Site Improvement Methods

Abstract

To provide a ground improvement method capable of suppressing the cost of using a solidifying material, and to provide a ground improvement method for not only volcanic ash soil but also organic soil and soil containing heavy metals.SOLUTION: A ground is mixed with a solidifying material containing cement and a water-soluble sulfur oxide salt. At this time, when a measured value of a content of alkali-soluble aluminum in the ground is equal to or less than a predetermined value, an aluminum compound is added to the solidifying material. Further, when a measured value of a content of soluble silicic acid in the ground is equal to or less than a predetermined value, a silicate compound is added to the solidifying material.SELECTED DRAWING: None

Description

[Technical field]

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

[0002] One method of improving ground is, for example, to mix the ground with a solidifying material containing cement or the like, thereby hardening the ground and improving its strength. However, with this method, poor solidification may occur when the ground is volcanic ash soil such as Kanto loam, or when the ground is soil containing organic matter or heavy metals. This poor solidification is thought to be caused by allophane, a type of amorphous inorganic component contained in volcanic ash soil, or by polysaccharide compounds such as lignin contained in organic matter-containing soil, or by Cu, Cr, Zn, etc. contained in heavy metal-containing soil. Volcanic ash soil contains allophane (Al 2 O 3 (1-2)SiO 2 nH 2 O), and the allophane adsorbs the calcium hydroxide that is produced during the hydration of the cement in the solidification material, inhibiting the hydration reaction of the cement and, as a result, inhibiting solidification.

[0003] As a method for solidifying ground where such poor solidification by cement occurs, a cement-based solidification material in which gypsum is added to cement is used, as shown in Patent Document 1. This cement-based solidification material solidifies the ground by generating ettringite, which is a highly hydrated composition, through a reaction between calcium derived from cement, sulfate ions derived from gypsum, and aluminum ions derived from cement and the ground. However, depending on the ground, the cement hardening inhibitor may not be an aluminum compound such as allophane, but may be heavy metals or organic matter, and sufficient strength may not be obtained even with the above-mentioned cement-based solidification material.

[0004] Also, a method has been proposed in which the mixing ratio of the ground and the solidification material is determined so that the strength of the improved soil is equal to or greater than a predetermined value based on the correlation between the amount of aluminum eluted from the ground and the strength of the improved soil containing the ground and the solidification material, and then the solidification material and ground are mixed (see Patent Document 2). However, this method increases or decreases the amount of solidification material mixed based on the correlation between the amount of aluminum and the improved soil strength that is prepared in advance, and there is a risk that the cost of using the solidification material will increase. In addition, this method assumes that the ground is volcanic ash soil, and does not assume that the ground is organic soil containing polysaccharide compounds such as lignin, or soil containing heavy metals including amphoteric metals such as lead, zinc, and chromium. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 7-149550 [Patent Document 2] Patent No. 6512472 Summary of the Invention [Problem to be solved by the invention]

[0006] The problem to be solved by the present invention is to provide a ground improvement method that can reduce the cost of using solidifying materials, and more preferably, to provide a ground improvement method that can be used for organic soil and soil containing heavy metals in addition to volcanic ash soil. [Means for solving the problem]

[0007] The conventional method described above is based on the premise that if the amount of allophane or eluted aluminum is known, the amount of solidifying material to be mixed can be set, and therefore the conclusion is that the amount of solidifying material should be increased or decreased. In contrast, the method of the present application does not have such a premise and was conceived with the objective of performing ground improvement in a favorable manner. In this respect, the conventional method and the method of the present application utilize the formation of ettringite from sulfate ions, aluminum ions, and calcium ions, and the mechanisms are similar, and it seems that it would be easy to conceive of the method once it is conceived. However, the conventional method is bound by the premise of determining the amount of solidifying material to be mixed, and the method of the present application could not be conceived. In addition, the conventional method uses gypsum, which is an insoluble sulfate, as a sulfate ion supply source, and uses sulfate ions that gradually dissolve in the reaction, so it is necessary to add an excess amount of sulfate, but the method of the present application uses a water-soluble sulfate, so the amount of sulfate ions required for the reaction is instantly supplied.

[0008] In addition, while alkali-soluble aluminum has the effect of inhibiting solidification, it also has the effect of promoting strength development (the formation of ettringite) due to sulfate ions. Therefore, it was conceived that by utilizing this effect, it would be possible to target organic soil and soil containing heavy metals. Based on the above background, the following means was conceived.

[0009] (Means described in claim 1) The ground is mixed with a solidification material containing cement and water-soluble sulfur oxide salts. In doing so , The content of alkali-soluble aluminum in the ground is measured, and if the measured value is below a predetermined value, an aluminum compound is added as an additive to the solidification material so that the measured value becomes equal to or greater than the predetermined value. , The content of soluble silicic acid in the ground is measured, and if the measured value is equal to or less than a predetermined value, a silicate compound is added as an additive to the solidification material so that the measured value becomes equal to or more than the predetermined value. A ground improvement method comprising the steps of:

[0010]

[0011]

[0012] (Claim 2 (Means described in The additive is an alkali-soluble aluminum silicate. Claim 1 The ground improvement method described in the above.

[0013] (Claim 3 (Means described in The additive is a dry clay containing allophane. Claim Claim 1 or claim 2 The ground improvement method described in the above. Effect of the Invention

[0014] According to the present invention, a ground improvement method is provided that can reduce the cost of using solidification materials. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Next, an embodiment of the present invention will be described. Note that the embodiment is an example of the present invention. The scope of the present invention is not limited to the scope of the embodiment.

[0016] In the soil improvement method of the present embodiment, soil and a solidification material are mixed. The solidification material contains at least cement and a water-soluble sulfur oxide salt.

[0017] In this embodiment, examples of ground to be treated include volcanic ash soils such as Kanto loam, Hachinohe loam, and Akaboku, organic soils containing polysaccharide compounds such as lignin, and soils contaminated with heavy metals including amphoteric metals such as lead, zinc, and chromium, and metals that inhibit cement hardening.

[0018] As mentioned above, volcanic ash soil contains allophane. The allophane content in Kanto loam, for example, is 10 to 80 mass %, and in most cases is 30 to 60 mass %.

[0019] On the other hand, in the case of organic soil or soil containing heavy metals, the allophane content may be low. In such a case, the above-mentioned effect of soluble aluminum in promoting the development of strength by sulfate ions may not be fully exerted. Therefore, in order not to limit the ground to be treated, it is preferable to measure the amount of alkali-soluble aluminum or soluble silicic acid in the ground as an additive to the solidification material, and if the measured value is below a predetermined value, to add an alkali-soluble aluminum compound or silicate compound, more preferably an alkali-soluble aluminum silicate or allophane-containing clay, so that the measured value becomes equal to or greater than the predetermined value.

[0020] The following method can be exemplified as a method for measuring alkali-soluble aluminum and soluble silicic acid. That is, first, the ground is dried. In addition, a 1N aqueous solution of sodium hydroxide is prepared. The aqueous solution of sodium hydroxide is added to the dried sample obtained as described above so that the mass volume ratio is 10%, and the mixture is stirred at room temperature for 2 hours. This stirring causes the alkali-soluble aluminum and soluble silicic acid to dissolve in the aqueous solution. The amount of the dissolved alkali-soluble aluminum and soluble silicic acid is measured using an inductively coupled plasma atomic emission spectrometer (ICP-AES). In this measurement using ICP-AES, an yttrium solution is added as an internal standard substance.

[0021] The predetermined value for the alkali-soluble aluminum is, for example, 0.1 to 10 mg / g, preferably 0.1 to 3 mg / g, more preferably 0.1 to 1 mg / g, as a content calculated from the amount of alkali elution. If the predetermined value is set to less than 0.1 mg / g, the strength development promoting effect of the alkali-soluble aluminum on sulfur oxide salts such as sodium sulfate may not be fully exerted. On the other hand, if the predetermined value is set to more than 10 mg / g, the solidification inhibition effect of the alkali-soluble aluminum may become significant.

[0022] The predetermined value for soluble silicic acid is, for example, 0.25 to 10 mg / g, preferably 0.5 to 8 mg / g, more preferably 0.8 to 5 mg / g, as a content calculated from the amount of alkali elution. If the predetermined value is set to less than 0.25 mg / g, the strength development promoting effect of sulfur oxide salts such as aluminum calcium sulfate by soluble silicic acid may not be fully exerted. On the other hand, if the predetermined value is set to more than 10 mg / g, the viscosity of the ground and cement milk when mixed may become very large.

[0023] Examples of the alkali-soluble aluminum compound to be added include amorphous aluminum silicate, fine particle akadama soil, colloidal alumina, γ-alumina, etc., and it is preferable to use alkali-soluble aluminum silicate. The alkali-soluble aluminum compound to be added may be added as one component of the solidification material, or may be added as a component separate from the solidification material.

[0024] More preferably, the alkali-soluble aluminum compound is a water-insoluble alkali-soluble aluminum compound, and the alkali-soluble silicic acid is a water-insoluble alkali-soluble silicic acid, such as water-insoluble alkali-soluble aluminum, water-insoluble alkali-soluble silicic acid, etc. For example, aluminum chloride, water glass, etc. are water-soluble alkali-soluble aluminum or water-soluble alkali-soluble silicic acid, while aluminum silicate, Akadama soil, etc. are water-insoluble alkali-soluble aluminum.

[0025] The amount of alkali-soluble aluminum compound added is such that the amount of alkali-soluble aluminum in the ground is a predetermined value or more, for example, a content calculated from the amount of alkali elution of 0.1 to 10 [mg / g], preferably 0.1 to 3 [mg / g], and more preferably 0.1 to 1 [mg / g].

[0026] The soluble silicic acid is added so that the content calculated from the amount of alkali elution is 0.25 to 10 mg / g, preferably 0.5 to 8 mg / g, and more preferably 0.8 to 5 mg / g.

[0027] In this embodiment, examples of the cement that can be used include various types of Portland cement, such as ordinary, early strength, and extra early strength, various mixed cements obtained by mixing Portland cement with blast furnace slag, silica, and fly ash, white cement, extra rapid hardening cement, alumina cement, blast furnace cement type B, cement bentonite (CB), and cement slurry.

[0028] The amount of cement mixed is based on the soil volume (1m 3 ) is preferably 20 to 800 kg, more preferably 30 to 500 kg, and particularly preferably 50 to 400 kg. If the amount of cement mixed is less than 20 kg, there is a risk that practical strength cannot be achieved. On the other hand, if the amount of cement mixed exceeds 800 kg, the volume of the cement-mixed soil increases significantly, which increases the amount of sludge discharged and results in huge processing costs.

[0029] In this embodiment, examples of the water-soluble sulfur oxide salts that can be used include sodium sulfate, potassium sulfate, various alums, sodium thiosulfate, and potassium thiosulfate. In this regard, cement contains oxidizing substances, and reducible sulfur compounds such as thiosulfates easily become sulfate ions in the cement slurry, leading to the formation of ettringite. In addition, when sodium thiosulfate or potassium thiosulfate is used, harmful hexavalent chromium in the cement can be reduced to trivalent chromium, so that it is effective in ground that is prone to elution of hexavalent chromium.

[0030] The amount of the water-soluble sulfur oxide salt is preferably 0.1 to 20% by mass, more preferably 0.5 to 15%, and particularly preferably 1 to 10% by mass, based on the mass (kg) of the solidifying material powder. If the amount of the water-soluble sulfur oxide salt is less than 0.1%, the effect of promoting strength development (ettringite formation) may be insufficient. On the other hand, if the amount of the water-soluble sulfur oxide salt is more than 20%, the amount of calcium ions fixed by sulfate ions in the solidifying material increases, and the hardening time may be significantly extended.

[0031] (others) In the ground improvement method of this embodiment, for example, various materials can be mixed in advance and injected into the target ground as one liquid, or two or more liquids can be injected into the target ground without mixing in advance, and mixed with the target ground. Examples of methods for mixing with the ground include a deep layer mixing method using a ground stirring blade, a shallow layer mixing method using a backhoe bucket, and a high-pressure jet mixing method. EXAMPLES

[0032] Next, an embodiment of the present invention will be described. Test specimens were prepared using the materials and mix ratios shown in Table 1, and tests were conducted. Test specimens were prepared by mixing a specified amount of sample soil and a specified mix of cement milk in a Hobart mixer, and filling a φ50 x H100 mold. The unconfined compressive strength of this test specimen at 7 and 28 days of age is shown in Table 2. For comparison, a case without copper (only No. 6 silica sand and water) is used as Test Example 1.

[0033] [Table 1]

[0034] [Table 2]

[0035] Test Examples 1 to 3 show the cement hardening inhibitory effect of heavy metals (copper), Test Example 4 shows the effect of adding sulfate alone, Test Examples 5 and 6 show the effect of adding an aluminum compound (aluminum silicate) alone, and Test Examples 7 to 9 show the effect of adding both sulfate and aluminum silicate. Note that in the test examples with two rows, the upper row shows the amount of soil elution, and the lower row shows the value calculated from the amount of simple substance eluted from the additive added to the cement milk. The same applies to the other tests below.

[0036] These results show that the strength of the sample soil decreases when it contains copper. Also, it is clear that adding both sulfate and aluminum silicate is more effective than adding either one alone.

[0037] Next, using the same method as above, a test was conducted to compare the effects of a conventional cement-based solidification material (with the addition of anhydrous gypsum (insoluble sulfate)) with the addition of a water-soluble sulfate (Miuranium sulfate). The materials and mixing ratios are shown in Table 3, and the results are shown in Table 4.

[0038] [Table 3]

[0039] [Table 4]

[0040] The effect of adding a water-soluble sulfate salt can be seen from Test Examples 4 and 7, while the effect of adding an insoluble sulfate salt can be seen from Test Examples 10 and 11. Specifically, it can be seen that the effect of adding a water-soluble sulfate salt is greater than that of an insoluble sulfate salt.

[0041] Next, a test was conducted on organic soil (soil containing CMC) using the same method as above. The materials and mixing ratios are shown in Table 5, and the results are shown in Table 6.

[0042] [Table 5]

[0043] [Table 6]

[0044] Test Examples 1 and 12 show the hardening inhibitory effect of CMC, Test Example 13 shows the effect of adding sulfate alone, and Test Example 14 shows the effect of adding both sulfate and aluminum silicate.

[0045] Next, a test was conducted on loamy sandy soil (containing a large amount of alkali-soluble aluminum) in the same manner as above. The materials and their mixing ratios are shown in Table 7, and the results are shown in Table 8.

[0046] [Table 7]

[0047] [Table 8]

[0048] Test Example 15 shows the strength of loamy sandy soil, and Test Example 16 shows the effect of adding sulfate. Although the effect is reduced in ground containing a large amount of alkali-soluble aluminum, it is clear that adding sulfate is effective.

[0049] Next, the type of sulfur oxide to be added (water-soluble sulfate (sodium sulfate) or water-soluble reduced sulfur oxide salt (sodium thiosulfate)) was examined using the same method as above. The materials and mixing ratios are shown in Table 9, and the results are shown in Table 10.

[0050] [Table 9]

[0051] [Table 10]

[0052] Test Example 17 shows the hardening inhibition effect of zinc, Test Example 18 shows the effect of adding sulfates, and Test Example 19 shows the effect of adding reduced sulfur oxide salts. Water-soluble sulfur oxide salts were the most effective.

[0053] Next, an alkaline elution test was conducted on the samples (sample soil and additives). The elution procedure was as follows: (1) drying the sample at 110°C, (2) elution with 10 g of sample (1 g for pure substances (samples 6 to 8)) + 100 ml of 1N-NaOH for 2 h at RT by shaking, and (3) quantitative analysis of the filtrate using a 0.45 μm membrane filter. The results are shown in Table 11.

[0054] [Table 11]

[0055] Next, the change in viscosity over time of cement milk to which each additive was added was examined. The results are shown in Table 12.

[0056] [Table 12]

[0057] Water-soluble aluminum salts (aluminum chloride) had good strength development, but lost fluidity very quickly, and at construction sites it is expected to cause problems such as blockages due to hardening in the cement milk delivery hose and uneven mixing due to hardening during mixing and stirring with the ground. [Industrial Applicability]

[0058] The present invention can be used as a ground improvement method that can be suitably used in cement hardening-inhibited ground regardless of inhibitors or ground components.

Claims

1. When mixing the ground with a solidification material containing cement and a water-soluble sulfur oxide salt, measuring the content of alkali-soluble aluminum in the ground, and if the measured value is equal to or less than a predetermined value, adding an aluminum compound as an additive to the solidification material so that the measured value becomes equal to or greater than the predetermined value; The content of soluble silicic acid in the ground is measured, and if the measured value is equal to or less than a predetermined value, a silicate compound is added as an additive to the solidification material so that the measured value becomes equal to or greater than the predetermined value. A ground improvement method comprising the steps of:

2. The additive is an alkali-soluble aluminum silicate. The ground improvement method according to claim 1.

3. The additive is a dry clay containing allophane. The ground improvement method according to claim 1 or 2.

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