JPS6020992A - Ground fortifier - Google Patents

Abstract

PURPOSE:To provide a low cost ground fortifier consisting mainly of an aqueous soln. of active silicic acid not contg. salt, which causes no environmental pollution and has high strength and excellent durability. CONSTITUTION:The ground fortifier consists mainly of an aqueous soln. of active silicic acid contg. substantially no salt. The silicic acid has an SiO2/NaO2 molar ratio of 50 or higher and a pH of 2-10, contains at least one silanol group which makes total of Si atoms in the aqueous soln. participate in condensation reaction and has a molecular weight of below 1,000. The soln. has a SiO2 concn. of below 12, pref. 2-10wt%. The aqueous soln. of active silicic acid is obtained, e.g., by removing alkali from water-soluble silicate such as sodium silicate, potassium silicate or ammonium silicate by ion exchange, electrophoresis, dialysis, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pollution-free ground improvement agent that has excellent strength and durability.

A common method for improving soft ground is to inject strips containing water glass as the main ingredient.

Water glass building materials are inexpensive and the gelation time can be easily adjusted, but they have two major drawbacks.

One is that water glass is a strongly alkaline substance, so even if an acidic reactant is used, the cured product must become alkaline in order to obtain a gelling time that is practically possible, and the leached alkali contaminates groundwater. That's true.

Theoretically, a neutral hardened product can be obtained by adding an acidic substance equivalent to the amount of alkali contained in water glass to neutralize it, but adding such an amount of an acidic substance instantly creates a non-uniform gel. Generally, an acidic substance with an alkali equivalent amount υ or less is used as a curing agent because of this, and therefore the problem of alkali contamination of groundwater as mentioned above arises.

Another major drawback is that the durability of the cured product is poor.

Unreacted water glass and salts generated by the reaction between the curing agent and water glass gradually elute from the cured product.

As a result, the strength of the cured product decreases.

Therefore, there is no problem when the purpose is short-term ground improvement, but it is not preferable when durability is required, such as ground improvement during dam construction.

The following methods are available to improve these drawbacks of water glass building materials. One method is to add water glass to a strong acid such as sulfuric acid to create acidic activated silicic acid, and neutralize and harden using this as the main ingredient and an alkaline curing agent.

This method is a preferred method for improving alkali contamination of groundwater, but since the main agent contains a large amount of salts such as Na2SO4 generated by acid and alkali of water glass, the elution of these salts is accompanied by the elution of these salts. There is a problem with changes in groundwater quality.

In addition, the acidic activated silicic acid aqueous solution maintains a long gelation time in an acidic region, but when an alkali is added to it to cause gelation in a neutral region, the gelation time is significantly shortened. If the city is between 5 and 8, the gelation time will be several minutes.
There was a problem that it took several seconds and sufficient permeability could not be obtained.

Another method is to use neutral colloidal silica as the main ingredient. This method generally involves condensing and stabilizing a product commercially available as a neutral silica sol, that is, an aqueous activated silicic acid solution obtained through an ion exchange resin, to a molecular weight of 20 to 30% by heating, etc.
This method uses a dispersion of particles with a diameter of about 10 mμ as the main ingredient.

This neutral colloidal silica has traditionally been used as a textile treatment agent, paper anti-slip agent, paint additive, etc., so it has been stabilized by adjusting the stability, particle size, and concentration to meet these purposes. ing.

According to the research conducted by the present inventors, when attempting to use such stabilized neutral colloidal silica as a ground consolidation agent, the SiO In particular, the initial strength is low, so the gel is easily washed away by running water. That is, for the purpose of ground injection, the unconfined compressive strength of consolidated sand is usually required to be 2 ky/(xn2 or more, but for this purpose, normal water glass grout has a water glass concentration of 30 (weight) 5 or more. This is 5
102 When converted to concentration, corresponds to S:9 (weight) 5 or more. However, in order to obtain the above strength using the above-mentioned neutral colloidal silica, the SiO2 concentration must be 20 (weight).
It turns out that 5 or more is required.

The present invention compensates for the drawbacks of the above-mentioned technologies and provides an economical ground improvement agent that is free from pollution, has excellent strength and durability.

That is, the ground improvement agent of the present invention is characterized in that the main ingredient is an activated silicic acid aqueous solution that is substantially salt-free. Here, the term "activated silicic acid aqueous solution that is substantially salt-free" means that the active silicic acid aqueous solution is substantially salt-free and has a SiO2/Na2O molar ratio of 50 or more and 1.
u2 to fO, and substantially all of the silicon atoms of all the silicic acids in the aqueous solution have a small number of silanol groups that can participate in condensation (both 1 and 1).
An aqueous solution of silicic acid with a molecular weight of 1,000 or less and whose silanol group does not act as a steric hindrance during the condensation reaction, and whose concentration of 5,102 is 12-fold or less,
Preferably, a 2 to 10% (by weight) solution is preferred.

The active silicic acid aqueous solution is stable without gelling during production, preparation for injection, or injection, and has a concentration of 8 to 1.
0 or 4-2 is preferable, and from the viewpoint of ease of production, pH 4-2.
2 is particularly preferred.

A method for obtaining such an active silicic acid aqueous solution is to obtain an active state by dealkalizing a water-soluble silicate, such as sodium silicate, potassium silicate, ammonium silicate, etc., by an ion exchange method, electrophoresis method, dialysis method, etc. can be mentioned.

As the above-mentioned water-soluble silicate, those having a molar ratio of 1 to 5 are preferably used, and from an industrial standpoint, it is preferable to use JIS No. S sodium silicate. Further, as the dealkalization method, an ion exchange method, particularly using an ion exchange resin, is particularly preferable since a highly concentrated activated silicic acid solution can be obtained.

This activated silicic acid aqueous solution is used for a short period of time without any stabilization treatment after production, but even if some condensation reaction occurs due to standing, it is still sufficient to achieve the purpose of the present invention. I don't mind if it's something.

In addition, the water-soluble silicate used as a raw material here is preferably a commercially available water-soluble silicate diluted from the viewpoint of ease of the dealkalization process and stability of the resulting activated silicic acid aqueous solution. The concentration is Si of the activated silicic acid aqueous solution obtained.
Preferably, it is diluted to an O2 content of 2 to 10%.

Unlike the commercially available neutral colloidal silica mentioned above, the activated silicic acid aqueous solution of the present invention has a low molecular weight, a small particle size, good reactivity, and gels in a short time, so it is stable depending on the usage time. It is preferable to manufacture the product at or near the injection site.

For example, an aqueous solution of SiO□ 5%, pH 5.4, obtained by passing JIS No. 5 sodium silicate through a cation exchange resin, is
It takes about one day to gel, so it can be used as a grout material.

The ground improvement agent of the present invention has the above-mentioned activated silicic acid aqueous solution as a main ingredient,
Depending on the purpose, commonly known pH adjusters or (and)
Contains a curing agent as appropriate.

Furthermore, the activated silicic acid aqueous solution in the ground improvement agent of the present invention can be used in an appropriate ratio depending on the purpose, but the 5102D in this solution
By using an activated silicic acid aqueous solution with a concentration of 2 to 10% by weight, it is possible to obtain the same strength as conventional water glass grout at a lower concentration than the 5102 concentration in conventionally used water glass grout. A product with excellent durability can be obtained. Of course, when neutral colloidal silica is used, a higher strength can be obtained with a thinner 5102°C concentration.

Furthermore, the noteworthy point of the present invention is that compared to conventional grout using an acidic silicic acid aqueous solution obtained by adding water glass to an acidic liquid, a longer gel time can be obtained in the neutral region.
The point is that higher consolidation strength can be obtained with the same gelation time and 8102 concentration.

In addition, as a gelling time adjusting agent or a gelling reaction agent, inorganic salts etc. can be used within the limits that achieve the purpose of the present invention, and from the viewpoint of shortening the gelling time and increasing the strength of the present invention, the amount used is Inorganic salts of polyvalent metals that require less are preferred. Examples of such inorganic salts include aluminum sulfate, magnesium chloride, sodium hydrogen carbonate, magnesium sulfate, aluminum nitrate, aluminum phosphate, calcium chloride, and the like.

Since the activated silicic acid of the present invention has a low molecular weight and high reactivity, the addition rate of the curing agent may be small, and in the case of a divalent metal salt, it is 0.1
If the hexavalent metal salt is added in an amount of ~1-layer precipitate, the gelation time can be reduced to within a few minutes with an even smaller amount.

In addition, the ground improvement agent of the present invention is preferably injected in a neutral state; if the activated silicic acid aqueous solution is acidic, an alkaline agent is used; Bye.

The soil improvement agent of the present invention solves the above-mentioned pollution problems (it can strengthen the soil with a low concentration of silica, and is excellent in its durability).

In other words, while ordinary water glass grout loses its strength over time, with the ground improvement agent of the present invention, the strength of the resulting sand gel gradually improves, so it can be used in a similar manner to soil improvement during dam construction. It can also be used for applications that require durability.

For example, when using neutral silica sol to obtain a sand gel strength comparable to that of water glass grout, the S io 2 concentration in the injection solution must be 20% or more. For ground improvement agents, it only takes about 5%.

The activated silicic acid aqueous solution of the present invention can be easily subjected to the ff method,
Since the silicic acid contained has a low molecular weight, an injection solution with less variation in curability and strength can be obtained.

Furthermore, since the ground improvement agent of the present invention does not use a strong acidic liquid such as sulfuric acid, there is no problem of corrosion of injection equipment. In addition, less salt elutes than when acidic silica sol is used (
Changes in groundwater quality are small. In addition, since the active silicic acid used in the ground improvement agent of the present invention has a small molecular weight and a low concentration, the initial viscosity is low (good permeability).

Furthermore, the ground improvement agent of the present invention has the advantage that greater strength can be obtained at a lower concentration of 5102 and the change in gelation time due to water dilution is smaller than when neutral colloidal silica is used.

The activated silicic acid aqueous solution of the present invention is, for example, placed in an ion exchange resin tower.
It is easily obtained by simply passing a diluted solution of IS No. silicate sodium silicate, and it is much more economical than commercially available neutral colloidal silica because it has a low 8102 content (even though a high-strength cured product can be obtained).

In addition, the ground improvement agent in the present invention can be injected into the ground under pressure or mixed with earth and sand to increase the strength and watertightness of the ground. Suspending substances such as cement, lime, or clay can also be mixed into the aqueous solution.

In addition to injection and mixing, the activated silicic acid aqueous solution and its suspension can be used for spraying, coagulation, precipitation, solidification, etc. of sludge, etc.

Examples of the present invention are shown below.

(Preparation of activated silicic acid aqueous solution) Preparation example 1 Sodium silicate JIS No. 5 product (Asahi Denka Kogyo Co., Ltd. product 5i)
n229.0%, Na2O9-0%) was diluted with water and 5i
A diluted sodium silicate aqueous solution containing 25.8% n and 1.8% Na2O was prepared. This aqueous solution was prepared in advance with 10% hydrochloric acid as a hydrogen type cation exchange resin (
Organo Co., Ltd. product, Amber 2ite IR-120B)
The solution was passed through the tower to obtain 5 inches of a 25.8% active silicic acid aqueous solution.

The value of this activated silicic acid aqueous solution was 2.5.

5to2/Na2o = 1 s o , this solution did not gel for 3 days at room temperature.

Preparation Example 2 Instead of the diluted sodium silicate aqueous solution in Preparation Example 1, SiO7,
Using 2% HNa2O2m2%, a 7-1% active silicic acid aqueous solution of 8102 was obtained in the same manner. The pH of this activated silicic acid aqueous solution was 3.0.

SiO2/Na2O=1000, this solution did not gel for 2 days at room temperature.

Examples 1 to 5, Comparative Examples 1 to 4 Using the activated silicic acid aqueous solutions produced in Preparation Examples 1 and 2, the gel time, the compressive strength of the sand gel, and the elution of 8102 from the homogel were measured.

The prescription is as shown in Table-1.

The raw materials used in Table 1 are as follows.

1) Neutral silica sol: Applied A manufactured by Kadenka Kogyo Co., Ltd.
T-30 2] Acidic silica sol: While vigorously stirring an aqueous solution of 6.3 g of 95% sulfuric acid and 55.7 g of water, silica JIS No. 5 (manufactured by Kadenka Kogyo Co., Ltd.)
A solution of 189 parts water was poured into 30I. 5io2Cl concentration 8.0%, PI (1,83) silica (JIS No. 5): manufactured by Kadenka Kogyo Co., Ltd. Other raw materials used were reagent grade 1.

The 51o2a degree, -'' and gel time in the chemical solution of the above example are as shown in Table 2.

Table 2 The chemical solution of the above prescription was poured into a mold of 5.0 mm φ x 10 (mL) and solidified with Toyoura standard sand to obtain a sand gel for strength measurement.

The strength measurement was performed according to JISA1216 soil unconfined compressive strength measurement. The wood age is indicated in the table (underwater curing).

The Sandgururi compressive strength is shown in Table-3.

Table 3 From Table 3, it can be seen that the soil improvement agent of the present invention can provide significantly greater strength at a lower concentration of 8102 than the neutral silica sorghum (Comparative Examples 3 and 4).

Furthermore, from Table 21 and Table 3, it can be seen that the soil improvement agent of the present invention can be adjusted to a sufficient gelation time to penetrate into the ground, compared to the acidic silica sol ground (Comparative Example 2).

It is also seen that the strength is greater and the long-term strength is superior compared to the alkaline water glass gel (Comparative Example 1).

Table 4 shows the measurement results of the elution amount of 5in2, which is one measure of the durability of the cured product.

The test specimen was prepared by preparing a 200I homogel using the above-mentioned drug solution and immersing it in 10 times the amount of distilled water. 2001 after a certain number of days! A sample of water was taken and 200 I of distilled water was added.

The analysis of 5in2 was carried out by evaporation to dryness and then weight measurement.

The elution rate of 5102 showed a constant value after 50 days, with the exception of Comparative Example 1, and almost no elution was observed thereafter. This shows that the product of the present invention has a low dissolution rate and excellent durability.

Next, in order to compare the grout characteristics of the activated silicic acid aqueous solution and the acidic silica sol according to the present invention, the SiO2 concentration was made the same for both grouts, and the relationship between the - value, gelation time, and compacted sand strength was measured. The results are shown in Tables 5 and 6.

The activated silicic acid aqueous solution was prepared according to Preparation Example 2 of the activated silicic acid aqueous solution with caustic soda, and the 5102 concentration was kept constant at 5% by weight.

On the other hand, the acidic silica sol shown in Table 1 was used, and Pf (Pf) was varied with caustic soda, and the concentration of 5102 was kept constant at 5% by weight.

From Tables 5 and 6, it can be seen that the activated silicic acid aqueous solution of the present invention can obtain the gelation time necessary for sufficient penetration even in the neutral region, and has high consolidation strength.

In the case of acidic silica sol Next, in order to compare the grout properties of the active silica aqueous solution according to the present invention and the neutral silica sol, the pH was set to a constant value (
is M6), and the unconfined compressive strength (
The strength after curing in a humid room for one day was measured.

In the case of an active silicic acid aqueous solution, the above preparation method is to add water to the solution obtained in Preparation Example 2 of an activated silicic acid aqueous solution to change the 5i02a degree, and add caustic soda to change the 5i02a degree.
6 and Nap/ was added to make the gelation time S: 10 minutes.

In addition, in the case of neutral silica sol, use the neutral silica sol shown in Table 15 and add water to change the concentration of 5in2, add sulfuric acid to make Pf (the value is 6g, and add aluminum sulfate to make the gel). The curing time was determined to be W2O minutes.

The results are shown in Table 7, and from this it can be seen that in the case of an active silicic acid aqueous solution, the concentration of 5102 is 2 kg/r when the concentration is 2.0% by weight or more.
In contrast to obtaining a consolidated sand strength of more than m2, in the case of neutral silica sol, the concentration of 5in2 must be 20in2 or more.
It is clear that it is impossible to reduce the strength of 5kg/1m2 or more.

On-site construction example Test injection was carried out in sandy ground with a hydraulic conductivity of 2 = 10-5 m/sea.

Three types of injection liquid were used: an activated silicic acid aqueous solution, a neutral silica sol, and an acidic silica sol, and each was injected at a distance of 20 m from each other. The injection depth is 5 to 3 m below the ground surface, and 0.
A total of 10,001 injections were made with 250 J at each stage using a 5 m injection scrubber.

The injection solutions were formulated so that the 5102 concentration was 5.0% by weight. For activated silicic acid aqueous solution and neutral silica sol, the formulation was the same as code 8 in Table 7, gelation time was 10 minutes, and pi (value was 6).Also, for acidic silica sol, as shown in Table 6, pH 6, Gel time 5
It was blended for 0 seconds.

As shown above, the pH value and 8102 concentration of the three types of mixed solutions can be kept constant, but the gelation time cannot be made the same as the others because the gelation time of acidic silica sol becomes faster in the neutral region. It's impossible. During the injection, an observation well was set up 10 meters away from the injection point, and groundwater was sampled before (January ago), during, and after the injection (3 days and 1 week later) to investigate changes in groundwater quality. .

In addition, the hydraulic conductivity before and after injection was measured, and after the injection, excavation was conducted to observe the consolidation status, and the consolidation was collected to measure the unconfined compressive strength.

The results are as follows.

The water quality test results are shown in Table 8, and it can be seen that the activated silicic acid aqueous solution causes almost no change compared to the acidic silica sol before, during, and after injection.

Table 8 Comparing the hydraulic conductivity before and after injection, the results are as shown in Table 9, which shows that the activated silicic acid aqueous solution improved the hydraulic conductivity extremely well.

Table 9 Also, regarding the solidification status according to the excavation survey, in the case of activated silicic acid aqueous solution, a semi-cylindrical solid with a diameter of rlm was obtained, and the unconfined compressive strength of the solidified sand was r5.4ky/son. It was 2. In the case of neutral silica sol, a cylindrical body with a diameter of about 3:80 was obtained, but the strength of the solid body was o, 8 Icy/
It was about an2. In the case of acidic silica sol, the gelation time is short, so pulsatile injection is observed considerably, and the gelation time is 0.5 to 1.
Consolidates at a straight q% of 5m, and its strength is 4.5 kg/c
It was m2.

Applicant's agent Kaoru Furutani

Claims (1)

[Claims] A ground improvement agent whose main ingredient is an activated silicic acid aqueous solution that contains virtually no salt.