Microbial foam light soil for embankment load reduction and construction method thereof

Abstract

The invention discloses microorganism foam light soil for embankment load reduction and a construction method of the microorganism foam light soil, and relates to the technical field of civil engineering materials. In order to solve the problems of non-uniform foam and unstable structure in the traditional foam light soil, the invention provides the following technical scheme: air bubbles generated by a foaming agent in the traditional foam light soil and a calcium carbonate cementation effect formed by denitrification are replaced by air bubbles generated by denitrification in situ in an MICP technology; the microbial foam light soil has the characteristics of light weight and high strength. The invention further discloses a construction method of the microorganism foam light soil for embankment load reduction. The construction method comprises the technical steps of direct excavation replacement, transverse small-diameter lead hole replacement and the like.

Description

Technical Field

[0001] The invention relates to the technical field of civil engineering materials, and in particular to a microbial foam lightweight soil for embankment load reduction and a construction method thereof. Background Art

[0002] Traditional foamed lightweight soil is a lightweight, porous material created by adding foam to a slurry composed of a curing agent, admixtures, and water in specific proportions. This material is then mixed, poured, and cured. It features low apparent density, high strength, and ease of construction. Using foamed lightweight soil for roadbed filling effectively reduces the roadbed's deadweight load and the added stress on soft foundations. The foam in traditional foamed lightweight soil is generated by a foaming agent and then added to the slurry. This foam is affected by environmental factors such as temperature and humidity, leading to structural instability. Furthermore, the compatibility of the foam with the cement slurry must be considered during the preparation and construction of foamed lightweight soil.

[0003] Prior to the present invention, microbial induced calcium carbonate precipitation (MICP) technology used microorganisms to react under specific conditions to generate calcium carbonate gel with a cementing effect to reinforce roadbed soil. It is an environmentally friendly, green and sustainable new soil reinforcement technology that can be used to reinforce foundations, treat liquefied soil, and biological plugging, etc., and has certain application prospects. After years of research by scientists, there are currently four main effective MICP methods: urea hydrolysis, denitrification, iron salt reduction, and sulfate reduction. Among them, denitrification is the process in which denitrifying bacteria reduce nitrates to release nitrogen in an anaerobic environment. This process consumes hydrogen ions in the environment to generate carbon dioxide, and the bicarbonate ions in the solution combine with calcium ions to form a precipitate. The chemical equation involved in this reaction is as follows:

[0004] 5C2H3O2 - +8NO3 - +13H + →10CO2+4N2+14H2O

[0005]

[0006] Ca2 + +HCO3 - +OH - →CaCO3(s)+H2O

[0007] In the past, microbial technology was primarily used for soil reinforcement, but its effectiveness was underutilized. Nitrogen (N2) produced by denitrification in MICP was directly emitted, resulting in a waste of resources. Traditional lightweight foam soil technology, on the other hand, requires cement and other curing agents, resulting in high costs and carbon emissions. Summary of the Invention

[0008] The purpose of the present invention is to provide a microbial foam lightweight soil for embankment load reduction and a construction method thereof, so as to solve the problems of high cost and large carbon emission of traditional foam lightweight soil.

[0009] The technical solution of the present invention to solve the above technical problems is as follows:

[0010] A microbial foam lightweight soil for embankment load reduction comprises 20-400 parts of raw material slurry, 20-50 parts of microbial solution and 20-100 parts of reaction liquid; the raw material slurry comprises water, aggregate, admixture and additive which are uniformly mixed in a certain proportion; the microbial solution is prepared from denitrifying bacteria liquid; and the reaction liquid comprises a denitrifying matrix and a calcium source.

[0011] Furthermore, the denitrifying bacterial liquid is a strain that has entered a stable period, the denitrifying matrix is an organic matter containing nitrate; and the calcium source is calcium acetate.

[0012] Furthermore, the water is tap water, purified water or distilled water; the aggregate is raw soil, and the raw soil is engineering waste soil, sandy soil, silt soil or clay soil.

[0013] A construction method of microbial foam lightweight soil for embankment load reduction comprises the following steps:

[0014] S1. Prepare raw materials: select and proportion water, aggregate, admixture and additives, and determine the amount of each raw material;

[0015] S2. Preparation of microbial solution: Denitrifying bacteria are selected for cultivation, bacterial liquid is obtained under suitable temperature and pH conditions, and bacterial liquid that has entered the stable phase and has high activity is detected and selected to prepare a solution;

[0016] S3. Prepare the reaction solution: construct a reaction system including a denitrification substrate and a calcium source, select nitrate-containing organic matter as the denitrification substrate, select calcium salt as the calcium source and determine the amount thereof;

[0017] S4. Mixing and stirring to prepare slurry: Aggregate, admixture and additive are added into a stirring device according to a proportion, and stirred at a speed of 100 r / min for 2-3 minutes to obtain a mixture; water is added to the mixture gradually, and the stirring device is started and stirred for 1-2 minutes after each addition of water to ensure that the slurry is uniform and free of sediment, until the water is added to obtain a raw material slurry; the pH value of the slurry is measured, and a pH adjuster is added according to the measurement result, and the stirring device is started and stirred for 1-2 minutes. After adjusting the pH value of the slurry to a range suitable for the survival of fungi, the microbial solution is added, and the stirring device is started and stirred evenly to obtain a microbial mixed slurry;

[0018] S5, gas production process: the reaction liquid and the microbial mixed slurry are mixed and the stirring device is started to stir evenly to obtain a microbial foam lightweight soil slurry; under an anaerobic environment, the denitrifying bacteria perform denitrification to reduce nitrate to produce nitrogen bubbles. The stirring device is continuously started during the reaction process to ensure uniform distribution of the nitrogen bubbles. At the same time, the denitrifying bacteria consume hydrogen ions in the environment to produce carbon dioxide, gradually increasing the alkalinity of the slurry environment;

[0019] S6. New embankment filling: Excavate the embankment foundation trench, compact the base, and ensure water and drainage of the base, and lay a crushed stone cushion. Formwork for the bottom plate and side plates is carried out. After the formwork is completed, the prepared microbial foam lightweight soil slurry is transported to the designated location via conveying equipment, and then pouring is carried out.

[0020] Replacement of existing embankments: For the replacement and load reduction of existing embankments, direct excavation replacement or horizontal small-diameter hole replacement is adopted; when direct excavation replacement is carried out, the original embankment to be replaced is first excavated, and after the excavation is completed, the base is cleaned and compacted to ensure that the base is flat and solid, and the waterproofing and drainage of the base are done well; then a suitable formwork is installed at the construction site, and after the formwork is supported, the prepared microbial foam lightweight soil slurry is transported to the designated location through the conveying equipment, and then the pouring operation is carried out; when horizontal small-diameter hole replacement is used, the slope of the original embankment is first excavated, Build a construction platform and prepare for the drilling. Then, use drilling equipment to drill small-diameter drilling holes in the embankment on both sides of the roadbed in batches. Reasonably set the drilling hole diameter and the vertical and horizontal spacing of the drilling holes. At the same time, make the drilling holes have a certain slope. After drilling, check the drilling quality. If the hole is qualified, transport the prepared microbial foam lightweight soil slurry into the hole through the conveying equipment. The microbial foam lightweight soil slurry is pumped, and the requirements for pumping distance and vertical pumping height are paid attention to. The pouring operation is carried out in blocks, layers, and batches to control the pouring volume of a single bin and the pouring thickness of a single layer.

[0021] S7. Cementation process: After the microbial foam lightweight soil slurry is poured, in an alkaline environment, bicarbonate ions and calcium ions gradually combine to produce calcium carbonate crystals, which cement the soil particles and form a soil skeleton. Over time, the cementation process gradually strengthens, and the strength of the microbial foam lightweight soil gradually increases;

[0022] S8. Curing and quality control: After the microbial foam lightweight soil slurry is poured, in an alkaline environment, bicarbonate ions and calcium ions gradually combine to produce calcium carbonate crystals, cementing soil particles to form a soil skeleton. After pouring, cover with geotextile for curing to prevent shrinkage cracks caused by rapid water loss. At the same time, regularly test the wet density and compressive strength of the foam lightweight soil, monitor microbial activity, bubble distribution and quantity, and calcium carbonate precipitation, and evaluate the MICP effect.

[0023] Furthermore, in step S1, the admixture includes fly ash, slag powder or silica fume.

[0024] Furthermore, in step S2, the denitrifying bacteria are specifically denitrifying Pseudomonas, and the culture temperature range is 20-40°C, and the pH value is adjusted to neutral or weakly alkaline.

[0025] Furthermore, in step S3, the denitrification matrix provides reaction substances for the denitrifying bacteria. Under an anaerobic environment, the denitrifying bacteria reduce the nitrate in the matrix to release nitrogen, forming nitrogen bubbles, and consume hydrogen ions in the environment to generate carbon dioxide. The calcium ions in the calcium source combine with the bicarbonate ions in the solution under an alkaline environment to form calcium carbonate crystals, which cement the soil particles together.

[0026] Furthermore, in step S8, the natural curing period is not less than 3 days, and the curing period is extended to not less than 7 days after the top layer is poured.

[0027] The present invention has the following beneficial effects:

[0028] 1. In the present invention, the gas produced by microorganisms is generated in situ in the soil, so that the distribution of bubbles in the soil is more uniform. Compared with chemical methods, the microbial reaction process is slower and therefore more controllable.

[0029] 2. The nitrogen generated by the microbial denitrification method of the present invention has stable chemical properties and low solubility, and the bubbles can remain in the soil for a longer time;

[0030] 3. The microbial reaction of the present invention generally uses microorganisms existing in nature. After completing their biological reaction, the residues of these microorganisms have little impact on the environment. The microbial method can reduce potential pollution to groundwater and the surrounding environment and does not involve the use of harmful chemicals.

[0031] 4. The microbial denitrification process of the present invention, under relatively alkaline conditions, generates bubbles that reduce the saturation of the soil while also depositing calcium carbonate. That is, while the soil saturation is reduced, it also has the effect of filling and cementing the soil particles. The synergistic effect of desaturation and cementation is beneficial in improving the stability of the soil, preventing liquefaction, and increasing the shear strength of the soil.

[0032] 5. The microbial foam lightweight soil of the present invention promotes the precipitation of calcium carbonate and cements soil particles during the microbial denitrification process, thereby building a stable soil skeleton structure. It no longer requires the reliance on curing agents such as cement in traditional processes, effectively reduces carbon emissions, and is an environmentally friendly, ecologically low-carbon material.

[0033] 6. The microbial foam lightweight soil of the present invention has light weight, high strength and good overall performance. While ensuring strength, it can effectively reduce the load of the overlying roadbed on the foundation, thereby achieving the effect of reducing settlement. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of MICP based on denitrification in the microbial foam lightweight soil of the present invention;

[0035] Figure 2 This is a cross-sectional schematic diagram of the direct excavation and placement technology of microbial foam lightweight soil according to the present invention;

[0036] Figure 3 This is a cross-sectional schematic diagram of the microbial foam lightweight soil transverse small-diameter hole replacement technology of the present invention;

[0037] Figure 4 yes Figure 2 Schematic diagram of the gas production process of microbial foam light soil in part A;

[0038] Figure 5 yes Figure 2 Schematic diagram of the microbial foam lightweight soil cementation process in Part B;

[0039] Figure 6 It is a technical flow chart of the preparation process and construction method of microbial foam lightweight soil of the present invention.

[0040] Figure numerals: 1-microbial foam lightweight soil; 2-pavement structure layer; 3-base; 4-original embankment; 5-small diameter inlet hole; 21-nitrogen bubbles; 22-microbial foam lightweight soil slurry; 23-calcium carbonate crystals; 24-soil particles. DETAILED DESCRIPTION

[0041] The following is a clear and complete description of the technical solution of the present invention in conjunction with the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0042] Please refer to Figure 1-6 The present invention provides a microbial foam lightweight soil for embankment load reduction and its construction method, addressing the high cost and high carbon emissions of traditional foam lightweight soil. When implementing this microbial foam lightweight soil for embankment load reduction and its construction method, the following steps must be strictly followed to ensure the quality of the final product and the effectiveness of the construction.

[0043] First, prepare the raw materials. Select water, aggregates, admixtures and additives, and accurately determine the amount of each raw material. Water can be tap water, purified water or distilled water to ensure the purity of the water quality and avoid impurities from having adverse effects on subsequent reactions. Aggregates are raw soil, which can be engineering waste soil, sandy soil, silt or clay soil. These raw soils are widely available and can effectively reduce costs while realizing the recycling of waste. Admixtures include fly ash, slag powder or silica fume, which can improve the performance of the raw material slurry and improve the strength and stability of the microbial foam lightweight soil 1. The type and amount of admixtures are selected according to the specific project needs and relevant standards to meet different construction requirements. When determining the amount of each raw material, it is necessary to comprehensively consider the performance indicators of the microbial foam lightweight soil 1, construction conditions and actual project needs, and obtain the best ratio scheme through experiments and calculations.

[0044] Next, prepare a microbial solution. Select Pseudomonas denitrificans as the denitrifying bacteria for cultivation. The cultivation process needs to be carried out under suitable temperature and pH conditions. The cultivation temperature range is controlled at 20-40°C, and the pH value is adjusted to neutral or weakly alkaline. Under such conditions, Pseudomonas denitrificans can grow and reproduce well. After a period of cultivation, the bacterial solution is tested and the bacterial solution that has entered the stable period and has high activity is selected. Whether the bacterial solution has entered the stable period and the level of activity can be determined by observing the growth state of the bacterial solution and measuring the activity index of the bacterial solution. The selected bacterial solution is prepared into a solution. During the preparation process, care should be taken to avoid contamination of the bacterial solution to ensure the quality of the microbial solution.

[0045] Then, prepare the reaction solution. Construct a reaction system including a denitrification matrix and a calcium source. Select nitrate-containing organic matter as the denitrification matrix. The denitrification matrix provides a reaction substance for the denitrifying bacteria. Under anaerobic conditions, the denitrifying bacteria can reduce the nitrate in the matrix to release nitrogen, forming nitrogen bubbles 21, and consume hydrogen ions in the environment to generate carbon dioxide. Calcium acetate is selected as the calcium source. The calcium ions in the calcium source combine with the bicarbonate ions in the solution in an alkaline environment to form calcium carbonate crystals 23, which cement the soil particles 24 together. When determining the amount of the calcium source, it is necessary to make reasonable calculations based on factors such as the amount of the denitrification matrix and the performance requirements of the microbial foam lightweight soil 1 to ensure that the proportions of the various components in the reaction solution are appropriate, thereby achieving the best cementation effect.

[0046] After preparing the raw material slurry, microbial solution, and reaction solution, mix and stir to form a slurry. Add the aggregate, admixture, and additives to the mixing device in the predetermined proportions. Start the mixing device and stir at 100 rpm for 2-3 minutes to thoroughly mix the aggregate, admixture, and additives, resulting in a uniform mixture. Add water to the mixture incrementally, stirring for 1-2 minutes after each addition to ensure a uniform slurry free of sediment. During the water addition process, carefully control the speed and amount of water addition to avoid adding too much water at once, which may result in uneven mixing. Continue stirring until all the water is added to obtain the raw material slurry. Measure the pH of the slurry and, based on the results, add an appropriate amount of pH adjuster. Start stirring and stir for 1-2 minutes to adjust the pH to a range suitable for bacterial survival. Different denitrifying bacteria may have different pH requirements, so the appropriate pH range should be determined based on the selected bacteria. After adjusting the pH, add the microbial solution and start stirring again to obtain a microbial mixed slurry. During the stirring process, it is necessary to ensure that the microbial solution is fully mixed with the raw material slurry to ensure that the microorganisms are evenly distributed in the slurry.

[0047] Subsequently, the gas production process begins. The reaction liquid is mixed with the microbial mixed slurry, and the stirring device is started to stir evenly to obtain a microbial foam lightweight soil slurry 22. In an anaerobic environment, denitrifying bacteria carry out denitrification, reducing nitrate to produce nitrogen bubbles 21. During the reaction, the stirring device is continuously started to stir so that the nitrogen bubbles 21 are evenly distributed. At the same time, denitrifying bacteria consume hydrogen ions in the environment to generate carbon dioxide, gradually increasing the alkalinity of the slurry environment. The creation of an anaerobic environment can be achieved by sealing the reaction vessel, controlling the oxygen content, etc. The stirring speed and time need to be adjusted according to the properties of the slurry and the reaction conditions to ensure that the nitrogen bubbles 21 can be evenly distributed and the reaction can proceed fully.

[0048] For the construction of a new embankment, the embankment foundation trench excavation operation is carried out first. The excavation process must be carried out strictly in accordance with the design requirements to ensure that the size and shape of the foundation trench meet the requirements. The base 3 is compacted, and the compaction degree must meet the relevant standards to ensure the bearing capacity of the base 3. At the same time, the waterproofing and drainage work of the base 3 is done well to prevent water accumulation in the base 3 from affecting the construction quality. Lay the gravel cushion layer, and the thickness and particle size of the gravel cushion layer must be selected according to the design requirements to play a good drainage and buffering role. Carry out the formwork construction operation of the base plate and side plate. The formwork must ensure the stability and accuracy of the formwork to ensure that the structural dimensions after pouring meet the design requirements. After the formwork is completed, the prepared microbial foam lightweight soil slurry 22 is transported to the designated location by conveying equipment, and then the pouring operation is carried out. During the pouring process, attention should be paid to controlling the pouring speed and height to avoid segregation of the slurry.

[0049] For the replacement and load reduction of existing embankments, direct excavation replacement or horizontal small-diameter lead holes 5 replacement can be used. When direct excavation replacement is carried out, the excavation operation of the original embankment 4 to be replaced is carried out first, and attention should be paid to protecting the surrounding environment and the original structure during the excavation process. After the excavation is completed, the base 3 is cleaned and compacted to ensure that the base 3 is flat and solid. At the same time, the waterproofing and drainage of the base 3 are done well. After that, a suitable formwork is installed at the construction site. After the formwork is supported, the prepared microbial foam lightweight soil slurry 22 is transported to the designated location through the conveying equipment, and then the pouring operation is carried out. When replacing the horizontal small-diameter lead holes 5, the slope of the original embankment 4 is first excavated, a construction platform is built, and preparations are made for the lead holes. Subsequently, the drilling equipment is used to carry out the horizontal small-diameter lead holes 5 of the embankment in batches on both sides of the roadbed. The lead hole diameter and the longitudinal and transverse spacing of the lead holes are reasonably set, and the lead holes have a certain slope to facilitate the pouring of the microbial foam lightweight soil slurry 22. After drilling, inspect the hole quality. If qualified, the prepared microbial foam lightweight soil slurry 22 is delivered into the hole via conveying equipment. Pumping of the microbial foam lightweight soil slurry 22 is performed, with attention to pumping distance and vertical height requirements. The slurry is poured in blocks, layers, and batches, controlling the volume and thickness of each layer. This ensures that the slurry fully fills the drilling hole, avoiding voids or looseness.

[0050] During the cementation process, after the microbial foam lightweight soil slurry 22 is poured, bicarbonate ions and calcium ions gradually combine in an alkaline environment to produce calcium carbonate crystals 23, which bind the soil particles 24 together to form a soil skeleton. Over time, the cementation process gradually intensifies, and the strength of the microbial foam lightweight soil 1 gradually increases. The formation of the alkaline environment is primarily due to the denitrifying bacteria consuming hydrogen ions to produce carbon dioxide during the reaction, which gradually increases the pH value of the slurry. The formation of calcium carbonate crystals 23 is a gradual process, requiring time to achieve sufficient strength.

[0051] Finally, maintenance and quality control are the key steps. After pouring, cover with geotextile for maintenance to prevent shrinkage cracks caused by rapid water loss. Geotextile can moisturize and insulate, providing a good environment for the cementation process of microbial foam lightweight soil 1. At the same time, regularly test the wet density and compressive strength of the foam lightweight soil, monitor microbial activity, bubble distribution and quantity, and calcium carbonate precipitation, and evaluate the MICP effect. The natural curing period is no less than 3 days, and after the top layer is poured, the curing period is extended to no less than 7 days. During the curing period, pay close attention to the curing situation and adjust the curing measures in a timely manner to ensure the quality of microbial foam lightweight soil 1.

[0052] Throughout the entire construction process, operations must be strictly adhered to relevant standards and specifications to ensure construction quality and safety. Furthermore, strict quality control is implemented for raw materials and the construction process, with each batch of raw materials inspected to ensure that their quality meets requirements. Every step of the construction process is monitored to promptly identify and resolve problems. Through the above-described specific implementation methods, the construction of microbial foam lightweight soil 1 for embankment load reduction can be effectively implemented, improving the embankment's stability and bearing capacity while reducing project costs and environmental impact.

[0053] In summary, this microbial foam lightweight soil for embankment load reduction and its construction method achieve excellent results and product quality by precisely controlling the ratio of various raw materials and strictly standardizing the operation of each construction step. In practical applications, the above implementation methods can be appropriately adjusted and optimized according to specific project requirements and conditions to achieve the best engineering results.

[0054] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A microbial foam lightweight soil for embankment load reduction, characterized in that: The method comprises 20-400 parts of raw material slurry, 20-50 parts of microbial solution and 20-100 parts of reaction liquid; the raw material slurry comprises water, aggregate, admixture and additive which are uniformly mixed in a certain proportion; the microbial solution is prepared from denitrifying bacterial liquid; and the reaction liquid comprises a denitrifying matrix and a calcium source.

2. The microbial foam lightweight soil for embankment load reduction according to claim 1, characterized in that: The denitrifying bacterial liquid is a bacterial strain that has entered a stable period, the denitrifying matrix is an organic matter containing nitrate; and the calcium source is calcium acetate.

3. The microbial foam lightweight soil for embankment load reduction according to claim 1, characterized in that: The water is tap water, purified water or distilled water; the aggregate is raw soil, which is engineering waste soil, sandy soil, silt soil or clay soil.

4. A construction method of microbial foam lightweight soil for embankment load reduction according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1. Prepare raw materials: select and proportion water, aggregate, admixture and additives, and determine the amount of each raw material; S2. Preparation of microbial solution: Denitrifying bacteria are selected for cultivation, bacterial liquid is obtained under suitable temperature and pH conditions, and bacterial liquid that has entered the stable phase and has high activity is detected and selected to prepare a solution; S3. Prepare the reaction solution: construct a reaction system including a denitrification substrate and a calcium source, select nitrate-containing organic matter as the denitrification substrate, select calcium salt as the calcium source and determine the amount thereof; S4. Mixing and stirring to prepare slurry: Aggregate, admixture and admixture are put into a stirring device according to a proportion, and stirred at a speed of 100 r / min for 2-3 minutes to obtain a mixture; water is added to the mixture gradually, and the stirring device is started and stirred for 1-2 minutes after each addition of water to ensure that the slurry is uniform and free of sediment, until the water is added to obtain a raw material slurry; Determine the pH value of the slurry, add a pH regulator according to the determination result, start the stirring device and stir for 1-2 minutes. After adjusting the pH value of the slurry to a range suitable for the survival of fungi, add the microbial solution, start the stirring device and stir evenly to obtain a microbial mixed slurry; S5, gas production process: the reaction liquid and the microbial mixed slurry are mixed, and the stirring device is started to stir evenly to obtain a microbial foam lightweight soil slurry (22); under an anaerobic environment, the denitrifying bacteria perform denitrification to reduce nitrate to produce nitrogen bubbles (21), and the stirring device is continuously started during the reaction process to stir so that the nitrogen bubbles (21) are evenly distributed. At the same time, the denitrifying bacteria consume hydrogen ions in the environment to generate carbon dioxide, gradually increasing the alkalinity of the slurry environment; S6. New embankment filling: excavation of the embankment foundation trench, compaction of the base (3), waterproofing and drainage of the base (3), laying of a gravel cushion layer; formwork construction of the bottom plate and side plates; after the formwork is completed, the prepared microbial foam lightweight soil slurry (22) is transported to the designated location through a conveying device, and then pouring is carried out; Existing embankment replacement: For the replacement and load reduction of existing embankments, direct excavation replacement or horizontal small-diameter hole replacement is adopted; when direct excavation replacement is carried out, the original embankment (4) to be replaced is first excavated, and after the excavation is completed, the base (3) is cleaned and compacted to ensure that the base (3) is flat and solid, and the waterproofing and drainage of the base (3) are done well; then, a suitable formwork is installed at the construction site. After the formwork is supported, the prepared microbial foam lightweight soil slurry (22) is transported to the designated location through the conveying equipment, and then the pouring operation is carried out; when horizontal small-diameter hole replacement is carried out, the slope of the original embankment (4) is first excavated and a construction platform is built. , make preparations for the lead holes, then use drilling equipment to carry out the transverse small-diameter lead holes (5) of the embankment in batches on both sides of the roadbed, reasonably set the aperture of the small-diameter lead holes (5) and the longitudinal and transverse spacing of the small-diameter lead holes (5), and at the same time make the small-diameter lead holes (5) have a certain slope, check the quality of the small-diameter lead holes (5) after the lead holes are drilled, and after the holes are qualified, transport the prepared microbial foam lightweight soil slurry (22) into the hole through the conveying equipment; the microbial foam lightweight soil slurry (22) is constructed by pumping, and at the same time, pay attention to the requirements of the pumping distance and the vertical pumping height, and adopt the block, layer and batch method to carry out the pouring operation, and control the pouring volume of a single bin and the pouring thickness of a single layer; S7, cementation process: After the microbial foam lightweight soil slurry (22) is poured, in an alkaline environment, bicarbonate ions and calcium ions gradually combine to produce calcium carbonate crystals (23), cementing soil particles (24) to form a soil skeleton. As time goes by, the cementation process gradually strengthens, and the strength of the microbial foam lightweight soil gradually increases; S8. Curing and quality control: After the microbial foam lightweight soil slurry is poured, in an alkaline environment, bicarbonate ions and calcium ions gradually combine to produce calcium carbonate crystals, cementing soil particles to form a soil skeleton; after pouring, cover with geotextile for curing operations to prevent shrinkage cracks caused by rapid water loss; at the same time, regularly test the wet density and compressive strength of the foam lightweight soil (1), monitor microbial activity, bubble distribution and quantity, and calcium carbonate precipitation (23), and evaluate the MICP effect.

5. The construction method of microbial foam lightweight soil for embankment load reduction according to claim 4, characterized in that: In step S1, the admixture includes fly ash, slag powder or silica fume.

6. The construction method of microbial foam lightweight soil for embankment load reduction according to claim 4, characterized in that: In step S2, the denitrifying bacteria are specifically denitrifying Pseudomonas, and the culture temperature range is 20-40°C, and the pH value is adjusted to neutral or weakly alkaline.

7. The construction method of microbial foam lightweight soil for embankment load reduction according to claim 4, characterized in that: In step S3, the denitrification matrix provides reaction substances for the denitrifying bacteria. Under an anaerobic environment, the denitrifying bacteria reduce the nitrate in the matrix to release nitrogen, forming nitrogen bubbles (21), and consume hydrogen ions in the environment to generate carbon dioxide. The calcium ions in the calcium source combine with the bicarbonate ions in the solution under an alkaline environment to form calcium carbonate crystals (23), which cement the soil particles (24) together.

8. The construction method of microbial foam lightweight soil for embankment load reduction according to claim 4, characterized in that: In step S8, the natural curing period is not less than 3 days, and the curing period is extended to not less than 7 days after the top layer is poured.

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