Method for manufacturing modified soil

Abstract

To provide a method for manufacturing granular soil which can obtain granular soil which has good handleability and high strength in re-use from weak soil having a high moisture ratio.SOLUTION: A method for manufacturing modified soil includes adding water absorptive particles (A) having a tapping flow value of 90 mm or less in swelling by water and quicklime (B) to weak soil having a moisture ratio of 100 mass% or more.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for producing improved soil, a method for constructing embankments, and an additive for soft soil. [Background technology]

[0002] Among soils, those with a high water content, such as sludge accumulated in rivers and lakes, highly organic soil, humus soil, soil and sand generated by flood damage, and construction sludge, are known as so-called soft soils. Soft soils are generally muddy and have very low strength, making them difficult to transport or reuse in their original state. Therefore, in order to improve the strength of soft soils and improve their handling, it is known to carry out a solidification treatment using a solidification material. As solidification materials, inorganic materials such as cement, quicklime, and slaked lime have traditionally been used, but the use of organic materials such as polymer compounds has also been proposed.

[0003] Patent Document 1 describes a method for modifying wet waste soil, which involves adding a water-absorbent resin and a water-soluble polymer compound to the wet waste soil, and which is applicable to wet waste soil with a wide range of moisture content, can be modified in a short time, and does not return to its original state even when the modified soil is subjected to vibration.The examples disclose that the amount of leachate and the flow value of the soil modified using a crosslinked sodium polyacrylate and a methyl chloride compound of dimethylamino methacrylate as a water-absorbent resin for soil with a moisture content of 65% are small.

[0004] Patent Document 2 describes a hardening agent for wet soil, which is made mainly of water-absorbent fibrous material and hydrophilic polymeric compound, as a hardening agent for wet soil that is environmentally friendly and can obtain soil strength without using lime-based hardening agents. It also discloses that water-absorbent polymeric compounds and even composites of lime and water-absorbent polymeric compounds are used as hardening agents as conventional techniques for hardening and stabilizing wet soil.

[0005] Patent Document 3 describes a soil granulation additive for granulating high-water content soil to prepare a soil granulation product, which is easy to handle when transporting or reusing the soil granulation product and can keep the pH of the soil granulation product within the environmental standard range of 5.8 to 8.6, and contains a nonionic polymer flocculant with a 90% weight cumulative particle size of 400 μm or less. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2-38615 [Patent Document 2] Japanese Patent Application Publication No. 8-302347 [Patent Document 3] JP 2019-182884 A Summary of the Invention [Problem to be solved by the invention]

[0007] Various techniques for solidifying soft soil have been proposed, but it is extremely difficult to solidify soft soil with a higher moisture content, for example, a moisture content of 100% by mass or more, and even if it is possible to solidify it, it is often obtained as a coarse, viscous mass, and it is not possible to obtain a loose, granular, improved soil that is easy to handle. Furthermore, when solidifying soft soil to be reused, for example as embankment, it is desired that the soil exhibits high strength in the form of use.

[0008] The present invention provides a method for producing improved soil, which can obtain improved soil that is easy to handle and has high strength when reused, from soft soil with a high moisture content. [Means for solving the problem]

[0009] The present invention relates to a method for producing improved soil, which comprises adding water-absorbing particles (A) having a tapping flow value of 90 mm or less when swollen with water and quicklime (B) to soft soil having a moisture content of 100 mass % or more.

[0010] The present invention also relates to a method for constructing an embankment, comprising the steps of: adding water-absorbing particles (A) having a tapping flow value of 90 mm or less when swollen with water and quicklime (B) to soft soil having a moisture content of 100 mass% or more to obtain modified soil; and constructing an embankment using the modified soil.

[0011] The present invention also relates to an additive for soft soil, which contains water-absorbing particles (A) having a tapping flow value of 90 mm or less when swollen with water, and quicklime (B). Effect of the Invention

[0012] According to the present invention, there is provided a method for producing improved soil, which can obtain improved soil that is easy to handle and has high strength when reused from soft soil with a high moisture content. The improved soil produced by the present invention can be used to construct embankments with excellent strength. [Brief description of the drawings]

[0013] [Figure 1] Photograph showing granular soil obtained in Example 1-1 [Diagram 2] Photograph showing lumpy soil obtained in Comparative Example 1-1 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The tapping flow value of the (A) component is an index showing the fluidity of the water-absorbing particles swollen with water, and this index is thought to be correlated with the degree of cross-linking of the water-absorbing particles, and it is presumed that the smaller the tapping flow value, the greater the degree of cross-linking of the water-absorbing particles. The greater the degree of cross-linking of the water-absorbing particles, the less likely the water-absorbing particles will swell even if they absorb water in soft soil. In the present invention, by using water-absorbing particles with a specific tapping flow value, the water content in the soft soil is reduced while the increase in viscosity of the modified soil due to the particles after water absorption is suppressed, and it is believed that the compactability is improved and strength is expressed after curing. In addition, the quicklime of the (B) component reacts with water to become calcium hydroxide, which generates a large amount of heat at that time. The (B) component reduces the amount of water in the wet soil by taking in water as a chemical reaction and promoting the evaporation of water by heat generation, and is thought to further synergistically improve the compactability improved by the (A) component.

[0015] [Method of manufacturing modified soil] In the present invention, modified soil is produced by adding components (A) and (B) to soft soil with a water content of 100% by mass or more. The modified soil obtained by the present invention is, for example, soft soil whose water content has been reduced by dehydration, and whose viscosity and adhesiveness have been reduced, and is preferably granulated soil (granular soil) from the viewpoint of convenience in transportation and reuse.

[0016] The soft soil targeted by the present invention has a water content of 100% by mass or more. Hereinafter, when soft soil is mentioned, it means a soil with a water content of 100% by mass or more unless otherwise specified. The water content of soil is the mass ratio of water to the solid content of soil. The water content of soft soil may be, for example, 100% by mass or more, preferably 110% by mass or more, more preferably 115% by mass or more, and 1000% by mass or less, preferably 800% by mass or less, more preferably 600% by mass or less, and more preferably 150% by mass or less. Soft soil with a water content of 100% by mass or more can be found, for example, in soils such as dredged soil, peat soil, excavated soil, and flooded soil. The water content may also be adjusted by drying or wetting the soil (for example, by adding water).

[0017] The component (A) used in the present invention is a water-absorbing particle having a tapping flow value of 90 mm or less when swollen with water. The tapping flow value of the component (A) is measured by the method described in the Examples. From the viewpoint of obtaining an improved soil having good handleability, for example, a granular shape, the tapping flow value of the component (A) is preferably 85 mm or less, more preferably 80 mm or less, and from the viewpoint of obtaining an improved soil having high strength when reused, it is preferably 51 mm or more, more preferably 60 mm or more, and even more preferably 70 mm or more. Hereinafter, unless otherwise specified, the tapping flow of the component (A) refers to the tapping flow when swollen with water.

[0018] The water-absorbing particles of component (A) are particles that have the property of absorbing water and swelling almost instantly when they come into contact with water, turning the entire water into a gel. An index of the properties of water-absorbing particles is the "water retention capacity (g / g)" which indicates the mass of water that the particle can retain within the particle relative to its own mass. In the present invention, particles with a water retention capacity of 10 (g / g) or more are called water-absorbing particles.

[0019] (A) Median diameter of component (D 50 The median diameter (D) of the component (A) may be, for example, 100 μm or more, or 200 μm or more, and 2000 μm or less, or 1000 μm or less, or 500 μm or less. 50 ) is measured by the method described in the Examples.

[0020] The component (A) may be water-absorbent resin particles. Examples of the resin include acrylic resin, polyacrylamide resin, acrylamide-acrylic acid resin, etc. Among these, the component (A) is preferably acrylic resin water-absorbent particles. As the component (A), a commercially available product can be used. Commercially available water-absorbent resin particles include, for example, the "Sunwet" series manufactured by Sanyo Chemical Industries, Ltd. and the "Aqualic" series manufactured by Nippon Shokubai Co., Ltd. Among these, a water-absorbent particle having a tapping flow value of 90 mm or less when swollen with water can be selected and used as the component (A).

[0021] The component (B) used in the present invention is quicklime. As quicklime, industrially available quicklime can be used. The component (B) has a median diameter (D 50 ) is preferably 10 μm or more and 1000 μm or less.

[0022] In the present invention, soft soil 1m 3 The component (A) can be added in an amount of preferably 10 kg or more, more preferably 15 kg or more, more preferably 20 kg or more, and preferably 60 kg or less, more preferably 50 kg or less, more preferably 30 kg or less.

[0023] In the present invention, soft soil 1m 3 The component (B) can be added in an amount of preferably 30 kg or more, more preferably 40 kg or more, and preferably 200 kg or less, more preferably 100 kg or less, and more preferably 75 kg or less.

[0024] In the present invention, the mass ratio (A) / (B) of the amount of component (A) added to the amount of component (B) added is preferably 0.05 or more, more preferably 0.1 or more, even more preferably 0.3 or more, and is preferably 2 or less, more preferably 1.7 or less, even more preferably 1.0 or less, even more preferably 0.5 or less.

[0025] In the present invention, components other than components (A) and (B) can be added to the soft soil as long as the effect of the present invention is not impaired. Such components include dispersants for clay particles that break up soil aggregates and discharge the water trapped inside the aggregates as free water. Common dispersants for clay particles include sodium polyacrylate and naphthalenesulfonic acid-formalin condensate. However, those that fall under component (A) are excluded.

[0026] There are no particular limitations on the method for adding component (A) and component (B) to soft soil. Component (A) and component (B) may be added in powder form to the soft soil, and if necessary, may be stirred and mixed using a known stirring means.

[0027] In addition, in order to simplify the addition of the (A) and (B) components to soft soil, an additive for soft soil containing the (A) and (B) components can be prepared in advance and added to the soft soil. The present invention provides an additive for soft soil containing the (A) and (B) components. The additive for soft soil of the present invention may be, for example, a modifier for soft soil. The additive for soft soil of the present invention may have a mass ratio (A) / (B) of the content of the (A) component to the content of the (B) component, which is preferably 0.05 or more, more preferably 0.1 or more, more preferably 0.3 or more, and preferably 2 or less, more preferably 1.7 or less, more preferably 1.0 or less, and more preferably 0.5 or less.

[0028] Soft soil to which components (A) and (B) have been added, for example, in amounts within the above-mentioned ranges, becomes improved soil with reduced viscosity and adhesiveness in a relatively short period of time, and also takes on a shape that is easy to handle, preferably granular. The improved soil obtained by the present invention has a bulk density of, for example, 1.1 g / cm 3 More than 1.5g / m 3 The following is the result.

[0029] The improved soil obtained by the present invention is in a low viscosity state, preferably in a free-flowing granular state, and therefore has good handling properties for transportation, etc. In addition, since it has high strength after being compressed by compaction, etc., it is highly useful in fields where this property is preferred. The improved soil obtained by the present invention can be used in various fields, and is particularly suitable for use as soil in the civil engineering field, and further as banking soil.

[0030] The improved soil obtained by the present invention has a soil strength after compaction of, for example, 150 kN / m 2 Above that, an additional 200kN / m 2 In addition, when the improved soil obtained by the present invention is used for a purpose in which a certain degree of strength is sufficient, such as a temporary embankment that is assumed to be removed, the upper limit of the soil strength is, for example, 1500 kN / m 2Below that, 500kN / m 2 The soil strength after compaction may be as follows: The soil strength after compaction is measured by the method described in the Examples.

[0031] [Embankment construction method] The present invention provides a method for constructing an embankment, comprising the steps of: adding highly cross-linked water-absorbent particles (A) [component (A)] having a tapping flow value of 90 mm or less and quicklime (B) [component (B)] to soft soil having a moisture content of 100 mass % or more to obtain modified soil; and using the modified soil to construct an embankment. The matters described in the modified soil manufacturing method of the present invention can be appropriately applied to the embankment construction method of the present invention. Specific examples and preferred examples of the (A) component and the (B) component in the embankment construction method of the present invention are the same as those in the modified soil manufacturing method of the present invention. In the embankment construction method of the present invention, the modified soil can be obtained by the modified soil manufacturing method of the present invention. The method of constructing embankments using the obtained modified soil can be based on known methods of constructing embankments. In the present invention, the modified soil can be compacted to construct an embankment. The compaction conditions are controlled, for example, by the degree of compaction, which is generally 90% or more for road embankments and 85% or more for river levees. The degree of compaction is the ratio between the dry density of soil compacted on-site and the maximum dry density of a standard compaction test. The modified soil can be compacted by known methods of compacting soil. EXAMPLES

[0032] <Soft soil for evaluation> As the soft soil, Kanto loam (red soil) with the following physical properties was used. Wet density: 1.376g / cm 3 ·Water content: 119% ·Dry density: 0.753g / cm 3

[0033] <Water-absorbing resin particles> The following water-absorbent resin particles were used as the water-absorbent resin particles. The tapping flow value and median diameter (D 50) were measured by the following method. The water retention capacity of each was 10 (g / g) or more. Invention product 1: Tapping flow value 79 mm, median diameter (D 50 ) 400μm, acrylic resin-based water-absorbing particles Invention product 2: Tapping flow value 77 mm, median diameter (D 50 ) 380μm, acrylic resin-based water-absorbing particles Comparison product 1: Tapping flow value 127 mm, median diameter (D 50 ) 400μm, acrylic resin-based water-absorbing particles Comparison product 2: Tapping flow value 102 mm, median diameter (D 50 ) 380μm, acrylic resin-based water-absorbing particles

[0034] <Method for measuring the tapping flow value of water-absorbent particles> (1) Weigh out 1 g of dry water-absorbing particles into a 500 mL plastic cup, add 200 g of ion-exchanged water, and then leave to stand at 20°C for 10 minutes. (2) After swelling, any free water present on the surface of the water-absorbing particles is removed. (3) A flow plate is placed on top of the tapping table, and a cylindrical plastic cone with an inner diameter of 50 mm, an outer diameter of 60 mm, and a height of 50 mm is placed on top of the flow plate, and the cone is filled with swollen water-absorbing particles. (4) Raise the cone vertically and then tap it 10 times. (5) The longest diameter of the spread of the water-absorbent particle and the diameter perpendicular to that diameter are measured with a vernier caliper, and the average value is the tapping flow value when swollen with water.

[0035] <Median diameter of water-absorbing particles (D 50 ) Measurement method> From the sieves specified in JIS Z 8801, select metal sieves with sieve openings of 710 μm, 500 μm, 300 μm, 150 μm, and a tray (150 μm or less). Sieve the dry water-absorbing particles, measure the mass of the sample remaining on each sieve, plot the cumulative distribution of the mass on a graph, read the particle diameter at which the cumulative distribution is 50%, and calculate the median diameter (D 50 )

[0036] <Quicklime> As the quicklime, special quicklime manufactured by Yoshimi Lime Industry Co., Ltd. was used.

[0037] <Evaluation method> The soft soil (Kanto loam), the (A) component shown in the table, and the (B) component shown in the table were charged into a mortar mixer in the amounts shown in the table, and mixed at low speed for 3 minutes. After mixing, granular soil was obtained in the example, but not in the comparative example, and instead a viscous, lumpy soil was obtained. The granular soil obtained in the example had a bulk density of 1.1 g / cm. 3 More than 1.5g / m 3 The soil obtained in Example 1-1 was in the following range. Figure 1 shows the granular soil obtained in Example 1-1. Figure 2 shows the lumpy soil obtained in Comparative Example 1-1. As shown in Figure 1, the soil obtained in Example 1-1 was in the form of fine particles and was in a loose state. On the other hand, as shown in Figure 2, the soil obtained in Comparative Example 1-1 was in the form of coarse, highly viscous lumps. The obtained soil was packed into a summit mold in three layers and compacted (using a 1.5 kg rammer; each layer was compacted 25 times). After compaction, the soil was left to cure in air at 20°C for 5 hours. After curing, the hardness index (spring contraction length) was measured using a Yamanaka soil hardness tester (Fujiwara Seisakusho Co., Ltd.: Standard soil hardness tester No. 351). Following the instruction manual for the soil hardness tester, the tip cone of the soil hardness tester was inserted until the flange touched the surface of the soil sample and then slowly pulled out. The hardness index (mm) on the scale at this time was read and the bearing strength (kg / cm) was calculated using the following formula: 2 ) and the bearing strength was converted to kN / m 2 The results were converted to soil hardness and are shown in Tables 1 and 2. P = (100X) / (0.7952(40-X) 2 〕 P: Supporting capacity strength (kg / cm 2 ) X: Hardness index (spring contraction length) (mm)

[0038] [Table 1]

Claims

1. A method for producing improved soil, comprising the steps of: placing a cylindrical plastic cone having an inner diameter of 50 mm, an outer diameter of 60 mm, and a height of 50 mm on soft soil having a moisture content of 100% by mass or more; filling the cone with swollen water-absorbing particles; vertically lifting the cone; and adding water-absorbing particles (A) (hereinafter referred to as component (A)) having a median diameter (D50) of 200 μm to 500 μm and a tapping flow value of 70 mm to 80 mm obtained by performing 10 tapping operations; and quicklime (B) (hereinafter referred to as component (B)). Add 10 kg to 50 kg of component (A) per 1 m3 of soft soil, A method for producing improved soil, wherein the mass ratio (A) / (B) of the amount of component (A) added to the amount of component (B) added is 0.1 or more and 1.0 or less.

2. Soft soil 1m ３ The method for producing improved soil according to claim 1, wherein 40 kg or more and 75 kg or less of component (B) is added to the soil.

3. The method for producing improved soil according to claim 1 or 2, wherein the component (A) is an acrylic resin-based water-absorbent resin particle.

4. A method for constructing embankments, comprising the steps of: placing a cylindrical plastic cone having an inner diameter of 50 mm, an outer diameter of 60 mm, and a height of 50 mm on soft soil having a moisture content of 100% by mass or more; filling the cone with swollen water-absorbing particles; lifting the cone vertically; and then adding water-absorbing particles (A) and quicklime (B) having a median diameter (D50) of 200 μm to 500 μm and a tapping flow value of 70 mm to 80 mm obtained by performing 10 tapping operations to obtain modified soil, and constructing an embankment using the modified soil, the method comprising the steps of: Add 10 kg to 50 kg of component (A) per 1 m3 of soft soil, A method for constructing embankments, wherein the mass ratio (A) / (B) of the amount of component (A) added to the amount of component (B) added is 0.1 or more and 1.0 or less.

5. 5. The method for constructing an embankment according to claim 4, wherein the embankment is constructed by compacting granular soil.

6. The method for constructing embankments according to claim 4 or 5, wherein improved soil is obtained by the manufacturing method according to any one of claims 1 to 3.

7. An additive for soft soil comprising water-absorbing particles (A) having a median diameter (D50) of 200 μm or more and 500 μm or less and a tapping flow value of 70 mm to 80 mm obtained by placing a cylindrical plastic cone having an inner diameter of 50 mm, an outer diameter of 60 mm, and a height of 50 mm, filling the cone with swollen water-absorbing particles, lifting the cone vertically, and then tapping 10 times, and quicklime (B) in a mass ratio (A) / (B) of 0.1 or more and 1.0 or less.

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