Method for improving expansive soil through combination of MICP and waste glass powder

Abstract

The invention discloses a method for improving expansive soil through combination of MICP and waste glass powder. The method comprises the following steps: pretreating the expansive soil, mixing the waste glass powder and the expansive soil according to a specific ratio, preparing and alternately injecting a microbial liquid and a cementing liquid, and curing at proper temperature and humidity to promote the precipitation reaction of calcium carbonate. The best mix proportion is determined through a multi-factor test, the waste glass powder and the MICP have a synergistic effect, the swelling-shrinkage property of the expansive soil is inhibited, the strength and stability are improved, and the method has the advantages of being environmentally friendly and low in cost, can be applied to engineering related scenes such as roads, buildings and water conservancy, and provides an innovative scheme for expansive soil improvement.

Description

Technical Field

[0001] The invention relates to the technical field of geotechnical engineering technology, and in particular to a method for improving expansive soil by combining MICP with waste glass powder. Background Art

[0002] Expansive soil is widely distributed around the world. Due to its special mineral composition (such as rich in hydrophilic clay minerals such as montmorillonite and illite), it has significant water absorption and expansion and water loss shrinkage characteristics, which poses a serious threat to engineering construction. In road engineering, the expansion and contraction deformation of the expansive soil roadbed will cause cracking, bulging, and subsidence of the road surface, seriously affecting the flatness, driving comfort and service life of the road; in construction engineering, the uneven deformation of the expansive soil foundation may cause cracking of the building wall, tilting of the foundation or even collapse, threatening the safety of life and property; in water conservancy projects, if facilities such as dams and channels are built on expansive soil, their expansion and contraction characteristics may cause leakage, landslides and other dangerous situations, affecting the normal operation of water conservancy facilities and flood control, irrigation and other functions.

[0003] At present, the improvement methods for expansive soil mainly include physical improvement, chemical improvement and biological improvement. Although physical improvement methods such as soil replacement and compaction can improve the engineering properties of expansive soil to a certain extent, they have problems such as waste of resources, high cost and limited effect. Chemical improvement methods such as lime improvement and cement improvement add chemical reagents to the expansive soil to react chemically with the mineral components in the soil to increase the strength of the soil and reduce the expansion. However, chemical improvement methods are prone to cause environmental pollution, and the long-term stability of the improved soil is difficult to guarantee. As an emerging technology, biological improvement methods have the advantages of environmental protection and sustainability, but when used alone, there are often problems such as insignificant improvement effects and limited scope of application.

[0004] On the other hand, with the rapid development of modern society, the amount of waste glass produced has shown an increasing trend year by year, and the treatment of waste glass has become an increasingly severe environmental challenge. At present, the recycling of waste glass is mainly focused on the reproduction of glass products, but there is still a large amount of waste glass that cannot be effectively recycled. These waste glasses not only occupy a large amount of land resources, but also have an extremely slow degradation process in the natural environment, causing long-term potential harm to the environment.

[0005] The application of waste glass powder in the field of expansive soil improvement provides a new way to dispose of waste glass. Waste glass powder has a certain activity, and its main components such as silicon dioxide (SiO2) and calcium oxide (CaO) can participate in chemical reactions under certain conditions. When used in conjunction with MICP technology, waste glass powder can not only fill the pores of expansive soil and improve the soil structure, but also its active components may undergo chemical reactions under the alkaline environment produced by microbial metabolism and the action of cementing liquid to generate substances with cementing properties, further enhancing the connection between soil particles, thereby synergizing with the MICP process, optimizing the improvement effect of expansive soil, and realizing resource recycling and environmental sustainable development.

[0006] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention and should not be regarded as an acknowledgment or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art. Summary of the invention

[0007] The technical problem to be solved by the present invention is to overcome the above technical defects and provide a method for improving expansive soil by combining MICP with waste glass powder. Waste glass powder is used to physically fill the pores of expansive soil and optimize the particle gradation. Its chemically active components react to form cementing substances under the alkaline environment produced by microbial metabolism and the action of cementing liquid; microorganisms in MICP induce the production of calcium carbonate precipitation, which fills the pores and cements the soil particles. The combined action of the two strengthens the connection between soil particles and reduces the porosity, thereby effectively inhibiting the expansion and contraction of expansive soil, significantly improving its strength and stability, and achieving the purpose of improving the performance of expansive soil.

[0008] In order to solve the above problems, the technical solution of the present invention is: comprising the following steps: Step 1: pre-treat the expansive soil to remove vegetation roots, stones and impurities in the expansive soil, then air-dry the expansive soil, crush the expansive soil using a mechanical crushing device, and sieve the expansive soil to obtain an expansive soil particle size of 1-3 mm; Step 2: Collect the waste glass, wash and dry it, grind it into powder with a ball mill, and sieve it to obtain waste glass powder with a fineness of 300-500 mesh; Step 3: selecting a microbial strain with calcium carbonate precipitation inducing ability, inoculating it into a culture medium containing yeast extract, ammonium chloride and calcium chloride, and culturing it for 36-60 hours. After the culturing, collecting the bacterial cells, washing them, and suspending them in a nutrient solution containing ammonium chloride and calcium chloride to prepare a microbial culture solution; Step 4: Dissolve calcium chloride in water to prepare a cementing solution, wherein the calcium ion concentration of the cementing solution is 0.6-0.9 mol / L, and add ammonium chloride, disodium hydrogen phosphate, and magnesium sulfate nutrients; Step 5: Conduct indoor tests. When the volume ratio of microbial liquid to cementing liquid is 1:1, study the effects of plain soil, waste glass powder improved soil, MICP soil, and composite improved soil on the performance of expansive soil. The amount of waste glass powder added is 2.5%-20% of the mass of the expansive soil. Step 6: Mix the expansive soil and waste glass powder evenly according to the optimal mix ratio, then spray the microbial solution evenly on the mixed soil sample, stir for 10-20 minutes, and then slowly inject the binder into the soil sample 2-4 times, stirring for 15-30 minutes after each injection; Step 7: Place the mixed soil sample injected with microbial liquid and binder liquid into a mold or container and cure it for 14 days at a temperature of 25℃-30℃ and a humidity of 85%-95%.

[0009] Furthermore, in step three, the microbial strain is Bacillus pasteurii.

[0010] Furthermore, in step three, the culture medium contains 5 g / L yeast extract, 10 g / L ammonium chloride, 5 g / L calcium chloride, and 10 g / L peptone.

[0011] Further, in step three, the ammonium chloride content in the nutrient solution is 5-8 g / L, and the calcium chloride content is 2-4 g / L.

[0012] Furthermore, in step 4, the ammonium chloride content in the binder liquid is 10-15 g / L, the disodium hydrogen phosphate content is 5-8 g / L, and the magnesium sulfate content is 1-3 g / L.

[0013] Furthermore, in step five, the dosage of different waste glass powders is 2.5%, 5%, 10%, 15% and 20%, and the volume ratio of the microbial liquid to the binder liquid is 1:1.

[0014] Furthermore, the pH value of the bacterial solution is 7.5-8.5, and the OD600 of the bacterial solution is 0.8-1.2.

[0015] Furthermore, the waste glass powder is prepared by grinding waste glass into powder using a ball mill, and sieving to obtain waste glass powder with a fineness of 300-500 meshes.

[0016] The advantages of the present invention compared with the prior art are: 1. The present invention utilizes the advantages of microorganisms' strong adaptability to the environment, high efficiency of enzyme catalysis, no secondary pollution and low cost.

[0017] 2. The present invention utilizes waste glass powder and turns waste into treasure. The amount of waste glass powder added can reach 2.5% - 15% of the mass of the expansive soil. It not only reduces the waste pressure on the environment caused by waste glass, but also reduces the cost of obtaining improved materials, achieving a win-win situation of environmental protection and economic benefits.

[0018] 3. The present invention accurately determines the best mix ratio through indoor tests, so that the waste glass powder dosage, microbial liquid concentration and cementing liquid concentration reach the optimal combination, effectively ensuring the stability and reliability of the improvement effect on the expansive soil and improving the improvement efficiency. Specifically, when the waste glass powder dosage is 15%, the improvement effect of various performance indicators is significant, and the unconfined compressive strength of the improved expansive soil can be increased from 207.53kPa to 659.94kPa.

[0019] 4. The present invention gives full play to the synergistic effect of various substances through reasonable stirring, injection and curing processes, significantly improves the mechanical properties of expansive soil such as unconfined compressive strength, enhances its bearing capacity in engineering applications, and prolongs the service life of related projects. According to tests, after 14 days of curing, the unconfined compressive strength can be increased by 2 times.

[0020] 5. The present invention can effectively reduce the no-load expansion rate of expansive soil, improve its expansion and contraction characteristics, reduce engineering problems such as deformation of foundation and roadbed caused by soil expansion and contraction, and improve the safety and stability of the foundation structure. Experimental data show that the no-load expansion rate of the improved expansive soil can be reduced from the original 10.13% to 5.95%.

[0021] 6. The present invention can effectively reduce the porosity of expansive soil, make the soil structure more compact, improve the density of the soil, and thus enhance the strength of the soil. Experimental data show that the porosity of the improved expansive soil can be reduced from the original 54.9% to 19.8%. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The present invention is a flow chart of the MICP combined with waste glass powder to improve expansive soil.

[0023] Figure 2 Graph showing the main chemical components and contents of the waste glass powder of the present invention.

[0024] Figure 3 It is the unconfined compressive strength diagram of each group of the present invention.

[0025] Figure 4 It is the no-load expansion rate diagram of each group of the present invention.

[0026] Figure 5 It is the porosity diagram of each group of the present invention. DETAILED DESCRIPTION

[0027] In order to make the contents of the present invention more clearly understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0028] A method for improving expansive soil by using MICP and waste glass powder. The soil used in the invention is expansive soil taken from a certain area in Wuhan City.

[0029] The MICP combined with waste glass powder method for improving expansive soil in this embodiment is to prepare a bacterial solution in the laboratory, and then mix it evenly with waste glass powder in proportion, use the waste glass powder to physically fill the pores of the expansive soil, optimize the particle grading, and its chemically active components react to form a cementing substance under the alkaline environment produced by microbial metabolism and the action of the cementing liquid; the microorganisms in the MICP induce the production of calcium carbonate precipitation, fill the pores and cement the soil particles, and the combined effect strengthens the connection between the soil particles and reduces the porosity, thereby effectively inhibiting the expansion and contraction of the expansive soil, and chemical reactions will also occur to generate calcium silicate hydrate (CSH), and the CSH gel will bond the soil particles, significantly improving their strength and stability, thereby achieving the purpose of improving the performance of the expansive soil.

[0030]

[0031] The above table shows the geotechnical properties data of expansive soil.

[0032]

[0033] The above table shows the main chemical composition data of waste glass powder.

[0034] The following is the chemical equation of the improved process:

[0035] The volume ratio of microbial liquid to cementing liquid is 1:1.

[0036] The waste glass powder is set to account for 2.5%-20% of the mass of the expansive soil.

[0037] Soil samples are divided into four categories: plain soil, MICP soil, waste glass powder improved soil, and composite improved soil.

[0038] The test plan is shown in the following table

[0039] Standard compaction tests were conducted on untreated soil and soil treated with waste glass powder. The optimum moisture content and maximum dry density of soil treated with soil and different waste glass powder addition ratios (2.5%, 5%, 10%, 15% and 20%) were determined. The unconfined compressive strength of soil treated with soil and different waste glass powder addition ratios (2.5%, 5%, 10%, 15% and 20%) was determined at the optimum moisture content and maximum dry density.

[0040] The test results are shown in the following table:

[0041] The results show that: The optimum moisture content of expansive soil is 18.5%. As the proportion of waste glass powder added increases, the optimum moisture content gradually decreases to 14.43%. This decrease is due to the replacement of expansive soil by waste glass powder, which has a lower water absorption capacity than expansive soil.

[0042] When the amount of waste glass powder added is increased to 15%, the maximum dry density increases from 1.71g / cm3 to 1.93g / cm3; after this point, the strength of the expansive soil begins to decrease with the addition of waste glass powder. In addition, the decrease in the maximum dry density when the amount of waste glass powder added exceeds 15% is caused by the replacement of a large amount of solids, which is related to the interaction between the expansive soil and the waste glass powder particles.

[0043] When the amount of waste glass powder added is increased to 15%, the peak compressive strength of the sample increases from 207.53 kPa to 362.10 kPa. However, when the amount of waste glass powder added exceeds 15%, the compressive strength drops sharply to 341.37 kPa. This is due to the decrease in the optimal moisture content after adding 15% waste glass powder.

[0044] The no-load expansion rate decreases with the increase of waste glass powder content, but when the waste glass powder content exceeds 15%, the no-load expansion rate begins to increase again. This shows that the addition of waste glass powder can inhibit the expansion of expansive soil, but when the waste glass powder content exceeds 15%, the expansion will increase instead.

[0045] As the amount of waste glass powder increases, the porosity gradually decreases. This is because the waste glass powder fills the gaps between the expansive soil particles, making the soil more compact.

[0046] In summary, it can be concluded that the optimal dosage of waste glass powder is 15%.

[0047] The engineering properties of composite improved expansive soil were studied by combining the microbial solution and the binder solution in a volume ratio of 1:1 and different waste glass powder dosages of 2.5%, 5%, 10%, 15% and 20%.

[0048] The test results are shown in the following table:

[0049] The results show that: When 20% of waste glass powder and MICP were added to the expansive soil to improve the expansive soil, its internal friction angle increased by about 63.33% (from 18.90 to 30.87); after adding 20% ​​of waste glass powder and MICP to improve the expansive soil, the cohesion of the soil sample decreased by 10.06%, from 38.56 kPa to 34.68 kPa.

[0050] It can be seen from the table that the strength of the composite improved soil gradually increases, and the compressive strength of the improved soil reaches a maximum of 659.94kPa. When the amount of waste glass powder exceeds 15%, the compressive strength of the improved soil decreases. When MICP is improved alone, the compressive strength increases from 207.53kPa to 473.46kPa. It can be seen that the composite improvement effect is better.

[0051] It can be seen from the table that the composite improved soil significantly reduces the porosity of the expansive soil, and it decreases with the increase of the amount of waste glass powder, and the improvement effect is better than that of MICP soil. The porosity comparison of each group shows that the porosity of the soil samples is in the order of plain soil, waste glass powder improved soil, MICP soil, and composite improved soil.

[0052] It can be seen from the table that the composite improved soil can reduce the no-load expansion rate. When the waste glass powder content is 15%, the combined improvement effect with MICP is the best, and the no-load expansion rate is reduced to 5.95%. The comparison of the no-load expansion rate of each group shows that the order of the no-load expansion rate of the soil samples is plain soil, MICP soil, waste glass powder improved soil, and composite improved soil.

[0053] In summary, the improved soil of the present invention has good comprehensive performance, can greatly improve the adverse characteristics of weak expansive soil, and reduce the engineering hazards caused by expansive soil.

[0054] The improved materials used in the present invention are MICP and waste glass powder; the addition of MICP and waste glass powder can make the internal structure of the improved expansive soil body bonded to each other to form a stable cementitious material to reinforce the soil body, and the waste glass powder can also enter the pores between the expansive soil particles to increase the density of the expansive soil and improve the integrity of the improved soil.

[0055] The present invention can utilize MICP and solid waste glass powder more scientifically, is simple to operate, and is economical and environmentally friendly.

[0056] The present invention and its embodiments are described above, and such description is not restrictive. The drawings show only one embodiment of the present invention, and the actual structure is not limited thereto. In short, if ordinary technicians in the field are inspired by it, without departing from the purpose of the invention, they can design a structure and embodiment similar to the technical solution without creativity, which should belong to the protection scope of the present invention.

Claims

1. A method for improving expansive soil by using MICP combined with waste glass powder, characterized in that: The following steps are involved: Step 1: pre-treat the expansive soil to remove vegetation roots, stones and impurities in the expansive soil, then air-dry the expansive soil, crush the expansive soil using a mechanical crushing device, and sieve the expansive soil to obtain an expansive soil particle size of 1-3 mm; Step 2: Collect the waste glass, wash and dry it, grind it into powder with a ball mill, and sieve it to obtain waste glass powder with a fineness of 300-500 mesh; Step 3: selecting a microbial strain with calcium carbonate precipitation inducing ability, inoculating it into a culture medium containing yeast extract, ammonium chloride and calcium chloride, and culturing it for 36-60 hours. After the culturing, collecting the bacterial cells, washing them, and suspending them in a nutrient solution containing ammonium chloride and calcium chloride to prepare a microbial culture solution; Step 4: Dissolve calcium chloride in water to prepare a cementing solution, wherein the calcium ion concentration of the cementing solution is 0.6-0.9 mol / L, and add ammonium chloride, disodium hydrogen phosphate, and magnesium sulfate nutrients; Step 5: Conduct indoor tests. When the volume ratio of microbial liquid to cementing liquid is 1:1, study the effects of plain soil, waste glass powder improved soil, MICP soil, and composite improved soil on the performance of expansive soil. The amount of waste glass powder added is 2.5%-20% of the mass of the expansive soil. Step 6: Mix the expansive soil and waste glass powder evenly according to the optimal mix ratio, then spray the microbial solution evenly on the mixed soil sample, stir for 10-20 minutes, and then slowly inject the binder into the soil sample 2-4 times, stirring for 15-30 minutes after each injection; Step 7: Place the mixed soil sample injected with microbial liquid and binder liquid into a mold or container and cure it for 14 days at a temperature of 25℃-30℃ and a humidity of 85%-95%.

2. The method for improving expansive soil by using MICP and waste glass powder according to claim 1, characterized in that: In step 3, the microbial strain is Bacillus pasteurii.

3. The method for improving expansive soil by MICP combined with waste glass powder according to claim 1, characterized in that: In step 3, the culture medium contains 5 g / L yeast extract, 10 g / L ammonium chloride, 5 g / L calcium chloride, and 10 g / L peptone.

4. The method for improving expansive soil by using MICP and waste glass powder according to claim 1, characterized in that: In step 3, the ammonium chloride content in the nutrient solution is 5-8 g / L, and the calcium chloride content is 2-4 g / L.

5. The method for improving expansive soil by using MICP and waste glass powder according to claim 1, characterized in that: In step 4, the ammonium chloride content in the binder is 10-15 g / L, the disodium hydrogen phosphate content is 5-8 g / L, and the magnesium sulfate content is 1-3 g / L.

6. The method for improving expansive soil by using MICP and waste glass powder according to claim 1, characterized in that: In step five, the dosage of different waste glass powders is 2.5%, 5%, 10%, 15% and 20%, and the volume ratio of microbial liquid to binder liquid is 1:

1.

7. The method for improving expansive soil by using MICP and waste glass powder according to claim 6, characterized in that: The pH value of the bacterial solution is 7.5-8.5, and the OD600 of the bacterial solution is 0.8-1.

2.

8. The method for improving expansive soil by using MICP and waste glass powder according to claim 6, characterized in that: The waste glass powder preparation method comprises the following steps: the waste glass powder is ground into powder by a ball mill, and then sieved to obtain waste glass powder with a fineness of 300-500 meshes.

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