Method for evaluating the fluidity of mixed soil

Abstract

This invention provides an evaluation method that can evaluate the fluidity of a mixed soil, which is obtained by mixing the target soil with a solidifying agent, with high sensitivity. [Solution] A method for evaluating the fluidity of a mixed soil obtained by mixing target soil and a solidifying agent, comprising the step of determining the penetration stress when the tip of the plunger 1 penetrates the mixed soil by a texture test using a plunger 1 having a conical tip shape.

Description

Technical Field

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[0001] The present invention relates to a method for evaluating the fluidity of mixed soil.

Background Art

[0002] In recent years, as part of the efforts towards carbon neutrality, in order to reduce the amount of cement used in the manufacturing process and suppress carbon dioxide emissions, the development of new solidifying materials using materials instead of cement has been urgently needed. One of the items for determining whether such a new solidifying material is suitable for on-site construction is the fluidity of the mixed soil obtained by mixing the local soil and the new solidifying material in a slurry state. Conventionally, the evaluation of the fluidity of mixed soil has been performed by a table flow test as shown in Patent Document 1.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] <00000,25> However, there have been cases where the table flow test has low sensitivity regarding fluidity and has not been able to appropriately evaluate the mixed soil containing the new solidifying material. <00000,27> [[ID=,38]] The present invention has been made in view of such problems of the conventional technology. The object of the present invention is to provide an evaluation method capable of highly sensitively evaluating the fluidity of the mixed soil obtained by mixing the target soil and the solidifying material.

Means for Solving the Problems

[0006] A method for evaluating the fluidity of a mixed soil according to an aspect of the present invention is a method for evaluating the fluidity of a mixed soil obtained by mixing a target soil with a solidifying agent, and comprises the step of determining the penetration stress when the tip of a plunger penetrates the mixed soil by a texture test using a plunger having a conical tip shape. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide an evaluation method that can evaluate the fluidity of a mixed soil obtained by mixing the target soil with a solidifying agent with high sensitivity. [Brief explanation of the drawing]

[0008] [Figure 1] This is a front view showing the plunger used for texture testing. [Figure 2] This is a view from the direction of arrow AA in Figure 1, and is a top view showing the plunger used for the texture test. [Figure 3] This figure compares the evaluation results of the texture test and the table flow test. [Figure 4] This figure compares the evaluation results of the texture test and the table flow test. [Modes for carrying out the invention]

[0009] The method for evaluating the fluidity of the mixed soil according to this embodiment will be described in detail below with reference to the drawings. Note that the dimensional ratios in the drawings are exaggerated for illustrative purposes and may differ from the actual ratios.

[0010] The soil fluidity evaluation method according to this embodiment is a method for evaluating the fluidity of soil mixed with a target soil and a solidifying agent. The target soil refers to the soil before the solidifying agent is mixed in, such as the original ground soil that is the target of ground improvement. The solidifying agent refers to a solidifying agent slurry such as cement slurry containing a cement-based solidifying agent. As one of the ground improvement methods, it is known that a solidifying agent such as a cement-based solidifying agent is mixed into the target soil in order to effectively solidify soil with a high water content or soil that contains a large amount of organic matter.

[0011] In promoting carbon neutrality, there is a need to shift to alternative materials with lower carbon dioxide emissions in deep mixing methods, which heavily utilize cement as a solidifying agent, a material that emits large amounts of carbon dioxide during its manufacturing process. One criterion for determining whether a new solidifying agent can be adapted to the site is the fluidity of the mixed soil, which is the mixture of the target soil and the solidifying agent. If the fluidity of the mixed soil is low, the mixing accuracy decreases and the quality is affected, so it is essential to use a solidifying agent that results in a mixed soil with appropriate fluidity. Conventionally, in vertical mixing methods such as the soil-cement diaphragm wall method (TRD method) and the power blender method, as well as in deep mixing methods, the table flow test was sometimes used to determine the fluidity of the mixed soil. However, the table flow test has low sensitivity regarding the fluidity of the mixed soil, and there have been cases where it has not been able to properly evaluate mixed soil containing new solidifying agents. For this reason, in deep mixing methods, the accuracy of mixing is determined empirically by the number of mixing cycles and mixing time, and a method for evaluating fluidity based on the characteristics of the mixed soil before construction has not been established.

[0012] The method for evaluating the fluidity of a mixed soil according to this embodiment evaluates the fluidity of the mixed soil by a texture test instead of a table flow test. Specifically, the method for evaluating the fluidity of a mixed soil according to this embodiment includes a step of determining the penetration stress when the tip of the plunger 1 penetrates the mixed soil by a texture test using a plunger 1 with a conical tip shape, as shown in Figures 1 and 2. The texture test is a method for quantitatively determining the hardness of the mixed soil by applying dynamic shear. Furthermore, by using a plunger 1 with a conical tip shape, it is possible to more clearly identify differences in the fluidity of the mixed soil that could not be evaluated when using a general cylindrical plunger, and to evaluate with high sensitivity. Furthermore, from the viewpoint of accuracy in fluidity evaluation, the angle θ of the tip of the plunger 1 is preferably 20° or more and 40° or less, and more preferably 25° or more and 35° or less.

[0013] The soil mixture evaluated by the soil mixture fluidity evaluation method according to this embodiment may be applied to shallow or intermediate soil improvement methods other than deep mixing treatment methods, which use solidification as the improvement principle. Specifically, it is preferable to apply it to various methods of mixing the original ground soil with cement slurry, such as mechanical mixing methods, high-pressure jet mixing methods, mechanical and jet combined mixing methods, or TRD methods. Among these, it is particularly preferable to apply it to methods with relatively small cement addition amounts, such as mechanical mixing methods and TRD methods. [Examples]

[0014] The embodiment will be described in more detail below with reference to examples, but the embodiment is not limited to these examples.

[0015] (Preparation of test samples) Solidifying agents were prepared according to the formulations shown in Table 1 (unit: parts by mass), and each was mixed with clay to produce mixed soil. Example 1 is a mixed soil made by mixing blast furnace cement type B and clay. On the other hand, Examples 2 to 4 are mixed soils with reduced cement usage, and were made by mixing a solidifying agent made by adding blast furnace slag fine powder to blast furnace cement type B with clay. Texture tests and table flow tests were then conducted in Examples 1 to 4. The evaluation results are shown in Table 1 and Figure 3.

[0016] (Texture test) First, the mixed soil prepared as described above was filled without any gaps into a container with an internal diameter of 80 mm and a depth of 40 mm, and then placed on a tabletop physical property measuring instrument manufactured by Yamaden Co., Ltd., which is a texture testing device. Subsequently, one test was performed in which the tip of a plunger was inserted into the mixed soil from the top surface at a penetration speed of 2.5 mm / s and a penetration distance of 30 mm. The penetration stress (Pa) was automatically measured by the above testing device and determined by converting the maximum load at the time of penetration into stress.

[0017] In Figures 1 and 2, the length and outer diameter of the plunger used in the texture test, as well as the angle of the plunger tip, were as follows. • Tip length L1: 22.4 mm · Length L2 of the middle part: 17.6 mm · Length L3 of the upper part: 10 mm · Total length L4 of the tip part, middle part and upper part: 50 mm · Outer diameter D1 of the tip part: 12 mm · Outer diameter D2 of the middle part: 10 mm · Outer diameter D3 of the upper part: 5 mm · Angle θ of the tip part: 30°

[0018] (Table flow test) The table flow test was carried out in accordance with the physical test method for cement (Japanese Industrial Standard JIS R5201: 2015), and the table flow value (mm) was obtained.

[0019]

Table 1

[0020] The penetration stress of the texture test in Example 1 was 12070 Pa, while in Examples 2 to 4 it was 12420 Pa, 12080 Pa, and 12340 Pa respectively. Therefore, a difference was found between Example 1 using blast furnace cement type B alone and Examples 2 to 4. On the other hand, the table flow value of the table flow test was 110 mm for all the mixtures in Examples 1 to 4. The result of this table flow test was a very low value showing almost no fluidity, and no difference was found between Example 1 using blast furnace cement type B alone and Examples 2 to 4. Even if it was difficult to correctly evaluate the fluidity in the table flow test in this way, based on the results of the texture test, it was possible to evaluate the fluidity of the mixtures with reduced cement usage such as in Examples 2 to 4 and determine whether it was adaptable to the site. That is, according to the fluidity evaluation method of the mixture according to this embodiment, it is possible to determine whether the stirring state of the blended cement slurry and the in-situ soil is suitable for construction and quality.

[0021] Next, solidifying agents were prepared according to the formulations shown in Table 2 (unit: parts by mass), and each was mixed with clay to produce mixed soil. Examples 5 to 10 are mixed soils with reduced cement usage, and consisted of a solidifying agent made by adding blast furnace slag powder and magnesium oxide to blast furnace cement type B, mixed with clay. Texture tests and table flow tests were then conducted in Examples 5 to 10 using the same method as described above. The evaluation results are shown in Figure 4.

[0022] [Table 2]

[0023] As shown in Figure 4, the penetration stress in the texture test for Examples 5-10 ranged widely from 11800 Pa to 16700 Pa. On the other hand, the table flow values ​​in the table flow test for Examples 5-10 remained within the range of 104 mm to 112 mm, showing little difference. Thus, even if it is difficult to accurately evaluate fluidity in the table flow test, it is possible to evaluate the fluidity of mixed soil with reduced cement usage, such as in Examples 5-10, based on the results of the texture test, and to determine whether it can be adapted to the site. In other words, according to the fluidity evaluation method of mixed soil according to this embodiment, it is possible to determine whether the mixing conditions between the mixed cement slurry and the in-situ soil are suitable for construction and quality.

[0024] Thus, according to the soil fluidity evaluation method of this embodiment, even for soil mixtures where fluidity cannot be correctly determined by a table flow test, the fluidity can be correctly determined by conducting a texture test.

[0025] As described above, the fluidity evaluation method for mixed soil according to this embodiment is a method for evaluating the fluidity of mixed soil obtained by mixing a target soil with a solidifying agent. This fluidity evaluation method includes a step of determining the penetration stress when the tip of a plunger penetrates the mixed soil by a texture test using a plunger with a conical tip. Therefore, it is possible to provide an evaluation method that can evaluate the fluidity of mixed soil obtained by mixing a target soil with a solidifying agent with high sensitivity.

[0026] Although this embodiment has been described above, this embodiment is not limited to these, and various modifications are possible within the scope of the gist of this embodiment. [Explanation of Symbols]

[0027] 1 Plunger θ Angle of the plunger tip

Claims

1. A method for evaluating the fluidity of a mixed soil obtained by mixing the target soil with a solidifying agent, A method for evaluating the fluidity of a mixed soil, comprising the step of determining the penetration stress when the tip of a plunger penetrates the mixed soil by a texture test using a plunger having a conical tip shape.

2. The method for evaluating the fluidity of a mixed soil according to claim 1, wherein the angle of the tip of the plunger is 20° or more and 40° or less.

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