Soil-cement walls and construction methods for soil-cement walls

Abstract

In soil-cement walls containing core materials, the performance of the wall is ensured while suppressing carbon dioxide emissions by appropriately using cement-based solidification agents with different blast furnace slag content. [Solution] A soil cement wall is made of soil cement, which is obtained by mixing a solidifying agent containing cement and blast furnace slag with soil, and discretely arranged steel core materials, wherein the solidifying agent has a blast furnace slag content of 60% by mass or more overall, does not contain a cement hardening retarder, or has a cement hardening retarder content of 2% by mass or less, and the uniaxial compressive strength of the soil cement is 0.2 N / mm 2 The above provides a soil-cement wall.

Description

[Technical Field]

[0001] The present invention relates to a soil-cement wall and a method for constructing a soil-cement wall. [Background technology]

[0002] A soil-cement wall is a continuous wall constructed by building a series of columns of soil-cement, which is a mixture of soil and a cement-based solidifying agent, or by constructing a continuous wall in ground excavated to a uniform thickness. As an example of technology related to soil-cement walls, Patent Document 1 describes a technology in which an excavation and pre-solidification process is performed at any time, in which excavation is performed while adding a non-hardening injection material to create a wall body made of a mixture of excavated soil and a non-hardening injection material; a core material insertion process is performed in which a core material is inserted into the wall body made of the mixed soil; and a solidification process is performed in which a solidifying agent is added to the mixed soil with the core material inserted, mixed, and solidified. By inserting a core material such as an H-shaped steel into the soil-cement wall in this way, the rigidity of the wall body can be improved. More specifically, the core material ensures the strength and rigidity against earth pressure and water pressure acting on the wall body, and the soil-cement connects, for example, discretely arranged core materials, giving the wall body watertightness, preventing soil from being drawn out through the wall body, and transmitting earth pressure to the core material.

[0003] On the other hand, as an example of technology related to soil cement, Patent Document 2 describes a soil cement slurry composition obtained by mixing a blast furnace slag composition containing 80-95% by mass of blast furnace slag fine powder and 5-20% by mass of gypsum (total 100% by mass) with water, adding an alkaline stimulant at a rate of 0.5-1.5 parts by mass or 5-45 parts by mass per 100 parts by mass of the mixture, and adding an admixture at a rate of 0.1-5 parts by mass per 100 parts by mass of the blast furnace slag composition. By increasing the blast furnace slag content in the solidifying agent, the generation of carbon dioxide during manufacturing can be suppressed, and the decrease in fluidity over time can be suppressed, ensuring the workability of the core material.

[0004] Regarding blast furnace cement used as a cement-based solidifying agent in soil cement construction, JIS R5211 classifies it into three types based on the amount of blast furnace slag: Type A (blast furnace slag more than 5% by mass and up to 30% by mass), Type B (blast furnace slag more than 30% by mass and up to 60% by mass), and Type C (blast furnace slag more than 60% by mass and up to 70% by mass). Generally, Type B, which has a good balance of performance, is used. However, Patent Document 2 describes how carbon dioxide generation during manufacturing is suppressed by including a large amount of blast furnace slag in the soil cement slurry composition. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2015-63888 [Patent Document 2] Japanese Patent Publication No. 2010-285466 [Overview of the project] [Problems that the invention aims to solve]

[0006] As mentioned above, using a solidifying agent with a high blast furnace slag content can suppress carbon dioxide emissions and ensure the workability of the core material. However, in terms of the strength of the soil cement after solidification, types A and B, which have a lower blast furnace slag content, are superior.

[0007] Therefore, the present invention aims to provide a soil-cement wall and a method for constructing a soil-cement wall that can suppress the generation of carbon dioxide while ensuring the performance of the wall, in a soil-cement wall including discretely arranged core materials. [Means for solving the problem]

[0008] [1] A soil cement wall comprising soil cement, which is obtained by mixing a solidifying agent containing cement and blast furnace slag with soil, and discretely arranged steel core materials, wherein the solidifying agent has a blast furnace slag content of 60% by mass or more overall, does not contain a cement hardening retarder, or has a cement hardening retarder content of 2% by mass or less, and the uniaxial compressive strength of the soil cement is 0.2 N / mm 2 That concludes the explanation of the soil cement wall. [2] The soil cement wall according to [1], wherein the core material has a length of 10 m or more and 60 m or less in the depth direction. [3] The soil cement wall according to [1] or [2], wherein the soil cement comprises a first soil cement having a relatively high blast furnace slag content and a second soil cement having a relatively low blast furnace slag content, and the core material is cast into the portion of the first soil cement. [4] In at least a portion of the soil cement, the solidifying agent is Portland cement (C), with a specific surface area of ​​3000 cm². 2 More than 10000cm 2 A soil cement wall according to any one of items [1] to [3], comprising the following blast furnace slag fine powder (GGBFS), water (W), and admixture (SP), wherein the mass ratio of each component satisfies the following conditions (1) to (3): 60% ≤ GGBFS / (C + GGBFS) ≤ 80% ···(1) 45% ≤ W / (C + GGBFS) ≤ 250% ···(2) 0.1% ≤ SP / (C + GGBFS) ≤ 5% ···(3) [5] The soil 1.0 m 3 The soil cement wall according to [4], wherein the amount of solidifying agent mixed with the soil cement wall is 100 kg or more and 500 kg or less. A method for constructing a soil-cement wall according to any one of items [6], [1] to [5], comprising the step of mixing cement and blast furnace slag on-site to produce the solidifying agent. A method for constructing a soil-cement wall according to any one of items [7], [1] to [5], wherein the table flow value 3 hours after immediately after the soil cement is poured into the ground is 150 mm or more. A method for constructing a soil-cement wall according to any one of items [8], [1] to [5], wherein the table flow value 6 hours after immediately after the soil cement is poured into the ground is 100 mm or more. [Effects of the Invention]

[0009] According to the above configuration, by using a solidifying agent with a high blast furnace slag content, it is possible to suppress the generation of carbon dioxide during the manufacturing of the solidifying agent while ensuring the workability of the core material. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic perspective view of a soil-cement wall according to one embodiment of the present invention. [Figure 2] Figure 1 is a top view of the soil-cement wall. [Figure 3] This figure shows another example of a soil-cement wall according to an embodiment of the present invention. [Modes for carrying out the invention]

[0011] Exemplary embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In this specification and the drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant descriptions will be omitted.

[0012] Figure 1 is a schematic perspective view of a soil-cement wall according to one embodiment of the present invention, and Figure 2 is a top view of the soil-cement wall shown in Figure 1. Note that the surrounding soil of the soil-cement wall is not shown in these figures. Furthermore, the group of columns constituting the soil-cement wall is constructed by mixing a solidifying agent with soil, but since the solidifying agent is fluid before solidification, a clear boundary as shown in the figures is not necessarily formed between the columns of the soil-cement wall and the surrounding soil, and between the columns themselves, and the two are mixed together at the boundary.

[0013] The soil-cement wall 1 includes a group of columns 2A to 2E made of soil-cement mixed with a solidifying agent, and core materials 3 inserted into the columns constituting the group of columns. Each column constituting the group of columns is constructed, for example, by injecting the solidifying agent while excavating the soil using a mixing auger, and then raising the auger while mixing the soil and solidifying agent. By constructing the columns so that adjacent columns slightly overlap, a soil-cement wall 1 can be created in which the group of columns is constructed continuously. The core material 3 is made of steel, and in the illustrated example, it is an H-beam. By inserting the core material 3 into the columns, the rigidity of the wall can be improved. However, the soil-cement wall 1 does not require rigidity to the extent that core materials are inserted into all columns, and as shown in the illustration, the core material 3 is placed discretely, specifically in every other column. The soil-cement wall 1 may include further continuous groups of columns on both sides of the illustrated group of columns 2A to 2E, but below we will further explain the configuration of the soil-cement wall 1 using the group of columns 2A to 2E as an example.

[0014] In this embodiment, the solidifying agent mixed with soil in the soil cement that constitutes the soil cement wall 1 contains cement and blast furnace slag, with a total blast furnace slag content of 60% by mass or more. Furthermore, the solidifying agent either does not contain a cement hardening retarder, or its cement hardening retarder content is 2% or less. The main components of the cement hardening retarder are, for example, lignin sulfonate, oxycarboxylic acid salt, or polycarboxylic acid. In the soil cement wall 1, these components are not detected in the soil cement, or the content of these components in the solidifying agent, calculated from the amount of these components detected in the soil cement and the mixing ratio of soil and solidifying agent, is 2% or less. The unconfined compressive strength of the soil cement is 0.2 N / mm². 2The above is the case. By configuring in this way, the content of blast furnace slag in the solidifying material is increased to suppress the generation of carbon dioxide during the production of the solidifying material, and the decrease in fluidity of the solidifying material over time can be suppressed without using a cement setting retarder. Since the decrease in fluidity of the solidifying material over time can be suppressed, that is, the solidification of the solidifying material can be delayed, the time for inserting the core material can be secured and the workability can be improved. Also, by setting the uniaxial compressive strength of the soil cement to 0.2 N / mm 2 or more, the strength of the wall body can also be ensured.

[0015] Furthermore, in the above soil cement wall 1, among the column bodies 2A to 2E, the column bodies 2A, 2C, 2E into which the core material 3 is inserted are regarded as the first column bodies, and the column bodies 2B, 2D into which the core material is not inserted are regarded as the second column bodies. In these column bodies, the solidifying material mixed with the soil contains cement and blast furnace slag. The first column bodies 2A, 2C, 2E are composed of the first soil cement with a relatively high content of blast furnace slag in the solidifying material, and the second column bodies 2B, 2D are composed of the second soil cement with a relatively low content of blast furnace slag in the solidifying material. Specifically, for example, when the solidifying material in the first column bodies 2A, 2C, 2E is a suspension of blast furnace cement type C containing more than 60% and not more than 70% of blast furnace slag by mass, the solidifying material in the second column bodies 2B, 2D is a suspension of blast furnace cement type A containing more than 5% and not more than 30% of blast furnace slag by mass, or a suspension of blast furnace cement type B containing more than 30% and not more than 60% of blast furnace slag by mass. In the above example, the solidifying material in the first column bodies 2A, 2C, 2E may be a suspension of a mixture of cement containing more than 70% of blast furnace slag and blast furnace slag (not included in the classification of blast furnace cement in JIS R5211). Note that since the content of blast furnace slag in the solidifying material in the soil cement is 60% by mass or more as a whole, solidifying materials with a content of blast furnace slag less than 60% by mass may be used partially as described above.

[0016] <00000९3>As already described, in the soil-cement wall 1, a clear boundary is not necessarily formed between the column bodies and the surrounding soil, nor between the column bodies themselves. In the boundary portion, the soil and solidifying materials of both column bodies are mixed. On the other hand, only the solidifying material used when constructing the column body is substantially observed at the center of the column body. Therefore, all the characteristics of the solidifying material components of each column body as described above can be clearly observed at the center of the column body. That is, in the example of the first column body 2C and the second column body 2D shown in FIG. 2, the blast furnace slag content of the solidifying material at the center P1 of the first column body 2C is higher than the blast furnace slag content of the solidifying material at the center P2 of the second column body 2D. The centers P1 and P2 of the column bodies are specified as the center of the planar shape of the column body, for example, the position of the rotation axis of the auger in the case of constructing a column body with a circular cross section using an auger. Since the core material 3 is inserted into the centers of the first column bodies 2A, 2C, and 2E, the soil-cement portion adjacent to the center of the web of the H-shaped steel, which is the core material 3, becomes the center P1 at the portion closest to the center other than the core material 3.

[0017] In the embodiment of the present invention as described above, the core material 3 is discretely arranged according to the rigidity required for the soil-cement wall 1, that is, the core material 3 is inserted only into the first column bodies 2A, 2C, and 2E of the column body group 2A to 2E, and not into the second column bodies 2B and 2D. By doing so, the material cost of the core material 3 can be reduced, and the amount of carbon dioxide emissions due to the production of the core material 3 can be suppressed. In addition, by using a solidifying material with a high blast furnace slag content, the generation of carbon dioxide during the production of the solidifying material is suppressed, and the reduction in fluidity over time is suppressed, that is, the solidification is delayed, so that the time for inserting the core material 3 can be ensured and the workability can be improved. If the construction time is ensured, it is also easy to longitudinally join the core material 3 when the wall height is high or there is a headspace limit. Although the cost increases when trying to suppress the reduction in fluidity over time of the solidifying material by adding a cement setting retarder, if the reduction in fluidity over time can be suppressed by increasing the blast furnace slag content, it is not necessary to add a cement setting retarder, which is economical.

[0018] In the soil cement wall 1 described above, the solidifying agent mixed with the soil to constitute the soil cement is preferably formulated so that the table flow value is 150 mm or more 3 hours after the completion of the core material construction, specifically immediately after the soil cement is poured into the ground. Furthermore, the solidifying agent is preferably formulated so that the table flow value is 100 mm or more, more preferably 200 mm or more 6 hours after the soil cement is poured into the ground. For example, if the core material 3 has a length of 10 m to 60 m in the depth direction, one longitudinal joint is required during the pouring of the core material 3. However, 3 to 6 hours after the pouring of the soil cement is sufficient to perform the longitudinal joint by welding or other means and then pour the core material 3. If the table flow value of the soil cement is maintained at 150 mm or more during this time, the core material 3 can be poured smoothly.

[0019] In the illustrated example of soil-cement wall 1, the first columns 2A, 2C, and 2E and the second columns 2B and 2D are arranged alternately, one of each. However, depending on the required rigidity of the soil-cement wall, two or more second columns may be arranged between the first columns into which the core material is inserted, that is, the core material 3 may be inserted into the columns at intervals of two or more columns. Furthermore, the core material 3 is not limited to H-shaped steel, but may be other shaped steel materials such as channel steel, angle steel, or T-shaped steel, or steel sheet piles or steel pipes. In addition, the soil-cement wall may be constructed of wall bodies of equal thickness, as shown in soil-cement wall 1A in Figure 3.

[0020] As an example of a solidifying agent, as mentioned above, a suspension of blast furnace cement type C can be used, as well as a solidifying agent with a high proportion of blast furnace slag, as described below. This solidifying agent is Portland cement (C), with a specific surface area of ​​3000 cm². 2 More than 10000cm 2 The following blast furnace slag fine powder (GGBFS), water (W), and admixture (SP) are included, and the mass ratio of each component satisfies the following conditions (1) to (3). Various types of Portland cement can be used, but ordinary Portland cement or low-heat Portland cement is more preferred. Also, soil 1.0 m3 The mixing amount of the solidifying material with respect to [it] is, for example, 100 kg or more and 500 kg or less.

[0021] 60% ≤ GGBFS / (C + GGBFS) ≤ 80% ···(1) 45% ≤ W / (C + GGBFS) ≤ 250% ···(2) 0.1% ≤ SP / (C + GGBFS) ≤ 5% ···(3)

[0022] The soil-cement wall 1 can be constructed by various known construction methods. For example, a process of manufacturing a solidifying material by kneading cement and blast furnace slag on-site may be carried out. When the solidifying material or components other than water of the solidifying material are kneaded in advance and transported to the site, it is necessary to prepare the solidifying materials of the first column body and the second column body separately. However, if the solidifying material is manufactured by kneading cement and blast furnace slag on-site, after transporting the same raw materials, the solidifying materials of the first column body and the second column body can be made separately while adjusting the content of blast furnace slag. More specifically, for example, Portland cement, blast furnace slag fine powder, water, and admixture may be kneaded on-site to manufacture the solidifying material.

Explanation of symbols

[0023] 1, 1A…soil-cement wall, 2A, 2B, 2C, 2D, 2E…column body, 3…core material, P1, P2…central part.

Claims

1. A soil cement wall is composed of soil cement, which is obtained by mixing a solidifying agent containing cement and blast furnace slag with soil, and discretely arranged steel core materials. The solidifying agent, as a whole, contains 60% by mass or more of the blast furnace slag and does not contain a cement hardening retarder, or contains 2% by mass or less of the cement hardening retarder. The unconfined compressive strength of the soil cement is 0.2 N / mm². ２ That concludes the explanation of the soil cement wall.

2. The soil cement wall according to claim 1, wherein the core material has a length of 10 m or more and 60 m or less in the depth direction.

3. The soil cement wall according to claim 1, wherein the soil cement comprises a first soil cement having a relatively high blast furnace slag content and a second soil cement having a relatively low blast furnace slag content, and the core material is cast into the portion of the first soil cement.

4. In at least a portion of the soil cement, the solidifying agent is Portland cement (C), with a specific surface area of ​​3000 cm². ２ More than 10000cm ２ The soil cement wall according to claim 1, comprising the following blast furnace slag fine powder (GGBFS), water (W), and admixture (SP), wherein the mass ratio of each component satisfies the following conditions (1) to (3). 60%≦GGBFS / (C+GGBFS)≦80%...(1) 45%≦W / (C+GGBFS)≦250%...(2) 0.1%≦SP / (C+GGBFS)≦5%...(3)

5. The aforementioned soil 1.0 m ３ The soil cement wall according to claim 4, wherein the amount of solidifying agent mixed with the soil cement is 100 kg or more and 500 kg or less.

6. A method for constructing a soil cement wall according to any one of claims 1 to 5, A method for constructing a soil-cement wall, comprising the step of mixing cement and blast furnace slag on-site to produce the solidifying agent.

7. A method for constructing a soil cement wall according to any one of claims 1 to 5, A method for constructing a soil-cement wall, wherein the table flow value three hours after the soil-cement is poured into the ground is 150 mm or more.

8. A method for constructing a soil cement wall according to any one of claims 1 to 5, A method for constructing a soil-cement wall, wherein the table flow value six hours after the soil-cement is poured into the ground is 100 mm or more.

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