Two-layer prestressed large-diameter shield tunnel structure and construction method

Abstract

The structure includes a segment ring and a multilayer prestressing system, the segment ring forming an annular structure with multiple joined segment pieces, the segment pieces including segment standard blocks and segment tension blocks, the segment tension blocks appear in pairs and are distributed on both sides of the segment ring, and the tensioning ends of the prestressing system are provided on the same or different segment tension blocks, the outer layer prestressing system is positioned on the outer surface of adjacent segment rings to resist the effect of negative bending moment, and the inner layer prestressing system is positioned on the inner surface of adjacent segment rings. [Effects] By effectively reducing the thickness of the segments, decreasing the amount of reinforcement required, and even adopting a reinforced design, the overall rigidity, crack load, deformation resistance capacity, and ultimate bearing capacity of the tunnel structure are greatly improved, avoiding problems such as leakage, deformation, and cracking, reducing operation and maintenance costs, and extending the service life.

Description

[Technical Field]

[0001] The present invention relates to the field of shield tunneling technology, and more particularly to a double-layer prestressed large-diameter shield tunnel structure and construction method. [Background technology]

[0002] Shield tunneling is widely used for tunnel structures such as railways, roads, rail transit, water conservancy, and power plants due to its advantages, including low construction costs, favorable construction environments, and safe and highly efficient construction. As underground construction continues to develop and the scenarios for shield tunneling become more diverse and complex, and especially as cross-sea tunneling projects continue to increase, shield tunneling is tending to evolve in terms of larger cross-sections, high groundwater heads, and long excavation distances.

[0003] While China has achieved some success in large-diameter shield tunnel construction technology, problems inherent in large-diameter shield tunnel structures are gradually emerging as construction areas expand and construction environments become increasingly complex. On the one hand, shield tunnel structures must withstand large soil and water loads in geological formations with thick overburden and high water head, and different parts of the structure experience different types of loads. In particular, the segment structure receives positive bending moments at the top and bottom, and negative bending moments on both sides, causing the segment thickness of the segment structure to constantly increase and the amount of reinforcement to gradually increase, which does not conform to the green and low-carbon development concept. On the other hand, during the operational phase, tunnels are subjected not only to vehicle vibration loads within the tunnel but also to eccentric loads from nearby construction in the surrounding area, which easily causes cracking, large deformation, and settlement of the segment structure, seriously affecting the durability and safety of the tunnel structure. Furthermore, after shield tunnel structures reach their design service life, there are no rational and effective treatment measures, requiring extensive manpower, financial resources, and time to modify the tunnel structure, which poses a major challenge to the continued operation of rail transport.

[0004] CN108729346A discloses a circumferential prestressed conduit structure and a method for manufacturing it, the circumferential prestressed conduit structure comprising two or more precast concrete arc-shaped segments joined to one another, two adjacent precast concrete arc-shaped segments connected by expansive concrete, a pre-groove extending circumferentially on the outer surface of the precast concrete arc-shaped segments, a tenon and a mortise provided at both circumferential ends of the precast concrete arc-shaped segments, the circumferential prestressed conduit structure further comprising an annular steel wire provided in the pre-groove and a push-up device for adjusting the spacing between two adjacent precast concrete arc-shaped segments.

[0005] This patent describes a method for connecting two adjacent arc-shaped precast concrete segments using expansive concrete, thereby integrating the expansive concrete and the precast concrete arc-shaped segments into a single unit, improving the water infiltration resistance of the pipeline. The expansive (self-stressing) concrete used in high-pressure grouting has characteristics such as strong penetration resistance, rapid initial hardening, high strength in the later stages, and excellent sulfate resistance. However, the construction process of this patent involves the precise joining of multiple precast concrete arc-shaped segments and adjustment of the extrusion device. To avoid problems such as low structural rigidity, weak deformation resistance, excessive deformation, cracking, water leakage, and bolt corrosion, the construction requires high complexity and precision. Furthermore, the reliance of prestressing on the extrusion device and the expansive properties of the expansive concrete may indirectly affect the efficiency and reliability of prestressing.

[0006] Furthermore, while there are differences in the understanding of those skilled in the art, the applicant studied many documents and patents when drafting the present invention, but due to the limitations of the specification, not all details and contents can be listed in detail. Therefore, the present invention does not lack the features of these prior art; on the contrary, the present invention possesses all the features of the prior art, and the applicant reserves the right to add relevant prior art to the background art. [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] In response to the shortcomings of conventional technology, the present invention provides a two-layer prestressed large-diameter shield tunnel structure. The present invention effectively reduces the thickness of the segments, decreases the amount of reinforcement, and allows for the adoption of an unreinforced design. Furthermore, it significantly improves the overall rigidity, crack load, deformation resistance capacity, and ultimate bearing capacity of the tunnel structure, thereby avoiding problems such as leakage, deformation, and cracking, reducing operation and maintenance costs, and extending the service life. [Means for solving the problem]

[0008] The present invention relates to a double-layer prestressed large-diameter shield tunnel structure, comprising a segment ring and a multi-layer prestressing system, wherein the segment ring constitutes an annular structure with a plurality of segment pieces joined together, the segment pieces include segment standard blocks and segment tension blocks, the segment tension blocks appear in pairs and are distributed on both sides of the segment ring, the prestressing system comprises an outer layer prestressing system and an inner layer prestressing system connecting the plurality of segment standard blocks and the plurality of segment tension blocks, and the tensioning ends of the prestressing systems are provided on the same or different segment tension blocks, the outer layer prestressing system is arranged on the outer surface of adjacent segment rings to resist deformation or opening on the outside of the segment pieces and their joints, and the inner layer prestressing system is arranged on the inner surface of adjacent segment rings to resist deformation or opening on the inside of the segment pieces and their joints.

[0009] This invention involves installing two layers of circumferential prestress on the outside and inside of the segment structure, thereby subjecting the entire cross-section of the segment structure to pressure, allowing the concrete to fully exert its pressure-bearing capacity, resulting in a more rational load distribution for the structure. Furthermore, it effectively reduces the thickness of the segments, decreases the amount of reinforcing steel used, and, in combination with steel fiber concrete technology, can achieve a reinforced concrete-free design. The inner prestress of this invention can resist positive bending loads in the tunnel structure, and the outer prestress can resist negative bending loads in the tunnel structure. This significantly improves the bending moment and crack load at the segment joint opening, strengthens the overall rigidity, deformation resistance, and ultimate bearing capacity of the segment structure, effectively avoids problems such as leakage, deformation, and cracking, and reduces the operation and maintenance costs of the tunnel structure in the future.

[0010] In a preferred embodiment, a tunnel structure is pre-embedded inside both the segment standard block and the segment tension block, and the tunnel structure includes a plurality of groups of outer tunnels and a plurality of groups of inner tunnels arranged symmetrically along the width direction of the segment piece, wherein the segment piece forms an internal two-layer tunnel structure that is staggered, with the outer tunnels positioned relatively outward and the inner tunnels positioned relatively inward.

[0011] According to a preferred embodiment, when the outer layer tunnel and the inner layer tunnel are the same, and the outer layer tension groove and the inner layer tension end are provided on the inner arc surface of the segment tension block, the shield tunnel structure includes two segment tension blocks of the same type and arranged symmetrically in one group. When the outer layer tunnel and the inner layer tunnel are different, and the outer layer tension groove and the inner layer tension end are provided on the inner arc surface of the segment tension block, the shield tunnel structure includes a total of four segment tension blocks in two groups, each group of the same type and arranged symmetrically. The inner layer tension end can be divided into an inner tooth block groove and an inner layer tension groove based on two different configurations of the segment tension block, where the segment tension block can be divided into a tooth block type tension block and a planar type tension block depending on the tensioning method.

[0012] According to a preferred embodiment, tooth blocks are arranged on the inner curved surface of a tooth block tensioning block, and the outer tension groove and inner tooth block groove are paired and arranged on both sides of the tooth block. The outer and inner tunnels pass through the tensioning surfaces on both sides of the tooth block in a crossing manner via large curvature tunnel steps and straight tunnel steps, and anchor plates are attached to the tensioning surfaces. The two-layer tunnel structure provides additional support, increasing the bending and torsional rigidity of the segment, thereby improving the overall structural stability during the tunnel construction process. The staggered tunnel structure can more effectively distribute and receive stress from external loads, reducing localized stress concentration, and thereby optimizing the mechanical performance of the segment. The design of the inner and outer tunnels allows for a wider variety of reinforcement arrangements, strengthens the connection strength between segments, and helps improve the overall integrity and sealing of the tunnel ring. By pre-creating tunnels inside the segment pieces, reinforcement can be placed and tensioned more quickly during construction, improving construction efficiency and reducing on-site construction time.

[0013] According to a preferred embodiment, the inner curved surface of the planar tensioning block has no protrusions, the outer tensioning grooves are arranged in pairs on both sides of the segment piece, the inner tensioning groove is a recessed groove arranged on the inner curved surface, the inner tunnel passes directly from the tensioning surface through large curvature tunnel steps and straight tunnel steps, and no anchor plate is provided on the tensioning surface. The outer tensioning grooves are arranged symmetrically on both sides of the segment piece, which helps to achieve a uniform distribution of prestress and improves the stability and support capacity of the segment structure. The symmetrical arrangement further helps to simplify the tensioning work, as tensioning operations on both sides can be performed simultaneously, thereby improving the efficiency and speed of construction. The inner tunnel is designed to pass through large curvature tunnel steps and straight tunnel steps, and such a design can optimize the path of the prestress cable, reduce losses in the prestress transmission process, and facilitate the routing and tensioning of the prestress cable. The large curvature tunnel helps to adapt to the geometric shape of the segment structure, and the straight tunnel helps to improve routing efficiency. Finally, the design that does not include anchor plates on the tensioning surface reduces the structural complexity of the tensioning block and lowers material and construction costs.

[0014] According to a preferred embodiment, the outer layer prestressing system is formed such that a prestressing cable enters from one side of the outer layer tensioning groove, circles the outer layer tunnel, and then passes through the other side of the outer layer tensioning groove, after which both ends of the prestressing cable are fixed to general anchor plates located on the tensioning surface to perform tensioning. By circling the tunnel, the prestressing cable can uniformly transmit prestress along the width direction of the segment, which helps to enhance the overall rigidity and crack resistance of the segment and resist the negative bending moment effect due to external loads. The uniform distribution of prestress helps to maintain the stability of the segment structure, and in large-diameter shield tunnels in particular, such a uniform prestress distribution can reduce structural deformation due to unevenness of geological pressure.

[0015] According to a preferred embodiment, an inner layer prestressing system using a planar tensioning block is formed such that one end of a prestress cable is fixed to the outer ring of a floating anchor placed in an inner layer tensioning groove, the prestress cable enters from one end of the inner layer tensioning groove, circles the inner layer borehole, passes through the other end of the inner layer tensioning groove, is fixed to the inner ring of the floating anchor, and is tensioned by a deflector. The use of a floating anchor allows for constant displacement of the prestress cable during the tensioning process, which helps reduce localized stress concentration due to tensioning force and can also accommodate minute deformations that may occur in the segment during construction and use.

[0016] In a preferred embodiment, the segment standard block and the segment tension block can be positioned and assembled using a positioning rod or a mortise and tenon joint as a connecting member. When a positioning rod is used as a connecting member, both ends of the segment piece are provided with elongated positioning grooves and multiple insertion grooves on the longitudinal joint surfaces, a hollow positioning rod is placed in the positioning groove and fixed in the insertion groove, and adjacent segment pieces are positioned and assembled by the positioning rod in the positioning groove. When a mortise and tenon joint is used as a connecting member, multiple convex pins are provided on the longitudinal joint surface of one end of the segment piece, and multiple recessed grooves are provided on the longitudinal joint surface of the other end, and adjacent segments are positioned and assembled by the convex pins and recessed grooves.

[0017] According to a preferred embodiment, the segment ring can be cast using steel fiber concrete with no internal reinforcement, and the prestressed cable can be selected from stranded wires made of fibrous materials with a tensile strength greater than 2000 MPa, including steel stranded wire and carbon fiber stranded wire, depending on the geological conditions and type of construction. The selection of prestressed cable can be flexibly adjusted according to different geological conditions and types of construction, ensuring the adaptability and economy of the structural design. For example, non-adhesive steel stranded wire is used when replacement or maintenance is required, and carbon fiber stranded wire is used in highly corrosive environments due to its excellent corrosion resistance. The combined use of steel fiber concrete and high-strength prestressed cable enables the unreinforced design of the segment ring, which is not achievable with conventional reinforced concrete structures, and helps to promote innovation and progress in structural design.

[0018] The present invention further relates to a construction method for a two-layer prestressed large-diameter shield tunnel structure, and the said method is The steps include placing two precast segment tension blocks on both sides of the tunnel structure and placing segment standard blocks in other parts of the tunnel structure, Using a wire passing machine, pass multiple prestressed cables from the tension groove to multiple outer layer pore channels and multiple inner layer pore channels on the outside or inside, fix them to a general anchor plate or a floating anchor, and reserve half of the pore channels so that the prestressed cables do not pass through. Using a tensioning device, cooperate with a deflector to tension. When tensioning, tension the outer layer pore channels and the inner layer pore channels simultaneously, or first tension the outer layer pore channels, and then tension the inner layer pore channels. After the tensioning is completed, grout the pore channels that adopt bonded steel strands, and seal the pore channels that adopt non-bonded steel strands and the reserved pore channels that do not pass through the wire. Sealing the anchor with concrete for all tension grooves.

Effect of the Invention

[0019] The two-layer prestress of the present invention can keep the total life cycle of the tunnel structure in a high axial force state. After the surrounding external disturbance load recovers, it can restore the deformation of the tunnel structure to the initial state and promote the closure of the open cracks. Also, combined with the technology of re-passing the wire through the reserved pore channels or cable replacement, it can reduce the reinforcement, improve the durability and safety of the tunnel structure, and extend the service life of the tunnel structure.

Brief Description of the Drawings

[0020] [Figure 1] It is Example 1 of the front view of the two-layer prestressed large-diameter shield tunnel structure provided by the present invention. [Figure 2] It is Example 2 of the front view of the two-layer prestressed large-diameter shield tunnel structure provided by the present invention. [Figure 3] It is Example 3 of the front view of the two-layer prestressed large-diameter shield tunnel structure provided by the present invention. [Figure 4] It is the plan view of the segment standard block of the first type of pore channel arrangement provided by the present invention. [Figure 5] It is the side view of the segment standard block of the first type of pore channel arrangement provided by the present invention. [Figure 6]This is a plan view of a segment standard block of the second type of hole arrangement provided in the present invention. [Figure 7] This is a side view of a segment standard block of the second type of tunnel arrangement provided in the present invention. [Figure 8] This is a plan view of one type of tension groove installation means for a tooth block type tension block provided in the present invention. [Figure 9] This is a plan view of one type of tension groove installation means for a planar tension block provided in the present invention. [Figure 10] This is a plan view of the second type of tension groove installation means for the tooth block type tension block provided in the present invention. [Figure 11] This is a plan view of the second type of tension groove installation means for a planar tension block provided in the present invention. [Figure 12] This is a schematic diagram of the structure of cross-section AA of the tooth block type tension block provided in the present invention. [Figure 13] This is a schematic diagram of the cross-sectional structure of the tooth block tension block BB provided in the present invention. [Figure 14] This is a schematic diagram of the structure of cross-section AA of the planar tension block provided in the present invention. [Figure 15] This is a schematic diagram of the cross-sectional structure of the planar tension block BB provided in the present invention. [Figure 16] This is a schematic diagram of the force bearing in the two-layer prestressed large-diameter shield tunnel structure provided by the present invention. [Modes for carrying out the invention]

[0021] The following will provide a detailed explanation with reference to the drawings. (Example 1)

[0022] The present invention provides a double-layer prestressed large-diameter shield tunnel structure, which, as shown in Figures 1 to 3, is composed of multiple segment rings 100 of uniform dimensions, each segment ring 100 being an arc-shaped structure with equal width, thickness, and diameter. The segment ring 100 can be composed of multiple segment pieces connected to each other, and these segment pieces include segment standard blocks 101 and segment tension blocks 102. Both sides of the shield machine are walkways, and the prestress loss increases with increasing distance from the tension end, and in particular, the prestress loss is maximized in the segment ring 100 at the symmetrical portion to the tension end. To ensure sufficient tensioning work space and a uniform circumferential prestress distribution, the segment tension blocks 102 are arranged in pairs and distributed symmetrically along both sides of the segment ring 100. This design aims to reduce the impact of prestress loss on structural performance and optimize tensioning efficiency. The segment standard block 101 is distributed to other parts of the tunnel structure, and its installation angle can be adjusted according to specific construction requirements to adapt to geometric changes in the tunnel track, such as curved sections or gradient sections, thereby ensuring the overall stability and continuity of the tunnel structure.

[0023] Preferably, as shown in Figures 1 to 3, the segment ring 100 is designed to integrate two independent prestressing systems to improve its structural performance. The outer prestressing system 103 is positioned in close contact with the outside of the segment ring 100, and the inner prestressing system 104 is provided close to the inside of the segment ring 100. The outer prestressing system 103 and the inner prestressing system 104 connect multiple segment standard blocks 101 and multiple segment tensioning blocks 102 to form a two-layer prestressed large-diameter shield tunnel structure. Both of these two-layer prestressing systems are tensioned by the segment tensioning blocks 102 to achieve precise prestressing. The main role of the outer prestressing system 103 is to increase the bending moment necessary to resist opening when the outside of the segment joint is subjected to load, thereby effectively resisting the negative bending moment effect generated on the outside of the segment structure by external water and soil loads. Accordingly, the inner prestressing system 104 strengthens the bending moment bearing capacity inside the segment joints, playing a role in resisting the positive bending moment action caused by soil and water loads at the top and bottom. With this arrangement of a double prestressing system, the segment ring 100 can more comprehensively respond to complex and variable underground environmental loads, ensuring the safety and stability of the tunnel structure. Furthermore, this design optimizes the distribution of prestress in the segment ring structure, improving the overall support efficiency and durability of the structure.

[0024] Preferably, as shown in Figures 1 to 3, in the tunnel structure design, when the structure needs to be subjected to significant loads and the segment thickness is sufficient to support the arrangement of a multi-layer prestressed system, the segment ring 100 can be optimized to accommodate the multi-layer prestressed system architecture. This architecture not only covers the outer layer prestressed system 103 and the inner layer prestressed system 104, but also leaves open the possibility of extending to more layers to adapt to more complex stress distribution demands.

[0025] Preferably, as shown in Figures 1 to 3, there are two types of arrangement policies for the tensioning ends of the prestressing system. One policy is to uniformly install the tensioning ends of the outer layer prestressing system 103 and the inner layer prestressing system 104 on the same segment tensioning block 102. This means simplifies the segment piece mode and promotes the convenience of assembly work. However, performing prestressing and tensioning work on multiple layers simultaneously within the same segment area may limit the working space and further challenge the efficiency of the tensioning work. Therefore, this means is applied when there is only one layer of walkway on both sides of the shield machine. Another policy is to distribute the tensioning ends of the outer layer prestressing system 103 and the inner layer prestressing system 104 on different segment tensioning blocks 102. This means increases the complexity of the segment piece and may slightly slow down the assembly speed, but it significantly expands the working area for prestressing and tensioning, providing workers with more sufficient working space, thereby effectively improving work efficiency and flexibility. Therefore, this means is applied to shield machines with two layers of walkway on both sides and a larger diameter. Preferably, Figures 4 to 7 show in detail the structural diagram of a segment standard block 101, in which a two-layer borehole structure is pre-embedded inside the segment standard block 101, and this structure includes a group of outer layer boreholes 201 located on the relative outside and a group of inner layer boreholes 203 located on the relative inside, and the borehole material can be selected from corrugated pipes, steel pipes or plastic pipes according to actual demand, and the bore diameter design must closely match the specific specifications of the prestressed cables 105 or prestressed reinforcing bars, and consideration must be given to the efficiency of routing the prestressed cables 105 during the construction process. In particular, depending on the width and thickness of the segment, the borehole structure can be installed to have three or more layers of boreholes.

[0026] Preferably, as shown in Figures 4 to 7, all outer layer channels 201 and inner layer channels 203 are located in independent horizontal planes and are distributed symmetrically along the width direction of the segment to ensure balance of structural force bearing. "Located in independent horizontal planes" means that in a cross section perpendicular to the width direction of the segment (i.e., the thickness direction of the segment), all outer layer channels 201 are at the same height, and all inner layer channels 203 are at different heights. To achieve an optimized prestress transfer effect, the spacing between adjacent channels must be determined by comprehensively considering the overall width of the segment and the specific layout of the tension grooves. To avoid potential positional collisions between the outer layer tension grooves 301 and the inner layer tension ends, the outer layer channels 201 and inner layer channels 203 employ a misaligned layout policy to ensure that they do not intersect in the same plane in the width direction.

[0027] Preferably, if both the outer layer boreholes 201 and the inner layer boreholes 203 are arranged in a 4-bore layout, each borehole can be sequentially numbered "upper 1-4" and "lower 1-4" according to the relative position of the boreholes to the edges of the segments. This embodiment provides two types of borehole arrangement means. The first arrangement order is lower 1, upper 1, lower 2, upper 2, upper 3, lower 3, upper 4, lower 4, as shown in Figures 4 and 5, and the second arrangement order is upper 1, lower 1, lower 2, upper 2, upper 3, lower 3, lower 4, upper 4, as shown in Figures 6 and 7. Both of these arrangement means aim to optimize the prestressing path and ensure that the segment structure has higher stability and safety when subjected to load.

[0028] Preferably, the principles to which the tunnel layout should adhere include the following: 1) The inner and outer tunnels are spaced apart along the width direction of the segment and cannot be located on the same width plane; that is, the inner and outer tunnels do not overlap in the plan view. 2) The spacing between each hole in the inner and outer layers must satisfy the arrangement of tooth blocks or grooves, and each hole must not be able to pass through the tensioned tooth block or groove, and must have a sufficient safety distance. 3) In order to satisfy the condition that the segments on both sides of the segment ring are arranged symmetrically, the number of holes with tensioned ends should be half the total number of holes and should be spaced apart.

[0029] Preferably, the segment ring 100 of the present invention uses a positioning rod or a mortise and tenon joint as a connecting member between segment pieces, enabling a highly efficient and precise positioning and assembly process. The purpose of providing such a connecting member is to replace conventional bolt connection designs and improve construction efficiency and structural stability.

[0030] Preferably, in a means of using a positioning rod as a connecting member, one or more elongated positioning grooves 205 with a semicircular cross-section are designed at an intermediate height position between the longitudinal joint surfaces of the segment standard block 101 and the segment tensioning block 102, and multiple insertion grooves 206 are further pre-provided inside the positioning groove to accommodate the connection requirements (shown in Figures 4 to 11). During the assembly process, a hollow positioning rod matching its dimensions (length and diameter) is first precisely installed in the positioning groove 205 of one segment, and then the positioning rod is firmly fixed in the insertion groove 206 with fastening elements such as bolts or key pins. Subsequently, the corresponding positioning groove 205 of another adjacent segment is precisely aligned and fixed based on the installed positioning rod, ensuring the accuracy and stability of the connection between segments.

[0031] Preferably, when using a mortise and tenon joint as the connecting means, the design of the segment standard block 101 and the segment tension block 102 adopts a complementary convex-pin / recessed groove structure. Specifically, multiple convex pins are arranged on the longitudinal joint surface of one end of the segment, and multiple corresponding recesses are provided on the other end. During the assembly process, adjacent segments are precisely inserted into the corresponding recesses by the convex pins, achieving seamless butting and a strong lock between segments, thereby simplifying the assembly flow and strengthening the overall integrity of the structure. This design not only improves assembly efficiency but also effectively reduces reliance on manual operation, ensuring the construction of high-quality tunnel segment rings.

[0032] Preferably, the arrangement policy described involves the outer layer tensioning end and the inner layer tensioning end being located on the same segment tensioning block 102. This policy is based on segment tensioning blocks 102 distributed symmetrically on both sides of the segment ring 100, employs a mirror-image symmetry design, and is implemented by an installation method that rotates 180° around a central point, with the aim of optimizing structural layout and construction efficiency. Specifically, each segment tensioning block 102 is designed to have tensioning grooves (i.e., inner layer tensioning end and outer layer tensioning end) in only half of its number of holes (preferably half of the outer layer holes 201 and half of the inner layer holes 203), while retaining the other half of the number of holes as through holes. Furthermore, in the detailed structural layer surface, the outer layer hole 201 has an outer layer tension groove 301 opened along a specific region of the inner arc surface of the segment, and the inner layer hole 203 has an inner layer tension end accumulated at its corresponding inner arc surface position, and the inner layer tension end is subdivided into an inner layer tooth block groove 306 and an inner layer tension groove 400 based on two different configurations of the segment tension block 102, thereby forming an inner layer tension force transmission structure. In view that the depth of the outer layer tension groove 301 is designed to exceed the overall depth of the inner layer hole 203 and its tension end assembly, the layout of the outer layer tension groove 301 is designed so that there is no physical intersection with the inner layer hole 203 and a certain safety distance is maintained, in order to avoid structural collision and stress concentration, thus meeting the requirements of structural safety and durability.

[0033] Furthermore, considering ease of construction and structural stability, the inner layer tensioning end is designed to be located in the vertically upper space of the outer layer borehole 201. This layout not only optimizes space utilization but also simplifies the tensioning work flow, improving overall construction efficiency and accuracy.

[0034] Preferably, in order to ensure the consistency of the types of the segment tensioning blocks 102 on both sides, to achieve a uniform distribution of prestress in the circumferential direction, and to strictly adhere to the principle that the boreholes and tension grooves do not intersect each other, it is necessary to perform accurate selection and optimization design for predetermined boreholes in which tension grooves are installed, and to match them to the borehole arrangement within the segment standard block 101. For example, if four boreholes are arranged in both the outer layer borehole 201 and the inner layer borehole 203, they are numbered sequentially as Lower 1 to Lower 4 (closer to the outer layer region of the segment) and Upper 1 to Upper 4 (closer to the inner layer region of the segment) based on the fixed position of the boreholes relative to the segment edge.

[0035] Based on the above layout, two types of tension groove installation methods are provided to be selected. In method 1, tension grooves are installed in two outer layer boreholes 201, lower 1 and lower 3, and in two inner layer boreholes 203, upper 2 and upper 4 (shown in Figures 8 and 9). In method 2, tension grooves are installed in two outer layer boreholes 201, upper 1 and upper 3, and in corresponding positions in two inner layer boreholes 203, lower 2 and lower 4 (shown in Figures 10 and 11). Both of these installation methods aim to optimize the prestressing path and ensure that the segment structure has higher stability and safety when subjected to load.

[0036] Preferably, Figures 12-15 show in detail the structural design overview of the segment tensioning block 102, and based on its tensioning mechanism, the segment tensioning block 102 is clearly divided into two types: a tooth block type tensioning block 106 and a planar tensioning block 107. Specifically, the structural feature of the tooth block type tensioning block 106 is that its inner layer tensioning end adopts the design of an inner layer tooth block groove 306. This design aims to provide a space that facilitates the arrangement and tensioning of the prestressed cable 105 in the inner layer borehole 203 by utilizing the tooth block 307 structure, which is higher than the segment surface. In contrast, the planar tensioning block 107 has its inner layer tensioning end arranged as an inner layer tensioning groove 400. This design uses a planar contact surface to transmit tensioning force, ensuring stability and uniformity in the tensioning process. The two types of tensioning blocks each have their own structural emphasis and together constitute a segment tensioning system that can adapt to different construction needs and tensioning conditions.

[0037] Preferably, as shown in Figures 12 and 13, tooth blocks 307 are designed to protrude from the inner arc surface of the tooth block tensioning block 106. These tooth blocks 307 have an arc-shaped structure of the same thickness, with both ends existing in a planar form, which can serve as the important tensioning surface 302. The thickness of the tooth block 307 area is set slightly higher than the thickness of the segment body, provided that it strictly adheres to the limiting regulations for the tunnel structure, to ensure sufficient tensioning strength. The outer tensioning groove 301 and the inner tooth block groove 306 are precisely positioned on both sides of the tooth block 307 and are arranged in pairs. The bottom structure of these two types of tensioning grooves includes a planar portion strictly perpendicular to the tensioning surface 302 and an arcar portion that smoothly transitions to the inner arc surface of the segment. The dimensions of the tensioning groove can meet the requirements of jack tensioning work, where the planar design is intended to facilitate the installation and operation of the operating device, and the arcar portion ensures a smooth structural transition between the tensioning groove and the tooth block tensioning block 106.

[0038] Preferably, as shown in Figures 12 and 13, in order to fully realize a 360° circumferential prestress distribution of the segment structure, the inner and outer two-layer boreholes of the tooth block tensioning block 106 adopt a cross layout, passing through the tensioning surfaces 302 on both sides of the tooth block 307, respectively. To accommodate the demands of complex tensioning paths, the outer layer borehole 201 and inner layer borehole 203 are specifically designed with large curvature borehole steps 304 and straight borehole steps 303 in the region adjacent to the tensioning surface 302. An anchor plate 305 is attached to each tensioning surface 302, and these anchor plates 305 are strictly perpendicular to the corresponding boreholes to ensure effective transmission of tensioning force and anchor fixation.

[0039] Preferably, as shown in Figures 14 and 15, the inner curved surface of the planar tensioning block 107 is smooth and without protrusions. This design does not require an additional increase in the segment thickness, thereby maintaining the original dimensions and characteristics of the structure. For the outer layer boreholes 201, the outer layer tensioning grooves 301 are precisely positioned on both sides of the segment in a paired configuration. The layout policy is similar to that of the outer layer tensioning grooves 301 in the toothed tensioning block 106, ensuring consistency and compatibility of the tensioning system. For the inner layer boreholes 203, the path design includes a continuous transition of large curvature borehole stages 304 and straight borehole stages 303, ultimately passing directly through the tensioning surface 302. The layout of the inner layer boreholes 203 in the planar tensioning block 107 does not employ a cross design, simplifying the tensioning path and improving construction efficiency. Furthermore, due to differences in structural characteristics, the tensioning surface 302 does not require the separate installation of anchor plates 305 in such tensioning blocks, further simplifying the structural configuration and reducing the complexity of construction.

[0040] Preferably, in the segment structure prestressing system of the present invention, the introduction of a design combining straight borehole stages 303 and large curvature borehole stages 304 is a significant improvement. This design aims to comprehensively optimize the distribution of prestress in the segment structure, ensuring high efficiency and uniformity of prestress transmission by the straight borehole stages 303 and reducing losses in the transmission process, while utilizing large curvature borehole stages to flexibly adapt to the demands of complex tensioning paths, ensuring that prestress is applied precisely and effectively to the designated location, especially in critical areas approaching the tensioning surface. Such a design not only overcomes the limitations of conventional single-borehole installation methods in terms of flexibility, construction efficiency, and structural performance, but also significantly improves the overall support capacity and crack resistance of the segment structure, extending the service life of the structure. Specifically, the straight tunnel section 303 simplifies the tensioning path, reduces construction difficulty, and improves construction efficiency, while the large curvature tunnel section, with its unique curvature design, precisely matches the geometric shape of the segment structure, achieving a comprehensive distribution of prestress within a 360° circumferential range. Therefore, the combined use of the straight tunnel section 303 and the large curvature tunnel section 304 provides strong support for improving the safety, durability, and economic efficiency of tunnel and underground construction structures.

[0041] Preferably, the outer layer prestressing system 103 is formed as follows: The prestressing cable 105 first enters through an outer layer tensioning groove 301 pre-formed in a segment tensioning block 102 on one side of the segment ring 100. Subsequently, the prestressing cable 105 circumnavigates the segment tensioning block 102 along a predetermined path and then passes through an outer layer hole 201 pre-formed inside a segment standard block 101 tightly connected to it. This path ensures that the prestressing cable 105 can distribute prestress uniformly and effectively. After the circumnavigation is complete, the prestressing cable 105 passes through the corresponding outer layer tensioning groove 301 in the segment tensioning block 102 on the other side of the segment ring 100, forming a complete prestressing cable circuit. Subsequently, to ensure the stability and effective tensioning of the prestressing cable 105, both ends are precisely fixed to specially made general anchor plates 308. Immediately after anchor fixing is complete, synchronized tensioning is performed to ensure that the prestressed cable 105 can be subjected to and maintained uniform prestress according to the design requirements through a precisely controlled tensioning process, further improving the support capacity and stability of the entire segment ring 100 and its constituent structures.

[0042] Preferably, the construction method of the inner layer prestress system 104 differs depending on the type of segment tension block 102. Specifically, when a tooth block type tension block 106 is used as the segment tension block 102, the construction process of the inner layer prestress system 104 is similar to that of the outer layer prestress system 103, but the prestress cable 105 must be placed in the inner layer borehole 203, introduced through the inner layer tooth block groove 306, and passed through, thereby achieving prestress. On the other hand, when a planar tension block 107 is used as the segment tension block 102, the construction method of the prestress cable 105 is different. In this case, one end of the prestress cable 105 is first fixed to the outer ring of the floating anchor 309, and then it circles the inner layer borehole 203 once to ensure a uniform distribution of prestress. After the circle is completed, the prestress cable 105 passes through the inner layer tension groove 400 and is fixed to the inner ring of the floating anchor 309. Finally, a deflector is used to perform precisely controlled tensioning work, thereby achieving effective construction of the inner layer prestress system 104.

[0043] Preferably, the tooth block tension block 106 has a greater thickness than the other segment pieces and has protrusions, but the dimensions of the tension grooves required for tensioning at both ends are smaller, resulting in less damping to the structure due to the tension grooves. The width of the segments of the planar tension block 107 does not change, and the contraction of the anchor plate tensioned by the floating anchor 309 is smaller, resulting in less prestress loss, however the floating anchor 309 moves during tensioning, and the inner layer tension groove 400 is larger in dimensions, resulting in greater damping to the structure.

[0044] Preferably, when selecting an anchor fixing method for tensioning the prestress cable 105, if a general anchor plate 308 is adopted as the fixing device, the tensioning operation must be performed synchronously on both ends of the prestress cable. In this method, contraction deformation of the anchor occurs at both tensioning ends, causing a relatively large prestress loss and affecting the prestress distribution effect of the structure. However, its advantage is that the required tension groove dimensions are relatively small, which is beneficial for the compactness of the structural design. Furthermore, this method requires tooth blocks 307 to be provided on the segment to provide the necessary anchor fixing support, and requires the anchor plate 305 to be precisely positioned on the tensioning surface 302 to ensure effective transmission and distribution of tensioning force. In contrast, if a floating anchor 309 is selected as the tensioning end fixing method, the tensioning operation only needs to be performed on one end of the prestress cable 105. This method significantly reduces prestress loss by avoiding the multiple contraction effect of the anchor when both ends are tensioned. However, the floating anchor 309 undergoes some movement during the tensioning process to adapt to prestressing. Therefore, the dimensions of the tension groove need to be increased accordingly to ensure smooth tensioning and stability of the anchor fixing system. This reduces prestress loss, and the movement characteristics of the floating anchor and their impact on the overall structural performance must be carefully considered during the design phase.

[0045] Preferably, the segment ring 100, through the cooperative action of the outer layer prestressing system 103 and the inner layer prestressing system 104, can maintain a continuous and uniform pressure-receiving state across its entire cross-section. Given that the segment ring 100 employs a large-diameter design and has a significant shield segment thickness, these structural characteristics provide a robust foundation for enhancing overall support capacity and stability. Furthermore, by combining it with steel fiber concrete during casting, it not only utilizes the high strength and excellent tensioning performance of the steel fibers but also significantly improves the toughness and durability of the concrete, effectively resisting external loads and the expansion of potential cracks. Based on the above design optimization and full utilization of material properties, the internal structure of the segment ring 100 still maintains excellent mechanical performance and structural integrity even without any conventional reinforcement. In particular, the prestress cables 105 of the inner layer prestressing system 104 and the outer layer prestressing system 103 can be set to different prestress values, and these prestress values ​​can be adjusted based on the internal force distribution of the segment ring 100.

[0046] Preferably, in the process of selecting the type of prestressed cable 105, it is necessary to comprehensively consider the geological conditions and specific requirements of the type of construction, and to flexibly select from steel stranded wire, carbon fiber stranded wire, or other stranded wires made of high-performance fiber materials with a tensile strength exceeding 2000 MPa. Each of these materials has its own unique advantages and application scenarios.

[0047] When non-adhesive stranded steel wire is selected as the prestressed cable 105, considering the demand for long-term use of the tunnel structure, it is preferable to design and install the tunnel shafts in advance, thereby extending the service life of the tunnel structure by providing a means to assist in cable replacement in the spare shafts after the tunnel has reached its design service life. This means involves performing initial tensioning on the spare shafts of the inner and outer layers, then replacing the non-adhesive stranded steel wire in the shafts where tensioning is complete, and finally removing the old non-adhesive stranded steel wire from the spare shafts. This process is repeatable and provides convenience for the long-term maintenance of the tunnel structure.

[0048] On the other hand, if bonded steel strands are used, the service life of the tunnel can be extended after it reaches its design service life by re-tensioning the pre-tensioned sections. This method involves directly re-tensioning the pre-tensioned sections of the inner and outer layers, leaving the completed tensioned sections unchanged and eliminating the need to replace the prestressed cables 105. However, it should be noted that this re-tensioning process is generally not repeatable multiple times, and its long-term effects must be carefully considered during the design phase.

[0049] Due to its unique corrosion resistance, carbon fiber strands are a preferred material for application in geological conditions with higher corrosiveness. The high strength and excellent durability of carbon fiber strands can effectively protect tunnel structures from erosion caused by harsh environments, ensuring the safe and stable operation of tunnels over long periods.

[0050] Preferably, Figure 16 shows the force bearing of a two-layer prestressed large-diameter shield tunnel structure, and when the segment ring is cast using unreinforced steel fiber concrete, the calculation method for the minimum prestress cable 105 area Ap' and Ap required for the inner layer prestress system 104 and the outer layer prestress system 103 is as follows. 1) Assume that the concrete stress patterns in the pressure-receiving and tension-reducing regions of the cross section are simplified into equivalent rectangular stress diagrams. 2) Calculate the height of the tension region in the rectangular stress diagram using the following formula.

number

number

[0051] Area A of the inner and outer layer prestressed cables 105 in a double-layer prestressed large-diameter shielded tunnel structure p 'and A p The value must simultaneously satisfy the requirements for both positive and negative bending loads.

[0052] In the formula, x t -- Height of the tension zone of the segment cross-section (mm), h-- Height of the segment cross-section (mm), x-- Height of the compression zone of the segment cross-section (mm), which is the value taken according to the current national standard "Code for Design of Concrete Structures" GB 50010, β1-- Coefficient, which is the value taken according to the current national standard "Code for Design of Concrete Structures" GB 50010, N-- Design value of the basic combined axial force (N) M-- Design value of the basic combined bending moment (kN·m), α1-- Influence coefficient of the equivalent stress value of the concrete in the compression zone, which is the value taken according to the current national standard "Code for Design of Concrete Structures" GB 50010, f fc -- Design value of the axial compressive strength of steel fiber concrete (MPa), b-- Width of the segment cross-section (mm), f ftu -- Design value of the residual tensile strength at the ultimate state of the bearing capacity of steel fiber concrete (MPa), f p 、f’ p -- Design values of the tension and compressive strengths of the outer and inner prestressed cables 105 (MPa), A p 、A’ p -- Cross-sectional areas of the outer and inner prestressed cables 105 (mm 2 ), h0-- Effective height of the segment cross-section (mm), a s -- Distance from the resultant force point of the outer prestressed cable 105 to the tension edge of the cross-section (mm), a’ s -- Distance from the resultant force point of the inner prestressed cable 105 to the compression edge of the cross-section (mm), σ’ p0 -- Prestressed reinforcement stress when the concrete normal stress at the resultant force point of the longitudinal prestressed reinforcement in the compression zone is equal to zero (Example 2)

[0053] This embodiment is a further improvement on Embodiment 1, and any overlapping content will be omitted from the explanation.

[0054] The present invention further relates to a construction method for a double-layer prestressed large-diameter shield tunnel structure, and the construction method includes S1 to S3.

[0055] In S1, the segment standard block 101 and the segment tension block 102 are precast.

[0056] Preferably, a dedicated mold is manufactured based on the design parameters of the segment standard block 101 and the segment tension block 102, then the outer layer hole 201 and inner layer hole 203 are bent according to the design requirements, then the anchor plate 305 is fixed to the outer layer tension groove 301 and inner layer tension groove 400 or inner layer tooth block groove 306 of the precast segment tension block 102, the outer layer hole 201 and inner layer hole 203 are fixed to the anchor plate, and finally steel fiber concrete is poured and cured.

[0057] In S2, the shield assembly machine first lifts multiple segment standard blocks 101 and attaches them to the lower part of the tunnel, positioning and assembling them using positioning rods or mortise and tenon joints. Subsequently, it lifts multiple segment tension blocks 102 and connects them to the attached segment standard blocks 101 on both sides of the tunnel, and finally lifts multiple segment standard blocks 101 and attaches them to the upper part of the tunnel.

[0058] Preferably, in the present invention, the segment tensioning blocks 102 are attached to both sides of the tunnel. On the one hand, both sides of the shield machine are generally walkways, allowing for the placement of equipment necessary for tensioning and providing a tensioning workspace. On the other hand, prestress loss increases with increasing distance from the anchor fixing end, meaning the prestress loss is greatest diagonally opposite the anchor fixing end. By positioning the anchor fixing ends on both sides of the tunnel, the prestress distribution throughout the tunnel structure can be made more uniform. Furthermore, by using positioning grooves and steel pipes to assist in the positioning and assembly of the segments, handhole attenuation of the inner arc surface of the segments can be avoided when connecting them with bolts, and the tunnel is more aesthetically pleasing.

[0059] In S3, a wire puller is used to pass multiple prestressed cables 105 through multiple outer or inner boreholes 201 and inner boreholes 203, and they are fixed to a general anchor plate 308 or floating anchor 309, leaving the other inner or outer boreholes as reserve, and then tensioning is performed using a tensioning device in conjunction with a deflector, during which the outer boreholes 201 and inner boreholes 203 may be tensioned simultaneously, or the outer boreholes 201 may be tensioned first and then the inner boreholes 203, after which grouting is performed in the boreholes where bonded steel strands are used, sealing in the boreholes where non-bonded steel strands are used and in the reserve boreholes where no wires are passed, and finally the anchors are sealed in concrete in all tensioning grooves.

[0060] Preferably, in the present invention, by installing two layers of circumferential prestress on the outside and inside of the segment structure, the entire cross-section of the segment structure is subjected to pressure, allowing the concrete to fully exhibit its pressure-receiving performance, resulting in a more rational force-bearing structure. Furthermore, the thickness of the segments can be effectively reduced, the amount of reinforcing steel used can be decreased, and in combination with steel fiber concrete technology, a reinforced concrete-free design can be achieved.

[0061] Preferably, in the present invention, the inner prestress can resist positive bending loads of the tunnel structure, and the outer prestress can resist negative bending loads of the tunnel structure, significantly improving the bending moment and crack load of the segment joint opening, strengthening the overall rigidity, deformation resistance capacity and ultimate bearing capacity of the segment structure, effectively avoiding problems such as leakage, deformation and cracking, and reducing the operation and maintenance costs of the tunnel structure in the later stages.

[0062] Preferably, in the present invention, the double-layer prestressing can keep the tunnel structure under a high axial force state for its entire lifecycle, restore the deformation of the tunnel structure to its initial state after the surrounding disturbance load has recovered, and promote the closing of any open cracks. Furthermore, by combining it with means for re-routing or replacing cables in the pre-prestressed borehole, it can improve the durability and safety of the tunnel structure and extend its service life.

[0063] The above specific embodiments are illustrative, and those skilled in the art can conceive of various solutions based on the implications of the disclosure of the present invention. These solutions also fall within the scope of the disclosure and the scope of protection of the present invention. As those skilled in the art will understand, the specification and its drawings are descriptive and do not limit the scope of the claims. The scope of protection of the present invention is defined by the claims and their equivalents. The specification of the present invention includes multiple inventive concepts, and for example, "preferably" or "based on a preferred embodiment" both indicate that the corresponding paragraphs disclose independent concepts, and the applicant reserves the right to file divisional applications based on each inventive concept. Throughout the specification, features introduced by "preferably" are merely optional forms and should not be understood as mandatory; therefore, the applicant reserves the right to waive or delete relevant preferred features at any time. [Explanation of Symbols]

[0064] 100: Segment ring, 101: Segment standard block, 102: Segment tension block, 103: Outer layer prestressing system, 104: Inner layer prestressing system, 105: Prestressed cable (muscle), 106: Tooth block type tension block, 107: Planar tension block, 201: Outer layer hole path, 203: Inner tunnel, 205: Positioning groove, 206: Insertion groove, 301: Outer layer tension groove, 302: Tension surface, 303: Straight hole road step, 304: Large curvature hole road, 305: Anchor plate, 306: Inner layer tooth block groove, 307: Tooth block, 308: General anchor plate, 309: Floating anchor, 400: Inner layer tension groove.

Claims

1. A double-layer prestressed large-diameter shield tunnel structure comprising a segment ring (100) and a multi-layer prestressing system, The segment ring (100) is formed by a plurality of segment pieces joined together to form an annular structure, and the segment pieces include segment standard blocks (101) and segment tension blocks (102), the segment tension blocks (102) appear in pairs and are distributed on both sides of the segment ring (100), The prestressing system includes an outer prestressing system (103) and an inner prestressing system (104) connecting a plurality of segment standard blocks (101) and a plurality of segment tensioning blocks (102), and the tensioning ends of the prestressing system are provided on the same or different segment tensioning blocks (102), where, The outer layer prestressing system (103) is positioned on the outer surface of the adjacent segment ring (100) to resist deformation or opening of the segment piece and its joint outside, The inner layer prestressing system (104) is positioned on the inner surface of the adjacent segment ring (100) to resist deformation or opening inside the segment piece and its joint. A double-layer prestressed large-diameter shield tunnel structure characterized by this feature.

2. Both the segment standard block (101) and the segment tension block (102) have pre-embedded borehole structures, and these borehole structures include a plurality of groups of outer boreholes (201) and a plurality of groups of inner boreholes (203) arranged symmetrically along the width direction of the segment piece, wherein the segment piece forms an internal two-layer borehole structure arranged at different levels from each other, with the outer boreholes (201) positioned relatively outward and the inner boreholes (203) positioned relatively inward. The shield tunnel structure according to feature 1.

3. When the outer layer tunnel (201) and the inner layer tunnel (203) are the same segment tensioning block (102) and an outer layer tensioning groove (301) and an inner layer tensioning end are provided on the inner arc surface of the same segment tensioning block (102), the shield tunnel structure includes two segments tensioning blocks (102) of the same type and arranged symmetrically in one group. When the outer layer tunnel (201) and the inner layer tunnel (203) are provided with outer layer tension grooves (301) and inner layer tension ends on the inner arc surfaces of different segment tension blocks (102), the shield tunnel structure includes a total of four segment tension blocks (102) in two groups, each group having the same type and arranged symmetrically. The inner layer tension end can be divided into an inner layer tooth block groove (306) and an inner layer tension groove (400) based on two different configurations of the segment tension block (102), and the segment tension block (102) can be divided into a tooth block type tension block (106) and a planar type tension block (107) depending on the tensioning method. The shield tunnel structure according to feature 2.

4. A tooth block (307) is arranged on the inner curved surface of the tooth block type tension block (106), the outer tension groove (301) and the inner tooth block groove (306) are paired and arranged on both sides of the tooth block (307), the outer hole (201) and the inner hole (203) pass through the large curvature hole step (304) and the straight hole step (303) in a crossing manner from the tension surfaces (302) on both sides of the tooth block (307), and an anchor plate (305) is attached to the tension surface (302). The shield tunnel structure according to feature 3.

5. The planar tensioning block (107) has no protrusions on its inner curved surface, the outer tensioning grooves (301) are arranged in pairs on both sides of the segment piece, the inner tensioning groove (400) is a recessed groove arranged on the inner curved surface, the inner holeway (203) passes directly through the tensioning surface (302) via the large curvature holeway step (304) and the straight holeway step (303), and no anchor plate (305) is provided on the tensioning surface (302). The shield tunnel structure according to feature 3.

6. The aforementioned outer layer prestressing system (103) is The prestress cable (105) enters from one side of the outer layer tension groove (301), circles around the outer layer borehole (201), and then passes through the other side of the outer layer tension groove (301), after which both ends of the prestress cable (105) are fixed to a general anchor plate (308) located on the tension surface (302), thereby performing tension. The shield tunnel structure according to claim 4 or 5, characterized by the features described above.

7. The inner layer prestressing system (104) employing the planar tensioning block (107) is, One end of the prestressed cable (105) is fixed to the outer ring of a floating anchor (309) positioned in the inner layer tension groove (400), and the prestressed cable (105) enters the inner layer tension groove (400) from one end, circles the inner layer borehole (203), passes through the other end of the inner layer tension groove (400), is fixed to the inner ring of the floating anchor (309), and is formed to be tensioned by a deflector. The shield tunnel structure according to claim 3 or 5, characterized by the above.

8. The segment standard block (101) and segment tension block (102) can be positioned and assembled using a positioning rod or a mortise and tenon joint as a connecting member. When a positioning rod is used as a connecting member, both ends of the segment piece are provided with elongated positioning grooves (205) and multiple insertion grooves (206) on the longitudinal joint surfaces, a hollow positioning rod is placed in the positioning groove (205) and fixed in the insertion grooves (206), and adjacent segment pieces are positioned and assembled using the positioning rod in the positioning groove (205). When using a mortise and tenon joint as a connecting member, multiple protruding pins are provided on the longitudinal joint surface of one end of the segment piece, and multiple recessed grooves are provided on the longitudinal joint surface of the other end, and adjacent segments are positioned and assembled by the protruding pins and recessed grooves. A shield tunnel structure according to any one of claims 1 to 5.

9. The segment ring (100) can be cast using steel fiber concrete with no internal reinforcement, and the prestressed cable (105) can be selected from stranded wires made of fibrous materials with a tensile strength greater than 2000 MPa, including steel stranded wire and carbon fiber stranded wire, depending on the geological conditions and type of construction. A shield tunnel structure according to any one of claims 1 to 5.

10. The steps include placing two precast segment tension blocks (102) on both sides of the tunnel structure and placing segment standard blocks (101) in other parts of the tunnel structure, The steps include using a cable puller to pass multiple prestressed cables (105) from the tension groove through multiple outer or inner boreholes (201) and multiple inner boreholes (203), fixing them to a general anchor plate (308) or floating anchor (309), and leaving half of the boreholes reserved so that the prestressed cables (105) are not passed through, The steps include using a tensioning device in conjunction with a deflector to tension the outer layer borehole (201) and inner layer borehole (203) simultaneously when pulling, or first tensioning the outer layer borehole (201) and then the inner layer borehole (203), grouting the boreholes where bonded steel strands are used after tensioning is complete, and sealing the boreholes where non-bonded steel strands are used and the spare boreholes that will not be used, The steps include sealing all tension grooves with concrete anchors, A construction method for a two-layer prestressed large-diameter shield tunnel structure, characterized by the following features.

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