JP6331514B2 - Slightly acidic solidification method for soil - Google Patents

Description

  The present invention relates to a stabilization technique by solidifying soft mud such as dredged soil and construction sludge. More specifically, the present invention relates to a method for solidifying soft soil, in which the pH of the solidified soil is adjusted to weak acidity and solidified.

  In many cases, construction sludge generated by civil engineering, construction generated soil, dredged sand generated by dredging work at harbors, etc. is solidified using cement-based solidifying material and stabilized. In this case, the pH of the solidified soil exhibits a high alkalinity of about 11 to 12, and there is a concern about the influence on animals / plants, and the reuse as soil may be limited.

  For example, alkali measures may be required for direct planting on solidified soil and construction near living wells, farmland, lakes, and ponds. In addition, when the soil to be solidified contains an ammonium salt, ammonia gas may be generated from the solidified soil that has become alkaline. Further, when the soil to be solidified is strongly acidic, the alkali component of the cement is consumed by the neutralization reaction, and sufficient solidification strength may not be obtained.

In order to solve these problems, a so-called neutral solidified material is required in which the solidified soil is neutral (drainage standard: pH 5.8 to 8.6) or close to neutrality. Until now, neutral solidified materials mainly consisted of hemihydrate gypsum, and this type of solidified material often has insufficient solidification strength, and is too reactive to stiffen during construction. May occur, which may hinder construction. In addition to this, it has recently been required that no harmful substances such as hexavalent chromium be eluted.
As already mentioned, there are gypsum-based solidification materials of this type that contain hemihydrate gypsum as the main component, and there are several neutral solidification materials that use both cement and gypsum as components and try to take advantage of the advantages of both systems. Proposed. For example, Patent Document 1 and Patent Document 2 disclose a solidified material made of a mixed material such as hemihydrate gypsum, cement and lime, blast furnace slag, and Patent Document 3 discloses a solidified material made of gypsum, Portland cement and aluminum sulfate. Is disclosed.

  Patent Document 4 discloses a solidified material composed of anhydrous or hemihydrate gypsum, cement, and an inorganic salt having a sulfate group. Further, Patent Documents 5 and 6 disclose a solidified material made of hemihydrate gypsum, alumina cement, or a mixed cement of alumina cement and Portland cement, and aluminum sulfate or iron sulfate.

JP-A-8-302346 JP-A-8-311446 JP-A-6-220451 JP-A-7-179854 JP-A-10-273660 Japanese Patent Laid-Open No. 10-273663

  However, in the above-described solidification method using a solidification material mainly composed of cement and hemihydrate gypsum, the strength of the solidified soil is relatively low, and because of its rapid hardness, the curing reaction proceeds during the mixing with the soil. The workability may be a problem.

  Therefore, the present invention shows that, in the method of solidifying soft soil, improved soil with high strength can be obtained, as well as excellent workability when cured at an appropriate time, and the solidified soil is neutral. An object of the present invention is to provide a solidification processing method that has a low environmental impact.

  As a result of intensive studies on the above problems, the present inventors have found that a solidification method in which aluminum sulfate and alumina cement are mixed at an appropriate ratio under a condition where the pH of the solidified soil is weakly acidic is a conventional half-water treatment. It has been found that a very high solidification strength can be obtained as compared with a gypsum-based neutral solidification material, and the present invention has been completed.

  That is, the present invention mixes a sample soil obtained by sampling a part of the soil to be solidified with a solidified material containing alumina cement and aluminum sulfate, and has a pH of more than 4.0 and not more than 6.0. A mixing ratio determining step for determining a mixing ratio of the solidification material with respect to the solidification target soil so as to obtain a predetermined strength, and a solidification process in which the solidification target soil and the solidification material are mixed at the mixing ratio. And a weakly acidic solidification treatment method for soil including the process. According to this treatment method, since the pH value of the solidified soil is a weakly acidic region, it is environmentally friendly, and it is possible to perform a solidified treatment with a wide range of applications and insolubilization of fluorine-contaminated soil. .

  The present invention also relates to a weakly acidic solidification treatment method for soil, wherein the pH is 5.0 to 6.0. By setting the pH within this range, sufficient effects can be obtained both in terms of strength and fluorine elution suppression.

  The present invention also relates to a weakly acidic solidification method for soil, wherein the solidifying material contains 30 to 80% by mass of alumina cement and 20 to 70% by mass of anhydrous aluminum sulfate. By using these materials for the solidifying material, it is possible to perform a solidification treatment that is more environmentally friendly and has a wide range of applications, and insolubilization of fluorine-contaminated soil.

  The present invention also relates to a weakly acidic solidification method for soil, wherein the alumina cement has an alumina content of 50 to 70% by mass. By setting the alumina content of the alumina cement within the above range, high solidification strength can be obtained.

According to the present invention, since the pH value of the solidified soil is in a weakly acidic region, it is environmentally friendly, and the fourth type improvement with a corn index of 200 kN / m ² or more, which is specified in the Construction Soil Utilization Technical Manual. The soil can be improved to a third type improved soil having a corn index of 400 kN / m ² or more and further to a second type improved soil having a corn index of 800 kN / m ² or more. Fluorine contaminated soil can be insolubilized.

It is the figure which showed the relationship between the pH of the solidified soil which solidified clay, and the corn index. It is the figure which showed the relationship between the pH of the solidified soil which solidified silt, and the corn index. It is the figure which showed the relationship between the pH of the solidification processing soil which solidified the fluorine simulation contaminated soil, and a fluorine elution amount.

Hereinafter, preferred embodiments of the present invention will be described below.
In the method for weakly acidifying and solidifying soil according to the present invention, a sample soil obtained by sampling a part of the soil to be solidified and a solidified material containing alumina cement and aluminum sulfate are mixed, and the pH exceeds 4.0. A mixing ratio determining step of determining a mixing ratio of the solidified material to the solidification target soil so that a predetermined strength is obtained under a condition of 0 or less;

  The pH of the solidified soil is more than 4.0 and preferably 6.0 or less, more preferably 4.5 to 6.0, and still more preferably 5.0 to 6.0. Within these ranges, a predetermined strength can be obtained. If the pH of the solidified soil is 5.0 to 6.0 and the soil to be solidified is fluorine-contaminated soil, the amount of fluorine elution from the solidified soil is below the soil environmental standard (0.8 mg / L or less) It is also possible. If the pH is 5.2 to 5.8, a sufficient effect is obtained in terms of strength with respect to a plurality of types of treated soil, and a sufficient effect is also obtained in terms of suppressing fluorine elution.

The soil to be solidified includes clay, silt, organic soil, volcanic ash clay, etc. as fine-grained soil, and sandy soil, etc. as coarse-grained soil. In the case of fine-grained soil, the water content is preferably 20 to 100%, more preferably 25 to 80%, still more preferably 30 to 70%.
In the case of coarse-grained soil, 5 to 40% is preferable, more preferably 8 to 30%, and still more preferably 10 to 25%. Here, the water content means a value expressed as a mass percentage of the ratio of the mass of soil water lost by oven drying at 110 ± 5 ° C. to the oven drying mass of the soil. Within these ranges, a predetermined strength can be obtained.

Predetermined strength as described above is preferably 600~4000kN / ^{m 2} in cone index at the age of 7 days, more preferably 650~3000kN / ^{m 2,} more preferably from 680~2500kN / ^{m 2.} If it is these strengths, it is prescribed in the construction generated soil use technical manual, and the required strength for reusing the solidified soil (cone index of 200 days of age 7 (type 4 improved soil) kN / m ^{2 to} 800 (Type 2 improved soil) kN / m ² or more).

  There are several types of alumina cement, such as for fire resistance and for building materials, all of which can be used by blending adjustment. However, it is necessary to use an alumina content of 50 to 70% by mass in terms of workability and solidification strength. More preferably, it is 51-60 mass%, More preferably, it is 52-55 mass%.

  When the alumina content is less than 50% by mass, the amount of solidified material required to obtain the same strength increases. Moreover, when there is more alumina content than 70 mass%, processing cost may become high significantly. Alumina cement not only acts as a neutralizing agent for aluminum sulfate, but also produces various hydrates by reaction with aluminum sulfate and solidifies firmly.

  In addition to anhydrous products, aluminum sulfate includes powdered products of hydrated crystal 18 hydrate with a small amount of alumina and aqueous solutions containing 8% alumina. Anhydrous is a preferred material because it is powdery and provides high strength. Other grades can also be used, but all of them require a greater amount to obtain the same strength compared to anhydrous salts.

  The solidifying material is 30-80% by mass of alumina cement, preferably 35-60% by mass, more preferably 40-50% by mass, and 20-70% by mass of anhydrous aluminum sulfate, preferably 40-65% by mass. Preferably it contains 50-60 mass%. Within these ranges, an appropriate strength can be obtained as described above, and the pH of the treated soil is also weakly acidic, so it is environmentally friendly.

Moreover, the weak acid solidification processing method of the soil of this invention includes the solidification process process which mixes the solidification process target soil and the solidification material in the ratio determined by the mixing ratio determination process.
The mixing ratio is preferably solidified material to solidify processed soil 1 m ³ is 50 to 200 kg / ^{m 3,} more preferably 70~150kg / ^{m 3,} more preferably from 90~100kg / ^{m 3.} If it is less than 50 kg / m ³ , the mixing with the soil cannot be made uniform, and if it is more than 200 kg / m ³ , the processing cost may be significantly increased. Within these ranges, an appropriate strength can be obtained as described above, and the pH of the treated soil is also weakly acidic, so it is environmentally friendly.

  When mixing the soil to be solidified and the solidified material, a general powder mixing device can be used without any problem. That is, in order to prepare an anhydrous aluminum sulfate and an alumina cement-based weakly acidic solidified material, both materials are general powders, so there is no need for special equipment and means, such as a high-speed mixer, a rocking mixer, etc. A powder mixing method using a normal powder mixing device can be applied. When mixing, it is preferable not to add extra water to the soil as much as possible. For this purpose, it is desirable to mix in a powder state. For mixing with soft soil, a plant mixing method or a normal method using a backhoe or a stabilizer can be applied.

  Hereinafter, the contents of the present invention will be specifically described with reference to examples. Note that the present invention is not limited to these examples.

(1) Preparation of solidified material Anhydrous aluminum sulfate (Daimei Chemical Co., Ltd.) and alumina cement (Asahi Glass Co., Ltd. No. 1) were used. Table 1 shows the chemical composition of anhydrous aluminum sulfate, and Table 2 shows the chemical composition of alumina cement. The pH of anhydrous aluminum sulfate is measured by JIS Z 8802: 2011 “pH measurement method”, the insoluble matter and iron are measured by the method shown in JIS K 1423-1970 “Aluminum sulfate”, and the chemical composition of the alumina cement is JIS R 5202. It was measured according to “Chemical Chemical Analysis Method”. A predetermined amount of these materials were weighed and manually mixed in an A4 size polyethylene bag for about 3 minutes to prepare a test solidified material. The compounding ratio of the solidifying material is shown in Tables 4-6.

(2) Preparation of sample soil Clay (water content 38.0%) and silt (water content 24.0%) collected at the construction site so that the water content is 70% for clay and 30% for silt. And sample soil was prepared by mixing at low speed for 3 minutes with a soil mixer. JIS A 1202: 2009 “Soil particle density test method”, JIS A 1204: 2009 “Soil particle size test method”, JIS A 1205: 2009 “Soil liquid limit / plastic limit test method” Measured according to The results are shown in Table 3.

(3) Preparation of simulated contaminated soil Next, in order to investigate the effect of suppressing elution of fluorine from the solidified soil, simulated contaminated soil to which fluorine was added in advance was prepared. The silt of (2) above was used as the simulated contaminated soil. First, silt having a water content of 24.0% was adjusted to a water content of 11.2% by natural drying. Thereafter, potassium fluoride dihydrate (manufactured by Wako Pure Chemical Industries, Ltd., reagent, Wako Grade 1) is added to the water necessary for a water content ratio of 30% to 1.35 g per kg of silt dry soil. The amount was dissolved. This aqueous solution was added to silt and kneaded at a low speed for 2.5 minutes with a soil mixer, and then the soil adhering to the container and paddle was scraped off and further kneaded at a low speed for 2.5 minutes to prepare a fluorine simulated contaminated soil. Then, it sealed in a 20 degreeC thermostatic chamber, and after 7-day curing, it used for experiment.

(4) Solidification treatment The solidification material prepared in (1) above was added to the sample soil prepared in (2) and (3) at 100 kg / m ^3, and then mixed for 3 minutes with a Hobart mixer. The mixed soil was filled in a φ10 × 12.5 cm mold by a tapping method, and hermetically sealed for 7 days in a constant temperature bath at 20 ° C.

(5) Cone index measurement The corn index at 7 days of age of the solidified soil obtained in the above (4) was measured in accordance with JIS A 1228: 2009 “Cone index test method for compacted soil”.

(6) pH measurement About the solidification processing soil before shaping | molding obtained by said (4), pH was measured according to Geotechnical Society standard JGS-0211-2009 "pH test method of soil suspension".

(7) Measurement of fluorine elution amount The simulated contaminated soil prepared in (3) above and the solidified soil obtained in (4) above were crushed at a material age of 7 days, spread on a bat and air-dried (temperature 20 ° C., 24 Time), the 2 mm sieve was passed through. Thereafter, the air-dried sample was put into pure water at a solid-liquid ratio of 1:10 and shaken for 6 hours. The liquid after shaking was filtered under reduced pressure using a 0.45 μm membrane filter, and the fluorine concentration of the obtained filtrate was measured according to JIS K 0102 “Industrial Wastewater Test Method”.

(8) Clay test results (Examples 2 to 4, Comparative Examples 1 to 6)
The test results when the clay is solidified are shown in Table 4, and the relationship between the pH of the solidified soil and the corn index is shown in Fig. 1 (Nos. 1 to 9). For comparison, the case of a conventional hemihydrate gypsum solidified material (No. 10) is also shown.
As shown in FIG. 1, by adjusting the pH to a weakly acidic region of more than 4.0 and not more than 6.0, the cone index increased rapidly, and Examples 2 to 4 (No. In 3 to 5), the solidified soil has a strength with a cone index of 600 kN / m ² or more. Among them, in Example 2 , it can be seen that a strength of a cone index of 1200 kN / m ² or more can be obtained.
In contrast, no. In the combination of 1, 6, and 7, the solidification strength is low (Comparative Examples 1 to 3). No. It can be seen that the strength of corn index 600 kN / m ² or more is obtained with the blending of 8 and 9, but the pH exceeds 11 and is strongly alkaline, which is not preferable in terms of environmental impact (Comparative Examples 4 and 5). .

  In addition, when compared with the conventional hemihydrate gypsum-based neutral solidified material (Comparative Example 6, No. 10), the solidified material related to the treatment method of the present invention has a high solidified strength by being weakly acidic. I understand.

(9) Silt test results (Examples 7 to 10, Comparative Examples 7 to 8)
Table 5 shows the test results when the silt was solidified, and Fig. 2 shows the relationship between the pH of the solidified soil and the corn index (Nos. 11 to 18).
As shown in FIG. 2, by adjusting the pH to a weakly acidic region exceeding 4.0 and not more than 6.0, the cone index increased rapidly, and Examples 7 to 10 (No. In 13 to 16), the solidified soil has a strength of a cone index of 1200 kN / m ² or more. Among them, in Examples 7 and 8, it can be seen that a strength of a cone index of 2500 kN / m ² or more can be obtained.
In contrast, no. In the composition of 17, the solidification strength is low (Comparative Example 7). No. It can be seen that the formulation of 18 is not preferable in view of environmental impact because the pH exceeds 11 and is strongly alkaline (Comparative Example 8).

  As described above, it can be seen that, even if the type of the sample soil is changed, the corn index is rapidly increased by adjusting the pH of the solidified soil to a weakly acidic region exceeding 4.0 and not more than 6.0.

(10) Test result of simulated contaminated soil (Example 11, Comparative Examples 9 to 10, Reference Example 1)
Table 6 shows the test results when the fluorine simulated contaminated soil was solidified, and Fig. 3 shows the relationship between the pH of the solidified soil and the fluorine elution amount (Nos. 19 to 21). For reference, the pH of the untreated soil and the fluorine elution amount are also shown.
As shown in FIG. 3, by adjusting the pH to a weakly acidic region of 5.0 to 6.0, the amount of fluorine elution from the solidified soil is drastically reduced compared to the untreated soil, and the scope of the present invention. In Example 11 (No. 20), the fluorine elution amount from the solidified soil is insolubilized to 0.8 mg / L or less of the soil environment standard.
In contrast, no. In the formulation of 19, the fluorine elution amount from the solidified soil is lower than that of the untreated soil, but exceeds the soil environmental standard (0.8 mg / L or less). (Comparative Example 9). No. In the formulation of No. 21, although the fluorine elution amount from the solidified soil was lower than that of the untreated soil, it exceeded the soil environmental standard (0.8 mg / L or less), and the pH reached nearly 11 and was strongly alkaline. Therefore, it can be seen that it is not preferable in view of the influence on the environment (Comparative Example 10).

  As described above, when the results of (8) to (10) are comprehensively evaluated, if the pH is 5.2 to 5.8, a sufficient effect in terms of strength can be obtained with respect to a plurality of types of treated soils such as clay and silt. Furthermore, a sufficient effect can be obtained in terms of suppressing fluorine elution.

Claims (6)

  The sample soil from which a part of the soil to be solidified is collected and the solidified material containing alumina cement and aluminum sulfate are mixed, and the pH is5.0-6.0A mixing ratio determining step for determining a mixing ratio of the solidified material with respect to the solidification target soil so that a predetermined strength is obtained in
  A solidification treatment step of mixing the solidification target soil and the solidification material at the mixing ratio. See
  The solidifying material is 30-80% by mass of alumina cement and 20% of anhydrous aluminum sulfate. Containing ~ 70% by mass,
  Fluorine elution amount from the solidification target soil is insolubilized to 0.8 mg / L or lessA method of weakly acidifying and solidifying soil. The alumina cement, alumina content is 50 to 70 wt%, weakly acidic solidification processing method according to claim 1 Symbol placing soil. The mixing ratio, the solidifying agent to the solidification target soil 1 m ³ is 50 to 200 kg / ^{m 3,} claim 1 or 2 Sat weakly acidic solidification method according. The method for weakly acidifying and solidifying soil according to any one of claims 1 to 3 , wherein the soil to be solidified is fine-grained soil and has a water content ratio of 20 to 100%. The fine soil, clay, silt, is at least one selected from the group consisting of organic soil and volcanic ash quality cohesive soil, weakly acidic solidification processing method according to claim 4 Symbol placing soil.
The method for weakly acidifying and solidifying soil according to any one of claims 1 to 5 , wherein the predetermined strength is 600 to 4000 kN / m ² in terms of a corn index of 7 days of age.

Images