JP4628082B2 - How to prevent ground liquefaction - Google Patents

Description

  The present invention relates to a ground liquefaction prevention method for preventing liquefaction of a sandy soil layer directly under a structure, for example.

  As a method for preventing liquefaction of this type of ground, there is a method shown in FIGS. 5 and 6 (see, for example, Patent Document 1). In this ground liquefaction prevention method, as shown in FIG. 5 and FIG. 6, first, a rectangular tubular water blocking wall in which the non-liquefied layer 4 is embedded in the outer periphery of the ground 2 on which the structure 1 is constructed. 5, an aqueous solution in which aluminum powder (foaming agent) is dissolved is injected into the sandy soil layer 3, which is a liquefied layer of the ground 2, from an injection hole 6 formed in the ground 2 in the water blocking wall 5.

Then, when the groundwater is pumped up by the pump 8 from the drainage hole 7 drilled in the ground 2 in the water blocking wall 5, the flow of the groundwater becomes the drainage hole 7 from the injection hole 6, and the aqueous solution in which the aluminum powder is dissolved is structured. It penetrates into the sandy soil layer 3 directly under the object 1. Next, when cement supernatant water (reactant) in which calcium hydroxide is dissolved is injected from the injection hole 6, this calcium hydroxide reacts with the aluminum powder to generate hydrogen gas (H ₂ ). Since the sandy soil layer 3 is unsaturated by the hydrogen gas, the liquefaction resistance of the ground 2 of the sandy soil layer 3 is increased, and liquefaction can be prevented.

Here, the liquefaction of the ground means that when the ground with high water content is deformed by an impact or vibration due to an earthquake, the water pressure of pore water existing in a saturated state between soil particles is more rapidly than the hydrostatic pressure. As a result, the frictional resistance between the soil particles disappears, and as a result, the ground behaves like a liquid and loses its proof strength. Further, the water pressure at a portion higher than the hydrostatic pressure is referred to as excess pore water pressure, and when this excess pore water pressure becomes equal to the effective upper loading pressure at that depth, the sand particles are disconnected from each other and floated in water. In the ground liquefaction prevention method described above, desaturation of the sandy soil layer 3 is attempted by reducing the degree of saturation of the sandy soil layer 3 with hydrogen gas.
JP 2001-355228 A Japanese Patent Laid-Open No. 2003-90032 JP-A-8-3975

  However, in the conventional ground liquefaction prevention method, in order to allow groundwater to flow from the injection hole 6 to the drain hole 7, the water stop wall 5 must be provided on the ground 2 around the structure 1. As it increased, construction work became large, and it took a long time for liquefaction countermeasures, resulting in high costs. Further, in order to generate hydrogen gas, two materials, a foaming agent such as aluminum powder and a reactive agent such as calcium hydroxide, are indispensable, which further increases the cost.

  Accordingly, the present invention has been made to solve the above-described problems, and an object of the present invention is to provide a ground liquefaction prevention method capable of reliably and inexpensively preventing ground liquefaction by simple work. And

According to a first aspect of the present invention, there is provided a ground liquefaction prevention method in which bubbles are diffused into a ground liquefied layer to bring the liquefied layer into an unsaturated state. A tube filled with dry ice is inserted into the plurality of sealed spaces, and then a plurality of sealed spaces are formed in the boring holes corresponding to the plurality of sealed spaces of the tubes. The closed spaces and the closed spaces in the boreholes are communicated with each other, carbon dioxide gas generated from the dry ice is diffused, and after the dry ice is completely vaporized, the pipes are opened from the borehole. The plugging material is injected into the boring hole while pulling out the material.

As described above , according to the first aspect of the present invention, a tube filled with dry ice is inserted into a boring hole formed in the ground, and after the dry ice is vaporized, the boring hole is pulled out with a closing material while the tube is pulled out. The liquefaction layer of the ground can be brought into an unsaturated state by a simple operation that only blocks. Thereby, the liquefaction resistance of the liquefied layer can be increased, and the liquefaction of the ground can be reliably prevented at low cost.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic enlarged cross-sectional view of the main part showing the unsaturated state of the ground by the ground liquefaction prevention method of the embodiment of the present invention, FIG. 2 is an overall schematic cross-sectional view showing the unsaturated state of the ground, FIG. Fig. 4 is a partial schematic view showing a state where a pipe is inserted into a borehole of the ground, and Fig. 4 is a partial schematic view showing a state where a shutter for opening and closing the opening window of the pipe is opened.

  As shown in FIGS. 1 and 2, the ground liquefaction prevention method according to the embodiment of the present invention is a sandy soil layer 12 that is a liquefied layer of the ground 11 on which an existing building (structure) 10 is constructed. It is applied to liquefaction measures.

  In this method for preventing liquefaction of the ground 11, first, as shown in FIG. 2, an oblique boring hole is formed in the sandy soil layer 12 of the ground 11 directly below the existing building 10 using a boring machine 9 such as a boring machine. (Drilling hole) 13 is formed. Next, a metal made by filling a predetermined amount of dry ice (solid to be vaporized) 30 in a closed space 24 formed by a plurality of shutters 23 for opening and closing each partition wall 21 and each opening window 22 in the boring hole 13. Then, a long tube (casing pipe) 20 is inserted.

Next, an air bag (shielding means) 25 made of rubber or the like attached to the outer periphery of each partition wall 21 of the tube 20 is inflated to form a plurality of sealed spaces S in the borehole 13. Next, the opening windows 22 formed in the sealed spaces 24 (between the pair of partition walls 21 and 21) of the pipe 20 are opened by moving the shutters 23 in the circumferential direction of the pipe 20. And the sealed spaces S in the borehole 13 are communicated with each other. Thereby, the dry ice 30 between each pair of partition walls 21 and 21 of the pipe 20 reacts with water or the like of the sandy soil layer 12 to generate carbon dioxide gas (CO ₂ ). Since this carbon dioxide gas is easily dissolved in water or the like, a large amount of carbon dioxide gas (bubbles) 15 can be contained in the ground 11 as shown in FIG.

  Next, after the dry ice 30 is completely vaporized, a grout material (blocking material) 14 is injected into the boring hole 13 from the tip of the pipe 20 while pulling out the pipe 20 from the boring hole 13. Then, the closing operation in the boring hole 13 by the grout material 14 is performed to the vicinity of the ground surface of the ground 11, and finally the boring hole 13 at the ground surface portion of the ground 11 is completely covered with the grout material 14 as shown in FIG. Block it. A predetermined number of boreholes 13 formed in this manner are formed obliquely in the sandy soil layer 12 immediately below the existing building 10. In addition, the solid to vaporize is not restricted to dry ice.

In this way, the tube 20 filled with the dry ice 30 is inserted into the boring hole 13 of the sandy soil layer 12 of the ground 11, and after the dry ice 30 is vaporized, the grout material 14 is drawn inside the boring hole 13 while pulling out the tube 20. The sandy soil layer 12 can be brought into an unsaturated state by a simple operation that is simply blocked by. That is, carbon dioxide gas (CO ₂ ) is generated when the dry ice 30 reacts with water or the like of the sandy soil layer 12. Since this carbon dioxide gas is easily dissolved in water or the like, a large amount of carbon dioxide gas 15 can be contained in the ground 11 as shown in FIG.

  Further, since carbon dioxide gas is heavier than air, the carbon dioxide gas does not escape to the ground surface side of the ground 11, and the carbon dioxide gas 15 dissolved in the water or the like diffuses around the borehole 13 of the sandy soil layer 12. The diffusion state is maintained over time. Thereby, the liquefaction resistance of the sandy soil layer 12 can be increased and the sandy soil layer 12 can be always kept in an unsaturated state, and the liquefaction of the ground 11 can be prevented reliably and at low cost. Since the carbon dioxide gas 15 dissolved in the water in the sandy soil layer 12 is further vaporized by vibration during an earthquake or the like, liquefaction of the sandy soil layer 12 of the ground 11 can be more effectively prevented. .

  Furthermore, even in the ground 11 directly under the existing building 10, the sandy soil layer 12 of the ground 11 can be easily and reliably brought into an unsaturated state. Moreover, since the displacement of the ground 11 is small at the time of this construction, the influence on the adjacent structures can be minimized.

  According to the embodiment, the slanted boring holes 13 are formed in the sandy soil layer 12 of the ground 11 to prevent the sandy soil layer 12 of the ground 11 from being liquefied. The boring hole 13 may be formed vertically.

Further, according to the embodiment, dry ice is used as the vaporized solid, but instead of the vaporized solid, the vaporized liquid such as highly volatile alcohol is sandy through a predetermined means such as a liquid supply pipe. Even if it is directly injected into the soil layer (liquefied layer) 12, the same effect as that of the above embodiment can be obtained. The vaporized liquid includes carbonated water in which a gas such as carbon dioxide gas (CO ₂ ) is dissolved. If carbonated water in which this gas is dissolved is injected into the sandy soil layer 12 through a predetermined means such as a liquid supply pipe, the carbonated water in which the gas is dissolved penetrates deeper into the sandy soil layer 12, for example, A large amount of carbon dioxide bubbles that have been melted by shaking due to vibration such as an earthquake are generated, and the sandy soil layer 12 can be more effectively prevented from being liquefied.

Further, carbon dioxide gas (CO ₂ ) is used instead of the vaporized solid, and this carbon dioxide gas is directly injected into the sandy soil layer (liquefied layer) 12 through a predetermined means such as a gas supply pipe. However, the same effect as the above embodiment can be obtained.

It is a general | schematic expanded sectional view of the principal part which shows the unsaturated state of the ground by the ground liquefaction prevention method of embodiment of this invention. It is the whole schematic sectional drawing which shows the unsaturated state of the said ground. It is the partial schematic which shows the state which inserted the pipe | tube in the boring hole of the said ground. It is the partial schematic diagram which shows the state which opened the shutter which opens and closes the opening window of the said pipe | tube. It is sectional drawing which shows the unsaturated state of the ground by the conventional liquefaction prevention method of the ground. It is explanatory drawing which shows the unsaturated state of the said conventional ground as a plane.

Explanation of symbols

11 Ground 12 Sandy soil layer (liquefaction layer)
13 Boring hole 14 Grout material (occlusion material)
15 Carbon dioxide gas 20 Tube 24 Sealed space 30 Dry ice (vaporized solid)
S sealed space

Claims (1)

In the method of preventing liquefaction of the ground by diffusing bubbles in the liquefied layer of the ground and making the liquefied layer unsaturated.
A boring hole is formed in the ground, a tube filled with dry ice is inserted into the plurality of sealed spaces, and then a plurality of holes are inserted into the boring holes corresponding to the plurality of sealed spaces of the tube. Next, each sealed space of these pipes and each sealed space in the borehole are communicated to diffuse carbon dioxide gas generated from the dry ice, and then the dry ice is completely A method for preventing ground liquefaction, wherein a plugging material is injected into the borehole while the tube is pulled out from the borehole after being vaporized .

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