Subway section air duct combined construction method

Abstract

The invention relates to the field of tunnel engineering, and discloses a subway section air duct combined construction method which comprises the following steps: S1, constructing an air duct vault advanced reinforcement measure from a constructed open-cut section air shaft, then excavating an air duct in a layered manner by a plurality of construction pilot tunnels, and constructing a primary support structure; s2, constructing an air duct secondary lining structure on the outer side of the rail-mounted area and the negative first layer part of the rail-mounted area, and reserving a hole for excavating a vertical shaft in a middle plate of the negative first layer of the air duct; s3, after the poured air duct secondary lining structure reaches the design strength, a vertical shaft is excavated through the reserved hole by adopting an inverted well wall hanging method, and soil around the shield tunnel is reinforced; s4, dismantling the temporary supports in the vertical shaft in sections from bottom to top, and constructing an air duct secondary lining structure in the vertical shaft; and S5, after the temporary reinforcement measures of the air duct secondary lining structure, the soil body around the shield tunnel and the shield segments are completed, the shield segments in the air duct range are dismantled step by step. The construction method has the beneficial effect that safe and efficient construction under the working condition that the shield is advanced and the air duct is built later is inverted.

Description

Technical Field

[0001] This invention relates to the field of tunnel engineering, and more specifically to a method for constructing combined ventilation ducts in subway sections. Background Technology

[0002] In the construction of subway tunnels, the ventilation ducts, as a key supporting facility to ensure ventilation and operational safety in long and complex sections, are usually planned and constructed simultaneously with the tunnel ventilation shafts. According to conventional construction procedures, the ventilation ducts must be completed before the tunnel boring machine (TBM) is built. Once the ventilation duct structure is stable, the TBM then either pushes through the ventilation shaft area or initiates its launch. This sequence ensures that the construction of the tunnel boring machine and the ventilation duct structure do not interfere with each other, representing a standard operating procedure in traditional subway construction.

[0003] However, in the practice of subway construction in urban centers, due to difficulties in land use coordination and delays in demolition, the construction of ventilation shafts and ducts in tunnel sections is often difficult to complete in a timely manner. This results in the tunnel boring machine (TBM) being unable to pass through the ventilation shaft area as planned, forcing it to remain stationary for extended periods or undergo multiple launches and receptions, severely impacting the continuity of TBM construction and the overall project schedule. More importantly, if subsequent construction of ventilation shafts is carried out after the TBM has already passed through the ventilation shaft area, it will face the complex situation of large-scale underground excavation work above and to the side of the existing TBM tunnel, and even the partial demolition of existing TBM segments. Existing construction methods lack a systematic solution for the reversed process of constructing ventilation shafts and demolishing segments after the TBM has already been completed, and cannot effectively control the structural deformation of the existing tunnel, becoming a core technical bottleneck restricting the project progress. Summary of the Invention

[0004] To address the aforementioned technical issues, the aim is to provide a combined construction method for ventilation ducts in subway sections, resolving the schedule conflict caused by delayed ventilation shaft construction leading to shield tunneling stagnation and multiple launches and receptions, and achieving safe and efficient construction under the reversed construction sequence of shield tunneling first and ventilation ducts later.

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

[0006] A combined construction method for ventilation ducts in subway sections, applicable to situations where the tunnel boring machine has already traversed the ventilation duct area, includes the following steps:

[0007] S1: Implement advanced reinforcement measures for the ventilation duct arch from the completed open-cut ventilation shaft section, and then excavate the ventilation duct in layers through multiple construction pilot tunnels, and construct the initial support structure; among them, the upper construction pilot tunnel crosses the existing shield tunnel and is excavated to the end wall for sealing, and a head wall is constructed; the lower construction pilot tunnel is excavated to the outer edge of the adjacent shield tunnel for sealing, and a head wall is constructed.

[0008] S2: The secondary lining structure of the ventilation duct outside the construction track area and the first basement level of the track area, and the opening for excavating the vertical shaft is reserved in the middle plate of the first basement level of the ventilation duct.

[0009] S3: After the secondary lining structure of the air duct has reached the design strength, the vertical shaft is excavated by using the inverted shaft wall method through the reserved opening, and the soil around the shield tunnel is reinforced by the side wall of the vertical shaft during the construction process.

[0010] S4: Remove the temporary supports inside the shaft in sections from bottom to top, and construct the secondary lining structure for the air duct inside the shaft;

[0011] S5: After the secondary lining structure of the ventilation duct reaches the design strength, the soil around the shield tunnel is reinforced, and the temporary reinforcement measures for the shield segments are completed, the shield segments within the ventilation duct area are dismantled in stages, and the bottom sealing, the remaining secondary lining structure of the ventilation duct, and the post-cast ring beam are promptly constructed.

[0012] The beneficial effects of this invention are as follows: By employing a differentiated sealing strategy—the upper-level construction guide tunnel in S1 crosses the shield tunnel to the end wall for sealing, and the lower-level construction guide tunnel is excavated to the outer edge of the adjacent shield tunnel for sealing—it creates working space for subsequent ventilation duct construction while avoiding direct disturbance to the existing shield tunnel bottom soil during lower-level excavation. Furthermore, by reserving a shaft opening in the middle slab of the first basement level of the ventilation duct in S2, a safe passage is provided for subsequent construction in the shield tunnel area. Finally, by simultaneously reinforcing the surrounding soil of the shield tunnel through the shaft sidewalls during the S3 shaft construction process, integrated soil improvement and shaft excavation are achieved, providing stable surrounding rock conditions in advance for segment removal. By dismantling the temporary supports inside the shaft in sections from bottom to top through S4 and promptly constructing the secondary lining, the stability of the shaft structure itself is ensured. In S5, the secondary lining of the ventilation duct achieves the required strength, the soil reinforcement is completed, and the temporary reinforcement measures for the tunnel segments are completed. Under the dynamic support protection of the trolley-type mobile internal support frame, the tunnel segments are dismantled in stages, and the bottom sealing and post-cast ring beam are constructed in a timely manner. This ensures that the stress state of the existing shield tunnel is always under control throughout the entire construction process, and the structural deformation is effectively suppressed. This systematically solves the contradiction between the delay in the construction of the ventilation shaft and the schedule of multiple launches and receptions caused by the delay in the construction of the ventilation shaft. It achieves safe and efficient construction under the reversed construction process of shield tunneling first and ventilation duct construction later.

[0013] In some embodiments, the number of construction pilot tunnels is 12, and they are excavated in a preset numbered sequence. Each construction pilot tunnel is excavated using a step method, with the step length controlled at 3-5m, and the longitudinal excavation lengths of each tunnel are staggered by no less than 15m. Due to the adoption of multiple refined excavation control measures—dividing the ventilation duct excavation section into 12 construction pilot tunnels, excavating in a preset numbered sequence, using a step method with a step length controlled at 3-5m, and staggering the longitudinal excavation lengths of each tunnel by no less than 15m—the single excavation exposure surface is minimized during large-scale underground excavation operations above and to the side of existing shield tunnels. The tunnel face remains stable, and the excavation disturbances of adjacent tunnels are staggered in time and space, effectively suppressing the superimposed settlement caused by the group tunnel effect and avoiding sudden changes in the stress on the shield tunnel structure due to concentrated excavation disturbances. This creates a stable surrounding rock environment for subsequent soil reinforcement and segment removal.

[0014] In some embodiments, the initial support structure includes a grid steel frame, steel mesh, anchor bolts, and shotcrete. After each excavation cycle is completed, the initial support is constructed in the following order: first, the grid steel frame is erected; then, steel mesh is welded onto the grid steel frame; anchor bolts are installed to secure the grid steel frame to the surrounding rock; then, temporary supports are erected; and finally, shotcrete is applied to form a closed support structure. By employing an initial support system composed of a grid steel frame, steel mesh, anchor bolts, and shotcrete, and strictly following a specific construction sequence—first erecting the grid steel frame → welding the steel mesh → installing anchor bolts → erecting temporary supports → and finally sealing with shotcrete—the initial support structure's load-bearing skeleton can immediately bear the surrounding rock load. The anchor bolts firmly anchor the steel frame to the surrounding rock to prevent subsidence, the temporary supports provide timely lateral restraint, and finally, the shotcrete encapsulates all components into a unified load-bearing structure. This sequential construction method ensures that the support structure after each excavation cycle in soft strata can play a timely and effective load-bearing role, avoiding the transmission of surrounding rock relaxation and deformation caused by delayed support or component connection failure to the existing shield tunnel.

[0015] In some embodiments, the reserved openings in the middle slab of the first basement level of the ventilation duct are temporary openings during construction and are sealed according to design requirements after the ventilation duct construction is completed. By adopting the technical measure of setting temporary reserved openings in the middle slab of the first basement level of the ventilation duct for construction only, and sealing them according to design requirements after the overall construction of the ventilation duct is completed, subsequent shaft construction does not require additional damage to the completed secondary lining structure of the ventilation duct. This ensures both the convenience of the construction access and the integrity of the ventilation duct structure and its permanent functionality, achieving separation of construction functions from the permanent structure and avoiding the drawback of permanently weakening the structural load-bearing performance for construction needs.

[0016] In some embodiments, when the shaft is excavated using the inverted shaft wall method, the temporary inverted arches within the range of the two shafts are broken in sections, and the bottom is sealed promptly after excavation to the bottom of the shaft. Because the construction method of breaking the temporary inverted arches within the range of the two shafts in sections, excavating the shaft from top to bottom using the inverted shaft wall method, and sealing the bottom promptly after excavation ensures that each cycle of shaft excavation is carried out under the protection of the already constructed shaft wall support, effectively controlling the disturbance of the surrounding soil during shaft construction; breaking the temporary inverted arches in sections avoids structural instability caused by demolishing too large an area at once, and timely sealing of the bottom quickly seals the bottom of the shaft, forming a complete load-bearing system, providing a stable working platform and grouting channel for subsequent reinforcement of the surrounding soil of the shield tunnel through the shaft sidewalls.

[0017] In some embodiments, the reinforcement of the soil surrounding the shield tunnel includes radial grouting reinforcement behind the segment walls before ventilation duct construction and auxiliary grouting reinforcement during the construction of the ventilation duct guide tunnel and shaft. Deep-hole grouting is used, and the reinforcement range is 3m outside the shield segments on both sides of the ventilation duct, with 5 rings of segments longitudinally on each side. Because a secondary reinforcement mode combining radial grouting behind the segment walls before ventilation duct construction with auxiliary grouting during the construction of the guide tunnel and shaft is adopted, and the grouting method is deep-hole grouting, with a clearly defined reinforcement range of 3m outside the shield segments and 5 rings of segments longitudinally, the soil surrounding the shield tunnel receives dual improvement before segment removal: the primary grouting fills the voids behind the segment walls that may be formed during shield construction, while the secondary grouting reinforces the disturbed area during ventilation duct construction. The clearly defined reinforcement range (3m outside and 5 rings longitudinally) ensures both improved soil strength in the core affected area and avoids waste caused by excessive grouting range, providing reliable mechanical protection for the smooth transfer of load to the surrounding rock during subsequent segment removal.

[0018] In some embodiments, the temporary reinforcement measures for the tunnel segments include: longitudinal tensioning connecting strips: six longitudinal tensioning connecting strips are installed along the tunnel circumference on the inner wall of 10 rings of permanent tunnel segments on both sides of the ventilation duct. The six connecting strips are respectively installed at the arch top, the two sides of the arch waist and the arch bottom of the segment ring. The two ends of each connecting strip are anchored to the segment bolt holes or embedded parts, thus longitudinally tensioning the 10 rings of tunnel segments into a whole; trolley-type mobile internal support frame: a trolley-type mobile internal support frame is installed in the inner wall of 4 rings of tunnel segments adjacent to the ventilation duct on both sides of the ventilation duct. The internal support frame is arranged longitudinally along the tunnel and is supported on the inner wall of the segment by hydraulic jacks to form a ring support system. The temporary reinforcement measures for the tunnel segments, consisting of a combination of longitudinal tensioning strips and a trolley-type mobile internal support structure, are adopted. Six longitudinal tensioning strips are installed along the circumferential direction on the inner wall of each of the 10 permanent tunnel segments on both sides of the duct, located at the arch top, the two sides of the arch waist, and the arch bottom, respectively. Both ends are anchored to the bolt holes or embedded parts of the tunnel segments, longitudinally tensioning the 10 rings of tunnel segments into a whole. The trolley-type mobile internal support frame is erected in the inner wall of each of the 4 tunnel segments adjacent to the duct on both sides, forming a ring support system supported by hydraulic jacks. Before the tunnel segments are dismantled, the longitudinal tensioning strips connect multiple rings of tunnel segments into a whole beam structure, enhancing the cooperative stress-bearing capacity between the rings and reinforcing the tunnel segment structure circumferentially. This effectively suppresses stress release and deformation transmission during the dismantling process, creating a safe premise for phased dismantling.

[0019] In some embodiments, the bottom of the inner support frame is provided with a traveling mechanism, which can move longitudinally along the tunnel during the dismantling of the tunnel segments to support the subsequent tunnel segments to be dismantled in sequence. When dismantling the shield tunnel segments in the ventilation duct, the trolley-type mobile inner support frame is first used to support the tunnel segments to be dismantled. Then, the shield tunnel segments are dismantled ring by ring longitudinally along the tunnel. Before dismantling each ring of tunnel segments, the trolley-type mobile inner support frame is moved to the ring of tunnel segments to be dismantled for support. After the ring of tunnel segments to be dismantled is dismantled, the trolley-type mobile inner support frame is moved to the next ring of tunnel segments. The above steps are repeated until all tunnel segments within the ventilation duct area are dismantled. By employing a modular dismantling and support system, the dismantling of tunnel segments is carried out by first supporting the segments to be dismantled with a trolley-type mobile internal support frame, then dismantling them ring by ring along the tunnel's longitudinal direction. Before dismantling each ring, the trolley is moved to the ring to be dismantled for support, and after dismantling one ring, it is moved to the next ring. This modular system, which combines dismantling and support in a coordinated manner, also provides radial support to the segments to be dismantled and their adjacent segments. This ensures that the dismantling process of each ring of segments is always under dynamic support protection. The traveling mechanism of the trolley-type mobile internal support frame allows it to move flexibly with the dismantling progress and always maintain tight support for the current working ring. This mode not only ensures the structural stability during the dismantling of a single ring, but also controls the gradual transfer of load during the overall dismantling process by advancing ring by ring, avoiding the risk of large-scale structural instability caused by the simultaneous dismantling of multiple rings or inadequate support.

[0020] In some embodiments, the radial grouting behind the shield tunnel segments and the temporary reinforcement measures for the shield tunnel segments should be completed before the ventilation duct construction. By adopting a time-series control requirement that the radial grouting behind the shield tunnel segments and the temporary reinforcement measures for the shield tunnel segments be completed before the main ventilation duct construction, all protective measures for existing shield tunnels are implemented before the ventilation duct excavation and segment removal operations begin. This time-series arrangement of reinforcement first, then disturbance ensures that the existing shield tunnel is always effectively protected during all subsequent construction operations, and any construction disturbance is within the bearing capacity of the reinforcement measures, avoiding structural safety risks caused by delayed protection measures.

[0021] In some embodiments, during the construction of the secondary lining structure of the ventilation duct, the length of temporary supports and temporary intermediate partitions removed at one time shall not exceed 6m. By adopting a refined dismantling control requirement that the length of temporary supports and temporary intermediate partitions removed at one time be strictly controlled within 6m during the construction of the secondary lining structure, the load transfer caused by a single dismantling during the gradual replacement of temporary supports is limited to the structurally bearable range. This avoids the risk of sudden release of surrounding rock stress, excessive deformation of initial supports, or even the transmission of impact loads to the existing shield tunnel due to excessive dismantling length, ensuring a smooth transition of the entire structural system during the stress system transformation.

[0022] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0023] 1. Systematically resolve the contradiction between the delay in tunnel boring machine (TBM) construction and the multiple launches and receptions caused by the lag in ventilation shaft construction, and achieve safe and efficient construction under the reversed construction process of TBM first and ventilation duct later.

[0024] 2. The technical measure of setting up temporary reserved openings in the middle slab of the first basement level of the ventilation duct for use only during construction, and sealing them according to the design requirements after the overall construction of the ventilation duct is completed, ensures that subsequent shaft construction does not require additional damage to the completed secondary lining structure of the ventilation duct. This ensures both the convenience of the construction passage and the integrity of the ventilation duct structure and its permanent use function are not affected, thus separating the construction function from the permanent structure and avoiding the drawback of permanently weakening the structural load-bearing performance for construction needs. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings:

[0026] Figure 1This is a schematic diagram of the structure after performing step S1 in this invention;

[0027] Figure 2 This is a schematic diagram of the structure after performing step S2 in this invention;

[0028] Figure 3 This is a schematic diagram of the structure after performing step S3 in this invention;

[0029] Figure 4 This is a schematic diagram of the structure after performing step S4 in this invention;

[0030] Figure 5 This is a schematic diagram of the structure after performing step S5 in this invention;

[0031] Figure 6 This is a schematic diagram of the excavation sequence of the pilot tunnel for ventilation duct construction in this invention;

[0032] Figure 7 This is a schematic diagram of the soil reinforcement around the shield tunnel and the temporary reinforcement of the shield tunnel segments in this invention;

[0033] Figure 8 This is a schematic diagram of the trolley-type mobile internal support frame in this invention.

[0034] The attached diagram shows the markings and corresponding component names:

[0035] Advanced reinforcement measures for the ventilation duct arch: 1. Initial support structure; 2. Temporary intermediate partition wall; 3. Temporary invert arch; 4. Temporary support; 5. Vertical shaft; 6. Head wall; 7. Reserved opening; 8. Secondary lining structure of the ventilation duct; 9. Post-cast ring beam; 10. Locking anchor bolt; 11. Shield segment; 12. Shield section; 13. Trolley-type mobile internal support frame; 14. Longitudinal tension connecting strip; 15. Open-cut section ventilation shaft; 16. Deep hole grouting; 17. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0037] Throughout this specification, references to "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in connection with that embodiment or example is included in at least one embodiment of the invention. Therefore, the phrases "an embodiment," "an example," "an example," or "an example" appearing in various places throughout the specification do not necessarily refer to the same embodiment or example. Furthermore, specific features, structures, or characteristics can be combined in one or more embodiments or examples in any suitable combination and / or sub-combination. Moreover, those skilled in the art will understand that the illustrations provided herein are for illustrative purposes and are not necessarily drawn to scale. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0038] In the description of this invention, the terms "front", "rear", "left", "right", "up", "down", "vertical", "horizontal", "high", "low", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the scope of protection of this invention.

[0039] The terms "first," "second," etc., used in this invention are merely for clarity of description and are not intended to limit any order or emphasize importance. Furthermore, the term "connection" as used herein, unless otherwise specified, can refer to a direct connection or an indirect connection via other components.

[0040] Example

[0041] like Figures 1-8 As shown, this embodiment provides a combined construction method for subway tunnel ventilation ducts, applicable to situations where the tunnel boring machine has already traversed the ventilation duct area. The method includes the following steps:

[0042] S1: Implement advanced reinforcement measures 1 for the ventilation shaft 16 in the already completed open-cut section, and then excavate the ventilation duct in layers through multiple construction pilot tunnels, and construct the initial support structure 2; among them, the upper construction pilot tunnel crosses the existing shield tunnel and is excavated to the end wall for sealing, and a head wall 7 is constructed; the lower construction pilot tunnel is excavated to the outer edge of the adjacent shield tunnel for sealing, and a head wall 7 is constructed.

[0043] S2: The secondary lining structure 9 of the ventilation duct outside the construction track area and the first basement level of the track area, and the opening for excavating the vertical shaft 6 is reserved in the middle plate of the first basement level of the ventilation duct.

[0044] S3: After the secondary lining structure 9 of the air duct has reached the design strength, the vertical shaft 6 is excavated through the reserved opening 8 using the inverted shaft wall method. During the construction of the vertical shaft 6, the soil around the shield tunnel is reinforced by grouting or shotcreting through the side wall of the vertical shaft 6.

[0045] S4: Remove the temporary support 5 inside the vertical shaft 6 in sections from bottom to top, and construct the secondary lining structure 9 of the ventilation duct inside the vertical shaft 6;

[0046] S5: After the secondary lining structure 9 of the ventilation duct has reached the design strength, the soil around the shield tunnel has been reinforced, and the temporary reinforcement measures for the shield segment 12 have been implemented, the shield segment 12 within the ventilation duct area will be dismantled in stages.

[0047] Temporary reinforcement measures for tunnel segment 12 include:

[0048] Longitudinal tensioning connector 15: On the inner wall of 10 rings of permanent segments on both sides of the ventilation duct, 6 longitudinal tensioning connectors 15 are installed along the tunnel circumference. They are respectively installed at the arch top, the waist of the arch on both sides and the bottom of the arch of the segment ring. The two ends of each connector are anchored to the bolt holes or embedded parts of the segment to longitudinally tension the 10 rings of segments into a whole.

[0049] A trolley-type mobile internal support frame 14 is installed within each of the four rings of shield tunnel segments 12 adjacent to the ventilation duct on both sides. This internal support frame is arranged circumferentially along the tunnel and is supported by hydraulic jacks against the inner wall of the segments, forming a ring-shaped support system. A traveling mechanism is provided at the bottom of the internal support frame, allowing it to move longitudinally along the tunnel during segment removal. The trolley-type mobile internal support frame 14 is equipped with an intelligent monitoring system. This system includes pressure sensors, displacement sensors, and a data acquisition and transmission module installed on the trolley-type mobile internal support frame 14. It monitors changes in support force and segment deformation in real time and transmits the data to the ground monitoring center. When the monitored data exceeds a preset threshold, the system automatically alarms and adjusts the supporting force of the hydraulic jacks to ensure a constant support state.

[0050] The segment removal operation shall be carried out in the following order:

[0051] 1. Pre-cut the first segment of the ring segment to be removed to a depth of 1 / 3 to 1 / 2 of the segment thickness to release some of the circumferential stress. After the stress release is stable, proceed with subsequent operations.

[0052] 2. Move the trolley-type mobile inner support frame 14 into the ring segment to be removed, and support it with hydraulic jacks;

[0053] 3. Under the protection of the trolley support, the ring segment is dismantled in sections in the order of first the arch, then the side walls, and finally the bottom slab;

[0054] 4. After each segment is removed, check the support condition and adjust the support force according to the monitoring data;

[0055] 5. After all the segments in the ring have been removed, move the trolley-type mobile inner support frame 14 to the next segment and repeat the above steps until all segments in the duct area have been removed.

[0056] After the tunnel lining segments are removed, the exposed surrounding rock surface is promptly sealed using a steel grid frame and shotcrete.

[0057] Timely construction of the bottom sealing concrete, the remaining secondary lining structure of the ventilation duct, and the post-cast ring beam 10. At the connection between the post-cast ring beam 10 and the existing shield tunnel segment 12, connecting steel bars are installed in the pre-reserved or planted steel bars in the segment. The steel bars of the post-cast ring beam 10 are tied or welded to the connecting steel bars. Before pouring concrete, the contact surface of the segment is roughened and an interface agent is applied to ensure reliable connection between the new and old structures and continuous stress.

[0058] Specifically, after the tunnel segments are removed, a post-cast ring beam 10 is constructed at the junction of the shield tunnel section 13 and the ventilation duct. The post-cast ring beam 10 is reliably anchored to the existing shield tunnel segments 12 through connecting steel bars to form a complete stress transition section, ensuring the structural safety and waterproof performance of the shield tunnel section 13 at the opening.

[0059] See Figure 1 It also includes shield tunnel section 13, which is a shield tunnel section that has been completed. It is located within the ventilation duct area to be constructed and is the core area for subsequent segment removal operations.

[0060] Throughout the entire segment dismantling process, the crown settlement and horizontal convergence of shield tunnel section 13 were monitored in real time, with the control targets being: crown settlement ≤10mm and horizontal convergence ≤15mm. When the monitored values ​​approached the warning values, the dismantling operation was suspended, and reinforcement measures such as enhanced grouting or temporary support were implemented.

[0061] See Figure 6 The number of construction pilot tunnels is 12, and they are excavated in a pre-set numbered sequence. Each construction pilot tunnel is excavated using the step method, with the step length controlled between 3 and 5 meters, and the longitudinal excavation lengths of each tunnel are staggered by no less than 15 meters. Due to the adoption of multiple refined excavation control measures—dividing the ventilation duct excavation section into 12 construction pilot tunnels, excavating in a pre-set numbered sequence, using the step method with a step length controlled between 3 and 5 meters, and staggering the longitudinal excavation lengths of each tunnel by no less than 15 meters—the single excavation exposure surface is minimized during large-scale underground excavation operations above and to the side of existing shield tunnels. The tunnel face remains stable, and the excavation disturbances of adjacent tunnels are staggered in time and space, effectively suppressing the superimposed settlement caused by the group tunnel effect and avoiding sudden changes in the stress on the shield tunnel structure due to concentrated excavation disturbances. This creates a stable surrounding rock environment for subsequent soil reinforcement and segment removal.

[0062] See Figure 1The initial support structure 2 includes a grid steel frame, steel mesh, anchor bolts 11, and shotcrete. After each excavation cycle, the initial support is constructed in the following order: first, the grid steel frame is erected, then the steel mesh is welded onto the grid steel frame, the anchor bolts 11 are installed to anchor the grid steel frame to the surrounding rock, then temporary supports 5 are erected, and finally shotcrete is applied to form a closed support structure. Because the initial support system, consisting of a grid steel frame, steel mesh, anchor bolts 11, and shotcrete, was adopted, and the construction was strictly carried out in a specific sequence: first erecting the grid steel frame → welding the steel mesh → installing the anchor bolts 11 for anchoring → erecting temporary supports 5 → finally sealing with shotcrete, the load-bearing skeleton of the initial support structure 2 can bear the surrounding rock load immediately. The anchor bolts 11 firmly anchor the steel frame to the surrounding rock to prevent subsidence, the temporary supports 5 provide timely lateral restraint, and finally the shotcrete wraps all components into an integral load-bearing structure. This sequential construction method ensures that the support structure after each excavation cycle in soft strata can play its load-bearing role in a timely and effective manner, avoiding the transmission of surrounding rock relaxation and deformation caused by delayed support or component connection failure to the existing shield tunnel.

[0063] See Figure 2 and Figure 6 The reserved opening 8 in the middle slab of the first basement level of the ventilation duct is a temporary opening during construction and will be sealed according to design requirements after the ventilation duct construction is completed. Because of the technical measure of setting a temporary reserved opening 8 in the middle slab of the first basement level of the ventilation duct for construction only, and sealing it according to design requirements after the overall construction of the ventilation duct is completed, the subsequent construction of the vertical shaft 6 does not require additional damage to the completed secondary lining structure 9 of the ventilation duct. This ensures both the convenience of the construction passage and the integrity of the ventilation duct structure and its permanent use function are not affected, achieving separation of construction function from the permanent structure and avoiding the drawback of permanently weakening the structural load-bearing performance for construction needs.

[0064] See Figures 3-4 When the vertical shaft 6 is excavated using the inverted shaft wall method, the temporary inverted arches 4 within the range of the two vertical shafts 6 are broken in sections, and the bottom of the vertical shaft 6 is sealed in a timely manner after excavation. Because the construction method of breaking the temporary inverted arches 4 within the range of the two vertical shafts 6 in sections, excavating the vertical shaft 6 from top to bottom using the inverted shaft wall method, and sealing the bottom in a timely manner after excavation ensures that each cycle of the vertical shaft 6 excavation process is carried out under the protection of the already constructed shaft wall support, effectively controlling the disturbance of the surrounding soil caused by the construction of the vertical shaft 6; breaking the temporary inverted arches 4 in sections avoids structural instability caused by demolishing too large an area at once, and timely sealing of the bottom quickly seals the bottom of the vertical shaft 6, forming a complete load-bearing system, providing a stable working platform and grouting channel for subsequent reinforcement of the surrounding soil of the shield tunnel through the sidewalls of the vertical shaft 6.

[0065] See Figure 5 and Figure 7The soil reinforcement around the shield tunnel includes radial grouting reinforcement behind the tunnel segments before ventilation duct construction and auxiliary grouting reinforcement during the construction of the ventilation duct guide tunnel and shaft 6. Deep-hole grouting 17 is used for grouting, and the reinforcement range is 3m outside the shield tunnel segments 12 on both sides of the ventilation duct, with 5 rings of segments longitudinally on each side. Because a two-stage reinforcement mode combining radial grouting behind the tunnel segments before ventilation duct construction and auxiliary grouting during the construction of the guide tunnel and shaft 6 is adopted, with deep-hole grouting 17 and a clearly defined reinforcement range of 3m outside the shield tunnel segments 12 and 5 rings of segments longitudinally, the soil around the shield tunnel receives dual improvement before segment removal: the first grouting fills the voids behind the tunnel segments that may be formed during shield construction, while the second grouting reinforces the disturbed area during ventilation duct construction. The clearly defined reinforcement range (3m outside and 5 rings longitudinally) ensures improved soil strength in the core affected area while avoiding waste caused by excessive grouting range, providing reliable mechanical protection for the smooth transfer of load to the surrounding rock during subsequent segment removal.

[0066] Specifically, the soil reinforcement around the shield tunnel adopts a multi-stage, multi-layer grouting system: the first stage is backfill grouting behind the tunnel segment wall to fill the gaps formed during shield construction; the second stage is radial deep hole grouting 17 to form a reinforcement ring within 3m outside the tunnel segment; the third stage is auxiliary grouting from the ventilation duct construction guide tunnel and vertical shaft construction to reinforce weak areas.

[0067] See Figure 7The temporary reinforcement measures for the shield tunnel segment 12 include: longitudinal tensioning connecting strips 15: six longitudinal tensioning connecting strips 15 are installed along the tunnel circumference on the inner wall of each of the 10 rings of permanent tunnel segments on both sides of the ventilation duct. The six connecting strips are respectively installed at the arch top, the two sides of the arch waist and the arch bottom of the segment ring. The two ends of each connecting strip are anchored to the bolt holes or embedded parts of the segment, thus longitudinally tensioning the 10 rings of segments into a whole; trolley-type mobile inner support frame 14: a trolley-type mobile inner support frame 14 is installed in each of the 4 rings of shield tunnel segments 12 adjacent to the ventilation duct on both sides. The inner support frame is arranged along the tunnel longitudinally and is supported on the inner wall of the segment by hydraulic jacks to form a ring support system; the bottom of the inner support frame is equipped with a traveling mechanism, which can move along the tunnel longitudinally during the dismantling of the segment to support the subsequent segments to be dismantled in sequence. The temporary reinforcement measures for the tunnel segments, consisting of a combined longitudinal tensioning connector 15 and a trolley-type mobile internal support frame 14, are employed. The longitudinal tensioning connector 15 consists of six longitudinally arranged connectors on the inner walls of ten permanent tunnel segments on each side of the duct, located at the arch top, the two sides of the arch waist, and the arch bottom, with both ends anchored to the segment bolt holes or embedded parts, thus longitudinally tensioning the ten tunnel segments into a unified structure. The trolley-type mobile internal support frame 14 is erected within four tunnel segments adjacent to the duct on each side, supported by hydraulic jacks to form a ring-shaped support system on the inner walls of the segments, and equipped with a traveling mechanism at the bottom. Before segment removal, the longitudinal tensioning connector 15 connects multiple tunnel segments into a unified beam structure, enhancing the collaborative stress-bearing capacity between the segment rings. The trolley-type mobile internal support frame 14 provides radial support to the segment to be removed and its adjacent segments. Both reinforce the tunnel segment structure from both longitudinal and circumferential dimensions, effectively suppressing stress release and deformation transmission during segment removal, creating a safe premise for phased removal.

[0068] Specifically, the longitudinal tensioning connecting strip 15 is installed on the inner wall of 10 rings of permanent tunnel segments on both sides of the ventilation duct in the shield tunnel section 13, and the trolley-type mobile inner support frame 14 is installed in 4 rings of shield tunnel segments 12 on both sides of the ventilation duct in the shield tunnel section 13, which are adjacent to the ventilation duct.

[0069] See Figures 1-5When dismantling the shield tunnel segments 12 in the ventilation duct, a trolley-type mobile inner support frame 14 is first used to support the segments to be dismantled. Then, the shield tunnel segments 12 are dismantled ring by ring along the longitudinal direction of the tunnel. Before dismantling each ring of segments, the trolley-type mobile inner support frame 14 is moved into the ring of segments to be dismantled for support. After the ring of segments to be dismantled is dismantled, the trolley-type mobile inner support frame 14 is moved to the next ring of segments. The above steps are repeated until all segments within the ventilation duct area are dismantled. By employing a method of first supporting the segments to be dismantled using a trolley-type mobile inner support frame 14, then dismantling them ring by ring along the tunnel's longitudinal direction, moving the trolley to the inner support of each ring before dismantling, and moving it to the next ring after dismantling one ring, and advancing ring by ring with coordinated dismantling and support operations, the dismantling process of each ring of segments is always under dynamic support protection. The traveling mechanism of the trolley-type mobile inner support frame 14 allows it to move flexibly with the dismantling progress and always maintain tight support for the current working ring. This method not only ensures the structural stability during the dismantling of a single ring, but also controls the gradual transfer of load during the overall dismantling process by advancing ring by ring, avoiding the risk of large-scale structural instability caused by the simultaneous dismantling of multiple rings or inadequate support.

[0070] See Figure 1 The radial grouting behind the shield tunnel segment 12 and the temporary reinforcement measures for the shield tunnel segment 12 should be completed before the ventilation duct construction. By adopting the time control requirement of arranging the radial grouting behind the shield tunnel segment 12 and the temporary reinforcement measures for the shield tunnel segment 12 before the main ventilation duct construction, all protective measures for the existing shield tunnel are implemented before the ventilation duct excavation and segment removal operations begin. This time sequence of reinforcement first, then disturbance ensures that the existing shield tunnel is always effectively protected during all subsequent construction operations, and any construction disturbance is within the bearing capacity of the reinforcement measures, avoiding structural safety risks caused by delayed protection measures.

[0071] See Figure 2 During the construction of the secondary lining structure 9 of the ventilation duct, the length of temporary support 5 and temporary central partition wall 3 removed at one time shall not exceed 6m. Because of the strict control requirement that the length of temporary support 5 and temporary central partition wall 3 removed at one time be kept within 6m during the construction of the secondary lining structure 9, the load transfer caused by a single removal during the gradual replacement of temporary supports is limited to the structural bearing capacity. This avoids the risk of sudden release of surrounding rock stress, excessive deformation of initial support, or even transmission of impact loads to the existing shield tunnel due to excessive removal length, ensuring a smooth transition of the entire structural system during the stress system transformation.

[0072] 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 construction method for combined ventilation ducts in subway sections, applicable to situations where the tunnel boring machine has already traversed the ventilation duct area, characterized in that, Includes the following steps: S1: Implement advanced reinforcement measures for the ventilation duct arch from the completed open-cut ventilation shaft section, and then excavate the ventilation duct in layers through multiple construction pilot tunnels, and construct the initial support structure; among them, the upper construction pilot tunnel crosses the existing shield tunnel and is excavated to the end wall for sealing, and a head wall is constructed; the lower construction pilot tunnel is excavated to the outer edge of the adjacent shield tunnel for sealing, and a head wall is constructed. S2: The secondary lining structure of the ventilation duct outside the construction track area and the first basement level of the track area, and the opening for excavating the vertical shaft is reserved in the middle plate of the first basement level of the ventilation duct. S3: After the secondary lining structure of the air duct has reached the design strength, the vertical shaft is excavated by using the inverted shaft wall method through the reserved opening, and the soil around the shield tunnel is reinforced by the side wall of the vertical shaft during the construction process. S4: Remove the temporary supports inside the shaft in sections from bottom to top, and construct the secondary lining structure for the air duct inside the shaft; S5: After the secondary lining structure of the ventilation duct reaches the design strength, the soil around the shield tunnel is reinforced, and the temporary reinforcement measures for the shield segments are completed, the shield segments within the ventilation duct area are dismantled in stages, and the bottom sealing, the remaining secondary lining structure of the ventilation duct, and the post-cast ring beam are promptly constructed.

2. The construction method for combined ventilation ducts in subway sections according to claim 1, characterized in that, The number of construction pilot tunnels is 12, and they are excavated in a preset order. Each construction pilot tunnel is excavated using the step method, with the step length controlled between 3 and 5 meters, and the longitudinal excavation lengths of each tunnel are staggered by no less than 15 meters.

3. The construction method for combined ventilation ducts in subway sections according to claim 1, characterized in that, The initial support structure includes a grid steel frame, steel mesh, anchor bolts, and shotcrete. After each excavation cycle, the initial support is constructed in the following order: first, the grid steel frame is erected; then, steel mesh is welded onto the grid steel frame; anchor bolts are installed to secure the grid steel frame to the surrounding rock; then, temporary supports are erected; and finally, shotcrete is applied to form a closed support structure.

4. The construction method for combined ventilation ducts in subway sections according to claim 1, characterized in that, The reserved opening in the middle slab of the first basement level of the air duct is a temporary opening during construction and will be sealed according to the design requirements after the air duct construction is completed.

5. The construction method for combined ventilation ducts in subway sections according to claim 1, characterized in that, When the vertical shaft is excavated using the inverted shaft wall method, the temporary inverted arches within the range of the two vertical shafts are broken in sections, and the bottom is sealed in time after excavation to the bottom of the vertical shaft.

6. The construction method for combined ventilation ducts in subway sections according to claim 1, characterized in that, The soil reinforcement around the shield tunnel includes radial grouting reinforcement behind the tunnel segments before ventilation duct construction and auxiliary grouting reinforcement during ventilation duct construction guide tunnel and shaft construction. Deep hole grouting is used, and the reinforcement range is 3m outside the shield tunnel segments on both sides of the ventilation duct, and 5 rings of tunnel segments in the longitudinal direction.

7. The construction method for combined ventilation ducts in subway sections according to claim 1, characterized in that, The temporary reinforcement measures for the tunnel segments include: Longitudinal tensioning strips: Six longitudinal tensioning strips are installed along the tunnel circumference on the inner wall of 10 rings of permanent pipe segments on both sides of the ventilation duct. The six strips are respectively installed at the arch top, the two sides of the arch waist and the arch bottom of the pipe segment ring. The two ends of each strip are anchored to the bolt holes or embedded parts of the pipe segment to longitudinally tension the 10 rings of pipe segments into a whole. Cart-type mobile internal support frame: Cart-type mobile internal support frames are installed in the four rings of shield tunnel segments adjacent to the ventilation duct on both sides. The cart-type mobile internal support frames are arranged longitudinally along the tunnel and are supported on the inner wall of the segment by hydraulic jacks to form a ring support system.

8. The construction method for combined ventilation ducts in subway sections according to claim 7, characterized in that, The trolley-type mobile inner support frame is equipped with a traveling mechanism at its bottom, which can move longitudinally along the tunnel during the dismantling of tunnel segments to support subsequent segments to be dismantled. When dismantling shield tunnel segments in the ventilation duct, the trolley-type mobile inner support frame is first used to support the segments to be dismantled. Then, the shield tunnel segments are dismantled ring by ring longitudinally along the tunnel. Before dismantling each ring of segments, the trolley-type mobile inner support frame is moved into the ring of segments to be dismantled for support. After the ring of segments to be dismantled is dismantled, the trolley-type mobile inner support frame is moved to the next ring of segments. The above steps are repeated until all segments within the ventilation duct area are dismantled.

9. The construction method for combined ventilation ducts in subway sections according to claim 1, characterized in that, The radial grouting behind the shield tunnel segment and the temporary reinforcement measures for the shield tunnel segment should be completed before the ventilation duct construction.

10. The construction method for combined ventilation ducts in subway sections according to claim 1, characterized in that, During the construction of the secondary lining structure of the air duct, the length of temporary supports and temporary intermediate partitions to be removed at one time shall not exceed 6m.

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