JPH11256161A - Cement composition for improving ground and improvement of ground - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject composition capable of realizing an improvement in operating efficiency, drilling properties and a reduction in discharged residual soil at the time of improving the ground and useful for the impovement, or the like, in the foundation ground of a structure, a retaining wall, or the like, by mixing a cement-based material with a specific powdery polymer. SOLUTION: This composition contains (A) a cement-based material, (B) a powdery polymer (salt) having functional groups which are carboxylate groups or sulfonate groups [e.g. a homopolymer (salt) of acrylic acid, an acrylic acid/ methacrylic acid copolymer (salt), a copolymer (salt) of an α,β-dicarboxylic acid-based monomer and an ethylenically unsaturated monomer or ligninsulfonic acid (salt)]. The composition preferably contains the components A and B so as to provide (99.99/0.01) to (80/20) weight ratio of the components A/B.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for soil improvement and is used for improving soil excavation and workability by improving the fluidity of soil cement, and for reducing residual soil discharged. The present invention relates to a cement composition and a ground improvement method.

[0002]

2. Description of the Related Art Conventionally, a shallow layer improvement treatment is called for the purpose of improving the foundation ground of a relatively lightweight structure, improving the foundation ground of retaining walls, culverts, pipes, etc., and preventing slope erosion. Ground improvement is underway. Further, ground improvement called deep layer improvement processing is performed for the purpose of constructing a structure having a high load strength on soft ground or strengthening a retaining wall. Further, soil cement continuous walls have been widely used for earth retaining and water stopping purposes.

However, in these ground improvement treatments, since the fluidity of soil cement is low, the burden on a device for driving an auger machine, which is an excavation machine, is large, and excavation performance is reduced and excavation efficiency is reduced. ,Also,
There is a drawback that the produced improved product is not homogeneous and the quality varies greatly.

There is also a method of securing fluidity by adding water to the soil in order to improve the workability. However, the addition of water increases the amount of treatment, and as a result, increases the disposal cost of the remaining soil and increases the cement cost. However, there has been a problem that the material cost increases.

On the other hand, since a large amount of residual soil generated during excavation becomes industrial waste, consideration for environmental issues such as extending the life of disposal sites and reduction of disposal costs have become major problems.

[0006] In order to solve such a drawback, conventionally, there have been proposed a number of methods for adding excipients such as a dispersant as well as water and cement to excavated soil (Japanese Patent Laid-Open No. 8-239).
662, JP-A-8-259947, JP-A-4-275961, JP-A-4-338144, JP-A-4-369548, JP-A-6-127
No. 993, JP-A-62-189217, JP-A-5-79033, JP-A-7-138566, JP-A-9-3453, JP-A-5-43283.
JP, JP-A-6-220835, JP-A-8-1
2403, JP-A-5-331833, JP-A-7-257951, and JP-A-9-31458.

However, in most cases, cement for soil improvement is produced by producing cement milk at or near the site of application and then mixing and mixing with excavated soil. Therefore, a liquid admixture is added on site. Needed. For this reason, there has been a problem that the addition amount management for the on-site measurement becomes complicated and the operation becomes complicated.

For such reasons, in the ground improvement treatment, there has been a strong demand for an admixture having a stable quality and a simple kneading operation. In addition, the fluidity of the manufactured soil cement and the reduction rate of the amount of discharged soil were not sufficient with the conventional method of separately adding a liquid admixture to the soil cement.

[0009]

DISCLOSURE OF THE INVENTION The present invention relates to a ground improvement for improving the workability in soil improvement, improving the excavation property by improving the fluidity of soil cement, and reducing the remaining soil discharged. An object of the present invention is to provide a cement composition and a soil improvement method.

[0010]

Means for Solving the Problems The present inventors have conducted studies to solve the above-mentioned problems, and as a result, have found that a cementitious material such as Portland cement, a mixed cement or a cementitious solidifying material and at least one kind of powdery material are used. When the powdery cement composition for ground improvement mixed with a molecular compound was manufactured by adding a dispersant to cement milk at or near the site of the enforcement, it facilitated the control of the amount added to the on-site measurement. It has been found that the kneading does not involve complication as in the case of post-addition of the agent, and that the efficiency of execution is dramatically improved, and the present invention has been completed.

That is, the present invention relates to a polymer compound having one or more functional groups selected from the group consisting of (a) a cement material and (b) a carboxylic acid group and a sulfonic acid group, and a salt thereof. Provided is a ground improvement powdery cement composition comprising at least one selected powdery polymer compound.

Further, in the powdery cement composition for ground improvement of the present invention, (b) the powdery polymer compound is a homopolymer of acrylic acid and a salt thereof, a copolymer of acrylic acid and methacrylic acid, and a copolymer thereof. It is preferably at least one selected from the group consisting of a salt, a copolymer of an α, β-dicarboxylic acid monomer and an ethylenically unsaturated monomer and a salt thereof, and ligninsulfonic acid and a salt thereof.

In the ground improvement powdery cement composition of the present invention, the weight ratio of (a) the cement material to (b) the powdery polymer compound is (a) / (b) = 99.
It is preferably in the range of 99 / 0.01 to 80/20.

[0014] The present invention also provides a soil improvement method comprising using, as a solidifying agent, a cement water slurry prepared by mixing the above-mentioned powdery cement composition for soil improvement preliminarily dry-mixed with water. I will provide a.

Further, the present invention provides a soil improvement method, which comprises mixing the above-mentioned powdery cement composition for soil improvement, which has been dry-mixed in advance, and soil with direct stirring, and then adding water.

In the present invention, since the amount of the admixture added to the cement is always constant, a cement water slurry of stable quality can be efficiently produced. In addition, since the cement is used in a state of being uniformly mixed with the cement, a highly fluid soil cement can be produced without localizing the admixture.

Further, as described above, the ground improvement powdery cement composition of the present invention provides a polymer compound having at least one functional group selected from the group consisting of carboxylic acid groups and sulfonic acid groups, and By using one or more kinds of powdery polymer compounds selected from the group consisting of salts,
Dramatically improved the fluidity of soil cement,
If you want to obtain the same fluidity as without adding an admixture,
It is possible to reduce the amount of added water and the amount of added cement water slurry for the soil to be improved, and as a result, it is possible to reduce the amount of residual soil discharged.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Next, the powdery cement composition for ground improvement of the present invention will be described in detail.

As the cement-based material (a) used in the present invention, various portland cements such as ordinary, fast and super fast, various mixed cements obtained by mixing blast furnace slag, silica and fly ash with these portland cements, white Cement, super-rapid hardening cement, alumina cement and the like can be used.

In the present invention, as the cement-based material, low heat-generating cement such as moderate heat cement or sulfuric acid-resistant cement can be used.

Further, a cement-based solidifying material generally used for ground improvement can also be used.

(A) The average particle diameter of the cement-based material is usually 5 to 30 μm, but larger or smaller ones can be used as long as they have hydraulic properties.

In the present invention, (a) various cement admixtures such as quick-setting materials, expanding materials, and high-strength admixtures used in ordinary cement concrete can be used in combination with the cement-based material. . The average particle diameter of these cement admixtures is usually 0.5 to 30 μm, but larger or smaller ones can be used without any problem. These cement admixtures may be used alone or in combination of two or more.

The component (b) used in the present invention is selected from the group consisting of (b) a carboxylic acid group and a sulfonic acid group.
At least one kind of powdered polymer compound selected from the group consisting of a polymer compound having at least one kind of functional group and a salt thereof.

The high molecular compound having at least one functional group selected from the group consisting of a carboxylic acid group and a sulfonic acid group includes acrylic acid, methacrylic acid, vinyl acetic acid, crotonic acid, maleic acid, and maleic anhydride. Acid, itaconic anhydride, citraconic anhydride, fumaric acid, itaconic acid, styrene sulfonic acid, 2-acrylamido-2-methyl-propanesulfonic acid, 3-acryloxy-2-
Hydroxy-propanesulfonic acid, vinylsulfonic acid,
Homopolymers of monomers such as allyl sulfonic acid and methallyl sulfonic acid, or alkyl acrylates, alkyl methacrylates, and hydroxyalkyl acrylates having 1 to 8 carbon atoms in the alkyl groups of these monomers and alkyl groups And a copolymer with at least one copolymerizable monomer selected from monomers such as acrylamide, styrene, isoprene, isobutylene, isoamylene, and vinyl acetate.

These (co) polymers can be used in acid or salt form. Further, the copolymerizable monomer is 1 to 9
9 mol%, preferably 10 to 90 mol%, can be copolymerized. The weight average molecular weight of the (co) polymer is
Preferably, those having a range of 1,000 to 500,000, more preferably 2,000 to 200,000 are suitably used.

The polymer compound having at least one functional group selected from the group consisting of a carboxylic acid group and a sulfonic acid group includes naturally occurring polymer compounds such as ligninsulfonic acid or a salt thereof, and naphthalenesulfonic acid. A formaldehyde condensate or a salt thereof, a melaminesulfonic acid formaldehyde condensate or a salt thereof, and the like are also preferably used.

Examples of the (co) polymer salts include water-soluble salts such as ammonium salts, alkali metal salts (eg, sodium salts, potassium salts, etc.) and alkaline earth metal salts (eg, calcium salts, magnesium salts, etc.). Salt,
It may be substituted with an amine salt such as monoethanolamine, diethanolamine, ethylamine, ethyleneamine, diethylenetriamine and the like, and an unneutralized portion may remain.

Among the above-mentioned (b) polymer compounds having one or more functional groups selected from the group consisting of carboxylic acid groups and sulfonic acid groups and salts thereof, homopolymers of acrylic acid and salts thereof, acrylic acid And a salt thereof with methacrylic acid, at least one selected from the group consisting of a copolymer of an α, β-dicarboxylic acid monomer and an ethylenically unsaturated monomer and a salt thereof, ligninsulfonic acid and a salt thereof Is particularly preferably used.

In the present invention, a powdery compound is used as the polymer compound. These polymer compounds are in a liquid form, and in the present invention, the liquid polymer compound is powdered by a conventional method such as spray drying to obtain (b)
A powdery polymer compound is produced.

The average particle diameter of the powdery polymer compound (b) is usually from 1 to 1000 μm, preferably from 5 to 500 μm. Larger or smaller powders can be used without any problem, but if it is larger than 1000 μm, the dissolution rate after the powder comes in contact with water may be reduced. If smaller than 1 μm, the specific surface area of the powder may be reduced. Therefore, it is necessary to pay attention to powder mixing properties and generation of powder as it is during the dissolution process.

In the present invention, the amounts of (a) the cement-based material and (b) the powdery high-molecular compound can be arbitrarily selected. Of (a) / (b) = 99.99 /
The range of 0.01 to 80/20 is preferable, and (a) /
(B) = 99.9 / 0.1 to 90/10 is more preferable.

In order to produce the ground improvement powdery cement composition of the present invention, (a) a cement-based material and (b)
What is necessary is just to mix with a powdery high molecular compound, and the usual dry-blending method of a powder can be applied as it is.

Further, the powdery cement composition for soil improvement according to the present invention is obtained by mixing (a) a cementitious material with (b) a powdery polymer compound little by little;
It can be produced by either a method in which the cement-based material is mixed little by little with the powdery polymer compound or a method in which both are mixed together.

The shape and material of the stirring vessel and the blades of the mixer used for producing the ground improvement powdery cement composition of the present invention are not particularly limited. A conventional mixer such as a mixer, a V-type mixer, an upright-type mixer, a double-cone-type mixer, a ribbon-type mixer, and a screw mixer may be used.

The amount of the powdery cement composition for ground improvement of the present invention to be used for the improved soil is variously used depending on the soil properties such as the water content and the particle diameter of the excavated soil, the purpose of use of the soil cement compact, and the like. for generally improving soil 1 m ^3, soil improvement for the powdery cement composition of the present invention 50
It is in the range of 600 kg, preferably 80-500 kg.

The powdery cement composition for soil improvement according to the present invention is prepared by mixing with water to prepare a water slurry, and then adding the resulting slurry to the soil and uniformly mixing the same to form a soil cement consolidated body.
After directly mixing and mixing the soil improvement cement composition with soil,
The method can be applied to a known ground improvement method using a cement-based material such as Portland cement, a mixed cement, or a cement-based solidifying material, such as a method of adding an appropriate amount of water.

When the ground is improved by using the ground improvement powdery cement composition of the present invention, the mixing ratio of water to the ground improvement cement composition (water / ground improvement cement composition ratio) is 50 to 50%. 400% by weight, preferably 70-30
0% by weight. If the mixing ratio of water is less than 50% by weight, the fluidity of the cement water slurry is insufficient and mixing with the soil becomes difficult. Conversely, if it exceeds 400% by weight, the amount of water increases and the strength decreases and This leads to a decrease in the rate of residual soil reduction.

Further, the powdery cement composition for soil improvement of the present invention can be used for landfill soil or soft ground by adding a solidifying material such as cement to the soil generated by dredging or excavation and solidifying. It is suitable for ground improvement methods such as reinforcement or soil cement wall formation. For example,
Ground improvement methods using the following kneading and placing methods can be exemplified.

(1) A method in which the solidified material and the soil are kneaded using a bucket and a rotary stirrer at a construction site using a backhoe, a clamshell, or the like.

(2) A method in which cement is directly injected into construction residual soil or soft soil by means of a transport pipe or a pressure pipe to knead the cement. In some cases, they are discharged once and re-kneaded with a backhoe.

(3) A method in which the solidified material and water are kneaded in the plant, transported to the excavation site by a pipe or a truck, an agitator vehicle, or the like, and kneaded with soil during excavation at the site. In some cases, the soil discharged by excavation is once transported to a plant, where the soil and cement are kneaded to produce soil cement, and then transported to the site.

(4) When excavating soil with an auger machine, a hardening liquid such as cement milk is ejected from the tip of the excavator, and the soil and cement milk are mixed in situ to form a soil cement wall. Method (earth retaining method,
Soil Mixing Wall method).

In this method, a core material is frequently buried as a stress material for securing the strength of the retaining wall and securing the waterproofness. As this core material, H-shaped steel,
Sheet pile, box sheet type steel sheet pile, PC pile and the like are used. These core materials need to be driven before the wall is hardened, and when embedded, the higher the fluidity of the wall, the quicker and more accurate the driving becomes possible. If the soil improvement cement composition of the present invention is used,
There is an advantage that these core materials can be easily embedded.

In particular, the powdery cement composition for ground improvement of the present invention is used in an excavating and kneading machine having both functions of excavating and kneading and having an outlet for cement milk at the tip of a kneading shaft. Is particularly preferred. When used in such an excavating kneader, at the same time as drilling the soil, the cement milk to which the soil improving cement composition of the present invention is added is discharged from the tip of the kneading shaft and mixed with the excavated soil by stirring. This is because a uniform soil cement compact can be manufactured.

Therefore, the powdery cement composition for ground improvement of the present invention is particularly preferably used in a ground improvement method using a water slurry method. Further, the stirring method of the ground improvement method using the water slurry method is roughly classified into a mechanical method and a high-pressure injection method, and is particularly preferably used in the mechanical method.

[0047]

EXAMPLES Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. In the following examples, "% by weight" and "parts by weight" are, unless otherwise specified.
Abbreviated as "%" and "part", respectively.

Examples 1 to 11 and Comparative Examples 1 to 4 Table 2 shows the results of measuring the fluidity and the uniaxial compressive strength of the soil cements manufactured by the following manufacturing examples using the following materials. In addition, the powdery cement composition for ground improvement and the test conditions are shown in Table 1, and the measurement methods of the fluidity and the uniaxial compressive strength test are also shown below.

(Production of ground improvement powdery cement composition) The ground improvement powdery cement composition used in the following soil cement production examples 1 and 2 was prepared so that the total amount of the ground improvement cement composition was 250 g. , Cement-based material and powdery polymer compound are weighed, and both are added at once,
It was manufactured by uniform mixing with a ribbon mixer.

(Production of Soil Cement) [Production Example 1] 250 g of powdery cement composition for ground improvement
And 650 g of water were uniformly mixed with a soil mixer to produce cement milk. 1440 g of excavated soil was added thereto and stirred to obtain a soil cement slurry. The weight ratio of the cement milk water to the ground improvement powdery cement composition was 260% of the cement milk water based on the ground improvement powdery cement composition.

[Production Example 2] 250 g of a powdery cement composition for ground improvement and 400 g of water were uniformly mixed with a soil mixer to produce cement milk. Excavated soil 144
0 g was added and stirred to obtain a soil cement slurry.
The weight ratio of the cement milk water to the ground improvement powdery cement composition was 160% of the cement milk water based on the ground improvement powdery cement composition.

[Production Example 3] 250 g of a cement-based material and a powdery polymer compound were separately added to 650 g of water, and uniformly mixed with a soil mixer to produce cement milk. 1440 g of excavated soil was added thereto and stirred to obtain a soil cement slurry. The weight ratio of the water of the cement milk to the total of the cement-based material and the powdery polymer compound was 260% of the total of the cement-based material and the powdery polymer compound.

[Production Example 4] Cement milk was produced by uniformly mixing 250 g of a cementitious material and 400 g of water with a soil mixer. 1440 g of excavated soil was added thereto and stirred to obtain a soil cement slurry. The weight ratio of the water of the cement milk to the cement-based material was 160% of the water of the cement milk with respect to the cement-based material.

Production Example 5 After dissolving 12.5 g (solid content: 40%) of a liquid polymer compound in 650 g of water, 237.5 g of a cement-based material was uniformly mixed with a soil mixer to produce cement milk. 1440 g of excavated soil was added thereto and stirred to obtain a soil cement slurry. The weight mixing ratio of the water of the cement milk and the sum of the cement-based material and the liquid polymer compound is such that the water of the cement milk is 260% of the total of the cement-based material and the liquid polymer compound.
Met.

[Production Example 6] 250 g of a cement material and 650 g of water were uniformly mixed with a soil mixer to produce a cement milk. 1440 g of excavated soil was added thereto and stirred to obtain a soil cement slurry. The weight ratio of the water of the cement milk to the cement-based material was such that the water of the cement milk was 260% of the cement-based material.

(Material used) [Cement-based material] A-1: Ordinary Portland cement (Ube Industries, Ltd.)
A-2: Blast furnace type B cement (Ube Industries, Ltd., average particle size 15 μm) A-3: Cement-based solidifying material (Ube Industries, Ltd., average particle size 20 μm)

[Powdered Polymer Compound] B-1: Copolymer of 50 mol% of sodium maleate and 50 mol% of isoamylene (weight average molecular weight of 10,000
B-2: copolymer of 80 mol% of sodium maleate and 20 mol% of isoamylene (weight average molecular weight 110,0)
B-3: sodium polyacrylate (weight average molecular weight 6,500, average particle diameter 17 μm) B-4: sodium polyacrylate (weight average molecular weight 5)
B-5: Sodium ligninsulfonate (weight average molecular weight 200,000, average particle diameter 20 μm) B-6: B-1 / B-5 = 3/7 (weight ratio) compounded B-7: B-1 / B-5 = 7/3 (weight ratio) blend (average particle diameter 16 μm) B-8: Sodium melamine sulfonate (weight average molecular weight 150,000, (Average particle diameter 50 μm)

The weight average molecular weight of the powdery polymer was measured by a gel permeation (GPC) method using polyethylene glycol as a standard product, and the average particle diameter was measured by a laser scattering diffraction method using alcohol as a dispersion medium. Was measured.

[Liquid Polymer Compound] B-3: 5 g of sodium polyacrylate (weight average molecular weight 6,500, average particle diameter 17 μm) was dissolved in 7.5 g of water to obtain a liquid polymer compound.

[Properties of sample soil] Unit weight 1.44 t / m ³ Water content 59.5% Soil particle density 2.69 g / cm ³ Particle size composition Clay 30.5% Silt 58.5% Sand 11 0.0%

(Method of Measuring Fluidity and Uniaxial Compressive Strength Test) [Fluidity Test] Fluidity was evaluated by the flow of the manufactured soil cement slurry. Evaluation method is JIS R
The mortar flow test according to 5201 was followed.

[Uniaxial compressive strength test] The uniaxial compressive strength is φ =
Molding was performed in a mold having a size of 5 cm and h = 10 cm, curing was performed until the material age was 28 days, and measurement was performed in accordance with JIS A 1108.

[0063]

The ratio of [Table 1] Soil Improvement cementitious composition soil cement (a) Seme (b) high molecular weight blending ratio manufacturing method water / soil improvement for cement species types of compounds (a) / (b) cement composition (% ) Example 1 A-2 B-1 (powder) 99/1 Production Example 1 260 Example 2 A-2 B-1 (powder) 99/1 Production Example 2 160 Example 3 A-1 B-2 (Powder) 99.5 / 0.5 Production Example 1 260 Example 4 A-1 B-3 (powder) 98/2 Production Example 1 260 Example 5 A-2 B-4 (powder) 93/7 Production Example 1 260 Example 6 A-3 B-5 (powder) 96/4 Production Example 1 260 Example 7 A-3 B-5 (powder) 97/3 Production Example 160 160 Example 8 A-1 B-6 (Powder) 99/1 Production Example 1 260 Example 9 A-1 B-6 (powder) 98/2 Production Example 2 160 Example 10 A-2 B-7 (powder) 97/3 Production Example 1 260 Example 11 A-1 B-8 (powder) 99/1 Production Example 1 260 Comparative Example 1 A-2 B-1 (powder) 99/1 Production Example 3 260 Comparative Example 2 A-1--Production Example 4 160 Comparative Example 3 A-3 B-3 (Liquid) 98/2 Production Example 5 260 Comparative Example 4 A-2 --- Production Example 6 260

[0064]

Table 2 Flow (mm) Uniaxial compressive strength (kgf / cm ² ) Example 1 171 9.1 Example 2 156 11.2 Example 3 165 9.3 Example 4 182 9.2 Example 5 239 9 0.0 Example 6 205 9.4 Example 7 177 11.4 Example 8 178 9.1 Example 9 163 11.4 Example 10 190 9.3 Example 11 161 8.0 Comparative Example 1 150 7. 8 Comparative Example 2 140 10.6 Comparative Example 3 159 8.1 Comparative Example 4 145 8.0

(Evaluation Results) From the above test results, when soil cement was manufactured using the ground cement powder-based cement composition of the present invention, and when cement-based material containing no powdery polymer compound was used. The fluidity after the production of the slurry is greatly increased as compared to In addition, the fluidity immediately after the production is greatly increased as compared with the case where the same soil cement is produced using a liquid polymer compound.

[0066]

When the powdery cement composition for ground improvement according to the present invention is used, when the admixture is added to the cement milk at the construction site or in the vicinity thereof, the additive amount can be easily controlled with respect to the on-site measurement. Therefore, the kneading is not complicated as in the case where the liquid admixture is added later, and the execution efficiency is dramatically improved.

Further, since the amount of the admixture added to the cement is always constant, it is possible to efficiently produce a cement water slurry of stable quality and to use the slurry in a state of being uniformly mixed with the cement. In addition, a highly fluid soil cement can be produced without localizing the admixture. Therefore, it is possible to improve excavation and workability during soil improvement, and to reduce the amount of water added to the soil to be improved, thereby reducing the amount of residual soil discharged. .

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C04B 28/02 C04B 28/02 C09K 17/22 C09K 17/22 P E02D 3/12 101 E02D 3/12 101 102 102 5/20 5/20 // C09K 103: 00

Claims (5)

[Claims] 1. A compound selected from the group consisting of (a) a cementitious material and (b) a polymer compound having at least one functional group selected from the group consisting of a carboxylic acid group and a sulfonic acid group, and a salt thereof. A powdery cement composition for ground improvement comprising the above powdery polymer compound. (B) the powdery polymer compound is a homopolymer of acrylic acid and a salt thereof, a copolymer of acrylic acid and methacrylic acid and a salt thereof, an α, β-dicarboxylic acid monomer and an ethylene The ground improvement powdery cement composition according to claim 1, which is at least one selected from the group consisting of a copolymer with an unsaturated monomer and a salt thereof, and ligninsulfonic acid and a salt thereof. 3. The weight ratio of (a) the cement-based material to (b) the powdery polymer compound is (a) / (b) = 99.9.
3. The method according to claim 1, wherein the ratio is in the range of 9 / 0.01 to 80/20.
The powdery cement composition for ground improvement according to item 1. 4. A cement water slurry prepared by mixing a powdery cement composition for ground improvement according to any one of claims 1 to 3, which has been dry-mixed in advance, and water as a solidifying agent. Ground improvement method characterized by the following. 5. The ground, wherein the powdery cement composition for ground improvement according to any one of claims 1 to 3, which has been dry-mixed in advance, is directly stirred and mixed with soil, and then water is added. Improvement method.