A method for gradually changing the layout of bifurcation tunnels on mountain highways

Abstract

This invention discloses a method for the gradual layout of bifurcation tunnels on mountain highways, including the construction of the small clearance section of the bifurcation tunnel using the three-stage excavation method with reserved core soil, the ring excavation method with reserved core soil, and the two-stage method, and the use of SF4x-1, SF4x-2, SF4x-3, SF4x-c, and SF4x-d type linings; the construction of the composite curved central wall arch tunnel section of the bifurcation tunnel using the two-stage method, and the use of FLjb type linings; the construction of the integral straight central wall gradually changing arch tunnel section of the bifurcation tunnel using the two-stage ring excavation method with reserved core soil, and the use of ZLjb-1 and ZLjb-2 type linings; the construction of the integral straight central wall arch tunnel section of the bifurcation tunnel using the three-guide tunnel method, and the use of Zlg type linings; and the construction of the arch open tunnel section of the bifurcation tunnel using ZLm type linings. The gradual layout method for bifurcation tunnels on mountain expressways employs a combination of excavation methods and sets up corresponding support structures for each method, providing a good solution for the excavation of continuous arch bifurcation tunnels.

Description

Technical Field

[0001] This invention relates to the field of tunnel construction technology, and in particular to a method for the gradual layout of bifurcated tunnels on mountain highways. Background Technology

[0002] Tunnels are structures built underground, underwater, or within mountains to carry railways or highways for motor vehicles. Based on their location, they can be categorized into three main types: mountain tunnels, underwater tunnels, and urban tunnels. Tunneling is frequently required in the construction of mountain highways, and highway branching tunnels are widely used due to their following functions:

[0003] 1. Improved safety: Traditional bifurcated tunnels have slow transitions between the two sides, which can easily lead to collisions and congestion between vehicles. Bifurcated tunnels with a gradual transition can make vehicle flow smoother and reduce the risk of accidents.

[0004] 2. Improve traffic capacity: The gradually changing bifurcated tunnel design can make better use of space and increase traffic capacity, especially in busy sections, which can alleviate traffic congestion.

[0005] 3. Reduced construction costs: Traditional bifurcated tunnels require construction in both directions, while bifurcated tunnels using a gradual transition method only require construction in one direction, which can reduce construction costs.

[0006] 4. Environmental protection and energy saving: The gradual branching of tunnels can reduce energy consumption because vehicles do not need to stop and wait, thus saving fuel.

[0007] In summary, the gradual transition of bifurcated tunnels on mountain highways improves traffic efficiency and safety, saves construction costs and energy consumption, and is a highly innovative and practical design approach.

[0008] However, bifurcated tunnels are difficult to excavate and may pose safety risks due to their complex stress structure and numerous construction procedures. Currently, there is no good solution. Summary of the Invention

[0009] To solve the above-mentioned technical problems, the present invention provides a method for gradually changing the layout of bifurcated tunnels on mountain highways.

[0010] The technical solution adopted in this invention is as follows:

[0011] A method for gradually changing the layout of bifurcation tunnels on mountainous expressways, which employs different construction methods and different lining types in different sections of the bifurcation tunnel; including the following steps:

[0012] The construction of the narrow clearance section of the bifurcation tunnel is divided into three steps:

[0013] The first step is to use the three-stage excavation method with reserved core soil and SF4x-1 type lining; the second step is to use the ring excavation method with reserved core soil and SF4x-2, SF4x-3, and SF4x-c type lining; the third step is to use the two-stage method and SF4x-4 and SF4x-d type lining.

[0014] Second, the composite curved wall arch tunnel section of the bifurcated tunnel is constructed using the two-stage method and FLjb type lining.

[0015] Third, the integral straight central wall gradually changing arch tunnel section of the bifurcation tunnel is constructed using the two-stage ring excavation method with reserved core soil, and ZLjb-1 and ZLjb-2 type linings are used.

[0016] Fourth, the integral straight-center wall arch tunnel section of the bifurcated tunnel is constructed using the three-guide tunnel method and adopts Zlg-type lining.

[0017] Fifth, the open-cut section of the bifurcated tunnel adopts ZLm-type lining.

[0018] Furthermore, in the first, second, and third steps of the construction of the small clearance section of the bifurcation tunnel, the cross-section is excavated from the outside to the inside and from high to low. After the outer cross-section is excavated, the corresponding initial support is installed. After the inner cross-section is excavated, the invert arch and invert arch filling are installed. Finally, the overall formwork secondary lining is carried out.

[0019] Furthermore, in the first and second steps of the construction of the small clearance section of the bifurcation tunnel, the lower section is excavated by skipping trenches, and the initial support is staggered on both sides to the bottom. The length of each bottoming on one side depends on the surrounding rock conditions, and is generally no more than 3m. The circumferential excavation advance is 0.5 to 1.0m, and the core soil area is not less than 50% of the entire upper half section area.

[0020] Furthermore, in the third step of the construction of the small clearance section of the bifurcation tunnel, after the excavation and initial support of the separated tunnel are completed, the secondary lining concrete of the invert arch is poured immediately, and the cyclic excavation of the upper bench is carried out with a maximum of 2 steel frame spacings for Class IV surrounding rock.

[0021] Furthermore, in the construction of the composite curved-middle-wall arch tunnel section, the integral straight-middle-wall gradually changing arch tunnel section, and the integral straight-middle-wall arch tunnel section of the bifurcated tunnel, the central pilot tunnel is excavated first, followed by the excavation of the pilot tunnel, and finally the excavation of the follow tunnel.

[0022] During the excavation of the central pilot tunnel, temporary support, central partition wall, and temporary formwork or temporary support or temporary cross bracing on the rear side are constructed.

[0023] During the excavation of both the pilot tunnel and the follow-up tunnel, the cross-sections were excavated from the outside to the inside and from high to low. After the outer cross-section was excavated, the corresponding initial support was installed. After the inner cross-section was excavated, the invert arch and invert arch were filled. Finally, the overall formwork was used for secondary lining.

[0024] Furthermore, during the construction of the composite curved wall arch tunnel section of the bifurcated tunnel, the excavation advance shall not exceed 3.0m; the temporary steel frame shall be dismantled after the initial support construction of the main tunnel structure is completed and stabilized, and the length of each dismantling shall not exceed 5m, and it shall be dismantled section by section; the invert arch shall be constructed immediately after dismantling, and the two processes shall be carried out alternately; after the length of the invert arch construction reaches the length of one lining by the lining trolley, the secondary lining of the arch wall shall be poured in a timely manner.

[0025] Furthermore, during the construction of the integral straight-center wall gradually changing arch tunnel section of the bifurcated tunnel, the excavation advance is 0.6 to 1.2 meters, and the core soil area should not be less than 50% of the entire upper half cross-section area.

[0026] Furthermore, in the construction of the integral straight-center wall arch tunnel section of the bifurcated tunnel, the cyclic advance is 0.6m when using the three-guide tunnel method, and the step length is controlled between 6 and 8 meters; the other side can only be excavated after the first side excavation and initial support are completed and the strength reaches 70%.

[0027] Furthermore, during the construction of each section of the bifurcated tunnel, the following necessary testing items are included: geological and support condition observation, surrounding displacement, arch settlement, surface settlement of the tunnel entrance with a burial depth of less than twice the excavation width and shallow buried section, and blasting vibration velocity of less than 15cm / s. By sorting out and regressing the above measurement data, the inherent laws are found, the stability of the surrounding rock and the support effect are evaluated, and then the displacement back analysis method is used to back-calculate the initial stress field and comprehensive physical and mechanical parameters of the surrounding rock, and compare and verify with the actual results.

[0028] The beneficial effects of this invention are:

[0029] This method for the gradual layout of bifurcation tunnels on mountainous highways employs three-stage excavation with reserved core soil, circular excavation with reserved core soil, and two-stage excavation in the small clearance sections of the bifurcation tunnels, using SF4x-1, SF4x-2, SF4x-3, SF4x-c, and SF4x-d type linings. In the composite curved-middle-wall arch tunnel section of the bifurcation tunnel, the two-stage method is used, employing FLjb type lining. In the integral straight-middle-wall gradually changing arch tunnel section of the bifurcation tunnel, the two-stage circular excavation with reserved core soil is used, employing ZLjb-1 and ZLjb-2 type linings. In the integral straight-middle-wall arch tunnel section of the bifurcation tunnel, the three-guide tunnel method is used, employing Zlg type lining. In the arch-open tunnel section of the bifurcation tunnel, ZLm type lining is used. This method for the gradual layout of bifurcation tunnels on mountainous highways utilizes multiple excavation methods in combination, and corresponding support structures are set for each excavation method, providing a good solution for the excavation of arch-bifurcation tunnels.

[0030] This method of gradually changing the layout of bifurcation tunnels on mountainous highways is the first in China to combine the construction methods of composite curved center walls, integral straight center wall transition sections, integral straight center walls, and open-cut sections. This combination of methods effectively improves the construction quality and efficiency of bifurcation tunnels on mountainous highways, and has the following significance:

[0031] 1. Increased construction flexibility: By adopting a combination of composite curved central wall, integral straight central wall transition section, integral straight central wall and open tunnel section, appropriate construction technology can be flexibly selected according to different geological conditions and shapes of tunnels, thus increasing construction flexibility.

[0032] 2. Improve construction efficiency: Combining multiple construction methods can maximize the advantages of different methods and improve the efficiency of tunnel construction.

[0033] 3. Ensure tunnel quality: By comprehensively utilizing construction methods such as composite curved central wall, integral straight central wall transition section, integral straight central wall and open-cut section, the structural stability and reliable quality of the tunnel can be ensured.

[0034] 4. Improve traffic safety: The comprehensive construction method fully considers traffic safety during the construction process, especially for tunnels constructed during traffic hours. This method can effectively shorten the construction period, reduce the impact on traffic, and ensure the traffic safety of drivers. Attached Figure Description

[0035] Figure 1 This is a plan view of the tunnel bifurcation section structure of the present invention;

[0036] Figure 2 and Figure 3 This is a schematic diagram of the construction process of the cross-section and longitudinal section of the three-step excavation with reserved core soil in the small clearance section of the present invention;

[0037] Figure 4 and Figure 5 This is a schematic diagram of the construction process of the cross-section and longitudinal section of the ring excavation reserved core soil method in the small clearance section of the present invention;

[0038] Figure 6 and Figure 7 This is a schematic diagram of the construction process of the cross-section and longitudinal section of the two-step method in the small clearance section of the present invention;

[0039] Figure 8 This is a schematic diagram of the structure of the tie rod with small clearance section of the present invention;

[0040] Figure 9 and Figure 10 This is a schematic diagram of the cross-section and planar construction procedures of the three-guide tunnel method for the integral straight central wall arch tunnel section in this invention;

[0041] Figure 11 and Figure 12 This is a schematic diagram of the cross-section and planar construction procedures of the two-stage annular excavation reserved core soil method for the integral straight central wall gradual section continuous arch tunnel in this invention.

[0042] Figure 13 and Figure 14 This is a schematic diagram of the cross-sectional and planar construction procedures of the composite curved-middle-wall-connected arch tunnel in this invention;

[0043] In the diagram, 1—small clearance section, 2—composite curved central wall arch tunnel section, 3—integral straight central wall gradually changing arch tunnel section, 4—integral straight central wall arch tunnel section;

[0044] 101—Intermediate Pilot Tunnel; 102—Temporary Support for Intermediate Pilot Tunnel; 103—Intermediate Divider Wall; 104—Temporary Cross Bracing on the Rear Side of the Intermediate Pilot Tunnel; 105—Side Pilot Pit of the Pilot Tunnel; 106—Initial Support for the Side Pilot Tunnel of the Pilot Tunnel; 107—Side Pilot Pit of the Rear Pilot Tunnel; 108—Initial Support for the Side Pilot Tunnel of the Rear Pilot Tunnel; 109—Upper Bench of the Main Tunnel of the Pilot Tunnel; 110—Initial Support for the Upper Section of the Pilot Tunnel; 111—Lower Bench of the Main Tunnel of the Pilot Tunnel. 112—Initial support of the lower section of the pilot tunnel; 113—Invert arch of the pilot tunnel; 114—Backfill of the invert arch of the pilot tunnel; 115—Secondary lining; 116—Upper bench of the main tunnel of the rear tunnel; 117—Initial support of the upper section of the main tunnel of the rear tunnel; 118—Lower bench of the main tunnel of the rear tunnel; 119—Initial support of the lower section of the main tunnel of the rear tunnel; 120—Invert arch of the rear tunnel; 121—Backfill of the invert arch of the rear tunnel; 122—Secondary lining.

[0045] 201—Central Pilot Tunnel; 202—Temporary Support for Central Pilot Tunnel; 203—Central Divider Wall; 204—Temporary Support on the Rear Side of Central Pilot Tunnel; 205—Upper Section of Pilot Tunnel; 206—Initial Support for Upper Section of Pilot Tunnel; 207—Arch Foot of Lower Section of Pilot Tunnel; 208—Initial Support for Arch Foot of Lower Section of Pilot Tunnel; 209—Core Soil of Upper Bench of Pilot Tunnel; 210—Lower Bench Section of Pilot Tunnel; 211—Initial Support for Lower Section of Pilot Tunnel; 212—Invert Arch of Pilot Tunnel 213—Backfill of the invert arch of the pilot tunnel; 214—Secondary lining; 215—Upper section of the pilot tunnel; 216—Initial support of the upper section of the pilot tunnel; 217—Arch foot of the lower section of the pilot tunnel; 218—Initial support of the arch foot of the lower section of the pilot tunnel; 219—Core soil of the upper step of the pilot tunnel; 220—Lower step section of the pilot tunnel; 221—Initial support of the lower section of the pilot tunnel; 222—Invert arch of the pilot tunnel; 223—Backfill of the invert arch of the pilot tunnel; 224—Secondary lining.

[0046] 301—Central pilot tunnel, 302—Temporary support for pilot tunnel, 303—Central partition wall, 304—Temporary formwork on the rear side of the central pilot tunnel, 305—Upper section of the pilot tunnel, 306—Initial support for the upper section of the pilot tunnel, 307—Lower bench section of the pilot tunnel, 308—Initial support for the lower section of the pilot tunnel, 309—Invert arch of the pilot tunnel, 310—Backfilling of the invert arch of the pilot tunnel, 311—Secondary lining, 312—Upper bench section of the rear tunnel, 313—Initial support for the upper section of the rear tunnel, 314—Lower bench section of the rear tunnel, 315—Initial support for the lower section of the rear tunnel, 316—Invert arch of the rear tunnel, 317—Backfilling of the invert arch of the rear tunnel, 318—Secondary lining;

[0047] 401—Initial support, 402—Initial support, 403—Initial support, 404—Initial support, 405—Invert arch, 406—Initial support, 407—Invert arch, 408—Invert arch filling, 409—Secondary lining.

[0048] 501—Initial support, 502—Initial support, 503—Initial support, 504—Invert arch initial support, 505—Invert arch, 506—Invert arch filling, 507—Secondary lining.

[0049] 601—Initial support, 602—Initial support, 603—Initial support, 604—Invert arch initial support, 605—Invert arch, 606—Invert arch filling, 607—Secondary lining.

[0050] 701—Anchor plate, 702—Tie bolt, 703—One section of anchor bolt, 704—The other end of anchor bolt. Detailed Implementation

[0051] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. The embodiments of the present invention are given for illustrative and descriptive purposes only, and are not intended to be exhaustive or to limit the invention to the forms disclosed. Many modifications and variations will be apparent to those skilled in the art. The embodiments were chosen and described to better illustrate the principles and practical application of the invention, and to enable those skilled in the art to understand the invention and design various embodiments with various modifications suitable for a particular purpose.

[0052] In view of the difficulties in excavation and potential safety risks caused by the complex stress structure and numerous construction procedures of bifurcation tunnels, this embodiment provides a method for the gradual layout of bifurcation tunnels on mountain highways. This method adopts multiple excavation methods in combination and sets up corresponding support structures for each excavation method, providing a good solution for the excavation of continuous arch bifurcation tunnels.

[0053] Specifically, such as Figure 1 As shown, the highway bifurcation tunnel includes a small clearance section 1, a composite curved central wall arch tunnel section 2, an integral straight central wall gradually changing arch tunnel section 3, an integral straight central wall arch tunnel section 4, and an arch open tunnel section 5.

[0054] The process from the excavation of the separated tunnel to the construction of the small clearance section 1 is divided into three steps:

[0055] The first step involves a three-stage excavation method with pre-reserved core soil, followed by the use of SF4x-1 type lining. For example... Figure 2 and Figure 3 As shown, the specific method is as follows: Circular excavation section I; Initial support 401; Excavation section II; Initial support 402; Skip-cut excavation section III; Initial support 403; Excavation section IV; Initial support 404; Skip-cut excavation section V; Invert arch 405; Excavation sections VI-1 and VI-2; Excavation section VII; Initial support 406; Invert arch 407; Invert arch filling 408; Overall casting secondary lining 409.

[0056] The second step involves construction using a ring-shaped excavation method with a pre-reserved core soil layer, and employing SF4x-2, SF4x-3, and SF4x-c type linings. For example... Figure 4 and Figure 5 As shown, the specific method is as follows: excavate the upper sections I, II, and III in a ring; construct the initial support of the upper section 501; excavate the lower section VI in a skip-slot manner; construct the initial support of the lower section 502; excavate the lower section V in a skip-slot manner; construct the initial support of the lower section 503; excavate the core soil VI and section VI; construct the initial support of the invert arch 504; construct the invert arch 505; construct the invert arch filling 506; and construct the secondary lining in a monolithic formwork 507.

[0057] In the first and second steps, the lower section is excavated by skipping trenches. The initial support is staggered on both sides to avoid the arch feet on both sides of the upper section being suspended at the same time. The length of each drop on one side depends on the surrounding rock conditions and is generally no more than 3m. Moreover, the advance of the ring excavation should be 0.5 to 1.0m, and the core soil area should be no less than 50% of the entire upper section area.

[0058] The third step involves construction using a two-stage method, employing SF4x-4 and SF4x-d type linings. For example... Figure 6 and Figure 7 As shown, the specific method is as follows: excavate the upper section I; construct the initial support of the upper section 601; excavate the lower section I in a skip-cutting manner; construct the initial support of the lower section 602; excavate the lower section II; construct the initial support of the lower section 603; excavate section IV; construct the initial support of the invert arch 604; construct the invert arch 605; construct the invert arch filling 606; and construct the secondary lining in a monolithic formwork 607.

[0059] After the excavation and initial support of the separated tunnel are completed, the secondary lining concrete of the invert arch should be poured immediately; the cyclic advance of the upper bench excavation should not exceed the spacing of two steel frames for Class IV surrounding rock.

[0060] In the construction of the small section, the construction steps for tie rods include: construction preparation → hole layout → drilling → anchor installation → grouting → tensioning → quality acceptance.

[0061] like Figure 8 As shown, the tie rod 702 adopts a Φ28 hollow grouting anchor rod, the length of which depends on the thickness of the intermediate rock column. The standard value of the anchor rod tension stress is 60KN. In actual construction, it is controlled by over-tensioning by 10%, that is, the maximum tension stress is 66KN, in order to compensate for stress loss.

[0062] The tensioning equipment uses a through-type jack, with one end fixed using 703 cement and the other end tensioned using 704 cement. The anchor bolt fixing end and the tensioning section are arranged in a row at intervals along the tunnel's longitudinal direction, with tensioning performed intermittently on the same cross-section to avoid localized stress concentration. When applying tension with the jack, the anchor is tensioned and tightened simultaneously. The corresponding hydraulic pressure value for applying the initial prestress is generally 10% of the design hydraulic pressure, which is used as the starting point for measuring the anchor bolt elongation. The tensioning of the prestressed anchor bolts uses a dual-control method; the error in the hydraulic pressure value must not exceed ±1.5%, and the error in the elongation must not exceed ±5%.

[0063] When the pressure gauge pointer stabilizes, anchor the anchor rod by tightening the anchor plate 701. Wrap hemp fibers around the ends of the anchor rod to fully compress and seal it against the borehole wall, achieving grout stoppage and fixation around the anchor rod. Grouting parameters: initial pressure 0.5 MPa; water:cement:water glass = 1:1:0.2; cement type 32.5R; water glass viscosity 30, modulus 2.4.

[0064] During construction, no personnel are allowed to stand on the top of the jacks or on the non-tensioned anchor rods; additional protective measures must be taken. After tensioning, the anchor rods must not be struck or kicked before grouting. Grouting work must avoid the ends of the anchor rods to prevent sudden breakage and injury from the prestressed anchor rods. Under hydraulic pressure, it is strictly forbidden to disassemble any parts of the hydraulic system.

[0065] When conducting anchor bolt pull-out tests, clamp the anchor bolt and slowly and evenly apply pressure until the pressure gauge reading reaches the value corresponding to the design value, or until the anchor bolt loosens. Destructive testing is generally not performed. For every 300 anchor bolts tested, at least 3 should be selected as a group for pull-out force testing. The bolts should be evenly selected from a row of anchor bolts within the same cross-section at the test point. The average pull-out force of the anchor bolts in the same group over 28 days should meet the design requirements, and the minimum pull-out force of each anchor bolt should not be less than 90% of the design value.

[0066] The construction of section 2 of the composite curved-arch tunnel includes:

[0067] like Figure 1 As shown, the excavation of section 2 of the composite curved-arch tunnel was carried out using the two-stage method, with FLjb-type lining. Figure 9 and Figure 10 As shown, the specific method is as follows: Excavate the central pilot tunnel 301; construct temporary support for the central pilot tunnel 302; construct the central partition wall 303; construct the temporary formwork for the rear side of the central pilot tunnel 304. Excavate the upper section of the pilot tunnel 305; construct initial support for the upper section of the pilot tunnel 306; excavate the lower bench section of the pilot tunnel 307; construct initial support for the lower section of the pilot tunnel 308; construct the invert arch of the pilot tunnel 309; backfill the invert arch of the pilot tunnel 310; integrally construct the secondary lining of the pilot tunnel 311. Excavate the upper bench section of the rear tunnel 312; construct initial support for the upper section of the rear tunnel 313; excavate the lower bench section of the rear tunnel 314; construct initial support for the lower section of the rear tunnel 315; construct the invert arch of the rear tunnel 316; backfill the invert arch of the rear tunnel 317; integrally construct the secondary lining of the rear tunnel 318.

[0068] The excavation advance should not exceed 3.0m; the temporary steel frame should be dismantled after the initial support construction of the main tunnel structure is completed and stabilized, and the length of each dismantling should not exceed 5m, and it should be dismantled section by section. The invert arch should be constructed immediately after dismantling, and the two processes should be carried out alternately. After the length of the invert arch construction reaches the length of one lining by the lining trolley, the secondary lining of the arch wall should be poured in a timely manner.

[0069] The composite curved-in-center wall, also known as the composite curved-in-center wall arch tunnel section 2, is a composite structure consisting of a reinforced concrete arch shell and reinforced concrete with a steel mesh. Recent research indicates that the composite curved-in-center wall can better adapt to larger deformations and geological conditions, improving the stability and safety of the tunnel. In terms of design, researchers have also proposed some new ideas, such as using a reinforced steel plate design to improve the load-bearing performance of the curved-in-center wall.

[0070] The transition section of the composite curved-wall arch tunnel segment 2 refers to the different structural forms adopted at both ends of the curved wall to adapt to different geological conditions. The application of the composite curved-wall transition section in bifurcated tunnels has the following innovative aspects:

[0071] 1. Employing Multiple Structural Forms: Traditional integral straight-center wall transition sections in bifurcation tunnels typically employ a single structural form, such as variable cross-section or variable thickness. Current innovations utilize multiple structural forms, such as variable cross-section, variable thickness, and variable materials, to adapt to different geological conditions and stress states, thereby improving tunnel stability and safety. 2. Using New Materials: To enhance the support effect and applicability of integral straight-center wall transition sections in bifurcation tunnels, the application of new materials is another innovation. For example, the use of high-strength steel fiber reinforced concrete and carbon fiber can improve the load-bearing performance and durability of the transition section. 3. Optimizing Structural Design: With the development of computer-aided design technology, the structural design of integral straight-center wall transition sections in bifurcation tunnels has been greatly improved. Optimizing the structural design can improve the load-bearing performance and seismic resistance of the transition section, reducing the deformation and risk of failure of the support structure. 4. Employing New Construction Methods: Traditional construction methods for integral straight-center wall transition sections in bifurcation tunnels generally involve manual casting or formwork casting, but these methods suffer from low efficiency and long construction periods. Current innovations involve adopting new construction methods, such as modular construction and prefabricated components, which can improve construction efficiency and quality while reducing construction difficulty and costs. 5. Utilizing intelligent technology: With the development of intelligent technology, some innovations have also emerged in the application of integral straight-center wall transition sections in bifurcated tunnels. For example, sensors and monitoring systems are used to monitor and analyze the deformation and stress of the transition section in real time, providing early warnings of potential damage risks to the tunnel support structure and ensuring the safe operation of the tunnel.

[0072] In summary, the application of integral straight center wall transition sections in bifurcation tunnels presents numerous innovations. These innovations contribute to improving the support effect and applicability of the transition sections, while also enhancing the stability and safety of the tunnel. In the future, with continuous technological development and progress, the application of integral straight center wall transition sections in bifurcation tunnels has significant room for growth, enabling better adaptation to different geological conditions and stress states, and providing more reliable support for tunnel engineering construction.

[0073] The construction of section 3 of the integral straight-center-wall gradually changing arch tunnel includes:

[0074] like Figure 1 As shown, the excavation of section 3 of the integral straight-center-wall gradually changing arch tunnel was carried out using the two-stage annular excavation method with reserved core soil, and ZLjb-1 and ZLjb-2 type linings were adopted. Figure 11 and Figure 12 As shown, the specific method is as follows: excavate the central pilot tunnel 201; construct temporary support for the central pilot tunnel 202; construct the central partition wall 203; construct temporary support for the rear side of the central pilot tunnel 204. Circularly excavate the upper section of the pilot tunnel 205; construct initial support for the upper section of the pilot tunnel 206; excavate the arch foot of the lower section of the pilot tunnel 207; construct initial support for the arch foot of the lower section of the pilot tunnel 208; excavate the core soil of the upper step of the pilot tunnel 209; excavate the lower step section of the pilot tunnel 210; construct initial support for the lower section of the pilot tunnel 211; construct the invert arch of the pilot tunnel 212; backfill the invert arch of the pilot tunnel 213; integrally construct the secondary lining of the pilot tunnel 214. 215. Construction of the upper section of the tunnel after ring excavation; 216. Construction of the initial support of the upper section of the tunnel; 217. Construction of the arch foot of the lower section of the tunnel after skip excavation; 218. Construction of the initial support of the arch foot of the lower section of the tunnel; 219. Excavation of the core soil of the upper bench of the tunnel; 220. Construction of the lower bench section of the tunnel; 221. Construction of the invert arch of the tunnel; 222. Backfilling of the invert arch of the tunnel; 224. Secondary lining of the tunnel after integral casting.

[0075] The excavation advance should be 0.6 to 1.2 meters, and the core soil area should be no less than 50% of the total upper half cross-sectional area.

[0076] The construction of section 4 of the integral straight-center-wall-connected arch tunnel includes:

[0077] like Figure 1 As shown, the excavation of section 4 of the monolithic straight-center-wall continuous arch tunnel was carried out using the three-guide tunnel method, with Zlg-type lining. Figure 13 and Figure 14As shown, the specific methods are as follows: excavate the central pilot tunnel 101; construct temporary support for the central pilot tunnel 102; construct the central partition wall 103; construct temporary horizontal bracing on the rear side of the central pilot tunnel 104. Excavate the pilot tunnel side pilot pit 105; construct initial support for the pilot tunnel side pilot tunnel 106; construct initial support for the rear tunnel side pilot tunnel 108; excavate the upper step of the main tunnel of the pilot tunnel 109; construct initial support for the upper section of the pilot tunnel 110; excavate the lower step of the main tunnel of the pilot tunnel 111; construct initial support for the lower section of the pilot tunnel 112; construct the invert arch of the pilot tunnel 113; backfill the invert arch of the pilot tunnel 114; and integrally construct the secondary lining of the pilot tunnel 115. 107. After excavation, the side pilot tunnel of the tunnel is opened; 116. The upper step of the main tunnel of the tunnel is opened; 117. Initial support of the upper section of the main tunnel of the tunnel is constructed; 118. The lower step of the main tunnel of the tunnel is opened; 119. Initial support of the lower section of the main tunnel of the tunnel is constructed; 120. The invert arch of the tunnel is constructed; 121. Backfilling of the invert arch of the tunnel; 122. Secondary lining of the tunnel is constructed in a monolithic formwork.

[0078] During the three-guide tunnel construction, the cyclic advance is 0.6m, and the step length is controlled between 6 and 8 meters. The other side can only be excavated after the first side excavation and initial support are completed and the strength reaches 70%.

[0079] In the integral straight-center-wall gradually changing arch tunnel section 3 and integral straight-center-wall arch tunnel section 4, the integral straight-center wall refers to a partition wall structure used in subway or other tunnel projects. Its construction is relatively complex and usually requires consideration of many factors, including safety, reliability, durability, and economy. In this embodiment, the minimum spacing between the straight-center walls in the composite curved-center-wall arch tunnel section 2, integral straight-center-wall gradually changing arch tunnel section 3, and integral straight-center-wall arch tunnel section 4 is 1.5m. The minimum spacing between the straight-center walls refers to the distance between the central partition walls 103, 203, and 303 and the curved sections of the bifurcated tunnels on both sides. This application has the following innovative points:

[0080] 1. Increased Tunnel Capacity: Using monolithic straight central walls with a minimum spacing of 1.5m increases tunnel capacity, reduces vehicle queuing time, alleviates traffic congestion, and improves road efficiency. 2. Reduced Tunnel Area: Using monolithic straight central walls with a minimum spacing of 1.5m reduces the tunnel's cross-sectional area, lowering construction and maintenance costs, and also reducing the tunnel's impact on the surrounding environment. 3. Improved Tunnel Safety: Using monolithic straight central walls with a minimum spacing of 1.5m improves tunnel stability and safety, reducing accidents caused by internal structural damage. Furthermore, the 1.5m spacing provides a more robust support structure, increasing the tunnel's seismic resistance and ensuring safe operation during natural disasters such as earthquakes. 4. Optimized Structural Design: With the development of computer-aided design technology, the structural design of monolithic straight central walls with a minimum spacing of 1.5m has been greatly improved. Optimized structural design enhances the tunnel's load-bearing capacity and seismic resistance, reducing deformation and the risk of damage to the support structure. 5. Improved construction efficiency: The integral straight central wall with a minimum spacing of 1.5m adopts some new construction technologies, such as prefabricated components and modular construction, which can improve construction efficiency and quality, and reduce construction difficulty and cost.

[0081] In summary, the application of monolithic straight centerwalls with a minimum spacing of 1.5m presents numerous innovations. These innovations contribute to improving tunnel capacity, reducing construction costs, enhancing tunnel safety and stability, and simultaneously improving construction efficiency and quality. In the future, with continuous technological development and progress, the application of monolithic straight centerwalls with a minimum spacing of 1.5m has significant room for further development, enabling them to better adapt to different geological conditions and stress states, providing more reliable support for tunnel engineering construction.

[0082] In the construction of integral straight-center-wall continuous tunnels in bifurcated tunnels, the lack of internal support, coupled with the complexity of the tunnel cross-section design and geological conditions, makes them prone to dangerous situations such as collapse. In this embodiment, during the construction of composite curved-center-wall continuous arch tunnel section 2, integral straight-center-wall gradual-arch tunnel section 3, and integral straight-center-wall continuous arch tunnel section 4, temporary formwork 304, temporary support 204, and temporary cross brace 104 are constructed on the rear side of the pilot tunnel. The specific significance of constructing these temporary formwork 304, temporary support 204, and temporary cross brace 104 is as follows:

[0083] 1. Improved Construction Safety: The special temporary cross bracing on the rear side provides effective support to the tunnel area, effectively preventing collapses and other accidents during construction. It also improves efficiency while ensuring construction safety. 2. Reduced Engineering Risks: Using special temporary cross bracing on the rear side significantly reduces the risks and uncertainties in tunnel construction. It also reduces the risk of traffic accidents caused by construction, thus ensuring road safety and smooth traffic flow. 3. Increased Construction Efficiency: Using special temporary cross bracing on the rear side improves construction efficiency, shortens construction time, and further reduces the time gap between construction and road opening, allowing roads to be put into use sooner and promoting regional economic development. 4. Promotion of New Technologies: Using special temporary cross bracing on the rear side not only has practical significance but also promotes the application of new construction technologies, contributing to the progress and development of the construction industry.

[0084] Conventional shotcrete is used on the upper part of the partition wall. However, conventional shotcrete can lead to problems such as incomplete compaction, poor waterproofing, and water leakage in the tunnel. It can also not withstand the force of the tunnel face, resulting in poor tunnel stability and partition wall tilting. In this embodiment, partition walls 103, 203, and 303 are all grouted using pre-embedded 42×4 grouting pipes, thereby avoiding the above problems.

[0085] The monolithic straight center wall, specifically the monolithic straight center wall transitional arch tunnel section 3 and monolithic straight center wall arch tunnel section 4, is a continuous support system installed inside the tunnel. It effectively disperses ground pressure and controls surrounding rock deformation. Recent research shows that, compared to traditional anchor mesh support, the monolithic straight center wall provides better control over surrounding rock deformation and reduces the amount of deformation in the support structure. Furthermore, in recent years, the application of new materials, such as high-strength steel fiber reinforced concrete, has also led to new breakthroughs in the support performance of monolithic straight center walls.

[0086] After the construction of the monolithic straight-center-wall continuous arch tunnel section 4 was completed, the excavation of the continuous arch open-cut tunnel section 5 commenced. Section 5 utilizes ZLm-type lining. The gradual layout method for the bifurcated tunnels of this mountainous expressway, employing both monolithic straight-center walls and composite curved-center walls, demonstrates the respective advantages and applicability of these two support methods in tunnel support. In the future, these two support forms have significant room for development, and their support effectiveness and applicability can be improved through the application of new materials and design innovation.

[0087] The gradual layout method for bifurcation tunnels on mountainous expressways integrates three forms: integral straight center wall, integral straight center wall transition section, and composite curved center wall. The integral straight center wall features a minimum spacing of 1.5m, while the transition section is long. In the design of bifurcation tunnels, various support structures are often used to adapt to different geological conditions and stress states. Integral straight center walls, integral straight center wall transition sections, and composite curved center walls are three commonly used forms. The significance of combining these three forms in the design of bifurcation tunnels is as follows:

[0088] 1. Enhanced Tunnel Stability and Safety: The combined use of three types of support structures—monolithic straight centerwalls, monolithic straight centerwall transition sections, and composite curved centerwalls—provides a more robust support structure, increases the tunnel's seismic resistance, and ensures safe operation during natural disasters such as earthquakes. This combination also reduces accidents caused by internal structural damage. 2. Adaptability to Different Geological Conditions and Stress: The combined use of these three types of support structures better adapts to different geological conditions and stress conditions. For example, composite curved centerwalls are suitable for curved sections, effectively reducing lateral displacement and settlement; monolithic straight centerwall transition sections are suitable for geologically variable conditions, improving the stability of the support structure.

[0089] 3. Optimize structural design: The combination of three forms—integrated straight central wall, integrated straight central wall transition section, and composite curved central wall—can optimize structural design, improve the tunnel's stress performance and seismic performance, and reduce the deformation and damage risk of the support structure.

[0090] 4. Improve construction efficiency and quality: The combination of three forms—integrated straight central wall, integrated straight central wall transition section, and composite curved central wall—allows for the adoption of new construction technologies, such as prefabricated components and modular construction, thereby improving construction efficiency and quality while reducing construction difficulty and costs.

[0091] In conclusion, the combined use of three forms—integrated straight center wall, integrated straight center wall transition section, and composite curved center wall—is of great significance in the design of bifurcated tunnels. It can improve the stability and safety of the tunnel, adapt to different geological conditions and stress conditions, optimize structural design, and improve construction efficiency and quality.

[0092] The data parameters for each lining in the gradual layout method of the bifurcation tunnel of the mountain expressway can be found in the table below.

[0093]

[0094] In addition, on-site monitoring and measurement are required during construction operations. Existing technologies will be used for monitoring and measurement, which will not be elaborated here. However, the following mandatory measurement items must be included in each section of construction.

[0095] Among them, the mandatory test items for separated tunnels are:

[0096] Four mandatory measurement items are: geological and support condition observation, surrounding displacement, arch subsidence, and surface subsidence of tunnel entrances with a burial depth of less than twice the excavation width and shallow buried sections.

[0097] Bifurcated tunnel arch section:

[0098] For arch tunnels, blasting vibration is listed as a mandatory test item based on the separate tunnel design, and the blasting vibration velocity is required to be less than 15cm / s.

[0099] By organizing and regressing the above measurement data, we can find its inherent patterns, evaluate the stability of the surrounding rock and the support effect, and then use the displacement back analysis method to calculate the initial stress field and comprehensive physical and mechanical parameters of the surrounding rock, and compare and verify them with the actual results.

[0100] Bifurcated Tunnel Small Clearance Section 1:

[0101] Required testing items: geological and support condition observation, surrounding displacement, arch subsidence, surface subsidence of tunnel entrances with a burial depth less than twice the excavation width and shallow buried sections, and blasting vibration (blasting vibration velocity less than 15cm / s).

[0102] In addition, the gradual layout method of the branching tunnels on mountainous highways can be optimized in the following ways: 1. Tunnel entrance design: A separate tunnel entrance design can be considered to separate the ramps and avoid traffic congestion caused by lane changes. 2. Autonomous driving technology: Introduce autonomous driving technology into the branching tunnels on mountainous highways, using intelligent transportation systems to help drivers quickly and accurately choose the correct route and avoid traffic accidents and congestion caused by wrong turns. 3. Risk warning and rescue system: Install risk warning and rescue systems in the branching tunnels on mountainous highways, such as LED electronic displays and emergency call systems, to help drivers respond quickly to emergencies. 4. Energy conservation and environmental protection: Promote energy conservation and environmental protection awareness in the branching tunnels on mountainous highways, for example, using new energy technologies such as solar energy to provide electricity for infrastructure such as lighting and ventilation systems. 5. Vehicle priority passage: For vehicle passage in the branching tunnels on mountainous highways, dedicated lanes can be set up for specific vehicles (such as buses and emergency vehicles) to ensure their priority passage. In addition, intelligent speed limit and distance monitoring systems can be installed in the tunnels to ensure vehicle driving safety.

[0103] Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art and related fields based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention. Structures, devices, and operating methods not specifically described and explained in the present invention, unless otherwise specified or limited, shall be implemented according to conventional means in the art.

Claims

1. A method for gradually changing the layout of bifurcated tunnels on mountain highways, characterized in that: The gradual layout method of the bifurcation tunnel of the mountain expressway adopts different construction methods and different lining types in different sections of the bifurcation tunnel; Includes the following steps: The construction of the narrow clearance section of the bifurcation tunnel is divided into three steps: The first step is to use the three-stage excavation method with reserved core soil and SF4x-1 type lining; the second step is to use the ring excavation method with reserved core soil and SF4x-2, SF4x-3, and SF4x-c type lining; the third step is to use the two-stage method and SF4x-4 and SF4x-d type lining. Second, the composite curved wall arch tunnel section of the bifurcated tunnel is constructed using the two-stage method and FLjb type lining. Third, the integral straight central wall gradually changing arch tunnel section of the bifurcation tunnel is constructed using the two-stage ring excavation method with reserved core soil, and ZLjb-1 and ZLjb-2 type linings are used. Fourth, the integral straight-center wall arch tunnel section of the bifurcated tunnel is constructed using the three-guide tunnel method and adopts Zlg-type lining. Fifth, the open-cut section of the bifurcated tunnel adopts ZLm-type lining; In the first, second, and third steps of the construction of the small clearance section of the bifurcation tunnel, the cross-section is excavated from the outside to the inside and from high to low. After the outer cross-section is excavated, the corresponding initial support is installed. After the inner cross-section is excavated, the invert arch and invert arch filling are installed. Finally, the overall formwork secondary lining is carried out. In the first and second steps of construction of the small clearance section of the bifurcation tunnel, the lower section is excavated by skip-cutting, and the initial support is laid down on both sides in a staggered manner. The length of each landing on each side depends on the surrounding rock conditions, and is generally no more than 3m. The circumferential excavation advance is 0.5 to 1.0m, and the core soil area is not less than 50% of the entire upper half section area. In the third step of the construction of the small clearance section of the bifurcation tunnel, after the excavation and initial support of the separated tunnel are completed, the secondary lining concrete of the invert arch is poured immediately, and the cyclic advance of the upper step excavation is no more than 2 steel frame spacings for Class IV surrounding rock. In the construction of the composite curved central wall arch tunnel section, the integral straight central wall gradually changing arch tunnel section, and the integral straight central wall arch tunnel section of the bifurcated tunnel, the central pilot tunnel is excavated first, followed by the excavation of the pilot tunnel, and finally the excavation of the follow tunnel. During the excavation of the central pilot tunnel, temporary support, central partition wall, and temporary formwork or temporary support or temporary cross bracing on the rear side are constructed. During the excavation of both the first and second tunnels, the cross-sections were excavated from the outside to the inside and from high to low. After the outer cross-section was excavated, the corresponding initial support was installed. After the inner cross-section was excavated, the invert arch and invert arch were filled. Finally, the overall formwork was used for secondary lining. In the construction of the composite curved wall arch tunnel section of the bifurcated tunnel, the excavation advance shall not exceed 3.0m; the temporary steel frame shall be dismantled after the initial support construction of the main tunnel structure is completed and stabilized, and the length of each dismantling shall not exceed 5m, and it shall be dismantled section by section; the invert arch shall be constructed immediately after dismantling, and the two processes shall be carried out alternately; after the length of the invert arch construction reaches the length of one lining by the lining trolley, the secondary lining of the arch wall shall be poured in a timely manner. In the construction of the integral straight-center wall arch tunnel section of the bifurcated tunnel, the cycle advance is 0.6m when using the three-guide tunnel method, and the step length is controlled between 6 and 8 meters; the other side can only be excavated after the first side excavation and initial support are completed and the strength reaches 70%. During the construction of each section of the bifurcated tunnel, the following necessary testing items are included: geological and support condition observation, surrounding displacement, arch settlement, surface settlement of the tunnel entrance with a burial depth of less than twice the excavation width and shallow buried section, and blasting vibration velocity of less than 15cm / s. By sorting out and regressing the above measurement data, the inherent laws are found, the stability of the surrounding rock and the support effect are evaluated, and then the displacement back analysis method is used to reverse the initial stress field and comprehensive physical and mechanical parameters of the surrounding rock, and compare and verify with the actual results.

2. The method for gradually changing the layout of bifurcated tunnels on mountain expressways according to claim 1, characterized in that: During the construction of the integral straight-center wall gradually changing arch tunnel section of the bifurcated tunnel, the excavation advance is 0.6 to 1.2 meters, and the core soil area should not be less than 50% of the entire upper half cross-section area.

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