Liquefaction prevention method

Abstract

By using materials that do not harden excessively and employing simple construction methods, liquefaction in the target area is prevented by natural processes. [Solution] The liquefaction prevention method for preventing liquefaction of the ground 1 includes an excavation step of excavating a cylindrical hole 3 in the ground 1 with an auger 2, a mixed material generation step of mixing a portion of the excavated soil 4 discharged from the hole 3 by the excavation step with fine and micro-grained natural soil from the outside to generate a mixed material 5, wherein the mixed material 5 does not contain cement-based solidifying agents or quicklime, and a column generation step of filling the hole 3 with the mixed material 5 generated in the mixed material generation step to compact the hole 3 and generate a column 6 of the mixed material 5 inside the hole 3, after the column 6 is generated, the fine and micro-grained particles inside the column 6 diffuse into the surrounding area by natural action.

Description

Technical Field

[0001] The present invention relates to a liquefaction prevention method.

Background Art

[0002] Liquefaction caused by seismic motion occurs, for example, in loose sandy soil layers with a high water content. When the ground vibrates strongly due to an earthquake, substances heavier than water sink, and relatively light water rises near the ground surface. Furthermore, when the rising water moves horizontally and upward, the ground and surface structures are damaged by the water pressure. These series of actions are one problem due to ground liquefaction.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As disclosed in Patent Document 1, a method of driving a columnar improvement body containing steel material as a core material into the ground is known. However, when such a strong improvement body is used for general liquefaction countermeasures, there is a problem that it becomes an obstacle when the ground is used for another purpose in the future.

[0005] To prevent liquefaction, it is generally preferable to reduce the gaps between particles that make up the ground and increase the bonding between particles in order to prevent the movement of pore water. Here, one might consider installing columns containing cement-based solidifying material or quicklime to prevent liquefaction, but these columns are excessively hard, posing a problem as they become obstacles that hinder future reuse of the ground. Furthermore, using cement-based solidifying material may have adverse environmental effects such as the leaching of hexavalent chromium and alkalization of the ground. Another method of preventing liquefaction could be to excavate the entire affected ground and replace it with another hard material, but this is not practical from the standpoint of securing scaffolding.

[0006] This invention has been made in view of the above circumstances, and its purpose is to provide a liquefaction prevention method that uses a material that does not harden excessively and can prevent liquefaction of a target area through natural processes using a simple construction method. [Means for solving the problem]

[0007] The first embodiment of the liquefaction prevention method is a liquefaction prevention method for preventing soil liquefaction, and the liquefaction prevention method includes an excavation step of excavating a cylindrical hole in the ground with an auger, a mixed material generation step of generating a mixed material by mixing only fine particles and microparticles obtained from natural soil with a portion of the excavated soil discharged from the hole by the excavation step, wherein the mixed material does not contain cement-based solidifying agents and quicklime, and a column generation step of generating a column of mixed material in the hole by compacting and filling the hole with the mixed material generated in the mixed material generation step, wherein after the column is generated, the column is left to stand so that the fine particles and microparticles in the column diffuse into the surrounding area by natural forces.

[0008] According to the first embodiment, by using a material that does not harden excessively and employing a simple construction method, liquefaction of the target ground can be prevented by natural processes. Furthermore, since the fine and micrograined components are derived from natural soil, they do not have an adverse effect on the environment.

[0009] In the liquefaction prevention method of the second aspect, when the volume of the ground to be prevented from liquefaction is V1, the volume of each column is VC, the number of columns is N, the volume of the fine particles added from the outside among the mixed materials of each column is V2 (V2 < VC), and the volume of the fine particles added from the outside among the mixed materials of each column is V3 (V3 < VC), V1 × 0.35 ≤ N × V2... (Equation 1) V1 × 0.10 ≤ N × V3... (Equation 2) The liquefaction prevention method according to the first aspect, wherein N, V2, and V3 are selected so that both of the above are satisfied.

[0010] According to the second aspect, when it is assumed that the fine particles and fine particles in the column are uniformly dispersed in the target ground by the action of nature over time, the target ground contains 35% or more of the fine particles and 10% or more of the fine particles, and liquefaction can be effectively prevented.

[0011] The liquefaction prevention method of the third aspect is the liquefaction prevention method according to the second aspect, in which a plurality of columns are arranged so as to be in contact with each other and form a row when viewed from above the target ground.

[0012] According to the third aspect, since a plurality of columns are arranged so as to form a continuous row, even before the fine particles and fine particles diffuse, the column becomes a water stop wall that prevents the long-distance movement of water in the target ground, and the damage of liquefaction can be effectively prevented.

[0013] The liquefaction prevention method of the fourth aspect is the liquefaction prevention method according to the third aspect, in which the rows are arranged so as to draw a closed line when viewed from above the target ground.

[0014] According to the fourth aspect, since the columns are arranged to draw closed lines, even before the fine particles and the microparticles diffuse, the columns serve as a cutoff wall that prevents the long-distance movement of water in the target ground closed in the horizontal direction, and can effectively prevent the damage caused by liquefaction. Further, the ground surrounded by the continuous columns in the target ground can be integrated to serve as a cutoff wall against the surroundings.

Effects of the Invention

[0015] According to the present invention, it is possible to prevent the liquefaction of the target area by the action of nature with a simple construction method using a material that does not become overly hard.

Brief Description of the Drawings

[0016] [Figure 1] It is a schematic cross-sectional view for explaining the state during the excavation process. [Figure 2] It is a schematic cross-sectional view for explaining the mixed material generation process. [Figure 3] It is a schematic cross-sectional view for explaining the state during the column generation process. [Figure 4] It is a schematic cross-sectional view after the column generation process is completed. [Figure 5] It is a plan view showing an arrangement example of a plurality of columns. [Figure 6] It is a plan view showing another arrangement example of a plurality of columns.

Modes for Carrying Out the Invention

[0017] An embodiment of a liquefaction prevention method for preventing the liquefaction of the ground will be described.

[0018] In the liquefaction prevention method, first, an excavation process is carried out. FIG. 1 is a schematic cross-sectional view for explaining the state during the excavation process. In the excavation process, as shown in FIG. 1, a generally cylindrical hole 3 is excavated in the ground 1 using an auger 2 for excavating the ground 1. During excavation, by rotating the auger 2 clockwise, the ground 1 is excavated, and at the same time, the excavated soil 4, which is the soil that constituted the ground 1, is sent upward by a spiral conveying section, and the excavated soil 4 is discharged outside the hole 3. As the auger 2, for example, the auger 2 disclosed in Japanese Patent No. 7073028 can be used.

[0019] FIG. 2 is a schematic cross-sectional view for explaining the mixed material generation process carried out after the excavation process. When the excavation process ends, a generally cylindrical hole 3 of a desired depth is formed as shown in FIG. 2. In the mixed material generation process, on the ground surface, fine particles and microparticles are externally mixed with a part of the excavated soil 4 discharged from the hole 3 by the excavation process, and the mixed material 5 is generated by sufficiently stirring using a heavy machine. The mixed material 5 does not contain a cement-based solidifying material and quicklime.

[0020] FIG. 3 is a schematic cross-sectional view for explaining the state during the column generation process carried out after the mixed material generation process. In the column generation process, while sending the mixed material 5 generated in the mixed material generation process from the ground surface to below the hole 3 by rotating the auger 2 counterclockwise, the hole 3 is filled with the mixed material 5. The auger 2 compresses the mixed material 5 downward and compresses it in such a way that the mixed material 5 is applied horizontally to the inner wall of the vertically extending hole 3.

[0021] FIG. 4 is a schematic cross-sectional view after the column generation process is completed. A cylindrical column 6 is generated in the hole 3 by the column generation process. In this example, the column 6 extends from the ground surface to the lowermost end of the hole 3. In other examples, the upper end of the column 6 may be lower than the ground surface, and the lower end of the column 6 may be above the lowermost end of the hole 3. For example, a stabilizing material for stabilizing the hole 3 may be introduced at the lowermost end of the hole 3, and the column 6 may be formed on the stabilizing material. For example, a material serving as a lid for the hole 3 may be placed above the column 6.

[0022] After the column generation process is completed and column 6 is generated, column 6 is left unattended, and the fine particles and microparticles in column 6 diffuse to the periphery by natural action. The diffusion by natural action includes, for example, diffusion due to vibrations in the vertical, horizontal, rotational, and other directions caused by an earthquake including initial ground motion, and diffusion associated with the movement of rainwater and groundwater, but is not limited thereto. The mixed materials 5 in column 6 are not adhered so as not to separate from each other, but are compacted to such an extent that they can be naturally dispersed later. Also, the formulation is determined such that the mixed materials 5 in column 6 do not combine integrally.

[0023] Here, the preparation of the mixed material 5 in the mixed material generation process will be described in detail. As shown in FIG. 4, a target ground 8 surrounded by, for example, a boundary 7 is determined in advance as a range for preventing liquefaction. Let the volume of the target ground 8 be V1. Assume that N columns 6 are formed in the target ground 8 by the above liquefaction prevention method. Let the volume of each column 6 be VC. Let the volume of the fine particles added from the outside among the mixed materials 5 of each column 6 be V2 (V2 < VC). Let the volume of the microparticles added from the outside among the mixed materials 5 of each column 6 be V3 (V3 < VC). Here, N, V2, and V3 are selected such that both of the following equations (1) and (2) are satisfied. V1×0.35≦N×V2 …(Equation 1) V1×0.10≦N×V3 …(Equation 2)

[0024] The fine particles include at least one of sand particles and soil particles. The sand particles are an aggregate of particles with a maximum particle size of less than 2 mm and a size of 0.2 mm or more. The soil particles are an aggregate of particles with a maximum particle size of less than 0.2 mm and a size of 0.02 mm or more. The microparticles, also called clay, are an aggregate of particles with a maximum particle size of less than 0.02 mm. The fine particles and microparticles are materials obtained from natural soil. Here, the natural soil is not limited to soil particles, but is assumed to include particles with a wide range of particle sizes including the fine particles and microparticles obtained from nature.

[0025] According to the research, assuming that the fine and micrograined particles in column 6 are uniformly dispersed within the target ground 8 by natural processes over time, liquefaction can be effectively prevented if the target ground 8 contains more than 35% fine particles and more than 10% micrograined particles. In one example, V2:V3 = 35:10. The time required for uniform dispersion is, for example, 40 years. However, even before complete uniform dispersion, liquefaction can be effectively suppressed in the vicinity of column 6.

[0026] Mixed material 5 does not contain solidifying agents. In particular, since mixed material 5 does not contain cement-based solidifying agents or quicklime, the column 6 does not become excessively hard, and liquefaction of the target ground 8 can be prevented by natural processes using a simple construction method. Since the column 6 does not become excessively hard, there is the advantage that the column 6 does not become an obstacle during construction even when the target ground 8 is reused. In addition, since mixed material 5 does not contain cement-based solidifying agents or quicklime, there are no adverse environmental impacts. In particular, since cement-based solidifying agents are not used, there is the advantage that there are no adverse environmental impacts such as the leaching of hexavalent chromium and alkalization of the ground.

[0027] Figure 5 is a plan view showing an example of the arrangement of multiple columns 6. As shown in Figure 5, when the target ground 8 is viewed from above, multiple columns 6 are arranged to form a continuous row. In this example, the columns 6 are arranged so that their outer edges are touching each other, and the arrangement as a whole forms a straight line. In other words, the centers of the columns 6 are aligned on a straight line. In other examples, the row may be arranged to form a curve. In other examples, two or more adjacent columns 6 may partially overlap.

[0028] Figure 6 is a plan view showing another example of the arrangement of multiple columns 6. As shown in Figure 6, when the target ground 8 is viewed from above, the multiple columns 6 are arranged in a continuous row that forms a closed line. In this example, the columns 6 are arranged so that their outer edges touch each other, forming a square as a whole. In other words, the centers of the columns 6 are located on the outer edge of the square. In other examples, the rows may be curved. In other examples, two or more adjacent columns 6 may partially overlap. In other examples, the multiple columns 6 may be arranged at a distance from each other.

[0029] (summary) According to this embodiment, by using a material that does not harden excessively and employing a simple construction method, liquefaction of the target ground 8 can be prevented by natural processes. Furthermore, since the fine and micrograined components are derived from natural soil, they do not have an adverse effect on the environment.

[0030] According to this embodiment, assuming that the fine particles and microparticles in column 6 are uniformly dispersed within the target ground 8 by natural processes over time, the target ground 8 will contain 35% or more fine particles and 10% or more microparticles, thereby effectively preventing liquefaction.

[0031] According to the embodiments illustrated in Figures 5 and 6, since the multiple columns 6 are arranged in a continuous row, even before the fine particles and microparticles diffuse, the columns 6 act as a watertight barrier that prevents the long-distance movement of water within the target ground 8, thereby effectively preventing liquefaction damage.

[0032] According to the embodiment illustrated in Figure 6, since the columns are arranged to form a closed line, even before fine and micro-grained particles diffuse, the columns 6 act as a watertight barrier that prevents the long-distance movement of water within the horizontally enclosed target ground 8, thereby effectively preventing liquefaction damage. Furthermore, the ground surrounded by the continuous columns 6 within the target ground 8 can act as a single unit, serving as a watertight barrier to the surrounding area. [Explanation of symbols]

[0033] 1...Ground, 2...Auger, 3...Hole, 4...Excavated soil, 5...Mixed material, 6...Column, 7...Boundary 8…Target ground

Claims

1. A liquefaction prevention method for preventing soil liquefaction, and the liquefaction prevention method is, An excavation process in which a cylindrical hole is excavated in the ground using an auger, A mixed material production step in which a portion of the excavated soil discharged from the hole by the excavation step is mixed with only fine particles and microparticles obtained from natural soil from an external source to produce a mixed material, wherein the mixed material does not contain cement-based solidifying agent and quicklime. A column generation step is performed in which the mixed material generated in the mixed material generation step is used to compact and fill the hole, thereby generating a column of the mixed material within the hole. Includes, After the column is generated, the column is left to stand so that the fine particles and microparticles within the column diffuse into the surrounding area by natural processes. Liquefaction prevention method.

2. Let V1 be the volume of the target ground to be prevented from liquefaction. Let VC be the volume of each of the aforementioned columns. Let N be the number of columns. Let V2 be the volume of the fine particles added from the outside of the mixed material in each column (V2 < VC). When the volume of the fine particles added from the outside of the mixed material in each of the columns is V3 (V3 < VC), V1×0.35≦N×V2…(Formula 1) V1×0.10≦N×V3…(Formula 2) N, V2, and V3 are selected such that both conditions are met. The liquefaction prevention method according to claim 1.

3. When the target ground is viewed from above, the multiple columns are arranged in a row, touching each other. The liquefaction prevention method according to claim 2.

4. When the aforementioned target ground is viewed from above, the rows are arranged to form a closed line. The liquefaction prevention method according to claim 3.

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