JP7265498B2 - 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, in a soil improvement method of placing Portland cement in soil and solidifying the soil, 20 to 30 parts by weight of sodium chloride, 20 to 30 parts by weight of magnesium chloride, An additive mainly composed of inorganic salts consisting of 35 to 45 parts by weight of potassium chloride, 5 to 15 parts by weight of calcium chloride and 4 to 8 parts by weight of citric acid is added in the form of an aqueous solution to 100 parts by weight of the Portland cement. A soil improvement method is disclosed in which the solid content of the agent is added at a ratio of 0.1 to 1 part by weight, stirred and mixed with soil, and pressurized from above to solidify the soil. .
In Patent Document 2, 20 to 40 parts by weight of calcium chloride, 30 to 50 parts by weight of magnesium chloride, and 30 to 50 parts by weight of magnesium chloride are added to 1,000 parts by weight of wood chip material, cement, and water in soil generated on site excavated from the ground to be constructed. Disclosed is a construction method characterized by adding and mixing a curing agent aqueous solution containing 15 to 30 parts by weight of aluminum chloride and 0.1 to 3 parts by weight of cobalt chloride, and then filling the excavated ground for construction with this mixture. It is

JP-A-60-229984 JP 2006-169065 A

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 is a soil improvement method comprising mixing hydraulic powder, water, and the following component (A) with soil having an organic mass content of 30% or more as determined by the ignition loss method, The present invention relates to a ground improvement method in which component (A) is mixed with hydraulic powder in an amount of 0.5% by mass or more and 10% by mass or less.
(A) component: one or more compounds that serve as a source of releasing aluminum ions and/or calcium ions and chloride ions in water (excluding hydraulic powder)

The present invention also provides a soil improvement additive containing the component (A), wherein the soil of the ground has an organic mass content of 30% or more determined by the ignition loss method. It relates to an additive composition.

The present invention also provides a soil improvement material containing soil having an organic mass content of 30% or more as determined by the ignition loss method, hydraulic powder, water, and the component (A), wherein the component (A) is It relates to a soil improvement material containing 0.5% by mass or more and 10% by mass or less with respect to hydraulic powder.

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]
The soil improvement method of the present invention exhibits its effect even when the soil has an organic mass content of 30% or more as determined by the ignition loss method.
In addition, in the ground 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 soil suspension measured by the method specified in the Japanese Geotechnical Society Standard JGS0211-2009. The effect is exhibited even in soil with a turbidity pH of 6 or less.

Although the mechanism by which the present invention expresses its effects is not clear, it is presumed as follows. It is known that supplying aluminum ions and/or calcium ions to the soil in addition to hydraulic powder accelerates the hydration reaction of the hydraulic powder and contributes to improving the strength of soil cement. Excessive addition of ions and/or calcium ions causes abnormal hydration (rapid hydration and pseudo-coagulation), resulting in a decrease in strength. Therefore, adding a large amount of aluminum ions and/or calcium ions was not usually performed. However, the present invention is intended for acidic soil containing organic matter such as humic acid, fulvic acid, humin, and bitumen. When supplied to the cement surface, the organic matter that inhibits the hydration reaction of the hydraulic powder forms a complex with the aluminum ions and/or calcium ions supplied in large amounts, thereby preventing the organic matter from adsorbing on the cement surface and relieving the hydration inhibition. , the inventors have found that it is possible to improve the strength of soil cement. At the same time, the present inventors have found that the presence of chloride ions has the effect of promoting the effect.

The soil has an organic matter content of 30% or more, preferably 35% or more, more preferably 40% or more, and preferably 90% or less, more preferably 80% or less, as determined by the ignition loss method. 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, humin, bitumen, and fulvic acid.

The soil is acidic soil with a soil suspension pH of preferably 6 or less, more preferably 5.5 or less, and still more preferably 5 or less, measured by the method specified by the Japanese Geotechnical Society Standard JGS0211-2009. good.

The hydraulic powder used in the present invention is a powder having a physical property of hardening by hydration reaction, and examples thereof include cement and the like (except for component (B) described later). From the viewpoint of improving the strength of soil cement containing acidic soil, the hydraulic powder is preferably cement, for example, portland cement such as ordinary portland cement, belite cement, moderate heat cement, high-early strength cement, super high-early strength cement, Cement such as sulfate resistant cement. Hydraulic powders include powders with pozzolanic action and/or latent hydraulicity such as blast furnace slag, steelmaking slag, fly ash, silica fume, etc., and blast furnace slag cement to which stone powder (calcium carbonate powder) etc. is added. , steelmaking slag cement, fly ash cement, silica fume cement, and the like. 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. and stone powder (calcium carbonate powder), the amount thereof is also included in the amount of hydraulic powder in the present invention (however, the amount of component (B) described later is excluded) .

The component (A) of the present invention is one or more compounds that serve as a source of releasing aluminum ions and/or calcium ions and chloride ions in water. However, hydraulic powder is excluded from the component (A).
Compounds serving as a source of releasing aluminum ions include one or more selected from aluminum chloride, aluminum sulfate, aluminum lactate, alum, and aluminum nitrate from the viewpoint of improving the strength of soil cement containing acidic soil.
From the viewpoint of improving the strength of soil cement containing acidic soil, the compound serving as a source of calcium ion release includes one or more selected from calcium chloride, calcium nitrate, and calcium thiocyanate.
Compounds serving as a supply source for releasing chloride ions include one or more selected from aluminum chloride, calcium chloride, sodium chloride, and potassium chloride from the viewpoint of improving the strength of soil cement containing acidic soil.

The (A) component is preferably the following (A1) component or (A2) component from the viewpoint of improving the strength of soil cement containing acidic soil.
(A1) component: one or more compounds selected from calcium chloride salts or aluminum chloride salts having a solubility in water at 20°C of 20 g/100 ml or more (A2) component: (A21) alkali metal chloride salt, and alkaline earth metal chloride salts (hereinafter referred to as component (A21)); A21) component (hereinafter referred to as (A22) component)

The (A1) component includes one or more selected from calcium chloride and aluminum chloride from the viewpoint of improving the strength of soil cement containing acidic soil.

Among the components (A2), from the viewpoint of improving the strength of soil cement containing acidic soil, the component (A21) includes one or more selected from sodium chloride, potassium chloride, and calcium chloride, and is preferable from the viewpoint of safety. is one or more selected from sodium chloride and calcium chloride.
Among the (A2) components, from the viewpoint of improving the strength of the soil cement containing acidic soil, the (A22) component includes one or more selected from aluminum lactate, alum, aluminum sulfate, and aluminum nitrate to improve the strength of the soil cement. from the viewpoint of, preferably one or more selected from alum and aluminum sulfate.

In the ground improvement method of the present invention, hydraulic powder is added to soil, and the mass ratio of hydraulic powder/soil is preferably 0.01 or more, more preferably 0.01 or more, more preferably 0.01 or more, from the viewpoint of mixability with soil cement. 1 or more, more preferably 0.25 or more, and from the viewpoint of workability of the soil cement, the mixing ratio is preferably 0.6 or less, more preferably 0.5 or less, and still more preferably 0.45 or less.

In the ground improvement method of the present invention, from the viewpoint of workability of soil cement, the weight ratio of water/hydraulic powder is preferably 40% by mass or more, more preferably 50% by mass. % or more, more preferably 60 mass % or more, and preferably 150 mass % or less, more preferably 120 mass % or less, and even more preferably 100 mass % or less. This mass ratio is calculated by (amount of water/amount of hydraulic powder)×100.

In the ground improvement method of the present invention, from the viewpoint of improving the strength of soil cement containing acidic soil, the component (A) is added to the hydraulic powder in an amount of 0.5% by mass or more, preferably 1.0% by mass. Above, more preferably 2.0% by mass or more, more preferably 3.0% by mass or more, and 10% by mass or less, preferably 8.0% by mass or less, more preferably 6.0% by mass or less. .

In the ground improvement method of the present invention, when the (A1) component is used as the (A) component, from the viewpoint of improving the strength of the soil cement containing acidic soil, the (A1) component is preferably used relative to the hydraulic powder. is 0.5% by mass or more, more preferably 1.0% by mass or more, still more preferably 2.0% by mass or more, even more preferably 3.0% by mass or more, and preferably 10% by mass or less, more preferably is 8.0% by mass or less, more preferably 6.0% by mass or less.

In the ground improvement method of the present invention, when using the (A2) component as the (A) component, from the viewpoint of improving the strength of soil cement containing acidic soil, the (A2) component ((A21) component and (A22) component total) is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, more preferably 2.0% by mass or more, and still more preferably 3.0% by mass or more, relative to the hydraulic powder , and preferably 10% by mass or less, more preferably 8.0% by mass or less.
In the ground improvement method of the present invention, when the (A2) component is used as the (A) component, from the viewpoint of improving the strength of the soil cement containing acidic soil, the (A21) component is preferably used relative to the hydraulic powder. is 0.25% by mass or more, more preferably 0.5% by mass or more, still more preferably 1.0% by mass or more, even more preferably 2.0% by mass or more, and preferably 6.0% by mass or less, It is more preferably 5.0% by mass or less, still more preferably 4.0% by mass or less, and the component (A22) is preferably 0.25% by mass or more, more preferably 0.5% by mass, relative to the hydraulic powder. % by mass or more, more preferably 1.0% by mass or more, even more preferably 2.0% by mass or more, and preferably 6.0% by mass or less, more preferably 5.0% by mass or less, still more preferably 4 .0% by mass or less.
In the ground improvement method of the present invention, when using the (A2) component as the (A) component, from the viewpoint of improving the strength of soil cement containing acidic soil, the (A21) component and the (A22) component are combined into the (A21) component. and (A22) component mass ratio (A21)/(A22) is preferably 0.1 or more, more preferably 0.5 or more, still more preferably 1.0 or more, and preferably 10 or less, more preferably is 5.0 or less, more preferably 3.0 or less, and even more preferably 2.0 or less.

In the ground improvement method of the present invention, further, as the component (B), from the viewpoint of improving the strength of soil cement containing acidic soil, at least one or more selected from anhydrite, dihydrate gypsum, hemihydrate gypsum and sodium sulfate It is preferred to mix the compounds.
In the ground improvement method of the present invention, when using the component (B), from the viewpoint of improving the initial strength of the soil cement, the component (B) is preferably added to the hydraulic powder in an amount of 0.1% by mass or more, More preferably 0.5% by mass or more, still more preferably 1.0% by mass or more, still more preferably 3.0% by mass or more, still more preferably 5.0% by mass or more, still more preferably 7.0% by mass % or more, preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less.

In the ground improvement method of the present invention, a cement dispersant may be mixed from the viewpoint of improving the fluidity of the soil cement. As the cement dispersant, one or more selected from polycarboxylic acid-based dispersants and naphthalenesulfonate-formaldehyde condensate-based dispersants are preferable.

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.

In the ground improvement method of the present invention, soil, hydraulic powder, (A) component, optionally (B) component, and water are mixed with soil by the following method (I). This is preferable from the viewpoint of uniformity of the improved product.
<Method (I)>
A slurry containing water, hydraulic powder, component (A), and optionally component (B), wherein component (A) is 0.5% by mass or more to 10% by mass of the hydraulic powder % or less, and mixing the slurry with soil.

The method (I) will be described below.
In method (I), the amount of slurry mixed per 1 m ³ of soil is preferably 150 kg or more and 800 kg or less from the viewpoint of improving the strength of soil cement containing acidic soil.
Moreover, in the method (I), from the viewpoint of improving the strength of the soil cement containing acidic soil, it is preferable that the mass ratio of hydraulic powder/soil in the soil cement is 0.01 or more and 0.6 or less.
In method (I), 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.

A specific method for preparing a slurry by mixing water, hydraulic powder, component (A), and optionally component (B) follows a known method for preparing a hydraulic composition such as cement milk. good.

In method (I), from the viewpoint of workability, the mass ratio of water/hydraulic powder in the slurry is preferably 40% by mass or more, more preferably 50% by mass or more, and still more preferably 60% by mass or more, and It is preferably 150% by mass or less, more preferably 120% by mass or less, and even more preferably 100% by mass 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 component (A) and component (B) are optionally dry-blended with hydraulic powder, it can also be used for shallow layer improvement using a powder mixing system DJM (Dry Jet Mixing) method and a stabilizer. can.

In method (I), from the viewpoint of mixability, the amount of slurry mixed per ^cubic meter of soil is preferably 150 kg or more, more preferably 200 kg or more, and still more preferably 250 kg or more, and from the viewpoint of workability of soil cement. , preferably 800 kg or less, more preferably 500 kg or less, still more preferably 400 kg or less.

A mixture of slurry and soil is solidified according to a known ground improvement method.

A more specific example of the method (I), which is the ground improvement method of the present invention, is a ground improvement method having the following steps 1 to 3.
<Step 1>
A step of preparing a slurry by mixing water, hydraulic powder, component (A), and optionally component (B), wherein the amount of component (A) is 0.5 to the hydraulic powder. Step <Step 2> of preparing a slurry by mixing so that the mass % or more and 10 mass % or less
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 amount of slurry mixed per 1 m ³ of soil is 150 kg or more and 800 kg or less, and water in the mixture Step <Step 3> in which the mass ratio of hard powder/soil is 0.01 or more and 0.6 or less
Solidifying the mixture of slurry and soil obtained in step 2

[Additive composition for ground improvement]
The soil improvement additive composition of the present invention is a soil improvement additive composition containing the component (A), wherein the soil of the ground has an organic mass of 30% or more as determined by the ignition loss method. It is a soil improvement additive composition used for a certain soil.
The soil improvement additive composition of the present invention may further contain component (B). The soil improvement additive composition of the present invention may consist of the (A) component and the (B) component.

Such a soil improvement additive composition 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 soil improvement method of the present invention can be appropriately applied to the soil improvement additive composition of the present invention.

[Soil improvement slurry]
The soil improvement slurry of the present invention is a soil improvement slurry containing water, hydraulic powder, and (A) component, wherein the component (A) is 0.5 mass with respect to the hydraulic powder % or more and 10% by mass or less, and the soil of the ground has an organic mass content of 30% or more determined by the ignition loss method. 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 soil improvement slurry of the present invention can further contain (B). 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 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
From the viewpoint of improving the strength of soil cement containing acidic soil, the soil improvement slurry of the present invention is preferably 150 kg or more, more preferably 200 kg or more, still more preferably 250 kg or more, and preferably 800 kg or less per 1 m ³ of soil. More preferably 500 kg or less, more preferably 400 kg or less, is mixed with soil and used. 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 preferably 0.01 or more, more preferably 0.1 or more, and further It is preferably 0.25 or more, and preferably 0.6 or less, more preferably 0.5 or less, still more preferably 0.45 or less, mixed with soil.

[Ground improvement body]
The soil improvement material of the present invention is a soil improvement material containing soil having an organic mass content of 30% or more as determined by the ignition loss method, hydraulic powder, water, and component (A), wherein (A) It is a soil improvement material containing 0.5% by mass or more and 10% by mass or less of the component with respect to the hydraulic powder. From the viewpoint of improving the strength of soil cement containing acidic soil, the soil improvement material preferably has a hydraulic powder/soil mass ratio of 0.01 or more and 0.6 or less. The soil improvement material may be a soil improvement material obtained by hardening a slurry containing the soil, water, hydraulic powder, and component (A).
The soil improvement body of the present invention may be a soil improvement body obtained by mixing the 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 may further contain component (B).
Specific examples and preferred aspects of the hydraulic powder, (A) component, (B) component, soil, etc., and quantitative definitions such as each mass ratio in the soil improvement body of the present invention are also the soil of the present invention. It is the same as the improvement method, soil improvement additive composition, and soil improvement slurry.

<Ingredients>
Components used in the following examples, comparative examples, and reference examples are shown below.
(A) Component (A1) Component Calcium chloride: Fujifilm Wako Pure Chemical Co., Ltd., solubility in water at 20 ° C. 74.5 g / 100 ml
· Aluminum chloride: Fujifilm Wako Pure Chemical Co., Ltd., solubility in water at 20 ° C. 45.8 g / 100 ml
(A2) Component (A21) Component Sodium chloride: Fuji Film Wako Pure Chemical Co., Ltd. Calcium chloride: Fuji Film Wako Pure Chemical Co., Ltd. (A22) Component Aluminum sulfate: Fuji Film Wako Pure Chemical Co., Ltd., 20 87g/100ml water solubility at °C
· Aluminum lactate: Fujifilm Wako Pure Chemical Co., Ltd., solubility in water at 20 ° C. 30.8 g / 100 ml
・ Alum: Fuji Film Wako Pure Chemical Co., Ltd., solubility in water at 20 ° C. 40.9 g / 100 ml

(B) Component Anhydrous gypsum: San-esu Gypsum Co., Ltd. Dihydrate gypsum: Fuji Film Wako Pure Chemical Co., Ltd.

Hydraulic powder/ordinary Portland cement: manufactured by Taiheiyo Cement Co., Ltd.

As the soil, peat and Sumiclay mud water shown in Table 1 were used. The organic matter content of peat and sumiclay mud was measured by the method specified in Japanese Engineering Standards JIS A1226:2009. Further, the pH of the soil suspension of peat and sumiclay mud was measured by the method specified in Japanese Geotechnical Society Standard JGS0211-2009. The pH of the peat soil suspension was 4.2, and the pH of the Sumiclay mud soil suspension was 7.

<Examples, Comparative Examples and Reference Examples>
A soil cement was prepared using the soil in Table 1, and the soil cement was evaluated as follows. Tables 2 and 3 show the results.

(1) Preparation of soil cement First, cement milk was prepared by the following procedure. The hydraulic powder, component (A), and component (B) were mixed in a 500 ml plastic cup (500 mL disposable cup, Nikko Hansen Co., Ltd.). Water was added to the mixture and kneaded with a hand mixer for 1 minute to prepare a cement slurry.
Tap water was used as water for preparing the cement slurry. The hydraulic powder and water were used so that the mass ratio of water/hydraulic powder was 60% by mass.
Components (A) and (B) were used in amounts as shown in Tables 2 and 3 with respect to the hydraulic powder.
After that, the soil was put into another 500 ml plastic cup, and the cement slurry was put into the injection amount shown in Tables 2 and 3 (hydraulic powder/soil mass ratio = 0.38), A soil cement was prepared by stirring for 3 minutes with a hand mixer. 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 and 3 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 Table 2, in Comparative Example 1 in which only the hydraulic powder was mixed with the peat, which is acidic soil containing organic matter, and the component (A) was not mixed, the soil cement could not be hardened. It can be seen that soil cement can be hardened in Examples 1 to 12 of the present invention in which the body and component (A) are mixed in specific amounts.
Further, from the results in Table 3, adding hydraulic powder and component (A) to Sumiclay mud, which is soil that does not contain organic matter, does not improve the 7-day strength of soil cement, and the ground of the present invention. It can be seen that the improved construction method is effective only for specific soil.

Claims (13)

A soil improvement method comprising mixing hydraulic powder, water, and the following component (A) with soil having an organic mass content of 30% or more as determined by the ignition loss method,
The hydraulic powder is Portland cement,
Hydraulic powder and water are mixed at a water/hydraulic powder mass ratio of 40% by mass or more and 120% by mass or less, and
(A) A ground improvement method in which the component (A) is mixed so as to be 2.0% by mass or more and 8.0% by mass or less with respect to the hydraulic powder.
Component (A): Component (A1) or (A2) below Component (A1): Calcium chloride salt with a solubility in water at 20°C of 20 g/100 ml or more (A2) Component: (A21) Alkali metal chloride One or more compounds selected from salts and alkaline earth metal chloride salts (hereinafter referred to as component (A21)); , excluding the (A21) component, hereinafter referred to as the (A22) component) 2. The soil improvement method according to claim 1, wherein the soil has a pH of 6 or less as measured by the method specified in JGS0211-2009 of the Japanese Geotechnical Society. The ground improvement method according to claim 1 or 2, wherein the soil, hydraulic powder, water, and component (A1) are mixed. The ground improvement method according to claim 3, wherein the component (A1) is calcium chloride. The ground improvement method according to claim 3 or 4, wherein the component (A1) is mixed in an amount of 2.0% by mass or more and 8.0% by mass or less with respect to the hydraulic powder. The ground improvement method according to claim 1 or 2, wherein the soil, hydraulic powder, water, and component (A2) are mixed. (A21) component is one or more selected from sodium chloride, potassium chloride and calcium chloride, and (A22) component is one or more selected from aluminum lactate, alum and aluminum sulfate, according to claim 6 Ground improvement method described. The ground improvement method according to claim 6 or 7, wherein the component (A2) is mixed in an amount of 2.0% by mass or more and 8.0% by mass or less with respect to the hydraulic powder. The ground improvement method according to any one of claims 6 to 8, wherein the mass ratio (A21) / (A22) of the (A21) component and the (A22) component is 0.1 or more and 10 or less. Further, (B) at least one compound selected from anhydrite, gypsum dihydrate, gypsum hemihydrate and sodium sulfate (hereinafter referred to as component (B)) is mixed with any one of claims 1 to 9. Ground improvement method described. The ground improvement method according to claim 10, wherein the component (B) is mixed in an amount of 0.1% by mass or more and 30% by mass or less with respect to the hydraulic powder. The soil improvement method according to any one of claims 1 to 11, wherein the soil is peat. A soil improvement material containing soil having an organic mass content of 30% or more as determined by the ignition loss method, hydraulic powder, water, and the following component (A),
The hydraulic powder is Portland cement,
The mass ratio of water/hydraulic powder is 40% by mass or more and 120% by mass or less,
(A) Soil improvement material containing 2.0% by mass or more and 8.0% by mass or less of component relative to hydraulic powder.
Component (A): Component (A1) or (A2) below Component (A1): Calcium chloride salt with a solubility in water at 20°C of 20 g/100 ml or more (A2) Component: (A21) Alkali metal chloride One or more compounds selected from salts and alkaline earth metal chloride salts (hereinafter referred to as component (A21)); , excluding the (A21) component, hereinafter referred to as the (A22) component)