CN111893988A - A kind of microbe-induced silty fine sand consolidation soft soil roadbed ecological improvement method - Google Patents

Abstract

The invention provides a microorganism-induced powder fine sand consolidation soft soil roadbed ecological improvement method, wherein the microorganism adopts Bacillus pasteurii, the strain starts as freeze-dried powder, and the bacteria are activated and cultured in the culture solution to obtain the Bacillus pasteurii Concentrate; then mix silt and fine sand into the soft soil, and the mixing ratio of silt and fine sand is 10-20%, and the silt and fine sand provides large-diameter aggregate for the soft soil road; mix the Bacillus pasteurii concentrate into the nutrient solution Inject the sand subgrade into the middle, and then inject the consolidation liquid until the subgrade does not reach the expected target. The invention applies interdisciplinary and uses biochemical technology to treat the soft soil roadbed, overcomes the problems of high pollution and high energy consumption of the traditional physical and chemical methods to deal with the roadbed, and can not only realize the strengthening treatment of the soft soil roadbed, but also reduce environmental pollution and pollution. energy consumption issues.

Description

A kind of microbe-induced silty fine sand consolidation soft soil roadbed ecological improvement method

technical field

The invention relates to the technical field of microbe-induced calcium carbonate precipitation reinforcement roadbed, in particular to a microbe-induced silty sand consolidation soft soil roadbed ecological improvement method.

Background technique

Soft soil subgrade, under the reciprocating action of increasing traffic load (high speed, heavy load), its fatigue life and working performance are not optimistic. If the bearing capacity of the subgrade soil is degraded and insufficient, or even liquefies, it may cause engineering disasters related to liquefaction, such as subsidence of subgrade, floating of underground pipes and tunnels, slope instability, and excessive erosion of coasts or river banks. affect its transportation function.

The traditional liquefaction roadbed remediation methods need to be improved and improved. For example, geotextile reinforcement technology has the problem of insufficient durability; chemical grouting based on cement, lime or organic glue is a high energy consumption and high emission industry; and physical reinforcement methods such as subgrade soil replacement, pile foundation and dynamic compaction are technically economical. Moreover, the construction cost in the built-up area is high, and the large-scale construction equipment is limited. Mechanical compaction and chemical grouting are the two most widely used methods for soil reinforcement treatment, but their high cost, high energy consumption, and the shortcomings of environmental pollution and damage have prompted the exploration of new soil reinforcement technologies.

SUMMARY OF THE INVENTION

The problem to be solved by the present invention is to provide a microorganism-induced silty sand consolidation soft soil roadbed ecological improvement method in view of the deficiencies of the above technologies. The microorganism adopts Bacillus Pasteurella, which is a non-pathogenic bacteria. When using urea-hydrolyzed microorganisms to induce calcium carbonate precipitation, there is no need to introduce foreign microorganisms, which helps to maintain the original soil ecological environment, and in a certain harsh environment ( Such as, acid-base, high salinity, etc.) conditions, can maintain strong biological activity. First, mix the silty sand into the soft soil subgrade to improve the soil structure of the subgrade. The soil mixed with enough silty sand not only contains a certain amount of coarse particles to make it have sufficient strength and water stability, but also contains a certain amount of The fine particles can bond the coarse particles together, but the fine sand is easy to loosen and has poor resistance to scouring by flowing water. The calcium carbonate precipitate produced by the microorganism-induced calcium carbonate deposition (MICP) process has a certain cementing function, which can bond the sand particles together and improve the engineering performance of the soil. This technology can significantly improve the strength, stiffness, and permeability of soil. , and compared with the traditional soil improvement process, its low energy consumption, low disturbance, and environment-friendly characteristics are more in line with the concept of sustainable development.

The technical scheme adopted by the present invention for solving the problems existing in the prior art is as follows:

A method for ecological improvement of soft soil roadbed by microbe-induced silt and fine sand consolidation is characterized in that: firstly, the silty fine sand is mixed with soft soil particles to improve the structure of the roadbed soil, and secondly, bacterial liquid, urea and calcium are transferred to the sandy soil Therefore, the pores of the sand, especially the sand particles, are filled and cemented with calcium carbonate, and the cemented crystallization of calcium carbonate rapidly precipitated in the pores of the sand can improve the consolidation of the soft soil roadbed and increase the bearing capacity. The mechanical properties of the subgrade have been greatly improved. The specific steps are as follows:

Step 1. Activation and cultivation of microorganisms: The microorganisms are Bacillus Pasteurella, an aerobic gram-positive bacteria that can produce a large amount of urease during the metabolic process. Bacterial activation and cultivation to obtain pasteurized bacillus concentrate;

Step 2. Add silt and fine sand: Mix silt and fine sand into the soft soil. The mixing ratio of silt and fine sand should be 10-20%. The silt and fine sand mainly provides large-sized aggregate for the soft soil road, and its purpose is to improve the roadbed. Soil structure, improve subgrade strength;

Step 3. Mix the Bacillus pasteurii concentrate into the nutrient solution and inject it into the sand subgrade: the bacterial solution and the nutrient solution are continuously injected into the soft soil subgrade in the longitudinal direction. The main purpose of the step is to activate the biological activity of Pasteurella and soil microorganisms as soon as possible, and to use the nutrient solution to spread the Pasteurella to the soft soil subgrade, so as to avoid excessive concentration of bacteria;

Step 4. Injecting the consolidation solution: This step is to provide hydrolyzed substances and calcium ions for the microorganisms. The consolidation solution is continuously injected into the soft soil subgrade in the longitudinal direction. consistent;

Step 5. Repeat steps 3 to 4. After 5 times, check the consolidation of the subgrade: if the subgrade does not reach the expected target, repeat steps 3 and 4. Check the consolidation of the subgrade every time it is repeated, and proceed to the next step if the target is reached.

The culture medium used for activation and culture in the step 1 is ATCC 1376 NH4-YE culture medium, the temperature of the culture medium is controlled at 30°C, PH8-9, and the culture time should be 17-19h. The bacteria should be stored in a refrigerator at 4°C, and the storage time should not exceed 30 days.

In the step 3, after injecting the bacterial liquid and the nutrient solution, it needs to stand for 1-2 hours.

The components of the nutrient solution in the step 3 are mainly the mixed solution of calcium chloride and urea, the concentration of CaCl ₂ is 0.60mol/L, and the concentration of urea is 0.65mol/L.

In the step 4, the bacterial solution is poured once and then the condensed solution is poured for five times, and each time the condensed solution is poured, the solution is allowed to stand for 6-8 hours.

The components of the consolidation solution in the step 4 are mainly the mixed solution of calcium chloride and urea, the concentration of CaCl is _0.60mol /L, and the concentration of urea is 0.65mol/L. The prepared consolidation solution should be used as soon as possible to avoid solidification. The composition of the condensate is deteriorated and the effect is affected.

The expected target in the step 5 adopts the CBR value as the inspection standard, and the expected target is achieved when the CBR value is not less than 4%.

The present invention has the following advantages:

The invention applies interdisciplinary and uses biochemical technology to treat the soft soil roadbed, and overcomes the problems of high pollution and high energy consumption of the traditional physical and chemical methods to treat the roadbed. Environmental pollution and energy consumption issues. The content of the present invention can not only consolidate the soft soil roadbed improvement method with silty fine sand, but also because the microorganism-induced calcium carbonate deposition can lock heavy metals and other harmful elements, the improvement method can be further improved, and the soft soil roadbed can be developed together with solid wastes such as steel slag. consolidation improvement.

Description of drawings

Fig. 1 is the schematic diagram of the microorganism-induced calcium carbonate precipitation technology adopted in the present invention;

Fig. 2 is that the microorganism that the present invention adopts provides nucleation process schematic diagram for calcium carbonate precipitation;

Fig. 3 is that calcium carbonate crystal of the present invention fills the gap between sand particles, and produces a cementation structure schematic diagram between sand particles;

Fig. 4 is the present invention in sandy soil, transmits the nutrient salt schematic diagram such as bacterial liquid and urea and calcium source;

5 is a schematic diagram of the present invention injecting the prepared consolidation liquid into a sandy soil roadbed;

Fig. 6 is the effect diagram of the microbe-induced silty sand accelerated consolidation soft soil roadbed of the present invention.

Detailed ways

The technical solution of the present invention will be further described in detail below by way of examples and in conjunction with the accompanying drawings. As shown in Figure 1 and Figure 2, it is a schematic diagram of the microstructure of the microbe-induced calcium carbonate consolidation and precipitation technology adopted in the present invention, including Pasteur Bacillus uses urea as energy, produces a large amount of highly active urease through metabolic activities, hydrolyzes urea to generate NH ₄ ⁺ and CO ₃ ^2- , and then pours calcium salt solution into the soil to provide calcium ions. Due to the special cell wall structure of microorganisms, Its surface generally has a large number of negative ions, and life activities transport CO ₃ ^2- to the cell surface to combine with Ca ²⁺ to form calcium carbonate crystals. The reaction equation is as follows:

NH ₂ -CO-NH ₂ +3H ₂ O→2NH ₄ ⁺ +CO ₃ ^2-

When the concentration _of CaCO3 in the void solution exceeds its solubility, calcium carbonate precipitates in the voids.

Further, the microorganisms should be activated before the microorganisms are cultured. The microorganisms are Bacillus Pasteurella, an aerobic gram-positive bacteria that can produce a large amount of urease in the metabolic process. The strains are lyophilized powder at first, which needs to be activated by bacteria, using ATCC 1376 NH4-YE culture medium for activation.

Further, the microorganisms are cultured. Inoculate the activated Bacillus Pasteurella into the ATCC 1376 NH4-YE medium, the temperature of the medium should be controlled at 30°C, PH8-9, the culture time should be 17-19h, and the cultured Bacillus Pasteurella should be placed in 4 It should be stored in the refrigerator at ℃, and the storage time should not exceed 30 days. When using it, take it out and use it for engineering.

Pasteurella plays two core roles in this reaction process: one is to provide urease for the hydrolysis of urea, and the other is to provide a nucleation point for the deposition of calcium carbonate crystals.

As shown in FIG. 3 , it is a schematic diagram of the structure of the calcium carbonate crystals of the present invention filling the gaps between the soil particles and producing cementation between the soil particles. Due to the special structure of the cell wall of Bacillus pasteuri, the cell surface is negatively charged. When the interstitial environment contains a certain concentration of calcium ions, the calcium ions will be adsorbed by the cells, so that the cells are crystals. Calcium carbonate crystals are deposited on the surface of soil particles, blocking soil pores and bonding soil particles, reducing soil permeability and increasing its strength.

The resulting calcium carbonate crystals play two roles in the soil. First, the calcium carbonate crystals will fill the gaps between the soil particles, increasing the compactness of the soil and the friction between the soil particles. Second, the calcium carbonate crystals will fill the gaps between the soil particles. There is a cementation effect between them, which is equivalent to a binder that binds the tiny soil particles together to form a dense block, which increases the cohesion between the soil particles, thereby improving the shear strength of the soil.

As shown in FIG. 4 and FIG. 5 , the present invention transmits bacterial liquid and urea nutrient solution to the sandy soil, and then injects the prepared consolidation liquid into the roadbed.

As shown in Figure 4, the pasteurized bacillus concentrate is added into the nutrient solution and injected into the sandy soil roadbed. The bacteria solution and the nutrient solution are continuously injected into the soft soil roadbed in the longitudinal direction. The horizontal interval should be between 0.4-0.7m. The main purpose of this step is to activate the biological activity of Bacillus Pasteurella and soil original microorganisms as soon as possible, and use the nutrient solution to spread Bacillus Pasteurella into the soft soil roadbed to avoid excessive bacteria. concentrated.

As shown in Figure 5, the consolidation liquid is injected into the roadbed. The main components of the consolidation liquid are calcium chloride and urea. The concentration of CaCl ₂ is 0.6mol/L and the concentration of urea is 0.65mol/L. Provide hydrolyzed substances and calcium ions for microorganisms. The consolidation liquid is continuously injected into the soft soil subgrade in the longitudinal direction. The horizontal interval should be between 0.4-0.7m, and it should be consistent with the injection path of the bacterial solution. After the bacterial solution is injected once, it is injected 5 times. The condensing liquid should be used as soon as possible, and the condensing liquid should be used as soon as possible to avoid the deterioration of the components of the consolidating liquid and affect the effect.

As shown in Figure 6, it is a schematic diagram of the subgrade reinforcement effect of the present invention. If the microbe-induced calcium carbonate reinforcement subgrade effect does not achieve the expected effect, steps 3, 4 and 5 should be repeated, and cycle until the subgrade engineering effect is achieved.

The construction steps of the microbe-induced silty sand to strengthen the soft soil roadbed of the present invention are carried out in sequence. In order to make the roadbed meet the engineering use requirements, steps 3, 4 and 5 should be repeated many times, so as to obtain the optimal material ratio and time for roadbed reinforcement. The relationship between.

The protection scope of the present invention is not limited to the above-mentioned embodiments. Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the scope and spirit of the present invention. If these changes and modifications belong to the scope of the claims of the present invention and their equivalents, the present invention is intended to include these changes and modifications.

Claims (7)

1. A microorganism-induced silty-fine sand consolidation soft soil roadbed ecological improvement method is characterized by comprising the following steps:

step 1, activation and culture of microorganisms: the microorganism adopts pasteurella, the strain is freeze-dried powder, and the bacteria is activated and cultured in the culture solution to obtain pasteurella concentrated solution;

step 2, adding fine sand: fine sand is mixed into the soft soil, the mixing proportion of the fine sand is 10-20%, and the fine sand provides large-particle-size aggregate for the soft soil road;

step 3, doping the bacillus pasteurii concentrated solution into the nutrient solution and injecting the nutrient solution into a sandy soil subgrade: continuously injecting the bacterial liquid and the nutrient solution into the soft soil roadbed according to the longitudinal direction, wherein the transverse interval is 0.4-0.7m, and then standing;

step 4, injecting consolidation liquid: continuously injecting consolidation liquid into the soft soil roadbed according to the longitudinal direction, wherein the transverse interval is 0.4-0.7m and is consistent with a bacterial liquid injection path;

and 5, repeating the steps 3-4, and detecting the roadbed consolidation condition after five times: and (4) repeating the step (3) and the step (4) when the roadbed does not reach the expected target, and performing the next construction when the roadbed is repeatedly checked to reach the expected target.

2. The method for ecologically improving the soft soil subgrade consolidated by the microorganism-induced fine sand powder as claimed in claim 1, wherein the method comprises the following steps: the culture solution adopted in the activation and culture in the step 1 is ATCC 1376 NH4-YE culture solution, the temperature of the culture medium is controlled at 30 ℃ during culture, the pH value is 8-9, the culture time is 17-19h, the cultured Paenibacillus pasteurianus is stored in a refrigerator at 4 ℃, and the storage time is not longer than 30 days.

3. The method for ecologically improving the soft soil subgrade consolidated by the microorganism-induced fine sand powder as claimed in claim 1, wherein the method comprises the following steps: and (3) standing for 1-2h after the bacterial liquid and the nutrient solution are injected in the step 3.

4. The method for ecologically improving the soft soil subgrade consolidated by the microorganism-induced fine sand powder as claimed in claim 1, wherein the method comprises the following steps: the nutrient solution in the step 3 mainly comprises a mixed solution of calcium chloride and urea and CaCl₂The concentration is 0.60mol/L and the urea concentration is 0.65 mol/L.

5. The method for ecologically improving the soft soil subgrade consolidated by the microorganism-induced fine sand powder as claimed in claim 1, wherein the method comprises the following steps: and (4) after the one-time bacterial liquid is poured in the step (4), pouring the consolidation liquid for 5 times, and standing for 6-8 hours every time the consolidation liquid is poured for 1 time.

6. The method for ecologically improving the soft soil subgrade consolidated by the microorganism-induced fine sand powder as claimed in claim 1, wherein the method comprises the following steps: the consolidation liquid in the step 4 mainly comprises a mixed liquid of calcium chloride and urea and CaCl₂The concentration is 0.60mol/L and the urea concentration is 0.65 mol/L.

7. The method for ecologically improving the soft soil subgrade consolidated by the microorganism-induced fine sand powder as claimed in claim 1, wherein the method comprises the following steps: and 5, adopting the CBR value as a check standard for the expected target in the step 5, wherein the expected target is achieved when the CBR value is not less than 4%.

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