Shield tunneling machine initial supporting and launching structure of small-clear-distance double-tunnel small-curvature-radius turning section

Abstract

According to the shield tunneling machine initial support starting structure of the small-clear-distance double-tunnel small-curvature-radius turning section, on the basis of conventional support, according to the characteristics of the small-clear-distance double tunnels, support strengthening measures are adopted, and a secant method is adopted for controlling the small-curvature-radius arc turning section; the duct pieces are specially prefabricated, and pea gravel backfilling and other technologies are adopted behind the initial duct pieces, so that the accuracy of the tunnel axis is guaranteed. According to the shield tunneling machine initial support starting structure of the small-clear-distance double-tunnel small-curvature-radius turning section, the risks of tunnel deformation and collapse caused by starting counter force are effectively avoided, it is ensured that the axis is accurate, the shield posture is controllable, the safety of shield starting of the small-clear-distance double-tunnel small-curvature-radius turning section under an initial support system is ensured, and the shield tunneling machine initial support starting structure of the small-clear-distance double-tunnel small-curvature-radius turning section is improved. Unpredictable workload of follow-up treatment is reduced, and the method has the characteristics of high construction safety and feasibility, remarkable economic benefits and the like.

Description

Technical Field

[0001] This application relates to the field of shield tunneling engineering, and in particular to the initial support and launching structure of a shield machine for a small-clearance double tunnel with a small radius of curvature turning section. Background Technology

[0002] Tunnel boring machine (TBM) technology is widely used in various tunnel projects. With its high efficiency and safety, the TBM has become an important tool for excavating tunnels and traversing complex geological conditions. However, many challenges remain in the initial support launching of double tunnels with small clearance and small radius of curvature turns. These projects not only require the TBM to have extremely high construction precision and ground control capabilities, but also need to achieve rapid and efficient tunneling operations while ensuring construction safety.

[0003] The challenges of shield tunneling in the narrow-clearance twin-tunnel, small-radius-of-curvature turning section lie in the mutual influence between the tunnels with small clearances and the complex alignment requirements brought about by the small-radius-of-curvature turns. To address these challenges, construction personnel need to precisely navigate and control the tunnel boring machine to ensure its stable passage through the strata during excavation, while avoiding damage to existing structures or adjacent tunnels.

[0004] Therefore, precise control of the tunnel boring machine (TBM) during construction is a major challenge. In sections with small radii of curvature, the TBM needs to achieve precise steering and positioning to adapt to complex track requirements. How to achieve rapid and efficient tunneling operations while ensuring construction safety has become a pressing technical problem to be solved. Utility Model Content

[0005] This application aims to solve the problem of precise control difficulties of tunnel boring machines (TBMs) in existing construction processes. It provides a TBM initial support and launching structure for a small-clearance double-tunnel small-radius-curvature turning section, including: two tunnels, an initial support structure, a reaction frame, a special segment structure for turning, and a backfill area.

[0006] The initial support structure is used to provide temporary support during the tunnel boring machine's excavation process;

[0007] The reaction frame is installed inside the launching tunnel, and the end face of the reaction frame is perpendicular to the secant line of the launching section axis.

[0008] The special tunnel segment structure for turning is used for the tunnel boring machine to make smooth turns during the tunneling process;

[0009] The backfill area is the void filled around the two tunnels to provide support for them.

[0010] In one feasible implementation, the two tunnels are excavated in a near-circular shape, with a width of 9.5m and a height of 9.9m, and the net distance between the two tunnels is 3.9m to 6.4m.

[0011] In one feasible implementation, the two tunnels are provided with small radius of curvature turning sections.

[0012] In one feasible implementation, the curve radius of the small curvature radius turning segment is 360m.

[0013] In one feasible implementation, the two tunnels originate in Class IV to V surrounding rock, which is slightly weathered granite and granite fracture rock, with the tunnel roof buried at a depth of 21.55m to 25.04m.

[0014] In one feasible implementation, the initial support structure includes anchor bolts, steel mesh, wet-sprayed concrete, and a grid steel frame structure.

[0015] In one feasible implementation, the anchor bolt is a φ25 hollow grouting anchor bolt; the steel mesh is a single-layer steel mesh of φ8@200*200; the wet-sprayed concrete has a strength grade of C25, a permeability grade of P6, and a thickness of 300mm; the main reinforcement diameter of the grid steel frame structure is φ22, and the grid steel frame spacing is 0.75m.

[0016] In one feasible implementation, the special segment structure for turning is set in the small radius of curvature turning section of the two tunnels and is assembled by a tunnel boring machine.

[0017] The special tube segments for turning are prefabricated according to the turning axis of the small radius of curvature turning segment.

[0018] In one feasible implementation, the gap behind the segments of the special segment structure for turning is the backfill area, which is backfilled with gravel and reinforced with grout.

[0019] This application provides a shield tunneling machine initial support and launching structure for a small-clearance double tunnel with a small radius of curvature turning section. Based on conventional support, and considering the characteristics of small-clearance double tunnels, enhanced support measures are adopted. For the small radius of curvature arc turning section, a secant method is used for control. Special prefabrication of tunnel segments and backfilling with gravel behind the initial segments are employed to ensure the accuracy of the tunnel axis. This technology effectively avoids the risk of tunnel deformation and collapse caused by the initial reaction force, ensuring axis accuracy and controllable shield attitude. It guarantees the safety of shield launching in the small-clearance double tunnel with a small radius of curvature turning section under the initial support system, reduces unforeseen workload in subsequent processing, and features high construction safety and feasibility, as well as significant economic benefits. Attached Figure Description

[0020] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present invention and, together with the description, serve to explain the principles of the embodiments of the present invention. Obviously, the drawings described below are merely some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0021] Figure 1 This is an exemplary plan view of the dual tunnels shown in an embodiment of this application;

[0022] Figure 2 This is a cross-sectional view of the initial support structure for the shield tunneling starting hole, as exemplarily shown in an embodiment of this application.

[0023] Figure 3 This is a schematic diagram of the reaction frame and permanent segment arrangement, exemplarily shown in an embodiment of this application;

[0024] Figure 4 This is an exemplary simulation diagram of the secant initiation in an embodiment of this application;

[0025] Figure 5 This is an exemplary diagram of the segment assembly structure shown in the embodiments of this application.

[0026] Explanation of icon numbers:

[0027] 10-Tunnel; 20-Initial support structure; 30-Reaction frame; 40-Special segment structure for turning; 50-Backfill area; 11-Small radius turning section; 21-Anchor bolt; 22-Wet shotcrete. Detailed Implementation

[0028] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided to make the present invention more comprehensive and complete, and to fully convey the concept of the exemplary embodiments to those skilled in the art. The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a full understanding of the implementation of embodiments of the present invention.

[0029] Shield tunneling technology still faces numerous challenges in the initial support and launching of tunnels in narrow-clearance, double-tunnel sections with small curvature radii. These projects require not only extremely high construction precision and ground control capabilities from the tunnel boring machine (TBM), but also rapid and efficient tunneling operations while ensuring construction safety. The difficulty in TBM construction of narrow-clearance, double-tunnel sections with small curvature radii lies in the mutual influence between the tunnels with small clearances and the complex alignment requirements brought about by the small curvature radius turns. To address these challenges, construction personnel need to precisely navigate and control the TBM to ensure its stable passage through the ground during tunneling, while avoiding damage to existing structures or adjacent tunnels. Therefore, precise control of the TBM during construction is a major challenge.

[0030] This application addresses the aforementioned problems through an embodiment, providing a shield machine initial support and launching structure for a small-clearance double-tunnel, small-radius-curvature turning section 11, as shown in the reference. Figures 1 to 5 As shown, it includes: two tunnels 10, initial support structure 20, reaction frame 30, special segment structure for turning 40, and backfill area 50.

[0031] The two parallel tunnels 10 are designed with a small clearance to accommodate space constraints in specific engineering environments. During excavation, the relative position and distance between the two tunnels 10 must be precisely controlled to ensure structural stability and construction safety. Specifically, in some embodiments of this application, the excavation shape of the two tunnels 10 is approximately circular, with a width of 9.5m and a height of 9.9m, and the clearance between the two tunnels 10 is 3.9m to 6.4m.

[0032] The excavation shape of the two tunnels 10 is designed to be near-circular, which not only facilitates the tunnel boring machine's excavation operation but also effectively reduces ground disturbance and improves the structural stability and safety of the tunnels 10. Specifically, the near-circular excavation shape can more evenly distribute the load during the excavation process, reduce stress concentration in the surrounding strata of the tunnels 10, and thus reduce the risk of ground deformation and damage.

[0033] The width of tunnel 10 is set at 9.5 meters, and the height of tunnel 10 is determined to be 9.9 meters. The wider tunnel 10 provides more spacious space to meet the layout requirements of infrastructure such as traffic, ventilation, and drainage, while the taller tunnel 10 provides better passage conditions to meet the vertical movement needs of vehicles, personnel, and equipment. At the same time, the height design must also take into account factors such as groundwater level, stratum stability, and ground load above tunnel 10 to ensure the structural safety and long-term stability of tunnel 10.

[0034] The net distance between the two tunnels 10 varies between 3.9 meters and 6.4 meters. This range was chosen based on a comprehensive assessment of the impact of the tunnel spacing on geological stability, construction difficulty, and engineering costs. A smaller net distance saves land resources and improves space utilization efficiency, but it also increases the risk of geological disturbance and mutual interference. Therefore, the spacing between tunnels 10 needs to be strictly controlled during the design and construction process to ensure the structural safety and stability of tunnels 10. Furthermore, the spacing needs to be dynamically adjusted and optimized according to specific geological conditions and construction requirements to achieve the best engineering benefits within the range of 3.9 meters to 6.4 meters.

[0035] In some embodiments of this application, the two tunnels 10 originate in Class IV to V surrounding rock, which is slightly weathered granite and granite fractured rock, with a tunnel roof burial depth between 21.55m and 25.04m. Therefore, during the actual excavation of tunnel 10, a detailed geological survey of the surrounding rock at the location of tunnel 10 is first conducted to confirm that it is slightly weathered granite and granite fractured rock, and to determine that the tunnel roof burial depth is between 21.55m and 25.04m.

[0036] Secondly, a SY485H + Belit BLTB-190B hydraulic breaker was selected as the main excavation equipment for breaking and excavating hard rock; simultaneously, a SY225 + Belit BLTB-100B was used for trimming operations to ensure the accuracy and smoothness of the excavation profile. This equipment configuration significantly improves excavation efficiency, reduces the labor intensity of construction workers, and ensures excavation quality.

[0037] The upper and lower bench excavation method was adopted, dividing the tunnel section 10 into two benches. The height of the upper bench was controlled between 5.8m and 6.3m to ensure sufficient working space for construction personnel and operational flexibility for equipment. The excavation advance of the upper bench was generally more than one grid spacing to accelerate the excavation speed; the excavation advance of the lower bench needed to be adjusted based on monitoring and measurement results, and was generally not to exceed three grid spacings, except in areas with poor geological conditions such as Class V surrounding rock, where it was not to exceed two grid spacings. The upper and lower bench excavation method reduces disturbance to the strata and is beneficial to the stability of the surrounding rock. At the same time, by controlling the excavation advance, the risk of strata deformation and collapse can be further reduced.

[0038] Finally, continuous monitoring and measurement are conducted during the excavation process, including monitoring indicators such as surface settlement and tunnel convergence. The excavation progress is adjusted promptly based on the monitoring results. If a sudden change occurs in the monitoring results or a yellow alert is triggered, the excavation progress should be immediately resumed at a rate of one slab at a time to ensure construction safety. After excavation is completed, the initial support structure 20 is immediately constructed, including the installation of anchor bolts 21, steel mesh, wet-sprayed concrete 22, and a lattice steel frame structure. The support measures should be closely integrated with the excavation work to ensure that the support structure can provide timely support. The initial support structure 20 is an important safety guarantee during the excavation of Tunnel 10, enhancing the overall stability of Tunnel 10 and preventing ground deformation and collapse. The close integration of the support measures with the excavation work ensures the effectiveness of the support structure and improves construction safety.

[0039] The initial support structure 20 is used to provide temporary support during the tunnel boring machine's excavation process. The initial support structure 20 is typically made of high-strength materials, such as steel bracing or concrete lining. It is installed behind the excavation face of tunnel 10 to effectively prevent ground collapse and ensure the safe conduct of the excavation operation. The design of the initial support structure 20 must fully consider factors such as geological conditions, excavation speed, and the dimensions of tunnel 10 to ensure optimal support performance.

[0040] Specifically, in some embodiments of this application, the initial support structure 20 includes anchor bolts 21, reinforcing mesh, wet-mixed shotcrete 22, and a grid steel frame structure. The anchor bolts 21 are φ25 hollow grouting anchor bolts; the reinforcing mesh is a single-layer φ8@200*200 reinforcing mesh; the wet-mixed shotcrete 22 has a strength grade of C25, a permeability grade of P6, and a thickness of 300mm; the main reinforcement of the grid steel frame structure has a diameter of φ22, and the grid steel frame spacing is 0.75m.

[0041] In actual construction, the initial support structure 20 will employ auxiliary measures such as advanced small-diameter pipe pre-support to ensure structural and construction safety in areas with poor surrounding rock conditions. The three stages of initial support – excavation, support, and shotcreting – will be closely coordinated to achieve seamless integration; the time from excavation completion to the end of initial support should not exceed 12 hours. Specific steps include:

[0042] S1: φ42 pre-support guide pipes (L=3m@0.4m) are installed within a 150° range of the arch crown. As a pre-support measure, the pre-support guide pipes can reinforce the surrounding rock in advance, enhance the stability of tunnel 10, and reduce the risk of ground disturbance and collapse during the excavation process.

[0043] S2: Install φ25 hollow grouting anchor rods (L=3m@1.0*0.5m) as an important component of the initial support structure 20; the anchor rods 21 are tightly bonded to the surrounding rock through grouting to form a strong anchoring force, further reinforcing the surrounding rock of tunnel 10 and improving the overall stability of tunnel 10.

[0044] S3: Lay a single layer of φ8@200*200 steel mesh. The steel mesh can enhance the crack resistance and integrity of the concrete, improve the bearing capacity of the initial support structure 20, and prevent the surrounding rock from cracking due to stress concentration.

[0045] S4: Sprayed wet-mixed concrete 22 with a strength grade of C25P6, a permeability grade of P6, and a thickness of 300mm. The wet-mixed concrete 22 can quickly form a strong protective layer, covering the steel mesh and anchor bolts 21, providing additional support and protection to prevent further deformation and damage to the surrounding rock.

[0046] S5: Install a grid steel frame structure with a main reinforcement diameter of φ22 and a spacing of 0.75m. The grid steel frame serves as the skeleton of the initial support structure 20, which can enhance the overall rigidity and stability of tunnel 10 and resist various loads and deformations during the tunneling process.

[0047] S6: A C45P12 reinforced concrete lining with a thickness of 350mm or 450mm is constructed locally at the starting end. For the sidewalls with small clearance, φ25 hollow grouted anchor bolts (L@1.5m*0.75m) are used for tie rods. The system anchor bolts 21 are removed at locations where tie rods 21 are installed. The angle of the system anchor bolts 21 at adjacent tie rod locations is adjusted according to actual conditions. Local lining further enhances the stability and bearing capacity of tunnel 10, especially in areas with poor geological conditions. The tie rods 21 strengthen the stability of the sidewalls with small clearance, preventing mutual compression and damage caused by excessively small clearances.

[0048] The reaction frame 30 is installed inside the starting tunnel, and the end face of the reaction frame 30 is perpendicular to the design secant line of the starting section axis. This setting not only helps the tunnel boring machine to obtain a stable direction of advancement in the early stage of tunneling, but also effectively disperses and resists the huge thrust generated during tunneling, prevents structural damage, and ensures construction safety.

[0049] The special-purpose tunnel segment structure 40 for turning is used for smooth turns during the tunnel boring machine's excavation process. Addressing the specific requirements of the small radius of curvature turning section 11, the special-purpose tunnel segment structure 40 employs a unique design, enabling it to achieve smooth turning movements during tunnel boring machine excavation. This ensures that the structural integrity of the tunnel 10 is maintained during turning while minimizing excavation resistance and improving construction efficiency.

[0050] Backfill area 50 is the void filled around the two tunnels 10, used to support the two tunnels 10. This area not only provides additional support for the tunnels 10, enhancing the overall stability of the structure, but also effectively isolates groundwater and other potential geological hazards, ensuring the safe operation of the tunnels 10.

[0051] In some embodiments of this application, the gap behind the segments of the special segment structure 40 for turning is a backfill area 50, which is backfilled with gravel and reinforced with grouting.

[0052] Specifically, during the installation of the reaction frame 30, the end face of the reaction frame 30 is perpendicular to the design secant line of the starting section axis to ensure that the shield axis remains parallel to the design axis of tunnel 10. The starting tunnel employs a negative ring segment technology, and the segments assembled inside the starting tunnel are permanent segments. To ensure the axis control requirements of the formed tunnel 10 and the goal of preventing leakage in tunnel 10 later, after each ring is completed during the segment assembly process inside the starting tunnel, gravel backfilling and grouting are immediately carried out behind the segment wall. Through gravel backfilling and grouting, the segment wall is quickly filled, preventing settlement and horizontal displacement of the segments after they detach from the tail shield.

[0053] In actual construction, during the initial excavation, the gaps behind the 40mm segments of the special tunnel segment structure for turning are first filled with gravel and then reinforced with grout. The gravel is made of a material with high compressive strength and good water stability. During the initial excavation, it can overcome the problem that the strength of the cement grouting method requires time to set. The strength of the filler between the tunnel segment and the rock mass is the key to ensuring that the tunnel segment does not deform and the axis is accurate during the initial excavation. Therefore, using gravel backfilling behind the tunnel segment can greatly ensure construction safety and quality and can significantly improve the construction speed.

[0054] In some embodiments of this application, two tunnels 10 are provided with small radius of curvature turning sections 11, the curve radius of the small radius of curvature turning sections 11 is 360m, the turning-specific segment structure 40 is set in the small radius of curvature turning sections 11 of the two tunnels 10 and is assembled by a tunnel boring machine, and the segments of the turning-specific segment structure 40 are prefabricated according to the turning axis of the small radius of curvature turning sections 11.

[0055] In this embodiment, special turning segments are prefabricated through calculation. The turning accuracy is further improved by installing special turning segments to ensure the accuracy of the axis and the safety of tunnel 10 operation in the later stage. First, the walking posture of the shield machine is simulated and the adjustment parameters of each ring are calculated. During the initial launch, dynamic adjustments are made in combination with actual parameters, with slow and gradual correction.

[0056] Specifically, the special tunnel segments for turning are prefabricated according to the turning axis of the small radius of curvature turning section 11 to ensure that each segment meets the specific curve requirements. Before prefabrication, the shape, size, and assembly sequence of the turning segments are determined through detailed calculations to ensure that the axis of the assembled tunnel 10 is consistent with the design requirements. Computer technology is used to simulate the walking posture of the tunnel boring machine (TBM) in the turning section to predict potential challenges and necessary adjustments. Based on the simulation results, the adjustment parameters required by the TBM during the installation of each ring of segments are calculated, including attitude angles and thrust.

[0057] During the initial launch, the tunnel boring machine's (TBM) walking posture is dynamically adjusted based on real-time monitoring data and calculated parameters to ensure precise navigation. During turns, a gradual and slow adjustment strategy is adopted to avoid instability or deviation caused by abrupt changes. Sensors and monitoring systems can also monitor the TBM's position and attitude, as well as changes in the tunnel's 10-axis, in real time, providing timely feedback to the operators for adjustments.

[0058] In this embodiment, by using a custom-made, turn-specific segment structure 40 and precise parameter calculations, the navigation and control accuracy of the tunnel boring machine (TBM) in turning sections can be significantly improved, ensuring the precision of the tunnel 10's axis. Precise navigation and control help reduce deviations and errors during construction, lowering the risk of ground deformation and collapse, thereby enhancing construction safety. Furthermore, precise control of the tunnel 10's axis ensures the stability and durability of the tunnel 10 structure, providing a safety guarantee for the later operation of the tunnel 10. This achieves precise navigation and control of the TBM in the small-radius-of-curvature turning section 11, thus ensuring the safety and efficiency of tunnel 10 construction.

[0059] This application provides a specific implementation case to illustrate the construction process of the initial support and launching structure of a tunnel boring machine in a small curvature radius turning section of a double tunnel with a clear distance.

[0060] Specifically, the Xiafu section of this project is equipped with a shield / TBM launching and track-exit shaft. The shield section uses two reinforced composite shield machines, which are launched separately from the small mileage end of the launching shaft, and excavate about 360m in a single line to the shield lifting shaft. The shield excavation diameter is 6490mm, with precast segment lining, segment thickness of 350mm, ring width of 1.5m, strength grade C50, and impermeability grade P12.

[0061] The project involves two tunnels for a two-way subway line. The two tunnels have an excavation diameter of 9.5m × 9.9m (width × height) and a net distance between them of 3.9m to 6.4m. The minimum diameter is 0.41 times the tunnel width, which far exceeds the criteria for determining the minimum net distance: the width of the rock pillar between the two tunnels is between that of a continuous arch tunnel and a double-track tunnel, and is generally less than 1.5 times the width of the tunnel excavation section.

[0062] The shield tunneling machine for this project has a starting curvature radius of 360m / 380m and a superelevation of 120mm. It starts from a small curvature radius turning section. The positional relationship between the tunnel centerline and the railway line centerline in the curved section of this project is shown in Table 1.

[0063] Table 1. Relationship between the centerline of the tunnel and the centerline of the railway line in the curved section of the tunnel.

[0064]

[0065] The section from YK12+903.349 to YK12+948.349 (ZK12+893.698 to ZK12+938.698) is the shield tunneling launch tunnel, constructed using the mining method. The pilot tunnel is 45m long, with a ground elevation of 29.2 to 30.8m and a tunnel roof burial depth of approximately 21.55 to 25.04m. The launch site is located in slightly weathered granite (fragmented) and granite fragmentation rock, with surrounding rock classified as Class IV to V.

[0066] The launching tunnel is excavated using a bench excavation method. SY485H excavators equipped with 190mm drill rods are used for rock breaking, while SY225 excavators equipped with 100mm drill rods are used for tunnel excavation contour trimming. A 50-ton side-tipping loader is used to transport excavated soil to the launching shaft, which is then vertically lifted to the upper slag pit by a 55t gantry crane. The shield tunnel launching shaft has a cross-section width of 7.3–9.5m and a height of 7.5–9.89m, employing a bench excavation method. The height of the upper bench is controlled between 5.8m and 6.3m. The excavation advance of the upper bench should, in principle, not exceed one grid spacing; the excavation advance of the lower bench should be based on monitoring and measurement results, and should, in principle, not exceed three grid spacings, and in areas with poor geological conditions such as Class V surrounding rock, not exceed two grid spacings. If the monitoring results change abruptly or trigger a yellow warning, the excavation advance should be one grid spacing at a time.

[0067] The initial support structure includes anchor bolts, steel mesh, wet-mixed shotcrete, and lattice steel frame. Key support parameters include: φ42 pre-support guide pipes (L=3m@0.4m) are installed at 150° on the arch crown; φ25 hollow grouting anchor bolts (L=3m@1.0*0.5m) are used for the system anchor bolts; φ8@200*200 single-layer steel mesh is used; C25P6 wet-mixed shotcrete with a thickness of 300mm is used; C22 lattice steel frame with main reinforcement is used at 0.75m spacing; C45P12 reinforced concrete with a thickness of 350mm / 450mm is used for local lining at the starting end; φ25 hollow grouting anchor bolts (L determined according to actual conditions @1.5m (ring) * 0.75m (longitudinal)) are used for double-ply tie rods on both sides of the small clear distance sidewalls. System anchor bolts are removed at locations where tie rods are installed, and the angle of system anchor bolts is adjusted for adjacent tie rod locations based on actual conditions.

[0068] The launching tunnel employs a negative-ring-free segment technology, and the segments assembled within the launching tunnel are permanent segments. Before connecting the tunnel boring machine (TBM) to its downstream equipment, the reaction frame is installed. During reaction frame installation, the end face of the reaction frame is perpendicular to the design secant line of the launching section axis to ensure that the TBM axis remains parallel to the tunnel design axis. (See attached diagram for reaction frame and permanent segment layout.) Figure 5 .

[0069] This project employs a secant-line launching technique. First, the tunnel boring machine's (TBM) walking posture is simulated, and adjustment parameters for each ring are calculated. During launching, dynamic adjustments are made based on actual parameters, with gradual and slow corrections. The TBM launch is conducted on a turning radius of R380 / R360 with a longitudinal slope of 28‰. The launching method is an arc-shaped inverted platform launch. During the first and second rings of tunneling, the main shield body is on the arc-shaped inverted platform, so the articulated cylinders cannot adjust the direction. Only after the front shield body descends the inverted platform can the direction be slowly adjusted using the articulated cylinders. Based on the initial launch posture simulation, the first ring's shield tail deflects 21mm to the right, and the cutterhead deflects 47mm to the left; the second ring's cutterhead posture is -37mm horizontally and +40mm vertically, while the shield tail posture is -5mm horizontally and +40mm vertically; after the third ring has advanced 1.2m, the front shield and articulated joint enter the surrounding rock and can be oriented, with the cutterhead posture at -24mm horizontally and +40mm vertically, and the shield tail posture at -23mm horizontally and +40mm vertically; the fourth ring's articulated joint cylinder has a left-right stroke difference of approximately 35mm, with the cutterhead posture at -24mm horizontally and +40mm vertically, and the shield tail posture... The horizontal position is -40mm, and the vertical position is +40mm. The left and right stroke difference of the fifth ring articulated cylinder is about 55mm. The main thrust cylinder can be slowly adjusted. The cutterhead position is -24mm horizontal and +40mm vertical. The shield tail position is -48mm horizontal and +40mm vertical. The left and right stroke difference of the sixth ring articulated cylinder is about 55mm. The left and right stroke difference of the main thrust cylinder is about 32mm. When the shield tail enters the surrounding rock, the horizontal position of the cutterhead is controlled at -10mm. Normal tunneling is carried out. The cutterhead position is -10mm horizontal and +40mm vertical. The shield tail position is -50mm horizontal and +40mm vertical.

[0070] The project features specially designed turning ring segments. First, through calculations, a layout of 5 turning ring segments + 1 straight ring segment was adopted. Special turning segments were prefabricated, and the installation of these specialized turning segments further improved the turning accuracy, ensured the precise alignment, and guaranteed the safety of the tunnel operation in the later stages.

[0071] To ensure the control requirements of the tunnel axis and the goal of preventing leakage in the later stages of tunnel construction, after each segment was assembled in the initial tunnel, gravel backfilling and grouting reinforcement were immediately carried out behind the segment wall. The gravel used was a high-compressive-strength, water-stable material. Through gravel backfilling and grouting, the segment wall was quickly filled, preventing settlement and horizontal displacement of the segments after detachment from the tail shield. This method overcomes the limitations of using cement grout, which requires time to set and provide strength. The strength of the filler between the segment and the rock mass is crucial to ensuring segment stability and accurate tunneling posture during initial excavation. Therefore, using gravel backfilling behind the segments greatly ensures construction safety and quality and significantly increases construction speed. The tunnel boring machine used in this project successfully started under the initial support conditions of a small-diameter, double-tunnel, small-radius-curvature turning section using these measures.

[0072] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the disclosure in the specification and the embodiments. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein.

Claims

1. A shield tunneling machine initial support and launching structure for a small-clearance double-tunnel turning section with a small radius of curvature, characterized in that, include: Two tunnels (10), initial support structure (20), reaction frame (30), special segment structure for turning (40) and backfill area (50); The initial support structure (20) is used to provide temporary support during the tunnel boring machine excavation process; The reaction frame (30) is installed inside the launching hole, and the end face of the reaction frame is perpendicular to the secant line of the launching section axis. The special segment structure (40) for turning is used for the tunnel boring machine to make smooth turns during the tunneling process; The backfill area (50) is the void filled around the two tunnels (10) to support the two tunnels (10).

2. The shield machine initial support launching structure for a small-clearance double-tunnel small-radius-of-curvature turning section according to claim 1, characterized in that, The two tunnels (10) are excavated in a near-circular shape, with a width of 9.5m and a height of 9.9m. The net distance between the two tunnels (10) is 3.9m to 6.4m.

3. The shield machine initial support launching structure for a small-clearance double-tunnel small-radius-of-curvature turning section according to claim 1, characterized in that, Both tunnels (10) are equipped with small radius of curvature turning sections (11).

4. The shield machine initial support launching structure for a small-clearance double-tunnel small-radius-of-curvature turning section according to claim 1, characterized in that, The curve radius of the small curvature radius turning segment (11) is 360m.

5. The shield machine initial support launching structure for a small-clearance double-tunnel small-radius-of-curvature turning section according to claim 1, characterized in that, The two tunnels (10) originate in Class IV to V surrounding rock, which is slightly weathered granite and granite fracture rock, with the tunnel top buried at a depth of 21.55m to 25.04m.

6. The shield machine initial support launching structure for a small-clearance double-tunnel small-radius-of-curvature turning section according to claim 1, characterized in that, The initial support structure (20) includes anchor bolts (21), steel mesh, wet sprayed concrete (22), and a grid steel frame structure.

7. The shield machine initial support and launching structure for a small-clearance double-tunnel small-radius-of-curvature turning section according to claim 6, characterized in that, The anchor rod (21) is a φ25 hollow grouting anchor rod; the steel mesh is a single-layer steel mesh of φ8@200*200; the wet sprayed concrete (22) has a strength grade of C25, a permeability grade of P6, and a thickness of 300mm; the main reinforcement diameter of the grid steel frame structure is φ22, and the grid steel frame spacing is 0.75m.

8. The shield machine initial support launching structure for a small-clearance double-tunnel small-radius-of-curvature turning section according to claim 1, characterized in that, The special segment structure (40) for turning is set in the small radius of curvature turning section (11) of the two tunnels (10) and is assembled by a tunnel boring machine; The special tube segment structure (40) for turning is prefabricated according to the turning axis of the small radius of curvature turning segment (11).

9. The shield machine initial support launching structure for a small-clearance double-tunnel small-radius-of-curvature turning section according to claim 1, characterized in that, The gap behind the segments of the special segment structure (40) for turning is the backfill area (50), which is backfilled with pea gravel and reinforced by grouting.

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