Ground improvement method

Abstract

To provide a soil improvement method which can uniformly mix soil and a solidification material by reducing a clay lump when improving the soil containing clay by using the solidification material, and can obtain a soil-improved body which is excellent in rigidity.SOLUTION: In a soil improvement method for mixing hydraulic setting powder (ii), a chemical compound (iii) expressed by the following general formula (1) and water (iv) to soil (i) which contains clay, the soil improvement method mixes (ii) to (i) at a ratio equal to or lower than 18 mass%, and in the method, (i) is the soil whose uniformity coefficient (D50 / D10) is equal to or higher than 2.6, and equal to or lower than 8.0: R-O-(AO)m-H (1). (In the general formula (1), R expresses a hydrogen atom, or a hydrocarbon group whose carbon number is equal to or larger 1, and equal to or smaller than 4, AO expresses an oxyethylene group or an oxypropylene, and m expresses an average addition mole number of AO, and is a number equal to or larger than 20, and equal to or smaller than 18,000.)SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a ground improvement method. [Background technology]

[0002] 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 the ground. In addition, the so-called replacement column method, in which ground soil is replaced with a solidification material, is known.

[0003] Patent Document 1 discloses a method for constructing a hydraulic solidification material liquid replacement column, which is characterized in that the tip of an excavation auger, which has a supply passage for hydraulic solidification material liquid inside, is provided with at least excavation claws and a discharge outlet for the hydraulic solidification material liquid, the excavation auger is rotated (forward or reverse) by a construction device equipped with an auger motor to excavate to a specified depth, and then the excavation auger is pulled up while rotating (forward or reverse) or without rotating while discharging hydraulic solidification material liquid from the discharge outlet, and a specified section of the excavated portion is filled with the hydraulic solidification material liquid.

[0004] 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 that contains 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. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2011-106253 A [Patent Document 2] JP 2020-26523 A [Patent Document 3] JP 2007-169547 A [Patent Document 4] JP 2009-286655 A Summary of the Invention [Problem to be solved by the invention]

[0006] 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 so-called co-rotation phenomenon may occur in which these blades and the soil rotate synchronously, preventing the soil and solidification material from being 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. [Means for solving the problem]

[0007] 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 soil with a uniformity coefficient (D50 / D10) of 2.6 or more and 8.0 or less, The (ii) component is mixed in an amount of 18 mass% or less relative to the (i) component. 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.) Effect of the Invention

[0008] According to the present invention, when improving soil containing clay using a solidification material, a ground improvement method is provided which can reduce clay lumps and uniformly mix the soil and solidification material, thereby obtaining a ground improvement body with excellent strength. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] <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).

[0010] 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 50% passing mass percentage) obtained by the method of JIS A 1204 by the effective diameter D10 (particle diameter at 10% passing mass percentage). The uniformity coefficient was calculated by 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.

[0011] From the viewpoint of improving the mixing uniformity and particle adhesion strength through water, the component (i) may be soil having a natural moisture content of 35% or more and 85% or less. The natural moisture content of the 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 the component (i) is more preferably 40% or more, even more preferably 45% or more, and more preferably 80% or less, even more preferably 75% or less.

[0012] Ingredient (i) is a sintered material with a BET specific surface area of ​​30 m in order to secure adhesion points between particles and increase strength. 2 / g or more 70m 2 The BET specific surface area of ​​the component (i) may be 35 m 2 / g or more, more preferably 40m 2 / g or more, and more preferably 65m 2 / g or less, more preferably 60m 2 / g or less. The BET specific surface area of ​​component (i) is calculated by a method in which gas molecules with a known adsorption occupancy area are adsorbed onto the surface of soil particles, the specific surface area of ​​the sample is calculated from the amount of gas molecules adsorbed, and the pore distribution is measured from the condensation of the gas molecules. Specifically, the BET specific surface area of ​​component (i) 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.) is used, and about 3 g of the sample is placed in a glass cell, and the adsorption gas (a mixed gas of nitrogen and helium in a ratio of 3:7) is injected at 60 cm into the sample cooled to liquid nitrogen temperature. 3 The gas was introduced at a flow rate of 100 / min and allowed to adsorb, and the amount of gas desorbed when the sample was returned to room temperature was measured. The specific surface area (single-point BET method) was obtained by dividing the amount by the sample mass.

[0013] The component (i) may be soil having a pore distance of 7 nm to 20 nm from the viewpoint of increasing the strength by bridging the particles with the compound (iii). The pore distance of the 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 the compound (iii) can crosslink, the pore distance of the 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.

[0014] The component (i) 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 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, and the soil just breaks into pieces. The plastic limit of the component (i) can be specifically 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 component (i) 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.

[0015] In the present invention, the physical properties (such as uniformity coefficient) of the component (i) are determined by using the soil (in situ soil) to which the ground improvement method of the present invention is applied as a sample. For example, the uniformity coefficient may be determined for the soil in situ.

[0016] j (i) The uniformity coefficient, natural moisture content, and BET specific surface area of ​​the components can be adjusted, for example, by mixing industrial sand, sand for grain adjustment, and water.

[0017] The average particle size of component (i) may be, for example, 1 μm or more, further 5 μm or more, and 150 μm or less, further 100 μm or less, further 50 μm or less. Here, the average particle size of component (i) is measured, for example, by preparing 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."

[0018] 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 its viscosity. According to the Geotechnical Society Standards, clayey soil, organic soil, and volcanic ash clayey soil are known as soils with a ratio of fine particles with a particle size of less than 75 μm of 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.

[0019] Clay is mainly composed of hydrous silicate minerals (hereinafter referred to as clay minerals) having 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.). The types and amounts of clay contained in soil are diverse, but the present invention can target soil containing clay minerals selected from, for example, kaolin and smectite.

[0020] Component (i) may be a soil containing halloysite. 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.

[0021] Component (i) may contain clay, for example, at least 15%, even at least 20%, even at least 25%, and at most 100%, even at most 95%, even at most 90% by weight.

[0022] The component (i) may be soil originating from volcanic ash. The component (i) may be a volcanic ash clay, for example, tuffaceous clay. Tuffaceous clay is soil that has been converted into clay through weathering, hydrolysis, etc., of volcanic ash. In general, tuffaceous clay has a milky white or milky gray appearance with little sand mixed in. Tuffaceous clay is a soil that is prone to be mixed with and formed as clay lumps 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. The 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.

[0023] The component (i) has a dry density of, for example, 1.9 g / cm 3 Above that, an additional 2.0g / cm 3 Above, and 2.9g / cm 3 Below that, 2.8g / cm 3 Here, the dry density of the component (i) is measured by the method of JIS A 1224.

[0024] Component (ii) is a hydraulic powder. The hydraulic powder of component (ii) is a powder having the physical property of hardening through a hydration reaction, and examples thereof include cement, gypsum, and the like. 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.

[0025] The hydraulic powder may contain powders having pozzolanic action and / or latent hydraulic properties, such as blast furnace slag, fly ash, and silica fume, and stone powder (calcium carbonate powder). These may be added to cement, such as blast furnace slag cement, fly ash cement, and silica fume cement. The hydraulic powder preferably contains blast furnace slag from the viewpoint of an aluminum ion source for ettringite, which is a hydration product. When the hydraulic powder contains blast furnace slag, the content of the 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.

[0026] In the present invention, the amount of hydraulic powder is the amount of powder having the physical property of hardening through a hydration reaction, such as the amount of cement or gypsum. However, in cases where the hydraulic powder includes a powder selected from a powder having pozzolanic action, a powder having latent hydraulic properties, and stone powder (calcium carbonate powder), the amounts of these powders are also included in the amount of hydraulic powder in the present invention.

[0027] 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, and AO is preferably an oxyethylene group. In the general formula (1), m represents the average number of moles of AO added, and 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.

[0028] The weight average molecular weight of component (iii) may be, for example, 1000 or more, further 2000 or more, further 3000 or more, and may be 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.

[0029] In the ground improvement method of the present invention, from the viewpoint of achieving 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 mass% or less to the (i) component. This ratio is preferably 3 mass% or more, more preferably 3.2 mass% or more, even more preferably 4 mass% or more, more preferably 5 mass% or more, even more preferably 6 mass% or more, even more preferably 8 mass% or more, and preferably 15 mass% or less, more preferably 12 mass% or less, more preferably 11 mass% or less, and even more preferably 10 mass% or less. This ratio is calculated by [amount of (ii) component / amount of (i) component]×100.

[0030] In the ground improvement method of the present invention, from the viewpoint of obtaining 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)]×100.

[0031] 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]×100.

[0032] 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 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, relative to the (ii) component. This ratio is calculated by [amount of (iv) component / amount of (ii) component]×100.

[0033] In the present invention, a water reducing agent (v) (hereinafter referred to as component (v)) may be mixed with component (i). Examples of the (v) component 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 (v) component include polycarboxylic acid polymers, naphthalene polymers, and polymers of (hydroxyalkyl) methacrylic acid esters of phosphoric acid. Specifically, examples of the (v) component include polyalkylene glycol monoester monomers having an oxyalkylene group with 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 with 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 (v) component include melamine sulfonic acid formalin condensates, aminosulfonic acid, and the like. (v) Component can be a commercially available water reducing agent or high-performance water reducing agent. 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)]×100.

[0034] 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 component (vi) 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 esters are more preferred among fatty acid ester-based defoamers, polyalkylene glycol alkyl ethers are more preferred among ether-based defoamers, and alkyldimethylamines or salts thereof are 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 with the (ii) component 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. This ratio is calculated by [amount of the (vi) component / amount of the (ii) component]×100.

[0035] In the present invention, it is preferable to mix a slurry containing the components (ii), (iii) and (iv) with the component (i). The slurry may be a solidifying agent slurry such as so-called cement milk. The slurry may contain the components (v) and (vi).

[0036] In the present invention, the component (i) can also be mixed with the components (ii), (iii) and (iv) separately.

[0037] In the ground improvement method of the present invention, the (i) component can be mixed with the (ii), (iii) and (iv) components in situ to prepare soil cement. As an example of the ground improvement method of the present invention, the prepared soil cement can be poured into the ground, and the soil cement hardens to become a ground improvement body, thereby improving the strength of the ground.

[0038] The ground improvement method of the present invention includes a construction method in which soil cement is poured into the ground. For example, the method can be implemented by a surface mixing method, a middle layer mixing method, a deep layer mixing method, a steel pipe pile method, a shield method, and the like. For example, the deep layer mixing improvement method includes a high pressure injection method, a TRD method, an SMW method, and the like. The method of the present invention is suitable for the deep layer mixing method.

[0039] 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 the 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 soil and add mechanical agitation. Examples of construction methods using such an agitator include the mud stabilizer method, the ARM method, the LVM method, the FAM method, the mud mixer M-II method, the SCM method, the ISM method, the WILL method, the eye mark method II, the VMS method, and the ST column method. Examples of these 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 and contraction column method, HEMS method, and MITS method.

[0040] In the present invention, from the viewpoint of achieving both the quality of the column and the shortening of the construction period, the number of times the blades are cut in the mixing by 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 with a blade cutting number in this range. In general, an agitator used for ground improvement is equipped with agitating blades, and the number of blade cutting is set in consideration of the shape of the agitating blades, the number of agitating blades, the agitating force, the amount of soil, the quality of the soil, etc.

[0041] 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 jet mixing methods (one-phase flow method, two-phase flow method, three-phase flow method), mechanical mixing methods (CDM method, etc.), and underground diaphragm wall methods (SMW method, TRD method, etc.). The solidification material mixture such as soil cement obtained by mixing the slurry with the (i) component can be solidified in accordance with known ground improvement methods.

[0042] In the present invention, the component (i) can be mixed and stirred while injecting the slurry into the ground, to form soil cement, and then a soil cement column can be constructed. In the present invention, the component (i) can be mixed with the slurry by rotating and drilling the ground while discharging the slurry from the tip of the mixing and stirring device. These methods can be combined. Such a method is suitable for a deep mixing treatment method.

[0043] 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 stirring and 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 at the original location of component (i). In general, when such a rod is used, component (i) and the slurry are stirred and mixed in an area shaped according to the rotation shape of the rod, for example, a circular area.

[0044] 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 excavating 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 stirring) is completed, the discharge of the slurry is stopped, the rotation direction of the auger rod is reversed, and then lifting (mixing and stirring) is started. The auger is pulled out to complete the process. In this method, the number of times the blades are cut 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.

[0045] <Ground improvement body> The present invention relates to a ground improvement body containing components (i), (ii), and (iii), in which the component (i) is soil having a uniformity coefficient (D50 / D10) of 2.6 to 8.0, and the component (ii) is contained in an amount of 18 mass% or less relative to the component (i). The matters described in the ground improvement method of the present invention can be appropriately applied to the ground improvement body of the present invention. Specific examples and preferred examples of the components (i), (ii), and (iii) in the ground improvement body of the present invention are also the same as those in the ground improvement method of the present invention.

[0046] 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 formed 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. EXAMPLES

[0047] (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 component (iii) to component (ii) was as shown in the table. Component (iv) was mixed to be 60% by mass relative to component (ii).

[0048] (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. Mixing was carried out for 1 minute using a mortar Hobart mixer. The solidification material slurry was used so that the ratio of (ii) component to (i) 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 the container was tapped 10 times to remove any coarse voids.

[0049] While the soil cement was still unhardened, the container was filled with soil cement, and the container was cut into two parts, 2.5 cm from the bottom, and 1% phenolphthalein (90% ethanol) was sprayed onto the cut surface 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, with clay lumps remaining. A transparent 5mm 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 the 5 mm grid that are all unstained) x 1 + (number of cells in the 5 mm grid that are partially unstained) x 0.5} / (total number of cells used in the measurement)

[0050] (3) Measurement of minimum needle penetration value The upper part of the soil cement cut in (2) above was left in the container and cured at 20°C for 24 hours. 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 the 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 was not bent. 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 of the needle penetration tester (needle, needle holder, and weight) was the specified mass (100g), a weight (50±0.05g) was attached to the needle holder of the needle penetration tester. The fastener was also pressed, and it was confirmed that the needle holder immediately fell. After curing, the sample was measured with the needle penetration tester to see how far the needle came to a stop. This measurement was performed at five different points randomly selected on the sample surface. The smallest of 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.

[0051] [Table 1]

[0052] *1 The preparation is soil prepared by mixing commercially available Kasaoka clay (manufactured by 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).

[0053] [Table 2]

Claims

1. 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 method. R-O-(AO) ｍ -+ (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.)

2. 2. The method for improving ground according to claim 1, wherein the component (i) is soil having a natural water content of 35% or more and 85% or less.

3. (i) Component has a BET specific surface area of ​​30 m ２ / g or more 70m ２ The soil improvement method according to claim 1 or 2, wherein the soil has a soil impurity concentration of 0.1 to 0.1 g / g or less.

4. The ground improvement method according to any one of claims 1 to 3, 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.

5. The ground improvement method according to any one of claims 1 to 4, wherein the component (i) is soil containing halloysite.

6. The ground improvement method according to any one of claims 1 to 5, wherein the component (i) is soil containing tuffaceous clay.

7. The ground improvement method according to any one of claims 1 to 6, wherein the component (iv) is mixed in a ratio of 40% by mass to 250% by mass to the component (ii).

8. The ground improvement method 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.

9. The method for improving ground according to any one of claims 1 to 8, wherein a water reducing agent (v) is mixed with the component (i).

10. 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).

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