A tunnel water conduction structure and reverse construction method applicable to large karst channels

Abstract

The present invention discloses a tunnel water diversion structure and a reverse construction method applicable to large karst channels, including a water-rich karst channel distributed horizontally or obliquely relative to the tunnel. The water-rich karst channel intersects with the tunnel and is truncated by the tunnel into a left channel section and a right channel section. A prefabricated spliced inverted siphon water conduit culvert structure for connecting the left channel section and the right channel section to each other is provided at the bottom of the tunnel. During construction, the excavation of the lower space of the tunnel is first carried out, and then the construction of structures such as the inverted siphon water conduit culvert is carried out. Subsequently, based on the lower structure of the tunnel, the excavation and support construction of the upper space of the tunnel are carried out. The structure of the present invention is simple and reliable, with good drainage performance, enabling the entire groundwater diversion process not to enter the tunnel, neither increasing the drainage pressure of the tunnel drainage structure nor having the operation risk of groundwater flowing in the tunnel. Moreover, by adopting the reverse construction method, the safety of tunnel construction and the reliability of the structure can be effectively guaranteed, with high construction safety and good economy.

Description

Technical Field

[0001] The present invention relates to a tunnel water guiding structure and a reverse construction method applicable to large karst channels, and belongs to the technical field of tunnel drainage facilities. Background Art

[0002] Under the action of chemical corrosion of karst water, a large number of underground karst structures such as karst caves and karst channels are developed inside soluble rock formations. When a tunnel crosses a soluble rock formation, it may intersect with an underground karst channel in space. At this time, in order to ensure the smoothness of the tunnel line, only the original karst channel can be blocked. It should be noted that if there is groundwater in the karst channel, blocking the karst channel also blocks the groundwater discharge channel, which will inevitably lead to the accumulation of groundwater on the top of the tunnel lining. The conventional countermeasure is to drain the groundwater into the tunnel through a drainage system, and then drain the water into the roadbed drainage system outside the tunnel entrance through an in-tunnel drainage structure such as a central drainage ditch. However, the entry of a large amount of groundwater into the tunnel, on the one hand, greatly increases the drainage pressure of the tunnel drainage system, and there may be problems of groundwater blockage and overflow in the tunnel during heavy rain; on the other hand, the groundwater in the karst channel is discharged outside the mountain through the tunnel, which will inevitably change the water environment state in the area connected by the karst channel, and may thus have a certain adverse impact on the natural environment or the lives of local residents. It can be seen that the existing treatment measures for large-scale discharge of karst groundwater through the tunnel drainage system have certain drawbacks and there is a large room for improvement.

[0003] In addition, the distribution of karst channels has characteristics such as randomness, diversity, and complexity. Some intersect the tunnel vertically, some horizontally, and the sizes of the karst caves also vary greatly. When the tunnel intersects with a horizontal or inclined karst channel, on the one hand, it is extremely difficult to drain the water in the karst channel, and on the other hand, it is difficult to ensure the construction safety and structural reliability of the tunnel. Especially when the tunnel intersects with a large karst channel, there will be a relatively long intersection section, which not only makes the stability of the intersection section poor, but also increases the construction range of the drainage structure, resulting in difficulties in ensuring construction safety, the waterproof and drainage reliability of the tunnel structure, etc. Therefore, it is of great practical significance to study a tunnel water guiding structure and a reverse construction method applicable to large karst channels. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a tunnel water guiding structure and a reverse construction method applicable to large karst channels, which can overcome the deficiencies of the prior art.

[0005] The purpose of the present invention is achieved by the following technical solutions:

[0006] A tunnel water diversion structure applicable to large karst channels, which includes water-rich karst channels distributed transversely or obliquely relative to the tunnel. The water-rich karst channels intersect with the tunnel and are truncated by the tunnel into a left channel section and a right channel section. A prefabricated spliced inverted siphon culvert structure for connecting the left channel section and the right channel section to each other is provided at the bottom of the tunnel.

[0007] The aforementioned inverted siphon culvert structure includes a transverse culvert arranged horizontally at the bottom of the tunnel. One end of the transverse culvert is connected to the left channel section through a high-level shaft, and the other end is connected to the right channel section through a low-level shaft. The high-level shaft, the transverse culvert, and the low-level shaft are all assembled from prefabricated structures, and their splicing joints are connected by a notch structure buckle. The outside of the joint is wrapped with an asphalt felt waterproof layer.

[0008] Drainage corrugated steel is provided on the outside of the secondary lining of the tunnel, and the drainage corrugated steel is connected to the drainage ditch in the invert of the tunnel through a transverse drain pipe.

[0009] A tunnel lower structure is provided at the inner bottom of the aforementioned inverted siphon culvert structure; and a waterproof concrete isolation structure is filled between the inner top of the inverted siphon culvert structure and the drainage corrugated steel.

[0010] Sealing templates are respectively provided at the ends of the aforementioned left channel section and right channel section close to the tunnel.

[0011] Shotcrete protective layers, anchor mesh shotcrete layers or grouting reinforcement layers are provided on the outside of the aforementioned inverted siphon culvert structure, the upper wall surface of the water-rich karst channel and the rock surface of the tunnel arch.

[0012] A reverse construction method for a tunnel water diversion structure applicable to large karst channels, which first excavates the lower space of the tunnel, then constructs structures such as inverted siphon culverts, and then, based on the tunnel lower structure, excavates and supports the upper space of the tunnel.

[0013] The aforementioned reverse construction method, the specific construction steps include:

[0014] S0. When the transverse water-rich karst channel is revealed during tunnel excavation, suspend the excavation construction of the upper bench, and then let the middle and lower benches of the tunnel catch up in turn, and then complete the initial support, invert and invert filling construction of the entire normal section before the intersection section of the tunnel and the transverse water-rich karst channel, so that the tunnel support structure in the front section of the intersection section is completely closed into a ring;

[0015] S1. Temporarily block the transverse water-rich karst channel, and use drainage equipment to temporarily drain the accumulated water inside the karst channel;

[0016] S2. Carry out the construction of the lower space of the tunnel in the intersection section with the karst channel:

[0017] (2.1) First, the sprayed concrete protective layer is constructed on the upper wall of the water-rich karst channel, and then the lower part of the tunnel is excavated by mechanical trenching and expansion on the left and right sides. After the excavation is completed, the sprayed concrete protective layer is immediately constructed on the rock surface to ensure the stability of the excavation surface and level the excavation surface;

[0018] (2.2) Assemble the prefabricated components of the inverted siphon water diversion structure in the excavated space of the surrounding rock below the tunnel: first construct the transverse culvert at the bottom of the excavated pit, then construct the connection between the high-level shaft, the low-level shaft and the transverse culvert, and then connect the high-level shaft to the designed elevation in sections according to the notch docking method; wrap the spliced ​​joints of the prefabricated components with an asphalt felt waterproof layer;

[0019] (2.3) The tunnel substructure is constructed by cast-in-place method on the inner side of the inverted siphon structure, followed by the infill and drainage ditch inside the invert;

[0020] (2.4) After the concrete has formed strength, fill the buffer layer with construction slag on the concrete surface;

[0021] S3, excavate the surrounding rock on the upper part of the horizontal water-rich karst channel, immediately construct a shotcrete protective layer on the surrounding rock surface after excavation, and then remove the cave slag and backfill the buffer layer;

[0022] S4. Set up karst channel blocking templates at the intersections of the left channel section, the right channel section and the tunnel respectively;

[0023] S5. Install drainage corrugated steel according to the assembly process;

[0024] S6. Construct waterproof concrete isolation structure in the gap between high-position shaft, low-position shaft, drainage corrugated steel and karst channel blocking formwork according to cast-in-place technology, and perform back grouting treatment on the corrugated steel of the arch;

[0025] S7. Construct the drainage structure inside the drainage corrugated steel, and then construct the secondary lining of the tunnel, and set a transverse drainage pipe at the foot of the side wall of the secondary lining of the tunnel, which is interconnected with the drainage corrugated steel and the drainage ditch; then carry out tunnel excavation construction according to normal construction procedures, and after the tunnel is penetrated, carry out the construction of the remaining structures in the tunnel, thus completing the construction of all tunnel structures in the section where the inverted siphon water diversion structure is located.

[0026] In the above step (2.2), each time the shaft is connected to a higher section, it is promptly fixed with shotcrete to avoid the risk of instability and collapse caused by the high and low shafts being exposed to the air on one side during the connection process.

[0027] In the above step (2.4), the thickness of the slag backfill buffer layer is not less than 0.5m to prevent the falling rocks caused by the blasting of the tunnel arch from damaging the tunnel structure.

[0028] Compared with the prior art, a tunnel water diversion structure and a reverse construction method applicable to large karst channels disclosed by the present invention include a water-rich karst channel distributed transversely or obliquely relative to the tunnel. The water-rich karst channel intersects with the tunnel and is truncated by the tunnel into a left channel section and a right channel section. A siphon water diversion culvert structure for connecting the left channel section and the right channel section to each other is provided at the bottom of the tunnel. During construction, the excavation of the lower space of the tunnel is carried out first, and then the construction of structures such as the siphon water diversion culvert is carried out. Thereafter, based on the lower structure of the tunnel, the excavation and support construction of the upper space of the tunnel are carried out. By arranging interconnected drainage channels on both sides and the bottom of the tunnel to form a siphon water diversion structure, the present invention can divert the water inside the karst channel on one side of the tunnel lining structure to the karst channel on the other side of the tunnel, thereby reconnecting the transverse karst channel blocked by the tunnel, effectively reducing the impact of tunnel construction on the original ecological environment, and being applicable to the tunnel drainage design in karst areas. At the same time, affected by the excavation construction of the lower part of the siphon water diversion structure, the conventional forward construction method of "constructing the arch part of the tunnel first and then the lower part of the tunnel" has the defect that the arch support is suspended for a long time, and thus the stability of the surrounding rock of the arch cannot be effectively guaranteed. However, by adopting the reverse construction method of "constructing the lower part of the tunnel first and then the upper part of the tunnel", the construction safety of the tunnel structure in the section where the siphon water diversion structure is located can be effectively ensured, and it is applicable to the situation where the tunnel intersects with the transverse water-rich karst channel. In addition, in view of the problems such as huge water accumulation and difficult drainage and poor tunnel stability when the tunnel intersects with the large karst channel, the present invention adopts a tunnel internal waterproof and drainage system composed of a drainage corrugated steel and a drainage ditch, which is not only efficient and convenient in construction, but also has good waterproof performance and drainage effect, and can effectively improve the overall impermeability of the tunnel; moreover, it can also improve the support strength in the tunnel, improve the overall structural stability of the tunnel, facilitate the smooth construction of the subsequent waterproof concrete isolation structure and the secondary lining, and improve the construction safety of the tunnel and the waterproof and drainage reliability of the tunnel structure.

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

[0030] (1) The structure of the present invention is simple and reliable, and has good drainage performance. By arranging interconnected siphon water diversion structures on both sides and the bottom of the tunnel, the karst water blocking one side of the tunnel lining structure can be diverted to the karst channel on the other side of the tunnel through the above siphon water diversion structure. Compared with the conventional measures of introducing groundwater into the tunnel, the whole diversion process of groundwater does not enter the tunnel, neither increasing the drainage pressure of the tunnel drainage structure nor having the operation risk of groundwater flowing in the tunnel.

[0031] (2) The inventive concept of the present invention is ingenious. Through the inverted siphon water conduction structure, it can reconnect the blocked large karst channels, ensuring the smooth flow of water in the karst channels, reducing the adverse effects of tunnel construction on the surrounding natural environment and the domestic water use of local residents. Moreover, the inverted siphon water conduction structure is composed of prefabricated parts spliced together, which is convenient for manufacturing and assembling, has high construction efficiency, and low dragging cost;

[0032] (3) The present invention makes full use of the relatively stable characteristics of the karst channel wall and innovatively adopts the reverse construction method of "constructing the lower part of the tunnel first and then the upper part of the tunnel", which can avoid the instability and collapse accidents of the surrounding rock and support structure of the upper part of the tunnel under the disturbance of the lower part excavation, thereby reducing the potential construction risks when the tunnel intersects with large karst channels in a long section; at the same time, the above reverse construction method can effectively avoid the adverse construction conditions brought by the "small upper part and large lower part" of the tunnel excavation section, and can effectively guarantee the construction safety and structural reliability of the tunnel;

[0033] (4) The present invention adopts the construction process from bottom to top. The lower structure of the tunnel is formed by one-time in-situ casting of concrete, and the upper structure of the tunnel uses drainage-type corrugated steel for assembly construction instead of the conventional initial support I-beam, greatly improving the construction efficiency; in addition, compared with the I-beam, the drainage-type corrugated steel structure has better waterproof and drainage performance and overall structural stability, and the corrugated steel can be directly used as the side formwork of the in-situ cast concrete, which is beneficial to the construction of the waterproof concrete isolation structure.

[0034] Other advantages, objectives and features of the present invention will be described to some extent in the subsequent specification, and to some extent, will be obvious to those skilled in the art based on the study of the following text, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the following specification. Brief Description of the Drawings

[0035] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the drawings, where:

[0036] Figure 1 is the construction process of the present invention Figure I ;

[0037] Figure 2 is the construction process of the present invention Figure II ;

[0038] Figure 3 is the construction process of the present invention Figure III ;

[0039] Figure 4 is the construction process of the present invention Figure IV ;

[0040] Figure 5 is the construction process of the present invention Figure V ;

[0041] Figure 6 is the construction process of the present invention Figure VI ;

[0042] Figure 7 is the construction process of the present invention Figure VII ;

[0043] Figure 8 is the construction process of the present invention Figure VIII ;

[0044] Figure 9 is the construction process of the present invention Figure IX ;

[0045] Figure 10 is the construction process of the present invention Figure X 。 Specific embodiments

[0046] The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the preferred embodiments are only for illustrating the present invention, rather than limiting the protection scope of the present invention.

[0047] As Figures 1 - 10 shown, a tunnel water diversion structure applicable to large karst channels includes a water-rich karst channel 1 distributed transversely or obliquely relative to the tunnel. The water-rich karst channel 1 intersects with the tunnel and is truncated by the tunnel into a left channel section 1-1 and a right channel section 1-2. A siphon culvert structure is provided at the bottom of the tunnel to connect the left channel section 1-1 and the right channel section 1-2 to each other.

[0048] The siphon culvert structure includes a transverse culvert 4 arranged horizontally at the bottom of the tunnel. One end of the transverse culvert 4 is connected to the left channel section 1-1 through a high-level shaft 3, and the other end is connected to the right channel section 1-2 through a low-level shaft 5. The high-level shaft 3, the transverse culvert 4, and the low-level shaft 5 are all prefabricated structures assembled together, and their splicing joints are connected by a notch structure buckle, and the outside of the joint is wrapped with an asphalt felt waterproof layer.

[0049] A drainage corrugated steel 8 is provided outside the secondary lining 11 of the tunnel, and the drainage corrugated steel 8 is connected to the drainage ditch 7 in the invert of the tunnel. The accumulated water in the upper part of the tunnel can pass through. The drainage corrugated steel 8 can adopt a tunnel drainage corrugated steel primary support structure disclosed in Patent No. 202121324965.8, which can improve the construction speed through an assembled process, and increasing the drainage corrugated steel 8 can effectively improve the waterproof and drainage performance and the overall structural stability of the tunnel structure in the section intersecting with the large karst channel.

[0050] At the inner bottom of the inverted siphon aqueduct culvert structure, there is a tunnel lower structure 6. The tunnel lower structure 6 is the bearing foundation of the tunnel, used to provide the lower support of the tunnel, and has high structural reliability.

[0051] Between the inner top of the inverted siphon aqueduct culvert structure and the drainage corrugated steel 8, there is a waterproof concrete isolation structure 10 filled. Specifically, the waterproof concrete isolation structure 10 is arranged at the intersection of the left channel section 1-1, the right channel section 1-2 and the drainage corrugated steel 8, and is used for the port isolation and plugging of the left channel section 1-1 and the right channel section 1-2. Preferably, in order to facilitate the pouring construction of the waterproof concrete isolation structure 10 and effectively improve the waterproof and drainage performance of the tunnel, plugging templates 9 are respectively arranged at the ports of the left channel section 1-1 and the right channel section 1-2 close to the tunnel, serving as the lateral templates for the pouring construction of the waterproof concrete isolation structure 10.

[0052] On the outer side of the inverted siphon aqueduct culvert structure, the upper wall surface of the water-rich karst channel 1 and the rock surface of the tunnel arch, shotcrete protective layers 2, anchor mesh shotcrete layers or grouting reinforcement layers are all arranged. The shotcrete protective layer 2 is used for the temporary protection of the excavated rock surface and ensuring the surface leveling of the excavated rock surface; further, if the surrounding rock excavated is weak, the anchor mesh shotcrete layer or other more effective surrounding rock reinforcement structures can be used to replace the shotcrete protective layer 2 to ensure the stability of the surrounding rock surface; if the foundation of the horizontal culvert 4 fails to meet the bearing capacity requirements, the grouting reinforcement layer or other surrounding rock reinforcement structures should be used to replace the shotcrete protective layer 2 to ensure that the foundation bearing capacity of the inverted siphon aqueduct culvert structure meets the requirements.

[0053] Based on the reverse construction method of the above-mentioned inverted siphon water conduction structure, first, the excavation of the lower space of the tunnel is carried out, then the construction of structures such as the inverted siphon aqueduct culvert is carried out, and then, based on the tunnel lower structure, the excavation and support construction of the upper space of the tunnel are carried out.

[0054] The specific construction steps include:

[0055] S0. When the tunnel excavation reveals the horizontal water-rich karst channel 1, suspend the excavation construction of the upper bench, and then let the middle and lower benches of the tunnel catch up in turn, and then complete the initial support, invert and invert filling construction of the entire normal section before the intersection section of the tunnel and the horizontal water-rich karst channel 1, so that the tunnel support structure in the front section of the intersection section is completely closed into a ring;

[0056] S1. Carry out temporary plugging of the horizontal water-rich karst channel 1, and use drainage equipment to temporarily drain the accumulated water inside the karst channel;

[0057] S2. Carry out the construction of the lower space of the tunnel in the intersection section with the karst channel:

[0058] (2.1) First, construct the shotcrete protective layer 2 on the upper wall surface of the water-rich karst channel 1. Then, conduct the excavation construction of the lower part of the tunnel in the way of mechanical cutting at the lower part of the tunnel and excavation and expansion on the left and right sides. After the excavation is completed, immediately construct the shotcrete protective layer 2 on the rock surface to ensure the stability of the excavation surface and level the excavation surface;

[0059] (2.2) Conduct the assembly construction of the precast components of the inverted siphon water diversion structure in the excavation space of the surrounding rock at the lower part of the tunnel: First, construct the horizontal culvert 4 at the bottom of the excavation pit. Then, conduct the construction of the connection parts between the high-level shaft 3, the low-level shaft 5 and the horizontal culvert 4. Then, gradually raise the shaft to the design elevation by means of notch docking; The splicing joints of the precast components are wrapped with asphalt felt waterproof layer;

[0060] In addition, considering that the high-level shaft 3 and the low-level shaft 5 are adjacent to the air on one side and there is a risk of instability and collapse during the raising process, therefore, every time a section of the shaft is raised, it should be fixed in time with shotcrete;

[0061] (2.3) Use the in-situ casting method to construct the lower tunnel structure 6 inside the inverted siphon structure. Among them, the initial support 11 at the upper part of the tunnel and the lower tunnel structure 6 should be just closed into a ring. The lower tunnel structure 6 serves as an isolation structure between the inverted siphon structure and the tunnel, playing roles such as support, waterproofing and isolation. Then, construct the filling inside the inverted arch and the drainage ditch 7;

[0062] (2.4) After the concrete forms strength, construct the crushed stone backfill buffer layer 13 on the concrete surface. Among them, the thickness of the crushed stone backfill buffer layer 13 should not be less than 0.5m. Its function is to prevent the falling stones generated by the blasting of the tunnel arch from damaging the tunnel structure and to reduce the height of the construction free face to a certain extent;

[0063] S3. Conduct the excavation of the surrounding rock at the upper part of the transverse water-rich karst channel 1. After the excavation, immediately construct the shotcrete protective layer 2 on the surrounding rock surface. Then, remove the crushed stone backfill buffer layer 13;

[0064] S4. Respectively erect the karst channel blocking formwork 9 at the intersections of the left channel section 1-1, the right channel section 1-2 and the tunnel. Among them, the karst channel blocking formwork 9 is made of waterproof concrete. Its function is to serve as a strengthened protective structure for blocking the karst channel to reduce the adverse impact of the karst channel on the tunnel structure;

[0065] S5. Install the drainage corrugated steel 8 according to the assembly process;

[0066] S6. Construct the waterproof concrete isolation structure 10 by the in-situ casting process in the gaps between the high-level shaft 3, the low-level shaft 5, the drainage corrugated steel 8 and the karst channel blocking formwork 9, and conduct the back grouting treatment for the drainage corrugated steel 8 at the arch part;

[0067] S7, construct the drainage structure inside the drainage corrugated steel 8, then construct the tunnel secondary lining 11, and set a transverse drainage pipe 12 interconnected with the drainage corrugated steel 8 and the drainage ditch 7 at the side wall foot of the tunnel secondary lining 11, so that the drainage corrugated steel 8 and the tunnel drainage ditch 7 are interconnected through the transverse drainage pipe 12 to form a drainage system in the tunnel;

[0068] Afterwards, the tunnel excavation construction is carried out according to the normal tunnel construction steps. After the tunnel is penetrated, the construction of the remaining structures in the tunnel is carried out. At this point, the construction of all tunnel structures in the section where the inverted siphon water diversion structure is located is completed.

[0069] In the step s5, the assembly process of the drainage type corrugated steel 8 is detailed in patent No. 202121324965.8, which discloses a construction process of a tunnel drainage type corrugated steel initial support structure, and will not be repeated here.

[0070] The above description is only a preferred embodiment of the present invention and does not constitute any form of confidentiality restriction on the present invention. Any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the technical solution of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A reverse construction method for a tunnel water diversion structure applicable to large karst channels, characterized in that: First, excavate the lower space of the tunnel, then construct the inverted siphon water pipe culvert structure, and then excavate and support the upper space of the tunnel based on the lower structure of the tunnel; The specific construction steps include: S0. When the tunnel excavation reveals the transversely distributed water-rich karst channel (1), the excavation construction of the upper step is suspended, and the middle and lower steps of the tunnel are allowed to catch up in sequence, and then the initial support, invert and invert filling construction of the entire normal section before the intersection of the tunnel and the transversely distributed water-rich karst channel (1) are completed, so that the tunnel support structure in front of the intersection section is completely closed into a ring; S1. Temporarily block the horizontally distributed water-rich karst channel (1), and temporarily drain the accumulated water inside the karst channel using drainage equipment; S2. Construction of the lower space of the tunnel that intersects with the karst channel: (2.1) First, the sprayed concrete protective layer (2) is constructed on the upper wall of the transversely distributed water-rich karst channel (1), and then the lower part of the tunnel is excavated by mechanical trenching and expansion on the left and right sides. After the excavation is completed, the sprayed concrete protective layer (2) is immediately constructed on the rock surface to ensure the stability of the excavation surface and level the excavation surface; (2.2) Assembling the prefabricated components of the inverted siphon water diversion structure in the excavated space of the surrounding rock below the tunnel: first, construct the transverse culvert (4) at the bottom of the excavated pit, then construct the connection between the high-position vertical shaft (3), the low-position vertical shaft (5) and the transverse culvert (4), and then connect the high-position vertical shaft section by section to the designed elevation in a notch-jointed manner; the spliced ​​joints of the prefabricated components are wrapped with an asphalt felt waterproof layer; (2.3) The tunnel substructure (6) is constructed by cast-in-place method on the inner side of the inverted siphon structure, followed by the infill and drainage ditch (7) inside the inverted arch; (2.4) After the concrete has reached sufficient strength, the construction slag is backfilled into a buffer layer (13) on the surface of the concrete. S3, excavating the surrounding rock above the transversely distributed water-rich karst channel (1), immediately constructing a shotcrete protective layer (2) on the surrounding rock surface after excavation, and then removing the slag and backfilling the buffer layer (13); S4, setting up karst channel blocking templates (9) at the intersections of the left channel section (1-1), the right channel section (1-2) and the tunnel respectively; S5. Install drainage corrugated steel (8) according to the assembly process; S6. A waterproof concrete isolation structure (10) is constructed in the gap between the high-position shaft (3), the low-position shaft (5), the drainage corrugated steel (8) and the karst channel blocking template (9) according to the cast-in-place process, and the drainage corrugated steel (8) of the arch is subjected to back grouting treatment; S7, construct the drainage structure inside the drainage corrugated steel (8), then construct the secondary lining (11) of the tunnel, and set a transverse drainage pipe (12) at the side wall foot of the secondary lining (11) of the tunnel, which is interconnected with the drainage corrugated steel (8) and the drainage ditch (7); then carry out tunnel excavation construction according to normal construction steps, and after the tunnel is penetrated, carry out the construction of the remaining structures in the tunnel, thus completing the construction of all tunnel structures in the section where the inverted siphon water diversion structure is located.

2. The reverse construction method according to claim 1, characterized in that: In step (2.2), after each section of the shaft is erected, it is promptly fixed with shotcrete to avoid the risk of instability and collapse caused by the unilateral airspace during the erection of the high-position shaft (3) and the low-position shaft (5).

3. The reverse construction method according to claim 1, characterized in that: In step (2.4), the thickness of the slag backfill buffer layer (13) is not less than 0.5 m to prevent the tunnel structure from being damaged by the falling rocks generated by the blasting of the tunnel arch.

4. A tunnel water conducting structure applicable to large karst channels, characterized in that: Constructed based on the reverse construction method described in any one of claims 1-3, the tunnel water diversion structure includes a water-rich karst channel (1) distributed transversely to the tunnel. The transversely distributed water-rich karst channel (1) intersects with the tunnel and is truncated by the tunnel into a left channel section (1-1) and a right channel section (1-2). A prefabricated spliced inverted siphon conduit culvert structure for connecting the left channel section (1-1) and the right channel section (1-2) to each other is provided at the bottom of the tunnel.

5. The tunnel water diversion structure applicable to large karst channels according to claim 4, characterized in that: The inverted siphon conduit culvert structure includes a transverse culvert (4) arranged horizontally at the bottom of the tunnel. One end of the transverse culvert (4) is connected to the left channel section (1-1) through a high-position shaft (3), and the other end is connected to the right channel section (1-2) through a low-position shaft (5). The high-position shaft (3), the transverse culvert (4), and the low-position shaft (5) are all assembled from prefabricated structures, and their splicing joints are connected by a notch structure snap connection, and the outside of the joints is wrapped with an asphalt felt waterproof layer.

6. The tunnel water diversion structure applicable to large karst channels according to claim 5, characterized in that: A drainage corrugated steel (8) is provided outside the secondary lining (11) of the tunnel, and the drainage corrugated steel (8) is connected to the drainage ditch (7) in the invert of the tunnel through a transverse drain pipe (12).

7. The tunnel water diversion structure applicable to large karst channels according to claim 6, characterized in that: A tunnel lower structure (6) is provided at the inner bottom of the inverted siphon conduit culvert structure; and a waterproof concrete isolation structure (10) is filled between the inner top of the inverted siphon conduit culvert structure and the drainage corrugated steel (8).

8. The tunnel water diversion structure applicable to large karst channels according to claim 7, characterized in that: Sealing forms (9) are respectively provided at the ends of the left channel section (1-1) and the right channel section (1-2) close to the tunnel.

9. The tunnel water diversion structure applicable to large karst channels according to claim 6, characterized in that: Shotcrete protective layers (2), anchor mesh shotcrete layers or grouting reinforcement layers are provided on the outer side of the inverted siphon conduit culvert structure, on the upper wall surface of the transversely distributed water-rich karst channel (1), and on the rock surface of the tunnel arch.

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