JP2020007897A - Ground improvement method - Google Patents

Abstract

To provide a ground improvement method that consolidates the ground using microorganisms, which can obtain stable consolidation ground having higher strength.SOLUTION: A ground improvement method using microorganisms precipitates calcium carbonate by reaction of carbon dioxide and a calcium source generated by the microorganisms while making the microorganisms, the calcium source, a silica component and an alkali agent coexist in the ground and making the ground neutral to alkali atmosphere, and consolidates the ground by curing a silica solution.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a ground improvement method. More particularly, the present invention relates to a soil improvement method for forming calcium carbonate in the ground by the metabolic action of microorganisms and consolidating the ground, and in particular, does not generate harmful substances when the ground is improved, which has an adverse effect on the environment. It is suitable for liquefaction countermeasures, seismic reinforcement under the foundation of structures, and waterproofing of earth and sand and rocks, etc., without giving large scale equipment and harmful chemicals.

  2. Description of the Related Art Conventionally, ground improvement by various construction methods has been performed to improve soft ground when constructing structures, prevent ground liquefaction and slope disasters due to earthquakes, and purify contaminated ground. As one of the methods, there is a ground improvement by injecting a chemical solution into the ground. Conventionally, a method of injecting water glass or cement into the ground to solidify the ground has been adopted. However, in the conventional method, there is a possibility that the injection material is a strong alkali, or a strong acid is used, which may have an adverse effect on the environment, requires careful handling, and also limits the usable ground. There was a difficult point that. On the other hand, as an environmentally friendly ground improvement technique, an injection method using biogrout utilizing metabolism of microorganisms and bacteria has been proposed.

  As a conventional technique, for example, Patent Literature 1 describes a manufacturing method in which water glass and carbon dioxide gas are supplied at a fixed ratio under pressure, and an aqueous solution of water glass in which carbon dioxide gas is absorbed is discharged to obtain a ground injection chemical solution. Have been. Patent Document 2 discloses a soil improvement method that does not cause environmental pollution by metabolizing and decomposing organic substances using yeasts and microorganisms inhabiting the soil. A method for improving the ground by utilizing the fluctuation of pH is described.

  Also, the applicant of the present application has proposed a ground improvement method utilizing microbial metabolism in Patent Documents 3 and 4. Furthermore, Patent Document 5 describes a microorganism that can be used for soil improvement, and Patent Document 6 describes a cement method using the microorganism.

Recently, among the above, the soil improvement method using calcified bacteria among microorganisms has attracted attention as a method for obtaining high solidification strength, and papers and patent applications have been filed. This means that calcifying bacteria (urease-producing microorganisms) can 1) penetrate deep into the soil through the medium, 2) survive in the ground as long as they are nourished, 3) on the surface of the soil particles It is possible to maintain the open porosity as required by causing the growth of carbonate in the soil, and 4) it is difficult to acidify the ground. The above Patent Documents 4 to 6 are based on the principle that, by the reaction between CO ₂ and calcium generated by the metabolism of organic matter by calcifying bacteria, CaCO ₃ is precipitated between soil particles to strengthen the ground. This is the method of strengthening the ground.

  U.S. Patent No. 5,064,086 discloses that a) introducing one or more solutions of calcifying bacteria into the soil; b) circulating the solutions in the soil; c) one or more nutrients for the calcifying bacteria. Introducing a solution to the soil and then circulating the solution in the soil; and d) introducing one or more solutions of the denitrifying bacteria to the soil and then circulating the solution in the soil. Is disclosed. U.S. Pat. No. 6,064,086 discloses that a high strength cement is formed in a permeable starting material, including the step of mixing the starting material with an effective amount of (i) a urease producing microorganism, (ii) urea, and (iii) calcium ions. The method is described, and it is disclosed that it is suitable for land improvement.

  On the other hand, as a method of injecting a chemical solution in ground improvement by injecting a chemical solution into the ground, in addition to forced injection such as pressurized injection and reduced pressure injection, natural permeation due to gravity or a head difference is known. For example, Patent Literature 7 describes that calcifying bacteria are injected by gravity. Further, Patent Document 9 discloses that, in an injection well composed of a perforated pipe (injection pipe) and a nutrient storage tank provided immediately above the nutrient, the nutrient is supplied at a pressure corresponding to the head difference from the storage tank to the groundwater table. Is supplied to the perforated tube. Further, Patent Document 10 discloses a process in which a microorganism having the property of solidifying sand and a nutrient source or a calcium source necessary for the microorganism to solidify the sand are mixed into the sand, and a structure is constructed using the sand. A coastal / river bank protection method including a step of performing the above is disclosed.

Japanese Patent Publication No. 07-057870 JP 2006-169940 A Japanese Patent No. 4709201 (Japanese Patent Application Laid-Open No. 2009-155855) Japanese Patent No. 5140879 Japanese Patent No. 5509471 (Japanese Patent Application Laid-Open No. 2011-45331) Japanese Patent No. 5547444 (Japanese Patent Application Laid-Open No. 2011-45333) JP 2008-508450 A JP 2008-524096 A JP 2011-218251 A JP 2018-25032 A

  As described above, various techniques for soil improvement using microorganisms have been studied, but it has been desired to realize a soil improvement method capable of obtaining a stronger and more stable solidified ground.

  Accordingly, an object of the present invention is to provide a ground improvement method for consolidating the ground using microorganisms, and to provide a ground improvement method capable of obtaining a more consolidated and stable consolidated ground.

  The present inventors have made intensive studies and found that, in the ground, calcium carbonate is formed using carbon dioxide generated by microorganisms, and the presence of a silica solution in the ground provides higher strength and stable solidification. The present inventor has found that a ground improvement method for obtaining a consolidated ground can be realized, and has completed the present invention.

That is, the present invention provides a soil improvement method using microorganisms,
The microorganism, a calcium source, a silica component, and an alkali agent are allowed to coexist in the ground, and while the ground is in a neutral to alkaline atmosphere, carbon dioxide is generated by the reaction between the carbon dioxide and the calcium source generated by the microorganism. The method is characterized in that calcium is precipitated and the ground is consolidated by hardening the silica solution.

  In the ground improvement method of the present invention, it is preferable that the microorganism is a calcifying bacterium, and urea is further allowed to coexist in the ground. In addition, it is preferable that an injection liquid containing the microorganism, the urea, and a nutrient is injected into the ground.

  In the ground improvement method of the present invention, the injection liquid preferably contains a pH adjuster, and also preferably contains a phosphate compound. It is also preferable that the injection liquid contains the silica component and / or a polyvalent metal compound.

  In the ground improvement method of the present invention, the ground containing calcium can be consolidated as the ground.

  In the soil improvement method of the present invention, the microorganism is cultured and grown together with the urea and a nutrient in a culture solution in a culture tank, and the grown microorganism, a culture solution containing the urea and the nutrient, It is preferably used as an infusion solution. In this case, using the microorganisms collected near the construction site as the microorganisms, the microorganisms grown, the culture solution containing the urea and the nutrient source, adding the calcium source and the silica solution, as the injection solution It can also be used.

  In the ground improvement method of the present invention, it is preferable that the culturing of the microorganism is performed until the culture reaches a range from a logarithmic growth phase to a stationary phase. Further, it is preferable to use a tank having a heating means capable of heating the culture solution as the culture tank.

  In the ground improvement method of the present invention, the injection liquid may further contain a gelling modifier. In this case, at least one selected from the group consisting of inorganic salts, organic salts and acids can be used as the gelling modifier.

  In the ground improvement method of the present invention, in the geotextile reinforced earth method, the embankment material as the ground may be consolidated.

Also, the present invention provides a soil improvement method using microorganisms,
An infusion solution containing any one or more of the above-mentioned microorganisms, a calcium source and nutrients as an active ingredient is supplied into the ground via geotextile, and calcium carbonate is produced by a reaction between the carbon dioxide produced by the microorganisms and the calcium source. Is deposited to consolidate the ground.

Furthermore, the present invention relates to a soil improvement method using an enzyme,
The enzyme, a calcium source, a silica component, and an alkali agent are allowed to coexist in the ground to form a neutral to alkaline atmosphere while the carbon dioxide generated by the enzyme reacts with the calcium source. And the hardening of the silica solution to solidify the ground.

  ADVANTAGE OF THE INVENTION According to this invention, it has become possible to implement | achieve the soil improvement method of solidifying the ground using microorganisms, and having a higher strength and a stable consolidated ground.

It is a perspective view which shows the cell grid expanded in the state of a honeycomb shape. It is explanatory drawing which shows one arrangement form of a cell grid. It is explanatory drawing which shows the other arrangement form of a cell grid. It is explanatory drawing which shows another arrangement form of a cell grid. It is explanatory drawing which shows embodiment which makes a consolidation material penetrate a geotextile by its own weight. It is explanatory drawing which shows other embodiment of this invention using geotextile.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
The present invention is a ground improvement method for consolidating the ground using microorganisms. It can also be used for repairing concrete structures. In this case, since the present invention is performed in a neutral to alkaline atmosphere, there is no possibility that the concrete will be deteriorated by the acid. In the present invention, a microorganism, a calcium source, a silica component, and an alkali agent are allowed to coexist in the ground, and while the ground is in a neutral to alkaline atmosphere, the reaction between the carbon dioxide and the calcium source generated by the microorganism is performed. Causes calcium carbonate to precipitate and hardens the silica solution to consolidate the ground.

  By allowing microorganisms and a calcium source to coexist in the ground, the carbon dioxide produced by the microorganisms reacts with the calcium of the calcium source to form calcium carbonate in the ground, and this calcium carbonate fills the ground. As a result, the ground is solidified. In addition, when the calcium carbonate is solidified, the silica in the silica component coexisting in the ground is bonded to gel in the gaps in the ground, and the ground can be more firmly consolidated.

Therefore, according to the present invention, the following effects can be obtained.
1) By introducing a silica component, it became possible to speed up the development of strength. As a result, it is possible to prevent calcium or the like from escaping due to surface water or infiltration water before reaching a high strength, thereby preventing consolidation strength from being obtained.
2) In the case of a solidified substance consisting of calcium carbonate alone, it is easily dissolved by acid rain, but since silica is introduced, a composite gel of CaCO ₂ and CaSiO ₃ is formed, and thus extremely durable against acid rain and acidic groundwater. Get higher.
3) The solidified body made only of calcium carbonate is easily eroded by groundwater because of its water permeability. However, by introducing silica, water stoppage can be imparted, and water stoppage can be controlled by the amount of silica. This is because silica gel binds calcium carbonate together with silica between soil particles.
4) When calcifying bacteria are used as microorganisms, the urea is restrained by silica gel in the process of hydrolysis of urea by the calcifying bacteria, thereby reducing the odor of urea and preventing escape of urea.
5) When calcifying bacteria are used as microorganisms, H ₂ S (hydrogen sulfide), which may be generated by the action thereof, can be neutralized with an alkaline agent to prevent the generation.

In general, about 10 ⁷ to 10 ⁹ microorganisms per gram are present in general soil, and typical examples of such microorganisms include bacteria, fungi, algae, protozoa, and algae. The microorganism used in the present invention may be any microorganism that can emit carbon dioxide due to metabolic activity or the like. Microorganisms existing in the ground to be improved may be used, and microorganisms not existing in the ground to be improved may be introduced from the outside and used.

As the microorganism, for example, calcifying bacteria (urea-decomposing bacteria) can be suitably used. Calcifying bacteria are broadly defined as "bacteria that grow or cause carbonate growth" and are called carbonate-producing bacteria, but in a narrower sense "urease (EC3.5). .1.5) Producing microorganisms, which hydrolyze urea to produce carbon dioxide and ammonia by the catalytic action of urease, an enzyme produced by calcifying bacteria, to generate carbonate ions. In the present invention, it refers to the latter narrow sense. Thereby, calcium carbonate is formed by the presence of the calcium source (calcium ion). Precipitation of calcium carbonate causes calcification, and carbon dioxide causes the silica component to gel, consolidating the ground. That is, in this case, since the silica component is solidified by a combination of urea, a calcium source such as CaCl ₂ , and urease derived from a microorganism, the silica component is simultaneously consolidated by using these components in combination. Further, it is also possible to cause the silica component and the calcium source to react with each other to generate calcium silicate, thereby consolidating the calcium silicate. Therefore, in this case, urea further coexists in the ground. In addition, Patent Document 10 discloses an embodiment in which a microorganism and silica colloid are used in combination, but in Patent Document 10, the pH value of the solution in the solution is lowered due to the metabolism of glucose by microorganisms, and siloxane bonds are generated accordingly. Thus, a network structure of silica colloid is formed, which is different from the solidification mechanism in the present invention.

The hydrolysis of urea by calcifying bacteria and the calcification (formation of calcium carbonate) by the reaction between carbonate ions generated by this hydrolysis and calcium ions from calcium chloride as a calcium source can be expressed by the following equation.
_{CO (NH 2) 2 + 3H} 2 O → 2NH 4 + + 2OH - + CO 2
CO ₂ + H ₂ O⇔H ₂ CO ₃
H ₂ CO ₃ ⇔HCO ₃ ⁻ + H ^{+
_{HCO 3 - ⇔ CO 3 2- +}} H +
CaCl ₂ ⇔Ca ²⁺ + 2Cl ⁻
Ca ²⁺ + CO ₃ ^2- → CaCO ₃ ↓

  The calcifying bacteria include bacteria selected from a genus list including Bacillus, sporosarcina, sporolactobacillus, clostridial, desulfotomacylum, and among them, calcium-resistant and fast-culturing speed Sporosarcina pasturi. Is preferred. In addition, calcium tolerance is urease activity in the presence of calcium, and can be confirmed by, for example, examining whether calcifying bacteria can survive in lime water or a calcium chloride solution and have urease activity.

  Further, as the microorganism, a microorganism that emits carbon dioxide by a metabolic action using a polysaccharide or the like as a nutrient under aerobic or anaerobic conditions can also be used. Such microorganisms, for example, emit carbon dioxide and water using a polysaccharide and oxygen as nutrients under aerobic conditions, and emit carbon dioxide and ethanol using a polysaccharide as nutrients under anaerobic conditions. Such microorganisms include, for example, cellulolytic bacteria having an enzyme that hydrolyzes an ether bond or an ester bond of sugar, aliphatic, or lactic acid, and are not limited to soil microorganisms, and if necessary, lactic acid bacteria and yeast bacteria. Alternatively, those conventionally used for foods may be used in combination.

  Microorganisms activated in the ground include fermentative bacteria and spoilage bacteria, which are facultative anaerobic bacteria that do not need to send air by explosion or stirring. Yeasts, lactic acid bacteria, and the like do not generate toxic substances such as ammonia and methane, but have a function of growing using organic substances and promoting metabolism. Anaerobic bacteria such as Lactobacillus (lactic acid bacteria) are all spore-free anaerobic bacteria, and produce alcohol and organic acids without exhausting enzymes. Aerobic basidiomycetes and filamentous fungi decompose vegetation in the soil about 1 to 10 cm from the ground surface. The Lactobacillus group is distributed in the surface, middle and lower layers.

  In the present invention, when microorganisms are introduced into the ground and used, those that have been cultured in a factory or a laboratory and stored in a lyophilized state or that stored in a culture solution are transported to a construction site. May be used, or those cultured at the construction site may be used. The use of the culture at the construction site allows bacteria and microorganisms to be used in the best condition at the peak of high activity, reducing the cost of construction because there is no need to manage during transportation. It is advantageous.

  In the present invention, similar effects can be obtained by using enzymes instead of microorganisms. The enzyme used here may be any enzyme that can generate carbon dioxide. Examples of such enzymes include urease and denitrifying enzyme. In addition, as such enzymes, those derived from plants can be used in addition to those derived from microorganisms.

  The calcium source may be any liquid or solid as long as it contains calcium, for example, slaked lime, slag, cement hydrate, calcium chloride or calcium hydroxide, calcium acetate, calcium compounds such as calcium saccharose, etc. One or more kinds can be used. As the calcium source, those existing in the ground may be used, or may be introduced into the ground before or after the injection of the injection material described below, or may be added to the injection material and introduced into the ground. Good. In other words, when consolidating ground containing calcium, it is not necessary to inject a new calcium source into the ground, but if there is a large amount of calcium source, it will be proportional to the amount of carbon dioxide emitted from microorganisms. Since a large amount of calcium carbonate can be precipitated, a calcium source may be further added to the ground.

  Here, when a magnesium source is present in the ground, carbon dioxide discharged from the microorganism may react with magnesium to form magnesium carbonate. Like calcium carbonate, magnesium carbonate also has a function of solidifying the ground by being filled in the ground.

  Further, in the present invention, the presence of an alkaline agent in the ground allows the ground to have a neutral to alkaline atmosphere. By setting the ground to a neutral to alkaline atmosphere, particularly an alkaline atmosphere, it is possible to speed up the expression of the consolidation strength, to suppress the dissolution of calcium carbonate formed in the ground, and to maintain durability. Can be.

  As the alkaline agent, one or more selected from the group consisting of a salt whose aqueous solution exhibits alkalinity, a hydroxide of a polyvalent metal, an alkaline silica solution, and a suspension of bentonite, slag, or cement can be used. . Further, a caking agent exhibiting alkalinity and containing at least one selected from the group consisting of lime, bentonite, slag and cement can also be used. In the present invention, when the calcium source or the silica component exhibits alkalinity, the calcium source or silica component exhibiting alkalinity can be used as an alkali agent.

  The silica component may be any one containing silica, such as water glass, active silica, colloidal silica, neutral or acidic silica sol, water glass, colloidal silica, slag and cement and the like. Powders such as minerals containing silica and silica fume can also be used. Here, as the water glass, a water glass aqueous solution, to which an acid, a salt, or an organic reactant, for example, an aldehyde compound such as glyoxal, or an ester such as an acetate, a diester, a triester, or a carbonate is added. Or a neutral to acidic silica solution obtained by neutralizing an alkali of water glass with an acid, activated silica, silica colloid, aqueous white carbon solution, and the like. Among these, examples of the silica component that also acts as an alkaline agent include water glass, colloidal silica, minerals containing silica, and silica fume.

  Activated silica is obtained by treating water glass with an ion exchange resin or an ion exchange membrane to remove part or all of the alkali in the water glass. Further, it may be obtained by passing water glass obtained by mixing water glass and an acid through an ion-exchange resin or an ion-exchange membrane, and desalting some or all of the salts in the water glass. .

  When the silica concentration of the active silica is low, the silica concentration can be increased by heat concentration or by appropriately adding colloidal silica, water glass or the like. The activated silica has a silica concentration of 1 to 8% by mass and a pH of 2 to 4.

  Such activated silica grows to a silica particle size of 1 to 5 nm and gels several days later, but is stabilized by adding an alkali such as caustic or water glass to a pH on the alkali side. An acid or a salt is added to the stabilized activated silica on site to adjust the alkaline pH and the gelation time, and then used.

  Further, an acid may be added to the activated silica to extend the pot life and adjust the gel time. This type of active silica not only can prolong the gelation time, but also gels even at a low concentration, and has excellent durability after consolidation. The viscosity is almost the same as that of water and is 2 cps or less.

  Colloidal silica is obtained by heating the above-mentioned activated silica to increase the particle size and stabilizing it by adjusting the pH to 9 to 10. The pH may be acidic to neutral. The colloidal silica thus obtained has a silica concentration of 5% or more, usually about 30%, and a particle size of 5 to 20 nm, but can be increased to more than that, for example, about 100 nm.

  The acidic to neutral silica sol is a neutral silica aqueous solution having a pH of about 5 to 9 obtained by mixing water glass with an excess or almost equivalent amount of an acid and neutralizing and removing alkali components in the water glass. It is usually prepared at the site of the injection and used in conventional ground injections at silica concentrations of 3 to 10% by weight. This silica sol is also excellent in durability since alkali has been removed, and gels even at a silica concentration of 1% by mass or less. The viscosity is almost the same as water, less than 2 cps.

  In the present invention, when each component such as a microorganism, a urea, a calcium source, an alkali agent and a silica component is introduced into the ground, each component may be separately injected, or may be injected in a mixed state. . Further, these components may be injected with a time difference before and after. In the present invention, when a microorganism is introduced into the ground and used, for example, an injection solution containing the microorganism, urea, and a nutrient can be injected into the ground.

  Nutrient sources are used to nourish, survive, and even proliferate microorganisms. Nutritional sources include monosaccharides such as glucose and fructose, sucrose, disaccharides such as maltose or galactose, other oligosaccharides, polysaccharides such as starch and maltodextrin, other saccharides, organic substances, salts and the like. One or more of them can be used. Since the metabolic rate changes depending on the microorganism or the nutrient source, these conditions need to be selected according to the construction ground.

Urea is composed of CO (NH ₂ ) ₂ and generates carbon dioxide (carbonate ion CO ₃ ²⁻ ) by hydrolysis, so that it can be used as a carbonate ion source. As the urea used for the injection, specifically, for example, a commercially available urea medium can be used.

  In the present invention, for example, in a culture solution in a culture tank, a microorganism is cultured and grown together with urea and a nutrient source, and a culture solution containing the grown microorganism, urea and a nutrient source can be used as an infusion solution. . The cultivation of the microorganism may be performed at a factory or the like, or may be performed at a construction site.

  As the culture tank, an existing culture tank may be used, and a tank having a stirring blade or a function of adjusting the temperature of the culture solution is preferable. Although one culture tank may be used, it is preferable to provide a plurality of culture tanks. By installing a plurality of them, switching at the time of failure and fine culture can be performed. There is a culture solution containing microorganisms, urea and nutrients in the culture tank in operation, where the microorganisms are cultured and proliferated. Culture conditions and culture method such as a culture solution can be determined according to a conventional method.

  In particular, it is preferable to use, as the culture tank, one having a heating means capable of heating the culture solution. Among the microorganisms, the culture temperature of calcified bacteria is particularly important. Therefore, the temperature of the culture solution is preferably set to 20 to 37 ° C. even when the culture is performed at the construction site. Therefore, the culture tank is preferably provided with a heating means capable of heating the culture solution so that the temperature in the above range can be maintained even in winter or the like when the outside air temperature is 20 ° C. or less.

  Examples of the heating means include an oil heater, a coiled tube heater, a throw-in heater, a sheet heater, and a ribbon heater. In addition, a heating effect can be obtained by performing the heating not only on the culture tank but also on the piping and the connection portion of the injection pipe.

  Further, it is preferable that the culture of the microorganism in the culture tank is performed until the range from the logarithmic growth phase to the stationary phase is reached. By using a microorganism cultured to this range, the microorganism can be used in the best condition with a high activity peak.

  In the present invention, using a microorganism collected near the construction site as a microorganism, it is grown in a culture tank, and a calcium source and a silica solution are further added to a culture solution containing the grown microorganism, urea, and a nutrient source. Then, it can be used as an injection solution.

  The injection solution may further contain a pH adjuster. This makes it possible to appropriately adjust the pH of the ground to activate microorganisms and increase the curing speed of silica.

  It is also preferable to mix a phosphoric acid compound in the above-mentioned injection solution. Since the phosphoric acid compound functions as a pH adjuster, it can solidify the silica solution and adjust the pH to a value at which hydrolysis can be performed efficiently. In addition, phosphoric acid is desirable for microbial growth and is effective because it reacts with a calcium source to form a solid compact of insoluble calcium phosphate.

  Further, the above-mentioned injectable solution may contain the above-mentioned silica component and / or polyvalent metal compound. That is, the microorganism and the silica component may be simultaneously injected into the ground or may be separately injected. Further, the polyvalent metal compound has a function of reacting with carbon dioxide to generate an insoluble polyvalent metal carbonate, adjusting the gelation reaction of the silica compound, and enhancing the strength of the solidified product. Such polyvalent metal compounds include, for example, calcium salts such as calcium chloride, magnesium salts such as magnesium chloride, polyvalent metal salts such as iron salts and aluminum salts, and polyvalent metal salts such as calcium hydroxide. One or more selected from the group consisting of oxides or oxides, fine lime, fine cement, fine slag, gypsum and calcium carbonate can be used. In addition, calcium and lime in shells and the like contained in the ground also affect the reaction.

  Furthermore, the injection solution may further contain a gelling regulator for controlling gelation of the silica solution. As such a gelling modifier, for example, one or more selected from the group consisting of inorganic salts such as calcium chloride and / or sodium chloride, organic salts, and trace amounts of acids can be used.

  In the present invention, the metabolic action of the microorganism and the gelation time of the silica solution can be adjusted using at least one selected from carbon dioxide, carbonated water, and oxygen.

  In the present invention, the neutral to alkaline atmosphere in the ground may be formed before the injection of the injection liquid, may be formed after the injection, or may be formed simultaneously with the injection. That is, the pH of the ground may be adjusted before or after the injection of the infusion by separately using an alkaline agent or the like. May be used.

  In the present invention, a microorganism, a calcium source, a silica component, and an alkali agent are allowed to coexist in the ground, and while the ground is in a neutral to alkaline atmosphere, a reaction between carbon dioxide and a calcium source generated by the microorganism is performed. As long as calcium carbonate is precipitated and the silica solution is hardened, any solidifying material such as microorganisms may be used as it is already present in the ground. They may be newly introduced into the ground and used in addition to those already existing in the ground, and there is no particular limitation. In the present invention, the injection of the injection material may be pressure injection into the ground or concrete structure, or may be mixed with infiltrated soil by natural flow, and may be performed using a conventional ground injection technique, and is not particularly limited.

  The ground improvement method of the present invention can be applied to ground requiring liquefaction countermeasures, ground requiring water stoppage, soft ground requiring increased strength, and the like.

  Further, the ground improvement method of the present invention may be used to consolidate an embankment material as a ground in a geotextile reinforced earth method. Geotextile is a sheet-like fiber material that is useful for, for example, a method for preventing scouring of seawalls and a method of reinforcing soil for buried or embankment surfaces. By applying the soil improvement method of the present invention to the ground on which geotextiles are arranged, the consolidation material is transmitted through the soil layer along the geotextile fibers, consolidating the surrounding soil layers together with the geotextile, and the entire ground It hardens homogeneously and eventually has the same environment as the unconstructed place. In addition, rainwater infiltrates, prevents drying, and supplies rainwater into the ground. In this case, a consolidation material such as an injection material may be sprayed or applied to the geotextile, or may be introduced into the ground by pouring. In addition, the infusion solution of the present invention can be permeated or mixed into the embankment reinforced in layers by geotextile to reinforce the reinforced soil structure. In this case, the reinforcing material resists external load, water pressure and scouring until the embankment material is solidified, and finally forms a high-strength repaired soil structure that withstands external forces as a wall surface and forms on slopes Being able to suppress the collapse of the back. Further, it can be used as a reinforced soil wall for coasts and seawalls or as an erosion prevention soil structure.

In the above, in addition to the soil reinforcing effect of the geotextile such as a nonwoven fabric, by utilizing the permeability of water or the infiltration of water by capillary action, the nutrients are contained in the fibers and voids constituting the geotextile. Utilizing the fact that microbial colonies are formed together with the existence, soil improvement of the ground can be performed in addition to embankment applications.
The ground may already contain microorganisms in the ground itself, may contain a calcium source, or may be rich in nutrients. In this case, by applying the water permeability of the geotextile to the ground to supply components that are insufficient for solidification by microorganisms through the geotextile, the ground can be strengthened by promoting the metabolism of the microorganism.
In FIG. 1 to FIG. 6 shown below, components that are not enough for microbial consolidation in the local ground are pre-infiltrated into the geotextile and installed in the ground, or supplied from the ground surface as shown in FIG. The microbial colony grows in the inside, the microbial metabolism progresses around the geotextile, and the consolidation can be expanded. In addition, it is possible to replenish the culture solution containing microorganisms and nutrients with the passage of time to expand the solidification. In this case, the underground geotextile will have a function similar to a microbial culture tank. Microorganisms are adsorbed on the fibers and nutrients are supplied, so that the inside of the nonwoven fabric becomes like a colony.

  Examples of the geotextile include, for example, a resin-impregnated cloth frame material obtained by forming a band-shaped nonwoven fabric impregnated with a resin and imparting water permeability and rigidity into a honeycomb shape, which is commercially available as Cell Grid (registered trademark). . FIG. 1 shows a perspective view of a cell grid 1 that has been expanded into a honeycomb shape at the time of construction. The cell grid 1 can be folded and packed in a reduced state during transport, and has the advantages of being lightweight and having excellent handling and workability. By arranging the cell grid in the ground, the soil particles in the ground are constrained by the lateral stress of the cell wall, the passive resistance of the surrounding cells, and the effect of friction between the replenisher and the cell wall, so the load is reduced. Even if it is added, destruction can hardly occur. The cell grid 1 may be, for example, installed on a riverbed on which concrete 11 is laid as shown in FIG. 2, or as a concrete lining form of a waterway as shown in FIG. As shown in FIG. 4, the sheet-shaped geotextile 2 can be used on a buried or embanked slope in which the geotextile 2 is buried. Specifically, after arranging geotextiles or cell grids at the target location and performing soil as desired, the consolidation material according to the present invention is injected into the ground by application, etc., and is introduced into the ground. The soil layer solidifies along the geotextile 2 or the cell grid 1, and the ground can be more firmly consolidated. Also, as shown in FIG. 5, the geotextile 2 is placed on the slope of the embankment, and one end of the geotextile 2 is immersed in the consolidation material 3 so that the consolidation material 3 penetrates the geotextile 2 by its own weight. The consolidation material 3 can also be made to penetrate into the ground through. In addition, the soil improvement method of the present invention provides an injection liquid containing any one or more of a microorganism, a calcium source, and a nutrient as an active ingredient through the geotextile into the ground, thereby reducing carbon dioxide generated by the microorganism. It may be one that solidifies the ground by precipitating calcium carbonate by reaction with a calcium source. In this case, as shown in FIG. 6, the geotextile 2 is impregnated in advance with a consolidation material according to the present invention containing a microorganism, a calcium source, nutrients, and, if necessary, a silica component, and is buried in the ground, or It is possible to use a method of infiltrating the consolidation material according to the embedded geotextile 2 and consolidating the surrounding ground.

  Hereinafter, the present invention will be described in more detail with reference to Examples. Note that the present invention is not limited to these examples.

  Since the microorganism used in the present invention may be one that emits carbon dioxide due to metabolic activity or the like, in the following experiments, it is assumed that calcifying bacteria are used as the microorganism, and urea generated by the calcifying bacteria is used. Urease, a degrading enzyme, was used with urea as an alternative to microorganisms.

The materials used this time are as follows. Here, calcium chloride and calcium hydroxide correspond to a calcium source, No. 5 water glass and colloidal silica correspond to a silica component, and calcium hydroxide, No. 5 water glass and colloidal silica also act as an alkaline agent.
Main agent: calcium chloride, calcium hydroxide Reactant: urea, urease Additive: phosphoric acid (10-fold diluted solution of 75% phosphoric acid solution), No. 5 water glass, colloidal silica, sodium hexametaphosphate Test container: φ1.5 × 17cm (30ml) test tube

The amount of each material used is the amount charged to 10 ml of water (ion-exchanged water), and the basic order of charging is as follows.
(1) water → (2) calcium source → (3) urea → (4) urease → (5) additive

[Test 1]
A confirmation test of solidification using urease, urea and a calcium source was performed. As shown in the table below, the reactants: urea (1 to 10 g) and urease (0.03 g) were mixed with the main agent: calcium chloride (2 to 6 g), and the reaction was confirmed. The charging order was (1) water, (2) calcium chloride, (3) urea, and (4) urease, and each was immediately stirred and dissolved with a stirring rod after charging the materials.

  Dissolution of urease was performed as described in No. From 5 onward, stirring was required. The colorimetric measurement range of ammonium ion is 0 to 20 mg / l. The measurement results of 1 to 8 were far beyond the range. No. 9 to 12 were in the colorimetric range, but could not be determined because the determination agent was not completely dissolved.

  As a result of the above experiment, based on the combination of 2 g of calcium chloride and 1 g of urea considered to be optimal, the following test was conducted by adding an additive thereto.

[Test 2-1]
As additives, a diluted phosphoric acid solution (0.5, 1.0 ml) and colloidal silica No. 5 water glass (0.5 ml) were used. The charging order was (1) water, (2) calcium chloride, (3) urea, (4) urease, and (5) additives. The observation results immediately after mixing are shown in Table 2 below, and the amount of precipitate, pH and ammonium ion amount after 2 days are shown in Table 3 below, and the observation results after 29 days and 2 months are shown in Table 4 below.

  As shown in the above table, a precipitate was generated immediately after mixing. After one week, the precipitate had hardened.

[Test 2-2]
In Test 2-1, the addition amount of No. 5 water glass as an additive was increased to 1, 2, 5 ml, and the test was carried out without adding urease. The charging order was (1) water, (2) calcium chloride, (3) urea, and (4) No. 5 water glass in that order. The observation results immediately after mixing are shown in Table 5 below, and the observation results after 1 month and 3 months are shown in Table 6 below.

  For all formulations, a coarse precipitate was generated.

[Test 2-3]
In Test 2-1, the amount of the phosphoric acid solution added as an additive was increased to 2.5 ml, and the test was performed. The charging order was (1) water, (2) calcium chloride, (3) urea, (4) urease, and (5) phosphoric acid solution. The observation results immediately after mixing and 3 days later are shown in Table 7 below, and the observation results after 1 month and 3 months are shown in Table 8 below.

  When the pH of the mixture was 1.1 or less, the acidity was high, and after 3 days, there was almost no precipitate.

[Test 2-4]
No. of Test 2-1. For 1 and 2, tests were performed in the case where calcium hydroxide was used instead of calcium chloride as a calcium source and a phosphoric acid solution was combined as an additive. In addition, a test was also conducted on a formulation using calcium chloride without adding any additive. The charging order is (1) water, (2) calcium hydroxide (calcium chloride), (3) urea, (4) urease, and (5) phosphoric acid solution. It was dissolved by stirring. The observation results immediately after mixing are shown in Table 9 below, and the amount of precipitate, pH and ammonium ion amount after 2 days are shown in Table 10 below, and the observation results after 1 month and 2 months are shown in Table 11 below. The amount of calcium hydroxide of 0.020 g is around the solubility.

  It was confirmed that solidification occurred even with calcium hydroxide.

[Test 2-5]
About test 2-4, the test was performed by returning calcium hydroxide to calcium chloride and changing the additive from a 75% phosphoric acid 10-fold diluted solution to sodium hexametaphosphate. The charging order was (1) water, (2) calcium chloride, (3) urea, (4) urease, and (5) additives. In addition, sodium hexametaphosphate has deliquescence, but when it is a lump, it has time to completely dissolve at room temperature. Therefore, it was decided to use as an aqueous solution. To prepare the sodium hexametaphosphate solution, 20 g of sodium hexametaphosphate was placed in a 200-ml volumetric flask, dissolved in hot water, and cooled, and water was added to make the total volume 200 ml (0.2 g / 2 ml). Further, in order to adjust the total amount of water, the amount contained in the sodium hexametaphosphate solution (ignoring the volume of sodium hexametaphosphate) was reduced from the amount of water charged. The observation results immediately after mixing are shown in Table 12 below, the precipitate amount, pH and ammonium ion amount after 3 days are shown in Table 13 below, and the observation results after 6 days and 19 days are shown in Table 14 below.

＊）添加剤の括弧内の数値はヘキサメタリン酸ナトリウムの量である。

*) The numerical value in parentheses of the additive is the amount of sodium hexametaphosphate.

  The combination of 2 g of calcium chloride and 1 g of sodium hexametaphosphate generated a hard consolidation after 6 days, and the combination of 2 g of sodium hexametaphosphate with an increased amount of the additive was partially hardened after 19 days. The formation of knots was observed.

[Test 2-6]
In Test 2-1, the test was performed by increasing the amount of colloidal silica added to 1, 2, and 5 ml. The charging order was (1) water, (2) calcium chloride, (3) urea, (4) urease, and (5) colloidal silica. The observation results immediately after mixing are shown in Table 15 below, and the amount of precipitate, pH and ammonium ion amount after 1 day are shown in Table 16 below, and the observation results after 7 days and 28 days are shown in Table 17 below.

  After 7 days of observation, the formulation of 5 ml of colloidal silica had the largest amount of hard consolidation in the test range.

  From the above, in the test range, a large amount of hard condensed matter was observed in a combination of 1 g of urea, 2 g of calcium chloride, and 0.03 g of urease and 5 ml of colloidal silica in the test range, and a large amount of hard consolidation was observed. Was found to be the best.

DESCRIPTION OF SYMBOLS 1 Cell grid 2 Geotextile 3 Consolidation material 11 Concrete

That is, the present invention provides a soil improvement method using microorganisms,
An infusion solution containing any one or more of the above-mentioned microorganisms, a calcium source and nutrients as an active ingredient is supplied into the ground via geotextile, and carbon dioxide produced by the microorganisms reacts with the calcium source to produce carbon dioxide. The method is characterized in that the ground is solidified by precipitating calcium.

  In the ground improvement method of the present invention, it is preferable that the injection liquid contains an alkaline agent, and the ground has a neutral to alkaline atmosphere. Further, it is preferable that the injection liquid contains a silica component.

  In the ground improvement method of the present invention, it is also preferable that the microorganism is a calcifying bacterium, and the injection liquid contains urea. It is also preferable that the injection liquid contains a pH adjuster, a phosphoric acid compound, and a polyvalent metal compound.

  In the ground improvement method of the present invention, the ground containing calcium can be consolidated as the ground.

  In the ground improvement method of the present invention, the injection liquid may contain a gelling modifier, and in this case, the gelling modifier may be one selected from the group consisting of inorganic salts, organic salts, and acids. The above can be used.

  In the soil improvement method of the present invention, the microorganisms are cultured and grown together with the urea and the nutrient in a culture solution in a culture tank, and the grown microorganism, a culture solution containing the urea and the nutrient, It can be used as the injection liquid. In this case, it is also possible to use the microorganism collected from the vicinity of the construction site as the microorganism, add the calcium source to a culture solution containing the grown microorganism, the urea and the nutrient source, and use the calcium source as the injection solution. .

  In the ground improvement method of the present invention, it is preferable that the culturing of the microorganism is performed until the culture reaches a range from a logarithmic growth phase to a stationary phase. Further, it is preferable to use a tank having a heating means capable of heating the culture solution as the culture tank.

Claims (16)

In the ground improvement method using microorganisms,
The microorganism, a calcium source, a silica component, and an alkali agent are allowed to coexist in the ground, and while the ground is in a neutral to alkaline atmosphere, the reaction between carbon dioxide generated by the microorganism and the calcium source is performed. A ground improvement method comprising precipitating calcium carbonate and consolidating the ground by hardening the silica solution.   The ground improvement method according to claim 1, wherein the microorganism is a calcifying bacterium, and urea is further coexisted in the ground.   The ground improvement method according to claim 2, wherein an injection liquid containing the microorganism, the urea, and a nutrient is injected into the ground.   The ground improvement method according to claim 3, wherein the injection liquid contains a pH adjuster.   The ground improvement method according to claim 3, wherein the injection liquid contains a phosphate compound.   The ground improvement method according to any one of claims 3 to 5, wherein the injection liquid contains the silica component and / or a polyvalent metal compound.   The ground improvement method according to any one of claims 1 to 6, wherein a ground containing calcium is consolidated as the ground.   The microorganism is cultured and grown together with the urea and a nutrient in a culture solution in a culture tank, and a culture solution containing the grown microorganism, the urea and the nutrient is used as the injection solution. The ground improvement method according to any one of the above.   Using the microorganisms collected near the construction site as the microorganisms, the microorganisms grown, the culture solution containing the urea and the nutrient source, the calcium source and the silica solution are added, and used as the injection solution. 8. The ground improvement method according to 8.   The soil improvement method according to claim 8 or 9, wherein the culturing of the microorganism is performed until reaching a range from a logarithmic growth phase to a stationary phase.   The ground improvement method according to any one of claims 8 to 10, wherein a tank provided with a heating means capable of heating the culture solution is used as the culture tank.   The ground improvement method according to any one of claims 3 to 11, wherein the injection liquid further contains a gelling modifier.   The ground improvement method according to claim 12, wherein the gelling agent is at least one selected from the group consisting of an inorganic salt, an organic salt, and an acid.   The ground improvement method according to any one of claims 1 to 13, wherein the embankment material as the ground is consolidated in the geotextile reinforced earth method. In the ground improvement method using microorganisms,
An infusion solution containing any one or more of the above-mentioned microorganisms, a calcium source and nutrients as an active ingredient is supplied into the ground via geotextile, and the carbon dioxide produced by the microorganisms reacts with the calcium source to produce carbon dioxide. A ground improvement method comprising solidifying the ground by precipitating calcium. In the ground improvement method using enzymes,
The enzyme, a calcium source, a silica component, and an alkali agent are allowed to coexist in the ground to form a neutral to alkaline atmosphere while the carbon dioxide generated by the enzyme reacts with the calcium source. And soil hardening by hardening the silica solution while precipitating calcium carbonate.

Images