Site improvement methods

Abstract

To provide a ground improvement method that can easily select a cement-based solidification material to be supplied to unimproved soil containing peat and can obtain solidified improved soil with excellent strength. [Solution] A ground improvement method comprising the steps of: collecting a sample of unimproved soil; measuring the wet density and water content of the unimproved soil; mixing the dried sample with an alkaline aqueous solution to obtain a mixture and then measuring the COD of the mixture; preparing one or more candidate cement-based solidification materials; selecting the cement-based solidification material to be supplied to the unimproved soil using the wet density, water content, COD, and content ratio of the one or more candidate cement-based solidification materials, expressed as (SO3 content of cement-based solidification material + Al2O3 content of cement-based solidification material) / CaO content of the cement-based solidification material, and a predetermined judgment formula; and supplying and mixing the selected cement-based solidification material to the unimproved soil to obtain solidified and improved soil.

Description

[Technical Field]

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

[0002] Conventionally, various soil improvement materials have been proposed for use in ground improvement. Patent Document 1 describes a solidification material for highly organic soil or humus soil that contains cement, ground granulated blast furnace slag, and anhydrous gypsum as a solidification material that can solidify highly organic soil with a high organic acid content and water content, characterized in that the total amount of the ground granulated blast furnace slag and anhydrous gypsum relative to the total amount of the cement, ground granulated blast furnace slag, and anhydrous gypsum is 15 to 40 mass%, and the ground granulated blast furnace slag is 10 mass% or more relative to the total amount of the cement, ground granulated blast furnace slag, and anhydrous gypsum. Furthermore, Patent Document 2 describes a method for easily selecting a cement-based solidification material to be supplied to peat containing humic substances. This method of ground improvement involves supplying a cement-based solidification material to unimproved soil containing peat and mixing the material to obtain solidified and improved soil. The method includes a sampling step of collecting a sample of the unimproved soil from the unimproved soil, a moisture content measuring step of measuring the moisture content of the unimproved soil using the sample, a COD measuring step of drying the sample, mixing the dried sample with an alkaline aqueous solution to obtain a mixture, and then measuring the COD (chemical oxygen demand) of the mixture. The method for improving ground is characterized by including a cementitious solidification material preparation step of preparing one or more types of cementitious solidification material; a selection step of selecting a cementitious solidification material to be supplied to the unimproved soil using the water content, the COD, and a content ratio of the one or more candidate cementitious solidification materials expressed as (SO3 content of cementitious solidification material + Al2O3 content of cementitious solidification material) / CaO content of cementitious solidification material, as well as a predetermined judgment formula; and a solidification treatment step of supplying the cementitious solidification material selected in the selection step to the unimproved soil, mixing them, and obtaining the solidified and improved soil. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-193515 [Patent Document 2] Japanese Patent Application Publication No. 2024-123933 Summary of the Invention [Problem to be solved by the invention]

[0004] When improving (solidifying) soil (ground) using a cement-based solidification material, if the soil contains organic humic substances, the solidification of the soil by the cement-based solidification material can be hindered. Among the components of humic substances, humic acid, which is soluble in alkali, particularly inhibits soil solidification. Therefore, when improving soil containing a large amount of humic acid, it is preferable to use a cement-based solidification material with superior hydration reactivity. However, measuring the amount of humic acid in soil requires complex procedures, reagents, equipment, etc. In addition, loss on ignition is an indicator used to evaluate the amount of organic matter contained in soil, but since the amount of organic matter evaluated by loss on ignition includes the amount of organic matter other than humic acid, it is difficult to use loss on ignition to accurately evaluate the degree to which cement-based solidification materials inhibit soil solidification. The object of the present invention is to provide a ground improvement method that can easily select a cement-based solidification material to be supplied to unimproved soil according to the unimproved soil to be solidified, so as to obtain solidified and improved soil with excellent strength, and that can obtain solidified and improved soil with excellent strength. [Means for solving the problem]

[0005] As a result of extensive research into solving the above-mentioned problems, the inventors have found that the above-mentioned objects can be achieved by a ground improvement method comprising the steps of: collecting a sample from unimproved soil; measuring the wet density and water content of the unimproved soil; mixing the sample with an alkaline aqueous solution to obtain a mixture and then measuring the COD of the mixture; preparing one or more candidate cement-based solidification materials; selecting a cement-based solidification material using the wet density, water content, COD, and the ratio of the total SO3 and Al2O3 contents of the cement-based solidification material to the CaO content, as well as a predetermined judgment formula; and supplying the selected cement-based solidification material to the unimproved soil and mixing them to obtain solidified and improved soil, and have completed the present invention. That is, the present invention provides the following [1] to [6]. [1] A ground improvement method for supplying and mixing a cement-based solidification material to unimproved soil containing peat and obtaining solidified and improved soil, comprising the steps of: a sampling step for collecting a sample of the unimproved soil from the unimproved soil; an unimproved soil measurement step for measuring the wet density and water content of the unimproved soil using the sample; a COD measurement step for drying the sample, mixing the dried sample with an alkaline aqueous solution to obtain a mixture, and then measuring the COD (chemical oxygen demand) of the mixture; a cement-based solidification material preparation step for preparing one or more candidates for the cement-based solidification material; a selection step for selecting the cement-based solidification material to be supplied to the unimproved soil using the wet density, water content, COD, and content ratio of the one or more candidate cement-based solidification materials expressed by the following formula (1), as well as a predetermined judgment formula; and a solidification treatment step for supplying and mixing the cement-based solidification material selected in the selection step to the unimproved soil to obtain the solidified and improved soil. (SO3 content of cement-based solidification material + Al2O3 content of cement-based solidification material) / CaO content of cement-based solidification material (1)

[0006] [2] The ground improvement method described in [1] above, wherein in the COD measurement step, the drying is carried out by leaving the sample to stand at 30 to 60°C for 10 hours or more, and the mixing is carried out by mixing the dried sample with 0.2 to 0.8 mol / L aqueous sodium hydroxide solution in an amount such that the mass ratio of the sample to the aqueous sodium hydroxide solution (sample / aqueous sodium hydroxide solution) is 0.005 to 0.10, and then leaving to stand at 10 to 30°C for 30 minutes or more. [3] The ground improvement method according to [1] or [2], wherein the cement-based solidification material contains Portland cement, ground granulated blast furnace slag, and gypsum powder. [4] A ground improvement method according to any one of [1] to [3], wherein in the selection step, the judgment formula is the following formula (2), and a cementitious solidification material for which the wet density, the water content, the COD, and the content ratio of the one or more candidate cementitious solidification materials expressed by the above formula (1), as well as a first value calculated using the following formula (2), are greater than 0, is selected as the cementitious solidification material to be supplied to the unimproved soil, and a cementitious solidification material for which the first value is 0 or less is not selected as the cementitious solidification material to be supplied to the unimproved soil. AXa-BXb-Clog 10 Xc+DXd (2) (In the above formula (2), Xa is the wet density (kg / m 3 ), Xb is the water content (%), Xc is the COD (mg / liter), Xd is the content ratio, A is a number between 8 and 22, B is a number between 0.07 and 0.14, C is a number between 9.3 and 17.0, and D is a number between 1.75 and 2.75.)

[0007] [5] A ground improvement method according to any one of [1] to [3], wherein in the selection step, the judgment formula is the following formula (3), and a cementitious solidification material for which the wet density, the water content, the COD, the content ratio of the one or more candidate cementitious solidification materials expressed by the above formula (1), the amount of the one or more candidate cementitious solidification materials to be added, and a second value calculated using the following formula (3) are greater than 0 is selected as the cementitious solidification material to be supplied to the unimproved soil, and a cementitious solidification material for which the second value is 0 or less is not selected as the cementitious solidification material to be supplied to the unimproved soil. αXa-βXb-γlog 10 Xc+δXd+εXe (3) (In the above formula (3), Xa is the wet density (kg / m 3 ), Xb is the water content (%), Xc is the COD (mg / liter), Xd is the content ratio, and Xe is the amount added (kg / m 3 ) where α is a number between 22 and 28, β is a number between 0.14 and 0.16, γ is a number between 12.0 and 13.8, δ is a number between 1.9 and 2.2, and ε is a number between 0.009 and 0.025.

[0008] [6] The ground improvement method according to any one of [1] to [3], wherein in the selection step, the judgment formulas are the following formulas (2) and (3), and a cementitious solidification material for which the wet density, the water content, the COD, and the content ratio of the one or more candidate cementitious solidification materials expressed by the formula (1), and a first value calculated using the following formula (2), and the wet density, the water content, the COD, the content ratio of the one or more candidate cementitious solidification materials expressed by the formula (1), and the amount of the one or more candidate cementitious solidification materials to be added, and a second value calculated using the following formula (3) are all greater than 0 are selected as the cementitious solidification material to be supplied to the unimproved soil, and a cementitious solidification material for which at least either the first value or the second value is 0 or less is not selected as the cementitious solidification material to be supplied to the unimproved soil. AXa-BXb-Clog 10 Xc+DXd (2) (In the above formula (2), Xa is the wet density (kg / m 3 ), Xb is the water content (%), Xc is the COD (mg / liter), Xd is the content ratio, A is a number between 8 and 22, B is a number between 0.07 and 0.14, C is a number between 9.3 and 17.0, and D is a number between 1.75 and 2.75.) αXa-βXb-γlog 10 Xc+δXd+εXe (3) (In the above formula (3), Xa is the wet density (kg / m 3 ), Xb is the water content (%), Xc is the COD (mg / liter), Xd is the content ratio, and Xe is the amount added (kg / m 3 ) where α is a number between 22 and 28, β is a number between 0.14 and 0.16, γ is a number between 12.0 and 13.8, δ is a number between 1.9 and 2.2, and ε is a number between 0.009 and 0.025. [Effects of the Invention]

[0009] According to the ground improvement method of the present invention, the cement-based solidification material to be supplied to unimproved soil can be selected according to the unimproved soil to be solidified, so that solidified and improved soil with excellent strength can be obtained, and solidified and improved soil with excellent strength can be obtained. Furthermore, the ground improvement method of the present invention does not require measuring the amount of humic acid contained in unimproved soil, nor does it require actual strength testing, making it easy to select a cement-based solidification material. DETAILED DESCRIPTION OF THE INVENTION

[0010] The ground improvement method of the present invention is a method of supplying a cement-based solidification material to unimproved soil containing peat (hereinafter simply referred to as "unimproved soil") and mixing the mixture to obtain solidified and improved soil, and includes a sampling step of collecting unimproved soil samples from the unimproved soil, an unimproved soil measurement step of measuring the wet density and water content of the unimproved soil using the samples, and a COD measurement step of drying the samples, mixing the dried samples with an alkaline aqueous solution to obtain a mixture, and then measuring the COD (chemical oxygen demand) of the mixture. The method includes a cementitious solidification material preparation process in which one or more cementitious solidification material candidates are prepared, a selection process in which the cementitious solidification material to be supplied to the unimproved soil is selected using the wet density, water content, COD, and content ratio (also called "SAC content ratio") of the one or more candidate cementitious solidification materials expressed by the following formula (1), as well as a predetermined judgment formula, and a solidification treatment process in which the cementitious solidification material selected in the selection process is supplied to the unimproved soil and mixed to obtain solidified improved soil. (SO3 content of cement-based solidification material + Al2O3 content of cement-based solidification material) / CaO content of cement-based solidification material (1) Each step will be explained in detail below.

[0011] [Sample collection process] This step involves collecting a sample of unimproved soil containing peat (peat soil that has not been subjected to solidification treatment). Unimproved soil containing peat is unimproved soil that is the target of solidification treatment (improvement treatment) in the present invention. Examples of peat contained in unimproved soil include tropical peat, woody peat, etc. Among them, tropical peat is suitable for the ground improvement method of the present invention because it is difficult to select an appropriate cement-based solidification material for it using conventional methods due to its high organic matter content. Tropical peat is the peat found in tropical peat soils (tropical peat bogs) found in the tropics, and is formed when the remains of dead trees and other plants accumulate as clumps of organic matter without decomposing. Peat usually contains organic matter (e.g., humus). Here, "humus" refers to the final product formed when the remains of plants and animals in the soil are decomposed by microorganisms, and contains a variety of organic compounds. The components that make up humic substances include humin (a component that is insoluble in alkali and acid), humic acid (a component that is soluble in alkali and acid), and fulvic acid (a component that is soluble in alkali and acid).

[0012] [Unimproved soil measurement process] This step is a step of measuring the wet density and water content of the unimproved soil using the sample collected in the sampling step. The wet density of the unimproved soil is not particularly limited, but is preferably 1.50 kg / m 3 or less, more preferably 0.50 to 1.45 kg / m 3 , and particularly preferably 0.80 to 1.40 kg / m 3 is. Generally, the lower the wet density of unimproved soil, the more organic matter it contains. 3 If the wet density is less than 1.50 kg / m, the strength development of the cement-based solidification material supplied and mixed with the unimproved soil is likely to be reduced, and it may be difficult to obtain solidified improved soil with sufficient strength. However, according to the method of the present invention, if the wet density is 1.50 kg / m, 3 Even for unimproved soil such as that described below, it is possible to easily select a cement-based solidification material that can produce solidified and improved soil with excellent strength, thereby obtaining solidified and improved soil with sufficient strength.

[0013] The moisture content of unimproved soil is not particularly limited, but is preferably 100% or more, more preferably 110 to 1,000%, even more preferably 120 to 700%, still more preferably 150 to 500%, and particularly preferably 200 to 400%. Generally, when the water content of unimproved soil is 100% or more, the strength development of the cement-based solidification material added and mixed with the unimproved soil is reduced, making it difficult to obtain solidified and improved soil with sufficient strength. However, according to the method of the present invention, even if the water content of unimproved soil is 100% or more, it is possible to easily select a cement-based solidification material that can produce solidified and improved soil with excellent strength, and to obtain solidified and improved soil with sufficient strength. The "moisture content" (unit: %) refers to the percentage of the mass of water contained in unimproved soil relative to the mass of solids contained in the unimproved soil ((water / solid) x 100%).

[0014] [COD measurement process] This step involves drying the sample collected in the sampling step, mixing the dried sample with an alkaline aqueous solution to obtain a mixture (suspension), and then measuring the COD (Chemical Oxygen Demand) of the mixture. Drying is performed, for example, by leaving the sample at 30 to 60°C (preferably 35 to 50°C, more preferably 40 to 50°C) for 10 hours or more (preferably 12 to 24 hours, more preferably 15 to 20 hours). By leaving the sample at 30°C or higher, the moisture contained in the sample can be sufficiently removed in a shorter time, allowing for more accurate measurement of the COD of the mixture. Furthermore, by leaving the sample at 60°C or lower, it is possible to more effectively prevent the organic matter contained in the sample from being altered by high temperatures, allowing for more accurate measurement of the COD of the mixture. Furthermore, from the viewpoint of measuring the COD of the mixture more accurately, the drying is preferably carried out until the moisture content of the sample after drying is 25% or less (preferably 20% or less).

[0015] The alkaline aqueous solution is not particularly limited, and examples thereof include an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, an aqueous calcium hydroxide solution, an aqueous sodium carbonate solution, etc. Among these, an aqueous sodium hydroxide solution is preferred from the viewpoint of ease of availability. The pH of the alkaline aqueous solution is preferably 12 or higher, more preferably 12.5 to 13.5. If the pH is 12 or higher, the COD of the mixture can be measured more accurately. The mixing is carried out, for example, by mixing the dried sample with 0.2 to 0.8 mol / L (preferably 0.3 to 0.7 mol / L, more preferably 0.4 to 0.6 mol / L) of an aqueous alkaline solution (e.g., sodium hydroxide) in amounts such that the mass ratio of the sample to the aqueous alkaline solution (sample / aqueous alkaline solution) is 0.005 to 0.10 (preferably 0.008 to 0.05, more preferably 0.010 to 0.03), and then allowing the mixture to stand at 10 to 30°C (preferably 12 to 28°C, more preferably 15 to 25°C) for 30 minutes or more (preferably 45 minutes to 5 hours, more preferably 1 to 2 hours). By carrying out the mixing under such conditions, the COD of the mixture can be measured more accurately. The above-mentioned standing still also includes the case where mixing (stirring) is continued using a stirrer or the like.

[0016] Before measuring the COD of the mixture, the mixture may be appropriately filtered to remove impurities, and the mixture may be appropriately diluted depending on the measurement method. The COD can be measured using, for example, a commercially available COD measuring device that meets the standards set forth in "JIS K 0806-1997 (Chemical Oxygen Demand (COD) Automatic Measuring Device)." The unimproved soil measurement step and the COD measurement step may be carried out between the sample collection step and the selection step, and the order of these steps is not particularly limited.

[0017] [Cement-based solidification material preparation process] This step is a step of preparing one or more candidates for the cement-based solidification material to be supplied to the unimproved soil in the solidification treatment step (described later). In this specification, the cement-based solidification material refers to a powdery material that contains cement and also contains an admixture (cement admixture) that can be arbitrarily blended. Examples of cements used in cement-based solidification materials include various types of Portland cement such as ordinary Portland cement, high-early-strength Portland cement, moderate-heat Portland cement, low-heat Portland cement, and sulfate-resistant Portland cement; blended cements such as blast-furnace cement, fly ash cement, and silica cement; ecocement; white cement; and ultra-rapid-hardening cement. Among these, various types of Portland cement are preferred from the viewpoints of availability and strength development, and ordinary Portland cement is more preferred. The cement content in the cement-based solidification material is preferably 20 to 90% by mass, more preferably 25 to 70% by mass. If the content is 20% by mass or more, the strength (e.g., uniaxial compressive strength) of the solidified improved soil can be increased. Furthermore, if the content is 90% by mass or less, material costs can be reduced and the amount of waste-derived raw materials used can be increased.

[0018] Furthermore, from the viewpoint of further improving the workability when supplying the cement-based solidification material in the solidification treatment step, a cement-based solidification material containing gypsum powder as an admixture is preferred. The proportion of gypsum powder in the cement-based solidification material is preferably 1 to 35 mass %, more preferably 5 to 30 mass %, calculated as SO3. The above ratio of gypsum powder does not include the gypsum powder contained in the cement. Examples of gypsum used in the gypsum powder include anhydrous gypsum, hemihydrate gypsum, dihydrate gypsum, etc. These may be used alone or in combination of two or more.

[0019] The cement-based solidification material may contain ground granulated blast furnace slag as an admixture from the viewpoint of increasing the strength (e.g., unconfined compressive strength) of the solidified improved soil, reducing material costs, and promoting the use of ground granulated blast furnace slag. The proportion of ground granulated blast furnace slag in 100% by mass of the cement-based solidification material is preferably 70% by mass or less, and more preferably 10 to 65% by mass. If the proportion is 70% by mass or less, the amount of cement is relatively large, and the strength (e.g., unconfined compressive strength) of the solidified improved soil can be increased. In addition, when the cement contained in the cement-based solidification material is blast furnace cement, the ground granulated blast furnace slag contained in the blast furnace cement is not included in the above ratio.

[0020] Examples of admixtures other than gypsum and ground granulated blast furnace slag include quicklime, slaked lime, fly ash, ground limestone, silica fume, etc. These may be used alone or in combination of two or more. The proportion of admixtures other than gypsum and ground granulated blast furnace slag in the cement-based solidification material (the total of all admixtures if two or more types of admixtures are included) is preferably 20 mass% or less, more preferably 0.1 to 10 mass%, and particularly preferably 1 to 5 mass%, from the viewpoint that the proportion of cement is relatively high and the strength of the solidified improved soil can be increased.

[0021] The Blaine specific surface area of ​​the cement-based solidification material is preferably 2,000 to 8,000 cm 2 / g, more preferably 2,500 to 7,000 cm 2 / g, and particularly preferably 3,000 to 6,000 cm 2 / g. The specific surface area of ​​the above Blaine is 2,000 cm 2 / g or more, the strength development of the cement-based solidification material is improved. 2 Cementitious solidification materials with a density of 0.1g or less are more readily available. The type of cement-based solidification material to be prepared is one or more, preferably 2 to 10 types, and more preferably 3 to 5 types. By preparing multiple types of cement-based solidification materials with different blend ratios, Blaine specific surface areas, etc., it is possible to more appropriately select the cement-based solidification material to be supplied to unimproved soil. The cement-based solidification material preparation step may be performed before the selection step, and the order is not particularly limited.

[0022] [Selection process] This process is a process of selecting the cement-based solidification material to be supplied to the unimproved soil using the wet density and water content of the unimproved soil measured in the unimproved soil measurement process, the COD of the mixture measured in the COD measurement process, and the content ratio expressed by the following formula (1) of one or more candidate cement-based solidification materials prepared in the cement-based solidification material preparation process, as well as a predetermined judgment formula. (SO3 content of cement-based solidification material + Al2O3 content of cement-based solidification material) / CaO content of cement-based solidification material (1) In this process, for each of one or more cement-based solidification materials that are candidates prepared in the cement-based solidification material preparation process, the content ratio value expressed by the above formula (1) (if formula (3) is used as the judgment formula, the amount of cement-based solidification material to be added) is calculated, and by using the obtained value, the wet density and water content values, the COD value, and a predetermined judgment formula, it is possible to select (determine) for each of one or more cement-based solidification materials whether it is a cement-based solidification material that should be supplied to unimproved soil. Examples of a method for selecting a cement-based solidification material to be supplied to unimproved soil using a predetermined judgment formula include the following method.

[0023] [Method for selecting cement-based solidification materials using Equation (2) as a judgment formula] In the selection process, a cement-based solidification material whose wet density and water content, COD, and content ratio of the one or more candidate cement-based solidification materials expressed by the formula (1) and the value calculated using the following formula (2) are greater than 0 is selected as the cement-based solidification material to be supplied to unimproved soil, and a cement-based solidification material whose value is 0 or less is not selected as the cement-based solidification material to be supplied to unimproved soil. AXa-BXb-Clog 10 Xc+DXd (2) (In the above formula (2), Xa is the wet density (kg / m 3 ), Xb is the water content (%), Xc is the COD (mg / liter), Xd is the content ratio of the one or more candidate cement-based solidification materials expressed by the above formula (1), A is a number from 8 to 22 (preferably 10 to 20, more preferably 12 to 16, and particularly preferably 14), B is a number from 0.07 to 0.14 (preferably 0.08 to 0.12, more preferably 0.09 to 0.11, and particularly preferably 0.10), C is a number from 9.3 to 17.0 (preferably 10.0 to 15.0, more preferably 12.0 to 14.0, and particularly preferably 13.0), and D is a number from 1.75 to 2.75 (preferably 1.90 to 2.50, more preferably 2.00 to 2.40, and particularly preferably 2.25).

[0024] [Method for selecting cement-based solidification materials using Equation (3) as a judgment formula] In addition, in order to take into account the numerical values ​​of the added amounts of candidate cement-based solidification materials and to easily select the cement-based solidification material to be supplied to unimproved soil with higher accuracy, the following formula (3) may be used as a judgment formula. The amount of cement-based solidification material added is the amount of the selected cement-based solidification material that is planned to be supplied to the unimproved soil in the solidification treatment step (described later). Specifically, in the selection process, the method selects cementitious solidification materials for which the values ​​of the wet density and water content, the COD value, the content ratio values ​​of the one or more candidate cementitious solidification materials expressed by the above formula (1), the amounts of the one or more candidate cementitious solidification materials to be added, and the value calculated using the following formula (3) are greater than 0 as cementitious solidification materials to be supplied to unimproved soil, and does not select cementitious solidification materials for which the values ​​are 0 or less as cementitious solidification materials to be supplied to unimproved soil. αXa-βXb-γlog 10 Xc+δXd+εXe (3) (In the above formula (3), Xa is the wet density (kg / m 3 ), Xb is the water content (%), Xc is the COD (mg / liter), Xd is the content ratio of one or more candidate cementitious solidification materials expressed by the formula (1), and Xe is the amount of one or more candidate cementitious solidification materials added (kg / m 3 ), α is a number from 22 to 28 (preferably 23 to 27, more preferably 24 to 26, and particularly preferably 25), β is a number from 0.14 to 0.16 (preferably a number of 0.16), γ is a number from 12.0 to 13.8 (preferably 12.5 to 13.5, more preferably 12.8 to 13.2, and particularly preferably 13.0), δ is a number from 1.90 to 2.20 (preferably 1.92 to 2.00, and more preferably 1.95), and ε is a number from 0.009 to 0.025 (preferably 0.010 to 0.020, more preferably 0.012 to 0.018, and particularly preferably 0.015). It should be noted that A to D and α to ε are numbers arbitrarily determined from specific numerical ranges.

[0025] [Method for selecting cement-based solidification materials using formulas (2) and (3) as judgment formulas] From the viewpoint of selecting a cement-based solidification material with higher accuracy, the cement-based solidification material may be selected using the above-mentioned formulas (2) and (3). Specifically, in the selection step, a cement-based solidification material for which the wet density, the water content, the COD, and the content ratio of the one or more candidate cement-based solidification materials expressed by the formula (1), and a first value calculated using the formula (2), and the wet density, the water content, the COD, the content ratio of the one or more candidate cement-based solidification materials expressed by the formula (1), and the amount of the one or more candidate cement-based solidification materials to be added, and a second value calculated using the formula (3) are all greater than 0 are selected as the cement-based solidification material to be supplied to the unimproved soil, and a cement-based solidification material for which at least one of the first value and the second value is 0 or less is not selected as the cement-based solidification material to be supplied to the unimproved soil.

[0026] If two or more types of cementitious solidification materials are prepared in the cementitious solidification material preparation step, a numerical value is calculated for each cementitious solidification material using at least one of the criteria (2) and (3), and the cementitious solidification material for which a numerical value greater than 0 is obtained is selected as the cementitious solidification material to be supplied to the unimproved soil. If there are multiple cementitious solidification materials for which a numerical value greater than 0 is obtained, any cementitious solidification material may be selected, but from the viewpoint of strength development, etc., it is preferable to select the cementitious solidification material for which the largest numerical value is obtained. If there is no cement-based solidification material for which a value greater than 0 is obtained, the process may return to the cement-based solidification material preparation step, prepare a new type of cement-based solidification material, and perform the selection step again.Furthermore, the value of the amount of cement-based solidification agent added in formula (3) may be changed, and then formula (3) may be used again for selection.

[0027] [Solidification process] This step involves supplying the cement-based solidification material selected in the selection step to unimproved soil and mixing it to obtain solidified and improved soil. The cement-based solidification material may be added and mixed in the form of a powder (dry addition method), or may be added and mixed in the form of a slurry (wet addition method). When using a cement-based solidification material in the form of a slurry, the water-to-powder ratio (the mass ratio (water / powder) of water to powder (cement-based solidification material) expressed as a percentage) is preferably 50 to 200%, more preferably 60 to 150%, and particularly preferably 70 to 120%, from the standpoint of increasing the strength of the solidified improved soil and making it easier to mix with unimproved soil. 1m of unimproved soil 3 The amount of cement-based solidification material supplied to the soil varies depending on the properties of the unimproved soil, the construction conditions, and the strength required for the solidified and improved soil obtained after treatment, but it is recommended to use a standard amount of cement-based solidification material per 1 m of unimproved soil. 3 The load is preferably 100 kg or more, more preferably 200 to 600 kg, and particularly preferably 250 to 550 kg. If the amount of supply is 100 kg or more, the strength of the solidified improved soil can be increased. If the amount of supply is 600 kg or less, an excessive increase in costs can be prevented. According to the ground improvement method of the present invention, even for unimproved soil containing peat, it is possible to select an appropriate cement-based solidification material in a simple manner without measuring the type and amount of organic matter (especially humic acid), and obtain solidified and improved soil with sufficient strength. [Example]

[0028] [Materials used] (1) Unimproved soils A to C (tropical peat soils A to C) (2) Cement-based solidification material A: Contains 20 to 90% by mass of Portland cement, 5 to 50% by mass of ground granulated blast furnace slag, and 5 to 30% by mass of gypsum powder. (3) Cement-based solidification material B: Contains 20 to 90% by mass of Portland cement, 5 to 50% by mass of ground granulated blast furnace slag, and 5 to 30% by mass of gypsum powder. (4) Cement-based solidification material C: containing 20 to 90% by mass of Portland cement, 5 to 50% by mass of ground granulated blast furnace slag, and 5 to 30% by mass of gypsum powder. For cement-based solidification materials A to C, the SO3 content (mass%), Al2O3 content (mass%), and CaO content (mass%) were measured in accordance with "JIS R 5204:2019 (Method for X-ray fluorescence analysis of cement)", and the content ratios obtained from these values ​​and expressed by the above formula (1) are shown in Table 1.

[0029] [Measurement of wet density and moisture content of unimproved soils A to C] The wet densities of unimproved soils A to C were measured in accordance with JIS A 1225:2020 (Testing method for wet density of soil). The moisture content of unimproved soils A to C was measured in accordance with JIS A 1203:2020 (Testing method for moisture content of soil). [COD measurement] For each of the unimproved soils A to C, a mixture was prepared according to the following procedure, and the COD of the mixture was measured. The unimproved soil was left to dry for 18 hours at 45°C to obtain a dried sample with a water content of 20% or less. The dried sample was mixed with 0.5 mol / L aqueous sodium hydroxide solution (pH: 13.4) in an amount such that the mass ratio of the sample to the aqueous sodium hydroxide solution (sample / aqueous sodium hydroxide solution) was 0.02, and then the mixture was left to stand for 1 hour in an environment of 20°C to produce a mixture. After appropriate filtration, the COD of the mixture was measured using a product called "Pack Test" manufactured by Kyoritsu Chemical Research Institute. The results are shown in Table 1.

[0030] [Example 1] The types and amounts of cement-based solidification materials shown in Table 1 were added (supplied) to the types of unimproved soil shown in Table 1 and mixed to produce solidified improved soils 1 to 9. The cement-based solidification material was added in the form of a slurry mixed with water so that the water-powder ratio (mass ratio of water to powder (cement-based solidification material)) was 80%. The unconfined compressive strength of the solidified improved soil at an age of 28 days was measured in accordance with JIS A 1216:2020 (Unconfined compression test method for soil). Unconfined compressive strength at 28 days is 1,000kN / mm 2If the unconfined compressive strength is 1,000kN / mm 2 If the value was less than this, it was evaluated as "x".

[0031] Wet density of unimproved soil (kg / m 3 The first value was calculated using the values ​​of the water content (%), COD (mg / liter) of the mixture obtained from the unimproved soil, and the above content ratio, as well as the following judgment formula (a). 14Xa-0.10Xb-13.0log 10 Xc+2.25Xd (a) (In the above formula (a), Xa is the wet density (kg / m 3 ), Xb is the water content (%), Xc is the COD (mg / liter), and Xd is the content ratio.

[0032] In addition, the wet density of unimproved soil (kg / m 3 ) and water content (%), COD (mg / liter) of the mixture obtained from unimproved soil, the above content ratio, and the amount of cement-based solidification material added (kg / m 3 The second value was calculated using the values ​​of (a) and (b) below. 25Xa-0.16Xb-13.0log 10 Xc+1.95Xd+0.015Xe (b) (In the above formula (b), Xa is the wet density, Xb is the water content (%), Xc is the COD (mg / liter), Xd is the content ratio, and Xe is the amount of cement-based solidification material added (kg / m 3 ) The measured value of the unconfined compressive strength, the first value calculated using formula (a), and the second value calculated using formula (b) are shown in Table 1. In Table 1, the case where the solidified improved soil did not solidify sufficiently and the sample broke when it was removed from the formwork is indicated as "unmeasurable."

[0033] [Table 1]

[0034] From Table 1, the solidified improved soils 1-3, 5-6, and 9, whose first and second values ​​are greater than 0, have a high unconfined compressive strength (1,070-1,820 kN / m 2 ) On the other hand, the solidified improved soils 4, 7-8, whose first and second values ​​are less than 0, have low unconfined compressive strength (253-385 kN / m 2 ) or does not solidify, and the unconfined compressive strength cannot be measured. From these results, it can be seen that by selecting one of cement-based solidification materials A to C as the cement-based solidification material to be supplied to unimproved soil A, one of cement-based solidification materials B to C as the cement-based solidification material to be supplied to unimproved soil B, and cement-based solidification material C as the cement-based solidification material to be supplied to unimproved soil C, it is possible to obtain solidified and improved soil with excellent strength.

Claims

1. A ground improvement method in which a cement-based solidification material is supplied to unimproved soil containing peat and mixed to obtain solidified and improved soil, a sampling step of collecting a sample of the unimproved soil from the unimproved soil; an unimproved soil measuring step of measuring the wet density and water content of the unimproved soil using the sample; a COD measurement step of drying the sample by leaving it to stand under conditions of 30 to 60°C for 10 hours or more, mixing the dried sample with 0.2 to 0.8 mol / L of aqueous sodium hydroxide in an amount such that the mass ratio of the sample to the aqueous sodium hydroxide solution (sample / aqueous sodium hydroxide solution) is 0.005 to 0.10 to obtain a mixture, and then leaving it to stand under conditions of 10 to 30°C for 30 minutes or more to measure the COD (chemical oxygen demand) of the mixture; a cement-based solidification material preparation step of preparing one or more candidates for the cement-based solidification material; a selection step of selecting, as a cementitious solidification material to be supplied to the unimproved soil, a cementitious solidification material for which the wet density, the water content, the COD, and the numerical value of the content ratio of the one or more candidate cementitious solidification materials expressed by the following formula (1), and a first value calculated using the following predetermined judgment formula (2) (wherein the first value is a dimensionless value without units obtained using only numerical values) are greater than 0, and not selecting, as a cementitious solidification material to be supplied to the unimproved soil, a cementitious solidification material for which the first value is 0 or less; a solidification treatment step of supplying the cement-based solidification material selected in the selection step to the unimproved soil and mixing them to obtain the solidified and improved soil; A ground improvement method comprising: (Cement-based solidification material SO ３ content + Al content of cement-based solidification material ２ O ３ (content of CaO) / CaO content of cement-based solidification material (1) AXa-BXb-Clog 10 Xc+DXd...(2) (In the above formula (2), Xa is the wet density (kg / m 3 ), Xb is the water content (%), Xc is the COD (mg / liter), Xd is the content ratio, A is a number from 12 to 16, B is a number from 0.09 to 0.11, C is a number from 12.0 to 14.0, and D is a number from 2.00 to 2.40.)

2. A ground improvement method in which a cement-based solidification material is supplied to unimproved soil containing peat and mixed to obtain solidified improved soil, a sampling step of collecting a sample of the unimproved soil from the unimproved soil; an unimproved soil measuring step of measuring the wet density and water content of the unimproved soil using the sample; a COD measurement step of drying the sample by leaving it to stand under conditions of 30 to 60°C for 10 hours or more, mixing the dried sample with 0.2 to 0.8 mol / L of aqueous sodium hydroxide in an amount such that the mass ratio of the sample to the aqueous sodium hydroxide solution (sample / aqueous sodium hydroxide solution) is 0.005 to 0.10 to obtain a mixture, and then leaving it to stand under conditions of 10 to 30°C for 30 minutes or more to measure the COD (chemical oxygen demand) of the mixture; a cement-based solidification material preparation step of preparing one or more candidates for the cement-based solidification material; a selection step of selecting, as a cementitious solidification material to be supplied to the unimproved soil, a cementitious solidification material for which the wet density, the water content, the COD, the content ratio of the one or more candidate cementitious solidification materials expressed by the following formula (1), the numerical value of the amount of addition of the one or more candidate cementitious solidification materials, and a second value (wherein the value is a dimensionless value without units obtained using only numerical values) calculated using the following predetermined judgment formula (3) are greater than 0, and not selecting, as a cementitious solidification material to be supplied to the unimproved soil, a cementitious solidification material for which the second value is 0 or less; a solidification treatment step of supplying the cement-based solidification material selected in the selection step to the unimproved soil and mixing them to obtain the solidified and improved soil; A ground improvement method comprising: (SO 3 content of cement-based solidification material+Al 2 O 3 content of cement-based solidification material) / CaO content of cement-based solidification material (1) αXa-βXb-γlog 10 Xc+δXd+εXe...(3) (In the above formula (3), Xa is the wet density (kg / m 3 ), Xb is the water content (%), Xc is the COD (mg / liter), Xd is the content ratio, Xe is the amount added (kg / m 3 ), α is a number from 24 to 25, β is a number from 0.14 to 0.16, γ is a number from 12.8 to 13.0, δ is a number from 1.95 to 2.00, and ε is a number from 0.012 to 0.015.)

3. A ground improvement method for producing solidified improved soil by supplying and mixing a cement-based solidification material to unimproved soil containing peat, a sampling step of collecting a sample of the unimproved soil from the unimproved soil; an unimproved soil measuring step of measuring the wet density and water content of the unimproved soil using the sample; a COD measurement step of drying the sample by leaving it to stand under conditions of 30 to 60°C for 10 hours or more, mixing the dried sample with 0.2 to 0.8 mol / L of aqueous sodium hydroxide in an amount such that the mass ratio of the sample to the aqueous sodium hydroxide solution (sample / aqueous sodium hydroxide solution) is 0.005 to 0.10 to obtain a mixture, and then leaving it to stand under conditions of 10 to 30°C for 30 minutes or more to measure the COD (chemical oxygen demand) of the mixture; a cement-based solidification material preparation step of preparing one or more candidates for the cement-based solidification material; the wet density, the water content, the COD, and the content ratio of the one or more candidate cement-based solidification materials expressed by the formula (1), and a first value calculated using the following predetermined judgment formula (2) (wherein the value is a dimensionless value without units that can be obtained using only numerical values); a selection step of selecting, as a cementitious solidification material to be supplied to the unimproved soil, a cementitious solidification material for which all of the values ​​of the wet density, the water content, the COD, the content ratio of the one or more candidate cementitious solidification materials expressed by the above formula (1), the numerical value of the added amount of the one or more candidate cementitious solidification materials, and a second value calculated using the following predetermined judgment formula (3) (however, the value is a dimensionless value without units obtained using only numerical values) are greater than 0, and not selecting, as a cementitious solidification material to be supplied to the unimproved soil, a cementitious solidification material for which at least either the first value or the second value is less than 0; a solidification treatment step of supplying the cement-based solidification material selected in the selection step to the unimproved soil and mixing them to obtain the solidified and improved soil; A ground improvement method comprising: (SO 3 content of cement-based solidification material+Al 2 O 3 content of cement-based solidification material) / CaO content of cement-based solidification material (1) AXa-BXb-Clog 10 Xc+DXd...(2) (In the above formula (2), Xa is the wet density (kg / m 3 ), Xb is the water content (%), Xc is the COD (mg / liter), Xd is the content ratio, A is a number from 12 to 16, B is a number from 0.09 to 0.11, C is a number from 12.0 to 14.0, and D is a number from 2.00 to 2.40.) αXa-βXb-γlog 10 Xc+δXd+εXe...(3) (In the above formula (3), Xa is the wet density (kg / m 3 ), Xb is the water content (%), Xc is the COD (mg / liter), Xd is the content ratio, Xe is the amount added (kg / m 3 ), α is a number from 24 to 25, β is a number from 0.14 to 0.16, γ is a number from 12.8 to 13.0, δ is a number from 1.95 to 2.00, and ε is a number from 0.012 to 0.015.)

4. The ground improvement method according to any one of claims 1 to 3, wherein the cement-based solidification material contains Portland cement, blast furnace slag ground powder, and gypsum powder.

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