Ecological roadbed structure of granite residual soil based on microorganism and discarded oyster shell modification and construction method thereof

Abstract

The application belongs to the field of road engineering, and relates to an ecological roadbed structure of modified granite residual soil based on microorganisms and waste oyster shells and a construction method thereof.The resource ecological roadbed structure comprises a bottom isolation layer, a modified granite residual soil filling area, a modified ecological slope protection area, a strength compensation layer, a pavement structure layer and a drainage structure.The top surface of the bottom isolation layer is the modified granite residual soil filling area, both side slopes of the modified granite residual soil filling area are covered with the modified ecological slope protection area, the modified ecological slope protection area comprises an oyster shell powder-vegetation base layer, an oyster shell coarse aggregate layer and a vegetation layer, the modified granite residual soil is mixed by a bacterial treatment liquid, granite residual soil and oyster shell powder, and the drainage structure is arranged at the bottom of the side slope.The ecological roadbed structure has good disintegration resistance, erosion resistance and impermeability, the mechanical properties meet the road engineering standards, and the ecological development concept is met.

Description

Technical Field

[0001] This invention belongs to the field of roadbed construction and relates to an ecological roadbed structure and construction method based on microorganisms and waste oyster shell modified granite residual soil. Background Technology

[0002] In my country, residual granite soil is mainly distributed in coastal areas such as Guangdong, Fujian, and Hainan. Due to its high natural water content, high liquid limit, difficulty in compaction, and easy disintegration upon contact with water, the roadbed's compaction degree and deflection value fail to meet design requirements, leading to softening, disintegration, and mudification damage. However, existing research shows that residual granite soil with a certain water content can actually meet the strength requirements of general soil roadbed fill, exhibiting good road performance. Currently, in actual roadbed construction, replacement methods or chemical slurries such as cement and lime are commonly used to modify residual granite soil. These methods have poor environmental protection and resource utilization, and also suffer from excessively high engineering costs.

[0003] Oysters (scientific name: *Crassostrea gigas*) are a popular and nutritious seafood. Currently, my country primarily processes and utilizes the edible parts of oysters, with a large amount of oyster shells being discarded as waste. The resource utilization of oyster shells is insufficient, and the organic matter within them can cause serious environmental pollution due to decomposition during long-term storage. Oyster shells have been utilized in various fields, such as as fertilizer for acidic soils to improve soil pH and increase fertilizer utilization, as aggregate in concrete building materials to enhance strength and durability, and for heavy metal adsorption in environmental remediation. To date, however, there is no engineering technology for using oyster shells to modify residual granite soil. This research aims to address the aforementioned problems of poor environmental protection, resource utilization, and high engineering costs associated with existing methods for modifying residual granite soil, while simultaneously resolving the issue of insufficient resource utilization of oyster shells. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides an ecological roadbed structure based on microorganisms and waste oyster shells modified granite residual soil, and its construction method.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] An ecological roadbed structure based on modified granite residual soil using microorganisms and waste oyster shells is characterized by comprising a bottom isolation layer, a modified granite residual soil filling area, a modified ecological slope protection area, a strength compensation layer, a pavement structure layer, and a drainage structure. The bottom of the modified granite residual soil filling area is the bottom isolation layer; the two side slopes of the modified granite residual soil filling area are covered by the modified ecological slope protection area; the top of the modified granite residual soil filling area consists of the strength compensation layer and the pavement structure layer; and the drainage structure is located at the bottom of the slopes.

[0007] Preferably, the modified granite residual soil filling area consists of several layers of modified granite residual soil; each modified granite residual soil layer comprises modified granite residual soil, a bacterial enzyme impermeable layer, and a reverse-wrapped geogrid layer; the modified granite residual soil is prepared by mixing oyster shell powder, granite residual soil, and bacterial treatment solution at a certain solid-liquid ratio; the particle size of the granite residual soil is less than 0.2 mm, and the granite residual soil excavated on-site is layered and dried in a natural environment until dry; the oyster shell powder-granite residual soil is prepared by mixing oyster shell powder and granite residual soil at a mass ratio not greater than 1:4, more preferably, at a mass ratio of 1:9; the particle size of the oyster shell powder is less than 0.2 mm; the bacterial treatment solution is a mixed solution of Pasteurella multocida concentrate and cementing solution, prepared by mixing Pasteurella multocida concentrate and cementing solution at a volume ratio of 1:1 to 2.5; the cementing solution includes a calcium chloride aqueous solution (providing Ca). 2+ ) and urea aqueous solution, calcium chloride in cementing solution (providing Ca) 2+ The molar concentrations of urea and urea are equal and both range from 0.5M to 1.5M (M is an abbreviation for mol / L, the same below, not elaborated further), more preferably, both are 1M; the solid-liquid ratio is determined based on the optimum moisture content of the granite residual soil, which is determined by indoor compaction tests; the modified granite residual soil is filled in layers, with each layer having a loose thickness of no more than 50cm, and adjacent wheel tracks overlapping by more than 1 / 3 during compaction, with the compaction degree controlled at more than 95%. The bacterial enzyme seepage barrier layer is formed by spraying a bacterial enzyme treatment solution onto the surface of the compacted modified granite residual soil; the amount of bacterial enzyme treatment solution used is 1.2 to 1.3 times the pore volume of the compacted granite residual soil. The reverse-wrapped geogrid layer is formed by a unidirectional geogrid made of high-density polyethylene (HDPE); the thickness of each layer of modified granite residual soil is 300-500mm; the unidirectional geogrid extends inward along the cross-section of the roadbed into the fill material for more than 0.9m, and the reverse-wrapping length of the unidirectional geogrid is reserved outward as needed, but the reinforcement quality and construction convenience must be ensured.

[0008] Preferably, the Pasteurella multocida concentrate is prepared by processing Pasteurella multocida bacterial solution, wherein the urease activity of the Pasteurella multocida bacterial solution is 10-15 mmol / (L·min).

[0009] Preferably, the bottom isolation layer is an oyster shell fine aggregate layer that has been treated with a bacterial enzyme treatment solution for 5 to 10 times; the oyster shell fine aggregate layer consists of geocells and oyster shell fine aggregate filling the geocells; the particle size of the oyster shell fine aggregate is less than 0.3 mm; and the thickness of the oyster shell fine aggregate layer is 10 cm to 15 cm.

[0010] Preferably, the modified ecological slope protection zone consists of, from bottom to top, an oyster shell powder-vegetated base layer, an oyster shell coarse aggregate layer, and a vegetation layer. The oyster shell powder-vegetated base layer comprises geocells and oyster shell powder-nutrient soil filling the geocells. The oyster shell powder-nutrient soil is prepared by mixing oyster shell powder and nutrient soil at a mass ratio of 1g-1.5g oyster shell powder: 1000g nutrient soil. The oyster shell powder has a particle size of less than 0.2mm. The nutrient soil contains plant seeds. The thickness of the oyster shell powder-vegetated base layer is 3cm-5cm. The oyster shell coarse aggregate layer is an oyster shell coarse aggregate layer treated with a bacterial enzyme treatment solution 3-5 times. The oyster shell coarse aggregate layer is composed of oyster shell coarse aggregate with a particle size of 2-4.75mm. The thickness of the oyster shell coarse aggregate layer is 3-5cm. The vegetation layer is formed by the growth of plant seeds sown on the surface of the oyster shell coarse aggregate layer and plant seeds mixed in the nutrient soil. The plant seeds can be one or more of the following: bermudagrass seeds, ryegrass seeds, white clover seeds, and tall fescue seeds.

[0011] Preferably, the road structure layer includes a subbase and a base course, both of which are cement-stabilized crushed stone layers, and the subbase and base course are full-width paved structures.

[0012] Preferably, the Pasteurella multocida concentrate is obtained by centrifuging and concentrating Pasteurella multocida bacterial solution; the volume ratio of the Pasteurella multocida concentrate to the Pasteurella multocida bacterial solution is 1 mL:10 mL.

[0013] Preferably, the Pasteurella multocida concentrate is obtained by concentrating the concentrate through the following steps:

[0014] Step 1): Prepare liquid culture medium for Bacillus pasteurellii and inoculate and culture the bacteria until the urease activity of the Bacillus pasteurellii culture is measured to be 10-15 mmol / (L·min), then stop the culture.

[0015] Step 2): Place the Bacillus pasteurellium culture obtained in Step 1) into a refrigerated centrifuge and centrifuge it. The centrifugation parameters are set as follows: speed 10000 rpm, temperature 4℃ and centrifugation time 15 min.

[0016] Step 3): After centrifugation in step 2), retain 1 / 10 of the volume of supernatant in each centrifuge tube. Use a long spoon to gently scrape the bacteria attached to the tube wall into the supernatant and stir gently to obtain Pasteurella multocida concentrate.

[0017] Preferably, the bacterial enzyme treatment solution is prepared by mixing a bacterial enzyme solution and a cementing solution at a volume ratio of 1:1 to 2.5; the cementing solution includes an aqueous solution of calcium chloride (providing Ca). 2+ ) and urea aqueous solution, wherein calcium chloride (providing Ca) in the cementing solution 2+The molar concentrations of urea and urea are equal and both are 2.0–2.5 M.

[0018] Preferably, the bacterial enzyme solution is extracted through the following steps:

[0019] Step 1): Prepare a culture medium for Bacillus pasteurellii and inoculate and culture the bacteria until the urease activity of the Bacillus pasteurellii culture solution is measured to be 10-15 mmol / (L·min), then stop the culture.

[0020] Step 2): Use an ultrasonic crusher to ultrasonically crush the Bacillus pasteurellium bacterial solution obtained in Step 1), while using an ice bath method to keep the temperature of the bacterial solution below 50°C during the crushing process, until the OD600 value of the bacterial solution reaches 0.20-0.25 and then stop crushing. The output power of the ultrasonic crusher is no more than 750W.

[0021] Step 3): Centrifuge the bacterial solution after the disruption in step 2) using a centrifuge, and take the supernatant as the bacterial enzyme solution;

[0022] Step 4): Dilute the bacterial enzyme solution to the target urease activity value of 10-15 mmol / (L·min).

[0023] A construction method for the above-mentioned ecological roadbed structure based on microorganisms and waste oyster shells modified granite residual soil, the construction method comprising the following steps:

[0024] 1) Construction preparation: On-site sampling and geotechnical tests such as moisture content, compaction, liquid limit, plastic limit, sieve analysis, and CBR are conducted to determine the specific gravity, liquid limit, plastic limit, permeability coefficient, natural moisture content, and optimum moisture content of the granite residual soil. Then, construction layout, material preparation, and site cleanup are carried out.

[0025] 2) Drying treatment of granite residual soil: The granite residual soil excavated on site is piled up in layers and dried in the natural environment. The soil layers are turned over regularly using mechanical equipment. After the granite residual soil is dry, a waterproof geomembrane is covered on its surface to keep the soil dry.

[0026] 3) Surcharge preloading: After step 2) is completed, a layer of non-woven fabric, a layer of 10cm thick filter layer and a layer of waterproof geotextile are laid from bottom to top on the surface of the proposed new roadbed; then, soil is filled on the waterproof geotextile for surcharge preloading. The surcharge preloading load is 150% to 200% of the design embankment load, and the surcharge preloading period is not less than 15 months.

[0027] 4) Construction of the bottom isolation layer: After step 3) is completed, the surcharge preload, waterproof geotextile, filter layer and non-woven fabric are removed, the site is leveled, and then geocells are laid on the roadbed surface. Oyster shell fine aggregate is filled into the geocells to the elevation. Finally, the oyster shell fine aggregate is uniformly sprayed with a bacterial enzyme treatment solution prepared on site by mixing cementing liquid and bacterial enzyme solution every 24 hours. The treatment is repeated 5 to 10 times to mineralize and form the bottom isolation layer.

[0028] 5) Construction of the modified granite residual soil filling area: After step 4) is completed, a geogrid is laid on the surface of the bottom isolation layer. Then, the prepared cementing liquid is mixed on-site with Bacillus pasteurellium concentrate and bacterial enzyme solution to prepare bacterial treatment solution and bacterial enzyme treatment solution. The pre-prepared oyster shell powder-granite residual soil is mixed and stirred on-site with the bacterial treatment solution to prepare modified granite residual soil. The evenly mixed modified granite residual soil is filled on the geogrid, compacted with a road roller, and covered with a waterproof film for curing for 20-28 hours. Then, every 20-28 hours, the bacterial enzyme treatment solution is sprayed on the compacted road surface and covered with a waterproof film for curing. After spraying and curing 5-7 times, the geogrid is wrapped around the compacted modified granite residual soil. After wrapping, a layer of modified granite residual soil is formed. Then, the next layer of modified granite residual soil is constructed until the design height is reached.

[0029] 6) Construction of oyster shell powder-vegetated base layer in modified ecological slope protection area: After step 5) is completed, geocells are laid on the slope surface of modified granite residual soil filling area. The prepared oyster shell powder and nutrient soil are mixed on site and filled into the geocells to the elevation. The nutrient soil contains one or more of the following: bermudagrass seeds, ryegrass seeds, white clover seeds, and tall fescue seeds.

[0030] 7) Construction of the oyster shell coarse aggregate layer in the modified ecological slope protection area: After step 6) is completed, oyster shell coarse aggregate is filled onto the surface of the oyster shell powder-vegetated base layer to the elevation to form the oyster shell coarse aggregate layer. Then, a bacterial enzyme treatment solution is prepared on-site by mixing a cementing liquid and a bacterial enzyme solution. The bacterial enzyme treatment solution is sprayed evenly onto the oyster shell coarse aggregate layer every 24 hours for 3-5 treatments to mineralize and form the oyster shell coarse aggregate layer. Then, a drainage structure is constructed at the bottom of the slope. Plant seeds are sown on the surface of the oyster shell coarse aggregate layer. The plant seeds can be one or more of the following: bermudagrass seeds, ryegrass seeds, white clover seeds, and tall fescue seeds.

[0031] 8) Construction of strength compensation layer and pavement structure layer: After step 7) is completed, strength compensation layer and pavement structure layer are constructed sequentially on the top surface of modified granite residual soil filling area.

[0032] Compared with the prior art, the beneficial effects and advantages of the present invention are as follows:

[0033] This invention provides an ecological roadbed structure and construction method for granite residual soil modified by microorganisms and waste oyster shells. The working principles of the bacterial treatment solution and the bacterial enzyme treatment solution for cementing the soil are essentially the same, respectively utilizing Bacillus pasteurella multocida to directly hydrolyze urea (CO(NH2)2) to produce carbonate ions, and using urease crudely extracted from Bacillus pasteurella multocida. Ammonium ions (as shown in Formula 1), and then a calcium source (Ca) is introduced. 2+ ) precipitates calcium carbonate crystals (CaCO3) with a cementing effect (as shown in Formula 2), which cement the loose rock and soil into a whole, thereby achieving the purpose of improving the engineering properties of the rock and soil.

[0034]

[0035]

[0036] In this invention: 1) On the one hand, *Pasteurella multocida*, a preferred bacterium, is a highly urease-producing alkaliphilic bacterium. Mixing alkaline oyster shell powder (pH = 9.0–10.0) with acidic granite residual soil in its natural state provides an alkaline environment for *Pasteurella multocida*, effectively improving the efficiency of bacterial mineralization and enhancing the disintegration resistance of the granite residual soil. On the other hand, incorporating oyster shell powder with a certain strength into the granite residual soil can, to some extent, improve the shear strength of the soil; 2) A cementing solution composed of *Pasteurella multocida* concentrate, urea, and calcium chloride solution is injected into the oyster shell powder-granite residual soil mixture and thoroughly mixed. *Pasteurella multocida* hydrolyzes the urea. The carbonate ions produced during the process combine with calcium ions in the cementing solution to form calcium carbonate precipitate. The calcium carbonate crystals cement the soil and form aggregates with good disintegration resistance, effectively improving the overall water resistance, strength, stiffness and stability of granite residual soil, thereby improving the road performance of granite residual soil subgrade; 3) The bacterial enzyme treatment solution is sprayed on the surface of the modified granite residual soil to form a layer of calcium carbonate hard shell with good water stability and seepage prevention and disintegration resistance, effectively optimizing the disintegration resistance and erosion resistance of granite residual soil; 4) Concentrated Bacillus pasteurellium bacterial solution is used to mix the soil to increase the number of bacteria per gram of soil, which greatly improves the efficiency of microbial mineralization and saves construction time. Meanwhile, the preferred Bacillus pasteurellii can maintain strong biological activity in harsh soil environments such as acidity, alkalinity, and high salinity, which can improve engineering efficiency and acceptance quality; 5) By first mixing the soil with bacterial treatment solution and then spraying the soil surface with bacterial enzyme treatment solution, the residual granite soil forms a micro-soil structure of soil particles-calcium carbonate cemented agglomerates + calcium carbonate hard shell surface layer. The mechanical stability provided by the mechanical force generated by the interlocking and embedding between soil particles, the chemical stability provided by the agglomerates formed by calcium carbonate cementation, and the protective effect of the calcium carbonate hard shell layer covering the surface in terms of collapse resistance, erosion resistance and seepage prevention are jointly improved, thus enhancing the collapse resistance and erosion resistance of the residual granite soil. Meanwhile, the combined treatment of mixing with Bacillus pasteurellii followed by spraying with bacterial enzymes means that even when the porosity of the granite residual soil decreases due to bacterial treatment, the molecular-sized bacterial enzymes (bacterial size approximately 0.5–3 μm, urease size approximately 12 nm) can still penetrate the soil, forming a thicker bacterial enzyme shell; 6) This invention uses modified granite residual soil compacted by geogrid backfilling. On the one hand, geogrids embedded in the subgrade can form a reinforced soil structure with composite stress, thereby improving the subgrade strength and stability, improving subgrade deformation performance, and having advantages such as saving investment, improving engineering quality, facilitating construction, and optimizing subgrade structure.On the other hand, the use of reverse-wrapped geogrids can reinforce and protect the slope surface of the roadbed, thereby improving the slope stability and resistance to rainwater erosion and wind erosion; 7) This invention can make full use of the granite residual soil excavated on site, reduce the amount of soil to be added from the outside, thereby reducing resource consumption during construction and reducing project costs; 8) The main component of oyster shells is calcium carbonate, and they also contain trace elements essential to animals, such as copper, magnesium, potassium, molybdenum, phosphorus, manganese, iron, zinc, etc. In addition, the pearl powder layer of oyster shells also contains a variety of amino acid components. Oyster shells can not only provide trace elements and amino acids for the growth of Bacillus pasteurellosis, but also effectively solve the environmental pollution problem caused by the disposal of oyster shells; 9) The bottom isolation layer uses a bacterial enzyme treatment solution to solidify a water-proof layer with extremely low permeability on the fine aggregate of oyster shells, which can effectively prevent capillary action and water migration caused by rising groundwater levels from entering the modified granite residual soil filling area. While maximizing resource utilization, the geocells can also improve the stability of the roadbed and coordinate the unevenness between the roadbed soil and the foundation. Uniform deformation; 10) The modified ecological slope protection zone on the slope surface of the modified granite residual soil filling area consists of oyster shell powder-vegetated base layer, oyster shell coarse aggregate layer, and vegetation layer from bottom to top, which can provide the following benefits: The oyster shell coarse aggregate layer has a certain strength and can prevent the roadbed from being eroded by water flow, thus preventing soil erosion; The vegetation layer formed by the growth of plant seeds in the oyster shell powder-vegetated base layer and plant seeds sown on the surface of the oyster shell coarse aggregate layer, with its roots and stems connecting each slope protection layer into a whole, further improves the erosion resistance and overall strength of the slope protection layer. It also has certain environmental benefits; 11) Oyster shell powder-vegetated base layer: Oyster shell powder and nutrient soil are mixed. Oyster shells themselves contain a large amount of calcium and other elements required for crop growth. As a soil conditioner, when mixed with nutrient soil, it can effectively improve soil acidification and passivate the activity of heavy metals in acid rain areas, thereby achieving the effects of acidification, calcium supplementation, soil repair, and promotion of plant growth; 12) Oyster shell coarse aggregate, due to its alkaline and porous structure, can adsorb heavy metal pollutants in surface runoff as a slope protection layer, and has a certain environmental purification capacity. Obviously, the ecological roadbed structure and construction method of granite residual soil modified by microorganisms and waste oyster shells provided by this invention can realize the resource utilization of granite residual soil and oyster shells, improve the disintegration resistance of granite residual soil, and maximize resource utilization, with good social, economic and environmental benefits. Attached Figure Description

[0037] Figure 1 A schematic diagram of the roadbed cross-section of the ecological roadbed structure based on microorganisms and waste oyster shells modified granite residual soil provided by the present invention.

[0038] Figure 2 This is a cross-sectional schematic diagram of the modified ecological slope protection area used in this invention.

[0039] Figure 3 This is a schematic cross-sectional view of the modified granite residual soil layer used in this invention.

[0040] In the diagram, 1-pavement structure layer, 2-strength compensation layer, 3-modified ecological slope protection area, 4-modified granite residual soil filling area, 5-bottom isolation layer, 6-drainage structure, 7-vegetation layer, 8-oyster shell coarse aggregate layer, 9-oyster shell powder-vegetated base layer, 10-reverse-wrapped geogrid layer, 11-bacterial enzyme seepage prevention layer, 12-plant root system.

[0041] Figure 4 This is a simplified diagram of the disintegration test apparatus used in the disintegration test of this invention.

[0042] Figure 5 This is a graph showing the disintegration amount-time curves of samples prepared under different treatment methods in the experimental and control groups in this invention.

[0043] Figure 6 The following are actual images showing the disintegration of samples obtained under different treatment methods in the experimental and control groups in this invention in water: Figure a shows the state of the soil group sample at t=3 min; Figure b1 shows the state of the bacterial treatment solution group sample at t=3 min; Figure c1 shows the state of the bacterial treatment solution + oyster shell powder mixture group at t=3 min; Figure d1 shows the state of the bacterial treatment solution + oyster shell powder mixture group at t=3 min; Figure b2 shows the state of the bacterial treatment solution group sample at t=10 min; Figure c2 shows the state of the bacterial treatment solution + oyster shell powder mixture group at t=30 min; Figure d2 shows the state of the bacterial treatment solution + oyster shell powder mixture group at t=20 min. Detailed Implementation

[0044] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0045] Granite residual soil was treated and samples were prepared using bacterial treatment solution, bacterial treatment solution + oyster shell powder (10%), and bacterial treatment solution + oyster shell powder (20%), respectively. Disintegration tests were then performed on the samples, and they were compared with samples prepared from untreated plain soil (i.e., samples obtained solely from granite residual soil). The physical and mechanical parameters of the granite residual soil are shown in Table 1. The sample preparation parameters for the experimental groups (corresponding to the three treatment methods) and the control group (i.e., the plain soil group) are shown in Table 2. Information on some raw materials and auxiliary materials is shown in Table 3.

[0046] Disintegration tests were conducted on samples of granite residual soil obtained from the above-mentioned different treatment methods. The disintegration tests were performed using a self-developed disintegration testing device, as described above. Figure 4As shown in the diagram, the prepared sample was placed on a perforated tray, and the tray and soil sample were simultaneously immersed in water. The tray was suspended from a tensile tester, which was connected to a computer via a data cable. When the sample disintegrated in the water, the disintegrated soil sample settled to the bottom of the beaker. At this point, the computer detected the sample mass loss value in real time. In this experiment, the disintegration amount = loss value / original mass, and the time required for the disintegration amount to reach 100% was used to measure the disintegration resistance of each group of samples.

[0047] In the disintegration experiment, the disintegration amount-time curves of the samples prepared under different treatments in each group are shown below. Figure 5 As shown in the figure, the bacterial treatment solution group only treated the granite residual soil with the bacterial treatment solution. This treatment generated cementing calcium carbonate crystals within the granite residual soil, improving the sample's resistance to disintegration. In the untreated soil group, the soil completely disintegrated in water in just 160 seconds. However, after treatment with the bacterial treatment solution, the bacterial treatment solution group took 685 seconds to completely disintegrate in water, approximately 4.3 times longer.

[0048] Due to the pH-regulating effect of oyster shell powder, a better pH environment was provided for Bacillus pasteurellii, and more nucleation sites were also provided for the bacteria, resulting in the formation of more calcium carbonate crystals within the granite residual soil. The bacterial treatment solution + 10% oyster shell powder group and the bacterial treatment solution + 20% oyster shell powder group required 1920s and 1320s respectively to reach 100% disintegration, approximately 2.8 times and 1.8 times that of the bacterial treatment solution group. This indicates that the combination of bacterial treatment solution and oyster shell powder effectively improves the disintegration resistance of granite residual soil.

[0049] Table 1 Physical and mechanical parameters of residual granite soil

[0050]

[0051] Table 2 Sample preparation parameters for experimental and control groups

[0052]

[0053] Note: A cementitious solution concentration of 1 mol / L refers to the concentration of calcium chloride (providing Ca). 2+ In a mixed solution of calcium chloride and urea, the molar concentrations of both calcium chloride and urea are 1 mol / L.

[0054] Table 3. Information on the names and models of raw and auxiliary materials

[0055] Raw material and auxiliary material name information and model source Calcium chloride Xilong Chemical Co., Ltd. urea Xilong Chemical Co., Ltd. Oyster shell powder Xiamen Mata Ecological Co., Ltd. Oyster shell coarse aggregate Xiamen Mata Ecological Co., Ltd. Oyster shell fine aggregate Xiamen Mata Ecological Co., Ltd. Pasteurella multocida China General Microbiological Culture Collection Center Nutrient soil Jiangsu Clover Trading Co., Ltd.

[0056] Example 1

[0057] (Corresponds to the bacterial treatment solution + 10% oyster shell powder group in Table 2)

[0058] like Figure 1 An ecological roadbed structure based on microbial mineralization of waste oyster shells and granite residual soil is disclosed, comprising a bottom isolation layer 5, a modified granite residual soil filling area 4, a modified ecological slope protection area 3, a strength compensation layer 2, a pavement structure layer 1, and a drainage structure 6. The modified granite residual soil filling area 4 is located above the bottom isolation layer 5. The modified ecological slope protection area 3 covers both sides of the modified granite residual soil filling area 4. The strength compensation layer 2 is located above the modified granite residual soil filling area 4, and the pavement structure layer 1 is located above the strength compensation layer 2. The drainage structure 6 is located at the bottom of the slope.

[0059] The bottom isolation layer 5 is a layer of fine oyster shell aggregate treated with a bacterial enzyme treatment solution five times; the bottom isolation layer 5 consists of geocells and fine oyster shell aggregate filling the geocells; the particle size of the fine oyster shell aggregate is less than 0.3 mm; the thickness of the fine oyster shell aggregate layer is 10 cm.

[0060] The pavement structure layer 1 includes a subbase and a base course. Both the subbase and the base course are cement-stabilized crushed stone layers, and the subbase and the base course are full-width paved structures.

[0061] like Figure 2 The modified granite residual soil filling area 4 consists of several layers of modified granite residual soil, which comprises modified granite residual soil, a bacterial enzyme seepage barrier layer 11, and a reverse-wrapped geogrid layer 10. The modified granite residual soil is prepared by mixing oyster shell powder, granite residual soil, and bacterial treatment solution at the optimal moisture content of the granite residual soil. The oyster shell powder-granite residual soil is prepared by mixing oyster shell powder and granite residual soil at a specific mass ratio; the oyster shell powder particle size is less than 0.2 mm. The reverse-wrapped geogrid layer 10 is formed by a unidirectional geogrid made of high-density polyethylene (HDPE). Each layer of modified granite residual soil is 300 mm thick. The geogrid extends inward along the cross-section of the roadbed into the filling material for more than 0.9 m. The bacterial enzyme seepage barrier layer 11 is formed by spraying a bacterial enzyme treatment solution onto the surface of the compacted modified granite residual soil.

[0062] like Figure 3 The modified ecological slope protection zone 3 consists of, from bottom to top, an oyster shell powder-vegetation base layer 9, an oyster shell coarse aggregate layer 8, and a vegetation layer 7. The oyster shell coarse aggregate layer 8 is an oyster shell coarse aggregate layer that has been treated with a bacterial enzyme treatment solution three times; the oyster shell coarse aggregate layer 8 is laid with oyster shell coarse aggregate with a particle size of 2-4.75mm; the thickness of the oyster shell coarse aggregate layer 8 is 3cm.

[0063] The oyster shell powder-vegetated base layer 9 is composed of geocells and oyster shell powder-nutrient soil filling the geocells; the oyster shell powder-nutrient soil is made by mixing oyster shell powder and nutrient soil at a mass ratio of oyster shell powder: nutrient soil of 1g: 1000g; the particle size of the oyster shell powder is less than 0.2mm; the thickness of the oyster shell powder-vegetated base layer is 3cm.

[0064] The bacterial treatment solution is a mixture of Pasteurella multocida concentrate and a gelling solution, prepared by mixing Pasteurella multocida concentrate and gelling solution at a volume ratio of 1:1; the gelling solution includes calcium chloride solution and urea solution, with the molar concentration of both calcium chloride and urea in the gelling solution being 1M; the Pasteurella multocida concentrate is obtained by concentrating the solution through the following steps:

[0065] Step 1): Prepare a liquid culture medium for Bacillus pasteurellii (20 g / L yeast extract, 15 g / L NH4Cl and 0.1 mM NiCl2, pH = 9.25; the same below) and inoculate and culture the bacteria until the urease activity of the Bacillus pasteurellii culture is measured to be 10 mmol / (L·min), then stop the culture.

[0066] Step 2): Place the Bacillus pasteurellium culture obtained in Step 1) into a refrigerated centrifuge and centrifuge it. Set the centrifugation parameters to 10,000 rpm / min, 4℃, and 15 min.

[0067] Step 3): After centrifugation in step 2), retain 1 / 10 of the volume of supernatant in each centrifuge tube. Use a long spoon to gently scrape the bacteria attached to the tube wall into the supernatant and stir gently to obtain Pasteurella multocida concentrate.

[0068] The bacterial enzyme treatment solution is prepared by mixing a bacterial enzyme solution and a cementing solution at a volume ratio of 1:1; the cementing solution includes a calcium chloride solution and a urea solution, both with a molar concentration of 2.0 M; the bacterial enzyme solution is extracted through the following steps:

[0069] Step 1): Prepare a culture medium for Bacillus pasteurellii and inoculate and culture the bacteria until the urease activity of the Bacillus pasteurellii culture solution is measured to be 10 mmol / (L·min), then stop the culture.

[0070] Step 2): Use an ultrasonic crusher to ultrasonically crush the Bacillus pasteurellium bacterial solution obtained in Step 1), while using an ice bath method to keep the temperature of the bacterial solution below 50°C during the crushing process, until the OD600 value of the bacterial solution reaches 0.25 and then stop crushing. The output power of the ultrasonic crusher is no more than 750W.

[0071] Step 3): Centrifuge the bacterial culture after the disruption in Step 2) using a centrifuge, and take the supernatant as the bacterial enzyme solution; set the centrifuge parameters as follows: speed 10000 rpm / min, temperature 4℃, and centrifugation time 15min.

[0072] Step 4): Dilute the bacterial enzyme solution to the target urease activity value.

[0073] The construction method for the resource-based ecological roadbed structure of waste oyster shells and granite residual soil based on microbial mineralization in this embodiment includes the following steps:

[0074] 1) Construction preparation: On-site sampling and geotechnical tests such as moisture content, compaction, liquid limit, plastic limit, sieve analysis, and CBR are conducted to determine the specific gravity, liquid limit, plastic limit, permeability coefficient, natural moisture content, and optimum moisture content of the granite residual soil. Then, construction layout, material preparation, and site cleanup are carried out.

[0075] 2) Drying treatment of granite residual soil: The granite residual soil excavated on site is piled up in layers and dried in the natural environment. The soil layers are turned over regularly using mechanical equipment. After the granite residual soil is dry, a waterproof geomembrane is covered on its surface to keep the soil dry.

[0076] 3) Surcharge preloading: After step 2) is completed, a layer of non-woven fabric, a layer of 10cm thick filter layer and a layer of waterproof geotextile are laid from bottom to top on the surface of the proposed new roadbed; then, soil is filled on the waterproof geotextile for surcharge preloading. The surcharge preloading load is 150% of the design embankment load, and the surcharge preloading period is not less than 15 months.

[0077] 4) Construction of the bottom isolation layer: After step 3) is completed, the surcharge preload, waterproof geotextile, filter layer and non-woven fabric are removed, the site is leveled, and then geocells are laid on the roadbed surface. Oyster shell fine aggregate is filled into the geocells to the elevation. Finally, the oyster shell fine aggregate is uniformly sprayed with a bacterial enzyme treatment solution prepared on site by mixing cementing liquid and bacterial enzyme solution every 24 hours for a total of 5 treatments to mineralize and form the bottom isolation layer.

[0078] 5) Construction of the modified granite residual soil filling area: After step 4) is completed, a geogrid is laid on the surface of the bottom isolation layer. Then, the prepared cementing liquid is mixed on-site with Bacillus pasteurellium concentrate and bacterial enzyme solution to prepare bacterial treatment solution and bacterial enzyme treatment solution. The pre-prepared oyster shell powder-granite residual soil is mixed and stirred on-site with the bacterial treatment solution to prepare modified granite residual soil. The evenly mixed modified granite residual soil is filled on the geogrid, compacted with a road roller, and covered with a waterproof film for curing for 20 hours. Then, every 20 hours, the bacterial enzyme treatment solution is sprayed on the compacted road surface and covered with a waterproof film for curing. After spraying and curing 5 times, the geogrid is wrapped around the compacted modified granite residual soil. After wrapping, a layer of modified granite residual soil is formed. Then, the next layer of modified granite residual soil is constructed until the design height is reached.

[0079] 6) Construction of oyster shell powder-vegetated base layer in modified ecological slope protection area: After step 5) is completed, geocells are laid on the slope of modified granite residual soil filling area. The prepared oyster shell powder and nutrient soil are mixed on site and filled into the geocells to the elevation. The nutrient soil contains bermudagrass seeds and ryegrass seeds.

[0080] 7) Construction of the oyster shell coarse aggregate layer in the modified ecological slope protection area: After step 6) is completed, oyster shell coarse aggregate is filled on the surface of the oyster shell powder-vegetated base layer to the elevation to form the oyster shell coarse aggregate layer. Then, a bacterial enzyme treatment solution is prepared on-site by mixing cementing liquid and bacterial enzyme solution. The bacterial enzyme treatment solution is sprayed evenly on the oyster shell coarse aggregate layer once every 24 hours for 3 treatments to mineralize and form the oyster shell coarse aggregate layer. Then, a drainage structure is constructed at the bottom of the slope. Plant seeds are sown on the surface of the oyster shell coarse aggregate layer. The plant seeds selected are white clover seeds and tall fescue seeds.

[0081] 8) Construction of strength compensation layer and pavement structure layer: After step 7) is completed, strength compensation layer and pavement structure layer are constructed sequentially on the top surface of modified granite residual soil filling area.

[0082] Example 2

[0083] (Corresponds to the bacterial treatment solution + 20% oyster shell powder group in Table 2)

[0084] like Figure 1 An ecological roadbed structure based on microbial mineralization of waste oyster shells and granite residual soil is disclosed, comprising a bottom isolation layer 5, a modified granite residual soil filling area 4, a modified ecological slope protection area 3, a strength compensation layer 2, a pavement structure layer 1, and a drainage structure 6. The modified granite residual soil filling area 4 is located above the bottom isolation layer 5. The modified ecological slope protection area 3 covers both sides of the modified granite residual soil filling area 4. The strength compensation layer 2 is located above the modified granite residual soil filling area 4, and the pavement structure layer 1 is located above the strength compensation layer 2. The drainage structure 6 is located at the bottom of the slope.

[0085] The bottom isolation layer 5 is a layer of fine oyster shell aggregate treated with a bacterial enzyme treatment solution 10 times; the bottom isolation layer 5 consists of geocells and fine oyster shell aggregate filling the geocells; the particle size of the fine oyster shell aggregate is less than 0.3 mm; the thickness of the fine oyster shell aggregate layer is 15 cm.

[0086] The pavement structure layer 1 includes a subbase and a base course. Both the subbase and the base course are cement-stabilized crushed stone layers, and the subbase and the base course are full-width paved structures.

[0087] like Figure 2The modified granite residual soil filling area 4 consists of several layers of modified granite residual soil, which comprises modified granite residual soil, a bacterial enzyme seepage barrier layer 11, and a reverse-wrapped geogrid layer 10. The modified granite residual soil is prepared by mixing oyster shell powder, granite residual soil, and bacterial treatment solution at the optimal moisture content of the granite residual soil. The oyster shell powder-granite residual soil is prepared by mixing oyster shell powder and granite residual soil at a specific mass ratio; the oyster shell powder particle size is less than 0.2 mm. The reverse-wrapped geogrid layer 10 is formed by a unidirectional geogrid made of high-density polyethylene (HDPE). Each layer of modified granite residual soil is 500 mm thick. The geogrid extends inward along the cross-section of the roadbed into the filling material for more than 0.9 m. The bacterial enzyme seepage barrier layer 11 is formed by spraying a bacterial enzyme treatment solution onto the surface of the compacted modified granite residual soil.

[0088] like Figure 3 The modified ecological slope protection zone 3 consists of, from bottom to top, an oyster shell powder-vegetation base layer 9, an oyster shell coarse aggregate layer 8, and a vegetation layer 7. The oyster shell coarse aggregate layer 8 is an oyster shell coarse aggregate layer that has been treated with a bacterial enzyme treatment solution five times; the oyster shell coarse aggregate layer 8 is laid with oyster shell coarse aggregate with a particle size of 2-4.75mm; the thickness of the oyster shell coarse aggregate layer 8 is 5cm.

[0089] The oyster shell powder-vegetated base layer 9 is composed of geocells and oyster shell powder-nutrient soil filling the geocells; the oyster shell powder-nutrient soil is made by mixing oyster shell powder and nutrient soil at a mass ratio of oyster shell powder: nutrient soil of 1.5g: 1000g; the particle size of the oyster shell powder is less than 0.2mm; the thickness of the oyster shell powder-vegetated base layer is 5cm.

[0090] The bacterial treatment solution is a mixture of Pasteurella multocida concentrate and a gelling solution, prepared by mixing Pasteurella multocida concentrate and gelling solution at a volume ratio of 1:2.5; the gelling solution includes calcium chloride solution and urea solution, with both calcium chloride and urea having a molar concentration of 1M; the Pasteurella multocida concentrate is obtained through the following steps:

[0091] Step 1): Prepare liquid culture medium for Bacillus pasteurellii and inoculate and culture the bacteria until the urease activity of the Bacillus pasteurellii culture is measured to be 15 mmol / (L·min), then stop the culture.

[0092] Step 2): Place the Bacillus pasteurellium culture obtained in Step 1) into a refrigerated centrifuge and centrifuge it. Set the centrifugation parameters to 10,000 rpm / min, 4℃, and 15 min.

[0093] Step 3): After centrifugation in step 2), retain 1 / 10 of the volume of supernatant in each centrifuge tube. Use a long spoon to gently scrape the bacteria attached to the tube wall into the supernatant and stir gently to obtain Pasteurella multocida concentrate.

[0094] The bacterial enzyme treatment solution is prepared by mixing a bacterial enzyme solution and a cementing solution at a volume ratio of 1:2.5; the cementing solution includes a calcium chloride solution and a urea solution, both with a molar concentration of 2.5M; the bacterial enzyme solution is extracted through the following steps:

[0095] Step 1): Prepare a culture medium for Bacillus pasteurellii and inoculate and culture the bacteria until the urease activity of the Bacillus pasteurellii culture solution is measured to be 15 mmol / (L·min), then stop the culture.

[0096] Step 2): Use an ultrasonic crusher to ultrasonically crush the Bacillus pasteurellium bacterial solution obtained in Step 1), while using an ice bath method to keep the temperature of the bacterial solution below 50°C during the crushing process, until the OD600 value of the bacterial solution reaches 0.30 and then stop crushing. The output power of the ultrasonic crusher is no more than 750W.

[0097] Step 3): Centrifuge the bacterial culture after the disruption in Step 2) using a centrifuge, and take the supernatant as the bacterial enzyme solution; set the centrifuge parameters as follows: speed 10000 rpm / min, temperature 4℃, and centrifugation time 15min.

[0098] Step 4): Dilute the bacterial enzyme solution to the target urease activity value.

[0099] The construction method for the resource-based ecological roadbed structure of waste oyster shells and granite residual soil based on microbial mineralization in this embodiment includes the following steps:

[0100] 1) Construction preparation: On-site sampling and geotechnical tests such as moisture content, compaction, liquid limit, plastic limit, sieve analysis, and CBR are conducted to determine the specific gravity, liquid limit, plastic limit, permeability coefficient, natural moisture content, and optimum moisture content of the granite residual soil. Then, construction layout, material preparation, and site cleanup are carried out.

[0101] 2) Drying treatment of granite residual soil: The granite residual soil excavated on site is piled up in layers and dried in the natural environment. The soil layers are turned over regularly using mechanical equipment. After the granite residual soil is dry, a waterproof geomembrane is covered on its surface to keep the soil dry.

[0102] 3) Surcharge preloading: After step 2) is completed, a layer of non-woven fabric, a layer of 10cm thick filter layer and a layer of waterproof geotextile are laid from bottom to top on the surface of the proposed new roadbed; then, soil is filled on the waterproof geotextile for surcharge preloading. The surcharge preloading load is 200% of the design embankment load, and the surcharge preloading period is not less than 15 months.

[0103] 4) Construction of the bottom isolation layer: After step 3) is completed, the surcharge preload, waterproof geotextile, filter layer and non-woven fabric are removed, the site is leveled, and then geocells are laid on the roadbed surface. Oyster shell fine aggregate is filled into the geocells to the elevation. Finally, the oyster shell fine aggregate is uniformly sprayed with a bacterial enzyme treatment solution prepared on site by mixing cementing liquid and bacterial enzyme solution every 24 hours for a total of 10 treatments to mineralize and form the bottom isolation layer.

[0104] 5) Construction of the modified granite residual soil filling area: After step 4) is completed, a geogrid is laid on the surface of the bottom isolation layer. Then, the prepared cementing liquid is mixed on-site with Bacillus pasteurellium concentrate and bacterial enzyme solution to prepare bacterial treatment solution and bacterial enzyme treatment solution. The pre-prepared oyster shell powder-granite residual soil is mixed and stirred on-site with the bacterial treatment solution to prepare modified granite residual soil. The uniformly mixed modified granite residual soil is filled on the geogrid, compacted with a road roller, and covered with a waterproof film for curing for 28 hours. Then, every 28 hours, the bacterial enzyme treatment solution is sprayed on the compacted road surface and covered with a waterproof film for curing. After 7 spraying and curing cycles, the geogrid is wrapped around the compacted modified granite residual soil. After wrapping, a layer of modified granite residual soil is formed. Then, the next layer of modified granite residual soil is constructed until the design height is reached.

[0105] 6) Construction of oyster shell powder-vegetated base layer in modified ecological slope protection area: After step 5) is completed, geocells are laid on the slope of modified granite residual soil filling area. The prepared oyster shell powder and nutrient soil are mixed on site and filled into the geocells to the elevation. The nutrient soil contains white clover seeds and tall fescue seeds.

[0106] 7) Construction of the oyster shell coarse aggregate layer in the modified ecological slope protection area: After step 6) is completed, oyster shell coarse aggregate is filled on the surface of the oyster shell powder-vegetated base layer to the elevation to form the oyster shell coarse aggregate layer. Then, a bacterial enzyme treatment solution is prepared on-site by mixing cementing liquid and bacterial enzyme solution. The bacterial enzyme treatment solution is sprayed evenly on the oyster shell coarse aggregate layer once every 24 hours for 5 treatments to mineralize and form the oyster shell coarse aggregate layer. Then, a drainage structure is constructed at the bottom of the slope. Plant seeds are sown on the surface of the oyster shell coarse aggregate layer. The plant seeds selected are bermudagrass seeds and ryegrass seeds.

[0107] 8) Construction of strength compensation layer and pavement structure layer: After step 7) is completed, strength compensation layer and pavement structure layer are constructed sequentially on the top surface of modified granite residual soil filling area.

[0108] It should be noted that in actual construction, the types of plant seeds mixed with the nutrient soil in the oyster shell powder-vegetated base layer and the types of plant seeds sown on the surface of the oyster shell coarse aggregate layer can be the same or different; the types of plant seeds mixed with the nutrient soil in the oyster shell powder-vegetated base layer or the types of plant seeds sown on the surface of the oyster shell coarse aggregate layer can be one type of plant seed or multiple types of plant seeds.

[0109] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Any equivalent modifications or substitutions to the technical solutions of the present invention that do not depart from the spirit and scope of the technical solutions of the present invention should fall within the scope of the patent of the present invention.

Claims

1. An ecological roadbed structure based on microorganisms and modified granite residual soil from waste oyster shells, the ecological roadbed structure comprising a pavement structure layer (1), a strength compensation layer (2), a modified ecological slope protection zone (3), a modified granite residual soil filling zone (4), a bottom isolation layer (5), and a drainage structure (6), characterized in that: The upper layer of the bottom isolation layer (5) is the modified granite residual soil filling area (4). The slopes on both sides of the modified granite residual soil filling area (4) are covered with modified ecological slope protection area (3). The top surface of the modified granite residual soil filling area (4) is successively constructed with strength compensation layer (2) and road structure layer (1). The modified ecological slope protection area (3) includes oyster shell powder-vegetation base layer (9), oyster shell coarse aggregate layer (8) and vegetation layer (7), and the drainage structure (6) is set at the bottom of the slope; The bottom isolation layer (5) is an oyster shell fine aggregate layer that has been sprayed with bacterial enzyme treatment solution 5 to 10 times. The oyster shell fine aggregate layer consists of geocells and oyster shell fine aggregate filling the geocells. The particle size of the oyster shell fine aggregate is less than 0.3 mm. The thickness of the oyster shell fine aggregate layer is 10 to 15 cm. The modified granite residual soil filling area (4) consists of several layers of modified granite residual soil, each layer of which is 300-500 mm thick. The modified granite residual soil layer consists of modified granite residual soil, a bacterial enzyme seepage prevention layer (11), and a reverse-wrapped geogrid layer (10). The modified granite residual soil is prepared by mixing oyster shell powder, granite residual soil, and bacterial treatment liquid at the optimal moisture content of the granite residual soil. The oyster shell powder and granite residual soil are mixed at a mass ratio of no more than 1:

4. The optimal moisture content is determined by indoor compaction test. The granite residual soil is prepared by layering and drying granite residual soil excavated on site under natural conditions. The particle size of the granite residual soil is less than 0.2 mm. The particle size of the oyster shell powder is less than 0.2 mm. The modified granite residual soil is filled in layers, with each layer having a loose thickness of no more than 50 mm. cm, during the rolling process, the adjacent wheel tracks overlap by more than 1 / 3, and the compaction degree is controlled at more than 95%; the bacterial enzyme seepage prevention layer (11) is formed by spraying bacterial enzyme treatment solution on the surface of the modified granite residual soil after compaction; the amount of bacterial enzyme treatment solution is 1.2 to 1.3 times the pore volume of the compacted granite residual soil; the reverse-wrapped geogrid layer (10) is formed by unidirectional geogrid of high-density polyethylene (HDPE) material, the unidirectional geogrid extends inward along the cross section of the roadbed to more than 0.9m into the fill material, and the reverse-wrapped length of the unidirectional geogrid is reserved outward as needed, but the reinforcement quality and construction convenience must be ensured.

2. The ecological roadbed structure based on microorganisms and waste oyster shells modified granite residual soil according to claim 1, characterized in that: The bacterial treatment solution is a mixture of Pasteurella multocida concentrate and a gelling solution, prepared by mixing Pasteurella multocida concentrate and gelling solution at a volume ratio of 1:1 to 2.

5. The Pasteurella multocida concentrate is obtained by processing Pasteurella multocida bacterial solution, and the urease activity of the Pasteurella multocida bacterial solution is 10 to 15 mmol / (L·min). The gelling solution includes calcium chloride solution and urea solution, and the molar concentrations of calcium chloride and urea in the gelling solution are equal and both are 0.5 to 1.5 M.

3. The ecological roadbed structure based on microorganisms and waste oyster shells modified granite residual soil according to claim 1, characterized in that: The modified ecological slope protection area (3) consists of, from bottom to top, oyster shell powder-vegetation base layer (9), oyster shell coarse aggregate layer (8), and vegetation layer (7); the oyster shell coarse aggregate layer (8) is an oyster shell coarse aggregate layer that has been treated with bacterial enzyme treatment solution for 3 to 5 times; the oyster shell coarse aggregate layer (8) is made of oyster shell coarse aggregate with a particle size of 2 to 4.75 mm; the thickness of the oyster shell coarse aggregate layer (8) is 3 to 5 cm.

4. The ecological roadbed structure based on microorganisms and waste oyster shells modified granite residual soil according to claim 1, characterized in that: The oyster shell powder-vegetated base layer (9) consists of geocells and oyster shell powder-nutrient soil filling the geocells; the oyster shell powder-nutrient soil is made by mixing oyster shell powder and nutrient soil at a mass ratio of 1~1.5:1000. The nutrient soil contains plant seeds; the oyster shell powder has a particle size of less than 0.2 mm; the thickness of the oyster shell powder-vegetation base layer is 3-5 cm; the vegetation layer is formed by the growth of plant seeds sown on the surface of the oyster shell coarse aggregate layer and plant seeds mixed in the nutrient soil, and the plant seeds are selected from one or more of bermudagrass seeds, ryegrass seeds, white clover seeds and tall fescue seeds.

5. The ecological roadbed structure based on microorganisms and waste oyster shells modified granite residual soil according to claim 2, characterized in that, The Pasteurella multocida concentrate is obtained by centrifuging and concentrating Pasteurella multocida bacterial solution; the volume ratio of the Pasteurella multocida concentrate to the Pasteurella multocida bacterial solution is 1:

10.

6. The ecological roadbed structure based on microorganisms and waste oyster shells modified granite residual soil according to claim 2, characterized in that, The Pasteurella multocida concentrate was prepared by the following steps: Step 1): Prepare liquid culture medium for Bacillus pasteurellii and inoculate and culture the bacteria until the urease activity of the Bacillus pasteurellii culture medium is measured to be 10~15 mmol / (L·min), then stop the culture. Step 2): Place the Bacillus pasteurellium culture obtained in Step 1) into a refrigerated centrifuge and centrifuge it. Set the centrifugation parameters to 10,000 rpm, 4°C and 15 min. Step 3): After centrifugation in Step 2), retain 1 / 10 of the volume of supernatant in each centrifuge tube. Use a long spoon to gently scrape the bacteria attached to the tube wall into the supernatant and stir gently to obtain Pasteurella multocida concentrate.

7. An ecological roadbed structure based on microorganisms and waste oyster shells modified granite residual soil according to claim 1 or 3, characterized in that, The bacterial enzyme treatment solution is prepared by mixing a bacterial enzyme solution and a cementing solution at a volume ratio of 1:1 to 2.5; the cementing solution includes a calcium chloride solution and a urea solution, wherein the molar concentrations of calcium chloride and urea in the cementing solution are equal and both are 2.0 to 2.5 M.

8. The ecological roadbed structure based on microorganisms and waste oyster shells modified granite residual soil according to claim 7, characterized in that, The bacterial enzyme solution is prepared by the following steps: Step 1): Prepare a culture medium for Bacillus pasteurellii and inoculate and culture the bacteria until the urease activity of the Bacillus pasteurellii culture is measured to be 10-15 mmol / (L·min), then stop the culture. Step 2): Use an ultrasonic crusher to ultrasonically crush the Bacillus pasteurellium culture obtained in Step 1), while using an ice bath method to keep the temperature of the culture during the crushing process below 50°C, until the OD600 value of the culture reaches 0.20~0.25 and then stop crushing. The output power of the ultrasonic crusher is not greater than 750 W. Step 3): Centrifuge the bacterial solution after the disruption in Step 2) using a centrifuge, and take the supernatant as the bacterial enzyme solution; Step 4): Dilute the bacterial enzyme solution to the target urease activity value.

9. An ecological roadbed structure based on microorganisms and waste oyster shells modified granite residual soil according to claim 1, characterized in that: The oyster shell powder-granite residual soil is made by mixing oyster shell powder and granite residual soil at a mass ratio of 1:

9.

10. An ecological roadbed structure based on microorganisms and waste oyster shells modified granite residual soil according to claim 2, characterized in that: The cementing solution contains equal molar concentrations of calcium chloride and urea, both of which are 1 M.

11. The construction method of the ecological roadbed structure based on microorganisms and waste oyster shell modified granite residual soil according to any one of claims 1-10, characterized in that, The construction method includes the following steps: 1) Construction preparation: On-site sampling and geotechnical tests were conducted to determine the specific gravity, liquid limit, plastic limit, permeability coefficient, natural moisture content, and optimum moisture content of the residual granite soil. Then, construction layout, material preparation, and site cleanup were carried out. 2) Drying treatment of granite residual soil: The granite residual soil excavated on site is piled in layers and dried in the natural environment. The soil layers are turned over regularly using mechanical equipment. After the granite residual soil is dry, a waterproof geomembrane is covered on its surface to keep the soil dry. 3) Surcharge preloading: After step 2) is completed, a layer of non-woven fabric, a layer of 10 cm thick filter layer and a layer of waterproof geotextile are laid from bottom to top on the surface of the proposed new roadbed; then, soil is filled on the waterproof geotextile for surcharge preloading. The surcharge preloading load is 150% to 200% of the design embankment load, and the surcharge preloading period is not less than 15 months. 4) Construction of the bottom isolation layer: After step 3) is completed, the surcharge preload, waterproof geotextile, filter layer and non-woven fabric are removed, the site is leveled, and then geocells are laid on the subgrade surface. Oyster shell fine aggregate is filled into the geocells to the elevation. Finally, the oyster shell fine aggregate is uniformly sprayed with a bacterial enzyme treatment solution prepared on site by mixing cementing liquid and bacterial enzyme solution every 24 hours. The treatment is repeated 5 to 10 times to mineralize and form the bottom isolation layer. 5) Construction of the modified granite residual soil filling area: After step 4) is completed, a geogrid is laid on the surface of the bottom isolation layer. Then, the prepared cementing liquid is mixed on-site with Bacillus pasteurellium concentrate and bacterial enzyme solution to prepare bacterial treatment solution and bacterial enzyme treatment solution. The pre-prepared oyster shell powder-granite residual soil is mixed and stirred on-site with the bacterial treatment solution to prepare modified granite residual soil. The evenly mixed modified granite residual soil is filled on the geogrid, compacted with a road roller, and covered with a waterproof film for curing for 20-28 hours. Then, every 20-28 hours, the bacterial enzyme treatment solution is sprayed on the compacted road surface and covered with a waterproof film for curing. After spraying and curing 5-7 times, the geogrid is wrapped around the compacted modified granite residual soil. After wrapping, a layer of modified granite residual soil is formed. Then, the next layer of modified granite residual soil is constructed until the design height is reached. 6) Construction of oyster shell powder-vegetated base layer in modified ecological slope protection area: After step 5) is completed, geocells are laid on the slope surface of modified granite residual soil filling area. The prepared oyster shell powder and nutrient soil are mixed on site and filled into the geocells to the elevation. The nutrient soil contains one or more of the following: bermudagrass seeds, ryegrass seeds, white clover seeds, and tall fescue seeds. 7) Construction of the oyster shell coarse aggregate layer in the modified ecological slope protection area: After step 6) is completed, oyster shell coarse aggregate is filled onto the surface of the oyster shell powder-vegetated base layer to the elevation to form the oyster shell coarse aggregate layer. Then, a bacterial enzyme treatment solution is prepared on-site by mixing a cementing liquid and a bacterial enzyme solution. The bacterial enzyme treatment solution is sprayed evenly onto the oyster shell coarse aggregate layer every 24 hours for 3-5 treatments to mineralize and form the oyster shell coarse aggregate layer. Then, a drainage structure is constructed at the bottom of the slope. Plant seeds are sown on the surface of the oyster shell coarse aggregate layer. The plant seeds can be one or more of the following: bermudagrass seeds, ryegrass seeds, white clover seeds, and tall fescue seeds. 8) Construction of strength compensation layer and pavement structure layer: After step 7) is completed, strength compensation layer and pavement structure layer are constructed sequentially on the top surface of modified granite residual soil filling area.

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