Shield tunnel portal ring beam construction method and shield tunnel portal ring beam structure

Abstract

The application discloses a shield tunnel portal ring beam construction method and a shield tunnel portal ring beam structure. After shield construction is completed, a short sleeve is reserved as a safety protection barrier during construction, grouting is carried out behind the short sleeve, the compactness is confirmed by nondestructive testing after grouting is completed, a steel sleeve end face is marked along the short sleeve in a closed safety space formed by the short sleeve, a static cutting mode is used to cut the short sleeve outside pipe piece, and the pipe piece is smoothly hoisted out, ring beam reinforcement binding is completed, the reinforcement is inserted into the remaining pipe piece after cutting and connected with a tunnel portal embedded steel ring and a main structure anchoring, a formwork trolley is installed as a ring beam inner form, side forms and outer forms are installed after fixation and sealing treatment is well done, and ring beam concrete is symmetrically poured in layers in the formwork system. In the construction process, the short sleeve is reserved as a closed safety barrier, the outside pipe piece is cut to release the ring beam construction space, and the risks of water and sand gushing and face instability caused by traditional sleeve dismounting are effectively avoided.

Description

Technical Field

[0001] This invention relates to the field of tunnel boring machine (TBM) construction technology, specifically to a method for constructing a tunnel portal ring beam and the structure of the tunnel portal ring beam. Background Technology

[0002] In subway, underground tunnel, and shield tunneling construction, the portal ring beam typically serves as a permanent connecting structure between the tunnel and the station or shaft, playing a crucial role in reinforcing the portal structure, providing permanent waterproofing, and transferring structural loads. During shield launching or receiving, the steel sleeve forms a closed pressure-bearing cavity, effectively isolating water and soil pressure and preventing sudden events such as face instability, water inrush, and sand inrush, providing a sealed protective space for the safe receiving of the shield. This steel sleeve sealing system is particularly important under complex geological conditions, serving as a safety barrier during shield construction and ensuring the safety of construction personnel and equipment in high-risk environments. In traditional construction processes, after the shield launch or receiving is completed, the construction unit must first remove the steel sleeve and initial support segments, and clean the working face at the portal before proceeding with ring beam construction operations such as reinforcement binding, formwork erection, and concrete pouring.

[0003] However, as the diameter of tunnel boring machines (TBMs) continues to increase, traditional construction techniques are revealing more and more safety risks and construction challenges. First, the removal of large-diameter steel sleeves is difficult, and the tunnel portal seal is prone to failure during construction, potentially leading to water inrush, sand inrush, or even face instability. This is particularly dangerous in high-water-pressure, water-rich soft soil layers, where even slight disturbance can damage the curtain sealing system, causing sudden water and soil inrush, ground subsidence, or even localized collapse. Second, the steel sleeves are heavy and bulky, making them prone to tipping and collisions that could cause injuries during hoisting in the confined space of the end shaft. Hot work operations also pose fire risks and the risk of poisoning from harmful gases. Furthermore, falling debris during removal can easily cause injuries from falling objects. These risks not only threaten construction safety but also complicate construction organization, increase costs, extend the construction period, and affect project efficiency and overall construction controllability. In addition, traditional methods of removing steel sleeves before constructing the ring beam can lead to exposed construction surfaces, discontinuous connections between the ring beam and the tunnel segments, or incomplete sealing, potentially causing problems for subsequent waterproofing and structural integrity. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention proposes a method for constructing a shield tunnel portal ring beam and a shield tunnel portal ring beam structure. During the construction process, a short sleeve is retained throughout as a closed safety barrier. The outer segments are cut to create space for the ring beam construction. Grouting is used to seal the gaps between the sleeve and the ground and the tunnel portal, thereby effectively avoiding the risks of water inrush, sand inrush, and tunnel face instability caused by traditional sleeve removal.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows: A method for constructing a shield tunnel portal ring beam includes the following steps: S1. After the shield tunneling is completed, the short sleeve is retained as a safety protection barrier during the construction period. S2, Grouting is performed behind the short sleeve to fill the gaps between the pipe segments and the short sleeve, the stratum and the portal structure, forming a fully enclosed water-proof curtain. A sealing steel plate is installed at the outer opening of the short sleeve to prevent the grout from overflowing. S3. After grouting is completed, non-destructive testing is used to confirm that the grouting density meets the design requirements. For areas that are not dense, additional grouting is performed, and the grouting is retested until the entire section meets the standard. S4. Within the enclosed safety space formed by the short sleeve, lay out the line along the end face of the short sleeve, and cut the outer tube segment of the short sleeve using a static cutting method. Cut in a symmetrical segmented order from top to bottom, and smoothly lift out the cut tube segment. S5, steel bars are tied inside and outside the short sleeve so that the steel cage of the ring beam completely wraps the short sleeve, and the steel bars are inserted into the remaining segments after cutting. At the same time, they are anchored to the pre-embedded steel ring of the tunnel portal and the main structure to ensure that the ring beam and the segments form a circumferential integral structure. S6. Install the template trolley as the inner mold of the ring beam. After fixing, install the side mold and outer mold of the ring beam and seal the joints. S7. Within the formwork system, the ring beam concrete is poured symmetrically in layers, vibrated to compact, and after curing, the formwork is removed to complete the ring beam construction.

[0006] Preferably, the grouting sequence in step S2 is from bottom to top and symmetrical and uniform grouting to avoid misalignment of the short sleeve.

[0007] Preferably, the grouting material in step S2 is a cement and water glass dual-liquid grout, and the grouting pressure is controlled at 0.3-0.5 MPa.

[0008] Preferably, the non-destructive testing in step S3 uses ground-penetrating radar to perform 100% full-coverage non-destructive testing, and the density needs to reach more than 95%.

[0009] Preferably, the static cutting method in step S4 uses diamond rope, and the leakage of the tunnel entrance is monitored throughout the process. If leakage occurs, work is stopped immediately, and grouting is performed to plug the leak before work resumes.

[0010] Preferably, in step S6, the template trolley is first precisely positioned, and the deviation between the center of the trolley and the center axis of the tunnel boring machine is controlled within 5mm. After fixing, it serves as the inner mold of the ring beam.

[0011] Preferably, in step S6, the side mold and outer mold are made of customized steel templates, and sealing strips are pasted at the joints of the templates. The overlaps with the short sleeve and the pre-embedded steel ring of the opening are also sealed to prevent grout leakage during concrete pouring.

[0012] On the other hand, the present invention also discloses a shield tunnel portal ring beam structure, constructed based on the above-mentioned shield tunnel portal ring beam construction method, comprising: Short sleeves are arranged along the central axis of the tunnel portal to form a closed safety barrier during construction and are retained without being removed. The ring beam is arranged around the short sleeve and is anchored to the pre-embedded steel ring of the tunnel portal and the main structure to form a circumferential integral structure that bears the load of the tunnel portal. The remaining portion of the cut tunnel segment is into which the ring beam reinforcement is inserted, and after pouring, it forms a circumferential integral structure with the ring beam. A sealing steel plate is placed at the opening on the outside of the short sleeve to prevent grout from overflowing.

[0013] Preferably, the short sleeve is a steel sleeve with the same diameter as the steel ring of the portal. It is composed of right-angled trapezoidal blocks, consisting of 9 blocks, each at 40°.

[0014] Preferably, the short sleeve is further provided with a curtain and a folding plate, and the sealing steel plate is welded between the short sleeve and the segment steel plate.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: The shield tunnel portal ring beam construction method of this invention retains short sleeves as a closed safety barrier throughout the construction process, avoiding safety risks such as water inrush, sand inrush, and tunnel face instability that may be caused by traditional sleeve removal operations, thus fundamentally improving construction safety. By grouting and sealing between the short sleeves and the strata, the tunnel portal, and the tunnel segments, and using sealing steel plates to prevent grout overflow, the safety of the ring beam construction space and the stability of the construction environment are ensured. Cutting the outer tunnel segments of the sleeves to free up the ring beam construction space, and connecting the ring beam reinforcement with the remaining tunnel segments to form a circumferential integrated structure, thereby ensuring the integrity of the ring beam and tunnel segments and the structural load-bearing capacity. Using a formwork trolley in conjunction with customized side and outer molds, the ring beam concrete is poured in layers symmetrically and vibrated to achieve compaction, improving construction efficiency and forming accuracy. In addition, static wire saw cutting is used to replace open flame or mechanical crushing operations, reducing construction noise, dust emissions, and construction waste, and improving the level of green construction. Through the above technical solution, the present invention not only effectively avoids the safety, construction efficiency and environmental problems of traditional processes, but also simplifies the construction process, reduces construction costs, and achieves safe, environmentally friendly and efficient shield tunnel portal ring beam construction. Attached Figure Description

[0016] Figure 1 This is a schematic flowchart of the shield tunnel portal ring beam construction method according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the shield tunnel portal ring beam structure according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the segment cutting of the shield tunnel portal ring beam structure according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the structure of the short sleeve according to an embodiment of the present invention; Figure 5 This is a schematic diagram of the sealing steel plate according to an embodiment of the present invention.

[0017] Reference numerals: 1-Short sleeve; 2-Ring beam; 3-Tunnel segment; 4-Sealing steel plate; 5-Portal embedded steel ring; 6-Curtain fabric; 7-Folding plate; 8-Tunnel segment steel plate. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention belong to the present invention.

[0019] Furthermore, the described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. Numerous specific details are provided in the following description to give a thorough understanding of embodiments of this application. However, those skilled in the art will recognize that the technical solutions of this application can be practiced without one or more of the specific details, or other methods, components, apparatuses, steps, etc., can be employed. In other instances, well-known methods, apparatuses, implementations, or operations are not shown or described in detail to avoid obscuring various aspects of this application.

[0020] Please see Figure 1-5 The present invention provides a method for constructing a shield tunnel portal ring beam, comprising the following steps: S1. After the shield tunneling is completed, short sleeve 1 is retained as a safety protection barrier during construction. Short sleeve 1 is arranged along the central axis of the shield tunnel entrance, providing a closed safety space throughout the entire ring beam construction process, isolating the stratum water and soil pressure, preventing water inrush, sand inrush and face instability, and providing a safe operating environment for construction personnel and equipment. S2, grouting is performed behind the short sleeve 1 to fill the gaps between the segment 3, the short sleeve 1, the stratum, and the portal structure, forming a fully enclosed water-proof curtain. A sealing steel plate 4 is installed at the outer opening of the short sleeve 1 to prevent the grout from overflowing. The grouting material can be cement grout or a two-component grout composed of cement and water glass. The sequence, pressure, and density are controlled through a closed loop to ensure that the grouting fills all circumferential gaps evenly, while avoiding the impact of sleeve 1 misalignment or grout leakage on construction safety. S3. After grouting is completed, non-destructive testing methods such as ground-penetrating radar are used to confirm that the grouting density meets the design requirements. For areas that are not dense, additional grouting is carried out, and the grouting is re-inspected until the entire section meets the standard, forming a reliable water-proof curtain and providing stable and safe construction conditions for subsequent ring beam construction. S4. Within the enclosed safety space formed by the short sleeve 1, lay out a line along the end face of the short sleeve 1 and cut the outer segment 3 of the short sleeve 1 using a diamond rope static cutting method. Cut the segment 3 in a symmetrical segmentation sequence from top to bottom and lift it out smoothly. This operation can free up the construction space of the ring beam 2 and avoid vibration and impact affecting the stability of the short sleeve 1 and the surrounding strata. S5, steel bars are tied inside and outside the short sleeve 1 so that the steel cage of the ring beam 2 completely wraps the short sleeve 1, and the steel bars are inserted into the remaining pipe segment 3 after cutting. At the same time, they are anchored to the pre-embedded steel ring 5 of the tunnel portal and the main structure to ensure that the ring beam 2 and the pipe segment 3 form a circumferential integral structure, thereby improving the overall load-bearing capacity and structural stability of the ring beam 2 after construction. S6. Install the template trolley as the inner formwork of ring beam 2. After fixing, install the side formwork and outer formwork of ring beam 2. Apply sealing strips to the template joints and seal the overlap with the short sleeve 1 and the pre-embedded steel ring 5 of the opening to ensure that no grout leakage occurs during the concrete pouring of ring beam 2. At the same time, control the construction center position and horizontal accuracy of ring beam 2 through the template trolley. S7. Within the formwork system, the concrete for ring beam 2 is poured in layers symmetrically, vibrated and compacted, and after curing, the formwork is removed according to the construction sequence to complete the construction of ring beam 2. At the same time, ring beam 2 and the remaining cut segments 3 form a circumferential integrated structure to ensure the integrity and load-bearing performance of ring beam 2, segments 3 and the portal structure.

[0021] Furthermore, the grouting sequence in step S2 is from bottom to top, symmetrical and uniform, to avoid misalignment of the short sleeve 1, ensure uniform filling of voids with grout, form a stable, fully enclosed waterproof curtain, and reduce possible minor displacements or localized uneven pressure on the short sleeve 1 during construction, thereby maintaining construction safety and the positioning accuracy of the ring beam 2. Specifically, the grouting material is a two-component grout composed of cement and water glass, and the grouting pressure is controlled at 0.3-0.5 MPa to ensure grout density while avoiding excessive grouting pressure that could cause deformation of the short sleeve 1 or surrounding strata. Simultaneously, it ensures that the sealing steel plate 4 effectively prevents grout overflow, forming a reliable seepage barrier.

[0022] Furthermore, in step S3, non-destructive testing is performed using ground-penetrating radar to conduct 100% full coverage testing of the grouting area. The density must reach more than 95%. For areas that are not dense, supplementary grouting is carried out. Cement grout with a water-cement ratio of 0.45:1 can be used for targeted supplementary grouting, and re-inspection is carried out until the entire section meets the standard, forming a closed-loop control to ensure that the grouting layer between the short sleeve 1 and the segment 3 and the portal structure is completely dense, providing a stable and reliable foundation for the construction of the ring beam 2.

[0023] In this embodiment, the segment to be cut is the 0-ring segment, and the segment immediately adjacent to its inner side is the +1-ring segment. The static cutting method in step S4 uses diamond wire to cut the outer segment 3 of the short sleeve 1. After the cutting is completed, a crane is used to lift it out smoothly, and the leakage of the tunnel entrance is monitored throughout the process. If leakage occurs, work is stopped immediately, and grouting is performed to plug the leak before work resumes.

[0024] In this embodiment, step S6 first completes the precise positioning of the template trolley, controlling the deviation between the trolley center and the shield machine's central axis within 5mm. After fixing, it serves as the inner formwork for the ring beam 2, ensuring that the construction axis of the ring beam 2 during concrete pouring is consistent with the central axis of the shield tunnel portal, thus improving construction accuracy and the continuity of the circumferential structure. Custom-made steel templates are used for the side and outer forms. Sealing strips are applied to the template joints, and the overlaps with the short sleeve 1 and the pre-embedded steel ring 5 at the tunnel portal are properly sealed to prevent grout leakage during concrete pouring, ensuring the compactness of the ring beam 2 concrete. The ring beam 2 and the remaining segments 3 after cutting form a circumferential integral structure, while maintaining the safety and stability of the construction space. After the template installation is completed, the ring beam 2 template system is inspected, including checking the verticality, flatness, and reinforcement strength of the inner, side, and outer forms, ensuring that the template trolley and custom steel templates are firm, stable, and meet construction requirements. Only after passing the inspection can the next construction process begin.

[0025] Please see Figure 2-5 Another embodiment of the present invention discloses a shield tunnel portal ring beam structure, constructed based on the above-described shield tunnel portal ring beam construction method, comprising: a short sleeve 1, arranged along the central axis of the shield tunnel portal, forming a closed safety barrier during construction and retained without removal; the short sleeve 1 not only forms a closed safety space during construction, isolating the ground water and soil pressure and providing a safe operating environment for construction personnel and equipment, but also maintains structural integrity to support the construction of the ring beam 2; the ring beam 2, arranged around the short sleeve 1, and anchored to the pre-embedded steel ring 5 of the portal and the main structure, forming a circumferential integral structure that bears the load of the portal; the ring beam 2 and the short sleeve 1... After being anchored and connected to the pre-embedded steel ring 5 in the tunnel portal and the main structure, an integrated load-bearing system is formed in the circumferential direction, improving the load-bearing capacity and structural stability of the tunnel portal. The remaining part of the cut segment 3 is into which the reinforcing bars of the ring beam 2 are inserted. After pouring, it forms an integrated circumferential structure with the ring beam 2. The remaining part of the cut segment 3 provides anchoring and insertion space for the reinforcing bars of the ring beam 2, ensuring that the cast ring beam 2 and segment 3 form a continuous, integrated circumferential structure, realizing the integrity of the structure and the continuity of the load-bearing capacity. The sealing steel plate 4 is located at the opening on the outside of the short sleeve 1 to prevent the grout from overflowing, ensure the stability of the construction space of the ring beam 2, and maintain the density and integrity of the grouting layer.

[0026] In this embodiment, the short sleeve 1 is a steel sleeve with the same diameter as the pre-embedded steel ring 5 of the tunnel portal. It is composed of right-angled trapezoidal segmented components, divided into 9 blocks, each at 40°. This segmented design facilitates on-site transportation, installation, and fixing, while ensuring that the overall circumferential shape of the short sleeve 1 precisely matches the shield tunnel portal structure, providing a stable enclosed space during construction. Specifically, the diameter of the short sleeve 1 at the tunnel entrance can be designed to be 14.9m, with the cutterhead 100mm from the working face. The length of the short sleeve 1 at the 12 o'clock position is 700mm, and the length at the 6 o'clock position is 1000mm, to meet the space requirements for shield tunneling and ring beam 2 construction. The minimum included angle between the segment 3 and the short sleeve 1 is 48.14° to ensure unobstructed space for grouting and ring beam 2 construction, while also ensuring the accuracy of structural connections. The bolt holes on the short sleeve 1 are spaced at 2° intervals, with the height of the bolt holes controlled at the front and rear. The stiffening plates are spaced at 4° intervals, with the length of the stiffening plates adjusted at different positions. M24 bolt holes are reserved at 15cm intervals between the stiffening plates to ensure the stability and structural strength of the short sleeve 1 assembly.

[0027] Furthermore, the short sleeve 1 is also equipped with a curtain 6 and a folding plate 7. The curtain 6 and the folding plate 7 together form a flexible sealing layer. Two folding plates 7 can be set. At the same time, the sealing steel plate 4 is welded between the short sleeve 1 and the segment steel plate 8, which can effectively prevent grout overflow during the grouting process, ensure the compactness and stability of the grouting layer around the short sleeve 1, and maintain the integrity and circumferential continuity of the structure after the ring beam 2 is constructed. Specifically, the length of the curtain 6 can be designed to be 650mm, the length of the folding plate 7 can be designed to be 600mm, and the sealing steel plate 4 can be designed to be 5mm thick, with a total of 36 pieces, a short side length of 1218mm, a long side length of 1325mm, and a plate length of 610mm.

[0028] This embodiment employs a construction process for the shield tunnel portal ring beam 2 without dismantling the short sleeve 1. Compared to the traditional method of "dismantling the steel sleeve first and then constructing the ring beam," it offers significant advantages in terms of cost, safety, environmental protection, and construction period. Taking a shield tunneling project as an example, in terms of construction period, by retaining the short sleeve 1 as a safety barrier during construction, the pre-construction procedures such as dismantling the steel sleeve, cleaning the portal working face, and handling leakage are eliminated in the traditional process. The total construction period for a single tunnel ring beam 2 is shortened from the conventional 25-30 days to 15-20 days, and the effective construction period for a single working face is shortened by approximately 30%. At the same time, the ineffective construction period for handling leakage after dismantling the sleeve 1 is completely avoided. In terms of construction cost, a single tunnel can directly save approximately 80,000 to 150,000 yuan in costs for large-scale hoisting, labor, and machinery rental required for dismantling the steel sleeve 1, resulting in a comprehensive reduction in construction cost of 18% to 28%. It also avoids the additional risk costs associated with emergency response to water and sand inrushes caused by dismantling the short sleeve 1, which typically amount to hundreds of thousands to millions of yuan. In terms of safety, the short sleeve 1 is retained throughout the entire process as a closed water and soil protection barrier, reducing the risk of exposure of the tunnel portal to zero. This completely avoids major safety accidents such as water inrush, sand inrush, tunnel face instability, and ground collapse that are common during the sleeve removal stage in traditional processes, reducing special investment in safety protection by approximately 65%. In terms of environmental protection, static wire saw cutting of the outer segment 3 of the short sleeve 1 is used to replace traditional open flame cutting or mechanical crushing operations. This reduces construction noise by approximately 40 dB, dust and welding fume emissions by approximately 85%, and construction waste generation by approximately 60%, fully meeting green construction standards and achieving the construction goals of safety, efficiency, and environmental protection.

[0029] In summary, this invention discloses a method for constructing a shield tunnel portal ring beam and a shield tunnel portal ring beam structure. After shield tunneling is completed, a short sleeve 1 is retained as a safety barrier during construction. Grouting is performed between the short sleeve 1 and the tunnel segments 3, the ground, and the portal structure, and sealing steel plates 4 are installed to prevent grout overflow, forming a fully enclosed water-proof curtain. Subsequently, the outer tunnel segments 3 are cut within the enclosed safety space formed by the short sleeve 1, the reinforcing steel of the ring beam 2 is tied and inserted into the remaining tunnel segments 3, and simultaneously anchored to the pre-embedded steel ring 5 of the portal and the main structure. A template trolley is installed as the inner mold of the ring beam 2, and after fixing, the side molds and outer molds are installed. After sealing, the concrete of the ring beam 2 is poured symmetrically in layers, vibrated to compact, and cured before demolding, ultimately forming a circumferential integrated structure of the ring beam 2, tunnel segments 3, and portal structure. The construction method of this invention retains the short sleeve 1 as a safety barrier throughout the entire process, effectively avoiding the risks of water inrush, sand inrush, and face instability caused by sleeve removal operations. Simultaneously, it ensures grout density, the structural integrity of the ring beam 2, and construction accuracy, reducing construction costs and safety protection investment, minimizing construction noise and waste, and meeting green construction requirements. This technical solution provides a safe, efficient, environmentally friendly, and controllable construction method for shield tunnel portal ring beam construction, offering reliable reference and promotional value for the construction of portal ring beams and the construction of vertical shaft and station interface structures in large-scale shield tunneling projects.

[0030] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Under the concept of the present invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of the present invention as described above. For the sake of brevity, they are not provided in detail. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for constructing a shield tunnel portal ring beam, characterized in that, Includes the following steps: S1, After the shield tunneling is completed, the short sleeve (1) is retained as a safety protection barrier during the construction period; S2, Grouting is performed behind the short sleeve (1) to fill the gap between the pipe segment (3) and the short sleeve (1), the stratum and the portal structure, forming a fully enclosed water-proof curtain. A sealing steel plate (4) is installed at the outer opening of the short sleeve (1) to prevent the grout from overflowing. S3. After grouting is completed, non-destructive testing is used to confirm that the grouting density meets the design requirements. For areas that are not dense, additional grouting is performed, and the grouting is retested until the entire section meets the standard. S4. In the closed safety space formed by the short sleeve (1), lay out the line along the end face of the short sleeve (1), and cut the outer tube segment (3) of the short sleeve (1) using the static cutting method. Cut in the order of first the upper part and then the lower part, and symmetrical segmentation, and lift out the cut tube segment smoothly. S5, tie the reinforcing bars inside and outside the short sleeve (1) so that the reinforcing cage of the ring beam (2) completely wraps the short sleeve (1), and insert the reinforcing bars into the remaining pipe segments after cutting, and at the same time anchor them to the pre-embedded steel ring (5) of the tunnel entrance and the main structure to ensure that the ring beam (2) and the pipe segments (3) form a circumferential integral structure. S6, install the template trolley as the inner mold of the ring beam (2), and after fixing, install the side mold and outer mold of the ring beam (2), and seal the joints; S7, pour the concrete of the ring beam (2) in layers symmetrically within the template system, vibrate and compact it, remove the formwork after curing, and complete the ring beam construction.

2. The method for constructing the shield tunnel portal ring beam according to claim 1, characterized in that, The grouting sequence in step S2 is from bottom to top and symmetrical and uniform grouting to avoid misalignment of the short sleeve (1).

3. The method for constructing the shield tunnel portal ring beam according to claim 2, characterized in that, The grouting material in step S2 is a cement and water glass dual-liquid grout, and the grouting pressure is controlled at 0.3-0.5 MPa.

4. The method for constructing the shield tunnel portal ring beam according to claim 1, characterized in that, The non-destructive testing in step S3 uses ground-penetrating radar to perform 100% full-coverage non-destructive testing, and the density needs to reach more than 95%.

5. The method for constructing the shield tunnel portal ring beam according to claim 1, characterized in that, The static cutting method in step S4 uses diamond wire, and the leakage of the tunnel entrance is monitored throughout the process. If leakage occurs, work is stopped immediately, and grouting is carried out to plug the leak before work resumes.

6. The method for constructing the shield tunnel portal ring beam according to claim 1, characterized in that, In step S6, the template trolley is first positioned precisely. The deviation between the center of the trolley and the center axis of the tunnel boring machine is controlled within 5mm. After fixing, it serves as the inner mold of the ring beam (2).

7. The method for constructing the shield tunnel portal ring beam according to claim 6, characterized in that, In step S6, the side mold and outer mold are made of customized steel templates. Sealing strips are pasted at the joints of the templates, and the overlap with the short sleeve (1) and the pre-embedded steel ring (5) of the opening is sealed to prevent grout leakage during concrete pouring.

8. A shield tunnel portal ring beam structure, constructed based on the shield tunnel portal ring beam construction method according to any one of claims 1 to 7, characterized in that, include: Short sleeves (1) are arranged along the central axis of the shield tunnel entrance to form a closed safety barrier during construction and are retained without being removed; The ring beam (2) is arranged around the short sleeve (1) and is anchored to the pre-embedded steel ring (5) of the tunnel portal and the main structure to form a circumferential integral structure that bears the load of the tunnel portal; The remaining part of the cut segment (3) is inserted into the ring beam reinforcement, and after pouring, it forms a circumferential integral structure with the ring beam (2); The sealing steel plate (4) is located at the opening on the outside of the short sleeve (1) to prevent the grout from overflowing.

9. The shield tunnel portal ring beam structure according to claim 8, characterized in that, The short sleeve (1) is a steel sleeve with the same diameter as the steel ring of the tunnel entrance. It is composed of right-angled trapezoidal blocks, consisting of 9 blocks, each at 40°.

10. The shield tunnel portal ring beam structure according to claim 9, characterized in that, The short sleeve (1) is also provided with a curtain (6) and a folding plate (7), and the sealing steel plate (4) is welded between the short sleeve (1) and the segment steel plate (8).

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