WO2021161637A1

WO2021161637A1 - Ground improvement method

Info

Publication number: WO2021161637A1
Application number: PCT/JP2020/045773
Authority: WO
Inventors: 聡之島田
Original assignee: 花王株式会社
Priority date: 2020-02-14
Filing date: 2020-12-09
Publication date: 2021-08-19
Also published as: JP2021127446A; JP7299869B2

Abstract

Provided is a ground improvement method capable of enhancing the compressive strength of soil cement even in the case where an acidic soil containing an organic substance such as a humic acid, a fulvic acid, a humin, or a bitumen is used. This ground improvement method comprises steps 1-3. <Step 1> A step for formulating a slurry by mixing water, a hydraulic powder, and a component (A). Component (A): A particle group having a particle size of 30 nm or less, 70 nm or less, and 100 nm or less when the respective cumulative number frequencies are 10%, 50%, and 90%, respectively, as determined by measuring the particle sizes of all contained particles by dynamic light scattering and plotting cumulative number frequencies with respect to particle size. <Step 2> A step for injecting the slurry obtained in step 1 into a ground to mix the slurry with a soil to obtain a mixture, wherein the mixed amount of the slurry per 1 m³ of the soil is 150-800 kg, and the mass ratio of the hydraulic powder and the soil in the mixture is 0.01-0.6. <Step 3> A step for solidifying the mixture of the slurry and the soil obtained in step 2.

Description

Ground improvement method

The present invention relates to a ground improvement method, an additive composition for ground improvement, and a ground improvement body.

Background technology As a method of improving the ground of the foundation for constructing a building, a ground improvement method in which a concrete or steel pipe ground improvement column is driven into the ground, or a cement-based solidifying material such as cement milk is injected while excavating the ground. A ground improvement method is known in which a column-shaped ground improvement body formed by mixing excavated soil and the cement milk is directly formed in the ground.

In ground improvement, which modifies the ground by adding and mixing cement-based solidifying material with soil, appropriate solidifying material, compounding ratio, additives, etc. are taken into consideration, such as the nature of the soil to be mixed and the type of construction method for ground improvement. It is desirable to select. In particular, when the soil to be mixed is acidic soil containing a large amount of organic matter such as humic acid, the desired strength can be obtained even if a cement solidifying material is used because the hydration reaction of the cement is hindered by the adsorption of the organic matter on the cement surface. However, it may be difficult to improve the ground.

Japanese Patent Application Laid-Open No. 2003-49165 describes that 1 to 20% by weight of volcanic ash having a particle size of 0.06 mm or less and silica sand sufficient to form an aqueous colloidal solution are formed on mud containing calcium ions in terms of the total amount of solid matter. A method for solidifying mud soil, which comprises mixing 0.02 to 1% by weight of special fine particles, and 1 to 20% by weight of volcanic ash having a particle size of 0.06 mm or less in terms of the total amount of solid matter in mud soil containing calcium ions. And a method for solidifying mud is disclosed, which comprises mixing 0.02 to 1% by weight of a special kira of fine particles made of silica sand sufficient for forming an aqueous colloidal solution.

Outline of the Invention The present invention provides a ground improvement method capable of increasing the compressive strength of soil cement even when using acidic soil containing organic substances such as humic acid, fulvic acid, humin, and bitumen.

The present invention relates to a ground improvement method having the following steps 1 to 3.
<Step 1>
Step of preparing a slurry by mixing water, a water-hard powder, and the following component (A) Component (A): A particle group whose particle size is measured by a dynamic light scattering method. When the cumulative number frequency with respect to the particle size is plotted, the particle size is 30 nm or less when the cumulative number frequency is 10%, and the particle size is 70 nm or less when the cumulative number frequency is 50%, and 90%. Particle group having a particle size of 100 nm or less <Step 2>
In the step of injecting the slurry obtained in step 1 into the ground and mixing the slurry and soil to obtain a mixture, ^{the mixing amount of the slurry per 1 m 3 of} soil is 150 kg or more and 800 kg or less, and water in the mixture. Step where the mass ratio of hard powder / soil is 0.01 or more and 0.6 or less <Step 3>
Step of solidifying the mixture of slurry and soil obtained in step 2

The present invention also relates to a ground improvement additive composition containing the component (A).

Further, the present invention is a ground improvement body containing soil, water-hard powder, water, and the above-mentioned component (A), and is a mass ratio of the content of water-hard powder to the content of soil (water-hard powder). It relates to a ground improvement body having a body / soil) of 0.01 or more and 0.6 or less.

According to the present invention, there is provided a ground improvement method capable of increasing the compressive strength of soil cement even when using acidic soil containing organic substances such as humic acid, fulvic acid, humin, and bitumen.

Form for carrying out the invention [ground improvement method]
<Step 1>
Step 1 is a step of preparing a slurry by mixing water, a hydraulic powder, and the component (A).

The hydraulic powder used in the present invention is a powder having physical properties that hardens by a hydration reaction, and examples thereof include cement. Preferred are cements such as Portland cement such as ordinary Portland cement, belite cement, moderate heat cement, early-strength cement, ultra-fast-strength cement, and sulfate-resistant cement. In addition, blast furnace slag cement, steel slag cement, blast furnace slag cement, steel slag cement, etc. Fly ash cement, silica fume cement and the like may be used. Further, a cement-based solidifying material may be used.
From the viewpoint of economy, the hydraulic powder is preferably one or more selected from ordinary Portland cement, blast furnace slag cement, and steelmaking slag cement.

In the present invention, the amount of the hydraulic powder is the amount of the powder having physical properties to be cured by the hydration reaction, but the hydraulic powder is a powder having a pozolan action or a powder having latent hydraulic property. When powders selected from body and stone powder (calcium carbonate powder) are contained, in the present invention, those amounts are also included in the amount of hydraulic powder.

The component (A) of the present invention is a particle group, and when the particle size of all the contained particles is measured by a dynamic light scattering method and the cumulative number frequency with respect to the particle size is plotted, the cumulative number frequency becomes 10%. It is a group of particles having a particle size of 30 nm or less at the time of becoming, a particle size of 70 nm or less at the time of 50%, and a particle size of 100 nm or less at the time of 90%.
The particle size (D10) when the cumulative number frequency of the component (A) is 10%, the particle size (D50) when the cumulative number frequency is 50%, and the particle size (D90) when the cumulative number frequency is 90% are included in the particle group. The particle size of all the particles is measured by the dynamic light scattering method using a laser particle analysis system (for example, manufactured by Otsuka Electronics Co., Ltd., trade name: ELSZ-1000), and the cumulative number frequency with respect to the particle size is plotted. Then, it is calculated by the Cumulant method analysis. More specifically, it is calculated by the method described in Examples.

The particle size (D10) when the cumulative number frequency of the particle group of the component (A) is 10% is 30 nm or less, preferably 25 nm or less, more preferably 20 nm or less, still more preferably, from the viewpoint of improving the strength of the soil cement. Is 15 nm or less, more preferably 12 nm or less, and preferably 0.1 nm or more, more preferably 0.5 nm or more, still more preferably 1.0 nm or more.
The particle size (D50) when the cumulative number frequency of the particle group of the component (A) is 50% is 70 nm or less, preferably 60 nm or less, more preferably 50 nm or less, still more preferably, from the viewpoint of improving the strength of the soil cement. Is 40 nm or less, more preferably 30 nm or less, still more preferably 25 nm or less, still more preferably 20 nm or less, and preferably 0.1 nm or more, more preferably 0.5 nm or more, still more preferably 1.0 nm or more. be.
The particle size (D90) when the cumulative number frequency of the particle group of the component (A) is 90% is 100 nm or less, preferably 90 nm or less, more preferably 80 nm or less, still more preferably, from the viewpoint of improving the strength of the soil cement. Is 70 nm or less, more preferably 60 nm or less, still more preferably 50 nm or less, still more preferably 40 nm or less, still more preferably 30 nm or less, and preferably 0.1 nm or more, more preferably 0.5 nm or more, further. It is preferably 1.0 nm or more.

Examples of the particle group of the component (A) of the present invention include one or more particle groups selected from silicon oxide, aluminum oxide, silicon nitride, titanium oxide, and iron oxide, which improve the strength of soil cement containing acidic soil. From the viewpoint, one or more kinds of particle groups selected from silicon oxide and aluminum oxide are preferable.

In step 1, from the viewpoint of improving the strength of soil cement containing acidic soil, the component (B) is further selected from calcium chloride salt or aluminum chloride salt having a solubility in water at 20 ° C. of 20 g / 100 ml or more. It is preferable to mix one or more compounds.

The component (B) is preferably one or more selected from calcium chloride and aluminum chloride from the viewpoint of improving the strength of soil cement containing acidic soil.

In step 1, from the viewpoint of improving the strength of soil cement containing acidic soil, it is preferable to further mix one or more compounds selected from calcium sulfate, sodium sulfate, and sodium thiosulfate as the component (C).

In step 1, a cement dispersant may be further mixed from the viewpoint of improving the fluidity of the cement slurry. As the cement dispersant, a polycarboxylic acid-based dispersant or a naphthalene sulfonic acid formaldehyde condensate-based dispersant is preferable.

In step 1, from the viewpoint of workability, the mass ratio of water / water-hard powder is preferably 40% by mass or more, more preferably 50% by mass or more, still more preferably 60% by mass. % Or more, preferably 150% by mass or less, more preferably 120% by mass or less, still more preferably 100% by mass or less. This mass ratio is calculated by (amount of water / amount of hydraulic powder) × 100.
In step 1, either fresh water or seawater can be used as the water used for preparing the slurry. At least part of the water in the slurry may be seawater.

In step 1, from the viewpoint of improving the strength of the soil cement containing acidic soil, the component (A) is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, based on the water-hard powder. More preferably 1% by mass or more, still more preferably 2% by mass or more, still more preferably 3% by mass or more, still more preferably 4% by mass or more, and preferably 10% by mass or less, more preferably 8% by mass. Hereinafter, the mixture is more preferably 6% by mass or less.

In step 1, when the component (B) is used, the component (B) is preferably 0.1% by mass or more, more preferably 0.1% by mass or more, based on the water-hard powder, from the viewpoint of improving the strength of the soil cement containing acidic soil. Is 0.5% by mass or more, more preferably 1% by mass or more, still more preferably 2% by mass or more, still more preferably 3% by mass or more, still more preferably 4% by mass or more, and preferably 10% by mass. Hereinafter, the mixture is more preferably 8% by mass or less, still more preferably 5% by mass or less.

In step 1, when the component (B) is used, the mass ratio of the component (A) and the component (B) to the component (A) and the component (B) (from the viewpoint of improving the strength of the soil cement containing acidic soil) A) / (B) is preferably 0.1 or more, more preferably 0.5 or more, further preferably 1 or more, and preferably 10 or less, more preferably 5 or less, still more preferably 3 or less. Mix in.

In step 1, when the component (C) is used, the component (C) is preferably 0.1% by mass or more, more preferably 0.1% by mass or more, based on the water-hard powder, from the viewpoint of improving the strength of the soil cement containing acidic soil. Is 0.5% by mass or more, more preferably 1% by mass or more, still more preferably 2% by mass or more, still more preferably 3% by mass or more, still more preferably 4% by mass or more, and preferably 20% by mass. Hereinafter, the mixture is more preferably 10% by mass or less, further preferably 8% by mass or less, still more preferably 6% by mass or less.

In the ground improvement method of the present invention, when the component (C) is used, the mass ratio of the component (A) to the component (C) and the component (A) to the component (C) is increased from the viewpoint of improving the strength of the soil cement. (A) / (C) is preferably 0.01 or more, more preferably 0.05 or more, still more preferably 0.1 or more, still more preferably 0.5 or more, and preferably 2 or less, more preferably. Is 1.5 or less, more preferably 1 or less.

Alkali metal carbonate may be further mixed in step 1, but the mixing amount of alkali metal carbonate is limited from the viewpoint of improving the strength of soil cement. Examples of the alkali metal carbonate include one or more selected from sodium carbonate, potassium carbonate, sodium hydrogen carbonate, and potassium hydrogen carbonate.

When the alkali metal carbonate is mixed in step 1, the mixing amount of the alkali metal carbonate is preferably 1% by mass or less, more preferably 0, with respect to the water-hard powder from the viewpoint of improving the strength of the soil cement. .1% by mass or less, more preferably 0.01% by mass or less. Further, in step 1, it is preferable not to mix the alkali metal carbonate.

When the alkali metal carbonate is mixed in step 1, the reason why the mixing amount is limited is not necessarily clear, but it is presumed as follows.
When an alkali metal carbonate is mixed in step 1, C3A contained in the water-hard powder reacts with carbonate ions to generate carbonic acid-based hydrates (monocarbonate, hemicarbonate), and ettringite from C3A. The strength is reduced due to the inhibition of the production of carbonic acid. The strength development of soil cement using acidic soil containing organic substances such as humic acid, fulvic acid, humin, and bitumen is due to the formation of ettrin guides from C3A contained in the water-hard powder. It will be extremely important. This is because the formation of CSH is strongly influenced by the type of soil, whereas the formation of ettrin guide is not easily influenced by the type of soil.
Therefore, it is preferable to limit the mixing amount of the alkali metal carbonate so as not to reduce the amount of ettringite produced.

The specific method for preparing the slurry in step 1 may be based on a known method for preparing a hydraulic composition such as cement milk.

<Process 2>
Step 2 is a step of injecting the slurry obtained in step 1 into the ground and mixing the slurry and soil to obtain a mixture, wherein ^{the mixing amount of the slurry per 1 m 3 of} soil is 150 kg or more and 800 kg or less. This is a step in which the mass ratio of the water-hard powder / soil in the mixture is 0.01 or more and 0.6 or less.

The ground improvement method of the present invention can be applied to grounds having various soils.
In the ground improvement method of the present invention, the soil is soil in which the organic content required by the ignition loss method is 30% or more, and the soil suspension is measured by the method specified by the Japanese Geotechnical Society Standard JGS0211-2009. The effect is exhibited even in soil where the pH of the liquid is 6 or less.

The amount of organic matter obtained by the ignition loss method of soil is preferably 30% or more, more preferably 35% or more, still more preferably 40% or more, from the viewpoint of further improving the strength of the component (A) having a small particle size. , And preferably 90% or less, more preferably 80% or less. Here, the ignition loss method is a method specified in the Japanese engineering standard JIS A1226: 2009.
Examples of the organic matter contained in the soil include one or more kinds of organic matter selected from humic acid, fulvic acid, humin, and bitumen.

The soil is acidic soil in which the pH of the soil suspension measured by the method specified by the Japanese Geotechnical Society Standard JGS0211-2009 is preferably 6 or less, more preferably 5.5 or less, still more preferably 5.0 or less. May be.

In step 2, from the viewpoint of the mixture of soil cement, ^{the mixing amount of the slurry per 1 m 3 of} soil is 150 kg or more, preferably 200 kg or more, more preferably 250 kg or more, further preferably 300 kg or more, and the construction of soil cement. From the viewpoint of sex, it is 800 kg or less, preferably 500 kg or less, and more preferably 400 kg or less.

In step 2, from the viewpoint of the mixture of soil cement, the water-hard powder is added to the soil, and the mass ratio of the water-hard powder / soil is 0.01 or more, preferably 0.1 or more, more preferably 0. 2 or more, more preferably 0.25 or more, and from the viewpoint of workability of soil cement, 0.6 or less, preferably 0.5 or less, more preferably 0.45 or less, still more preferably 0.4 or less. Mix.

The specific method for injecting the slurry into the ground may be based on a known ground improvement method.
As a method of injecting the slurry into the ground, for example, an injection stirring method (one-phase flow method, two-phase flow method, three-phase flow method), a mechanical stirring method (CDM method, etc.), and an underground continuous wall method (SMW method, SMW method, etc.) TRD method, etc.). Furthermore, in a system in which the component (A) and the component (B) are optionally dry-blended into a hydraulic powder, it is also used for the DJM (Dry Jet Mixing) method of powder mixing method and shallow layer improvement using a stabilizer or the like. can.

<Step 3>
Step 3 is a step of solidifying the mixture of the slurry and soil obtained in Step 2. The mixture of slurry and soil is solidified according to a known ground improvement method.

The ground improvement method of the present invention can be applied to a surface layer improvement method, a deep layer improvement method, a steel pipe pile method, a shield method, and the like. For example, the deep layer improvement method can be applied to the high pressure injection method, the TRD method, the SMW method, and the like.

[Additive composition for ground improvement]
The ground improvement additive composition of the present invention is a ground improvement additive composition containing the component (A). The additive composition for ground improvement of the present invention can further contain the component (B) from the viewpoint of improving the strength. Further, the additive composition for ground improvement of the present invention can further contain the component (C) from the viewpoint of improving the strength. The ground improvement additive composition of the present invention may consist of a component (A), a component (B) and a component (C).

Such a ground improvement additive composition is an additive composition used for a ground improvement material to be mixed with soil for ground improvement, for example, a hydraulic composition such as cement milk.
The amount of the additive composition for ground improvement of the present invention can be set in consideration of the type of ground improvement material, the type of soil (ground), etc., but the ground improvement method of the present invention and the ground improvement body of the present invention can be set. It is preferable that the amount is as described in. The matters described in the ground improvement method of the present invention can be appropriately applied to the ground improvement additive composition of the present invention.
The ground improvement additive composition of the present invention may be for acidic soil. Further, the additive composition for ground improvement of the present invention is soil in which the organic content required by the ignition weight loss method is 30% or more, and the soil is measured by the method specified by the Japanese Geotechnical Society standard JGS0211-2009. It may be for soil where the pH of the suspension is 6 or less.

[Slurry for ground improvement]
The ground improvement slurry of the present invention is a ground improvement slurry containing water, a hydraulic powder, and the component (A). The slurry has a water / hydraulic powder mass ratio of preferably 40% by mass or more and 150% by mass or less. The ground improvement slurry of the present invention may be a ground improvement slurry obtained by mixing water, a hydraulic powder, and the ground improvement additive composition of the present invention. The ground improvement slurry of the present invention is preferably used in the ground improvement method of the present invention. In addition, the ground improvement slurry of the present invention can contain one or more components selected from the component (B) and the component (C). The matters described in the ground improvement method and the ground improvement additive composition of the present invention can be appropriately applied to the ground improvement slurry of the present invention. The ground improvement slurry of the present invention may be for acidic soil. The soil improvement slurry of the present invention is soil having an organic content of 30% or more required by the ignition loss method, and is a soil suspension measured by the method specified by the Japanese Geotechnical Society Standard JGS0211-2009. May be for soils with a pH of 6 or less.

The ground improvement slurry of the present invention is a ground improvement slurry that is mixed with soil for ground improvement, for example, a hydraulic composition such as cement milk.
The amount of the ground improvement slurry used of the present invention can be set in consideration of the composition of the ground improvement slurry, the type of soil (ground), etc., but will be described in the ground improvement method of the present invention and the ground improvement body of the present invention. It is preferable that the amount is increased.
The soil improvement slurry of the present invention weighs 150 kg or more, preferably 200 kg or more, more preferably 250 kg or more, still more preferably 300 kg or more, and 800 kg or less, preferably 500 kg or less, more preferably 400 kg or less per ^{1 m 3 of soil.} It is used in combination with. Further, in the ground improvement slurry of the present invention, the water-hard powder and soil in the slurry have a water-hard powder / soil mass ratio of 0.01 or more, preferably 0.1 or more, more preferably 0. It is used by mixing with soil in an amount of .2 or more, more preferably 0.25 or more, and 0.6 or less, preferably 0.5 or less, more preferably 0.45 or less, still more preferably 0.4 or less.

[Ground improvement body]
The ground improvement body of the present invention is a ground improvement body containing soil, water-hard powder, water, and component (A), and is a mass ratio (water) of the content of water-hard powder to the content of soil. Hard powder / soil) is a ground improvement body of 0.01 or more and 0.6 or less. This ground improvement body may be a ground improvement body obtained by curing a slurry containing soil, water, hydraulic powder, and component (A).
The ground improvement body of the present invention may be a ground improvement body formed by mixing soil and the ground improvement slurry of the present invention.

The matters described in the ground improvement method of the present invention, the additive composition for ground improvement, and the slurry for ground improvement can be appropriately applied to the ground improvement body of the present invention. The ground improvement body of the present invention can contain one or more components selected from the component (B) and the component (C).
Specific examples of the water-hard powder, the component (A), the component (B), the component (C), the soil, etc. in the ground improvement body of the present invention, preferred embodiments, and quantitative specifications such as each mass ratio are also specified. , The same as the ground improvement method of the present invention, the ground improvement additive composition, and the ground improvement slurry. For example, the soil is acidic soil, preferably soil having an organic content of 30% or more determined by the ignition loss method, and is a soil suspension measured by the method specified by the Japanese Geotechnical Society Standard JGS0211-2009. The soil may have a pH of 6 or less.

Example <Ingredients>
The components used in the following examples and comparative examples are shown below.
(A) Component-Silicon oxide (1): Silicon oxide (coloidal silica), particle size (D10) 5 nm when the cumulative number frequency is 10%, particle size (D50) when the cumulative number frequency is 50%. 8 nm, particle size (D90) when the cumulative number frequency is 90%, silicon oxide (2) manufactured by Nikki Catalyst Kasei Co., Ltd .: silicon oxide (colloidal silica), particles when the cumulative number frequency is 10% Diameter (D10) 7 nm, particle size (D50) 10 nm when the cumulative number frequency is 50%, particle size (D90) 15 nm when the cumulative number frequency is 90%, silicon oxide manufactured by Nikki Catalyst Kasei Co., Ltd. 3): Silicon oxide (coloidal silica), particle size (D10) 10 nm when the cumulative number frequency is 10%, particle size (D50) 14 nm when the cumulative number frequency is 50%, cumulative number frequency 90% Particle size (D90) 27 nm, manufactured by Nikki Catalyst Kasei Co., Ltd. Aluminum oxide: γ-alumina, particle size (D10) 15 nm when the cumulative number frequency is 10%, cumulative number frequency is 50% Particle size (D50) of 23 nm, particle size (D90) of 31 nm when the cumulative number frequency is 90%, (A') component manufactured by Baikowski Japan (comparative component of (A) component)
-Silicon oxide (4): Silicon oxide (coloidal silica), particle size (D10) 83 nm when the cumulative number frequency is 10%, particle size (D50) 100 nm when the cumulative number frequency is 50%, cumulative number Particle size (D90) 130 nm when the frequency reaches 90%, manufactured by JGC Catalysts and Chemicals Co., Ltd.

The particle size (D10) when the cumulative number frequency of the component (A) and the component (A') is 10%, the particle size (D50) when the frequency is 50%, and the particle size (D90) when the cumulative number frequency is 90%. Uses a laser particle analysis system (manufactured by Otsuka Electronics Co., Ltd., trade name: ELSZ-1000) to dynamically scatter all particles contained in the particle group of component (A) and component (A') under the following conditions. The particle size was measured by the method, and the cumulative number frequency with respect to the particle size was plotted and calculated by the Cumulant method analysis.
[Measurement condition]
-Measurement sample: Weigh the measurement sample into a screw tube and add water as a dispersion solvent so that the solid content concentration becomes 0.4% by mass.-Temperature: 23.6 ° C.
-Angle between incident light and detector: 90 °
-Number of integrations: 50-Refractive index of water as a dispersion solvent: 1.333

(B) Ingredients-Calcium chloride: Fuji Film Wako Pure Chemical Industries, Ltd.-Aluminum chloride: Fuji Film Wako Pure Chemical Industries, Ltd. (C) Ingredients-Calcium sulfate: Fuji Film Wako Pure Chemical Industries, Ltd.-Sodium sulfate: Fuji Film Wako Pure Chemical Industries, Ltd. ・ Sodium thiosulfate: Fuji Film Wako Pure Chemical Industries, Ltd.

Hydraulic powder ・ Ordinary Portland cement: Taiheiyo Cement Co., Ltd. ・ Blast furnace slag cement: Nittetsu Blast Furnace Cement Co., Ltd.

The soil used was the peat shown in Table 1. The organic content of peat was measured using the ignition loss method specified in Japanese Industrial Standard JIS A1226: 2009. The pH of the peat soil suspension was measured by the method specified by the Japanese Geotechnical Society Standard JGS0211-2009.

<Examples and comparative examples>
Soil cement was prepared using the soil shown in Table 1, and the soil cement was evaluated as follows. The results are shown in Table 2.

(1) Preparation of soil cement First, cement milk was prepared by the following procedure. The component (A) or the component (A'), the component (B) and water are mixed to prepare an aqueous additive solution, and the aqueous additive solution is prepared in a 500 ml plastic cup (500 mL disposable cup, Nikko Hansen Co., Ltd.). The water-hard powder and the component (C) were mixed and kneaded with a hand mixer for 1 minute to prepare cement milk.
Tap water was used as the water for preparing the additive aqueous solution. The aqueous solution of the water-hard powder and the aqueous solution of the additive were used so that the mass ratio of the aqueous solution of the additive / the aqueous solution of the additive was 60% by mass. The mass ratio of the additive aqueous solution / water-hard powder substantially corresponds to the water / water-hard powder ratio.
The component (A), the component (A'), the component (B), and the component (C) were used so that the amount added to the hydraulic powder was as shown in Table 2.
Then, the soil is poured into another 500 ml plastic cup, and the cement milk is poured so as to have the injection amount shown in Table 2 (mass ratio (hydraulic powder / soil) is 0.38), and the hand. Soil cement was prepared by stirring with a mixer for 3 minutes. After stirring, the upper surface was leveled by applying vibration, sealed with a wrap film, and allowed to stand at 22 ° C. for a predetermined time.

(2) Evaluation The strength of the ground improvement body obtained by using the prepared soil cement was evaluated by the following method. Soil cement was filled in a mold (diameter 50 mm × height 100 mm). Filling was done with a table vibrator for 30 seconds in two layers. Two specimens were prepared. The strength of the cured product (ground improvement product) of the specimen obtained above in air at 20 ° C. for 7 days was measured by a uniaxial compression tester. Table 2 shows the average value of the intensities of the two specimens as the intensities for 7 days.

In Table 2, in the comparative example in which the 7-day strength was described as 0, the strength was not measured because the soil cement could not be removed from the mold because it did not harden.

<Reference example>
In addition to the above component (A), the component (A') used in the reference example is shown below.
-Silicon oxide (5): Silicon oxide (coloidal silica), particle size (D10) 120 nm when the cumulative number frequency is 10%, particle size (D50) 160 nm when the cumulative number frequency is 50%, cumulative number Particle size (D90) 200 nm when the frequency reaches 90%, manufactured by JGC Catalysts and Chemicals Co., Ltd.

(3) Preparation of cement paste Cement was prepared by the following procedure. The additive aqueous solution is prepared by mixing the component (A) or the component (A') with water, and the additive aqueous solution and the water-hard powder (ordinary) are prepared in a 500 ml plastic cup (500 mL disposable cup, Nikko Hansen Co., Ltd.). Portland cement (manufactured by Taiheiyo Cement Co., Ltd.) was mixed and kneaded with a hand mixer for 1 minute to prepare a cement paste. After stirring, the upper surface was leveled by applying vibration, sealed with a wrap film, and allowed to stand at 22 ° C. for a predetermined time.
Tap water was used as the water for preparing the additive aqueous solution. The water-hard powder and the additive aqueous solution were used so that the water content / water-hard powder mass ratio in the additive aqueous solution was 60% by mass.
The component (A) or the component (A') was used so that the amount added to the hydraulic powder was as shown in Table 3.

(4) Evaluation The strength of the prepared cement paste was evaluated by the following method. The cement paste was filled in a mold (diameter 50 mm × height 100 mm). Filling was done with a table vibrator for 30 seconds in two layers. Two specimens were prepared. The strength of the cured product (ground improvement product) of the specimen obtained above in air at 20 ° C. for 7 days was measured by a uniaxial compression tester. Table 3 shows the average value of the intensities of the two specimens as the intensities for 7 days.

In Table 2, in Comparative Example 1 in which the component (A) is not mixed only with the water-hard powder in the soil which is peat, and in Comparative Example 2 in which the water-hard powder and the particle group not satisfying the conditions of the present invention are mixed, the soil is used. Although the cement cannot be hardened, in Examples 1 to 12 of the present invention in which the water-hard powder and the specific particle group which is the component (A) are mixed in the soil, the soil cement can be hardened. I understand.
On the other hand, as shown in the results of Table 3, it can be seen that when the particle group is added to the cement paste containing no soil, the strength can be improved for 7 days even when the particle group that does not satisfy the conditions of the present invention is added. As described above, the present invention has been found that the curing strength of soil cement can be improved by adding a particle group satisfying a specific condition to soil cement containing soil and hydraulic powder. I understand.

Claims

A ground improvement method having the following steps 1 to 3.
<Step 1>
Step of preparing a slurry by mixing water, a water-hard powder, and the following component (A) Component (A): A particle group whose particle size is measured by a dynamic light scattering method. When the cumulative number frequency with respect to the particle size is plotted, the particle size is 30 nm or less when the cumulative number frequency is 10%, and the particle size is 70 nm or less when the cumulative number frequency is 50%, and 90%. Particle group having a particle size of 100 nm or less <Step 2>
In the step of injecting the slurry obtained in step 1 into the ground and mixing the slurry and soil to obtain a mixture, the mixing amount of the slurry per 1 m 3 of soil is 150 kg or more and 800 kg or less, and water in the mixture. Step where the mass ratio of hard powder / soil is 0.01 or more and 0.6 or less <Step 3>
Step of solidifying the mixture of slurry and soil obtained in step 2
The soil is a soil in which the organic content required by the ignition loss method is 30% or more, and the pH of the soil suspension measured by the method specified by the Japanese Geotechnical Society standard JGS0211-2009 is 6 or less. The ground improvement method according to claim 1, which is soil.
The ground improvement method according to claim 1 or 2, wherein the component (A) is one or more particle groups selected from silicon oxide and aluminum oxide.
The ground improvement method according to any one of claims 1 to 3, wherein in step 1, the component (A) is mixed with the hydraulic powder in an amount of 0.1% by mass or more and 10% by mass or less.
The ground improvement method according to any one of claims 1 to 4, wherein the hydraulic powder is one or more selected from ordinary Portland cement, blast furnace slag cement, and steelmaking slag cement.
The ground improvement method according to any one of claims 1 to 5, wherein the following component (B) is further mixed in step 1.
(B) Ingredient: One or more compounds selected from calcium chloride salt or aluminum chloride salt having a solubility in water at 20 ° C. of 20 g / 1000 ml or more.
The ground improvement method according to claim 6, wherein the component (B) is at least one selected from calcium chloride and aluminum chloride.
The ground improvement method according to claim 6 or 7, wherein in step 1, the component (B) is mixed with the hydraulic powder in an amount of 0.1% by mass or more and 10% by mass or less.
The present invention according to any one of claims 1 to 8, wherein in step 1, one or more compounds (hereinafter referred to as (C) component) selected from (C) calcium sulfate, sodium sulfate, and sodium thiosulfate are further mixed. Ground improvement method.
The ground improvement method according to claim 9, wherein in step 1, the component (C) is mixed with the hydraulic powder in an amount of 0.1% by mass or more and 10% by mass or less.
The ground improvement method according to any one of claims 1 to 10, wherein in step 1, the mixed amount of the alkali metal carbonate is 1% by mass or less with respect to the water-hard powder.
An additive composition for ground improvement containing the following component (A).
(A) Component: A particle group, in which the particle size of all contained particles is measured by a dynamic light scattering method and the cumulative number frequency with respect to the particle size is plotted, and the particles when the cumulative number frequency becomes 10%. A group of particles having a diameter of 30 nm or less, a particle size of 70 nm or less when it reaches 50%, and a particle size of 100 nm or less when it reaches 90%.
(B) The additive for ground improvement according to claim 12, further comprising (B) one or more compounds selected from calcium chloride salt or aluminum chloride salt having a solubility in water at 20 ° C. of 20 g / 1000 ml or more. Composition.
It is a ground improvement body containing soil, water-hard powder, water, and the following component (A), and the mass ratio (water-hard powder / soil) between the content of water-hard powder and the content of soil is Ground improvement body of 0.01 or more and 0.6 or less.
(A) Component: A particle group, in which the particle size of all contained particles is measured by a dynamic light scattering method and the cumulative number frequency with respect to the particle size is plotted, and the particles when the cumulative number frequency becomes 10%. A group of particles having a diameter of 30 nm or less, a particle size of 70 nm or less when it reaches 50%, and a particle size of 100 nm or less when it reaches 90%.