JP2023154217A - Ground improvement method - Google Patents

Abstract

To provide a ground improvement method capable of forming a lightweight ground with more stable quality by suppressing disappearance or connection of air bubbles contained in a lightweight ground material.SOLUTION: When forming a lightweight ground LG having a large number of air bubbles B by preparing a lightweight ground material LM by mixing slurry-like muddy water 3, a foamed foam 5 having a large number of air bubbles B, and a solidifying material 4, and pouring and solidifying the lightweight ground material LM, the lightweight ground material LM is mixed with cellulose nanofibers F.SELECTED DRAWING: Figure 1

Description

The present invention relates to a ground improvement method, and more specifically, to a ground improvement method that can suppress the disappearance of air bubbles contained in lightweight ground materials and the connection of air bubbles to form a lightweight ground with more stable quality.

A slurry-like muddy water created by adding water to the raw soil, foamed foam with a large number of air bubbles, and a solidifying material are mixed to create a slurry-like lightweight ground material, and the lightweight ground material is poured. A ground improvement method (so-called SGM lightweight earthwork method) is being carried out in which a lightweight ground having a large number of air bubbles is formed by solidification (see, for example, Patent Document 1). Conventionally, since the film of air bubbles contained in lightweight ground material was in a relatively unstable state, the air bubbles contained in lightweight ground material were relatively easy to disappear from the time the lightweight ground material was created until it solidified. . In addition, the air bubbles contained in the lightweight ground material were relatively easy to connect with each other, and the size of the air bubbles contained in the lightweight ground material tended to vary. Therefore, there was a problem in that the quality of the lightweight ground was likely to vary.

Japanese Patent Application Publication No. 2008-25126

An object of the present invention is to provide a ground improvement method that can suppress the disappearance of air bubbles contained in a lightweight ground material and the connection of air bubbles to form a lightweight ground with more stable quality.

In order to achieve the above object, the ground improvement method of the present invention prepares a lightweight ground material by mixing slurry-like mud water, foamed foam having a large number of cells, and a solidifying material, and then pours the lightweight ground material. A ground improvement method for forming a lightweight ground having a large number of air bubbles by solidification, characterized in that the lightweight ground material is mixed with cellulose nanofibers.

According to the present invention, by mixing the lightweight ground material with cellulose nanofibers, it is possible to improve the stability of the film of each bubble contained in the lightweight ground material. Thereby, it is possible to suppress the disappearance of air bubbles contained in the lightweight ground material and the connection of air bubbles, and it is possible to form a lightweight ground with more stable quality.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram schematically illustrating an embodiment of a ground improvement method of the present invention. FIG. 2 is an explanatory diagram schematically illustrating a lightweight ground material to which cellulose nanofibers are added.

EMBODIMENT OF THE INVENTION Hereinafter, the ground improvement method of this invention is demonstrated based on embodiment shown in the figure.

The ground improvement method of the present invention involves creating a slurry-like lightweight ground material by mixing slurry-like muddy water created by adding water to raw material soil, foamed foam having a large number of air bubbles, and a solidifying agent such as cement. This is an improved ground improvement method (so-called SGM lightweight earth construction method) in which lightweight ground material with many air bubbles is formed by pouring and solidifying the lightweight ground material.

In recent years, in order to suppress global warming, reducing emissions of carbon dioxide (CO ₂ ), a greenhouse gas, in civil engineering and construction work has become an important issue. In the conventional SGM lightweight earthwork method, the air bubbles contained in the lightweight ground material are formed with air, and the air is held in the air bubbles (voids) in the lightweight ground. If it can be replaced with a gas with a higher volume ratio of carbon dioxide, it will be possible to store a large amount of carbon dioxide in lightweight soil, contributing to the reduction of carbon dioxide during civil engineering and construction work.

However, the solubility of carbon dioxide in water is significantly higher than that in air. Furthermore, carbon dioxide reacts with the alkali of the cement-based solidifying agent used in the SGM lightweight earthwork method (Ca(OH) ₂ +CO ₂ →CaCO ₃ +H ₂ 0). Therefore, in the SGM lightweight earthwork method, it is difficult to prevent the disappearance of carbon dioxide-rich bubbles in lightweight ground materials by simply using a gas with a higher volume ratio of carbon dioxide than air as a substitute for air. It is not possible to form a quality stable lightweight ground with air bubbles.

The present inventors have studied various methods for suppressing the disappearance of bubbles formed with a gas having a higher volume ratio of carbon dioxide than air in lightweight ground materials. As a result, it was found that when cellulose nanofibers are mixed into a lightweight ground material, the cellulose nanofibers adhere to the coating (interface) of each bubble B, thereby increasing the mechanical strength of the bubble interface. Furthermore, by mixing cellulose nanofibers into the lightweight ground material to improve the stability of the film of each bubble contained in the lightweight ground material, the air bubbles in the lightweight ground material have a higher volume ratio of carbon dioxide than air. It has been found that even when formed with gas, it is possible to form a lightweight foundation with stable quality and having a large number of air bubbles. It was also found that when forming air bubbles in a lightweight ground material, by mixing cellulose nanofiber with the lightweight ground material, it is possible to form a lightweight ground with more stable quality.

Therefore, in the present invention, in a ground improvement method for forming a lightweight ground (SGM lightweight earthwork method), a lightweight ground having a large number of air bubbles is formed by mixing cellulose nanofibers with a lightweight ground material. Cellulose nanofiber is a material obtained by subdividing cellulose from trees, flowers, etc. to the nano level through mechanical processing, chemical processing, or a combination of these processes.

Typical specifications of cellulose nanofibers include a fiber length of several nm to several nanometers and a fiber width of several nm to several tens of micrometers. There is some variation in fiber width, and for example, fibers that are poorly defibrated during the process of manufacturing cellulose nanofibers from wood also fall into the category of cellulose nanofibers. As raw materials for cellulose nanofibers, for example, wood pulp, bamboo pulp, softwood pulp, etc. are used.

Hereinafter, the ground improvement method of the present invention will be explained in more detail with reference to FIG. In the embodiment illustrated below, a case will be exemplified in which the bubbles B of the lightweight ground material LM are formed with a gas CG having a higher volume ratio of carbon dioxide C than air.

The volume percentage of carbon dioxide C contained in the air (atmosphere near the earth's surface) varies somewhat depending on the altitude, etc., but the volume percentage of carbon dioxide C in normal air is about 0.03 to 0.04%. When forming the bubbles B of the lightweight ground material LM with gas CG having a higher volume ratio of carbon dioxide C than air, for example, the volume ratio of carbon dioxide C is 0.4% or more, more preferably 2% or more. , more preferably 10% or more gas CG to form the bubbles B of the lightweight ground material LM. Alternatively, lightweight ground can be created using gas CG in which the volume ratio of carbon dioxide C is, for example, 10 times or more, more preferably 50 times or more, still more preferably 250 times or more, the volume ratio of carbon dioxide C contained in the air at the construction site. Form bubbles B of material LM. The upper limit of the volume ratio of carbon dioxide C contained in the gas CG with a higher volume ratio of carbon dioxide C forming the bubbles B of the lightweight ground material LM is, for example, 97% or less.

As illustrated in FIG. 1, in the ground improvement system 1 of this ground improvement method, a slurry-like muddy water 3 made by adding water to raw material soil 2 collected from the water bottom or land, and a foamed foam having a large number of air bubbles B. 5 and a solidifying material 4 such as cement, a slurry-like lightweight ground material LM is prepared and poured. The expanded foam 5 is obtained by coating the cells B with a film of a highly surface-active substance (surfactant).

In this ground improvement method, a slurry-like muddy water 3, a solidification material 4 (for example, cement), and a foamed foam 5 are supplied to a lightweight soil mixer 6. In the line that supplies muddy water 3 to the lightweight soil mixer 6, raw soil 2 is collected from the bottom of the water or on land, and gravel and foreign matter contained in the raw soil 2 are removed. Next, the raw soil 2 is put into a vibrating sieve 9 using a construction machine 8 or the like, and the raw soil 2 is classified by the vibrating sieve 9, so that particles with relatively large particle sizes (for example, Remove particles with a particle size of 5 mm to 10 mm or more. Thereafter, the raw material soil 2 that has been classified by the vibrating sieve 9 is desilted by the desilting machine 10, and the desilted raw material soil 2 is put into the mud storage tank 11. In the mud storage tank 11, water is added to the raw material soil 2 to produce muddy water 3 in the form of slurry.

As in this embodiment, when the bubbles B of the lightweight ground material LM are formed with a gas CG having a higher volume ratio of carbon dioxide C than air, the carbon dioxide C contained in the gas CG forming the bubbles B is It is preferable to increase the carbon dioxide concentration of the muddy water 3 in anticipation of dissolving it in the moisture of the lightweight ground material LM and reacting with the alkali of the solidification material 4. Preferably, the carbon dioxide concentration of the muddy water 3 is saturated.

In this embodiment, the carbon dioxide concentration of the muddy water 3 is increased by using a carbonate solution CW (carbonated water) in which carbon dioxide C is dissolved as water added to the raw material soil 2. For example, by connecting a high-pressure container 40 in which carbon dioxide C is stored in advance to the mud storage tank 11 and supplying carbon dioxide C into the mud storage tank 11 by the high-pressure container 40, carbon dioxide C can be added to the muddy water 3. It is also possible to mix and dissolve.

Next, the muddy water 3 stored in the mud storage tank 11 is sent to the lightweight soil conditioning mud machine 13 by the mud pump 12. Then, the density and flow value of the muddy water 3 are adjusted using the lightweight soil conditioning mud machine 13. When the raw material soil 2 is sandy soil, additives such as bentonite are added as necessary to adjust the muddy water 3 to a predetermined density and flow value. The muddy water 3 (adjusted mud) whose density and flow value have been adjusted by the lightweight soil conditioning mud machine 13 is pumped to the lightweight soil kneading machine 6 .

In the line for supplying the solidifying material 4 to the lightweight soil kneading machine 6, the solidifying material 4 is supplied to the lightweight soil kneading machine 6 from the storage facility 14 (silo) in which the solidifying material 4 is stored. As in this embodiment, when the bubbles B of the lightweight ground material LM are formed with a gas CG having a higher volume ratio of carbon dioxide C than air, the carbon dioxide C contained in the gas CG forming the bubbles B is In anticipation of the reaction with the alkali of the solidifying material 4, it is preferable to mix carbon dioxide C into the solidifying material 4 in advance to increase the carbon dioxide concentration of the solidifying material 4. In this embodiment, a high-pressure container 40 (40A) in which carbon dioxide C is stored in advance is connected to the storage facility 14, and carbon dioxide C is mixed and dissolved in the solidifying material 4 stored in the storage facility 14. I have to.

In addition, when the bubbles B of the lightweight ground material LM are formed with gas CG having a higher volume ratio of carbon dioxide C than air, the alkali of the solidification material 4 and carbon dioxide C react, so that the lightweight ground material LM pH may decrease. When the pH of the lightweight ground material LM becomes lower than the specified value, the long-term strength of the lightweight ground LG may decrease. Therefore, it is preferable to know in advance the mixing amount of the solidifying agent 4 (cement addition amount) that can suppress the pH of the lightweight ground material LM from becoming lower than the specified value, through an indoor mixing test or the like.

In the line for supplying the expanded foam 5 to the lightweight soil kneader 6, a diluted liquid 17 obtained by diluting a foaming agent 15 with water 16 is supplied to the foaming machine 19 by a diluted liquid pump 18. In this embodiment, by supplying a liquid emulsifier containing cellulose nanofibers F stored in a storage tank 22 to a diluent pump 18, a diluted liquid 17 containing cellulose nanofibers F is supplied to a foaming machine 19. It is configured to do this.

As in this embodiment, when the bubbles B of the lightweight ground material LM are formed with a gas CG having a higher volume ratio of carbon dioxide C than air, the carbon dioxide C contained in the gas CG forming the bubbles B is diluted. In order to suppress dissolution in the water contained in the liquid 17, it is preferable to increase the carbon dioxide concentration of the diluent 17. Preferably, the carbon dioxide concentration of the diluent 17 is saturated.

In this embodiment, a carbonic acid solution CW (carbonated water) in which carbon dioxide C is dissolved is used as the water 16 used for dilution. For example, by connecting a high-pressure container 40 in which carbon dioxide C is stored in advance to a water storage tank 20 storing water 16 used for dilution, and supplying carbon dioxide C into the water storage tank 20 by the high-pressure container 40, dilution can be performed. It is also possible to adopt a configuration in which carbon dioxide C is mixed and dissolved in the water 16 used for the purpose. Further, for example, by connecting the high pressure container 40 to the liquid storage tank 21 storing the foaming agent 15 and supplying carbon dioxide C into the liquid storage tank 21 by the high pressure container 40, the foaming agent 15 can be filled with carbon dioxide. It is also possible to have a structure in which C is mixed and dissolved.

The foaming machine 19 is further supplied with gas CG for forming the cells B of the foaming foam 5 by a compressor 30 (30A). In this embodiment, a high-pressure container 40 (40B) in which carbon dioxide C is stored in advance is connected to a compressor 30A, and carbon dioxide C is supplied from the high-pressure container 40B to the compressor 30A. The structure is such that gas CG with a higher volume ratio of carbon dioxide C than the air at the construction site is supplied to the machine 19. The compressor 30 to which the high-pressure container 40B can be connected can be easily manufactured, for example, by improving the air supply structure of a conventionally used air compressor.

The foaming machine 19 uses the supplied diluent 17 and the gas CG to produce a foamed foam 5 having a large number of fine bubbles B. The foam 5 produced by the foaming machine 19 is sent to the lightweight soil kneading machine 6. In the lightweight soil kneading machine 6, the supplied mud water 3 (adjusted mud), solidifying material 4, and foam 5 are stirred and mixed by a mixer to produce a slurry-like lightweight ground material LM containing a large number of air bubbles B.

As in this embodiment, when the bubbles B of the lightweight ground material LM are formed with gas CG having a higher volume ratio of carbon dioxide C than air, in the process of producing the lightweight ground material LM using the lightweight soil kneading machine 6. , a part of the carbon dioxide C contained in the gas CG forming the bubbles B of the expanded foam 5 may be consumed by dissolving in the water contained in the muddy water 3 or reacting with the alkali of the solidification material 4. be. Therefore, when the bubbles B of the lightweight ground material LM are formed with gas CG having a higher volume ratio of carbon dioxide C than air, the foam 5 of the lightweight ground material LM is It is better to increase the mixing ratio. An appropriate mixing ratio of the expanded foam 5 that can sufficiently secure the air bubbles B in the lightweight ground material LM can be determined in advance by conducting an indoor mixing test.

As shown in the image diagram shown in FIG. 2, in the lightweight ground material LM mixed with cellulose nanofibers F, the coating (interface) of each cell B is between the surfactant contained in the foam 5 and the cellulose. It is covered and protected by nanofibers F. Therefore, the mechanical strength of the interface of each air bubble B contained in the lightweight ground material LM increases due to the emulsification stability of cellulose nanofiber F than when cellulose nanofiber F is not added, and each air bubble B disappears. This makes it more difficult for the bubbles B to connect with each other. Furthermore, since the film of each bubble B is protected by the cellulose nanofibers F, carbon dioxide C contained in the gas CG forming the bubble B is suppressed from dissolving to the outside of the film and from reacting with alkali. Ru.

As illustrated in FIG. 1, the lightweight ground material LM before solidification produced by the lightweight soil kneading machine 6 is pumped to the pouring machine 7, and the lightweight soil material LM is transferred to the water bottom or on land where the ground is being improved. to be poured. In the process of pumping the lightweight ground material LM before solidification to the casting machine 7, in order to suppress the escape of air bubbles B from the lightweight ground material LM, the internal pressure of the pressure feeding pipe 24 that pumps the lightweight ground material LM is set to a positive pressure. It is best to keep it in good condition.

In this embodiment, the lightweight ground material LM before solidification is pumped through the pressure feed pipe 24 by the pressure pump 23, and the volume proportion of carbon dioxide C is higher than that of the air at the construction site by the compressor 30 (30B). By supplying compressed gas CG with increased pressure, the lightweight ground material LM before solidification is pumped to the pouring machine 7 while the internal pressure of the pressure feeding pipe 24 that pumps the lightweight ground material LM is maintained in a positive pressure state. It is configured. In this embodiment, a high-pressure container 40 (40C) storing carbon dioxide C is connected to the compressor 30B, and carbon dioxide C is supplied from the high-pressure container 40C to the compressor 30B. Note that if the amount of gas CG compressed by the compressor 30B exceeds the amount of gas CG supplied from the high-pressure container 40C and having a high volume ratio of carbon dioxide C, the compressor 30B will supply the compressed gas CG from the high-pressure container 40C. The structure is such that air at the construction site is supplied together with gas CG having a high volume ratio of carbon dioxide C, and compressed gas CG having a higher volume ratio of carbon dioxide C than the air at the construction site is supplied. You can also do it.

When the cast lightweight ground material LM hardens, a lightweight ground LG is formed in which a large number of independent voids formed by air bubbles B are retained. Inside the lightweight ground LG, a gas CG having a higher volume ratio of carbon dioxide C than air is retained in a large number of independent voids. The unit volume weight of the lightweight ground material LM in the hardened state is approximately 8 to 13 kN/ ^m3 , which is lighter than general ground materials, and the lightweight ground material LM has sufficient strength against ground subsidence, earthquakes, liquefaction, etc. have. Therefore, by placing the lightweight ground material LM using this ground improvement method, a stable lightweight ground LG can be formed.

As described above, according to the present invention, by mixing the lightweight ground material LM with the cellulose nanofibers F, the emulsification stability of the cellulose nanofibers F causes each air bubble B contained in the lightweight ground material LM to form a coating. stability can be improved. Thereby, it is possible to suppress the disappearance of the bubbles B contained in the lightweight ground material LM and the connection of the bubbles B with each other, and it is possible to form a lightweight ground LG with more stable quality.

As in this embodiment, when cellulose nanofibers F are added in the process of producing the lightweight ground material LM before casting the lightweight ground material LM, before the lightweight ground material LM is cast by the casting machine 7, The cellulose nanofibers F stabilize the film of the bubbles B contained in the lightweight ground material LM. Therefore, it is advantageous to reduce the rate at which the bubbles B contained in the lightweight ground material LM disappear.

In particular, as in this embodiment, when cellulose nanofibers F are added to the foam 5 in the process of producing the foam 5 using the foaming machine 19, the lightweight soil kneader 6 produces muddy water 3, solidifying material 4 and At a stage before the step of mixing the foam 5, the film of the cells B contained in the foam 5 is stabilized by the cellulose nanofibers F. Therefore, it is more advantageous to reduce the rate at which the air bubbles B disappear in the mixing process using the lightweight soil kneader 6. Further, when cellulose nanofibers F are added in the process of producing the foamed foam 5, the air bubbles B contained in the foamed foam 5 are uniformly dispersed due to the dispersibility of the cellulose nanofibers F. Therefore, in the mixing process using the lightweight soil kneader 6, the muddy water 3, the solidifying material 4, and the expanded foam 5 are easily mixed uniformly in a short time, which is advantageous in shortening the mixing time using the lightweight soil kneader 6. Since the mixing time by the lightweight soil kneader 6 can be shortened, it is also advantageous to reduce the rate at which the air bubbles B contained in the lightweight soil material LM disappear.

In addition, in the present invention, the cellulose nanofibers F may be mixed with the lightweight ground material LM before the lightweight ground material LM is completely solidified, and the cellulose nanofibers F may be mixed with the lightweight ground material LM in a process other than the process of producing the expanded foam 5 exemplified above. Fiber F can also be added and mixed. For example, in the process of producing slurry-like muddy water 3, cellulose nanofibers F can be added to raw material soil 2, water added to raw material soil 2, adjusted muddy water 3, and the like. Furthermore, for example, cellulose nanofibers F can also be added to the solidifying material 4. Furthermore, for example, the cellulose nanofibers F can be added in the step of mixing the muddy water 3, the expanded foam 5, and the solidifying material 4 using the lightweight soil kneader 6. In this case, it is only necessary to put the cellulose nanofibers F into the lightweight soil kneading machine 6 along with the muddy water 3, the solidification material 4, and the foam 5, so it is very easy to create a lightweight ground material LM to which cellulose nanofibers F have been added. can be created. Furthermore, for example, cellulose nanofibers F can be added and mixed in the step of pumping the produced lightweight ground material LM to the pouring machine 7. Further, for example, after the lightweight ground material LM is cast by the pouring machine 7, the cellulose nanofibers F can be added and mixed with the lightweight ground material LM before solidification. In this embodiment, a liquid emulsifier containing cellulose nanofibers F was used, but for example, powdered cellulose nanofibers F may also be added.

As mentioned above, in the conventional method in which cellulose nanofibers F are not added, the air bubbles B of the lightweight ground material LM are formed with gas CG having a higher volume ratio of carbon dioxide C than air to form a lightweight ground LG with stable quality. It was difficult to do so. In contrast, in the present invention, by mixing cellulose nanofibers F with the lightweight ground material LM, even when the volume ratio of carbon dioxide C contained in the bubbles B of the lightweight ground material LM is high, cellulose The emulsion stability of the fibers F can effectively suppress the disappearance of the bubbles B. Therefore, even when the air bubbles B of the expanded foam 5 are formed with gas CG having a higher volume ratio of carbon dioxide C than the air at the construction site, a lightweight ground LG having a large number of air bubbles B can be formed with stable quality. becomes possible.

In the lightweight ground LG formed by mixing cellulose nanofibers F, many independent air bubbles B (voids) of the lightweight ground LG are each covered with cellulose nanofibers F, so air bubbles B are formed. The carbon dioxide C contained in the gas CG is difficult to flow out to the outside of the coating of the bubbles B. Therefore, by adopting the ground improvement method of the present invention, it becomes possible to stably store carbon dioxide C, which is a cause of global warming, in the soil after improvement (lightweight ground LG), making it possible for civil engineering and construction It can contribute to reducing carbon dioxide C during construction.

Furthermore, in this ground improvement method, in the process of producing the lightweight ground material LM, a gas CG with a higher volume ratio of carbon dioxide C than the air at the construction site or a carbonic acid solution CW in which carbon dioxide C is dissolved is mixed. By doing so, it is possible to mix a large amount of carbon dioxide C into the lightweight ground material LM. Specifically, for example, a large amount of carbon dioxide C can be added to the lightweight ground material LM by mixing carbon dioxide C with water added to the raw material soil 2, water 16 diluting the solidification agent 4, foaming agent 15, etc. Can be mixed. Further, for example, by using the carbonic acid solution CW for the water added to the raw soil 2 or the water 16 for diluting the foaming agent 15, a large amount of carbon dioxide C can be mixed into the lightweight ground material LM.

By mixing a large amount of carbon dioxide C into the lightweight ground material LM, the carbon dioxide C contained in the gas CG forming the bubbles B of the lightweight ground material LM becomes difficult to dissolve due to the moisture in the lightweight ground material LM. Therefore, when forming the bubbles B of the lightweight ground material LM with gas CG having a higher volume ratio of carbon dioxide C than air, by bringing the carbon dioxide concentration of the lightweight ground material LM close to the saturated state, a large number of bubbles B It is advantageous to form lightweight ground LG with stable quality.

As in this embodiment, compressed gas CG with a higher volume ratio of carbon dioxide C than the air at the construction site is sent into the pressure pipe 24 connected to the pouring machine 7 for pouring the lightweight ground material LM. If the structure is such that the lightweight ground material LM is force-fed to the pouring machine 7, carbon dioxide C can be effectively mixed into the lightweight ground material LM in the process of force-fed the light-weight ground material LM. In addition, by pumping the lightweight ground material LM under positive pressure using compressed gas CG with a high volume ratio of carbon dioxide C, it is possible to eliminate the carbon dioxide contained in the lightweight ground material LM before pouring the lightweight ground material LM. It is also advantageous to suppress carbon C from flowing out.

As in this embodiment, when carbon dioxide C previously stored in the high-pressure container 40 or the like is mixed into the lightweight ground material LM, carbon dioxide C can be mixed into the lightweight ground material LM relatively easily. In particular, when the high-pressure container 40 is used, gas CG having a high volume ratio of carbon dioxide C can be easily supplied, so that a large amount of carbon dioxide C can be efficiently mixed into the lightweight ground material LM. Therefore, it is advantageous to increase carbon dioxide C stored in the lightweight ground LG. Furthermore, by using the high-pressure container 40, it is also possible to store carbon dioxide C discharged outside the construction site in the soil.

The method of mixing carbon dioxide C into the lightweight ground material LM (mud water 3, solidification material 4, foam 5) is not limited to the case of using the high pressure container 40 or the carbonic acid solution CW, but there are various other methods to mix the lightweight ground material LM. Carbon dioxide C can be mixed into the material LM. For example, carbon dioxide C emitted by machines used at the construction site can be mixed into the lightweight ground material LM.

Machines used at construction sites include construction machines used to collect soil from the bottom of the water or on land, diesel engines from ships (crane ships equipped with grab buckets, etc.), and construction machines that feed the raw material soil 2 into the vibrating sieve 9. 8. Machines (compressor 30A, diluent pump 18, foaming machine 19, etc.) used for producing the lightweight ground material LM can be exemplified. Further, examples include a compressor 30B that pumps the lightweight ground material LM to the pouring machine 7, a generator that supplies power to each machine used in construction, and the pouring machine 7.

When using carbon dioxide C discharged by a machine at a construction site, for example, the exhaust port of the machine that discharges carbon dioxide C and the air supply port of the compressor 30 that supplies carbon dioxide C are connected by piping. In addition, for example, equipment (for example, mud storage tank 11, storage equipment 14, water storage tank 20, storage tank 20, Piping for sending carbon dioxide C to the liquid tank 21 and storage tank 22) is provided. At construction sites where it is not permissible to contain pollutants contained in the exhaust gas emitted by machinery into the soil, for example, the above-mentioned piping is installed to contain particulate matter (PM) and nitrogen oxides ( For example, a filter is provided to remove pollutants such as NO, NO ₂ ), and volatile organic compounds (VOC).

By mixing carbon dioxide C emitted from machines at the construction site into the lightweight ground material LM, carbon dioxide C emitted into the atmosphere during construction using this ground improvement method can be effectively reduced. In particular, in this ground improvement method, since the amount of carbon dioxide C emitted by the pouring machine 7 and the compressor 30 is relatively large, the carbon dioxide C discharged by the pouring machine 7 and the compressor 30 is recovered to improve the lightweight soil. When used as carbon dioxide C mixed into the material LM, the amount of carbon dioxide C discharged in this ground improvement method can be effectively reduced. In addition, when exhaust gas emitted by machines used at the construction site is used, the heat of the exhaust gas can heat the lightweight ground material LM before solidification during the process of pumping the lightweight ground material LM in the pressure feeding pipe 24. I can do it. Being able to heat the lightweight ground material LM before solidification is advantageous in shortening the curing period until the cast lightweight ground material LM solidifies.

In addition, in the embodiment described above, the case where the bubbles B of the lightweight ground material LM are formed with the gas CG having a higher volume ratio of carbon dioxide C than air is exemplified, but even when the bubbles B are formed with air, the lightweight By mixing cellulose nanofibers F with the ground material LM, it is possible to further improve the stability of the film of each bubble B contained in the lightweight ground material LM. Therefore, compared to the conventional method in which cellulose nanofibers F are not mixed, it is more advantageous in reducing the rate of disappearance of air bubbles B contained in the lightweight ground material LM, and it is possible to form a lightweight ground LG with more stable quality. It becomes possible.

1 Ground improvement system 2 Raw material soil 3 Mud water 4 Solidifying material 5 Foam foam 6 Light-weight soil kneading machine 7 Casting machine 8 Construction machinery 9 Vibrating sieve 10 De-sludge machine 11 Sludge storage tank 12 Sludge pump 13 Light-weight soil conditioning machine 14 Storage Equipment 15 Foaming agent 16 Water 17 Diluent 18 Diluent pump 19 Foaming machine 20 Water tank 21 Liquid storage tank 22 Storage tank 23 Pressure pump 24 Pressure pipes 30, 30A, 30B Compressor 40, 40A to 40C High pressure container F Cellulose nano Fiber LM Lightweight ground material B Bubbles LG Lightweight ground C Carbon dioxide CG (with a higher volume ratio of carbon dioxide than air) Gas CW Carbonic acid solution

Claims (5)

A lightweight ground material is prepared by mixing slurry-like muddy water, foamed foam having a large number of cells, and a solidifying material, and by pouring and solidifying the lightweight ground material, a lightweight ground having a large number of cells is formed. In the ground improvement method,
A ground improvement method characterized in that the lightweight ground material is mixed with cellulose nanofibers. The soil improvement method according to claim 1, wherein the cellulose nanofibers are added in the process of producing the lightweight soil material before the lightweight soil material is cast. The ground improvement method according to claim 1 or 2, wherein the cells of the expanded foam are formed with gas having a higher volume ratio of carbon dioxide than air at the construction site. The ground improvement method according to claim 1 or 2, wherein in the process of producing the lightweight ground material, a gas with a higher volume ratio of carbon dioxide than air at the construction site or a carbonic acid solution in which carbon dioxide is dissolved is mixed. . Supplying compressed gas with a higher volume ratio of carbon dioxide than the air at the construction site into a pipe connected to a casting machine that performs pouring of the lightweight ground material and through which the lightweight ground material passes, The ground improvement method according to claim 1 or 2, wherein the lightweight ground material is pumped to the pouring machine.

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