A method for improving sand consolidation uniformity and strength by alternately injecting bacteria and enzymes

Abstract

The present invention relates to a method for improving the uniformity and strength of sand consolidation by alternately grouting bacteria and enzymes, and belongs to the technical field of sand consolidation. This method deposits the product on the surface and joints of sand particles through the microbial induced calcium carbonate precipitation (MICP) technical process to form preliminary strength, and then utilizes the urease induced calcium carbonate precipitation (EICP) technical process to fill the gaps between the particles, or adopts a process route of first EICP and then MICP, that is, first reducing the gaps between sand particles through EICP, and then enhancing the bonding force between particles with the help of MICP. This innovative process effectively overcomes the technical defects of disordered deposition of products in the simple mixed combination process of bacteria and enzymes, and achieves a significant improvement in the strength of sand columns. The alternating grouting process of bacteria and enzymes in the present invention has the characteristics of uniform product distribution, high structural density, and excellent mechanical properties.

Description

Technical Field

[0001] The invention belongs to the technical field of sand consolidation, and more specifically, relates to a method for improving the uniformity and strength of sand consolidation by alternately perfusing bacteria and enzymes. Background Art

[0002] With the acceleration of urbanization and the continuous expansion of infrastructure construction, sand, a widespread foundation material, has become increasingly important for its mechanical properties and stability, crucial to engineering safety. However, natural sand often suffers from low bearing capacity, liquefaction, and significant settlement. These characteristics can pose serious safety risks under dynamic loads such as earthquakes and traffic vibrations. Therefore, the development of effective sand consolidation technologies is urgently needed to improve foundation safety and ensure engineering security.

[0003] Traditional sand fixation methods include tamping, chemical and plant-based sand fixation. The tamping method uses heavy compacting equipment to increase the density of sand. The construction is simple but the effect is limited, and it may cause vibrations to surrounding structures. The chemical method is to add cement or lime to the sand to significantly increase the bearing capacity, but the cost is high and may cause groundwater and ecological pollution. The plant-based sand fixation method uses plant roots to improve the soil structure, but the effect is slow to show and is limited by environmental conditions. At the same time, emerging sand fixation technologies, such as biological sand fixation technology, have shown broader application prospects and better performance. Compared with traditional sand fixation methods, the microorganisms or enzymes used in biological sand fixation technology are derived from soil or plants. They have the characteristics of low energy consumption, environmental friendliness and low cost, and solve the problems of low cohesion and poor water retention between sand particles.

[0004] In recent years, bioinduced carbonate precipitation (BICP), an emerging bioremediation technology for geotechnical reinforcement, has gained widespread recognition and application both domestically and internationally. It includes two main categories: microbial induced calcium carbonate precipitation (MICP) and urease-induced calcium carbonate precipitation (EICP). MICP primarily uses microorganisms as indirect catalysts, utilizing urease, produced by the metabolic activity of specific microorganisms, to decompose urea, releasing ammonia. This, in turn, elevates the pH of the environment, promoting the binding of calcium ions with carbonate ions, another decomposition product, to form calcium carbonate precipitate (biocement). This is often used as a bioremediation technique for sand consolidation. EICP, on the other hand, uses urease as a direct catalyst. Because the process involves no living organisms, it can be classified as a biomimetic mineralization technique. BICP has been applied to numerous geotechnical engineering problems, such as stratum grouting and sealing, stone or concrete repair, sandy foundation soil improvement, construction site dust suppression, heavy metal stabilization, and underground pollution control. However, with its widespread use, its shortcomings have become increasingly apparent. For example, the formation of biofilms during MICP applications negatively impacts grouting processes, resulting in prolonged treatment cycles and uneven consolidation. EICP grouting technology suffers from rapid surface sealing and poor deep-layer consolidation. Furthermore, most soil consolidation tests involving MICP and EICP rely on mixing the cementing fluid with pure sand, which lacks practical value.

[0005] Therefore, there is no mature practice on how to realize biological reinforcement of rock and soil. There is an urgent need for a sand consolidation process that can improve the uniformity and strength of sand consolidation to effectively consolidate sand and soil, improve the consolidation strength and uniformity, and have the advantages of being environmentally friendly, sustainable, and having a short processing cycle.

[0006] When a single MICP technology is applied, it is easy to have uneven sand consolidation effects and insufficient mechanical properties. This is mainly because the distribution of microorganisms in sand is usually uneven, and the microbial density and metabolic activity in different areas vary greatly, resulting in local mineralization reactions, which in turn affects the uniformity of the distribution of sedimentary products with grouting depth. In addition, by-products (such as biofilms or additional polymers, etc.) may be produced during microbial metabolism. These by-products can cause biological blockages and further lead to uneven deposition. In the paper "Experimental Study on the Solidification Effect of Urease-Deposited Calcium Carbonate in Soil", scholars found that the calcium carbonate content of the specimens reinforced with bacteria was mainly distributed in the space area near the outside of the specimen, while the distribution of calcium carbonate in the middle of the entire specimen area was extremely uneven. The advantage of MICP is that the negatively charged groups on the surface of the microorganisms used can enrich the Ca in the environmental solution surrounding the cells. 2+ It also provides nucleation sites for the formation of calcium carbonate, which is conducive to the formation of calcium carbonate crystals, and the products are mostly attached to the surface of sand particles.

[0007] In contrast, EICP technology utilizes free urease extracted from leguminous plants. The resulting calcium carbonate crystals are smaller in size and are distributed between sand particles. However, the resulting calcium carbonate is brittle and not conducive to improving strength. EICP also offers advantages such as low cost, simple preparation, and stable product.

[0008] In the invention patent "A method for solidifying desert aeolian sand by combining bacteria and enzymes" with publication number CN 116769681A, a bacteria-enzyme combination method for solidifying desert aeolian sand is provided, which combines two types of Bacillus, urease and carbonic anhydrase to improve the efficiency and effect of solidifying desert aeolian sand. In this method, Bacillus pasteurianus, Bacillus colloidus that can secrete carbonic anhydrase, urease and a cementing fluid are first mixed in proportion, filled into a solidification culture medium, and then solidified and naturally dried for a certain period of time to obtain a solidified sand column. In the process of solidifying desert aeolian sand, this method has the advantages of a shorter solidification cycle, a faster solidification rate, and a larger increase in the unconfined compressive strength of the solidified sample (up to 1.96 times) compared with traditional single MICP and EICP technologies. However, this mixing process may be limited by factors such as economy and ease of operation during large-scale application.

[0009] Both MICP and EICP have limitations in their environmental adaptability. Microbial cultivation in MICP is complex, and the bacteria have specific requirements for their survival environment. Their activity is difficult to control, and they may not function properly in certain extreme environments (such as anaerobic conditions and low pH). While urease activity in EICP applications is unaffected by oxygen concentration, changes in ambient temperature can significantly affect the urease's catalytic action, potentially inhibiting the reaction at best and causing denaturation and inactivation at worst.

[0010] MICP and EICP technologies each have advantages and disadvantages in terms of curing effectiveness and applicability. While existing technologies utilize a combined bacterial and enzyme process, they simply mechanically mix the bacterial and enzyme solutions once, failing to fully utilize the synergistic advantages of MICP and EICP technologies in sand consolidation applications, including their enhanced microstructure, deposition sites, distribution, and environmental adaptability. This results in unstable mineralization reaction efficiency and curing effectiveness, as well as limited applicability. Summary of the Invention

[0011] The present invention provides a method for improving the uniformity and strength of sand consolidation by alternating grouting of bacteria and enzymes. The method deposits the product on the surface of sand particles through the microbial induced calcium carbonate precipitation technology MICP process, and then uses the urease induced calcium carbonate precipitation technology EICP process to fill the gaps between the particles, or adopts a process route of first EICP and then MICP, that is, first reducing the gaps between sand particles through EICP, and then using MICP to enhance the bonding force between particles. This innovative process effectively overcomes the technical defect of disordered deposition of products in the simple mixed combination process of bacteria and enzymes, and achieves a significant improvement in the strength of sand columns. The alternating grouting process of bacteria and enzymes in the present invention has the characteristics of uniform product distribution, high structural density, and excellent mechanical properties, providing a new technical solution for geotechnical engineering and ecological restoration projects that is environmentally friendly, sustainable, and has a short treatment cycle.

[0012] According to the purpose of the present invention, a method for improving the uniformity and strength of sand consolidation by alternating bacterial and enzyme perfusion is provided, in which microbial mineralization and biomimetic mineralization are carried out alternately until the sand column is sealed; the microbial mineralization is specifically as follows: the mineralized bacterial solution is perfused into the sand column, and after standing for 1h-3h, the cementing solution is perfused and allowed to stand for 10h-15h for mineralization; the biomimetic mineralization is specifically as follows: the urease solution is perfused into the sand column, and after standing for 1h-3h, the cementing solution is perfused and allowed to stand for 10h-15h for mineralization.

[0013] Preferably, the last step is to carry out microbial mineralization and biomimetic mineralization simultaneously, specifically, using a mixture of mineralizing bacteria solution and urease solution for perfusion, letting it stand for 1h-3h, and then perfusing the cementing solution and letting it stand for 10h-15h for mineralization.

[0014] Preferably, the binder is a mixed solution of urea and calcium chloride.

[0015] Preferably, the molar ratio of the urea to calcium chloride is 1:(0.5-2).

[0016] Preferably, the optical density value OD of the mineralized bacterial solution is 600 The urease solution is a plant urease extract with a concentration of 30-100 g / L.

[0017] Preferably, the volume ratio of the mineralized bacteria solution to the urease solution in the mixed solution is 1:(0.5-9).

[0018] Preferably, the mineralized bacterial solution is a Bacillus pasteurianus bacterial solution, a Bacillus subtilis bacterial solution, a Bacillus sphaericus bacterial solution, a Bacillus mucilaginosus bacterial solution or an alkaliphilic Bacillus bacterial solution.

[0019] Preferably, the grouting method is gravity flow grouting or pressure grouting.

[0020] Preferably, the temperatures of the microbial mineralization and biomimetic mineralization are each independently selected from 10°C to 30°C.

[0021] In general, the above technical solutions conceived by the present invention have the following technical advantages compared with the existing technology:

[0022] (1) The bacterial and enzyme combined sand consolidation process disclosed in the present invention achieves a dual reinforcement effect by regulating crystal morphology and organic matter filling through alternating grouting, thereby significantly improving the strength of the sand column. Compared with the traditional single grouting method, the grouting process of first using bacterial solution and then enzyme solution, the first use of bacterial solution will cause large particles of calcium carbonate to form on the surface and joints of sand particles, and the subsequent addition of enzyme solution can further cause calcium carbonate to form on the surface of sand particles, and the gaps between sand particles are filled with organic matter and calcium carbonate. At the same time, the organic matter also has a cementing effect, making the connection between particles inside the sand column tighter; in the present invention's alternating grouting process of first using enzyme solution and then using bacterial solution, the enzyme solution pretreatment causes organic matter and small-sized calcium carbonate crystals to evenly fill the gaps between sand particles, and the subsequent bacterial solution perfusion uses these areas as nucleation sites to generate large-sized rhombohedral grains.

[0023] (2) The bacterial-enzyme combined sand consolidation process disclosed in the present invention can improve the uniformity, strength and efficiency of sand consolidation. Compared with the traditional single MICP method, the calcium carbonate crystals produced are larger in size and tend to aggregate on the surface and contact points of the particles, which has little effect on pore filling, resulting in most of the bacterial solution and cementing liquid injected into the grouting first accumulating at the bottom of the sand column to form calcium carbonate, causing uneven sand consolidation. The participation of protein-like organic matter in EICP makes the generated calcium carbonate smaller in size and distributed on the surface and gaps of the sand particles. At the same time, the organic matter plays a role of bonding and filling, so that the gaps between the sand particles are filled more densely. The method of carrying out bacterial-enzyme sand consolidation separately according to the present invention can not only generate large-particle calcium carbonate crystals, but also play a bonding role of organic matter, thereby filling the sand column more densely, and enabling the sand column to achieve higher strength and toughness in a shorter period of time.

[0024] (3) The bacterial-enzyme combined sand consolidation process disclosed in the present invention can improve the uniformity of sand consolidation. This process achieves the effect of uniform sand consolidation by uniformly generating high-content calcium carbonate in different parts of the sand column (upper, middle and lower parts).

[0025] (4) The bacterial-enzyme combined sand consolidation process disclosed in the present invention can significantly improve the strength of sand consolidation. The process uses a mixed bacterial-enzyme solution for perfusion in the last step, which can further promote the formation of calcium carbonate inside the sand column. At the same time, the generated calcium carbonate and the added organic matter can cement and fill the sand column more densely, thereby significantly improving the strength of the sand column.

[0026] (5) The bacterial-enzyme combined sand consolidation process disclosed in the present invention significantly improves the environmental adaptability of the mineralization process. The mineralization efficiency of this process in an anaerobic and low-temperature environment is better than that of a single MICP method or EICP method.

[0027] (6) The present invention can effectively consolidate sandy soil, improve consolidation strength, uniformity and environmental adaptability, and has the advantages of being environmentally friendly, sustainable, and having a short treatment cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is the unconfined compressive strength of sand columns with different treatments.

[0029] Figure 2 The microscopic morphology of sand columns with different treatments.

[0030] Figure 3 The microscopic morphology of glass beads after grouting and bonding under different mineralization process conditions.

[0031] Figure 4 Effects of different temperatures on calcium carbonate yield: (a) 10℃; (b) 20℃; (c) 30℃. DETAILED DESCRIPTION

[0032] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0033] A sand consolidation process for improving the uniformity and strength of sand consolidation by combining bacteria and enzymes, comprising the following steps:

[0034] (1) Prepare materials: Use PVC pipe to make a cylindrical mold with a length of 11-11.5 cm and an inner diameter of 36.9 mm, and cut plastic film to the appropriate size;

[0035] (2) Make a sand-consolidating mold: Place a perforated rubber plug and permeable stone at the bottom of the PVC tube, and press the inner wall against a plastic film coated with Vaseline to isolate the sand particles from the PVC tube for subsequent demolding. Evenly sprinkle 100g of clean quartz sand into the PVC tube and gently tap the outer wall with a rubber hammer until the sand is densely packed. The height of the sand in the mold is H = 60mm, and then press the permeable stone on top.

[0036] (3) Grouting treatment: Inject clean water from the top of the sand column to saturate the sample. Inject a bacterial solution (referred to as bacterial solution) or a plant urease solution (referred to as enzyme solution) of 1 times the pore volume of the sand, about 30 ml, and let it stand for 2 hours to ensure that the bacteria / urease are fully diffused in the sand column and adsorbed on the surface of the sand particles. Then inject the same volume of cementing fluid (a mixed solution containing 0.5M urea and 0.5M calcium chloride) and carry out biomineralization for 12 hours. Every four cementing fluid groutings complete a round of biomineralization treatment cycle. Fresh bacterial solution / enzyme solution must be added again and the above steps repeated. A total of more than two stages of biomineralization are completed, in which the first stage (1-2 rounds) uses bacterial solution for grouting and the second stage (3-4 rounds) uses enzyme solution for grouting; or the first stage (1-2 rounds) uses bacterial solution for grouting and the second stage (3-4 rounds) uses enzyme solution for grouting;

[0037] (4) Demolding and drying: The sample densely filled with biocement is demolded, washed and dried, and then analyzed for physical and chemical indicators.

[0038] The following are specific embodiments

[0039] Example 1: Comparison of the effects of different grouting methods on the unconfined compressive strength and calcium carbonate content of bioreinforced sand columns

[0040] The present invention provides a sand consolidation process for improving the uniformity and strength of sand consolidation by combining bacteria and enzymes, comprising the following steps:

[0041] Step S1: Expansion Culture of Bacterial Liquid: Bacillus pasteurianus powder is added to 1 L of high-temperature sterilized yeast extract-ammonium salt medium (i.e., YE-NH4 medium, containing 20 g yeast extract, 10 g (NH4)2SO4, 12 μg / L MnSO4·H2O, 24 μg / L NiCl2·6H2O, and adjusted to pH 8.5). The culture is activated over 36-48 hours to form a mother culture (first generation culture). The mother culture is then inoculated into an expansion medium at a ratio of 1:100 and continued for 12-18 hours. The bacterial culture is completed when the medium becomes noticeably turbid or the OD600 value is 0.8-2.0.

[0042] Extraction of plant urease: (1) Pretreatment of plant seeds: Weigh an appropriate amount of soybean seeds and place them in an oven at 40°C for 6 hours to dry. Then, place them in a grinder and grind them to obtain soybean powder. After sieving (60-150 mesh) to remove soybean powder with large particle size, the sieved soybean powder is placed in a low-temperature dry environment for storage; (2) Extraction: Weigh 5g soybean powder and place it in a beaker. Add 50ml of distilled water to the beaker and stir continuously with a magnetic stirrer for 30 minutes. Place the uniformly stirred soybean powder solution in a Place in a low temperature environment (4°C) and let it stand for 3 hours; the optimal solid-liquid ratio used for extraction is 1g:10mL (soybean powder mass unit g: distilled water volume unit mL); (3) Centrifugation: The soybean powder solution is divided into centrifuge tubes, and the same mass of solution is poured into each centrifuge tube. The tubes are placed in a centrifuge and centrifuged at room temperature (centrifugal speed 3000rpm, centrifugal time 15min). After centrifugation, the supernatant is collected and the creamy oil floating on the surface of the supernatant is filtered out with gauze to obtain the plant urease solution.

[0043] Step S2: Bacteria-enzyme combined grouting process: inject a bacterial solution (referred to as bacteria solution) or a plant urease solution (referred to as enzyme solution) of about 30 ml with a volume 1 times the pore volume of the sand, let it stand for 2 hours to ensure that the bacteria / urease are fully diffused in the sand column and adsorbed on the surface of the sand particles, and then inject the same volume of cementing fluid (a mixed solution of 0.5M urea and 0.5M calcium chloride) for 12 hours of biomineralization. Every four cementing fluid groutings complete a round of biomineralization treatment cycle, and the bacteria solution / enzyme solution needs to be replenished again before repeating the above steps. A total of no less than four rounds of biomineralization are completed, of which the 1st-2nd round / the 3rd-4th round uses bacteria solution for grouting, and correspondingly, the 3rd-4th round / the 1st-2nd round uses enzyme solution for grouting.

[0044] Step S3: Obtain the solidified sand column and analyze its compressive strength and calcium carbonate content in different parts.

[0045] Methods 1-9 in Table 1 below study the effects of different grouting methods on unconfined compressive strength and calcium carbonate content in different parts.

[0046] In step 3 of the technical solution, there are three stages of biological grouting treatment. The grouting of bacterial liquid / enzyme liquid is carried out according to methods 1-9 (Table 1). The rest of the methods are the same as above. The results are shown in Figure 1 Table 2:

[0047] Table 1 Sand column grouting process methods for the control group and experimental group

[0048]

[0049] Depend on Figure 1As can be seen, the compressive strengths of Methods 1, 4, and 5 were comparable, exceeding those of Methods 2 and 3. Method 1 was blocked after only four grouting cycles, while the combined bacterial and enzyme grouting process allowed for continued grouting, increasing the number of grouting cycles. After five grouting cycles, the strength of the alternating bacterial and enzyme grouting processes (Methods 8 and 9) was significantly higher than that of the other methods by more than 100%. This demonstrates that optimizing the grouting process can achieve higher mechanical strength in a shorter period of time.

[0050] Table 2 Calcium carbonate content in various parts of sand column in different treatment groups

[0051]

[0052] Testing the calcium carbonate product content in various locations of the sand column specimens (Table 2) revealed that the experimental group specimens exhibited significant advantages in both uniformity and product content. For the two-stage grouting test, the calcium carbonate products in the Method 4 and Method 5 specimens were more uniform than those in the control group (Method 1 and Method 2). Furthermore, while the control group (Method 3) exhibited better uniformity, its total mineralized product content was low, resulting in lower strength. Furthermore, the higher uniformity of the sand columns grouted by Methods 4 and 5 allowed them to achieve compressive strengths similar to those achieved by Method 1, even though the total amount of mineralized calcium carbonate produced was lower than that of Method 1. For the three-stage grouting test, compared to the control group (Method 6 and Method 7), the total calcium carbonate content of the sand columns in the experimental group (Method 8 and Method 9) significantly increased while maintaining uniformity comparable to that of the control group (Method 6-7), a phenomenon consistent with their higher strength performance. These experiments demonstrate that the combined bacterial and enzyme-assisted grouting method offers the combined advantages of both uniformity and high mineralized product content.

[0053] The advantages of the above-mentioned bacteria-enzyme combined alternating grouting in terms of uniformity and strength are due to the optimization effect of this process on the microstructure of the specimens ( Figure 2 ). For the specimen of method 1 of pure EICP mineralization, the organic matter in the enzyme solution participates in the mineralization process, making the generated spherical calcium carbonate smaller in size, mainly distributed on the surface and gaps of the sand particles. At the same time, the organic matter plays a role of bonding and filling, making the gaps between the sand particles filled more densely. However, the easy blocking characteristics of the EICP grouting process greatly limit the development of the final specimen strength. For the specimen of method 7 of pure MICP mineralization, the rhombohedral calcium carbonate crystals generated by mineralization are larger in size and easily aggregated on the surface and contact points of the particles, which has little effect on pore filling. Therefore, there are larger gaps between the particles ( Figure 2). The above characteristics of MICP also cause most of the bacterial solution and cementing fluid injected into the grouting to accumulate at the bottom of the sand column first to form calcium carbonate, resulting in uneven sand consolidation effect. Compared with the separate EICP and MICP processes, the simple mixed perfusion process method 6 of the combined bacteria and enzyme combines the advantages of both. The spherical and diamond-shaped calcium carbonate generated in the sample are distributed on the surface of the sand particles and in the gaps between the particles. Furthermore, compared with the simple mixed bacteria and enzyme combined process, in the specimens of the alternating perfusion bacteria and enzyme combined methods 8 and 9, the deposited calcium carbonate not only formed a better bond on the surface of the sand particles, but also the mineralized products in the gaps between the sand particles showed higher compactness, which confirmed that the alternating perfusion bacteria and enzyme combined process, through the synergistic advantage of optimizing the grouting sequence, can break through the limitations of a single MICP or EICP, and has the effect of optimizing the microstructure of the material.

[0054] To further verify the optimization effect of the above-mentioned alternating perfusion of bacteria and enzymes on microstructure, the sand particles in the above experiment were replaced with glass beads, which can more clearly reveal the distribution characteristics of the products under various process conditions. Compared with single MICP, single EICP or bacteria-enzyme mixed perfusion, the specimens with alternating perfusion of bacteria and enzymes showed a denser and more uniform product distribution on the surface and gaps of the sand particles ( Figure 3 ). In the method where enzyme solution participates in mineralization, the product will be generated in the gap, while in the method where only bacterial solution participates in mineralization, the product will be concentrated on the surface of the particles, such as Figure 3 As shown in the red circle. Specifically, in the enzyme-first, then bacterial process (method 4), enzyme pretreatment allows organic matter and small calcium carbonate crystals to evenly fill the interstices between sand particles. Subsequent bacterial perfusion uses these areas as nucleation sites to produce large rhombohedral crystals. In the bacterial-first, then enzyme process (method 5), the initial application of bacterial solution results in the formation of large calcium carbonate particles on the surfaces and joints of the sand particles. The subsequent addition of enzyme solution further increases the formation of calcium carbonate on the sand particle surfaces, filling the interstices between the sand particles with organic matter and calcium carbonate. The organic matter also acts as a cementing agent, making the internal connections of the sand column tighter. In summary, the alternating bacterial-enzyme process is the key to improving the strength and uniformity of sand columns.

[0055] Example 2: Comparison of the effects of different ambient temperatures on biomineralization deposition rates

[0056] This implementation case is based on an aqueous solution mineralization test, which aims to demonstrate the mineralization effect of the bacteria-enzyme combination technology under different temperature mineralization conditions, thereby verifying its adaptability to sand consolidation applications under different temperature conditions. By using three different treatment methods: mixing a single bacterial solution, a 1:1 volume ratio mixed solution of bacterial solution and enzyme solution, and a single enzyme solution with a cementing solution (containing 0.5M calcium chloride and 0.5M urea), the volume ratio of the bacteria / enzyme solution to the cementing solution is 1:5. The specific experimental ratio is shown in Table 3. Place it in an oscillating incubator with a temperature gradient of 10°C, 20°C and 30°C, respectively. React at a speed of 90rpm for 2h, 6h and 24h, then take it out and measure the yield of calcium carbonate (determined by the acid washing method: 5% hydrochloric acid is used to wash the mineralized precipitate) to study the effect of ambient temperature on the yield of calcium carbonate under different treatment conditions.

[0057] Table 3 Aqueous solution experiments at different temperatures

[0058]

[0059] like Figure 4 As shown in (a), when the ambient temperature is 10°C, at 2 hours, the mineralized deposition of enzymes and bacterial enzyme complexes is significantly higher than that of bacteria (P < 0.05). At 6 hours, the order of mineralized deposition is: bacterial enzyme complex > bacteria > enzyme. Low temperature limits the mineralization rate of enzymes, but has a smaller limiting effect on bacterial enzyme complexes and bacteria. Figure 4 As shown in (b), when the ambient temperature is 20℃, the mineralization deposition of bacteria is significantly higher than that of enzyme and bacterial enzyme composite at 2h and 6h (P<0.05). Figure 4 As shown in (c), at an ambient temperature of 30°C, the order of mineralized deposition after 2 hours was: enzyme > bacterial-enzyme combination > bacteria. At 6 hours, the mineralized deposition of the bacterial-enzyme combination surpassed that of the enzyme (P < 0.05). The mineralization rate of the enzyme increased with increasing temperature. The mineralization rates of the bacterial-enzyme combination, bacteria, and enzyme were highest at 10°C, 20°C, and 30°C, respectively. These results demonstrate that the combined use of bacteria and enzymes can improve the environmental adaptability of biosand consolidation technology and maintain substantial mineralization efficiency at low temperatures.

[0060] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements 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 method for improving the uniformity and strength of sand consolidation by alternate perfusion of bacteria and enzymes, characterized in that: The microbial mineralization and biomimetic mineralization are carried out alternately until the sand column is blocked; the microbial mineralization is specifically as follows: the mineralized bacterial solution is injected into the sand column, and after standing for 1 hour to 3 hours, the cementing solution is injected and the sand column is allowed to stand for 10 hours to 15 hours for mineralization; the biomimetic mineralization is specifically as follows: the urease solution is injected into the sand column, and after standing for 1 hour to 3 hours, the cementing solution is injected and the sand column is allowed to stand for 10 hours to 15 hours for mineralization; The last step is to carry out microbial mineralization and biomimetic mineralization simultaneously. Specifically, a mixture of mineralizing bacteria solution and urease solution is injected, and after standing for 1-3 hours, the cementing solution is injected and allowed to stand for 10-15 hours for mineralization. The optical density value OD of the mineralized bacterial solution 600 is 0.8-2.0; the urease solution is a plant urease extract with a concentration of 30-100 g / L; The volume ratio of the mineralized bacteria solution to the urease solution in the mixed solution is 1:(0.5-9).

2. The method for improving the uniformity and strength of sand consolidation by alternate perfusion of bacteria and enzymes as claimed in claim 1, characterized in that: The binder solution is a mixed solution of urea and calcium chloride.

3. The method for improving the uniformity and strength of sand consolidation by alternate perfusion of bacteria and enzymes as claimed in claim 2, characterized in that: The molar ratio of the urea to the calcium chloride is 1:(0.5-2).

4. The method for improving the uniformity and strength of sand consolidation by alternate perfusion of bacteria and enzymes as claimed in claim 1, characterized in that: The mineralized bacterial solution is Bacillus pasteurianus bacterial solution, Bacillus subtilis bacterial solution, Bacillus sphaericus bacterial solution, Bacillus colloids bacterial solution or Bacillus alkaliphilus bacterial solution.

5. The method for improving the uniformity and strength of sand consolidation by alternate perfusion of bacteria and enzymes as claimed in claim 1, characterized in that: The grouting method is gravity flow grouting or pressure grouting.

6. The method for improving the uniformity and strength of sand consolidation by alternate perfusion of bacteria and enzymes as claimed in claim 1, characterized in that: The temperatures of the microbial mineralization and biomimetic mineralization are independently selected from 10°C to 30°C.

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