A trenchless micro-disturbance external prestress system

Abstract

This invention relates to a trenchless, micro-disturbance external prestressing system, belonging to the field of tunnel structures. The system includes prestressed strands and an anchoring system. External prestress is applied to the tunnel structure through shafts and holes constructed on both sides of the existing tunnel structure in the following manner: both ends of the prestressed strands are inserted into the anchoring system, one end is fixed, and the other end is connected to a jack and tensioned to apply external prestress to the tunnel structure. During prestressing tensioning, the prestressed strands cut through the soil under the tension of the jacks and continuously tighten towards the outer wall of the tunnel structure, eventually adhering tightly to the outer wall. This invention, by applying an external prestressing system to the outside of the tunnel structure, not only provides circumferential prestress but also generates radial forces pointing towards the center of the tunnel structure and tangential forces tangential to the outer surface of the tunnel structure. This results in a self-stabilizing structural system, significantly enhancing its overall stiffness and deformation resistance, and improving its ultimate bearing capacity.

Description

[0001] The original basis for this divisional application is patent application No. 202510230524.8, filed on February 28, 2025, entitled "A method for treating shield tunnel defects by non-excavation micro-disturbance external prestressing". Technical Field

[0002] This invention relates to the field of tunnel structure technology, and in particular to a trenchless micro-disturbance external prestressing system. Background Technology

[0003] Based on years of subway monitoring data, many operating tunnels have entered a stage of service with defects, with various defects occurring frequently, such as tunnel convergence, deformation, cracks, water leakage, and lining detachment. Therefore, addressing the defects in shield tunnels is of significant practical importance and necessity.

[0004] The main causes of defects in shield tunnels are as follows: First, the shield tunnel structure may have problems such as insufficient overall integrity and weak deformation resistance. In particular, the segment joints, as the weakest link, are prone to deformation, cracking, and leakage under complex soil and water loads, leading to large deformation and instability. Second, shield tunnels are usually located in strata of different properties. When encountering train vibrations inside the tunnel or nearby construction, adverse geological effects may occur. With changes in the bearing capacity of the surrounding soil, the shield tunnel may experience longitudinal uneven settlement and deformation. Third, if the construction process is not standardized or the procedures are not strictly followed during the construction of the shield tunnel, voids and cavities may appear around the tunnel structure, leading to a series of problems such as water leakage, cracking, frost damage, and corrosion.

[0005] To address tunnel structural defects, common current treatment methods mainly include grouting reinforcement on the outside of the tunnel structure or bonding high-strength materials inside the tunnel. For example, CN112901212A discloses a method for treating tunnel defects that allows for repeated grouting and is applicable to special grouts. The method is as follows: Step 1: In sections of the tunnel prone to water leakage and before and after them, multiple sets of repeatable grouting components are installed at intervals along the longitudinal direction of the tunnel, between the initial support and the waterproof layer. Step 2: Connect two adjacent connecting pipes of two adjacent overflow grout cylinders near the tunnel surface to a horizontal pipe that horizontally penetrates the waterproof layer and secondary lining, extending into the tunnel interior. The upper connecting pipe serves as the discharge end, and the lower connecting pipe serves as the grouting end, used for connection to the grouting machine. Step 3: Seal the discharge end, start the grouting machine, and inject grout from the grouting end. The grout is then transported through the annular grout delivery channel, sequentially filling each overflow grout cylinder. However, the effect of external grouting reinforcement is often unsatisfactory and requires long-term maintenance; while internal bonding of high-strength materials can improve the strength of the tunnel structure, these materials may separate from the original structure after secondary deformation of the tunnel structure, affecting the reinforcement effect.

[0006] Therefore, there is an urgent need in this field for a more effective treatment method to alleviate existing defects in tunnel structures such as large deformation, cracking, and water leakage, and to fundamentally avoid various defects in the subsequent operation of tunnel structures, so as to improve the durability and safety of tunnel structures and reduce subsequent operation and maintenance costs.

[0007] Furthermore, on the one hand, there are differences in understanding among those skilled in the art; on the other hand, the applicant studied a large number of documents and patents when making this invention, but due to space limitations, not all details and contents were listed in detail. However, this does not mean that the present invention does not possess the features of these prior art. On the contrary, the present invention already possesses all the features of the prior art, and the applicant reserves the right to add relevant prior art to the background art. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a trenchless, micro-disturbance external prestressing system. This system permanently improves the overall stiffness and deformation resistance of tunnel structures, alleviates existing problems such as large deformation, cracking, and water leakage, and fundamentally avoids various problems during subsequent operation, thereby enhancing the durability and safety of the tunnel structure and reducing subsequent operation and maintenance costs. This invention applies external prestress to the tunnel structure through its side shafts and boreholes without significantly disturbing the original tunnel structure. This permanently improves the overall stiffness and deformation resistance of the tunnel structure, alleviates existing problems such as large deformation, cracking, and water leakage, and fundamentally avoids various problems during subsequent operation, thereby enhancing the durability and safety of the tunnel structure and reducing subsequent operation and maintenance costs.

[0009] This invention discloses a method for treating shield tunnel defects using non-excavation micro-disturbance external prestressing, which includes the following steps:

[0010] S1. Determine the spatial location of the tunnel structure to be treated for defects, and construct the first shaft, the second shaft, and the shaft support structure on both sides of the tunnel structure respectively.

[0011] S2. Construct the first vertical hole between the tunnel structure and the first vertical shaft, and push the prestressed strand to the bottom of the first vertical hole;

[0012] S3. The strata are locally reinforced through the first and second cable-passing openings at the bottom of the vertical shaft support structure on both sides, and then the first and second operating openings are excavated. The telescopic rod is used to cross the strata from the second operating opening to the first operating opening, and the prestressed strand is pulled back to the second operating opening.

[0013] S4. Reinforce the strata locally through the third cable-passing opening according to the strata conditions and excavate to form the third operating opening. Then, construct the second vertical hole between the tunnel structure and the second vertical shaft, and pull the prestressed strand from the second operating opening to the third operating opening.

[0014] S5. Based on the geological conditions, the stratum is locally reinforced and excavated through the tensioning port to form a tensioning operation port. A telescopic rod is used to cross the stratum from the tensioning operation port to the third operation port, and the prestressed strand is pulled back to the tensioning operation port.

[0015] S6. Insert both ends of the prestressed strand into the anchoring system, fix one end, and connect the other end to the jack and tension it to apply external prestress to the tunnel structure.

[0016] According to a preferred embodiment, the first and second vertical shafts are excavated simultaneously and the shaft support structure is constructed in a timely manner. The bottom of the shaft is reinforced with concrete. The depth of the shaft is greater than the bottom burial depth of the tunnel structure, and the inner diameter is designed to allow construction personnel to move and operate the jacks.

[0017] According to a preferred embodiment, the first shaft and the second shaft are respectively provided with a first cable-passing port and a second cable-passing port at the same burial depth below the bottom of the tunnel structure, and a third cable-passing port and a tensioning port are respectively provided at the same burial depth above the top of the tunnel structure.

[0018] According to a preferred embodiment, the first cable-threading opening, the second cable-threading opening, the third cable-threading opening, and the tensioning opening are pits with a thickness less than that of the surrounding area, and the size of the tensioning opening is larger than that of the cable-threading openings. The pits can be chiseled out and the outer soil can be reinforced and excavated to form the first operating opening, the second operating opening, the third operating opening, and the tensioning operating opening with a size larger than that of the operating openings.

[0019] According to a preferred embodiment, the telescopic rod used for pulling prestressed strands is a multi-section telescopic round rod with hooks at the ends. The length of the telescopic rod in its unextended state is less than the inner diameter of the shaft support structure, and the length in its fully extended state is greater than the distance between the first shaft and the second shaft.

[0020] According to a preferred embodiment, the end of the prestressed strand is a circular lifting ring, which is connected to the hook of the telescopic rod. Depending on the sand and gravel content of the stratum, the prestressed strand should preferably be carbon fiber strand or other high-strength strand with strong corrosion resistance.

[0021] According to a preferred embodiment, the anchoring system includes an anchor plate, a clamp, a jack, and a protective cover. The anchor plate includes an arc-shaped base, a tensioning surface, a first duct cluster, and a second duct cluster. The radius of the arc-shaped base is consistent with the outer diameter of the tunnel structure. The duct cluster consists of variable-diameter circular inclined holes penetrating the anchor plate, including a duct inlet located below the tensioning surface and a duct outlet located above the tensioning surface. The slope design of the duct cluster ensures that the prestressed strands do not deflect at the duct inlet. The tensioning surface is approximately perpendicular to the duct cluster.

[0022] According to a preferred embodiment, one end of the prestressed strand is inserted through the inlet of the first duct cluster and exits through the outlet of the duct, and is fixed at the outlet of the duct by a clamp; the other end of the prestressed strand is inserted through the inlet of the second duct cluster and exits through the outlet of the duct, and is fixed at the outlet of the duct by a clamp after being tensioned by a jack.

[0023] According to a preferred embodiment, the components of the anchoring system are made of corrosion-resistant materials, and the anchoring system is wrapped with a protective cover. The protective cover is filled with grease or the anchoring system is coated with a polyurea coating or other materials to ensure corrosion resistance. A waterproof gasket is provided between the protective cover and the outer surface of the tunnel structure, and expansion bolts are used for fixing.

[0024] According to a preferred embodiment, the first vertical shaft is transformed into a maintenance shaft after treatment. The bottom of the maintenance shaft is located below the tensioning opening, and the bottom is a concrete-cast maintenance shaft bottom. The opening is sealed with a manhole cover.

[0025] This invention applies an external prestressing system to the outside of the tunnel structure, providing not only circumferential prestress but also radial forces pointing towards the center of the tunnel structure and tangential forces along its outer surface. The radial force helps reduce the ellipticity of the tunnel structure, while the tangential force adds additional axial force. Together, these forces effectively reduce tunnel deformation and joint opening, thus mitigating existing problems such as large deformation, cracking, and water leakage. This external prestressing system creates a self-stabilizing structural system, significantly enhancing its overall stiffness and deformation resistance, and improving its ultimate bearing capacity. These improved mechanical properties enable the tunnel structure to more effectively cope with various external load changes that may occur during operation, thus effectively preventing further large deformation, cracking, or water leakage, while reducing subsequent operation and maintenance costs. Furthermore, this invention can use carbon fiber strand as the prestressing material, which has good corrosion resistance and mechanical strength. All components of the anchoring system are treated with anti-corrosion coatings and encased in protective covers filled with grease or other anti-corrosion measures to further enhance the system's durability. These measures ensure that the entire external prestressing system can meet the design service life requirements of the tunnel structure. Finally, this invention only requires the excavation of small-sized first and second shafts on both sides of the tunnel structure, with vertical holes and necessary operating and tensioning openings between them for applying external prestress. The first and second shafts are constructed symmetrically and synchronously, minimizing the impact of external prestressing construction on the existing tunnel structure, ensuring micro-disturbance characteristics during construction, and guaranteeing the safety and stability of the original structure. In summary, this invention provides an efficient, reliable, and durable technical solution, bringing significant technical and economic benefits to the treatment of shield tunnel defects. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of step S1 of the method for treating shield tunnel defects using non-excavation micro-disturbance external prestressing provided by the present invention;

[0027] Figure 2 This is a schematic diagram of step S2 of the method for treating shield tunnel defects using non-excavation micro-disturbance external prestressing provided by the present invention;

[0028] Figure 3 This is a schematic diagram of step S3 of the method for treating shield tunnel defects using non-excavation micro-disturbance external prestressing provided by the present invention;

[0029] Figure 4 This is a schematic diagram of step S4 of the method for treating shield tunnel defects using non-excavation micro-disturbance external prestressing provided by the present invention;

[0030] Figure 5This is a schematic diagram of step S5 of the method for treating shield tunnel defects using non-excavation micro-disturbance external prestressing provided by the present invention;

[0031] Figure 6 This is a schematic diagram of step S6 of the method for treating shield tunnel defects using non-excavation micro-disturbance external prestressing provided by the present invention;

[0032] Figure 7 This is a plan view of step S6 of the method for treating shield tunnel defects using non-excavation micro-disturbance external prestressing provided by the present invention;

[0033] Figure 8 This is a plan view of step S7 of the method for treating shield tunnel defects using non-excavation micro-disturbance external prestressing provided by the present invention;

[0034] Figure 9 This is a schematic diagram of the anchoring system provided by the present invention;

[0035] Figure 10 This is a schematic diagram of the structure of the anchor plate provided by the present invention;

[0036] Figure 11 This is a schematic diagram of the tensioning surface of the anchor plate provided by the present invention;

[0037] Figure 12 This is a schematic diagram illustrating the mechanism of action of external prestress on tunnel structures provided by the present invention;

[0038] Figure 13 This is a schematic diagram of the effective prestress of the prestressed strand after considering the prestress loss terms σ1 and σ2 under different layout schemes of the anchoring system provided by the present invention;

[0039] Figure 14 This is a software simulation diagram of shaft excavation under the external prestressing treatment scheme provided by the present invention;

[0040] Figure 15 This is a schematic diagram of the horizontal deformation of the tunnel structure before and after the vertical shaft excavation under the external prestressing treatment scheme provided by the present invention;

[0041] Figure 16 This is a comparison diagram of the axial force distribution between the external prestressing treatment scheme and the ordinary scheme under unloading conditions provided by this invention;

[0042] Figure 17 This is a comparison diagram of the bending moment distribution between the external prestressing treatment scheme and the ordinary scheme under unloading conditions provided by this invention;

[0043] Figure 18 This is a comparison diagram of the overall deformation of the external prestressing treatment scheme under unloading conditions provided by this invention and the ordinary scheme.

[0044] List of reference numerals

[0045] 100: Tunnel structure; 101: First vertical shaft; 102: Second vertical shaft; 103: Shaft support structure; 104: First cable-passing opening; 105: Second cable-passing opening; 106: Third cable-passing opening; 107: Tensioning opening; 108: Shaft bottom reinforcement structure; 200: First vertical opening; 201: Second vertical opening; 202: Prestressed strand; 203: Lifting ring; 204: Telescopic rod; 205: Hook; 301: First operating port; 302: Second operating port; 303: Third operating port; 304: Tensioning operating port; 400: Anchoring system; 401: Anchor plate; 402: Arc-shaped base; 403: Tensioning surface; 404: First duct cluster; 405: Second duct cluster; 406: Duct entrance; 407: Duct exit; 408: Clamping plate; 409: Jack; 500: Protective cover; 501: Waterproof gasket; 502: Expansion bolt; 600: Inspection well; 601: Bottom of inspection well; 602: Well cover. Detailed Implementation

[0046] The following is a detailed explanation with reference to the accompanying drawings.

[0047] like Figures 1 to 8 This invention discloses a method for treating shield tunnel defects using non-excavation micro-disturbance external prestressing, which may include the following steps:

[0048] S1. Determine the spatial location of the tunnel structure 100 to be treated for defects, and construct the first vertical shaft 101, the second vertical shaft 102, and the shaft support structure 103 on both sides of the tunnel structure 100.

[0049] Preferably, the spatial location of the tunnel structure 100 includes parameters such as tunnel coordinates, burial depth, diameter, and surrounding pipelines. At the same time, considering that the tunnel structure 100 will experience structural settlement and convergence deformation during construction and operation, the actual location of the tunnel structure 100 needs to take into account the impact of deformation.

[0050] S2. A first vertical hole 200 is constructed between the tunnel structure 100 and the first vertical shaft 101, and the prestressed strand 202 is pushed to the bottom of the first vertical hole 200.

[0051] Preferably, the first vertical hole 200 can be drilled after the shaft structure is constructed. It is located between the tunnel structure 100 and the shaft, and as close as possible to the cable-passing or tensioning opening 107 of the shaft. This is because the first vertical hole 200 needs to be located within the subsequently formed operating opening to facilitate the encirclement of the prestressed strand 202 at the operating opening. Preferably, the first vertical hole 200 can be excavated using mud slurry wall protection to avoid hole collapse. Further, a telescopic rod 204 or any rod with a hook 205 at one end, exceeding the depth of the shaft, can be used to push the prestressed strand 202 to the bottom of the first vertical hole 200. During the pushing process, the rod or the prestressed strand 202 should be prevented from scraping against the hole wall of the first vertical hole 200, thus avoiding hole collapse. Preferably, the purpose of constructing the shaft and the vertical hole is to facilitate the encirclement of the prestressed strand 202 around the tunnel structure 100. This is an optional auxiliary measure or structure of the present invention. The present invention can also use other methods that can achieve the encirclement of the prestressed strand 202 around the tunnel structure 100.

[0052] S3. The strata are locally reinforced according to the strata conditions through the first cable-passing port 104 and the second cable-passing port 105 at the bottom of the vertical shaft support structure 103 on both sides. Then, the first operating port 301 and the second operating port 302 are excavated. The telescopic rod 204 is used to cross the strata from the second operating port 302 to the first operating port 301, and the prestressed strand 202 is pulled back to the second operating port 302.

[0053] Preferably, the grouting reinforcement area should be larger than the size of the operating opening to ensure the stability of the stratum after the operating opening is excavated.

[0054] Preferably, for strata with good permeability and abundant groundwater, grouting with water-glass materials or local treatment using weak freezing methods can be employed to stabilize the soil and provide waterproofing. Simultaneously, the reinforced soil has very low strength, facilitating construction and not affecting subsequent prestressed strand 202 tensioning. For strata with low permeability or good stability, reinforcement treatment is not necessary.

[0055] S4. The third access point 106 is used to locally reinforce the strata according to the strata conditions and excavate to form the third operating point 303. Then, the second vertical hole 201 is constructed between the tunnel structure 100 and the second vertical shaft 102, and the prestressed strand 202 is pulled from the second operating point 302 to the third operating point 303.

[0056] S5. The stratum is locally reinforced and excavated through tensioning port 107 according to the stratum conditions to form tensioning operation port 304. The telescopic rod 204 is used to cross the stratum from tensioning operation port 304 to the third operation port 303, and the prestressed strand 202 is pulled back to tensioning operation port 304.

[0057] S6. Insert both ends of the prestressed strand 202 into the anchoring system 400, fix one end, and connect the other end to the jack 409 and tension it to apply external prestress to the tunnel structure 100.

[0058] Preferably, in step S6, before the prestressed strand 202 is inserted into the anchoring system 400, the outer surface of the tunnel structure 100 at the third operating port 303 can be cleaned. This cleaning not only removes loose material, dirt, or other impurities that may be present on the surface of the tunnel structure 100, ensuring good contact between the prestressed strand 202 and the tunnel structure 100 and the bonding effect during subsequent mortar filling, but also allows the tension force to be effectively transferred from the prestressed strand 202 to the tunnel structure 100, improving the reinforcement effect. Simultaneously, a clean surface facilitates the inspection of the tunnel structure 100 by construction personnel, confirming the absence of cracks or other defects, thus ensuring construction quality. It also helps to identify and address potential corrosion problems of the prestressed strand 202 or the anchoring system 400, such as damp areas or sources of chemical corrosion, ensuring the long-term stability and durability of the system. Furthermore, a clean and unobstructed working surface makes the installation of the anchoring system 400 more convenient and allows for adjustments as needed to ensure the correct positioning of the prestressed strand 202.

[0059] Preferably, the purpose of applying external prestress to the tunnel structure 100 is to adjust the existing deformation of the tunnel structure 100 and resist its further deformation during subsequent operation. The applied prestress value is related to the current conditions of the tunnel structure 100 and the conditions that may occur in the future, including the design parameters of the tunnel structure 100, the existing deformation characteristics, the geological conditions, and the planned close-in construction.

[0060] Preferably, in addition to the steps described above, the method of the present invention may further include:

[0061] S7. The anchoring system 400 is treated with anti-corrosion and anti-rust treatment. The first vertical hole 200, the second vertical hole 201 and the second vertical shaft 102 are filled with mortar. The bottom of the first vertical shaft 101 is filled to the bottom of the tensioning port 107 and the top is covered to form the inspection well 600.

[0062] Preferably, the above steps can be repeated until multiple external prestressing points are applied within a length of 100 mm of the tunnel structure to be treated for the proposed defects. Preferably, the reasonableness of the assumed conditions for applying multiple external prestressing points can be verified through numerical simulation. For example, based on the previous design and experimental foundation of the prestressed segment structure, the following reference design can be obtained: using 4 to 6 prestressed strands 202 with a diameter of 15.2 mm and a tensile strength of 3000 MPa, controlling the tension at 2400 MPa, and the spacing between the prestressed strands 202 is about 2 m.

[0063] Preferably, the multiple external prestressing anchoring systems 400 arranged longitudinally along the tunnel structure 100 can be symmetrically arranged on both sides of the tunnel structure 100. That is, the previous anchoring system 400 is arranged on the left side of the tunnel structure 100 and tensioned, while the next anchoring system 400 is arranged on the right side of the tunnel structure 100 and tensioned, and so on in a cycle. This arrangement takes into account that during the tensioning process, the prestressed strands 202 will suffer prestress loss due to factors such as anchor deformation, prestressed strand shrinkage, friction between the prestressed strands 202 and the duct, and concrete creep. Moreover, as the distance from the anchoring system 400 increases, this prestress loss gradually increases, resulting in uneven stress on the tunnel structure 100. By symmetrically arranging the anchoring systems 400 on both sides of the tunnel structure 100, the parts with the greatest prestress loss of adjacent external prestressing systems can be staggered. This not only improves the uniformity of prestressing on the tunnel structure 100 as a whole, but also makes the stress on the tunnel structure 100 more reasonable and stable. The above arrangement helps ensure the prestressing effect at each anchorage point, reduces potential structural risks caused by excessive local prestress loss, and optimizes the mechanical properties of the entire tunnel structure. Furthermore, the symmetrical arrangement facilitates operational balance during construction, reducing potential structural displacement problems caused by unilateral loading.

[0064] Preferably, the first shaft 101 and the second shaft 102 should be excavated simultaneously. The shafts should be circular, with a smaller rather than larger outer diameter, and a larger rather than smaller clear distance from the tunnel structure 100. This avoids uneven load distribution on both sides of the tunnel structure 100 due to differences in shaft excavation depth and reduces disturbance to the tunnel structure 100 caused by unloading during shaft construction. Simultaneously, the shaft support structure 103 should be constructed promptly during shaft excavation to prevent deformation of the shaft itself. The outer diameter of the shaft can be limited to approximately 1.2m to 1.5m, and the clear distance from the tunnel structure 100 can be limited to greater than 0.5m. The shaft support structure 103 can be a precast reinforced concrete structure with waterproofing treatment at the joints. After the shaft excavation is completed, a concrete bottom reinforcement structure 108 can be constructed at the bottom of the shaft and waterproofed. After the shaft is constructed, the depth of the bottom reinforcement structure 108 should be greater than the bottom burial depth of the tunnel structure 100 to facilitate the threading of the prestressed strands 202 at the bottom. Since the control equipment such as the tensioning machine required for prestressing is placed on the ground outside the shaft, the inner diameter of the shaft only needs to be sufficient to allow construction personnel to move and operate the jacks 409.

[0065] Preferably, the first shaft 101 and the second shaft 102 are respectively provided with a first cable-passing port 104 and a second cable-passing port 105 at the same burial depth below the bottom of the tunnel structure 100, and a third cable-passing port 106 and a tensioning port 107 are respectively provided at the same burial depth above the top of the tunnel structure 100. When the shaft support structure 103 adopts a precast structure, the tunnel burial depth should be considered during the precast structure preparation stage to determine the setting of the cable-passing ports (first cable-passing port 104, second cable-passing port 105, and third cable-passing port 106) and the tensioning port 107. If the burial depth of the cable-passing ports and the tensioning port 107 is not set properly, the subsequent telescopic rod 204 will not be able to reach the corresponding operating port after crossing the strata, resulting in the inability to pull the prestressed strand 202.

[0066] Preferably, the cable-threading opening and the tensioning opening 107 have different functions. The cable-threading opening mainly serves the traction of the prestressed strand 202 by the telescopic pole 204 and is relatively small in size. The tensioning opening 107, in addition to serving the function of the cable-threading opening, also needs to serve the tensioning of the prestressed strand 202 and is relatively large in size. Furthermore, both the cable-threading opening and the tensioning opening 107 need to be removed during construction, and the structural thickness of this area should be thinner than other areas. Therefore, the first cable-threading opening 104, the second cable-threading opening 105, and the third cable-threading opening 106 are designed as small-sized pits with a thickness less than the surrounding area, while the tensioning opening 107 is designed as a large-sized pit with a thickness less than the surrounding area. The first cable-threading opening 104, the second cable-threading opening 105, and the third cable-threading opening 106 can be removed in one go, and the outer soil can be grouted for reinforcement. Then, small-sized first operating opening 301, second operating opening 302, and third operating opening 303 are excavated. The tensioning opening 107 is relatively large, and its complete removal at once could easily cause soil instability. Therefore, small holes can be drilled first for soil grouting reinforcement before the entire opening is removed to create the larger tensioning operating opening 304. Preferably, the main purpose of designing the operating opening as small is to assist the prestressed strand 202 in encircling the tunnel structure 100. This area requires the connection between the hook 205 of the telescopic rod 204 and the lifting ring 203 of the prestressed strand 202 to facilitate the telescopic rod 204 pulling the prestressed strand 202. The dimensions of the small operating opening can be, for example, 15cm × 15cm × 15cm. Preferably, the main purpose of designing the tensioning operating opening 304 as large is to serve the fixing and tensioning of the prestressed strand 202. Therefore, it needs to meet the space requirements for the installation of the anchoring system 400 and the construction of the jack 409. The dimensions of the large tensioning operating opening 304 can be, for example, 50cm × 50cm × 50cm.

[0067] Preferably, the inner diameter of the shaft support structure 103 is much smaller than the distance between the first shaft 101 and the second shaft 102. Therefore, the traction of the prestressed strand 202 requires the use of a telescopic rod 204 with a telescopic function and hooks 205 at the ends. If the same telescopic rod 204 is used for both lateral and vertical traction of the prestressed strand 202, the length of the telescopic rod 204 in its unextended state is less than the inner diameter of the shaft support structure 103, and the length in its fully extended state is greater than the depth of the first shaft 101 and the second shaft 102. If the telescopic rod 204 is only used for lateral traction of the prestressed strand 202, the length of the telescopic rod 204 in its fully extended state is greater than the distance between the first shaft 101 and the second shaft 102. The vertical traction of the prestressed strand 202 can use any rod with hooks 205 at the ends whose length exceeds the depth of the shaft.

[0068] Preferably, the end of the prestressed strand 202 is a circular lifting ring 203, which can be connected to the hook 205 of the telescopic rod 204. Considering that the external prestressing system is located in a groundwater environment, which is corrosive, ordinary prestressed strands 202 are prone to corrosion when exposed to this environment for a long time, thus affecting the durability and long-term safety of the external prestressing system. At the same time, since the prestressed strand 202 is located in the soil, the friction between the prestressed strand 202 and the tunnel structure 100 and the soil can be reduced during tensioning to ensure the uniform distribution of circumferential prestress as much as possible. Carbon fiber strands have advantages such as good corrosion resistance, wear resistance, lightweight and high strength, and can be used in environments such as nuclear industry and seawater, which can meet the durability requirements of external prestressing in tunnel structure 100.

[0069] Preferably, Figures 9 to 11 A structural schematic diagram of the anchoring system 400 and the anchor plate 401 is shown. The anchoring system 400 includes the anchor plate 401, the clamping plate 408, the jack 409, and the protective cover 500. The anchoring system 400 is used for tensioning and fixing (i.e., anchoring) the prestressed strands 202. Due to limited operating space, the external prestressing system can adopt a scheme of fixing one end and tensioning the other end. The anchoring system 400 is not fixed to the tunnel structure 100 and can move freely during the tensioning process.

[0070] Preferably, the anchor plate 401 includes an arc-shaped base 402, a tensioning surface 403, a first cluster of ducts 404, and a second cluster of ducts 405. The contact area between the anchor plate 401 and the tunnel structure 100 can utilize the arc-shaped base 402, with the radius of the arc being the same as the outer diameter of the tunnel structure 100. This means the entire surface of the arc-shaped base 402 can be in close contact with the outer surface of the tunnel structure 100. This facilitates movement of the arc-shaped base 402 during tensioning and increases the contact area between the anchor plate 401 and the tunnel structure 100, preventing damage to the tunnel structure 100 due to excessive stress exerted by the anchor plate 401 after tensioning. The first cluster of ducts 404 and the second cluster of ducts 405 can be arranged in a rectangular or circular array, consisting of variable-diameter circular oblique holes penetrating the anchor plate 401, including a small-diameter duct inlet 406 located below the tensioning surface 403 and a large-diameter duct outlet 407 located above the tensioning surface 403. Since the clamping piece 408 is a frustum shape with a circular through hole in the middle, the prestressed strand 202 can pass through the circular channel of the clamping piece 408. The clamping piece 408 is installed at the duct outlet 407. The variable diameter circular inclined hole design is beneficial for the clamping piece 408 to clamp the prestressed strand 202 during tensioning, and the greater the tension force, the greater the clamping force. In addition, since the duct inlet 406 is higher than the outer surface of the tunnel structure 100, the prestressed strand 202 is inserted obliquely into the duct inlet 406. Therefore, the slope of the duct cluster should be designed so that the prestressed strand 202 does not bend at the duct inlet 406, and the tensioning surface 403 should also be kept as perpendicular as possible to the duct cluster to reduce the prestress loss during tensioning.

[0071] Preferably, the external prestressing system can adopt a one-end fixed and one-end tensioning scheme. One end of the prestressed strand 202 is inserted through the duct inlet 406 of the first duct cluster 404 and exits through the duct outlet 407, and is fixed at the duct outlet 407 by a clamp 408. The other end of the prestressed strand 202 is inserted through the duct inlet 406 of the second duct cluster 405 and exits through the duct outlet 407, and is fixed by the clamp 408 after tensioning by the jack 409. To facilitate the operation of the jack 409, the jack 409 should face one side of the shaft (first shaft 101 or second shaft 102). During prestressing tensioning, the prestressed strand 202 cuts the soil under the tension of the jack 409 and continuously tightens towards the outer wall of the tunnel structure 100, eventually adhering tightly to the outer wall.

[0072] Preferably, all components of the anchoring system 400 can be made of corrosion-resistant materials. After tensioning, a corrosion-resistant protective cover 500 can be used to enclose the entire anchoring system 400, and the protective cover 500 can be filled with grease. A waterproof gasket 501 is provided between the protective cover 500 and the outer surface of the tunnel structure 100, and it can be fixed to the outer surface of the tunnel structure 100 using expansion bolts 502.

[0073] Preferably, the external prestressing system is located in a harsh environment, requiring regular inspection and maintenance. Except for the first shaft 101, all other excavated shafts, holes, and operating openings need to be sealed promptly after the external prestressing tensioning is completed. The first shaft 101 can be converted into a maintenance shaft 600. Due to the considerable depth of the first shaft 101, it is difficult for workers to inspect the anchoring system 400 for prestress loss and structural corrosion at the tensioning opening 107. When constructing the maintenance shaft 600, the bottom of the first shaft 101 needs to be backfilled to a depth below the tensioning opening 107, and the bottom of the maintenance shaft 601 should be constructed of concrete. Simultaneously, the opening of the maintenance shaft 600 can be fitted with a reinforced concrete cover 602. The strength of the cover 602 should meet traffic safety requirements, and the opening can be waterproofed and sealed if necessary.

[0074] According to a preferred embodiment, the mechanism of action of the external prestressing system constructed based on the method of the present invention on the tunnel structure 100 is as follows:

[0075] (1) Calculation of external prestress loss

[0076] During tensioning and anchoring, the prestressed strand 202 will experience prestress loss due to factors such as anchor deformation, strand shrinkage, concrete elastic deformation, and concrete creep. Among these, the prestress loss (σ1) caused by anchor deformation and prestressed strand shrinkage, and the prestress loss (σ2) caused by friction between the prestressed strand 202 and the outer wall of the tunnel structure 100, account for a large proportion of all prestress losses. Therefore, this invention mainly considers the prestress losses caused by σ1 and σ2, and their calculation formulas are as follows:

[0077]

[0078] σ²=σ con [1-e -(kr+μ)θ ],

[0079] In the formula, σ con The tension control stress value for prestressed strand 202 should be deducted from the anchorage friction loss; μ is the friction coefficient between the prestressed steel bar and the outer wall of the tunnel structure 100; k is the friction coefficient considering the misalignment of the segment assembly; r is half the outer diameter of the segment; θ is the angle from the tensioning end to the tangent of the duct section of the calculated cross-section curve; θ0 is the angle of reverse friction influence of prestressed strand 202, which can be calculated by the following formula:

[0080]

[0081] In the formula, 'a' represents the deformation of the tensioning end anchorage and the inward shrinkage value of the prestressed strand 202; E s The elastic modulus of the prestressed strand 202 is given.

[0082] Effective prestress (σ) of prestressed strand 202 e The prestress control stress value of prestressed strand 202 is calculated by subtracting various prestress losses from the prestressing control stress value. The expression is as follows:

[0083] σ e =σ con -σ1-σ2.

[0084] (2) Mechanism of action of external prestress on tunnel structure 100

[0085] like Figure 12 As shown, after the prestressed strand 202 is tensioned, the prestress will act on the tunnel structure 100, and through decomposition, it can form a radial force (σ) pointing towards the center of the tunnel structure 100. n ) and the tangential force (σ) tangential to the outer surface of the tunnel structure 100 t Force analysis was performed on a micro-segment of prestressed strand 202 and tunnel structure 100. The equilibrium equation of prestressed strand 202 can be expressed as:

[0086]

[0087] In the formula, dσ e dθ is the effective prestress increment of the prestressed strand 202; dθ is the wrap angle of the differential segment of the prestressed strand 202; t is the equivalent width of the working surface of the prestressed strand 202, which can be taken as the width of the anchor groove; θ is the included angle from the tensioning end to the tangent of the duct section of the calculated cross section curve.

[0088] Since dθ is very small, the following conclusion can be derived:

[0089]

[0090] Based on the above conclusions, the radial force (σ) can be calculated. n ) and tangential force (σ t The expression for ) is:

[0091]

[0092] (3) Effect of external prestressing on the internal force enhancement of tunnel structure 100

[0093] The tangential force (σ) generated on the tunnel structure 100 by external prestressing after tensioning and anchoring t This refers to the axial force provided to tunnel structure 100. Compared to ordinary tunnel structures, the axial force of tunnel structure 100 under this scheme can be divided into two parts: one part is the axial force generated by external soil and water loads, and the other part is the axial force formed by external prestressing. That is, the axial force borne by tunnel structure 100 under this scheme will be greater than that of ordinary tunnel structures.

[0094] Figure 13 The effective prestress of the prestressed strand 202 is calculated considering prestress loss terms σ1 and σ2 under different layout schemes for the anchoring system 400. The prestressed strand 202 consists of 6 bundles, each bundle composed of multiple strands of prestressed carbon fiber strands, with a single strand diameter of 15.2 mm and a tensile strength of 3000 MPa. Taking the top of the tunnel structure 100 as 0°, the angle increases clockwise. The right anchorage position of the tunnel structure 100 is at 60°, and the left anchorage position is at 300°. σ con The pressure is 2400 MPa, and the pressure μ is 0.2 rad. -1 k is 0.0015m -1 a is 1mm, E s The effective prestress of a single prestressed strand 202 is between 1101 and 1892 kN, with a maximum and minimum effective prestress difference of 790 kN, when the anchorage system 400 is arranged alternately on the right and left sides of the tunnel structure 100. When the anchorage system 400 is arranged on both sides, the average effective prestress of the prestressed strands 202 on both sides is between 1357 and 1700 kN, with a maximum and minimum effective prestress difference of 342 kN, which is only 43% of the difference when arranged on one side. When the anchorage system 400 is arranged on either the right or left side of the tunnel structure 100, the effective prestress is asymmetrically distributed along both sides of the tunnel structure 100, causing the tunnel structure 100 to bear a large eccentric load. When the anchoring system 400 is arranged at intervals on the right and left sides of the tunnel structure 100, the effective prestress is symmetrically distributed along both sides of the tunnel structure 100, resulting in a more uniform and reasonable stress distribution on the tunnel structure 100.

[0095] According to a preferred embodiment, the impact of shaft excavation on the deformation of tunnel structure 100 under the external prestressing treatment scheme of the present invention is analyzed. The specific analysis process is as follows:

[0096] (1) Model parameter settings

[0097] Figure 14 This is a software simulation diagram of the shaft excavation under the external prestressed treatment scheme established using a geological structure model. Tunnel structure 100 has an outer diameter of 6.0m, a thickness of 0.3m, a ring width of 1.5m, a total of 5 rings, and a top burial depth of 15m. The two side shaft structures have an outer diameter of 1.2m, an inner diameter of 0.8m, a burial depth of 23m, a spacing of 2m, and a net distance of 1.8m from tunnel structure 100. Both shafts and tunnel structure 100 are made of C50 concrete. The geological stratum is silty fine sand; using a modified Mohr-Coulomb model, the soil elastic modulus is 24.14MPa, Poisson's ratio is 0.3, and the unit weight is 20.3kN / m³. 3 Triaxial test secant stiffness 5000kN / m 2The unloading elastic modulus is 50 MPa, and the final expansion angle is 10°.

[0098] (2) Simulation steps

[0099] a. Establish a soil model and perform ground stress balance; b. Excavate the tunnel and construct the tunnel structure 100; c. Excavate the shaft and construct the support structure.

[0100] (3) Simulation results

[0101] The horizontal deformation of the tunnel structure before and after the excavation of the shaft under the external prestressing treatment scheme is as follows: Figure 15 As shown, the maximum horizontal deformation of tunnel structure 100 before and after shaft excavation was 6.71 mm and 6.74 mm, respectively, with a deformation increment of only 0.03 mm, or 0.4%. This indicates that shaft excavation had almost no effect on the deformation of tunnel structure 100; in other words, external prestressing construction caused only minor disturbance to tunnel structure 100.

[0102] According to another preferred embodiment, the method for treating external prestressing defects in shield tunnels according to the present invention is compared with a conventional method. The specific comparison process is as follows:

[0103] (1) Model parameter settings

[0104] A three-dimensional model of tunnel structure 100 was established using Abaqus software. The external prestressing treatment scheme of this invention and a conventional scheme were used to treat shield tunnel defects under two-sided unloading conditions. Tunnel structure 100 has an outer diameter of 6.0m, a thickness of 0.3m, a ring width of 1.5m, and consists of one ring. The material is C50 concrete. The external prestressing treatment scheme involves placing a bundle of six 15.2mm prestressed carbon fiber strands with a tensile strength of 3000MPa outside tunnel structure 100. This is a truss-linear elastic model, with a tension control stress value of 2400MPa. The conventional scheme does not use external prestressing. A load structure model was used to apply loads around tunnel structure 100, including a vertical pressure and bottom reaction of 220kPa and a lateral pressure of 80kPa.

[0105] (2) Simulation steps

[0106] For the external prestressing treatment scheme, the simulation steps are as follows: a. Establish a model of tunnel structure 100 and perform ground stress balance; b. Apply peripheral loads to tunnel structure 100; c. Establish a prestressed strand model and apply prestress to the prestressed strand 202; d. Reduce the pressure on both sides of tunnel structure 100 to 40 kPa. Preferably, for the ordinary scheme, simulation step c can be deleted.

[0107] (3) Simulation results

[0108] The internal forces of the external prestressing treatment scheme and the ordinary scheme under unloading conditions are as follows: Figure 16 and Figure 17 As shown, the axial force per meter of the external prestressing treatment scheme and the ordinary scheme are 2005.5 kN and 925 kN, respectively. The axial force of the external prestressing treatment scheme is 117% higher than that of the ordinary scheme. The bending moments of the external prestressing treatment scheme and the ordinary scheme are 343 kN·m and 323 kN·m, respectively. The bending moment of the external prestressing treatment scheme is slightly larger than that of the ordinary scheme, but overall, it significantly improves the internal forces of the existing tunnel and greatly enhances the ultimate bearing capacity of the existing tunnel.

[0109] The overall deformation increments of the external prestressing treatment scheme and the ordinary scheme under unloading conditions are shown in the figure. Figure 18 The horizontal convergence deformation increments of the external prestressing treatment scheme and the conventional scheme were 26 mm and 46.4 mm, respectively, representing a 44% reduction in horizontal convergence. The vertical convergence deformation increments of the external prestressing treatment scheme and the conventional method were 24 mm and 35 mm, respectively, representing a 31% reduction in vertical convergence. Therefore, compared to the conventional scheme, the external prestressing treatment scheme resulted in reduced deformation.

[0110] Based on the simulation comparison results, it can be seen that applying external prestress can significantly increase the axial force of the tunnel structure 100 and reduce deformation, making the structure more rationally stressed, effectively improving tunnel deformation problems, and reducing deformation hazards in later operation.

[0111] It should be noted that the specific embodiments described above are exemplary. Those skilled in the art can devise various solutions inspired by the disclosure of this invention, and these solutions all fall within the scope of this invention and its protection. Those skilled in the art should understand that this specification and its accompanying drawings are illustrative and do not constitute a limitation on the claims. The scope of protection of this invention is defined by the claims and their equivalents. This specification contains multiple inventive concepts; phrases such as "preferred" or "according to a preferred embodiment" indicate that the corresponding paragraph discloses an independent concept. The applicant reserves the right to file divisional applications based on each inventive concept. Throughout the text, the feature introduced by "preferred" is only an optional mode and should not be construed as mandatory. Therefore, the applicant reserves the right to abandon or delete relevant preferred features at any time.

Claims

1. A trenchless micro-disturbance external prestressing system, characterized in that, It includes: prestressed Stranded wire (202) and anchoring system (400). It applies external prestress to the tunnel structure (100) by constructing shafts and openings on both sides of the existing tunnel structure (100) in the following manner: The two ends of the prestressed strand (202) are inserted into the anchoring system (400), one end is fixed, and the other end is connected to the jack (409) and tensioned to apply external prestress to the tunnel structure (100). When the prestress is tensioned, the prestressed strand (202) cuts the soil under the action of the jack (409) and continuously tightens towards the outer wall of the tunnel structure (100), eventually adhering closely to the outer wall. A first vertical shaft (101) and a second vertical shaft (102) are constructed on both sides of the tunnel structure (100). A first vertical hole (200) is constructed between the tunnel structure (100) and the first vertical shaft (101), and a second vertical hole (201) is constructed between the tunnel structure (100) and the second vertical shaft (102). The prestressed strand (202) can be pushed and / or pulled in the first vertical hole (200) and the second vertical hole (201). The first shaft (101) and the second shaft (102) are respectively provided with a first cable-passing port (104) and a second cable-passing port (105) at the same burial depth below the bottom of the tunnel structure (100), and a third cable-passing port (106) and a tensioning port (107) are respectively provided at the same burial depth above the top of the tunnel structure (100). The first cable-piercing opening (104), the second cable-piercing opening (105), the third cable-piercing opening (106), and the tensioning opening (107) can be removed and the outer soil can be grouted and excavated to form the first operating opening (301), the second operating opening (302), the third operating opening (303), and the tensioning operating opening (304) which is larger than the above operating openings. The telescopic rod (204) can pull the prestressed strand (202) from the first operating port (301) to the second operating port (302), from the second operating port (302) to the third operating port (303), and from the third operating port (303) to the tensioning operating port (304).

2. The system according to claim 1, characterized in that, The telescopic rod (204) used for traction of prestressed strand (202) is a multi-section telescopic round rod with hooks (205) at the ends. The length of the telescopic rod (204) in the unextended state is less than the inner diameter of the shaft support structure (103), and the length in the fully extended state is greater than the distance between the first shaft (101) and the second shaft (102).

3. The system according to claim 1, characterized in that, The end of the prestressed strand (202) is a circular lifting ring (203) that can be connected to the hook (205) of the telescopic rod (204).

4. The system according to claim 1, characterized in that, The anchoring system (400) includes an anchor plate (401), a clamp (408), a jack (409), and a protective cover (500). The anchor plate (401) includes an arc-shaped base (402), a tensioning surface (403), a first duct cluster (404), and a second duct cluster (405). The radius of the arc of the arc-shaped base (402) is consistent with the outer diameter of the tunnel structure (100). The duct cluster is a variable-diameter circular oblique hole that penetrates the anchor plate (401), including a duct inlet (406) located below the tensioning surface (403) and a duct outlet (407) located above the tensioning surface (403).

5. The system according to claim 4, characterized in that, One end of the prestressed strand (202) is inserted through the duct inlet (406) of the first duct cluster (404) and exits through the duct outlet (407), and is fixed at the duct outlet (407) by a clamp (408); the other end of the prestressed strand (202) is inserted through the duct inlet (406) of the second duct cluster (405) and exits through the duct outlet (407), and is fixed at the duct outlet (407) by a clamp (408) after being tensioned by a jack (409).

6. The system according to claim 1, characterized in that, The components of the anchoring system (400) are made of corrosion-resistant materials and are wrapped with a protective cover (500). The protective cover (500) is filled with grease or coated with a coating to ensure corrosion resistance. A waterproof gasket (501) is provided between the protective cover (500) and the outer surface of the tunnel structure (100) and is fixed with expansion bolts (502).

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