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

Abstract

In a soil-cement wall containing a core material, the required strength level for the soil-cement is reduced by continuously arranging the core material in the direction of the wall's extension, thereby ensuring the wall's performance while suppressing carbon dioxide emissions by using a solidifying agent with a high blast furnace slag content. [Solution] A soil cement wall is constructed of soil cement, which is a mixture of soil and a solidifying agent containing cement and blast furnace slag, and a steel core material is cast into the soil cement, which is continuously arranged in the direction of extension of the wall, 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 2.0 N / mm 2 The following soil-cement wall is provided.

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 reduce the required strength level of the soil cement by continuously arranging the core material in the extensional direction of the wall, thereby ensuring the performance of the wall while suppressing the generation of carbon dioxide by using a solidifying agent with a high blast furnace slag content. [Means for solving the problem]

[0008] [1] A soil cement wall in which the wall body is constructed of soil cement, which is obtained by mixing a solidifying agent containing cement and blast furnace slag with soil, and steel core materials are cast into the soil cement, which are arranged continuously in the direction of extension of the wall body, wherein the solidifying agent has a blast furnace slag content of 60% by mass or more as a whole, 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 2.0 N / mm 2 The following is a 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 height direction of the wall body. [3] The soil cement wall according to [1], wherein the core material includes a first core material having a first length in the height direction of the wall and a second core material having a second length shorter than the first length in the height direction, and the second core material is arranged between one or more of the first core materials at a predetermined period. [4] The soil cement wall according to [3], wherein the upper end of the second core material is lower than that of the first core material. [5] The soil cement wall according to [3], wherein the second core material has a lower end that is higher than the first core material. [6] 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 as described in [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) [7] 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 [8], [1] to [7], 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 [9], [1] to [7], 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

[10] , [1] to [7], 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 continuously arranging the core material in the direction of extension of the wall, the required strength level for the soil cement can be reduced, and by using a solidifying agent with a high blast furnace slag content, carbon dioxide generation during the manufacturing of the solidifying agent can be suppressed while ensuring the workability of the core material. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic perspective view showing a first example of a soil-cement wall according to one embodiment of the present invention. [Figure 2] This is a schematic perspective view showing a second example of a soil-cement wall according to one embodiment of the present invention. [Figure 3] This figure shows an example of the arrangement of core materials in 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] Figs. 1 and 2 are schematic perspective views showing two examples of soil-cement walls according to embodiments of the present invention. In these figures, the surrounding soil of the soil-cement wall is not shown. Further, the soil-cement constituting the soil-cement wall is constructed by mixing a solidifying material with soil. However, since the solidifying material before solidification has fluidity, a clear boundary as shown in the figures is not necessarily formed between the soil-cement and the surrounding soil, and the two are mixed at the boundary portion.

[0013] In the soil-cement wall 1A shown in Fig. 1, the soil-cement 2 forms a wall body composed of a group of continuously constructed columns. In the soil-cement wall 1B shown in Fig. 2, the soil-cement 2 forms a wall body with a uniform thickness. The soil-cement 2 is a mixture of a solidifying material and soil. For example, the group of columns forming the wall body of the soil-cement 2 in the soil-cement wall 1A is constructed by repeating the process of injecting the solidifying material while excavating the soil using a kneading auger machine, and pulling up the auger while kneading the soil and the solidifying material, such that adjacent columns overlap slightly. The wall body of the soil-cement wall 1B is constructed, for example, by the TRD method, in which a chain saw-type cutter post built into the ground is moved horizontally, and the solidifying material and soil are kneaded in the vertical direction while excavating the ground with a bit. The core material 3 is made of steel, and in the illustrated example, it is an H-shaped steel. The core material 3 is not limited to H-shaped steel, and may be other shaped steel materials such as channel steel, angle steel or T-shaped steel, or steel sheet piles or steel pipes.

[0014] In the present embodiment, the core materials 3 are arranged in the extending direction of the wall body and are continuously arranged by being connected to each other with joints. By inserting the continuous core materials 3 into the wall body of the soil-cement 2, the rigidity of the wall body can be greatly improved. In this case, high strength is not required for the soil-cement 2, and the uniaxial compressive strength of the soil-cement 2 is 2.0 N / mm 2 as follows. The uniaxial compressive strength of general ground, that is, soil without a solidifying material mixed therein, is 0.2 N / mm 2The following values are obtained when ensuring a uniaxial compressive strength of approximately 10 times that of the ground in the soil cement so that the ground does not collapse toward the soil cement wall side. The lower limit value of the uniaxial compressive strength of the soil cement 2 is not particularly limited, but from the viewpoint of ensuring the minimum strength of the wall body, it is preferably 0.2 N / mm 2 or more.

[0015] The solidifying agent mixed with the soil in the soil cement walls 1A and 1B includes cement and blast furnace slag, and the content of blast furnace slag as a whole is 60% by mass or more. More specifically, the solidifying agent may be a suspension of blast furnace cement type C containing 60% to 70% by mass of blast furnace slag, or a suspension of a mixture of cement and blast furnace slag containing more than 70% of blast furnace slag (not included in the classification of blast furnace cement in JIS R5211).

[0016] In the present embodiment, the solidifying agent does not contain a cement hardening retarder or the content of the cement hardening retarder is 2% or less. The main components of the cement hardening retarder are, for example, lignin sulfonate, oxycarboxylate or polycarboxylic acid. In the soil cement walls 1A and 1B, these components are not detected from the soil cement 2, or the detected amount of the above components in the soil cement 2 and the content rate of the above components in the solidifying agent calculated inversely from the mixing ratio of the soil and the solidifying agent are 2% or less.

[0017] If the strength level of the soil cement 2 as described above, that is, the uniaxial compressive strength is 2.0 N / mm 2 or less, the content of blast furnace slag in the solidifying agent can be increased to suppress the generation of carbon dioxide during the production of the solidifying agent, and the decrease in the fluidity of the solidifying agent over time can be suppressed without using an expensive cement hardening retarder. When the core materials 3 are connected to each other by joints and arranged continuously, the construction time becomes long because the joints of the core materials 3 are inserted into the soil cement 2 while being fitted together, but the decrease in the fluidity of the solidifying agent over time can be suppressed, that is, the solidification of the solidifying agent can be delayed, so that the construction time for this purpose can be easily ensured.

[0018] As previously mentioned, in soil-cement walls 1A and 1B, a clear boundary is not necessarily formed between the soil-cement and the surrounding soil, and the surrounding soil and soil-cement are mixed together at the boundary. Therefore, the characteristics of the solidifying agent components described above can be observed in the central part of the wall, more specifically in the soil-cement portion adjacent to the center of the web of the H-shaped steel core 3.

[0019] Figure 3 shows an example of the arrangement of core material in an embodiment of the present invention. The earth pressure acting on the soil cement walls 1A and 1B generates a bending moment throughout the entire wall. The bending moment acts almost none at the upper and lower ends of the wall, but acts largely at intermediate depths. Therefore, for example, in the soil cement walls 1A and 1B described above, the core material 3 may be composed of two or more members with different lengths in the height direction of the wall. In the illustrated example, the core material includes a core material 3A having a length L1 in the height direction of the wall and a core material 3B having a length L2 shorter than length L1, with one core material 3B arranged between the two core materials 3A. The present invention is not limited to this example, and it is possible to have a configuration in which a first core material having a first length (core material 3A in the above example) and a second core material having a second length shorter than the first length (core material 3B in the above example) are arranged between one or more first core materials at a predetermined period. Furthermore, in the illustrated example, the upper end height H2 of core material 3B is lower than the upper end height H1 of core material 3A, and the lower end height H3 of core material 3B is higher than the lower end height H4 of core material 3A. Considering the range of earth pressure as described above, such differences in the heights of the core materials (H1-H2 and H3-H4) may be within a range of, for example, 1 / 3 or less of the total height of the wall. Also, the heights of the core materials may differ only at the upper end and be the same at the lower end, or they may differ only at the lower end and be the same at the upper end, or they may differ at both the upper and lower ends, as in the illustrated example.

[0020] The shape of the joints connecting the core materials 3 in the soil cement walls 1A and 1B is not particularly limited, but for example, a combination of a C-shaped joint and a T-shaped joint as shown in Figure 3 may be used. Alternatively, a combination of C-shaped joints or a joint with a shape similar to that of a straight steel sheet pile joint may be used. In the example shown in Figure 3, joints are formed along the entire length of the core materials 3A and 3B, but joints do not necessarily have to be formed along the entire length of the core material; for example, they may be formed intermittently along the length of the core material.

[0021] In the embodiments of the present invention described above, the rigidity of the wall can be greatly improved by continuously arranging the core material 3 in the soil cement walls 1A and 1B. In this case, since high strength is not required for the soil cement 2, by using a solidifying agent with a high blast furnace slag content, the generation of carbon dioxide during the production of the solidifying agent can be suppressed, and the decrease in fluidity over time can be suppressed, that is, solidification can be delayed, thereby securing time to insert the core material 3 and improving workability. This also allows time to be secured to fit the joints of the core material 3 together during pouring, and makes it easier to vertically join the core material 3 when the wall height is high or when there are headroom restrictions. Adding a cement hardening retarder to suppress the decrease in fluidity over time of the solidifying agent is costly, but if the decrease in fluidity over time can be suppressed by increasing the blast furnace slag content, it is not necessary to add a cement hardening retarder, which is economical.

[0022] In the soil-cement walls 1A and 1B as described above, the solidifying agent mixed with the soil to form the soil-cement is preferably formulated such that the table flow value is 150 mm or more from immediately after the completion of the construction of the core material, specifically, from immediately after the soil-cement is placed in the ground to 3 hours later. Further, the solidifying agent is preferably formulated such that the table flow value is 100 mm or more, more preferably 200 mm or more, from immediately after the soil-cement is placed in the ground to 6 hours later. Thereby, it is possible to secure sufficient construction time for placing the core materials 3 while fitting the joints of the core materials 3 together. Further, for example, when the core material 3 has a length of 10 m or more and 60 m or less in the depth direction, at least one longitudinal joint is required during the placement of the core material 3. However, if 3 to 6 hours have elapsed since the placement of the soil-cement, it is sufficient for placing the core material 3 after making a longitudinal joint by welding or a joint. If the table flow value of the soil-cement is maintained at the above value during this time, the core material 3 can be placed smoothly.

[0023] The soil-cement walls 1A and 1B can be constructed by various known construction methods. For example, a process of manufacturing a solidifying agent by kneading cement and blast furnace slag on site may be carried out. In this case, for example, the formulation of the solidifying agent of the soil-cement to be constructed later can be adjusted while checking the above table flow value for the soil-cement constructed on site first. More specifically, for example, Portland cement, blast furnace slag fine powder, water, and a admixture may be kneaded on site to manufacture a solidifying agent.

[0024] As an example of the solidifying agent, in addition to using a suspension of blast furnace cement type C as described above, a solidifying agent with a high blast furnace slag content as described below may be used. This solidifying agent contains Portland cement (C), blast furnace slag fine powder (GGBFS) with a specific surface area of 3000 cm 2 or more and 10000 cm 2 or less, water (W), and an admixture (SP), and the mass ratio of each component satisfies the following conditions (1) to (3). Various types of Portland cement are used, but ordinary Portland cement or low-heat Portland cement is more preferable. Also, for 1.0 m of soil3 The amount of solidifying agent to be mixed is, for example, between 100 kg and 500 kg.

[0025] 60%≦GGBFS / (C+GGBFS)≦80% (1) 45%≦W / (C+GGBFS)≦250% (2) 0.1%≦SP / (C+GGBFS)≦5% (3) [Explanation of Symbols]

[0026] 1A, 1B... Soil cement wall, 2... Soil cement, 3, 3A, 3B... Core material.

Claims

1. A soil cement wall is constructed of soil cement, which is a mixture of soil and a solidifying agent containing cement and blast furnace slag, and steel core materials are cast into the soil cement, with the core material being continuously arranged in the direction of extension of the wall. 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 2.0 N / mm². ２ The following is a 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 height direction of the wall body.

3. The core material includes a first core material having a first length in the height direction of the wall and a second core material having a second length shorter than the first length in the height direction. The soil cement wall according to claim 1, wherein the second core material is arranged between one or more of the first core materials at a predetermined period.

4. The soil cement wall according to claim 3, wherein the upper end of the second core material is lower than that of the first core material.

5. The soil cement wall according to claim 3, wherein the lower end of the second core material is higher than that of the first core material.

6. 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)

7. 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.

8. A method for constructing a soil cement wall according to any one of claims 1 to 7, 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.

9. A method for constructing a soil cement wall according to any one of claims 1 to 7, 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.

10. A method for constructing a soil cement wall according to any one of claims 1 to 7, 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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