A method for constructing a suspension bridge type tunnel across a super-large cave

Abstract

The application discloses a suspension bridge type tunnel construction method for crossing super-large karst caves, and the specific implementation steps are as follows: step one, positioning a tunnel contour line on the ground according to the location condition of the karst cave, and determining the position of a sling installation; step two, excavating a sling anchorage zone and pouring concrete in the sling anchorage zone; step three, lowering a cable from a borehole to the design elevation below the bottom surface of the tunnel, and fixing the ground end of the cable; step four, hanging and connecting main beams section by section into a whole; step five, pouring the tunnel structure; step six, paving inside the tunnel; step seven, setting tunnel protection facilities; and step eight, adjusting the sling force, so that the structure stress reaches the best state. The construction method is simple and reliable, the tunnel load is transmitted to the anchorage structure on the ground through the sling structure, and the tunnel can effectively cross super-large karst caves.

Description

Technical Field

[0001] This invention belongs to the field of tunnel engineering technology, and in particular relates to a construction method for a suspension bridge-type tunnel spanning an extra-large karst cave. Background Technology

[0002] For tunnel crossings in extremely large karst caves, traditional methods primarily involve filling the surrounding karst cavities with excavated slag. However, for such large karst caves with exceptionally long longitudinal spans and deep bottoms, this approach is problematic due to the enormous amount of filling material required, poor drainage, long construction periods, and significant post-construction settlement, making it difficult to meet structural and operational safety requirements. Conventional bridge spans, on the other hand, have limited spanning capacity, require large piers, pose significant construction risks within the cave, and are economically unfeasible. Suspension and cable-stayed bridges, relying on anchorage within the cave, present significant construction challenges and risks, especially given the poor rock wall conditions within the karst cave. Summary of the Invention

[0003] The purpose of this invention is to address the shortcomings of existing technologies by providing a suspension bridge-type tunnel construction method for crossing extra-large karst caves. In the construction of extra-large karst caves with shallow burial depth, deep bottom, and particularly large longitudinal spans, this invention utilizes a suspension bridge-type tunnel for crossing, effectively overcoming the disadvantages of difficult access to large amounts of fill materials, poor drainage, long construction period, large post-construction settlement, high risk, and poor economic efficiency. It also eliminates the need for internal anchoring, significantly improving the efficiency of karst tunnel construction, reducing costs, and minimizing risks.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A method for constructing a suspension bridge-type tunnel spanning an extra-large karst cave includes the following construction steps:

[0006] Step 1: Based on the location of the karst cave, locate the tunnel outline on the ground to determine the installation position of the suspension cables;

[0007] Step 2: Excavate the anchorage area for the suspension cables and pour concrete for the anchorage area, specifically as follows:

[0008] Main construction of the anchorage area: surveying and setting out the anchorage area—excavation of the foundation pit—compacting and leveling the bottom of the foundation pit—pouring 20cm thick C20 plain concrete as the anchorage ground formwork—drilling the suspension cable holes—tying the anchorage reinforcement bars, embedding the anchorage tie rods, and pre-embedding the prestressed corrugated pipes—installing the anchorage support formwork—pouring the anchorage concrete—curing, completing the main construction of the anchorage;

[0009] Step 3: Lower the cable from the borehole to below the designed elevation of the tunnel floor and fix the ground end of the cable; specifically:

[0010] Installation of anchorage anchoring device: Remove all anchorage formwork - complete anchorage concrete curing - install suspension cables - tension suspension cables in the prestressed corrugated pipe section and grout - pour anchorage cavity and top slab concrete - backfill anchorage foundation pit.

[0011] Step 4: Install the main beams section by section and connect them into a whole; specifically:

[0012] The process involves: traction cables for the first section of the main beam; installation of the main beam and fixing of the cable heads; control of cable force according to the formwork elevation; binding of main beam reinforcement; pouring of concrete for the joint section; curing until the concrete strength reaches 90% of the design value; tensioning of longitudinal prestressed steel bars in the main beam; and installation of the main beam section by section according to the above process until the entire bridge is connected.

[0013] Step 5: Tunnel structure pouring;

[0014] Step Six: Tunnel Interior Paving;

[0015] Step 7: Install tunnel protection facilities;

[0016] Step 8: Adjust the cable tension to achieve optimal structural stress. Based on the actual elevation and stress conditions of each segment after bridge completion, and comparing them with the original design values, recalculate and analyze the overall bridge stress. Adjust the cable tension as needed based on the calculation results to ensure that bending moment, shear force, axial force, etc., meet the requirements of the construction and operation phases.

[0017] The present invention further explains that, in step one, the transverse construction spacing between the suspenders in the anchorage range is determined according to the tunnel width, and the longitudinal construction spacing is determined according to the bearing capacity of a single suspender and the range of the tunnel length.

[0018] The present invention further explains that, in step two, the size of the excavated cable anchorage area is determined by the bearing capacity of the foundation; the size of the anchorage reinforcement, anchorage tie rod, pre-embedded prestressed corrugated pipe and other structural components is determined by the load transmitted by the cable.

[0019] The present invention further explains that, in step three, the installation sling is fixed to the anchor rod by means of a straddle or pin connection at one end;

[0020] The present invention further explains that, in step four, the installation of the main beam and the fixing of the cable ends involve transporting the main beam to the previously constructed bridge deck using a bridge erecting machine or hoisting method for installation; the fixing of the cable ends involves connecting the lower end of the suspender cable to the main beam using an anchor-head bearing type or a pin-connection type, with the suspender cable placed within the secondary lining on both sides of the tunnel. The main beam mainly includes structural forms such as steel truss beams, steel box beams, concrete beams, and steel-concrete composite beams;

[0021] The present invention further explains that the tunnel structure mentioned in step five refers to the sidewall and roof structure of the tunnel, the cross-section of which is rectangular, arched or straight-walled arched, and is cast with reinforced concrete or other lightweight materials with a thickness of not less than 20cm; the other lightweight materials include foamed concrete and light steel structure.

[0022] The present invention further explains that, in step six, the tunnel refers to the general term for the structure excluding the suspension cable system and the anchorage system. The tunnel interior paving includes the bridge deck subbase paving, the tunnel lining paving, and the carriageway paving layer. When railway transportation is involved, it also includes ballast, sleepers, and rails.

[0023] The present invention further illustrates that, in step seven, the tunnel protection facility includes a rockfall prevention buffer layer and a rockfall protection net, wherein the rockfall prevention buffer layer is a rubber buffer protection layer.

[0024] In this invention, the suspension cables, main beams, and tunnel structure together form a cable-stayed tunnel structure system, serving as the main load-bearing structure and jointly absorbing the structural weight, vehicle loads, and rockfall impacts. The rockfall protection facilities effectively protect the tunnel structure and mitigate the impact of rockfalls on the entire structural system.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] 1. The suspension bridge tunnel construction method of the present invention is scientific, reasonable, simple and reliable. By transferring the tunnel load to the ground anchorage structure through the suspension cable structure, it can effectively realize the tunnel crossing of extra-large karst caves with a large longitudinal span.

[0027] 2. The suspension bridge-type tunnel structure of the present invention can be connected in series with multiple sets of structures, with flexible arrangement, and can meet the requirements of structural crossing over longer distances;

[0028] 2. The suspension bridge tunnel construction method of the present invention effectively overcomes the difficulties such as large filling volume of karst caves, difficulty in controlling post-construction settlement, and long construction period, improves the construction efficiency of karst tunnels, reduces costs, and reduces risks;

[0029] 3. The construction method of the present invention has good effect, high construction efficiency, and strong operability, and can meet the requirements of project implementation in terms of safety and quality;

[0030] 4. The construction method of the present invention can be widely applied to tunnel engineering in highways, railways, municipal engineering, military and other fields. It has a wide range of applications and broad application value. Attached Figure Description

[0031] To illustrate the technical solutions in the embodiments of the present invention or the prior art more specifically and intuitively, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0032] Figure 1 This is a schematic diagram of the construction process of the present invention;

[0033] Figure 2 This is a schematic diagram of the structure of the suspension bridge-type tunnel spanning an extra-large karst cave in this invention.

[0034] Figure 3 This is a schematic diagram of the cross-sectional structure of the cable-stayed bridge spanning a super-large karst cave in this invention;

[0035] Figure 4 This is a schematic diagram of the structure in which the main sling and the branch slings of the present invention are connected by a sling divider;

[0036] Figure 5 This is a schematic diagram of the structure in the anchorage area of ​​the present invention, showing the connection between the main suspending cable and the anchorage tie rod via cable clamps.

[0037] In the diagram: 1. Cavern; 2. Anchorage area; 21. Anchorage tie rod; 22. Cable clamp; 23. Prestressed corrugated pipe; 24. Anchorage ground formwork; 25. Anchorage reinforcement; 3. Suspension cable; 31. Cable splitter; 32. Cable splitter; 4. Tunnel; 5. Main beam; 6. Tunnel structure; 7. Roadway pavement layer; 8. Cable head; 9. Tunnel protection facilities. Detailed Implementation

[0038] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0039] Reference Figure 1 The construction method for a suspension bridge-type tunnel spanning an extra-large karst cave, as described above, includes the following construction steps:

[0040] Step 1: Based on the location of the karst cave (1), locate the tunnel outline on the ground and determine the installation position of the suspension cable (3);

[0041] Step 2: Excavate the anchorage area (2) and pour concrete for the anchorage area (2), specifically as follows:

[0042] Main construction of anchorage area (2): Measurement and layout of anchorage area - excavation of foundation pit - compaction and leveling of foundation pit bottom - pouring 20cm thick C20 plain concrete as anchorage ground formwork (24) - drilling of cable holes - binding of anchorage reinforcement (25), installation of anchorage tie rods (21), pre-embedding of prestressed corrugated pipes (23) - installation of support anchorage formwork - pouring of anchorage concrete - curing, and completion of main construction of anchorage;

[0043] Step 3: Lower the sling (3) from the borehole to the designed elevation of the bottom surface of the tunnel (4), and fix the ground end of the sling (3); specifically:

[0044] Install anchorage anchoring device: Remove all anchorage formwork - complete anchorage concrete curing - install suspension cable (3) - tension suspension cable (3) in the prestressed corrugated pipe (23) and grout - pour anchorage cavity and top plate concrete - backfill anchorage pit;

[0045] Step 4: Install the main beam (5) segment by segment and connect them into a whole; specifically:

[0046] The slings (3) for pulling the first section of the main beam are installed (5) and the cable head is fixed (8). The cable force is controlled according to the formwork elevation. The main beam reinforcement is tied. The joint section concrete is poured. The concrete is cured until the concrete strength reaches 90% of the design value. The longitudinal prestressed steel bars of the main beam are tensioned. The main beam (5) is installed section by section according to the above process until the entire bridge is connected.

[0047] Step 5, Tunnel Structure (6) Pouring;

[0048] Step 6: Interior paving of tunnel (4);

[0049] Step 7: Install tunnel protection facilities (9);

[0050] Step 8: Adjust the tension of the suspenders (3) to achieve the optimal stress state of the structure. Based on the actual elevation and stress of each segment after the bridge is completed, compare the original design values, recalculate and analyze the stress of the entire bridge, and adjust the tension of the suspenders (3) as needed according to the calculation results, so that the bending moment, shear force, axial force, etc. all meet the requirements of the construction and operation stages.

[0051] In this implementation plan, the transverse construction spacing between the suspenders (3) in the anchorage area (2) described in step one is determined according to the tunnel width, and the longitudinal construction spacing is determined according to the bearing capacity of a single suspender (3) and the length range of the tunnel (4) it supports;

[0052] In this implementation plan, the size of the excavation cable anchorage area (2) in step two is determined by the bearing capacity of the foundation; the size of the anchorage steel bars (25), anchorage tie rods (21), pre-embedded prestressed corrugated pipes (23) and other structural accessories is determined by the load transmitted by the cable (3);

[0053] In addition to meeting the requirements for punching shear, shear and bending bearing capacity, the construction of the anchorage zone (2) should also meet the following basic requirements:

[0054] The minimum width of the anchorage zone (2) shall not be less than 1500 mm, and the minimum thickness of the anchorage zone (2) shall not be less than 800 mm. The minimum thickness of the anchorage zone for flat plate and beam-slab raft anchorage shall not be less than 500 mm. The concrete material and its strength grade shall meet the requirements for the durability and impermeability of structural concrete. The reinforcing bars in the anchorage zone shall be installed along the entire length.

[0055] The main reinforcement bars in the anchorage zone (2) shall comply with the provisions of the current national standard "Code for Design of Concrete Structures" GB 50010 regarding the minimum reinforcement ratio. The diameter of the main reinforcement bars shall not be less than 12mm, the diameter of the stirrup bars shall not be less than 10mm, and the diameter of the stirrups shall not be less than 6mm.

[0056] The thickness of the concrete cover for the bottom reinforcement, excluding the concrete cushion, should not be less than 50 mm; furthermore, it should not be less than the thickness of the anchor rod (21) embedded in the anchorage zone (2). The anchorage length of the anchor rod (21) should not be less than 8 times the diameter of the longitudinal main reinforcement.

[0057] In this implementation scheme, step three involves installing the sling by fixing one end of the sling to the anchor rod (21) using either a straddle-type or pin-type connection. The straddle-type sling uses two steel wire ropes with anchor heads at both ends, wrapped around the cable groove at the top of the cable clamp (22), and then connecting the anchor head (8) to the tunnel main beam (5). The pin-type sling uses two steel wire ropes with anchor heads at the lower end and connecting sleeves at the upper end, connecting the upper end of the sling to the ear plate (sling plate) below the cable clamp via a pin connection. The ear plate extends from the lower half of the cable clamp. The sling (3) is usually made of galvanized twisted steel wire rope, closed-lock steel wire rope, or parallel galvanized steel wire bundle, and the surface is painted or wrapped with HDPE sheath for corrosion protection. They are usually arranged at equal intervals and with equal cross sections. The sling (3) structure is a sling system consisting of a single sling (3) or a main sling (3) and multiple branch slings (32). The main sling (3) and the branch slings (32) are connected by a branch slinger (31) to transfer the load.

[0058] In this implementation plan, step four, installing the main beam (5) and fixing the cable head (8), involves transporting the main beam (5) to the previously constructed bridge deck using a bridge erecting machine or hoisting method for installation. Fixing the cable head (8) involves connecting the lower end of the suspending cable (3) or branch cable (32) to the main beam (5) using an anchor-bearing or pin-connected method. The suspending cable (3) or branch cable (32) is placed within the secondary lining on both sides of the tunnel structure (4). The main beam (5) includes structural forms such as steel truss beams, steel box beams, concrete beams, and steel-concrete composite beams.

[0059] In this implementation plan, the tunnel structure (6) mentioned in step five refers to the sidewall and roof structure of the tunnel. Its casting cross section is rectangular, arched or straight-walled arched, and it is cast with reinforced concrete or other lightweight materials with a thickness of not less than 20cm. The other lightweight materials include foamed concrete and light steel structure.

[0060] In this implementation plan, the tunnel (4) mentioned in step six refers to the general term for the structure excluding the suspension cable system and the anchorage system. The internal paving of the tunnel (4) includes the bridge deck sub-layer paving, the tunnel lining paving, and the carriageway paving layer (7). When railway transportation is involved, it also includes ballast, sleepers, and rails.

[0061] In this implementation scheme, the tunnel protection facility (9) mentioned in step seven includes a rockfall buffer layer and a rockfall protection net. The rockfall buffer layer is a rubber buffer protection layer. The rubber buffer protection layer has good buffering, deformation, and energy dissipation characteristics under impact load, which increases the impact time of falling rocks on the tunnel roof, thereby effectively reducing the impact force of falling rocks and ensuring the safety of the tunnel structure (6) under the impact of falling rocks. The rockfall protection net adopts a passive protection net and a guiding protection net, which can effectively dissipate the impact force of falling rocks;

[0062] In this implementation plan, the suspension cables (4), main beams (5), and tunnel structure (6) together form a suspension tunnel structure system, which serves as the main load-bearing structure and jointly bears the loads of the structure's own weight, vehicles, and falling rocks. The tunnel protection facilities (9) can effectively protect the tunnel structure (6) and reduce the impact of falling rocks on the entire structural system.

[0063] In this implementation plan, the suspension bridge tunnel construction method for crossing a super-large karst cave is a type of suspension bridge tunnel in which the load of the tunnel (4) and its own weight are borne by a set of suspension cables (3) system.

[0064] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for constructing a suspension bridge-type tunnel spanning an extra-large karst cave, characterized in that, Includes the following steps: Step 1: Based on the location of the karst cave (1), locate the tunnel outline on the ground and determine the installation position of the suspension cable (3); Step 2: Excavate the cable anchorage area (2) and pour concrete for the anchorage area (2), specifically as follows: Main construction of anchorage area (2): Measurement and layout of anchorage area - excavation of foundation pit - compaction and leveling of foundation pit bottom - pouring 20cm thick C20 plain concrete as anchorage ground formwork (24) - drilling of cable holes - binding of anchorage reinforcement (25), installation of anchorage tie rods (21), pre-embedding of prestressed corrugated pipes (23) - installation of support anchorage formwork - pouring of anchorage concrete - curing, and completion of main construction of anchorage; Step 3: Lower the sling (3) from the borehole to the designed elevation of the bottom surface of the tunnel (4), and fix the ground end of the sling (3); specifically: Install anchorage anchoring device: Remove all anchorage formwork - complete anchorage concrete curing - install suspension cable (3) - tension suspension cable (3) in the prestressed corrugated pipe (23) and grout - pour anchorage cavity and top plate concrete - backfill anchorage pit; Step 4: Install the main beam (5) segment by segment and connect them into a whole; specifically: The slings (3) for pulling the first section of the main beam are installed (5) and the cable head is fixed (8). The cable force is controlled according to the formwork elevation. The main beam reinforcement is tied. The joint section concrete is poured. The concrete is cured until the concrete strength reaches 90% of the design value. The longitudinal prestressed steel bars of the main beam are tensioned. The main beam (5) is installed section by section according to the above process until the entire bridge is connected. Step 5, Tunnel Structure (6) Pouring; Step 6: Interior paving of tunnel (4); Step 7: Install tunnel protection facilities (9); Step 8: Adjust the tension of the suspenders (3) to achieve the optimal stress state of the structure. Based on the actual elevation and stress of each segment after the bridge is completed, compare the original design values, recalculate and analyze the stress of the entire bridge, and adjust the tension of the suspenders (3) as needed according to the calculation results, so that the bending moment, shear force, axial force, etc. all meet the requirements of the construction and operation stages.

2. The construction method for a suspension bridge-type tunnel spanning an extra-large karst cave according to claim 1, characterized in that, In step one, the transverse construction spacing between the suspenders (3) in the anchorage area (2) is determined according to the tunnel width, and the longitudinal construction spacing is determined according to the bearing capacity of a single suspender (3) and the length range of the tunnel (4).

3. The construction method for a suspension bridge-type tunnel spanning an extra-large karst cave according to claim 1, characterized in that, The dimensions of the excavated cable anchorage area (2) in step two are determined by the bearing capacity of the foundation; the dimensions of the anchorage steel bars (25), anchorage tie rods (21), pre-embedded prestressed corrugated pipes (23) and other structural components are determined by the load transmitted by the cable (3).

4. The construction method for a suspension bridge-type tunnel spanning an extra-large karst cave according to claim 1, characterized in that, In step three, the installation of the sling is to fix one end of the sling (3) to the anchor rod (21) by means of straddling or pin connection.

5. The construction method for a suspension bridge-type tunnel spanning an extra-large karst cave according to claim 1, characterized in that, In step four, the installation of the main beam (5) and the fixing of the cable head (8) involves transporting the main beam (5) to the previously constructed bridge deck using a bridge erecting machine or hoisting method for installation; the fixing of the cable head (8) involves connecting the lower end of the suspending cable (3) to the main beam (5) using an anchor head bearing type or a pin connection type, with the suspending cable (3) placed inside the secondary lining on both sides of the tunnel (4). The main beam (5) includes structural forms such as steel truss beams, steel box beams, concrete beams, and steel-concrete composite beams.

6. The construction method for a suspension bridge-type tunnel spanning an extra-large karst cave according to claim 1, characterized in that, In step five, the tunnel structure (6) refers to the sidewall and roof structure of the tunnel. Its casting cross-section is rectangular, arched or straight-walled arched, and it is cast with reinforced concrete or other lightweight materials with a thickness of not less than 20cm. The other lightweight materials include foamed concrete and light steel structure.

7. The method for constructing a suspension bridge-type tunnel spanning an extra-large karst cave according to claim 1, characterized in that, In step six, tunnel (4) refers to the general structure excluding the suspension cable system and the anchorage system. The internal paving of tunnel (4) includes bridge deck sub-layer paving, tunnel lining paving, and carriageway paving layer (7). When railway transportation is involved, it also includes ballast, sleepers, and rails.

8. The construction method for a suspension bridge-type tunnel spanning an extra-large karst cave according to claim 1, characterized in that, The tunnel protection facility (9) in step seven includes a rockfall prevention buffer layer and a rockfall protection net. The rockfall prevention buffer layer is made of rubber buffer protection layer.

9. A method for constructing a suspension bridge-type tunnel spanning an extra-large karst cave according to claim 1, characterized in that, The aforementioned suspension cables (3), main beams (5), and tunnel structure (6) together form a suspension tunnel structure system, serving as the main load-bearing structure and jointly bearing the loads of the structure's own weight, vehicles, and falling rocks. The aforementioned rockfall prevention facilities can effectively protect the tunnel structure (6) and reduce the impact of falling rocks on the entire structural system.

10. A method for constructing a suspension bridge-type tunnel spanning an extra-large karst cave according to claim 1, characterized in that, The suspension bridge-type tunnel spanning a super-large karst cave includes the form in which the load of the tunnel (4) and its self-weight are borne by a set of suspension cable (3) systems and the load of the tunnel (4) and its self-weight are borne by multiple sets of suspension cable (3) systems.

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