A self-repairing system for water seepage cracks of a shield tunnel and a preparation method and application thereof

Abstract

This invention belongs to the field of seepage crack repair, specifically relating to a self-repairing system for seepage cracks in shield tunnels, its preparation method, and its application. The self-repairing system for seepage cracks in shield tunnels provided by this invention includes a polyvinyl alcohol (PVA) bag and a composite capsule of polyacrylonitrile fiber and microorganisms disposed within the cavity of the PVA bag. It has a high seepage barrier recovery rate, reaching over 90%, and requires no manual operation during the repair process, reducing tunnel maintenance costs.

Description

Technical Field

[0001] This invention belongs to the field of water seepage crack repair, specifically relating to a self-repairing system for water seepage cracks in shield tunnels, its preparation method, and its application. Background Technology

[0002] With the rapid expansion of urban underground space development, shield tunnels, as a common tunnel structure, have been widely designed and used. Due to complex geological conditions, adjacent tunnel construction, and harsh operating conditions, concrete shield tunnels are prone to problems such as segment cracking, misalignment, and tensioning under the long-term influence of multiple factors. This allows free water from the outside of the tunnel to seep into the interior. Early water seepage problems in shield tunnels generally occur on the outer layer of the concrete segments and are difficult to detect in time. As the seepage cracks in the shield tunnel increase, a series of problems such as piping can occur, seriously threatening the safe operation of the tunnel. Timely repair of tunnel seepage problems has become a research hotspot both domestically and internationally.

[0003] Microbial self-healing technology, as a type of biomimetic self-healing method, has attracted widespread attention due to its environmental friendliness and self-healing potential. Its core working principle is to pre-embed alkali-resistant microorganisms and specific substrates into concrete during mixing. Once the concrete cracks, the entry of moisture and oxygen activates the dormant microorganisms. Through a series of biochemical reactions, the pre-embedded culture medium in the concrete is metabolized into calcium carbonate precipitate, filling the cracks and achieving self-healing. However, due to various factors such as technical defects, high process difficulty, and stringent application requirements, existing self-healing systems have relatively poor self-healing effects and high costs.

[0004] Existing research indicates that microbial-induced calcium carbonate deposition technology can effectively improve the self-healing ability of concrete cracks, restoring the concrete's impermeability after repair. However, current research mainly focuses on water seepage caused by concrete fragmentation. No solutions have yet been proposed for water seepage caused by the failure of waterstops in shield tunnels. Waterstops are an integral part of the waterproofing design of tunnel segments. According to the "Technical Specification for Safety Protection of Urban Rail Transit Structures," when the opening at the joint of tunnel segments is less than 6mm, the waterstop can effectively prevent water from entering the tunnel. When the opening at the joint is greater than 6mm, water from outside the tunnel can seep into the segments. Waterstops are generally made of rubber-based materials. Compared to concrete, although they are widely used in tunnel segments due to their advantages such as lighter weight, relatively lower cost, and faster action, they are prone to aging and corrosion, and are more difficult to repair. Water seepage caused by the failure of waterstops in shield tunnels leads to a reduced service life and high maintenance costs for shield tunnel structures. Therefore, developing a solution to overcome the water seepage problem caused by the failure of waterstops in shield tunnels is crucial. Summary of the Invention

[0005] In view of the problems of water seepage caused by the failure of the waterstop in shield tunnels mentioned above, the present invention will provide a self-repairing system for water seepage gaps in shield tunnels, its preparation method and application.

[0006] To achieve the above objectives, the following technical solutions are specifically included:

[0007] A self-repairing system for water seepage cracks in shield tunnels includes a polyvinyl alcohol (PVA) bag and a polyacrylonitrile fiber and microbial composite capsule disposed in the cavity inside the PVA bag. In the PVA bag, the volume percentages of the polyacrylonitrile fiber and the microbial composite capsule are 60-80% and 20-40%, respectively.

[0008] The microbial composite capsule is composed of a core, an inner wall, and an outer protective wall, from the inside out.

[0009] The core comprises the following components in weight percentage: sodium silicate 20-40%, sodium carbonate 10-30%, sodium hydroxide 5-15%, bentonite 5-15%, quicklime 5-15%, and penetrating crystallizing additive 15-25%.

[0010] The inner wall comprises the following components by weight percentage: 10-15% porous media material, 2-5% microbial powder, 18-25% fly ash, 15-22% silica fume, 13-25% metakaolin, and 20-30% calcium carbonate powder. The microbial powder includes at least one of alkali-resistant Bacillus, Bacillus subtilis, and urease-producing bacteria.

[0011] The self-repairing system for water seepage gaps in shield tunnels of the present invention includes a polyvinyl alcohol (PVA) filling bag and a polyacrylonitrile fiber and microbial composite capsule disposed in the internal cavity of the PVA filling bag. The microbial composite capsule contains microorganisms (aerobic) and a culture medium for microbial growth. The PVA filling bag encapsulates the polyacrylonitrile fiber and the microbial composite capsule, ensuring that the microorganisms are in a dormant state under anhydrous conditions. On the other hand, when water seeps into the tunnel, the filling bag dissolves in water and releases the internal microbial capsules. The metabolism of the microorganisms in the composite capsules drives calcium carbonate deposition. At the same time, the polyacrylonitrile fiber can fix the microorganisms and increase the repair width, thereby improving the water seepage prevention capability of the shield tunnel and increasing the tunnel's durability.

[0012] In the core, sodium silicate and sodium carbonate react with calcium ions to form hydrated calcium silicate and calcium carbonate, filling the cracks; sodium hydroxide creates an alkaline environment in the cracks, improving CO2 utilization; quicklime provides calcium ions and reacts with water to form an alkaline environment; bentonite has water-swelling properties, and as it expands with water, it fills the remaining pores; penetrating crystallizing additives penetrate microcracks and promote the self-healing of the core material.

[0013] The core also includes a binder with a mass percentage of 0.5-5%.

[0014] Preferably, the diameter of the self-repairing system for water seepage gaps in the shield tunnel is 3-7 mm.

[0015] When the opening at a conventional tunnel joint exceeds 6mm, water from outside the tunnel can seep into the tunnel segments. When the self-repairing system for water seepage gaps in shield tunnels of this invention is placed directly on the waterstop at the tunnel segment joint, the selected self-repairing system for water seepage gaps in shield tunnels of the above-mentioned size can be suitable for the waterstop at the conventional tunnel segment joint, effectively preventing the opening or crack from continuing to expand in advance, playing a timely repair role, effectively improving the tunnel's water-proof capability, and increasing the tunnel's durability.

[0016] Preferably, the thickness of the polyvinyl alcohol filling bag is 20 μm or more.

[0017] Polyvinyl alcohol (PVA) filling bags are made from PVA film materials such as the NT type. The melting temperature of this type of filling bag is 25℃, the tensile strength reaches 44MPa or more, the tensile strength reaches 50MPa or more, and the elongation can reach 150-400%. The thickness of a single layer of film is about 20μm. This type of PVA filling bag not only has room temperature water solubility, but also has good mechanical strength, which can effectively protect the internal polyacrylonitrile fibers and microbial composite capsules.

[0018] Preferably, the diameter of the polyacrylonitrile fiber is 1-5 mm.

[0019] Polyacrylonitrile (PA) fiber is characterized by high strength, good toughness, and aging resistance. Compared to steel fiber, it has better flexibility. When the filling belt is compressed, the hardness of PA fiber is insufficient to damage the polyvinyl alcohol (PVA) filling belt; fibers that are too hard (such as steel fiber) are prone to puncturing the filling belt, leading to the loss of internal material. PVA filling bags are insoluble in water, and microbial composite capsules are easily adsorbed onto the surface of PA fiber. The soft texture of PA fiber can act as a buffer, ensuring the integrity of the microbial composite capsules and preventing them from rupturing when compressed.

[0020] When the polyvinyl alcohol filling bag dissolves in water, the poor hygroscopicity of the polyacrylonitrile fiber ensures that it will not dissolve in the water environment. The high surface density of the polyacrylonitrile fiber can effectively fill the pores of the concrete pipe joints and prevent the microbial capsules from being washed away by water. When the microbial composite capsules release microorganisms and generate calcium carbonate deposits, the calcium carbonate can be deposited along the polyacrylonitrile fibers, reducing the area of ​​the gaps that need to be repaired and improving the repair efficiency.

[0021] Preferably, the mass percentages of the core, inner wall, and outer protective wall are 30-40%, 55-60%, and 5-10%, respectively.

[0022] Preferably, the porous media material comprises a carbonate, wherein the carbonate comprises at least one of sodium carbonate, ammonium carbonate, and potassium carbonate.

[0023] The porous media material of the inner wall of the microbial composite capsule is carbonate, which can further increase the ability of internal microorganisms to induce carbonate formation, improve the ability of calcium carbonate deposition inside the cracks, and at the same time improve the tunnel's impermeability and durability.

[0024] Preferably, the outer protective wall comprises at least one of polyvinyl alcohol, acrylic resin, polyurethane rubber, polyurea, cellulose acetate butyrate, vinyl acetate copolymer, urea-formaldehyde resin, and polyurethane.

[0025] The outer protective wall of the microbial composite capsule made of the above-mentioned material has excellent hydrophilicity, alkali resistance, brittleness and sealing performance. It can also rupture when external microcracks occur, allowing microorganisms to flow out, thus ensuring the release efficiency of internal aerobic microorganisms.

[0026] Preferably, the diameter of the microbial composite capsule is 20-100 μm.

[0027] This invention provides a method for preparing the self-repairing system for water seepage gaps in shield tunnels, comprising the following steps:

[0028] (1) The raw materials of the core are mixed and granulated to obtain core particles; the raw materials of the inner wall are mixed with water to obtain a pre-impregnation solution; the core particles are then immersed in the pre-impregnation solution and dried to obtain core particles coated with the inner wall; the raw materials of the outer protective wall are then coated or sprayed onto the surface of the core particles coated with the inner wall and dried to obtain the microbial composite capsule.

[0029] (2) Polyacrylonitrile fiber and microbial composite capsules are wrapped in polyvinyl alcohol bags to obtain the self-repairing system for water seepage gaps in shield tunnels.

[0030] The present invention also provides an application of the aforementioned self-healing system for seepage cracks in shield tunnels in shield tunnel waterstops.

[0031] The self-repair system for water seepage gaps in shield tunnels is pre-embedded in the grooves of precast concrete tunnel segments, wherein the grooves are at least one type: an outer groove and an inner groove.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) The self-repair system for seepage gaps in shield tunnels provided by the present invention, under waterless conditions, the external polyvinyl alcohol filling bag plays a protective and fixing role for polyacrylonitrile fibers and microbial composite capsules, and the waterless and oxygen-free environment inside the filling bag is conducive to the long-term preservation of microbial composite capsules.

[0034] (2) When the tunnel segment waterstop fails, the free water in the soil comes into contact with the polyvinyl alcohol bag, causing the polyvinyl alcohol bag to dissolve and the polyacrylonitrile fiber and microbial composite capsule are released. The polyacrylonitrile fiber can fix the microorganisms and reduce the gap of the tunnel joint, which is conducive to the deposition of calcium carbonate.

[0035] (3) The self-repairing system for seepage cracks in shield tunnels provided by the present invention has a high seepage prevention and recovery rate of over 90%. No manual operation is required during the repair process, which reduces the cost of tunnel maintenance. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the transverse plan of a shield tunnel.

[0037] Figure 2 This is a schematic diagram of the transverse plane of a shield tunnel joint.

[0038] Figure 3 This is a longitudinal cross-sectional view of the fiber microbial composite capsule filling bag.

[0039] Figure 4 This is a cross-sectional view of a microbial complex capsule.

[0040] Figure 5 This is a schematic diagram illustrating the release of polyacrylonitrile fiber and microbial composite capsules.

[0041] Figure 6 This is a schematic diagram of the repair of joint gaps in a shield tunnel.

[0042] The following are explanations of the reference numerals used in the accompanying drawings: 1. Concrete segment of shield tunnel; 2. External groove of segment; 3. Internal groove of segment; 4. Waterstop; 5. Polyacrylonitrile fiber and microbial capsule filling bag; 6. Polyvinyl alcohol filling bag; 7. Microbial composite capsule; 8. Polyacrylonitrile fiber; 9. Outer wall of microbial composite capsule; 10. Inner wall of microbial composite capsule; 11. Core of microbial composite capsule; 12. Calcium carbonate deposit.

[0043] Figure 7 The graphs show the barrier effect of Example 1 and Comparative Example 1. Detailed Implementation

[0044] To better illustrate the purpose, technical solution, and advantages of this invention, specific embodiments will be used to further explain the invention below. Unless otherwise specified, the test methods used in the embodiments and / or comparative examples are conventional methods; the materials and reagents used, unless otherwise specified, are commercially available.

[0045] The polyvinyl alcohol (PVA) bags used below can be obtained by cutting and sewing PVA film material directly. Commercially available PVA bags can be used directly, with their length and width dimensions controlled within 7mm.

[0046] The core particles can be selected from commercially available particle products, or they can be prepared from the raw materials in the specific examples and comparative examples below.

[0047] Example 1

[0048] This embodiment discloses a self-repairing system for water seepage cracks in a shield tunnel, comprising a polyvinyl alcohol (PVA) bag and a polyacrylonitrile fiber and microbial composite capsule disposed in the cavity inside the PVA bag. In the PVA bag, the volume percentages of the polyacrylonitrile fiber and the microbial composite capsule are 70% and 30%, respectively.

[0049] The microbial composite capsule is composed of a core, an inner wall, and an outer protective wall from the inside out, with the following mass percentages: core 35%, inner wall 55%, and outer protective wall 10%.

[0050] The core comprises the following components by mass percentage: 30% sodium silicate, 20% sodium carbonate, 10% sodium hydroxide, 10% bentonite, 10% quicklime, and 20% penetrating crystallizing additive (model: XYPEX).

[0051] The inner wall comprises the following components by weight percentage: 12% porous media material (sodium carbonate), 3% microbial powder (alkali-resistant Bacillus), 20% fly ash, 20% silica fume, 20% metakaolin, and 25% calcium carbonate powder.

[0052] The outer protective wall is polyvinyl alcohol;

[0053] A detailed structural diagram is attached. Figure 1-5 As shown, the inner and outer groove dimensions of the segment are 3-5mm, so the diameter of the self-repairing system for water seepage gaps in the shield tunnel, which is formed by the entire filling strip, is controlled within 7mm. To facilitate filling the filling bag, the diameter of the microbial composite capsule is 20-100μm, which is easy to adhere to the surface of polyacrylonitrile fiber. The diameter of the polyacrylonitrile fiber is 1-5mm, which is more suitable.

[0054] A method for preparing a self-repairing system for water seepage gaps in shield tunnels, specifically including the following steps:

[0055] (1) Preparation of polyvinyl alcohol filling: Polyvinyl alcohol film material with a thickness of 20 micrometers is directly cut and sewn to form polyvinyl alcohol filling with a length and width of about 6-7 mm.

[0056] (2) The preparation steps of the microbial complex capsules include:

[0057] (2-1) Preparation of core particles: Weigh and mix the raw material powders of the core particles evenly; then put them into a disc granulator. The inclination angle of the disc granulator is adjusted to 45° and the rotation speed is 30 rpm. Add a small amount of binder (such as adding 1% water glass solution as a binder, which is alkaline and has good viscosity). The powder is gradually added during the rolling process until the particles reach the required size. Then, sieve them and dry them at 40°C to obtain core particles.

[0058] (2-2) Inner wall composition and outer protective wall preparation: Disperse or dissolve all the raw materials of the inner wall in water (the mass ratio of all raw materials of the inner wall to the mass of water is 1:1) to obtain the inner wall prepreg; Impregnate the core obtained in step (2-1) into the inner wall prepreg, stir and mix, and then dry to obtain the core covering the inner wall material.

[0059] (2-3) Preparation of outer protective wall: The raw material of the outer protective wall is evenly sprayed or coated on the surface of the core covering the inner wall material, and then dried to obtain the microbial composite capsule;

[0060] (3) Preparation of the entire self-healing system: Polyacrylonitrile fiber (commercially available) and the microbial composite capsule are wrapped in a polyvinyl alcohol bag to obtain a self-healing system for water seepage gaps in shield tunnels, and the system is pre-embedded in the grooves inside and outside the precast concrete tunnel segments.

[0061] Example 2

[0062] The difference between this embodiment and Embodiment 1 is that:

[0063] This embodiment discloses a self-repairing system for water seepage cracks in a shield tunnel, comprising a polyvinyl alcohol (PVA) bag and a polyacrylonitrile fiber and microbial composite capsule disposed in the cavity inside the PVA bag. In the PVA bag, the volume percentages of the polyacrylonitrile fiber and the microbial composite capsule are 60% and 40%, respectively.

[0064] The microbial composite capsule is composed of a core, an inner wall, and an outer protective wall from the inside out, with the following mass percentages: core 40%, inner wall 55%, and outer protective wall 5%.

[0065] The core comprises the following components in weight percentage: 20% sodium silicate, 30% sodium carbonate, 15% sodium hydroxide, 5% bentonite, 15% quicklime, and 15% penetrating crystallizing additive.

[0066] The inner wall comprises the following components by weight percentage: 10% porous media material (ammonium carbonate), 2% microbial powder (1% Bacillus subtilis and 1% urease-producing bacteria), 18% fly ash, 15% silica fume, 25% metakaolin, and 30% calcium carbonate powder.

[0067] The outer protective wall is made of acrylic resin.

[0068] Example 3

[0069] The difference between this embodiment and Embodiment 1 is that:

[0070] This embodiment discloses a self-repairing system for water seepage cracks in a shield tunnel, comprising a polyvinyl alcohol (PVA) bag and a polyacrylonitrile fiber and microbial composite capsule disposed in the cavity inside the PVA bag. In the PVA bag, the volume percentages of the polyacrylonitrile fiber and the microbial composite capsule are 80% and 20%, respectively.

[0071] The microbial composite capsule is composed of a core, an inner wall, and an outer protective wall, from the inside out, with the three components accounting for 30%, 60%, and 10% of their respective mass percentages.

[0072] The core comprises the following components in weight percentage: sodium silicate 40%, sodium carbonate 10%, sodium hydroxide 5%, bentonite 15%, quicklime 5%, and penetrating crystallizing additive 25%.

[0073] The inner wall comprises the following components by weight percentage: 15% porous media material (potassium carbonate), 5% microbial powder (2.5% urease-producing bacteria), 25% fly ash, 22% silica fume, 13% metakaolin, and 20% calcium carbonate powder.

[0074] The outer protective wall is cellulose acetate butyrate.

[0075] Comparative Example 1

[0076] The difference between this comparative example and Example 1 is that no polyacrylonitrile fiber was added in this comparative example, and all of them were filled with microbial composite capsules in polyvinyl alcohol bags.

[0077] Test method for permeability recovery rate:

[0078] A seepage tank and a water level gauge are installed at the joint to record the water level changes in the seepage tank. The joint permeability coefficient is then calculated based on these water level changes.

[0079]

[0080] In the formula, k is the permeability coefficient, V is the volume of infiltrated water, and T is the infiltration time. The initial permeability coefficient, the permeability coefficient during repair, and the permeability coefficient without gaps are then tested separately. The seepage resistance recovery rate is calculated using the following formula:

[0081]

[0082] Where η is the seepage prevention recovery rate, k0, k t and k t0 These are the initial permeability coefficient, the permeability coefficient during repair, and the permeability coefficient without gaps, all in L / s.

[0083] The test results are attached. Figure 6 As shown, when the opening at the joint exceeds 6mm after 28 days, water from outside the tunnel will seep into the tunnel segments. At this point, the self-healing system in the inner and outer grooves of this invention will activate. This system plays a dual role, repairing the gaps at the joints through the combined action of polyacrylonitrile fibers and microbial composite capsules. In Example 1, the self-healing system restored 97% of the seepage resistance, while in Comparative Example 1, it only restored 68%. This demonstrates that adding polyacrylonitrile fibers can effectively improve the seepage resistance efficiency of tunnel segment joints.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A self-repairing system for water seepage gaps in shield tunnels, characterized in that, The product includes a polyvinyl alcohol (PVA) filling bag and a polyacrylonitrile fiber and microbial composite capsule disposed in the internal cavity of the PVA filling bag. In the PVA filling bag, the volume percentages of the polyacrylonitrile fiber and the microbial composite capsule are 60-80% and 20-40%, respectively. The microbial composite capsule is composed of a core, an inner wall, and an outer protective wall, from the inside out. The core comprises the following components by mass percentage: sodium silicate 20-40%, sodium carbonate 10-30%, sodium hydroxide 5-15%, bentonite 5-15%, quicklime 5-15%, and penetrating crystallizing additive 15-25%; The inner wall comprises the following components by mass percentage: 10-15% porous media material, 2-5% microbial powder, 18-25% fly ash, 15-22% silica fume, 13-25% metakaolin, and 20-30% calcium carbonate powder. The microbial powder includes at least one of alkali-resistant Bacillus, Bacillus subtilis, and urease-producing bacteria.

2. The self-repairing system for water seepage gaps in shield tunnels as described in claim 1, characterized in that, The diameter of the self-repairing system for water seepage gaps in shield tunnels is 3-7mm.

3. The self-repairing system for water seepage gaps in shield tunnels as described in claim 1, characterized in that, The porous media material includes carbonates, and the carbonates include at least one of sodium carbonate, ammonium carbonate, and potassium carbonate.

4. The self-repairing system for water seepage gaps in shield tunnels as described in claim 1, characterized in that, The outer protective wall comprises at least one of polyvinyl alcohol, acrylic resin, polyurethane rubber, polyurea, cellulose acetate butyrate, vinyl acetate copolymer, urea-formaldehyde resin, and polyurethane.

5. The self-repairing system for water seepage gaps in shield tunnels as described in claim 1, characterized in that, The diameter of the microbial complex capsule is 20-100 μm.

6. The self-repairing system for water seepage gaps in shield tunnels as described in claim 1, characterized in that, The diameter of the polyacrylonitrile fiber is 1-5 mm.

7. The self-repairing system for water seepage gaps in shield tunnels as described in claim 1, characterized in that, The thickness of the polyvinyl alcohol filling bag is 20 μm or more.

8. The self-repairing system for water seepage gaps in shield tunnels as described in claim 1, characterized in that, The mass percentages of the core, inner wall, and outer protective wall are 30-40%, 55-60%, and 5-10%, respectively.

9. The method for preparing the self-repairing system for seepage cracks in shield tunnels as described in any one of claims 1-8, characterized in that, Includes the following steps: (1) The raw materials of the core are mixed and granulated to obtain core particles; the raw materials of the inner wall are mixed with water to obtain a pre-impregnation solution; the core particles are then immersed in the pre-impregnation solution and dried to obtain core particles coated with the inner wall; the raw materials of the outer protective wall are then coated or sprayed onto the surface of the core particles coated with the inner wall and dried to obtain the microbial composite capsule. (2) Polyvinyl alcohol packaging bags are used to wrap polyacrylonitrile fibers and microbial composite capsules; The self-repairing system for water seepage gaps in shield tunnels was obtained.

10. The application of a self-healing system for seepage cracks in shield tunnels in shield tunnel waterstops, characterized in that, The system is the self-repairing system for water seepage gaps in shield tunnels as described in any one of claims 1-8.

Images