the top of the tunnel; An air bag (5) is located below the flexible protective net and is arranged corresponding to the bottom opening of the collapsed cavity (1) at the top of the tunnel; The airbag (5) is constructed to be able to conformally seal the bottom opening of the collapsed cavity (1) at the top of the tunnel after being inflated, so as to form a temporary support; The airbag (5) is also constructed so that concrete can be injected into the interior of the airbag when the temporary support is inflated, so that the airbag (5) is converted from a temporary support to a permanent support.

2. The protection system according to claim 1, characterized in that: The airbag (5) comprises a top face portion, a bottom face portion and a side face portion connecting the top face portion and the bottom face portion and forming a circle on the side; an inflation port and an exhaust port are arranged on the bottom face portion of the airbag (5); and a tubular exhaust passage (53) is arranged in the airbag (5) and is connected to the exhaust port and extends into the inner cavity of the airbag (5).

3. The protection system according to claim 2, characterized in that: The tubular exhaust passage (53) is constructed in an L-shape, comprising a transverse passage portion attached to the inner wall of the top surface portion of the airbag (5) and connected to the inner cavity of the airbag (5) at its end, and a vertical passage portion attached to the inner wall of the side surface portion of the airbag (5) and connected to the exhaust port at its end, wherein the end of the transverse passage portion of the tubular exhaust passage (53) is close to or located at the center of the airbag (5).

4. The protection system according to claim 3, characterized in that: The tubular exhaust passage (53) comprises a water-permeable spring steel tube (531) located inside and a rubber shell wrapped around the water-permeable spring steel tube (531), wherein the rubber shell is connected to the inner wall of the airbag (5).

5. The protection system according to claim 4, characterized in that: The flexible protection net comprises a first flexible protection net and a second flexible protection net arranged from top to bottom, wherein the first flexible protection net is constructed as a steel wire rope protection net (4), and the second flexible protection net is constructed as a double-twisted hexagonal flexible net (8) laid on the steel wire rope protection net (4).

6. The protection system according to claim 5, characterized in that: The steel wire rope protection net (4) is made of galvanically coated steel wire rope and is woven in a diamond mesh weaving manner; the twisted hexagonal flexible net (8) is woven from grade A galvanically coated steel wire.

7. The protection system according to claim 6, characterized in that: Each steel wire rope protection net (4) is formed by splicing a plurality of prefabricated steel wire rope mesh pieces of different specifications.

8. The protection system according to any one of claims 1 to 7, characterized in that: The flexible protective net and the airbag (5) are both manufactured on-site at the construction site based on the three-dimensional structural data of the collapsed cavity (1) at the top of the tunnel.

9. An on-site construction method for realizing the protection system for tunnel top collapse cavity according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1, cleaning the cavity area of ​​the collapsed cavity (1) at the top of the tunnel found during tunnel excavation and then performing spray anchor support; S2, scanning the collapsed cavity (1) at the top of the tunnel to obtain three-dimensional structural data of the collapsed cavity (1) at the top of the tunnel, and then constructing a collapsed cavity model according to the three-dimensional structural data; S3, based on the data of the collapsed cavity model, a flexible protective net and an air bag (5) which can form a conformable fit with the bottom opening of the collapsed cavity (1) at the top of the tunnel after being inflated are manufactured on site; S4, arranging at least one flexible protection net from top to bottom inside the collapsed cavity (1) at the top of the tunnel, and connecting the flexible protection net to the inner wall of the collapsed cavity (1); S5, installing the airbag (5) below the flexible protective net and at the bottom opening of the collapsed cavity (1) at the top of the tunnel, and inflating it until it fits with the surrounding side walls of the bottom opening of the collapsed cavity (1) at the top of the tunnel; S6, when the tunnel excavation construction passes the position of the collapsed cavity (1) at the top of the tunnel, concrete is injected into the airbag (5) to convert the airbag (5) from a temporary support to a permanent support.

10. The on-site application method according to claim 9, characterized in that: In step S4, two flexible protection nets are arranged, including a first flexible protection net and a second flexible protection net from top to bottom, wherein the first flexible protection net is a steel wire rope protection net (4), and the second flexible protection net is a double-twisted hexagonal flexible net (8) laid on the steel wire rope protection net (4); Before step S1, the method further includes step S0 of prefabricating a plurality of steel wire rope meshes of different specifications; In step S3, the steel wire rope protection net (4) is formed on site by splicing a plurality of prefabricated steel wire rope mesh sheets of different specifications based on the data of the collapsed cavity model.

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