Tunnel wall post-grouting material with self-repairing function and preparation method thereof

Abstract

A tunnel wall backfill grouting material with self-healing function and its preparation method are disclosed. The grouting material is formed by mixing a high-silica-alumina content grouting substrate, sodium silicate, calcium oxide, self-healing capsules, and water in a mass ratio of 2.0-5.0:1.0-1.5:1.0:0.08-0.45:3.2-9.0. The self-healing capsules include capsule A and capsule B, with a shell thickness of 0.105±0.005 mm, composed of ethyl cellulose and urea-formaldehyde resin in a mass ratio of 10.0-20.0. Capsule A contains sodium silicate, sodium hydroxide, and potassium hydroxide in a mass ratio of 1.0:0.007-0.014:0.003-0.006; capsule B contains quicklime and hydroxyl graphene oxide in a mass ratio of 100.0:0.001-0.01. The self-healing function of this invention refers to the fact that after the grouting anti-seepage layer behind the tunnel wall is cracked under load, capsules A and B crack accordingly. Sodium silicate dissolves in an alkaline environment and reacts with calcium hydroxide generated by the hydration of quicklime to form hydrated calcium silicate gel. Together with the covalent polymer gel formed by the decondensation and polymerization of the silicon and aluminum components in the grouting material, it fills the cracks and pores in the grouting layer, thereby achieving the purpose of tunnel anti-seepage self-healing.

Description

Technical Field

[0001] This invention relates to the field of building construction, and in particular to a tunnel wall backfill grouting material with self-healing function and its preparation method. Background Technology

[0002] Backfill grouting is a crucial method for tunnel seepage prevention and has been widely applied in practical engineering. When a tunnel is below the groundwater level or surrounded by fissure water, the grouting anti-seepage layer can rupture under environmental load disturbances, allowing groundwater to rapidly seep in along the fissures. This leads to tunnel leakage, water inrush, and even further structural damage, seriously threatening traffic safety and causing unpredictable economic losses, such as severe corrosion of equipment within the tunnel, reduced equipment efficiency, erosion of the lining, steel reinforcement corrosion, and ultimately structural failure. Furthermore, secondary grouting is often required after tunnel leakage occurs. Grouting construction can disrupt tunnel operations, and when the surrounding groundwater environment is complex, open-hole grouting also carries significant risks. Moreover, secondary grouting can only repair macroscopic cracks; microscopic cracks (less than 0.05 mm wide) remain prevalent. Therefore, it is difficult to completely eliminate tunnel defects. How to enable the grouting anti-seepage layer to self-repair during the micro-crack incubation stage, starting from the grouting material itself, is an important research direction for comprehensively eliminating tunnel leakage.

[0003] However, so far, the relevant results have been very limited.

[0004] Application number CN202010034165.6 discloses a multi-component composite grouting material for shield tunnel walls made from industrial waste and its preparation method. The grouting material is characterized by being formed by mixing 50-70 parts of fly ash, 10-30 parts of blast furnace slag powder, 10-30 parts of inert steel slag powder, 35-55 parts of alkaline activator, 150-200 parts of fine sand, 1-2 parts of water-reducing agent, 0-0.5 parts of retarder, and 80-120 parts of water. It has high early strength and short setting time, but this patent does not have a self-healing function.

[0005] Application No. 202210460927.8 describes an environmentally responsive, homogeneous, expansive self-healing microcapsule for concrete and its preparation method. The microcapsule material is characterized by comprising 80-100 parts bentonite repair agent, 10-30 parts clay curing agent, 15-35 parts MgO expansive agent, and 2-8 parts binder. Its self-healing mechanism involves the microcapsule rupturing under stress. The inorganic salts in the curing agent react with the alkali metals in the repair agent to form alum, which slowly expands into an amorphous gel under alkali activation. The MgO expansive agent also generates expansive products upon contact with water. This invention is primarily applied to the repair of concrete structures and does not conflict with the application field of this invention.

[0006] Application number CN202110373495.2 discloses a method for preparing a self-healing cement-based composite material. The composite material is characterized by being formed by mixing 20-50 parts of repair material (one of slag, fly ash, or metakaolin), 5-15 parts of expansion agent (one of MgO, calcium sulfoaluminate, or alunite), 20-35 parts of active mineral powder (slag powder or silica fume), 1-3 parts of activator (one of CaO, NaOH, Na2CO3, Na2SO4, or water glass), and 10-20 parts of deionized water. Graphene oxide and SiO2 are added to the mixture, with their mass ratio to the repair material ≤10% and not 0. This patented method has a complex manufacturing process and high cost, is difficult to prepare on-site, and is mostly used for secondary grouting to seal cracks. Summary of the Invention

[0007] The purpose of this invention is to provide a tunnel wall backfill grouting material with self-healing function and its preparation method. The grouting material is formed by mixing a high-silica-alumina content grouting substrate, sodium silicate, calcium oxide, and water in a specific ratio, and adding a certain number of self-healing capsules. Based on the principle that aluminosilicates undergo depolymerization and condensation under alkaline activation to form a covalently polymerized gel, this method preventively solves the problems of damage and cracking of the tunnel wall backfill grouting seepage prevention layer caused by environmental load disturbances, which can lead to water leakage, water inrush, steel corrosion, and poor lining durability. Furthermore, because the grout has a self-healing function, as long as the self-healing capsule material remains in the damaged and cracked area of ​​the tunnel lining, it will continuously form gel, sealing the cracks, avoiding secondary grouting, ensuring the quality of the seepage prevention layer, and resulting in significant economic and social benefits.

[0008] To address the problems in the existing technology, the technical solution adopted by this invention is as follows:

[0009] A tunnel wall backfill grouting material with self-healing function is formed by mixing a high-silica-alumina content grouting substrate, sodium silicate, calcium oxide, self-healing capsules, and water. The water-to-solid ratio of the grouting material is 0.8-1.2, and the grout specific gravity is 1.4-1.8. The high-silica-alumina content grouting substrate contains 65-75% silicon and aluminum elements. The mass ratio of the high-silica-alumina content grouting substrate to sodium silicate and calcium oxide is 1.0-2.0:1, and the mass ratio of sodium silicate to calcium oxide is 1.0-1.5:1.

[0010] As an improvement, the high-silicon-aluminum content grouting substrate is a powdered mixture composed of solid waste steel slag, mineral powder, fly ash, and red mud with high silicon-aluminum content.

[0011] As an improvement, the self-healing capsule is composed of a mixture of self-healing capsule A and self-healing capsule B, with a mass ratio of 2-6% to the solid phase material. The mass ratio of self-healing capsule A to self-healing capsule B is 0.75-1.25. The solid phase material includes a grouting substrate, sodium silicate, and calcium oxide.

[0012] A further improvement is that the shells of both self-healing capsule A and self-healing capsule B are made of a mixture of ethyl cellulose and urea-formaldehyde resin, wherein the mass ratio of ethyl cellulose to urea-formaldehyde resin is 10.0-20.0, the shell particle size is 0.5-1.0 mm, and the shell thickness is 0.105±0.005 mm.

[0013] A further improvement is that the cavity material of the self-healing capsule A is a powder made of anhydrous sodium silicate, sodium hydroxide and potassium hydroxide, all with a particle size of less than 50 mesh. The proportion of sodium hydroxide is 0.7-1.4% of the mass of anhydrous sodium silicate, and the proportion of potassium hydroxide is 0.3-0.6% of the mass of anhydrous sodium silicate.

[0014] A further improvement is that the volume ratio of the dry-mixed powder of anhydrous sodium silicate, sodium hydroxide, and potassium hydroxide in the cavity of the self-healing capsule A is 0.6-0.7.

[0015] A further improvement is that the cavity material of the self-healing capsule B is composed of quicklime powder with a particle size of less than 300 mesh and hydroxyl graphene oxide with a particle size of less than 3000 mesh, and the mass ratio of hydroxyl graphene oxide to quicklime powder is 0.001%-0.01%.

[0016] A further improvement is that the volume ratio of quicklime powder and hydroxyl graphene oxide in the cavity of the self-healing capsule B is 0.45-0.55, so as to ensure that the density of the self-healing capsule A, the self-healing capsule B and the grouting material behind the tunnel wall are close, and that they are uniformly distributed in the grout.

[0017] The above-mentioned method for preparing a tunnel wall backfill grouting material with self-healing function includes the following steps: 1) preparing intracavitary mixtures of self-healing capsule A and self-healing capsule B respectively; 2) preparing the shell of the self-healing capsule using ethyl cellulose and urea-formaldehyde resin, and injecting the repair material into it; 3) mixing the grouting substrate with high silica-alumina content, sodium silicate, calcium oxide and water according to the specified water-solid ratio to form a slurry with uniform consistency; 4) adding self-healing capsule A and self-healing capsule B to the slurry and mixing them thoroughly so that the self-healing capsules are evenly distributed in the slurry to form the grouting material.

[0018] The self-healing principle of the grouting material of this invention is as follows: under alkaline activation, aluminosilicates undergo depolymerization and condensation to form a covalent polymer gel. When the grouting anti-seepage layer behind the tunnel wall ruptures under load, the capsules A and B sealed inside it crack, and groundwater seeps in along the crack surface, causing anhydrous sodium silicate to dissolve in the alkaline environment created by sodium hydroxide and potassium hydroxide. On the one hand, it reacts with the calcium hydroxide formed by the hydration of quicklime to form hydrated calcium silicate gel. On the other hand, the aluminosilicate component in the grouting material behind the wall further undergoes depolymerization and condensation under the activation of sodium hydroxide and potassium hydroxide to form a covalent polymer gel, thereby filling the cracks and pores of the grouting layer together with the hydrated gel, achieving the purpose of tunnel anti-seepage self-healing.

[0019] Beneficial effects:

[0020] Compared with existing technologies, this invention provides a tunnel wall backfill grouting material with self-healing function and its preparation method.

[0021] (1) The advantage of this invention is that by adding self-healing capsules to the grout in advance, the problem of tunnel water leakage and poor durability that may occur after the tunnel seepage prevention layer is cracked under load is solved in the crack initiation stage. At the same time, it also avoids the shortcomings of secondary grouting, such as incomplete elimination of tunnel defects, high construction risk, and serious impact on operational safety.

[0022] (2) The self-healing capsule is designed with a specific gravity range similar to that of the grouting material, which solves the problem of uniform mixing with the grouting material and can prevent secondary problems caused by uneven distribution of the capsule in the seepage prevention layer.

[0023] (3) The grouting substrate behind the tunnel wall is industrial solid waste, which is a resource-based reuse of industrial solid waste. It can effectively save cement, reduce energy consumption and CO2 emissions, and reduce engineering construction costs.

[0024] (4) The raw materials for grouting are dry powder mixtures, similar to cement, which are convenient for storage and transportation. Attached Figure Description

[0025] Figure 1 This is a flowchart illustrating a method for preparing a self-healing tunnel wall backfill grouting material according to the present invention.

[0026] Figure 2 The change in compressive strength of silty soil with 10% self-healing geopolymer content;

[0027] Figure 3 The change in compressive strength of silty soil with 15% self-healing geopolymer content;

[0028] Figure 4 The change in compressive strength of silty soil with 20% self-healing geopolymer content;

[0029] Figure 5The change in compressive strength of coarse-grained filler in group A of geopolymer stabilization;

[0030] Figure 6 The change in compressive strength of coarse-grained filler in group B for geopolymer stabilization. Detailed Implementation

[0031] The following embodiments are provided to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way.

[0032] The specific implementation methods of this invention include:

[0033] 1) Check if the grouting holes are blocked and check if the grouting pump is working properly;

[0034] 2) Check if the pressure display system is functioning properly;

[0035] 3) Install the sealing seams for the grouting holes;

[0036] 4) Use steel slag powder and mineral powder to make grouting substrate, with a mass ratio between 0.4 and 0.6. The mass ratio of grouting substrate to (sodium silicate and calcium oxide) is between 1.0 and 2.0, the mass ratio of sodium silicate to calcium oxide is between 1.0 and 1.5, and the water-solid ratio is 0.8 and 1.2 to prepare grouting.

[0037] 5) Add 1-6% of self-healing capsules to the grouting and mix thoroughly;

[0038] 6) Use a mortar pump to transport the prepared slurry to the tunnel boring machine's slurry storage tank;

[0039] 7) Use a grouting pump to grout multiple reserved grouting holes simultaneously. The grouting pressure should be controlled at more than twice the soil pressure at the top of the tunnel arch and slightly greater than the soil pressure at the bottom of the tunnel arch, but not more than 0.4 MPa.

[0040] 8) During the grouting process, the grout should be continuously stirred to prevent segregation, and the stirring time should be controlled to not exceed 45 minutes.

[0041] 9) After grouting is completed, check the grouting holes and continuously revise the grouting parameters and design based on the pressure-flow-time curve, the grout discharge from the outlet hole, and the deformation of the tunnel lining segments and the deformation of the ground and surrounding buildings.

[0042] 10) Re-grout the unmet parts until the tunnel wall is completely grouted.

[0043] Example 1

[0044] Geopolymer grouting material was prepared by mixing steel slag and mineral powder as base materials with sodium silicate and calcium oxide in a certain proportion and then adding water and stirring evenly. 4% self-healing capsules were added to the mixture to obtain the self-healing grouting material. Then, 10%, 15%, and 20% of the self-healing grouting material were added to silty sand, and cylindrical samples with a diameter of 3.91 cm and a coverage of 8 cm were prepared at a water-cement ratio of 1.2.

[0045] Sample preparation was completed within 25 minutes, with 9 parallel samples for each working condition. After 24 hours of standard curing (temperature 20℃±3℃, relative humidity not less than 90%), the samples were carefully demolded to ensure no breakage or deformation, and then cured for another 28 days. To compare and evaluate the effect of self-healing capsules on sample strength development, 9 parallel samples with the same self-healing material dosage were divided into 3 groups. The first group underwent unconfined compressive strength testing using a universal pressure testing machine to obtain the average compressive strength of the polymer-stabilized silt. The second group underwent 5 saturated freeze-thaw cycles to induce internal damage in the samples before unconfined compressive strength testing to obtain the compressive strength of the frost-damaged polymer-stabilized silt before repair. The third group underwent 5 saturated freeze-thaw cycles to induce internal damage in the samples before being placed under standard curing conditions for 14 days, and then unconfined compressive strength testing to obtain the compressive strength of the frost-damaged polymer-stabilized silt after repair. The test results are as follows: Figure 2-4 As shown in Table 1, the strength of frost-damaged geopolymer-stabilized siltstone significantly recovers under self-healing action, with the 10% self-healing material admixture example showing the most significant repair effect. Furthermore, although it cannot reach the initial strength in a short period, the difference between its strength and the initial strength will gradually decrease over time.

[0046] Table 1 Strength test results of Example 1

[0047]

[0048] Example 2:

[0049] The self-healing material differs from Example 1 in that the self-healing capsule dosage is 6%. Group A and B coarse-grained fillers, conforming to the design requirements of high-speed railway subgrade, were prepared using clay particles smaller than 0.075mm, fine sand of 0.075-0.25mm, medium sand of 0.25-0.5mm, coarse sand of 0.5-2mm, and boulders of 2-20mm. Then, 15% geopolymer material was added to fillers A and B respectively, and cylindrical specimens were prepared by controlling the water content at maximum moisture content + 2%. Specimen preparation was controlled within 25 minutes, with 9 parallel samples for each working condition. After the specimens were placed in a standard curing environment (temperature 20℃±3℃, relative humidity not less than 90%) for 24 hours, they were carefully demolded to ensure no breakage or deformation, and then cured for another 28 days.

[0050] To compare and evaluate the effect of self-healing capsules on the strength development of samples, nine parallel samples with the same self-healing material dosage were divided into three groups. In the first group, unconfined compressive strength tests were directly conducted using a universal pressure testing machine to obtain the average compressive strength of the geopolymer-stabilized coarse-grained filler. In the second group, all samples underwent five saturated freeze-thaw cycles to induce internal damage before unconfined compressive strength tests were conducted to obtain the compressive strength of the frozen-damaged geopolymer-stabilized coarse-grained filler before repair. In the third group, all samples underwent five saturated freeze-thaw cycles to induce internal damage before being placed under standard curing conditions for 14 days, followed by unconfined compressive strength tests to obtain the compressive strength of the frozen-damaged geopolymer-stabilized coarse-grained filler after repair. The test results are as follows: Figure 5-6 As shown in Table 2, the strength of both groups A and B packings recovered significantly after freeze-thaw damage, with group A showing better recovery. This indicates that the present invention can improve the resistance of high-speed railway subgrades to freeze-thaw damage.

[0051] Table 2 Strength test results of Example 2

[0052]

[0053] In summary, this invention has promising engineering applications. Based on the principle that aluminosilicates depolymerize and condense under alkaline activation to form a covalent polymer gel, when the grouting anti-seepage layer behind the tunnel wall ruptures under load, its inner capsules rupture accordingly. Sodium silicate dissolves in the created alkaline environment, and the hydrated calcium silicate gel formed by its reaction with calcium hydroxide formed by the hydration of quicklime, along with the aluminosilicate components in the grouting material, further depolymerize and condense under the activation of sodium hydroxide and potassium hydroxide to form a covalent polymer gel. Together, they fill the cracks and pores in the grouting layer, achieving the purpose of self-repairing tunnel anti-seepage. This method exhibits high damage repair sensitivity and good repair effect. Furthermore, the raw materials required for this invention are readily available and inexpensive. The grouting substrate is mainly composed of solid waste, providing a new approach to treating engineering waste, making it environmentally friendly.

[0054] The above are merely preferred embodiments of the present invention and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should recognize that any equivalent substitutions and obvious changes made based on the content of this specification should be included within the protection scope of the present invention.

Claims

1. A tunnel wall backfill grouting material with self-healing function, characterized in that, A grouting material is formed by mixing a high-silicon-aluminum content grouting substrate, sodium silicate, calcium oxide, self-healing capsules, and water. The grouting material has a water-to-solid ratio of 0.8-1.2 and a grout specific gravity of 1.4-1.

8. The high-silicon-aluminum content grouting substrate contains 65-75% silicon and aluminum. The mass ratio of the high-silicon-aluminum content grouting substrate to sodium silicate and calcium oxide is 1.0-2.0:1, and the mass ratio of sodium silicate to calcium oxide is 1.0-1.5:

1. The self-healing capsules are composed of self-healing capsule A and self-healing capsule B, with a mass ratio of 2-6% to the solid phase material. The self-healing capsules A and B... The mass ratio is 0.75-1.25, and the solid phase material includes grouting substrate, sodium silicate, and calcium oxide; the cavity material of the self-healing capsule A is a powder made of anhydrous sodium silicate, sodium hydroxide, and potassium hydroxide with a particle size of less than 50 mesh, wherein the sodium hydroxide content is 0.7-1.4% of the mass of anhydrous sodium silicate, and the potassium hydroxide content is 0.3-0.6% of the mass of anhydrous sodium silicate; the cavity material of the self-healing capsule B is a mixture of quicklime powder with a particle size of less than 300 mesh and hydroxyl graphene oxide with a particle size of less than 3000 mesh, and the mass ratio of hydroxyl graphene oxide to quicklime powder is 0.001%-0.01%.

2. The tunnel wall backfill grouting material with self-healing function according to claim 1, characterized in that, The high-silicon-aluminum content grouting substrate is a powdery mixture composed of solid waste steel slag, mineral powder, fly ash, and red mud with high silicon-aluminum content.

3. The tunnel wall backfill grouting material with self-healing function according to claim 1, characterized in that, The shells of both self-healing capsule A and self-healing capsule B are made of a mixture of ethyl cellulose and urea-formaldehyde resin, wherein the mass ratio of ethyl cellulose to urea-formaldehyde resin is 10.0-20.0, the shell particle size is 0.5-1.0 mm, and the shell thickness is 0.105±0.005 mm.

4. The tunnel wall backfill grouting material with self-healing function according to claim 1, characterized in that, The volume ratio of the dry-mixed powder of anhydrous sodium silicate, sodium hydroxide, and potassium hydroxide in the cavity of the self-healing capsule A is 0.6-0.

7.

5. The tunnel wall backfill grouting material with self-healing function according to claim 1, characterized in that, The volume ratio of quicklime powder and hydroxyl graphene oxide in the cavity of the self-healing capsule B is 0.45-0.55, so as to ensure that the density of the self-healing capsule A, the self-healing capsule B and the grouting material behind the tunnel wall are close, and that they are uniformly distributed in the grout.

6. A method for preparing a tunnel wall backfill grouting material with self-healing function according to claim 1, characterized in that, Includes the following steps: 1) Prepare the cavity mixtures of self-healing capsule A and self-healing capsule B separately; 2) Prepare the shell of the self-healing capsule using ethyl cellulose and urea-formaldehyde resin, and inject the repair material into it; 3) Mix the grouting substrate with high silica-alumina content, sodium silicate, calcium oxide and water according to the specified water-solid ratio to form a slurry with uniform consistency; 4) Add self-healing capsule A and self-healing capsule B to the slurry and mix thoroughly so that the self-healing capsules are evenly distributed in the slurry to form the grouting material.

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