Method for repairing loess erosion rill by micro-channel fiber reinforced micp multistage grouting

Abstract

The present application relates to the technical field of putting solidifying material or filling material into soil for consolidation, and discloses a method for repairing loess erosion rill by using micro-channel fiber reinforced MICP multistage grouting, wherein before injecting the bacteria solution and calcium urea required by MICP, mud slurry doped with plant vessel fiber and gel salt is first injected, the mud slurry with weak diffusion capacity is used to block the large cracks that cause the loss of the bacteria solution and calcium urea, and only the micro cracks suitable for MICP repair are left; the gel salt in the mud slurry generates gel quickly after injection, and the mud slurry is shaped before solidification, so that the mud slurry loss is avoided and the repair speed is kept up with the development speed of the loess erosion rill; the plant vessel fiber forms micro migration channels to avoid complete blockage after solidification; combined with the facultative anaerobic characteristics of bacillus megaterium, the engineering bacteria can still infiltrate the micro cracks and play a biological cementation role in the relatively anoxic environment in the mud slurry. Meanwhile, the grouting and consolidation body is not easy to be damaged. The above points are combined, and the MICP is successfully applied to repair the loess erosion rill.

Description

Technical Field

[0001] This invention relates to the field of consolidation technology by placing solidifying material or pore-filling material into soil, and in particular to a method for repairing loess erosion gullies by multi-stage grouting with microchannel fiber-reinforced MICP. Background Technology

[0002] MICP, short for Microbial Induced Calcium Carbonate Precipitation, is a biotechnology that utilizes the metabolic activities of specific microorganisms to generate calcium carbonate precipitates, thereby cementing loose particles or repairing cracks. At its core is a common biochemical reaction process—urea hydrolysis. Urease produced by microorganisms (often Bacillus pasteurellii, a strict aerobic bacterium) catalyzes the hydrolysis of urea. The resulting carbonate ions react with soil / rock or additionally injected calcium to form calcium carbonate precipitates, thus repairing micro-cracks.

[0003] MICP differs significantly from conventional grouting repair processes. Its grout is entirely a dilute aqueous solution with extremely low viscosity and excellent fluidity, allowing it to penetrate even the finest cracks for repair. Simultaneously, the generated calcium carbonate crystals grow from the surface of soil / rock particles, forming a strong physicochemical bond with the original matrix, resulting in better overall integrity. Furthermore, if dormant bacteria and nutrients remain in the treated material, when new cracks form and come into contact with moisture, the surviving bacteria may be reactivated, producing new calcium carbonate to "heal" the cracks—a smart self-healing mechanism.

[0004] Loess is a type of soil with low viscosity and weak resistance to water erosion. Water erosion is a problem in many loess areas, including the Loess Plateau of my country. Water erosion initially forms fine gullies, which deepen and erode further to form crisscross gullies. These crisscross gullies have distinct edges, and small steep scarps form at their mouths, reaching 1-2 meters in width and depth. Further erosion of these crisscross gullies forms gullies with distinct scarps at their heads. Landslides and collapses frequently occur along the gully edges, causing the gullies to widen continuously, reaching depths of several meters to tens of meters and lengths of several hundred meters. As gullies further develop, their slopes gradually become gentler due to collapse, and the bottom fills with debris, forming wide and shallow dry valleys called ravines. Therefore, in addition to vegetation restoration, another important aspect of loess soil and water conservation is to eliminate erosion gullies as soon as they appear, preventing their further development.

[0005] MICP technology, due to its environmental friendliness and self-healing capabilities, shows promise for the repair of loess erosion gullies. However, in practical applications, the inventors have discovered that the following characteristics of loess lead to difficulties in applying MIP technology to the repair of loess erosion gullies: 1. The problem of customer churn: Loess is a soil with very low clay content, which makes it prone to cracking. The erosion gullies are often connected to multiple larger fissures. The MICP solution injected into the erosion gullies will not only be lost in large quantities during grouting, but will also be quickly washed away during subsequent precipitation. Bacteria and reactants have difficulty adhering and cannot form effective cementation.

[0006] 2. Structural strength challenges: The loess matrix has low strength, and the cement formed by loess and calcium carbonate is easily destroyed by continuous water erosion and freeze-thaw cycles.

[0007] 3. Efficiency Challenges: In loess regions, erosion gullies develop rapidly, necessitating a repair method that can quickly fill gullies, possess a certain initial strength, and maintain long-term stability. However, the effectiveness of MICP technology relies on relatively slow biochemical reactions and crystal growth, often leaving insufficient time for timely repairs.

[0008] The inventors attempted to pre-fill the erosion grooves, but found that the MICP solution could not be injected normally after filling, and the corresponding microorganisms (Pasteurella multocida) could not grow normally. Summary of the Invention

[0009] This invention provides a method for repairing loess erosion gullies by multi-stage grouting with microchannel fiber-reinforced polymer (MICP).

[0010] The technical problem to be solved is that while MIP technology is environmentally friendly and self-healing, it cannot be applied to repair loess erosion gullies because MIP solution is easily lost from loess, the cementitious body formed by loess and calcium carbonate is not strong enough, and the repair speed cannot keep up with the development speed of erosion gullies in loess areas.

[0011] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a method for repairing loess erosion gullies by microchannel fiber-reinforced (MICP) multi-stage grouting, comprising the following steps: Step 1: Investigate the condition of loess erosion gullies, and adjust the grouting material and grouting method according to the investigation results; Step 2: Prepare grouting material, which includes microchannel fiber slurry, bacterial solution, and urea calcium agent; The microchannel fiber slurry is a slurry mixed with plant vascular fibers and gelling salts. The gelling salts are soluble polymeric salts that can produce gels after being injected into loess erosion gullies to prevent the microchannel fiber slurry from being lost. The bacterial solution is a suspension of engineered bacteria that are facultative anaerobic and can secrete urease. The urea calcium agent is a calcium salt solution doped with urea and engineered bacteria as a carbon source. Step 3: Based on the survey results of Step 1, inject microchannel fiber slurry into the loess erosion gullies. After the microchannel fiber slurry solidifies, it blocks the cracks outside the micro-cracks in the loess erosion gullies. Step 4: After the microchannel fiber slurry has solidified, inject the bacterial solution into the loess erosion gullies; Step 5: After the bacterial solution has seeped into the loess erosion furrows along the plant's vascular fibers, inject urea-calcium agent into the loess erosion furrows. Engineered bacteria decompose urea to produce carbonate ions, which combine with calcium ions to form calcium carbonate stones, thus repairing the microcracks that were not filled by the microchannel fiber slurry in step three.

[0012] Furthermore, in step one, based on the different conditions of loess erosion gully exposure, the following two working conditions are identified: Condition 1: If the loess erosion gullies are open trenches, then in step two, it is not necessary to control the length of the plant vascular fibers and the fluidity of the microchannel fiber slurry. In step three, the surface filling method guided by the vascular fibers is used for grouting. Condition 2: If the loess erosion gullies are partially exposed underground gullies, then in step three, steel pipe pressurized grouting is used. In step two, the length of the plant vascular fibers is 4-6 mm, and the viscosity of the microchannel fiber slurry is 40-50 seconds, based on the Marsh funnel viscosity.

[0013] Furthermore, in step two, the gelling salt is sodium alginate, and before sodium alginate is mixed into the microchannel fiber slurry, a slurry sample is taken for a premixing test. If sodium alginate does not gel after being mixed into the slurry sample, it indicates that the calcium ion content of the microchannel fiber slurry is qualified and sodium alginate can be directly mixed in. Otherwise, it indicates that the calcium ion content of the microchannel fiber mud exceeds the standard. In this case, sodium carbonate is first used as a pretreatment agent to reduce the calcium ion content in the microchannel fiber mud to the qualified level, and then sodium alginate is mixed in. The minimum amount of sodium carbonate is determined through gradient experiments, and the minimum amount of sodium carbonate is used to reduce the calcium ion content.

[0014] Furthermore, in step two, the preparation process of the microchannel fiber slurry includes the following sub-steps: Step 2.1a: Take loess soil from the area where the loess erosion gullies are located, crush it, dry it in the sun, and sieve it; Step 2.2a: Mix no less than 2.5 parts by weight of plant vascular fibers into 100 parts by weight of loess, and then add water to make a slurry; Step 2.3a: Adjust the calcium ion content in the mud to the acceptable level; Step 2.4a: Add 0.5-0.7 parts by weight of sodium alginate to the mud.

[0015] Furthermore, the plant vascular fibers are made from wood fibers, bamboo fibers, or straw fibers made from barkless wood or straw after the leaves have been removed. The plant vascular fibers are pretreated by soaking in an alkaline solution and then washing before being mixed into the microchannel fiber slurry to optimize interfacial adhesion.

[0016] Furthermore, the content of engineered bacteria in the bacterial solution is not less than 100 million CFU / ml, and in step four, free bacterial solution appears at the end of the loess erosion gully below the intermittent grouting of the bacterial solution.

[0017] Furthermore, the engineered bacteria are Bacillus megaterium isolated from the soil where loess erosion gullies are located, and strains with high urease activity are screened using a culture medium with urea as the sole nitrogen source.

[0018] Furthermore, in step five, urea-calcium agent is intermittently injected until free urea-calcium agent appears at the end of the loess erosion gully; The carbon source in the urea calcium preparation is glucose, and the calcium salt is calcium chloride. Each liter of urea calcium preparation contains 55-65 grams of urea, 50-60 grams of calcium chloride, and 8-12 grams of glucose.

[0019] Compared with existing technologies, the microchannel fiber-reinforced polymeric acid (MICP) multi-stage grouting method for repairing loess erosion gullies, as described in this invention, has the following advantages: In this invention, the different diffusion capabilities of different grouting materials are fully utilized. Before injecting the bacterial solution and urea calcium agent required for MIP, a slurry mixed with plant vascular fibers and gelling salts is injected first. The slurry has a weak diffusion capability, which blocks the large cracks that cause the loss of bacterial solution and urea calcium agent, leaving only micro cracks suitable for MIP repair. After the gelling salts in the mud are injected, they quickly form a gel, which shapes the mud before it solidifies. This not only prevents mud loss but also allows the repair speed to keep up with the development of erosion gullies in the loess region. The plant vascular fibers in the mud provide microscopic migration channels for subsequent engineered bacteria, avoiding physical blockage after the mud solidifies. This design, combined with the facultative anaerobic characteristics of Bacillus megaterium used in this invention, solves the core problem of traditional MIP technology (which often uses strictly aerobic Bacillus pasteurellium) where engineered bacteria cannot survive and function due to internal hypoxia after mud injection, thus ensuring the repair effect.

[0020] Meanwhile, the plant vascular fibers make the grouting solidified body formed by the solidification of mud a reinforced soil with high strength and strong resistance to wind / water erosion. The mixture of reinforced soil and calcium carbonate crystals formed by MIP is not easily destroyed under the continuous scouring of water flow and freeze-thaw cycles.

[0021] Combining the above points, MICP was successfully applied to the repair of loess erosion gullies, thus enabling the repair to have long-term stability and ecological compatibility. Attached Figure Description

[0022] Figure 1 This is a flowchart of a method for repairing loess erosion gullies using microchannel fiber-reinforced microchannel grouting (MICP) according to the present invention. Detailed Implementation

[0023] Taking the key technology project for efficient vegetation restoration in difficult sites (project number 2024YFD2200500) as an example, a method for repairing loess erosion gullies by microchannel fiber-reinforced MIP multi-stage grouting includes the following steps: Step 1: Investigate the condition of loess erosion gullies, and adjust the grouting material and grouting method according to the investigation results; Loess erosion gullies exhibit various forms, thus requiring investigation.

[0024] Step 2: Prepare the grouting material, which includes microchannel fiber slurry, bacterial solution, and urea calcium agent; Microchannel fiber mud is a mud mixed with plant vascular fibers and gelling salts; The "plant vascular bundle fibers" mentioned here refer to fibers composed of plant vascular bundles. Vascular bundles are structures formed by a vertical row of interconnected dead cells in the plant stem; they are very thin tubes primarily used for water transport. Placed here, they provide pathways for the migration of engineered microorganisms. Because the vascular bundles are very thin, with a cross-section smaller than soil particles, even if they become blocked, they cannot be completely blocked, always leaving pathways for microbial migration. Simultaneously, the outer surface of the vascular bundles also allows for microbial migration, as plant fibers cannot be perfectly seamlessly integrated with the soil.

[0025] Gel-forming salts are soluble polymeric salts that can produce gels after being injected into the fine erosion gullies of loess, thus preventing the loss of microchannel fiber slurry. Although microchannel fiber mud has high viscosity, its solidification is slow, and it can still be lost in larger fissures. Furthermore, due to the rapid development of erosion gullies in the Loess Plateau, sometimes the microchannel fiber mud, before it has solidified, can be washed away by light rainfall or soil deformation, causing these gullies to widen or deepen. In such cases, gelling salts can help stabilize the microchannel fiber mud and overcome these problems.

[0026] The bacterial solution is a suspension of engineered bacteria that are facultative anaerobic and can secrete urease; Here, because microchannel fiber slurry needs to be injected first, and then MIP technology is used, even with plant vascular fibers, there will still be varying degrees of oxygen deficiency in the deep soil. At this time, commonly used strictly aerobic engineered bacteria cannot grow normally.

[0027] Urea calcium preparation is a calcium salt solution doped with urea and engineered bacteria as a carbon source; Step 3: Based on the survey results of Step 1, inject microchannel fiber slurry into the loess erosion gullies. After the microchannel fiber slurry solidifies, it blocks the cracks in the loess erosion gullies except for the micro-cracks (generally referring to cracks with a width of less than 100 micrometers). This approach takes advantage of the weak diffusion capacity of mud, which cannot repair those tiny cracks, but MICP technology can. Furthermore, the cracks that mud can seal can lead to the loss of bacterial solution and urea calcium agent; in this combination, the disadvantages of the two methods are offset.

[0028] Step 4: After the microchannel fiber slurry has solidified, inject the bacterial solution into the loess erosion gullies; Step 5: After the bacterial solution has seeped into the loess erosion furrows along the plant's vascular fibers, inject urea-calcium agent into the loess erosion furrows. Engineered bacteria decompose urea to produce carbonate ions, which combine with calcium ions to form calcium carbonate stones, thus repairing the microcracks that were not filled by the microchannel fiber slurry in step three.

[0029] In step one, based on the different conditions of loess erosion gully exposure, the work is divided into the following two scenarios: Condition 1: If the loess erosion gullies are open trenches, then in step two, it is not necessary to control the length of the plant vascular fibers and the fluidity of the microchannel fiber slurry. In step three, the surface filling method guided by the vascular fibers is used for grouting. Loess erosion gullies may be open channels, completely exposed. In this case, it is easy to handle, and microchannel fiber slurry can be directly poured into the channel along the open channel.

[0030] Condition 2: If the loess erosion gullies are partially exposed underground gullies, then in step three, steel pipe pressurized grouting is used. In step two, the length of the plant vascular fibers is 4-6 mm, and the viscosity of the microchannel fiber slurry is 40-50 seconds, based on the Marsh funnel viscosity.

[0031] However, loess erosion gullies can also become hidden channels. Hidden channels have limited points where mud can be injected, requiring specialized grouting tools (such as steel perforated pipes). In this case, the fluidity of the mud and the length of the plant vascular fibers must be considered. The basic principle of the Marsh funnel viscometer is to allow a certain amount (946 ml) of liquid to flow freely through a funnel under gravity, recording the time required for outflow. This time is usually expressed in seconds; the longer the outflow time, the higher the viscosity of the liquid. Experiments show that a viscosity of 40-50 seconds ensures smooth injection of microchannel fiber mud without loss along micro-cracks. A plant vascular fiber length of 4-6 mm ensures sufficient reinforcement without tangling and affecting grouting through the steel perforated pipe.

[0032] In step two, the gelling salt is sodium alginate. Before mixing sodium alginate into the microchannel fiber slurry, a slurry sample is taken for a premixing test. If sodium alginate does not gel after being mixed into the slurry sample, it indicates that the calcium ion content of the microchannel fiber slurry is qualified and sodium alginate can be directly mixed in. Otherwise, it indicates that the calcium ion content of the microchannel fiber mud exceeds the standard. In this case, sodium carbonate is first used as a pretreatment agent to reduce the calcium ion content in the microchannel fiber mud to the qualified level, and then sodium alginate is mixed in. The minimum amount of sodium carbonate is determined through gradient experiments, and the minimum amount of sodium carbonate is used to reduce the calcium ion content.

[0033] Sodium alginate is a high-molecular-weight salt that forms a gel upon contact with calcium ions. Since soil has a high calcium ion content, sodium alginate rapidly gels after being injected into the soil, solidifying the microchannel fiber slurry in contact with the soil. However, the microchannel fiber slurry itself can also cause sodium alginate to gel prematurely, so the calcium ion content must be controlled. Sodium carbonate is used for decalcification, and a step-wise test is employed to determine the minimum dosage. The step-wise test is a commonly used dosage measurement method. Here, multiple slurry samples are taken, and different dosages of sodium carbonate are mixed in for decalcification. Then, sodium alginate is added to assess the decalcification effect. The group with the best decalcification effect and the lowest sodium carbonate dosage is used to determine the minimum sodium carbonate dosage (e.g., the minimum amount of sodium carbonate to be mixed in per 100 kg of slurry). This is then used as the standard for formal decalcification treatment. Excessive use of sodium carbonate is not advisable; otherwise, the subsequent injection of urea calcium will cause premature precipitation, affecting permeability.

[0034] Step two involves the following sub-steps in the preparation of the microchannel fiber slurry: Step 2.1a: Take loess soil from the area where the loess erosion gullies are located, crush it, dry it in the sun, and sieve it; Use local materials as much as possible. If possible, add some bentonite to improve the slurry's crack resistance or some fly ash to improve its fluidity.

[0035] Step 2.2a: Mix no less than 2.5 parts by weight of plant vascular fibers into 100 parts by weight of loess, and then add water to make a slurry; Here, the plant vascular fibers need to be dry-mixed into the loess because it is difficult to distribute them evenly when mixed into the mud, but dry mixing allows for this. 2.5 parts by weight is the minimum amount of plant vascular fibers required to ensure that they can form a three-dimensional network in the mud. There is no specific upper limit on the amount of plant vascular fibers used, but the amount should not affect the fluidity of the microchannel fiber mud and should be cost-effective.

[0036] Step 2.3a: Adjust the calcium ion content in the mud to the acceptable level; Step 2.4a: Add 0.5-0.7 parts by weight of sodium alginate to the mud. The amount of sodium alginate used within this range is effective.

[0037] In this embodiment, the plant vascular fibers are wood fibers, bamboo fibers, or straw fibers made from peeled wood or straw after the leaves have been removed. The plant vascular fibers are pretreated by soaking in alkaline solution and then washing before being mixed into the microchannel fiber slurry to optimize the interfacial adhesion.

[0038] Since this method utilizes plant vascular fibers, the bark, which primarily consists of sieve tubes (non-connected vessels), needs to be removed. Similarly, the stalks and leaves, containing a large amount of irrelevant biomass, also need to be removed. A good option is peeled hemp stalks. While the economic value of hemp (cannabis, flax, nettle, and velvet hemp) lies in its bark, peeled stalks are considered a major form of solid waste. However, they are perfectly suited to the needs of this embodiment, as they are relatively tough, have many vascular bundles, and have already been peeled. In practical use, the peeled stalks can be crushed radially into long strips, then twisted into filaments, and finally cut into sections.

[0039] The amount of engineered bacteria in the bacterial solution is no less than 100 million CFU / ml, based on CFU, to ensure sufficient bacterial quantity.

[0040] Furthermore, in step four, the bacterial solution is intermittently injected until free bacterial solution appears at the end of the loess erosion gullies. The specific timing of this intermittent injection can be determined by the individual; generally, after each injection, a five-minute pause is allowed to allow the bacterial solution to fully penetrate before continuing injection.

[0041] The engineered bacteria were Bacillus megaterium isolated from the soil in which loess erosion gullies are located, and strains with high urease activity were screened using a culture medium with urea as the sole nitrogen source.

[0042] Bacillus megaterium is a facultative anaerobe, and locally isolated strains are used to avoid causing ecological problems.

[0043] In step five, urea-calcium agent is intermittently injected until free urea-calcium agent appears at the end of the loess erosion gully; the intermittent injection method here is the same as the bacterial solution above.

[0044] The carbon source in urea calcium preparation is glucose, and the calcium salt is calcium chloride. Each liter of urea calcium preparation contains 55-65 grams of urea, 50-60 grams of calcium chloride, and 8-12 grams of glucose.

[0045] Each urea molecule decomposes to release one carbonate ion. Ideally, the molar ratio of urea to calcium chloride should be 1:1. However, in practice, excess urea effectively prevents the premature formation of a complex precipitate between calcium chloride and urea in the solution, ensuring the reaction is controlled by bacterial urease activity and resulting in a more uniform precipitation. Therefore, a 2:1 molar ratio is used. As for glucose, the amount should not be excessive, otherwise it will produce a large number of contaminating bacteria. Approximately 10 grams per liter is an amount sufficient to maintain the growth of Bacillus megaterium without causing excessive proliferation of other bacteria.

[0046] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for repairing loess erosion gullies using microchannel fiber-reinforced microchannel grouting (MICP) multi-stage grouting, characterized in that: Includes the following steps: Step 1: Investigate the condition of loess erosion gullies, and adjust the grouting material and grouting method according to the investigation results; Step 2: Prepare grouting material, which includes microchannel fiber slurry, bacterial solution, and urea calcium agent; The microchannel fiber slurry is a slurry mixed with plant vascular fibers and gelling salts. The gelling salts are soluble polymeric salts that can produce gels after being injected into loess erosion gullies to prevent the microchannel fiber slurry from being lost. The bacterial solution is a suspension of engineered bacteria that are facultative anaerobic and can secrete urease. The urea calcium agent is a calcium salt solution doped with urea and engineered bacteria as a carbon source. Step 3: Based on the survey results of Step 1, inject microchannel fiber slurry into the loess erosion gullies. After the microchannel fiber slurry solidifies, it blocks the cracks outside the micro-cracks in the loess erosion gullies. Step 4: After the microchannel fiber slurry has solidified, inject the bacterial solution into the loess erosion gullies; Step 5: After the bacterial solution has seeped into the loess erosion furrows along the plant's vascular fibers, inject urea-calcium agent into the loess erosion furrows. Engineered bacteria decompose urea to produce carbonate ions, which combine with calcium ions to form calcium carbonate stones, thus repairing the microcracks that were not filled by the microchannel fiber slurry in step three.

2. The method for repairing loess erosion gullies using microchannel fiber-reinforced microchannel grouting (MICP) according to claim 1, characterized in that: In step one, based on the different conditions of loess erosion gully exposure, the work is divided into the following two scenarios: Condition 1: If the loess erosion gullies are open trenches, then in step two, it is not necessary to control the length of the plant vascular fibers and the fluidity of the microchannel fiber slurry. In step three, the surface filling method guided by the vascular fibers is used for grouting. Condition 2: If the loess erosion gullies are partially exposed underground gullies, then in step three, steel pipe pressurized grouting is used. In step two, the length of the plant vascular fibers is 4-6 mm, and the viscosity of the microchannel fiber slurry is 40-50 seconds, based on the Marsh funnel viscosity.

3. The method for repairing loess erosion gullies using microchannel fiber-reinforced microchannel grouting (MICP) according to claim 2, characterized in that: In step two, the gelling salt is sodium alginate. Before mixing sodium alginate into the microchannel fiber slurry, a slurry sample is taken for a premixing test. If sodium alginate does not gel after being mixed into the slurry sample, it indicates that the calcium ion content of the microchannel fiber slurry is qualified and sodium alginate can be directly mixed in. Otherwise, it indicates that the calcium ion content of the microchannel fiber mud exceeds the standard. In this case, sodium carbonate is first used as a pretreatment agent to reduce the calcium ion content in the microchannel fiber mud to the qualified level, and then sodium alginate is mixed in. The minimum amount of sodium carbonate is determined through gradient experiments, and the minimum amount of sodium carbonate is used to reduce the calcium ion content.

4. The method for repairing loess erosion gullies using microchannel fiber-reinforced microchannel grouting (MICP) according to claim 3, characterized in that: Step two involves the following sub-steps in the preparation of the microchannel fiber slurry: Step 2.1a: Take loess soil from the area where the loess erosion gullies are located, crush it, dry it in the sun, and sieve it; Step 2.2a: Mix no less than 2.5 parts by weight of plant vascular fibers into 100 parts by weight of loess, and then add water to make a slurry; Step 2.3a: Adjust the calcium ion content in the mud to the acceptable level; Step 2.4a: Add 0.5-0.7 parts by weight of sodium alginate to the mud.

5. The method for repairing loess erosion gullies using microchannel fiber-reinforced microchannel grouting (MICP) according to claim 1, characterized in that: The plant vascular fibers are made from wood fibers, bamboo fibers, or straw fibers made from barkless wood or straw after the leaves have been removed. The plant vascular fibers are pretreated by soaking in alkaline solution and then washing before being mixed into the microchannel fiber slurry to optimize interfacial adhesion.

6. The method for repairing loess erosion gullies using microchannel fiber-reinforced microchannel grouting (MICP) according to claim 1, characterized in that: The content of engineered bacteria in the bacterial solution is not less than 100 million CFU / ml, and in step four, free bacterial solution appears at the end of the loess erosion gully below the intermittent grouting of the bacterial solution.

7. The method for repairing loess erosion gullies using microchannel fiber-reinforced MICP multi-stage grouting according to claim 6, characterized in that: The engineered bacteria are Bacillus megaterium isolated from the soil where loess erosion gullies are located, and strains with high urease activity are screened using a culture medium with urea as the sole nitrogen source.

8. The method for repairing loess erosion gullies using microchannel fiber-reinforced microchannel grouting (MICP) according to claim 1, characterized in that: In step five, urea-calcium agent is intermittently injected until free urea-calcium agent appears at the end of the loess erosion gully; The carbon source in the urea calcium preparation is glucose, and the calcium salt is calcium chloride. Each liter of urea calcium preparation contains 55-65 grams of urea, 50-60 grams of calcium chloride, and 8-12 grams of glucose.

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