Soil conditioner and soil improvement method

Abstract

To provide a soil improver which can obtain a sufficient improving effect even on extremely soft soil for which conventional soil improvers have not been able to obtain a sufficient improving effect, and which does not significantly change the properties of the improved soil. The present invention provides a soil conditioner for improving the quality of water-containing soil, based on porous ore with a bulk specific gravity of 0.7 or more, which contains the following components (contents in parentheses): (a) Polymer flocculant [a mass%] (b) Magnesium oxide [b mass%] (c) pH buffer with a buffer range of pH 7 or higher [c mass %] The soil conditioner contains the above components, wherein the content relationships of the components satisfy a≦b, b≧c, and a≧c, and the total content [a+b+c] of the components (a) to (c) is 25 to 60 mass%.

Description

[Technical Field]

[0001] The present invention relates to a soil conditioner for improving the quality of wet soil and a soil improvement method. [Background technology]

[0002] For example, soil generated during dredging work is generally very soft and contains a large amount of water. It is difficult to handle such soft soil as it is, and it is necessary to improve the soil quality using soil conditioners before transporting or reusing it.

[0003] BACKGROUND ART Soil conditioners that combine inorganic materials with polymeric agents are known as soil conditioners used to improve the quality of soft soil (water-containing soil) (see, for example, Patent Documents 1 and 2).

[0004] The soil conditioner described in Patent Document 1 consists of (A) hydraulic gypsum, (B) a coagulant, (C) porous inorganic particles, and (D) a pH adjuster. Examples of the coagulant (B) include a metal acrylate-acrylamide copolymer, an anionic polyacrylamide polymer, a partial hydrolyzate of polyacrylamide, and an acrylic acid-vinyl alcohol copolymer.

[0005] The soil conditioner described in Patent Document 2 is composed of (A) water-absorbing particles and (B) quicklime. Examples of the (A) water-absorbing particles include acrylic resin, polyacrylamide resin, and acrylamide-acrylic acid resin. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-1397 [Patent Document 2] Japanese Patent Application Publication No. 2023-8326 Summary of the Invention [Problem to be solved by the invention]

[0007] In order to reuse soil by backfilling or other means, it is necessary for the amended soil to have sufficient strength and for the properties of the amended soil to remain largely unchanged from the soil before amendment (pH to be stable at around neutral).

[0008] In this regard, the soil conditioner described in Patent Document 1 contains hydraulic gypsum as component (A), which can increase the sulfate concentration in the soil after amendment, making it unsuitable for reuse. Furthermore, the soil conditioner in Patent Document 1 contains a pH adjuster as component (D), but the amount of pH adjuster added must be adjusted depending on the soil to be amended. If the amount of pH adjuster added is excessive, the amount of amended soil will increase, which can make it difficult to handle.

[0009] The soil conditioner described in Patent Document 2 also contains quicklime as component (B), which increases the pH of the soil, potentially making it difficult to reuse the soil after it has been improved.

[0010] The soil conditioners described in Patent Documents 1 and 2 use a combination of inorganic materials (hydraulic gypsum, quicklime) and polymeric chemicals (polymeric flocculants, water-absorbent polymers), but extremely soft soil (high-moisture soil) occurs at actual construction sites, and conventional soil conditioners are unlikely to improve such soft soil. Therefore, there is a demand for soil conditioners with a stronger improvement effect.

[0011] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a soil conditioner that can achieve sufficient improvement effects even in extremely soft soil that has not been improved sufficiently by conventional soil conditioners, without significantly changing the properties of the improved soil. Another aim is to provide a soil improvement method using such a soil conditioner with excellent improvement effects. [Means for solving the problem]

[0012] The characteristic configuration of the soil improver according to the present invention for solving the above problems is as follows: A soil conditioner for improving the quality of water-containing soil, based on porous ore with a bulk density of 0.7 or more, containing the following components (contents in parentheses): (a) Polymer flocculant [a mass%] (b) Magnesium oxide [b mass%] (c) pH buffer with a buffer range of pH 7 or higher [c mass %] Including, The relationship of the content of each component satisfies a≦b, b≧c, a≧c, and the total content [a+b+c] of the components (a) to (c) is 25 to 60 mass %.

[0013] The soil conditioner of this configuration, which sets the respective contents of the above components (a) to (c) in a specific relationship and further sets the total content to 25 to 60 mass%, achieves sufficient soil improvement without significantly changing the soil properties, even in extremely soft soil (high-moisture soil) that has not been sufficiently improved with conventional soil conditioners. Furthermore, since it is based on a porous ore with a bulk specific gravity of 0.7 or greater, moisture in the moist soil is absorbed by the porous ore, reducing the stickiness of the improved soil. Furthermore, instead of the pH adjuster contained in conventional soil conditioners, it contains a pH buffer with a buffer range of pH 7 or greater, which stabilizes the pH of the improved soil near neutral, resulting in improved soil suitable for reuse. Furthermore, magnesium oxide generates magnesium hydroxide through hydration, but magnesium hydroxide is weakly alkaline and does not inhibit the effect of the polymer flocculant, allowing the above components (a) to (c) to reliably perform their respective functions.

[0014] In the soil improver according to the present invention, The content [a% by mass] of the polymer flocculant is preferably 5 to 15% by mass.

[0015] According to the soil conditioner of this configuration, by setting the content of component (a) to 5 to 15 mass %, the fluidity of the wet soil is reduced (i.e., solidified), and further, by coating the wet soil with the polymer flocculant, it is possible to effectively prevent the soil from turning into mud again.

[0016] In the soil improver according to the present invention, The content of the magnesium oxide [b % by mass] is preferably 10 to 40% by mass.

[0017] According to the soil conditioner of this configuration, by setting the content of component (b) to 10 to 40 mass %, the soil will exhibit self-hardening properties and be able to have sufficient strength.

[0018] In the soil improver according to the present invention, The content [c% by mass] of the pH buffering agent is preferably 5 to 10% by mass.

[0019] With the soil conditioner of this configuration, by setting the content of component (c) at 5 to 10 mass %, immediately after adding the soil conditioner to moist soil, the soil becomes weakly alkaline due to the hydration reaction of magnesium oxide. However, once the soil has been modified (hardened) to a certain extent, the alkaline ions are used in the hardening reaction and no longer redissolve, making it possible to stabilize the pH of the soil at around neutral.

[0020] In the soil improver according to the present invention, The pH buffer is preferably sodium bicarbonate and / or potassium bicarbonate.

[0021] According to the soil conditioner of this configuration, the selection of sodium bicarbonate and / or potassium bicarbonate as the pH buffer accelerates the hardening reaction of magnesium oxide, resulting in earlier strength development. In addition, because sodium bicarbonate and potassium bicarbonate are relatively inexpensive, they can improve the quality of wet soil at low cost.

[0022] In the soil improver according to the present invention, The porous ore is preferably obsidian perlite and / or zeolite.

[0023] According to the soil conditioner of this configuration, by selecting obsidian perlite and / or zeolite as the porous ore, the soil becomes dry and granular (in a loose state), and improved soil that is easy to reuse can be obtained.

[0024] The characteristic configuration of the soil improvement method according to the present invention for solving the above problems is as follows: A soil improvement method for improving the quality of wet soil, comprising: The method includes adding a soil improver according to the present invention to the water-containing soil, The soil containing water to which the soil conditioner was added had a cone index of 400 kN / m after 48 hours in a cone index test according to JIS A 1228. 2 It is more than that.

[0025] According to the soil improvement method of this configuration, the soil improvement agent of the present invention is used to improve moist soil, so that even extremely soft soil (high moisture soil) that has not been improved sufficiently by conventional soil improvement agents can be improved sufficiently, and the pH of the improved soil is stabilized at around neutral, making it suitable for reuse. The improved soil obtained has a cone index of 400 kN / m after 48 hours in a cone index test according to JIS A 1228. 2 For these reasons, the soil can be reused as improved soil of type 3 or higher as specified by the Ministry of Land, Infrastructure, Transport and Tourism.

[0026] In the soil improvement method according to the present invention, In the addition step, the amount of the soil improver added to the water-containing soil is 10 to 40 kg / m 3 It is preferable to set it to .

[0027] According to the soil improvement method of this configuration, the amount of soil improver added to the wet soil is 10 to 40 kg / m 3 By setting the value at , a high improvement effect can be obtained without significantly changing the properties of the soil.

[0028] In the soil improvement method according to the present invention, It is preferable that the pH of the moist soil to which the soil improver has been added fluctuates within a range of ±1.0 or less after 48 hours relative to the pH of the moist soil before the addition of the soil improver.

[0029] According to the soil improvement method of this configuration, the pH of the obtained improved soil fluctuates within ±1.0 or less after 48 hours compared to the pH of the wet soil before the soil improver was added, making it easy to reuse. DETAILED DESCRIPTION OF THE INVENTION

[0030] The soil conditioner and soil improving method according to the present invention will be described below. However, the present invention is not limited to the configurations described in the following embodiments and examples.

[0031] <Hydrous soil> The present invention is a soil conditioner for improving the quality of water-containing soil, and is particularly suitable for improving high-water content soil with a water content of 80% or more (approximately 44% water content). Examples of high-water content soil include dredged soil generated during dredging work. Dredged soil is included in the "soft soil requiring soil improvement" according to the Ministry of Land, Infrastructure, Transport and Tourism's recycling guidelines, and has a cone index of 200 kN / m as defined in the Ministry's standards for the use of generated soil. 2 Dredged soil is generally characterized by low strength due to its high water content and high organic matter content.

[0032] <Soil conditioner> When treating water-containing soil (particularly high-water content soil), the main requirements for a soil conditioner (or improved soil) include the following (A) to (E). (A) The amended soil is neutral. (B) The improved soil has solidified into granular form to some extent. (C) The self-hardening property of the improved soil appears after a short period of curing. (D) Solidification can be achieved with less addition than conventional inorganic solidifying agents. (E) The improved soil does not re-mutate.

[0033] The present inventors have conducted extensive research into soil conditioners that satisfy the requirements (A) to (E) and have found that a soil conditioner based on porous ore and containing a polymer flocculant (hereinafter sometimes referred to as component (a)), magnesium oxide (hereinafter sometimes referred to as component (b)), and a pH buffer (hereinafter sometimes referred to as component (c)) is particularly effective for improving high-moisture soil. Each component of the soil conditioner of the present invention will be described below.

[0034] [Porous ore] The porous ore is the main component of the soil conditioner, and it contributes to removing moisture from the wet soil and making it dry (crumbly). Here, "main component" means that its content in the soil conditioner is 40% by mass or more, preferably 50% by mass or more. In particular, when a porous ore with a bulk density of 0.7 or more is used, the moisture in the wet soil is quickly absorbed by the porous ore, resulting in high-quality improved soil particles with reduced stickiness.

[0035] Porous ores that can be used include obsidian perlite and zeolite. Obsidian perlite and zeolite have excellent water release properties from hydrated soil, making it possible to obtain improved soil that is easy to reuse. Obsidian perlite and zeolite can be used alone or in a mixed state.

[0036] [(a) Polymer flocculant] Polymer flocculants contribute to reducing the fluidity of wet soil (i.e., solidifying it). Furthermore, adding an appropriate amount of polymer flocculant to wet soil coats the soil with the polymer flocculant, effectively preventing the soil from becoming muddy again. While anionic, cationic, amphoteric, and nonionic polymer flocculants can all be used as polymer flocculants, anionic polymer flocculants are preferred due to their excellent soil adhesion prevention properties and minimal environmental impact. Furthermore, among amphoteric polymer flocculants, anionic-rich amphoteric polymer flocculants, which have more anionic groups than cationic groups, can also be used in the same way as anionic polymer flocculants. In other words, polymer flocculants containing anionic groups in their molecular structure (anionic polymer flocculants or anionic-rich amphoteric polymer flocculants) are preferably used.

[0037] Examples of anionic polymer flocculants include polycarboxylates or copolymers of polycarboxylates and acrylamide, polysulfonates or copolymers of polysulfonates and acrylamide, and derivatives thereof. Examples of polycarboxylic acids for forming polycarboxylates include acrylic acid, methacrylic acid, itaconic acid, and maleic acid. Examples of polysulfonic acids for forming polysulfonates include acrylamido-2-methylpropanesulfonic acid, vinylsulfonic acid, and styrenesulfonic acid.

[0038] Examples of cationic polymer flocculants include alkylaminoacrylate salt polymers or copolymers of alkylaminoacrylate salt polymers and acrylamide, alkylaminomethacrylate salt polymers or copolymers of alkylaminomethacrylate salt polymers and acrylamide, and derivatives thereof. Examples of alkylaminoacrylate salt polymers include dimethylaminoethyl acrylate, dimethylaminopropyl acrylamide, acryloyloxyethyl trimethylammonium chloride, acryloylaminopropyl trimethylammonium chloride, and acryloyl 2-hydroxypropyl fluoride. Examples of alkylaminomethacrylate salt polymers include dimethylaminoethyl methacrylate, dimethylaminopropyl methacrylamide, methacryloyloxyethyl trimethylammonium chloride, methacryloylaminopropyl trimethylammonium chloride, and methacryloyl 2-hydroxypropyl fluoride.

[0039] Examples of amphoteric polymer flocculants include random copolymers, alternating copolymers, block copolymers, and graft copolymers of anionic monomers, which are constituent units of anionic polymer flocculants, cationic monomers, which are constituent units of cationic polymer flocculants, and nonionic monomers (if necessary). Random copolymers or alternating copolymers are preferred from the viewpoint of stability. The polymerization ratio of anionic monomers to cationic monomers is 30 to 45 mol%, preferably 35 to 42 mol%, of anionic groups, 0.1 to 10.0 mol%, preferably 0.1 to 4.0 mol%, of cationic groups, with the remainder being nonionic groups. In amphoteric polymer flocculants, the anionic groups of the anionic polymer flocculant and the cationic groups of the cationic polymer flocculant exist in the same polymer structure, but they do not undergo phase separation like a mixture of anionic and cationic polymer flocculants, and therefore can exhibit stable performance.

[0040] The molecular weight of the polymer flocculant is 1.0 x 10 as the weight average molecular weight (Mw). 7 ~2.5×10 7 is preferred, and 1.3 × 107 ~2.2×10 7 When the molecular weight of the polymer flocculant is within the above range, the polymer flocculant has an excellent ability to sequester water contained in the water-containing soil and is easy to handle.

[0041] The polymer flocculant may be in the form of a powder or a liquid dissolved or dispersed in a solvent such as water. In the case of a liquid polymer flocculant, the solid content is preferably 10 to 80% by weight, more preferably 20 to 60% by weight, and even more preferably 40 to 50% by weight.

[0042] The content of the polymer flocculant in the soil conditioner is preferably 5 to 15 mass %. If the content of the polymer flocculant is set within the above range, re-mudification of the soil can be more effectively prevented.

[0043] [(b) Magnesium oxide] Magnesium oxide contributes to the development of self-hardening properties in moist soil. When an appropriate amount of magnesium oxide is added to moist soil, the water in the soil reacts with the magnesium oxide through a hydration reaction to produce magnesium hydroxide. Because magnesium hydroxide is weakly alkaline, it does not inhibit the effects of polymer flocculants. The magnesium hydroxide thus produced forms crystal nuclei in the moist soil, which are the starting points for solidification, and as the crystal growth progresses, the soil solidifies.

[0044] The content of magnesium oxide in the soil conditioner is preferably 10 to 40 mass %. If the content of magnesium oxide is set within the above range, the soil will exhibit sufficient self-hardening properties and will have high strength.

[0045] [(c) pH buffer] The pH buffer promotes the hydration reaction of magnesium oxide and maintains the soil in a neutral pH range after amendment. A pH buffer with a buffer range of pH 7 or higher is used. While some conventional soil conditioners contain pH adjusters, none contain a pH buffer like the one used in the present invention. The soil conditioner of the present invention, particularly one with a buffer range of pH 7 or higher, allows the pH fluctuation range after 48 hours to be ±1.0 or less relative to the pH of the hydrated soil before addition of the soil conditioner. This stabilizes the pH of the amended soil near neutral, resulting in amended soil suitable for reuse.

[0046] Examples of pH buffers with a buffer range above pH 7 include sodium bicarbonate and potassium bicarbonate. The use of sodium bicarbonate and potassium bicarbonate accelerates the hardening reaction of magnesium oxide, resulting in earlier development of strength. Furthermore, because sodium bicarbonate and potassium bicarbonate are relatively inexpensive, they can be used to improve water-containing soil at low cost. Sodium bicarbonate and potassium bicarbonate can be used alone or in a mixed state.

[0047] The content of the pH buffer agent in the soil conditioner is preferably 5 to 10% by mass. If the content of the pH buffer agent is set within this range, immediately after adding the soil conditioner to wet soil, the soil will become weakly alkaline due to the hydration reaction of magnesium oxide. However, once the soil has been improved (hardened) to a certain extent, the alkaline ions are used in the hardening reaction and will no longer redissolve, so the pH of the soil can be stabilized at around neutral.

[0048] [Other ingredients] Other ingredients can be added to the soil conditioner as needed. Examples of other ingredients include antifoaming agents, pH adjusters, solvents, thickeners, stabilizers, colorants, deodorizers, antibacterial agents, and antioxidants. These ingredients can be added alone or in combination.

[0049] [Relationship between the content of each ingredient] As described above, the soil conditioner of the present invention is based on porous ore and contains (a) a polymer flocculant, (b) magnesium oxide, and (c) a pH buffer. After extensive research, the inventors have found that the relationship between the contents of each component affects the improvement effect on moist soil.

[0050] Specifically, when the content of (a) polymer flocculant in the soil conditioner is a mass %, the content of (b) magnesium oxide is b mass %, and the content of (c) pH buffer is c mass %, if the relationship of the contents of components (a) to (c) satisfies a≦b, b≧c, a≧c, and the total content of components (a) to (c) [a+b+c] is 25 to 60 mass %, it becomes possible to obtain a sufficient improvement effect without significantly changing the properties of the soil, even in extremely soft soil (high-moisture soil) for which conventional soil conditioners have not been able to provide a sufficient improvement effect.

[0051] [Soil conditioner performance] When the soil conditioner of the present invention is added to moist soil, (i) after 48 hours, the cone index in the cone index test according to JIS A 1228 is 400 kN / m 2 And finally, (ii) the cone index is 800kN / m 2 It is preferable that the soil has the above properties (i). The soil having the above properties (ii) corresponds to soil of Class 3 improved soil or higher as specified by the Ministry of Land, Infrastructure, Transport and Tourism. The soil having the above properties (ii) corresponds to soil of Class 2 improved soil or higher as specified by the Ministry of Land, Infrastructure, Transport and Tourism. The improvement test of the wet soil will be explained in the examples below.

[0052] <Soil improvement method> The soil improving method of the present invention uses the above soil improver to improve the quality of moist soil, and includes an addition step of adding the above soil improver to the moist soil. The moist soil to which the soil improver has been added will have at least the property (i) above.

[0053] The amount of soil conditioner to be added to wet soil is 10 to 40 kg / m 3It is preferable to set the amount of soil improver to within the above range. By setting the amount of soil improver added within the above range, a high improvement effect can be achieved without significantly changing the properties of the soil. Furthermore, the pH of the improved soil obtained through the addition step preferably fluctuates within ±1.0 or less, more preferably ±0.5 or less, of the pH of the hydrated soil before adding the soil improver, after 48 hours. The pH value of the improved soil is preferably 7 to 8. In this case, the improved soil can be easily reused. [Example]

[0054] In order to confirm the performance of the soil conditioner of the present invention, simulated soil with a high moisture content was prepared and various tests were carried out. Examples etc. are explained below.

[0055] <Simulated soil> As a simulated soil for various tests, the Ministry of Land, Infrastructure, Transport and Tourism notified "Standards for the Use of Generated Soil" (Kokukangi No. 112, Kokukanso No. 309, dated August 10, 2006) that the soil has a cone index of 200 kN / m 2 We reproduced organic clayey soil, which is muddy soil with a water content of about 80% or more.

[0056] Specifically, Kasaoka clay (clay from Kasaoka City, Okayama Prefecture) and black soil (surface soil from Kanuma City, Tochigi Prefecture) were mixed at a weight ratio of 5:5, then water was added to a moisture content of approximately 100% and stirred until no lumps remained. After two days of standing, the moisture content was measured. If it remained above 80%, it was used as simulated soil. The properties of the simulated soil prepared were 100% moisture content, specific gravity 1.45, pH 6.8, and mini-slump value 11 cm. The moisture content was measured using a heat-drying moisture meter (model: MF-50, manufactured by A&D Co., Ltd.). The specific gravity was calculated from the volume and weight of the simulated soil placed in a beaker (500 mL). The pH was measured using a pH meter (manufactured by AS ONE Corporation, part number: 1-062-01-20). The mini-slump value was measured by a mini-slump test using a mini-slump cone (top inner diameter 50 mm × bottom inner diameter 100 mm × height 150 mm).

[0057] <Medications used> The following chemicals were used to prepare the soil conditioners of the Examples and Comparative Examples. [High molecular weight drugs] Polymer flocculant (main component: polyacrylic acid / polyacrylamide copolymer, "Water Floc" manufactured by Technica Godo Co., Ltd., particle size: 75 μm or less) Water-absorbing polymer (main component: sodium polyacrylate, "SAP" manufactured by Technica Godo Co., Ltd., particle size: 75-150 μm, water absorption ratio: 100-300 times) [Inorganic drugs] Magnesium oxide (Maehata Industries Co., Ltd., particle size: 150 μm or less) Gypsum (hemihydrate gypsum) (manufactured by E-Plus Co., Ltd., particle size: 300 μm or less) Slaked lime (Kawai Lime Industry Co., Ltd., particle size: 300 μm or less) Calcium carbonate (manufactured by Nitto Funka Kogyo Co., Ltd., particle size: 150-425 μm) [pH buffer] Sodium bicarbonate (buffer range: pH 8-9, particle size: 150-425 μm) Potassium bicarbonate (buffer range: pH 8-9, particle size: 150-425 μm) Aluminum sulfate (buffer range: pH 2-4, particle size: 150 μm or less) (Reference) Sodium tripolyphosphate (not a pH buffer, particle size: 150 μm or less) [Porous ore] Obsidian perlite (manufactured by Pacific Perlite Co., Ltd., pore size: 100-500 nm, particle size: 45-600 μm, bulk density: 0.8-1.2) Perlite (manufactured by Pacific Perlite Co., Ltd., pore size: several hundred nm to several tens of μm, particle size: 0.6 mm or less, bulk density: 0.1 to 0.6) Zeolite (manufactured by Nitto Funka Kogyo Co., Ltd., pore size: several nm, particle size: 150-600 μm, bulk density: 0.8-1.2)

[0058] <Soil conditioner> The components and contents of the soil conditioners in the examples and comparative examples are shown in Table 1 below.

[0059] [Table 1]

[0060] <Amount of soil conditioner to be added> To determine the amount of soil conditioner to be added to the simulated soil, a table flow test was conducted according to the following procedure. (1) Put 1 L of simulated soil into a stand mixer (Waring, model: WSM7Q). (2) Add a small amount (e.g., 5 g) of the soil conditioner of Example 1 to a stand mixer (addition amount: 5 kg / m 3 ). (3) Mix in a stand mixer for 3 minutes. (4) After stirring is stopped, a table flow test is carried out in accordance with JIS R 5201 to measure the table flow value. (5) Collect the simulated soil used in the table flow test, and repeat steps (2) to (4) above until the table flow value is 105 mm x 105 mm or less. (6) The total amount of soil conditioner added when the table flow value reaches 105 mm x 105 mm or less is considered to be the optimal amount of soil conditioner to be added to the simulated soil.

[0061] The optimum amount of soil conditioner to be added to the simulated soil determined by the above table flow tests is 30 kg / m 3 This amount was about the same as that of a conventional inorganic solidifying agent (approximately 50 kg / m 3 Therefore, the amount of soil conditioner added to the water-containing soil is 30 kg / m 3 If the amount is set at this level, then of the requirements (A) to (E) required for soil conditioners (or improved soil) explained above, the requirement (D) "solidifying with less addition than conventional inorganic solidifying agents" will be met. In the test results described below, this will be evaluated as "(D) amount added."

[0062] <Appearance evaluation of improved soil> The appearance of the improved soil obtained by adding the soil improvers of the Examples and Comparative Examples to the simulated soil was evaluated as follows. (1) 1 L of simulated soil was placed in a stand mixer, and 30 g of the soil conditioner of the Examples and Comparative Examples was added (addition amount: 30 kg / m 3 ). (2) Mix in a stand mixer for 3 minutes. (3) After stirring has stopped, place the simulated soil (amended soil) on the floor (concrete floor covered with newspaper) of a test room where the temperature (15±3°C) and humidity (45±10%) have been adjusted, and spread it evenly over an area of ​​approximately 30cm x 30cm. In order to reduce the effects of drying due to air currents, the amended soil should be placed away from the ventilation openings of the test room. (4) Visually check the appearance of the amended soil after it has been left for 48 hours.

[0063] Based on the above appearance evaluation test, it is determined whether or not the soil conditioner (or improved soil) satisfies the requirements (A) to (E) of "(B) The improved soil is solidified into a granular shape to a certain extent." In the test results described below, this is evaluated as "(B) Appearance."

[0064] <Strength evaluation of improved soil> The strength of the improved soil obtained by adding the soil improvers of the Examples and Comparative Examples to the simulated soil was evaluated by the cone index. Specifically, the improved soil was collected from the test room after 48 hours, and the cone index was measured by conducting the cone index test in accordance with JIS A 1228.

[0065] Based on the above cone index test, among the requirements (A) to (E) required for soil conditioners (or improved soil), it is judged whether or not "(C) The improved soil exhibits self-hardening properties after a short period of curing" is met. Note that in the test results described below, this is evaluated as "(C) Self-hardening properties."

[0066] <pH of modified soil and re-mudification> The soil conditioners of the Examples and Comparative Examples were added to the simulated soil, and the pH and the presence or absence of re-mudification were confirmed for the improved soil obtained by adding the soil conditioners of the Examples and Comparative Examples to the simulated soil according to the following procedures. (1) The modified soil after 48 hours is placed in a container, and water is added to adjust the content of the modified soil in the water to 10% by weight. (2) Gently stir the water containing the amended soil with a spoon 20 times. (3) The turbidity of the water after stirring is measured using a turbidity meter (manufactured by Kasahara Chemical Industries Co., Ltd., model: TR-55). (4) After measuring the turbidity, the water containing the amended soil is transferred to a sealed container, shaken for 2 hours using a shaker, and then allowed to stand for 30 minutes. The hydrogen ion concentration of the water is then measured using a pH meter (manufactured by AS ONE Corporation, product number: 1-062-01-20).

[0067] Based on the above turbidity and pH measurements, it is determined whether the soil conditioner (or amended soil) satisfies the requirements (A) to (E) of "(E) The amended soil does not re-mudify" and "(A) The amended soil is neutral." In the test results described below, the soil conditioner is evaluated as "(E) Re-mudify" and "(A) Neutral."

[0068] <Evaluation of improved soil (soil conditioner)> The evaluation of the improved soil obtained with the soil conditioners of the Examples and Comparative Examples is shown in Table 2. In Table 2, the improved soils of the Examples and Comparative Examples were assigned scores based on the following evaluation criteria for each of the evaluation items: (A) neutrality, (B) appearance, (C) self-hardening, (D) amount added, and (E) re-mudiness. The improved soils with a total score of 40 or more were evaluated as good. (A) Neutral pH fluctuation range is ±0.5 or less: 10 points pH fluctuation range: more than ±0.5, less than ±1.0: 5 points pH fluctuation range exceeds ±1.0: 0 points (B) Appearance - The soil particles are fine and crumbly: 10 points The soil has a variety of particle sizes, but is loose: 5 points -Soil particles are large and sticky: 0 points (C) Self-hardening Cone index after 48 hours is 400kN / m 2The final value is 800kN / m 2 Reached: 10 points Cone index after 48 hours is 400kN / m 2 Above: 5 points Cone index after 48 hours is 400kN / m 2 Less than: 0 points (D) Addition amount -Soil conditioner dosage: 50kg / m 3 Below: 10 points -Soil conditioner dosage: 50kg / m 3 Super, 100kg / m 3 Below: 5 points -Soil conditioner dosage of 100 kg / m 3 Super :0 points (E) Re-silting Turbidity 35 or less: 10 points Turbidity over 35 and up to 50: 5 points Turbidity over 50: 0 points

[0069] [Table 2]

[0070] In Tests 1 to 10, when the polymer flocculant content was fixed at 10% by mass, the soil conditioners of Examples 1 to 6 (Tests 4 to 9), which had magnesium oxide contents of 10 to 40% by mass, sodium bicarbonate contents of 5 to 10% by mass, and obsidian perlite contents of 40 to 75% by mass, received a total evaluation score of 40 points or more, and were evaluated as good improved soil. In particular, the soil conditioner of Example 4 received a total evaluation score of 50 points, the full score, and was evaluated as very good improved soil. In contrast, the soil conditioners of Comparative Examples 1 to 3 (Tests 1 to 3), which had magnesium oxide contents of 5% by mass or less, and the soil conditioner of Comparative Example 4 (Test 10), which had magnesium oxide contents of 50% by mass or more, received a total evaluation score of 30 points or less, and the improved soil obtained was not evaluated as good.

[0071] From Tests No. 11 to 15, the soil conditioners of Comparative Examples 5 and 6 (Tests No. 11 and 12), which used water-absorbent polymers instead of polymer flocculants, and the soil conditioners of Comparative Examples 7 to 9 (Tests No. 13 to 15), which used inorganic agents other than magnesium oxide, received a total evaluation score of 35 points or less, and the resulting improved soils were not rated as good.

[0072] The soil conditioner of Example 7 (Test No. 16), which used potassium bicarbonate as a pH buffer, received a total evaluation score of 50 points, the full score, just like the soil conditioner of Example 4 (Test No. 7), which used sodium bicarbonate as a pH buffer, and the resulting improved soil was evaluated as very good.

[0073] From Tests Nos. 17 to 19, the soil conditioner of Comparative Example 10 (Test No. 17), which used aluminum sulfate as a pH buffer with a buffer range of less than pH 7, the soil conditioner of Comparative Example 11 (Test No. 18), which used sodium tripolyphosphate, which is not a pH buffer, and the soil conditioner of Comparative Example 12 (Test No. 19), which used perlite as the porous ore with a bulk specific gravity of less than 0.7, received a total evaluation score of 35 points or less, and the resulting improved soils were not rated as good.

[0074] The soil conditioner of Example 8 (Test No. 20), which used zeolite as the porous ore, was slightly inferior to the soil conditioner of Example 4 (Test No. 7), which used obsidian perlite as the porous ore, but the total evaluation score was 40 points, and the resulting improved soil was evaluated as good.

[0075] In Tests Nos. 7 and 21 to 25, the soil conditioners of Examples 4 and 9 to 11 (Tests Nos. 7 and 22 to 24), which contained 5 to 15% by mass of polymer flocculant, received a total evaluation score of 40 or more, and were evaluated as having good improved soil. In contrast, the soil conditioner of Comparative Example 13 (Test No. 21), which contained 2.5% by mass of polymer flocculant, and the soil conditioner of Comparative Example 14 (Test No. 25), which contained 20% by mass of polymer flocculant, received a total evaluation score of 30 or less, and the improved soil obtained was not evaluated as having good improved soil.

[0076] The soil conditioners of Examples 1 to 11 (Test Nos. 4 to 9, 16, 20, 22 to 24) that were evaluated as good in the above tests were based on porous ore with a bulk density of 0.7 or more, and when the content of (a) polymer flocculant is a mass%, the content of (b) magnesium oxide is b mass%, and the content of (c) pH buffer is c mass%, the relationship of the contents of components (a) to (c) satisfies a≦b, b≧c, a≧c, and the total content of components (a) to (c) [a+b+c] is 25 to 60 mass%. [Industrial Applicability]

[0077] The soil conditioner and soil improvement method of the present invention can be used to improve soft soil (wet soil) containing a large amount of water, which is generated during dredging work or the like.

Claims

1. A soil conditioner based on porous ore with a bulk density of 0.7 or more, which improves the quality of water-containing soil to a soil of at least Class 3 improved soil as specified by the Ministry of Land, Infrastructure, Transport and Tourism, and prevents a significant change in the pH of the improved soil, and contains the following components (contents in parentheses): (a) Polymer flocculant [a mass %] (b) Magnesium oxide [b mass %] (c) pH buffer having a buffer range of pH 7 or higher [c mass %] Including, The porous ore is obsidian perlite and / or zeolite, The relationship between the contents of each component satisfies a≦b, b≧c, a≧c, and the total content [a+b+c] of the components (a) to (c) is 25 to 60% by mass. A soil conditioner.

2. The soil conditioner according to claim 1, wherein the content [a mass%] of the polymer flocculant is 5 to 15 mass%.

3. The soil conditioner according to claim 1, wherein the content [b mass %] of the magnesium oxide is 10 to 40 mass %.

4. The soil improver according to claim 1, wherein the content [c% by mass] of the pH buffer agent is 5 to 10% by mass.

5. The soil conditioner according to claim 1, wherein the pH buffer is sodium bicarbonate and / or potassium bicarbonate.

6. A soil improvement method for improving the quality of wet soil, comprising: The method includes adding the soil improver according to any one of claims 1 to 5 to the water-containing soil, The water-containing soil to which the soil conditioner was added had a cone index of 400 kN / m after 48 hours in a cone index test according to JIS A 1228. ２ This is the soil improvement method.

7. In the addition step, the amount of the soil improver added to the water-containing soil is 10 to 40 kg / m ３ The soil improving method according to claim 6, wherein the above formula is set to

8. 7. The soil improvement method according to claim 6, wherein the pH of the moist soil to which the soil improver has been added fluctuates within a range of ±1.0 or less after 48 hours compared to the pH of the moist soil before the addition of the soil improver.

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