Site improvement methods

Abstract

To provide a soil improvement method that mixes soil and hydraulic powder, with improved mixability of the soil and the hydraulic powder, and also improved strength of a cured mixture of the soil and the hydraulic powder.SOLUTION: A soil improvement method includes mixing a hydraulic slurry with soil comprising clay to cure the mixture, wherein the hydraulic slurry comprises (A) a nonionic surfactant comprising a C15-55 hydrophobic group and an oxyalkylene group with an average number of added moles of 8 or more and 30 or less, hydraulic powder and water.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a ground improvement method and a hydraulic slurry for ground improvement. [Background technology]

[0002] One method for improving ground is to mix cement-based slurry with the soil at the site to be improved, and then the mixture of cement-based slurry and soil hardens to strengthen the ground. Examples of this method include the DCS method and the CDM method. The DCS method is a cement-based deep mixing ground improvement method in which hydraulic slurry (cement-based slurry) is injected into the ground and mixed with the soil to create a DCS column (soil cement column). The CDM method is a deep mixing method using mechanical stirring, in which a slurried cement-based hardening material is injected into soft ground, stirred and mixed with the soft ground, and chemically solidified.

[0003] Patent Document 1 discloses a ground improvement method in which hydraulic powder and triethanolamine or a salt thereof are mixed into soil, and the amount of the setting retarder mixed into the soil is less than 0.5 mass% of the amount of hydraulic powder mixed into the soil. In the working examples, it is disclosed that a powder mixture containing cement and an additive containing triethanolamine is prepared, the powder mixture is mixed with water to prepare cement milk, and the cement milk is injected into and mixed with simulated clayey soil. Patent Document 2 discloses a ground improvement method including the steps of: forming a borehole and excavating generated soil to the surface; spreading a powdered cement composition on the excavated soil and stirring it; mixing a hardening auxiliary composition with a nonionic surfactant; and backfilling the borehole with the improved soil mixture obtained in the hardening auxiliary composition mixing step. In the examples, the method uses polyoxyethylene sorbitan oleate as the nonionic surfactant. Patent Document 3 discloses a method for producing a hydrous soil treatment agent containing a water-soluble polymer and a surfactant as components, in which the surfactant is allowed to coexist when the water-soluble polymer is synthesized by solution polymerization of one or more monomers. The examples disclose that the soil treatment agent and a hydraulic substance are mixed with the soil to be evaluated, and that Rheodol SP-S10 (trade name), a sorbitan fatty acid ester, is used as the surfactant. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-178062 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-211382 [Patent Document 3] Japanese Patent Application Laid-Open No. 2005-154653 Summary of the Invention [Problem to be solved by the invention]

[0005] Clay lumps contained in soil are difficult to crumble, and if clay lumps remain in a mixture containing soil and hydraulic powder, the structure of the hardened mixture containing soil and hydraulic powder will be uneven, resulting in a decrease in strength. Therefore, it is desirable to reduce the amount of clay lumps remaining in a mixture containing soil and hydraulic powder, improve the mixability of the soil and hydraulic powder, and increase the strength of the hardened body of the mixture containing soil and hydraulic powder, thereby achieving stable ground reinforcement.

[0006] The present invention provides a ground improvement method for mixing soil, particularly clay-containing soil, with a hydraulic slurry containing hydraulic powder and water, which improves the mixability of the soil and hydraulic powder and increases the strength of the hardened body of the mixture containing the soil and hydraulic powder. [Means for solving the problem]

[0007] The present invention relates to a ground improvement method in which a hydraulic slurry containing (A) a nonionic surfactant having a hydrophobic group having from 15 to 55 carbon atoms and an oxyalkylene group having an average added mole number of from 8 to 30 (hereinafter referred to as component (A)), hydraulic powder, and water is mixed with clay-containing soil and hardened.

[0008] The present invention also relates to a hydraulic slurry for ground improvement, which contains (A) a nonionic surfactant having a hydrophobic group with a carbon number of 15 to 55 and an oxyalkylene group with an average number of added moles of 8 to 30, a hydraulic powder, and water, and which is mixed with underground soil to harden the soil. [Effects of the Invention]

[0009] According to the present invention, in a ground improvement method for mixing soil with a hydraulic slurry containing hydraulic powder and water, it is possible to provide a ground improvement method in which the mixability of the soil and the hydraulic powder is improved and the strength of the hardened body of the mixture containing the soil and hydraulic powder is improved. DETAILED DESCRIPTION OF THE INVENTION

[0010] In the ground improvement method of the present invention, for example, by mixing a hydraulic slurry containing component (A), hydraulic powder, and water with clay-containing soil, the mixability of the soil and hydraulic powder and the mixability of the soil and hydraulic slurry are improved, and the amount of clay lumps remaining in the mixture of soil and hydraulic slurry is reduced. As a result, the hardened product of the mixture also has excellent uniformity and the strength of the hardened product is improved. The ground improvement method of the present invention can strengthen the stable ground.

[0011] <Hydraulic slurry> The hydraulic slurry used in the ground improvement method of the present invention contains (A) a nonionic surfactant having a hydrophobic group having from 15 to 55 carbon atoms and an oxyalkylene group having an average added mole number of from 8 to 30 (hereinafter referred to as component (A)), hydraulic powder, and water. The hydraulic slurry of the present invention may be a hydraulic slurry for ground improvement.

[0012] Component (A) is a nonionic surfactant having a hydrophobic group having from 15 to 55 carbon atoms and an oxyalkylene group having an average number of added moles of from 8 to 30. One or more types of component (A) can be used.

[0013] Examples of the hydrophobic group of component (A) include palmityl, stearyl, oleyl, phenyl substituted with a styrene group, and phenyl substituted with a benzyl group. From the viewpoint of uniformity of the mixture of soil and hydraulic slurry, stearyl, oleyl, and phenyl substituted with a benzyl group are preferred. The number of carbon atoms in the hydrophobic group of component (A) is 15 or more, preferably 17 or more, from the viewpoint of uniformity of the mixture of soil and hydraulic slurry, and is 55 or less, preferably 37 or less, more preferably 27 or less, from the viewpoint of product stability.

[0014] Component (A) may be one or more nonionic surfactants selected from (A1) polyoxyalkylene sorbitan fatty acid esters (hereinafter referred to as component (A1)) and (A2) substituted polyoxyalkylene phenyl ethers (hereinafter referred to as component (A2)). The fatty acid of component (A1) may be a fatty acid having from 12 to 22 carbon atoms. Furthermore, the number of substituents of component (A2) may be from 1 to 4.

[0015] When component (A) is component (A1), the hydrophobic group of component (A) may be one or more selected from palmityl, stearyl, and oleyl groups, and from the viewpoint of uniformity of the mixture of soil and hydraulic slurry, one or more selected from stearyl and oleyl groups are preferred. Furthermore, when component (A) is component (A2), the hydrophobic group of component (A) may be a phenyl group substituted with a styrene group or a phenyl group substituted with a benzyl group, and from the viewpoint of uniformity of the mixture of soil and hydraulic slurry, a phenyl group substituted with two or more styrene groups or a phenyl group substituted with two or more benzyl groups is preferred, a phenyl group substituted with two styrene groups or a phenyl group substituted with three benzyl groups is more preferred, and a phenyl group substituted with three benzyl groups is even more preferred.

[0016] When component (A) is component (A1), the number of carbon atoms in the hydrophobic group of component (A) is 15 or more, preferably 17 or more, from the viewpoint of uniformity of the mixture of soil and hydraulic slurry, and is 55 or less, preferably 37 or less, more preferably 27 or less, from the viewpoint of product stability. When the component (A) is the component (A1), the number of carbon atoms in the hydrophobic group is the total number of carbon atoms in the fatty acids bonded to one molecule of sorbitan. Furthermore, when component (A) is component (A2), the number of carbon atoms in the hydrophobic group of component (A) is 15 or more, preferably 17 or more, from the viewpoint of uniformity of the mixture of soil and hydraulic slurry, and is 55 or less, preferably 37 or less, more preferably 27 or less, from the viewpoint of product stability. When the component (A) is the component (A2), the number of carbon atoms in the hydrophobic group is the total value of the number of carbon atoms in the substituted phenyl group and the number of carbon atoms in the modifying group that modifies the phenyl group.

[0017] The oxyalkylene group of component (A) may be one or more types selected from oxyalkylene groups having from 2 to 4 carbon atoms, and from the viewpoint of product stability, one or more types selected from oxyethylene groups and oxypropylene groups are preferred. When the oxyalkylene group of component (A) contains two or more types of oxyalkylene groups, they may be randomly bonded or block bonded.

[0018] The average number of moles of oxyalkylene groups added in component (A) is 8 or more, preferably 12 or more, more preferably 14 or more, and 30 or less, preferably 26 or less, more preferably 22 or less, from the viewpoint of uniformity of the mixture of soil and hydraulic slurry.

[0019] The component (A) is preferably one or more nonionic surfactants selected from (A3) polyoxyethylene distyrenated phenyl ether, polyoxyethylene tribenzyl phenyl ether, and polyoxyethylene sorbitan fatty acid esters (having 13 to 60 carbon atoms) [hereinafter referred to as component (A3)], and more preferably polyoxyethylene tribenzyl phenyl ether and polyoxyethylene sorbitan fatty acid esters (having 17 to 21 carbon atoms).

[0020] The hydraulic powder is a powder that has the physical property of hardening through a hydration reaction, and examples thereof include cement and gypsum. The hydraulic powder is preferably cement. Examples of cement include Portland cement such as ordinary Portland cement, belite cement, moderate-heat cement, high-early-strength cement, ultra-high-early-strength cement, and sulfate-resistant cement. The hydraulic powder contains cement, especially Portland cement, in an amount of preferably 25% by mass or more, more preferably 35% by mass or more, even more preferably 50% by mass or more, still 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, still more preferably 90% by mass or less, and even more preferably 85% by mass or less.

[0021] The hydraulic powder may also contain powders with pozzolanic activity 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, such as blast furnace slag cement, fly ash cement, and silica fume cement. The hydraulic powder preferably contains blast furnace slag, as it serves as an aluminum ion source for ettringite, a hydration product. When the hydraulic powder contains blast furnace slag, its content 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.

[0022] 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 powder with pozzolanic action, 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.

[0023] The water that can be used includes tap water, lake water, river water, and groundwater.

[0024] <Composition of hydraulic slurry and other components> The hydraulic slurry of the present invention may contain component (A) in an amount of preferably 0.02% by mass or more, more preferably 0.04% by mass or more, and even more preferably 0.08% by mass or more, from the viewpoint of uniformity of the mixture of soil and hydraulic slurry, and preferably 1.0% by mass or less, more preferably 0.4% by mass or less, and even more preferably 0.2% by mass or less, from the viewpoint of injectability into the ground.

[0025] The hydraulic slurry of the present invention may contain hydraulic powder in an amount of preferably 30% by mass or more, more preferably 45% by mass or more, and even more preferably 60% by mass or more, from the viewpoint of improving the strength of the hardened mixture of soil and hydraulic slurry (hereinafter also referred to as ground improvement body), and in an amount of preferably 80% by mass or less, more preferably 75% by mass or less, and even more preferably 70% by mass or less, from the viewpoint of the fluidity of the hydraulic slurry.

[0026] In the hydraulic slurry of the present invention, the ratio of the content of component (A) to the content of hydraulic powder [component (A) / hydraulic powder] is preferably 0.05% by mass or more, more preferably 0.10% by mass or more, and even more preferably 0.15% by mass or more, from the viewpoint of uniformity of the mixture of soil and hydraulic slurry, and is preferably 1% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.30% by mass or less, from the viewpoint of cost and suppression of foaming.

[0027] In the hydraulic slurry of the present invention, the ratio of the content of water (W) to the content of hydraulic powder (C) [(W) / (C)] is preferably 0.4 or more, more preferably 0.5 or more, and even more preferably 0.6 or more, in terms of mass ratio, from the viewpoint of the injectability of the hydraulic slurry into the ground, and is preferably 2.0 or less, more preferably 1.0 or less, and even more preferably 0.8 or less, from the viewpoint of the strength of the ground improvement body and reducing the amount of waste.

[0028] The hydraulic slurry of the present invention may contain a nonionic surfactant other than component (A). The proportion of component (A) in the total nonionic surfactants contained in the hydraulic slurry of the present invention may be, for example, 30 mass% or more, further 50 mass% or more, further 80 mass% or more, and 100 mass% or less. The hydraulic slurry of the present invention may be a hydraulic slurry containing 100 mass% of component (A) as a nonionic surfactant.

[0029] The proportion of the (A3) component in the total nonionic surfactants contained in the hydraulic slurry of the present invention may be, for example, 10 mass% or more, further 20 mass% or more, further 30 mass% or more, and 100 mass% or less. The hydraulic slurry of the present invention may be a hydraulic slurry containing 100 mass% of the (A3) component as a nonionic surfactant.

[0030] The hydraulic slurry of the present invention may optionally contain antifoaming agents, thickeners, dispersants and preservatives.

[0031] <Additives for hydraulic slurry> The present invention provides a hydraulic slurry additive to be mixed with clay-containing soil in a soil improvement method in which a hydraulic slurry containing hydraulic powder and water is mixed with the soil and hardened, the additive containing (A) a nonionic surfactant having a hydrophobic group with a carbon number of 15 to 55 and an oxyalkylene group with an average number of added moles of 8 to 30. The nonionic surfactant is the same as the component (A) described in the hydraulic slurry of the present invention.

[0032] <Hydraulic premix> The present invention provides a hydraulic premix for ground improvement, which contains (A) a nonionic surfactant having a hydrophobic group having from 15 to 55 carbon atoms and an oxyalkylene group having an average number of added moles of from 8 to 30, and hydraulic powder, and which is mixed with underground soil to harden the soil. Preferred embodiments of the component (A) and hydraulic powder of the hydraulic premix for ground improvement of the present invention are the same as the preferred embodiments of the component (A) and hydraulic powder explained in the hydraulic slurry of the present invention.

[0033] <Soil improvement method> The present invention provides a ground improvement method that involves mixing (A) a nonionic surfactant having a hydrophobic group with 15 to 55 carbon atoms and an oxyalkylene group with an average added mole number of 8 to 30 (hereinafter referred to as component (A)), hydraulic powder, and water with clay-containing soil, followed by hardening. The ground improvement method may be a method of mixing clay-containing soil with the hydraulic slurry in situ. The present invention also provides a ground improvement method in situ, which comprises mixing (A) a nonionic surfactant having a hydrophobic group with a carbon number of 15 to 55 and an oxyalkylene group with an average number of added moles of 8 to 30 (hereinafter referred to as component (A)), hydraulic powder, and water with clay-containing soil and allowing the mixture to harden. The ground improvement method may comprise mixing a hydraulic slurry containing hydraulic powder and water with the soil. These ground improvements may be ground strengthening. In the ground improvement method of the present invention, the hydraulic slurry of the present invention can be preferably used. Therefore, in the ground improvement method of the present invention, the component (A), hydraulic powder, etc. described in the hydraulic slurry of the present invention can be preferably used. The ground improvement method of the present invention will be described below with reference to specific embodiments, but the ground improvement method of the present invention is not limited to the following embodiments. For example, when using the hydraulic premix of the present invention, a hydraulic slurry obtained by mixing the hydraulic premix with water can be used, and the soil can be hardened after mixing the hydraulic premix with soil.

[0034] The ground improvement method of the present invention comprises step 1 of mixing component (A), hydraulic powder, and water to obtain a hydraulic slurry, step 2 of mixing the hydraulic slurry with clay-containing soil to obtain a mixture of soil and hydraulic slurry, and step 3 of hardening the mixture of soil and hydraulic slurry.

[0035] In step 1, from the viewpoint of uniformity of the mixture of soil and hydraulic slurry, the amount of component (A) can be preferably 0.02 mass % or more, more preferably 0.04 mass % or more, and even more preferably 0.08 mass % or more, based on the total amount of the mixed components of the hydraulic slurry, and from the viewpoint of injectability into the ground, the amount can be preferably 1.0 mass % or less, more preferably 0.4 mass % or less, and even more preferably 0.2 mass % or less.

[0036] Furthermore, from the viewpoint of the strength of the ground improvement body and reducing waste, the hydraulic powder can be mixed in an amount of preferably 30% by mass or more, more preferably 45% by mass or more, and even more preferably 60% by mass or more, based on the total amount of mixed components of the hydraulic slurry, and from the viewpoint of the injectability of the hydraulic slurry into the ground, the amount can be preferably 80% by mass or less, more preferably 75% by mass or less, and even more preferably 70% by mass or less.

[0037] The ratio of the amount of component (A) mixed to the amount of hydraulic powder mixed in the total amount of mixed components of the hydraulic slurry [component (A) / hydraulic powder] is preferably 0.05% by mass or more, more preferably 0.10% by mass or more, and even more preferably 0.15% by mass or more, from the viewpoint of uniformity of the mixture of soil and hydraulic slurry, and is preferably 1% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.30% by mass or less, from the viewpoint of cost and suppression of foaming.

[0038] The ratio of the amount of water (W) mixed to the amount of hydraulic powder (C) mixed in the total amount of mixed components of the hydraulic slurry [(W) / (C)] is preferably 0.4 or more by mass, more preferably 0.5 or more, and even more preferably 0.6 or more, from the viewpoint of injectability into the ground, and is preferably 2.0 or less, more preferably 1.0 or less, and even more preferably 0.8 or less, from the viewpoint of the strength of the ground improvement body and reducing waste.

[0039] In step 2, the hydraulic slurry is mixed with clay-containing soil. In this case, from the viewpoint of uniformity of the mixture of soil and hydraulic slurry, the amount of component (A) mixed with respect to the soil [component (A) / soil] is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, and even more preferably 0.01% by mass or more, and from the viewpoint of cost reduction and defoaming properties, the hydraulic slurry and soil are mixed so that the amount is preferably 0.5% by mass or less, more preferably 0.3% by mass or less, and even more preferably 0.1% by mass or less.

[0040] Clay contained in soil is, for example, mainly composed of hydrous silicate minerals (hereinafter 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.). The types and amounts of clay contained in soil vary, but the present invention can target, for example, soil containing clay minerals selected from kaolin and smectite.

[0041] Clay-containing soil may contain, for example, 30% by mass or more, further 40% by mass or more, further 50% by mass or more, and 100% by mass or less, further 95% by mass or less, further 90% by mass or less of clay.

[0042] The clay-containing soil may be soil originating from volcanic ash. The soil may be a volcanic ash clay, for example, tuffaceous clay. Tuffaceous clay is soil that has been converted into clay through weathering, hydrolysis, or the like of volcanic ash. Generally, tuffaceous clay contains little sand and has a milky white to milky gray appearance. Tuffaceous clay is a type of soil that is prone to the formation of clay lumps during the production of soil cement, but these clay lumps are difficult to deflocculate. However, in the present invention, even clay lumps derived from such tuffaceous clay can be easily deflocculated.

[0043] The ground improvement method of the present invention is preferably applied to a construction method in which hydraulic slurry is mixed with in-situ soil, from the viewpoint of being able to reduce the amount of clay lumps remaining in a mixture containing soil and hydraulic powder. The ground improvement method of the present invention can be applied specifically to deep layer mixing treatment methods, mid-layer mixing treatment methods, shallow layer mixing treatment methods, etc. Deep mixing treatment methods include, for example, the DCS method, JST method, CDM-LODIC method, CDM-Column method, CDM method, CDM method, CDM-SSC method, CDM-Mega method, CDM-Land4 method, CDM-Lemni2 / 3 method, CDM-FLOAT method, DCS method, Tenocolumn method, MR-IIC method, Twin Blade Mixing method, Open Wing method, Double Mixing method, USP method, MT-CMC method, Esumicolumn method, Three S G method, Soil Master method, PROP method, CI-CMC method, Ascolumn method, DJM method, TRD method, Epocolumn method, NC column method, RAS column method, KS-B·MIX method, DCM-L method, Expanding and Contracting Column method, HEMS method, and MITS method. Examples of mid-layer mixing methods include the ARM method, LVM method, FAM method, SCM method, ISM method, i-mark method II, VMS method, ST column method, three-dimensional mixing method, MMB method, and WILL method. Examples of shallow mixing treatment methods include the Mud Stabilizer method, Power Blender method, Mud Mixer M-II method, Chemi-Colizer method, Soil Primer method, STB method, RM method, BH-RM method, VM method, and FSM method. [Example]

[0044] <Examples 1 and 2 and Comparative Examples 1 and 2> (1) Preparation of hydraulic slurry The components (A) and water shown in Tables 1 and 2 were mixed in the proportions shown in Tables 1 and 2, and then hydraulic powder was added to prepare hydraulic slurries. The components (A) and water were stirred with a glass rod until they were visually uniform and transparent. The mixture of water containing component (A) and hydraulic powder was stirred for 30 seconds with a hand mixer. The hydraulic slurries were prepared so that the mass ratio of component (A) to hydraulic powder (C) ((A) / (C)) and the mass ratio of water (W) to hydraulic powder (C) (W / C) were as shown in Tables 1 and 2. The hydraulic powder used was "Eustabiler 50" (Ube Industries, Ltd.), a special soil solidification material for ground improvement.

[0045] (2) Measurement of the clay remaining area ratio Soil cement was prepared by mixing hydraulic slurry with clay-containing soil (tuffaceous clay collected from a construction site in Kashiwa City, Chiba Prefecture, clay content 90% by mass). The soil cement was mixed using a mortar Hobart mixer for 30 seconds, simulating the mixing conditions of a construction method in which hydraulic slurry is mixed with in-situ soil. The hydraulic slurry was used so that the ratio of hydraulic powder (C) to soil ((C) / soil) 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. While the soil cement was still unhardened, the container was filled with soil cement and cut into two halves, 2.5 cm from the bottom, from the outside, and 1% phenolphthalein (90% ethanol) was sprayed onto the cross section of the lower part. The areas containing cement were stained, but the areas without cement were not. The areas without cement were unstained areas where clay lumps remained. A transparent 5mm grid was placed over 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. The clay lump residual rate is shown in Tables 1 and 2. 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 hydraulic slurry are mixed. Clay lump remaining rate (%) = {(Number of cells in the 5 mm grid that are entirely unstained) x 1 + (Number of cells in the 5 mm grid that are partially unstained) x 0.5} / (Number of all cells used in the measurement)

[0046] Furthermore, the cement uniformity of the soil cement of each example was calculated based on the following formula: The higher the cement uniformity, the higher the uniformity of the soil cement. Cement uniformity (%) = [1 - [(clay lump residual rate (%) calculated for soil cement of Example / clay lump residual rate (%) calculated for soil cement of Comparative Example 1-1)]] × 100

[0047] (3) Compressive strength measurement (3-1) Preparation of the specimen As with the measurement of the clay remaining area ratio, the soil cement shown in Table 2, prepared using a mortar Hobart mixer, was immediately filled into a formwork (diameter 50 mm x height 100 mm). The filling was carried out using a table vibrator, packing in two layers for 15 seconds. Four specimens were prepared. (3-2) Measurement of the strength of the hardened body The formwork filled with soil cement was left to stand at 20±2°C and demolded after 28 days. The strength of the resulting hardened body (ground improvement body) was measured in accordance with JIS A1216, the unconfined compression test method for soil. The strength measurement results are shown in Table 2. Note that when the strength of the hardened soil cement body in Table 1 is measured in the same way, the same tendency as the hardened soil cement body in Table 2 is observed.

[0048] [Table 1]

[0049] [Table 2]

Claims

1. A method for improving ground, comprising mixing a hydraulic slurry containing (A) a nonionic surfactant having a hydrophobic group having from 15 to 55 carbon atoms and an oxyalkylene group having an average added mole number of from 8 to 30, the nonionic surfactant being one or more selected from polyoxyethylene distyrenated phenyl ether, polyoxyethylene tribenzyl phenyl ether, and polyoxyethylene sorbitan fatty acid ester (hereinafter referred to as component (A)), hydraulic powder, and water with clay-containing soil, and allowing the mixture to harden.

2. The ground improvement method according to claim 1, which is used in a construction method in which a hydraulic slurry is mixed with the soil in situ.

3. 3. The ground improvement method according to claim 1, wherein the mixing amount of component (A) relative to the hydraulic powder is 0.05% by mass or more and 1% by mass or less.

4. The ground improvement method according to any one of claims 1 to 3, wherein the mixing amount of component (A) to the soil is 0.001% by mass or more and 0.5% by mass or less.

5. The ground improvement method according to any one of claims 1 to 4, wherein the ratio (W / C) of the amount of water (W) mixed to the amount of hydraulic powder (C) mixed is 0.4 or more and 2.0 or less in mass ratio.

6. The ground improvement method according to any one of claims 1 to 5, wherein the hydraulic slurry is mixed with clay-containing soil in situ.

7. 7. The method for improving ground according to claim 1, wherein the hydraulic slurry is injected into the ground and mixed with soil.

8. (A) A hydraulic slurry for ground improvement comprising: a nonionic surfactant having a hydrophobic group having from 15 to 55 carbon atoms and an oxyalkylene group having an average added mole number of from 8 to 30, the nonionic surfactant being one or more selected from polyoxyethylene distyrenated phenyl ether, polyoxyethylene tribenzyl phenyl ether, and polyoxyethylene sorbitan fatty acid ester; hydraulic powder; and water; the hydraulic slurry being mixed with underground soil to harden the soil.

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