Open type TBM passes through soft and broken stratum cavity treatment and collaborative support method

Abstract

The application provides an open TBM cavity treatment and collaborative support method for soft and broken strata, comprising: detecting and acquiring spatial form information of a cavity above a shield and in front of a cutter head, and performing segmented and layered backfilling on the cavity, wherein the cavity above the shield and in front of the cutter head is backfilled first to form a shell-shaped protective structure, and the cavity behind the shield is backfilled layer by layer; based on the height of the radial cavity, dynamic adjustment is performed according to structural deformation monitoring data to implement differentiated support; a steel arch frame and a prestressed anchor cable collaborative bearing frame are constructed, and a pad of the prestressed anchor cable is fixed on a longitudinal connecting steel of the steel arch frame; two rows of composite angle advanced pipe roofs are constructed by using the structure space of the TBM, and the two rows of composite angle advanced pipe roofs are arranged at intervals and supplemented by grouting. The application forms a complete TBM support system for passing through soft and broken strata by means of cavity segmented and layered backfilling, dynamic decision of support parameters, collaborative bearing of anchor cables and steel arch frames and composite pipe roof advanced reinforcement.

Description

Technical Field

[0001] This invention relates to the field of tunnel engineering construction technology, specifically to a method for treating and supporting cavities in soft and fractured strata using an open-type TBM. Background Technology

[0002] Open-face TBMs, with their advantages of high-efficiency and integrated construction, have been widely used in deep-buried long tunnel projects. However, they face two major challenges when traversing weak and fractured geological sections: (1) The risk of TBM jamming is prominent: Due to the poor self-stabilizing ability of the surrounding rock, continuous large-scale collapses are likely to occur above the shield and in front of the cutterhead, forming cavities several meters high. This causes the TBM shield to lose the enclosure and constraint of the surrounding rock. On the one hand, uneven stress may lead to loss of machine attitude control; on the other hand, the continuous expansion of the collapsed cavity will lead to excessive muck discharge. The collapsed rock muck accumulates above the cutterhead and shield, and the shield pressure increases abnormally. This not only greatly reduces the tunneling efficiency, but also generates huge frictional resistance, which may cause the TBM to get stuck and construction to stop.

[0003] (2) The support structure is prone to failure: When the initial support is constructed in the case of a large cavity at the top, the back of the support is suspended. Since the cavity cannot provide effective resistance to the surrounding rock, the initial support structure is subjected to uneven stress. Under the action of the surrounding rock pressure, the initial support (especially the steel arch frame) will arch and deform towards the cavity with the least resistance, forming an "egg-shaped" structure, losing its designed circular bearing capacity, resulting in the failure of the support system and seriously threatening construction safety.

[0004] Existing technologies typically address the aforementioned problems by using simple concrete backfilling to treat cavities, but this approach suffers from three major drawbacks: First, core parameters such as backfill timing and thickness lack clear quantitative decision-making standards; second, the backfill and subsequent anchor (cable) support do not form a coordinated load-bearing system, resulting in low load-bearing efficiency; and third, the lack of a linkage decision-making mechanism between the arrangement and parameter selection of pre-support and cavity treatment leads to unsatisfactory treatment results and recurring problems. Existing technologies cannot fundamentally solve the construction challenges of open-face TBMs traversing soft, fractured strata and other adverse geological conditions. Summary of the Invention

[0005] This invention addresses the aforementioned shortcomings by providing a method for treating and supporting cavities in open-type TBMs penetrating weak and fractured strata. This method utilizes segmented and layered backfilling of cavities, dynamic decision-making of support parameters, coordinated load-bearing by anchor cables and steel arches, and advanced reinforcement with composite pipe roofs to form a complete TBM support system for penetrating weak and fractured strata. This achieves multiple objectives, including preventing TBM jamming, controlling support structure deformation, and improving construction efficiency.

[0006] To achieve the above objectives, this invention provides a method for treating and coordinating the support of open-type TBMs penetrating cavities in weak and fractured formations, comprising: The spatial morphology information of the cavity above the shield and in front of the cutterhead is obtained by detection, and the cavity is backfilled in sections and layers. The cavity above the shield and in front of the cutterhead is backfilled first to form a shell-shaped protective structure, and the cavity behind the shield is backfilled in layers. Based on the radial cavity height, dynamic adjustments are made according to structural deformation monitoring data to implement differentiated support. Construct a steel arch frame and a prestressed anchor cable co-supporting frame, and fix the pad of the prestressed anchor cable to the longitudinal connecting steel of the steel arch frame; Utilizing the TBM's own structural space, two rows of advanced pipe roofs with composite angles are constructed. The two rows of advanced pipe roofs with composite angles are arranged at intervals and supplemented with grouting to form a three-dimensional reinforcement zone in front of the cutterhead.

[0007] Furthermore, the cavity above the shield and in front of the cutterhead is first backfilled to a height of 2-3m to form a shell-shaped protective structure. After the shield is installed, steel arches and shotcrete are used for initial support. Then, backfilling is carried out in layers and at multiple points according to the principle of from far to near and from bottom to top.

[0008] Furthermore, the layered backfilling of the cavity behind the shield includes three layers: The first layer of backfilling is carried out on the cavity of the top arch within 5m behind the shield. The second layer of backfilling is carried out on the arch cavity within a range of 5 to 10 meters behind the shield. The third layer of backfilling involves full-height compaction of the cavity in the arch 10-20m behind the shield.

[0009] Furthermore, the first layer of backfill is carried out after the shotcrete strength of the initial support reaches 75% of the design strength, with a backfill height of 2-3m and a backfill thickness of not less than 1.5m at the top of the steel arch; the second layer of backfill has a height of 2-3m; the third layer of backfill is carried out by multi-point symmetrical pumping, and the backfill is closely attached to the original rock surface.

[0010] Furthermore, the differentiated support includes: When the radial cavity height H < 5m, after the backfill reaches the set strength, prestressed anchor cables with a length of 10 to 12m are installed along the excavation outline to reinforce the shallow surrounding rock and backfill as a whole. When the radial cavity height H≥5m, prestressed anchor cables with a length of 10-12m are installed along the excavation outline outside the cavity. System anchors with an outward octagonal arrangement are installed within the cavity. The tail of the system anchor is fixed to the steel arch frame, and the head is anchored into the stable bedrock behind the cavity at a set outward inclination angle. The outward inclination angle is set to be 30°-50° with the vertical section of the tunnel axis.

[0011] Furthermore, the dynamic adjustment based on structural deformation monitoring data includes: If the monitoring data shows that the steel arch frame deforms towards the cavity, it indicates that there is still room for compression in the backfill at the cavity, and the prestressed anchor cable will not be installed at that location. If monitoring data shows that the steel arch frame deforms toward the open face inside the tunnel, then prestressed anchor cables shall be installed within the cavity. The installation length L of the prestressed anchor cables within the cavity shall be determined by the formula L=H+6m, where H is the radial cavity height, and the installation length L of the prestressed anchor cables within the cavity shall not be less than 12m.

[0012] Furthermore, the system anchor bolts arranged in an outward octagonal shape have a length of 6 to 8 meters, which are used to transfer and distribute the load of the backfill to the stable bedrock, preventing the backfill from sinking as a whole and compressing the steel arch frame.

[0013] Furthermore, the prestress applied by the prestressed anchor cable is transferred to the steel arch frame through the pad, and the steel arch frame provides active support resistance; when the surrounding rock deforms, the load is transferred to the pad of the longitudinal connecting steel and the prestressed anchor cable through the steel arch frame, so as to achieve coordinated deformation and synergistic force of active support and passive support.

[0014] Furthermore, the two rows of composite-angle advanced pipe sheds include: The first row of pipe roofs is constructed using the guide holes pre-drilled on the TBM shield. The pipe roof angle is 7° to 7.5°, and the effective range is concentrated in the relatively shallow surrounding rock in front of the cutterhead. The second row of pipe roofs is constructed in the middle of the first row of pipe roofs, utilizing the space at the tail of the shield. The pipe roofs are at an angle of 30° to 45°, extending deep into the surrounding rock to form a deep surrounding rock bearing arch.

[0015] Furthermore, the spatial morphology information includes the radial cavity height and horizontal range; the segmented and layered backfilling of the cavity uses high-fluidity, early-strength, micro-expansion concrete pumped into the cavity through a high-pressure pipeline.

[0016] Compared with the prior art, the present invention has the following beneficial effects: Firstly, this invention organically integrates advanced detection, cavity treatment, dynamic initial support, and advanced support, breaking the traditional single and passive response mode and forming a complete problem solution, achieving full-chain coverage from risk prediction to subsequent prevention and control.

[0017] Secondly, this invention is based on a dual decision-making mechanism of "radial cavity height" and "deformation monitoring trend", which enables the support parameters to be dynamically adjusted according to actual geological conditions and structural response. This avoids the cost waste caused by excessive support and eliminates the safety risks caused by insufficient support, thus balancing safety and economy.

[0018] Thirdly, this invention, through the anchor-frame collaborative structural design, enables active support and passive support to form a force-bearing community, thereby improving the integrity and deformation resistance of the support system and fundamentally solving the "egg-shaped" deformation problem of the support structure.

[0019] Fourth, this invention makes full use of the spatial characteristics of the TBM structure and constructs a deep and three-dimensional advanced pre-support system by combining pipe roofs at different angles, which effectively prevents the collapse of subsequent tunneling sections and ensures the continuity of construction.

[0020] Fifth, the treatment method of this invention closely combines the characteristics of TBM construction technology and space constraints, and has strong operability in each step. It can effectively solve the two core pain points of TBM jamming and support deformation failure, and greatly improve tunneling efficiency while ensuring construction safety. Attached Figure Description

[0021] Figure 1 This is a flowchart of an embodiment of the open-type TBM method for treating and coordinating support of cavities in weak and fractured strata according to the present invention. Figure 2 This is a schematic diagram of the segmented and layered backfilling along the TBM fuselage cavity; Figure 3 Detailed drawing of the cooperative load-bearing structure of the longitudinal connection steel of the anchor cable and the steel arch frame; Figure 4 A schematic diagram of cavity backfilling and outward-pointing octagonal anchor bolts and anchor cables for support; Figure 5 A schematic diagram of the advanced pipe shed layout with two rows of composite angles; In the diagram: 1-Cutoff head, 2-Shield, 3-Steel arch frame, 4-Plate, 5-Longitudinal connecting steel, 6-Cavity backfill concrete, 7-First layer backfill, 8-Second layer backfill, 9-Third layer backfill, 10-Prestressed anchor cable within the cavity, 11-Outward octagonal anchor rod, 12-Prestressed anchor cable outside the cavity, 13-Excavation outline, 14-Emergency backfill, 15-Collapse, 16-First row of pipe sheds, 17-Second row of pipe sheds. Detailed Implementation

[0022] The following examples illustrate the implementation of the present invention in detail, but they do not constitute a limitation on the invention and are merely illustrative. Furthermore, the advantages of the present invention will become clearer and easier to understand by explaining them.

[0023] The present invention provides a method for treating and supporting cavities in soft and fractured strata using an open-type TBM, comprising the following steps: (1) Cavity detection and segmented backfilling Spatial morphology information of the cavity above shield 2 and in front of cutterhead 1 was obtained using detection methods, including the radial cavity height and horizontal range. These methods included laser scanning, advanced geological prediction, and drilling. High-fluidity, early-strength, micro-expansion concrete was selected for segmented and layered backfilling.

[0024] For the cavity above shield 2 and in front of cutterhead 1, high-flow, early-strength, and micro-expansion concrete is backfilled for 2-3m through high-pressure pipelines to quickly form a "shell-like" protective structure, preventing further collapse of the surrounding rock and creating conditions for subsequent tunneling and support.

[0025] After the shield 2 is installed, the steel arch frame 3 is installed first. The steel arch frame 3 is made of steel with high load-bearing capacity. Then, 5-10cm of concrete is initially sprayed. After that, backfilling is carried out in layers and at multiple points according to the principle of "from far to near and from bottom to top" to ensure that the backfill is dense and continuous and closely adheres to the original rock surface.

[0026] The cavity behind Shield 2 is treated using a three-layer backfilling method: The first layer of backfilling 7 targets the area within 5m behind Shield 2. After the initial support, such as the arch frame and initial shotcrete, is constructed outside Shield 2, the cavity within the top arch area within 5m behind Shield 2 is backfilled after the shotcrete reaches 75% of its design strength. The backfill height is 2-3m, ensuring that the thickness of the backfill material at the top of the steel arch frame is not less than 1.5m. The second layer of backfilling 8 targets the cavity within 5-10m behind Shield 2, with a backfill height of 2-3m. The third layer of backfilling 9 targets the cavity within 10-20m behind Shield 2, performing full-height dense backfilling using multi-point symmetrical pumping to ensure that the backfill material is tightly adhered to the original rock surface.

[0027] (2) Dynamic support decision-making and implementation based on dual criteria This invention implements a differentiated support strategy based on "radial cavity height" and "structural deformation monitoring data" for dynamic adjustment.

[0028] When the radial cavity height H < 5m, after the backfill reaches the set strength, prestressed anchor cables with a length of 10 to 12m are installed along the excavation contour 13 to reinforce the shallow surrounding rock and backfill as a whole.

[0029] When the radial cavity height H≥5m, the surrounding rock of the cavity is relatively stable. Prestressed anchor cables with a length of 10-12m are installed outside the cavity along the excavation outline 13. Within the cavity, 6-8m of system anchor rods (i.e., outward-octagonal anchor rods) are installed first. The tail is fixed on the steel arch frame, and the head is anchored into the stable bedrock behind the cavity at a set outward inclination angle. The outward inclination angle is set to be 30°-50° with the vertical section of the tunnel axis.

[0030] The main function of the outward-facing octagonal anchor rod 11 is to transfer and distribute the load of the collapsed cavity backfill concrete 6 to the stable bedrock, preventing the backfill body from sinking as a whole and compressing the steel arch frame.

[0031] Based on the deformation monitoring data, the deformation trend of the arch frame in the cavity is judged: if the monitoring data shows that the steel arch frame deforms towards the surrounding rock side, i.e., the cavity direction, it indicates that the backfill in the cavity still has compression space, the need for active support of the anchor cable is reduced, and the prestressed anchor cable 10 in the cavity area can be discontinued. If monitoring data shows that the steel arch frame deforms toward the open face inside the tunnel, it indicates that the surrounding rock pressure is large and reinforcement support needs to be started immediately. The length L of the prestressed anchor cable within the cavity is determined by the following formula: L=H+6m, where H is the radial cavity height. The length L of the prestressed anchor cable within the cavity is not less than 12m. This ensures that the anchoring section of the anchor cable is always located in the deep and stable rock mass, forming a reliable tensile bearing.

[0032] (3) Cooperative load-bearing structure of anchor cables and steel arch frame The longitudinal connecting steel section 5 is made of T62.5×125 steel. It is tightly bonded to the initial shotcrete and firmly welded to the adjacent steel arch frame 3. Two sections of longitudinal connecting steel section 5 are used at locations where prestressed anchor cables are designed; otherwise, a single section is used. Specifically, at the prestressed anchor cable locations, after the anchor cable drilling is completed, two sections of T62.5×125 steel are welded to the steel arch frame 3 at a circumferential interval of 5cm. Then, a base plate 4 is directly welded and fixed to the two sections of longitudinal connecting steel welded to the steel arch frame, constructing a spatially coordinated load-bearing frame. The prestress applied by the prestressed anchor cables is transferred to the steel arch frame 3 through the base plate 4, enabling the steel arch frame to actively provide support resistance. After the anchor cables are installed, the remaining shotcrete is applied.

[0033] When the surrounding rock deforms, the load is transferred through the steel arch frame 3 and the pad plate 4, which further activates the resistance of the prestressed anchor cable, realizing the coordinated deformation and synergistic stress of the "active + passive" support, and greatly improving the integrity and bearing capacity of the support system.

[0034] (4) Composite angle advanced pipe roof system during subsequent tunneling To prevent large-scale collapses from occurring again in subsequent excavation sections, two rows of advanced pipe roofs with composite angles were constructed using the TBM's own structural space before tunneling.

[0035] The first row of pipe sheds 16 is a small-angle pipe shed, constructed using the guide holes reserved on the TBM shield 2. The angle of this row of pipe sheds is relatively small, about 7° to 7.5°, and its effective range is mainly concentrated in the relatively shallow surrounding rock in front of the cutterhead 1, providing timely "umbrella-shaped" protection.

[0036] The second row of pipe roofs 17 is a large-angle pipe roof. Considering that the pipe roofs constructed through the pre-reserved guide holes on the shield 2 are located in relatively shallow surrounding rock and have a large spacing (generally 0.9 to 1.1 m), the second row of pipe roofs 17 is constructed in the middle of the first row of pipe roofs 16, arranged at intervals. The angle of this row of pipe roofs is limited by space and can be controlled between 30° and 45°. It mainly reinforces the first row of pipe roofs 16, and at the same time, by constructing at a large angle to penetrate deep into the surrounding rock in front, it promotes the formation of a deep surrounding rock "bearing arch".

[0037] The first row of pipe sheds 16 and the second row of pipe sheds 17, with their combined angles and grouting, form a three-dimensional reinforced zone in front of the cutterhead 1, effectively preventing subsequent collapse.

[0038] The following describes specific embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with the techniques or conditions described in the literature in this field.

[0039] A deep-buried water diversion tunnel project employed open-face TBM excavation with a tunnel diameter of 9.83m. It needed to traverse a Class V soft and fractured stratum within a fault zone and influence zone. The surrounding rock of this stratum had a uniaxial compressive strength of approximately 5MPa and well-developed joints and fissures. During excavation, cavities repeatedly appeared in front of the cutterhead and at the top of the shield, reaching a maximum height of 9.0m. This resulted in excessive muck discharge from the TBM, abnormally increased shield pressure, deformation of the initial support steel arch into an "egg-shell" shape, and slow excavation.

[0040] like Figures 1-5 As shown, the method of the present invention is used to treat the above-mentioned engineering situation. The specific implementation steps are as follows: Step 1: Cavity Detection Within 30 minutes after the TBM excavation was stopped, the maximum radial cavity height was determined to be approximately 8.5m, and the horizontal range was approximately 8.0m, using detection methods such as laser scanning.

[0041] Step Two: Emergency Backfilling and Layered Backfilling Emergency Backfill 14: High-fluidity, early-strength, micro-expansion concrete was used. Four Φ76 steel pipes were installed at the tail of shield 2, and C25 concrete was pumped to backfill in front of cutterhead 1. The backfill height was about 2m, quickly forming a shell-shaped protective structure.

[0042] First layer backfill 7: After shield 2 is erected, H175 steel arch frames are set up at 0.55m intervals. An emergency shotcrete system is used to initially spray 5-10cm of concrete. The longitudinal connection of the arch frames uses T62.5×125 steel. After the shotcrete reaches 75% of its design strength, the cavity within 5m behind shield 2 is backfilled for about 2.5m.

[0043] Second layer backfill 8: Backfill the cavity 5-10m behind shield 2, with a backfill height of about 2.5m.

[0044] Third layer backfill 9: The cavity is backfilled and compacted within 20m behind the shield 2. A multi-point symmetrical pumping method is used to ensure that the backfill body is in close contact with the original rock surface.

[0045] After completing the three-layer backfilling process as described above, a complete and dense cavity backfill concrete 6 is formed inside the cavity.

[0046] Step 3: Dynamic Support Adjustment 240° range of foundation support for tunnel side arch: Since the radial cavity height H=8.5m>5m in this embodiment is a large cavity, 12 prestressed anchor cables are installed outside the cavity range for 12m, with a pretension force of 200kN and a spacing of 1.0m×1.1m; the pad plate 4 is welded and fixed to the two longitudinal connecting steel sections welded to the steel arch frame, and the size of the pad plate is not less than 15cm×15cm.

[0047] An external octagonal anchor rod 11 (self-propelled hollow grouting anchor rod) with a diameter of 38mm and a length of 6m is installed within the cavity. The anchor rod has a deflection angle of 49° relative to the vertical section of the tunnel axis and a spacing of 1.0m×1.0m between rows to transfer the load of the backfill to the stable bedrock.

[0048] Deformation Adjustment: Monitoring revealed a daily deformation of 6mm in the steel arch, with deformation extending inwards into the tunnel, indicating significant surrounding rock pressure. Based on the formula L=H+6m, the calculated length of prestressed anchor cables within the cavity is L=8.5+6=14.5m. Prestressed anchor cables 10 are installed within the cavity for reinforcement support, and pads 4 are welded and fixed to the two longitudinal connecting steel sections welded to the steel arch. After the anchor cable installation is completed, the remaining shotcrete is applied.

[0049] After adopting the above methods, the daily deformation was reduced to 2mm, and the deformation was effectively controlled.

[0050] Step 4: Construction of advanced pipe roof Two rows of advanced pipe roofs were constructed before subsequent tunneling: the first row of pipe roofs, 16, was a small-angle pipe roof with an angle of 7.5° and a length of 15m, constructed using the guide holes pre-reserved on the TBM shield 2; the second row of pipe roofs, 17, was a large-angle pipe roof with an angle of 40° and a length of 20m, arranged at intervals between the first row of pipe roofs in the tail space of the shield. The two rows of pipe roofs were combined and supplemented with grouting to provide advanced support for the surrounding rock in the arch area in front of the shield 2 and the tunnel face, forming a three-dimensional reinforced zone.

[0051] Implementation effect After adopting the method of this invention, the collapse of the TBM crown area was significantly controlled, the amount of muck removed was reduced, and the pressure on shield 2 was lowered. The tunneling speed in the regional fault fracture zone increased from about 1.0 m / d to about 3.0 m / d, and the tunneling efficiency increased by about 200%. The deformation of the steel arch frame was effectively controlled, and the "eggshell" deformation no longer occurred. The support system was stable and reliable, and construction safety was guaranteed.

[0052] The above are merely specific embodiments of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the protection scope of the present invention. Any other aspects not described in detail are prior art.

Claims

1. A method for treating and coordinating the support of open-type TBMs penetrating cavities in weak and fractured formations, characterized in that, include: The spatial morphology information of the cavity above the shield and in front of the cutterhead is obtained by detection, and the cavity is backfilled in sections and layers. The cavity above the shield and in front of the cutterhead is backfilled first to form a shell-shaped protective structure, and the cavity behind the shield is backfilled in layers. Based on the radial cavity height, dynamic adjustments are made according to structural deformation monitoring data to implement differentiated support. Construct a steel arch frame and a prestressed anchor cable co-supporting frame, and fix the pad of the prestressed anchor cable to the longitudinal connecting steel of the steel arch frame; Utilizing the TBM's own structural space, two rows of advanced pipe roofs with composite angles are constructed. The two rows of advanced pipe roofs with composite angles are arranged at intervals and supplemented with grouting to form a three-dimensional reinforcement zone in front of the cutterhead.

2. The method for treating and coordinating support of cavities in weak and fractured strata using an open-type TBM according to claim 1, characterized in that, The cavity above the shield and in front of the cutterhead is first backfilled to a height of 2-3m to form a shell-shaped protective structure. After the shield is installed, steel arches and shotcrete are used for initial support. Then, backfilling is carried out in layers and at multiple points according to the principle of from far to near and from bottom to top.

3. The method for treating and coordinating support of cavities in weak and fractured strata using an open-type TBM according to claim 2, characterized in that, The layered backfilling of the cavity behind the shield includes three layers: The first layer of backfilling is carried out on the cavity of the top arch within 5m behind the shield. The second layer of backfilling is carried out on the arch cavity within a range of 5 to 10 meters behind the shield. The third layer of backfilling involves full-height compaction of the cavity in the arch 10-20m behind the shield.

4. The method for treating and coordinating support of cavities in weak and fractured strata using an open-type TBM according to claim 3, characterized in that, The first layer of backfill is carried out after the shotcrete strength of the initial support reaches 75% of the design strength, with a backfill height of 2-3m and a backfill thickness of not less than 1.5m at the top of the steel arch; the second layer of backfill has a height of 2-3m; the third layer of backfill is carried out by multi-point symmetrical pumping, and the backfill is closely attached to the original rock surface.

5. The method for treating and coordinating support of cavities in weak and fractured strata using an open-type TBM according to claim 4, characterized in that, The differentiated support includes: When the radial cavity height H < 5m, after the backfill reaches the set strength, prestressed anchor cables with a length of 10 to 12m are installed along the excavation outline to reinforce the shallow surrounding rock and backfill as a whole. When the radial cavity height H≥5m, prestressed anchor cables with a length of 10-12m are installed along the excavation outline outside the cavity. System anchors with an outward octagonal arrangement are installed within the cavity. The tail of the system anchor is fixed to the steel arch frame, and the head is anchored into the stable bedrock behind the cavity at a set outward inclination angle. The outward inclination angle is set to be 30°-50° with the vertical section of the tunnel axis.

6. The method for treating and coordinating support of cavities in weak and fractured strata using an open-type TBM according to claim 5, characterized in that, The dynamic adjustment based on structural deformation monitoring data includes: If the monitoring data shows that the steel arch frame deforms towards the cavity, it indicates that there is still room for compression in the backfill at the cavity, and the prestressed anchor cable will not be installed at that location. If monitoring data shows that the steel arch frame deforms toward the open face inside the tunnel, then prestressed anchor cables shall be installed within the cavity. The installation length L of the prestressed anchor cables within the cavity shall be determined by the formula L=H+6m, where H is the radial cavity height, and the installation length L of the prestressed anchor cables within the cavity shall not be less than 12m.

7. The method for treating and coordinating support of cavities in weak and fractured strata using an open-type TBM according to claim 6, characterized in that, The outward-octagonal arrangement of the system anchor bolts has a length of 6-8m and is used to transfer and distribute the load of the backfill to the stable bedrock, preventing the backfill from sinking as a whole and compressing the steel arch frame.

8. The method for treating and coordinating support of cavities in weak and fractured strata using an open-type TBM according to claim 7, characterized in that, The prestress applied by the prestressed anchor cable is transferred to the steel arch frame through the pad, and the steel arch frame provides active support resistance. When the surrounding rock deforms, the load is transferred to the pad of the longitudinal connecting steel and the prestressed anchor cable through the steel arch frame, so as to achieve coordinated deformation and synergistic force of active support and passive support.

9. The method for treating and coordinating support of cavities in weak and fractured strata using an open-type TBM according to any one of claims 1 to 8, characterized in that, The two rows of composite-angle advanced pipe sheds include: The first row of pipe roofs is constructed using the guide holes pre-drilled on the TBM shield. The pipe roof angle is 7° to 7.5°, and the effective range is concentrated in the relatively shallow surrounding rock in front of the cutterhead. The second row of pipe roofs is constructed in the middle of the first row of pipe roofs, utilizing the space at the tail of the shield. The pipe roofs are at an angle of 30° to 45°, extending deep into the surrounding rock to form a deep surrounding rock bearing arch.

10. The method for treating and coordinating support of cavities in weak and fractured strata using an open-type TBM according to any one of claims 1 to 8, characterized in that, The spatial morphology information includes the radial cavity height and horizontal range; the segmented and layered backfilling of the cavity uses high-fluidity, early-strength, micro-expansion concrete pumped into the cavity through a high-pressure pipeline.

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