A method for improving the crack resistance of fluidized solidified soil based on MICP technology

Abstract

The application discloses a method for improving the crack resistance of flow-state solidified soil based on MICP technology, and comprises the following steps: (1) uniformly mixing and stirring raw soil after crushing treatment with water to obtain raw soil slurry; (2) mixing microbial spore resuspension liquid with a cementing liquid containing urea and a calcium source to obtain a MICP treatment liquid; (3) uniformly mixing the raw soil slurry, a solidifying agent and the MICP treatment liquid to obtain a flow-state solidified soil slurry; and (4) filling the flow-state solidified soil slurry, and performing at least twice spraying treatment on the surface of the flow-state solidified soil slurry after initial setting by using the MICP treatment liquid to obtain flow-state solidified soil. The water stability of the flow-state solidified soil is significantly improved by the composition design and treatment mode regulation of the MICP treatment liquid, and the crack resistance of the solidified soil is further enhanced.

Description

Technical Field

[0001] This invention belongs to the field of microbial reinforcement of fluidized solidified soil technology, specifically relating to a method for improving the crack resistance of fluidized solidified soil based on MICP technology. Background Technology

[0002] Fluidized solidified soil is a self-leveling, self-compacting composite material composed of soil, solidifying agent, water, and admixtures. Due to its advantages such as good fluidity, convenient construction, low pressure on surrounding structures, and the ability to utilize waste soil, it is widely used in projects such as pipe gallery backfilling, roadbed filling, and foundation pit backfilling. To meet the requirements of high fluidity construction, fluidized solidified soil is typically designed with a high water-cement ratio and low cementitious material content. This can lead to shrinkage cracking during curing due to significant water loss, severely affecting the durability and safety of the project.

[0003] Currently, crack resistance improvement technologies for fluidized solidified soils mainly fall into two categories: material composition optimization and construction and curing process control. Material composition optimization includes adding fibers to bridge cracks, incorporating expanding agents to compensate for shrinkage, and using shrinkage-reducing agents to lower the surface tension of pore water. However, these methods have limitations: fibers can reduce material fluidity; the effectiveness of expanding agents is limited by humidity conditions and may cause unstable expansion in the later stages; shrinkage-reducing agents are expensive and contribute little to strength improvement. Construction and curing process control includes strengthening early wet curing, but for scenarios such as deep backfilling or concealed works, implementing sufficient and uniform wet curing is often very difficult in practice, limiting its practical application.

[0004] Microbial-induced calcium carbonate precipitation (MICP) is an emerging biomineralization technology. Its core principle is to utilize the metabolic activity of microorganisms to decompose urea, producing carbonate ions. These carbonate ions combine with free calcium ions in the environment, depositing calcium carbonate crystals on and around the microbial cells, thereby cementing loose particles and filling pores. However, the interior of fluidized bed solidified soil typically exhibits a high pH, ​​high salt ion concentration, and low oxygen environment, making it difficult for ordinary microbial vegetative cells to survive for extended periods, thus limiting the application of MIP technology in the field of fluidized bed solidified soil. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for improving the crack resistance of fluidized solidified soil based on MIP technology to address the shortcomings of the prior art. This method significantly improves the water stability of fluidized solidified soil by designing the composition of the MIP treatment liquid and controlling the treatment method, thereby enhancing the crack resistance of the solidified soil.

[0006] To achieve the above objectives, according to one aspect of the present invention, a method for improving the crack resistance of fluidized solidified soil based on MICP technology is provided, comprising the following steps: (1) After crushing the raw soil, mix it with water and stir evenly to obtain raw soil slurry; (2) The microbial spore resuspension was mixed with a gel containing urea and calcium source to obtain the MICP treatment solution; (3) Mix the raw soil slurry, solidifying agent and MIP treatment liquid evenly to obtain a fluidized solidified soil slurry; (4) Fill the fluidized solidified soil slurry, and after initial setting, spray the surface of the slurry with MIP treatment liquid at least twice to obtain fluidized solidified soil.

[0007] In the above scheme, the microbial spore resuspension is obtained by activating urease-producing microorganisms, inducing spore culture, lysing vegetative somatic cells, purifying and washing them, and then resuspending them in a sterile medium, wherein the spore concentration is ≥7×10⁻⁶. 9 CFU / mL.

[0008] In the above scheme, the method for preparing the microbial spore resuspension includes the following steps: (1) Inoculate the urease-producing microorganisms onto a medium containing CASO agar + 10~30g / L urea, adjust the pH to 7.3±0.5, and incubate at a constant temperature of 25~35℃ for 12~36h to obtain activated single colonies; (2) Pick a single colony and inoculate it into liquid culture medium. Shake and culture at 25-35℃ and 150-200rpm for 48-72h until most bacteria form spores and release them. (3) Centrifuge the cultured bacterial solution to collect the precipitate, add sterile water to resuspend it, add lysozyme to a final concentration of 1~2 mg / mL, add sodium dodecyl sulfate (SDS) to a final concentration of 0.1%~0.5%, and incubate at 35~40℃ for 1~2 h; (4) Centrifuge again to discard the supernatant, add sterile water to resuspend, centrifuge and wash 3-5 times to obtain pure spore precipitate; (5) Resuspend the purified spores in 0.8-0.9% sterile physiological saline to obtain a microbial spore resuspension; take a small amount of the spore suspension from the microbial spore resuspension, smear it onto a slide, and perform heat shock treatment to induce germination. Count viable cells using the dilution plating method. The spore concentration should be ≥7×10⁻⁶. 9 CFU / ml.

[0009] In the above scheme, the cementing solution is composed of urea, calcium chloride and water; the concentration of urea in the cementing solution is 1~2 mol / L and the concentration of calcium chloride is 2~3 mol / L.

[0010] Preferably, both the urea and calcium chloride are of analytical grade.

[0011] In the above scheme, the curing agent is composed of lime, bentonite and gypsum; the mass ratio of lime, bentonite and gypsum is 1:(1~3):(1~2).

[0012] In the above scheme, the moisture content of the raw soil is ≤15%, the organic matter content is ≤5%, and the maximum particle size is ≤10mm.

[0013] In the above scheme, the lime is calcareous lime with an effective calcium oxide content of ≥75% and a sieve residue of ≤10% on an 80μm square hole sieve.

[0014] In the above scheme, the bentonite is sodium-based bentonite with a montmorillonite content of ≥80% and a sieve residue of ≤20% on an 85μm square hole sieve.

[0015] In the above scheme, the gypsum is phosphogypsum or natural dihydrate gypsum, and the calcium sulfate dihydrate content in the gypsum is ≥90%.

[0016] In the above scheme, the mass ratio of the raw soil and water in the raw soil slurry, the solidifying agent, the microbial spore resuspension and the cementing liquid in the MICP treatment solution in step (3) is as follows: 100-200 parts of raw soil, 200-300 parts of water, 50-100 parts of solidifying agent, 20-30 parts of microbial spore resuspension, and 30-50 parts of cementing liquid.

[0017] In the above scheme, the initial setting time in step (4) is 4 to 8 hours after the slurry is poured; the interval between two consecutive sprayings of MICP treatment liquid is 12 to 36 hours. The dosage of MIP treatment solution for a single spray is 0.004~0.008 kg / m³. 2 ; In the above scheme, the raw material soil crushing treatment in step (1) is specifically as follows: the raw material soil is crushed and pre-treated, and then passed through a 10mm sieve.

[0018] According to another aspect of the present invention, a fluidized solidified soil prepared by the above-described method for improving the crack resistance of fluidized solidified soil based on MICP technology is provided. The fluidized solidified soil has a uniformly distributed microbial-induced calcium carbonate filler inside, a continuous mineralized layer on the surface, and active microbial spores inside. The material has the function of self-healing triggered by water. Its 28-day unconfined compressive strength is ≥2.0 MPa.

[0019] According to another aspect of the invention, the above-described fluidized solidified soil is provided for use in deep backfilling projects, concealed works, pipe gallery backfilling, roadbed filling, or foundation pit backfilling.

[0020] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects: (1) This invention provides a method for improving the crack resistance of fluidized solidified soil based on MICP technology. By internally mixing microbial spore suspension and cementing liquid with fluidized solidified soil slurry and spraying it on the surface multiple times after initial setting, the synergistic effect of microbial mineralization process inside and on the surface of the material is realized. This method can ensure that calcium carbonate is evenly distributed in the whole material, filling pores and improving microstructure. It can also form a continuous calcium carbonate mineralization layer with a certain thickness on the surface, thereby effectively inhibiting water evaporation, compensating for shrinkage stress, and significantly improving the crack resistance of fluidized solidified soil. It also has the ability to self-repair early microcracks and achieve healing through continuous mineralization after microcracks are generated. This is an active crack resistance mechanism that traditional external fibers, expansion agents or shrinkage reduction agents do not have.

[0021] (2) The method of this invention uses microbial spores instead of vegetative cells, which significantly improves the survival rate of microorganisms in the complex environment of fluidized solidified soil. Fluidized solidified soil usually has a high pH, ​​high salt ion concentration and low oxygen environment, making it difficult for ordinary microbial vegetative cells to survive for a long time. The spore morphology has extremely strong stress resistance and can withstand the alkaline environment and high osmotic pressure inside the solidified soil. After the slurry hardens and the environment tends to stabilize, the spores can germinate into vegetative cells under suitable conditions, continuously inducing calcium carbonate precipitation, thereby achieving long-term reinforcement. At the same time, microbial spores can remain dormant in the hardened fluidized solidified soil for a long time. When the solidified soil produces microcracks due to shrinkage or external force, water and air enter the crack channels, triggering spore germination. After germination, the microorganisms use the residual nutrients in the environment to induce the formation of calcium carbonate crystals on the surface and inside of the cracks, filling the cracks and preventing their expansion. This "dormant-trigger-repair" mechanism gives fluidized solidified soil the ability to actively repair itself, overcoming the defect of traditional crack-resistant technology that can only passively resist and cannot repair existing cracks.

[0022] (3) This invention adopts a composite treatment method of "internal admixture + multiple surface spraying", which not only ensures that the initial fluidity and self-compacting properties of the fluidized solidified soil are not affected, but also strengthens the weak crack-resistant areas of the surface after initial setting. Compared with traditional crack-resistant methods such as adding fibers, expansion agents or shrinkage-reducing agents, the method of this invention does not affect the fluidity of the fluidized solidified soil, does not depend on humidity conditions, and the mineralized products are stable, without the problem of unstable expansion in the later stage. At the same time, it requires little modification to the existing construction process, and is especially suitable for complex scenarios such as deep backfilling and hidden works where it is difficult to implement sufficient wet curing. It is convenient to construct and has uniform and long-lasting effects. Attached Figure Description

[0023] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 This is a scanning electron microscope image of the fluidized solidified soil prepared in Example 1 of the present invention.

[0024] Figure 2 The room temperature water loss rate of the fluidized solidified soil sample prepared in this invention.

[0025] Figure 3 The evaporation rate at room temperature of the fluidized solidified soil sample prepared in this invention.

[0026] Figure 4 These are photographs of the samples from Examples 2 and 5 and Comparative Examples 1-3 of the present invention, showing the changes over time. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0028] It should be understood that the sequence number of each step in the embodiment does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0029] This invention provides a method for improving the crack resistance of fluidized solidified soil based on MICP technology. Please refer to [link / reference]. Figure 1 This includes the following steps: (1) The raw soil is crushed and pretreated, passed through a 10mm sieve, and mixed with water until it is evenly stirred to obtain raw soil slurry; (2) Mix lime, bentonite, and gypsum evenly to obtain a solidifying agent. Mix the microbial spore suspension with a cementing solution containing urea and calcium source to obtain a MICP treatment solution; wherein the cementing solution is composed of urea, calcium chloride and water. (3) Mix the raw soil slurry, solidifying agent and MIP treatment liquid evenly to obtain a fluidized solidified soil slurry; (4) The fluidized solidified soil slurry is filled by pumping. After filling to the design elevation, its self-leveling properties are utilized, and a simple scraper is used to level it before covering the surface with a plastic film. After initial setting, the surface is sprayed with MIP treatment liquid 2-3 times to obtain fluidized solidified soil.

[0030] The method for preparing the microbial spore resuspension used in this invention specifically includes the following steps: Bacillus pasteurellii was inoculated onto CASO agar medium supplemented with 20 g / L urea, the pH was adjusted to 7.3, and the culture was maintained at 30°C for 24 hours to obtain activated single colonies. One to two morphologically typical single colonies were picked from the activated plate and inoculated into an Erlenmeyer flask containing liquid culture medium. The Erlenmeyer flask was placed in a shaker and cultured at 30°C and 150-200 rpm for 72 hours, until most bacteria were observed to have formed spores and released under a microscope. The culture was transferred to a centrifuge tube and centrifuged at 4°C for 10-15 minutes. The supernatant was discarded, and the bottom precipitate was collected. The precipitate was resuspended in sterile water. Lysozyme was then added to a final concentration of 1-2 mg / mL, and SDS (sodium dodecyl sulfate) was added to a final concentration of 0.1-0.5%. The mixture was incubated at 37°C for 1-2 hours to lyse any remaining vegetative cells. The lysed solution was centrifuged again, and the supernatant containing cell debris was discarded. Add sterile water to the precipitate, resuspend by refluxing, and repeat centrifugation and washing 3-5 times to thoroughly remove chemical reagents and impurities. Resuspend the final purified spore precipitate in 0.85% sterile physiological saline to obtain a microbial spore resuspension. Take a small amount of the spore resuspension and smear it on a slide, subjecting it to heat shock to induce germination. Perform viable cell counting using the dilution plating method; the spore concentration should be ≥7 × 10⁻⁶. 9 CFU / ml.

[0031] In this invention, the cementing solution is composed of urea and calcium chloride; the urea concentration in the cementing solution is 1~2 mol / L, and the calcium chloride concentration is 2~3 mol / L, both of which are analytical grade. The mass ratio of lime, bentonite, and gypsum in the curing agent is 1:(1~3):(1~2). The lime is calcareous lime with an effective calcium oxide content ≥75%, and a residue of ≤10% on an 80μm square-hole sieve; the bentonite is sodium-based bentonite with a montmorillonite content ≥80%, and a residue of ≤20% on an 85μm square-hole sieve; the gypsum is phosphogypsum or natural dihydrate gypsum, with a calcium sulfate dihydrate content ≥90%. The moisture content of the raw soil is ≤15%, the organic matter content is ≤5%, and the maximum particle size is ≤10mm.

[0032] Example 1 The fluidized solidified soil in this embodiment includes the following raw materials in parts by weight: 100 parts raw soil, 200 parts water, 50 parts solidifying agent, 20 parts microbial spore resuspension, and 30 parts cementing liquid.

[0033] The raw soil is manually crushed and sieved, then mixed with water in corresponding mass proportions and stirred evenly to obtain a raw soil slurry. The solidifying agent is prepared with lime, bentonite, and gypsum in a mass ratio of 1:1.5:1. A small amount of spores from the microbial spore resuspension is heat-shocked to induce germination, and viable cell counts are performed using the dilution plating method; the spore concentration should be greater than 7 × 10⁻⁶. 9CFU / ml. The concentrations of urea and calcium chloride in the cementitious solution were 1 mol / L and 2 mol / L, respectively. Microbial spore suspension was mixed with the cementitious solution to obtain the MIP treatment solution. The raw soil slurry, solidifying agent, and MIP treatment solution were mixed and stirred evenly with a mixer to obtain a fluidized solidified soil slurry. After the solidified soil slurry was poured, its surface was smoothed and covered with a plastic film. After 6 hours of initial setting, the surface of the fluidized solidified soil was sprayed with the MIP treatment solution, with a single spraying dosage of 0.004 kg / m³. 2 After 24 hours of mineralization, this operation was repeated, for a total of 3 spraying treatments. Samples were taken at 7, 14, and 28 days after treatment, with the ambient temperature set at 0±5℃. Water loss from the test blocks was observed at room temperature, and the sample mass was measured every 12 hours. Unconfined compressive strength tests were conducted using an electronic universal testing machine according to the "Standard for Geotechnical Testing Methods" (GBT50123-2019). Three parallel samples were prepared for each test scheme, and the average value of the test results was taken.

[0034] Example 2 The fluidized solidified soil in this embodiment includes the following raw materials in parts by weight: 125 parts raw soil, 225 parts water, 50 parts solidifying agent, 20 parts microbial spore resuspension, and 35 parts cementing liquid.

[0035] The raw soil is manually crushed and sieved, then mixed with water in corresponding mass proportions and stirred evenly to obtain a raw soil slurry. The solidifying agent is prepared with lime, bentonite, and gypsum in a mass ratio of 1:2:1. A small amount of spores from the microbial spore resuspension is subjected to heat shock treatment to induce germination. Viable cell counts are performed using the dilution plating method; the spore concentration should be greater than 7 × 10⁻⁶. 9 CFU / ml. The concentrations of urea and calcium chloride in the cementitious solution were 1.5 mol / L and 2.5 mol / L, respectively. Microbial spore suspension was mixed with the cementitious solution to obtain the MIP treatment solution. The raw soil slurry, solidifying agent, and MIP treatment solution were mixed and stirred evenly with a mixer to obtain a fluidized solidified soil slurry. After the solidified soil slurry was poured, its surface was leveled and covered with a plastic film. After 6 hours of initial setting, the surface of the fluidized solidified soil was sprayed with the MIP treatment solution, with a single spraying dosage of 0.004 kg / m³. 2 After 24 hours of mineralization, this operation was repeated, for a total of 3 spraying treatments. Samples were taken at 7, 14, and 28 days after treatment, with the ambient temperature set at 0±5℃. Water loss from the test blocks was observed at room temperature, and the sample mass was measured every 12 hours. Unconfined compressive strength tests were conducted using an electronic universal testing machine according to the "Standard for Geotechnical Testing Methods" (GBT50123-2019). Three parallel samples were prepared for each test scheme, and the average value of the test results was taken.

[0036] Example 3 The fluidized solidified soil in this embodiment includes the following raw materials in parts by weight: 150 parts raw soil, 250 parts water, 75 parts solidifying agent, 25 parts microbial spore resuspension, and 40 parts cementing liquid.

[0037] The raw soil is manually crushed and sieved, then mixed with water of the corresponding mass ratio and stirred evenly to obtain a raw soil slurry. The solidifying agent is prepared with lime, bentonite, and gypsum in a mass ratio of 1:2.5:1.5. A small amount of spores from the microbial spore resuspension is heat-shocked to induce germination, and viable cell counts are performed using the dilution plating method; the spore concentration should be greater than 7 × 10⁻⁶. 9 CFU / ml. The concentrations of urea and calcium chloride in the cementitious solution were 1.5 mol / L and 2.5 mol / L, respectively. Microbial spore suspension was mixed with the cementitious solution to obtain the MIP treatment solution. The raw soil slurry, solidifying agent, and MIP treatment solution were mixed and stirred evenly with a mixer to obtain a fluidized solidified soil slurry. After the solidified soil slurry was poured, its surface was leveled and covered with a plastic film. After 6 hours of initial setting, the surface of the fluidized solidified soil was sprayed with the MIP treatment solution, with a single spraying dosage of 0.006 kg / m³. 2 After 24 hours of mineralization, this operation was repeated, for a total of 4 spraying treatments. Samples were taken at 7, 14, and 28 days after treatment, with the ambient temperature set at 0±5℃. Water loss from the test blocks was observed at room temperature, and the sample mass was measured every 12 hours. Unconfined compressive strength tests were conducted using an electronic universal testing machine according to the "Standard for Geotechnical Testing Methods" (GBT50123-2019). Three parallel samples were prepared for each test scheme, and the average value of the test results was taken.

[0038] Example 4 The fluidized solidified soil in this embodiment includes the following raw materials in parts by weight: 175 parts raw soil, 275 parts water, 100 parts solidifying agent, 30 parts microbial spore resuspension, and 45 parts cementing liquid.

[0039] The raw soil is manually crushed and sieved, then mixed with water in corresponding mass proportions and stirred evenly to obtain a raw soil slurry. The solidifying agent is prepared with lime, bentonite, and gypsum in a mass ratio of 1:3:1.5. A small amount of spores from the microbial spore resuspension is subjected to heat shock treatment to induce germination. Viable cell counts are performed using the dilution plating method; the spore concentration should be greater than 7 × 10⁻⁶. 9CFU / ml. The concentrations of urea and calcium chloride in the cementitious solution were 2 mol / L and 3 mol / L, respectively. Microbial spore suspension was mixed with the cementitious solution to obtain the MIP treatment solution. The raw soil slurry, solidifying agent, and MIP treatment solution were mixed and stirred evenly with a mixer to obtain a fluidized solidified soil slurry. After the solidified soil slurry was poured, its surface was leveled and covered with a plastic film. After 6 hours of initial setting, the surface of the fluidized solidified soil was sprayed with the MIP treatment solution, with a single spraying dosage of 0.006 kg / m³. 2 After 24 hours of mineralization, this operation was repeated, for a total of 4 spraying treatments. Samples were taken at 7, 14, and 28 days after treatment, with the ambient temperature set at 0±5℃. Water loss from the test blocks was observed at room temperature, and the sample mass was measured every 12 hours. Unconfined compressive strength tests were conducted using an electronic universal testing machine according to the "Standard for Geotechnical Testing Methods" (GBT50123-2019). Three parallel samples were prepared for each test scheme, and the average value of the test results was taken.

[0040] Example 5 The fluidized solidified soil in this embodiment includes the following raw materials in parts by weight: 200 parts raw soil, 300 parts water, 100 parts solidifying agent, 30 parts microbial spore resuspension, and 50 parts cementing liquid.

[0041] The raw soil is manually crushed and sieved, then mixed with water in corresponding mass proportions and stirred evenly to obtain a raw soil slurry. The solidifying agent is prepared with lime, bentonite, and gypsum in a mass ratio of 1:3:2. A small amount of spores from the microbial spore resuspension is subjected to heat shock treatment to induce germination. Viable cell counts are performed using the dilution plating method; the spore concentration should be greater than 7 × 10⁻⁶. 9 CFU / ml. The concentrations of urea and calcium chloride in the cementitious solution were 2 mol / L and 3 mol / L, respectively. Microbial spore suspension was mixed with the cementitious solution to obtain the MIP treatment solution. The raw soil slurry, solidifying agent, and MIP treatment solution were mixed and stirred evenly with a mixer to obtain a fluidized solidified soil slurry. After the solidified soil slurry was poured, its surface was leveled and covered with a plastic film. After 6 hours of initial setting, the surface of the fluidized solidified soil was sprayed with the MIP treatment solution, with a single spraying dosage of 0.008 kg / m³. 2 After 24 hours of mineralization, this operation was repeated, for a total of 5 spraying treatments. Samples were taken at 7, 14, and 28 days after treatment, with the ambient temperature set at 0±5℃. Water loss from the test blocks was observed at room temperature, and the sample mass was measured every 12 hours. Unconfined compressive strength tests were conducted using an electronic universal testing machine according to the "Standard for Geotechnical Testing Methods" (GBT50123-2019). Three parallel samples were prepared for each test scheme, and the average value of the test results was taken.

[0042] Comparative Example 1 The difference between this comparative example and Example 1 is that in Example 1, a curing agent was used instead of MICP treatment liquid in the raw materials for preparing the fluidized solidified soil slurry, and no spraying treatment was performed after the solidified soil slurry was poured.

[0043] The fluidized solidified soil in this embodiment includes the following raw materials in parts by weight: 100 parts raw soil, 200 parts water, and 100 parts curing agent.

[0044] The raw soil was manually crushed and sieved, then mixed with water of the corresponding mass ratio and stirred evenly to obtain a raw soil slurry. The solidifying agent consisted of lime, bentonite, and gypsum in a mass ratio of 1:1.5:1. The raw soil slurry and solidifying agent were mixed and stirred evenly with a mixer to obtain a fluidized solidified soil slurry. After the solidified soil slurry was poured, its surface was smoothed and covered with a plastic film. Samples were taken at 7, 14, and 28 days of curing, with the ambient temperature set at 0±5℃. Water loss from the test blocks was observed at room temperature, and the sample mass was measured every 12 hours. Unconfined compressive strength tests were conducted using an electronic universal testing machine according to the "Standard for Geotechnical Testing Methods" (GBT50123-2019). Three parallel samples were prepared for each test scheme, and the average value of the test results was taken.

[0045] Comparative Example 2 The difference between this comparative example and Example 1 is that: in Example 1, a curing agent was used instead of the MIP treatment liquid in the raw materials for preparing the fluidized solidified soil slurry; after the solidified soil slurry was poured, it was sprayed with the MIP treatment liquid from Example 1.

[0046] The fluidized solidified soil in this embodiment includes the following raw materials in parts by weight: 100 parts raw soil, 200 parts water, and 100 parts curing agent.

[0047] The raw soil is manually crushed and sieved, then mixed with water of the corresponding mass ratio and stirred evenly to obtain a raw soil slurry. The solidifying agent is prepared with lime, bentonite, and gypsum in a mass ratio of 1:1.5:1. The raw soil slurry and solidifying agent are mixed and stirred evenly with a mixer to obtain a fluidized solidified soil slurry. After the solidified soil slurry is poured, its surface is smoothed and covered with a plastic film. After 6 hours of initial setting, the surface of the fluidized solidified soil is sprayed with MIP treatment solution, with a single spray dosage of 0.004 kg / m³. 2 After 24 hours of mineralization, this operation was repeated, for a total of 3 spraying treatments. Samples were taken at 7, 14, and 28 days after treatment, with the ambient temperature set at 0±5℃. Water loss from the test blocks was observed at room temperature, and the sample mass was measured every 12 hours. Unconfined compressive strength tests were conducted using an electronic universal testing machine according to the "Standard for Geotechnical Testing Methods" (GBT50123-2019). Three parallel samples were prepared for each test scheme, and the average value of the test results was taken.

[0048] Comparative Example 3 The difference between this comparative example and Example 1 is that after 6 hours of initial setting, the surface of the fluidized solidified soil is not sprayed with MIP treatment liquid.

[0049] The fluidized solidified soil in this embodiment includes the following raw materials in parts by weight: 100 parts raw soil, 200 parts water, 50 parts solidifying agent, 20 parts microbial spore resuspension, and 30 parts cementing liquid.

[0050] The raw soil is manually crushed and sieved, then mixed with water in corresponding mass proportions and stirred evenly to obtain a raw soil slurry. The solidifying agent is prepared with lime, bentonite, and gypsum in a mass ratio of 1:1.5:1. A small amount of spores from the microbial spore resuspension is heat-shocked to induce germination, and viable cell counts are performed using the dilution plating method; the spore concentration should be greater than 7 × 10⁻⁶. 9 CFU / ml. The concentrations of urea and calcium chloride in the cementing solution were 1 mol / L and 2 mol / L, respectively. The raw soil slurry, solidifying agent, microbial spore resuspension, and cementing solution were mixed and stirred evenly with a mixer to obtain a fluidized solidified soil slurry. After the solidified soil slurry was poured, its surface was smoothed and covered with a plastic film. Samples were taken at 7, 14, and 28 days of curing, with an ambient temperature of 0±5℃. Water loss from the test blocks was observed at room temperature, and the sample mass was measured every 12 hours. Unconfined compressive strength tests were conducted using an electronic universal testing machine according to the "Standard for Geotechnical Testing Methods" (GBT50123-2019). Three parallel samples were prepared for each test scheme, and the average value of the test results was taken.

[0051] The unconfined compressive strength test results of different embodiments and comparative examples of the present invention are shown in Table 1.

[0052] Table 1. Test results of unconfined compressive strength of fluidized solidified soil

[0053] The unconfined compressive strength test results show that the fluidized solidified soil samples prepared in Examples 1-5 of this invention exhibit continuously increasing unconfined compressive strength at all curing ages. The 28-day strength all exceeded 2.5 MPa, and the 7-day strength all reached over 1 MPa, meeting the engineering strength standards for fluidized solidified soil. The monotonically increasing strength with age indicates that the matrix structure of the sample samples in the examples continuously densifies with curing time, without the accumulation of internal damage.

[0054] To demonstrate the technical effectiveness of this invention, multiple comparative tests were conducted. Table 1 shows that Comparative Example 1 (without any MIP treatment) exhibited the lowest strength among all experimental groups, and a significant strength reduction occurred between 14 and 28 days—the 28-day strength was significantly lower than the 14-day strength. The fundamental reason for this strength reduction is that the untreated solidified soil matrix develops microcracks during drying shrinkage. These cracks expand and connect with the continuous evaporation of moisture, leading to the accumulation of structural damage to the matrix and ultimately a decrease in compressive strength. Comparative Example 2 (only surface-sprayed with MIP treatment liquid, without internal admixture) showed higher strength than Comparative Example 1, but still significantly lower than Examples 1-5, and also exhibited a strength reduction trend. This result reveals the limitations of surface spraying treatment: while the surface mineralization layer can slow down the evaporation rate of surface moisture to some extent, it cannot form a continuous calcium carbonate cement network within the matrix. Microcracks caused by internal drying shrinkage can still initiate and expand, thus limiting the strength improvement. Comparative Example 3 (with only internal MIP treatment solution and no surface spraying) showed improved strength compared to Comparative Examples 1-2, and its 7-day strength was roughly the same as that of the Examples. However, its later strength was still lower than that of Examples 1-5, and a strength reduction phenomenon also occurred from 14 to 28 days. This indicates that although internal MIP can induce calcium carbonate precipitation and fill some pores and cement soil particles in the matrix, thereby improving early strength, the lack of protection from the closed mineralization layer formed by surface spraying means that the moisture inside the matrix can still be continuously lost through surface evaporation, leading to the continuous accumulation of drying shrinkage stress, which causes cracking and strength reduction.

[0055] The above comparative results fully demonstrate the synergistic effect of the "internal admixture + multiple surface spraying" composite treatment method of the present invention: the uniformly distributed microbial spores and cementing liquid inside can continuously induce calcium carbonate precipitation during the sample hardening process, fill the pores and cement the particles, and form a three-dimensional reinforced skeleton; while multiple surface spraying can build a continuous mineralized dense layer on the surface, effectively inhibiting the outward migration of internal moisture and reducing the concentration of drying shrinkage stress; the synergistic effect of the two achieves full-section crack resistance enhancement of the fluidized solidified soil from the inside out.

[0056] Figure 1 The image shown is a scanning electron microscope image of the fluidized solidified soil prepared in Example 1 of this invention. It can be clearly seen that calcium carbonate is uniformly distributed in the whole material, filling the pores and improving the microstructure.

[0057] Figure 2 , Figure 3 The results of observing water loss at room temperature show that Comparative Example 1 had the highest water loss rate and evaporation rate. Comparative Example 3 had a significantly lower water loss rate and evaporation rate than Comparative Example 1, but was still significantly higher than Examples 1-5. The results indicate that the technology of this invention can significantly reduce the water loss rate and evaporation rate of fluidized solidified soil.

[0058] Figure 4 The images shown are photographs of the specimens from Examples 2 and 5 and Comparative Examples 1-3, showing the changes over time. It should be noted that the photographs are taken from representative specimens in the experimental groups and are not necessarily the same specimen. Figure 4 It can be seen that the samples in Examples 2 and 5 were well preserved over time without obvious cracks; while in Comparative Examples 1-3, large cracks were clearly observed in the samples after 28 days of curing, and their compressive strength was significantly lost. This further illustrates that the present invention has a significant improvement effect.

[0059] It should be noted that, depending on the implementation needs, the various steps described in this application can be broken down into more steps, or two or more steps or parts of the steps can be combined into new steps to achieve the purpose of this invention.

[0060] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for improving the crack resistance of fluidized solidified soil based on MICP technology, characterized in that, Includes the following steps: (1) After crushing the raw soil, mix it with water and stir evenly to obtain raw soil slurry; (2) The microbial spore resuspension was mixed with a gel containing urea and calcium source to obtain the MICP treatment solution; (3) Mix the raw soil slurry, solidifying agent and MIP treatment liquid evenly to obtain a fluidized solidified soil slurry; (4) Fill the fluidized solidified soil slurry, and after initial setting, spray the surface of the slurry with MIP treatment liquid at least twice to obtain fluidized solidified soil.

2. The method for improving the crack resistance of fluidized solidified soil based on MICP technology according to claim 1, characterized in that, The microbial spore resuspension was obtained by activating urease-producing microorganisms, inducing spore culture, lysing vegetative somatic cells, purifying and washing them, and then resuspending them in a sterile medium, wherein the spore concentration was ≥7×10⁻⁶. 9 CFU / mL.

3. The method for improving the crack resistance of fluidized solidified soil based on MICP technology according to claim 2, characterized in that, The method for preparing the microbial spore resuspension includes the following steps: (1) Inoculate the urease-producing microorganisms onto a medium containing CASO agar + 10~30g / L urea, adjust the pH to 7.3±0.5, and incubate at a constant temperature of 25~35℃ for 12~36h to obtain activated single colonies; (2) Pick a single colony and inoculate it into liquid culture medium. Shake and culture at 25-35℃ and 150-200rpm for 48-72h until most bacteria form spores and release them. (3) Centrifuge the cultured bacterial solution to collect the precipitate, add sterile water to resuspend it, add lysozyme to a final concentration of 1~2 mg / mL, add SDS to a final concentration of 0.1%~0.5%, and incubate at 35~40℃ for 1~2 h; (4) Centrifuge again to discard the supernatant, add sterile water to resuspend, centrifuge and wash 3-5 times to obtain pure spore precipitate; (5) The purified spore precipitate is resuspended in 0.8%~0.9% sterile physiological saline to obtain a microbial spore resuspension; the spore concentration in the microbial spore resuspension is ≥7×10⁻⁶. 9 CFU / mL.

4. The method for improving the crack resistance of fluidized solidified soil based on MICP technology according to claim 1, characterized in that, The cementing solution is composed of urea, calcium chloride and water; the concentration of urea in the cementing solution is 1~2 mol / L and the concentration of calcium chloride is 2~3 mol / L.

5. A method for improving the crack resistance of fluidized solidified soil based on MICP technology according to claim 1, characterized in that, The curing agent is composed of lime, bentonite and gypsum; the mass ratio of lime, bentonite and gypsum is 1:(1~3):(1~2); The raw soil has a moisture content of ≤15%, an organic matter content of ≤5%, and a maximum particle size of ≤10mm.

6. A method for improving the crack resistance of fluidized solidified soil based on MICP technology according to claim 5, characterized in that, The lime is calcareous lime with an effective calcium oxide content of ≥75% and a sieve residue of ≤10% on an 80μm square hole sieve; the bentonite is sodium-based bentonite with a montmorillonite content of ≥80% and a sieve residue of ≤20% on an 85μm square hole sieve; the gypsum is phosphogypsum or natural dihydrate gypsum, and the gypsum contains ≥90% calcium sulfate dihydrate.

7. A method for improving the crack resistance of fluidized solidified soil based on MICP technology according to claim 1, characterized in that, The mass ratio of the raw soil and water in the raw soil slurry, the solidifying agent, the microbial spore resuspension and the cementing liquid in the MICP treatment solution in step (3) is as follows: 100-200 parts of raw soil, 200-300 parts of water, 50-100 parts of solidifying agent, 20-30 parts of microbial spore resuspension, and 30-50 parts of cementing liquid.

8. A method for improving the crack resistance of fluidized solidified soil based on MICP technology according to claim 1, characterized in that, The initial setting time mentioned in step (4) is 4 to 8 hours after the slurry is poured; the interval between two consecutive sprayings of MICP treatment liquid is 12 to 36 hours. The dosage of MIP treatment solution for a single spray is 0.004~0.008 kg / m³. 2 ; The specific process of raw material soil crushing in step (1) is as follows: the raw material soil is crushed and pre-treated, and then passed through a 10mm sieve.

9. A type of fluidized solidified soil prepared using the method for improving the crack resistance of fluidized solidified soil based on MICP technology as described in any one of claims 1 to 8, characterized in that, The fluidized solidified soil has a uniform distribution of microbial-induced calcium carbonate filler inside, a continuous mineralized layer on the surface, and retains active microbial spores inside. Its 28-day unconfined compressive strength is ≥2.0 MPa.

10. The application of the fluidized solidified soil according to claim 9 in deep backfilling projects, concealed works, pipe gallery backfilling, roadbed filling or foundation pit backfilling.

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