Method for solidifying soft soil through biomineralization effect of guar gum and urease-producing strain

Abstract

The invention provides a method for solidifying soft soil through the biological mineralization effect of guar gum and a urease-producing strain, the urease-producing strain is bacillus pasteurii DC419, and the preservation number of the urease-producing strain is CCTCC (China Center for Type Culture Collection) NO: M 20222038. The method for solidifying the soft soil comprises the following steps: mixing urease-producing strain fermentation liquor and cementing liquid to obtain mixed liquor; soft soil and guar gum are evenly mixed, the mixed solution is added, the mixture is evenly mixed and then stands still, and solidification of the soft soil is achieved. The soft soil cured by the method disclosed by the invention has relatively high compressive strength and relatively good waterproof capability.

Description

Technical Field

[0001] This invention relates to the field of biotechnology, specifically to a method for solidifying soft soil through the biomineralization process of guar gum and urease-producing strains. Background Technology

[0002] Loose, clayey soils are characterized by high water content, low strength, high compressibility, significant sensitivity, and susceptibility to disturbance. They are widely distributed in coastal areas and river valleys. Rapid urbanization has generated large quantities of this type of soil material. If not properly managed, these soils can pose geological engineering risks, including foundation settlement and slope instability, potentially compromising structural integrity and transportation infrastructure.

[0003] Biopolymer additives show great potential in absorbing soil moisture and enhancing soil stability, but their applicability in soil stabilization applications is limited, and they may be prone to secondary softening. Microbial-induced carbonate precipitation (MICP) is an emerging soil stabilization method. This process promotes the sequestration of atmospheric carbon dioxide by forming calcium carbonate crystals, which then fill soil pores and enhance particle bonding. However, its post-stabilization strength is low, and it is easily eroded by rainwater. This invention provides a method for stabilizing soft soil through the biomineralization of guar gum and urease-producing strains. Summary of the Invention

[0004] Purpose of the invention: The technical problem to be solved by the present invention is to provide a method for solidifying soft soil by biomineralization of guar gum in conjunction with urease-producing strains, addressing the shortcomings of the existing technology.

[0005] To address the aforementioned technical problems, this invention discloses a method for solidifying soft soil through the biomineralization process of guar gum and urease-producing bacterial strains. The specific technical solution is as follows:

[0006] This invention provides a method for stabilizing soft soil through the biomineralization process of guar gum and urease-producing strains, the method comprising the following steps:

[0007] (1) Mix the fermentation broth of the urease-producing strain and the gelling liquid to obtain a mixture;

[0008] (2) Mix the soft soil and guar gum evenly, add the mixture prepared in step (1), mix evenly and let stand to solidify the soft soil.

[0009] In step (1), the urease-producing strain includes *Sporosarcina pasteurii*. Preferably, it is *Sporosarcina pasteurii* DC419, with accession number CCTCCNO: M20222038, the details of which are disclosed in Chinese patent CN116445343A.

[0010] In step (1), the fermentation broth of the urease-producing strain is prepared as follows: the urease-producing strain is inoculated into a fermentation medium and fermented at 28–35°C for 16–24 h; wherein the fermentation medium contains 1–10 g / L urea, preferably 3–5 g / L urea. Preferably, the urease-producing strain is inoculated into a fermentation medium and fermented at 30°C and 180 r / min for 20 h, wherein the pH of the fermentation medium is 9, and the fermentation medium further includes 10–15 g / L peptone, 20–25 g / L yeast extract, 16–17 g / L dipotassium hydrogen phosphate, 0.2–0.8 g / L anhydrous magnesium sulfate, and 10–20 g / L glycerol. More preferably, the urease-producing strain is inoculated into the fermentation medium in the form of a strain seed liquid for fermentation culture. The strain seed liquid is prepared by taking the urease-producing strain preservation tube out of the -80℃ freezer, inoculating it into LB medium, and culturing it in a constant temperature shaker at 28-35℃ and 150-200r / min for 10-12h.

[0011] Preferably, in step (1), the urease-producing strain fermentation broth has a cell concentration OD0 600 It is 2 to 3.

[0012] In step (1), the cementing solution comprises 0.3–1.2 mol / L urea and 0.3–1.2 mol / L calcium formate; the pH of the cementing solution is 8–12. Preferably, the solvent is water. More preferably, the cementing solution is a mixture of 0.9 mol / L urea and 0.9 mol / L calcium formate, and the solvent is distilled water. The pH of the cementing solution is preferably 9.

[0013] In step (1), the mixing volume ratio of the urease-producing strain fermentation broth to the gelling liquid is 1:1 to 3, preferably 1:2.

[0014] In step (2), the mass of guar gum added is 0.5% to 3% of the mass of the soft soil. Preferably, it is 1%.

[0015] In step (2), the mass of the mixture added is 15% to 20% of the mass of the soft soil. Preferably, it is 16.5%.

[0016] In step (2), the standing time is 5 to 7 days at room temperature.

[0017] Among them, the compressive strength of the soft soil after solidification is >3.5MPa.

[0018] Beneficial effects:

[0019] This invention provides a method for solidifying soft soil through biomineralization by guar gum synergistically with a urease-producing strain. The strain used in this invention, Sporosarcina pasteurii DC419, is from the China Center for Type Culture Collection (CCTCC), accession number: CCTCC NO: M 20222038. This invention utilizes the biomineralization effect of guar gum synergistically with the strain Sporosarcina pasteurii DC419 to solidify soft soil. The solidified soft soil exhibits excellent compressive strength, waterproofing properties, and self-healing capabilities. Attached Figure Description

[0020] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0021] Figure 1 It is a molding mold for soft soil, with a diameter of 50mm and a height of 100mm.

[0022] Figure 2 It is a universal tensile testing machine.

[0023] Figure 3 The image shows the scanning electron microscopy characterization of the solidified soil in Example 3. Detailed Implementation

[0024] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0025] The following examples are provided to better understand the present invention, but do not limit the invention. Unless otherwise specified, the experimental methods in the following examples are conventional methods. Unless otherwise specified, the experimental materials used in the following examples were purchased from conventional biochemical reagent stores. All quantitative experiments in the following examples were performed in triplicate, and the results were averaged.

[0026] In the following examples, the LB medium was prepared as follows: 10 g / L tryptone, 5 g / L yeast extract, and 10 g / L sodium chloride, with the remainder being distilled water. The pH was adjusted to 9 with 4 M sodium hydroxide solution, and then sterilized.

[0027] In the following examples, the fermentation medium was prepared as follows: 12 g / L peptone, 24 g / L yeast extract, 16.43 g / L dipotassium hydrogen phosphate, 0.49 g / L anhydrous magnesium sulfate, 10 g / L glycerol, with the balance being distilled water. The pH was adjusted to 9 with 4M sodium hydroxide solution, and then sterilized.

[0028] In the following embodiments, the Sporosarcina pasteuriiDC419, with accession number CCTCC NO: M20222038, has its detailed information disclosed in Chinese Patent CN116445343A.

[0029] Example 1: Preparation of bacterial culture

[0030] Remove the culture tube from the -80℃ freezer, inoculate 50 μL of L. pasteurii DC419 strain and 100 μL of urea (urea concentration of 200 g / L) into 5 mL of LB medium, and then place it in a constant temperature shaker at 30℃ and 180 r / min for 12 h to obtain the seed culture.

[0031] In a clean bench, 1 mL of the seed culture and 2 mL of urea (urea concentration of 200 g / L) were added to 100 mL of fermentation medium for enrichment. The mixture was then incubated at 30°C and 180 rpm in a shaker for 20 h. After enrichment, the bacterial concentration was measured using a spectrophotometer to be OD0.05. 600 =2.1, and the fermentation broth is obtained.

[0032] Example 2: Optimization of Fermentation Broth Dosage

[0033] The cementing solution and the fermentation broth prepared in Example 1 were mixed at a certain volume ratio (cementing solution: fermentation broth ratio of 1:3, 1:2, 1:1, 2:1, or 3:1), resulting in a total volume of 20 mL. The mixture was allowed to stand at 30°C for 48 h to obtain a final mixture. This mixture was then centrifuged at 6000 rpm for 5 min in a high-speed rotary centrifuge. The waste liquid after centrifugation was discarded, and the resulting sample was dried in an oven and weighed. The weight of the precipitate obtained after drying was recorded. The results showed:

[0034] When the volume ratio of the cementing solution to the fermentation broth is 1:3, the resulting precipitate is 0.786g.

[0035] When the volume ratio of the cementing solution to the fermentation broth is 1:2, the amount of precipitate produced is 1.065g.

[0036] When the volume ratio of cementing liquid to fermentation liquid is 1:1, the amount of precipitate produced is 1.433g.

[0037] When the volume ratio of cementing liquid to fermentation liquid is 2:1, the amount of precipitate produced is 1.603g.

[0038] When the volume ratio of cementing liquid to fermentation liquid is 3:1, the resulting precipitate is 1.529g.

[0039] Therefore, a volume ratio of 2:1 for the cementing liquid to the fermentation broth was chosen for subsequent experiments.

[0040] Example 3: Soft Soil Consolidation Strength Test

[0041] This embodiment designs a method for guar gum synergistically combined with MIP to solidify soft soil, which specifically includes the following steps:

[0042] (1) Take a soil sample from a construction site at the Jiangpu Campus of Nanjing University of Technology, crush it with a pulverizer and weigh it.

[0043] (2) Add 1% w / w guar gum sample by weight of soil to the soft soil and mix well.

[0044] (3) The cementing solution and the fermentation broth prepared in Example 1 are mixed at a volume ratio of 2:1 to obtain a mixture. The mixture is then poured into the soft soil obtained in step (1) at 16.5% w / w of the soil mass and stirred evenly. The mixture is then compacted into a mold (e.g., Figure 1 (As shown), and cured under laboratory conditions at room temperature. The cementitious solution was prepared as follows: 0.9 mol / L urea and 0.9 mol / L calcium formate were mixed, with distilled water as the solvent and a pH of 9.

[0045] (4) After curing for 7 days, test in a universal tensile testing machine (e.g.) Figure 2 The soil was tested and fractured under pressure (as shown), and the required pressure P was recorded. Its compressive strength was calculated as p = P / A, where A is the cross-sectional area under stress. The results showed that the compressive strength of the solidified soil was 3.70 MPa. Fractured soil samples were photographed and analyzed using a scanning electron microscope. Figure 3 As shown, the specific manifestations are: (1) the precipitation fills the pores in the soil; (2) the spatial distribution is more uniform; and (3) larger crystals are formed.

[0046] In addition, this embodiment also includes multiple control experiments, as detailed below:

[0047] Guar gum concentration optimization group: Similar to steps (1) to (4) above, except that in step (2), 1% w / w, 2% w / w, and 4% w / w guar gum samples were added to the soft soil. After the soft soil was solidified according to the above steps and left for 7 days, the compressive strength was calculated to be 3.70 MPa, 1.91 MPa, and 0.64 MPa, respectively. Among them, the solidification effect was the best when the guar gum added was 1% w / w of the soil mass.

[0048] Guar gum group: 1% w / w guar gum sample by soil mass was added to the soil, followed by 16.5% w / w distilled water by soil mass, mixed evenly, compacted into a mold, and cured under constant temperature conditions in the laboratory. The compressive strength was calculated after 7 days and was 2.20 MPa.

[0049] MICP group: Same as step (3) above, prepare cementing liquid, mix cementing liquid and fermentation liquid prepared in Example 1 at a volume ratio of 2:1, pour into soil at 16.5% w / w of soil mass and stir evenly, compact into mold, and solidify under constant temperature conditions in the laboratory. After 7 days of solidification, calculate the compressive strength, which is 0.38 MPa.

[0050] Example 4: Soft Soil Solidification and Waterproofing Test

[0051] This embodiment conducted a waterproofing test on the solidification of soft soil. The waterproofing test method is as follows:

[0052] (1) Prepare solidified soil according to steps (1) to (4) of the method of solidifying soft soil with guar gum and MICP in Example 3, put it into a mold, weigh it and record its weight as m1, record the self-weight of the mold as m0, and take it out after completely immersing the mold in water for 7 days.

[0053] (2) After being removed from the water, the soil was left to dry for 7 days. Its weight was recorded as m2. The soil loss rate Y was calculated using the formula Y = (m1 - m2) / (m1 - m0). The soil was removed from the mold and tested on a universal tensile testing machine to break the soil under pressure. The required pressure P was recorded. The compressive strength p = P / A was calculated, where A is the cross-sectional area under force. The results showed that the compressive strength of the soil after soaking for 7 days was 1.62 MPa, and the soil loss rate was 6.44%.

[0054] In the curing and waterproofing test, this embodiment also tested the curing and waterproofing effects of other polymers, specifically:

[0055] Xanthan gum group: The curing method is the same as steps (1) to (4) in Example 3, except that the guar gum sample in step (2) is replaced with an equal mass of xanthan gum sample.

[0056] Dextran group: The curing method is the same as steps (1) to (4) in Example 3, except that the guar gum sample in step (2) is replaced with an equal mass of dextran sample.

[0057] In this embodiment, waterproof tests were conducted on the xanthan gum group and the dextran group according to the waterproof test method described in this embodiment. The results showed that the compressive strength of the soil obtained from the xanthan gum group after immersion in water for 7 days was 1.58 MPa, and the soil loss rate was 7.64%. The compressive strength of the soil obtained from the dextran group after immersion in water for 7 days was 0.67 MPa, and the soil loss rate was 18.5%. Both were lower than the curing and waterproofing effect of guar gum.

[0058] Example 5: Self-healing test of soft soil

[0059] (1) Solidified soil was prepared according to steps (1) to (4) of the method for solidifying soft soil with guar gum and MICP as described in Example 3. After testing the compressive strength of the specimens obtained after 7 days of solidification, the soil samples were crushed using a mechanical crusher.

[0060] (2) The solidified soil sample was crushed with a mixer. After crushing, 16.5% w / w of deionized water was added and stirred evenly. The moistened soil mixture was then compacted and put into a mold for specimen remolding.

[0061] (3) After 7 days, the soil was removed from the mold and tested on a universal tensile testing machine to break the soil. The required pressure P was recorded.

[0062] (4) Calculate its compressive strength p=P / A, where A is the cross-sectional area under force. The results show that the compressive strength of the remolded soil is 1.68MPa.

[0063] Meanwhile, this embodiment also conducted self-healing tests on the MIP group described in Example 3 and the xanthan gum group and dextran group described in Example 4. The test methods were the same as above. The results showed that the compressive strength of the soil after remodeling of the MIP group, xanthan gum group and dextran group were 0.59 MPa, 1.50 MPa and 0.83 MPa, respectively.

[0064] Based on the above experimental results, this method can significantly improve the strength and waterproofing ability of solidified soft soil, and also has a certain self-healing effect, showing good application prospects.

[0065] This invention provides a method for solidifying soft soil through the biomineralization process of guar gum and urease-producing strains. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. A method for solidifying soft soil through the biomineralization process of guar gum and urease-producing strains, characterized in that, Includes the following steps: (1) Mix the fermentation broth of the urease-producing strain and the gelling liquid to obtain a mixture; (2) Mix the soft soil and guar gum evenly, add the mixture prepared in step (1), mix evenly and let stand to solidify the soft soil.

2. The method according to claim 1, characterized in that, In step (1), the urease-producing strain includes Sporosarcina pasteurii.

3. The method according to claim 2, characterized in that, The aforementioned Bacillus pasteurii includes Bacillus pasteurii DC419, whose accession number is CCTCC NO: M 20222038.

4. The method according to claim 1, characterized in that, In step (1), the fermentation broth of the urease-producing strain is prepared by the following method: the urease-producing strain is inoculated into the fermentation medium and fermented at 28-35°C for 16-24 hours; wherein the fermentation medium contains 1-10 g / L urea.

5. The method according to claim 1, characterized in that, In step (1), the cementing solution includes 0.3-1.2 mol / L urea and 0.3-1.2 mol / L calcium formate; the pH of the cementing solution is 8-12.

6. The method according to claim 1, characterized in that, In step (1), the mixing volume ratio of the fermentation broth of the urease-producing strain to the gelling liquid is 1:1 to 3.

7. The method according to claim 1, characterized in that, In step (2), the mass of guar gum added is 0.5% to 3% of the mass of the soft soil.

8. The method according to claim 1, characterized in that, In step (2), the mass of the mixture added is 15% to 20% of the mass of the soft soil.

9. The method according to claim 1, characterized in that, In step (2), the standing time is 5 to 7 days at room temperature.

10. The method according to claim 1, characterized in that, The compressive strength of the soft soil after solidification is >3.5MPa.

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