Ground injection method and ground injection material used therein

Abstract

The present invention provides a new ground injection method and a ground injection material for utilizing silica material derived from geothermal water for ground improvement without causing soil contamination. [Solution] This is a ground grouting method that uses silica grout derived from geothermal water to produce sand gels and / or homogels with heavy metal contents below environmental standards for soil contamination and / or uniform wastewater standards. Silica grout with a target silica concentration is prepared using silica materials, which is then used to prepare solidified soil specimens. If the heavy metal concentrations in the test solution of the solidified soil measured in a test specified in the "Environmental Standards for Soil Contamination" are below the standard values, the silica grout is used as is; or, if the heavy metal concentrations exceed both the standard values, the silica concentration is reduced by reducing the amount of silica materials so that the heavy metal concentrations are below the standard values. Then, silica colloid obtained by the ion exchange method or the metallic silica method is added to the resulting mixture to adjust the silica concentration to the target value.

Description

[Technical Field]

[0001] The present invention relates to a ground grouting method using silica derived from geothermal water and a ground grouting material used therein. [Background technology]

[0002] Because silica materials derived from geothermal water are naturally occurring, they are preferable from the perspective of reducing CO2 emissions compared to silica materials obtained using conventional ion exchange or metal silica methods. However, because silica materials derived from geothermal water contain heavy metals at levels exceeding environmental standards, they can cause soil contamination when used to improve ground, which is problematic from an environmental perspective.

[0003] In response to this, the present applicant has proposed in Patent Documents 1 and 2 a technique for using silica materials derived from geothermal water for ground improvement without causing soil contamination. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6796305 [Patent Document 2] Patent No. 7072818 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a new ground grouting method for utilizing silica material derived from geothermal water for ground improvement without causing soil contamination, and a ground grouting material to be used therefor. [Means for solving the problem]

[0006] The inventors have discovered that by using the heavy metal concentration in the solidified body formed by silica grout using geothermal water or silica material derived from geothermal water as the standard, rather than the heavy metal content in geothermal water or silica material derived from geothermal water as has been studied in the past, it is possible to confirm the state of soil contamination in a more realistic manner, and have discovered that it is possible to carry out ground improvement using silica material derived from geothermal water while more reliably preventing the occurrence of soil contamination, which has led to the completion of the present invention.

[0007] That is, in the ground injection method of the present invention, when injecting silica grout containing a silica material obtained by collecting silica in geothermal water into the ground, In the ground grouting method, the content of heavy metals contained in the sand gel and / or homogel made from the silica grout is below the environmental standard value for soil contamination and / or below the uniform wastewater standard value, A silica grout having a desired silica concentration is prepared using the silica material, and a test specimen of solidified soil is prepared using the silica grout having the desired silica concentration. The test specimen is then subjected to a test specified in the Ministry of the Environment Notification No. 46 "Environmental Standards for Soil Contamination" to measure the heavy metal concentration in the test solution of the solidified soil. i) If the obtained heavy metal concentration is below the environmental standard value for soil contamination and / or below the uniform wastewater standard value, the silica grout having the desired silica concentration is used as is; ii) If the obtained heavy metal concentration exceeds both the environmental standard value for soil contamination and the uniform effluent standard value, the amount of the silica material is reduced to prepare a silica grout with a low silica concentration so that the heavy metal concentration is not more than the environmental standard value for soil contamination and / or the uniform effluent standard value, and then a silica colloid obtained by an ion exchange method or a metal silica method is added to the low silica grout to adjust the low silica concentration to the desired silica concentration before use.

[0008] In the ground grouting method of the present invention, the heavy metals may be second-class specified hazardous substances, particularly chromium and arsenic.

[0009] In the ground injection method of the present invention, the following procedure iii) can be carried out instead of the above procedure ii). iii) If the obtained heavy metal concentration exceeds both the environmental standard value for soil contamination and the uniform wastewater standard value, the content of heavy metals in the silica grout having the desired silica concentration is reduced using an insolubilizing material so that the heavy metal concentration is not more than the environmental standard value for soil contamination and / or the uniform wastewater standard value.

[0010] In the ground grouting method of the present invention, it is preferable to prepare the consolidated soil using Toyoura sand, and in particular, the consolidated soil can be prepared using Toyoura sand at a relative density of 60%.

[0011] The ground grouting material of the present invention is a ground grouting material used in the above-mentioned ground grouting method, The heavy metal concentration is below the environmental standard value for soil contamination and / or the uniform wastewater standard value, and the grout is made of silica having the desired silica concentration. The grout is characterized by containing, together with the silica material, one or more selected from the group consisting of water glass, acid, salt and alkali, and being non-alkaline.

[0012] The ground grouting material of the present invention may have a silica concentration of 0.4 to 50.0 w / vol % and a pH in the range of 1.5 to 10.0.

[0013] In addition, another ground injection method of the present invention includes injecting silica grout containing a silica material obtained by collecting silica in geothermal water into the ground, measuring the heavy metal content in the silica material, and estimating the heavy metal content in the sand gel and / or homogel produced by the silica grout based on the measured heavy metal content in the silica material; The silica grout is injected into the ground so that the estimated content of heavy metals is below the environmental standard value for soil contamination and / or the uniform wastewater standard value. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a new ground grouting method and a ground grouting material to be used therefor, which can utilize silica material derived from geothermal water for ground improvement without causing soil contamination. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a graph showing the uniaxial compressive strength of the sand gel in Example 1. [Figure 2] 1 is a graph showing the uniaxial compressive strength of the homogel in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0017] [Ground injection method] In the ground injection method of the present invention, when silica grout containing silica material obtained by collecting silica from geothermal water is injected into the ground, the heavy metal content of the sand gel and / or homogel produced from the silica grout is set to be below the environmental standard value for soil contamination and / or below the uniform wastewater standard value.

[0018] In this invention, silica grout with the desired silica concentration is prepared using silica material obtained by collecting silica from geothermal water, and then a specimen of consolidated soil is prepared using the silica grout with the desired silica concentration. This specimen of consolidated soil is subjected to the test specified in the Ministry of the Environment Notification No. 46, "Environmental Standards for Soil Contamination," to obtain the measured value of the heavy metal concentration in the test solution of the consolidated soil.

[0019] Next, it is confirmed whether the heavy metal concentration in the above-mentioned consolidated soil is i) below the environmental standard value for soil contamination and / or below the uniform wastewater standard value, or ii) above both the environmental standard value for soil contamination and the uniform wastewater standard value.

[0020] If the heavy metal concentration in the above-mentioned consolidated soil is i) below the environmental standard value for soil contamination and / or below the uniform wastewater standard value, the ground can be improved without causing soil contamination, so silica grout with the desired silica concentration is used as is to be injected into the ground.

[0021] On the other hand, if the heavy metal concentration in the consolidated soil exceeds both the environmental standard value for soil contamination and the uniform wastewater standard value, ii) the amount of silica material derived from the geothermal water is reduced to prepare a silica grout with a low silica concentration so that the heavy metal concentration is equal to or less than the environmental standard value for soil contamination and / or the uniform wastewater standard value, thereby improving the ground without causing soil contamination.

[0022] However, since the desired strength cannot be achieved in this state, heavy metal-free silica colloid obtained by the ion exchange method or the metal silica method is added to this low-silica concentration silica grout to adjust the silica concentration to the desired level, and then the grout is injected into the ground. This allows ground improvement to be achieved with the desired strength while using silica material derived from geothermal water and without causing soil contamination.

[0023] In prior art, soil contamination caused by silica grout was prevented by reducing the heavy metal content of the silica-containing geothermal water itself or by reducing the heavy metal content of silica material derived from geothermal water. However, in the present invention, the heavy metal concentration in solidified soil solidified with silica grout using silica material derived from geothermal water is suppressed to below a specified standard value, making it possible to establish a more practical soil contamination prevention technology.

[0024] In the present invention, the following procedure iii) can also be carried out instead of the above procedure ii). That is, when the heavy metal concentration in the solidified soil exceeds both the environmental standard value for soil contamination and the uniform wastewater standard value, iii) the heavy metals in the silica grout having the desired silica concentration may be insolubilized with an insolubilizing material to reduce the heavy metal concentration so that the heavy metal concentration is equal to or less than the environmental standard value for soil contamination and / or the uniform wastewater standard value. This also makes it possible to use a silica material derived from geothermal water and achieve the desired strength without causing soil contamination.

[0025] In the present invention, the heavy metal specifically refers to a type 2 specified hazardous substance. The environmental standards for soil contamination list 26 specified hazardous substances, of which 9 are type 2 specified hazardous substances (heavy metals, etc.). Specific examples of heavy metals include chromium, arsenic, lead, fluorine, boron, mercury, cadmium, selenium, and chromium, with chromium and arsenic being representative.

[0026] In the present invention, the sand used to prepare the above-mentioned consolidated soil is not particularly limited, but it is preferable to use Toyoura sand. For example, the above-mentioned consolidated soil can be prepared using Toyoura sand at a relative density of 60%.

[0027] In the present invention, the insolubilizing material used for insolubilizing heavy metals is not particularly limited, and commercially available products can be used.

[0028] [Ground injection material] The grout of the present invention is a grout for use in the above-mentioned grouting method, and is composed of silica grout having a heavy metal concentration below the environmental standard value for soil contamination and / or below the uniform wastewater standard value, and having the desired silica concentration. The grout of the present invention contains the above-mentioned silica material derived from geothermal water, as well as one or more selected from the group consisting of water glass, acid, salt, and alkali, and is non-alkaline. Here, "non-alkaline" means a pH in the range of 1.5 to 10.0.

[0029] Examples of acids that can be used include inorganic acids such as sulfuric acid, phosphoric acid, nitric acid, hydrochloric acid, and sulfamic acid, as well as mixed acids thereof. A wide variety of other mineral acids, such as citric acid, glycolic acid, malic acid, and tartaric acid, and other organic acids can also be used, but at least one of sulfuric acid, phosphoric acid, and organic acids is preferred.

[0030] Examples of salts that can be used include inorganic salts of polyvalent metals such as sodium chloride, calcium chloride, magnesium chloride, iron chloride, aluminum chloride, sodium hydrogen carbonate, aluminum sulfate, magnesium sulfate, aluminum nitrate, and aluminum phosphate.

[0031] Examples of alkalis include slaked lime, magnesium hydroxide, magnesium carbonate, and caustic alkali.

[0032] The ground grouting material of the present invention may further contain a polyvalent metal compound. Preferably, the ground grouting material of the present invention has a silica concentration of 0.4 to 50.0 w / vol% and a pH in the range of 1.5 to 10.0.

[0033] In addition, in the present invention, the content of heavy metals in the silica material derived from the geothermal water may be reduced using an insolubilizing material, thereby reducing the content of heavy metals in the silica grout to below the environmental standard value and / or the uniform wastewater standard value, and further, the ground injection material of the present invention may be used in combination with an insolubilizing material.

[0034] Another ground injection method of the present invention involves injecting into the ground a silica grout containing a silica material obtained by collecting silica from geothermal water, measuring the heavy metal content of the silica material, estimating the heavy metal content of the sand gel and / or homogel produced from the silica grout based on the measured heavy metal content of the silica material, and injecting into the ground a silica grout whose estimated heavy metal content is below the environmental standard value for soil contamination and / or the uniform wastewater standard value. This allows for a simpler method of improving the ground to the desired strength while using silica material derived from geothermal water and without causing soil contamination.

[0035] [experiment] (Strength test) Geothermal water-derived colloids are considered highly useful in terms of preventing global warming by reducing CO2 emissions, but because they are naturally derived, they contain heavy metals. Therefore, in this study, we used a commercially available geothermal water-derived colloid, GEO40 SOL-1030Na (GEO40 Co., Ltd.) (hereafter referred to as "1030Na"), to prepare a solution with a silica concentration of 12 w / v% (hereafter, silica grout containing silica derived from geothermal water is referred to as "geothermal silica." Note that "geothermal silica" is a registered trademark (1,16,37) of Kyotei Do Engineering Co., Ltd., registration number 6611742). Homogel and sand gel specimens were prepared using Toyoura sand by a mixing method. These specimens were analyzed and tested in accordance with the Environmental Agency's Notification No. 46, "Environmental Standards for Soil Contamination." Table 1 shows the formulation.

[0036] (Materials used) Geothermal water-derived silica colloid 1030Na (GEO40 SOL-1030Na, manufactured by GEO40): specific gravity 1.21, silica concentration 30 w / w% Colloidal silica (1): specific gravity 1.21, silica concentration 30 w / w% No. 5 water glass: specific gravity 1.32, silica concentration 25.5 w / w% ·Sulfuric acid: Specific gravity 1.674, 75w / w% concentration Hardener: specific gravity 2, chloride

[0037] [Table 1]

[0038] In Example 1, the proportion of silica colloid 1030Na derived from geothermal water in the chemical solution was 4.7%, and in the comparative example, the proportion of silica colloid not derived from geothermal water in the chemical solution was also 4.7%.

[0039] (Test method and test results) (Preparation of specimen) Sand gel specimens using Toyoura sand and geothermal silica as a chemical solution containing 1030Na were prepared using the formulation shown in Table 1, with a silica concentration of 12 w / v%, a relative density of 60%, a diameter of 50 mm, and a height of 100 mm. Table 1 also shows the unconfined compressive strength after 28 days. Example 1 showed slightly higher results than the comparative example.

[0040] As in Example 2, 1030Na can be used to reduce the silica concentration and keep the heavy metals within the standard value. In this case, the sand gel strength after 28 days is 0.2 MN / m 2 has been obtained.

[0041] Even in the case of a formulation with a high silica concentration, as in Example 5, even when the amount of 1030Na reduced from the formulation of Example 4 was replaced with colloidal silica (1), the strength of the sand gel and homogel was equivalent.

[0042] (Test method and results of analysis of liquid samples from sand gel specimens) Analysis of heavy metal concentrations in the test solution of sand gel specimens using Toyoura sand, a geothermal silica, as a chemical solution using 1030Na was carried out using the methods specified in the appendix and attached tables of the Environment Agency's Notification No. 46, "Environmental Standards for Soil Contamination." Table 2 shows the measurement results along with the geothermal water-derived colloid (GEO40 SOL-1030Na). Table 2 lists only Type 2 specified hazardous substances (heavy metals, etc.).

[0043] The specific test method is as follows: First, the sand gel specimen is air-dried at a temperature not exceeding 30°C, and then the sample and solvent (water) are mixed at a ratio of approximately 10% by weight and volume, and shaken for 6 hours to allow elution. Next, after centrifuging the mixture, the supernatant is used for testing.

[0044] The heavy metal content of the geothermal water-derived colloid (1030Na) is defined as A (mg / L), and the heavy metal content of the test solution from the Toyoura sand gel specimen treated with the agent shown in Example 1 of Table 1 (geothermal silica: 12 w / v% solution of 1030Na) is defined as B (mg / L). The value of α = B / A, where B = αA, is also shown in Table 2. The standard value in Environment Agency Notification No. 46 is defined as D (mg / L).

[0045] (Test method and results of liquid analysis from homogel specimen) The analysis of heavy metal concentrations in the test solution of homogel specimens of geothermal silica using 1030Na as a chemical solution was carried out according to the method specified in the appendix and attached table of the Ministry of the Environment Notification No. 46 "Environmental Standards for Soil Contamination."

[0046] [Table 2]

[0047] 1030Na is the measurement result of geothermal water-derived colloid (GEO40 SOL-1030Na) obtained from Geo40, but testing is not conducted for each lot, and the most recent test results by Geo40 are listed.

[0048] In the case of 1030Na only, arsenic, lead, fluorine, boron, and total mercury exceed the standard values ​​(however, the measurement value listed as "less than" is presumably the lower measurement limit of Geo40).

[0049] On the other hand, for the sand gel specimens using Toyoura sand and geothermal silica (silica concentration 12 w / v%) as a chemical solution using 1030Na, it was found that all items were below the "standard value" (all 26 items other than the 9 items were below the standard value). Note that the "lower limit of quantification" in the table indicates the lower limit of reliable measurement.

[0050] In other words, it can be seen that the content of Type 2 specified hazardous substances (heavy metals, etc.) was significantly reduced in the geothermal silica sand gel specimens prepared as a chemical solution using 1030Na. Since 1030Na accounts for 4.7% of the solution in geothermal silica as a chemical solution, this dilution rate is thought to be a major factor. If the heavy metal concentration in the chemical solution exceeds the standard value, the formulation can be changed to bring the heavy metal concentration within the standard value by reducing the proportion of 1030Na. Furthermore, colloidal silica produced by ion exchange or water glass can be added to make up for the amount of 1030Na reduced.

[0051] In addition, from the results in the table, the range of α for each heavy metal was determined so that α (= B / A) ≦ D / A when the content of geothermal water-derived colloid 1030Na in the geothermal silica chemical solution was 12%.

[0052] Table 2 shows that the heavy metal content of geothermal water-derived colloids is significantly reduced in the test solution of Toyoura sand gel specimens solidified with chemical solutions. The maximum heavy metal content in the test solution of Toyoura sand gel specimens solidified with geothermal water-derived colloids is chromium, and the chromium (or selenium) content is found to be less than one-fifth of that. Therefore, if one-fifth of the chromium content of the heavy metals in geothermal water is below the environmental standard value, the contents of the other heavy metals will also be below the environmental standard value. In other words, if one-fifth of the chromium content exceeds the standard value, the proportion of geothermal water-derived colloids in the chemical solution should be set low.

[0053] Furthermore, in the above test, the heavy metal content in the test solution of Toyoura sand sand gel specimens was measured using a chemical solution, but if the on-site soil contains clay, heavy metals are more likely to be adsorbed, and it is thought that the amount of heavy metals detected will be lower than in the case of Toyoura sand.Chemical grouting is mainly applied to sandy ground, and Toyoura sand has a low ion adsorption rate, so there is thought to be no problem if the amount of heavy metals detected in the test solution of Toyoura sand sand gel specimens is below the standard value.

[0054] From the above, if the heavy metal content of the geothermal water-derived colloid to be blended is known, it becomes possible to formulate a chemical solution whose heavy metal content is below environmental standards and / or uniform wastewater standards, without measuring the heavy metal content in the test solution of the chemical solution.

[0055] The present invention is a further development of the invention of the applicant's prior patent, Japanese Patent No. 6796305. While the heavy metal content of 1030Na as a geothermal water-derived silica colloid exceeds environmental standards and uniform wastewater standards when used as is, the present invention makes it possible to produce a chemical solution that satisfies the conditions of being below environmental standards and / or uniform wastewater standards. In particular, as mentioned above, the measured strengths of the homogel and sandgel after 7 days and 28 days have been found to be nearly the same as those of silica colloids prepared using the ion exchange method.

Claims

1. When injecting silica grout containing silica material obtained by collecting silica in geothermal water into the ground, In the ground grouting method, the content of heavy metals contained in the sand gel made from the silica grout is equal to or less than the environmental standard value for soil contamination and / or the uniform wastewater standard value, A silica grout having a desired silica concentration is prepared using the silica material, and a sand gel specimen is prepared by solidifying Toyoura sand using the silica grout having the desired silica concentration. The test specified in the Ministry of the Environment Notification No. 46 "Environmental Standards for Soil Contamination" is conducted to measure the heavy metal concentration in the test solution of the sand gel specimen. i) If the obtained heavy metal concentration is equal to or less than the environmental standard value for soil contamination and / or the uniform wastewater standard value, the silica grout having the desired silica concentration is used as is; ii) If the obtained heavy metal concentration exceeds both the environmental standard value for soil contamination and the uniform effluent standard value, a ground injection method characterized by: reducing the amount of silica material to prepare silica grout with a low silica concentration so that the heavy metal concentration is not more than the environmental standard value for soil contamination and / or the uniform effluent standard value; and then adding silica colloid obtained by an ion exchange method or a metal silica method to the low silica grout to adjust the low silica concentration silica grout to the desired silica concentration before use.

2. 2. The ground injection method according to claim 1, wherein the heavy metal is a type 2 specified hazardous substance.

3. 3. The ground grouting method according to claim 2, wherein the heavy metals are chromium and arsenic.

4. 2. The ground grouting method according to claim 1, wherein the following procedure iii) is carried out instead of the procedure ii). iii) If the obtained heavy metal concentration exceeds both the environmental standard value for soil contamination and the uniform wastewater standard value, the content of heavy metals in the silica grout having the desired silica concentration is reduced using an insolubilizing material so that the heavy metal concentration is not more than the environmental standard value for soil contamination and / or the uniform wastewater standard value.

5. 2. The ground grouting method according to claim 1, wherein the sand gel specimen is made of Toyoura sand with a relative density of 60%.

6. A ground injection material used in the ground injection method according to any one of claims 1 to 5, A ground grout comprising silica grout having a target silica concentration, the heavy metal concentration of which is below the environmental standard value for soil contamination and / or below the uniform wastewater standard value, and the ground grout containing, together with the silica material, one or more selected from the group consisting of water glass, acid, salt and alkali, and being non-alkaline.

7. 7. The grouting material according to claim 6, wherein the silica concentration is 0.4 to 50.0 w / vol % and the pH is in the range of 1.5 to 10.

0.

8. When injecting silica grout containing silica material obtained by collecting silica in geothermal water into the ground, measuring the heavy metal content in the silica material, and estimating the heavy metal content in the sand gel and / or homogel produced by the silica grout based on the measured heavy metal content in the silica material; A ground injection method, characterized by injecting the silica grout into the ground, such that the estimated content of heavy metals is below the environmental standard value for soil contamination and / or below the uniform wastewater standard value.

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