JP2008184741A - Soil improvement method including calcium by use of microorganism - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for improving soil in a wide range by use of only the substances existing in the natural condition without generating toxic substance even after the soil improvement to prevent the environment from being affected by the soil improvement. <P>SOLUTION: A mixture liquid prepared by mixing nutrient source with polyvalent metallic compound to increase solubility of the polyvalent metallic compound is poured into the ground, and the product prepared by metabolic action of the microorganisms living in the ground is reacted with the polyvalent metallic compound to consolidate the ground. In the ground containing large amount of polyvalent metallic compound, the product prepared by the metabolic action of the microorganisms living in the ground is reacted with the polyvalent metallic compound after the nutrient source is poured into the ground and the polyvalent metallic compound, is dissolved to consolidate the ground. Sugar can be used as the nutrient source. In addition, one or a plurality of kinds of substances among microorganisms, slightly soluble silicate compound, nutrient source, and pH regulator or hardener are charged into the ground as required. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a ground improvement method in which a nutrient source, a polyvalent metal compound, and a microorganism are introduced into the ground, and a product resulting from the metabolic action of the microorganism reacts with the polyvalent metal compound to solidify the ground. It does not generate harmful substances when consolidated, so it does not adversely affect the environment, and does not require large-scale equipment or harmful chemicals. It is suitable for liquefaction countermeasure construction, seismic reinforcement under the structure foundation, etc. The present invention relates to a ground improvement method.

  As a method of solidifying the ground with an injection material to improve the ground, conventionally, a method of solidifying the ground by injecting water glass or cement as an injection material into the ground has been adopted.

  However, this method may cause adverse effects on the environment, such as the use of strong alkalis or strong acids in the injection material, and requires careful handling, and the ground that can be used is limited. Has been.

  In the ground where liquefaction of the ground may occur, there are many grounds containing calcium such as shells along the coast. However, when a ground improvement method that does not affect the surrounding environment is required during ground improvement, there is a possibility that unreacted substances will dissolve after the ground improvement with a strong alkali such as a conventional silica compound or an acid as a reaction material. was there. Moreover, in the injection material using water glass and calcium, since the gelation time is short, it does not penetrate into the ground and it is difficult to improve the ground in a wide range.

  A liquid containing a polyvalent metal compound as an active ingredient by the applicant, and a B liquid containing one or more selected from the group of carbonic acid, bicarbonate, sulfuric acid, phosphoric acid and their polyvalent metal salts as active ingredients An invention has been already known in which water is not contaminated by infiltrating or injecting into the soil, or mixing with the soil to form an insoluble salt so that there is little alkali contamination or silica does not elute. Yes. (Patent Document 1)

  A cement admixture made of calcium saccharate obtained by reacting slaked lime or quicklime with sugar is already known (Patent Document 2, Patent Document 3, Patent Document 4).

  The present inventors further improve the above method, and generate carbon dioxide by metabolic action of microorganisms to obtain a stable gel having a long gelation time even if the amount of acid or alkali used is reduced. Furthermore, the present invention was completed by developing a grout that has a high ground improvement effect in the ground and does not adversely affect the environment by previously mixing a nutrient source and a polyvalent metal compound.

JP 2004-67819 A Japanese Patent Application Laid-Open No. 08-183957 Japanese Patent No. 3325250 Japanese Patent No. 3357670

  Therefore, the object of the present invention is to further reduce the impact on the environment, and to use only substances that exist in the natural state to generate harmful substances on and around the improved ground and after ground improvement. First, it is an object to provide a method for improving a wide range of ground, which has improved the above-mentioned drawbacks of the known technology.

  In order to solve the above-mentioned problems, the present invention injects a mixed solution in which the nutrient source and the polyvalent metal compound are mixed to increase the solubility of the polyvalent metal compound into the ground, and the metabolic action of microorganisms living in the ground. It is characterized by solidifying the ground by reacting the produced product with a polyvalent metal compound.

  In addition, in the ground containing a large amount of polyvalent metal compound, after injecting nutrient sources and dissolving the polyvalent metal compound, the product produced by the metabolic action of microorganisms living in the ground is reacted with the polyvalent metal compound. It is characterized by solidifying the ground.

  At this time, sugar can be used as a nutrient source.

  Further, in the above method, one or more of microorganisms, hardly soluble silicate compounds, nutrient sources, pH adjusters, or curing agents are added.

  By mixing the nutrient source and the polyvalent metal compound in advance according to the present invention, the solubility of the polyvalent metal compound can be increased and the permeability into the ground can be increased.

  Furthermore, when nutrient sources are consumed due to the metabolism of microorganisms and metabolites are produced, the solubility of the polyvalent metal compound decreases and precipitates in the ground, thereby improving the water-stopping property and causing harmful substances when the ground is consolidated. It is a ground improvement method suitable for liquefaction countermeasures, seismic reinforcement under the structure foundation, etc., without causing adverse effects on the environment and without requiring large equipment and harmful chemicals. is there.

Microorganisms produce carbon dioxide from a nutrient source (glucose) in metabolic activity, for example, as shown in the following formula.
_{C 6 H 12 O 6 + 6O} 2 → 6CO 2 + 6H 2 O ( aerobic conditions)
C ₆ H ₁₂ O ₆ → 2CO ₂ + 2C ₂ H ₅ OH (anaerobic condition)

At this time, calcium as a polyvalent metal compound injected into the ground reacts with carbon dioxide generated by microorganisms, and calcium carbonate precipitates and settles between the soil particles as shown in the following formula, thereby hardening the ground.
Ca ²⁺ + CO ₂ → H ₂ O → CaCO ₃ + 2H ⁺

  Furthermore, by injecting nutrient sources, the metabolic rate of microorganisms changes depending on the type and amount of nutrient sources, and the precipitation amount of calcium salt changes with changes in the amount of carbon dioxide produced, so the hardening time and strength of the ground, The hydraulic conductivity etc. can be adjusted. When the amount of dissolved calcium in the ground is small or when the ground is improved with high strength, a polyvalent metal compound can be further injected into the ground to increase the amount of precipitated calcium salt.

  In addition, in the ground where many microorganisms exist, by adjusting the metabolism of microorganisms in the ground by organic nutrient sources, it reacts with the polyvalent metal compound in the ground and the injected polyvalent metal compound to precipitate the metal salt. be able to.

  However, conventionally used polyvalent metal salts such as lime have a low solubility in water and a small amount of precipitation in the ground. In order to obtain a sufficient amount of calcium to improve the ground, it must be dissolved in a large amount of water, diluting other infusion materials. Therefore, in the present invention, the polyvalent metal compound reacts with, for example, sucrose as a nutrient source to generate calcium saccharate, thereby increasing the solubility in water.

  Calcium saccharate can be produced at a temperature ranging from room temperature to about 100 ° C., and a saccharide and a polyvalent metal compound are sufficiently added, and unreacted substances are filtered and used.

  In the present invention, the polyvalent metal compound is one or more selected from the group consisting of chlorides of polyvalent metals, fine lime, and fine cement, and is preferably a water-soluble compound. For example, a metal component composed of calcium, manganese, magnesium, copper, zinc, potassium, aluminum and iron, a salt and an oxide can be used.

Calcium carbonate has three different crystal forms (calcite, aragonite, and vaterite), and calcite usually precipitates in calcium solutions at room temperature and pressure, but Mg ²⁺ and certain organic components When a small amount of is added to the solution, aragonite and vaterite are precipitated. In particular, aragonite and vaterite have a remarkable direction during crystal growth, so if the crystal morphology of calcium carbonate can be controlled, the anisotropy of the mechanical and hydraulic characteristics of the ground is relatively free. There is a possibility that it can be controlled.

  The nutrient source in the present invention is a nutrient source for microorganisms, and preferably one that is metabolically decomposed by microorganisms in the soil. Examples include monosaccharides such as glucose and fructose, disaccharides such as sucrose, maltose and galactose, other oligosaccharides, polysaccharides such as dextrose, starch and maltodextrin, and other saccharides. Since the metabolic rate varies depending on the microorganism or organic nutrient source, it is necessary to select it according to the construction ground.

  In addition, glycine, lysine, glutamic acid, and other amino acids, dipeptides, polypeptides, protein hydrolysates, milk solids, creams, egg solids, gelatin and whey proteins are used as complexes with polyvalent metal compounds. An amino component selected from the group may be used (see JP 2005-145965 A). These nutrient sources may be used alone or in combination.

  In addition, by repeatedly injecting the same or different types of nutrients, polyvalent metal compounds, and microorganisms into the ground in advance or once into the ground, the microorganisms in the ground and the metabolism of the injected microorganisms are activated. The ground can be strongly improved.

  The microorganism used in the present invention can be used as long as it hardly affects the human body and the environment. In particular, lactic acid bacteria, yeast bacteria, and the like that have been used for foods in the past, and those that exist in general ground can be used.

  The calcium salt precipitated according to the present invention is a calcium salt such as calcium carbonate, calcium hydroxide, calcium lactate or calcium nitrate, an aluminum salt such as aluminum hydroxide, or a polyvalent metal salt such as magnesium salt. It is influenced by the compound and the microorganisms to be injected or inhabiting the ground.

  Furthermore, in order to increase the strength in the ground in the present invention, clay minerals such as diatomaceous earth, white clay, bentonite, and natural silicate minerals such as quartzite powder and volcanic ash, incineration ash, blast furnace slag, etc. may be added as a hardly soluble silicate compound. Good.

  Moreover, in order to activate the metabolism of microorganisms, you may use a pH adjuster and a hardening | curing agent further.

Measurement of Solubility Using Sucrose and Calcium Hydroxide Changes in water solubility when calcium hydroxide and sucrose were used were measured.

1. Test method Add sucrose to 100 ml of distilled water, stir until sucrose is dissolved, then add 7.41 g of calcium hydroxide, heat to 70 ° C. and stir for 24 hours. Thereafter, the liquid temperature was cooled to room temperature (25 ° C.), and the calcium concentration of the filtered liquid was measured.

2. Measuring apparatus An ICP emission spectroscopic analyzer was used.

3. Test results

  From the results in Table 1, it was found that the calcium content of the filtrate was higher when the sucrose was added than when the sucrose was not added. Moreover, the result that the correlation of the addition amount of sucrose and the calcium content of a filtrate was small was obtained.

Calcium carbonate precipitation test To the calcium solution obtained in Experimental Case No. 1 of Example 1, yeast was added and the calcium concentration was measured.

1. Test Method The filtrate of the calcium solution obtained in Experimental Case No. 1 of Example 1 was put in a 4 ml test tube, and 0.1 g of yeast was added. Then, the calcium concentration after 24 hours was measured.

2. Test result The calcium concentration 24 hours after adding yeast to the calcium solution was 27 kg / m ³ .

On the other hand, the calcium concentration before adding yeast was 33.5 kg / m ³ from Example 1, indicating that the calcium concentration in the solution was reduced. From this, it was confirmed that calcium carbonate was precipitated by the metabolism of microorganisms.

Permeability test of an improved standard sand specimen Test case No. 1 of Example 1 The filtrate obtained by blending 2 and 2% of yeast (trade name: Nissin Super Camellia) were stirred and passed through a standard sand specimen, and the water permeability coefficient was measured. In addition, as a comparison, yeast was similarly added to the filtrate obtained in the comparative example of Example 1, and water was passed through the standard sand specimen, and the water permeability coefficient was measured.

1. Test method 90 cm of standard sand is filled into a 1 m plastic mold (relative density 60%, water permeability 2.02 × 10 ^-2 cm / s), and 2 g of yeast per 100 ml of the calcium-containing solution in test case No. 2 of Example 1 The prepared 1500 ml of the chemical solution was passed through 5 cycles, the prepared specimen was demolded and cut to 10 cm, sealed with a wrapping material, and the permeability coefficient after curing at room temperature for 28 days was measured.

  The water permeability test was a pressurized water permeability test according to the Geotechnical Society standards. Similarly, a water permeation test was performed on the filtrate of the comparative example of Example 1. Furthermore, it measured also with the liquid which added 68.4g of sucrose as a nutrient source per 100 ml of filtrates.

2. Test results The results are shown in Table 2.

  The calcium hydroxide filtrate without sucrose (No. 1) showed only a slight decrease in the hydraulic conductivity compared to water alone (No. 4), whereas the calcium hydroxide filtrate did not In the filtrate with sucrose added (No. 2), the permeability coefficient decreased by about an order of magnitude. Moreover, in the experiment (No. 3) with the filtrate which added 68.4g of sucrose as a nutrient source to the calcium hydroxide solution, the water permeability coefficient decreased greatly and became smaller than the value of experiment case No. 2.

  From this, by adding sucrose at the time of blending calcium solution, the solubility of calcium increases, so the nutrient source of microorganisms increases the solubility of calcium by mixing at the time of blending polyvalent metal compound rather than at the time of injection, effectively The ground can be improved.

Claims (7)

  A mixed liquid in which the solubility of the polyvalent metal compound is increased by mixing the nutrient source and the polyvalent metal compound is injected into the ground, and the product produced by the metabolic action of microorganisms living in the ground reacts with the polyvalent metal compound. A ground improvement method characterized by allowing the ground to solidify.   After injecting nutrients into the ground rich in polyvalent metal compounds and dissolving the polyvalent metal compounds, the product produced by the metabolic action of microorganisms living in the ground reacts with the polyvalent metal compounds to create the ground. A ground improvement method characterized by consolidation.   The ground improvement construction method according to claim 1 or 2, wherein sugar is used as a nutrient source.   The ground improvement method according to any one of claims 1 to 3, further comprising introducing a microorganism.   The ground improvement method according to any one of claims 1 to 4, further comprising adding a hardly soluble silicate compound.   The ground improvement method according to any one of claims 1 to 5, wherein one or more of a pH adjuster and a curing agent are further added. The ground improvement method according to any one of claims 1 to 6, wherein one or a plurality of nutrient sources, polyvalent metal compounds, and microorganisms are injected into the ground in advance or additionally.