JP-7856956-B2 - Ground improvement method

Inventors

• 森澤 友博
• 御手洗 義夫
• 中道 正人
• 高橋 英紀
• 栗原 大

Assignees

• 東亜建設工業株式会社
• 国立研究開発法人 海上・港湾・航空技術研究所

Dates

Publication Date

20260512

Application Date

20220406

Claims (5)

1. In a ground improvement method in which a lightweight ground material is prepared by mixing a slurry-like muddy water, foamed foam having numerous air bubbles, and a solidifying agent, and then the lightweight ground material is poured and solidified to form a lightweight ground with numerous air bubbles, A ground improvement method characterized by forming the bubbles in the foamed foam with a gas having a higher volume ratio of carbon dioxide than the air at the construction site, and mixing cellulose nanofibers with the lightweight ground material.
2. The ground improvement method according to claim 1, wherein when preparing the lightweight ground material, the foamed foam to which the cellulose nanofibers have been added, the muddy water, and the solidifying agent are mixed.
3. The ground improvement method according to claim 1 or 2, wherein when preparing the lightweight ground material, the muddy water in which carbon dioxide has been dissolved to increase the carbon dioxide concentration, the foamed foam, and the solidifying agent are mixed.
4. The ground improvement method according to claim 1 or 2, wherein the lightweight ground material is mixed with a liquid emulsifier containing cellulose nanofibers.
5. A ground improvement method according to claim 1 or 2, wherein compressed gas with a higher volume ratio of carbon dioxide than the air at the construction site is supplied to a pipe connected to a concrete-casting machine that casts the lightweight ground material, and through which the lightweight ground material passes, thereby pressurizing the lightweight ground material to the concrete-casting machine.

Description

This invention relates to a ground improvement method, and more specifically, to a ground improvement method that can form a lightweight ground with more stable quality by suppressing the disappearance of air bubbles contained in lightweight ground material and the bonding of air bubbles with each other. A ground improvement method (the so-called SGM lightweight soil method) is being used, which involves mixing a slurry-like mud mixture, prepared by adding water to raw soil, with foamed foam containing numerous air bubbles and a solidifying agent to create a slurry-like lightweight ground material, and then placing and solidifying this lightweight ground material to form a lightweight ground with numerous air bubbles (see, for example, Patent Document 1). Conventionally, because the air bubble coating contained in the lightweight ground material is relatively unstable, the air bubbles contained in the lightweight ground material tend to disappear relatively easily between the time the lightweight ground material is prepared and when it solidifies. Furthermore, the air bubbles contained in the lightweight ground material tend to connect with each other relatively easily, leading to variations in the size of the air bubbles in the lightweight ground. Therefore, there was a problem of variations in the quality of the lightweight ground. Japanese Patent Publication No. 2008-25126 This is an explanatory diagram illustrating a schematic embodiment of the ground improvement method of the present invention.This is a schematic diagram illustrating a lightweight ground material with added cellulose nanofibers. The ground improvement method of the present invention will be described below based on the embodiment shown in the figure. The present invention is an improved ground improvement method (so-called SGM lightweight soil method) that involves mixing a slurry-like mud mixture, prepared by adding water to raw soil, with foamed foam having numerous air bubbles and a solidifying agent such as cement to create a slurry-like lightweight ground material, and then pouring and solidifying this lightweight ground material to form a lightweight ground with numerous air bubbles. In recent years, reducing carbon dioxide ( CO2 ) emissions, a greenhouse gas, has become a crucial issue in civil engineering and construction work in order to mitigate global warming. In conventional SGM lightweight earthworks, air is used to form air bubbles in the lightweight ground material, and air is retained in these air bubbles (voids) in the lightweight ground. However, if the gas that forms these air bubbles in the lightweight ground material can be replaced with a gas that has a higher volume ratio of carbon dioxide than air, it will be possible to store a large amount of carbon dioxide in the lightweight ground, contributing to the reduction of carbon dioxide emissions in civil engineering and construction work. However, the solubility of carbon dioxide in water is significantly higher than that of air. Furthermore, carbon dioxide reacts with the alkali in the cement-based solidifying agent used in the SGM lightweight earthwork method (Ca(OH) ₂ + CO₂ → CaCO₃ + H₂O ). Therefore, in the SGM lightweight earthwork method, simply using a gas with a higher volume percentage of carbon dioxide than air as a substitute for air makes it difficult to prevent the disappearance of carbon dioxide-rich bubbles in the lightweight ground material, and it is not possible to form a lightweight ground with stable quality and a large number of bubbles. The inventors investigated various methods to suppress the disappearance of bubbles formed with a gas that has a higher volume proportion of carbon dioxide than air in lightweight ground materials. As a result, it was found that mixing cellulose nanofibers with the lightweight ground material increased the mechanical strength of the bubble interfaces because the cellulose nanofibers adhered to the coating (interface) of each bubble B. Furthermore, it was found that by mixing cellulose nanofibers with the lightweight ground material to improve the stability of the coating of each bubble contained in the lightweight ground material, it becomes possible to form a lightweight ground with stable quality and a large number of bubbles, even when the bubbles in the lightweight ground material are formed with a gas that has a higher volume proportion of carbon dioxide than air. It was also found that even when forming bubbles in the lightweight ground material with air, mixing in cellulose nanofibers allows for the formation of a lightweight ground with even more stable quality. Therefore, in this invention, in a ground improvement method for forming lightweight ground (SGM lightweight earthwork method), lightweight ground with numerous air bubbles is formed by mixing cellulose nanofibers with the lightweight ground material. Cellulose nanofibers are materials obtained by subdividing cellulose from trees, plants, etc.,