A construction method for enhancing the impermeability of cement-soil mixing piles based on biocapsules

Abstract

This invention relates to a construction method for enhancing the impermeability of cement-soil mixing piles based on biocapsules, comprising the following steps: S1, mixing biocapsules into cement slurry; S2, constructing triaxial mixing piles using a two-stirring-one-spraying process, followed by temperature gradient curing of the pile body after construction; the preparation of the biocapsules includes the following steps: dispersing amino-modified silica microspheres in a urease solution for adsorption, then dispersing the obtained urease-loaded biocapsules in a sodium alginate-polylactic acid-chitosan mixed solution for emulsification, and then adding the resulting suspension dropwise to a calcium ion-containing solution for cross-linking and solidification, thus obtaining the final product. This invention introduces a double-layered biocapsule into the cement slurry, which maintains structural integrity during construction and triggers the controlled release of internal active components such as urease when cracks encounter water, significantly improving the impermeability and self-healing performance of the pile body.

Description

Technical Field

[0001] This invention relates to the field of foundation treatment technology, and in particular to a construction method for enhancing the impermeability of cement-soil mixing piles based on biological capsules. Background Technology

[0002] In underground engineering projects such as subway foundation pits and diaphragm walls, cement-soil mixing piles are widely used in foundation reinforcement and seepage prevention projects due to their convenient construction and controllable costs. However, piles obtained by traditional cement grouting have drawbacks such as poor pile uniformity, insufficient durability, difficult maintenance, and poor environmental performance, making them increasingly difficult to adapt to complex geological conditions and the development needs of green buildings.

[0003] In recent years, microbial induced calcium carbonate precipitation (MICP) technology has attracted widespread attention as a green and environmentally friendly soil reinforcement solution. This technology utilizes the urease secreted by microorganisms to induce the formation of calcium carbonate cement, thereby achieving soil reinforcement and seepage prevention. However, directly applying MIP technology to cement-soil mixing piles presents the problem that microbial activity is easily affected by the engineering environment. On the one hand, the cement hydration process creates a highly alkaline environment with a pH > 11, leading to microbial inactivation (survival rate of less than 10% after 48 hours); on the other hand, the low underground temperature environment (<15℃) significantly reduces the microbial metabolic rate, resulting in a decrease in the urea hydrolysis rate and a significantly prolonged reaction cycle.

[0004] To address these issues, existing methods attempt to protect microorganisms through encapsulation technology. However, existing encapsulation materials still face two major challenges: first, their mechanical properties are insufficient to withstand the high shear and vibration physical damage during the construction of mixing piles, causing microorganisms to leak out prematurely and become inactive upon exposure to the cement environment; second, their release performance is poor, failing to respond promptly to the need for crack repair.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a construction method for enhancing the impermeability of cement-soil mixing piles based on biocapsules.

[0007] The technical solution adopted in this invention is as follows:

[0008] This invention provides a construction method for enhancing the impermeability of cement-soil mixing piles based on biocapsules, comprising the following steps:

[0009] S1. Mix the biological capsules into the cement slurry and stir evenly.

[0010] S2. The three-axis mixing piles are constructed using a two-mixing-one-spraying process. After construction, the piles are subjected to temperature gradient curing treatment.

[0011] In step S1, the preparation of the biological capsule includes the following steps:

[0012] Amino-modified silica microspheres were dispersed in a urease solution for adsorption. The resulting urease-loaded bio-microspheres were then dispersed in a sodium alginate-polylactic acid-chitosan mixed solution for emulsification. The resulting suspension was then added dropwise to a calcium ion-containing solution for cross-linking and solidification, thus obtaining the final product.

[0013] This invention proposes a construction method for enhancing the impermeability of cement-soil mixing piles based on biocapsules. By introducing a double-layered biocapsule into the cement slurry, the biocapsule maintains its structural integrity during construction and triggers the controlled release of internal active ingredients such as urease when water enters cracks. Ultimately, urease induces the formation of calcium carbonate precipitate, filling pores and cracks, significantly improving the impermeability and self-healing performance of the pile. The inner layer of the biocapsule uses amino-modified silica microspheres as a carrier, efficiently loading internal active ingredients such as urease while creating a relatively isolated microenvironment to enhance its stability during construction. The outer layer uses a sodium alginate-polylactic acid-chitosan composite system as the wall material. The sodium alginate, cross-linked with calcium ions, forms a hydrophilic gel network that rapidly swells and degrades when cracks appear in the cement-soil mixture and water seeps in, providing a release channel for the internal active ingredients. Polylactic acid, as a polymer framework, further enhances the mechanical strength of the biocapsule, effectively resisting damage caused by shearing and vibration during construction and preventing premature release of internal active ingredients.

[0014] Preferably, in step S1, the dosage of the biocapsule is 0.5-3% of the pile volume, the particle size of the biocapsule is 50-500μm, the water-cement ratio of the cement slurry is 0.55-0.6, and the pH of the cement slurry is 9-11.

[0015] Preferably, in step S1, the amino-modified silica microspheres are obtained by modifying silica microspheres with an aminosilane coupling agent, and the mass ratio of the aminosilane coupling agent to the silica microspheres is 0.05~0.15:1.

[0016] Preferably, in step S1, the raw material components of the urease solution include: 10~50 g / L of urease, 0.5~1.5 mol / L of urea, 0.5~1.65 mol / L of calcium chloride, 0.2~0.3 mol / L of sucrose, and 0.1~0.3 mol / L of ammonium chloride, wherein the molar ratio of urea to calcium chloride is 1:1~1.1.

[0017] Preferably, in step S1, the raw material composition of the sodium alginate-polylactic acid-chitosan mixed solution includes: 25~35g / L polylactic acid, 15~25g / L sodium alginate, and 0.5~2g / L chitosan.

[0018] Preferably, the polylactic acid has a crystallinity of 40-60%.

[0019] Preferably, the molecular weight of the polylactic acid is 50,000 to 100,000 Da.

[0020] Preferably, in step S1, the concentration of calcium ions in the calcium ion-containing solution is 2-5 wt%.

[0021] Preferably, in step S2, the two-stirring-one-spraying process specifically includes the following steps: the drill bit is equipped with a high-frequency vibration module and a rotary jet nozzle. The drill bit rotates and sinks to the designed depth. After continuously spraying grout at the bottom of the pile for 30 seconds, it rotates in the opposite direction to lift and spray grout. During grouting, the intelligent layered grouting system is used to regulate the grouting pressure to increase gradually from bottom to top along the pile body and dynamically regulate the grouting volume. Then, a second sinking and lifting stirring is performed. When the drill bit is lifted to the top of the pile, grout is continuously sprayed at the top of the pile for 30 seconds. Grouting is then stopped to complete the construction.

[0022] The construction parameters for the two-mixing-one-spraying process are as follows: vibration frequency of 80~120Hz, amplitude of 2~5mm, spray nozzle inclination angle of 15~30°, rotation speed of 100~150rpm, sinking speed of 0.6~0.8m / min, lifting speed of 0.5~0.6m / min, spraying pressure of the lower part of the pile body of 0.4~0.6MPa, spraying pressure of the middle part of the pile body of 0.6~0.8MPa, and spraying pressure of the upper part of the pile body of 0.8~1.0MPa.

[0023] Preferably, in step S2, the temperature gradient curing treatment specifically includes the following steps: covering the pile body and surrounding soil with plastic film or geotextile, curing for 7 to 14 days in an environment with a humidity of 80 to 90%, and after the pile body is formed, first circulating hot air at 40 to 50°C is introduced for 2 hours, and then low temperature curing at 10 to 15°C is used for 48 hours. Attached Figure Description

[0024] Figure 1 This is a comparison chart of the cement-soil permeability coefficients before and after construction in Example 1. Detailed Implementation

[0025] To better understand the above technical solutions, exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the present invention can be understood more clearly and thoroughly, and that the scope of the present invention can be fully conveyed to those skilled in the art.

[0026] This invention provides a construction method for enhancing the impermeability of cement-soil mixing piles based on biocapsules, comprising the following steps:

[0027] S1. Mix the biological capsules into the cement slurry and stir evenly.

[0028] S2. The three-axis mixing piles are constructed using a two-mixing-one-spraying process. After construction, the piles are subjected to temperature gradient curing treatment.

[0029] In step S1, the preparation of the biological capsule includes the following steps:

[0030] Amino-modified silica microspheres were dispersed in a urease solution for adsorption. The resulting urease-loaded bio-microspheres were then dispersed in a sodium alginate-polylactic acid-chitosan mixed solution for emulsification. The resulting suspension was then added dropwise to a calcium ion-containing solution for cross-linking and solidification, thus obtaining the final product.

[0031] After construction using the bio-capsule-containing cement grout of this invention, the bio-capsules are dispersed and sealed within the cement-soil matrix. When cracks appear in the cement-soil and water seeps in, the water triggers a response mechanism on the outer wall of the bio-capsule: the sodium alginate hydrophilic gel network rapidly swells, opening channels for the diffusion of internal active ingredients; while polylactic acid undergoes gradual hydrolysis. Both mechanisms work synergistically to achieve efficient and controllable release of the internal active ingredients. Subsequently, the released urease catalyzes the hydrolysis of urea in the crack's water environment, inducing the formation of calcium carbonate precipitate and filling the crack pores, thereby achieving self-repair and long-term enhancement of the cement-soil's impermeability.

[0032] In a preferred embodiment of the present invention, in step S1, the dosage of the biocapsules is 0.5-3% of the pile volume, the particle size of the biocapsules is 50-500 μm, the water-cement ratio of the cement slurry is 0.55-0.6, and the pH of the cement slurry is 9-11. In this invention, by screening the biocapsules with the above-mentioned dosage and particle size, and the cement slurry with the above-mentioned water-cement ratio and pH, on the one hand, it is beneficial for the biocapsules to be uniformly dispersed in the cement slurry; on the other hand, it provides a suitable survival environment for the biocapsules while maintaining normal cement hydration.

[0033] In a preferred embodiment of the present invention, in step S1, the amino-modified silica microspheres are obtained by modifying silica microspheres with an aminosilane coupling agent, and the mass ratio of the aminosilane coupling agent to the silica microspheres is 0.05~0.15:1. The inner layer of the biocapsule of the present invention uses amino-modified silica microspheres as a carrier. Firstly, the amino modification achieves efficient loading of urease; secondly, this carrier can construct a physical barrier that relatively isolates urease from the high-alkaline environment of cement, reducing urease inactivation, and works synergistically with the outer wall material to resist shearing and vibration during construction, preventing the biocapsule from rupturing. For example, the mass ratio of aminosilane coupling agent to silica microspheres can be 0.05:1, 0.07:1, 0.1:1, 0.13:1, 0.15:1, etc.; further examples include N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, etc.; the particle size of silica microspheres can be 1~10μm. In addition, during the preparation process, the aminosilane coupling agent can first be prepared into a solution with a concentration of 0.5~2wt%, and then the silica microspheres can be added for modification.

[0034] In a preferred embodiment of the present invention, in step S1, the raw material components of the urease solution include: 10-50 g / L urease, 0.5-1.5 mol / L urea, 0.5-1.65 mol / L calcium chloride, 0.2-0.3 mol / L sucrose, and 0.1-0.3 mol / L ammonium chloride, wherein the molar ratio of urea to calcium chloride is 1:1-1.1. The present invention uses the above-mentioned proportions of raw material components to construct the urease solution, which ensures that the urease maintains stable activity in the highly alkaline environment of cement soil, thereby efficiently inducing the formation of calcium carbonate precipitation. Sucrose, as a stabilizer, when added in appropriate amounts, can form a hydration layer around the urease molecules, effectively slowing down its deactivation in an alkaline environment without affecting its diffusion; an appropriate amount of ammonium chloride can adjust the pH and ion balance of the reaction system, creating a favorable environment for the urease activity and the smooth progress of the precipitation reaction.

[0035] In a preferred embodiment of the present invention, in step S1, the raw material composition of the sodium alginate-polylactic acid-chitosan mixed solution includes: 25-35 g / L polylactic acid, 15-25 g / L sodium alginate, and 0.5-2 g / L chitosan. In the composite outer wall material system of the present invention, sodium alginate, as the core hydrophilic component, crosslinks with calcium ions to form a stable hydrophilic gel network; polylactic acid, as the hydrophobic polymer backbone, provides the main mechanical strength of the capsule wall material and regulates release; chitosan strengthens the structure of the capsule outer wall material through electrostatic composite with sodium alginate, and its amphiphilic properties can improve the interfacial compatibility between hydrophilic and hydrophobic components. Furthermore, the embodiments of the present invention employ a typical method for preparing the sodium alginate-polylactic acid-chitosan mixed solution, comprising the following steps: mixing a polylactic acid solution formed by dissolving polylactic acid in dichloromethane with a sodium alginate solution formed by dissolving sodium alginate in water, then adding chitosan and stirring until homogeneous to obtain the final product.

[0036] In a preferred embodiment of the present invention, the crystallinity of polylactic acid (PLA) is 40-60%. This choice of PLA within this crystallinity range not only provides the biocapsule with sufficient mechanical strength to withstand construction shear and vibration, preventing premature rupture, but also gives the capsule outer wall material a moderately dense structure. This allows for a synergistic response with the sodium alginate hydrophilic gel network after water seepage into cracks—the sodium alginate hydrophilic gel network swells first to form release channels, promoting the gradual hydrolysis of PLA, thereby ensuring the full and controlled release of internal active ingredients and achieving efficient formation and filling of calcium carbonate precipitate at the cracks. For example, the crystallinity of PLA can be 40%, 45%, 50%, 55%, 60%, etc.

[0037] In a preferred embodiment of the present invention, the molecular weight of polylactic acid (PLA) is 50,000 to 100,000 Da. The present invention controls the molecular weight of PLA within this range to avoid the following: too low a molecular weight would result in a loose outer wall structure of the capsule, leading to premature rupture during the mixing stage; and too high a molecular weight would result in an excessively dense outer wall structure, hindering the release of internal active ingredients in a water-permeable environment. For example, the molecular weight of PLA can be 50,000 Da, 60,000 Da, 70,000 Da, 80,000 Da, 90,000 Da, 100,000 Da, etc.

[0038] In a preferred embodiment of the present invention, in step S1, the concentration of calcium ions in the calcium ion-containing solution is 2-5 wt%. This concentration range of calcium ion-containing solution is beneficial for forming a hydrophilic gel network with moderate cross-linking degree with the sodium alginate in the capsule outer wall material. For example, the concentration of calcium ions in the calcium ion-containing solution can be 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, etc. Furthermore, for curing conditions, curing at a temperature of 20-40°C for 30-100 min can be selected.

[0039] In a preferred embodiment of the present invention, step S2, the two-stirring-one-spraying process specifically includes the following steps: the drill bit is equipped with a high-frequency vibration module and a rotary jet nozzle; the drill bit rotates and sinks to the designed depth; after continuously spraying grout at the bottom of the pile for 30 seconds, it rotates in the opposite direction to lift and spray grout; during grouting, the intelligent layered grouting system is used to regulate the grouting pressure to increase gradually in sections along the pile body from bottom to top and dynamically regulate the grouting volume; then, a second sinking and lifting stirring is performed; when the drill bit is lifted to the top of the pile, grout is continuously sprayed at the top of the pile for 30 seconds, grouting is stopped, and the construction is completed.

[0040] The construction parameters for the two-mixing-one-spraying process are as follows: vibration frequency of 80~120Hz, amplitude of 2~5mm, spray nozzle inclination angle of 15~30°, rotation speed of 100~150rpm, sinking speed of 0.6~0.8m / min, lifting speed of 0.5~0.6m / min, spraying pressure of the lower part of the pile body of 0.4~0.6MPa, spraying pressure of the middle part of the pile body of 0.6~0.8MPa, and spraying pressure of the upper part of the pile body of 0.8~1.0MPa.

[0041] The two-stirring-one-spraying process of this invention is used for construction, which ensures the efficiency and uniformity of pile formation while avoiding damage to the biocapsules, thus laying the technological foundation for the realization of the biocapsules' anti-seepage and self-repairing functions in the later stage.

[0042] In a preferred embodiment of the present invention, step S2, the temperature gradient curing treatment specifically includes the following steps: covering the pile body and surrounding soil with plastic film or geotextile, curing for 7-14 days in an environment with a humidity of 80-90%; after the pile body is formed, first circulating hot air at 40-50℃ is introduced for 2 hours, followed by low-temperature curing at 10-15℃ for 48 hours. The present invention employs a temperature gradient curing process, initially raising the temperature to accelerate cement solidification and strengthening, and later lowering the temperature to protect the activity of urease within the biological capsule. Additionally, the pile body can be wrapped with a phase change material (such as paraffin-graphene composite material) before curing to reduce the interference of temperature fluctuations on the curing effect.

[0043] Preparation Examples 1-7: Preparation of Biocapsules

[0044] Preparation Example 1

[0045] Amino-modified silica microspheres (obtained by modifying silica microspheres with γ-aminopropyltriethoxysilane, where the mass ratio of γ-aminopropyltriethoxysilane to silica microspheres is 0.1:1, and the particle size of the silica microspheres is 2 μm) were dispersed in a urease solution (the raw material components include: 30 g / L urease, 1 mol / L urea, 1 mol / L calcium chloride, 0.2 mol / L sucrose, and 0.2 mol / L ammonium chloride) for adsorption, and then the obtained... Urease-loaded biospheres were dispersed in a sodium alginate-polylactic acid-chitosan mixed solution (raw material composition includes: 30 g / L polylactic acid (50% crystallinity, 75000 Da molecular weight), 20 g / L sodium alginate (150000 Da molecular weight), and 1 g / L chitosan) for emulsification. The resulting suspension was then added dropwise to a 3 wt% calcium chloride solution at a rate of 1 drop / second for cross-linking. The mixture was then cured at 25 °C for 50 min to obtain biocapsules.

[0046] Preparation Example 2

[0047] Amino-modified silica microspheres (obtained by modifying silica microspheres with N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, where the mass ratio of N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane to silica microspheres is 0.05:1, and the particle size of the silica microspheres is 1 μm) were dispersed in a urease solution (the raw material components include: 15 g / L urease, 0.8 mol / L urea, 0.8 mol / L calcium chloride, 0.2 mol / L sucrose, and 0.15 mol / L ammonium chloride). Adsorption was performed, and then the obtained urease-loaded biospheres were dispersed in a sodium alginate-polylactic acid-chitosan mixed solution (the raw material composition included: 25 g / L polylactic acid (crystallinity of 55%, molecular weight of 60000 Da), 15 g / L sodium alginate (molecular weight of 150000 Da), and 0.8 g / L chitosan) for emulsification. The resulting suspension was then added dropwise to a 2.5 wt% calcium chloride solution at a rate of 1 drop / second for cross-linking, and solidified at 25 °C for 30 min to obtain biocapsules.

[0048] Preparation Example 3

[0049] Amino-modified silica microspheres (obtained by modifying silica microspheres with γ-aminopropyltriethoxysilane, the mass ratio of γ-aminopropyltriethoxysilane to silica microspheres was 0.15:1, and the particle size of the silica microspheres was 5 μm) were dispersed in a urease solution (the raw material components included: 45 g / L urease, 1.2 mol / L urea, 1.3 mol / L calcium chloride, 0.25 mol / L sucrose, and 0.25 mol / L ammonium chloride) for adsorption, and then... The obtained urease-loaded biospheres were dispersed in a sodium alginate-polylactic acid-chitosan mixed solution (the raw material composition included: 35 g / L polylactic acid (crystallinity of 45%, molecular weight of 90,000 Da), 25 g / L sodium alginate (molecular weight of 150,000 Da), and 1.5 g / L chitosan) for emulsification. The resulting suspension was then added dropwise to a 4 wt% calcium chloride solution at a rate of 1 drop / second for cross-linking. The mixture was then cured at 30 °C for 40 min to obtain biocapsules.

[0050] Preparation Example 4

[0051] The difference between this preparation example and Preparation Example 1 is that the crystallinity of polylactic acid is adjusted from 50% to 30%. The remaining steps remain unchanged.

[0052] Preparation Example 5

[0053] The difference between this preparation example and Preparation Example 1 is that the crystallinity of polylactic acid is adjusted from 50% to 70%. The remaining steps remain unchanged.

[0054] Preparation Example 6

[0055] The difference between this preparation example and Preparation Example 1 is that the molecular weight of polylactic acid was adjusted from 75,000 Da to 40,000 Da. The remaining steps remained unchanged.

[0056] Preparation Example 7

[0057] The difference between this preparation example and Preparation Example 1 is that the molecular weight of polylactic acid was adjusted from 75,000 Da to 110,000 Da. The remaining steps remain unchanged.

[0058] The biocapsules obtained in Examples 1-7 were subjected to performance tests, and the results are recorded in Table 1.

[0059] The testing method is as follows:

[0060] (1) Mixing breakage rate: According to the cement-soil specimen design (using dry standard quartz sand to simulate soil, cement content of 15% of dry sand mass, deionized water as mixing water, water-cement ratio of 0.6, pH=10, and biocapsule content of each group of 2% of cement-soil volume), the raw materials were weighed, and under the conditions of 150 rpm rotation speed and 100 Hz vibration frequency, the mixing construction was simulated for 5 min. The number of biocapsules that had broken (leaked contents) was counted by the optical microscope statistical method. The mixing breakage rate % was calculated as: number of broken capsules / total number of biocapsules × 100%.

[0061] (2) Release efficiency: Each group of biological capsules was placed in deionized water and left to stand at 25°C for 24 hours. The key contents were quantified: the urease activity or urea concentration in the solution was determined by spectrophotometry, and the calcium ion concentration was determined by atomic absorption spectrometry or EDTA titration. The release efficiency % was calculated as: actual released contents mass / total contents of the biological capsule initially packaged × 100%.

[0062] (3) Permeability coefficient: The mixture obtained by stirring in step (1) was made into a cement-soil specimen of 50×50×50mm. The cement-soil specimen prepared by urease solution in Preparation Example 1 without capsule encapsulation was used as the control group. After curing for 14 days, the permeability coefficient was determined by the variable head method.

[0063] Table 1

[0064]

[0065] As shown in Table 1, the biocapsules prepared in Examples 1-3 of this invention can balance high protection during construction and high responsiveness to water seepage through cracks, exhibiting excellent impermeability. Comparing Preparation Example 1 with Preparation Examples 4-7, it can be seen that when the crystallinity of polylactic acid is too low or the molecular weight is too small, the mechanical strength of the capsule wall material is insufficient, leading to a high rate of breakage during stirring and premature release of active ingredients; when its crystallinity is too high or the molecular weight is too large, the wall material is too dense, which hinders release and results in insufficient repair response.

[0066] Example 1

[0067] This invention provides a construction method for enhancing the impermeability of cement-soil mixing piles based on biocapsules, comprising the following steps:

[0068] S1. Based on the target pile volume (cement-soil volume), 3% of the biocapsules prepared in Example 1 (pre-screened biocapsules with a particle size of 50~500μm) are added to the cement slurry (water-cement ratio of 0.6, pH of 10) and stirred at 120rpm for 2min.

[0069] S2. The three-axis mixing piles are constructed using a two-mixing-one-spraying process. After construction, the piles are subjected to temperature gradient curing treatment.

[0070] The two-mixing-one-spraying process specifically includes the following steps: The drill bit is equipped with a high-frequency vibration module and a rotary spray nozzle with an inclination angle of 15°. The drill bit rotates and sinks to the designed depth with a vibration frequency of 90Hz, an amplitude of 3mm, a sinking speed of 0.6m / min, and a rotation speed of 120rpm. After continuous spraying of grout at the bottom of the pile for 30s, the drill bit rotates in the opposite direction and is lifted and sprayed with grout. The vibration frequency is 80Hz, the amplitude is 3mm, the lifting speed is 0.5m / min, and the rotation speed is 120rpm. During spraying, the intelligent layered spraying system is used to regulate the spraying pressure to increase in a gradient from bottom to top along the pile body (the spraying pressure of the lower, middle, and upper parts of the pile body is 0.5MPa, 0.7MPa, and 0.9MPa, respectively). The pressure sensor integrated into the drill rod provides real-time feedback on the soil resistance and dynamically regulates the spraying volume within a range of ±15%. A second sinking and lifting mixing process is then performed to enhance the uniformity of the pile body. When the drill bit is lifted to the top of the pile, continuous spraying of grout is performed at the top of the pile for 30s. The spraying is then stopped, and the single pile construction is completed.

[0071] The temperature gradient curing treatment includes the following steps: cover the pile body and surrounding soil with plastic film or geotextile, and cure for 14 days in an environment with 90% humidity. After the pile body is formed, first circulate hot air at 40℃ for 2 hours, and then cure at a low temperature of 15℃ for 48 hours.

[0072] Sampling tests were conducted on the cement-soil mixing piles prepared using the construction method of Example 1: Before on-site construction, a designed pile point was selected for drilling and sampling. Soil samples were taken at depths of 2.1~2.3m, 2.3~2.5m, 2.7~2.9m, 5.0~5.2m, 5.2~5.4m, 5.4~5.6m, 7.5~7.7m, 7.7~7.9m, and 7.9~8.1m below the ground surface. The permeability coefficient was determined using the variable head method and recorded. Fourteen days after the completion of the cement-soil mixing pile construction, the same location was sampled again to determine the permeability coefficient, and the magnitudes of the permeability coefficients before and after the test were compared.

[0073] Combination Figure 1 It can be seen that when cement slurry containing the biocapsules of this invention is used for cement-soil mixing pile construction, the average permeability coefficient increases from the initial 7.935 × 10⁻⁶. -5 cm / s decreased to 3.033×10 -6 The speed of cm / s further demonstrates that this construction method can significantly enhance the anti-seepage and self-healing performance of cement-soil mixing piles.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A construction method for enhancing the impermeability of cement-soil mixing piles based on biological capsules, characterized in that, Includes the following steps: S1. Mix the biological capsules into the cement slurry and stir evenly. S2. The three-axis mixing piles are constructed using a two-mixing-one-spraying process. After construction, the piles are subjected to temperature gradient curing treatment. In step S1, the preparation of the biological capsule includes the following steps: Amino-modified silica microspheres were dispersed in a urease solution for adsorption. The resulting urease-loaded bio-microspheres were then dispersed in a sodium alginate-polylactic acid-chitosan mixed solution for emulsification. The resulting suspension was then added dropwise to a calcium ion-containing solution for cross-linking and solidification, thus obtaining the final product. The raw material composition of the sodium alginate-polylactic acid-chitosan mixed solution includes: 25~35g / L polylactic acid, 15~25g / L sodium alginate, and 0.5~2g / L chitosan.

2. The construction method for enhancing the impermeability of cement-soil mixing piles based on bio-capsules according to claim 1, characterized in that, In step S1, the dosage of the biocapsule is 0.5-3% of the volume of the pile body, the particle size of the biocapsule is 50-500μm, the water-cement ratio of the cement slurry is 0.55-0.6, and the pH of the cement slurry is 9-11.

3. The construction method for enhancing the impermeability of cement-soil mixing piles based on biocapsules as described in claim 1, characterized in that, In step S1, the amino-modified silica microspheres are obtained by modifying silica microspheres with an aminosilane coupling agent, and the mass ratio of the aminosilane coupling agent to the silica microspheres is 0.05~0.15:

1.

4. The construction method for enhancing the impermeability of cement-soil mixing piles based on biocapsules as described in claim 1, characterized in that, In step S1, the raw material components of the urease solution include: 10~50 g / L of urease, 0.5~1.5 mol / L of urea, 0.5~1.65 mol / L of calcium chloride, 0.2~0.3 mol / L of sucrose, and 0.1~0.3 mol / L of ammonium chloride, wherein the molar ratio of urea to calcium chloride is 1:(1~1.1).

5. The construction method for enhancing the impermeability of cement-soil mixing piles based on biocapsules as described in claim 1, characterized in that, The polylactic acid has a crystallinity of 40-60%.

6. The construction method for enhancing the impermeability of cement-soil mixing piles based on biocapsules as described in claim 1, characterized in that, The molecular weight of the polylactic acid is 50,000 to 100,000 Da.

7. The construction method for enhancing the impermeability of cement-soil mixing piles based on biocapsules as described in claim 1, characterized in that, In step S1, the concentration of calcium ions in the calcium ion-containing solution is 2-5 wt%.

8. The construction method for enhancing the impermeability of cement-soil mixing piles based on biocapsules as described in claim 1, characterized in that, In step S2, the two-stirring-one-spraying process specifically includes the following steps: the drill bit is equipped with a high-frequency vibration module and a rotary jet nozzle. The drill bit rotates and sinks to the designed depth. After continuously spraying grout at the bottom of the pile for 30 seconds, it rotates in the opposite direction to lift and spray grout. During grouting, the intelligent layered grouting system is used to regulate the grouting pressure to increase gradually from bottom to top along the pile body and dynamically regulate the grouting volume. Then, a second sinking and lifting stirring is performed. When the drill bit is lifted to the top of the pile, grout is continuously sprayed at the top of the pile for 30 seconds. Grouting is then stopped to complete the construction. The construction parameters for the two-mixing-one-spraying process are as follows: vibration frequency of 80~120Hz, amplitude of 2~5mm, spray nozzle inclination angle of 15~30°, rotation speed of 100~150rpm, sinking speed of 0.6~0.8m / min, lifting speed of 0.5~0.6m / min, spraying pressure of the lower part of the pile body of 0.4~0.6MPa, spraying pressure of the middle part of the pile body of 0.6~0.8MPa, and spraying pressure of the upper part of the pile body of 0.8~1.0MPa.

9. The construction method for enhancing the impermeability of cement-soil mixing piles based on biocapsules as described in claim 1, characterized in that, In step S2, the temperature gradient curing treatment specifically includes the following steps: covering the pile body and surrounding soil with plastic film or geotextile, curing for 7 to 14 days in an environment with a humidity of 80 to 90%, and after the pile body is formed, first circulating hot air at 40 to 50°C is introduced for 2 hours, and then low temperature curing at 10 to 15°C is used for 48 hours.

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