CN110438974B - Microbial solidification kit and method for in-situ solidification of calcareous sand - Google Patents
Microbial solidification kit and method for in-situ solidification of calcareous sand Download PDFInfo
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Abstract
The invention discloses a microbial curing kit and a method for curing calcareous sand in situ, and belongs to the field of geological engineering-microbial interdisciplinary science. The invention discloses a microbial solidification kit for in-situ solidification of calcareous sand, which comprises: a first component comprising a carboxylic acid; a second component comprising a urease-producing microorganism; a third component comprising urea and a nutrient solution. A method of in situ microbial solidification of calcareous sand comprising the step of partially dissolving the calcareous sand with the first component described above. The invention can effectively obtain calcium source in the sandy soil of the calcareous sandy soil body in situ or in the nearby area, and further react with microorganisms to deposit calcium carbonate, thereby realizing the in-situ curing effect.
Description
Technical Field
The invention belongs to the field of geological engineering-microorganism interdisciplines, and particularly relates to a microorganism curing kit and a method for curing calcareous sand in situ.
Background
The mineralization of microorganisms is widely existed in nature, some microorganisms can generate a plurality of minerals in vitro by utilizing own physiological activities or metabolism, and the crystallization products can generate certain influence on the physical and mechanical properties of rock and soil mass, so that the microorganisms are widely concerned by the geological engineering community in recent years. Because calcite has stable property, better strength and durability and can well solidify sandy soil, the Microbial induced calcium carbonate precipitation (MICP) is a hotspot of the technical research of Microbial rock soil. The MICP method utilizes certain specific urease-producing bacteria, such as Sporosarcina pasteurii (Sporosarcina), to hydrolyze urea in an alkaline environment to produce CO3 2-By providing it with a calcium ion (Ca) enrichment2+) The nutrient salt quickly separates out calcium carbonate crystals with excellent cementation effect, and precipitates fill the pores between adjacent sandy soil particles, so that loose sand grains are agglomerated into massive solids. The technology has low cost, quick effect and no pollution, is applied to the plugging of porous medium materials at first, is popularized and applied to the repair of surface crack defects of stone materials and cement-based materials later, and the research on soil body reinforcement is started later.
In the process of island reef development and construction, a calcareous sand stratum is inevitably encountered, and a calcareous sand body must be reinforced, improved and treated due to poor mechanical property and low foundation bearing capacity which cannot meet the normal engineering construction requirements. The traditional foundation reinforcing method is to use mechanical energy or artificial materials to physically or chemically reinforce the soil body, the physical reinforcing method comprises the measures of dynamic consolidation of the foundation, soil replacement of a cushion layer, cement mixing pile arrangement and the like, the construction period is long, the cost consumption is high, large-scale mechanical equipment needs to be supported on site, and the application is limited under many conditions. The chemical reinforcing method is to pour chemical grout into the target rock-soil body, but the grouting material mostly has strong alkalinity and biotoxicity, so the solidified rock-soil body cannot grow vegetation, and the environmental hazard is too great.
The prior art with publication number CN 108718586 a discloses a method for solidifying sandy soil by microorganism-induced calcium carbonate precipitation by using a regenerated calcium source, which comprises the following steps: s1: preparing a culture solution; s2: preparing a bacterial liquid; s3: preparing a regenerated calcium source nutrient solution; s4: and (4) preparing the biological mortar. The regenerated calcium source is raw oyster shells, scallop shells and egg shells from kitchen waste, calcium ions are obtained by pickling the regenerated calcium source from the sources in the prior art, the regenerated calcium source is applied to a sandy soil solidifying technology, kitchen waste is utilized, sandy soil can be further reinforced and solidified, the obtained material is good in strength and appearance, and compared with the chemical analysis calcium adopted in the prior art, the cost is greatly reduced, and the economic and environment-friendly effects are good.
Disclosure of Invention
1. Problems to be solved
Although the MICP cost can be reduced by adding a method for regenerating a calcium source in the prior art, the method is still in a laboratory research stage, in the actual construction process, the regenerated calcium source obtained in the prior art is difficult to ensure continuous and sufficient supply, and aiming at the problem, the invention provides the microorganism curing kit and the method for in-situ curing the calcareous sand, the calcium source can be efficiently obtained in the sandy soil of the calcareous sand body in situ or in the nearby area, and then the calcium carbonate is deposited by reacting with microorganisms, so that the in-situ curing effect is realized.
2. Technical scheme
In order to solve the problems, the technical scheme adopted by the invention is as follows:
at present, a precedent for combining the MICP technology with in-situ cementation and reinforcement of the calcareous sand is absent, the MICP is carried out by utilizing the self characteristics of the sand body, a cementation hardening shell layer with certain strength can be formed in the calcareous sand foundation, and the engineering stability and safety of the calcareous sand as a building/construction foundation are improved.
A microbial immobilization kit for in situ immobilization of calcareous sand comprising: a first component comprising a carboxylic acid; a second component comprising a urease-producing microorganism; a third component comprising urea and a nutrient solution. The role of the first component is mainly twofold: firstly, the acid-containing first component and calcium sand rich in calcium carbonate are subjected to acidolysis reaction, calcium ions required in the subsequent MICP process are produced in situ, and the cost of additionally adding calcium salt as a calcium source is saved; and secondly, the pores in the sandy soil can be gradually enlarged in the acidolysis reaction process of the first component and the calcareous sandy soil, and a permeable channel is manufactured, so that the uniform dispersion and permanent planting of microorganisms in the sandy soil body in the subsequent MICP process are facilitated.
Preferably, the carboxylic acid of the first component is one or more organic weak acids selected from formic acid, acetic acid, propionic acid, butyric acid and lactic acid, and the acids are low in cost and the reaction product has no influence on the environment.
Preferably, the second component comprises a mixture of urease producing bacteria and liquid medium.
Preferably, the urease producing bacteria is sarcina pasteurii (sporosarcina paseurii) with deposit number ATCC 11859. The sporosarcina pasteurii is an alkalophilic bacterium rich in natural soil, and the produced urease can rapidly hydrolyze urea in the stationary liquid to generate carbonate ions and ammonium ions, so that the pH value in the soil body is gradually increased, and the forward progress of the calcium carbonate deposition reaction is facilitated. The bacterial culture medium adopts 20g/L yeast extract, 10g/L ammonium sulfate and 15.73 g/L0.13 mol Tris-Buffer, is alkalescent, and compared with the prior art that neutral mixed solution of 10-20 g/L tryptone, 10-20 g/L sodium chloride and 20g/L urea is adopted as culture solution in the experimental research on the solidified coral sand by depositing calcium carbonate by microorganisms, the alkalescent nutrient solution is more suitable for the growth and the propagation of microorganisms, and can create an environment suitable for the activity of urease-producing bacteria in advance.
Preferably, the formula of the liquid medium of the urease-producing bacteria is as follows: 20g/L yeast extract, 10g/L ammonium sulfate, and 15.73 g/L0.13 mol Tris-Buffer.
Preferably, the nutrient solution contains 3g/L of nutrient broth (peptone: 10 g/L; sodium chloride: 5 g/L; beef powder: 3 g/L). The Nutrient Broth was purchased from the supplier Oxoid under the english name Nutrient Broth, model M1168. The nutrient solution has the functions of maintaining the nutrient supply required by growth and propagation of microorganisms after field planting in sandy soil and inducing mineralization.
A method of microbial in situ solidification of calcareous sand comprising the step of partially dissolving the calcareous sand with the first component described above. The method can only dissolve the calcareous sand on the shallow surface layer, and can also partially dissolve the calcareous sand in a certain depth according to the actual construction condition.
Preferably, the method for in-situ curing the calcareous sand specifically comprises the following steps:
1) spraying the first component on the surface of the calcareous sand;
2) spraying the activated second component to the sand body treated in the step 1);
3) spraying the third component to the sand body treated in the step 2).
The specific infiltration depth of the sprayed acid in the step 1) is related to the spraying amount, the particle size of sandy soil particles, the porosity, the water content and the like, when the carboxylic acid in the first component is acetic acid, the acetic acid can firstly dissolve sand particles on a shallow surface layer, the dissolving capacity is weakened along with the consumption and the range diffusion of reactants, and calcium ions dissolved in the early stage can be generally carried to infiltrate by about 2-5 m in the keeping period; the above steps lead calcium sand rich in calcium carbonate to be decomposed under an acid environment to generate enough calcium ions (Ca)2+) The urease-producing bacteria with negative charges on the cell surface can be promoted to be adsorbed and planted in the soil body along with the gradual diffusion of the downward seepage of the solution, and a material basis is created for the subsequent MICP process; meanwhile, along with the infiltration of the acid solution, the dissolution of the sand particles on the shallow surface layer also leads to the increase of the porosity of the sandy soil body, which is beneficial to the infiltration of the microbial liquid and the stationary liquid in the subsequent process and the formation of a thicker solidified layer.
Preferably, the spraying in the step 1) is kept for 12-24 hours after the spraying is finished, the spraying in the step 2) is kept for 0.5-2 hours after the spraying is finished, and the spraying in the step 3) is kept for 6-24 hours after the spraying is finished.
Preferably, the method for curing the calcareous sand in situ can also adopt a grouting mode through a grouting hole or a mode of combining spraying and grouting through the grouting hole to replace the step of spraying each component.
Preferably, the step 1) is repeated for 1-2 times, so that the acetic acid is fully permeated and reacted in the calcareous sand body.
Preferably, repeating the step 2) and the step 3) 3-5 times for large-scale building engineering with high requirements on the bearing capacity and stability of the foundation, and waiting for the completion of natural cementation.
Preferably, the steps 3) and 4) are repeated for small-scale site modification projects such as coastal pavements and dustproof shells for 2-4 times.
The step of repeatedly spraying specifically comprises the steps of spraying the microbial liquid once, spraying the third component containing urea and the nutrient solution for multiple times after the bacterial liquid is infiltrated, or alternately and repeatedly spraying the bacterial liquid and the third component containing urea and the nutrient solution for multiple times.
Preferably, the ambient temperature of the operation site in the steps 1) to 3) is 20-40 ℃, the temperature range is favorable for optimally keeping the activity of microorganisms, the forward reaction is ensured, the rain cannot be drenched in the construction stage, if the rain is drenched within 24 hours after the construction, the strength test needs to be carried out, and secondary spraying reinforcement measures are taken if necessary.
Preferably, the method for in-situ curing the calcareous sand specifically comprises the following steps:
1) the method comprises the steps of obtaining calcareous sand on site, soaking the obtained calcareous sand by adopting a first component, uniformly stirring to obtain calcium ions, filtering, injecting supernatant into a calcareous sand body in a target area along a grouting hole, keeping for a specific time, and waiting for the calcium ions to diffuse;
2) arranging grouting holes in the calcareous sand body of the target area, and injecting the activated second component into the grouting holes of the calcareous sand body of the target area along the grouting holes;
3) injecting a third component into the calcareous sand body treated in the step 2) along the grouting holes.
Preferably, the calcareous sand is coarse sand with the particle content of more than 50% of the total weight and the particle content of more than 2mm of the particle size of more than 0.50mm of the coarse sand is less than 25% of the total weight, or medium sand with the particle content of more than 50% of the total weight and the particle content of more than 0.50mm of the particle size of more than 0.25mm of the medium sand is less than 50% of the total weight, or fine sand with the particle content of more than 85% of the total weight and the particle content of more than 0.25mm of the fine sand is less than 50% of the total weight, or silt with the particle content of more than 0.075mm of the fine sand is more than 50% of the total weight and less than. Wherein, the classification source of the sand is 'building foundation basic design standard' (GB 50007-2011), and the table 4.1.7 classifies the sand and the soil.
Preferably, the concentration of calcium ions in the supernatant in the step 1) is 0.1-1.5 mol/L. Too high a concentration may affect the bacterial activity, or the cementation reaction is too rapid and subsequent penetration after surface cementation cannot be continued.
Preferably, the first component in the step 1) is acetic acid with the mass concentration of 5-25%. The efficiency of the high-concentration acid is not increased too much, which causes waste due to increased cost.
Preferably, in the step 1), the inner diameter of each grouting hole is 0.1-0.5 m, the hole depth is 0.1-1.0 m, and the interval between adjacent grouting holes is 1.0-2.0 m. The inner diameter of the grouting hole can be enlarged or reduced and the depth and the interval of the hole can be adjusted according to actual conditions.
Preferably, the molar concentration of the urea and the calcium ions in the step 3) is 1: 1.
Preferably, the urea content in step 3) is 60.06 g/L.
Preferably, the urease-producing bacteria in the second component of step 2) are activated at 25 deg.C, pH 8.1, and the rotation speed of the constant temperature shaker is 180 rpm/min. The rotating speed can promote oxygen in the air to be fully mixed with bacteria liquid, and natural growth and propagation of bacteria are guaranteed.
Preferably, a spectrophotometer is adopted to control the concentration of the urease-producing bacterial liquid, namely, the light absorption value is 1.0-2.0 (OD 600) when the wavelength is set to be 600nm, and a conductivity meter is adopted to control the urease activity level of the bacterial liquid to be 1.8-2.0 mS/(cm-min)-1). The specific method for detecting urease activity by the conductivity meter comprises the following steps: under the condition of room temperature, 5mL of urease-producing bacterial liquid cultured for 24h is taken, 45mL of 1.6mol/L urea solution is added for mixing, a conductivity meter is used for detecting the conductivity change of the mixed liquid, data is recorded every 5min, the urea amount hydrolyzed by bacterial urease in unit time is calculated out, and the urea amount hydrolyzed by urease in unit minute is used for expressing the activity of urease.
3. Advantageous effects
Compared with the prior art, the invention has the beneficial effects that:
(1) the invention relates to a microbial solidification kit for in-situ solidification of calcareous sand, which adopts a first component containing acid; the method can dissolve the calcareous sand on the shallow surface layer of the target area and generate calcium ions in situ on the surface layer of the sandy soil, thereby not only saving the cost of adding the calcium ions additionally, but also increasing the pore channels of the sandy soil, solving the problems of infiltration and diffusion of the microbial inoculum along the depth direction of the sandy soil, and being beneficial to the permanent planting of microorganisms in the second component;
(2) the acid in the first component is preferably acetic acid in carboxylic acid, and the reason is that the strong acid can cause the sand body to be acidolyzed too fast, so that the sand body is easy to collapse; meanwhile, compared with strong acids such as hydrochloric acid, sulfuric acid, nitric acid and the like, carboxylic acids such as acetic acid and the like can avoid additionally introducing Cl-、SO4 2-、NO3 -Chemical elements which harm ecological environment and engineering safety enter into the cementing body; the calcium acetate source generated in the dissolving process can ensure that the MICP generates needle-shaped calcium carbonate with stable structure and tight occlusion, thereby reducing the raw material cost of the curing liquid, facilitating construction, enhancing the curing effect and achieving multiple purposes;
(3) the method for in-situ solidifying the calcareous sand by the microorganisms comprises the step of partially dissolving the calcareous sand by adopting the first component, although the calcium carbonate can be dissolved by acid, the prior MICP technical thought is that calcium carbonate is generated under the action of the microorganisms by adopting additional calcium ions, and the method utilizes the characteristic of high natural calcium content of the calcareous sand, firstly gradually dissolves the calcium carbonate in the calcareous sand on the superficial layer part of a target area, and then supplements urease-producing microorganisms and urea to generate the calcium carbonate with a cementing effect in situ, and the thought is not applied to the MICP technology;
(4) aiming at the technical problems of site limitation, environmental pollution and the like in the traditional sand foundation solidification technology, the invention fully combines foundation treatment and MICP technology, considers different site conditions (such as calcium sand grain composition) and different engineering construction purposes, respectively provides a targeted treatment scheme and gives medicines to the symptoms;
(5) the invention adopts a method for dissolving calcareous sand by acetic acid to obtain a calcium source on site, adopts a grouting method through grouting holes for large-scale projects needing deeper underground foundations, takes the sand on site to mix and stir with the acetic acid, and prepares a supernatant containing calcium ions to be injected into the calcareous sand body in a target area; for small-scale engineering, no foundation is needed, only one layer of hardened shell is needed, acetic acid is sprayed to wait for natural permeation and reaction; for fine sand and silt with low porosity and poor permeability.
Drawings
FIG. 1 is a schematic diagram showing the effect of in situ solidification of calcareous sand by microorganisms;
FIG. 2 is a schematic diagram of acetic acid solution spraying;
FIG. 3 is a schematic view of stirring and acid hydrolysis of calcareous sand and grouting of calcium-containing clear liquid;
FIG. 4 is a schematic view of microbial liquid grouting;
FIG. 5 is a schematic view of microbial inoculum spray;
FIG. 6 is a schematic illustration of a curing fluid grouting;
FIG. 7 is a schematic view of the solidification liquid spray;
in the figure: 1. a cementing layer; 2. a calcareous sand body; 3. acetic acid solution; 4. grouting holes; 5. bacterial liquid; 6. solidifying liquid; 7. a container; 8. supernatant containing calcium ions; 9. hardening the shell; 10. and (4) a water pump.
Detailed Description
As a green and environment-friendly new process method, the MICP technology uses urease-producing microorganisms as a medium, and under the condition of the existence of urea and calcium ions, the calcium carbonate with certain strength and cementing function is generated by utilizing natural biological induced mineralization, and can replace cement chemical cementing materials to a certain extent, as shown in figure 1, so that the engineering requirements are met, the carbon dioxide emission can be greatly reduced, and the adverse effects of greenhouse effect and other chemical harmful substances on the environment are reduced. The calcium carbonate mainly plays two roles in the cementing body, and firstly, the calcium carbonate can bear the load with certain strength; secondly, calcium carbonate is deposited in pores among the calcareous sand particles to firmly bond the loose sand particles together to form a compact whole. The hardened layer formed by cementing the calcareous sand by the MICP technology not only can improve the bearing capacity of the soil body, but also has certain liquefaction resistance.
A microbial curing kit is used for curing calcareous sand in situ, and the first component is 5-25% by massAcetic acid; the second component is Sporosarcina pasteurii (OD 600 is 0.5-2.0, urease activity level is 1.8-2.0 mS/(cm-min)-1) And liquid medium, the medium formulation is: 20g/L of yeast extract, 10g/L of ammonium sulfate and 15.73g/L of 0.13mol Tris-Buffer; the third component was 60.06g/L urea and a solidified liquid containing 3g/L of a Nutrient Broth from a supplier of Oxoid, under the English name Nutrient Broth, model M1168.
The surface calcareous sand 2 is required to be sprayed or soaked by acetic acid 3 with specific concentration before the microorganism is solidified so as to obtain sufficient calcium ions, and the calcium ions are used as a material basis for assisting the microorganism planting and inducing the production of calcium carbonate. In order to determine the optimal mass fraction of acetic acid in the first fraction, the following protocol was used in this example to study the 12h dissolution rate of calcareous sands with different concentrations of acetic acid: respectively and uniformly mixing 6g of glacial acetic acid and unequal pure water according to the preset mass concentrations of 5%, 10%, 15%, 20% and 25%, soaking 5g of calcareous sand in each part of acetic acid solution, carrying out 12-hour full reaction, filtering, washing with deionized water, drying residual calcareous sand, calculating the dissolution rate of acetic acid with different concentrations on calcium carbonate, and selecting the optimal acetic acid concentration by comprehensively considering the dissolution efficiency and the engineering economic benefit. The test results are shown in the following table:
TABLE 1 dissolution rate of calcareous sands in acetic acid of different concentrations for 12h
The test result of calcium carbonate acidolysis by acetic acid shows that when the concentration of acetic acid is 20%, calcium carbonate close to 90% can be dissolved in 12h, the advantage is obvious compared with the result of low concentration, when the concentration is 25%, the change of the concentration of acetic acid of 5% only increases the dissolution rate of 3%, and the economic benefit is greatly reduced. Therefore, 20% is selected as the optimal acetic acid concentration, so that the dissolution rate of the calcareous sand is ensured, and unnecessary engineering expenditure is avoided.
The invention is further described with reference to specific examples. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present invention is not limited thereby.
Example 1
The cured object in this example was a south China sea calcareous sand with a calcium content of 95.13%, and the particle size distribution is shown in Table 2.
Table 2 calcareous sand composition used in example 1
A method for in-situ solidifying calcareous sand by microorganisms utilizes a microorganism induced mineralization technology, aiming at coarse sand with the particle content of more than 0.50mm and less than 25% of the total weight, or medium sand with the particle content of more than 50% of the total weight and more than 2mm and less than 50% of the total weight, or medium sand with the particle content of more than 0.25mm and less than 50% of the total weight, acetic acid solution with the mass fraction of 20%, microbial solution and solidification solution consisting of urea and nutrient solution are sequentially sprayed inside a calcareous sand body 2, so that the calcareous sand body 2 is solidified to form a cementing block body 1, the specific structure is shown in figure 1, and the method for in-situ solidifying the calcareous sand specifically comprises the following steps:
1) as shown in figure 2, at 25 ℃, 20 percent of acetic acid solution is sprayed on the surface of the calcareous sand in the target area, and the spraying amount is 120kg/m2The acetic acid solution gradually infiltrates along pores along with the process of acid hydrolysis of the calcareous sand, and calcium ions gradually diffuse along infiltration channels in the process and are kept for 12 hours (generally, more than or equal to 12 hours); one or a combination mode of mechanical spraying and manual spraying can be adopted for acetic acid spraying, microbial liquid spraying and urea fixing liquid spraying, and uniform coverage in a target area is ensured; the spraying amount is designed according to the actual engineering requirements, and reaction and free infiltration are waited after spraying;
2) as shown in fig. 5, the liquid culture medium mixture of activated sarcina pasteurii was sprayed on the sand treated in step 1): spraying Paecilomyces pasteurianus for one time, wherein the spraying amount is 60kg/m2Keeping for 1.5h until bacterial liquid infiltration and field planting are completed;
3) as shown in FIG. 7, 60.06g/L of urea and urea containing 3g/L of ureaSpraying the sand body treated in the step 2) with a nutrient solution mixture of nutrient broth (the nutrient broth comprises 10g/L of peptone, 5g/L of sodium chloride and 3g/L of beef powder) in an amount of 200kg/m2And keeping for 0.5 h.
Repeating the step 2) and the step 3) once respectively, wherein the unconfined uniaxial compressive strength of the coarse sand cemented body and the hardened shell reaches 2.1MPa, and the unconfined uniaxial compressive strength of the medium sand cemented body and the hardened shell reaches 2.9 MPa.
The results show that the method is used for reinforcing the calcareous sand, the urease-producing microorganisms fully utilize calcium ions dissolved by acetic acid and subsequently supplemented urea molecules to induce and generate sufficient calcium carbonate with bearing and cementing capabilities in the soil body, and the strength of a cementing hardened layer can reach several MPa, so that the bearing capacity of the calcareous sand foundation can be effectively improved. Calcium ions required by the cementing material are generated by in-situ or nearby acidolysis, and no additional configuration is needed; toxic and harmful substances such as chloride ions, sulfate ions, nitrate ions and the like are not additionally introduced in the cementing process, and the microorganism induced mineralization is a natural process and has strong adaptability to the construction environment; after the cementation is finished, later maintenance is not needed, and other materials are not needed to cover and support. The method saves a large amount of manpower and material resources and effectively reduces the engineering investment.
Example 2
The solidified object in this example was the calcareous sand of south China sea with a calcium content of 95.13%, and the grain size composition is shown in Table 3.
Table 3 calcareous sand composition used in example 2
1) such asAs shown in fig. 3, a sufficient amount of calcareous sands are collected in situ near a target area, poured into a stirring container containing 20 mass percent of acetic acid solution, soaked for 12 hours, and stood to take supernatant after the acetic acid reacts with the calcareous sands; the concentration of calcium ions in the obtained supernatant is 1.0 mol/L. Injecting the supernatant rich in calcium ions into the calcareous sand body in the target area along the injection hole, wherein the injection amount is 150kg/m2Keeping for 6h after injection;
2) as shown in FIG. 4, the activated liquid culture mixture of sarcina pasteurii is injected into the sand body treated in step 1) along the injection hole: injecting primary bacteria liquid along the grouting hole, wherein the injection amount is 50kg/m2Keeping for 0.5h until the bacterial liquid field planting is finished;
3) as shown in fig. 6, a mixture of 60.06g/L urea and a nutrient solution containing 3g/L nutrient broth is injected into the sand body treated in the step 2) along the injection hole; the injection amount was 150kg/m2Waiting for 6h for natural induction and mineralization of the microorganisms;
and (3) repeating the step 2) and the step 3) for four times respectively to obtain a hardened shell with the thickness of 10cm, the unconfined uniaxial compressive strength of the fine sand cement body and the hardened shell reaching 1.8MPa, and the unconfined uniaxial compressive strength of the powder sand cement body and the hardened shell reaching 1.5 MPa.
In this example, sufficient calcareous sands were collected in situ near the target area in step 1), poured into a stirred vessel containing acetic acid solution, and the concentration of acetic acid and the soaking time were controlled to obtain supernatant with calcium ion concentrations of 0.1mol/L and 1.5mol/L, respectively. The two solutions are respectively adopted to carry out the steps 1) to 3) in the embodiment, and the step 2) and the step 3) are repeated for four times respectively, so that the solidified calcareous sand with the hardened shell is obtained.
Example 3
In the embodiment, aiming at large-scale building engineering with high requirements on foundation bearing capacity and stability, the cured object is Chinese south-sea calcareous sand with the calcium content of 95.13%, the grain composition is medium sand, see table 2, a spraying and grouting combined mode is adopted, grouting holes are formed in the calcareous sand body to be treated, the inner diameter of each grouting hole is 0.2m, the hole depth is 1.0m, the interval between every two adjacent grouting holes is 1.5m, and square grids are uniformly distributed.
1) As shown in the figure2, spraying 25 percent of acetic acid solution on the surface of the calcareous sand in the target area at 25 ℃, wherein the spraying amount is 2500kg/m2Keeping for 12 h;
2) injecting the activated mixed liquid of the liquid culture medium of the sarcina pasteurianum into the soil body along the grouting holes by a water pump 10, wherein the injection amount is 500kg/m2Keeping for 1.5 h; the microorganisms gradually diffuse along the original pores and the pore canals dissolved by the acetic acid and are adsorbed and planted on the surfaces of the sand particles by the calcium ions along the way;
3) after the microbial field planting is finished, a water pump 10 is adopted to inject a curing liquid along a grouting hole through a grouting pipe, wherein the curing liquid comprises 60.06g/L urea and 3g/L nutrient broth, and the injection amount is 4000kg/m2Keeping for 24 hours; under the condition that calcium ions and urease-producing microorganisms exist, the production process of calcium carbonate with cementing capacity can be efficiently completed by adding urea, nutrient broth (10 g/L of peptone; 5g/L of sodium chloride; 3g/L of beef powder) can provide necessary nutrients for the microorganisms participating in reaction in sandy soil, and precipitation and solidification calcareous sand can be gradually generated in the process of infiltration of solidification liquid to form a firm cementing body;
and (3) repeating the steps 2) and 3) for five times alternately, wherein the thickness of the finally obtained hardened shell is 3m, and the unconfined uniaxial compressive strength of the cementing body and the hardened shell reaches 5.3 MPa. By adopting the method, the sand body with the range of 1.0m of a single-hole square circle can be effectively solidified by taking each grouting hole as the center.
Example 4
In the embodiment, aiming at small-scale site modification projects such as coastal sidewalks and dustproof shells, the solidification object is the south China sea calcareous sand with the calcium content of 95.13%, the grain composition is medium sand, see table 2, and a spraying mode is adopted.
1) Firstly, spraying 5% acetic acid solution on the surface of calcareous sand body, wherein the spraying amount is 1500kg/m2Keeping for 12 hours after spraying;
2) spraying the liquid culture medium mixture of activated Sporosarcina pasteuri on the surface of calcareous sand body at a spray amount of 50kg/m2Waiting for natural infiltration;
3) spraying the curing liquid on the calcareous sand body by adopting a spraying modeSurface, spraying amount is 150kg/m2Waiting for natural infiltration, and gradually blocking pores along the way and hardening the sand body penetrated in the surface layer by calcium carbonate precipitates generated in the infiltration process;
and (3) alternately repeating the step 2) and the step 3) for three times to form a hardened shell with the thickness of 5cm, wherein the unconfined uniaxial compressive strength of the cementing body and the hardened shell reaches 2.4 MPa.
During spraying and grouting construction operation, the environmental temperature needs to be 20-40 ℃, the rain cannot be drenched within 24 hours, if precipitation occurs, strength test needs to be carried out, an unconfined compression test is proposed for testing, a specific implementation scheme is implemented according to JTJ 051-93 'road geotechnical test regulations', and secondary spraying and grouting reinforcement measures are adopted under necessary conditions.
The foregoing is merely a preferred description of the invention and its embodiments, and it should be understood that this description is not limiting, that what is shown in the drawings is only one embodiment of the invention, and that the actual construction and process are not limited thereto. Without departing from the inventive concept, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (5)
1. The method for in-situ curing the calcareous sand by microorganisms is characterized by comprising the following steps of: a first component comprising a carboxylic acid; a second component comprising a urease-producing microorganism; a third component comprising urea and a nutrient solution;
the method for in-situ curing the calcareous sand comprises the following specific steps: 1) spraying the first component on the surface of the calcareous sand to partially dissolve the calcareous sand;
2) spraying the activated second component to the sand body treated in the step 1);
3) spraying the third component to the sand body treated in the step 2);
the calcareous sand is coarse sand with the particle size of more than 0.50mm and the particle content of more than 2mm being less than 25% of the total weight, or medium sand with the particle size of more than 0.25mm and the particle content of more than 0.50mm being less than 50% of the total weight.
2. The method for in-situ microbial solidification of calcareous sands as claimed in claim 1, wherein the carboxylic acid of the first component is one or more organic weak acids selected from formic acid, acetic acid, propionic acid, butyric acid and lactic acid.
3. The method of claim 1, wherein the second component comprises a mixture of urease-producing bacteria and a liquid medium.
4. The method for in-situ curing of calcareous sands by microorganisms according to claim 1, wherein the step of spraying each component can be replaced by grouting through a grouting hole or by a combination of spraying and grouting through the grouting hole.
5. The method for curing calcareous sands in situ by microorganisms according to any one of claims 1 to 4, wherein the first component in the step 1) is acetic acid with a mass concentration of 5 to 25%.
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| CN111576390A (en) * | 2020-04-01 | 2020-08-25 | 中国水利水电科学研究院 | Method for reducing expansibility of expansive soil |
| CN113605315B (en) * | 2021-07-30 | 2022-08-12 | 海南大学 | Seawall construction device |
| CN113979677A (en) * | 2021-10-29 | 2022-01-28 | 海南大学 | Preparation method of mixed calcareous sand made of microorganism reinforced nano material |
| CN114208727B (en) * | 2021-12-20 | 2023-05-12 | 东南大学 | Modularized airtight coral culture system |
| CN114396038A (en) * | 2022-01-21 | 2022-04-26 | 中煤航测遥感集团有限公司 | Method for reinforcing soil strength by using microorganism induced calcium carbonate deposition |
| CN115075221B (en) * | 2022-07-15 | 2023-03-14 | 中国科学院武汉岩土力学研究所 | Quick curing method for calcareous sand |
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