JP4940462B1 - Ground improvement method - Google Patents

Abstract

[PROBLEMS] To improve the ground by preventing the liquefaction of the ground by unsaturating the ground by simply generating carbon dioxide bubbles in the ground under the groundwater surface without the need for a special air bubble generator or process. Provide construction methods.
An acidic solution and a carbonate compound are combined in the ground to generate carbon dioxide bubbles, thereby desaturating the ground and preventing liquefaction of the ground. An inorganic acid such as sulfuric acid or phosphoric acid is suitable as the acidic liquid, and a sodium hydrogen carbonate liquid is suitable as the carbonate compound.
[Selection] Figure 3

Description

  The present invention relates to a ground improvement method, and in particular, can prevent liquefaction in an area where the ground is loosely accumulated such as alluvium and coastal landfill.

  In areas where the ground is loosely deposited, such as alluvial deposits and coastal landfills, there are concerns about large-scale liquefaction damage during earthquakes, so various liquefaction measures have been implemented so far.

  Sand volume changes due to dilatancy phenomenon due to shear deformation such as earthquake. In particular, sand saturated with water increases the excess pore water pressure, reduces the effective stress, and decreases the sand resistance. As a result, a liquefaction phenomenon occurs and drains and the volume decreases.

  The conventional liquefaction countermeasure methods include a method of preventing liquefaction by eliminating excess pore water pressure at the time of an earthquake by creating piles of crushed stone with good water permeability in the ground (drainage method). There is known a method (consolidation method) in which a sand pile compacted by press-fitting sand is formed, and the surrounding ground is compressed sideways to perform vibration compaction.

  Furthermore, a method of lowering the groundwater level by pumping up groundwater with a pump (groundwater lowering method), and a chemical solution (solidifying material) injected into the ground permeates and solidifies in the gaps between the soil particles, which becomes an adhesive. A construction method (chemical solution injection construction method) that exhibits effects such as strengthening and water stopping (improving water permeability) is also known.

  However, the conventional liquefaction countermeasure methods described above are currently generally applied to relatively important structures that meet the economic efficiency due to the fact that construction costs are considerably high. It was not something.

  In particular, the groundwater level lowering method requires the pump to be operated at all times, so there are problems such as land subsidence and running costs that are considerably increased due to the groundwater level drop. There were problems such as water pollution.

  In addition, the liquefaction countermeasure work that can be applied directly under an existing structure has a problem that the injected solution is difficult to penetrate in a wide range and the workability is difficult. In addition, construction in places that touch the surroundings, such as residential land, has the effect on the groundwater due to chemical injection, the impact on the residential land due to ground deformation, and economic problems. Most of them were not done, and it was urgent to develop more economical liquefaction countermeasures.

  By the way, in recent years, a bubble mixing method (micro bubble water mixing method) has been proposed in which high-concentration air-dissolved water containing a large number of ultrafine bubbles having a diameter of 10 μm to 100 μm is mixed into the ground to increase the unsaturation of the ground. .

  This method absorbs excess pore water pressure generated during liquefaction by shrinkage of air bubbles mixed between soil particles, prevents increase of excess pore water pressure, and keeps the soil particles in mesh to improve liquefaction strength. It is expected to be a new countermeasure against liquefaction.

JP2008-2170 JP2007-211537 JP 5-16498 Japanese Patent Publication No. 3-54153 JP 2007-23396

  Conventional liquefaction countermeasures are divided into consolidation and desaturation. Consolidation is a method of solidification with a solution-type injection material having excellent durability, especially around existing structures and Excellent workability directly underneath. For consolidation, silica grout with water glass as the main ingredient is mainly used. Especially, gel glass is prepared by mixing water glass and acid, or adding calcium carbonate or sodium carbonate to change pH slowly. The present inventors have developed an acidic silica sol for adjusting the above.

  In addition, water glass and water glass using carbon dioxide or carbonated water have been developed. In any case, carbon dioxide or carbonated water is used to neutralize the alkali of the water glass and gel the water glass. Yes. In addition, a grout in which air bubbles are mixed in a silica solution has been proposed, but there is a system for forming an aqueous solution containing a predetermined amount of bubbles, feeding liquid under pressure up to the ground, and generating bubbles in the ground. Difficulties and the economics of silica grout become a problem.

  In any of these silica grouts, since the strength of the injected ground is determined by the concentration of the silica grout, a sufficient silica concentration corresponding to that is required to obtain a sufficient injection effect.

  However, since the liquefaction strength in chemical injection as described above is determined by the silica concentration of the chemical, and because permeability and durability are required, it is necessary to use special materials and blending, and there is a problem in economic efficiency. It was.

  On the other hand, in the bubble mixing method, since the raw materials are water and air, it is excellent in economic efficiency, and research results having sufficient liquefaction strength are shown.

  However, when there is a groundwater flow such as directly under a river embankment, there is a possibility that the expected quality cannot be secured and maintained over a long period of time because the injected bubbles flow out and diffuse.

  In addition, because it is based on the principle that fine particle bubbles are adsorbed on the surface of the soil particles, an aqueous solution containing fine particle bubbles is manufactured and injected into the ground while maintaining a pressurized state through an injection tube to release the pressure. In order to generate air bubbles, the system and operation corresponding to that had been required.

  That is, an air bubble mixed liquid is generated using a device that generates air bubbles, and is introduced into the ground through the injection pipe while maintaining the pressurized state, and the pressure is released in the ground. There is a problem that the system in which bubbles are generated and become unsaturated is complicated and it is difficult to maintain a pressurized state until the bubbles are generated by opening to the ground.

  The present invention has been made to solve the above-described problems, and does not require a special bubble generating device or process, and easily generates carbon dioxide bubbles in the ground to unsaturate the ground and An object of the present invention is to provide a ground improvement method capable of preventing liquefaction.

The ground improvement method according to claim 1 is an acidic silica solution having a silica concentration of 0.1 wt% to 40 wt% obtained by adding an acid to water glass or silica colloid through a plurality of pipes of an injection pipe installed below the groundwater surface in the ground. Carbon dioxide or bicarbonate is chemically reacted at the junction of the injection pipe to generate CO ₂ in the gap in the ground, and the degree of unsaturation of the ground is increased to 3% or more. It is characterized by performing liquefaction countermeasure work by consolidation.
The ground improvement method according to claim 2 is the ground improvement method according to claim 1, wherein the amount of CO ₂ consumed by reacting with the Ca compound contained in the ground or groundwater is calculated to determine the degree of unsaturation of the ground. It is characterized in that the required amount of CO ₂ is generated by setting the amount of acid and carbonate or bicarbonate to generate the amount of CO ₂ required to be 3% or more .
Ground improvement method according to claim 3, wherein, in the ground improvement method according to claim 1 or 2, in which carbonate is characterized by a carbonate of alkaline earth metal compound.
The ground improvement method according to claim 4 is the ground improvement method according to claim 3 , wherein seawater is used as the alkaline earth metal compound.
The ground improvement construction method according to claim 5 is characterized in that in the ground improvement construction method according to any one of claims 1 to 4 , air bubbles are generated by the combined use of an air generator or a microbubble generator. is there.
The ground improvement method according to claim 6 is the ground improvement method according to any one of claims 1 to 5 , wherein the volume of carbon dioxide required by setting a target degree of unsaturation in a predetermined improvement region is set. It is characterized by being generated in the ground.

The formation of the ground unsaturated with carbon dioxide bubbles is not only possible by a simple method, but also has a high liquefaction strength even when the degree of unsaturation is the same as compared with the desaturation caused by air fine particle bubbles. This seems to be because carbon dioxide reacts with the calcium and magnesium components present more or less in the ground below the groundwater surface to deposit insoluble calcium carbonate and magnesium carbonate on the contact surface between the soil particles.

Especially in coastal areas where countermeasures against liquefaction are required, there is a large amount of calcium such as coral sand caused by shells and corals. Often the amount can reach around 10% calcium content. For this reason, the liquefaction strength has an effect of carbon dioxide bubbles and a soil particle fixing effect of calcium carbonate, and a greater liquefaction strength can be obtained even with the same degree of unsaturation as fine air bubbles.

In the practice of the present invention, in such a case, the amount of carbon dioxide that reacts with the calcium content and is consumed to calculate the amount of carbon dioxide that is consumed to obtain a predetermined degree of unsaturation is formed. You can do so.

  The present invention solves the problem of bubble formation and pumping into the ground by the conventional physical (or mechanical) method, and easily generates carbon dioxide bubbles in the ground by applying a chemical method. The soil can be desaturated to obtain liquefaction strength.

  The principle of the present invention is to generate carbon dioxide bubbles by reacting a carbonic acid compound and an acid under the groundwater surface to desaturate the ground under the groundwater surface. If carbon dioxide is generated by joining a carbonate-containing liquid as the A liquid and an acidic liquid as the B liquid at the junction of the injection pipe having the flow path, it is rapidly generated by a chemical reaction at the injection pipe junction. The carbon dioxide bubbles are fine particles that enter the soil particle gaps, and can easily desaturate the ground.

  For this reason, as in the method of injecting fine particle bubbles, a special bubble generator and a pipeline from the injection tube to the ground keep the pressurized state and keep the air volume reduced to release the pressurized state in the ground. Thus, the process of desaturation is simplified, and an epoch-making advantage that workability is easily performed without requiring a special apparatus is obtained.

  In the present invention, carbon dioxide may be formed by supplying liquefied carbon dioxide from a carbon dioxide cylinder. Moreover, the exhaust gas from a factory or a thermal power plant may be sufficient. Moreover, you may mix air with these with an air compressor. It may be liquid carbon dioxide mixed with microbubbles known as microbubbles.

  In this case, when fine bubbles of carbon dioxide are adsorbed on the surface of the soil particles and the excess pore water pressure increases due to the seismic load, the volume of carbon dioxide contracts to absorb the excess pore water pressure and prevent liquefaction. Can do.

Also, if carbon dioxide is generated by joining a carbonate compound-containing liquid as the A liquid and an acidic liquid as the B liquid at the junction of the injection pipe having a plurality of channels provided in the ground, the junction at the injection pipe The bubbles of carbon dioxide generated by the rapid chemical reaction become fine particles and enter the soil particle gap, and the ground can be easily desaturated.

  Examples of acids in the present invention include inorganic acids such as sulfuric acid and phosphoric acid, sodium hydrogen sulfate, acidic salts such as aluminum chloride, organic acids such as citric acid, acetic acid, and succinic acid, glyoxal, etheric bonate, triacetin, Examples thereof include organic compounds that act as an acid in the presence of water glass or silica colloid alkali, such as organic esters such as diacetin.

  Examples of carbonates include bicarbonate, alkali metal carbonates, and poorly water-soluble carbonates such as calcium carbonate and magnesium carbonate. Water-soluble alkali metal salts are particularly suitable. Any other acid or salt can be used in combination to adjust the gelation and pH.

  The present invention can prevent liquefaction in areas where the ground is loosely accumulated, such as alluvium and coastal landfill.

Further, in the present invention, by adding silica as an active ingredient as a composition, the surrounding area of carbon dioxide in the ground is covered with silica gel produced by the reaction of silica and acid, regardless of the flow of groundwater. It is possible to prevent the desaturation from being reduced because the carbon dioxide is retained in the injection region and carbon dioxide dissolves in the groundwater and the saturation due to the groundwater can be prevented from increasing.

  In the silica solution containing carbon dioxide, the silica particles adhere to the contact surfaces of the soil particles, and bubbles of carbon dioxide are adsorbed on the surface of the soil particles. For this reason, the excess pore water pressure due to the seismic load is absorbed by the contraction of the carbon dioxide bubbles, and at the same time, the skeleton structure of the soil particles is maintained by the adhesive force of the silica particles.

  As a result, since the shear stress is reduced with respect to the repeated shear stress caused by the large earthquake motion and the skeletal structure of the soil is prevented from being destroyed, the ground subsidence due to the liquefaction phenomenon does not occur. In addition, it can withstand large earthquake motions due to the synergistic effect of carbon dioxide bubbles and silica adhesion, and can exhibit high liquefaction strength even at low silica concentrations.

  In addition, even if the amount of carbon dioxide generated is increased, many unsaturated soil blocks that contain soil particles in blocks are formed, and the soil particles are fixed with silica gel, which increases the degree of unsaturation of the entire injected ground. High liquefaction strength can be expected.

  This means that a sufficient liquefaction strength can be obtained even if the silica concentration is small, and an excellent ground improvement effect can be obtained.

  In this case, the low-concentration silica gel present in the gaps between the soil particles deforms and follows the load without breaking. For this reason, the gel existing between the soil particles is deformed without breaking against the shear stress of a large earthquake and acts on carbon dioxide bubbles to contract the volume of carbon dioxide to absorb the seismic load. Seem.

Moreover, in general chemical injection, sufficient liquefaction strength cannot be obtained unless the silica concentration is increased and the gap filling rate is sufficiently increased. However, in the present invention, since the gel becomes agar-like by lowering the silica concentration, it can be deformed without breaking against an increase in excess pore water pressure due to an earthquake, so carbon dioxide bubbles are deformed in the gel. It is possible to express the seismic effect of unsaturated ground by adapting to the increase in excess pore water pressure, and in addition to the fixing effect of silica gel sand particles, the skeleton of soil particles even if the silica concentration is low Large liquefaction strength can be obtained without breaking the structure. In addition, it is possible to increase the degree of unsaturation by increasing the amount of carbon dioxide generated. In that case, a large unsaturated soil block is wrapped with a thin silica gel membrane by increasing the silica concentration and decreasing the injection amount. It is possible to hold the unsaturated soil block against the flow of groundwater, and at the time of an earthquake, even if it is hard, the thin gel film is easily broken and the internal gas is compressed to absorb the seismic load and become large Liquefaction strength can be obtained. These findings (Figure 1, Table 1) than the silica concentration can be 0.1 to 40%, in particular 0.1～6Wt% is preferred.

In addition, the silica solution is gelated due to the presence of an acid, and the silica gel becomes neutral to acidic region by dealkalization, whereby the durability of silica is obtained and the solubility of carbon dioxide is lowered. This is because carbon dioxide is easily dissolved in water in the presence of alkali. Silica is water glass or silica colloid.

  FIG. 1 shows the relationship between the silica concentration after gelling of the silica solution and the 28-day curing, and Table 1 shows the silica concentration and the gel state.

  Silica gel has lower strength as the silica concentration decreases, but the fracture strain increases. Or it becomes a jelly-like gel, and the distortion increases without showing a peak indicating fracture. Even in such a case, if the silica concentration is such that the gel is precipitated, the adhesive force of the silica particles acts and the skeleton structure of the soil particles is maintained. Silica gel forms a loose gel at a silica concentration of about 2%, and at 0.1 wt% or more, it has no ability to contain the entire amount of water, but silica gel precipitates and works effectively to bind soil particles.

In addition, it is preferable to use a silica solution having a silica concentration of 0.1 wt% to 40 wt% for the ground improvement method . When the silica concentration is 40 wt% or more, the strength increases, and even if carbon dioxide is present, the liquefaction strength is determined by the silica concentration. Further, when the silica concentration is 6% wt or more, the amount of silica to be used is reduced by increasing the degree of unsaturation, the effect of desaturation by carbon dioxide is increased, and an economic effect can be obtained at the same time. The degree of unsaturation should be 3% or more. The higher the degree of unsaturation, the less liquefaction will occur due to the formation of unsaturated ground below the groundwater surface, but a large amount of carbon dioxide will be generated. However, the unsaturated soil block may be fixed below the groundwater surface with silica so as not to escape to the ground. Specifically, the degree of unsaturation should be within 95%.

Moreover, the saturation can be adjusted as necessary by generating air bubbles by using an air generator or a microbubble generator. In this case, carbon dioxide gas that can be obtained by subtracting the air amount from the gas amount corresponding to the target degree of unsaturation to obtain the remaining gas amount may be set.

Further, sticking between the soil particles may be precipitated alkaline earth metal carbonate insoluble among alkaline earth metal salts or hydroxides are reacted with the soil particles, such as calcium compounds and magnesium compounds to carbon dioxide . When slaked lime is used as the calcium compound, the same effect can be obtained even when calcium carbonate is deposited or reacted with Ca ions and Mg ions in the waste liquid by-produced during seawater or salt production. In this case, the design may be such that the amount of carbon dioxide consumed by the reaction between the alkaline earth metal salt contained and carbon dioxide is calculated to obtain the amount of carbon dioxide corresponding to the target degree of unsaturation. Further, seawater is used as the alkaline earth metal compound .

In addition, by setting the target degree of unsaturation in a given improvement area and setting the amount of carbon dioxide so that the required volume of carbon dioxide bubbles is obtained, carbon dioxide bubbles are generated in the ground. The ground can be desaturated.
When carbon dioxide is formed by blending a carbonic acid compound and an acid, the blending design may be performed as such. Also, when air bubbles are used together, or when Ca compound is contained in the ground or groundwater, calculate the amount of carbon dioxide consumed and set the amount of carbon dioxide that can obtain the required degree of unsaturation do it.

  As a result of research on the present invention, it has been found that the present invention has the following characteristics.

  (1) In the case of unsaturated sand due to carbon dioxide bubbles, the liquefaction strength increases compared to that of untreated saturated sand more than the same as in the case of unsaturated sand due to fine particle bubbles. That is, the liquefaction strength can be expressed by a simple method. The effect is remarkable especially in the ground containing Ca.

  (2) When the degree of unsaturation is the same, the liquefaction strength of the carbon dioxide bubbles added with silica is greatly increased as compared with the case of only air bubbles.

  (3) In the case of carbon dioxide bubbles to which silica is added, the liquefaction strength is greatly increased even if the silica concentration is the same as in the case of only the silica solution. In this case, the liquefaction strength is larger than the total strength of the liquefaction strength of only the silica solution and the liquefaction strength of only carbon dioxide, and the synergistic effect is obtained. For this reason, sufficient liquefaction strength can be obtained even if low-concentration silica, which cannot be obtained by liquefaction countermeasures only by gelation of the silica solution, is used.

  (4) In the above, the silica concentration is effective even at a thin concentration where an injection effect cannot be obtained with a grout of only a silica solution. In other words, the silica solution alone is effective even at such a thin concentration that the silica gel cannot contain the total amount of water in the blended solution. It is thought to do.

  (5) Carbon dioxide has the effect of reacting with alkali of water glass or colloidal Syria to precipitate silica and improving the durability of silica gel. Therefore, when air bubbles are further added to the carbon dioxide solution to which silica is added, the air bubbles are fixed between the soil particles in the ground with silica gel, and the liquefaction strength is further improved.

  According to the present invention, a special bubble generating device or a special process for injecting bubbles into the ground is not required, and carbon dioxide bubbles are simply generated in the ground to desaturate the ground. It can prevent liquefaction of the ground, and is particularly suitable for prevention of liquefaction in areas where the ground is loosely deposited, such as alluvium and coastal landfill.

  In particular, by adding silica, the excess pore water pressure is reduced by maintaining the skeletal structure of the soil particles at the time of the earthquake by silica gel produced by the reaction of silica and acid around the carbon dioxide in the ground, and until the earthquake occurs In this period, it is possible to prevent the desaturation due to the groundwater by preventing the reduction of the unsaturation due to the flow of the groundwater.

It is a graph which shows the fracture strain with respect to the silica concentration of a silica sol. It is a graph which shows the relationship (carbon dioxide absorption coefficient table | surface) of the dissolved amount (gas volume) of the carbon dioxide in aqueous solution, temperature, and a pressure. It is the schematic which shows an example of a carbon dioxide generator. It is a graph which shows the result of the undrained repeated triaxial test done about each specimen.

  Embodiments of the present invention will be described below.

  In order to verify the effect of the ground injected with carbon dioxide and the ground injected with carbon dioxide and silica solution, specimens shown in Table 2 were prepared and the liquefaction strength was measured.

  In Example 1, bubbles of carbon dioxide were generated in the specimen to adjust the saturation to 90%. Further, as Comparative Example 1, the degree of saturation was set to 100%, and the liquefaction strength was compared with the presence or absence of carbon dioxide. In Example 2, the silica solution was injected and carbon dioxide bubbles were generated in the specimen, and the saturation was 90%. Further, as Comparative Example 2, only the silica solution was injected to obtain a saturation degree of 100%, and the liquefaction strength with and without carbon dioxide was compared.

  In this embodiment, in order to generate and desaturate a predetermined volume of carbon dioxide in the improved ground, the amount of carbon dioxide dissolved in the pore water pressure in the ground is adjusted.

  Carbon dioxide is soluble. The amount of carbon dioxide dissolved in the aqueous solution (gas volume) is affected by temperature and pressure. FIG. 2 shows a carbon dioxide absorption coefficient table.

In the ground with a pore water pressure of 0.1 MPa at 20 ° C, 1.745 L of carbon dioxide dissolves per liter of groundwater.
・ Volume (L) = Volume of water (L) x GV = 1 x 1.745 = 1.745 L
In order to lower the saturation of the ground, it is necessary to generate carbon dioxide in an amount corresponding to the degree of unsaturation.

  Therefore, in this embodiment, in order to generate 10% of the volume of carbon dioxide, it is necessary to excessively generate 0.1 L of carbon dioxide by the above chemical reaction. Therefore, 1.845L of carbon dioxide per liter was created in the ground.

  Similarly, the amount of carbon dioxide required to generate 20% carbon dioxide in the gap is 1.945 L per liter.

  As a method for generating carbon dioxide in the ground, carbon dioxide was generated by the reaction of citric acid and sodium hydrogen carbonate (bicarbonate) as shown in Formulas 1 and 2.

  The carbon dioxide generation method in the present invention may be any method in which carbonate and acid are reacted. As the carbonate, sodium hydrogen carbonate, sodium carbonate, potassium carbonate, magnesium carbonate, calcium carbonate or the like can be used. . As the acid, an acid salt such as phosphoric acid, sulfuric acid, citric acid or sodium hydrogen sulfate can be used.

  In the present invention, 1.845 L per 1 L of carbon dioxide required to generate 10% carbon dioxide in the gap is mixed with a gas density of carbon dioxide of 1.98 and a molar mass of carbon dioxide of 44.01 g / mol. Carbon dioxide is needed.

・ Mass (g): Volume (L) × Carbon dioxide gas density (g / L)
= 1.845 × 1.98 = 3.65g
-Number of moles (mol): Mass (g) ÷ Molar mass (g / mol)
= 3.65 ÷ 44.01 = 0.083mol

From the reaction formula of Equation 2, citric acid required to produce 1.845 L of carbon dioxide (anhydrous, molar mass 192.12 g / mol)
Is 5.38 g.

-Number of moles (mol): 1/3 of carbon dioxide
= 0.083 ÷ 3 = 0.028 (mol)
・ Mass (g): Number of moles (mol) × molar mass (g / mol)
= 0.028 x 192.12 = 5.38g

From the reaction formula, 6.97 g of sodium hydrogen carbonate necessary to produce 1.845 L of carbon dioxide is obtained.
(Molar mass 84.007 g / mol)
-Number of moles (mol): Same amount as carbon dioxide
= 0.083 mol
・ Mass (g): Number of moles (mol) × molar mass (g / mol)
= 0.083 x 84.007 = 6.97g

  By adding 5.38 g of citric acid to the A liquid and 6.37 g of sodium hydrogen carbonate to the B liquid and reacting them in the ground, 1.745 L of carbon dioxide is dissolved and 0.1 L of carbon dioxide is generated.

  The formulation used for the experiment is shown below.

(1) Example 1
Carbonic acid was generated by mixing 500 ml of an aqueous citric acid solution and 500 ml of an aqueous sodium bicarbonate solution as an acidic solution.

(2) Example 2
Carbon dioxide was generated by mixing 500 ml of an aqueous solution in which citric acid was dissolved in a silica sol having a silica concentration of 4 wt% as an acidic silica sol solution and 500 ml of an aqueous sodium hydrogen carbonate solution. The silica concentration in the specimen was set to 2 wt%.

(3) Comparative Example 1
Degassed water was used.

(4) Comparative example 2
An acidic silica sol solution having a silica concentration of 2% was injected.

  In the apparatus shown in FIG. 3, Toyoura sand was placed in the specimen 12 in the apparatus so that Dr = 60%, and injection was performed from the 5, 6, and 7 tanks. In Examples 1 and 2, an acidic solution or an acidic silica sol solution was combined with the A liquid at the 13 inlet, and an aqueous sodium hydrogen carbonate (bicarbonate) solution was combined with the B liquid, and reacted in 12 test bodies to generate carbon dioxide. .

  The prepared specimens were cured at room temperature for 7 days, and repeated undrained triaxial tests.

  The test conditions were cell pressure (200 kPa) −back pressure (100 kPa) = initial effective restraint pressure (100 kPa), and the number of repetitions N was such that both amplitude strains DA reached 5%. The shear stress ratio after 20 repetitions is defined as liquefaction strength Rl, and the results are shown in FIG.

  From the results, the liquefaction strength of Comparative Example 1 in which only water was injected was 0.15, whereas the liquefaction strength of Example 1 in which carbon dioxide was generated was 0.25. The liquefaction strength of Comparative Example 2 was 0.28, whereas the liquefaction strength of Example 2 was 0.6. From this, the liquefaction strength is increased by generating carbon dioxide, and further, a viscoelastic specimen can be created by generating carbon dioxide in the silica sol, and a high liquefaction strength is obtained by a synergistic effect. be able to.

  In addition, when a microbubble generator was installed in the 5 water tank shown in FIG. 3 and a specimen having a saturation of 90% was prepared and the liquefaction strength was measured, the same value as in Example 1 was obtained. It can be seen that the saturation can be adjusted by generation.

  Further, when an alkaline earth metal compound is present in the improved ground, the liquefaction strength can be increased by reacting with carbon dioxide and crystallizing.

  In the case of using sea sand mixed with shells in the specimen shown in Fig. 3, the liquefaction strength of the specimen with 90% saturation by the microbubble generator was 0.25, the same as that of Toyoura sand. On the other hand, the liquefaction strength when saturation was 90% using carbon dioxide increased to 0.29.

  Similarly, when carbon dioxide is mixed into a chemical solution with a silica concentration of 2% and the saturation level due to carbon dioxide is 90%, the liquefaction strength is 0.64, which is higher than that of Toyoura sand. It can be seen that the carbonates of the above precipitate and increase the liquefaction strength. In addition, when sea sand mixed with shells of this example is used, magnesium ions 1.27 g / kg and calcium ions 0.40 g / kg are present in the groundwater as the groundwater, and magnesium ions, calcium ions, and carbon dioxide. The reaction is represented by the following formula:

_{^{Mg 2+ + CO 3 - → Mg}} 2 CO 3
_{^{Ca 2+ + CO 3 - → Ca}} 2 CO 3

  As a result, 0.052 mol magnesium ion and 0.010 mol calcium ion are present in the above ground and react with an equal amount of carbon dioxide. As a result, when the present invention was applied to this ground, 0.062 mol of carbon dioxide was generated.

Furthermore, in the present invention, the saturation is preferably set to 97% or less, and desirably 95% or less, and the saturation can be adjusted by using an air generator or a microbubble generator.

  In addition, carbon dioxide discharged from factories, etc., collected in gas cylinders, liquefied by a liquefier, dissolved in water, converted to dry ice by a compressor, or chemically reacted into carbonates such as baking soda Can also be used.

  In these cases as well, the amount of carbon dioxide contained may be calculated, and an amount corresponding to a predetermined degree of unsaturation may be injected into the ground to desaturate the target ground.

  The present invention prevents liquefaction particularly in areas where the ground is loosely deposited, such as alluvium and coastal landfill, by simply generating carbon dioxide bubbles in the ground and desaturating the ground. be able to.

Claims (6)

Carbonate or bicarbonate is injected into an acidic silica solution with a silica concentration of 0.1 wt to 40 wt% by adding acid to water glass or silica colloid through multiple pipes of injection pipes installed under the groundwater surface in the ground A chemical reaction is generated at the junction of the pipe to generate CO ₂ in the gap in the ground, and the soil unsaturation and solidification are achieved by setting the degree of unsaturation to 3% or more. A ground improvement method characterized by performing. In the ground improvement construction method according to claim 1, CO consumed by reacting with a Ca compound contained in the ground or groundwater ₂ The amount of CO required to calculate the amount of soil and bring the degree of unsaturation to 3% or more ₂ Set the amount of acid and carbonate or bicarbonate to generate the amount of CO required ₂ A ground improvement method characterized by generating   The ground improvement construction method according to claim 1 or 2, wherein the carbonate is a carbonate of an alkaline earth metal compound.   The ground improvement construction method according to claim 3, wherein seawater is used as the alkaline earth metal compound.   The ground improvement construction method according to any one of claims 1 to 4, wherein air bubbles are generated by the combined use of an air generation device or a microbubble generation device.   The ground improvement construction method according to any one of claims 1 to 5, wherein a desired volume of carbon dioxide is generated in the ground by setting a target degree of unsaturation in a predetermined improvement region. Ground improvement method.

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