Ground improvement methods

Abstract

The present invention relates to a method for improving a ground which comprises adding a hydraulic powder, calcium silicate, and water to the soil, wherein the soil, at the time when at least the calcium silicate is added, has a bitumen content of 3 mass% or greater with respect to the amount of the hydraulic powder to be added to the soil.

Description

Technical Field

[0001] The present invention relates to a method for improving ground.

[0002] Background Art As a method for improving the foundation ground for constructing a building, there are known ground improvement methods such as driving ground improvement columns made of concrete or steel pipes into the ground, and injecting cement-based solidifying materials such as cement milk while excavating the ground, and directly forming a columnar ground improvement body formed by mixing the excavated soil and the cement milk in the ground. <00OO012> In ground improvement where a cement-based solidifying material is mixed with soil to modify the ground, it is considered to select a solidifying material, an additive, a mixing ratio, etc. in consideration of the properties of the soil to be mixed, the type of the ground improvement method, and the like.

[0004] Japanese Patent Application Laid-Open No. 2018-178062 discloses a ground improvement method for providing a ground improvement method having high initial strength of about 7 days and long-term strength of about 28 days of a ground improvement body, in which a hydraulic powder and triethanolamine or a salt thereof are mixed with soil, and the mixing amount of a setting retarder added to the soil is less than 0.5% by mass with respect to the mixing amount of the hydraulic powder added to the soil. And in the examples thereof, sodium gluconate is used as the setting retarder.

[0005] Japanese Patent Application Laid-Open No. 2006-8765 discloses a soil strengthening material capable of increasing the strength of the ground despite the presence of a hydration inhibitor, which is a soil strengthening material containing a cement-based solidifying material and a porous powder having a BET specific surface area of 30 m

[0005] , , 2 , <00000ZO>,

[0006] , , / g or more, and is used for soil containing organic matter. And as a typical example of the hydration inhibitor contained in the soil, humic acid is mentioned.

[0006] Summary of the Invention The present invention provides a novel ground improvement method that can effectively improve the ground by reducing the heat of hydration when improving the ground using hydraulic powder.

[0007] The present invention relates to a method for improving ground, comprising adding hydraulic powder, calcium silicate, and water to soil, wherein the bitumen content in the soil when at least calcium silicate is added is 3% by mass or more relative to the amount of hydraulic powder added to the soil.

[0008] The present invention provides a novel method for improving ground that can effectively improve ground by reducing the amount of heat of hydration when improving ground using hydraulic powder.

[0009] Modes for carrying out the invention Bitumen is known as an organic substance found in soil, but the inventors have found that in ground improvement using hydraulic powder and calcium silicate, the presence of a certain amount or more of bitumen brings about a desirable ground improvement effect. Gluconic acid, which is used as a setting retarder, and organic substances found in soil, such as humic acid (a component soluble in alkali and insoluble in acid), fulvic acid (a component soluble in alkali and acid), and humin (a component insoluble in both alkali and acid), are thought to tend to inhibit the hydration reaction of hydraulic powders such as cement. However, unlike these organic substances, bitumen, under the predetermined conditions of the present invention, exhibits a desirable effect in ground improvement using hydraulic powder and calcium silicate. This is an unexpected effect for those skilled in the art. Bitumen is a lipid-soluble component that dissolves in organic solvents such as benzene, alcohol, and dichloromethane, and does not readily react with calcium ions eluted from cement, thus not significantly reducing the calcium ion concentration. Furthermore, because bitumen is lipid-soluble, it is thought to provide a partial hydrophobic field when present near cement, thus slowing down the hydration reaction. These effects suggest that the ground improvement method of the present invention may suppress the heat generated by rapid hydration reactions while still achieving long-term strength.

[0010] This invention has found that when improving soil by adding hydraulic powder, calcium silicate, and water, the soil improvement effect is good when the bitumen content in the soil is 3% by mass or more relative to the amount of hydraulic powder added to the soil when at least calcium silicate is added. When the bitumen content in the soil is less than 3% by mass relative to the amount of hydraulic powder added to the soil and at least calcium silicate is added, the heat of hydration of the mixture of hydraulic powder, calcium silicate, water, and soil (ground improvement body) increases. In ground improvement methods using hydraulic powder, an increase in the heat of hydration of the ground improvement body can induce thermal cracking of the soil-cement columns formed in the ground, potentially preventing the desired strength from being achieved. This invention can solve this problem.

[0011] In the ground improvement method of the present invention, when at least calcium silicate is added to the soil, the bitumen content in the soil is 3% by mass or more relative to the amount of hydraulic powder added to the soil. Under these conditions, the bitumen content may be 3% by mass or more, preferably 4% by mass or more, preferably 30% by mass or less, more preferably 20% by mass or less, even more preferably 10% by mass or less, and even more preferably 8% by mass or less, relative to the amount of hydraulic powder added to the soil. In the present invention, after adjusting the bitumen content in the soil to 3% by mass or more relative to the amount of hydraulic powder added to the soil, at least calcium silicate can be added to the soil. For example, as a ground improvement method of the present invention, a method of adding hydraulic powder, calcium silicate, and water is given under the condition that the bitumen content in the soil is 3% by mass or more relative to the amount of hydraulic powder added to the soil.

[0012] Hydraulic powder refers to powder that hardens through a hydration reaction, and examples include cement and gypsum. Preferably, the hydraulic powder is cement such as ordinary Portland cement, beelite cement, moderate-heat cement, rapid-hardening cement, ultra-rapid-hardening cement, or sulfate-resistant cement. The cement may also be blast furnace slag cement, fly ash cement, silica fume cement, etc., which are made by adding powders having pozzolanic properties and / or latent hydraulic properties, such as blast furnace slag, fly ash, or silica fume, or stone powder (calcium carbonate powder), to the above-mentioned cements. Here, if the hydraulic powder includes powders selected from pozzolanic properties, latent hydraulic properties, and stone powder (calcium carbonate powder) in addition to powders that harden through a hydration reaction, such as cement, the amounts of these are also included in the amount of hydraulic powder in this invention. Furthermore, if a powder that hardens through a hydration reaction contains a high-strength admixture, the amount of the high-strength admixture is also included in the amount of the hydraulic powder. This also applies to mass percentages and mass ratios that are related to the mass of the hydraulic powder.

[0013] In the ground improvement method of the present invention, hydraulic powder can be added to the soil when the mass ratio of hydraulic powder to soil is, for example, preferably 0.01 or more, more preferably 0.02 or more, even more preferably 0.05 or more, even more preferably 0.1 or more, and preferably 0.6 or less, more preferably 0.5 or less, even more preferably 0.45 or less, and even more preferably 0.2 or less.

[0014] Examples of calcium silicate include calcium metasilicate and calcium orthosilicate. Calcium silicate may also be in hydrate form. In this invention, calcium silicate refers to a component added separately from the calcium silicate component contained in hydraulic powders, such as cement. Calcium silicate can be produced by reacting a silicate with a calcium salt. For example, a reaction product of sodium metasilicate and calcium chloride can be used as calcium metasilicate.

[0015] In the ground improvement method of the present invention, calcium silicate can be added to the soil in an amount equivalent to calcium metasilicate (CaSiO3) relative to the hydraulic powder, for example, preferably 0.1% by mass or more, more preferably 1% by mass or more, more preferably 3% by mass or more, even more preferably 4% by mass or more, even more preferably 5% by mass or more, and preferably 30% by mass or less, more preferably 20% by mass or less, even more preferably 10% by mass or less, and even more preferably 8% by mass or less.

[0016] In the ground improvement method of the present invention, tap water, groundwater, seawater, river water, lake water, etc., can be used as water.

[0017] In the ground improvement method of the present invention, water can be added to the soil in an amount relative to the hydraulic powder, for example, preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 55% by mass or more, even more preferably 60% by mass or more, and preferably 150% by mass or less, more preferably 120% by mass or less, even more preferably 100% by mass or less, and even more preferably 80% by mass or less.

[0018] In this invention, the hydraulic powder, calcium silicate, and water may be added to the soil separately, or they may be added simultaneously as a slurry or the like.

[0019] In this invention, the hydraulic powder, calcium silicate, and water may each be added to the soil in separate amounts. In this invention, the bitumen content in the soil when calcium silicate is first added may be 3% by mass or more relative to the amount of hydraulic powder added to the soil.

[0020] Bitumen is an organic substance contained in soil that is extracted by dissolving in organic solvents such as dichloromethane, benzene, and alcohol. While organic substances in soil extracted by alkaline solutions (e.g., 1 mol / L sodium hydroxide aqueous solution) are sometimes defined as humus, in this invention, bitumen refers to organic substances in soil that are not extracted by alkaline solutions. Furthermore, while bitumen is sometimes defined as an asphalt component, in this invention, asphalt is not considered bitumen. Therefore, in this invention, bitumen can be defined as an organic substance contained in soil that is extracted by the organic solvent dichloromethane, is not extracted by the alkaline solution 1 mol / L sodium hydroxide aqueous solution, and is not asphalt. In this invention, bitumen can be either bitumen naturally present in the soil or bitumen prepared separately. In addition, the bitumen content in the soil can be adjusted by mixing separately prepared bitumen with the soil.

[0021] In this invention, the bitumen content in the soil can be measured, for example, by the following method. <Method for measuring the bitumen content in soil> A predetermined amount of soil and water are placed in a container of a predetermined capacity and stirred under alkaline conditions. Then, the soil and water mixture is removed from the container, the supernatant (alkaline-soluble components) is discarded by centrifugation or other means, and the residue is added to another container. An organic solvent such as dichloromethane is added to this and stirred. The mixture of residue and organic solvent is removed from the container, and the supernatant (organic solvent-soluble components) is recovered by centrifugation or other means. The organic solvent is removed from the recovered supernatant to recover bitumen. The amount of bitumen in the soil is calculated from the amount of bitumen recovered.

[0022] More specifically, the bitumen content in soil can be measured, for example, by the following method: Place 1 kg of soil in a 3 L airtight plastic container, add 1 L of 1 mol / L sodium hydroxide solution, seal the container, and stir for 1 hour at 100 rpm using a rotary stirrer (Ito Seisakusho Co., Ltd., BMU-100). Then, remove the soil and sodium hydroxide solution mixture from the container and centrifuge it using a centrifuge (Kokusan Co., Ltd., multi-tube centrifuge H-80) at 1000 rpm for 5 minutes, discard the supernatant, and add the residue to a new container (a 3 L airtight plastic container). Add 500 ml of dichloromethane to this mixture, seal the container, and stir for 1 hour using the same rotary stirrer under the same conditions as above. Remove the residue and dichloromethane mixture from the container and centrifuge it using the same centrifuge under the same conditions as above to collect the supernatant. Transfer the collected supernatant to a 1 L round-bottom flask and remove the dichloromethane using an evaporator to recover the bitumen. Calculate the amount of bitumen in the soil from the amount of bitumen recovered.

[0023] In the ground improvement method of the present invention, it is preferable to add a slurry containing hydraulic powder, calcium silicate, and water (hereinafter also referred to as the slurry of the present invention) to the soil. The specific method for preparing the slurry of the present invention may be similar to known methods for preparing hydraulic compositions such as cement milk.

[0024] The slurry of the present invention may have a water / hydraulic powder ratio of, for example, preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 60% by mass or more, and preferably 150% by mass or less, even more preferably 120% by mass or less, and even more preferably 100% by mass or less. This water / hydraulic powder ratio is the mass percentage (mass%) of water and hydraulic powder in the slurry, and is calculated as (mass of water / mass of hydraulic powder) × 100.

[0025] In the ground improvement method of the present invention, the slurry of the present invention is applied to 1 m of soil. 3It can be added, for example, preferably 150 kg or more, more preferably 200 kg or more, still more preferably 250 kg or more, still more preferably 300 kg or more, and preferably 800 kg or less, more preferably 500 kg or less, still more preferably 400 kg or less.

[0026] The specific method of adding the slurry of the present invention to the ground may conform to known ground improvement methods. Examples of the method of injecting and adding the slurry to the ground include, for example, the jet mixing method (single-phase flow method, two-phase flow method, three-phase flow method), the mechanical mixing method (CDM method, etc.), and further the diaphragm wall method (SMW method, TRD method, etc.).

[0027] The mixture of the slurry and soil of the present invention is cured according to known ground improvement methods.

[0028] In the present invention, in a system in which calcium silicate is dry-blended with hydraulic powder, it can also be used for shallow improvement using the powder mixing method of the DJM (Dry Jet Mixing) method or a stabilizer.

[0029] The ground improvement method of the present invention can be applied to a method for improving the foundation ground for constructing a building. Examples of the method to which the ground improvement method of the present invention can be applied include, for example, a ground improvement method in which a ground improvement column made of concrete or steel pipe is driven into the ground, and a ground improvement method in which a cement-based solidifying material such as cement milk is injected while excavating the ground, and a columnar ground improvement body formed by mixing the excavated soil and the cement milk is directly formed in the ground. The ground improvement method of the present invention can be applied to methods such as surface improvement methods, deep improvement methods, steel pipe pile methods, and shield methods. For example, in the deep improvement method, it can be applied to the high-pressure jet method, the TRD method, the SMW method, etc.

[0030] In the ground improvement method of the present invention, components such as retarders, hardening accelerators, air-entraining agents, expanding agents, foaming agents, thickeners, fluidizing agents, foaming agents, waterproofing agents, and defoaming agents can be added to the soil. These optional components may also be blended into the slurry of the present invention. Examples of optional components include polymer compounds with a weight-average molecular weight of 1000 or more having a main chain and side chains, wherein the main chain contains monomers selected from acrylic acid, methacrylic acid, maleic acid, and fumaric acid as constituent monomers, and the side chains contain ether functional groups and / or acid functional groups. Aggregates can also be blended into the slurry of the present invention. Examples of aggregates include fine aggregates and coarse aggregates. Examples of fine aggregates include those specified in number 2311 of JIS A0203-2014. Examples of fine aggregates include river sand, land sand, mountain sand, sea sand, and stones.

[0031] The present invention provides a method for reducing the heat of hydration when improving the ground by adding hydraulic powder to the soil, Add hydraulic powder, calcium silicate, and water to the soil. At a minimum, the bitumen content in the soil when calcium silicate is added is 3% by mass or more relative to the amount of hydraulic powder added to the soil. A method for reducing the heat of hydration is provided. The matters described in the ground improvement method of the present invention can be appropriately applied to the method for reducing the heat of hydration of the present invention. In the method for reducing the heat of hydration of the present invention, the bitumen content in the soil when calcium silicate is added can be adjusted to be 3% by mass or more relative to the amount of hydraulic powder added to the soil. One method for adjusting the bitumen content is to mix separately prepared bitumen into the soil.

[0032] The present invention provides a method for using a composition comprising hydraulic powder, calcium silicate, and water in soil, wherein the bitumen content in the soil when at least calcium silicate is added is 3% by mass or more relative to the amount of hydraulic powder. The matters described in the ground improvement method of the present invention can be appropriately applied to the use of the present invention.

[0033] Examples <Ingredients used> The following examples, reference examples, and comparative examples were carried out using the following components. • Test soil: Peat from Hokkaido, bitumen content 0.1% by mass (measurement method as described above) • Cement: Ordinary Portland cement manufactured by Taiheiyo Cement Corporation • Calcium silicate: Calcium metasilicate manufactured by the following method. <Method for producing calcium metasilicate> Calcium metasilicate (CaSiO3) was produced by reacting sodium metasilicate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and calcium chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) in water. The amounts of sodium metasilicate and calcium chloride used were determined based on the theoretical amounts assuming complete reaction and the formation of calcium metasilicate. • Bitumen: Bitumen extracted using the following method <Method for extracting bitumen> 1 kg of the test soil was added to a 3 L resealable plastic container, and 1 L of 1 mol / L sodium hydroxide aqueous solution was added to it. The container was sealed and stirred for 1 hour using a rotary stirrer. Then, the mixture of test soil and sodium hydroxide aqueous solution was removed from the container and centrifuged (1000 rpm, 5 minutes) using a centrifuge (Kokusan Co., Ltd., multi-tube centrifuge H-80). The supernatant was discarded, and the residue was added to a new container (a 3 L resealable plastic container). 500 ml of dichloromethane was added to this mixture, the container was sealed, and stirred for 1 hour using the same rotary stirrer as before. The mixture of residue and dichloromethane was removed from the container, and the supernatant was recovered by centrifugation. The recovered supernatant was transferred to a 1 L round-bottom flask, and the dichloromethane was removed by distillation using an evaporator to recover bitumen.

[0034] [Examples 1-3] A sample was prepared by adding 12 g of tap water, 1 g of calcium silicate (5% by mass relative to the cement), and 1 g of bitumen (5% by mass relative to the cement), 1.2 g (6% by mass relative to the cement), or 0.6 g (3% by mass relative to the cement) to 20 g of ordinary Portland cement, which is a hydraulic powder, and stirring with a glass rod for 1 minute. 20 g of the prepared sample was taken into a 30 ml plastic container and measured using a calorimeter (TAM AIR: TA instruments). The amount of water was 60% by mass relative to the hydraulic powder. The cumulative heat generation (J / g) 24 hours after contact with water is shown as the heat generation of hydration. A lower heat generation of hydration indicates a higher crack reduction effect.

[0035] [Reference example 1] The heat of hydration was measured in the same manner as in Examples 1 to 3, except that the composition of the sample was 20 g of ordinary Portland cement, 12 g of tap water, and 0.02 g of bitumen (0.1% by mass relative to the cement).

[0036] [Comparative Example 1] The heat of hydration was measured in the same manner as in Examples 1 to 3, except that the composition of the sample consisted of 20 g of ordinary Portland cement, 12 g of tap water, 1 g of calcium silicate (5% by mass relative to the cement), and 0.02 g of bitumen (0.1% by mass relative to the cement).

[0037] [Table 1]

[0038] In Reference Example 1, although the heat of hydration is low, when applied to soil, the strength of the hardened mixture (ground improvement body) becomes significantly lower, resulting in inferior ground improvement. In Comparative Example 1, the hardening of the mixture is accelerated by the use of calcium silicate, but because calcium silicate is added under conditions where the amount of bitumen is small, thermal cracking is likely to occur due to large hydration heat, and the strength of the hardened body tends to be inferior. On the other hand, in Examples 1 to 3, the strength of the hardened body of the mixture can be improved without thermal cracking by accelerating hardening with the use of calcium silicate while allowing for moderate hydration heat. Although only bitumen was used in Examples 1-3 and Comparative Example 1, and no soil was used, the difference in the heat of hydration between Examples 1-3 and Comparative Example 1 shows the same trend even when soil containing bitumen is used in the test. In Examples 1-3, bitumen extracted from soil with a bitumen content of 0.1% by mass was used. The hydraulic powder / soil mass ratios in Examples 1-3, when simply converted assuming the soil was used before bitumen extraction, are 0.020, 0.017, and 0.033, respectively. Furthermore, in Examples 1 to 3, ordinary Portland cement was mixed with tap water, calcium silicate, and bitumen. However, it is preferable to prepare a slurry containing hydraulic powder, calcium silicate, and water, and add this slurry to bitumen (or soil containing bitumen) from the viewpoint of improving workability in ground improvement.

Claims

1. A method for improving ground, comprising adding hydraulic powder, calcium silicate, and water to soil, wherein the bitumen content in the soil when at least calcium silicate is added is 4% by mass or more and 30% by mass or less relative to the amount of hydraulic powder added to the soil.

2. A method for improving ground according to claim 1, wherein hydraulic powder, calcium silicate, and water are added under the condition that the bitumen content in the soil is 4% by mass or more relative to the amount of hydraulic powder added to the soil.

3. A method for improving ground according to claim 1 or 2, wherein hydraulic powder is added in a mass ratio of hydraulic powder to soil of 0.01 or more and 0.6 or less.

4. Calcium silicate is used in relation to hydraulic powders, and calcium metasilicate (CaSiO2) is used in relation to the hydraulic powder. ３ A method for improving the ground according to any one of claims 1 to 3, wherein the substance is added in an amount of 0.1% by mass or more and 30% by mass or less, on a conversion basis.

5. A method for improving ground according to any one of claims 1 to 4, comprising adding a slurry containing hydraulic powder, calcium silicate, and water to the soil.

6. A method for improving ground according to any one of claims 1 to 5, wherein water is added to the hydraulic powder in an amount of 40% by mass or more and 100% by mass or less.

7. A method for improving ground according to any one of claims 1 to 6, wherein the hydraulic powder is cement.

8. A method for improving ground according to any one of claims 1 to 7, wherein calcium silicate is a reaction product of sodium metasilicate and calcium chloride.

9. A method for improving ground according to any one of claims 1 to 8, wherein the bitumen content in the soil is adjusted by mixing separately prepared bitumen into the soil.

10. A method for improving the foundation ground for constructing a building, as described in any one of claims 1 to 9.

11. A method for improving ground according to any one of claims 1 to 10, wherein bitumen is defined as organic matter contained in the soil that is not extracted with an alkaline solution, a 1 mol / L aqueous sodium hydroxide solution, is extracted with an organic solvent, dichloromethane, and is not asphalt.

12. A method for reducing the heat of hydration when improving the ground by adding hydraulic powder to soil, Add hydraulic powder, calcium silicate, and water to the soil. At a minimum, the bitumen content in the soil when calcium silicate is added is 4% by mass or more and 30% by mass or less relative to the amount of hydraulic powder added to the soil. Methods for reducing the heat of hydration.

13. Use of a composition comprising hydraulic powder, calcium silicate, and water in soil, wherein the bitumen content in the soil when at least calcium silicate is added is 4% by mass or more and 30% by mass or less relative to the amount of hydraulic powder.

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