JP5017620B1 - Ground improvement method, silica grout and its raw materials - Google Patents

Abstract

[Problem] To provide a ground improvement method using silica-based grout that can generate a uniform gel in the ground even when water containing salt such as seawater is used as mixing water. To do.
[Solution]
In order to inject and solidify silica-based grout, which contains a silica-based compound, a curing agent, and water mixed and has a pH of neutral or acidic region into the ground, the silica-based compound solution and the curing agent-containing liquid are mixed. Prepare and add each of the silica-based compound solution and the curing agent compounding solution to each of the silica-based compound solution and the salt-containing water as kneaded water. adjusted according to the amount of salt contained in the water containing Na 2 _O in an amount and salt contained in the system compound solution.
[Selection] Figure 2

Description

  The present invention is a ground improvement method for performing permanent ground improvement such as liquefaction prevention, suction prevention and permanent reinforcement by injecting and solidifying silica-based grout into the ground, in particular, mixing silica-based grout. The present invention relates to a ground improvement method using silica containing salt water such as seawater or spring water, silica-based grout, and raw materials thereof.

  In recent years, chemical injection methods are not limited to conventional temporary injection methods, but are used in ground improvement work for the purpose of permanent improvement or long-term improvement. In this ground improvement work, application of silica grout has been required. By injecting and solidifying silica-based grout into the ground, permanent ground improvement such as liquefaction prevention, suction prevention and permanent reinforcement can be performed. Silica-based grouts are used especially for water stoppages such as liquefaction countermeasures near rivers and coasts and bank protection works such as dikes due to recent earthquakes.

  In the vicinity of the coast where liquefaction countermeasures are performed, it is difficult to obtain tap water, and therefore, it has been desired to use seawater that is easily available as the blended water for silica grout. However, when seawater is used as the blended water for the silica grout in the alkaline region, the silica content reacts with sodium chloride, magnesium chloride, etc. in the seawater to cause cloudiness and precipitate a heterogeneous silica content. For this reason, even if it was a liquefaction countermeasure work near the shore, tap water had to be used as the blended water. In addition, when water glass grout in the alkaline region is injected into the ground containing seawater, the injected solution reacts with the seawater in the ground and whitens to form a heterogeneous gel, thus obtaining sufficient ground improvement effect. It was difficult.

  In recent years, as shown in FIG. 1, acidic silica injecting material obtained by mixing water glass and acid, and further neutralizing non-alkaline by adjusting pH and neutralizing agent to acidic silica to adjust gelation time. Silica injection materials have been proposed. Non-alkaline silica colloids made by adding colloidal silica, water glass and acid are also known as durable silica grouts.

  These acidic or non-alkaline silica-based injection materials have a long gelation time because they have a long gelation time, are excellent in a wide range of permeability, and have removed alkali that causes deterioration of the water glass injection material with an acid or the like. In terms of obtaining a consolidated region that is excellent in long-term durability over time and excellent in durability over a wide range, it has unique characteristics that cannot be obtained with water glass injection materials in other alkaline regions.

  Further, it is already known that an acidic silica injection material obtained by mixing water glass and acid forms a uniform gel without white turbidity even when injected into the ground containing seawater and obtains an excellent effect. Yes.

  These acidic or non-alkaline silica-based injection materials, in the step of removing the alkali of the water glass as the main agent, when the acid is added to the water glass as it is, the silica concentration in the water glass is usually as high as 20 to 50%, instantly It is difficult to inject into the ground due to non-uniform gelation. Therefore, each of water glass and acid was diluted with water with low electrolyte concentration, such as tap water, industrial water, and river water. Dilution makes it possible to create a uniform gel, and it is easy to adjust the pH after kneading and the silica concentration, so that the desired gelation time and strength can be obtained in the ground, which is efficient. Formulation can be performed.

  The place where it is difficult to obtain tap water or industrial water, etc., where the silica-based grout produced by diluting in this way is injected and ground improvement work is carried out around liquefaction countermeasures, revetments, bedrock, etc. It may be. In this case, it is conceivable to use seawater or spring water as mixing water instead of fresh water having a low electrolyte concentration such as tap water or industrial water.

  However, in order to produce an acidic or non-alkaline silica-based injection material, when sea water or spring water is used as a blended water of non-alkaline silica solution or silica colloid solution using water glass and acid, It is thought that water glass and seawater or spring water react with the electrolyte contained to precipitate heterogeneous bulk silica. Therefore, conventionally, water glass and acid were diluted with water having a low electrolyte concentration, such as tap water, industrial water, and river water, so that heterogeneous massive silica was not precipitated. Therefore, since water with low electrolyte concentration, such as tap water, industrial water, river water, etc. which are kneaded with a construction site with a container etc. in advance, was economically expensive.

  In order to solve these problems, there are a method of reducing the molar ratio of the water glass as the main agent and a method of adding an alkali material (Patent Document 1). However, since these methods are highly alkaline, they are leached when used in silica-based grout and durability cannot be obtained.

JP-A-1-192912

  As described above, in order to produce an acidic or non-alkaline silica-based injection material, when seawater or spring water is mixed and used as water, the silica compound causes gelation of silica molecules due to the electrolyte contained in seawater or spring water. Therefore, even if mixing can be performed before injection, non-uniform gelation occurs in the ground or gelation occurs in the injection path. For this reason, conventionally, it is necessary to transport water with low electrolyte concentration such as tap water, industrial water, and river water as kneaded water to a construction site in advance by a container or the like, which is economically expensive.

  The present invention has been made in order to advantageously solve the above-mentioned problem. In a solution-type silica grout having a neutral or acidic pH range, water containing salt such as seawater in mixed water, that is, kneaded water. The purpose of the present invention is to provide a ground improvement method using silica-based grout so that a uniform gel can be formed in the ground, together with the silica-based grout and raw materials. is there.

  The present inventors conducted research and development on the suppression of gelation in the case of using seawater as the mixing water used when blending the solution type silica grout having a medium acidic pH range based on the following facts.

Water glass and silica colloid are stabilized over a long period of time by containing an alkali such as Na ₂ O. When water glass or silica colloid is used as the ground improvement injecting material, it is gelled in the ground by neutralizing sodium ions with an acid or aggregating silica with an electrolyte such as a salt. Since the gelation time is adjusted by adjusting the amount of acid and electrolyte added as a curing agent at this time, the kneading water has little influence on the gelation time, and the electrolyte concentration of industrial water, tap water, etc. is low Use things.

  Seawater usually has physical properties of a specific gravity of 1.02-1.03 and a salinity of 3.1-3.8%. Therefore, when mixed with a silica compound, it acts like a curing agent. If mixed water is used instead of tap water or the like, it is difficult to adjust the target gelation time.

Thus, as a result of intensive studies, the present inventors have found that even silica compounds having different Na ₂ O do not gel by changing the amount of seawater added. The present invention is based on this finding.

The ground improvement method of the present invention includes a silica-based compound, a curing agent, and water to be mixed. When the silica-based grout having a neutral or acidic pH is injected into the ground and solidified, the silica-based compound The salt content to be added to the silica-based compound solution is prepared by adding a solution and a curing agent-comprising solution and adding water containing salt as kneaded water to each of the silica-based compound solution and the curing agent-comprising solution. The amount of water containing is adjusted according to the amount of Na ₂ O contained in the silica-based compound solution and the amount of salt contained in the water containing salt.

In the ground improvement method of the present invention, the amount of salt-containing water added to the silica-based compound solution is adjusted to the Na ₂ O concentration (g) of the silica-based compound solution and the salt concentration (g) of the salt-containing water. It is preferable to set the ratio to be 0.7 or more and to add the remaining kneading water required for the silica-based grout to the curing agent compounding liquid. The silica compound in the ground improvement method of the present invention may be one or more selected from water glass, silica colloid, active silica and active silica colloid, and the curing agent is phosphoric acid, sulfuric acid, salt 1 type or 2 types or more selected from. Furthermore, in the ground improvement construction method of the present invention, the silica compound is two or more kinds having different Na ₂ O amounts, and two or more silica-based compound solutions are prepared for each silica compound. Among them, to the solution with a small amount of Na ₂ O, water containing a salt concentration lower than that of the other silica compound solution is added, fresh water having a salt concentration of 0 is added, or kneaded water is added. It can also be set as the structure which does not.

The silica-based grout of the present invention includes a silica-based compound, a curing agent, and kneaded water, and was prepared by adding water containing salt as kneaded water to each of the silica-based compound solution and the curing agent blending solution. The amount of water containing salt added to the silica-based compound solution is a mixture of raw materials, depending on the amount of Na ₂ O contained in the silica-based compound solution and the amount of salt contained in water containing the salt. It is characterized by being adjusted.

The silica-based grout of the present invention is a silica-based grout used in the ground improvement method, and one of the raw materials is prepared by adding water containing salt as water mixed with the silica-based compound solution. The amount of water containing salt to be added to is adjusted according to the amount of Na ₂ O contained in the silica-based compound solution and the amount of salt contained in the water containing salt.

According to the present invention, the amount of salt-containing water added to the silica-based compound solution is adjusted according to the amount of Na ₂ O contained in the silica-based compound solution and the amount of salt contained in the salt-containing water. Therefore, it is possible to use water containing an electrolyte that is advantageous in cost for mixing water, for example, seawater or spring water that can be obtained near the construction site, and therefore, without limiting the molar ratio of the silica compound to low alkali. A uniform and permanent improvement effect of the ground can be secured.

It is a graph which shows the general relationship of the pH area | region of a silica type grout, a water glass density | concentration, gelation time, and intensity | strength. It is a graph which shows the influence which ratio of the amount of Na2O of several silica compounds from which molar ratio differs differs in the amount of salt content of seawater has on gelation time.

Hereinafter, the ground improvement method of the present invention, the silica grout and its raw materials will be described more specifically.
The ground improvement method of the present invention is to prepare a silica-based compound solution and a curing agent blending solution, and add water containing salt as kneaded water to each of the silica-based compound solution and the curing agent blending solution. It is important to adjust the amount of water containing salt added to the silica-based compound solution according to the amount of Na ₂ O contained in the silica-based compound solution and the amount of salt contained in the water containing salt. And

According to the experiment of the present inventors, for example, Na ₂ O (%), SiO ₂ (%), and silica compounds I to III having different molar ratios shown in Table 1, specific gravity 1.23, salinity concentration 3.5%. When various amounts of seawater are added and the gelation time is measured, a graph as shown in FIG. 2 is obtained.

From the results shown in FIG. 2, the present inventor shows that the stability depending on the silica compound and seawater concentration does not depend on the molar ratio of the silica compound, but depends on the ratio of the Na ₂ O concentration in the silica compound and the salt concentration in the kneaded water. I found out.

  In liquefaction countermeasures, when the silica-based injection material is blended in the tank and injected into the ground from the injection pipe installed in the ground with a pump, the stabilization time of the mixture of silica compound and mixed water is 30 minutes As described above, preferably one hour or more is required.

For this purpose, if the ratio of the Na ₂ O concentration and the salt concentration (salt content) in the kneaded water in FIG. 2 is set to 0.7 or more, preferably 1.0 or more, the mixture can be stably mixed without causing cloudiness.

  Seawater and spring water may be diluted with low electrolyte water such as groundwater or rivers, but the present invention can also be applied to water with different salt concentrations as shown in Table 3.

×：ゲル化、△：白濁または３０分以上安定化、○：透明な状態で６０分以上安定化

×: Gelled, Δ: Cloudy or stabilized for 30 minutes or more, ○: Stabilized for 60 minutes or more in a transparent state

In the injection, the optimal amount of silica-containing water added to the silica-based compound solution for the optimal silica-injecting material that can be expected to have the required strength during the service period in consideration of the strength change of the target ground, the silica-based compound solution By adjusting and blending according to the amount of Na ₂ O contained in the water and the amount of salt contained in the water containing salt, the ground improvement having durability can be performed.

  The silica-based compound solution used in the present invention is water glass, non-alkaline water glass (silica sol) removed with water glass acid, silica colloid (colloidal silica), active silica, and active silica colloid. The mixture is the active ingredient.

  As the active ingredient water glass, water glass having a molar ratio of 1.0 to 4.5 can be used, but a glass having a higher molar ratio can also be used. As an active ingredient silica colloid, there is a colloid which is stabilized in weak alkalinity with a particle size of 5 to 50 nm. In addition, the active ingredient may be water glass, or active silica obtained by treating acidic water glass obtained by mixing water glass and acid with an ion exchange resin or an ion exchange membrane, or active silica colloid obtained by further increasing the particle size. Further, the active ingredient may be an active silica colloid obtained by adding water glass, an acid or a salt to the active silica colloid.

  The silica colloid in the present invention can be obtained by removing most of the alkali metal ions from a liquid alkali metal silica salt aqueous solution (water glass). For example, a zeolite cation exchanger, an ammonium ion It is obtained by passing water glass through the ion exchange resin of the exchanger, adding the generated silica colloid to the water glass at a temperature of 80 ° C. to 90 ° C., and passing the ion exchange resin again to perform ion exchange. Yes, this process yields a relatively pure (dilute) silica colloid (active silica colloid).

  Furthermore, in order to obtain a pure silica colloid, the above-mentioned dilute silica colloid is prepared to be slightly alkaline, and the above-mentioned silica colloid is further evaporated and further evaporated to stabilize and concentrate simultaneously, or ion exchange. A method is used in which the subsequent active silica colloid is heated under an appropriate alkali and further stabilized by adding an active silica colloid.

Silica colloidal solution in the present invention may use a colloidal silica as described above, since the Na ions are little separated off, normally a pH indicates the 10 following weak alkaline, Na 2 _O, the concentration in the liquid Is in the range of 0.2% by mass to 4.0% by mass. When the concentration of Na ₂ O in the liquid exceeds 4% by mass, the silica colloid dissolves and becomes an aqueous solution of silicate. On the other hand, when the amount of Na ₂ O is less than 0.2% by mass, the silica colloid cannot exist stably and aggregates. That is, when Na ₂ O is in the range of 0.2% by mass to 4.0% by mass, Na ions can be distributed on the surface of the silica colloid and kept in a stable colloidal state. Therefore, a silica colloid solution in which Na ₂ O is in the range of 0.2% by mass to 4.0% by mass is preferable.

  The colloidal silica solution prepared in this way is almost neutral and semi-permanently stable. When this is used as an infusion solution, it is gelled during delivery from the factory to the site and during the infusion operation. There is no worry to do.

  Further, water glass and colloidal silica having a small molar ratio can be gelled with a small amount of a curing agent because they contain a small amount of Na ions, and dehydration condensation hardly occurs even after gelation, and volume shrinkage is small. Therefore, silica-based grouts using these silica-based compounds as raw materials can improve the quality of the ground with little shrinkage or deterioration of the gel after injection and an improvement effect in the long term.

The silica-based compound solution in the present invention has a pH range of neutral or acidic. Specifically, the pH can be in the range of 1-8. In the case of water glass, the amount of Na ₂ O contained in the silica-based compound solution is defined by JIS standard water glass. Further, sodium hydroxide may be added in order to improve stability.

  Examples of the salt-containing water in the present invention include seawater and spring water. The salt contained in the water containing the salt includes sodium chloride, magnesium chloride, magnesium sulfate, calcium sulfate, potassium chloride and the like, and these analysis methods include flame atomic absorption method, ICP emission spectroscopic analysis method, ion chromatographic method. Can be measured. It is also measured with a simple salinity meter.

Since the ratio of the amount (g) of Na ₂ O in the silica-based compound solution to the amount of salt water-containing salt (g) is 0.7 or more, it can be stably blended without becoming cloudy. ,preferable. A more preferable ratio is 1.0 or more.

In the present invention, when two or more types of silica compounds having different amounts of Na ₂ O are used as the silica compounds, two or more silica-based compound solutions are prepared for each silica compound, and the salinity is set for each solution. Water containing salt may be added to each solution at this time, and the amount of Na ₂ O contained in the silica-based compound solution and the amount of salt contained in the water containing salt are added to each solution. Adjust according to. Of the two or more silica-based compound solutions, water containing a lower salt concentration than other silica compound solutions is added to a solution having a small amount of Na ₂ O, or fresh water having a salt concentration of 0 is added. Or a mode in which kneading water is not added.

  Examples of the curing agent used in the present invention include mineral acids such as phosphoric acid and sulfuric acid, sodium hydrogen sulfate, aluminum sulfate, aluminum chloride and the like, salts that dissolve in water and exhibit relatively strong acidity, carbon dioxide, carbonates, and the like. Inorganic salts, metal organic acids and the like. Among them, in particular, sequestering agents such as phosphoric acid and phosphoric acid compounds, chelating agents, and further reactive agents used in combination with sulfuric acid, etc. are hardly soluble silica by masking the underground concrete structure together with silica. Forming a coating film of the compound is preferable because it has an effect of protecting concrete from salt damage caused by salt in seawater and deterioration due to the formation of ettringite due to the binding of sulfate ions and calcium in the hardener. In addition, silica containing a sequestering agent such as phosphate ions reacts with trace metals in the soil and calcium such as shells to form an insoluble or hardly soluble silica compound when injected into the ground. It is presumed that the alkali component in the ground can be passivated and the shortening of gelation due to the rapid increase in pH of the soil silica during infiltration can be suppressed.

  The phosphoric acid compound and / or chelating agent used in the present invention has a chelating effect, and examples thereof include phosphoric acid, various acidic phosphates, neutral phosphates, and basic phosphates. , Tetrapolyphosphates, hexametaphosphates, tripolyphosphates, pyrophosphates, acidic hexametaphosphates, acidic pyrophosphates, and the like, and the condensed phosphates are sodium salts Is preferred. As the phosphoric acid compound forming the non-alkaline silica solution, sodium hexametaphosphate is preferable because it forms a particularly strong masking silica. Examples of the chelating agent include ethylenediaminetetraacetic acid, nitrilotriacetic acid, gluconic acid, tartaric acid, and salts thereof in addition to the phosphoric acid compound. In the present invention, the phosphoric acid compound is present in the presence of a silica solution. Underneath it forms the most effective coating on the concrete surface.

Reactive agents include water-soluble sodium chloride, potassium chloride, calcium chloride and other mineral acid alkali metal salts, alkaline earth metal salts, or aluminum salts such as sulfate bands, aluminum chloride, polyaluminum chloride, and alum. In addition, a small amount of these may be added or used in combination to increase the buffer capacity and retain the function as a gelling time adjusting agent. Furthermore, in the present invention, a metal ion sequestering agent other than the phosphoric acid compound can be used to expect metal ion masking. Such sequestering agents include tetrapolyphosphates, hexametaphosphates (especially sodium salts are good), tripolyphosphates, pyrophosphates, acidic hexametaphosphates, acidic pyrophosphates and other condensed phosphates, ethylenediamine Examples thereof include tetraacetic acid, nitrilotriacetic acid, gluconic acid, tartaric acid, and salts thereof.
Further, an alkali material or a polymer material can be added as a gel time adjusting material.

Example 1
Hereinafter, the present invention will be described more specifically based on examples.
Four types of silica compounds I to IV shown in Table 3 were prepared.

In Example 1 and Comparative Example 1, silica-based grout was produced using the silica compound I described above. Under the present circumstances, the hardening | curing agent compounding liquid (A liquid) and the silica compound solution (B liquid) were prepared. The injection material obtained after blending was a silica grout having a silica concentration of 6% by mass and a pH of 3. Table 4 shows the composition of this silica-based grout. From Example 1 and Comparative Example 1, when the pH after kneading with an acidic curing agent is acidic to neutral, the amount of kneading water used for diluting the silica compound is set in relation to the amount of Na ₂ O. According to the invention, the silica concentration after mixing can be adjusted by adjusting the remaining mixing water to 0.7 or more and mixing the remaining mixing water with the acidic curing agent.

Ｔｏｔａｌ １０００ｍｌ
×：ゲル化、△：白濁または３０分以上安定化、○：透明な状態で６０分以上安定化

Total 1000ml
×: Gelled, Δ: Cloudy or stabilized for 30 minutes or more, ○: Stabilized for 60 minutes or more in a transparent state

(Example 2, Example 3)
In Example 2 and Example 3, silica-based grout was produced using the above-mentioned silica compound II. Under the present circumstances, the hardener compounding liquid (A liquid) and the silica compound solution (B liquid) were prepared like Example 1. FIG. The injection material obtained after blending was a silica grout having a silica concentration of 6% by mass and a pH of 3. Table 5 shows the composition of these silica grouts. Since Example 2 and Example 3 differ from Example 1 in the amount of Na ₂ O derived from the silica compound, the amount of kneading water added is different in order to maintain the stability of the B liquid. Moreover, when the comparative example 1 and Example 3 are compared, the silica density | concentration after kneading is the same, but it turns out by changing a silica compound that stability to seawater becomes high even if it is the same amount of B liquid.

Ｔｏｔａｌ １０００ｍｌ
×：ゲル化、△：白濁または３０分以上安定化、○：透明な状態で６０分以上安定化

Total 1000ml
×: Gelled, Δ: Cloudy or stabilized for 30 minutes or more, ○: Stabilized for 60 minutes or more in a transparent state

Example 4
Example 4 shows an example in which silica compound IV having a high molar ratio was used, and in the case where two or more silica compounds were used. A silica-based grout was produced using the silica compound I and the silica compound IV. Under the present circumstances, the hardening | curing agent compounding liquid (A liquid), the silica compound solution (B liquid), and the silica compound solution (C liquid) were prepared. The injection material obtained after blending was a silica grout having a silica concentration of 6% by mass and a pH of 3. Table 6 shows the composition of these silica-based grouts, and Table 7 shows the results of stability evaluation of the B and C solutions.

When silica compound IV is used, as shown in Comparative Example 2 and Comparative Example 3, when seawater having a salt concentration of 3.5% is used and 25 ml is added to the kneaded water, Na ₂ O (g) / salt (g) The quantity ratio becomes less than 0.7, and the stability of the B liquid is deteriorated. In order to stabilize the liquid B, according to the present invention, the silica compound IV is mixed with 25 ml of water so that the amount ratio of Na ₂ O (g) / salt (g) is 0.7 or more. Must be 3 ml or less. Therefore, in Example 4, the addition amount of the kneading water was 0 ml, that is, no seawater was added to the B liquid. As a result, Example 4 was excellent in the stability of the B liquid and the stability of the C liquid.

In Example 4, seawater was not added to the B liquid, but if seawater with a low salt concentration was added to the B liquid instead of adding seawater, the amount of water mixed into the B liquid was increased. can do. For example, when seawater having a salt concentration of 0.4% is used, even if the same amount of mixing water is added to silica compound IV (if silica compound IV is 25 ml, 25 ml of mixing water is added), Na ₂ Since the amount ratio of O (g) / salt (g) is 0.7 or more, blending with which stability is obtained becomes possible.

Ｔｏｔａｌ １０００ｍｌ

Total 1000ml

×：ゲル化、△：白濁または３０分以上安定化、○：透明な状態で６０分以上安定化

×: Gelled, Δ: Cloudy or stabilized for 30 minutes or more, ○: Stabilized for 60 minutes or more in a transparent state

(Example 5, Example 6)
Examples 5 and 6 are examples in which they become neutral (pH 7.6) after blending. In the blending of these examples, as shown in Table 8, it is divided into a curing agent blending solution and a silica compound solution. As in the present invention, the ratio of the silica compound and the kneaded water in the B solution is Na ₂ O (g) / It sets so that the quantity ratio of salt (g) may be 0.7 or more, and mixes with A liquid.

×：ゲル化、△：白濁または３０分以上安定化、○：透明な状態で６０分以上安定化

×: Gelled, Δ: Cloudy or stabilized for 30 minutes or more, ○: Stabilized for 60 minutes or more in a transparent state

  The present invention relates to a ground improvement method for expecting a permanent improvement effect such as prevention of liquefaction, prevention of sucking and permanent reinforcement by injecting and solidifying silica-based grout into the ground. It can be used to secure a permanent improvement effect.

Claims (7)

Injecting and solidifying silica-based grout, which contains a silica-based compound, a curing agent, and water mixed, and the pH is neutral or acidic, into the ground,
A silica-based compound solution and a curing agent blending solution are prepared, and each of the silica-based compound solution and the curing agent blending solution is kneaded into each of the silica-based compound solution and salt-containing water as water to be added. A ground improvement method characterized by adjusting the amount of water containing salt to be added according to the amount of Na ₂ O contained in the silica-based compound solution and the amount of salt contained in water containing the salt. The amount of salt-containing water added to the silica-based compound solution is such that the ratio of the amount of Na ₂ O (g) in the silica-based compound solution to the amount of salt-containing water salt (g) is 0.7 or more. The ground improvement construction method according to claim 1, wherein the remaining kneading water required for the silica-based grout is added to the curing agent blending solution.   The ground improvement method according to claim 1 or 2, wherein the silica compound is one or more selected from water glass, silica colloid, active silica and active silica colloid. Two or more types of silica compounds having different Na ₂ O amounts are prepared, and two or more silica-based compound solutions are prepared for each silica compound. Among these silica-based compound solutions, a solution having a small amount of Na ₂ O is used. The ground improvement method according to claim 3, wherein water containing a salt concentration lower than that of the other silica compound solution is added, fresh water having a salt concentration of 0 is added, or kneading water is not added.   The ground improvement construction method according to any one of claims 1 to 4, wherein the curing agent is one or more selected from phosphoric acid, sulfuric acid, and a salt. A mixture of raw materials prepared by adding water containing salt to each of the silica compound solution and the curing agent compounded liquid, and containing salty water as the kneaded water. The amount of water containing salt added to the silica-based compound solution is adjusted according to the amount of Na ₂ O contained in the silica-based compound solution and the amount of salt contained in the water containing salt. Silica-based grout. A silica-based grout used in the ground improvement method, wherein one of the raw materials is prepared by kneading a silica-based compound solution and adding water containing salt as water, and adding the salt-containing water added to the silica-based compound solution. A silica-based grout, characterized in that the amount is adjusted according to the amount of Na ₂ O contained in the silica-based compound solution and the amount of salt contained in water containing salt.

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