Construction method for structural conversion of complex tunnel section

Abstract

The present invention relates to a construction method for structural conversion of a complex tunnel section, comprising the following steps: A. Excavate the small tunnel (1), and conduct initial support during excavation; B. Gradually expand the excavation area of the half-width (A) where the small tunnel (1) converges with the large tunnel (2) at an obtuse angle within the convergence area; C. Within the convergence area, excavate the other half-width of the small tunnel in a direction opposite to the above-mentioned excavation direction of the small tunnel (1), and gradually expand the excavation area at the same time; D. Conduct initial support on the top of the convergence area and adopt temporary support; E. Continue the excavation construction of the small tunnel (1), and conduct initial support during excavation; F. Within the convergence area, simultaneously excavate the large tunnel in the reverse direction, and conduct initial support during excavation. The method of the present invention is directed at the structural conversion of a complex tunnel section formed after the convergence of multiple tunnels with different cross-sectional sizes, controls the deformation of the tunnel stratum in the convergence section, and can accelerate the construction progress and ensure construction safety.

Description

Technical Field

[0001] The present invention relates to the construction technical field of tunnel engineering, and particularly to a construction method for structural conversion of a complex tunnel section. Background Art

[0002] At present, with the development of the urbanization process in China, the tunnel construction project has also entered a new peak period of development. The urban development space extends underground, and the urban underground engineering projects are gradually increasing. Many cities have planned a large number of underground tunnel engineering projects.

[0003] During tunnel construction, in order to ensure the construction period and site, multiple tunnels are often constructed simultaneously. Therefore, complex tunnel situations such as large-span, variable-section, and confluent tunnel construction will inevitably occur. Due to the influence of the geological structure and the limitation of construction technology, the structural conversion construction of complex tunnel sections is difficult. The erection of support and reinforcement structures affects each other, engineering accidents are likely to occur, there are certain construction risks, and the control during the construction process is prone to deviation, affecting the construction period and quality.

[0004] Therefore, in order to ensure the stability of complex tunnels, it is necessary to reasonably arrange the construction and study a construction method for structural conversion applicable to complex tunnel sections. Summary of the Invention

[0005] In order to overcome the above defects existing in the prior art, the present invention provides a construction method for structural conversion of a complex tunnel section. The method of the present invention is aimed at the structural conversion of a complex tunnel section formed after the confluence of multiple tunnels with different cross-section sizes, controls the deformation of the tunnel strata in the confluence section, and can accelerate the construction progress and ensure construction safety.

[0006] To achieve the above object, the present invention provides a construction method for structural conversion of a complex tunnel section, including the following steps:

[0007] A. Excavate a small tunnel with a small excavation cross-section size according to a predetermined size, and carry out the initial support of the small tunnel while excavating.

[0008] B. When excavating to one side line of the confluence area with another large tunnel having a large excavation cross-section size, continue to excavate half of the small tunnel in the longitudinal direction of the small tunnel towards the confluence area. At the same time, gradually expand the excavation area of the half of the small tunnel that converges with the large tunnel at an obtuse angle in the confluence area until excavating to the other side line of the confluence area with the large tunnel.

[0009] C. In the confluence area, starting from the other side line of the large tunnel, excavate the other half of the small tunnel in the direction opposite to the above excavation direction of the small tunnel, and gradually expand the excavation area until excavating to the above-mentioned one side line of the large tunnel.

[0010] D. Carry out initial support on the top excavation part of the small tunnel within the confluence area, and use a temporary support structure to temporarily support the top and side wall parts of the small tunnel within the confluence area;

[0011] E. Within the confluence area, starting from the other side line of the large tunnel, continue to carry out the excavation construction of the small tunnel in the excavation direction of step A according to a predetermined size, and carry out the initial support of the small tunnel while excavating;

[0012] F. After step E has been carried out for 10 - 15 meters, within the confluence area, remove the temporary support structure, and then starting from the gradually expanding excavation area part of the small tunnel, respectively along the longitudinal direction of the large tunnel, simultaneously and reversely excavate the large tunnel according to a predetermined size, and carry out the initial support of the large tunnel while excavating.

[0013] Preferably, in step B, the half-width gradually expanding excavation area means that the top and side wall parts of the half-width are gradually extended outward to the small tunnel along the longitudinal direction of the large tunnel, and the extended side wall part forms an angle of 45 - 60 degrees with the side wall part in the normal longitudinal direction of the small tunnel.

[0014] Preferably in any of the above solutions, in step C, the gradually expanding excavation area is symmetrically opposite to the half-width gradually expanding excavation area in step B with respect to the center line of the small tunnel.

[0015] Preferably in any of the above solutions, in steps B and C, in order to eliminate the influence brought by stress concentration, the confluence part where the extended side wall part forms an angle with the side wall part in the normal longitudinal direction of the small tunnel is subjected to arc trimming treatment, and the radian is (2 / 3 - 3 / 4)*π.

[0016] Preferably in any of the above solutions, in step D, the temporary support structure is a plurality of detachable and assembled steel frame structures, which are processed from I-beams. The top of the steel frame structure is adaptively extended according to the height and width of the tunnel top in the confluence area; the component members of the steel frame structure are connected by mortise and tenon joints to achieve convenient and stable connection, and the connection between multiple steel frame structures adopts a strengthening structure.

[0017] Preferably in any of the above solutions, during the excavation process, the pre-grouting process is used to reinforce the excavated small tunnel and large tunnel; the radial spacing of each grouting pipe is maintained at 2 - 2.5 m, and the cross-section of the overall grouting pipe is arranged in a regular hexagon; and through numerical analysis method simulation, the excavation footage and support plan are determined.

[0018] The beneficial effects of the present invention are:

[0019] 1. The method of the present invention is directed to the structural conversion of a complex tunnel section formed after the convergence of multiple tunnels with different cross-sectional sizes. It comprehensively considers factors such as the stress conditions of the complex cross-sectional structure, adopts specific excavation methods and excavation sequences, successfully realizes the structural conversion and transition, strictly controls the deformation of the tunnel strata in the convergence section, and can accelerate the construction progress and ensure construction safety.

[0020] 2. The present invention solves the problem of temporary support in the structural conversion area of the complex tunnel section, facilitates the smooth progress of the project construction, and ensures the safety of the construction environment at the same time; the temporary support structure can be well integrated with the initial support structure, has good support effect, and ensures the construction space in the structural conversion area without affecting the normal construction progress.

[0021] 3. The construction method of the present invention has clear stress and construction safety. Through numerical analysis and simulation, it can provide an optimization basis for the construction footage and support plan, so as to achieve the purpose of saving the construction period and reducing costs.

[0022] 4. The present invention provides key technical support for the construction of large spaces in excavated tunnels. The method provided is not limited by the project scale and has wide applicability; during the excavation process of the underground space, the impact on the above-ground traffic, production, and life is small, the technical difficulty during the construction process is relatively small, the construction speed is fast, and the safety and economy are high, greatly improving the technical competitiveness. Brief Description of the Drawings

[0023] Figure 1 It is a schematic diagram of the complex tunnel section targeted by the construction method according to the present invention. Detailed Embodiments

[0024] The technical solutions of the present application will be described in detail below in combination with the specific embodiments and drawings of the present application. However, the following embodiments are only for understanding the present invention. The embodiments in the present application and the features in the embodiments can be combined with each other. The present application can be implemented in many different ways defined and covered by the claims.

[0025] Embodiment 1

[0026] See Figure 1 , a construction method for the structural conversion of a complex tunnel section, including the following steps:

[0027] A. Excavate the small tunnel 1 with a small excavation cross-sectional size according to the predetermined size, and carry out the initial support of the small tunnel 1 while excavating.

[0028] B. When excavating to one side line of the convergence area with the large tunnel 2 having a large excavation cross-section size, continue to excavate half-width A of the small tunnel 1 along the depth direction of the small tunnel 1 towards the convergence area. At the same time, gradually expand the excavation area of half-width A where the small tunnel 1 converges with the large tunnel 2 at an obtuse angle until excavating to the other side line of the convergence area with the large tunnel 2;

[0029] C. Within the convergence area, starting from the other side line of the large tunnel 2, excavate the other half-width of the small tunnel in the direction opposite to the above excavation direction of the small tunnel 1, and gradually expand the excavation area until excavating to the said one side line of the large tunnel 2;

[0030] D. Carry out primary support for the top excavation part of the small tunnel 1 within the convergence area, and use a temporary support structure to temporarily support the top and side wall parts of the small tunnel 1 within the convergence area;

[0031] E. Within the convergence area, starting from the other side line of the large tunnel 2, continue to carry out the excavation construction of the small tunnel 1 in accordance with the predetermined size along the excavation direction in step A, and carry out the primary support of the small tunnel 1 while excavating;

[0032] F. After step E has been carried out for 10 meters, within the convergence area, remove the temporary support structure, and then starting from the part where the excavation area of the small tunnel 1 is gradually expanded, excavate the large tunnel in the depth direction of the large tunnel 2 in the reverse direction at the same time in accordance with the predetermined size, and carry out the primary support of the large tunnel 2 while excavating.

[0033] In step B, the gradual expansion of the excavation area of half-width A means that the top and side wall parts of half-width A are gradually extended outward from the small tunnel 1 along the depth direction of the large tunnel 2, and the extended side wall part forms an angle of 60 degrees with the side wall part in the normal depth direction of the small tunnel 1.

[0034] In step C, the gradual expansion of the excavation area is symmetrically opposite to the gradual expansion of the excavation area of half-width A in step B with respect to the center line X of the small tunnel 1.

[0035] In steps B and C, in order to eliminate the influence brought by stress concentration, the converging part where the extended side wall part forms an angle with the side wall part in the normal depth direction of the small tunnel 1 is subjected to arc trimming treatment, and the radian is 2π / 3.

[0036] In step D, the temporary support structure is multiple detachable and assembled steel frame structures, which are processed from I-beams. The top of the steel frame structure is adaptively expanded according to the height and width of the tunnel top in the convergence area; the component members of the steel frame structure are connected by mortise and tenon joints to achieve convenient and stable connection, and the connection between multiple steel frame structures adopts a strengthening structure.

[0037] During the excavation process, the pre-grouting process is used to reinforce the small tunnel 1 and the large tunnel 2 being excavated; the radial spacing of each grouting pipe is maintained at 2.5 m, and the cross-section of the overall grouting pipe is arranged in a regular hexagon; and through numerical analysis simulation, the excavation footage and support plan are determined.

[0038] Embodiment 2

[0039] See Figure 1 , a construction method for structural conversion of a complex tunnel section, comprising the following steps:

[0040] A. The small tunnel 1 with a small excavation section size is excavated according to a predetermined size, and the initial support of the small tunnel 1 is carried out while excavating.

[0041] B. When excavating to one side line of the confluence area with another large tunnel 2 with a large excavation section size, continue to excavate the half-width A of the small tunnel 1 along the depth direction of the small tunnel 1 in the confluence area, and at the same time gradually expand the excavation area of the half-width A where the small tunnel 1 and the large tunnel 2 meet at an obtuse angle until excavating to the other side line of the confluence area with the large tunnel 2.

[0042] C. In the confluence area, starting from the other side line of the large tunnel 2, excavate the other half-width of the small tunnel in the direction opposite to the above excavation direction of the small tunnel 1, and at the same time gradually expand the excavation area until excavating to the said one side line of the large tunnel 2.

[0043] D. Carry out the initial support for the top excavation part of the small tunnel 1 in the confluence area, and use a temporary support structure to temporarily support the top and side wall parts of the small tunnel 1 in the confluence area.

[0044] E. In the confluence area, starting from the other side line of the large tunnel 2, continue to excavate the small tunnel 1 according to a predetermined size along the excavation direction of step A, and carry out the initial support of the small tunnel 1 while excavating.

[0045] F. After step E has been carried out for 15 m, in the confluence area, remove the temporary support structure, and then starting from the part where the excavation area of the small tunnel 1 is gradually expanded, respectively along the depth direction of the large tunnel 2, excavate the large tunnel in the reverse direction according to a predetermined size while excavating, and carry out the initial support of the large tunnel 2 while excavating.

[0046] In step B, the gradual expansion of the excavation area of the half-width A means that the top and side wall parts of the half-width A are gradually extended outward along the depth direction of the large tunnel 2 towards the outside of the small tunnel 1, and the extended side wall part forms an angle of 45 degrees with the side wall part in the normal depth direction of the small tunnel 1.

[0047] In step C, the gradually expanding excavation area is symmetrically opposite to the gradually expanding excavation area of half-width A in step B with respect to the center line X of the small tunnel 1.

[0048] In steps B and C, in order to eliminate the influence brought by stress concentration, arc trimming treatment is carried out on the confluence part where the extended side wall part and the side wall part in the normal depth direction of the small tunnel 1 form an angle, and the radian is 3π / 4.

[0049] In step D, the temporary support structure is composed of multiple detachable and assembled steel frame structures, which are processed from I-beams. The top of the steel frame structure is adaptively expanded according to the height and width of the tunnel top in the confluence area; the component parts of the steel frame structure are connected by mortise and tenon joints to achieve convenient and stable connection, and the connection between multiple steel frame structures adopts a strengthening structure.

[0050] During the excavation process, the pre-grouting process is used to reinforce the excavated small tunnel 1 and large tunnel 2; the radial spacing of each grouting pipe is kept at 2 m, and the cross-section of the overall grouting pipe is arranged in a regular hexagon; and the excavation footage and support plan are determined through numerical analysis simulation.

[0051] In order to further improve the technical effect of the present invention, in this embodiment, the steel frame structures are evenly spaced according to the space size of the confluence area and are formed by stamping, and its overall structure conforms to the space form in the confluence area. Connection strengthening members are arranged at the joints of the component parts of the steel frame structure, and the connection strengthening members and the component parts are fastened together by bolts.

[0052] In this embodiment, in view of the influence brought by stress concentration generated after the side walls of different tunnels in the structure conversion area are confluent, special arc trimming treatment is taken. In addition to the aforementioned arc treatment for the tunnel side walls, the following measures are also taken for the arc trimming treatment:

[0053] a. After the arc treatment is carried out on the confluence part where the extended side wall part and the side wall part in the normal depth direction of the small tunnel 1 form an angle, prestressed anchor rods are evenly drilled to half of the preset depth in the entire area of the treatment position, and a metal grid is anchored on the surface of the treatment position to completely cover the surface of the treatment position;

[0054] b. Continue to drill the prestressed anchor rods until the preset depth is reached; a second layer of metal grid is anchored again on the surface of the above-mentioned metal grid;

[0055] c. A plurality of grouting holes and pressure-relieving anchor cable holes are evenly drilled around the prestressed anchor rods in the treatment position, and prestressed pressure-relieving anchor cables are installed; the orifices of the grouting holes are temporarily blocked;

[0056] d. Spray shotcrete on the entire surface area of the treatment location to evenly distribute the tunnel's underlying load on the above-mentioned structure and avoid stress concentration.

[0057] e. Remove the temporary plugging of the grouting holes and carry out closed grouting reinforcement; then spray shotcrete again on the entire surface area of the treatment location to seal the grouting holes.

[0058] The above-mentioned arc trimming treatment utilizes the change in structural form and the coordinated cooperation of rock bolts, grouting, metal grids, yielding anchor cables, and shotcrete to cause appropriate and controllable expansion of deep formation fissures, transfer the stress concentration area to deeper depths, and then strengthen it to achieve the coupling of the formation and the strengthening treatment, eliminate the influence brought by stress concentration, enable the structure in this area to have the characteristics of adapting to long-term tunnel deformation and wide failure range, and improve the ability to jointly resist formation deformation.

[0059] Example 3

[0060] See Figure 1 , a construction method for structural conversion of a complex tunnel section, including the following steps:

[0061] A. Excavate the small tunnel 1 with a small excavation section size according to the predetermined dimensions, and carry out the initial support of the small tunnel 1 while excavating.

[0062] B. When excavating to one side edge of the convergence area with the large tunnel 2 having a large excavation section size, continue to excavate the half-width A of the small tunnel 1 in the depth direction of the small tunnel 1 in the convergence area, and at the same time gradually expand the excavation area of the half-width A where the small tunnel 1 converges with the large tunnel 2 at an obtuse angle until excavating to the other side edge of the convergence area with the large tunnel 2.

[0063] C. In the convergence area, starting from the other side edge of the large tunnel 2, excavate the other half-width of the small tunnel in the direction opposite to the above excavation direction of the small tunnel 1, and at the same time gradually expand the excavation area until excavating to the said one side edge of the large tunnel 2.

[0064] D. Carry out the initial support for the top excavation part of the small tunnel 1 in the convergence area, and use a temporary support structure to temporarily support the top and side wall parts of the small tunnel 1 in the convergence area.

[0065] E. In the convergence area, starting from the other side edge of the large tunnel 2, continue to excavate the small tunnel 1 according to the predetermined dimensions in the excavation direction of step A, and carry out the initial support of the small tunnel 1 while excavating.

[0066] F. After step E has advanced 13 meters, within the confluence area, remove the temporary support structure, and then starting from the gradually expanding excavation area part of the small tunnel 1, respectively along the longitudinal direction of the large tunnel 2, simultaneously and reversely excavate the large tunnel according to a predetermined size, and carry out the initial support of the large tunnel 2 while excavating.

[0067] In step B, the gradually expanding excavation area of the half-width A means that the top and side wall parts of the half-width A are gradually extended outward along the longitudinal direction of the large tunnel 2 to the outside of the small tunnel 1, and the extended side wall part forms an angle of 50 degrees with the side wall part in the normal longitudinal direction of the small tunnel 1.

[0068] In step C, the gradually expanding excavation area is symmetrically opposite to the gradually expanding excavation area of the half-width A in step B with respect to the center line X of the small tunnel 1.

[0069] In steps B and C, in order to eliminate the influence brought by stress concentration, the confluence part where the extended side wall part forms an angle with the side wall part in the normal longitudinal direction of the small tunnel 1 is subjected to arc trimming treatment, and the radian is 7π / 10.

[0070] In step D, the temporary support structure is a plurality of detachable and assembled steel frame structures, which are processed from I-beams. The top of the steel frame structure is adaptively extended according to the height and width of the tunnel top in the confluence area; the component members of the steel frame structure are connected by mortise and tenon joints to achieve convenient and stable connection, and the connection between multiple steel frame structures adopts a strengthening structure.

[0071] During the excavation process, the pre-grouting process is used to reinforce the excavated small tunnel 1 and large tunnel 2; the radial spacing of each grouting pipe is maintained at 2.3 m, and the cross-section of the overall grouting pipe is arranged in a regular hexagon; and through numerical analysis method simulation, the excavation footage and support plan are determined.

[0072] In order to further improve the technical effect of the present invention, in this embodiment, in steps B and C, the specific steps of gradually expanding the excavation area are as follows:

[0073] (1) Excavate the central core soil in a three-step structure form to the middle position of the confluence area;

[0074] (2) Excavate the upper 1 / 3 height of the left soil to the 1 / 4 position of the confluence area, and excavate the upper 1 / 3 height of the right soil to the 1 / 4 position of the confluence area;

[0075] (3) Excavate the upper 1 / 3 height of the left soil to the middle position of the confluence area, and excavate the middle 1 / 3 height of the left soil to the 1 / 4 position of the confluence area;

[0076] (4) Excavate the upper 1 / 3 height of the soil on the right side to the middle position of the convergence area, and excavate the middle 1 / 3 height of the soil on the right side to the 1 / 4 position of the convergence area;

[0077] (5) Excavate the upper 1 / 3 height of the soil on the left side to the edge line position of the convergence area, excavate the middle 1 / 3 height of the soil on the left side to the middle position of the convergence area, and excavate the lower 1 / 3 height of the soil on the left side to the 1 / 4 position of the convergence area;

[0078] (6) Excavate the upper 1 / 3 height of the soil on the right side to the edge line position of the convergence area, excavate the middle 1 / 3 height of the soil on the right side to the middle position of the convergence area, and excavate the lower 1 / 3 height of the soil on the right side to the 1 / 4 position of the convergence area;

[0079] (7) Excavate the remaining soil on the left and right sides simultaneously until the edge line position of the convergence area; finally, excavate the middle core soil to the edge line position of the convergence area, and the excavation is completed.

[0080] During the above process, support can be carried out while excavating.

[0081] The above excavation method can effectively control the formation deformation, reduce the settlement amount, maintain the stability of the working face, ensure the construction safety, and reduce the delay in the construction progress caused by the structural conversion; moreover, after excavation, it can bring a larger working space, providing convenience for the advancement of subsequent processes.

[0082] It can be seen from the above embodiments that the method of the present invention aims at the structural conversion of the complex tunnel section formed after the convergence of multiple tunnels with different cross-sectional sizes, comprehensively considers factors such as the stress conditions of the complex cross-sectional structure, adopts a specific excavation method and excavation sequence, successfully realizes the structural conversion and transition, strictly controls the deformation of the tunnel formation in the convergence section, and can accelerate the construction progress and ensure the construction safety.

[0083] The present invention solves the problem of temporary support in the structural conversion area of the complex tunnel section, facilitates the smooth progress of the engineering construction, and at the same time ensures the safety of the construction environment; the temporary support structure can be well integrated with the initial support structure, has good support effect, and ensures the construction space in the structural conversion area without affecting the smooth progress of the normal construction.

[0084] The construction method of the present invention has clear stress and construction safety. Through numerical analysis methods for simulation, it can provide an optimization basis for the construction footage and support scheme, so as to achieve the purpose of saving the construction period and reducing the cost.

[0085] The present invention provides key technical support for the construction of large spaces in excavated tunnels. The provided method is not limited by the project scale and has wide applicability; during the excavation process of the underground space, the impact on the above-ground traffic, production, and life is small, the technical difficulty during the construction process is relatively small, the construction speed is fast, the safety and economy are high, and the technical competitiveness is greatly improved.

[0086] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention in any other form. Any person skilled in the art may use the technical content disclosed above to make changes or modifications into equivalent embodiments with equivalent changes. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the technical solution content of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A construction method for structural conversion of a complex tunnel section, characterized in that, it includes the following steps: A. Excavate the small tunnel (1) with a small excavation section size according to the predetermined size, and carry out the initial support of the small tunnel (1) while excavating. B. When excavating to one side line of the confluence area with the large tunnel (2) having a large excavation section size, continue to excavate half of the small tunnel (1) (A) along the depth direction of the small tunnel (1) towards the confluence area. At the same time, gradually expand the excavation area of the half (A) where the small tunnel (1) converges with the large tunnel (2) at an obtuse angle until excavating to the other side line of the confluence area with the large tunnel (2). Gradually expanding the excavation area of the half (A) means gradually expanding the top and side wall parts of the half (A) along the depth direction of the large tunnel (2) towards the outside of the small tunnel (1), where the expanded side wall part forms an angle of 45 - 60 degrees with the side wall part in the normal depth direction of the small tunnel (1). C. In the confluence area, starting from the other side line of the large tunnel (2), excavate the other half of the small tunnel in the direction opposite to the above excavation direction of the small tunnel, and gradually expand the excavation area at the same time until excavating to one side line of the large tunnel (2). D. Carry out the initial support for the top excavation part of the small tunnel (1) in the confluence area, and use a temporary support structure to temporarily support the top and side wall parts of the small tunnel (1) in the confluence area. E. In the confluence area, starting from the other side line of the large tunnel (2), continue to excavate the small tunnel (1) according to the predetermined size along the excavation direction in step A, and carry out the initial support of the small tunnel (1) while excavating. F. After step E has been carried out for 10 - 15 meters, in the confluence area, remove the temporary support structure, and then starting from the part where the excavation area of the small tunnel (1) is gradually expanded, respectively excavate the large tunnel in the opposite direction along the depth direction of the large tunnel (2) according to the predetermined size, and carry out the initial support of the large tunnel (2) while excavating.

2. The construction method for structural conversion of a complex tunnel section according to claim 1, characterized in that, in step C, the gradually expanding excavation area is symmetrically opposite to the gradually expanding excavation area of the half (A) in step B with respect to the center line (X) of the small tunnel (1).

3. The construction method for structural conversion of a complex tunnel section according to claim 2, characterized in that, in steps B and C, in order to eliminate the influence brought by stress concentration, the confluence part where the expanded side wall part forms an angle with the side wall part in the normal depth direction of the small tunnel (1) is subjected to arc trimming treatment, and the radian of the arc is (2 / 3 - 3 / 4)*π.

4. The construction method for structural conversion of a complex tunnel section according to claim 2 or 3, characterized in that, In step D, the temporary support structure is composed of multiple detachable and assembled steel frame structures, which are processed from I-beams. The top of the steel frame structure is adaptively expanded according to the height and width of the tunnel top in the confluence area. The component members of the steel frame structure are connected by mortise and tenon joints to achieve convenient and stable connection, and the connection between multiple steel frame structures adopts a strengthening structure.

5. The construction method for structural conversion of a complex tunnel section according to claim 4, characterized in that, During the excavation process, the pre-grouting process is used to reinforce the excavated small tunnel (1) and large tunnel (2); the radial spacing of each grouting pipe is maintained at 2-2.5 m, and the cross-section of the overall grouting pipe is arranged in a regular hexagon; and through numerical analysis simulation, the excavation footage and support plan are determined.

Images