A construction method for vertically entering multiple subway interval tunnels by continuous roof picking of a construction passage

Abstract

The present application belongs to the technical field of tunnel construction, and discloses a construction method for vertically entering multiple subway interval tunnels by continuous roof picking of a construction passage, which comprises six steps of simulation calculation and analysis, auxiliary passage construction, horizontal passage roof picking construction, intersection reinforcement treatment, interval main line tunnel construction, and main line tunnel outer horizontal passage backfilling. The technical principle of the present application is based on the New Austrian Tunneling Method, combined with the mine shed method as a temporary support system, and follows the principles of "strong support, short footage, frequent measurement, and early closure". The present application implements step-by-step excavation, timely support, and information-based construction.

Description

Technical Field

[0001] This invention belongs to the field of tunnel construction technology, and specifically relates to a construction method for vertically entering multiple subway tunnel sections by continuously lifting the top of the construction passage. Background Technology

[0002] Against the backdrop of regional integration and high-quality urban development, the design and construction of large high-speed rail hub stations integrates intercity railways and urban rail transit systems, striving to create convenient transfers, multi-level access, and seamless connections to create comprehensive urban transportation hubs, promoting the integrated development of stations and cities. However, in the construction of high-speed rail hub stations, due to limited construction space, some subway tunnel sections cannot be constructed from the underground level of the station building, requiring the establishment of construction access channels from outside the site to enter the subway tunnel sections for construction.

[0003] Currently, the methods for opening the roof of a subway tunnel from the construction access point mainly fall into two categories: vertical opening and inclined opening. These can be further subdivided into the scaffolding arch opening method, the pilot tunnel opening method, and the inclined shaft beam construction method. However, in areas with weak and fractured surrounding rock, and where the main structure of the station building has already been completed, and drilling and blasting construction cannot be used for the subway section tunnel, there are no established methods for continuously traversing three large-section tunnels (2 lines + 1 line + 4 lines) to enter the main subway section tunnel. Existing conventional technologies are insufficient to meet the requirements for construction safety and quality. Summary of the Invention

[0004] This invention provides a construction method for vertically entering multiple subway tunnel sections through a continuous overhead tunnel. Based on the New Austrian Tunneling Method (NATM), it combines the mining scaffolding method as a temporary support system. It follows the principles of "strong support, short advance, frequent measurement, and early closure," and implements step-by-step excavation, timely support, and information-based construction.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A construction method for vertically entering multiple subway tunnel sections via a continuous cantilevered access channel includes the following steps:

[0007] Step 1: Simulation and Calculation Analysis: Before the construction of the cross passage and the tunnel section, based on the mechanical properties of the surrounding rock of the cross passage cantilever section and the tunnel section, the MIDAS NX finite element analysis software is used to simulate and analyze different working conditions of the cantilever section construction entering the subway tunnel section, determine the support design parameters of each intersection of the cantilever section and the tunnel section, optimize the construction plan, and provide a basis for the construction of the cross passage and the tunnel section.

[0008] Step 2, Auxiliary passage construction: Since the excavation height of the construction passage is lower than that of the main tunnel in the section, when using the transverse passage to vertically enter the section tunnel for top-lifting construction, the construction passage will be widened and heightened 20m away from the main tunnel of the first section tunnel to reduce the height of subsequent top-lifting construction, increase the working space, and create conditions for the use of large equipment and to speed up the top-lifting construction.

[0009] Step 3: Construction of the Transverse Passage using the Overhead Excavation Method: Before passing through the double-track tunnel and the four-track tunnel in the section, the transverse passage requires two overhead excavations to reach the arch height required for the main tunnel construction. During the overhead excavation, the excavation slope line is determined based on the starting elevation and the arch height of each main tunnel, and the bench method is used. The scope of the upper bench overhead excavation is controlled according to the designed excavation outline of the arch, gradually increasing the slope of the elevated section to the designed arch elevation, with each cycle advancing no more than 1m, and initial support is promptly implemented. After the upper bench is excavated to the arch position, construction begins on the horizontal slope section of the transverse passage, maintaining the arch excavation height unchanged until the horizontal slope section is completed. The lower bench excavation maintains a distance of at least 5m from the upper bench excavation surface, and initial support is promptly implemented, completing the construction of the elevated and horizontal slope sections of the transverse passage.

[0010] Step 4: Intersection Reinforcement: During the construction of the transverse passage perpendicularly crossing the tunnel section, due to the large cross-section of the main tunnel, the rock mass at the intersection is in a suspended state and subjected to complex stresses. Based on on-site simulation calculations and analysis, the added steel arches here will not only bear the load transmitted from the main tunnel section but also the load of the transverse passage's cantilevered section itself. To ensure the safety of the transverse passage construction, portal arches are installed at each intersection location according to the simulation analysis results to support the surrounding rock deformation during the construction of the transverse passage's cantilevered section, ensuring that the deformation meets design requirements.

[0011] Step 5: Construction of the Main Line of the Intersection Tunnels: After the completion of the cross passage construction, the initial section of each section's main line tunnel will be constructed using the pilot tunnel widening method. Starting from the intersection of the cross passage centerline and the centerline of each section's tunnel, and based on the survey control network, pilot tunnel construction will proceed perpendicular to the cross passage for each main line tunnel. The pilot tunnels will be excavated according to the support design scheme, based on different surrounding rock grades. Once the pilot tunnel construction reaches the arch elevation of the main line tunnel after a certain distance, the tunnel face will be closed, and the initial section of the main line tunnel will be constructed in the opposite direction using the widening method. Each cycle of excavation will be controlled at 1m, with initial support construction carried out simultaneously according to the main line tunnel design. The initial support of the pilot tunnel will be removed at the same time, until construction passes through the intersection influence zone and reaches the design mileage, completing the initial section construction of the main line tunnel. Subsequently, the excavation direction will be reversed, and the remaining section tunnels will be constructed in sections according to the designed excavation method. During this process, invert construction should be carried out promptly to ensure that the initial support and invert are closed into a ring as early as possible. During the construction of the main line tunnels in each section, deformation monitoring inside and outside the tunnel will be conducted in a timely manner according to the plan to provide a basis for information-based construction.

[0012] Step 6: Backfilling of the external cross passage: After the construction cross passage is completed, the area outside the tunnel entrance will be backfilled with slag and soil, and the 6m section around the entrance will be backfilled with C20 concrete. The 10m section connecting the cross passage to the tunnel section will be backfilled with C35 concrete, and the upper 3m of the remaining section will be backfilled with C20 concrete, while the lower part will be backfilled with soil and rock.

[0013] The beneficial effects of this invention are as follows:

[0014] (1) Given the limited construction site and the fact that the main structure of the high-speed rail hub station has been completed, making it impossible to use the drill-and-blast method for the construction of cross passages and main tunnels of subway sections, a construction method was developed through finite element simulation analysis. This method involves excavation using mechanical crushing, setting up portal-type support steel frames at intersections, and reinforcing the surrounding rock with self-propelled locking anchor bolts installed above the steel frames. The cross passages are then continuously jacked up vertically to enter multiple subway tunnel sections. This technology has advantages such as high rigidity of the support structure, good stability of the surrounding rock, and safe and reliable construction process.

[0015] (2) The present invention is a construction method for vertically entering multiple subway tunnel sections by two vertical cantilever sections through a transverse passage. Through information-based construction, the deformation of the surrounding rock can be effectively controlled, the disturbance to the surrounding rock is small, no special machinery and equipment are required, and the construction operation is simple and the overall cost is low.

[0016] (3) This invention employs a longitudinal climbing pilot tunnel method for the initial section construction of the main line tunnel. By gradually expanding the pilot tunnel to form a working space, and then expanding it in the opposite direction, the transition from a small cross section to a large cross section of the surrounding rock structure is achieved. It features high construction efficiency, fast progress, and easy control of the excavation outline. Attached Figure Description

[0017] Figure 1 This is a longitudinal section view of the transverse passage cantilever construction of the present invention;

[0018] Figure 2 This is a schematic diagram of the reinforcement section at the intersection of the transverse cantilevered roof of the present invention;

[0019] Figure 3 This is a schematic diagram of the intersection portal steel arch frame of the present invention;

[0020] Figure 4 This is a schematic diagram of the horizontal channel backfill plane of the present invention;

[0021] Figure 5 This is a construction flowchart of the present invention, which involves vertically entering multiple subway tunnel sections from a horizontal passage.

[0022] Among them, 1. Auxiliary passage; 2. Cross passage; 3. Double-track tunnel in the section; 3a. Portal steel arch frame on the left side of the double-track tunnel; 3b. Portal steel arch frame on the right side of the double-track tunnel; 4. Single-track tunnel in the section; 5. Four-track tunnel in the section; 5a. Portal steel arch frame on the left side of the four-track tunnel; 6. Concrete retaining wall; 7. Backfill concrete for the cross passage. Detailed Implementation

[0023] To better illustrate the objectives, technical solutions, and advantages of this invention, the invention will be further described below in conjunction with specific embodiments. This invention can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the inventive concept to those skilled in the art. This invention will be defined only by the claims.

[0024] like Figure 1-5 As shown, this invention provides a construction method for vertically entering multiple subway tunnel sections via a continuous cantilevered access channel, comprising the following steps:

[0025] Step 1: Simulation and Calculation Analysis: Before the construction of the cross passage and the tunnel section, based on the mechanical properties of the surrounding rock of the cross passage 2 cantilever section and the tunnel section, the MIDAS NX finite element analysis software was used to simulate and analyze different working conditions of the cantilever section construction entering the subway tunnel section. The design parameters of the support of each intersection of the cantilever section and the tunnel section were determined, and the construction plan was optimized to provide a basis for the vertical entry of the cross passage 2 into the tunnel section.

[0026] S11. Computational Model Creation: In this example, the tunnel excavation and support process simulation uses ideal elastic-plasticity and the Mohr-Coulomb yield criterion for numerical analysis. The tunnel excavation and surrounding rock are both treated as solid elements. The initial support adopts an elastic constitutive model, the anchor bolts are assumed to be embedded truss elements, and the secondary lining is analyzed as shell elements.

[0027] S12. Boundary Condition Setting: Set the boundary conditions of the calculation model reasonably according to the surrounding rock conditions. The boundary constraint conditions of the model are normal displacement around the perimeter, the lower boundary is fixed, and the upper boundary is free.

[0028] Step 2, Auxiliary Passage Construction: Since the excavation height of the construction passage is lower than that of the main tunnel in the section, before the transverse passage 2 enters the section tunnel vertically for construction, auxiliary passage 1 is set up 20m before the main tunnel of the double-track tunnel 3. The original construction passage is widened and heightened to reduce the height of the cantilever construction, increase the working space, and create conditions for the use of large equipment and to accelerate the cantilever construction progress. When auxiliary passage 1 reaches the left side intersection of the double-track tunnel 3, the intersection is reinforced using the left side portal steel arch 3a of the double-track tunnel according to the simulation calculation results, completing the auxiliary passage construction.

[0029] S21 and Auxiliary Passage 1 were excavated using the step method. Construction followed the principles of "strong support, short advances, frequent measurements, and early closure." Mechanical crushing was used for excavation, and the step distance between upper and lower steps was strictly controlled. The entire cross-section of Auxiliary Passage 1 was supported by 16-type steel arch frames, with a cyclic advance of 1-2 meters and an arch frame spacing of 3 frames / 2 meters. After the arch frames were installed, wire mesh was promptly installed, followed by anchor spraying. A simple working platform was manually erected, mechanical crushing was used for excavation, small excavators were used for slag removal and loading, and dump trucks were used for transportation.

[0030] Step 3, Construction of the transverse passage using the cantilever method: In this embodiment, the transverse passage 2 needs to undergo two cantilever constructions before passing through the left side of the double-track tunnel 3 and the left side of the four-track tunnel 5 in the section. See details. Figure 1 The first overpass construction began 5 meters from the end of the auxiliary passage, with its excavation slope line drawn from the tangent line of the excavation line of the starting arch crown to the arch crown excavation line of the double-track tunnel 3 in the section. The second overpass construction took place on the left side of the cross passage 2, which traverses the fourth-track tunnel 5 in the section. The starting point was the line drawn from the tangent line of the excavation line of the cross passage's flat slope section 5 meters from the left side wall of the fourth-track tunnel 5 to the excavation line of the arch crown excavation line of the fourth-track tunnel 5 in the section. Following the left-to-right construction sequence of cross passage 2, the two overpasses and the flat slope section construction were completed sequentially using the step method. During the construction of cross passage 2, deformation monitoring inside and outside the tunnel was conducted in a timely manner according to the plan to provide a basis for information-based construction.

[0031] S31. Upper and Lower Bench Excavation: The construction range of the upper bench is controlled according to the arch excavation outline. Through small-step excavation, the upper arch pilot tunnel is gradually raised to the designed arch crown position, with the upper arch pilot tunnel raised at a slope of 10-20%. For each cycle of excavation and support work on the upper bench, the advance should not exceed the spacing of two steel frames for Class IV surrounding rock, and the advance should not exceed the spacing of two steel frames for the sidewalls. The steel frame foundation and connection should be excavated alternately on the left and right sides or in skip sections. The bench height should not exceed 1 / 2 of the total excavation height. Before excavating the lower bench, the upper steel frame anchor bolts must be completed, and longitudinal connecting steel bars should be installed and welded securely between steel frames in a timely manner. After the upper bench excavation reaches the arch crown position, construction proceeds to the flat slope section, maintaining the same excavation height until the flat slope section is completed. The lower bench excavation surface should maintain a distance of no more than 5m from the upper bench excavation surface, and initial support should be implemented promptly. After completing the elevated section of the transverse passage 2, which crosses the double-track tunnel 3, construction of the transverse passage 2 continues in accordance with the principles of "intersection reinforcement, initial support, and step excavation" until the four-track tunnel 5 is completed.

[0032] S32. Initial Support Construction: During the cantilever construction of the transverse passage 2, erect 25b@1000mm steel frames according to the height changes of the cantilever section, and install anchor bolts. When installing the steel mesh, a protective layer thickness of not less than 30mm should be left between the mesh and the rock surface, and the overlap length of the mesh should not be less than 200mm. Connect the mesh using binding or welding methods, and firmly weld the steel mesh to the anchor bolts. After the steel mesh installation is completed and inspected for compliance, spray concrete to the designed thickness, and promptly install radial anchor bolts to complete the initial support construction. The initial support construction process for the flat slope section of transverse passage 2 is the same as that for the cantilever section.

[0033] Step 4, Intersection Reinforcement: Through simulation analysis, the supporting steel arches at the intersections of the left and right sides of the double-track tunnel 3 and the left side of the four-track tunnel 5 with the cross passage 2 not only bear the loads transmitted from the main tunnel of the section, but also the load of the cantilever section of the cross passage 2 itself. To ensure the stability of the surrounding rock at the intersection, according to the simulation analysis results, portal steel arches 3a / 3b / 5a are added at the intersection to ensure the safety of the construction process of the cantilever section of the cross passage 2. Because the excavation outline of the cross passage 2 is larger than the excavation outline of the single-track tunnel 4 of the section, no reinforcement support is required when the cross passage 2 passes through the single-track tunnel 4 of the section. See details. Figure 2 .

[0034] S41. Portal Steel Arch Frame Fabrication: The portal steel arch frame consists of I-beam columns, arched arch frames, and I-beam support beams. See details... Figure 3 The portal steel arch frame is welded from 25b I-beams. A longitudinal I-beam support beam is installed at the top of the arch. I-beam columns are installed between the support beam and the arch, corresponding to the spacing of the initial support steel frame of the main tunnel, and are welded to the arch and support beam. In addition to butt welding, the welded ends to the support beams should also be welded on all four sides to ensure the rigidity and strength of the joint. After all parts are fabricated according to the design drawings, they should be trial-assembled on site, and only after passing the test can they be used.

[0035] S42. Installation of Portal Steel Arches: Based on simulation calculations and analysis, following the construction sequence of cross passage 2, two 25b portal steel arches 3a will be erected sequentially at the left intersection of the double-track tunnel 3 in the section, three 25b portal steel arches 3b at the right intersection, and four 25b portal steel arches 5a at the left intersection of the four-track tunnel 5 in the section. The surrounding rock at each intersection will be supported to maintain the stability of the upper rock mass. To ensure the stability of the portal steel arches, the steel frame bases should rest on solid bedrock during construction. Eight Φ50 locking steel pipes will be installed on the outside of the portal frame to ensure its stable installation.

[0036] S43. Self-advancing anchor bolt construction: After the portal steel arch frame is installed at each intersection, T51 type self-advancing anchor bolts with a length of 6.0m and a diameter of 500mm are driven on top of the steel arch frame to reinforce the surrounding rock.

[0037] S44. Wire mesh installation and initial shotcrete construction: After the portal steel arch frames at each intersection are installed in sequence and the self-propelled top anchor bolts are driven, wire mesh installation and shotcrete construction should be carried out in a timely manner according to the initial support design.

[0038] Step 5: Construction of the main tunnels in the section: After completing the excavation and initial support construction of the double-track tunnel 3 to the four-track tunnel 5 and the cross passage 2 in sequence, the main tunnels in the section will be constructed at a 90-degree angle perpendicular to the cross passage 2, according to the survey control network. During the construction of the main tunnels, the excavation and initial support methods for each main tunnel section should be organized according to the designed surrounding rock grade. During construction, deformation monitoring inside and outside the tunnels should be strengthened to ensure that the top elevation of the pilot tunnel is consistent with the top elevation of the main tunnel, providing a basis for information-based construction.

[0039] S51. Small Pilot Tunnel Excavation: The initial section of each tunnel section will be constructed using the small pilot tunnel expansion method. Starting from the intersection of the centerline of the cross passage 2 and the centerline of each tunnel section, pilot tunnel construction will proceed perpendicularly to the cross passage 2 for tunnels 3 (double-track), 4 (single-track), and 5 (four-track). Pilot tunnel excavation will be carried out according to the corresponding design support scheme based on different surrounding rock grades. After a certain distance of pilot tunnel construction, a 5cm thick layer of concrete will be initially sprayed onto the surrounding rock face, and the working face will be sealed. Excavation will then proceed in the opposite direction to the designed cross-section of the tunnel section. The initial support of the pilot tunnel will be removed, and support will be provided according to the initial support of the main tunnel for every 1m of excavation until the construction passes through the intersection influence zone and reaches the design mileage. For tunnels 3 (double-track), 4 (single-track), and 5 (four-track), initial support and invert construction should be carried out promptly to ensure early closure of the initial support and invert into a ring. When the three tunnel sections are excavated synchronously in parallel, the distance between the front and rear excavation faces should not be less than 15m.

[0040] S52. Grouting behind the initial support: After the initial support is completed, grouting and backfilling should be carried out promptly behind the initial support. The backfilling grouting should follow the excavation face and maintain a distance of no more than 5m from the excavation face. The grouting pipe is a Φ42 seamless steel pipe with a wall thickness of 4mm, 0.5m long, with a circumferential and longitudinal spacing of 2m×3m, arranged in a staggered pattern. The grouting pressure is controlled between 0.1 and 0.3MPa. The grouting sequence starts from the arch foot and moves towards the arch crown, and from the waterless holes to the water-bearing holes. During the grouting process, the changes in pressure and flow rate should be constantly monitored and recorded to ensure that the grouting is dense.

[0041] S53. Waterproofing Membrane and Secondary Lining Construction: The waterproofing membrane shall be laid without nails. At the top, bottom, and invert sections, it should be laid longitudinally along the tunnel. Joints between waterproofing membranes shall be hot-melt welded using a double-seam welder, with an overlap length of not less than 10cm. After the waterproofing membranes pass inspection, secondary lining shall be constructed in sections.

[0042] Step 6: Backfilling of the External Crosspass: After the construction passage is completed, according to design requirements, the external crosspass outside the main tunnel needs to be sealed and backfilled to ensure the stability of the mountain. Four concrete retaining walls 6, each 50cm thick, are constructed within the crosspass area, using C30 concrete. See details. Figure 4 The backfill area for cross passage 2 is as follows: excavated soil is used for backfilling outside the tunnel entrance; C20 concrete is used for backfilling within a 6m section around the entrance. For the remaining sections, the upper 3m is backfilled with C20 concrete, and the lower section is backfilled with soil and rock. The compaction degree of the soil and rock is not less than 90%.

[0043] S61. Construction of concrete retaining wall: At the junction of cross passage 2 with double-track tunnel 3, single-track tunnel 4, and four-track tunnel 5 in the section, the position of the retaining wall is marked according to the design drawings. After the formwork is erected, concrete is poured to complete the construction of the retaining wall.

[0044] S62. Cross-passage backfilling construction: Backfill material should be laid in layers, leveled, and compacted. The layer thickness and number of compaction passes should be determined through testing based on the soil and rock properties and the equipment used. Moderately weathered sandstone or sandy mudstone should be used for backfilling, with a particle size not exceeding 10cm, a soil-rock compaction degree of not less than 90%, a solid volume fraction of not less than 83%, and the maximum solid particle size not exceeding 2 / 3 of the thickness of each layer. When backfilling concrete at openings and intersection sealing sections, tenons should be installed according to design requirements to ensure a firm connection between the backfill concrete layers.

[0045] Furthermore, to prevent water accumulation in the cross passage 2 during the backfilling process, a φ500 fiberglass drainage pipe was buried on one side of the water ditch in the concrete sealing section at the intersection of cross passage 2 and the main tunnel, and encased with 15cm thick C20 concrete.

[0046] Furthermore, C20 concrete was used for backfilling at the cantilevered section of the transverse passage 2. Before backfilling, connecting steel bars were installed between the surrounding rock and the concrete using anchor bolts, spaced 2m x 3m in a staggered pattern. The anchor bolts were embedded 2.5m into the surrounding rock and extended 0.5m to the backfill area, with a 10cm hook pre-installed at the end to ensure backfill quality.

[0047] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A construction method for vertically entering multiple subway tunnel sections via a continuous cantilevered access passage, characterized in that: The construction method includes the following steps: Step 1, Simulation Calculation and Analysis: Before the construction of the transverse passage (2) into the tunnel section, based on the top section of the transverse passage (2) and the mechanical properties of the surrounding rock of the tunnel section, the MIDAS NX finite element analysis software was used to simulate and analyze different working conditions of the top section construction into the subway tunnel section, determine the support design parameters of each intersection of the top section and the tunnel section, optimize the construction plan, and provide a basis for the vertical construction of the transverse passage (2) into the tunnel section. Step 2, construction of auxiliary passage: Since the excavation height of the construction passage is lower than that of the main tunnel of the section, before the cross passage (2) enters the section tunnel vertically for construction, an auxiliary passage (1) is set up 20m away from the main tunnel of the double-track tunnel (3) of the section, and the original construction passage is widened and heightened; when the auxiliary passage (1) is constructed to the left side interface of the double-track tunnel (3), the intersection is reinforced with the left side portal steel arch frame (3a) of the double-track tunnel according to the simulation calculation results, and the construction of the auxiliary passage is completed. Step 3, Construction of the transverse passage using the overhang method: The transverse passage (2) will undergo two overhang constructions before passing through the left side of the double-track tunnel (3) and the left side of the four-track tunnel (5). The starting point of the first overhang is 5m away from the end point of the auxiliary passage (1), and its excavation slope line is the line connecting the starting arch and the tangent of the arch excavation line of the double-track tunnel (3). The second overhang construction will be carried out on the left side of the transverse passage (2) passing through the four-track tunnel (5). The starting point is the line connecting the excavation line of the arch of the transverse passage (2) at the left side wall of the four-track tunnel (5) at the left side wall of the four-track tunnel (5) and the tangent of the arch excavation line of the four-track tunnel (5). The second overhang excavation slope line will be the line connecting the arch excavation line of the transverse passage (2) at the left side wall of the four-track tunnel (5). According to the construction sequence of the transverse passage (2) from left to right, the two overhangs and the construction of the flat section of the transverse passage (2) will be completed in sequence using the step method. During the construction of the transverse passage (2), the deformation monitoring inside and outside the tunnel will be carried out in a timely manner according to the plan to provide a basis for information-based construction. Step 4, Intersection reinforcement: Add a portal steel arch frame (3a) on the left side of the double-track tunnel, a portal steel arch frame (3b) on the right side of the double-track tunnel, and a portal steel arch frame (5a) on the left side of the four-track tunnel at the intersection to ensure the safety of the construction process of the cantilever section of the cross passage (2); no reinforcement support is required when the cross passage (2) passes through the single-track tunnel (4) in the section; Step 5, Construction of the main line of the tunnel in the section: After completing the excavation and initial support construction of the double-line tunnel (3) to the four-line tunnel (5) and the cross passage (2) in sequence, according to the measurement control network, turn 90 degrees perpendicular to the cross passage (2) to carry out the construction of each main line tunnel in the section. Step 6: Backfilling of the cross passage outside the tunnel: After the construction passage is used up, the cross passage (2) outside the main tunnel is sealed and backfilled to ensure the stability of the mountain.

2. The construction method according to claim 1, characterized in that: In step 1, the specific steps of the simulation calculation and analysis are as follows: S11. Calculation Model Creation: Simulation of Engineering Tunnel Excavation and Support Process. Ideal elastic-plastic and Mohr-Coulomb yield criteria are selected for numerical analysis. Tunnel excavation and surrounding rock are both treated as solid elements. The initial support adopts an elastic constitutive model. The anchor bolt is assumed to be an embedded truss element. The secondary lining is analyzed as a shell element. S12. Boundary Condition Setting: Set the boundary conditions of the calculation model reasonably according to the surrounding rock conditions. The boundary constraint conditions of the model are normal displacement around the perimeter, the lower boundary is fixed, and the upper boundary is free.

3. The construction method according to claim 1, characterized in that: In step 2, the auxiliary passage (1) is excavated using the step method. During construction, the principles of strong support, short advance, frequent measurement, and early closure are followed. Mechanical crushing is used for excavation, and the step distance between the upper and lower steps is strictly controlled. The entire cross-section of the auxiliary passage (1) is supported by 16-type steel arch frames, with a cyclic advance of 1-2m and an arch frame spacing of 3 frames / 2m. After the arch frames are installed, the netting is hung in time, and anchor spraying is carried out. A simple working platform is set up manually, mechanical crushing is used for excavation, small excavators are used to scoop and load slag, and dump trucks are used for transportation.

4. The construction method according to claim 1, characterized in that: In step 3, the specific steps of the horizontal passage cantilever construction method are as follows: S31. Upper and Lower Bench Excavation: The construction range of the upper bench is controlled according to the arch excavation outline. Through small-step excavation, the upper arch pilot tunnel is gradually raised to the designed arch crown position, with the upper arch pilot tunnel raised at a slope of 10-20%. For each cycle of excavation and support work on the upper bench, the advance should not exceed the spacing of two steel frames for Class IV surrounding rock, and the advance should not exceed the spacing of two steel frames for the sidewalls. The steel frame foundation and connection should be excavated alternately on the left and right sides or in skip sections. The bench height should not exceed 1 / 2 of the total excavation height. Before the lower bench excavation, all work must be completed. The upper steel frame is anchored with foot bolts. Longitudinal connecting steel bars should be installed and welded firmly between the steel frames in a timely manner. After the upper step is excavated to the arch position, the construction of the flat slope section is carried out. The excavation height remains unchanged until the flat slope section is completed. The lower step excavation and the upper step excavation surface are kept at a distance of no more than 5m, and the initial support is installed in a timely manner. After the cross passage 2 of the elevated section is completed and crosses the double-line tunnel 3 of the section, the construction of the cross passage 2 continues in accordance with the principles of cross intersection reinforcement, initial support, and step method excavation until the cross passage 4-line tunnel (5) is completed. S32. Initial support construction: During the construction of the cantilever section of the transverse passage (2), a 25b@1000mm steel frame is erected according to the height change of the cantilever section, and anchor bolts are installed. When the steel mesh is installed, a protective layer thickness of not less than 30mm should be left between it and the rock surface. The overlap length of the mesh should not be less than 200mm. It is connected by binding or welding. The steel mesh is welded firmly to the anchor bolts. After the steel mesh is installed and inspected and qualified, the concrete is sprayed to the design thickness. Radial anchor bolts are installed in time to complete the initial support construction. The initial support construction process of the flat slope section of the transverse passage (2) is the same as that of the cantilever section.

5. The construction method according to claim 1, characterized in that: In step 4, the specific steps for reinforcing the intersection are as follows: S41. Portal Steel Arch Frame Fabrication: The portal steel arch frame consists of I-beam columns, an arched frame, and I-beam support beams. The portal steel arch frame is welded from 25b I-beams. A longitudinal I-beam support beam is installed at the top of the arch. The gap between the support beam and the arch is determined by the spacing of the initial support steel frame of the main tunnel, and I-beam columns are installed accordingly, welded to the arch and support beams. In addition to butt welding, the welded ends to the support beams are also welded on all four sides to ensure the rigidity and strength of the joint. After all parts are fabricated according to the design drawings, they should be trial-assembled on-site. Only after passing the trial assembly can the arch be used. S42. Installation of portal steel arch frame: According to the simulation calculation analysis, in accordance with the construction sequence of the cross passage (2), the portal steel arch frame (3a) of the double-line tunnel (3) is erected on the left side of the intersection of the double-line tunnel (3) in the section, the portal steel arch frame (3b) of the double-line tunnel (3b) is erected on the right side of the intersection, and the portal steel arch frame (5a) of the four-line tunnel (5) is erected on the left side of the intersection of the four-line tunnel (5) in the section. The surrounding rock at each intersection is supported to keep the upper rock stable. In order to ensure that the portal steel arch frame is erected firmly, the steel frame base should be placed on solid bedrock during construction. A total of 8 Φ50 locking steel pipes are set on the outside of the portal frame to ensure that the portal frame is installed firmly. S43. Self-advancing anchor bolt construction: After the portal steel arch frame is installed at each intersection, T51 type self-advancing anchor bolts with a length of 6.0m and a diameter of 500mm are driven on top of the steel arch frame to reinforce the surrounding rock. S44. Wire mesh installation and initial shotcrete construction: After the portal steel arch frames at each intersection are installed in sequence and the self-propelled top anchor bolts are driven, wire mesh installation and shotcrete construction should be carried out in a timely manner according to the initial support design.

6. The construction method according to claim 1, characterized in that: In step 5, the specific steps for the main line construction of the tunnel section are as follows: S51. Small pilot tunnel expansion construction: The small pilot tunnel expansion construction method is adopted for the starting section of each tunnel. Starting from the intersection of the center line of the cross passage (2) and the center line of each tunnel, the pilot tunnel construction of the double-line tunnel (3), single-line tunnel (4), and four-line tunnel (5) of the section is carried out perpendicular to the cross passage (2) according to the measurement control network. According to different surrounding rock grades, the pilot tunnel is excavated according to the corresponding design support scheme. After the pilot tunnel is constructed to a certain distance, 5cm thick concrete is initially sprayed onto the surrounding rock surface and the working face is sealed. The excavation is carried out in the opposite direction of the section tunnel design cross section. The initial support of the pilot tunnel is removed. Every 1m of working face is excavated and the initial support of the main line tunnel is supported in a timely manner until the construction passes through the intersection influence area to the design mileage. The initial support and invert construction are carried out in a timely manner for the construction of the section double-line tunnel (3), section single-line tunnel (4), and section four-line tunnel (5) so that the initial support and invert are sealed into a ring as soon as possible. When the three section tunnels are excavated in parallel at the same time, the distance between the front and rear excavation faces is not less than 15m. S52. Grouting behind the initial support: After the initial support is completed, grouting and backfilling should be carried out behind the initial support in a timely manner. The backfilling grouting should follow the excavation face and maintain a distance of no more than 5m from the excavation face. The grouting pipe is a Φ42 seamless steel pipe with a wall thickness of 4mm, 0.5m long, with a circumferential and longitudinal spacing of 2m×3m, arranged in a quincunx pattern. The grouting pressure should be controlled between 0.1 and 0.3MPa. The grouting sequence should start from the arch foot and move towards the arch crown, and from the waterless holes to the water-bearing holes. During the grouting process, the changes in pressure and flow rate should be monitored at all times and recorded to ensure that the grouting is dense. S53. Waterproofing membrane and secondary lining construction: The waterproofing membrane shall be laid without nails. At the top, bottom and invert arches, it is advisable to lay it along the longitudinal direction of the tunnel. The joints between the waterproofing membranes shall be hot-melted using a double-seam welding machine, with an overlap length of not less than 10cm. After the waterproofing membranes pass inspection, the secondary lining shall be constructed in sections.

7. The construction method according to claim 1, characterized in that: In step 6, a total of 4 concrete retaining walls (6) are set up within the cross passage (2). The retaining walls are 50cm thick and are cast with C30 concrete. The backfilling range of the cross passage (2) is as follows: the area outside the opening is backfilled with slag soil, the 6m range of the opening section is backfilled with C20 concrete, and the upper 3m of the remaining section is backfilled with C20 concrete and the lower part is backfilled with soil and rock. The compaction degree of soil and rock is not less than 90%.

8. The construction method according to claim 1, characterized in that: In step 6, the specific steps for backfilling the cross passage outside the tunnel are as follows: S61. Construction of concrete retaining wall: At the junction of the cross passage (2) with the double-track tunnel (3), the single-track tunnel (4), and the four-track tunnel (5) in the section, the position of the retaining wall is marked according to the design drawings. After the formwork is erected, concrete is poured to complete the construction of the retaining wall. S62. Cross passage backfilling construction: The fill material is laid in layers during backfilling, leveled, and then compacted. The layer thickness and number of compaction passes are determined by testing based on the properties of the soil and rock and the equipment. The backfill uses moderately weathered sandstone or sandy mudstone, with a particle size control not exceeding 10cm, a soil-rock compaction degree of not less than 90%, a solid volume ratio of not less than 83%, and the maximum solid particle size not exceeding 2 / 3 of the thickness of each layer. When backfilling concrete at the opening and intersection sealing sections, tenons are arranged according to the design requirements to ensure that the backfill concrete layer is firmly connected.

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