Combined construction method for shallow-buried three-hole large-section tunnel underpassing existing railway

Abstract

The application discloses a combined construction method for shallow-buried and excavated three-hole large-section tunnel underpassing an existing railway, which comprises the following steps: S1, model analysis; S2, reinforcing the roadbed of the existing railway; S3, proving the surrounding rock in front of the tunnel face; S4, implementing advanced support, reinforcing the tunnel face, and adopting annular excavation reserved core soil non-blasting excavation technology to perform hole body excavation and support; S5, performing inverted arch excavation and support, and performing inverted arch bottom grouting construction; and S6, performing secondary lining mold concrete closed loop. The application adopts the comprehensive construction technology combining "slope batch grouting + root pile + pipe shed support beam + inverted arch bottom grouting + non-blasting excavation technology", reinforces the undisturbed soil, reduces the soil permeability coefficient, realizes the purpose of reinforcing the undisturbed soil and plugging water, prevents the tunnel underpassing the existing railway influence section from causing excessive ground surface settlement and existing railway roadbed settlement, and improves the safety factor of the underpassing tunnel and the existing railway.

Description

Technical Field

[0001] This invention relates to the field of long tunnel construction technology, specifically to a combined construction method for a shallow-buried, three-tunnel, large-section tunnel passing under an existing railway. Background Technology

[0002] In recent years, my country's highway construction has developed rapidly, with an increasing number of newly built expressway tunnels. Due to terrain constraints, new tunnels often pass under existing railways. Tunnel excavation not only adversely affects the safety of new tunnel construction but also endangers the operational safety of existing railways. This is especially true for large-section tunnels in high-altitude, cold regions that pass under existing railways, which present high construction difficulties, risks, and technical requirements. Inappropriate reinforcement measures and excavation methods can lead to significant plastic deformation of the surrounding rock and surface, even causing cracks and collapses, impacting both tunnel construction and railway safety.

[0003] Combining a 22.13km-long extra-long highway tunnel, a separated design was adopted. The tunnel, with a total length of 22.13km, is a key control project of the entire line. The tunnel adopts a "3-tunnel + 4-shaft" design scheme. The tunnel exit is located in a high-altitude and cold region. The lithology consists of medium-dense, relatively thin, glacial-deposited gravelly soil on the upper part, with underlying granite bedrock and Class V surrounding rock, exhibiting poor stability. Furthermore, it is located in a freeze-thaw zone, with a maximum freezing depth of 2.0–5.0m at the tunnel site. The exit of the three tunnels, from YK97+727 to 783.1, passes under the Southern Xinjiang Railway (railway chainage K243+423–544). The distances from the top elevation of the existing railway rail 1 to the top of the secondary lining of the left tunnel, right tunnel, and central guide tunnel are 10.25m, 9.18m, and 11.12m, respectively. Preventing and controlling the settlement of the railway embankment caused by the excavation of the three large-section tunnels ("two main tunnels + central guide tunnel") presents a major technical challenge. Summary of the Invention

[0004] In view of the technical problems mentioned above, the present invention provides a combined construction method for shallow buried, three-hole, large-section tunnels to pass under an existing railway.

[0005] This invention is achieved through the following technical solution:

[0006] A method for constructing a shallow-buried, three-tunnel, large-section tunnel under an existing railway, characterized by the following steps:

[0007] S1: Model Analysis;

[0008] S2: Reinforce the existing railway subgrade;

[0009] S3: Investigate the surrounding rock ahead of the tunnel face;

[0010] S4: Implement advanced support and reinforce the tunnel face. Use a non-blasting excavation process with a ring-shaped excavation and reserved core soil for tunnel excavation and support.

[0011] S5: Excavation and support of the invert arch, and grouting construction at the bottom of the invert arch;

[0012] S6: Secondary lining is formed by casting concrete to create a closed ring.

[0013] Further, step S1 specifically involves using geotechnical numerical software to perform finite element simulation analysis on the deformation of the ground surface and rails when the tunnel is constructed under the newly built three-hole tunnel to the bottom of the railway embankment and when it passes through the railway embankment, in order to obtain construction parameters to guide the construction.

[0014] Furthermore, in step S2, the reinforcement of the existing railway subgrade adopts a combination of "slope grouting in batches + tree root piles + pipe roof support beams".

[0015] Furthermore, the slope grouting process in batches is as follows:

[0016] S2.1.1: Hole drilling is performed, and the hole is cleaned by high-pressure air.

[0017] S2.1.2: Insert the grouting pipe to seal the gap between the grouting pipe and the soil, and at the same time seal the tail end of the grouting pipe; the tail end of the grouting pipe is blocked with geotextile to prevent the pipe from being blocked when sprayed concrete.

[0018] S2.1.3: Lay n layers of steel mesh and spray concrete;

[0019] S2.1.4: Connect the grouting pipeline for grouting via the small grouting pipe.

[0020] Further, in step 2, the root piles are located at both ends of the bottom of the pipe roof support beam on both sides of the railway embankment and are arranged in a quincunx pattern. A grouting pipe is arranged in a quincunx pattern between the root piles at both ends. The tail of the root piles and the grouting pipe are embedded at least 10cm into the bottom of the pipe roof support beam (5).

[0021] The construction process for the tree root piles is as follows:

[0022] S2.2.1: Drill holes with a down-the-hole machine and clean the holes with high-pressure air;

[0023] S2.2.2: Insert a seamless steel pipe and pour a concrete grout stop pad, wherein the tail end of the seamless steel pipe protrudes at least 40cm above the ground and the grout stop pad is at least 30cm thick;

[0024] S2.2.3: Connect the grouting pipeline for root pile grouting construction;

[0025] The construction procedure for the grouting guide pipe between the two tree root piles is as follows:

[0026] A1: Hole drilling is performed, followed by high-pressure air cleaning.

[0027] A2: Insert a small grouting guide pipe to seal the gap between the small grouting guide pipe and the soil, and at the same time seal the tail end of the small grouting guide pipe; the tail end of the small grouting guide pipe is blocked with geotextile to prevent the pipe body from being blocked when sprayed concrete.

[0028] A3: Pour concrete grout stop pad, wherein the thickness of the grout stop pad is at least 30cm;

[0029] A4: Connect the grouting pipeline and perform grouting with the small grouting pipe.

[0030] Furthermore, the specific construction process for the pipe roof support beam in step S2 is as follows:

[0031] S2.3.1: Construct a pipe roof support beam on one side of the construction site and install guide pipes;

[0032] S2.3.2: Drill holes with a down-the-hole drill and clean the holes with high-pressure air;

[0033] S2.3.3: Guided measurement and insertion of the large pipe shed;

[0034] S2.3.4: Construction of the pipe shed support beam on the other side;

[0035] S2.3.5: Connect the grouting pipeline for grouting of the large pipe shed.

[0036] Furthermore, in step S4, the advanced support adopts a central pipe roof, with the outer insertion points evenly distributed within the angle range of the tunnel arch at a certain circumferential spacing, and overlaps with the previous cycle of advanced support by 2m; wherein, to ensure the stability of the tunnel face during excavation, the surrounding rock of the tunnel face needs to be reinforced; the non-blasting process for reserving core soil in the ring excavation is as follows:

[0037] B1: Excavation and support of the arc-shaped upper pilot tunnel;

[0038] B2: Excavate and reserve core soil;

[0039] B3: The lower left and lower right steps are excavated separately; specifically, the side with the worse surrounding rock on the lower left and lower right steps is excavated first.

[0040] B4: Excavation and support of the invert arch, and grouting construction at the bottom of the invert arch;

[0041] B5: Construction of invert arch lining concrete and invert arch filling construction;

[0042] B6: Secondary lining cast-in-place concrete construction.

[0043] It should be further explained that the specific methods for reinforcing the surrounding rock at the tunnel face are: shotcrete reinforcement at the tunnel face, shotcrete reinforcement at the tunnel face + local glass fiber anchor grouting reinforcement, shotcrete reinforcement at the tunnel face + full-section glass fiber anchor grouting reinforcement, shotcrete reinforcement at the tunnel face + full-section borehole grouting, and advanced curtain grouting.

[0044] Another preferred option is that once the arc-shaped pilot tunnel, core soil, left and right lower steps, and inverted arch reach a safe distance from each other, n blasting machines can be used to work simultaneously to speed up the excavation, and the excavation advance per cycle shall not exceed 1 arch frame, n≥1;

[0045] At the same time, the invert arch should be constructed closely following the face construction, and the secondary lining and formwork concrete should be poured in close loop following the invert arch filling construction to form a strong arch structure.

[0046] Furthermore, the grouting construction process at the bottom of the invert arch is as follows:

[0047] B4.1: Excavation of the invert arch and installation of the steel arch frame:

[0048] B4.2: Drill holes with a pneumatic drill, clean the holes with high-pressure air, and insert a small grouting guide pipe;

[0049] B4.3: Pouring initial support concrete for the invert arch;

[0050] B4.4: Connect the grouting pipeline for grouting construction using small grouting pipes.

[0051] Furthermore, when constructing the new three-tunnel tunnel under the existing railway embankment, the excavation and support of the nth tunnel body must be carried out first, followed by the excavation and support of the (n+1)th tunnel body, and finally the excavation and support of the (n+2)th tunnel body, while maintaining a certain distance between the tunnel faces, where n≥1.

[0052] Preferably, before constructing the three-hole tunnel under the existing railway embankment, it is necessary to set up horizontal displacement and vertical settlement monitoring points at the top of the rails, the top of the sleepers, and the embankment slope. Among them, monitoring and measurement points are buried at certain intervals at the top of the initial support arch, the waist of the arch, and the bottom of the invert arch.

[0053] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0054] 1. This invention employs a comprehensive construction technology combining "slope grouting in batches + root piles + pipe roof support beams + grouting at the bottom of the invert arch + non-blasting excavation" to reinforce the loose soil of the railway subgrade. This technology strengthens the original soil, reduces the soil permeability coefficient, and achieves the purpose of reinforcing the original soil and blocking water. The tunnel excavation is carried out using a non-blasting process. During the tunnel excavation, the maximum cumulative settlement monitored by the track top settlement monitoring was only -6mm, demonstrating a significant reinforcement effect. This invention can quickly and effectively prevent excessive surface settlement and existing railway subgrade settlement caused by the tunnel passing under the existing railway, greatly improving the safety factor of the tunnel and the existing railway, achieving the expected results, and having no adverse impact on railway operation. It has significant technical value and economic significance.

[0055] 2. This invention reduces the impact of overlapping construction work with existing railways during underpass tunnel construction, improves construction efficiency, shortens construction time, and reduces construction costs. Simultaneously, it successfully solves the problem of safely, quickly, and with high quality carrying out normal excavation construction of a new three-tunnel large-section tunnel without relocation of existing railways; that is, it eliminates the need to negotiate railway relocation with railway-related units, and avoids pausing construction to wait for the relocation of the underpass railway, saving significant railway relocation costs, reducing the impact of railway relocation on the progress of the central tunnel + double main tunnel excavation project, ensuring the continuity of the three-tunnel large-section tunnel excavation, and accelerating the tunnel excavation construction progress.

[0056] 3. This invention improves the physical and mechanical properties of the railway embankment soil by grouting and reinforcing it, thereby increasing the self-stability of the railway embankment soil, reducing the soil permeability coefficient, ensuring the stability of the railway embankment when the tunnel passes under it, and controlling the surface settlement after the tunnel excavation. This effectively ensures the safety and quality of the rapid construction process of the tunnel passing under the railway.

[0057] 4. This invention employs a combination of techniques including "slope grouting in batches + root piles + pipe roof support beams + grouting at the bottom of the invert arch," which is highly feasible and innovative. This ensures construction quality, accelerates construction progress, significantly shortens the construction period and reduces safety risks of tunnels passing under railways, and solves the problem of difficult tunnel excavation under railways. The new process used in the construction method, employing ring excavation with reserved core soil non-blasting excavation technology, greatly reduces environmental pollution, generates significant environmental benefits, saves on manpower, machinery, and materials input, reduces material consumption, and has significant energy-saving benefits. Attached Figure Description

[0058] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings:

[0059] Figure 1 This is a schematic diagram of the longitudinal section of the three tunnels passing under the railway in an embodiment of the present invention;

[0060] Figure 2 This is a schematic diagram of the cross-section of the reinforcement of the support beam for the three-hole underpass railway pipe shed in an embodiment of the present invention;

[0061] Figure 3 This is a schematic diagram of the ring-shaped excavation with reserved core soil in an embodiment of the present invention.

[0062] In the above figures, the component names corresponding to the reference numerals are as follows:

[0063] 1-Steel rail; 2-Railway embankment; 3-Shotcrete; 4-Grouting pipe; 5-Pipe roof support beam; 6-Large pipe roof; 7-Tree root pile; 8-Advanced large pipe roof; 9-Advanced support; 10-Upper arc-shaped pilot tunnel; 11-Core soil; 12-Lower step; 13-Inverted arch; 14-Hydraulic inverted arch trestle bridge; 15-Secondary lining cast-in-place concrete. Detailed Implementation

[0064] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of this invention are only for explaining this invention and are not intended to limit this invention. Example

[0065] like Figure 1 As shown in the figure, this embodiment provides a combined construction method for shallow-buried, three-tunnel, large-section tunnels passing under an existing railway, including the following steps:

[0066] S1: Model Analysis;

[0067] S2: Reinforce the existing railway subgrade;

[0068] S3: Investigate the surrounding rock ahead of the tunnel face;

[0069] S4: Implement advanced support 9 and reinforce the tunnel face. Use non-blasting excavation technology with ring excavation and reserved core soil 11 for tunnel excavation and support.

[0070] S5: Excavation and support of invert arch 13, and grouting construction at the bottom of invert arch 13;

[0071] S6: Secondary lining cast-in-place concrete 15 closed into a ring.

[0072] This plan adopts a combination of technical measures for the 22.13km-long tunnel passing under the existing railway, namely, "partial grouting of both sides of the slope + 7 tree root piles + 5 pipe roof support beams + 13 inverted arch bottom grouting + non-blasting excavation technology", to form an effective reinforcement structure and solve the technical problem of settlement control of the three-tunnel large-section tunnel of "double main tunnel + middle guide tunnel" passing under the existing railway embankment 2.

[0073] Specifically, the railway embankment 2 is reinforced with a combination of measures to improve the railway subgrade soil, forming a rod-shaped reinforced solid body to restrict the relative displacement of the railway subgrade, strengthen the overall integrity of the subgrade, and enhance the shear failure resistance of the overlying soil. Furthermore, a combination of "root piles 7 + pipe roof support beams 5 + bottom grouting of the invert arch 13" is used to form a good "simply supported beam" support structure, leveraging the "simply supported beam" effect to support the railway subgrade and prevent its subsidence. Simultaneously, the tunnel excavation adopts a non-explosive excavation process with a ring-shaped excavation and reserved core soil 11 to prevent the large-scale surface subsidence caused by tunnel blasting vibrations and shock waves, which could lead to tunnel arch collapse and railway subgrade deformation and settlement.

[0074] Furthermore, the model analysis in step S1 involves using Midas GTS NX geotechnical numerical software to perform finite element simulation analysis on the deformation of the ground surface and rail 1 during the construction of the new three-tunnel tunnel under the railway embankment 2 and when it passes through the railway embankment 2, in order to obtain construction parameters to guide the construction.

[0075] In step S2, the existing railway subgrade is reinforced by a combination of "slope grouting in batches + root piles 7 + pipe roof support beams 5".

[0076] It should be noted that the slope grouting process in batches is as follows:

[0077] S2.1.1: Hole drilling is performed, and the hole is cleaned by high-pressure air.

[0078] S2.1.2: Insert the grouting pipe 4 to seal the gap between the grouting pipe 4 and the soil, and at the same time seal the tail end of the grouting pipe 4 to prevent the pipe from being blocked when spraying concrete;

[0079] S2.1.3: Lay n layers of steel mesh and spray 3 layers of concrete;

[0080] S2.1.4: Connect the grouting pipeline and perform grouting through the small grouting pipe 4.

[0081] It should also be noted that in step 2, the root piles 7 are located at both ends of the bottom of the pipe roof support beams 5 on both sides of the railway embankment 2 and are arranged in a quincunx pattern. There are grouting pipes 4 arranged in a quincunx pattern between the root piles 7 at both ends. The tail ends of the root piles 7 and the grouting pipes 4 are embedded at least 10cm into the bottom of the pipe roof support beams 5.

[0082] The construction process for the root pile 7 is as follows:

[0083] S2.2.1: Drill holes with a down-the-hole machine and clean the holes with high-pressure air;

[0084] S2.2.2: Insert a seamless steel pipe and pour a concrete grout-stopping pad, wherein the tail end of the seamless steel pipe protrudes at least 40cm above the ground and the grout-stopping pad is at least 30cm thick;

[0085] S2.2.3: Connect the grouting pipeline to carry out grouting construction for the root pile 7;

[0086] The construction procedure for the grouting guide pipe 4 between the two end root piles 7 is as follows:

[0087] A1: Hole drilling is performed, followed by high-pressure air cleaning.

[0088] A2: Insert the grouting pipe 4 to seal the gap between the grouting pipe 4 and the soil, and at the same time seal the tail end of the grouting pipe 4 to prevent the pipe from being blocked when spraying concrete;

[0089] A3: Grout stop pad for concrete pouring, wherein the thickness of the grout stop pad is at least 30cm;

[0090] A4: Connect the grouting pipeline and perform grouting through the small grouting pipe 4.

[0091] Furthermore, the specific construction process of the pipe roof support beam 5 in step S2 is as follows:

[0092] S2.3.1: Construct pipe roof support beam 5 on one side of the construction site and install guide pipes;

[0093] S2.3.2: Drill holes with a down-the-hole drill and clean the holes with high-pressure air;

[0094] S2.3.3: Guide measurement and insertion of the large pipe shed 6;

[0095] S2.3.4: Construction of the pipe shed support beam 5 on the other side;

[0096] S2.3.5: Connect the grouting pipeline for grouting of the large pipe shed 6.

[0097] For the loose soil of the railway subgrade crossing the railway, a comprehensive construction technology combining "slope grouting in batches + 7 root piles + 5 pipe roof support beams + 13 invert arches with bottom grouting + non-blasting excavation" was adopted to reinforce the original soil, reduce the soil permeability coefficient, and thus achieve the purpose of reinforcing the original soil and blocking water. This also reduced the impact of the underpass tunnel construction on the existing railway, improved construction efficiency, shortened construction time, and reduced construction costs. Furthermore, it successfully solved the problem of safely, quickly, and with high quality carrying out the normal excavation of the new three-tunnel large-section tunnel without relocating the existing railway. This eliminated the need to negotiate railway relocation with railway authorities and to pause construction while waiting for the railway relocation, saving significant railway relocation costs and reducing the impact of railway relocation on the progress of the central tunnel and double main tunnel excavation. This ensured the continuity of the three-tunnel large-section tunnel excavation and accelerated the tunnel construction progress. This not only saved construction costs for the construction unit, but also saved project investment costs for the construction unit, and saved a series of expenses for relocation and rerouting of railway-related units, indirectly saving the country a huge amount of expenditure.

[0098] Furthermore, in step S4, the advanced support 9 adopts a central pipe roof and is evenly distributed at certain intervals within the angle of the tunnel arch, with at least a 2m overlap between adjacent advanced supports 9; wherein, to ensure the stability of the tunnel face during excavation, the surrounding rock of the tunnel face needs to be reinforced; the non-blasting process for reserving the core soil 11 in the ring excavation is as follows:

[0099] B1: Excavation and support of the arc-shaped upper pilot tunnel;

[0100] B2: Excavate and reserve 11 cubic meters of core soil;

[0101] B3: The lower left step 12 and the lower right step 12 will be excavated separately. Specifically, the side with the worse surrounding rock on the lower left or right step will be excavated first.

[0102] B4: Excavation and support of invert arch 13, and grouting construction at the bottom of invert arch 13;

[0103] B5: Construction of concrete lining for arch 13 and filling of arch 13;

[0104] B6: Secondary lining cast-in-place concrete construction 15.

[0105] The tunnel excavation adopted a non-blasting method. During the excavation, the maximum cumulative settlement of the rail top was only -6mm, demonstrating a significant reinforcement effect. This method can quickly and effectively prevent excessive surface settlement and existing railway subgrade settlement caused by the tunnel passing under the existing railway. The non-blasting excavation method eliminates the disturbance of surrounding rock and surface caused by blasting vibrations and shock waves, greatly improving the safety factor of the tunnel and the existing railway. It achieved the expected results and had no adverse impact on railway operations, demonstrating significant technical and economic value.

[0106] It should be noted that the specific methods for reinforcing the surrounding rock at the tunnel face are as follows: shotcrete reinforcement at the tunnel face, shotcrete reinforcement at the tunnel face plus localized glass fiber anchor grouting, shotcrete reinforcement at the tunnel face plus full-section glass fiber anchor grouting, shotcrete reinforcement at the tunnel face plus full-section borehole grouting, and pre-grouting. By reinforcing the railway embankment 2 with grouting, the physical and mechanical properties of the embankment soil are improved, the self-stability of the railway embankment 2 soil is enhanced, and the permeability coefficient of the soil is reduced, ensuring the stability of the railway embankment 2 when the tunnel passes under it. Surface settlement after tunnel excavation is controllable, effectively ensuring the safety and quality of the rapid construction process of the tunnel section passing under the railway.

[0107] Another preferred option is that once the arc-shaped pilot tunnel, core soil 11, left and right lower steps 12, and inverted arch 13 reach a safe distance from each other, n blasting machines can be used to operate simultaneously to speed up the excavation. Moreover, the excavation advance per cycle shall not exceed one arch frame, and n≥1. In other words, by using n blasting machines for non-blasting excavation, the construction efficiency can be greatly improved, the construction cycle can be shortened, and the construction cost can be reduced.

[0108] At the same time, the invert arch 13 should be constructed closely following the face construction, and the secondary lining cast concrete 15 should be constructed closely following the invert arch 13 filling construction to close the loop and form a strong arch structure.

[0109] It should be further noted that the grouting construction process at the bottom of invert arch 13 is as follows:

[0110] B4.1: Excavation of the invert arch (section 13), installation of the steel arch frame:

[0111] B4.2: Drill holes with a pneumatic drill, clean the holes with high-pressure air, and insert the grouting guide tube 4;

[0112] B4.3: Pour the initial support concrete for the invert arch 13;

[0113] B4.4: Connect the grouting pipeline and carry out grouting construction with the grouting small guide pipe 4.

[0114] When constructing the new three-tunnel tunnel under the existing railway embankment 2, the excavation and support of the nth tunnel body must be carried out first, followed by the excavation and support of the (n+1)th tunnel body, and finally the excavation and support of the (n+2)th tunnel body, while maintaining a certain distance between the tunnel faces, where n≥1. It should also be noted that the YT-28 pneumatic drilling rig is used for drilling in the above construction process.

[0115] Preferably, before the construction of the three-hole tunnel under the existing railway embankment 2, it is necessary to set up horizontal displacement and vertical settlement monitoring points at the top of the rail 1, the top of the sleeper, and the embankment slope. Among them, monitoring and measurement points are buried at a certain distance at the top of the initial support arch, the waist of the arch, and the bottom of the invert arch 13. The monitoring data of each monitoring point are collected and received by the tunnel construction monitoring center, so as to monitor and grasp the situation of the construction site at all times and ensure the safety of the entire construction process.

[0116] Example 2

[0117] This embodiment only describes the differences from Embodiment 1. It should be noted that in tunnel construction, due to the complex geological environment and high construction difficulty, dynamic construction monitoring has become an urgent guarantee technology to ensure the safety and efficiency of tunnel construction. Based on this, this embodiment proposes a tunnel construction monitoring system, which includes: a construction environment monitoring unit and a construction personnel monitoring unit. The construction environment monitoring unit includes detection modules corresponding to each construction point in the tunnel, and the detection modules integrate humidity and temperature sensors, dust and gas sensors, and ZigBee wireless communication modules. The construction personnel monitoring unit includes a portable module carried by the construction personnel. The portable module includes a signal activation module connected to the ZigBee wireless communication module, an alarm module, and a transmission module connected to the dispatch center of the construction headquarters. Multiple ZigBee wireless communication modules form a local communication network covering the construction tunnel.

[0118] It should be noted that the detection modules installed at various construction points in the tunnel can monitor the construction environment inside the tunnel, thus providing a basic guarantee for the personal safety of construction personnel. At the same time, when the portable modules carried by the tunnel construction personnel communicate with the ZigBee wireless communication module of the detection module during construction, the signal activation module can emit a signal and transmit it to the dispatch center through the transmitter module, thereby realizing the location of the construction personnel. In addition, when the detection module detects changes in the environment of the construction point inside the tunnel (posing a safety hazard to the construction personnel), the ZigBee wireless communication module can also transmit information to the warning module through its local area communication network, so that the warning module can provide warning information to the construction personnel (such as issuing an audible and visual alarm).

[0119] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A combined construction method for shallow-buried, three-tunnel, large-section tunnels passing under an existing railway, characterized in that... Includes the following steps: S1: Model analysis, specifically: using geotechnical numerical software to perform finite element simulation analysis on the deformation of the ground surface and rail (1) when the tunnel under the newly built three tunnels is constructed to the bottom of the railway embankment (2) and when it passes through the railway embankment (2), and to obtain construction parameters to guide the construction; S2: Reinforce the existing railway subgrade by adopting a combination of "slope grouting in batches + root piles (7) + large pipe shed (6) and pipe shed support beams (5)"; S3: Investigate the surrounding rock ahead of the tunnel face; S4: Implement advance support (9) and reinforce the tunnel face. Use the non-blasting excavation process with reserved core soil in a ring for tunnel excavation and support. The advance support (9) adopts a central pipe roof and is evenly distributed within the angle range of the tunnel arch at a certain circumferential spacing, and overlaps with the previous cycle of advance support (9) by at least 2m. In order to ensure the stability of the tunnel face during excavation, the surrounding rock of the tunnel face needs to be reinforced. The non-blasting process with reserved core soil in a ring is as follows: B1: Excavation and support of the arc-shaped upper pilot tunnel; B2: Excavate and reserve core soil; B3: The lower left and lower right steps should be excavated separately; B4: Excavation and support of the invert arch (13), and grouting construction at the bottom of the invert arch (13); B5: Construction of concrete lining for inverted arch (13) and construction of filling for inverted arch (13); B6: Construction of secondary lining cast-in-place concrete (15); S5: Excavation and support of the invert arch (13), and grouting construction at the bottom of the invert arch (13); S6: Secondary lining cast concrete (15) closed into a ring.

2. The method for combined construction of a shallow-buried, three-tunnel, large-section tunnel passing under an existing railway, as described in claim 1, is characterized in that... The slope grouting process in batches is as follows: S2.1.1: Hole drilling is performed, and the hole is cleaned by high-pressure air. S2.1.2: Insert the grouting pipe (4) to seal the gap between the grouting pipe (4) and the soil, and at the same time seal the tail end of the grouting pipe (4). The tail end of the grouting pipe (4) is blocked with geotextile to prevent the pipe from being blocked when sprayed concrete. S2.1.3: Lay n layers of steel mesh and spray concrete (3); S2.1.4: Connect the grouting pipeline and perform grouting with the small grouting pipe (4) Grouting.

3. The method for combined construction of a shallow-buried, three-tunnel, large-section tunnel passing under an existing railway, as described in claim 1, is characterized in that... In step S2, the pipe shed support beam (5) is located on both sides of the railway embankment (2), and the tree root piles (7) are arranged in a plum blossom shape at both ends of the bottom of the pipe shed support beam (5); A grouting pipe (4) is arranged in a plum blossom shape between the two ends of the root pile (7). The tail of the root pile (7) and the grouting pipe (4) are embedded at least 10cm into the bottom of the pipe shed support beam (5). The construction procedure for the root pile (7) is as follows: S2.2.1: Drill holes with a down-the-hole machine and clean the holes with high-pressure air; S2.2.2: Insert a seamless steel pipe and pour a concrete grout stop pad, wherein the tail end of the seamless steel pipe protrudes at least 40cm above the ground and the grout stop pad is at least 30cm thick; S2.2.3: Connect the grouting pipeline for root pile (7) grouting construction; The construction procedure for the grouting guide pipe (4) between the two end root piles (7) is as follows: A1: Hole drilling is performed, followed by high-pressure air cleaning. A2: Insert the grouting pipe (4) to seal the gap between the grouting pipe (4) and the soil, and at the same time seal the tail end of the grouting pipe (4). The tail end of the grouting pipe (4) is blocked with geotextile to prevent the pipe from being blocked when sprayed concrete. A3: Grout stop pad for concrete pouring, wherein the thickness of the grout stop pad is at least 30cm; A4: Connect the grouting pipeline and perform grouting with the small grouting guide pipe (4) Grouting.

4. The method for combined construction of a shallow-buried, three-tunnel, large-section tunnel under an existing railway, as described in claim 1, is characterized in that... The construction process of the pipe roof support beam (5) is as follows: S2.3.1: Construct the pipe shed support beam (5) on one side and install the guide pipe; S2.3.2: Drill holes with a down-the-hole drill and clean the holes with high-pressure air; S2.3.3: Guide measurement and insertion of large pipe shed (6); S2.3.4: Construction of the pipe shed support beam on the other side (5); S2.3.5: Connect the grouting pipeline for grouting of the large pipe shed (6).

5. The method for combined construction of a shallow-buried, three-tunnel, large-section tunnel under an existing railway, as described in claim 1, is characterized in that... The grouting construction process at the bottom of the invert arch (13) is as follows: B4.1: Excavation of the invert arch (13), installation of the steel arch frame: B4.2: Drill holes with a pneumatic drill, clean the holes with high-pressure air, and insert a small grouting guide pipe (4). B4.3: Pour the initial support concrete for the invert arch (13); B4.4: Connect the grouting pipeline for grouting small guide pipe (4) Grouting construction.

6. A combined construction method for shallow-buried, three-tunnel, large-section tunnels passing under an existing railway, as described in any one of claims 1-5, characterized in that... When constructing the new three-tunnel tunnel under the existing railway embankment (2), the excavation and support of the nth tunnel body must be carried out first, followed by the excavation and support of the (n+1)th tunnel body, and finally the excavation and support of the (n+2)th tunnel body. The tunnel faces must be kept at a certain distance from each other, where n≥1.

7. The method for combined construction of a shallow-buried, three-tunnel, large-section tunnel under an existing railway, as described in claim 6, is characterized in that... Before the construction of the three tunnels under the existing railway embankment (2), it is necessary to set up horizontal displacement and vertical settlement monitoring points at the top of the rails (1), the top of the sleepers and the embankment slope. Among them, monitoring and measurement points are buried at a certain distance at the top of the initial support arch, the waist of the arch and the bottom of the inverted arch (13).

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