Stability control method for eccentric door type reinforcement combined with bag grouting of sharp curve shield tunnel

Abstract

The present application relates to a kind of acute curve shield tunnel eccentric door type reinforcement combined with bag grouting stability control method, its steps are as follows: (1) construction preparation;(2) eccentric door type reinforcement;(3) acute curve segment shield tunneling;(4) segment assembly;(5) bag grouting;(6) remove ball valve and grouter;(7) secondary grouting.The present application is aimed at silt ground acute curve segment "eccentric door type" MJS soil reinforcement method combined with bag grouting segment stability control method under synchronous grouting mode, effectively guarantee the stability of soil layer and the stability of tunnel segment during acute curve segment shield tunnel construction, solve the problem of insufficient lateral reaction and unstable longitudinal force transmission of silt ground acute curve segment tunnel, provide guarantee for silt layer acute curve segment high-precision shield tunnel safe construction.

Description

Technical Field

[0001] This invention relates to the field of underground engineering construction technology, applicable to shield tunnel construction, and particularly to a method for eccentric portal reinforcement combined with bag grouting for stability control of shield tunnels with steep curves in soft silt strata. Background Technology

[0002] With the continuous advancement of in-depth development and organic renewal in urban centers, the development of underground space in central urban areas has entered a new stage. In the increasingly complex and dense underground transportation network, the shield tunneling method, with its advantages of speed, environmental friendliness, intelligence, efficiency, and minimal impact on the surrounding environment, has become the preferred method for tunnel construction in central urban areas. However, current shield tunneling faces challenges such as existing dense underground pipe networks, the need to avoid and protect adjacent buildings, resulting in complex and diverse tunnel alignments, a sharp increase in steep curves, and a decreasing radius-to-diameter (R / D) ratio, making curvature control increasingly difficult. Currently, Japan is a world leader in shield tunneling technology for steep curves, having completed several successful cases (minimum R / D = 29.3). However, the vast majority of these successful cases involve shield tunneling in relatively hard soil or rock layers; there are currently no cases of shield tunneling with a steep curve R / D of 25 in soft, silty, and unfavorable geological conditions.

[0003] The soft silty soil layers in Shanghai and similar areas are characterized by low strength, poor permeability, high water content, high compressibility, and high sensitivity. They also exhibit thixotropic and rheological properties, making them susceptible to disturbance during construction and prone to instability at the excavation face. This is extremely unfavorable for shield tunneling on sharp curves. The main problems encountered in shield tunneling on sharp curves in soft silty soil layers are: ① During shield tunneling on sharp curves, the tunnel axis forms an angle with the normal direction of the segment end face. Under the action of the jacks, a lateral force is generated on the segment exiting the shield tail, resulting in a stress state of compression on the inside and tension on the outside of the tunnel on the sharp curve, causing the segment to move outwards from the curve. The extremely low strength of the soft silty soil layer cannot provide sufficient lateral reaction force for sharp curve tunnels. ② Over-excavation is inevitable during shield tunneling on sharp curves, causing soil loss and significant disturbance to the soil, which can easily lead to substantial settlement. ③ Due to the high water content of the silty soil layer, there is a possibility of segment floating after the shield excavation is completed. ④ In addition, due to the extremely poor self-stabilizing performance of the soft silty soil layer, the shield attitude is also difficult to control. If the horizontal and vertical deviations of the shield machine are too large, the shield machine will have an excessive amount of serpentine movement, causing excessive disturbance to the strata or causing segment misalignment and cracking.

[0004] To address issues such as insufficient ground reaction force, easy segment misalignment or floating, significant ground settlement, and unstable shield posture during shield tunneling in steep curve sections of the Shanghai Taopu Wastewater Treatment Plant's initial rainwater storage project (TP1.2 and TP1.5 sections), various process parameter tests and on-site implementations were conducted in the soft silty strata where the steep curve shield tunnels (approximately 185.29m in length, with a minimum turning radius of 115m and an overlying soil layer thickness of approximately 13.87–11.98m, primarily located in ③1 silty clay and ④1 silty clay) are situated. Ultimately, an independently developed method combining the "eccentric portal" MJS soil reinforcement method with bag-mounted grouting segment stability control in sharp curve sections was formed. This method effectively balances the pressure difference between the inner and outer sides of the curve section through "eccentric portal" MJS soil reinforcement, preventing tunnel uplift. Simultaneously, the bag-mounted grouting in the synchronous grouting mode provides timely inter-segment filling and support for the segments, effectively ensuring the stability of the soil layer and tunnel segments during shield tunnel construction in sharp curve sections. On-site, shield tunneling and segment assembly were successfully carried out on a sharp curve with a small radius (R=115m, D=5.935R / D=21.3) in soft silty soil conditions. This solved the problems of insufficient lateral reaction force and unstable longitudinal force transmission in sharp curve sections of silty soil, providing a guarantee for the safe and high-precision shield tunnel construction in sharp curve sections of silty soil. Summary of the Invention

[0005] To achieve the above objectives, the present invention aims to provide a method for stabilizing shield tunnels with eccentric portal reinforcement combined with bag grouting in soft silty strata and steep curves.

[0006] The technical solution adopted in this invention is: a method for stabilizing and controlling eccentric portal reinforcement combined with bag grouting in steep curve shield tunnels, comprising the following steps:

[0007] S1: Construction Preparation

[0008] Before the formal construction of a steep curve shield tunnel, the following work should be carried out: axis re-measurement, shield attitude adjustment, shield machine construction parameter confirmation, equipment maintenance, material quality inspection, and technical and emergency material inspection.

[0009] S2: Eccentric gate reinforcement

[0010] For shield tunnels with sharp curves in soft silt strata, the MJS method was used for ground pre-reinforcement. The reinforcement range was determined by combining three-dimensional numerical simulation analysis to control the shield settlement Δs ≤ 20mm and the principal compressive stress σmax ≤ 0.5MPa during the sharp curve section. The distance between the reinforcement starting point on the inner side of the sharp curve and the tangent of the inner arc of the tunnel was 0.3–0.5m, and the reinforcement width b1 was 0.45–0.5D. The distance between the reinforcement starting point on the outer side of the sharp curve and the tangent of the outer arc of the tunnel was 0.5–1.0m. The outer reinforcement width b2 is 0.85~1.0D; the reinforcement depth on both sides of the curve section should exceed the bottom of the tunnel pipe by 0.3m, the distance s between the reinforcement bottom surface of the upper part of the tunnel and the outside of the tunnel segment should be 300mm~500mm, and the reinforcement height h1 should not be less than 3m. Based on this standard, an eccentric portal reinforcement is formed; through eccentric portal reinforcement, the reinforcement on the inner side of the sharp curve can reduce the settlement caused by over-excavation, the reinforcement on the outer side can increase the lateral reaction force, and the reinforcement of the top plate can reduce the adverse effects of shield tunnel settlement and uplift in soft soil.

[0011] S3: Shield tunneling on a sharp curve section

[0012] During the construction of the sharp curve section, the advancing speed is controlled within 1 to 2 cm / min, and one ring of tunneling is completed in stages: after each certain distance of tunneling, the tunneling is stopped and the jacks are retrieved in batches and the segments are re-pressed, and the tunneling continues. This process is repeated multiple times to complete one ring of tunneling. During the shield tunneling process, synchronous grouting is strengthened. Grouting is carried out in a diagonal alternating injection method to ensure that the injected grout evenly and continuously fills the construction voids behind the tunnel wall.

[0013] S4: Segment Assembly

[0014] During segment assembly, a staggered assembly method is adopted, following a bottom-up principle. Starting from the bottom, the bottom standard blocks are assembled first, followed by the standard blocks on both sides and adjacent blocks in a symmetrical order, and finally the capping blocks are assembled. After the segment assembly is completed, the assembly head is removed. The first ring after the shield tail is selected to open the grouting holes and install bag grouters. 4-5 bag grouters are installed on the outer segments of each sharp curve. At the junction of the straight-to-straight point and the transition point of the sharp curve, a ring is selected to install 3-4 bag grouters on the inner segments of the sharp curve.

[0015] S5: Grouting with Bag

[0016] After the fourth ring of the shield tail was deployed, a one-way three-way ball valve was installed on the bag grouting device, and the grouting machine was turned on to perform double-liquid grouting of the bag. Grouting was carried out promptly and solidified at the junction of the straight and gentle curve sections and the transition points between the straight and gentle curve sections, as well as on the back side of the straight curve sections. This effectively ensured the timely and effective support and stability of the tunnel segments in the soft soil and silty clay. Simultaneously, on the horizontal curve, the triangular stability of the starting, ending, and back sides of the straight curve tunnel was achieved.

[0017] S6: Remove the ball valve and grouting device

[0018] Four hours later, the ball valve and grouting device were removed.

[0019] S7: Secondary grouting

[0020] For formed tunnels, secondary grouting is carried out in a timely manner. Every 5 rings of segment assembly are grouted with double liquid to form rings, and the soil settlement is controlled within 20mm.

[0021] Furthermore, in step S2, MJS pile diameter control Ordinary Portland cement of grade P.O42.5 is used, with a cement content of not less than 40%, a water-cement ratio of 0.6 to 0.8, and the uniaxial compressive strength of the solidified body is controlled at 0.8 to 1.2 MPa.

[0022] Furthermore, in step S3, during the shield tunneling process on the sharp curve section, to ensure the shield tunneling can smoothly turn through the sharp curve section, a limited, large-scale over-excavation is carried out on the soil inside the sharp curve using a contour cutter. Before the curve construction, the contour cutter begins to over-excavate on the inside, slowly and uniformly extending from an angle of 90° until the contour cutter reaches its maximum stroke at an angle of 120°, in preparation for the curve construction. When officially entering the curve end, the contour cutter continues to over-excavate on the inside while maintaining its maximum stroke, with the contour cutter angle α controlled between 120° and 240°. After leaving the curve section, the contour cutter begins to slowly retract from an angle of 240°, and is fully reset at an angle of 270°. The over-excavation amount δ is strictly controlled between 10mm and 50mm, and a two-liquid mixed plastic flow gel material is used as the over-excavation filling material to fill the over-excavation gap.

[0023] Furthermore, in step S3, the grouting pressure is controlled to be 1.5 to 1.8 times the at-rest earth pressure, and the synchronous grouting volume is maintained at 3.27 to 4.36 m³. 3 / meter, ensuring a filling rate of 150% to 200%.

[0024] Furthermore, in step S4, when assembling the capping block, first overlap 2 / 3 of the ring width, push it radially upward, and then insert it longitudinally; after aligning the second segment with the previous ring segment and the first segment of this ring, first longitudinally press the circumferential waterstop strip, then circumferentially press the longitudinal waterstop strip, and finely adjust the alignment bolt holes; tighten the longitudinal and circumferential connecting bolts while assembling the segments; after the entire ring segment comes out of the shield tail, tighten all connecting bolts again; the gap between adjacent ring surfaces is ≤1mm, and the gap between adjacent blocks in the longitudinal joint is ≤1mm.

[0025] Furthermore, in step S5, the grouting uses cement grout and water glass concentrate at a 1:1 ratio. The cement grout mix ratio is 1:1, and the water glass concentration is not less than 38. The grout is prepared in advance according to the above parameters to control the initial setting time of the two-component grout to be 25-35 seconds and the final setting time to be no more than 20 minutes. The grouting volume is controlled to be approximately 0.07 m³. 3The entire process involves double-liquid grouting to achieve an effective umbrella-shaped opening diameter of approximately 70-80cm and a thickness of 8-12cm for the attached bag.

[0026] Furthermore, after the above steps are completed, the axial deviation of the tunnel segment behind the shield tail is checked periodically, and the measured value is compared with the previous measured value. If the segment deviates outward after exiting the shield tail, the grouting holes on the segment are used to inject a double-liquid grout group behind the outer wall of the curve to prevent the tunnel deviation from continuing to develop. At the same time, according to the magnitude of the deviation, the inner wall thickness of the curve is appropriately supplemented with secondary grout to prevent the inner soil from loosening and deforming, ensuring that the axial deviation is less than 20mm.

[0027] The beneficial effects of this invention are as follows: This invention employs an "eccentric portal" MJS soil reinforcement mode for sharp curve sections in soft silty soil strata, combined with a bag-mounted grouting segment stability control method under synchronous grouting mode, effectively ensuring the stability of the soil layer and tunnel segments during shield tunnel construction in sharp curve sections. On-site, shield tunneling and segment assembly were successfully carried out on a 115m sharp curve with a small radius under soft silty soil conditions. This solves the problems of insufficient lateral reaction force and unstable longitudinal force transmission in tunnels with sharp curves in silty soil strata, providing a guarantee for the safe construction of high-precision shield tunnels in sharp curve sections of silty soil. Attached Figure Description

[0028] Figure 1 This is a process flow diagram of the present invention;

[0029] Figure 2 This is diagram AA, showing the cross-section of the MJS eccentric portal reinforced shield tunnel section on a sharp curve.

[0030] Figure 3 This is a partial enlarged view of the AA section of the MJS shield tunnel with eccentric portal reinforcement on a sharp curve.

[0031] Figure 4 This is the BB diagram of the eccentric portal reinforced section of the MJS shield tunnel for the steep curve segment (straight-to-gradient, gradient-to-straight point);

[0032] Figure 5 This is a partial enlarged view of the reinforced section BB of the MJS eccentric portal type shield tunnel in the sharp curve section (straight-to-gradient, gradient-to-straight point);

[0033] Figure 6 This is a cross-sectional view of the over-excavation area inside the sharp curve section;

[0034] Figure 7 This is a longitudinal plan view of eccentric gate-type reinforcement and synchronous grouting with attached bags. Detailed Implementation

[0035] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0036] like Figures 1 to 7As shown, the present invention provides a method for stabilizing shield tunnels in soft silty strata with steep curves using eccentric portal reinforcement combined with bag grouting, comprising the following steps:

[0037] S1: Construction Preparation

[0038] Before the formal construction of a steep-curve shield tunnel, it is necessary to carry out tasks such as axis re-measurement, shield attitude adjustment, confirmation of shield machine construction parameters, equipment maintenance, material quality inspection, and inspection of technical and emergency supplies.

[0039] S2: Eccentric gate reinforcement:

[0040] For shield tunnels with sharp curves in soft silt strata, the MJS method was used for ground pre-reinforcement. The reinforcement range was determined based on three-dimensional numerical simulation analysis, controlling the shield settlement Δs ≤ 20mm and the principal compressive stress σmax ≤ 0.5MPa during the sharp curve section. The distance between the reinforcement starting point on the inner side of the sharp curve and the tangent of the inner arc of the tunnel was 0.3–0.5m, and the reinforcement width b1 was 0.45–0.5D. The distance between the reinforcement starting point on the outer side of the sharp curve and the tangent of the outer arc of the tunnel was 0.5–1.0m, and the reinforcement width b2 on the outer side of the sharp curve was 0.85–1.0D. The reinforcement depth on both sides of the curve section should exceed the bottom of the tunnel by 0.3m. The distance s between the bottom of the reinforcement on the upper part of the tunnel and the outside of the tunnel segment should be 300mm–500mm, and the reinforcement height h1 should not be less than 3m. This standard forms an eccentric portal reinforcement system.

[0041] MJS pile diameter control Ordinary Portland cement of grade P.O42.5 is used, with a cement content of not less than 40% and a water-cement ratio of 0.6 to 0.8. The uniaxial compressive strength of the solidified body is controlled at 0.8 to 1.2 MPa.

[0042] By using eccentric portal reinforcement, reinforcement on the inner side of sharp curves can reduce settlement caused by over-excavation, reinforcement on the outer side can increase lateral reaction force, and reinforcement of the top plate can reduce the adverse effects of shield tunnel settlement and uplift in soft soil.

[0043] S3: Shield tunneling on a sharp curve section:

[0044] During the construction of the sharp curve section, the advancing speed is controlled within 1 to 2 cm / min, and one ring of tunneling is completed in stages: after each certain distance of tunneling, the tunneling is stopped and the jacks are retrieved in batches, the segments are re-pressed, and the tunneling continues. This process is repeated multiple times to complete one ring of tunneling.

[0045] During the tunnel boring machine (TBM) advancement on sharp curves, to ensure smooth passage through these curves, a limited, large-scale over-excavation is performed on the inner side of the curve using a contour cutter. Before curve construction, the contour cutter begins over-excavation on the inner side, slowly and uniformly extending from an angle of 90° until reaching its maximum stroke at 120°, preparing for curve construction. Upon entering the curve's end, the contour cutter continues over-excavation on the inner side while maintaining its maximum stroke, with the contour cutter angle α controlled between 120° and 240°. After leaving the curve, the contour cutter begins to slowly retract from an angle of 240°, fully resetting at 270°. The over-excavation amount δ is strictly controlled between 10mm and 50mm, and a two-liquid mixed plastic-fluid gelled material is used as the over-excavation filler in the over-excavation gaps.

[0046] During the tunnel boring machine (TBM) advancement process, synchronous grouting should be strengthened. Grouting should be carried out using a diagonal alternating injection method to ensure that the injected grout evenly and continuously fills the structural voids behind the tunnel wall. The grouting pressure should be controlled at 1.5 to 1.8 times the static earth pressure, and the synchronous grouting volume should be maintained at 3.27 to 4.36 m³ / s. 3 / meter), ensuring a filling rate of 150% to 200%.

[0047] S4: Segment Assembly:

[0048] When assembling the tunnel segments, a staggered assembly method is adopted, following a bottom-up principle. Starting from the bottom, the bottom standard blocks are assembled first, followed by the standard blocks on both sides and adjacent blocks in a symmetrical order, and finally the capping blocks are assembled. When assembling the capping blocks, they are first overlapped by 2 / 3 of the ring width, pushed upwards radially, and then inserted longitudinally.

[0049] After aligning the second segment with the previous segment and the first segment of this ring, first tighten the circumferential waterstop strip longitudinally, then tighten the longitudinal waterstop strip circumferentially, and fine-tune the alignment bolt holes; tighten the longitudinal and circumferential connecting bolts while assembling the segments; after the entire ring of segments is removed from the shield tail, tighten all connecting bolts again. The gap between adjacent ring surfaces is ≤1mm, and the gap between adjacent segments in the longitudinal joint is ≤1mm.

[0050] After the segments are assembled, the assembly head is removed. The first ring after the shield tail is selected to open the grouting holes and install bagged grouters. Four to five bagged grouters are installed on the outer segments of each sharp curve. At the junction of the straight-to-gradual point and the gradual-to-straight point of the sharp curve, one ring is selected to install three to four bagged grouters on the inner segments of the sharp curve.

[0051] S5: Grouting with attached bags:

[0052] After the fourth ring of the shield is deployed, a one-way three-way ball valve is installed on the bag grouting device, and the grouting machine is started to perform bag grouting with two-component grout. The grouting uses cement grout and water glass concentrate at a ratio of 1:1. The cement grout ratio is 1:1, and the water glass has a Baume degree of not less than 38. The grout is prepared in advance according to the above parameters to control the initial setting time of the two-component grout to 25-35 seconds and the final setting time to not exceed 20 minutes. The grouting volume is controlled to be approximately 0.07m. 3 The entire process involves double-liquid grouting to achieve an effective umbrella-shaped opening diameter of approximately 70-80cm and a thickness of 8-12cm for the attached bag.

[0053] By promptly injecting and solidifying grout into the inner and outer sides of the tunnel segments at the transition points between straight and gradual curves, and at the back side of the tunnel segments on sharp curves, timely and effective support and stability of the tunnel segments in soft soil and silty clay were effectively ensured. Simultaneously, on horizontal curves, triangular stability was achieved at the beginning, end, and back sides of the sharp curve tunnel.

[0054] S6: Remove the ball valve and grouting device:

[0055] Four hours later, the ball valve and grouting device were removed.

[0056] S7: Secondary grouting:

[0057] For formed tunnels, secondary grouting is carried out in a timely manner. Every 5 rings of segment assembly are grouted with double liquid to form rings, and the soil settlement is controlled within 20mm.

[0058] Regularly check the axial deviation of the tunnel segments behind the shield tail and compare the measured values ​​with previous measurements. If the segments deviate outward after exiting the shield tail, use the grouting holes on the segments to inject a double-liquid grout group behind the outer wall of the curve to prevent the tunnel deviation from continuing. At the same time, depending on the magnitude of the deviation, perform secondary grouting on the inner wall thickness of the curve to prevent the inner soil from loosening and deforming, ensuring that the axial deviation is less than 20mm.

Claims

1. A method for stabilizing a steeply curved shield tunnel using eccentric portal reinforcement combined with bag grouting, characterized in that... Includes the following steps: S1: Construction Preparation Before the formal construction of a steep curve shield tunnel, the following work should be carried out: axis re-measurement, shield attitude adjustment, shield machine construction parameter confirmation, equipment maintenance, material quality inspection, and technical and emergency material inspection. S2: Eccentric gate reinforcement For shield tunnels with sharp curves in soft silt strata, the MJS method was used for ground pre-reinforcement. The reinforcement range was determined by combining three-dimensional numerical simulation analysis to control the shield settlement Δs ≤ 20 mm and the principal compressive stress σmax ≤ 0.5 MPa during the sharp curve section. The distance between the reinforcement starting point on the inner side of the sharp curve and the tangent of the inner curve of the tunnel was 0.3~0.5 m, and the reinforcement width b1 was 0.45~0.5D. The distance between the reinforcement starting point on the outside of the sharp curve and the tangent of the outer arc of the tunnel is 0.5~1.0m, and the reinforcement width b2 on the outside of the sharp curve is 0.85~1.0D; the reinforcement depth on both sides of the curve section should exceed the bottom of the tunnel pipe by 0.3m, the distance s between the reinforcement bottom surface on the upper part of the tunnel and the outside of the tunnel segment should be 300mm~500mm, and the reinforcement height h1 should not be less than 3m. Based on this standard, an eccentric portal reinforcement is formed; through eccentric portal reinforcement, the reinforcement on the inside of the sharp curve can reduce the settlement caused by over-excavation, the reinforcement on the outside can increase the lateral reaction force, and the reinforcement of the top plate can reduce the adverse effects of shield tunnel settlement and uplift in soft soil; S3: Shield tunneling on a sharp curve section During the construction of the sharp curve section, the advancing speed is controlled within 1 to 2 cm / min, and one ring of tunneling is completed in stages: after each certain distance of tunneling, the tunneling is stopped and the jacks are retrieved in batches and the segments are re-pressed, and the tunneling continues. This process is repeated multiple times to complete one ring of tunneling. During the shield tunneling process, synchronous grouting is strengthened. Grouting is carried out in a diagonal alternating injection method to ensure that the injected grout evenly and continuously fills the construction voids behind the tunnel wall. S4: Segment Assembly During segment assembly, a staggered assembly method is adopted, following a bottom-up principle. Starting from the bottom, the bottom standard blocks are assembled first, followed by the standard blocks on both sides and adjacent blocks in a symmetrical order, and finally the capping blocks are assembled. After the segment assembly is completed, the assembly head is removed, and the grouting holes are opened in the first ring after the shield tail to install the bag grouting device. 4-5 bag grouting devices are installed on the outer segment of each sharp curve. At the junction of the straight-to-straight point and the transition point of the sharp curve, a ring is selected to install 3-4 bag grouting devices on the inner segment of the sharp curve. S5: Grouting with Bag After the fourth ring of the shield tail is launched, a one-way three-way ball valve is installed on the bag grouting device, and the grouting machine is turned on to carry out bag double liquid grouting; through the junction of the straight and gentle points of the sharp curve section and the gentle straight point, the bag grouting on the back side of the sharp curve segment is injected and solidified in time, which effectively ensures the timely and effective support and stability of the tunnel segment of the sharp curve in soft soil and silty soil. At the same time, on the horizontal curve, the starting, ending and back side triangular stability of the sharp curve tunnel are achieved. S6: Remove the ball valve and grouting device Four hours later, the ball valve and grouting device were removed. S7: Secondary grouting For formed tunnels, secondary grouting is carried out in a timely manner. Every 5 rings of segment assembly are grouted with double liquid to form rings, and the soil settlement is controlled within 20mm.

2. The method for stabilizing and controlling eccentric portal reinforcement combined with bag grouting in steep curve shield tunnels according to claim 1, characterized in that: In step S2, MJS pile diameter control 2400@1800mm, using P.O42.5 grade ordinary Portland cement, with a cement content of not less than 40%, a water-cement ratio of 0.6~0.8, and the uniaxial compressive strength of the solidified body controlled at 0.8~1.2MPa.

3. The method for stabilizing and controlling eccentric portal reinforcement combined with bag grouting in steep curve shield tunnels according to claim 1, characterized in that: In step S3, during the shield tunneling process on the sharp curve section, to ensure the shield tunneling can smoothly turn through the sharp curve section, a limited, large-scale over-excavation is carried out on the soil inside the sharp curve using a contour cutter. Before the curve construction, the contour cutter begins to over-excavate on the inside, slowly and uniformly extending from an angle of 90° until the contour cutter reaches its maximum stroke at an angle of 120°, in preparation for the curve construction. When officially entering the curve end, the contour cutter continues to over-excavate on the inside while maintaining its maximum stroke, with the contour cutter angle α controlled between 120° and 240°. After leaving the curve section, the contour cutter begins to slowly retract from an angle of 240°, and is fully reset at an angle of 270°. The over-excavation amount δ is strictly controlled between 10mm and 50mm, and a two-liquid mixed plastic flow gel material is used as the over-excavation filling material to fill the over-excavation gaps.

4. The method for stabilizing and controlling eccentric portal reinforcement combined with bag grouting in steep curve shield tunnels according to claim 1, characterized in that: In step S3, the grouting pressure is controlled at 1.5 to 1.8 times the at-rest earth pressure, and the synchronous grouting volume is maintained at 3.27 to 4.36 m³. 3 / meter, ensuring a filling rate of 150%~200%.

5. The method for stabilizing and controlling eccentric portal reinforcement combined with bag grouting in steep curve shield tunnels according to claim 1, characterized in that: In step S4, when assembling the capping block, first overlap 2 / 3 of the ring width, push it radially upward, and then insert it longitudinally; after aligning the second segment with the previous ring segment and the first segment of this ring, first tighten the circumferential waterstop strip longitudinally, then tighten the longitudinal waterstop strip circumferentially, and finely adjust the alignment bolt holes; tighten the longitudinal and circumferential connecting bolts while assembling the segments; after the entire ring segment comes out of the shield tail, tighten all connecting bolts again; the gap between adjacent ring surfaces is ≤1mm, and the gap between adjacent blocks in the longitudinal joint is ≤1mm.

6. The method for stabilizing and controlling eccentric portal reinforcement combined with bag grouting in steep curve shield tunnels according to claim 1, characterized in that: In step S5, the grouting uses cement grout and water glass concentrate at a 1:1 ratio. The cement grout mix ratio is 1:1, and the water glass concentration is not less than 38. The grout is prepared in advance according to the above parameters to control the initial setting time of the two-component grout to be 25-35 seconds and the final setting time to be no more than 20 minutes. The grouting volume is controlled to be approximately 0.07 m³. 3 The entire process involves double-liquid grouting to achieve an effective umbrella-shaped opening with a diameter of 70-80cm and a thickness of 8-12cm for the attached bag.

7. The method for stabilizing and controlling eccentric portal reinforcement combined with bag grouting in steep curve shield tunnels according to claim 1, characterized in that: After the above steps are completed, the axial deviation of the tunnel segment behind the shield tail is checked regularly, and the measured value is compared with the previous measurement value. If the segment deviates outward after exiting the shield tail, the double liquid grout group is injected into the outer wall of the curve using the grouting holes on the segment to prevent the tunnel deviation from continuing to develop. At the same time, according to the magnitude of the deviation, the inner wall thickness of the curve is appropriately supplemented with secondary grout to prevent the inner soil from loosening and deforming, ensuring that the axial deviation is less than 20mm.

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