Method for producing liquefied treated soil and liquefied treated soil

Abstract

To provide a method for producing liquefied treated soil and liquefied treated soil, which can reduce the environmental load and increase the solidification strength.SOLUTION: A method for producing liquefied treated soil involves adding biochar 1, cement-based solidification material 2, and water 3 to mud 4. Then, a mixing process 5 is performed to agitate the mud 4 to which biochar 1, cement-based solidification material 2, and water 3 have been added. The mixing process 5 involves agitating the mud 4 to which biochar 1, cement-based solidification material 2, and water 3 have been added for 30 to 180 seconds. After this mixing process 5, liquefied treated soil 6 is obtained.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing liquefied treated soil and liquefied treated soil. More specifically, the present invention relates to a method for producing liquefied treated soil and liquefied treated soil for use in, for example, backfilling. [Background technology]

[0002] Traditionally, construction work known as "backfilling" has been carried out, in which excavated ground is filled back in. This is because when holes are formed in the ground after excavation, the ground's strength weakens, causing land subsidence and reducing earthquake resistance.

[0003] Furthermore, if the backfilling is insufficient, there is a risk that the backfilled soil and sand will liquefy during an earthquake, causing the building to tilt or collapse. Therefore, it is necessary to select the appropriate soil and to compact or solidify the backfilled area.

[0004] In addition, sand and liquefied soil are used for backfilling. "Fluidized treated soil" is a fluid, resource-recycling backfill material that is made by mixing water and cement-based solidification materials, or bentonite, slag, etc., with the soil to be treated, such as construction waste, to create a fluidized material.

[0005] By the way, when budget is of the essence or cement cannot be used, sand is used as backfill material. However, depending on the type of sand, compaction may not be possible reliably, and although sand is inexpensive, it must be used with careful consideration of where it is used.

[0006] On the other hand, liquefied treated soil has fluidity and self-hardening properties and does not require compaction, which reduces operating costs. In addition, because liquefied treated soil has fluidity, it is used to backfill narrow spaces and areas where compaction is difficult. Furthermore, liquefied treated soil is a material made by mixing construction waste soil generated during construction with water and cement, and since it uses excavated soil, it is environmentally friendly and reduces industrial waste. For these reasons, various types of liquefied treated soil have been proposed.

[0007] For example, Patent Document 1 describes a liquefied treated soil that is a mixture of adjusted muddy water containing water and soil particles and a solidification material. In this liquefied treated soil, the specific gravity of the adjusted muddy water is 1.1 to 1.3, the water content of the adjusted muddy water is 62 to 85%, the soil particles contain 50 to 65% fine particles with a particle size of less than 75 μm, and the solidification material has an unconfined compressive strength of 200 kN / m at 28 days. 2 It contains blast furnace type C cement in an amount of 97% or more and has a recycling rate of 97% or more. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2023-20068 Summary of the Invention [Problem to be solved by the invention]

[0009] Incidentally, Japan's cement industry emits carbon dioxide equivalent to approximately 4% of total greenhouse gas emissions, making measures to reduce emissions an important issue.

[0010] In this context, it has been reported that carbonation treatment of improved soils made by mixing cement with sand or bentonite can increase their strength. By making good use of this technology, it is expected that a significant reduction in the environmental impact can be achieved through carbon dioxide fixation. Securing disposal sites for the mud has become an issue, and coupled with the need for effective use of the mud, a solidification process is being carried out in which the mud is solidified with cement.

[0011] However, when cement is used to solidify mud, the clay minerals and organic components in the mud may inhibit the formation of cement hydrate, which may result in the elution of chromium that is not fixed in the cement hydrate.

[0012] For these reasons, there has been a demand for technology that can sufficiently fix carbon dioxide to reduce the environmental impact while also increasing the solidification strength of mud.

[0013] The present invention was devised in consideration of the above points, and aims to provide a method for manufacturing liquefied treated soil that can reduce the environmental load while increasing the solidification strength, as well as liquefied treated soil that can reduce the environmental load while increasing the solidification strength. [Means for solving the problem]

[0014] In order to achieve the above-mentioned objectives, the method for producing liquefied treated soil of the present invention is a method for producing liquefied treated soil using raw soil, which is construction sludge or excavated soil, as the main raw material, and includes a mixing step in which a solidification material, a specified biochar, and water are mixed with the raw soil.

[0015] Here, by mixing biochar with the raw soil, the carbon dioxide fixed as a carbon compound in the biochar can be stored in the liquefied treated soil of the present invention.

[0016] In addition, by mixing biochar into the raw soil, the strength of the liquefied treated soil of the present invention can be improved. Therefore, a specified strength (for example, uniaxial compressive strength of 100 kN / m as a liquefaction countermeasure by backfilling with cement-based improved soil) 2 This reduces the amount of solidification material required to obtain the above-mentioned results. In other words, the solidification material can be replaced with biochar. Furthermore, by reducing the amount of solidification material (e.g., cement-based solidification material) used, the amount of cement-based solidification material produced can also be reduced accordingly, resulting in a reduction in the amount of carbon dioxide generated during the production of cement-based solidification material.

[0017] In addition, in the method for producing liquefied treated soil of the present invention, biochar can be added to the raw soil in an amount of 10% by weight or less in the mixing step.

[0018] Here, the amount of biochar added is based on the total amount of the liquefied treated soil of the present invention. In this case, even if the amount of biochar added is a maximum of 10% by weight, the liquefied treated soil of the present invention can have sufficient strength.

[0019] Furthermore, in the mixing step of the method for producing liquefied treated soil of the present invention, a predetermined weighting material can be added together with the solidification material and biochar to obtain liquefied treated soil with a specific gravity of 1.3 to 1.8.

[0020] In this case, since the specific gravity is 1.3 or more, the resulting liquefied treated soil can be prevented from becoming excessively light, making it easier for the strength of the ground backfilled with the resulting liquefied treated soil to meet the desired value. Furthermore, since the specific gravity is 1.8 or less, the resulting liquefied treated soil is prevented from becoming excessively heavy. As a result, the soil pressure exerted by the resulting liquefied treated soil on the surrounding soil and structures is not high, making it less likely to cause the walls of the backfilled areas to collapse.

[0021] Furthermore, in the mixing step of the method for producing fluidized treated soil of the present invention, a specified admixture can be added together with the solidification material and the biochar to obtain fluidized treated soil with a flow value of 110 to 400 mm.

[0022] In this case, since the flow value is 110 mm or more, it is easy to obtain liquefied treated soil with improved fluidity to the extent that insufficient filling in small areas can be suppressed. Furthermore, since the flow value is 400 mm or less, the resulting liquefied treated soil does not become excessively soft, preventing the backfilled area from becoming soft ground.

[0023] In order to achieve the above-mentioned object, the liquefied treated soil of the present invention is a liquefied treated soil obtained by solidifying raw soil such as construction sludge or excavated soil, contains a predetermined amount of biochar, and has an unconfined compressive strength of 130 kN / m at 28 days. 2 The specific gravity is 1.3 to 1.8, the flow value is 110 to 400 mm, and the bleeding rate is less than 1%.

[0024] Here, by containing biochar in the liquefied treated soil of the present invention, carbon dioxide fixed as a carbon compound in the biochar can be stored in the liquefied treated soil of the present invention.

[0025] Furthermore, by including biochar in the liquefied treated soil of the present invention, the strength of the liquefied treated soil of the present invention can be improved. Therefore, the amount of solidification material required to obtain a given strength can be reduced. In other words, the solidification material can be replaced with biochar. Furthermore, by reducing the amount of solidification material (for example, cement-based solidification material) used, it is possible to reduce the amount of carbon dioxide generated during the production of the cement-based solidification material.

[0026] In addition, the unconfined compressive strength of the liquefied treated soil of the present invention at 28 days is 130 kN / m 2 As described above, by using the liquefied treated soil of the present invention as backfill material, it is possible to satisfy the specified strength according to the target of each type of construction work (construction type).

[0027] In addition, since the specific gravity of the liquefied treated soil of the present invention is 1.3 or more and 1.8 or less, the "specific gravity of the ground before excavation" and the "specific gravity of the backfilled area" can be made approximately the same. Furthermore, it is easy to achieve the specific gravity according to the target type of work.

[0028] Furthermore, since the flow value of the liquefied treated soil of the present invention is 110 mm or more and 400 mm or less, it can satisfy the fluidity and specified strength according to the target type of work.

[0029] In addition, since the bleeding rate is less than 1%, the soil particles are kept uniform in the depth direction, resulting in uniform strength development. [Effects of the Invention]

[0030] The method for producing liquefied treated soil according to the present invention can reduce the environmental load and increase the solidification strength. The liquefied treated soil according to the present invention can reduce the environmental load and has high solidification strength. [Brief explanation of the drawings]

[0031] [Figure 1] 1 is a schematic diagram showing the manufacturing process of liquefied treated soil to which the present invention is applied. DETAILED DESCRIPTION OF THE INVENTION

[0032] FIG. 1 is a schematic diagram showing the manufacturing process of liquefied treated soil to which the present invention is applied. As shown in FIG. 1, in the method for producing liquefied treated soil of the present invention, first, biochar 1, cement-based solidification material 2, and water 3 are added to mud 4. Here, the mud 4 is raw soil that is the main raw material of liquefied treated soil.

[0033] Then, a mixing process 5 is performed in which the mud 4 to which the biochar 1, cement-based solidification material 2, and water 3 have been added is stirred. Specifically, the liquefied treated soil 6 of the present invention can be obtained by stirring mud 4 to which biochar 1, cement-based solidification material 2, and water 3 have been added for 30 to 180 seconds.

[0034] In addition to biochar 1 and cement-based solidification material 2, at least one weighting agent or admixture can be added to mud 4 as appropriate, and a mixing process 5 can be performed to obtain the fluidized treated soil 6 of the present invention.

[0035] [About the mud] "Mud" refers to, for example, "construction mud" generated at construction sites such as tunnel construction (shield construction), excavation work (boring, pile installation), and building construction.

[0036] [About solidification materials] The "solidification material" is, for example, a cement-based solidification material.

[0037] (Cement-based solidification material) As the cement-based solidification material, a common one can be used, and specific examples include mixed cements such as blast furnace cement, fly ash cement, and silica cement, and ecocement.

[0038] Specific examples of solidification-promoting components include aluminum oxide, aluminum hydroxide, slag (blast furnace slag, converter slag, electric furnace slag), aluminum, silica sand, iron oxide, iron hydroxide, magnesium oxide, silica gel, and calcium aluminate.

[0039] [About biochar] Biochar is a carbonized material obtained by pyrolyzing (carbonizing) biomass in a carbonization furnace or gasification furnace. Biomass is a reusable organic resource (excluding fossil fuels such as petroleum) derived from plants and animals.

[0040] Furthermore, any carbonized material obtained by pyrolyzing (carbonizing) biomass in a carbonization furnace or gasification furnace can be used as biochar.Specific examples include carbonized wood, carbonized bamboo, and carbonized plant shells (rice husks, soybean pods, etc.).

[0041] [About weighted materials] As the weighting material, any common material can be used, and specific examples include sand, calcium carbonate, silica sand, fly ash, iron powder, and finely powdered granulated blast furnace slag.

[0042] [About admixtures] Common admixtures can be used, and specific examples include air-entraining agents, air-entraining water-reducing agents, high-performance air-entraining water-reducing agents, water-reducing agents, high-performance water-reducing agents, superplasticizers, hardening accelerators, rust inhibitors, adhesive mortar stabilizers, setting retarders, accelerators, quick-setting agents, shrinkage-reducing agents, separation-reducing agents, foaming agents, foaming agents, antifreeze agents, and cold-resistance accelerators.

[0043] [effect] The method for producing liquefied treated soil of the present invention adds biochar (i.e., the obtained liquefied treated soil 6 contains biochar), thereby achieving carbon storage by trapping carbon dioxide fixed in the biochar as a carbon compound in the soil, and contributing to reducing carbon dioxide in the atmosphere.

[0044] Carbon dioxide from the atmosphere is absorbed by the leaves of plants, such as agricultural crops, and converted into sugars through photosynthesis, which then turn into various carbon compounds that make up plant biomass. Approximately half of the carbon that was in the biomass before carbonization remains in biochar. In addition, because the carbon bonds that make up biochar are strong, it is difficult for soil microorganisms to decompose, and it is expected to remain underground for a long period of time, perhaps more than 100 years. Therefore, the method for producing liquefied treated soil of the present invention makes it possible to achieve carbon storage as described above.

[0045] In addition, because biochar can improve the strength of the resulting liquefied soil, it is possible to reduce the amount of solidification material added to the mud (amount used), and as a result, the desired strength can be achieved with a small amount of solidification material. Furthermore, by reducing the amount of solidification material (e.g., cement-based solidification material) used, the amount of cement-based solidification material produced can also be reduced accordingly, resulting in a reduction in the amount of carbon dioxide generated during the production of cement-based solidification material.

[0046] In other words, the manufacturing method of liquefied treated soil of the present invention can achieve both "carbon dioxide reduction through carbon storage" and "carbon dioxide reduction through reduced use of solidification material" by producing biochar.

[0047] <Example> Below, we will explain the tests conducted to demonstrate the effects of adding biochar to mud.

[0048] The mud used for the test was construction waste soil, which was in a sludge-like state. The physical properties of the tested mud are shown in Table 1.

[0049] [Table 1]

[0050] In addition, in the present examples, carbonized rice husks were used as biochar (Examples 1 to 8). In addition, a cement-based solidification material (trade name "Geoset", manufactured by Taiheiyo Cement Corporation) was used as the solidification material.

[0051] In the examples, biochar and cement-based solidification materials were added to mud having the physical properties shown in Table 1 in the amounts shown in Table 2 and mixed together (Examples 1 to 8). Specifically, 840 g of mud was placed in a Hobart mixer, and biochar and solidification material were then added to the mud and stirred.

[0052] The density (specific gravity) of the soil particles of the liquefied soil was also measured. The results are shown in Table 2. Furthermore, a flow test was conducted on the liquefied treated soil in accordance with "12 Flow Test" of JIS R 5201 "Physical Testing Methods for Cement," and the flow values ​​of the liquefied treated soil were measured "immediately after mixing," "1 hour after mixing," and "1.5 hours after mixing." The average values ​​obtained from the measurements are shown in Table 2.

[0053] The bleeding rate of the liquefied treated soil was also measured in accordance with the Japan Society of Civil Engineers standard "Test method for bleeding rate and expansion of injection mortar for prepacked concrete" (JSCE-1986). The measured values ​​are shown in Table 2.

[0054] [Comparative Example] For comparison, a similar test was also conducted without adding biochar to the mud. In the comparative examples, no biochar was added to mud having the physical properties shown in Table 1, and a cement-based solidification material was added in the amount shown in Table 2, and mixed (Comparative Examples 1 to 4). Specifically, as in the above-mentioned examples, a cement-based solidifying material was added to the mud and stirred.

[0055] [Table 2]

[0056] Here, for example, in the case of the liquefied treated soil of Example 1, the calculation is that 4.3% by weight of biochar was added to the mud, based on the total amount of liquefied treated soil. Furthermore, for example, in the case of the liquefied treated soil of Example 5, it is calculated that 8.2% by weight of biochar was added to the mud, based on the total amount of liquefied treated soil.

[0057] As can be seen from Table 2, the flow values ​​of the fluidized soils to which biochar was added (Examples 1 to 8) were almost the same as the flow values ​​of the fluidized soils to which biochar was not added (Comparative Examples 1 to 4), and the addition of biochar had no effect on the flow values ​​or bleeding rate.

[0058] The liquefied treated soil obtained in this manner (liquefied treated soil of this example, liquefied treated soil of the comparative example) was discharged from the Hobart mixer and allowed to cure naturally, and the unconfined compressive strength of the liquefied treated soil was measured 3 days, 7 days, 14 days, and 28 days after mixing. The unconfined compressive strength was measured three times, and the average values ​​are shown in Table 3. The unconfined compressive strength was measured in accordance with JIS A 1216 "Unconfined compression test method for soil."

[0059] [Table 3]

[0060] As can be seen from Tables 2 and 3, the liquefied treated soil of the present invention (Examples 1-8) contains a predetermined amount of biochar and has an unconfined compressive strength of 130 kN / m at 28 days. 2 The specific gravity was 1.3 to 1.8, the flow value was 110 to 400 mm, and the bleeding rate was less than 1%.

[0061] Furthermore, as can be seen from Table 3, when comparing "Example 1 and Example 5" with "Comparative Example 1," which all have the same amount of solidification agent added, and when comparing "Example 2 and Example 6" with "Comparative Example 2," and when comparing "Example 3 and Example 7" with "Comparative Example 3," and when comparing "Example 4 and Example 8" with "Comparative Example 4," the unconfined compressive strength of the liquefied treated soil with added biochar was higher than the unconfined compressive strength of the liquefied treated soil without added biochar.

[0062] In other words, although the amount of solidification material added was the same (50 g), the uniaxial compressive strength of the fluidized soil with biochar added (Examples 1 and 5) was higher than the uniaxial compressive strength of the fluidized soil without biochar added (Comparative Example 1). Furthermore, although the amount of solidification material added was the same at 60 g, the uniaxial compressive strength of the fluidized soil with biochar added (Examples 2 and 6) was higher than that of the fluidized soil without biochar added (Comparative Example 2).

[0063] Furthermore, although the amount of solidification material added was the same (120 g), the uniaxial compressive strength of the fluidized soil with added biochar (Examples 3 and 7) was higher than that of the fluidized soil without added biochar (Comparative Example 3). Furthermore, although the amount of solidification material added was the same (180 g), the uniaxial compressive strength of the fluidized soil with biochar added (Examples 4 and 8) was higher than that of the fluidized soil without biochar added (Comparative Example 4).

[0064] These results show that the liquefied treated soil of the present invention can increase its unconfined compressive strength by containing biochar. Therefore, in order to obtain fluidized soil with high uniaxial compressive strength, instead of adding a solidification material such as a cement-based solidification material to the mud, biochar can be added, thereby reducing the amount of solidification material used. [Explanation of symbols]

[0065] 1. Biochar 2. Cement-based solidification materials 3 water 4 Mud 5 Mixing process 6. Liquefied soil

Claims

1. A method for producing liquefied treated soil using raw soil, such as construction sludge and excavated soil, as the main raw material, A mixing step is included in which a solidifying material, a predetermined biochar, and water are mixed with the raw soil. Manufacturing method of liquefied treated soil.

2. The mixing step The biochar is added to the raw soil in an amount of 10% by weight or less. A method for producing the liquefied treated soil according to claim 1.

3. By mixing the biochar, it is possible to obtain fluidized soil with higher strength than when the biochar is not mixed. A method for producing liquefied treated soil according to claim 1 or claim 2.

4. By mixing the biochar, it is possible to obtain liquefied treated soil that stores carbon dioxide as a carbon compound. A method for producing liquefied treated soil according to claim 1 or claim 2.

5. In the mixing step, a predetermined weighting material is added together with the solidification material and the biochar, and liquefied treated soil having a specific gravity of 1.3 to 1.8 can be obtained. A method for producing liquefied treated soil according to claim 1 or claim 2.

6. In the mixing step, a predetermined admixture is added together with the solidification material and the biochar, and fluidized treated soil having a flow value of 110 to 400 mm can be obtained. A method for producing liquefied treated soil according to claim 1 or claim 2.

7. By mixing the biochar, it is possible to obtain fluidized soil with strength equal to or greater than that obtained by mixing the same amount of the solidification material instead of the biochar. A method for producing liquefied treated soil according to claim 1 or claim 2.

8. By mixing the biochar, the amount of the solidification material used can be reduced, resulting in a reduction in carbon dioxide emissions compared to when the same amount of the solidification material is mixed in place of the biochar. A method for producing liquefied treated soil according to claim 1 or claim 2.

9. This is liquefied soil obtained by solidifying raw soil such as construction sludge and excavated soil, Contains a specified biochar, The unconfined compressive strength at 28 days is 130 kN / m ２ The specific gravity is 1.3 to 1.8, the flow value is 110 to 400 mm, and the bleeding rate is less than 1%. Fluidized treated soil.

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