JP7640371B2 - Ground improvement methods - Google Patents

Description

The present invention relates to a ground improvement method.

In the fields of civil engineering and architecture, compositions containing various components such as soil and cement are used for various purposes. For example, soil cement is known as a composition used in ground improvement methods, earth retaining methods, foundation pile methods, and backfilling methods. Soil cement is a mixture of soil and a cement-based solidification material or water. Soil cement used in the fields of civil engineering and architecture is often prepared by adding cement milk, which is a mixture of a cement-based solidification material and water, to soil. The required properties of soil cement, such as viscosity and fluidity, differ depending on the construction method. Cement milk and soil cement are used in columnar ground reinforcement methods such as the so-called soil cement method, in which cement milk is injected into the ground to construct a soil cement column. In addition, the so-called replacement column method, in which ground soil is replaced with a solidification material, is known.

Patent Document 1 discloses a method for constructing a hydraulic solidification liquid replacement column, which is characterized in that the tip of an excavation auger, which has a supply passage for hydraulic solidification liquid inside, is provided with at least an excavation claw and a discharge port for the hydraulic solidification liquid, the excavation auger is rotated (forward or reverse) by a construction device equipped with an auger motor while digging to a specified depth, and then the excavation auger is pulled up while rotating (forward or reverse) or without rotating while discharging hydraulic solidification liquid from the discharge port, and a specified section of the excavated portion is filled with the hydraulic solidification liquid.

On the other hand, it is known to add various components to cement-based solidification materials.
Patent Document 2 discloses a soil cement containing a compound having an ortho-position polyhydric phenol skeleton.
Patent Document 3 discloses an additive for soil cement containing a phosphate polymer obtained by copolymerizing a specific monomer 1 having a polyoxyalkylene group, a phosphate monoester monomer 2, and a phosphate diester monomer 3 at a pH of 7 or less.
Patent Document 4 discloses a powdered premixed cement composition for ground improvement, which contains 0.5 to 15 parts by mass of a powdered ground improvement additive composed of sodium lignin sulfonate, an alkali metal carbonate, and a specified polyether antifoaming agent per 100 parts by mass of a powdered cement-based solidifying material.

JP 2011-106253 A JP 2020-26523 A JP 2007-169547 A JP 2009-286655 A

In soil cement, clay may exist in the form of lumps due to incorporation from the soil or aggregation during mixing. If clay lumps remain in the soil cement, for example, the soil may easily adhere to the excavation blades and mixing blades of the excavation and mixing device, and the blades and the soil may rotate synchronously, which is called a corotation phenomenon, and the soil and the solidification material may not be mixed uniformly. If fine particles such as clay are not mixed uniformly, clay lumps will be localized in the soil cement column, resulting in a decrease in the strength of the ground improvement body, which is the hardened product of the soil cement.
The present invention provides a ground improvement method that, when improving soil containing clay using a solidification material, can reduce clay lumps, uniformly mix the soil and the solidification material, and obtain a ground improvement body with excellent strength.

The present invention relates to a method for improving ground, which comprises mixing a clay-containing soil (i) (hereinafter referred to as component (i)), a hydraulic powder (ii) (hereinafter referred to as component (ii)), a compound (iii) represented by the following general formula (1) (hereinafter referred to as component (iii)), and water (iv) (hereinafter referred to as component (iv)):
(i) The component is a soil having a uniformity coefficient (D50/D10) of 2.6 or more and 8.0 or less;
The component (ii) is mixed in an amount of 18% by mass or less relative to the component (i);
This relates to ground improvement methods.
RO-(AO) _m -H (1)
(In general formula (1), R represents a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms, AO represents an oxyethylene group or an oxypropylene group, and m represents the average number of moles of AO added.)

The present invention provides a method for improving soil containing clay using a solidification material, which can reduce clay lumps and mix the soil and solidification material uniformly, resulting in a soil improvement body with excellent strength.

<Soil improvement method>
The ground improvement method of the present invention is a method for mixing component (i) having a uniformity coefficient (D50/D10) of 2.6 to 8.0 with component (ii), component (iii), and component (iv), in which component (ii) is mixed in a ratio of 18 mass % or less relative to component (i).

The (i) component is a soil containing clay, and has a uniformity coefficient (D50/D10) of 2.6 to 8.0. The uniformity coefficient (D50/D10) of the (i) component is calculated by dividing the effective diameter D50 (particle diameter at a passing mass percentage of 50%) obtained by the method of JIS A 1204 by the effective diameter D10 (particle diameter at a passing mass percentage of 10%). The uniformity coefficient was calculated using this method in the examples described later. The uniformity coefficient (D50/D10) of the (i) component is 2.6 or more, preferably 2.8 or more, more preferably 3.0 or more, and 8.0 or less, preferably 7.6 or less, more preferably 7.0 or less, and even more preferably 6.0 or less, from the viewpoint that the strength of the ground improvement body can be improved by reducing the sand component and making the particles dense.

From the viewpoint of improving the mixing uniformity and particle adhesion strength through water, component (i) may be soil with a natural moisture content of 35% or more and 85% or less. The natural moisture content of component (i) means the ratio of the mass of water contained in the soil divided by the dry mass of the soil, and is calculated by the soil moisture content test method of JIS A 1203. The natural moisture content was measured by this method in the examples described later. The natural moisture content of component (i) is more preferably 40% or more, even more preferably 45% or more, and even more preferably 80% or less, even more preferably 75% or less.

The (i) component may be soil having a BET specific surface area of 30 m ² /g or more and 70 m ² /g or less, from the viewpoint of securing the adhesion points between particles and increasing the strength. The BET specific surface area of the (i) component is more preferably 35 m ² /g or more, even more preferably 40 m ² /g or more, and more preferably 65 m ² /g or less, even more preferably 60 m ² /g or less. The BET specific surface area of the (i) component is calculated by a method in which gas molecules with a known adsorption occupation area are adsorbed on the surface of soil particles, the specific surface area of the sample is calculated from the amount of gas molecules, and the pore distribution is measured from the condensation of the gas molecules. Specifically, the BET specific surface area of the (i) component can be measured by a one-point BET method using, for example, a fully automatic specific surface area measuring device (for example, MacSorb manufactured by Mountec Co., Ltd.). In the examples described later, a fully automatic specific surface area measuring device (MacSorb manufactured by Mountec Co., Ltd.) was used. Approximately 3 g of a sample was placed in a glass cell, and the sample was cooled to liquid nitrogen temperature. An adsorption gas (a mixed gas of nitrogen and helium in a ratio of 3:7) was introduced at a flow rate of 60 ^cm3 /min to adsorb the sample. The amount of gas desorbed when the sample was returned to room temperature was measured, and the specific surface area (single-point BET method) was obtained by dividing the amount by the mass of the sample.

Component (i) may be soil having a pore distance of 7 nm or more and 20 nm or less, from the viewpoint of increasing strength by compound (iii) bridging particles together. The pore distance of component (i) is calculated by dividing the volume of water contained in the soil by the BET specific surface area. From the viewpoint of the short distance at which compound (iii) can crosslink, the pore distance of component (i) is more preferably 8 nm or more, even more preferably 9 nm or more, and even more preferably 18 nm or less, even more preferably 16 nm or less.

The (i) component may be soil in which the difference between the natural water content and the plastic limit is 0% or more and 80% or less, from the viewpoint that the compound (iii) fixes the water on the particle surface and increases the strength. Here, the plastic limit is the water content at the boundary when the soil changes from a plastic state to a semi-solid state, and may be, for example, the water content at which a lump of soil is kneaded well and rolled with the palm of the hand on a glass plate to a diameter of 3 mm, at which it just breaks into pieces. Specifically, the plastic limit of the (i) component can be measured, for example, by JIS A 1205 "Test method for liquid limit and plastic limit of soil", and the plastic limit was measured by this method in the examples described later. The difference between the natural water content and the plastic limit of the (i) component is more preferably 20% or more, even more preferably 40% or more, and even more preferably 70% or less, even more preferably 60% or less, from the viewpoint of high concentration of the compound (iii) and uniform mixing.

In the present invention, the physical properties (such as uniformity coefficient) of the (i) component are determined by measuring the soil sample (soil in situ) on which the ground improvement method of the present invention is to be performed. For example, the uniformity coefficient may be determined for the soil in situ.

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The uniformity coefficient, natural water content, and BET specific surface area of component (i) can be adjusted by mixing, for example, industrial sand, sand for grain adjustment, and water.

The average particle size of component (i) may be, for example, 1 μm or more, or even 5 μm or more, and 150 μm or less, or even 100 μm or less, or even 50 μm or less. Here, the average particle size of component (i) is measured, for example, by creating a suspension in which particles are suspended in water, and measuring the change in density of the suspension over time to determine the particle size. Specifically, the average particle size of component (i) can be measured, for example, by JIS A 1223 "Test method for fine particle content of soil."

Component (i) preferably contains fine particles having a particle size of less than 75 μm.
The classification criteria for soil as a ground material are summarized in the Geotechnical Society Standards (Geotechnical Society of Japan, 2009). According to these, particles with a particle size of 5 μm or more and less than 75 μm are classified as silt, and particles with a particle size of less than 5 μm are classified as clay. These fine particles are the components that give the soil viscosity. According to the Geotechnical Society Standards, clayey soil, organic soil, and volcanic ash clayey soil are known as soils in which the proportion of fine particles with a particle size of less than 75 μm is 50 mass % or more. Such soils can be targeted in the present invention.
An example of component (i) is soil in which the proportion of fine particles having a particle size of less than 75 μm is preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 60% by mass or more, even more preferably 70% by mass or more, and preferably 100% by mass or less.

Clay is mainly composed of hydrous silicate minerals (hereafter referred to as clay minerals) with a layered structure, and examples of clay minerals contained as fine particles in this clay include kaolin (kaolinite, dickite, nacrite, etc.), serpentine (lizardite, antigorite, chrysotile, etc.), mica clay minerals (illite, sericite, glauconite, celadonite, etc.), chlorite, vermiculite, smectite (montmorillonite, beidellite, nontronite, saponite, hectorite, etc.). Soils contain a wide variety of clays in terms of type and amount, but the present invention can be applied to soils containing clay minerals selected from, for example, kaolin and smectite.

The component (i) may be a soil containing halloysite. The component (i) may contain halloysite in an amount of, for example, 5% by mass or more, further 10% by mass or more, further 15% by mass or more, and 50% by mass or less, further 40% by mass or less, further 30% by mass or less.

The (i) component may contain clay, for example, at least 15% by weight, further at least 20% by weight, further at least 25% by weight, and up to 100% by weight, further up to 95% by weight, further up to 90% by weight.

Component (i) may be soil originating from volcanic ash. Component (i) may be volcanic ash clay, for example, tuffaceous clay. Tuffaceous clay is soil formed by weathering volcanic ash and turning it into clay through hydrolysis. Tuffaceous clay generally has a milky white or milky gray appearance with little sand mixed in. Tuffaceous clay is a soil in which clay lumps are easily mixed and formed during the production of soil cement, but the clay lumps are difficult to deflocculate. In the present invention, even clay lumps from such tuffaceous clay can be easily deflocculated. Component (i) may contain tuffaceous clay in an amount of, for example, 5% by mass or more, further 10% by mass or more, further 15% by mass or more, and 50% by mass or less, further 40% by mass or less, further 30% by mass or less.

The dry density of the component (i) may be, for example, 1.9 g/cm or ^more , further 2.0 g/cm ^{or more} , and 2.9 g/cm ^{or less} , further 2.8 g/cm ^{or less} . Here, the dry density of the component (i) is measured by the method of JIS A 1224.

Component (ii) is a hydraulic powder. The hydraulic powder of component (ii) is a powder having the physical property of being hardened by a hydration reaction, and examples of such powder include cement and gypsum.
The hydraulic powder is preferably cement. The cement is, for example, Portland cement such as ordinary Portland cement, belite cement, moderate heat cement, early strength cement, ultra early strength cement, sulfate resistant cement, etc. The hydraulic powder contains cement, further Portland cement, preferably 25% by mass or more, more preferably 35% by mass or more, even more preferably 50% by mass or more, even more preferably 60% by mass or more, even more preferably 70% by mass or more, and preferably 95% by mass or less, more preferably 92% by mass or less, even more preferably 90% by mass or less, even more preferably 85% by mass or less.

The hydraulic powder may contain powders having pozzolanic action and/or latent hydraulic properties, such as blast furnace slag, fly ash, and silica fume, as well as stone powder (calcium carbonate powder). These may be added to cement to form blast furnace slag cement, fly ash cement, silica fume cement, etc. The hydraulic powder preferably contains blast furnace slag from the viewpoint of providing an aluminum ion source for ettringite, which is a hydration product. When the hydraulic powder contains blast furnace slag, the content of blast furnace slag in the hydraulic powder is preferably 10% by mass or more, more preferably 15% by mass or more, and preferably 60% by mass or less, more preferably less than 50% by mass.

In the present invention, the amount of hydraulic powder is the amount of powder that has the physical property of hardening through a hydration reaction, such as the amount of cement or gypsum. However, if the hydraulic powder includes a powder selected from a powder with pozzolanic action, a powder with latent hydraulic properties, and stone powder (calcium carbonate powder), the amount of these powders is also included in the amount of hydraulic powder in the present invention.

The component (iii) is a compound represented by the following general formula (1).
RO-(AO) _m -H (1)
(In general formula (1), R represents a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms, AO represents an oxyethylene group or an oxypropylene group, and m represents the average number of moles of AO added.)
In the general formula (1), R is a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms. Examples of the hydrocarbon group include an alkyl group and an alkenyl group. R is preferably a hydrogen atom.
In the general formula (1), AO is an oxyethylene group or an oxypropylene group. AO is preferably an oxyethylene group.
In the general formula (1), m represents the average number of moles of AO added. m may be, for example, 50 or more, further 100 or more, further 150 or more, and 50,000 or less, further 25,000 or less, further 12,500 or less.

The weight average molecular weight of component (iii) may be, for example, 1000 or more, further 2000 or more, further 3000 or more, and 2,000,000 or less, further 1,000,000 or less, further 500,000 or less, further 200,000 or less. It is preferable to select m in general formula (1) so that component (i) has this weight average molecular weight.

In the ground improvement method of the present invention, in order to achieve both the strength of the column and the reduction of the amount of sludge generated during construction, the (ii) component is mixed in a ratio of 18% by mass or less to the (i) component. This ratio is preferably 3% by mass or more, more preferably 3.2% by mass or more, even more preferably 4% by mass or more, more preferably 5% by mass or more, even more preferably 6% by mass or more, even more preferably 8% by mass or more, and preferably 15% by mass or less, more preferably 12% by mass or less, more preferably 11% by mass or less, and even more preferably 10% by mass or less. This ratio is calculated by [amount of (ii) component / amount of (i) component] x 100.

In the ground improvement method of the present invention, in order to obtain a homogeneous solidification material mixture (meaning a mixture containing components (i), (ii), (iii) and water; the same applies below) with few clay lumps, component (iii) is mixed in a ratio of preferably 0.01% by mass or more, more preferably 0.02% by mass or more, even more preferably 0.03% by mass or more, and preferably 1% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.2% by mass or less relative to component (i). This ratio is calculated by [amount of component (iii) / amount of component (i)] x 100.

In the ground improvement method of the present invention, from the viewpoint of preparing a uniformly mixed cement slurry in a short time, the (iii) component is mixed in a ratio of preferably 0.007% by mass or more, more preferably 0.008% by mass or more, even more preferably 0.009% by mass or more, and preferably 12% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass or less, relative to the (ii) component. This ratio is calculated by [amount of (iii) component/amount of (ii) component] x 100.

In the ground improvement method of the present invention, from the viewpoint of ensuring the fluidity of the cement slurry and reducing the amount of sludge discharged, the (iv) component is mixed with the (ii) component in a ratio of preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 60% by mass or more, and preferably 250% by mass or less, more preferably 150% by mass or less, even more preferably 80% by mass or less. This ratio is calculated by [amount of (iv) component / amount of (ii) component] x 100.

In the present invention, a water reducing agent (v) (hereinafter referred to as component (v)) may be mixed with component (i).
Examples of the component (v) include polymer compounds having a group selected from a carboxyl group, a sulfonic acid group, and a phosphoric acid group. The weight-average molecular weight of the polymer compound may be 3,000 or more and 100,000 or less. Examples of the component (v) include polycarboxylic acid polymers, naphthalene polymers, and polymers of (hydroxyalkyl) methacrylic acid esters of phosphoric acid. Specific examples include polyalkylene glycol monoester monomers having an oxyalkylene group having 2 or 3 carbon atoms and acrylic acid polymers, polymers containing amide macromonomers, polymers containing polyethyleneimine, copolymers of polyalkylene glycol monoester monomers having an oxyalkylene group having 2 or 3 carbon atoms, di-[(2-hydroxyethyl) methacrylic acid] phosphate, and mono(2-hydroxyethyl) methacrylic acid phosphate, and naphthalene sulfonic acid formaldehyde condensates. Examples of the component (v) include melamine sulfonic acid formalin condensates, aminosulfonic acid, and the like. As component (v), commercially available water reducing agents or high-performance water reducing agents can be used.
In the ground improvement method of the present invention, from the viewpoint of reducing the load on the cement milk pump, component (v) is mixed in a ratio of preferably 0.01 mass % or more, more preferably 0.02 mass % or more, even more preferably 0.03 mass % or more, and preferably 1 mass % or less, more preferably 0.5 mass % or less, even more preferably 0.2 mass % or less, relative to component (ii). This ratio is calculated by [amount of component (v) / amount of component (ii)] x 100.

In the present invention, a defoaming agent (vi) (excluding component (iii)) (hereinafter referred to as component (vi)) may be mixed with component (i).
Examples of the (vi) component include silicone-based defoamers, fatty acid ester-based defoamers, ether-based defoamers, aliphatic amine-based defoamers, etc. Dimethylpolysiloxane is more preferred among silicone-based defoamers, polyalkylene glycol fatty acid ester is more preferred among fatty acid ester-based defoamers, polyalkylene glycol alkyl ether is more preferred among ether-based defoamers, and alkyldimethylamine or a salt thereof is more preferred among aliphatic amine-based defoamers.
In the ground improvement method of the present invention, from the viewpoint of preventing outflow of materials from the milk plant, the (vi) component is mixed in a ratio of preferably 0.0001% by mass or more, more preferably 0.0002% by mass or more, even more preferably 0.0003% by mass or more, and preferably 0.01% by mass or less, more preferably 0.005% by mass or less, even more preferably 0.001% by mass or less, relative to the (ii) component. This ratio is calculated by [amount of (vi) component/amount of (ii) component]×100.

In the present invention, it is preferable to mix component (i) with a slurry containing components (ii), (iii), and (iv). The slurry may be a solidifying material slurry such as cement milk. The slurry may contain components (v) and (vi).

In the present invention, component (i) can also be mixed with components (ii), (iii), and (iv) separately.

In the ground improvement method of the present invention, component (i) can be mixed with components (ii), (iii), and (iv) in situ to prepare soil cement. As an example of the ground improvement method of the present invention, the prepared soil cement is poured into the ground, and the soil cement hardens to become a ground improvement body, thereby improving the strength of the ground.

The ground improvement method of the present invention includes a construction method in which soil cement is poured into the ground. For example, it can be implemented by a surface mixing method, a mid-layer mixing method, a deep mixing method, a steel pipe pile method, a shield method, and the like. For example, deep mixing improvement methods include a high-pressure injection method, a TRD method, and an SMW method. The method of the present invention is suitable for a deep mixing method.

In the ground improvement method of the present invention, it is preferable to use the above-mentioned slurry. In that case, the above-mentioned slurry can be mixed into component (i) using a slurry mixing type agitator. Here, the slurry mixing type agitator is an agitator used in a construction method involving mechanical agitation of soil and slurry, and is an agitator that can inject a slurry containing hydraulic powder such as cement into the soil and add mechanical agitation. Examples of construction methods that use such agitators include the Mud Stabi method, ARM method, LVM method, FAM method, Mud Mixer M-II method, SCM method, ISM method, WILL method, Eyemark method II, VMS method, and ST column method. Examples include three-dimensional mixing method, power blender method, MMB method, MR-IIC method, twin blade mixing method, open wing method, double mixing method, USP method, MT-CMC method, Esmi column method, Three S G method, Soil Master method, CDM-SSC method, PROP method, CI-CMC method, Ascolumn method, DJM method, TRD method, Epo column method, NC column method, RAS column method, JST method, CDM-LODIC method, CDM-column method, CDM method, Teno column method, KS-B MIX method, CDM-Mega method, CDM-Land4 method, CDM-Lemni 2/3 method, CDM-FLOAT method, DCM-L method, DCS method, expansion/contraction column method, HEMS method, and MITS method.

In the present invention, from the viewpoint of achieving both column quality and shortening of construction time, the number of times the blades are cut when mixing with the agitator is preferably 100 times or more, more preferably 200 times or more, and preferably 1000 times or less, more preferably 500 times or less. It is preferable to use an agitator that has a blade cutting number within this range. In general, agitators used for ground improvement are equipped with blades, and the number of blade cutting times is set taking into consideration the blade shape, number of blades, mixing force, soil volume, soil quality, etc.

When using the slurry, the specific method of injecting the slurry into the ground (i), component, may be in accordance with known ground improvement methods. Examples of methods for injecting the slurry into the ground include the jet mixing method (one-phase flow method, two-phase flow method, three-phase flow method), mechanical mixing method (CDM method, etc.), and underground continuous wall method (SMW method, TRD method, etc.). The solidification material mixture such as soil cement obtained by mixing the slurry with component (i) can be solidified in accordance with known ground improvement methods.

In the present invention, the slurry is injected into the ground while mixing and stirring component (i), forming soil cement, and then a soil cement column can be constructed. In the present invention, the slurry can be discharged from the tip of the mixing and stirring device while rotary drilling the ground, and component (i) and the slurry can be mixed. These methods can be combined. Such a method is suitable for deep mixing treatment.

The ground improvement method of the present invention includes a method of penetrating component (i) while rotating a rod equipped with an agitating blade and a slurry outlet, and injecting a slurry containing components (ii), (iii), and (iv) into component (i) from the outlet while mixing component (i) and the slurry with the agitating blade, in which component (ii) is mixed in a ratio of 18% by mass or less relative to component (i). This method is also preferably performed in the original location of component (i). In general, when such a rod is used, component (i) and the slurry are mixed and stirred in an area shaped according to the rotational shape of the rod, for example, a circular area.

In the present invention, as the agitator for the slurry mixing method, for example, an earth auger for excavation having an auger rod, a nozzle for ejecting the solidification material (slurry) provided on the auger rod, an excavation blade provided on the auger rod, and an anti-corotation blade provided on the auger rod as necessary can be used. Such an earth auger for excavation can be any known one used in the method for constructing soil cement columns.
The excavation earth auger is set at a predetermined position in the ground where a soil cement column is to be constructed, and excavation is performed to a predetermined dry excavation depth while rotating the mixing blade. During this process, the slurry is discharged from the auger rod while excavation is performed. Although excavation may be performed without discharging the slurry, when the predetermined depth is reached, the slurry is discharged while excavation is performed. When the injection excavation process (mixing and mixing) is completed, the discharge of the slurry is stopped, the rotation direction of the auger rod is reversed, and then lifting (mixing and mixing) is started. The auger is pulled out to complete the process. In this method, the number of blade cuts can be calculated from the rotation speed of the mixing blade.
In the present invention, the clay lumps in the soil cement column are reduced, and the clay lumps that exist are small, so that the decrease in the strength of the soil cement column can be suppressed. The slurry has excellent fluidity, so that the workability is improved.

<Ground improvement body>
The present invention relates to a soil improvement body containing (i), (ii), and (iii), in which the (i) component is a soil having a uniformity coefficient (D50/D10) of 2.6 to 8.0, and the (ii) component is contained in an amount of 18% by mass or less relative to the (i) component. The matters described in the soil improvement method of the present invention can be appropriately applied to the soil improvement body of the present invention. Specific examples and preferred examples of the (i), (ii), and (iii) components in the soil improvement body of the present invention are also the same as those in the soil improvement method of the present invention.

The ground improvement body of the present invention may be a ground improvement body obtained by mixing component (i), component (ii), and component (iii), in which component (i) is soil having a uniformity coefficient (D50/D10) of 2.6 or more and 8.0 or less, and the mixed amount of component (ii) is 18 mass% or less relative to the mixed amount of component (i).
Furthermore, the ground improvement body of the present invention may be a ground improvement body obtained by hardening a mixture obtained by mixing component (i), component (ii), component (iii), and component (vi), in which component (i) is soil having a uniformity coefficient (D50/D10) of 2.6 or more and 8.0 or less, and the content of component (ii) in the mixture is 18 mass% or less relative to the content of component (i) in the mixture.

(1) Preparation of solidification material slurry The solidification material slurry was prepared by mixing the components (ii), (iii), and (iv) shown in the table. Mixing was performed for 1 minute using a hand mixer. The ratio of the component (iii) to the component (ii) was as shown in the table. The component (iv) was mixed to be 60% by mass relative to the component (ii).

(2) Measurement of the clay remaining area ratio The solidification material slurry was mixed with the (i) component shown in the table to prepare soil cement. The mixing was carried out for 1 minute using a mortar Hobart mixer. The solidification material slurry was used so that the ratio of the (ii) component to the (i) component was as shown in the table.
The soil cement was filled into a container (soft plastic cup) with a diameter of 10 cm and a height of 5 cm, and tapped 10 times to remove any coarse voids.

While the soil cement was still unhardened, the container was filled with soil cement, and the container was cut into two parts, one above the other, at a position 2.5 cm from the bottom, and 1% phenolphthalein (90% ethanol) was sprayed onto the cross section of the lower part. The parts containing cement were stained, but the parts not containing cement were not stained. The parts not containing cement were unstained parts where clay lumps remained.
A transparent 5 mm square mesh was placed on the cross section after the dyeing process, and the number of unstained cells was counted. The clay lump residual rate was calculated using the following formula, which was used as an index of mixability. This formula assumes that a cell that is partially unstained is equivalent to 0.5 unstained cells. The smaller the clay lump residual rate, the more uniformly the soil and solidification material slurry are mixed.
Clay lump remaining rate (%) = {(number of cells in which all 5 mm squares are unstained) x 1 + (number of cells in which some 5 mm squares are unstained) x 0.5} / (number of all cells used in the measurement)

(3) Measurement of minimum needle penetration value The upper part of the soil cement cut in (2) above was cured at 20°C for 24 hours while still in the container. In order to prevent the cross section from drying out, the cross section of the soil cement was covered with a wet towel during curing. After curing, the minimum needle penetration value was measured using a penetration tester. A specified penetration needle (hereinafter referred to as needle) was used for the penetration tester. Here, the needle was made of stainless steel (SUS440C as specified in JIS G 4303), had a conical tip, was 40 mm long and 1 mm in diameter, was free of rust, and had no bends. In addition, the surface roughness of the tapered part of the needle was 0.3 μm or less when measured according to JIS B 0651.
After confirming that the total mass of the load part (needle, needle holder, weight) of the needle penetration tester was the specified mass (100 g), a weight (50±0.05 g) was attached to the needle holder of the needle penetration tester. In addition, the clasp was pressed and it was confirmed that the needle holder immediately fell. The distance until the needle stopped was measured with the needle penetration tester for the sample after curing. This measurement was performed by randomly selecting five different points on the sample surface. The smallest distance among these distances is shown in the table as the minimum needle penetration value. The smaller the minimum needle penetration value, the higher the strength of the hardened body.

*1 The preparation is soil prepared by mixing commercially available Kasaoka clay (Kasanen Factory, product name Kasaoka clay (powder) (250 mesh)), No. 6 silica sand, and water in a ratio of Kasaoka clay/silica sand/water = 10/70/20 (mass ratio).

Claims (10)

A method for improving ground comprising mixing a clay-containing soil (i) (hereinafter referred to as component (i)), a hydraulic powder (ii) (hereinafter referred to as component (ii)), a compound (iii) represented by the following general formula (1) (hereinafter referred to as component (iii)), and water (iv) (hereinafter referred to as component (iv)),
(i) The component is a soil having a uniformity coefficient (D50/D10) of 2.6 to 8.0 and a pore distance of 7 nm to 20 nm ;
The component (ii) is mixed in an amount of 18% by mass or less relative to the component (i);
Ground improvement methods.
RO-(AO) _m -H (1)
(In general formula (1), R represents a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms, AO represents an oxyethylene group or an oxypropylene group, and m represents the average number of moles of AO added.) The ground improvement method according to claim 1, wherein component (i) is soil having a natural water content of 35% or more and 85% or less. 3. The method for improving ground according to claim 1 or 2, wherein the component (i) is soil having a BET specific surface area of 30 m ² /g or more and 70 ^{m 2} /g or less. 4. The method for improving ground according to claim 1 , wherein the component (i) is soil having a difference between its natural water content and its plastic limit of 0% or more and 80% or less. The method for improving ground according to any one of claims 1 to 4 , wherein the component (i) is soil containing halloysite. The method for improving ground according to any one of claims 1 to 5 , wherein the component (i) is soil containing tuffaceous clay. The method for improving ground according to any one of claims 1 to 6 , wherein the component (iv) is mixed in a ratio of 40 mass% to 250 mass% based on the component (ii). The method for improving ground according to any one of claims 1 to 7 , wherein the weight average molecular weight of the component (iii) is 1,000 or more and 2,000,000 or less. The ground improvement method according to any one of claims 1 to 8, in which a water reducing agent (v) is mixed with component (i). The method for improving ground according to any one of claims 1 to 9 , wherein an antifoaming agent (vi) is mixed with the component (i).