JP5252754B2 - Ground improvement method using microorganisms - Google Patents
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- JP5252754B2 JP5252754B2 JP2012022145A JP2012022145A JP5252754B2 JP 5252754 B2 JP5252754 B2 JP 5252754B2 JP 2012022145 A JP2012022145 A JP 2012022145A JP 2012022145 A JP2012022145 A JP 2012022145A JP 5252754 B2 JP5252754 B2 JP 5252754B2
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Landscapes
- Foundations (AREA)
- Soil Conditioners And Soil-Stabilizing Materials (AREA)
- Investigation Of Foundation Soil And Reinforcement Of Foundation Soil By Compacting Or Drainage (AREA)
Description
本発明は、地盤改良工法に関し、特に、微生物の代謝産物によって地盤の液状化抵抗を高める地盤改良工法に関するものである。 The present invention relates to a ground improvement method, and more particularly, to a ground improvement method for increasing the liquefaction resistance of a ground by a microbial metabolite.
地盤の液状化現象とは、地震の際に地下水位の高い砂地盤が液体状の挙動を示す現象をいう。結果的に砂地盤状に建設された建物が不等沈下を起こしたり、地中の比重の軽い構造物（例えば下水管など）が浮き上がったりする現象が起き、大きな被害を与え得ることが知られている。一方、地盤が液状化する条件としては、地盤が水で飽和しているか飽和に近い状態にあること、振動によって間隙水圧が上昇して地盤のせん断耐力が減少すること等がある（吉見吉昭著「砂地盤の液状化 第２版」技法堂１９９１年：非特許文献１）。 The ground liquefaction phenomenon is a phenomenon in which sand ground with a high groundwater level behaves like a liquid during an earthquake. As a result, it is known that buildings constructed in the shape of sandy ground may cause unequal subsidence and structures with low specific gravity in the ground (such as sewer pipes) may occur, causing significant damage. ing. On the other hand, the conditions for liquefaction of the ground include that the ground is saturated with water or close to saturation, and that the pore water pressure increases due to vibration and the shear strength of the ground decreases (by Yoshiaki Yoshimi) "Liquefaction of sand ground 2nd edition" Technique Hall 1991: Non-Patent Document 1).
地震時の地盤の液状化を防止する方策は種々提案されている。例えば、特開２００８−５７２４７号公報（特許文献１）は、地上に敷設されたパイプラインの両側に壁状に連続する地下壁体を建設する方法を提案するものである。 Various measures for preventing liquefaction of the ground during an earthquake have been proposed. For example, Japanese Patent Application Laid-Open No. 2008-57247 (Patent Document 1) proposes a method for constructing underground wall bodies that are continuous in a wall shape on both sides of a pipeline laid on the ground.
特開平１０−１８３０８号公報（特許文献２）は、建物の基礎構造の周囲に構築した連続する包囲壁と、前記包囲壁の外面に沿って所定の間隔をおいて複数構築した控え壁とよりなる建物基礎地盤の液状化防止構造を構築することによって建物の基礎地盤のせん断変形を効果的に抑制して液状化を防止する方法を提案するものである。 Japanese Patent Application Laid-Open No. 10-18308 (Patent Document 2) includes a continuous surrounding wall constructed around the foundation structure of a building, and a plurality of retaining walls constructed at predetermined intervals along the outer surface of the surrounding wall. It proposes a method to prevent liquefaction by effectively suppressing shear deformation of the foundation ground of the building by constructing a liquefaction prevention structure of the building foundation ground.
上記特許文献１と２に記載された方法はいずれも、地盤中にコンクリート壁等を構築して地盤の変形を拘束することによって液状化を防止するものであるが、建設コストが高く、かつ、撤去する際にも大きなコストがかかることになる。 Both of the methods described in Patent Documents 1 and 2 prevent liquefaction by constructing a concrete wall or the like in the ground and restraining deformation of the ground, but the construction cost is high, and It will be very expensive to remove.
特開２００３−１１９７６２号公報（特許文献３）は、対象地盤に井戸を設け、井戸にアルカリ及びアルカリ土類金属のうち少なくとも一つを含む塩化物を水に溶解したアルカリ金属塩の水溶液を注入し、炭酸イオンを含んだ炭酸水溶液を井戸に注入し、対象地盤内部でアルカリ及びアルカリ土類金属のうち少なくとも一つを含む難溶解性塩を形成する方法を提案するものである。当該方法は地盤を構成する粒子の間隙に難溶解性塩を充填することによって流動化抵抗を向上させるが、対象地盤のボリュームに相当する莫大な量の塩化物と炭酸水溶液を必要とする。 Japanese Patent Laid-Open No. 2003-119762 (Patent Document 3) discloses that a well is provided in a target ground, and an aqueous solution of an alkali metal salt in which a chloride containing at least one of alkali and alkaline earth metal is dissolved in water is injected into the well. The present invention proposes a method of injecting an aqueous carbonate solution containing carbonate ions into a well to form a hardly soluble salt containing at least one of alkali and alkaline earth metal inside the target ground. This method improves fluidization resistance by filling the gaps between the particles constituting the ground with a hardly soluble salt, but requires an enormous amount of chloride and aqueous carbonate solution corresponding to the volume of the target ground.
特開２００７−２１１５３７号公報（特許文献４）は、地盤中に微細な気泡を注入することで地盤の水飽和度を低下させ、液状化を起こりにくくする技術を開示したものである。この技術の場合、地盤の不飽和状態を維持するためには気泡注入を持続する必要があり、継続的な維持費が必要になると共に、気泡注入システムに高い耐震性が必要になるなどの問題もある。 Japanese Patent Laying-Open No. 2007-211537 (Patent Document 4) discloses a technique for reducing the water saturation of the ground by injecting fine bubbles into the ground and making it difficult to cause liquefaction. In the case of this technology, in order to maintain the unsaturated state of the ground, it is necessary to continue the bubble injection, which requires continuous maintenance costs, and the bubble injection system requires high earthquake resistance. There is also.
一方、微生物を用いた地盤改良技術としては、有機栄養源、カルシウム塩、およびｐ Ｈ 緩衝剤を注入することによって地盤の透水性を低下させる地盤改良工法（特開２００６−１６９９４０号公報：特許文献５）や、バクテリアセルロース産生能を有する微生物によって土中に不透水壁を構築して石油の改修を増進する方法（特開２００１−３２１１６４号公報：特許文献６）などが公開されている。しかし、特許文献５、６に記載された技術はいずれも地盤の液状化防止を対象とした技術ではない。これらの公報に記載された技術は、いずれも地盤を不透水化するものであり、それ自体は地盤の飽和度を低下させて流動化を起こりにくくすることとは相反する技術である。
本発明は、従来技術が有する上記の課題を解決することを目的としたものであって、さらに、建設コストおよび維持コストが低廉で、建設前の敷地および既存の建築物の地下地盤に適用でき、容易に地盤の液状化抵抗を高め、地震時に液状化しにくい地盤に改良する方法を提供する。 The object of the present invention is to solve the above-mentioned problems of the prior art. Further, the construction cost and the maintenance cost are low, and the invention can be applied to a site before construction and an underground ground of an existing building. To provide a method for easily increasing the liquefaction resistance of the ground and improving the ground to be difficult to liquefy during an earthquake.
上記の目的を達成するために、本発明は、地盤中に存在する液状化抵抗を高める作用のある微生物の代謝に必要な養分として有機物および／または無機物を地盤中に供給して該微生物の代謝を促進し、該微生物の代謝産物および／または増殖した菌体集合体によって前記地盤の液状化抵抗を高める地盤改良工法である。 In order to achieve the above object, the present invention provides an organic substance and / or an inorganic substance as nutrients necessary for the metabolism of microorganisms having an action of increasing the liquefaction resistance existing in the ground, thereby metabolizing the microorganisms. Is a ground improvement method for enhancing the liquefaction resistance of the ground by the metabolite of the microorganism and / or the expanded cell aggregate.
本明細書に於いて微生物とは、原核生物、真核生物などの微小な生物を指し、土壌中に生息する（または生息できる）細菌、放線菌、糸状菌、原生動物などを含む意味で用いる。代謝とは、物質代謝およびエネルギー代謝を包括する言葉として用い、異化、発酵、好気呼吸、嫌気呼吸、同化を含む。養分は有機物と無機物のそれぞれを単独または混合して使用する微生物の代謝に必要な物質を指し、目的とする代謝産物の生成によるが、有機物としては、炭水化物、糖類、タンパク質、アミノ酸、脂質、高級脂肪酸、低級脂肪酸など、無機物としては窒素化合物、リン化合物が含まれる。これらとは別に微生物の呼吸に必要な電子受容体（酸素、硝酸塩など）が地盤環境中に不足する場合には供給する必要がある。 In the present specification, the microorganism refers to minute organisms such as prokaryotes and eukaryotes, and is used to include bacteria, actinomycetes, filamentous fungi, protozoa, etc. that inhabit (or can live in) soil. . Metabolism is used as a term encompassing substance metabolism and energy metabolism, and includes catabolism, fermentation, aerobic respiration, anaerobic respiration, and assimilation. Nutrient refers to substances necessary for the metabolism of microorganisms that use organic and inorganic substances alone or in combination, depending on the production of the desired metabolite, but organic substances include carbohydrates, sugars, proteins, amino acids, lipids, Examples of inorganic substances such as fatty acids and lower fatty acids include nitrogen compounds and phosphorus compounds. Apart from these, it is necessary to supply electron acceptors (oxygen, nitrate, etc.) necessary for the respiration of microorganisms when the ground environment is insufficient.
地盤に養分を供給する方法は、液状化防止対策の対象となる構造物に影響を与えない方法であれば特定の方法に限定されない。一例として、液状化防止対象地盤および／または周辺近傍に設けた（どのような方法でも掘削によって地盤に形成した）ボーリング孔あるいは井戸から、リチャージ工法または圧入工法などにより養分および有用な菌体を注入する。また、建物の建設前においては対象地盤を掘削して必要な微生物と養分を混合した後に埋め戻すこともできる。液状化抵抗とは、地震時に液状化しにくい地盤の性質を指し、本発明においては、使用される微生物と代謝反応によって異なるが、液状化の要件のうち、主として地盤の水飽和度の低下および粘性の増加によって液状化抵抗を高める。 The method of supplying nutrients to the ground is not limited to a specific method as long as it does not affect the structure that is the target of liquefaction prevention measures. As an example, nutrients and useful cells are injected from the borehole or well provided near the liquefaction-prevented ground and / or the vicinity (by any method formed on the ground by excavation) or by a recharge method or press-fitting method. To do. In addition, before construction of the building, the target ground can be excavated and mixed with necessary microorganisms and nutrients and then backfilled. Liquefaction resistance refers to the nature of the ground that is difficult to liquefy during an earthquake, and in the present invention, depending on the microorganism used and the metabolic reaction, among the requirements for liquefaction, mainly the decrease in water saturation and viscosity of the ground. Increased resistance to liquefaction.
本発明においては、地盤の液状化抵抗を高めるにあって、養分と微生物を共に地盤中に供給しても良い。対象地盤中に自然に存在する微生物の代謝産物によって地盤改良を行う場合は当該微生物の養分だけを地盤に供給してもよいが、養分と微生物を共に地盤に供給すれば、対象地盤には存在しない微生物の代謝産物によって地盤改良を行うこともできる。 In the present invention, in order to increase the liquefaction resistance of the ground, both nutrients and microorganisms may be supplied into the ground. When the ground is improved by metabolites of microorganisms that naturally exist in the target ground, only the nutrients of the microorganisms may be supplied to the ground. However, if both nutrients and microorganisms are supplied to the ground, they are present in the target ground. It is also possible to improve the ground by metabolites of microorganisms that do not.
地盤の水飽和度の低下させる方法として、微生物（群）を利用して窒素ガスを生成させることも可能である。微生物としては窒素の生成を促進する細菌である脱窒菌を用いることができる。脱窒菌は、硝酸還元菌のうち、硝酸イオンを窒素にまで還元する能力を備えたものを指し、例えば、Pseudomonas属、Paracoccus属、Thiobacillus属等に属する細菌を挙げることができる。この場合、前記養分は硝酸イオンあるいは最終的に硝酸性イオンとなる窒素化合物であり、前記代謝産物は窒素ガスである。脱窒菌の代謝によって産生した窒素ガスが、地盤中に滞留することにより地盤の水飽和度が低減し、液状化抵抗を高めることができる。 As a method of reducing the water saturation of the ground, it is also possible to generate nitrogen gas using microorganisms (group). As the microorganism, denitrifying bacteria, which are bacteria that promote the production of nitrogen, can be used. A denitrifying bacterium refers to a nitrate-reducing bacterium that has the ability to reduce nitrate ions to nitrogen, and examples include bacteria belonging to the genus Pseudomonas, Paracoccus, and Thiobacillus. In this case, the nutrient is a nitrogen compound which finally becomes nitrate ions or nitrate ions, and the metabolite is nitrogen gas. Nitrogen gas produced by the denitrifying bacteria's metabolism stays in the ground, thereby reducing the water saturation of the ground and increasing the liquefaction resistance.
地盤の水飽和度の低下させる方法として、微生物（群）を利用して二酸化炭素ガスを生成させる。本明細書で有効利用する微生物は、酸素を電子受容体として二酸化炭素を生成する代謝機構を備えた微生物を指しており、好気性細菌だけでなく、通性好気性菌や偏性好気性菌も包括する。このような微生物は地盤中に多数存在しているため、請求項１に示す液状化抵抗を高める能力の有る菌体を地盤に導入する必要はないが、地盤中には酸素が不足しているため、酸素の供給が必要である。酸素の供給には、エアスパージングまたは徐放性酸素供給薬剤（過酸化マグネシウム等）の使用などが可能である。好気性菌による前記代謝産物は二酸化炭素ガスであり、地盤中に滞留した二酸化炭素ガスにより地盤の水飽和度を低減することを通じて液状化抵抗を高める。 As a method of reducing the water saturation of the ground, carbon dioxide gas is generated using microorganisms (groups). The microorganism effectively used in the present specification refers to a microorganism having a metabolic mechanism that generates carbon dioxide using oxygen as an electron acceptor, and includes not only aerobic bacteria but also facultative aerobic bacteria and obligate aerobic bacteria. Also encompass. Since a large number of such microorganisms exist in the ground, it is not necessary to introduce the cells having the ability to increase liquefaction resistance according to claim 1 to the ground, but oxygen is insufficient in the ground. Therefore, it is necessary to supply oxygen. For oxygen supply, air sparging or a sustained-release oxygen supply agent (magnesium peroxide or the like) can be used. The metabolite produced by the aerobic bacteria is carbon dioxide gas, and the liquefaction resistance is increased by reducing the water saturation of the ground by the carbon dioxide gas retained in the ground.
地盤の間隙水中の粘性増加によって液状化抵抗を高める方法として、微生物（群）を利用して粘度の高い代謝産物（バイオポリマー）を生成させる。微生物によって生成されるバイオポリマーは様々な性質のものが存在するが、ここでは特に水に不溶性または難溶性のバイオポリマーであり、且つ間隙水中の粘度をできるだけ大きくするバイオポリマーを生成する細菌が望ましい。長期的な液状化防止のためには、難分解性の不溶性バイオポリマー生成菌を利用して長期的に間隙水中の粘度を高めることが必要であり、有用なバイオポリマーを生成する細菌を栄養と共に供給する方法が有効である。不溶性ポリマー生成菌としては、登録3896564に記載の微生物がある。当該特許に記載されたEnterobacter sp. CJF-002株は安価な糖類を用いて大量培養できる通性嫌気性細菌であり、本件発明においても利用可能である。この場合、前記養分は糖類または糖類を含む組成物であり、前記代謝物はバイオポリマーである。 As a method of increasing the liquefaction resistance by increasing the viscosity in the pore water of the ground, a highly viscous metabolite (biopolymer) is generated using microorganisms (group). Biopolymers produced by microorganisms have various properties, but here, bacteria that produce biopolymers that are insoluble or sparingly soluble in water and have the highest possible viscosity in pore water are desirable. . In order to prevent long-term liquefaction, it is necessary to increase the viscosity in pore water over the long term using persistent biodegradable insoluble biopolymer producing bacteria. The supply method is effective. Examples of insoluble polymer-producing bacteria include microorganisms described in Registration 3895654. The Enterobacter sp. CJF-002 strain described in the patent is a facultative anaerobic bacterium that can be cultured in large quantities using inexpensive sugars, and can also be used in the present invention. In this case, the nutrient is a saccharide or a composition containing a saccharide, and the metabolite is a biopolymer.
地盤の間隙水中の粘性増加は、間隙水中に存在する微生物バイオマス量が増加し、それらがバイオフィルム等を形成することによっても促進される。バイオフィルムとは、微生物が土壌間隙中に増殖した際に代謝産物によって形成されるフィルム状の高粘性体である。バイオフィルムの存在は高濃度の微生物が多糖類やポリマーなどの中で集合体を形成して間隙を塞ぎ、井戸の目詰まりを生じさせる現象などで知られている。バイオフィルムは間隙水と比較すると比重や粘性が大きいために、バイオフィルムの存在によって液状化抵抗は大きくなる。また、バイオフィルムの生成量は、微生物数に概ね比例すると考えられるため、微生物のエネルギー獲得が容易な酸化還元条件である好気条件が有利になる。通常、ガス生成とバイオフィルムの生成には相関関係があるため、バイオガスと同一の手法で養分（酸素）を供給する請求項3の条件によって液状化抵抗能力を高めることが可能である。 The increase in the viscosity of the pore water in the ground is also promoted by an increase in the amount of microbial biomass present in the pore water, which forms a biofilm or the like. A biofilm is a film-like high-viscosity body that is formed by metabolites when microorganisms grow into soil gaps. The existence of biofilms is known as a phenomenon in which high concentrations of microorganisms form aggregates in polysaccharides and polymers to close gaps and cause clogging of wells. Since biofilm has a higher specific gravity and viscosity than pore water, liquefaction resistance increases due to the presence of biofilm. In addition, since the amount of biofilm produced is considered to be approximately proportional to the number of microorganisms, aerobic conditions, which are oxidation-reduction conditions that facilitate the acquisition of microorganism energy, are advantageous. Usually, since there is a correlation between gas generation and biofilm generation, it is possible to enhance the liquefaction resistance capability under the conditions of claim 3 in which nutrient (oxygen) is supplied by the same technique as biogas.
前記微生物はバイオフィルムを生成するものであれば特定の微生物を限定されない。それらを活性化させる必須供給源は酸素であり、付随する栄養源としては、有機物としては炭水化物、糖類、タンパク質、アミノ酸、脂質、高級脂肪酸、低級脂肪酸など、無機物としては、窒素化合物、リン化合物などを選択して地盤に供給する。前記代謝物はバイオフィルムを形成する様々な高分子化合物あり、地盤中のバイオフィルムによって地盤の地震時の粘性を増大させて液状化抵抗を高める。バイオフィルム生成菌は、例えば、アセトバクター属、アルカリゲネス属、シュードモナス属、アグロバクテリウム属、リゾビウム属、スファエロチルス属、サルシナ属、アクロモバクター属、アエロバクター属、アゾトバクター属およびズーグレア属に属する各種の菌である。 The microorganism is not particularly limited as long as it produces a biofilm. The essential source to activate them is oxygen, and the accompanying nutrient sources include carbohydrates, saccharides, proteins, amino acids, lipids, higher fatty acids, lower fatty acids, etc. as organic substances, and nitrogen compounds, phosphorus compounds, etc. as inorganic substances Select and supply to the ground. The metabolites are various polymer compounds that form a biofilm, and the biofilm in the ground increases the viscosity of the ground during an earthquake to increase liquefaction resistance. Biofilm-producing bacteria, for example, various species belonging to the genus Acetobacter, Alkagenes, Pseudomonas, Agrobacterium, Rhizobium, Sphaerotilus, Sarsina, Achromobacter, Aerobacter, Azotobacter and Zoogrea It is a fungus.
前記必要な養分の地盤中への供給は、液状化防止対象地盤および／または周辺近傍に設けた井戸、またはそれと同等の機能を持つ養分の供給施設よって行うことができ、必要に応じて揚水井戸等の施設を設けて対象地盤の飽和土壌内の間隙水を循環させる。 The supply of the necessary nutrients into the ground can be performed by a liquefaction-prevented ground and / or a well provided in the vicinity of the ground, or a nutrient supply facility having an equivalent function, and if necessary, a pumping well Establish a facility such as to circulate pore water in the saturated soil of the target ground.
本発明によった場合、建設コストおよび維持コストが低廉で、建設前の敷地および既存の建築物の地下地盤に適用でき、撤去が容易な方法による地盤の液状化抵抗を高めることが可能になる。 According to the present invention, the construction cost and the maintenance cost are low, and it can be applied to the site before construction and the underground ground of an existing building, and it becomes possible to increase the liquefaction resistance of the ground by a method that is easy to remove. .
以下に、実施例に基づいて本発明の具体的な態様を説明するが、本発明は以下に記載する実施例に限定されるものではなく、実施例は発明の理解を助けるために記載するに過ぎないことはいうまでも無い。 Hereinafter, specific embodiments of the present invention will be described based on examples. However, the present invention is not limited to the examples described below, and the examples are described to help the understanding of the invention. It goes without saying that it is not too much.
図１は、本発明に基づく地盤改良方法を実施するための設備を示す概念図である。
図１において、液状化抵抗力を高める対象である飽和地盤１００の地上には建築物５００が建設されている。建築物の周囲に、第１の井戸２００を掘削し、硝酸塩・有機物貯留タンク４００に貯蔵された硝酸塩および／または有機物を混入させた水溶液を注水ポンプ３００によって第１の井戸２００に注入する。一方、建物周囲の別の場所（例えば第１の井戸２００とは対角線上の位置）に第２の井戸２２０を掘削して、揚水ポンプ３２０によって地下水をくみ出す。くみ出した地下水は、注水ポンプ３００に戻して循環させてもよい。
FIG. 1 is a conceptual diagram showing equipment for implementing the ground improvement method according to the present invention.
In FIG. 1, a building 500 is constructed on the ground of a saturated ground 100 that is a target for increasing liquefaction resistance. The first well 200 is excavated around the building, and an aqueous solution mixed with nitrate and / or organic matter stored in the nitrate / organic matter storage tank 400 is injected into the first well 200 by the water injection pump 300. On the other hand, the second well 220 is excavated to another place around the building (for example, a position on a diagonal line with the first well 200), and groundwater is pumped out by the pumping pump 320. The pumped-up groundwater may be returned to the water injection pump 300 and circulated.
このように構成することによって、飽和地盤１００には硝酸塩および／または有機物が供給される。したがって、構造物直下の地盤中の脱窒菌には有機物から供給される電子供与体（水素）と電子受容体となる硝酸イオンが供給されうることになり、脱窒反応によって窒素ガスが生成され、飽和間隙水中に拡散する。結果的に地盤の飽和度が低下して、液状化抵抗が高められることになる。窒素は時間の経過と共に次第に地表から逸散することになるので、硝酸塩および／または有機物の供給は、継続的または断続的に行われるのが望ましい。 By comprising in this way, nitrate and / or organic substance are supplied to the saturated ground 100. FIG. Therefore, denitrifying bacteria in the ground directly under the structure can be supplied with electron donors (hydrogen) supplied from organic matter and nitrate ions as electron acceptors, and nitrogen gas is generated by the denitrification reaction, Diffuses into saturated pore water. As a result, the degree of saturation of the ground is lowered and the liquefaction resistance is increased. Since nitrogen will gradually dissipate from the surface over time, it is desirable that the nitrate and / or organic supply be carried out continuously or intermittently.
図２は、地盤中で微生物を増殖させた状態を示す写真である。左写真で示す通常の飽和地盤中にも１０7cells/g程度の微生物は当然存在するが、微生物の増殖に好適な環境を創出した結果（図２、右写真）、その数は約１００倍に増加し、代謝活性も大幅に増大している。すなわち、微生物の増殖に好適な環境を創出した環境では、土壌間隙水中に多数の微生物が占めることが確認され、これらがバイオフィルムを形成して地盤間隙水中の粘性増加によって液状化抵抗を高める。図３は、図２で示した微生物によるガス生成の例であるが、単位容積中の細胞数が増大するに伴って水に対するガスの比率が増大することが示されている。すなわち、微生物を増殖させることによって、地盤の飽和度は低下し、液状化抵抗が高まることが示されている。図３は、糖類を発酵利用する細菌のガス生成に関するデータであるが、上記の傾向は、糖類でなく有機物を利用した場合においても、また発酵利用以外のガス生成に関しても同様に見出されるものである。 FIG. 2 is a photograph showing a state in which microorganisms are grown in the ground. Although there are naturally 10 7 cells / g of microorganisms in the normal saturated ground shown in the left photograph, as a result of creating a suitable environment for the growth of microorganisms (Fig. 2, right photograph), the number is about 100 times The metabolic activity is also greatly increased. That is, in an environment that has created an environment suitable for the growth of microorganisms, it is confirmed that a large number of microorganisms occupy the soil interstitial water, and these form a biofilm and increase the liquefaction resistance by increasing the viscosity in the ground interstitial water. FIG. 3 shows an example of gas generation by the microorganism shown in FIG. 2, but it is shown that the ratio of gas to water increases as the number of cells in a unit volume increases. That is, it has been shown that the growth of microorganisms decreases the saturation of the ground and increases the liquefaction resistance. FIG. 3 shows data related to the gas generation of bacteria using fermentation of saccharides, but the above-mentioned tendency can be found in the same way in the case of using organic substances instead of saccharides and also in the generation of gases other than the use of fermentation. is there.
図１に示した同様の構成で、通性嫌気性微生物であるEnterobacter sp. CJF-002株（前記）の代謝を活性化させることによりバイオポリマーの産生を行わせることもできる。生成されるポリマーは、長期間にわたって安定的に地盤の粘性を高めることができる難分解性の不溶性バイオポリマーであることが望ましい。その場合は、バイオポリマーの効果が維持されている間は養分の供給を休止することができる。 微生物によって生成した不溶性のバイオポリマーの写真を参考のために図４に示す。 With the same configuration shown in FIG. 1, biopolymers can be produced by activating the metabolism of Enterobacter sp. CJF-002 strain (described above), which is a facultative anaerobic microorganism. The produced polymer is desirably a hardly degradable insoluble biopolymer that can stably increase the viscosity of the ground over a long period of time. In that case, the nutrient supply can be suspended while the effect of the biopolymer is maintained. A photograph of an insoluble biopolymer produced by a microorganism is shown in FIG. 4 for reference.
図５は、本発明の１実施例に基づいて、酸素と養分を供給して好気性微生物または通性好気性微生物の代謝を促進する場合を示す概念図である。図１と同じ構成要素には同一の番号を付して説明を省略する。図５において新たに設けられているのはコンプレッサ４２０である。コンプレッサ４２０によって空気を強制的に飽和地盤に供給（スパージング）する。こうすることによって地下水中に酸素が供給され、好気性微生物の増殖と活性化に好適な環境が創出される。酸素以外に養分を供給する方法としては、「特開2005-131533 汚染地下水の原位置浄化システム」が有効である。好気性微生物の増殖によって二酸化炭素とバイオフィルムが生成されれば、それらによって地盤の液状化抵抗が高められる。 FIG. 5 is a conceptual diagram showing a case where oxygen and nutrients are supplied to promote metabolism of aerobic microorganisms or facultative aerobic microorganisms according to one embodiment of the present invention. The same components as those in FIG. In FIG. 5, a compressor 420 is newly provided. The compressor 420 forcibly supplies air to the saturated ground (sparging). By doing so, oxygen is supplied to the groundwater, and an environment suitable for the growth and activation of aerobic microorganisms is created. As a method for supplying nutrients other than oxygen, “JP 2005-131533 In-situ purification system for contaminated groundwater” is effective. If carbon dioxide and biofilms are generated by the growth of aerobic microorganisms, they will increase the liquefaction resistance of the ground.
この時、コンプレッサ４２０の代わりに、マイクロバブル発生装置を用いてマイクロバブルを含む栄養水を地盤に供給する方法を用いれば、上記同様、好気性微生物の代謝を促進して代謝産物によって地盤の液状化抵抗を高めると同時に、地盤中のマイクロバブルによる直接的な不飽和化によっても液状化抵抗を高めることができる。マイクロバブルは、さらに次第に地下水中に溶け込むことによって長期間にわたって地下水中の酸素濃度を高い値に維持することができる利点もある。 At this time, if a method of supplying nutrient water containing microbubbles to the ground using a microbubble generating device instead of the compressor 420 is used, the metabolism of the aerobic microorganisms is promoted and the liquid of the ground is metabolized as described above. While increasing the liquefaction resistance, the liquefaction resistance can also be increased by direct desaturation by microbubbles in the ground. Microbubbles also have the advantage that the oxygen concentration in the groundwater can be maintained at a high value over a long period of time by gradually dissolving in the groundwater.
１００ 飽和地盤
２００、２２０ 第1の井戸、第2の井戸
３００、３２０ 注水ポンプ、揚水ポンプ
４００ 硝酸塩・有機物貯留タンク
４２０ コンプレッサ
５００ 建築物
100 Saturated ground 200, 220 First well, second well 300, 320 Water injection pump, water pump 400 Nitrate / organic matter storage tank 420 Compressor 500 Building
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