Double shield tunneling butt joint construction method for underground road junction and merging sections in soft soil areas

Abstract

The present invention discloses a double-shield, dark-excavation, butt-jointed construction method for underground road junction and confluence sections in soft soil areas. The mainline tunnel and ramp tunnel are constructed using a shield tunneling method. A pipe curtain and freezing pipes are installed in the irregularly shaped transition section and end area. The freezing pipes within the pipe curtain freeze and reinforce the soil, forming a stable frozen curtain. A servo support system is applied inside the mainline and ramp tunnels. Localized hole excavation is performed in controlled areas, and the soil at the junction of the end and the transition section is gradually excavated. The irregularly shaped transition space is formed through dark-excavation. The advantages of this invention are that it eliminates the need for open-cut working pit construction on the ground and is unaffected by the ground environment. This increases the flexibility of setting up the junction and confluence sections of the underground road and selecting entrances and exits, thereby improving the traffic capacity of the underground road and surrounding areas.

Description

Technical Field

[0001] The present invention relates to the technical field of shield tunneling, in particular to a double-shield tunneling butt joint construction method for a junction and diversion section of an underground road in a soft soil area. Background Art

[0002] With the acceleration of urbanization, underground road construction is expanding as an important means to alleviate surface traffic pressure and improve urban traffic efficiency. In soft soil areas, underground road construction is particularly complex, especially in diverging and merging sections. Changes in traffic direction cause significant changes in the tunnel cross-section, forming an irregular, gradient section. In addition, the soft soil geology affects the stability of the tunnel structure, significantly increasing the construction difficulty and safety risks. Traditional methods for constructing diverging and merging sections of underground roads rely on open-cut or caisson techniques. These methods not only have long construction cycles and significant environmental impacts, but are also prone to causing ground subsidence and other problems in soft soil areas. Furthermore, open-cut construction requires the occupation of surface land and involves demolition and other work, making it difficult to implement in urban core areas.

[0003] In recent years, the use of shield methods for mainline tunnel construction has been gradually explored, and combined with dark excavation technology to form irregular gradient sections. CN115163094A discloses a construction method for urban underground road divergence and confluence points, which realizes the construction of urban underground road divergence and confluence points by combining the mainline shield tunnel, open-cut working shaft and connecting dark excavation technology. This method still requires the construction of open-cut working shaft, only the foundation pit size is smaller than the traditional technology. JP2003148086A discloses a construction method for tunnel divergence and confluence sections in soft rock formations, which realizes efficient and safe connection between tunnels by minimizing the excavation part and reducing the road surface occupation by using rectangular shields and U-shaped retaining walls; JP2006132567A discloses a shield top plate construction method, which realizes accurate and low-impact branch connection point construction by pre-forming a structure of multiple top plates surrounding the excavation area outside the excavation position. CN108868814A discloses a shield tunnel ventilation shaft connected to a concealed duct in collapsible loess and gravelly soil. This dual-layer structure, combined with concealed ducts and open-cut ventilation shafts, addresses several issues associated with traditional open-cut ventilation shaft construction. However, the technical solutions provided by these patents struggle to meet the requirements for excavation in soft soil, an area that this application addresses. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a double-shield underground excavation docking construction method for the junction and merging sections of underground roads in soft soil areas. By optimizing the shield tunnel layout and underground excavation technology, the full underground excavation construction of the junction and merging sections of underground roads is realized without occupying ground space and reducing environmental impact, which greatly increases the flexibility of the setting of the junction and merging sections of underground roads and the site selection of entrances and exits, and greatly improves the traffic function of underground roads.

[0005] In order to solve the above technical problems, the present invention provides a double shield tunneling and butting construction method for the junction and diversion section of an underground road in a soft soil area, comprising the following steps:

[0006] Step S1: construct the main line and ramp tunnel using the shield method;

[0007] According to the requirements of the underground road line shape, the main line tunnel and ramp tunnel are constructed using the shield method respectively. The middle partition wall is set up inside the tunnel as needed. The main line tunnel and ramp tunnel are excavated separately before the special-shaped gradient section in the connection area, and the docking interface is reserved;

[0008] Step S2: constructing pipe curtains and freezing pipes on the special-shaped gradient sections and ends;

[0009] A pipe curtain structure is pre-installed in the irregular transition section and end section of the connection area where the main line tunnel and the ramp tunnel meet. The pipe curtain is composed of a series of steel pipes and is arranged along the excavation contour in the irregular transition section of the connection area.

[0010] Freezing pipes are arranged in the pipe roof for soil freezing and reinforcement. The freezing pipes are pre-set in the steel top pipe or directly arranged in the soil. The specific freezing pipe arrangement plan is determined based on the on-site construction conditions and factors such as soil properties and cover thickness.

[0011] Step S3: using pipe curtains to freeze and reinforce the soil;

[0012] Circulating refrigerant through the freezing pipes freezes the soil around the pipe curtain into frozen ground, forming a water-stop curtain. The freezing process must meet the requirements of bearing capacity and waterproof performance, while also considering frost heave control;

[0013] Step S4: Applying a servo support system inside the mainline tunnel and the ramp tunnel;

[0014] A servo support system is applied to key stress-bearing areas inside the mainline tunnel and ramp tunnel, where the servo support system is adjusted and optimized according to the actual on-site construction process;

[0015] Step S5: excavating the upper soil through local holes and installing assembled steel-concrete pipe segments;

[0016] Under the protection of the frozen soil curtain, local holes were broken to excavate the upper soil, and assembled steel-concrete segments were installed, gradually advancing into the tunnel;

[0017] Step S6: gradually excavating the soil at the junction of the end and the transition section, replacing supports, and removing the frozen zone segments;

[0018] When excavation reaches the junction of the end and the gradient section, the soil is gradually excavated and the support system is replaced to ensure construction safety. After the excavation is completed, the frozen area segments are removed to form a complete tunnel structure;

[0019] Step S7: constructing the end wall;

[0020] Construct end walls at the ends of the tunnel to seal the tunnel structure and ensure the overall stability of the tunnel;

[0021] Step S8: excavating the soil at the irregular-shaped gradient section and removing the segments;

[0022] After the excavation of the soil in the irregular gradient section is completed, the pipe segments are removed to form a smooth tunnel transition section.

[0023] The step S1 includes the following specific steps:

[0024] Step S11: Determine the line type, cross-sectional dimensions, and center partition wall locations of the main line tunnel and ramp tunnel based on the planning of the multi-point entry, divergence, and merging sections of the underground road;

[0025] Step S12: Complete the construction of the starting shaft to ensure the smooth start of the shield machine. According to the tunnel section size and geological conditions, select the appropriate shield machine model and excavate according to the predetermined route and slope.

[0026] The step S2 includes the following specific steps:

[0027] Step S21: Design the structure of the curved pipe curtain and the steel pipe specifications based on the special-shaped cross-section profile formed by the double shield and the soil conditions, and prepare sufficient steel pipes and connectors;

[0028] Step S22: using a pipe jacking method or a horizontal directional drilling method to push or drill the steel pipe into the soil along a predetermined trajectory to form a pipe curtain structure;

[0029] Step S23: Arrange freezing pipes around the pipe roof to ensure that the freezing pipes are in close contact with the pipe roof.

[0030] The step S3 includes the following specific steps:

[0031] Step S31: Install the refrigeration unit, the refrigerant circulation system, and the temperature monitoring system, and perform debugging to ensure the normal operation of the freezing system;

[0032] Step S32: The soil circulates the refrigerant through the freezing pipes, gradually freezing the soil around the pipe curtain into frozen soil, while monitoring parameters such as the thickness, strength and temperature of the frozen soil curtain.

[0033] The step S4 includes the following specific steps:

[0034] Step S41: Arrange servo heads for force and displacement control in key stress-bearing areas of the mainline tunnel and ramp tunnel segments, and design the truss structure of the servo support system;

[0035] Step S42: During the construction process, the stress condition of the support system is monitored in real time, and data such as stress, strain, and displacement of the support system are collected using sensors and monitoring equipment.

[0036] The step S5 includes the following specific steps:

[0037] Step S51: Under the protection of the frozen soil curtain, a combination of mechanical and manual methods is used to perform local hole excavation in the upper area of ​​the main line and ramp tunnels, and the excavation footage and speed are controlled;

[0038] Step S52: Prefabricated assembled steel-concrete segments are installed in the space of the special-shaped gradient section excavated at the upper part. The segments are connected with bolts or mortise and tenon structures to form a steel arch shell structure connected by arch segments, and a segment structure of the main line and ramp tunnel with a multi-arch steel section with an approximately elliptical cross-section.

[0039] The step S6 includes the following specific steps:

[0040] Step S61: When excavating to the junction of the end and the gradient section, excavate the soil step by step in a segmented and layered manner;

[0041] Step S62: After the soil excavation is completed, when the forces on the soil and the tunnel tend to be stable, replace the unnecessary support truss structure and change the servo support system;

[0042] Step S63: After excavation reaches the frozen area and it is confirmed that the soil in the area is stable, the interior of the special-section tunnel structure of the main line and ramp tunnel is closed, and the pipe segments in the frozen area are removed.

[0043] The step S7 includes the following specific steps:

[0044] Step S71: Accurately measure the spatial dimensions of the end of the tunnel's irregularly shaped gradient section to determine the specific position and contour of the end wall;

[0045] Step S72: Install the steel frame, set up a stable formwork with tight joints, pour the prepared concrete evenly into the formwork, and vibrate it thoroughly to ensure that the concrete is dense;

[0046] Step S73: After the concrete has initially set, appropriate maintenance measures are taken in a timely manner. After the concrete reaches the designed strength, the formwork is removed and a comprehensive quality inspection is carried out to ensure that the end wall meets the design requirements before acceptance.

[0047] The step S8 includes: gradually removing the pipe segments in the special-shaped gradient section, and performing necessary processing on the space after the removal of the pipe segments, such as pouring concrete and installing prefabricated components, to form a smooth tunnel transition section, while the special-shaped gradient section tunnel structure meets the strength and stability requirements.

[0048] This invention addresses the construction challenges of irregularly shaped, gradually changing sections of underground roads by integrating shield, freezing, and pipe-curtain methods. The shield method is used to form the main and branch tunnels, and the freezing method is then used to strengthen the soil strength in the excavation area, minimizing environmental impact and lowering the probability of excavation instability. Finally, the pipe-curtain method, along with a special-shaped structure and internal support system, is used to form irregularly shaped, gradually changing spaces through covert excavation. This is the first time that the fully covert excavation method for irregularly shaped, gradually changing sections of underground roads with diverging and merging flows has been proposed in soft soil areas. This eliminates the need for open-cut working well construction on the ground and is unaffected by the ground environment. This significantly increases the flexibility of setting up diverging and merging sections and selecting entrances and exits, significantly improving the underground road's function for traffic flow.

[0049] The superior effects of the present invention are:

[0050] 1) By adopting the double shield tunneling technology and combining it with pipe curtain freezing reinforcement measures, the soil stability and groundwater control problems encountered during underground road construction in soft soil areas were effectively solved;

[0051] 2) The present invention adopts refined construction methods in key areas of tunnel construction, such as the irregular transition section and the end area, to ensure the stability and durability of the tunnel structure during construction and subsequent use;

[0052] 3) The use of concealed excavation and docking technology minimizes interference with ground traffic and the need to relocate underground pipelines, reducing the impact on surrounding buildings and underground facilities. This environmentally friendly construction method is in line with the sustainable development concept of modern urban construction;

[0053] 4) The present invention improves construction efficiency, ensures safety during construction and the long-term stability of the tunnel structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0055] Figure 1 It is a flowchart of a specific embodiment of the present invention;

[0056] Figure 2 This is a schematic diagram of the construction of a double shield tunnel for connecting the diversion and merging sections of an underground road according to a specific embodiment of the present invention;

[0057] Figure 3 This is a schematic diagram of a curved tube curtain constructed with a special-shaped gradient section according to a specific embodiment of the present invention;

[0058] Figure 4 This is a schematic diagram of pipe curtain freezing at the end section of a specific embodiment of the present invention;

[0059] Figure 5 A schematic diagram of an internal servo support system according to a specific embodiment of the present invention;

[0060] Figure 6 This is a schematic diagram of assembling steel-concrete pipe segments according to a specific embodiment of the present invention;

[0061] Figure 7 Schematic diagram of excavation, support conversion and segment removal according to a specific embodiment of the present invention;

[0062] Description of the numbers in the figure

[0063] 1—mainline tunnel segment; 2—ramp tunnel segment;

[0064] 3—Curved pipe curtain; 4—Frozen pipe;

[0065] 5—end pipe curtain; 6—servo support truss structure;

[0066] 7—Servo control device; 8—Arched steel-concrete pipe segment;

[0067] 9—Segment assembly device. DETAILED DESCRIPTION

[0068] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0069] like Figure 1 As shown, the present invention provides a double shield tunneling method for connecting and constructing a junction and diversion section of an underground road in a soft soil area, comprising the following steps:

[0070] Step S1: construct the main line and ramp tunnel using the shield method;

[0071] According to the requirements of the underground road line shape, the main line tunnel and ramp tunnel are constructed using the shield method respectively. The middle partition wall is set up inside the tunnel as required. The main line tunnel and ramp tunnel are excavated separately before the special-shaped gradient section in the connection area, and the docking interface is reserved;

[0072] Step S2: constructing pipe curtains and freezing pipes on the special-shaped gradient sections and ends;

[0073] A pipe curtain structure is pre-installed in the irregular transition section and end section of the connection area where the main line tunnel and the ramp tunnel meet. The pipe curtain is composed of a series of steel pipes and is arranged along the excavation contour in the irregular transition section of the connection area.

[0074] Freezing pipes are arranged in the pipe roof for soil freezing and reinforcement. The freezing pipes are pre-set in the steel top pipe or directly arranged in the soil. The specific freezing pipe arrangement plan is determined based on the on-site construction conditions and factors such as soil properties and cover thickness.

[0075] Step S3: using pipe curtains to freeze and reinforce the soil;

[0076] Circulating refrigerant through the freezing pipes freezes the soil around the pipe curtain into frozen ground, forming a water-stop curtain. The freezing process must meet the requirements of bearing capacity and waterproof performance, while also considering frost heave control;

[0077] Step S4: Applying a servo support system inside the main line and ramp tunnels;

[0078] A servo support system is applied to the key stress-bearing areas inside the mainline tunnel and ramp tunnel, and the servo support system is adjusted and optimized according to the actual on-site construction process;

[0079] Step S5: excavating the upper soil through local holes and installing assembled steel-concrete pipe segments;

[0080] Under the protection of the frozen soil curtain, local holes were broken to excavate the upper soil, and assembled steel-concrete segments were installed, gradually advancing into the tunnel;

[0081] Step S6: gradually excavating the soil at the junction of the end and the transition section, replacing supports, and removing the frozen zone segments;

[0082] When excavation reaches the junction of the end and the gradient section, the soil is gradually excavated and the support system is replaced to ensure construction safety. After the excavation is completed, the frozen area segments are removed to form a complete tunnel structure;

[0083] Step S7: constructing the end wall;

[0084] Construct end walls at the ends of the tunnel to seal the tunnel structure and ensure the overall stability of the tunnel;

[0085] Step S8: excavating the soil at the irregular-shaped gradient section and removing the segments;

[0086] After the excavation of the soil in the irregular gradient section is completed, the pipe segments are removed to form a smooth tunnel transition section.

[0087] Furthermore, step S1 includes the following specific steps:

[0088] Step S11: Determine the line type, cross-sectional dimensions, and center partition wall locations of the main line tunnel and ramp tunnel based on the planning of the multi-point entry, divergence, and merging sections of the underground road;

[0089] Step S12: Complete the construction of the starting shaft to ensure that the shield machine can start smoothly. According to the tunnel section size and geological conditions, select the appropriate shield machine model and excavate according to the predetermined route and slope;

[0090] like Figure 2As shown, the diverging and merging sections are where vehicles diverge from the main road and enter the ramp, or where vehicles on the ramp merge and enter the main road. The main line and ramp are constructed using the double shield tunneling method to connect the tunnels. Ramps, as auxiliary roads in the road system, are usually used to connect the main line with other roads or provide vehicle access. The main line, as the main traffic section of the underground road, carries the majority of traffic. The irregular gradient section is located between the ramp and the main line, forming the transition area between the two. Due to the differences in parameters such as line shape and width between the ramp and the main line, a smooth transition is required through the irregular gradient section to ensure smooth and safe vehicle travel. The end section usually refers to the cross-section at the starting or ending position of a tunnel or underground structure.

[0091] Furthermore, step S2 includes the following specific steps:

[0092] Step S21: Design the structure of the curved pipe curtain and the steel pipe specifications based on the special-shaped cross-section profile formed by the double shield and the soil conditions, and prepare sufficient steel pipes and connectors;

[0093] Step S22: using a construction method such as pipe jacking or horizontal directional drilling to push or drill the steel pipe into the soil along a predetermined trajectory to form a pipe curtain structure;

[0094] Step S23: Arrange freezing pipes around the pipe roof to ensure that the freezing pipes are in close contact with the pipe roof;

[0095] like Figure 3 As shown, when this embodiment is implemented, the special-shaped gradient section is constructed as a curved pipe curtain. The curved pipe curtain is composed of a series of steel pipes that are tightly arranged and arranged along the excavation contour of the special-shaped gradient section to form a continuous support structure. The steel pipes are overlapped with lock joints, and water-stop lubricant is applied at the lock joints of the steel pipes. Water-stop agent is injected at the joints of the steel pipes to enhance the stability and bearing capacity of the overall structure; freezing pipes are arranged inside or around the curved pipe curtain for soil freezing and reinforcement. The freezing liquid circulates through the freezing pipes to freeze the soil around the pipe curtain into frozen soil to form a water-stop curtain.

[0096] like Figure 4 As shown, when this embodiment is implemented, pipe curtain freezing is applied to the end section, a pipe curtain structure is arranged at the end section of the connection area where the main line tunnel and the ramp tunnel are connected, and grouting or concrete is injected inside. Freezing pipes for soil freezing and reinforcement are arranged inside the pipe curtain or in the soil adjacent to the pipe curtain.

[0097] Furthermore, step S3 includes the following specific steps:

[0098] Step S31: Install the refrigeration unit, the refrigerant circulation system, and the temperature monitoring system, and perform debugging to ensure the normal operation of the freezing system;

[0099] Step S32: The soil circulates the freezing liquid through the freezing pipes, gradually freezing the soil around the pipe curtain into frozen soil, while monitoring parameters such as the thickness, strength and temperature of the frozen soil curtain.

[0100] Furthermore, step S4 includes the following specific steps:

[0101] Step S41: Arrange servo heads for force and displacement control in key stress-bearing areas of the mainline tunnel and ramp tunnel segments, and design the truss structure of the servo support system;

[0102] Step S42: During the construction process, the stress condition of the support system is monitored in real time, and data such as stress, strain, and displacement of the support system are collected using sensors and monitoring equipment;

[0103] like Figure 5 As shown, when this embodiment is implemented, a servo support system is applied internally, including a servo support truss structure and a servo control device. The servo support truss structure serves as the main support structure and is distributed in the key stress-bearing areas inside the mainline tunnel and ramp tunnel, including the junction between the arched segments and the mainline and ramp tunnel segments, and the connection between the middle structure and the mainline and ramp tunnel segments. The servo support truss structure is composed of multiple interconnected rods to form a stable frame structure that can withstand various forces and deformations generated during tunnel boring and excavation. The servo control device is responsible for precisely controlling the operation of the servo support system, including a servo control system, sensors, and hydraulic jacks. It monitors and adjusts the status of the servo support system in real time to ensure that it provides stable and precise support during tunnel construction. The existence of the servo control device enables the support system to be dynamically adjusted according to the actual conditions inside the tunnel, improving the safety and efficiency of construction. Through the adjustment of the servo control device, the servo support truss structure flexibly adapts to changes in tunnel shape and stress, providing the necessary support and stability.

[0104] Furthermore, step S5 includes the following specific steps:

[0105] Step S51: Under the protection of the frozen soil curtain, a combination of mechanical and manual methods is used to perform local hole excavation in the upper area of ​​the main line and ramp tunnels, and the excavation footage and speed are controlled;

[0106] Step S52: Prefabricated assembled steel-concrete segments are installed in the space of the special-shaped gradient section excavated at the upper part. The segments are connected with bolts or mortise and tenon structures to form a steel arch shell structure connected by arch segments, and a segment structure of the main line and ramp tunnel with a multi-arch steel section with an approximately elliptical cross-section.

[0107] like Figure 6As shown, during implementation of this embodiment, assembled steel-concrete segments are constructed. The upper half of the mainline and ramp tunnels are connected to the arched steel-concrete segments of the vault to form an arch structure, with the segments connected using bolts. During the steel-concrete segment assembly process, local excavation is performed under the protection of a frozen soil curtain to provide space for the steel-concrete segments. Following a predetermined design and installation sequence, the arched steel-concrete segments are gradually advanced into the tunnel interior, completely covering the entire tunnel interior with assembled steel-concrete segments, forming a complete tunnel lining structure.

[0108] Furthermore, step S6 includes the following specific steps:

[0109] Step S61: When excavating to the junction of the end and the gradient section, excavate the soil step by step in a segmented and layered manner;

[0110] Step S62: After the soil excavation is completed, when the forces on the soil and the tunnel tend to be stable, replace the unnecessary support truss structure and change the servo support system;

[0111] Step S63: After excavation reaches the frozen area and confirming that the soil in the area is stable, the interior of the special-shaped tunnel structure of the main line and ramp tunnel is closed, and the segments in the frozen area are removed;

[0112] like Figure 7 As shown, when this embodiment is implemented, the excavation work at the junction of the end and the gradient section is carried out by a combination of mechanical and manual methods. In the initial stage of excavation, the mechanical excavator will first perform large-scale rough excavation to quickly remove the surface soil. As the excavation deepens, the mechanical operation will gradually switch to manual fine excavation to ensure the flatness and accuracy of the excavation surface. When the tunnel structure with a special-shaped gradient section tends to be stable under stress, the temporary support servo truss structure installed at the joint of the pipe segment is removed, and only the servo support truss structure at the junction of the arched steel-concrete pipe segment and the main line and ramp tunnel is retained. If necessary, new support rods are installed to form a new servo support structure system. The new support system is required to effectively withstand the loads generated during the excavation process and maintain the overall stability of the tunnel structure. After the support conversion, the soil in the middle part and the temporary pipe segment removal operations are carried out. After the removal is completed, the removal area is cleaned and tidied to ensure the cleanliness and safety of the construction site.

[0113] Furthermore, step S7 includes the following specific steps:

[0114] Step S71: Accurately measure the spatial dimensions of the end of the tunnel's irregularly shaped gradient section to determine the specific position and contour of the end wall;

[0115] Step S72: Install the steel frame, set up a stable formwork with tight joints, pour the prepared concrete evenly into the formwork, and vibrate it thoroughly to ensure that the concrete is dense;

[0116] Step S73: After the concrete has initially set, appropriate curing measures are taken in a timely manner. After the concrete reaches the designed strength, the formwork is removed and a comprehensive quality inspection is carried out to ensure that the end wall meets the design requirements before acceptance.

[0117] Furthermore, step S8 includes the following specific steps:

[0118] The pipe segments in the special-shaped gradient section are gradually removed, and the space after the removal of the pipe segments is processed as necessary, such as pouring concrete, installing prefabricated components, etc., to form a smooth tunnel transition section. At the same time, the tunnel structure of the special-shaped gradient section meets the strength and stability requirements.

[0119] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for constructing a double shield tunnel for a junction and diversion section of an underground road in a soft soil area, characterized in that: The steps include: Step S1: construct the main line and ramp tunnel using the shield method; According to the requirements of the underground road line shape, the main line tunnel and ramp tunnel are constructed using the shield method respectively. A central partition wall is set inside the tunnel. The main line tunnel and ramp tunnel are excavated separately before the special-shaped gradient section in the connecting area, and a docking interface is reserved. Step S2: constructing pipe curtains and freezing pipes on the special-shaped gradient sections and ends; A pipe curtain structure is pre-installed in the irregular transition section and end section of the connection area where the mainline tunnel and the ramp tunnel meet. The pipe curtain is composed of a series of steel pipes and is arranged along the excavation contour in the irregular transition section of the connection area. Freezing pipes for soil freezing and reinforcement are arranged in the pipe roof. The freezing pipes are preset in the steel top pipe or directly arranged in the soil. The specific freezing pipe arrangement plan is determined according to the soil properties, cover thickness, on-site construction conditions and factors. Step S3: using pipe roof to freeze and reinforce the soil; The refrigerant circulates through the freezing pipes to freeze the soil around the pipe curtain into frozen soil, forming a water-stop curtain; Step S4: Applying a servo support system inside the main line and ramp tunnels; A servo support system is applied to the key stress-bearing areas inside the mainline tunnel and ramp tunnel, and the servo support system is adjusted and optimized according to the actual on-site construction process; Step S5: excavating the upper soil through local holes and installing assembled steel-concrete pipe segments; Under the protection of the frozen soil curtain, local holes were broken to excavate the upper soil, and assembled steel-concrete segments were installed, gradually advancing into the tunnel; Step S6: gradually excavating the soil at the junction of the end and the transition section, replacing supports, and removing the frozen zone segments; When excavation reaches the junction of the end and the transition section, the soil is gradually excavated and the support system is replaced. After the excavation is completed, the frozen zone segments are removed to form a complete tunnel structure. Step S7: constructing the end wall; Construct end walls at the ends of the tunnel to seal the tunnel structure; Step S8: excavating the soil at the irregular-shaped gradient section and removing the segments; After the excavation of the soil in the irregular gradient section is completed, the pipe segments are removed to form a smooth tunnel transition section.

2. The method for constructing a double shield tunneling joint for a junction and merging section of an underground road in a soft soil area according to claim 1 is characterized in that: The step S1 includes the following specific steps: Step S11: Determine the line type, cross-sectional dimensions, and center partition wall locations of the main line tunnel and ramp tunnel based on the planning of the multi-point entry, divergence, and merging sections of the underground road; Step S12: Complete the construction of the starting shaft to ensure that the shield machine can start smoothly. Select the shield machine model according to the tunnel section size and geological conditions, and excavate according to the predetermined route and slope.

3. The method for constructing a double shield tunneling joint for a junction and merging section of an underground road in a soft soil area according to claim 1, characterized in that: The step S2 includes the following specific steps: Step S21: Design the structure of the curved pipe curtain and the steel pipe specifications based on the special-shaped cross-section profile formed by the double shield and the soil conditions, and prepare sufficient steel pipes and connectors; Step S22: using a pipe jacking method or a horizontal directional drilling method to push or drill the steel pipe into the soil along a predetermined trajectory to form a pipe curtain structure; Step S23: Arrange freezing pipes around the pipe roof so that the freezing pipes are in close contact with the pipe roof.

4. The method for constructing a double shield tunneling joint for a junction and merging section of an underground road in a soft soil area according to claim 1, characterized in that: The step S3 includes the following specific steps: Step S31: Install the refrigeration unit, the refrigerant circulation system, and the temperature monitoring system, and perform debugging; Step S32: The soil circulates the freezing liquid through the freezing pipes, gradually freezing the soil around the pipe curtain into frozen soil, while monitoring the thickness, strength and temperature of the frozen soil curtain.

5. The method for constructing a double shield tunneling joint for a junction and merging section of an underground road in a soft soil area according to claim 1, characterized in that: The step S4 includes the following specific steps: Step S41: Arrange servo heads for force and displacement control in key stress-bearing areas of the mainline tunnel and ramp tunnel segments, and design the truss structure of the servo support system; Step S42: During the construction process, the stress condition of the support system is monitored in real time, and the stress, strain and displacement data of the support system are collected using sensors and monitoring equipment.

6. The method for constructing a double shield tunneling joint for a junction and diversion section of an underground road in a soft soil area according to claim 1, characterized in that: The step S5 includes the following specific steps: Step S51: Under the protection of the frozen soil curtain, a combination of mechanical and manual methods is used to perform local hole excavation in the upper area of ​​the main line and ramp tunnels, and the excavation footage and speed are controlled; Step S52: Prefabricated assembled steel-concrete segments are installed in the space of the special-shaped gradient section excavated at the upper part. The segments are connected with bolts or mortise and tenon structures to form a steel arch shell structure connected by arch segments, and a segment structure of the main line and ramp tunnel with a multi-arch steel section with an approximately elliptical cross-section.

7. The method for constructing a double shield tunneling joint for a junction and merging section of an underground road in a soft soil area according to claim 1, characterized in that: The step S6 includes the following specific steps: Step S61: When excavating to the junction of the end and the gradient section, excavate the soil step by step in a segmented and layered manner; Step S62: After the soil excavation is completed, when the forces on the soil and the tunnel tend to be stable, replace the unnecessary support truss structure and change the servo support system; Step S63: After excavation reaches the frozen area and it is confirmed that the soil in the area is stable, the interior of the special-section tunnel structure of the main line and ramp tunnel is closed, and the pipe segments in the frozen area are removed.

8. The method for constructing a double shield tunneling joint for a junction and merging section of an underground road in a soft soil area according to claim 1, characterized in that: The step S7 includes the following specific steps: Step S71: Accurately measure the spatial dimensions of the end of the tunnel's irregularly shaped gradient section to determine the specific position and contour of the end wall; Step S72: Install the steel frame, set up a stable formwork with tight joints, pour the prepared concrete evenly into the formwork, and vibrate it thoroughly to ensure that the concrete is dense; Step S73: After the concrete has initially set, appropriate maintenance measures are taken in a timely manner. After the concrete reaches the designed strength, the formwork is removed and a comprehensive quality inspection is carried out.

9. The method for constructing a double shield tunneling joint for a junction and diversion section of an underground road in a soft soil area according to claim 1, characterized in that: The step S8 includes: gradually removing the pipe segments in the special-shaped gradient section, processing the space after the removal of the pipe segments to form a smooth tunnel transition section, and at the same time, the special-shaped gradient section tunnel structure meets the strength and stability requirements.

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