Test method for improving expansive soil based on microorganism-mineral interaction

Abstract

The invention discloses an experimental method for improving expansive soil based on microorganism-mineral interaction, which utilizes the physiological characteristics of microorganisms to interact with montmorillonite and other minerals of the expansive soil, promotes the montmorillonite minerals to be weathered into non-expansive minerals, and reduces the content of montmorillonite in the expansive soil, thereby reducing the expansive property of the expansive soil and improving the expansive soil quality. The problems that the expansion and shrinkage of the expansive soil are not thoroughly improved through a microbial technology, calcium ion deposition is not easy to control, and long-term stability is poor are solved. Meanwhile, compared with a traditional expansive soil chemical improvement method, the method adopts a microbial technology, does not need to add a large number of chemical agents, and is low in cost, environmentally friendly, simple in test step and easy to popularize and apply.

Description

Technical Field

[0001] The invention relates to the technical field of expansive soil improvement tests, and in particular to a test method for improving expansive soil based on microorganism-mineral interaction. Background Art

[0002] Expansive soil contains strong hydrophilic minerals such as montmorillonite, which has significant water absorption and expansion, and water loss and shrinkage characteristics. Due to the expansion and contraction characteristics of expansive soil, it is easy to cause harm to buildings. Therefore, civil engineering technicians need to study ways to improve expansive soil and avoid harm to construction projects by suppressing its expansion characteristics.

[0003] The crystal structure of montmorillonite mineral is a 2:1 layered structure, with aluminum oxide octahedron in the middle and silicon oxide tetrahedron above and below, and water and some exchange cations in the interlayer. This 2:1 layered structure gives montmorillonite a strong cation exchange and a large amount of water molecule adsorption capacity. The higher its content, the more obvious the expansion and contraction effect of the expansive soil. The content of montmorillonite has a decisive control effect on the expansion and contraction of the expansive soil.

[0004] Traditional expansive soil improvement technologies mainly include physical improvement and chemical improvement. The physical improvement method mainly involves adding materials such as fiber and sand to the expansive soil to change the particle size distribution of the expansive soil and increase the friction between soil particles to achieve the purpose of reducing the expansion rate of the expansive soil. The chemical improvement method improves the engineering properties of the expansive soil by adding materials such as lime, cement, and water glass to the expansive soil through certain chemical reactions. Although physical and chemical improvement methods can achieve certain improvement effects, there are also problems such as large engineering workload, long construction period, and environmental pollution. In recent years, the microbial technology that has emerged has become a new method for improving special soils due to its environmental friendliness and good improvement effect. At present, the research on the improvement of expansive soil by microbial technology mainly focuses on microbial induced calcium carbonate precipitation technology (MICP). Its basic principle is to use the metabolic activities of microorganisms to produce a large amount of highly active urease, using urea in the environment or added externally as a nitrogen source, thereby decomposing urea into ammonium ions and carbonate ions. Subsequently, carbonate ions combine with calcium ions to form calcium carbonate precipitation, which adheres to the surface of soil particles to improve the swelling and shrinkage, strength, and stiffness of the soil. Although this technology can improve the swelling and shrinkage of expansive soil, it also has some limitations, such as the decomposition of urea to produce ammonia, which is polluting, the poor controllability of calcium ion deposition, and long-term stability issues. Summary of the invention

[0005] In view of the above problems, the purpose of the present invention is to provide an experimental method for improving expansive soil through microbial-mineral interaction, which qualitatively and quantitatively utilizes the physiological characteristics of microorganisms themselves to promote the weathering of montmorillonite minerals into non-expandable minerals, thereby reducing the montmorillonite content in the expansive soil, and provides a component ratio reference for microbial improvement of expansive soil.

[0006] The present invention provides an experimental method for improving expansive soil based on microorganism-mineral interaction, comprising the following steps:

[0007] S1. Select a microbial strain, prepare a culture medium, and culture it according to preset conditions to obtain a microbial culture solution;

[0008] S2. Obtaining expansive soil and pre-treating it to obtain an expansive soil sample;

[0009] S3. Mix the expansive soil sample obtained in step S2 with the culture medium, divide it into several experimental groups and put it into a container, connect a preset number of experimental groups with the microbial solution obtained in step S1, and connect the rest as a control group with distilled water, and all experimental groups are cultured at a constant temperature according to a time gradient, and the experimental groups after the culture is completed are centrifuged; the supernatant obtained by centrifugation is subjected to trace element determination to obtain trace element data of the supernatant; the solid obtained by centrifugation is dried to obtain a soil sample to be tested; microstructure experiments and mineral phase and component content analysis experiments are carried out on the soil sample to be tested to obtain test data of the soil sample to be tested; based on the geotechnical test method standard, a free expansion rate experiment is carried out on the obtained soil sample to be tested to obtain expansion rate data of the soil sample to be tested;

[0010] S4. Set up parallel experimental groups according to the time gradient of step S3, mix the microbial solution and the culture medium evenly with the expansive soil sample according to a preset ratio, and prepare the ring knife specimens after constant temperature culture for a corresponding time. Based on the geotechnical test method standard, perform the load expansion rate and contraction rate experiment under the preset load to obtain the ring knife specimen experimental data;

[0011] S5. According to the trace element data of the supernatant obtained in step S3 and the test data of the soil sample to be tested, qualitative analysis is performed on the improvement of the expansive soil by the interaction between microorganisms and minerals;

[0012] S6. Based on the swelling rate data of the soil sample to be tested in step S3 and the ring cutter sample experimental data obtained in step S4, quantitatively analyze the improvement of the expansive soil by the interaction between microorganisms and minerals.

[0013] Step S1 specifically comprises: preparing a nitrogen-free culture medium, inoculating the selected microbial strain seed solution into the nitrogen-free culture medium, and culturing in a shaking table at 28° C. to 30° C. and a rotation speed of 145 r / min to 150 r / min for 36 h to 42 h to obtain a microbial bacterial solution;

[0014] The microbial strain is Bacillus mucilaginosus CSUFT21698, classified and named Paenibacillus mucilaginosus, deposited in China Center for Type Culture Collection on November 28, 2024, with the deposit address being Wuhan University, and the deposit number being CCTCC NO: M 20242650;

[0015] The activity concentration OD of the microbial solution 600 The value is 1.8-2.0, and the pH value is 7.0-7.5;

[0016] The nitrogen-free culture medium comprises 9 to 10 g / L sucrose -1 , CaCO3·2H2O 0.10~0.12g·L -1 、K2HPO40.20~0.22g·L -1 、CaCO35.0~5.1g·L -1 , MgSO4·7H2O 0.20~0.21g·L -1 、NaCl 0.20~0.21g·L -1 After the nitrogen-free culture medium is prepared according to the above components, the pH value is adjusted to 7.0-7.5 using dilute hydrochloric acid.

[0017] The pretreatment in step S2 is as follows: drying the expansive soil at 105-110° C. for 8-10 h, crushing it and passing it through a 0.075 mm sieve to obtain an expansive soil sample;

[0018] 9% to 10% of calcified montmorillonite particles are added to the expansive soil;

[0019] The fundamental reason for the significant swelling and shrinkage of expansive soil is that it is rich in montmorillonite minerals. Adding a certain amount of montmorillonite to the original soil to interact with microorganisms is more targeted and representative, and can better reflect the effect of microbial-promoted mineral phase change on the swelling and shrinkage of expansive soil.

[0020] The expansive soil sample meets the liquid limit of 50.0% to 58.1%, the plastic limit of 30.0% to 35.5%, and the free expansion rate of 90% to 171%;

[0021] Step S3 specifically includes the following steps:

[0022] The expansive soil sample obtained in step S2 is mixed with the culture medium in a ratio of 1:(5-5.5), and then divided into 2S experimental groups and placed in a container;

[0023] S of the experimental groups are inoculated as positive experimental groups with the microbial solution obtained in step S1, the inoculation volume of the microbial solution is 6.0-6.2 mL, and the liquid volume is 98-100 mL; the remaining S experimental groups are inoculated with distilled water as control groups to keep the quality of each experimental group consistent;

[0024] S positive experimental groups are divided into t1 day, t2 day, ..., t i day, ..., t m The culture was carried out at a constant temperature of 35°C and shaking at 150 r / min for a time gradient of 1 day, and the positive experimental group after the culture was completed was centrifuged to obtain the supernatant and residual solid;

[0025] The S control groups are the same as the positive experimental group, and the number of i day, ..., t m The culture was carried out at a constant temperature of 35°C and shaking at 150 r / min for a time gradient of 1 day, and the positive experimental group after the culture was completed was centrifuged to obtain the supernatant and residual solid;

[0026] The supernatants obtained from the above 2S experimental groups were subjected to trace element experiments to determine the Si content in the supernatants. 4+ 、Al 3 + Mg 2+ and K + Ion concentration, obtain the trace element data of the supernatant; the ion concentration in the trace element experiment was determined by inductively coupled plasma optical emission spectrometry (ICP-OES);

[0027] The residual solids obtained from the above 2S experimental groups are dried at 105-110°C for 8-10 hours to obtain soil samples to be tested, and microstructure experiments and mineral phase and component content analysis experiments are performed on the soil samples to be tested, so as to obtain the vibration behavior of all atoms in the montmorillonite mineral lattice in the expansive soil after the action of microorganisms and its influence on the groups or chemical bonds, and obtain the test data of the soil samples to be tested;

[0028] The microstructure experiment was tested using a Fourier transform infrared spectrometer (FTIR) with a spectral range of 600 to 4000 cm -1 , resolution 4cm -1 ;

[0029] The mineral phase and component content analysis experiment was conducted using a powder X-ray diffractometer (XRD), with a radiation source of CuKα1 (λ=0.154nm) and a step width of 0.02°; the mineral phase and component content analysis experiment used wide-angle X-ray diffraction, with a scanning range of 5°~70° and a scanning speed of 5~5.2° / min; the mineral phase and component content analysis experiment used software to perform phase qualitative analysis, using the K value to calculate the percentage of clay minerals in the sample, and then multiplying it by the dry weight of the sample to finally obtain the absolute content of each clay mineral;

[0030] Based on the geotechnical test method standard, a free expansion rate experiment is carried out on the soil sample to obtain the expansion rate data of the soil sample to be tested.

[0031] Step S4 specifically comprises: uniformly mixing the microbial liquid, the culture medium and the expansive soil sample in a ratio of 1:1:(8-8.5) to obtain a mixed sample; the water content of the mixed sample is 25.0-25.2%;

[0032] The mixed samples were divided into S groups and cultured at 35°C for t1 day, t2 day, ..., t i day, ..., t m Days of time gradient, obtaining ring knife samples;

[0033] Based on the geotechnical test method standard, the ring knife specimen was subjected to the lateral load expansion rate and contraction rate test under the preset load, and the ring knife specimen experimental data was obtained.

[0034] Step S5 is specifically as follows: according to the supernatant trace element data obtained in step S3, the Si content in the centrifugal supernatant of the experimental groups with different time gradient culture time is compared. 4+ 、Al 3+ Mg 2+ and K + Ion concentration, through the changes in the dissolution of four cations, indirectly proves the influence of microorganisms on the metal elements in the crystal structure of montmorillonite;

[0035] The keratinous Bacillus secretes carbonic anhydrase (CA) during the growth and metabolism process. The enzyme can fix CO2 to produce bicarbonate, which can enhance the flow of cell membranes and promote the release of mineral cations. At the same time, the extracellular polysaccharides produced by the CA can promote the release of mineral ions through complexation.

[0036] According to the test data of the soil sample obtained in step S3, the vibration behavior of all atoms in the montmorillonite mineral lattice in the expansive soil under the action of microorganisms in the centrifugal solid of the experimental group with different time gradient incubation times and its influence on the groups or chemical bonds are obtained, which directly proves that the microorganisms convert montmorillonite into illite, thereby achieving the improvement of the expansive soil.

[0037] The Bacillus horniferus can promote the transformation of montmorillonite to illite at room temperature and 1 atmosphere, and can destroy the mineral lattice structure to a certain extent.

[0038] Step S6 specifically comprises: according to the experimental data of the ring knife sample obtained in step S4, by changing the load expansion rate and contraction rate data of the ring knife samples with different incubation times, obtaining the relationship between the microbial action time and the expansion rate and contraction rate of the expansive soil;

[0039] According to the swelling rate data of the tested soil sample in step S3, the improvement of the expansive soil by the interaction between microorganisms and minerals is quantitatively analyzed through the swelling rate of the tested soil sample at different microbial action times and the montmorillonite mineral conversion rate data.

[0040] Beneficial effects of the present invention:

[0041] (1) Compared with the traditional expansive soil improvement method, the method of the present invention adopts microbial technology to reduce the montmorillonite content in the expansive soil, has obvious effect, does not need to add a large amount of chemical agents, has simple steps, low cost and environmental protection, and is easy to promote and apply;

[0042] (2) Compared with the existing technology of improving expansive soil by microbial induced calcium carbonate deposition, the method of the present invention solves the problems of poor controllability of calcium ions and easy weathering of calcium carbonate over a long period of time, and fundamentally solves the significant expansion and contraction of expansive soil caused by rich montmorillonite. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 Schematic diagram of the interaction between Bacillus subtilis CICC 21698 and expansive soil;

[0044] Figure 2 This is a schematic diagram of the principle of improving the swelling and shrinkage of expansive soil by Bacillus colloids CICC 21698;

[0045] Figure 3 This is the data diagram of trace elements in the supernatant in Example 1;

[0046] Figure 4 This is the experimental data analysis diagram of the microstructure of the soil sample to be tested in Example 1;

[0047] Figure 5 The mineral phase analysis diagram of the soil sample to be tested in Example 1;

[0048] Figure 6 This is the experimental data diagram of the ring knife sample in Example 1;

[0049] Figure 7 This is the experimental data diagram of the free expansion rate of the soil sample to be tested in Example 1. DETAILED DESCRIPTION

[0050] The present invention and the effects produced are further described in detail below in conjunction with specific implementation methods.

[0051] The expansive soil in the embodiment is taken as an example of a soil sample from a project in Nanning, Guangxi Zhuang Autonomous Region, and the test is carried out according to the above technical scheme. The specific steps are as follows:

[0052] S1. Select a microbial strain, prepare a culture medium, and culture it according to preset conditions to obtain a microbial culture solution, specifically:

[0053] A nitrogen-free culture medium is prepared, and the selected microbial strain seed solution is inoculated into the nitrogen-free culture medium, and cultured in a shaking incubator at 30° C. and a rotation speed of 150 r / min for 36 hours to obtain a microbial bacterial solution;

[0054] The microbial strain is Bacillus mucilaginosus CSUFT21698, classified and named Paenibacillus mucilaginosus, deposited in China Center for Type Culture Collection on November 28, 2024, with the deposit address being Wuhan University, and the deposit number being CCTCC NO: M 20242650;

[0055] The activity concentration OD of the microbial solution 600 value is 1.82, pH value is 7.1;

[0056] The nitrogen-free culture medium includes 10 g·L sucrose -1 、CaCO3·2H2O 0.1g·L -1 、K2HPO40.2g·L -1 、CaCO35.0g·L -1 、MgSO4·7H2O 0.2g·L -1 、NaCl 0.2g·L -1 After the nitrogen-free culture medium is prepared according to the above components, the pH value is adjusted to 7.0 using dilute hydrochloric acid.

[0057] S2. Obtaining expansive soil and pre-treating it to obtain an expansive soil sample;

[0058] The pretreatment is as follows: drying the expansive soil at 105° C. for 8 hours, crushing it and passing it through a 0.075 mm sieve to obtain an expansive soil sample;

[0059] The expansive soil sample meets the liquid limit of 58.1%, the plastic limit of 35.5%, and the free expansion rate of 171%, and is a strong expansive soil;

[0060] 10% of calcified montmorillonite particles are added to the expansive soil;

[0061] S3. Mix the expansive soil sample obtained in step S2 with the culture medium, divide it into several experimental groups and put it into a container, connect a preset number of experimental groups with the microbial solution obtained in step S1, and connect the rest as a control group with distilled water, and all experimental groups are cultured at a constant temperature according to a time gradient, and the experimental groups after the culture is completed are centrifuged; the supernatant obtained by centrifugation is subjected to trace element determination to obtain trace element data of the supernatant; the solid obtained by centrifugation is dried to obtain a soil sample to be tested; microstructure experiments and mineral phase and component content analysis experiments are performed on the soil sample to be tested to obtain test data of the soil sample to be tested; based on the geotechnical test method standard, a free expansion rate experiment is performed on the obtained soil sample to be tested to obtain the expansion rate data of the soil sample to be tested, which specifically includes the following steps:

[0062] The expansive soil sample obtained in step S2 was mixed with the culture medium at a ratio of 1:5, and then divided into 8 experimental groups and placed in conical flasks;

[0063] Four of the experimental groups were used as positive experimental groups and inoculated with the microbial solution obtained in step S1, with an inoculation volume of 6 mL and a liquid volume of 100 mL; the remaining four experimental groups were used as control groups and inoculated with distilled water to keep the quality of each experimental group consistent;

[0064] The four positive experimental groups were cultured at 35°C and 150 r / min with a time gradient of 7 days, 14 days, 28 days, and 42 days. The positive experimental groups were centrifuged at a speed of 10,000 r / min for 15 minutes to obtain supernatant and residual solids.

[0065] The four control groups were the same as the positive experimental group, and were cultured at 35°C and 150 r / min with a time gradient of 7 days, 14 days, 28 days, and 42 days. The positive experimental group was centrifuged at a speed of 10,000 r / min for 15 minutes to obtain the supernatant and residual solids.

[0066] The supernatants obtained from the above 8 experimental groups were subjected to trace element experiments to determine the Si content in the supernatants. 4+ 、Al 3+ Mg 2+ and K + Ion concentration, obtain the trace element data of the supernatant; the ion concentration in the trace element experiment was determined by inductively coupled plasma optical emission spectrometry (ICP-OES);

[0067] The residual solids obtained in the above 8 experimental groups were dried at 105°C for 8 hours and ground through a 0.075 mm mesh to obtain soil samples to be tested. Microstructure experiments and mineral phase and component content analysis experiments were performed on the soil samples to obtain the vibration behavior of all atoms in the montmorillonite mineral lattice in the expansive soil after the action of microorganisms and its influence on groups or chemical bonds, and the test data of the soil samples to be tested were obtained;

[0068] The microstructure experiment was tested using a Fourier transform infrared spectrometer (FTIR) with a spectral range of 600 to 4000 cm -1 , resolution 4cm -1 ;

[0069] The mineral phase and component content analysis experiment was carried out by powder X-ray diffractometer (XRD), with the radiation source being CuKα1 (λ=0.154nm) and the step width being 0.02°; the mineral phase and component content analysis experiment was carried out by wide-angle X-ray diffraction, with a scanning range of 5° to 70° and a scanning speed of 5° / min; the mineral phase and component content analysis experiment was carried out by jade9.0 software for phase qualitative analysis, and the percentage of clay minerals in the sample was calculated using the K value, and then multiplied by the dry weight of the sample to finally obtain the absolute content of each clay mineral;

[0070] Based on the geotechnical test method standard, a free expansion rate experiment is carried out on the soil sample to obtain the expansion rate data of the soil sample to be tested.

[0071] S4. Set up parallel experimental groups according to the time gradient of step S3, mix the microbial solution and culture medium with the expansive soil sample in a preset ratio, and prepare the ring knife specimen after constant temperature culture for a corresponding time. Based on the geotechnical test method standard, perform the lateral load expansion rate and contraction rate experiment under the preset load to obtain the ring knife specimen experimental data, specifically:

[0072] The microbial liquid, the culture medium and the expansive soil sample were uniformly mixed in a ratio of 1:1:8 to obtain a mixed sample; the water content of the mixed sample was 25.2%;

[0073] The mixed samples were divided into 4 groups and cultured at 35°C for 7, 14, 28, and 42 days to obtain ring knife samples.

[0074] Based on the geotechnical test method standard, the ring knife specimen was subjected to the lateral load expansion rate and contraction rate test under the preset load, and the ring knife specimen experimental data was obtained.

[0075] S5. According to the trace element data of the supernatant obtained in step S3 and the test data of the soil sample to be tested, a qualitative analysis is performed on the improvement of the expansive soil by the interaction between microorganisms and minerals, specifically:

[0076] The trace element data of the supernatant obtained in step S3 is as follows: Figure 3 As shown in the figure, Si in the expansive soil under microbial action 4+ 、Al 3+ , K + and Mg 2+ Continuous dissolution, dissolution efficiency Mg 2+ >K + >Si 4+ >Al 3+ The dissolution of metal ions will cause changes in the original element content in the mineral structure of the expansive soil, leading to the destruction of the mineral structure.

[0077] In the soil sample test data obtained in step S3, the microstructure test results are as follows: Figure 4 As shown in the figure, Al in the montmorillonite structure after 42 days under the action of microorganisms 3+ At the same time, the Si-O bonds, Al-O bonds, -OH bonds and main cations in the montmorillonite crystal structure are affected, and the montmorillonite crystal structure is destroyed.

[0078] In the soil sample test data obtained in step S3, the mineral phase analysis results are as follows: Figure 5 As shown in the figure, the main phases of quartz, plagioclase, illite and montmorillonite in the test group and the blank control group basically did not change, but the illite peak appeared at 2θ angle of 48.07° in the 28-day and 42-day samples, indicating that montmorillonite in the expansive soil was transformed into illite under the action of microorganisms.

[0079] In the test data of the soil sample to be tested obtained in step S3, the component content analysis experimental results are shown in Table 1.

[0080] Table 1 Mineral content of soil samples tested at different days of microbial action

[0081]

[0082] Note: M: montmorillonite I: illite K: kaolinite C: chlorite

[0083] From the data in Table 1, it can be seen that the interaction between Bacillus colloidalis and expansive soil in the present invention causes the montmorillonite content to gradually decrease, while the illite content to gradually increase, wherein the increase in illite is the result of the combined action of montmorillonite and illite / montmorillonite mixed-layer minerals.

[0084] S6. According to the swelling rate data of the soil sample to be tested in step S3 and the experimental data of the ring cutter sample obtained in step S4, quantitative analysis is made on the improvement of the expansive soil by the interaction between microorganisms and minerals, specifically:

[0085] The experimental data of the ring knife sample in step S4 is as follows: Figure 6As shown, it can be seen that the expansion rate and shrinkage rate of the expansive soil samples decreased after 7, 14, 28 and 42 days of microbial action, and the decrease was more significant with the extension of the action time.

[0086] The relationship between the expansion rate data of the soil sample to be tested in step S3 and the montmorillonite mineral conversion rate is as follows: Figure 7 As shown in the figure, the different stages of bacterial action can be divided into three main transformation stages: the slow transformation stage (7 days-14 days), during which the decrease in free expansion rate is mainly affected by the cation exchange of montmorillonite crystals, resulting in the transformation of montmorillonite to disordered illite-montmorillonite mixed-layer minerals. The deceleration transformation stage (14 days-28 days), at this time, some illite has been initially generated, most clay minerals exist in the form of illite-montmorillonite mixed-layer minerals, and the rate of decrease in free expansion rate is relatively slow. The accelerated transformation stage (28 days-42 days) during this stage, the montmorillonite content decreases significantly, a large amount of K+ enters the montmorillonite interlayer, and through cation replacement, the transformation of illite-montmorillonite mixed-layer minerals to illite is accelerated, and the free expansion rate decreases rapidly.

Claims

1. An experimental method for improving expansive soil based on microbial-mineral interaction, characterized in that: The following steps are involved: S1. Select a microbial strain, prepare a culture medium, and culture it according to preset conditions to obtain a microbial culture solution; S2. Obtaining expansive soil and pre-treating it to obtain an expansive soil sample; S3. Mix the expansive soil sample obtained in step S2 with the culture medium, divide it into several experimental groups and put it into a container, connect a preset number of experimental groups with the microbial solution obtained in step S1, and connect the rest as a control group with distilled water, and all experimental groups are cultured at a constant temperature according to a time gradient, and the experimental groups after the culture is completed are centrifuged; the supernatant obtained by centrifugation is subjected to trace element determination to obtain trace element data of the supernatant; the solid obtained by centrifugation is dried to obtain a soil sample to be tested; microstructure experiments and mineral phase and component content analysis experiments are carried out on the soil sample to be tested to obtain test data of the soil sample to be tested; based on the geotechnical test method standard, a free expansion rate experiment is carried out on the obtained soil sample to be tested to obtain expansion rate data of the soil sample to be tested; S4. Set up parallel experimental groups according to the time gradient of step S3, mix the microbial solution and the culture medium evenly with the expansive soil sample according to a preset ratio, and prepare the ring knife specimens after constant temperature culture for a corresponding time. Based on the geotechnical test method standard, perform the load expansion rate and contraction rate experiment under the preset load to obtain the ring knife specimen experimental data; S5. According to the trace element data of the supernatant obtained in step S3 and the test data of the soil sample to be tested, qualitative analysis is performed on the improvement of the expansive soil by the interaction between microorganisms and minerals; S6. Based on the swelling rate data of the soil sample to be tested in step S3 and the ring cutter sample experimental data obtained in step S4, quantitatively analyze the improvement of the expansive soil by the interaction between microorganisms and minerals.

2. The experimental method for improving expansive soil based on microorganism-mineral interaction according to claim 1, characterized in that: Step S1 specifically comprises: preparing a nitrogen-free culture medium, inoculating the selected microbial strain seed solution into the nitrogen-free culture medium, and culturing in a shaking table at 28 to 30° C. and a rotation speed of 145 to 150 r / min for 36 to 42 hours to obtain a microbial bacterial solution; The activity concentration OD of the microbial solution 600 The value is 1.8-2.0, and the pH value is 7.0-7.5; The nitrogen-free culture medium comprises 9 to 10 g / L sucrose -1 , CaCO3·2H2O 0.10~0.12g·L -1 、K2HPO40.20~0.22g·L -1 、CaCO35.0~5.1g·L -1 , MgSO4·7H2O 0.20~0.21g·L -1 、NaCl 0.20~0.21g·L -1 After the nitrogen-free culture medium is prepared according to the above components, the pH value is adjusted to 7.0-7.5 using dilute hydrochloric acid.

3. The experimental method for improving expansive soil based on microorganism-mineral interaction according to claim 2, characterized in that: The microbial strain is Bacillus mucilaginosus CSUFT21698, classified and named Paenibacillus mucilaginosus, deposited in the China Center for Type Culture Collection on November 28, 2024, with the deposit address being Wuhan University, and the deposit number being CCTCC NO: M 20242650.

4. The experimental method for improving expansive soil based on microorganism-mineral interaction according to claim 1, characterized in that: The pretreatment in step S2 is as follows: drying the expansive soil at 105-110° C. for 8-10 hours, crushing it and passing it through a 0.075 mm sieve to obtain an expansive soil sample; 9% to 10% of calcified montmorillonite particles are added to the expansive soil; The fundamental reason for the significant swelling and shrinkage of expansive soil is that it is rich in montmorillonite minerals. Adding a certain amount of montmorillonite to the original soil to interact with microorganisms is more targeted and representative, and can better reflect the effect of microbial-promoted mineral phase change on the swelling and shrinkage of expansive soil.

5. The experimental method for improving expansive soil based on microorganism-mineral interaction according to claim 4, characterized in that: The expansive soil sample meets the following requirements: liquid limit is 50.0% to 58.1%, plastic limit is 30.0% to 35.5%, and free expansion rate is 90% to 171%.

6. The experimental method for improving expansive soil based on microorganism-mineral interaction according to claim 1, characterized in that: Step S3 specifically includes the following steps: The expansive soil sample obtained in step S2 is mixed with the culture medium in a ratio of 1:(5-5.5), and then divided into 2S experimental groups and placed in a container; S of the experimental groups are inoculated as positive experimental groups with the microbial solution obtained in step S1, the inoculation volume of the microbial solution is 6.0-6.2 mL, and the liquid volume is 98-100 mL; the remaining S experimental groups are inoculated with distilled water as control groups to keep the quality of each experimental group consistent; S positive experimental groups are divided into t1 day, t2 day, ..., t i day, ..., t m The culture was carried out at a constant temperature of 35°C and shaking at 150 r / min for a time gradient of 1 day, and the positive experimental group after the culture was completed was centrifuged to obtain the supernatant and residual solid; The S control groups are the same as the positive experimental group, and the number of i day, ..., t m The culture was carried out at a constant temperature of 35°C and shaking at 150 r / min for a time gradient of 1 day, and the positive experimental group after the culture was completed was centrifuged to obtain the supernatant and residual solid; The supernatants obtained from the above 2S experimental groups were subjected to trace element experiments to determine the Si content in the supernatants. 4+ 、Al 3+ Mg 2+ and K + Ion concentration, obtain the trace element data of the supernatant; the ion concentration in the trace element experiment was determined by inductively coupled plasma optical emission spectrometry (ICP-OES); The residual solids obtained from the above 2S experimental groups were dried at 105-110°C for 8-10 hours to obtain soil samples to be tested, and microstructure experiments and mineral phase and component content analysis experiments were performed on the soil samples to obtain the vibration behavior of all atoms in the montmorillonite mineral lattice in the expansive soil after the action of microorganisms and its influence on groups or chemical bonds, and the test data of the soil samples to be tested were obtained; The microstructure experiment was tested using a Fourier transform infrared spectrometer (FTIR) with a spectral range of 600 to 4000 cm -1 , resolution 4cm -1 ; The mineral phase and component content analysis experiment was conducted using a powder X-ray diffractometer (XRD), with a radiation source of CuKα1 (λ=0.154nm) and a step width of 0.02°; the mineral phase and component content analysis experiment used wide-angle X-ray diffraction, with a scanning range of 5°~70° and a scanning speed of 5~5.2° / min; the mineral phase and component content analysis experiment used software to perform phase qualitative analysis, using the K value to calculate the percentage of clay minerals in the sample, and then multiplying it by the dry weight of the sample to finally obtain the absolute content of each clay mineral; Based on the geotechnical test method standard, a free expansion rate experiment is carried out on the soil sample to obtain the expansion rate data of the soil sample to be tested.

7. The experimental method for improving expansive soil based on microorganism-mineral interaction according to claim 1, characterized in that: Step S4 specifically comprises: uniformly mixing the microbial liquid, the culture medium and the expansive soil sample in a ratio of 1:1:(8-8.5) to obtain a mixed sample; the water content of the mixed sample is 25.0%-25.2%; The mixed samples were divided into S groups and cultured at 35°C for t1 day, t2 day, ..., t i day, ..., t m Days of time gradient, obtaining ring knife samples; Based on the geotechnical test method standard, the ring knife specimen was subjected to the lateral load expansion rate and contraction rate test under the preset load, and the ring knife specimen experimental data was obtained.

8. The experimental method for improving expansive soil based on microorganism-mineral interaction according to claim 1, characterized in that: Step S5 is specifically as follows: according to the supernatant trace element data obtained in step S3, the Si content in the centrifugal supernatant of the experimental groups with different time gradient culture time is compared. 4+ 、Al 3+ Mg 2+ and K + Ion concentration, through the changes in the dissolution amount of four cations, indirectly proves the influence of microorganisms on the metal elements in the crystal structure of montmorillonite.

9. The experimental method for improving expansive soil based on microorganism-mineral interaction according to claim 8, characterized in that: According to the test data of the soil sample obtained in step S3, the vibration behavior of all atoms in the montmorillonite mineral lattice in the expansive soil under the action of microorganisms in the centrifugal solid of the experimental groups with different time gradient incubation times and its influence on the groups or chemical bonds are obtained.

10. The experimental method for improving expansive soil based on microorganism-mineral interaction according to claim 1, characterized in that: Step S6 specifically comprises: according to the experimental data of the ring knife sample obtained in step S4, by changing the load expansion rate and contraction rate data of the ring knife samples with different incubation times, obtaining the relationship between the microbial action time and the expansion rate and contraction rate of the expansive soil; According to the swelling rate data of the tested soil sample in step S3, the improvement of the expansive soil by the interaction between microorganisms and minerals is quantitatively analyzed through the swelling rate of the tested soil sample at different microbial action times and the montmorillonite mineral conversion rate data.

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