JP7044339B2 - Improved ground and ground improvement method - Google Patents

Description

The present invention relates to an improved ground and a method for improving the ground.

The following Patent Document 1 discloses a ground improvement method for forming a columnar consolidated body in the ground to prevent liquefaction. This columnar consolidated body is formed by forming an excavation hole using an excavator and filling the excavation hole with grout and earth and sand mixed by stirring. In addition, grout is press-fitted in a pulse shape around the excavation hole to prevent the columnar consolidated body from collapsing and floating when the surrounding ground is liquefied.

Japanese Unexamined Patent Publication No. 2013-68017

In the ground improvement method described in Patent Document 1, a columnar solidified body is formed through steps such as excavation, stirring and mixing, and press-fitting. If the ground is to be improved over a wide area, it is necessary to repeat these steps to provide a plurality of columnar consolidated bodies, which requires a lot of construction work. Therefore, the range in which the ground can be improved is limited.

It is an object of the present invention to provide an improved ground and a ground improvement method capable of freely setting a ground improvement range in consideration of the above facts.

One aspect of the ground improvement body is formed of a supercooled solution in a solidified state in the ground and does not include a panel for freezing the ground.

One aspect of the ground improvement body is formed by infiltrating a supercooled solution into the ground and stimulating it at an arbitrary timing or adding a crystallization agent to solidify it. Therefore, the ground improvement range can be freely set.

On the other hand, for example, when the ground is improved over a wide area by using cement that does not easily penetrate into the ground, a stirring device such as an auger is required to form a ground improvement body in which the cement and the soil in the ground are mixed. Furthermore, since it is necessary to provide a plurality of these, it takes time and effort to construct. In addition, when injecting a drug solution, solidification progresses over time, depending on the type and composition of the drug used. Therefore, there is a limit to the range of ground improvement in one construction.
In one aspect of the improved ground, the supercooled solution has a melting point higher than the temperature of the ground.
The ground improvement method according to claim 1 is to solidify the supercooled solution in the ground by injecting a crystallization agent into the ground in which a supercooled solution having a melting point higher than the temperature of the ground surrounded by an impermeable wall has permeated. To form an improved ground.

The ground improvement method according to claim 2 includes a step of constructing an impermeable wall surrounding a predetermined area on the ground, a step of constructing a water injection well and a pumping well on the ground inside the impermeable wall, and the pumping well. A step of pumping groundwater from the water injection well, a step of injecting a supercooled solution from the water injection well into the ground, and a crystallization agent being poured into the ground in which the supercooled solution has permeated to solidify the supercooled solution to shield the water. It has a step of hardening the ground inside the wall.

In the ground improvement method of claim 2 , the supercooled solution is infiltrated into the ground surrounded by the impermeable wall, and a crystallization agent is added to solidify the supercooled solution. Since the supercooled solution does not solidify until the crystallization agent is added, it can be solidified after permeating the entire area of the ground surrounded by the impermeable wall. Therefore, regardless of the scale of the part surrounded by the impermeable wall, the entire area can be improved. That is, the ground improvement range can be freely set.

On the other hand, for example, when improving the ground using cement that does not easily penetrate into the ground, it is necessary to form a pile-shaped ground improvement body that is a mixture of cement and soil in the ground, and it is necessary to provide multiple of these. It takes time and effort. In addition, when injecting a drug solution, solidification progresses with the passage of time, although it depends on the type and composition of the drug used, so there is a limit to the adjustment of the solidification time.

In the ground improvement method of claim 3 , a surfactant that lowers the freezing point is added to the supercooled solution.

In the ground improvement method of claim 3 , the freezing point of the supercooled solution is lowered by the surfactant. The lower the temperature of the supercooled solution than the melting point and the closer the temperature is to the freezing point, the more unstable the supercooled state becomes, and the more easily the supercooled solution is stimulated and solidified without giving a crystallization agent. That is, it becomes easy to solidify at an unintended timing. By lowering the freezing point of the supercooled solution with a surfactant, the supercooled state can be stabilized even in a low temperature state.

According to the improved ground and the ground improvement method according to the present invention, it is easy to improve the ground in a wide range.

It is a graph which shows the relationship between the cooling time at the time of cooling the supercooled solution used in the improved ground and the ground improvement method which concerns on embodiment of this invention, and the temperature of a supercooled solution. It is a plot figure which shows the uniaxial compression strength according to the mixing ratio of water in the strength test body using the sodium acetate trihydrate as a supercooling solution which concerns on embodiment of this invention. 6 is a graph showing the relationship between strain and compressive stress according to the mixing ratio of water in a strength test piece using sodium acetate trihydrate as a supercooled solution according to the embodiment of the present invention. It is sectional drawing which shows the ground improvement method which concerns on embodiment of this invention, (A) shows the state which the impermeable wall, the water injection well and the pumping well were constructed in the ground, (B) injects the supercooling solution into the ground. (C) shows the state in which the crystallization agent is charged into the water injection well, (D) shows the state in which the solidification reaction of the supercooled solution is proceeding by the crystallization agent, and (E). Shows the state where the supercooled solution solidified and the improved ground was formed.

(Improved ground)
As shown in FIG. 4 (E), the improved ground G2 according to the present embodiment is a ground G in which sodium acetate trihydrate (CH ₃ COONa · 3H ₂ O) as a supercooling solution is surrounded by an impermeable wall 50. It is a hardened ground formed by solidifying inside.

(Supercooled solution)
As shown in FIG. 1, the supercooled solution retains a liquid state in a temperature range higher than the melting point, like liquids other than the supercooled solution (A to B). The supercooled solution does not solidify even when cooled to a temperature range below the melting point and maintains a liquid state (BC). This phenomenon is called "supercooling", and this state is called "supercooling state". The supercooled solution in the liquid state (A to C) has a viscosity lower than that of cement, and can be infiltrated into the ground by press-fitting into the permeable layer or the impermeable layer in the ground.

When a stimulus such as vibration is given to the supercooled solution in the supercooled state, crystallization starts from the place where the stimulus is given and solidifies while generating heat of solidification (C to D). In addition to the method of stimulating the supercooled solution in the supercooled state, a method of adding a crystallizing agent (crystallized solid supercooled solution) into the supercooled solution in the supercooled state is used. , A method of injecting a supercooled solution in a supercooled state toward a crystallization agent, a method of cooling to a freezing point, and the like.

The supercooled solution in the supercooled state is maintained in a liquid state when it is continuously cooled without giving any irritation and without contacting it with a crystallization agent. If cooling is continued while maintaining the liquid state, it will eventually reach the freezing point and solidify. The difference between this melting point and the freezing point is called the degree of supercooling. The smaller the degree of supercooling, the more unstable the supercooled state becomes, and the weaker the stimulus is, the more unstable the supercooled state becomes. In other words, when there are two types of supercooled solutions in the supercooled state, the supercooled solution having a high freezing point is in an unstable state than the supercooled solution having a low freezing point, and it is highly probable that the supercooled solution will solidify by an unintended stimulus.

Once solidified, the supercooled solution retains its solid state unless heated to its melting point (DE). The improved ground G2 in the present embodiment hardens the ground G by utilizing the compressive strength of the supercooled solution in a solid state that has penetrated between the soil particles to improve the ground.

The "melting point" in the present embodiment is the temperature at which the supercooled solution in the solidified state melts, and the "freezing point" is the temperature at which the supercooled solution in the liquefied state solidifies. ..

The supercooled solution in the present embodiment contains sodium acetate trihydrate produced by mixing water at a ratio of 100:66 (molecular weight ratio) to anhydrous sodium acetate and heating and melting. The supercooled solution containing sodium acetate trihydrate is a substance that maintains a supercooled state at an underground temperature (10 to 20 ° C.), and has a melting point of about 58.0 ° C. The freezing point is 0 ° C. or lower. This freezing point is adjusted by a surfactant described later. As a result, the supercooled solution is maintained in a supercooled state in the ground where the temperature is lower than the melting point and the temperature is higher than the freezing point, and the supercooled solution can be solidified by stimulation or addition of a crystallization agent. Further, after solidification, the ground does not melt unless it is heated to 58.0 ° C. or higher.

(Surfactant)
In addition to sodium acetate trihydrate, oxycarboxylate-based Floric (registered trademark) T is added to the supercooled solution in the present embodiment as a surfactant. As a result, the freezing point of the supercooled solution is adjusted to an arbitrary temperature (0 ° C. or lower in this embodiment).

By using this surfactant, for example, the freezing point of the supercooled solution can be lowered. The lower the freezing point of the supercooled solution, the higher the stability in the supercooled state, so it is possible to suppress solidification due to unintended stimuli (vibration of vehicles running on the road surface, minute seismic motion, etc.).

(Ground improvement method)
In the ground improvement method in the present embodiment, in the ground G shown in FIGS. 4A to 4E, an impermeable wall 50 is constructed so as to surround the target range for improving the soil quality, and the impermeable wall 50 surrounds the ground G. It is a method of constructing the improved ground G2 inside the ground.

In order to construct the improved ground G2, first, as shown in FIG. 4A, an impermeable wall 50 surrounding a predetermined area is constructed on the ground G. The impermeable wall 50 is also formed on the back side and the front side of the paper surface in FIGS. 4A to 4E, and is formed in a frame shape in a plan view.

The ground G includes a permeable layer GH through which groundwater flows and an impermeable layer GE through which groundwater does not flow.

The impermeable wall 50 is an impermeable means formed of a cement improved body, and the lower end thereof is embedded in the impermeable layer GE. As a result, the flow of groundwater in the ground G "outside" of the impermeable wall 50 and the flow of groundwater in the ground G "inside" of the impermeable wall 50 are prevented from affecting each other. The impermeable wall 50 is not limited to the improved cement body, and may be formed of a steel sheet pile (sheet pile), concrete, or the like.

After the impermeable wall 50 is constructed, the water injection well 52 and the pumping well 54 are constructed inside the impermeable wall 50. The water injection well 52 is an injection means for injecting the supercooled solution generated by the ground improvement device 60 into the ground G, and the supercooled solution can be sent into the ground G by a pump or the like (not shown). Further, the pumping well 54 is a pumping means for pumping groundwater from the ground G, and the groundwater of the permeable layer GH can be sucked up by the pumping pump P and sent to the ground improvement device 60. The pump P is controlled by the ground improvement device 60. A plurality of water injection wells 52 and pumping wells 54 can be installed inside the impermeable wall 50, respectively.

Next, as shown in FIG. 4B, the ground improvement device 60 is operated to pump groundwater from the pumping well 54. The groundwater pumped from the pumping well 54 is discharged to the outside of the impermeable wall 50. Further, the ground improvement device 60 sends a supercooled solution in a supercooled state to the water injection well 52, and the supercooled solution is injected from the water injection well 52 into the permeable layer GH. By pumping groundwater from the pumping well 54, a flow of groundwater from the water injection well 52 to the pumping well 54 is formed, whereby the groundwater in the permeation layer GH in the ground G inside the impermeable wall 50 is gradually overcooled. Replaced by the solution.

The temperature of the ground G is generally 10 to 20 ° C., which is lower than the melting point (about 58.0 ° C.) of the supercooled solution and higher than the freezing point (0 ° C. or lower). The cooling solution is maintained in a supercooled state.

After the supercooled solution has penetrated into the permeable layer GH inside the impermeable wall 50, the crystallization agent 32 is charged into the water injection well 52 as shown in FIG. 4 (C). The permeation of the supercooled solution into the permeable layer GH means that the groundwater was collected from the observation well separately provided in the ground G inside the pumping well 54 or the impermeable wall 50, and the concentration of the supercooled solution became higher than the measured value. It is judged by that. Groundwater can also be collected from the water injection well 52 and the pumping well 54, and the concentration of the supercooled solution can be suitably measured.

The crystallization agent 32 charged into the water injection well 52 is a solidified crystal of sodium acetate trihydrate, and is charged into the water injection well 52 and comes into contact with the supercooled solution in a supercooled state to solidify the supercooled solution. Further, as shown in FIG. 4D, the supercooled solution propagates the solidification reaction from the solidified portion by contacting with the crystallization agent 32, and gradually begins to solidify from the peripheral portion of the solidified portion. After that, as shown in FIG. 4 (E), the improved ground G2 formed by solidifying the supercooled solution is constructed inside the impermeable wall 50.

(Action / effect)
In the ground improvement method in the present embodiment, a supercooled solution having a viscosity lower than that of cement is infiltrated into the ground G. Further, since the supercooled solution does not solidify until the crystallization agent 32 is added, the supercooled solution can be permeated into the entire area of the ground G surrounded by the impermeable wall 50 and then solidified. Therefore, the ground can be improved regardless of the scale of the portion surrounded by the impermeable wall 50. For example, it is possible to improve the ground on various scales, such as the scale of one house or the scale of multiple blocks.

Further, in the ground improvement method in the present embodiment, it is sufficient to secure a place for installing the water injection well 52, the pumping well 54, and the ground improvement device 60 in the above-ground portion. That is, the ground can be improved even on the ground where an existing building is built on the ground.

On the other hand, in the case of ground improvement using cement that does not easily penetrate into the ground, in order to improve the ground over a large area, a pile-shaped ground improvement body is formed by mixing cement and soil in the ground. It is necessary to provide multiple of these. Therefore, it takes time and effort for construction. Further, since this ground improvement body is formed by excavating the ground from the upper part, it is difficult to improve the ground when a building is built on the upper part of the ground.

As described above, in the ground improvement method in the present embodiment, it is possible to improve the ground in a wide range on which the existing building is built. Further, in the improved ground G2, since the groundwater in the permeable layer GH is replaced with a solidified supercooled solution, it is difficult to liquefy even if a seismic motion is applied, for example. Therefore, it is effective as a countermeasure against liquefaction.

Further, in the ground improvement method in the present embodiment, the ground G (see FIG. 4C) in which the liquid supercooled solution has permeated undergoes a solidification reaction from the portion in contact with the crystallization agent 32 charged into the water injection well 52. Propagate. Therefore, for example, it can be solidified more quickly than the hardening reaction of cement. Therefore, the construction speed of the improved ground G2 can be increased.

Further, in the ground improvement method in the present embodiment, the supercooled solution in the supercooled state (15 ° C.) is injected into the ground G. Therefore, after injection into the ground G, it can be solidified at any timing (for example, immediately).

On the other hand, when a supercooled solution that is not in a supercooled state (the temperature is higher than the melting point, for example, 60 ° C.) is injected into the ground G, the ground heat (10 to 20) of the ground G is required to solidify the supercooled solution. It is necessary to cool down to the melting point (58 ° C) or lower depending on the temperature. Therefore, the supercooled solution cannot be solidified until it is cooled and the temperature becomes lower than the melting point.

In the present embodiment, the groundwater pulled up from the pumping well 22 is discharged to the outside of the impermeable wall 50, but the embodiment of the present invention is not limited to this. For example, groundwater may be mixed with sodium acetate anhydrous and melted by heating to generate a supercooled solution after removing impurities. By generating a supercooled solution from the groundwater pulled up from the pumping well 22, the amount of drainage can be reduced.

Further, in the present embodiment, the ground improvement device 60 is used to generate a supercooled solution and control the pump P, but the embodiment of the present invention is not limited to this. For example, instead of using the ground improvement device 60, the supercooled solution may be generated in advance at a factory or the like and injected into the water injection well 52, and the pump P may be operated by an operator. If the ground improvement device 60 is not provided, the number of devices installed on the ground surface can be reduced, so that it is easy to improve the ground even in a place where buildings are densely packed.

Further, in the present embodiment, the crystallization agent 32 is charged into the water injection well 52, but the embodiment of the present invention is not limited to this. For example, it may be charged into the pumping well 54, or may be charged into both the water injection well 52 and the pumping well 54. Further, a charging hole may be separately provided in the ground G inside the impermeable wall 50, and the crystallization agent 32 may be charged into the charging hole. By adding the crystallization agent 32 from a plurality of places, the starting point of solidification of the supercooled solution increases, so that the reaction can be promoted. In addition, "injecting a crystallization agent into the ground" in the present invention means a generic term for these embodiments.

Further, the sodium acetate trihydrate used in the supercooled solution in the present embodiment is produced by mixing water at a ratio of 100:66 with respect to anhydrous sodium acetate and heating and melting. The embodiment is not limited to this.

For example, the mixing ratio of sodium acetate anhydrous and water may be changed. Increasing the mixing ratio of water increases the stability of the supercooled solution in the supercooled state.

As specific examples of the supercooled solution in which the mixing ratio of sodium acetate anhydrous and water is changed, FIGS. 2 and 3 show sodium acetate 3 in which the molecular weight ratio of water to sodium acetate anhydrous is 100: 66, 75, 80, 90. Data on hydrates are shown.

The data shown in FIG. 2 shows the molecular weight ratio of water to sodium acetate anhydrous in a columnar body filled with silica sand No. 5 (glass sand having a particle size of about 5 mm) at a gap ratio of 35%: 100: 66, 75, 80. , 90 is the uniaxial compression strength of the test piece impregnated with sodium acetate trihydrate and solidified. Further, the data shown in FIG. 3 is the relationship between the compressive stress and the strain generated when pressure is applied to each test piece in the uniaxial compressive strength test.

As the molecular weight ratio of water to sodium acetate anhydrous increases, the uniaxial compressive strength decreases, as shown in FIG. On the other hand, as shown in FIG. 3, the strain due to the compressive stress increases. That is, when the mixing ratio of water in the sodium acetate trihydrate increases, the bearing capacity of the ground improvement body decreases, but the malleability is high and brittle fracture is difficult.

In this way, by changing the mixing ratio of sodium acetate anhydrous and water, it is possible to form a ground improvement body according to the required performance.

In the present embodiment, sodium acetate trihydrate was used as the supercooled solution, but the embodiment of the present invention is not limited to this. For example, sodium sulfate decahydrate (Na ₂ SO _{4.10H 2} O, melting point 32.0 to 38.0 ° C.), sodium thiosulfate pentahydrate (Na ₂ S ₂ O _{3.5H 2} O, melting point 48. 3 ° C), disodium phosphate dodecahydrate (Na ₂ HPO _{4.12H 2} O, melting point 35.0 ° C), calcium chloride hexahydrate (CaCl _{2.6H 2 O} , melting point 30.0 ° C), Calcium acetate monohydrate (C ₄ H ₆ CaO ₄ · H ₂ O, melting point 100-150 ° C), magnesium acetate tetrahydrate (C ₄ H ₆ MgO _4.4 H ₂ O, melting point 79.0 ° C), Potassium acetate (C ₂ H ₃ KO ₂ , melting point 292 ° C), potassium fluoride tetrahydrate (KF · 4H ₂ O, melting point 18.5 ° C), erythritol (C ₅ H ₁₂ O ₄ , melting point 119 ° C), Various substances having a melting point higher than the temperature of the ground G, such as mannitol (C ₆ H ₁₄ O ₆ , melting point 167 ° C.), can be used.

Further, these supercooled solutions can adjust the freezing point to an arbitrary temperature by adding a surfactant, and can maintain a stable supercooled state in the ground. It is not always necessary to add a surfactant to the supercooled solution, and the presence or absence of application can be selected according to the ground temperature, the need to keep the supercooled state stable, and the like.

32 Crystallizer 50 Impermeable wall 52 Water injection well 54 Pumping well G Ground G2 Improved ground

Claims (3)

A ground improvement method for forming an improved ground by solidifying the supercooled solution in the ground by injecting a crystalline agent into the ground in which a supercooled solution having a melting point higher than the temperature of the ground surrounded by an impermeable wall has permeated. .. The process of constructing an impermeable wall on the ground that surrounds a predetermined area,
The process of constructing a water injection well and a pumping well on the ground inside the impermeable wall, and
The process of pumping groundwater from the pumping well and
The step of injecting a supercooled solution from the water injection well into the ground,
A step of pouring a crystallization agent into the ground in which the supercooled solution has permeated and solidifying the supercooled solution to harden the ground inside the impermeable wall.
Ground improvement method with. The ground improvement method according to claim 2 , wherein a surfactant that lowers the freezing point is added to the supercooled solution.

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