JP7326384B2 - Ground improvement method - Google Patents

Description

The present invention relates to a soil improvement method, a soil improvement additive composition, and a soil improvement body.

As a method to improve the foundation for building a building, there is a ground improvement method in which a concrete or steel pipe ground improvement column is driven into the ground, and a cement-based solidification material such as cement milk is injected while excavating the ground, and the excavated soil is removed. A soil improvement method is known in which a column-shaped soil improvement body formed by mixing cement milk with the cement milk is directly formed in the ground.

In ground improvement that improves the ground by adding and mixing cement-based solidifying materials with soil, appropriate solidifying materials, compounding ratios, additives, etc. should be selected. Especially when the soil to be mixed is acidic soil containing a large amount of organic matter such as humic acid, the hydration reaction of cement is inhibited by the adsorption of organic matter on the surface of the cement. Therefore, ground improvement may be difficult.

In Patent Document 1, a special kira fine particle consisting of 1 to 20% by weight of volcanic ash with a particle size of 0.06 mm or less and silica sand sufficient to form an aqueous colloidal solution is added to mud containing calcium ions. 0.02 to 1% by weight of volcanic ash having a particle size of 0.06 mm or less and an aqueous colloidal solution are added to the mud containing calcium ions, in terms of the total amount of solid matter. Disclosed is a mud solidification method characterized by mixing 0.02 to 1% by weight of special kira fine particles consisting of silica sand sufficient to form .

JP-A-2003-49165

The present invention provides a ground improvement method that can increase the compressive strength of soil cement even when acidic soil containing organic matter such as humic acid, fulvic acid, humin and bitumen is used.

The present invention relates to a ground improvement method having steps 1 to 3 below.
<Step 1>
A step of mixing water, hydraulic powder, and (A) colloidal silica having a surface potential of 0 mV or more and +50 mV or less (hereinafter referred to as component (A)) to prepare a slurry.
<Step 2>
A step of injecting the slurry obtained in step 1 into the ground and mixing the slurry and soil to obtain a mixture.
<Step 3>
Solidifying the mixture of slurry and soil obtained in step 2.

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

The present invention also provides a soil improvement material containing soil, hydraulic powder, water, and component (A), wherein the mass ratio of the content of hydraulic powder to the content of soil (hydraulic powder / soil) is 0.01 or more and 0.6 or less.

INDUSTRIAL APPLICABILITY According to the present invention, a ground improvement method is provided that can increase the compressive strength of soil cement even when acidic soil containing organic matter such as humic acid, fulvic acid, humin and bitumen is used.

[Ground improvement method]
<Step 1>
Step 1 is a step of mixing water, hydraulic powder, and (A) colloidal silica having a surface potential of 0 mV or more and +50 mV or less (hereinafter referred to as component (A)) to prepare a slurry.

The hydraulic powder used in the present invention is a powder having a physical property of hardening by a hydration reaction, and examples thereof include cement and the like. Preferred are cements such as Portland cement such as ordinary Portland cement, belite cement, moderate heat cement, high-early-strength cement, ultra-high-early-strength cement, and sulfate-resistant cement. In addition, powders with pozzolanic action and/or latent hydraulicity such as blast furnace slag, steelmaking slag, fly ash, silica fume, etc., blast furnace slag cement, steelmaking slag cement, etc. added with stone powder (calcium carbonate powder), etc. Fly ash cement, silica fume cement, and the like may also be used. A cement-based solidifying material may also 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 hydraulic powder refers to the amount of powder having a physical property to harden by hydration reaction. When powders selected from solids and stone powders (calcium carbonate powders) are included, their amounts are also included in the amount of hydraulic powders in the present invention.

The component (A) of the present invention is colloidal silica having a surface potential of 0 mV or more and +50 mV or less.
In the present invention, colloidal silica is a colloidal solution in which silica particles are dispersed in water, and refers to a concept including modified colloidal silica modified by modifying the surface of silica particles with a modifier.

Colloidal silica is preferably cationic colloidal silica from the viewpoint of improving the strength of soil cement containing acidic soil.
In the present invention, cationic colloidal silica is colloidal silica whose surface is cationic. For example, the surface of colloidal silica is modified with a compound having a cationic group, or a certain It is obtained by adding a compound to denature it.

As a method for obtaining cationic colloidal silica,
(1) A method of treating the surface of colloidal silica particles with a silane coupling agent or a titanium coupling agent having a cationic group. Examples include a method of introducing aluminum atoms into the inside to make the surface cationic.

The surface potential (zeta potential) of the component (A) is 0 mV or more, preferably +3.0 mV or more, more preferably +6 mV or more, and +50 mV, from the viewpoint of improving the strength of soil cement containing acidic soil and dispersion stability. Below, it is preferably +40 mV or less, more preferably +30 mV or less, still more preferably +20 mV or less, still more preferably +15 mV or less, and even more preferably +10 mV or less.
The surface potential (zeta potential) of component (A) refers to the zeta potential obtained by converting the electrophoretic mobility of colloidal silica using Henry's formula. For example, an aqueous solution with a concentration of component (A) of 0.5% by mass is prepared, and colloidal silica is measured at 25° C. using a zeta-potential measuring device (for example, “Zetasizer Nano” manufactured by Malvern), and laser Doppler The zeta potential using the electrophoretic mobility obtained by detection electrophoresis is used as the surface potential.

The component (A) of the present invention is a particle group, and the particle diameter of all the particles contained is measured by a dynamic light scattering method, and when the cumulative number frequency is plotted against the particle diameter, the cumulative number frequency is 10%. It is a particle group having a particle diameter of 30 nm or less at 0, 70 nm or less at 50%, and 100 nm or less at 90%.
The particle size (D10) when the cumulative number frequency of component (A) is 10%, the particle size (D50) when it is 50%, and the particle size (D90) when it is 90% are included in the particle group. For all particles, the particle size is measured by dynamic light scattering using a laser particle analysis system (for example, Otsuka Electronics Co., Ltd., trade name: ELSZ-1000), and the cumulative number frequency is plotted against the particle size. calculated by the cumulant method analysis. More specifically, it is calculated by the method described in Examples.
The particle diameter (D10) when the cumulative number frequency of the particle groups of component (A) is 10% is 30 nm or less, preferably 25 nm or less, more preferably 20 nm or less, and still more preferably 15 nm or less, from the viewpoint of improving strength. , more preferably 12 nm or less, and preferably 0.1 nm or more, more preferably 0.5 nm or more, and even more preferably 1.0 nm or more.
The particle diameter (D50) when the cumulative number frequency of the particle groups of component (A) is 50% is 70 nm or less, preferably 60 nm or less, more preferably 50 nm or less, and still more preferably 40 nm or less, from the viewpoint of improving strength. , 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, and even more preferably 1.0 nm or more.
The particle diameter (D90) when the cumulative number frequency of the particle groups of component (A) is 90% is 100 nm or less, preferably 90 nm or less, more preferably 80 nm or less, and still more preferably 70 nm or less, from the viewpoint of improving strength. , 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, still more preferably 1 0 nm or more.

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

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

In step 1, a cement dispersant may be further mixed from the viewpoint of improving the fluidity of the cement slurry. The cement dispersant is preferably a polycarboxylic acid-based dispersant or a naphthalenesulfonate-formaldehyde condensate-based dispersant.

In step 1, from the viewpoint of workability, the hydraulic powder and water are mixed so that the mass ratio of water/hydraulic powder is preferably 40% by mass or more, more preferably 50% by mass or more, and still more preferably 60% by mass. % or more, and preferably 150% by mass or less, more preferably 120% by mass or less, even more preferably 100% by mass or less, and even more preferably 80% 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 to prepare 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 soil cement containing acidic soil, the amount of component (A) in terms of solid content is preferably 0.1% by mass or more, more preferably 1% by mass, based on the hydraulic powder. % or more, more preferably 3 mass % or more, still more preferably 5 mass % or more, and preferably 20 mass % or less, more preferably 10 mass % or less, and even more preferably 8 mass % or less.

In step 1, when component (B) is used, from the viewpoint of improving the strength of soil cement containing acidic soil, the content of component (B) is preferably 0.1% by mass or more, more preferably 0.1% by mass or more, relative to the hydraulic powder. is 1% by mass or more, more preferably 3% by mass or more, even more preferably 5% by mass or more, and preferably 10% by mass or less, more preferably 20% by mass or less, and even more preferably 8% by mass or less. .

In step 1, when the component (B) is used, from the viewpoint of improving the strength of the soil cement containing acidic soil, the component (A) and the component (B) are adjusted to the mass ratio of the component (A) and the component (B) ( A)/(B) is preferably 0.1 or more, more preferably 0.5 or more, still more preferably 1 or more, and preferably 10 or less, more preferably 5 or less, still more preferably 3 or less, and still more It is preferable to mix so that the ratio is 2 or less.

Although an alkali metal carbonate may be further mixed in step 1, the amount of the alkali metal carbonate to be mixed is limited from the viewpoint of improving the strength of the soil cement. Alkali metal carbonates include one or more selected from sodium carbonate, potassium carbonate, sodium hydrogencarbonate, and potassium hydrogencarbonate.

When the alkali metal carbonate is mixed in step 1, the amount of the alkali metal carbonate mixed is preferably 1% by mass or less, more preferably 0% by mass, based on the hydraulic powder, from the viewpoint of improving the strength of the soil cement. 0.1% 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.

The reason why the amount of the alkali metal carbonate to be mixed is limited when mixed in step 1 is not necessarily clear, but is presumed as follows.
In step 1, when an alkali metal carbonate is mixed, C3A contained in the hydraulic powder reacts with carbonate ions to produce carbonate-based hydrates (monocarbonate, hemicarbonate), and ettringite from C3A. Inhibition of the generation of the strength lowers the strength. The formation of etrin guides from C3A contained in hydraulic powder is essential for the strength development of soil cement, especially soil cement that uses acidic soil containing organic matter such as humic acid, fulvic acid, humin, and bitumen. extremely important. This is because the formation of CSH is strongly affected by the type of soil, whereas the formation of etrin guide is less affected by the type of soil.
Therefore, it is preferable to limit the amount of alkali metal carbonate to be mixed so as not to reduce the amount of ettringite produced.

A specific method for preparing the slurry in step 1 may follow a known method for preparing a hydraulic composition such as cement milk.

<Step 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.

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

In the soil, the organic matter content determined by the ignition loss method is preferably 30% or more, more preferably 35% or more, still more preferably 40% or more, from the viewpoint of further improving the strength with the component (A). is 90% or less, more preferably 80% or less. Here, the ignition loss method is a method defined in Japanese Engineering Standards JISA1226:2009.
Organic matter contained in soil includes one or more organic matter selected from humic acid, fulvic acid, humin, and bitumen.

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

In step 2, from the viewpoint of mixability of soil cement, the amount of slurry mixed per 1 m ³ of soil is preferably 150 kg or more, more preferably 200 kg or more, still more preferably 250 kg or more, and even more preferably 300 kg or more, and From the viewpoint of workability of the soil cement, it is preferably 800 kg or less, more preferably 500 kg or less, and even more preferably 400 kg or less.

In step 2, from the viewpoint of the mixability of the soil cement, the hydraulic powder is added to the soil, and the hydraulic powder/soil mass ratio is preferably 0.01 or more, more preferably 0.1 or more, and still more preferably is 0.2 or more, more preferably 0.25 or more, and from the viewpoint of workability of soil cement, preferably 0.6 or less, more preferably 0.5 or less, further preferably 0.45 or less, and more It is more preferably mixed at 0.4 or less.

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

<Step 3>
Step 3 is a step of solidifying the mixture of slurry and soil obtained in Step 2. A 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 construction methods such as a surface layer improvement method, a deep layer improvement method, a steel pipe pile method, and a shield method. For example, in the deep improvement construction method, it can be applied to the high pressure injection construction method, the TRD construction method, the SMW construction method, and the like.

[Additive composition for ground improvement]
The present invention is a soil improvement additive composition containing the component (A).
The soil improvement additive composition of the present invention may further contain component (B) from the viewpoint of improving the strength of soil cement containing acidic soil.
The soil improvement additive composition of the present invention may further contain water from the viewpoint of dispersion stability.
The components (A) and (B) are the same as those described in the ground improvement method of the present invention.

In the soil improvement additive composition of the present invention, the component (A) is preferably 1% by mass or more, more preferably 2.0% by mass in terms of solid content, from the viewpoint of improving the strength of soil cement containing acidic soil. % or more, more preferably 5 mass % or more, and preferably 30 mass % or less, more preferably 15 mass % or less, still more preferably 20 mass % or less.

In the soil improvement additive composition of the present invention, the component (B) is preferably 1% by mass or more, more preferably 5% by mass or more, still more preferably 10% by mass, from the viewpoint of improving the strength of soil cement containing acidic soil. % by mass or more, preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less.

In the soil improvement additive composition of the present invention, the mass ratio (A) / (B) of the content of component (A) and the content of component (B) is the strength improvement of soil cement containing acidic soil. From the viewpoint, it is preferably 0.1 or more, more preferably 0.5 or more, still more preferably 1 or more, and preferably 10 or less, more preferably 5 or less, still more preferably 3 or less, and even more preferably 2 or less. be.

The soil improvement additive composition of the present invention contains water, preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 20% by mass or more, and preferably 90% by mass or less, more preferably The content is 80% by mass or less, more preferably 70% by mass or less.

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

[Soil improvement slurry]
The soil improvement slurry of the present invention is a soil improvement slurry containing water, hydraulic powder and component (A). The slurry preferably has a water/hydraulic powder mass ratio of 40% by mass or more and 150% by mass or less.
The soil improvement slurry of the present invention may be a soil improvement slurry obtained by mixing water, hydraulic powder, and the soil improvement additive composition of the present invention. The soil improvement slurry of the present invention is preferably used in the soil improvement method of the present invention.
In addition, the ground improvement slurry of the present invention can contain the component (B).
Specific examples and preferred aspects of the hydraulic powder, component (A), component (B), soil, etc. in the soil improvement slurry of the present invention are the same as those of the soil improvement method of the present invention. In addition, the quantitative definition of the hydraulic powder, (A) component, (B) component, etc. described in the ground improvement method of the present invention is replaced by the content of the mixed amount, respectively, and the ground improvement of the present invention. It can be applied to slurry for
The matters described in the soil improvement method and the soil improvement additive composition of the present invention can be appropriately applied to the soil improvement slurry of the present invention. The soil improvement slurry of the present invention may be used for acidic soil. In addition, the soil improvement slurry of the present invention is a soil having an organic matter content of 30% or more determined by the ignition loss method, and is a soil suspension measured by the method specified in the Japanese Geotechnical Society Standard JGS0211-2009. of pH 6 or less.

The soil improvement slurry of the present invention is a soil improvement slurry mixed with soil for soil improvement, for example, a hydraulic composition such as cement milk.
The amount of the soil improvement slurry of the present invention used can be set in consideration of the composition of the soil improvement slurry, the type of soil (ground), etc., 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
The soil improvement slurry of the present invention is 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. used in combination with Further, in the soil improvement slurry of the present invention, the hydraulic powder and soil in the slurry have a hydraulic powder/soil mass ratio of 0.01 or more, preferably 0.1 or more, more preferably 0 0.2 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, mixed with soil.

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

The matters described in the soil improvement method, the soil improvement additive composition, and the soil improvement slurry of the present invention can be appropriately applied to the soil improvement body of the present invention. The soil improvement body of the present invention can contain component (B).
Specific examples and preferred aspects of the hydraulic powder, component (A), component (B), soil, etc. in the soil improvement material of the present invention are the same as those of the soil improvement method of the present invention. In addition, the quantitative definition of the hydraulic powder, (A) component, (B) component, soil, etc. described in the ground improvement method of the present invention is replaced by the content of the mixed amount, respectively. It can be applied to soil improvement bodies. For example, the soil is acidic soil, preferably soil having an organic mass content of 30% or more determined by the ignition loss method, and the soil suspension measured by the method specified in the Japanese Geotechnical Society Standard JGS0211-2009. The soil may have a pH of 6 or less.

<Ingredients>
Components used in the following examples and comparative examples are shown below.
(A) Component Colloidal silica (1): Cationic colloidal silica, surface potential (zeta potential) 6.7 mV, particle diameter (D10) 6 nm when cumulative number frequency reaches 10%, cumulative number frequency reaches 50% Particle diameter (D50) 11 nm when it becomes, Particle diameter (D90) 15 nm when the cumulative number frequency is 90% Colloidal silica manufactured by Nissan Chemical Co., Ltd. (2): cationic colloidal silica, surface potential (zeta potential) 15.1 mV, particle diameter (D10) 8 nm when cumulative number frequency is 10%, particle diameter (D50) 14 nm when cumulative number frequency is 50%, particle diameter when cumulative number frequency is 90% (D90) 22 nm, manufactured by Nissan Chemical Co., Ltd.

(A') component (comparative component of (A) component)
・ Colloidal silica (3): anionic colloidal silica, surface potential (zeta potential) -20 mV, particle size (D10) 5 nm when cumulative number frequency is 10%, particle size when cumulative number frequency is 50% (D50) 8 nm, particle diameter when the cumulative number frequency is 90% (D90) 10 nm, manufactured by JGC Catalysts and Chemicals Co., Ltd.

The surface potential (zeta potential) of the components (A) and (A') was measured by preparing an aqueous solution with a concentration of 0.5% by mass of the component (A) or (A'), and subjecting it to a zetasizer at 25°C. Measured with Nano (manufactured by Malvern).

Particle diameter (D10) when the cumulative number frequency of components (A) and (A') is 10%, particle diameter (D50) when the cumulative number frequency is 50%, particle diameter (D90) when the cumulative number frequency is 90% uses a laser particle analysis system (manufactured by Otsuka Electronics Co., Ltd., trade name: ELSZ-1000) for all particles contained in the particle group of components (A) and (A'), dynamic light scattering under the following conditions. The particle size was measured by the method, the cumulative number frequency was plotted against the particle size, and calculated by the cumulant method analysis.
[Measurement condition]
・Measurement sample: Weigh the measurement sample into a screw tube and prepare by adding water as a dispersion solvent so that the solid content concentration is 0.4% by mass ・Temperature: 23.6 ° C
・Angle between incident light and detector: 90°
・The number of accumulation times: 50 times ・The refractive index of water as a dispersion solvent: 1.333

(B) Component Calcium chloride: Fuji Film Wako Pure Chemical Co., Ltd. Calcium nitrate: Fuji Film Wako Pure Chemical Co., Ltd.

Hydraulic powder/ordinary Portland cement: Taiheiyo Cement Co., Ltd. Blast furnace slag cement: Nippon Steel Blast Furnace Cement Co., Ltd.

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

<Examples and Comparative Examples>
A soil cement was prepared using the soil in Table 1, and the soil cement was evaluated as follows. The results are shown in Tables 2-4.

(1) Preparation of soil cement First, cement milk was prepared by the following procedure. Component (A), component (B) and water are mixed to prepare an aqueous additive solution, and the hydraulic powder and the aqueous additive solution are mixed in a 500 ml plastic cup (500 mL disposable cup, Nikko Hansen Co., Ltd.). and kneaded with a hand mixer for 1 minute to prepare cement milk.
Tap water was used as water for preparing the additive aqueous solution. The hydraulic powder and the aqueous additive solution were used so that the mass ratio of the aqueous additive solution/hydraulic powder was 60% by mass. The additive aqueous solution/hydraulic powder weight ratio substantially corresponds to the water/hydraulic powder ratio.
Components (A) and (B) were used so that the amounts added to the hydraulic powder were as shown in Tables 2-4.
After that, put the soil into another 500 ml plastic cup, and add the cement milk so that the injection amount shown in Tables 2 to 4 is obtained (mass ratio (hydraulic powder/soil) is 0.38). , and stirred for 3 minutes with a hand mixer to prepare soil cement. After stirring, the mixture was shaken to level the top surface, sealed with a wrap film, and allowed to stand at 22° C. for a predetermined period of time.

(2) Evaluation The strength of the soil improvement body obtained using the prepared soil cement was evaluated by the following method. The soil cement was filled into a formwork (diameter 50 mm x height 100 mm). Filling was carried out in two layers for 30 seconds using a table vibrator. Two specimens were produced. The 7-day strength in air at 20° C. of the hardened body (soil improvement body) obtained above was measured with a uniaxial compression tester. Tables 2 to 4 show the average strength of the two specimens as the 7-day strength.

In Table 2, the strength of the comparative examples whose 7-day strength was 0 was not measured because the soil cement could not be removed from the formwork because the soil cement did not harden.
In addition, Examples 1-1 and 1-2 in which colloidal silica was mixed with soil cement, and Comparative Example 1-2 compared with Comparative Example 1-1 in which colloidal silica was not mixed, the soil of acidic soil containing organic matter was improved. Although the 7-day strength of soil cement containing soil cement can be improved, Examples 1-1 and 1-2, in which colloidal silica, which is the component (A) of the present invention, is mixed are mixed with colloidal silica, which is a comparative component. As compared with Comparative Example 1-2, the 7-day strength of soil cement containing acidic soil containing organic matter can be further improved.

In Table 3, in a soil cement system in which colloidal silica is mixed with calcium chloride as component (B). Examples 2-1 and 2-2, in which colloidal silica, which is the component (A) of the present invention, is mixed are more acidic than those in Comparative Example 2-1, which is mixed with colloidal silica as a comparative component. The 7-day strength of soil cement containing earthen soil can be further improved.

In Table 4, in a soil cement system in which colloidal silica is mixed with calcium nitrate as component (B). Example 3-1, in which colloidal silica, which is the component (A) of the present invention, was mixed, compared with Comparative Example 3-1, in which colloidal silica, which was a comparative component, was mixed, and soil of acidic soil containing organic matter was improved. The 7-day strength of the containing soil cement can be further improved.

Claims (11)

A ground improvement method that includes the following steps 1 to 3.
<Step 1>
A step of mixing water, hydraulic powder, and (A) cationic colloidal silica having a surface potential of +3 mV or more and +50 mV or less (hereinafter referred to as component (A)) to prepare a slurry. The powder and water have a water/hydraulic powder mass ratio of 40% by mass or more and 150% by mass or less, and the component (A) is 0.1% by mass based on the hydraulic powder in terms of solid content. A step of mixing at not less than 10% by mass.
<Step 2>
A step of injecting the slurry obtained in step 1 into the ground and mixing the slurry and soil to obtain soil cement , wherein the soil has an organic mass content of 30% or more as determined by the ignition loss method. Soil, the pH of the soil suspension measured by the method specified by the Japanese Geotechnical Society Standard JGS0211-2009 is 6 or less, and the amount of the slurry mixed per 1 m 3 of soil is 150 kg or more and 800 kg or less ^. and mixing at a mass ratio of hydraulic powder/soil in the soil cement of 0.01 or more and 0.6 or less.
<Step 3>
A step of solidifying the soil cement obtained in step 2. The ground improvement method according to claim 1 , 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 claim 1 or 2 , wherein (B) a calcium salt having a solubility in water at 20°C of 20 g/100 ml or more (hereinafter referred to as component (B)) is further mixed in step 1. The ground improvement method according to claim 3 , wherein the component (B) is one or more selected from calcium chloride and calcium nitrate. 5. The ground improvement method according to claim 3 or 4, wherein in step 1, the component (B) is mixed in an amount of 0.1% by mass or more and 10% by mass or less with respect to the hydraulic powder. In step 1, the (A) component and the (B) component are mixed so that the mass ratio (A)/(B) of the (A) component and the (B) component is 0.1 or more and 10 or less. The ground improvement method according to any one of claims 3 to 5. A soil improvement material containing soil, hydraulic powder, water, and (A) cationic colloidal silica having a surface potential of +3 mV or more and +50 mV or less, wherein the soil has an organic mass content determined by the ignition loss method The soil is 30% or more, the pH of the soil suspension measured by the method specified in the Japanese Geotechnical Society standard JGS0211-2009 is 6 or less, and the content of hydraulic powder and water The content (water/hydraulic powder) is 40% by mass or more and 150% by mass or less, and the content of component (A) is, in terms of solid content, 0.00% relative to the hydraulic powder. A soil improvement material having a content of 1% by mass or more and 10% by mass or less, and a mass ratio of a content of hydraulic powder to a content of soil (hydraulic powder/soil) of 0.01 or more and 0.6 or less. The soil improvement material according to claim 7, further comprising (B) a calcium salt having a solubility in water at 20°C of 20 g/100 ml or more (hereinafter referred to as component (B)). The soil improvement material according to claim 8, wherein the component (B) is one or more selected from calcium chloride and calcium nitrate. The soil improvement material according to claim 8 or 9, wherein the content of component (B) is 0.1% by mass or more and 10% by mass or less relative to the hydraulic powder. The mass ratio (A)/(B) between the content of component (A) and the content of component (B) is 0.1 or more and 10 or less, according to any one of claims 8 to 10. Soil improver.